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Neogene history of the West Pacific Warm Pool, Kuroshio and Leeuwin currents

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Neogene history of the West Pacific Warm Pool, Kuroshio and Leeuwin currents

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Abstract

Foraminiferal analysis of Miocene to recent strata of the Northwest Shelf of Australia is used to chart West Pacific Warm Pool (WPWP) influence. The assemblage is typified by ``larger'' foraminifera with ingressions of the Indo-Pacific ``smaller'' taxa Asterorotalia and Pseudorotalia at around 4 Ma and from 1.6 to 0.8 Ma. A review of recent and fossil biogeography of these taxa suggests their stratigraphic distribution can be used to document WPWP evolution. From 10 to 4.4 Ma a lack of biogeographic connectivity between the Pacific and Indian Ocean suggests Indonesian Throughflow (ITF) restriction. During this period, the collision of Australia and Asia trapped warmer waters in the Pacific, creating a central WPWP biogeographic province from the equator to 26°N. By 3 Ma Indo-Pacific species migrated to Japan with the initiation of the ``modern'' Kuroshio Current coinciding with the intensification of the North Pacific Gyre and Northern Hemisphere ice sheet expansion. Indo-Pacific taxa migrated to the northwest Australia from 4.4 to 4 Ma possibly because of limited ITF. The absence of Indo-Pacific taxa in northwest Australia indicates possible ITF restriction from 4 to 1.6 Ma. Full northwest Australian biogeographic connectivity with the WPWP from 1.6 to 0.8 Ma suggests an unrestricted stronger ITF (compared to today) and the initiation of the modern Leeuwin Current. The extinction of some Indo-Pacific species in northwest Australia after 0.8 Ma may be related to the effects of large glacial/interglacial oscillations and uplift of the Indonesian Archipelago causing Indonesian seaway restriction.

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... More limited data are available for benthic foraminifera on the middle-and outer-shelf regions. Benthic foraminifera from the coast of Western Australia have been previously studied by Betjeman (1969), Loeblich and Tappan (1994), Haig (1997), James et al. (1999), Li et al. (1999), Orpin et al. (1999), Semeniuk (2001), Quilty and Hosie (2006), Mays (2007), Gallagher et al. (2009), andParker (2009). Betjeman (1969) published the first major study, reporting 397 benthic foraminiferal species between 0 and 300 m water depth from Cape Leeuwin in the south to the Rowley Shelf in the north. ...
... More pertinent to our study, Gallagher et al. (2009) assessed abundances of LBF from 4.4 Ma to modern from the northwestern shelf as indicators for dynamic LC paleoflow and connectivity with the Western Pacific Warm Pool. Mays (2007), in his thesis, analyzed benthic and planktonic foraminifera from six transects (24-318S) on the Rottnest Shelf and Carnarvon Ramp, reporting evidence for influence of upwelling and saline downwelling along the shelf. ...
... Our data will be useful in the interpretation of regional biogeography and habitat preferences of benthic foraminifera in the eastern Indian Ocean. Furthermore, the resulting data will aid in studies of the paleoecology of the Western Australian province (e.g., Corliss 1979b, Chaproniere 1984, Moss et al. 2004, Renema 2007, Gallagher et al. 2009), water-mass circulation (Corliss 1979a;De Deckker 2005, 2007;Spooner et al. 2011), and carbonate ramps in general (Parker and Gischler 2015 (Hocking et al. 1987, Stagg andColwell 1994). The Mesozoic section of the Northern Carnarvon Basin has been of geological interest for hydrocarbon extraction in the recent decades (Bradshaw and Bernecker 2015). ...
Chapter
The carbonate sediments of the Western Australian shelf in the Indian Ocean host diverse assemblages of benthic foraminifera. These shelf environments are dominated by the southward-flowing Leeuwin Current, which impacts near-surface circulation and influences biogeographic ranges of Indo-Pacific warm-water foraminifera. Analyses of outer-ramp to upper-slope sediments (127-264 m water depth) at four different sites (some with replicates) revealed 185 benthic species. A shift from benthic to planktonic foraminifera was accompanied by a decrease in ''larger'' benthic foraminifera below the lowermost euphotic zone. Fisher a and proportions of buliminid and textulariid taxa increased with water depth, as miliolids and rotaliids decreased in proportion. Cluster analyses on the 125 to 250 lm and 250 to 850 lm size fractions revealed distinct assemblages, with the former distinguishing between deeper and shallower sites, and the latter distinguishing between the Carnarvon Ramp site and the three sites on the northwestern shelf (NWS). The assemblage shift with depth was likely caused by rapidly changing physical conditions in the upper thermocline. The assemblage differences between the NWS and the Carnarvon Ramp site indicate limited horizontal transport and migration rates on the outer shelf below the influence of the Leeuwin Current. Similarity in bottom-water temperature at the studied sites indicates that water mass characteristics, biogeographic history, and/or possibly diversity in benthic shelf habitats, rather than temperature and depth, are responsible for differences between the two regions.
... The lines indicate the multi-annual surface isotherms (available at http://www.nodc.noaa. gov/OC5/WOA09/pr_woa09.html): ECC, Eastern Countercurrent; LC, Leeuwin Current; SEC, South Equatorial Current; SJC, South Java Current; WAC, West Australian Current (modified from Takahashi & Okada, 2000;Gallagher et al., 2009). Solid circles indicate site locations. ...
... Ma. (Karas et al., 2009(Karas et al., , 2011. These paleoceanographic changes induced by the tectonic evolution of the Indonesian seaway are supported by the inference, mainly from foraminiferal evidence, that the modern oligotrophic Kuroshio Current formed during the late Pliocene (< 3 Ma; Gallagher et al., 2009Gallagher et al., , 2015. ...
... The abundance of Discoaster at ODP Hole 757B suggests shallowing of the thermocline/nutricline during the late Pliocene (ca 3.0 Ma), confirming the reduced ITF by tectonic restriction of the Indonesian seaway and intensified cooling of the Benguela upwelling system (Karas et al., 2011). These factors led to the development of the WPWP and the modern oligotrophic Kuroshio Current in the western Pacific Ocean (Gallagher et al., 2009;K. Sato et al., 2008). ...
Article
We studied the calcareous nannofossil assemblages from Ocean Drilling Program Hole 757B in the eastern Indian Ocean to reconstruct the sea‐surface conditions, especially changes in thermocline/nutricline depth, from the middle Miocene to the Pleistocene. Nutrient levels at the sea surface were reconstructed from the nannofossil accumulation rate, abundance of Discoaster, and coccolith size variations in Reticulofenestra. The sea‐surface conditions were likely to have been oligotrophic with a deep thermocline/nutricline during 11.8–7.5 and 6.7–6.2 Ma. The change from oligotrophic to eutrophic conditions at 7.5–6.7 Ma was caused by an influx of nutrient‐rich terrestrial material or upwelling of nutrient‐rich water induced by intensified southeast trade winds. This conclusion is supported by a marked increase in the magnetic susceptibility of the sediment that is coincident with the change from oligotrophic to eutrophic assemblages. The diminished abundance of Discoaster after ~ 3.0 Ma indicates shallowing of the thermocline/nutricline after that time, which confirms the reduced Indonesian Throughflow resulting from tectonic restriction and intensified cooling of the Benguela upwelling system. Decreases in the modal coccolith size of Reticulofenestra, indicating eutrophic conditions, are observed in three horizons. Two of these events (at 7.5 and 5.0 Ma) correspond to biogenic blooms in the Indian Ocean at 7.6 Ma and 6.0–5.0 Ma, respectively.
... An early study focusing on microfossil biogeographic connectivity between the western Pacific Ocean and the northwest shelf of Australia suggested relatively stronger ITF and LC during 1.6-0.8 Ma (Gallagher et al., 2009). Recently, based on TEX 86 temperature records derived from glycerol dialkyl glycerol tetraethers (GDGTs) at Site U1460, Petrick et al. (2019) proposed cooling and weak ITF conditions at ∼0.65 and ∼1.55 Ma, which were caused by global sea level lowering and regional tectonic changes. ...
... Since the MPT, large glacial-interglacial oscillations become an important signature in the climatic setting of the northwestern Australian area (Gallagher et al., 2009;Spooner et al., 2011). Although the northwestern Australian continent was generally dry, moisture availabilities during some interglacial periods over the late Pleistocene could be comparable with those in the early Pliocene (Site 762; Fig. 4c; Stuut et al., 2019). ...
... It is possible that during the interglacial periods over the late Pleistocene, the stronger LC potentially contributed to the wetness over the northwestern Australian continent by providing more moisture availability and enhancing austral summer monsoon (Molnar and Cronin, 2015). This is perhaps the reason for large-amplitude hydrological swings on the Australian continent on orbital scales over the late Pleistocene (Gallagher et al., 2009;Spooner et al., 2011). Therefore, although the intensified LC after ∼1.2 Ma may have potentially brought additional moisture to the northwestern Australian continent during the interglacial periods over the late Pleistocene, it could not overturn the long-term drying trend associated with the global cooling over the Pliocene-Pleistocene period. ...
Article
Although the Leeuwin Current (LC) is thought to play a pivotal role in climatic and oceanic systems of the western Australian region, how the LC developed through the Pliocene-Pleistocene period remains elusive. Here we used biomarker records to reconstruct variations of temperatures and primary productivity on the northwest shelf of Australia over the last 6 million years. Since ∼1.2 million years ago (Ma), our sea surface temperature record indicates progressive warming, with temperature values comparable to those in the Indo-Pacific Warm Pool, in contrast with the long-term global cooling trend. The regional surface warming was accompanied by suppressed primary productivity, together indicating prevailing warm, low-salinity, nutrient-deficient surface water, and thus a stronger LC since the Mid-Pleistocene Transition. During 4–1.2 Ma, greater surface temperature gradient between the Indo-Pacific Warm Pool and the northwest shelf of Australia and higher primary productivity seem to suggest a generally weaker LC. Warmer temperatures and lower productivity suggest a plausible existence of the LC during 6–4 Ma, but more work is required to confirm this. Impact of sea level and the Indonesian Throughflow on the LC strength may exist, but did not dominate through the Pliocene-Pleistocene period, considering different variation patterns among them. We propose the stronger LC after ∼1.2 Ma was more likely triggered by enhanced atmospheric circulation. Although the increased LC after ∼1.2 Ma may have potentially brought additional moisture to the Australian continent during the interglacial periods, it has not overturned the long-term drying trend through the Pliocene-Pleistocene period.
... Microfaunas can be influenced by a variety of parameters such as oxygen, gradients in light, temperature, salinity, organic matter, sediment substrate, water masses, and velocity and turbulence of surface-water currents (Gooday, 2003;Hohenegger, 2005;Fellowes et al., 2017). Assemblage variability reflects habitat shifts (Gallagher et al., 2009;Langer and Mouanga, 2016), extinctions (Mateo et al., 2017), stress factors (Quilty and Hosie, 2006), and inter-species competition (Debenay et al., 2009). Furthermore, benthic assemblages can be associated with processes occurring at the surface of the ocean (e.g., surface currents, upwelling) and respond to changes in environmental conditions (Smith, 1992;Gooday, 2003;Murray, 2006;Murgese and De Deckker, 2007). ...
... The eastern region is dominated by the effects of the Indonesian Throughflow (ITF), which connects the Indo-Pacific Warm Pool (~28°C) with the Indian Ocean and the Western Australian shelf (Wyrtki, 1987;Potemra, 2005). The warm water facilitates the growth of the Ningaloo Reef (Collins et al., 2003), Houtman Abrolhos Reef Complex (Collins et al., 1998), and larger benthic foraminifera (Gallagher et al., 2009). ...
... Expansion of subtropical faunas such as zooxanthellate corals, which require minimum temperatures of 14°C to survive, have been used to indicate enhanced LC reaching the Houtman Abrolhos Reef Complex Collins et al., 2003;Greenstein and Pandolfi, 2008). Gallagher et al. (2009) showed that temperature sensitive shelfal benthic foraminiferal species (Asterorotalia spp., Pseudorotalia spp., and Heterolepa margaritiferus) migrated from the southwest Pacific to the Western Australian shelf during periods of expanded influence of the ITF. Kendrick et al. (1991) found the subtropical estuarine arcoid bivalve Anadara trapezia in marine isotope stages 5 (~130 ka) and 7 (~243 ka) in the Perth and Carnarvon basins, where it is now extinct. ...
Article
Benthic foraminiferal assemblages from a ~300 m deep core from an outer carbonate-ramp site off Western Australia (International Ocean Discovery Program Core U1460A) were examined to reconstruct the paleoceanographic evolution of the Carnarvon Ramp and the warm surficial Leeuwin Current (LC) for the last 3.54 Ma. Of the identified 179 benthic foraminiferal species, occurrences of the 15 most abundant taxa were assessed using Q-mode Cluster Analysis and Non-Metric Dimensional Scaling. Diversity, equitability, planktonic/benthic index, microhabitat preference, and sedimentary parameters such as lithology and sponge spicule content were analyzed to gather information about past intermediate- and surface-water circulation. Relative abundances of infaunal and epifaunal species were applied to indicate changes in organic-matter supply and oxygenation at the sea floor. Influence of upwelling was recognized by a high infaunal species ratio, with dominance by Uvigerina peregrina, Lagena annellatrachia and Trifarina bradyi. Epifaunal species such as Hanzawaia nipponica and Hyalinea florenceae gradually became more abundant around 1.14 Ma, indicating increased ventilation and establishment of the paleo-LC. A more substantial change was initiated by 0.91 Ma as marked by key species Spirorutilus carinatus and Rotorbinella sp., together with increased faunal diversity, benthic foraminiferal accumulation rates, and evidence for suspension feeding sponges. With the LC flow suppressing upwelling, and better ventilated waters entering the shelf, the environment favored epifaunal agglutinates, rotalids, and miliolids, while buliminids decreased. Under high-flow conditions of the LC, sponge spicules and skeletal carbonate production reached an optimum at ~0.6 Ma before returning to modern conditions. Supported by these observations, we propose the following paleoceanographic evolution of the Carnarvon Ramp: During the late Pliocene to mid Pleistocene (3.54–0.91 Ma) conditions of deep-water upwelling from the Western Australian Current and Indian Ocean Gyre indicate the absence of the capping LC on the outer carbonate ramp. A transitional phase started in the mid Pleistocene (1.14–0.61 Ma). The paleo-LC triggered gradual oxygenation at the sediment-water interface, which coincided with an increase in carbonate sedimentation rates, and waning sea-surface productivity. During a third phase, mid Pleistocene to present (0.91–0 Ma), the LC's intensity and flow rates peaked at ~0.6 Ma. Benthic foraminiferal accumulation rates reached a high, then decreased to present-day rates. For short periods, sea-surface productivity was moderately enhanced, likely due to fluctuating LC persistence or landward shift during glacial maxima.
... A dramatic increase in subsidence rates, beginning at around 10 Ma, also occurred on the northwest margin of Australia (Czarnota et al., 2013). Uplift of the Indonesian Archipelago from 10 to 4.4 Ma changed regional oceanographic conditions by trapping warm waters in the central Pacific, forming the West Pacific Warm Pool north of Papua New Guinea (Gallagher et al., 2009(Gallagher et al., , 2014. Intermittent connectivity between the West Pacific Warm Pool and the Indian Ocean via the Indonesian Seaway occurred between 1.6 and 0.8 Ma and led to the establishment of the south-flowing Leeuwin Current down the Western Australian coast (Gallagher et al., 2009(Gallagher et al., , 2014. ...
... Uplift of the Indonesian Archipelago from 10 to 4.4 Ma changed regional oceanographic conditions by trapping warm waters in the central Pacific, forming the West Pacific Warm Pool north of Papua New Guinea (Gallagher et al., 2009(Gallagher et al., , 2014. Intermittent connectivity between the West Pacific Warm Pool and the Indian Ocean via the Indonesian Seaway occurred between 1.6 and 0.8 Ma and led to the establishment of the south-flowing Leeuwin Current down the Western Australian coast (Gallagher et al., 2009(Gallagher et al., , 2014. Today the Leeuwin Current transports warm, low salinity, nutrient-deficient water southwards, extending tropical reef development to 30°S off Western Australia. ...
... Collins et al. (1997) suggested that this dual carbonate geometry may be due to the influence of the shallow warm-water Leeuwen Current as this is a major factor in the extreme southerly extent of reefs on present day Western Australian margin. However, there is evidence to suggest that the modern form of the Leeuwin Current only began in the Pliocene and intensified to its modern extent in the Pleistocene (Gallagher et al., 2009(Gallagher et al., , 2014De Vleeschouwer et al., 2018). This suggests that the Oligo-Miocene reef development and growth on a heterozoan carbonate system was not related to the Leeuwin Current. ...
Article
The Great Barrier Reef of Australia is the largest modern coral reef system on Earth. However, a similar-sized barrier reef (~2000 km long) existed on Australia’s north-western margin in the middle Miocene and to some extent, still exists today. Seismic profiles reveal that this reef system was first initiated in the late Paleogene (~34-28 Ma) and reached its zenith as a prograding barrier reef during the middle Miocene (16-15 Ma). This giant reef system backstepped in the late Miocene (~10 Ma), forming a series of isolated atolls and pinnacle reefs. These remaining reefs were gradually extinguished, leaving only a few surviving isolated atolls today (Rowley Shoals, Scott Reef, Seringapatam Reef and Ashmore Reef). The distribution of these extant reefs therefore outlines the former presence of the mid-Miocene Great Barrier Reef of the Australian North West Shelf. This middle Miocene shallow-water rimmed-reefal shelf grew contemporaneously on a deeper-water heterozoan ramp, producing an unusual mixed heterozoan/photozoan carbonate system for most of its length. The initiation of reef growth appears related to Australia’s northward drift into lower latitudes, combined with warm mid-Miocene climatic optimum conditions. However, the sudden and simultaneous initiation of reef growth in the mid-Miocene across the North West Shelf was probably also related to changes in paleoceanography (increased aragonite saturation and/or nutrient-depletion) perhaps influenced by changing climatic conditions (increased aridity). From the late Miocene (~10 Ma) to Holocene, high rates of subsidence across the North West Shelf probably set the scene for ultimate demise of this giant barrier reef system and led to widespread backstepping with the development of a series of isolated atolls and pinnacle reefs. It is likely that other paleoceanographic and climatic events (like nutrient supply, carbonate saturation, eustasy etc) combined with continued high subsidence rates acted to gradually extinguish the reef system in a series of steps over a period of 10 million years. The onset (~1 Ma) of a strong Leeuwin Current (with the delivery of warm and nutrient depleted water from the north) and its effect on the Quaternary reefs of the Western Australian coast is a good example of a paleoceanographic process that would be difficult to recognize in an ancient setting. It is likely that similar paleoceanographic events have controlled the rich and complex history of reef growth and drowning since the mid-Miocene on the North West Shelf.
... The long history of intense hydrocarbon exploration using large seismic and well datasets (Longley et al., 2002) and the recent International Ocean Discovery Program (IODP) Expedition 356 (Gallagher et al., 2017) have revealed the existence of thick (>2 km) sequences of Cenozoic upper bathyal to shelfal marine strata (see summaries in Keep et al., 2018;deMenocal & Gallagher, 2019). These strata record long and short-term climate/ocean variability (Auer et al., 2019;Christensen et al., 2017;De Vleeschouwer et al., 2019Gallagher et al., 2009;Groeneveld et al., 2017;Ishiwa et al., 2019;Karatsolis et al., 2020;Moss et al., 2004) and have increased our understanding of reef evolution (Gallagher et al., 2014;Gorter et al., 2002;McCaffrey et al., 2020;Power, 2008;Rosleff-Soerensen et al., 2012;Ryan et al., 2009) and subtropical to tropical siliciclastic/carbonate platform development (Anell & Wallace, 2019;Cathro et al., 2003;Gallagher et al., 2018;Goktas et al., 2016;Sanchez et al., 2012;Tagliaro et al., 2018). In addition, these strata host substantial mass-transport deposits (with volumes ∼17 to >162 km 3 ) (Hengesh et al., 2013;Scarselli et al., 2013) that were triggered by ongoing neo-tectonism as the Australian plate is colliding with the Asian plate (Keep et al., 2018) or subsidence variability (Gurnis et al., 2020). ...
... Analyses of industry seismic and downhole log datasets/samples have contributed significantly to our knowledge of the Cenozoic evolution of the NWS. However, until IODP Expedition 356 (Gallagher et al., 2017), the only samples of the upper Cenozoic strata of the region were cuttings, sidewall cores (Gallagher et al., 2009;Moss et al., 2004;Rosleff-Soerensen et al., 2012;Wallace et al., 2003), limited engineering cores of the upper 80 m (Collins, 2002;Gallagher et al., 2014) and samples of the modern sedimentary veneer (James et al., 2004;Jones, 1973). ...
... From east to west, these industry wells are Finucane-1, Angel-2, Goodwyn-6, and Goodwyn-2; their well logs can be sourced from the Geoscience Australia online NOPIMS database (http://www.ga.gov.au/nopims; last access May 21, 2020). We interpreted the approximate stratigraphic position of the latest Miocene in the industry wells by using previously-published biostratigraphic data from cuttings by Gallagher et al. (2009Gallagher et al. ( , 2014 and by extrapolating from the detailed IODP age-depth models in the Carnarvon Basin. ...
... The known "letter stages" biozonation, introduced by Leupold and van der Vlerk (1936) and constantly used in shallow carbonate facies (Adams, 1970;Chaproniere, 1984;Boudagher-Fadel and Banner, 1999;Cotton et al., 2014), could not be applied in this study as the deposits are mostly siliciclastic. However, some studies in siliciclastic settings in the Indopacific region indicate that it is possible to use larger rotaliid foraminifera as regional index fossils due to their relatively fast phylogenetic evolution (Huang, 1964;Billman and Kartaadiputra, 1974;Billman and Scrutton, 1976;Billman et al., 1980;Gallagher et al., 2009;van Gorsel et al., 2014). ...
... This recent study reported rotaliids as the major component of all samples and as most abundant above 20 m water depth, where organic-rich muddy sediments prevail. Focused studies on these rotaliids and their ecological conditions point to their dominance being restricted to eutrophic settings with a muddy sea bottom (Murray, 1991;Gallagher et al., 2009); this further supports the results obtained in our study. ...
... The abundance of rotaliid foraminifera is also a clear indication that this group of foraminifera could be successfully used for biostratigraphic determination if similar facies with different ages can be sampled in the region, as has already been suggested by a number of authors (Huang, 1964;Billman et al., 1980;Gallagher et al., 2009). This in turn would lead to important advances in the stratigraphic identification of major sequences used in petroleum studies. ...
Article
Palaeonvironmental interpretations and biostratigraphic zonations in northwest Borneo are still a matter of debate but are important for petroleum related applications. The outcrop of Ambug Hill, a late Miocene marine siliciclastic sequence in Brunei Darussalam, has been investigated for its foraminifera assemblage. From a 9.5 m clay-rich interval 50 taxa have been recognized and classified, whenever possible to species level. The studied fauna is characterized by mostly hyaline foraminifera, dominated by two rotaliid species: Cavarotalia annectens and Heterolepa dutemplei. Additionally, a number of miliolids, lageniids, bolivinids and also planktonic foraminifera are present but in much lower abundance. The dominance of the rotaliids points to a sea floor rich in organic carbon characterized by muddy substrates with very low light penetration and the possible growth of patchy sea grass or macroalgae in the system, as indicated by epiphytic foraminifera in the samples. The results obtained give additional insights on how the environmental conditions might have been during the deposition of the deltaic sequences very widespread in the region, and how the fauna coped with such settings. Throughout the investigated samples, the dominance of the assemblages clearly shows alternating stress conditions, typical of pro- deltaic environments. The large abundance of rotaliid foraminifera, points toward possible biostratigraphic applications as several taxa within this group have short biozones in the region even though have strong facies dependency. If their role as biostratigraphic indicators could be finally proven, they might be used to date the large depositional sequences occurring in the region, since planktonic index fossils are scarce due to the very proximal settings of the sediments.
... There is evidence suggesting that an important uplift phase began during the Late Miocene to Early Pliocene (Cane & Molnar, 2001;Hall, 2002;Hall et al., 2011;Kuhnt et al., 2004;Molnar & Cronin, 2015;Tate et al., 2017), with tectonic restriction of the ITF having a major effect on global thermohaline circulation by the late Early Pliocene (Cane & Molnar, 2001;Gallagher et al., 2009;Karas et al., 2009Karas et al., , 2011bKaras et al., 2017). The ITF reorganization during the Pliocene has also been causally linked to the marine isotope stage (MIS) M2 glacial event at~3.3 ...
... Our study provides novel insights into the temporal evolution of Pliocene ITF restriction in relation to global climatic changes and investigates how tectonic ITF restriction and the transport of tropical waters from the Pacific into the Indian Ocean may have increased the sensitivity of the Indian Ocean to orbitally driven Antarctic ice sheet dynamics (Patterson et al., 2014), which potentially amplified the cooling during the MIS M2 glacial event at 3.3 Ma in the Southern Hemisphere (De Vleeschouwer et al., 2018). To achieve this, we present a detailed timeline of how changes in ITF configuration heralded major changes in the eastern Indian Ocean, which in turn affected global climatic patterns De Schepper et al., 2014;Gallagher et al., 2009;Karas et al., 2009Karas et al., , 2011bKaras et al., 2017;Sarnthein et al., 2017). We also provide the first evidence for the increasingly important role glacio-eustatic sea level changes had on the Indian Ocean hydroclimate after MIS M2 and show how they are linked to the shift in the Australian climate system from a "humid interval (5.5-3.3 ...
... Their study suggests that sea level drops around 30 m are enough to significantly alter the hydroclimatic conditions along northwest Australia, leading to stronger upwelling and reduced humidity via the Sahul-Indian Ocean Bjerknes mechanism with an increased east-west tilt of the Indian Ocean thermocline. In summary, it appears that the heightened glacial/interglacial variability after 3.3 Ma resulted in oceanographic conditions along the NWS that were already comparable to its proposed Pleistocene configuration implying a stronger ITF and Leeuwin current during interglacials and a weaker ITF during glacials leading to increased seasonal upwelling of cool nutrient-rich water masses of the Leeuwin Undercurrent (Gallagher et al., 2009;Godfrey & Mansbridge, 2000;Ridgway & Godfrey, 2015;Spooner et al., 2011;Wijeratne et al., 2018). ...
Article
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The Pliocene was characterized by a gradual shift of global climate toward cooler and drier conditions. This shift fundamentally reorganized Earth's climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high-resolution sediment geochemistry, calcareous nannofossil, and X-ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue-based interpretations of nannofossil assemblages indicate that ITF configuration culminated ~3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (~3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul-Indian Ocean Bjerknes mechanism and increased the response to glacio-eustatic variability.
... Rainfall is more important in the cool winter months when the subtropical highs (or subtropical ridges) move to the north and the cold fronts embedded in the westerly circulation bring moisture over the continent [39,40]. [41]). The blue star indicates the location of MD00-2361 [12]. ...
... All specimens of benthic foraminifera were identified [41,[49][50][51] and clustered into seven groups using the Ward's clustering method in the software Past [52]. This method groups species based on the similarity of their abundances. ...
Article
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International Ocean Discovery Program (IODP) Expedition 356 Site U1461 represents one of the few records from the North West Australian shelf that provides information about aridity fluctuations in Australia during the Quaternary. A combination of chronostratigraphic indicators revealed the (partial) preservation of two major glaciations (Marine Isotope Stage (MIS) 2 and MIS 12) in the sedimentary record. The faunal content (mainly benthic foraminifera, corals and bryozoans) was analyzed to estimate paleo-environments and paleo-depths in order to determine if these sediments have been remobilized by reworking processes. Despite the occurrence of a depositional hiatus (including MIS 5d to MIS 9-time interval), the excellent preservation of faunal content suggests that the preserved sediment is in situ. The geochemical composition of the sediments (Nd and major elements) indicates that during MIS 12 riverine input was likely reduced because of enhanced aridity, and the sediment provenance (mainly atmospheric dust) is likely in the central (Lake Eyre) or eastern (Murray Darling Basin) parts of the Australian continent. MIS 2 is confirmed to be one of the driest periods recorded in Australia but with mixed dust sources from the eastern and western parts of the continent. More humid conditions followed the glacial maximum, which might correspond to the peak of the Indian-Australian Summer Monsoon.
... The KC is a northward deflection of the horizontal North Equatorial Current (near 13°N, Samar and Leyte, Philippines). The KC is a strong ocean current that runs constantly northward along the east of Taiwan to Ryukyu, reaching ~ 30°N off the coast of Japan 14,15 . The KC carries warm water (> 25 °C) from equatorial regions. ...
... The samples from Penghu, where at the end of KBC, the genotypes are mixed throughout a year. Summarized by Hu et al. (2000), Jan et al. (2002), Gallagher et al. (2009), and Gallagher et al. (2015)[13][14][15][16] . The ANOVA results of the gonadosomatic index (GSI) collected from the female (blue bars)/male (orange bars) samples of (a) Dashi, (b) Penghu, and (c) Kaohsiung. ...
Article
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Abstract Many fisheries management and conservation plans are based on the genetic structure of organisms in pelagic ecosystems; however, these structures tend to vary over time, particularly in cyclic ocean currents. We performed genetic analyses on the populations of the pelagic fish, Megalaspis cordyla (Osteichthyes: Carangidae) in the area surrounding Taiwan during 2000–2001. Genotyping was performed on M. cordyla collected seasonally around Taiwan as well as specimens collected from Singapore (Malacca strait) and Indonesia (Banda Sea). Gonadosomatic indices (GSI) revealed that M. cordyla does not spawn near Taiwan. Data related to the mitochondrial control region revealed that the samples from Singapore and Indonesia represented two distinct genetic cohorts. Genotyping revealed that during the summer (June–August 2000), the Indonesian variant was dominant in eastern Taiwan (presumably following the Kuroshio Current) and in the Penghu region (following the Kuroshio Branch Current). During the same period, the Singapore genotype was dominant along the western coast of Taiwan (presumably following the South China Sea Current); however, the number dropped during the winter (December–February 2001) under the effects of the China Coast Current. Divergence time estimates indicate that the two genetic cohorts split during the last glacial maximum. Despite the fact that these results are based on sampling from a single year, they demonstrate the importance of seasonal sampling in unravelling the genetic diversity in pelagic ecosystems.
... During the mid-to late Pleistocene with the weak ITF and the strong LC, a generally drier conditions in northwestern and southeastern Australia were recognized (McLaren & Wallace, 2010;Sniderman, 2011;Sniderman et al., 2016;Stuut et al., 2019). Besides, larger glacial-interglacial monsoonal oscillations become another important signature in the Australian area (Gallagher et al., 2009;Spooner et al., 2011). However, due to sparse records covering the Pliocene-Pleistocene period, how the continental environments evolved along with the ITF constriction and the general aridification remains elusive and requires further investigations. ...
... Nevertheless, the δ 13 C org values still add another dimension of the terrestrial OC story, by suggesting fragile environments with large-amplitude hydrological swings. Over the late Pleistocene, large glacial-interglacial oscillations and strong sea level variations become important climatic signatures in northwestern Australia (Auer et al., 2021;Gallagher et al., 2009;Spooner et al., 2011;Stuut et al., 2019). This is perhaps the reason for large-amplitude hydrological swings on the Australian continent at orbital scales, signaling the larger variation in the δ 13 C org values after the mid-Pleistocene transition (MPT, ∼1.2 Ma). ...
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Plain Language Summary Terrestrial material indicators recorded in nearshore marine sedimentary cores are useful for studying the continental climates in northwestern Australia. Here, we present biomarker‐based data from cores at International Ocean Discovery Program Site U1461 to reconstruct the history of the terrestrial material input to the northwest shelf of Australia over the last 5 million years. We aim to reveal how the vegetation and soil organic transportations responded to climate changes in northwestern Australia through the Pliocene‐Pleistocene period. Our results show a continuous decrease in the vegetational organic input since 5 million years ago (Ma), an increased soil input at ∼2.5–2.2 Ma, a stronger variability in bulk terrestrial organic input since ∼1.7 Ma, and a shift in soil source between ∼1.5 and 1.2 Ma. All these changes together indicate that the climates in northwestern Australia shifted from a generally wet condition during the early Pliocene to a drier and more variable phase during the late Pleistocene, which is controlled by ongoing Indonesian Throughflow constriction and global atmospheric circulations.
... Rainfall is more important in the cool winter months when the subtropical highs (or subtropical ridges) move to the north and the cold fronts embedded in the westerly circulation bring moisture over the continent [39,40]. [41]). The blue star indicates the location of MD00-2361 [12]. ...
... All specimens of benthic foraminifera were identified [41,[49][50][51] and clustered into seven groups using the Ward's clustering method in the software Past [52]. This method groups species based on the similarity of their abundances. ...
Article
nternational Ocean Discovery Program (IODP) Expedition 356 Site U1461 represents one of the few records from the North West Australian shelf that provides information about aridity fluctuations in Australia during the Quaternary. A combination of chronostratigraphic indicators revealed the (partial) preservation of two major glaciations (Marine Isotope Stage (MIS) 2 and MIS 12) in the sedimentary record. The faunal content (mainly benthic foraminifera, corals and bryozoans) was analyzed to estimate paleo-environments and paleo-depths in order to determine if these sediments have been remobilized by reworking processes. Despite the occurrence of a depositional hiatus (including MIS 5d to MIS 9-time interval), the excellent preservation of faunal content suggests that the preserved sediment is in situ. The geochemical composition of the sediments (Nd and major elements) indicates that during MIS 12 riverine input was likely reduced because of enhanced aridity, and the sediment provenance (mainly atmospheric dust) is likely in the central (Lake Eyre) or eastern (Murray Darling Basin) parts of the Australian continent. MIS 2 is confirmed to be one of the driest periods recorded in Australia but with mixed dust sources from the eastern and western parts of the continent. More humid conditions followed the glacial maximum, which might correspond to the peak of the Indian-Australian Summer Monsoon.
... The numbered locations are listed in Table 1. (b) Oolites around Australia and their relationship to global seawater pH estimates (Royal Society, 2005) and regional oceanography (adapted from Gallagher et al., 2009Gallagher et al., , 2014 red are warm and blue are cool currents. Isl. ...
... The tropical carbonates that host modern oolites on the Northwest Shelf of Northern Australia are strongly influenced by shallow (50e300 m) currents that originate in the West Pacific Warm Pool (Fig. 1b, Gallagher et al., 2009Gallagher et al., , 20142017a). Northwest Shelf oceanography from 5 S to 15 S is dominated by the South Table 1 Age and environmental setting of Indo-Pacific oolites. ...
... The modern-day configuration of continents and island arcs developed during this time, through tectonic orogeny in the Andean and Eurasian belts, formation of backarc basins along the Pacific margin, and the northward movement of the Australian plate (Potter and Szatmari, 2015). Modern oceanic gateways were established by the closure of the Paratethys Ocean (18-12 Ma; Rögl, 1997), closure of the Isthmus of Panama (~3 Ma; O'Dea et al., 2016) and by the constriction of the Indonesian gateway in the Indo-Pacific (5-2 Ma; Cane and Molnar, 2001;Gallagher et al., 2009). In the Mediterranean Basin, restriction of the Strait of Gibraltar in the late Miocene resulted in the Messinian salinity crisis and desiccation of the Mediterranean Sea (~6 Ma; Rouchy and Caruso, 2006). ...
... The northward movement of the Australian plate shifted the continent towards a warmer equatorial climate (Dicaprio et al., 2011). Variability in the southward-flowing Indonesian Throughflow (ITF) and the onset of the southward-flowing Leeuwin Current affected oceanic temperatures along the western margin of the continent, leading to the appearance of tropical carbonate platforms and reefs on the Australian Northwest Shelf (NWS; Gallagher et al., 2009Gallagher et al., , 2017b. Furthermore, dynamic topography models and paleoshoreline analysis indicate that Western Australia has undergone an anomalous tectonic tilting of the continent to the northeast since the Eocene, which resulted in inundation of the NWS (Dicaprio et al., 2011;Heine et al., 2010). ...
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The Bare Formation represents a unique episode of Neogene siliciclastic deposition on the carbonate-dominated Australian Northwest Shelf (NWS). Seismic interpretation coupled with age control from International Ocean Discovery Program (IODP) Expedition 356 Sites U1462, U1463 and U1464, allow us to constrain the timing of siliciclastic deposition and the associated sedimentary processes. The Bare Formation is preceded by middle to late Miocene shelf exposure and karstification (~12 Ma). Elongate sandbars deposits with small lobate deltas developed during the late Miocene. Fluvial deposition increased markedly in the Zanclean (5.3–3.6 Ma), resulting in development of a large wave dominated delta, with evidence of channels, comprising the thickest component of the Bare Formation. Siliciclastic input decreased in the Piacenzian (3.6–2.58 Ma), leading to margin retreat and final termination in the early Pleistocene (~2.39 Ma). The results correlate with regional climate and sedimentary records from Sites U1463 and U1464, which indicate an arid middle to late Miocene on the NWS, followed by a humid interval in the Zanclean and a return to arid conditions during the Piacenzian. We suggest that fluctuation of surface runoff patterns in the continental hinterland was the primary control on Bare Formation evolution. Sedimentary and climate transitions are linked to reorganization of Indian Ocean paleoceanography, accompanying northward migration of the Australian continent and progressive restriction of the Indonesian Throughflow.
... The Cenozoic oceanography of the North West Shelf was closely controlled by the Indo nesian Throughflow ( Fig. 1; McGowran et al., 1997;Gallagher et al., 2009;Kuhnt et al., 2004;RosleffSoerensen et al., 2012). The Indonesian Throughflow flooded the North West Shelf with warm, lowsalinity water, delivering Pacific and Asian reef species (Collins, 2010;Rosleff Soerensen et al., 2012). ...
... The Indonesian Throughflow flooded the North West Shelf with warm, lowsalinity water, delivering Pacific and Asian reef species (Collins, 2010;Rosleff Soerensen et al., 2012). Bathymetric controls on the Indonesian Seaway during Miocene con vergence between Australia and the Banda arc (McGowran et al., 1997) strengthened the Indo nesian Throughflow (Gallagher et al., 2009;RosleffSoerensen et al., 2012) and are thought to have extended carbonate production up to 29°S, along Australia, by the Holocene (Zhu et al., 1993). ...
Article
We investigated pinnacle features at the base of late Oligocene–Miocene isolated carbonate buildups using three-dimensional seismic and borehole data from the Browse Basin, Northwest Australia. Brightened seismic reflections, dim spots, and other evidence of fluid accumulation occur below most pinnacle features. An important observation is that all pinnacles generated topography on successive late Oligocene–Miocene paleoseafloors, therefore forming preferential zones for the settlement of reef-building organisms by raising the paleo-seafloor into the photic zone. Their height ranges from 31 m to 174 m, for a volume varying from 33 km3 to 11,105 km3. Most of the pinnacles, however, are less than 2000 km3 in volume and present heights of 61–80 m. As a result of this work, pinnacles are explained as the first patch reefs formed in association with mud volcanoes or methanogenic carbonates, and they are considered as precluding the growth of the larger isolated carbonate buildups. We postulate that pinnacle features above fluidflow conduits demonstrate a valid seep-reef relationship, and we propose them to be refined diagnostic features for understanding fluid flow through geological time.
... Paleoceanographic studies using sediments from either side of the Isthmus of Panama indicate CAS constriction reached a critical threshold between 4.8-4 Ma (Haug and Tiedemann 1998;Steph et al. 2006;Steph et al. 2010). Similarly, the ITF constriction occurred from the Miocene (Kuhnt et al. 2004) into the Late Pliocene, and likely onward (Gallagher et al. 2009;Karas et al. 2011;Gallagher et al. 2014;Christensen et al. 2017), with increased constriction from 3-4 Ma inferred to alter Australian and African climates (e.g., Cane and Molnar 2001;De Vleeschouwer et al. 2018). Disentangling the effects of the CAS and ITF on the development of the North Pacific subtropical gyre and equatorial circulation (e.g., Kennett et al. 1985), and their likely influence on low to mid-latitude planktic foraminiferal diversity and evolution are confounding and beyond the scope of this contribution. ...
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Patterns of diversity in the modern planktic foraminifera indicate a latitudinal diversity gradient (LDG), which peaks in the mid-latitude regions. Plankton distributional patterns are often most strongly associated with temperature and are expected to change in response to expanded tropical water masses. Defining the underlying causes of climatic and oceanographic processes, however, requires detailed, local-scale diversity curves and evolutionary metrics, as well as solid taxonomic concepts of planktic foraminifera, to test the oceanographic processes driving evolution of marine plankton. Currently, diversity estimates for the planktic foraminifera are mainly based on global datasets skewed towards tropical to subtropical sites and conducted at coarse resolutions that hamper investigations of evolutionary processes, especially for short-lived climate perturbations. Here, we present 10-kyr resolution diversity curves and 25-kyr resolution local first appearance and extirpation rates of planktic foraminifera for four Ocean Drilling Program sites that extend from the temperate northern edge of the modern-day position of the Kuroshio Current Extension (KCE) to the tropics. We provide an updated taxonomic review of late Neogene planktic foraminiferal species from within the influence of the KCE. These data allow for investigations of the western Pacific LDG and patterns of evolution through the late Neogene in response to tectonic and climate events. Our results indicate that a mid-latitude diversity peak has been prominent in the western Pacific since at least 12.1 Ma, with highest diversity generally on the northern edge of the KCE. These data contradict previous studies indicating highest diversity is located ±20°, as our data reveal highest diversity for the planktic foraminifera at ±35° N, likely due to strong seasonality. Development of the modern North Pacific gyre system due to closure of the Central American Seaway and constriction of the Indonesian Throughflow increased the LDG between the tropics and the northernmost site, likely in response to KCE intensification. Diversity was only slightly affected during the mid-Piacenzian Warm Period (~3.2–2.9 Ma), with diversity gradients between the equatorial site and southernmost mid-latitude sites becoming similar, perhaps indicating a weaker thermal gradient developing in the northwest Pacific as the KCE and warmer waters were displaced northwards. With intensification of Northern Hemisphere glaciation came a decrease in diversity at the northernmost site, hypothesized to be caused by subtropical gyre constriction and southward displacement of subpolar surface waters. The beginning of the mid-Pleistocene transition marks an increase in diversity gradients, especially between the northernmost and tropical sites. A detailed taxonomic evaluation of planktic foraminiferal species has led to synonymization of what we consider regional morphological variants, as well as revised taxonomic concepts of key subtropical to temperate late Neogene planktic foraminifera. Scanning electron micrographs capture the morphological variability within a species concept for the first time in great detail for this part of the world ocean. These data and updated taxonomic concepts provide a framework for future studies to link evolutionary patterns with high-resolution geochemical and sedimentological data to further interpret localized drivers of diversification in the planktic foraminifera.
... The evolution of Paleogene climates in eastern Eurasia in general and Primorye in particular is tied to the history of the East Asian Monsoon and is complicated by tectonic events such as uplift of the Tibetan Plateau, and the Sea of Japan back-arc opening (Akhmetiev, 2004(Akhmetiev, , 2015Akhmetiev & Zaporozhets, 2017;An, Kutzbach, Prell, & Porter, 2001;Liu et al., 2015;Liu & Yin, 2002;Pavlyutkin & Golozubov, 2010;Quan, Liu, & Utescher, 2012a, 2012bSato et al., 2006;Tada, Zheng, & Clift, 2016;Yamanoto & Hoang, 2009). Moreover, past climates of eastern Eurasia are supposed to reflect the varying intensity of the warm Kuroshio and cold subarctic currents (Gallagher et al., 2009;Matthiessen, Knies, Vogt, & Stein, 2009). ...
Article
Paleogene vegetation changes in Primorye (Far East of Russia) are studied using the Plant Functional Types (PFT) Approach, for the first time applied on the large palaeobotanical records of this region. The palaeobotanical data for this reconstruction are based on the analysis of 30 palynofloras and 24 leaf floras covering the Early Palaeocene to Late Oligocene. The vegetation reconstruction at the level of PFTs in general points to the presence of mesophytic forest vegetation in Primorye throughout the Paleogene. While in the Palaeocene vegetation of Primorye was of temperate deciduous type, warm temperate-mixed evergreen-deciduous forests dominated in the Eocene and Early Oligocene. In the Late Oligocene, the vegetation of Primorye was again primarily deciduous, mixed evergreen-deciduous forests persisted at places. The observed vegetation patterns and their changes through time in many cases can be correlated with spatial climate patterns and the overall continental palaeoclimate evolution, as recently reconstructed from the same palaeobotanical record. The higher-than-present spatial homogeneity of Paleogene vegetation coincides with shallow temperature gradients and a significantly more humid regional rainfall pattern over Primorye during the Paleogene.
... Increased upwelling is likely to both decrease temperatures and increase nutrient levels, both favouring heterozoan carbonate production. The introduction of a shallow, warm-water current (for example, the modern Leeuwin Current on the Western Australian margin; Gallagher et al., 2009) would obviously favour the reefal photozoan carbonate factory over the deeper heterozoan factory. ...
Article
The concurrent development of a cool‐carbonate Miocene clinoform system and the tropical reef which developed on its shelf in the North Carnarvon Basin is studied. The study, based on seismic interpretation and geometrical analysis, seeks to investigate how the architecture of the clinoforms develops in relation to the advance of the reef‐margin, providing a proxy for discussing contemporaneous shoreline versus shelf‐edge development. The progradation of the reef and shelf‐edge often display a closely mirrored development, although the reef twice advances an order of two to three times the concurrent advance of the shelf‐edge. The forced regression of the second advance, as compared to the normal regression during the first, is observed in proportionally higher input of sediment towards advance of the shelf‐edge and toe, along with a gentler slope. The inability of the shelf‐edge to keep pace with the reef‐margin (and by proxy the shoreline) during lower accommodation/sedimentation is a result of the increased volume of sediment required to match reef‐margin advance beyond the shelf‐edge. Increased accommodation/sedimentation ratios promote higher trajectories where the volumes on shelf and slope are more balanced and the development more closely matched. The observed matched development of reef and shelf‐edge during both limited and increased slope sedimentation, suggest that accommodation is the dominant control on the location and trajectory of both ‘shoreline’ and shelf‐edge, and that excess sediment is deposited along the slope. This article is protected by copyright. All rights reserved.
... Moreover, past climates of eastern Eurasia are supposed to reflect the varying intensity of the warm Kuroshio and cold subarctic currents (e.g. Gallagher et al. 2009;Matthiessen et al. 2009). ...
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The Paleogene climate dynamics in Primorye (Far East of Russia) are studied using the Coexistence Approach, based on palaeobotanical records. Palaeobotanical data for the reconstruction comprises 54 palaeofloras covering the early Paleocene to late Oligocene, a time span of ca. 42 myr. The climate inferences obtained are consistent with independently derived global trends, demonstrating general climate cooling through the Paleogene. Cooling is most striking regarding the cold month mean temperature, while the decline of mean annual temperature was less marked. Our data indicate that the Paleogene climate of Primorye was significantly warmer than present, in general, with the warmest conditions prevailing throughout the Eocene and in the southeast of the study area. Negligible Paleogene temperature gradients over Primorye are related to the global pattern and specific regional aspects. The precipitation reconstruction points to conditions considerably wetter than at present. A distinct increase in mean annual precipitation is observed for the early Eocene and persisted throughout the Eocene and Oligocene. The regional rainfall pattern fundamentally differed from modern conditions, and this holds for all studied variables. The inland region and the south of Primorye were significantly more humid than today. The Paleogene pattern was possibly related to a monsoon-type circulation and enhanced landward flow of humid air masses, due to an overall flatter geomorphology of the East Asian coastal areas.
... Segundo diversos autores (Veevers, Powell e Roots 1991, Gallagher et al. 2009, Gallagher et al. 2012), a sedimentação da bacia de margem passiva do noroeste da Austrália resume a história geológica da margem norte do país desde o Mioceno Superior até os dias atuais. A NWS, região de estudo, oferece condições singulares para a compreensão de elementos-chave da circulação termohalina global, devido à sua proximidade da chamada "Piscina Aquecida do Indo-Pacífico" (IPWP, sigla em inglês) e Fluxo Indonésio de Correntes (ITF, sigla em inglês; Fig. 1 (James et al. 2004), levou-se em consideração a atuação das monções e a Corrente de Leewuin como principais controladores da sedimentação na região, sob a influência do ITF, que afasta a corrente fria da região da costa noroeste australiana (Fig. 2). ...
... Zhang et al., 2016). Among these arcs, the Philippine Arc may contribute the least because the Western Pacific boundary current (the Kuroshio Current) initiated and influenced this area no earlier than the late Pliocene (Gallagher et al., 2009;. For the same reason, coupled with DSDP Site 296 being located on the (Chen et al., 2007), the Gobi Desert (Biscaye et al., 1997;W. ...
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Plain Language Summary The Northern Hemisphere Westerly wind is a significant component of planetary‐scale atmospheric circulation and has a large impact on regional and global climate change. Although numerous modern observations and orbital time‐scale studies of the Westerly wind have been conducted, we still know little about its evolution on million‐year time‐scales, which may modulate the overall amplitude of short‐term variations. Eolian deposition in the North Pacific has preserved precious information about the westerlies in the past. A continuous and high resolution eolian flux record dating from 23 Ma was reconstructed from sediments at Deep Sea Drilling Project Site 296 in the Northwest Pacific. Combined with dust records at Ocean Drilling Program Site 1208 to the east, we constrain how the path and strength of the Northern Hemisphere Westerlies have changed since the early Miocene. The two eolian records indicate a northwards shift of the westerlies between 23 and 9 Ma and a relatively stable state since then. We suggest that stepwise uplift of the Tibetan Plateau since at least the early Miocene began to drive the northwards shift of the Northern Hemisphere Westerlies until about 9 Ma, after which the westerlies remained relatively stable over Asia‐North Pacific on million‐year timescales.
... Paleoceanographic studies using sediments from either side of the Isthmus of Panama indicate CAS constriction reached a critical threshold between 4.8-4 Ma (Haug and Tiedemann 1998;Steph et al. 2006;Steph et al. 2010). Similarly, the ITF constriction occurred from the Miocene (Kuhnt et al. 2004) into the Late Pliocene, and likely onward (Gallagher et al. 2009;Karas et al. 2011;Gallagher et al. 2014;Christensen et al. 2017), with increased constriction from 3-4 Ma inferred to alter Australian and African climates (e.g., Cane and Molnar 2001;De Vleeschouwer et al. 2018). Disentangling the effects of the CAS and ITF on the development of the North Pacific subtropical gyre and equatorial circulation (e.g., Kennett et al. 1985), and their likely influence on low to mid-latitude planktic foraminiferal diversity and evolution are confounding and beyond the scope of this contribution. ...
... distribution. A. trispinosa is abundant in silty sand and muddy substrate (Inoue, 1989;Rao et al., 1990;Orpin et al., 1999;Gallagher et al., 2009;Gandhi and Solai, 2010;Panchang and Nigam 2012;Natsir et al., 2012;Rao et al., 2013). Ghose (1966) discussed the significance of spines in A. trispinosa and inferred that the long slender spines helped the species to increase its buoyancy to remain suspended just above the substrate. ...
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A total of 97 surface sediment samples were collected from the continental shelf and slope of the western Bay of Bengal to assess the potential application of Asterorotalia trispinosa as a paleomonsoon proxy. The relative abundance of living as well as total (living and dead) A. trispinosa ranges from being absent to a maximum of ∼31%. The highest abundance of A. trispinosa is close to the outfall region of the Ganga-Brahmaputra Rivers and decreases away from the river mouths. Contrary to that, A. trispinosa is rare in front of both the Cauvery and Pennar river outfall regions, in the central part of the western Bay of Bengal. The living A. trispinosa abundance is the lowest in between two major river systems, viz. Ganga-Brahmaputra-Mahanadi and Krishna-Godavari. The relative abundance of both the total and living A. trispinosa is strongly positively correlated with ambient seawater temperature, and negatively correlated with %Corg and salinity. Based on the spatial distribution, we conclude that A. trispinosa is stenohaline in nature, rather than euryhaline, and further that the increased relative abundance of A. trispinosa indicates warmer and only marginally hyposaline environment. Even though the ecological preference of A. trispinosa suggests it as a potential paleomonsoon proxy, the restricted distribution implies limited application.
... Today, the relative strength of the Leeuwin Current is largely controlled by the ITF and influences warm water delivery to the Western Australian coast and toward higher latitudes (Feng et al., 2003). It is thought that constriction and shallowing of the Indonesian Gateway in the Pliocene reduced the strength of the ITF and the Leeuwin Current, thereby reducing the amount of warm equatorial Pacific water reaching the northwest coast of Australia Gallagher et al., 2009;Song et al., 2007). ...
Article
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Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio‐Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX86 and the long‐chain diol index, provide insight into past ITF variability (3.5–1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of ~5°C occurs within the mid‐Pliocene Warm Period (3.3–3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and long‐chain diol index records is a strong cooling from ~1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.
... Since the middle Miocene, it has been proximal to the western edge of the present day Indonesian Throughflow, which transports cool, low-salinity North Pacific thermocline water to the Indian Ocean. Additionally it is directly under the influence of the modern Leeuwin Current, a narrow, shallow current that transports warm, low-salinity, nutrient-deficient water southward along the west coast of Australia (Gallagher et al., 2009;Pattiaratchi & Woo, 2009), derived from water formed within the Indonesian Throughflow and the Central Indian Ocean (Domingues et al., 2007;Wijffels et al., 2002). Surface salinity estimates from nearby sites are 34.15 ...
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Across the middle Miocene, Earth's climate underwent a major cooling and expansion of the Antarctic ice sheet. However, the associated response and development of the tropical climate system is not fully understood, in part because this is influenced by both global climate and also low-latitude tectonic gateways and paleoceanography. Here we use combined δ¹⁸O and Mg/Ca of planktic foraminifera to reconstruct the thermal history and changes in hydrology from the Indo-Pacific region from 16.5 to 11.5 Ma. During the warmth of the early middle Miocene, our records indicate a dynamic ocean-atmosphere system in the Indo-Pacific region, with episodes of saltier and warmer tropical surface waters associated with high pCO2 and retreat of the Antarctic ice sheet. We show that across the Middle Miocene Climate Transition (MMCT) surface ocean temperatures in the Indo-Pacific cooled by ~2°C, synchronous with the advance of the Antarctic ice sheet. The associated cooling in the Southern Ocean appears to have started earlier and was stronger. Further, we show that western Pacific Ocean warmed and eastern tropical Indian Ocean freshened following the MMCT, likely caused by the constriction of the Indonesian Seaway and reduced connectivity between the Pacific and Indian Oceans following Antarctic glaciation. The MMCT therefore represented a key phase in the evolution of the West Pacific Warm Pool and associated tropical climate dynamics.
... The migration of Indo-Pacific species northward to Japan by the latest Pliocene (after 3 Ma) with the initiation of the modern nutrient deficient Kuroshio Current coincided with the intensification of the North Pacific Gyre caused by Northern Hemisphere ice sheet expansion (Gallagher et al., 2009). Some could reach to as far as the northern Pacific end, close to Japan as the sublittoral fauna, from off Sendai, with warm 'Kuroshio currents' (Matoba 1976). ...
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Comparative morphology of the benthic foraminiferal fauna from the east coast of India and the southern part of the east coast of Japan have been discussed in the light of the view that the biogeographic connectivity was lost between the Pacific and Indian Oceans between a period from 10 to 4.4 Ma, due to the restriction of the Indonesian Through flow (caused due to collision of Australia and Southeast Asia). An overview on the intraspecific variations in the 41 Indo-Pacific benthic foraminiferal species of Recent foraminifera (out of the 122 common reported species) from the east coast of India and the southern part of the east coast of Japan has been presented together with the foramgeographical affinity between the regions, located in the two fairly distal ends of the warm-water Indo-Pacific province.
... The Northwest margin of Australia is strongly influenced by shallow (50e300 m) currents that originate in the West Pacific Warm Pool (Fig. 1e, Gallagher et al., 2009;2017). Regional oceanography from 5 S to 15 S is dominated by the South Equatorial Current (Collins, 2002). ...
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The bathyal Ocean Drilling Program Site 765 at 5725 m water depth, offshore northwest Australia at 16°S is directly under the influence of the Australian monsoon during the Austral summer and is the recipient of continental dust during the Austral winter. It is downstream of the Indonesian Throughflow, which is a major arm of the global thermohaline circulation. As such it is ideally situated to record the climate and oceanic consequences of Quaternary climate variability. Despite being over 400 km from northwest Australia, palynomorphs (pollen and spores) are relatively common in this section, sourced via aeolian (during the dry winter) and benthic transportation processes and sediment plumes (during the summer monsoon). Detailed palynological analyses of this flora in the upper part of this core reveals intermittent snap shots of environmental and climate change over the last 300 kyrs. Interglacial stages are interpreted to be characterised by palynomorph-rich turbidite and calcareous ooze deposition whereas palynomorph-poor slowly accumulating siliceous oozes (deposited below the Calcium Carbonate Compensation Depth) are present during glacials. The dominance of Poaceae sourced from the Australian mainland in interglacial periods suggests that vegetation during these periods was similar to today. Interglacial palynofloral assemblages suggest a more intense wet season (Australian monsoon) with higher rainfall that allowed more active erosion and deposition onto the shelf. The presence of Indonesian sourced pollen and fern spore taxa, as well as warm water dinoflagellate species suggest enhanced Leeuwin Current and monsoonal intensity during interglacials times. The youngest part of the core is dominated by siliceous ooze, likely deposited during the Last Glacial Maximum and the early Holocene. The lack of calcareous ooze near the top of the core is likely caused by Holocene to Recent erosive processes or core disturbance. The presence of common charcoal in all samples over the last 300 kyrs shows that fire was a constant feature of the landscape in northwest Australia prior to human occupation of the region 65,000 years ago.
... This resulted in a sub-surface cooling (4 • C) of the eastern Indian Ocean due to the switching of the ITF source water from the southern Pacific to the Northern Pacific. This cooling also affected the strength of the ITF sourced currents and associated low latitude climatic changes (Christensen et al., 2017;De Vleeschouwer et al., 2019;Gallagher et al., 2009;Smith et al., 2020). ...
Article
Understanding the response of the South Asian Summer Monsoon (SASM) to high atmospheric pCO2 is required to predict future SASM changes under the current global warming scenario. The mid-Piacenzian Warm Period (mPWP), 3.0 to 3.3 Ma (million years ago) during the late Pliocene, provides us with such an opportunity as it had atmospheric pCO2 comparable to the present. To reconstruct SASM variability during this period, we studied multiple proxies of terrigenous input (Ti), clasticity (Ti/Ca), chemical weathering (K/Al, Mg/Al), and productivity (Ba/Al, Caexcess) in sediment collected during IODP Expedition 355 (Site U1456) spanning the mid to late Piacenzian (3.3–2.6 Ma). We find that the SASM intensified (weakened) during interglacials (glacials) of the mPWP and beyond in close correspondence with the global climate. However, we note that the SASM shifted to a higher mean state at 2.95 Ma. It could be because of the tectonically induced reorganization of the Indonesian Throughflow (ITF), which enhanced the cross-equatorial pressure gradient by changing the source of water to the southern equatorial Indian Ocean. This enhanced pressure gradient resulted in the intensification of the SASM during the late Piacenzian. During the northern hemisphere glaciation after 2.95 Ma, the SASM shows a long-term decline over and above the glacial-interglacial variability. The spectral and wavelet transform analysis indicates the control of the earth's orbital parameters, especially eccentricity, over the SASM variations during the late Piacenzian.
... Higher interglacial LC activity after the MPT is further supported by evidence from benthic foraminifer assemblages (Gallagher et al., 2009) and contemporary La Niña like conditions in the equatorial Pacific (e.g., McClymont and Rosell-Mel e, 2005), which are known to cause strong LC activity (Feng et al., 2009;Furnas, 2007;He et al., 2021;Wijffels et al., 2008). ...
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The Middle Pleistocene Transition (MPT) represents a major change in Earth's climate state, exemplified by the switch from obliquity-dominated to ∼100-kyr glacial/interglacial cycles. To date, the causes of this significant change in Earth's climatic response to orbital forcing are not fully understood. Nonetheless, this transition represents an intrinsic shift in Earth's response to orbital forcing, without fundamental changes in the astronomical rhythms. This study presents new high-resolution records of International Ocean Discovery Program (IODP) Site U1460 (eastern Indian Ocean, 27°S), including shallow marine productivity and organic matter flux reconstructions. The proxy series covers the interval between 1.1 and 0.6 Ma and provides insights into Pleistocene Leeuwin Current dynamics along the West Australian shelf. The large >45 m global sea level drop during the marine isotope stage (MIS) 22–24 is marked in our data, suggesting that the MPT led to large-scale changes in Indian Ocean circulation patterns and surface water conditions. We consider shelf exposure (and thus the “Sahul-Indian Ocean Bjerknes mechanism”) as a possible key process to increase the upwelling of nutrient-rich sub-Antarctic Mode waters through the Leeuwin Undercurrent along the Australian shelf. We conclude that the shoaling of nutrient-rich lower-thermocline waters enhanced mid-latitude productivity patterns in the eastern Indian Ocean across the 900-ka event.
... Pseudorotalia spp. have been reported to be typical warm member of the Indo-Pacific shelf assemblage in tropical water characterized by coarse substrate and being less sensitive to water depth (Murray, 1991;Gallagher et al., 2009;Minhat et al., 2016). Ammonia spp., such as Ammonia beccarii, is a shallow infaunal and low salinity tolerant species occurring in the inner-middle shelf. ...
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The Miocene epoch marks the most crucial period during the Cenozoic cooling trend, characterized by the Middle Miocene Climatic Optimum (MMCO) and a series of short–lived cooling events (Miocene isotope events). To understand the paleoenvironmental evolution along the shallow water shelf in the South China Sea during the Miocene, the benthic foraminiferal assemblage and total organic carbon content (TOC) were analyzed at Hole LF 14 located in the Lufeng Sag, northern South China Sea. Three benthic foraminiferal assemblages (e.g., the Uvigerina spp. assemblage, the Cibicides spp. assemblage, and the Cibicidoides spp. assemblage), corresponding to different watermass conditions, were recognized based on Q–mode factor analysis. Early studies suggested that Hole LF14 was deposited under semienclosed bay, middle to outer shelf or even upper bathyal environment during ~18.7–4.53 Ma. The dominant Uvigerina spp. assemblage was characterized by low diversity and shallow infaunal to infaunal species, indicating a warm, low–oxygenation and eutrophic conditions since the Early Miocene to MMCO (~18.7–14.24 Ma). An abrupt sea level drop and significant faunal changes were recorded during 14.24–13.41 Ma, suggesting development of the East Antarctic Ice Sheets, which resulted in a drop of sea level and change in benthic foraminiferal assemblages along the shallow water shelf. Beyond the Uvigerina spp. assemblage, the Cibicides spp. assemblage became important during the middle–late Middle Miocene (14.24–11.54 Ma). This assemblage was dominated by epifaunal species with relative high diversity, suggesting high–energy, high–oxygenation and oligotrophic conditions with episodic supply of organic food. The dominant Cibicidoides spp. assemblage with high diversity, indicates a mesotrophic conditions with relative high–oxygen content during the Late Miocene to Pliocene (11.54–4.53 Ma). The appearance and continuous occurrence of Ammonia spp. and Pseudorotalia spp. since 10.02 Ma, may reflect the influence of the Kuroshio Current.
... Planktic foraminiferal diversity (Lam & Leckie, 2020a) and assemblage data (Kennett et al., 1985) indicate that the KCE has been present in the northwest Pacific through much of the late Neogene. Studies that have investigated the paleobiogeography of neritic benthic foraminifera indicate the KC likely reached its present northern extent by the latest Pliocene at ∼3.0 Ma (Gallagher et al., 2009(Gallagher et al., , 2015, after mid-Pliocene warmth. At this time, molluscan data indicate that the current underwent an intensification (Tsuchi, 1997), possibly related to final closure of the Central American Seaway (CAS) and initiation of Northern Hemisphere glaciation (NHG) (Maier-Reimer et al., 1990). ...
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The Kuroshio Current Extension (KCE) is the major western boundary current of the North Pacific Subtropical Gyre. To better understand how the KCE behaved under elevated CO2 conditions and how it came into its modern configuration, we use stable isotopic analyses from mixed‐layer planktic foraminifera from three Ocean Drilling Program sites that lie to the north, underneath of, and south of the present day KCE. Our data support previous hypotheses suggesting that the KCE played a significant role in delivering moisture to the high latitudes and contributed to extensive ice growth. Samples span from 5 to 2.5 Ma and cover three tectonic and climate events. In response to constriction of the Central American Seaway, the KCE region warmed then cooled, with a potential equatorward shift of the current and intensification of the North Pacific Subtropical Gyre. During the mid‐Piacenzian Warm Period, we define the mid‐Piacenzian 1 and 2 events, which were times when the KCE warmed and subsequently developed a strong temperature/salinity gradient between the two northernmost sites. Northern Hemisphere ice growth at ∼2.9 Ma brought the KCE into its modern‐day configuration. Paradoxically, the southernmost Hole 1209A appears coolest through the study interval. This paradox is resolved by invoking seasonal preferences of the species analyzed, a finding that highlights the need to consider seasonal and ecological preferences of plankton when interpreting geochemical records in midlatitude regions. We propose several hypotheses for drivers of KCE behavior that require further testing using higher‐resolution proxy data tied to additional regional and global records.
... Cane & Molnar (2001) suggested that closure of Indonesian seaway around 3-4 Ma is responsible for this event. The constriction of Indonesian Throughflow (ITF) instigated from the Miocene (Kuhnt et al., 2004) and continued up to the late Pliocene and likely onward (Gallagher et al., 2009;Karas et al., 2011;Gallagher et al., 2014;Christensen et al., 2017). In the central Indian Ocean between 3.5 and 2.95 Ma, sea surface conditions remained stable, whereas, subsurface waters cooled (Karas et al., 2009(Karas et al., , 2011 and that was associated with the ongoing ITF constriction (Christensen et al., 2017). ...
Article
Thirty-two planktonic foraminiferal taxa have been identified based on Bright Field microscopic study as well as Scanning Electron Microscopy on the samples collected from the outcrop adjacent to the type section of Neill West Coast Formation at Neil Island of Ritchie's Archipelago, northern Indian Ocean. The planktonic foraminiferal taxa belong to ten genera viz., Dentoglobigerina, Globigerina, Globigerinoides, Globoconella, Globorotalia, Globorotaloides, Globoturborotalita, Neogloboquadrina, Orbulina, and Trilobatus. A number of statistical analyses have been done in addition to taxonomic study to interpret the palaeocenographic scenario. We performed PCA analysis on the foraminiferal content of the samples to test the relatedness. Two biozones have been established by Stratigraphically Constrained Cluster Analysis (CONISS). We used SHEBI (SHE analysis for biozone identification) analysis to precisely demarcate seven biozones. Attempts have been made to decipher the Plio–Pleistocene boundary in the Neill West Coast Formation based on specific zonal markers. The presence of some taxa (e.g., Globoconella inflata, Globigerina bulloides, and Neogloboquadrina pachyderma) indicates the initiation of a cooling event from late Pliocene onwards. An event of ocean upwelling also has been identified based on the presence of Globigerina bulloides, Neogloboquadrina pachyderma, and N. dutertrei from the late Pliocene to early Pleistocene of the northern Indian Ocean that also correlates with palaeoceanographic records known from other upwelling regions.
... Later, during the late Miocene, due to the continuous collision of Australia and Southeast Asia, the gateway was further restricted, enabling the exchange of upper bathyal water or shallow sea water at ∼6 Ma (Gaina & Müller, 2007;Kuhnt et al., 2004). The progressive constriction was also revealed by changes in foraminiferal assemblages and oxygen and carbon isotope records for the late Middle Miocene-late Miocene (Gallagher et al., 2009;Nathan & Leckie, 2009). Therefore, we assigned a maximum depth of ∼1,200 m to the Indonesian Gateway at ∼14 Ma and a maximum depth of ∼500 m at ∼6 Ma. ...
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During the Miocene, major global cooling occurred during two intervals: the middle Miocene (∼14–13 Ma) and the late Miocene (∼7‐6 Ma). The Antarctic Ice Sheet expanded substantially at ∼14–13 Ma, and glaciation in the Northern Hemisphere was initiated at ∼7–6 Ma. Although the causes of these two global cooling events remain unclear, paleoclimate modeling provides an important approach for investigating the mechanisms. However, paleoclimate modeling relies on paleogeographic boundary conditions, and many uncertainties remain regarding the land–sea distribution, topography, and bathymetry of the Miocene; specifically, previous published paleogeographic reconstructions for the middle and late Miocene show several discrepancies with each other. Here, we present two new sets of global topographic and bathymetric boundary conditions for the middle Miocene (∼14 Ma) and late Miocene (∼6 Ma). Our new reconstructions use a published plate kinematics model, oceanic lithospheric paleo‐ages, and oceanic sediment thicknesses and incorporate global fossil records, stratigraphy, lithofacies, paleoenvironment, and paleoelevation data. With these data, we further constrain the conditions of several important intercontinental and marginal seas surrounding Eurasia and the Arctic, the depth of major seaways in tropical latitudes and middle‐high latitudes of the Northern Hemisphere, and global paleotopography, especially that of the Tibetan Plateau and the Andes.
... Ces exemples soulignent le rôle important du MC dans la dynamique climatique de la région Indo-Pacifique et permettent de mieux comprendre le lien entre paléogéographie du Continent Maritime et climat. [Gallagher et al., 2009]. Les flèches noires représentent les principaux courants marins. ...
Thesis
En défléchissant la Terre, la topographie dynamique module l'extension des zones inondées dans les régions où l'altitude est proche du niveau marin. Ce phénomène contribue ainsi à modifier la paléogéographie à grande échelle et ont un impact sur les sphères externes (atmo-, hydro- et bio-sphère) en altérant notamment les circulations atmosphériques et océaniques. Ces travaux de thèse, qui s’appuient sur une approche interdisciplinaire, illustrent la chaîne de connections entre dynamique mantellique et climat à travers l'étude de l'évolution Quaternaire du Continent Maritime. Le caractère insulaire de la région et la présence de mers peu profondes comme la mer de Java, permettent des modifications rapides de la répartition terre-océan à grande échelle, et en font un cas idéal pour étudier les connections entre géodynamique et climat. D’autre part, la dynamique mantellique, excitée par les nombreuses subductions, y est très active et contribue à déformer la surface et la dynamique climatique régionale est étroitement associée à la géographie particulière de l’archipel Indonésien.Les changements paléogéographiques sont d'abord révélés par la cartographie des morphologies côtières. Celle-ci souligne la répartition contrastée de la déformation Quaternaire en soulignant le soulèvement général de la région centrale (Wallacea), alors que les deux plateformes continentales localisées à l'Ouest et au Sud-Est subsident. L'utilisation combinée des observations et de la modélisation de la croissance des récifs coralliens est utilisée afin de quantifier la vitesse verticale de déformation. Notre méthode est basée sur la comparaison entre la morphologie des récifs observés sur la plateforme de la Sonde, à l'ouest de l'Asie du Sud-Est, et les morphologies récifales issues des simulations numériques et permet une quantification inédite de la vitesse de subsidence de la plateforme. Les résultats suggèrent que la Sonde était émergée de manière permanente avant 400 000 ans, formant une masse continentale entre les îles de l'Ouest Indonésien et le continent asiatique. Les causes de ces changements paléogéographiques sont appréhendées à l'aide de la modélisation mécanique de la géodynamique. Un modèle numérique en trois dimensions d'une zone de subduction a été utilisé afin de d'explorer les causes dynamiques de la déformation. L'analyse des simulations permet de décrire l'évolution spatio-temporelle de la déformation à l'aplomb d'une zone de subduction, lors d'une perturbation provoquée par l'arrivée dans la fosse d'un bloc continental ou d'un plateau océanique, un cas simplifié similaire à l'Asie du Sud-Est. Les résultats montrent que lors d'un épisode de collision, l'initiation d'une déchirure dans la plaque en subduction générée par l'entrée dans la fosse de matériel peu dense entraîne une modification de l'écoulement mantellique. Cette modification provoque un épisode de subsidence dynamique qui fait suite à un épisode de surrection provoquée par la collision. Les vitesses de déformations calculées ont un ordre de grandeur comparable aux vitesses de déformations enregistrées et modélisées à l'échelle régionale. Les conséquences des changements paléogéographiques sont appréhendées à l'aide d'un modèle du climat IPSL-CM5A2. Les résultats montrent que la présence d'une plateforme de la Sonde émergée provoque une augmentation saisonnière des précipitations sur le Continent Maritime. Cette augmentation est engendrée par une intensification de la convergence à l'échelle régionale contrôlée par le chauffage radiatif des surfaces continentales exposées. L'exposition de la plateforme de la Sonde engendre également une modification du transport dans le détroit de Makassar avec un impact local sur la salinité et les températures de surface de l'océan. Nos analyses montrent par ailleurs que l'augmentation de la saisonnalité des précipitations est indépendante de la paramétrisation de la convection et des nuages dans le modèle.
... Water circulation along the Rowley Shelf is influenced by shallow currents that originate in the West Pacific Warm Pool, including the shallow (i.e., <300 m deep) and warm, low salinity Leeuwin Current, which carries warm waters southward along the coast of Western Australia and suppresses coastal upwellings (Gallagher et al., 2018;Haller et al., 2018;Hatcher et al., 1991;Holloway, 1995;James et al., 2004;Stephen et al., 2009). Water circulation is also influenced by tide, with the tidal range reaching up to 6 m along the coast and generating strong tide-induced currents in the cross-shelf direction, which in turn generate internal tides (Condie and Andrewartha, 2008;Holloway, 2001;Katsumata, 2006). ...
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Palaeoshorelines and associated palaeo-coastal features are studied to reconstruct past sea level, climate, and depositional environments. Their identification typically depends on direct field observations and is therefore challenging in marine environment, where the interpretation mostly relies on sparse geophysical data. This review presents, based on 118 published case studies, a summary of morphological evidences that can be used to identify submerged relict coastal features worldwide, using only geophysical data. Four coastal feature categories that can be used as palaeoshoreline indicators were identified: (1) beach ridges of wind and wave origin; (2) shoreface strata; (3) marine terraces; and (4) coral-reef terraces. In light of this proposed classification, an area of ~200,000 km² was investigated along the Rowley Shelf (North West Shelf, Australia), a carbonate-dominated platform, based on the integration of high-resolution bathymetry (i.e., seismic-derived bathymetry, satellite-derived bathymetry, multibeam echosounder bathymetry, spot depth soundings) and 2D reflection seismic lines. Relict features were discriminated from modern bedforms using five criteria: (1) stratigraphic position; (2) emersion features; (3) similarity with modern and published analogues; (4) integration of modern ocean conditions; and (5) evidence of early cementation. In total, over 500 submerged relict coastal features were identified, making this review the most comprehensive catalogue published to date. Relict features are concentrated over specific depths, referred to as modal sea-level depths (MSLDs), which correspond to depths where the relative sea level remained stable over long periods of time. Nine MSLDs are observed at 20, 35, 50, 60, 70, 80, 90, 105 and 125 m below sea level. Each MSLD is the result of the accumulation of coastal features through multiple glacial/ interglacial cycles. Most of the features may nevertheless be related to the last glacial sea-level fall and were likely formed between Marine Isotopes Stages (MIS) 5 and 2. The analysis of the submerged coastal features indicates that the overall shelf morphology is controlled by the repartition of these features, and that, while in a carbonate province, their formation is related to wind, tide, fluvial and wave processes. The higher concentration of fluvial relict features at shallower depths and of tide-influenced relict features at greater depths suggest that fluvial runoffs were limited during glacial periods. This, in turn, supports the hypothesis of a prevalent dry climate during glacial periods and in contrast, of a humid climate during interglacial periods. Finally, the study reveals that most of modern coral reefs of the Rowley Shelf are growing on top of relict coastal features and that seabed ridges previously interpreted as drowned coral reefs are, in fact, likely to be relict coastal features formed through clastic processes. Results from this study will support the identification of submerged palaeoshorelines on continental shelves around the globe and highlight the influence of associated relict coastal features on shelf morphologies. Additionally, this study provides new insights on processes shaping carbonate provinces.
... The sea is connected to the East China Sea through the Tsushima Strait (< 140 m), to the Pacific Ocean via the Tsugaru Strait (< 130 m), and to the Okhotsk Sea through the Soya (< 55 m) and Mamiya (< 12 m) Straits ( Figure 1). The modern surface water of the Japan Sea is strongly influenced by the TWC, an offshoot of the Kuroshio Current ( Figure 1; Gallagher et al., 2009Gallagher et al., , 2015. The warm saline Kuroshio Current mixes with the less saline nutrient-rich East China Sea Coastal Water (ECSCW) south of Japan (Figure 1; Qiu, 2001;Usami et al., 2013) before flowing into the Japan Sea via the Tsushima Strait as the TWC (Figure 1). ...
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The Japan Sea is directly influenced by the Asian monsoon, a system that transports moisture and heat across southeast Asia during the boreal summer, and is a major driver of the Earth's ocean-atmospheric circulation. Foraminiferal and facies analyses of a 460-kyr record from Integrated Ocean Drilling Program Expedition 346 Site U1427 in the Japan Sea reveal a record of nutrient flux and oxygenation that varied due to sea level and East Asian monsoon intensity. The East Asian summer monsoon (EASM) was most intense during marine isotope stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c when the Tsushima Warm Current flowed into an unrestricted well-mixed normal salinity Japan Sea, whereas East Asian winter monsoon (EAWM) conditions dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level minima restricted the Japan Sea resulting in low-salinity and oxygen conditions in the absence of Tsushima flow. Reduced oxygen stratified, low-salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI when East China Sea coastal waters breached the Tsushima Strait. Chinese loess, cave, and Lake Biwa (Japan) and U1427 proxy records suggest EASM intensification during low to high insolation transitions, whereas the strongest EAWM prevailed during lowest insolation periods or high to low insolation transitions. Ice sheet/CO2 forcing leads to the strongest EAWM events in glacials and enhanced EASM in interglacials. Mismatches between proxy patterns suggest that latitudinal and land/sea thermal contrasts played a role in East Asian monsoon variability, suggesting that a complex interplay between ice sheet dynamics, insolation, and thermal gradients controls monsoonal intensity.
... In modern Western Australia, the south-flowing Leeuwin current allows the growth of coral reefs at latitudes as far south as 32 °S (Hatcher, 1991). A primitive form of this current, known as the proto-Leeuwin current, may have flowed along the western margin of Australia during the Miocene (Feary and James, 1995;McGowran et al., 1997;O'Connell et al., 2012), although the southward flow of the modern Leeuwin current only started during the Pliocene (Gallagher et al., 2009(Gallagher et al., , 2014De Vleeschouwer et al., 2018). Proximal shallow-water carbonate production along the modern Western Australian margin is low overall, possibly because of fluctuations in water quality by saline downwelling coming from marginal lagoon (e.g., Shark Bay) or by influx of siliciclastic sediments (Dix, 1989;Dix et al., 2005). ...
Thesis
Miocene evolution of one of the world's largest carbonate systems on Australia's NW Shelf is investigated here through an integrated outcrop, sample, petrographic and seismic study. Early Miocene foraminiferal deposits formed a ramp despite palaeoenvironmental analysis suggesting accumulation in warm waters. Coral-rich, lagoonal facies, dated through foraminiferal biostratigraphy, are present in Middle Miocene strata post-dating the Miocene Climatic Optimum. The switch from a ramp to rimmed platform and the development of a >2,000 km long reef province may have been influenced by eustatic variations, increased tectonic activity associated with Australia-SE Asia collision, oceanic current reorganisation and climate change.
Article
The Indonesian Throughflow (ITF) is the unique low-latitude connector between the Pacific and Indian oceans. During the Plio–Pleistocene, the ITF may have played a significant role in the global climate associated with the tectonic constriction of the Indonesian gateway, which was possibly one of the factors spurring the Northern Hemisphere glaciation. Persistent constriction of the gateway would have restricted the ITF intermediate water (ITF-IW) with a high priority over the ITF upper waters. Due to limited availability of sediment archives, however, no investigations have been carried out on the Plio–Pleistocene evolution of the ITF-IW. In this study, we present our work on a total of 1368 sediment samples spanning the past ∼3.17–1.07 Ma from Site U1482, which was drilled during the International Ocean Discovery Program Expedition 363 in the Timor Passage, the main exit of the ITF to the Indian Ocean. Site U1482 is bathed by the ITF-IW, the evolution of which could thus be monitored by benthic foraminiferal shells preserved in the sediments of the site. Based on establishment of the first high-resolution (∼1.53 kyr) Plio–Pleistocene benthic δ¹⁸O stratigraphy within the ITF region, we recognized that, superimposed over the prominent 41-kyr glacial–interglacial cycles, the long-term change of Site U1482 benthic δ¹⁸O was punctuated at ∼2.51–2.43 Ma (Marine oxygen isotope stage (MIS)100/99–96/95) and at ∼1.6 Ma (MIS 56/55), followed by an interval of decreased glacial–interglacial amplitudes in the duration of ∼1.6–1.2 Ma. We propose that Site U1482 benthic δ¹⁸O was mainly driven by the global ice-sheet growth prior to ∼1.6 Ma, in addition to possibly influenced by the tectonic constriction of the Indonesian gateway. In contrast, the decreased glacial–interglacial amplitudes in the benthic δ¹⁸O during the interval of ∼1.6–1.2 Ma more likely indicate the regional signal carried by the ITF-IW, which is attributed to a freshening of the ITF surface waters that was subsequently transmitted to the intermediate depths via vertical mixing in the Banda Sea, caused by enhanced regional precipitation related to monsoonal and western Pacific warm pool conditions.
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Inorganic precipitation of aragonite is a common process within tropical carbonate environments. Across the Northwest Shelf of Australia (NWS) such precipitates were abundant in the late Pleistocene, whereas present-day sedimentation is dominated by calcitic bioclasts. This study presents sedimentological and geochemical analyses of core data retrieved from the upper 13 meters of IODP Site U1461 that provide a high-resolution sedimentary record of the last ~15 thousand years. Sediments that formed from 15 to 10.1 ka BP are aragonitic and characterised by small needles (<5 µm) and ooids. XRF elemental proxy data indicate that these sediments developed under arid conditions in which high marine alkalinity favoured carbonate precipitation. A pronounced change of XRF-proxy values around 10.1 ka BP indicates a transition to a more humid climate and elevated fluvial runoff. This climatic change coincides with a shelf-wide cessation of inorganic aragonite production and a switch to carbonate sedimentation dominated by skeletal calcite. High ocean water alkalinity due to an arid climate and low fluvial runoff therefore seems to be a prerequisite for the formation of shallow water aragonite-rich sediments on the NWS. These conditions are not necessarily synchronous to interglacial periods, but are linked to the regional hydrological cycle.
Article
Meridional heat transport of the western Pacific boundary current (the Kuroshio Current) is one of the key factors in global climate change. This current is important because it controls the temperature gradient between low latitudes and the North Pacific and so significantly influences mid-latitude atmosphere-ocean interactions. Here we reconstruct changes in hydrological conditions within the mid-latitude mainstream of the Kuroshio Current based on faunal analysis of planktonic foraminifera in core DSDP 296 from the Northwest Pacific Ocean. This approach enabled us to deduce evolutionary processes within the Kuroshio Current since the Pliocene. A total of 57 species in the coarser section (>150 µim) were identified; results indicate that planktonic foraminiferal faunal evolution has mainly been characterized by three major stages, the first of which comprised mixed-layer warm-water species of Globigerinoides ruber which first appeared between 3.5 and 2.7 Ma and then gradually increased in content. Percentages of another warm-water species of G. conglobatus also gradually increased in number over this interval. Variations in warm-water species indicate a gradual rise in sea surface temperature (SST) and imply initiation of Kuroshio Current impact on the Northwest Pacific Ocean since at least 3.5 Ma. Secondly, over the period between 2.7 and 2.0 Ma, thermocline species of Globigerina calida, Neogloboquadrina humersa, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata started to appear in the section. This fauna was dominated by G. ruber as well as increasing G. conglobatus contents. These features imply a further rise in SST and its gradually enhanced influence on thermocline water, suggesting strengthening of the Kuroshio Current since 2.7 Ma. Thirdly, between 2.0 Ma and present, increasing contents of thermocline species (i.e., G. calida, N. dutertrei and P. obliquiloculata) indicate a gradual rise in seawater temperature at this depth and also imply more intensive Kuroshio Current during this period. On the basis of comparative records from cores ODP 806 and DSDP 292 from the low latitude Western Pacific, we propose that initiation of the impact of the Kuroshio Current in the Northwest Pacific and it subsequent stepwise intensifications since 3.5 Ma can be closely related to the closure and restriction of the Indonesian and Central American seaways as well as variations in the Western Pacific Warm Pool (WPWP) and equatorial Pacific region.
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Phytoclasts in the form of plant debris in terrestrial sediments can be transported by water to distant areas because they are lighter than inorganic particles. The semi-enclosed East Sea, which is connected by narrow straits to other seas, is adjacent to continental shelves that are the source area of terrestrial sediment flowing into the East Sea. These shelves alternated repeatedly between terrestrial and marine environments as a result of eustatic sea-level changes during the Late Quaternary. Palynofacies analyses of the IODP Exp. 346 U1430 core, located in the Eastern South Korea Plateau (ESKP) of the East Sea, have revealed changes in the size and concentration of phytoclasts associated with glacial–interglacial cycles. These changes are generally negatively correlated with the global sea-level curve, and their anti-phase cycles with high amplitude are clearly evident during the last ca. 750 ka with the geotectonic stabilization period. In particular, several coarse-grained phytoclasts were observed during the glacial period, including the Last Glacial Maximum (LGM). These findings suggest that the concentration and size of phytoclasts flowing into the East Sea were influenced by changes in the distance of the source area, depending on the water depth of the strait and nearby shelves owing to sea-level changes in tandem with glacial–interglacial cycles and geotectonic events.
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We collected a suite of core top samples during R/V Sonne Cruise SO257 in May 2017 along the southwestern front of the Indo‐Pacific Warm Pool (IPWP) to monitor the variability of Southern Hemisphere tropical and subtropical sea surface hydrology and to assess temperature and salinity reconstructions with data sets reflecting conditions in the post‐monsoonal season. In our core top samples, a steep increase in planktic δ¹⁸O, associated with a decrease in sea surface temperature (SST), indicates that the southwestern front of the IPWP is located between 23° and 24°S during austral fall. We additionally reconstructed SST, sea surface salinity ,and δ¹⁸O seawater (δ¹⁸Osw) over the last 450 kyr in two sediment successions located within and beyond the monsoonal rain belt. Our records show that SST was highly coherent and phase‐locked with atmospheric pCO2 during the last 450 kyr. The regional differences in the δ¹⁸Osw records reveal that the Western Australian Margin north of 15°S remained seasonally under the influence of IPWP water masses, even during glacials. The temporal variability in upper ocean hydrology along the Western Australian Margin is not directly coupled to local monsoonal precipitation, but is strongly affected by advective mixing of Indonesian Throughflow derived water masses.
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The East China Sea (ECS) seasonally receives a high organic input due to the terrestrial organic matter influx, which is controlled by the East Asian Summer Monsoon (EASM), and the increased productivity driven by upwelling of the subsurface Kuroshio Current (KC). Changes in benthic foraminiferal assemblage composition in combination with paleoceanographic proxy data (CaCO3 (%), TOC (%), δ¹³Cpf, and δ¹⁸Obf) are used to reconstruct bottom water oxygenation and organic export flux variability over the last 400 kyr in the ECS. Multivariate analyses of benthic foraminiferal census data identified six biofacies characteristic of varying environmental conditions. These results suggest that enhanced EASM precipitation and KC upwelling directly influenced organic export flux and bottom water oxygen content in the ECS. The ECS bottom water was suboxic during Marine Isotope Stage (MIS) 11 to 8; suboxic to dysoxic between MIS 7 and 6, strongly dysoxic between mid‐MIS 5 and 4, and exhibited high variability between MIS 3 and 1. Spectral analysis of relative abundances of representative genera Quinqueloculina (oxic), Bulimina (suboxic), and Globobulimina (dysoxic) reveals a robust 23 kyr signal, which we attribute to precessionally‐paced changes in surface productivity and bottom water oxygenation related to KC variability over the past 400 kyr.
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During the late Miocene, global cooling occurred alongside the establishment of near-modern terrestrial and marine ecosystems. Significant (3 to 5 °C) sea surface cooling from 7.5 to 5.5 Ma is recorded by proxies at mid to high latitudes, yet the magnitude of tropical cooling and the role of atmospheric carbon dioxide (pCO2) in driving this trend are debated. Here, we present a new orbital-resolution sea surface temperature (SST) record spanning the late Miocene to earliest Pliocene (9 to 5 Ma) from the eastern equatorial Indian Ocean (International Ocean Discovery Program Site U1443) based on Mg/Ca ratios measured in tests of the planktic foraminifer Trilobatus trilobus. Our SST record reveals a 3.2 °C decrease from 7.4 to 5.8 Ma, significantly increasing previous estimates of late Miocene tropical cooling. Analysis of orbital-scale variability shows that before the onset of cooling, SST variations were dominated by precession-band (19-23 kyr) variability, whereas tropical temperature became highly sensitive to obliquity (41 kyr) after 7.5 Ma, suggesting an increase in high latitude forcing. We compare a revised global SST database with new paleoclimate model simulations and show that a pCO2 decrease from 560 ppm to 300 ppm, in the range suggested by pCO2 proxy records, could explain most of the late Miocene sea surface cooling observed at Site U1443. Estimation of meridional sea surface temperature gradients using our new Site U1443 record as representative of tropical SST evolution reveals a much more modest increase over the late Miocene than previously suggested, in agreement with modelled gradients.
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During the late Miocene, global cooling occurred alongside the establishment of near-modern terrestrial and marine ecosystems. Significant (3 to 5 °C) sea surface cooling from 7.5 to 5.5 Ma is recorded by proxies at mid to high latitudes, yet the magnitude of tropical cooling and the role of atmospheric carbon dioxide (pCO2) in driving this trend are debated. Here, we present a new orbital-resolution sea surface temperature (SST) record spanning the late Miocene to earliest Pliocene (9 to 5 Ma) from the eastern equatorial Indian Ocean (International Ocean Discovery Program Site U1443) based on Mg/Ca ratios measured in tests of the planktic foraminifer Trilobatus trilobus. Our SST record reveals a 3.2 °C decrease from 7.4 to 5.8 Ma, significantly increasing previous estimates of late Miocene tropical cooling. Analysis of orbital-scale variability shows that before the onset of cooling, SST variations were dominated by precession-band (19-23 kyr) variability, whereas tropical temperature became highly sensitive to obliquity (41 kyr) after 7.5 Ma, suggesting an increase in high latitude forcing. We compare a revised global SST database with new paleoclimate model simulations and show that a pCO2 decrease from 560 ppm to 300 ppm, in the range suggested by pCO2 proxy records, could explain most of the late Miocene sea surface cooling observed at Site U1443. Estimation of meridional sea surface temperature gradients using our new Site U1443 record as representative of tropical SST evolution reveals a much more modest increase over the late Miocene than previously suggested, in agreement with modelled gradients.
Article
The Kuroshio Current (KC) is the biggest western boundary current in the northwest Pacific Ocean and plays an essential role in the Cenozoic climate evolution and ocean circulation changes. Paleoceanography of the Shikoku Basin, located downstream of the KC region, is sensitive to the evolution of the KC. In this study, the Miocene hemipelagic sediment supply in the Shikoku Basin has been investigated on sediments from lithologic Unit III of IODP Site C0011 using a combination of rock magnetism, Sr isotope composition, grain size analysis, and calcareous nannofossil study. Integrated results reveal that multidomain (MD) (titano-) magnetite concentration increases in the upper part of Unit III since ~10–11 Ma with elevated ⁸⁷Sr/⁸⁶Sr values (0.712–0.714) and fining up sediment grain size. Magnetic parameters, Sr isotope composition, and grain size, as reliable indicators of sediment sources, have been used to discriminate the geological sources of the sediments and attribute the increase in MD (titano-) magnetite concentration to the increasing detrital input from the East China Sea (ECS), which is rich in fine-grained particles and coarse-grained magnetite and have high ⁸⁷Sr/⁸⁶Sr ratio (0.712–0.727). Furthermore, the intensified western boundary current later became known as the KC is interpreted as a plausible reason for increasing fine-grained flux from the ECS. Our study provides a much earlier record of the KC at ~10–11 Ma, giving new insight into understanding the Cenozoic ocean circulation changes and climate evolution in the northwest Pacific Ocean.
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The distribution of modern benthic foraminifera is studied from offshore mixed carbonate-siliciclastic settings of Brunei Darussalam located in northwestern Borneo (South China Sea). The sediments were collected from 17 sites (i.e., shallow reefs, sunken wrecks, and two depth transects). A total of 231 species were identified from 8 to 63 m water depth. We conducted several analyses to understand the patterns of faunal composition, including: (1) Cluster analysis and Principal Component Analysis together with correlation to define relation among the sites; (2) Diversity indices, such as Shannon Index and Fisher's Alpha Index to assess diversity patterns at sites; and (3) Foram Index (FI) to determine whether the water quality indicates conditions that support reef growth. The most abundant foraminiferal groups from the reef and most wreck samples are larger benthic foraminifera (LBF), especially Calcarinidae and Amphisteginidae, whereas in the muddier sites the most abundant are smaller benthic foraminifera (SBF) with the genera Pseudorotalia and Asterorotalia. Certain species from the groups have shown patterns that do or do not correlate with depth and clay content.
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Late Miocene to Pliocene sediments from the NW Australian shelf provide unique records of paleoclimatic variations under warmer-than-present conditions. During the period from 6–3.5 million years ago (Ma), the area was dominated by warm, tropical waters supplied by an intensified, uninterrupted Indonesian Throughflow and characterised by prevailing humid conditions and increased precipitation. Despite the available information regarding the general paleoclimatic conditions, little is known about the concurrent regional ocean circulation patterns and the relative intensity of seasonally flowing boundary currents, such as the Leeuwin Current. Recent investigations of sediments recovered from the shelf during International Ocean Discovery Program (IODP) Expedition 356, have produced a number of well-dated time-series that cover the late Neogene and can therefore assist with more detailed reconstructions. In this study, we investigate two astronomically-tuned calcareous nannofossil records from IODP Sites U1463 and U1464 that can help us trace and understand long-term changes in ocean circulation and seasonality, as well as their effect on nutrient replenishment in the upper photic zone. By looking into shifts in the dominant species within the nannofossil assemblage, and comparing them with paleotemperature gradients between the NW Australian shelf and the eastern Indian Ocean, we identify the main periods of change in stratification and nutrient availability that occurred over the continental shelf. Our results indicate a significant change in ecological and oceanographic regime that occurred across the Miocene to Pliocene boundary (5.4–5.2 Ma), which can be attributed to an increase in seasonality and an overall intensification of the upper water column mixing over the shelf. Major changes in the nannofossil assemblages that reflect broader-scale processes and evolutionary events, such as the extinction of Sphenolithus spp. (~3.54 Ma) and the termination of the late Miocene to early Pliocene biogenic bloom in the eastern Indian Ocean (4.6–4.4 Ma), occurred long after this regional regime shift.
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Pliocene foraminifera and calcareous nannofossils from a borehole section “Kainosawa Onsen” in the eastern part of Akita City, Akita Prefecture, Japan Sea borderland of northern Japan were examined. The information on biostratigraphy and inferred paleoenvironment from the study section will furnish basis for further study on the Pliocene formations in the Sea of Japan region. The studied section is correlated to the uppermost part of the Onnagawa Formation or the lowermost part of the Funakawa Formation, Tentokuji Formation, and Sasaoka Formation, in ascending order. The Globorotalia ikebei/Orbulina universa Zone and the Globigerina pachyderma (dextral)/Globorotalia orientalis Zone were recognized as planktonic foraminiferal zones, the Miliammina echigoensis Zone and the Uvigerina akitaensis Zone were defined as benthic foraminiferal zones, and CN12a Subzone were recognized as calcareous nannofossil zone. From these fossil zones, a geologic age of Pliocene was elucidated for the Funakawa and the Tentokuji Formations. Assemblages of planktonic foraminifera in the Globorotalia ikebei/Orbulina universa Zone indicate a paleoenvironment with cold surface water whereas those in the G. orientalis/G. pachyderma (dextral) Zone indicate relatively warm surface water. Such assemblages suggestive of warm water are supposed to have been brought into the Sea of Japan by the influx of transitional surface water between the warm Kuroshio Current and the cold Oyashio Current. Upper Bathyal Zone or deeper paleobathymetric paleoenvironment is estimated for both the M. echigoensis Zone and the U. akitaensis Zone. Generally a paleoenvironment with cold water is assumed from the assemblages of these two zones. On the contrary, influx of relatively warm water is assumed from parts of the assemblages of the U. akitaensis Zone. Furthermore, fluctuations of primary productivity during the deposition of the studied interval were suggested by the analysis of microhabitat preferences of benthic foraminiferal assemblages.
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“Located between the Pacific and Indian Oceans and between the Asian and Australian continents, the seas of the Indonesian Archipelago have a significant role in global weather patterns and oceanic circulation. The dynamic interplay between geological, physical, chemical and biological processes has given rise to one of the most diverse marine regions on the planet. The exceptional marine and coastal ecosystem diversity of the Indonesian Archipelago, coupled with monsoonal tropical climate, provides hundreds of habitats that support thousands of marine species. This treasure of marine biodiversity has sustained the people of the archipelago for thousands of years. Current population pressures and rapid economic development have, however, placed many of the natural resources at risk due to overexploitation, lack of management and environmental degradation. Development and implementation of ecologically sound management plans for sustainable use of Indonesian marine resources are essential, as is the understanding of the various physical, chemical, biological and ecological processes that maintain the integrity of marine ecosystems. The challenging task of documenting Indonesia’s marine realm is presented here in a two-volume set, the result of worldwide literature reviews and extensive new field observations. The first volume provides a review of geology, physical oceanography and meteorology of the archipelago. Coral reefs, one of the most important, yet least known ecosystems in Indonesia are introduced in this volume through discussions of the geologic history of reefs, followed by a review of the major theories of coral reef formation, development and their worldwide distribution. Corals and other coral reef-associated organisms are then examined. The chapter on foraminifera, major producers of present and past carbonate deposits, presents some little-known Indonesian assemblages. Next the authors look at the natural environmental factors that affect coral reef development and survival. A chapter on coral reef growth and development concludes the first volume. The second volume discusses the origin, formation and distribution of various reef types in the Indonesian Archipelago, and provides new estimates on their extent. The second volume also provides a review of the ecology of the Indonesian seagrass, mangrove and open-ocean ecosystems. The chapter on marine biodiversity focuses on a number of marine and coastal habitats and threatened marine organisms. The final two chapters discuss what recent effects the human race has had on marine resources, and what we can do to protect and preserve our marine and coastal zones for generations to come.” XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Individual Chapters can be accessed through the “LINKED DATA” tab below
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During survey of SEAFDEC vessel in May, 1999, 39 samples of bottom sediments of Vietnamese coastline were collected. The samples were analyzed for their sedimentological, micropaleontological characteristics as well as for their total organic matter and mineralogical composition of sediments. The study area can be divided into three parts: northern, central and southern part. Northern and southern parts are characterized by a wide, shallow continental shelf, while central part has very narrow continental shelf. Generally, in the southern part sand is more spread, especially in the front of the Maekong river mouth (25.64% of total sediments), sediments is coarser than in others (average mean size is 0.162mm), better sorted, less skewed. In the northern part, clayish silts, clayish, sandy silts are most spread, sediments are poor sorted, moderate skewed. Average mean size is 0.088mm. In the central part, clayish, silty sand is dominant. Average mean size is 0.1507mm. Sediments are poor sorted. Result of study revealed an occurrence of 98 foraminifers species in the bottom sediments, 19 of them are plankton and 79 are benthos. A content of total organic matter in the study area varies from 0.125% to 1.344%. High content of TOM is observed in the central part, as well as in the south western part. A study on mineralogical composition has pointed out a presence of 35 minerals in bottom sediment.
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ABSTRACT Ecologic distribution of brackish water foraminifera Census data on 89 species of benthic foraminiferal tests from 131 samples from brackish water environments throughout New Zealand are analysed by cluster and correspondence analyses. Ten brackish water faunal associations are recognised. When mapped in study areas they can be seen to inhabit distinct estuarine and tidal inlet environments. The associations are characterised by Trochamminita salsa, Haplophragmoides wilberti, Trochammina inflata, Jadammina macrescens, Miliammina fusca, Elphidium excavatum and Ammonia parkinsoniana, on their own or in combinations. Canonical correspondence analysis indicates that the factors most influential in determining the faunal distribution in brackish environments are, in descending order of importance: salinity, tidal exposure, and presence of intertidal vegetation. Associations characterised by agglutinated species occur in the more extreme brackish water environments - in the least saline environments and also above mean high water. Ecologic distribution of normal marine salinity foraminifera Census data on 327 species of benthic foraminiferal tests from 197 samples from shallow water (<100 m), normal marine environments around New Zealand are analysed by cluster and correspondence analyses. Eighteen faunal associations inhabiting distinct coastal environments are recognised. The associations are characterised by various combinations of species of Elphidium, Haynesina, Pileolina, Rosalina, Gaudryina, Notorotalia, Planoglabratella, Quinqueloculina, Cibicides, Zeaflorilus, Virgulopsis, Patellinella, Nonionellina, Trifarina, Bulimina and Cassidulina. Canonical correspondence analysis indicates that the following factors in decreasing order of importance are most influential in determining the faunal distribution in normal marine environments: factors linked to depth, factors linked to wave and current energy, factors linked to biogeography, bottom water oxygen concentrations and substrate type. Taxonomy 419 species are listed from shallow water (<100 m) around New Zealand. The 233 most common or distinctive species are fully illustrated and their diagnostic features outlined. Four new species are described: Glabratellina kermadecensis n.sp., Neoconorbina cavalliensis n.sp., Pileolina gracei n.sp. and Notorotalia hornibrooki n.sp.. Frequency of species occurrence To assess species frequency, species duration and biogeography, we used a data set containing the presence/absence records of 353 species in 50 composite shallow water localities from around the New Zealand region. The frequency of species occurrence follows a log series curve with 35% of the species occurring rarely (1-2 localities) and 20% occurring commonly (>16 localities). Rotaliinid species have the greatest frequency of occurrence (35% are common), whereas lageninids and textulariinids have the greatest number of rare species (44%, 55%). Unlike reported North American results, there appears to be no significant difference in the percentage of endemic or cosmopolitan species that are rare or common. Species duration 128 Recent benthic species (36%) have a recorded New Zealand fossil record (50% of rotaliinids, <35% of other suborders). One species first appears in each of the late Cretaceous and Paleocene, 22 in Eocene, 25 in Oligocene, 67 in Miocene, 14 in Pliocene, 4 in Pleistocene, with major influxes in the latest Eocene-early Oligocene, and early Miocene (31 species each). Species with a fossil record have a mean partial species duration of 21 m.yrs. Deeper water species (live dominantly >100 m) have a longer mean duration (24 m.yrs.), than dominantly shallow species (20 m.yrs.) or brackish species (9 m.yrs.). Commonly occurring species have a far greater percentage with a fossil record (55%) than rarely occurring species (19%). Contrary to findings elsewhere, the rarely occurring species with a fossil record have a longer mean duration (27 m.yrs.) than the intermediate class (21.5 m.yrs.) and the common class (15.5 m.yrs.). 66% of the 50 endemic New Zealand species have a fossil record (mean duration 14 m.yrs.), whereas only 40% of the 180 cosmopolitan species have a New Zealand fossil record (mean duration 25 m.yrs.). Biogeography Fifty percent of our species are cosmopolitan, 14% endemic and 10% have a South-west Pacific distribution. All 21 brackish-restricted species are cosmopolitan. There is one endemic genus (Zeaflorilus) and one third of the endemic species belong to three genera - Notorotalia (6 spp.), Pileolina (5 spp.) and Quinqueloculina (5 spp.). New Zealand appears to be the centre of greatest diversity for the former two genera. 38% of the endemic species occur commonly around New Zealand with many as characterising species of faunal associations - Spiroplectinella proxispira, Elphidium novozealandicum, Nonionellina flemingi, Notorotalia finlayi, Pileolina zealandica, Virgulopsis turris, Zeaflorilus parri. All the New Zealand brackish and mid shelf faunal associations occur overseas, but 13 of the 16 normal marine salinity, inner shelf associations appear to be restricted to New Zealand. Most endemic species are widespread around New Zealand with just 6 having distributions restricted to a single province - Glabratellina kermadecensis (Kermadecian), Discorbinella deflata (Moriorian), Fissurina baccata, Elphidium excavatum f. oirgi, Pileolina calcarata, P. harmeri (Aupourian). A simplified version of the composite locality presence/absence data set on New Zealand’s normal marine, shallow water foraminifera was analysed by clustering Jaccard coefficients. Six mappable biogeographic provinces were identified from the resulting dendrogram - Kermadecian, Aupourian (north-east North Island), New Zealand (most of the three main islands), Fiordland, Moriorian (Chatham Islands) and Antipodean (Subantarctic Islands). These foraminiferal provinces are closely similar to the classic, molluscan-defined marine provinces, except that the classic Cookian and Forsterian Provinces are combined into the New Zealand Province and a separate Fiordland Province is recognised. Another minor difference is that the Far North and Waitemata Harbour are excluded from the foraminiferal Aupourian province and group with the New Zealand Province. The number of shallow water benthic foraminiferal species present in the Fiordland and outlying island provinces is considerably fewer than in the two mainland provinces, because of less extensive study, reduced range of habitats, less likelihood of successful trans-oceanic dispersal (islands), young age of island group (Kermadecian), or cooler water (Fiordland, Antipodean). Diversity decreases from north to south in the well-studied mainland provinces, with 304 species in Aupourian and 270 in the New Zealand. Thirty warm, shallow-water species are restricted to the Aupourian Province, which is strongly influenced by the warm East Auckland Current, and a further 8 species are restricted to the Aupourian plus the Kermadecian. Few species are restricted to the other provinces - Kermadecian (6), New Zealand (9), Fiordland (0), Moriorian (1) and Antipodean (0). The pattern of brackish water foraminiferal biogeography in New Zealand differs from that of the normal marine species and appears to be more similar to that displayed by terrestrial plants and animals. Dispersal Our results show that there are two groups of shallow water foraminiferal species. One group has been able to rapidly disperse widely around the world, crossing oceanic barriers of up to 1500 km width (Tasman Sea), whereas the other group (including the New Zealand endemics) have not successfully dispersed to other countries. Transport on the feet or feathers of migratory wading seabird is postulated as the most likely dispersal mechanism for the cosmopolitan brackish foraminiferal fauna. Trans-oceanic current transport of suspended juveniles is the most favoured dispersal mechanism for the majority of the widespread normal marine, shallow water species, possibly assisted at times by “island-hopping” across the wider oceanic barriers. We infer from their modern New Zealand distribution patterns that three species (Elphidium vellai, Virgulinella fragilis, Siphogenerina raphana) have been introduced in ships’ ballast water within the last century or so. A fourth (Spiroloculina carinata) may also but is less certain. Paleoenvironmental assessment A multiplicity of physical and biological factors determine the modern ecologic distribution patterns of foraminifera. The correlation of some of these factors with the presence or abundance of certain foraminiferal taxa or associations has been documented in modern faunas and may be used to assess the paleoenvironment of fossil foraminiferal faunas. The validity of this uniformitarian approach is largely accepted for the Quaternary and Neogene but becomes less reliable going back in time through the Paleogene and Cretaceous. Fossil foraminiferal faunas can provide assessments, at varying levels of accuracy, of a number of paleoenvironmental factors of value to geological, paleoclimatic and paleoceanographic studies. Planktic foraminiferal percentage, maximum size, encrustation, diversity, coiling ratios and taxonomic census data can be used to estimate oceanicity and paleotemperature and to give an indication of water depth. Benthic foraminiferal diversity and composition by suborder sometimes provide a general indication of the past environment, but the benthic taxonomic composition and recognition of faunal associations allow more detailed assessments of water depth, intertidal level, salinity, exposure to water turbulence, bottom oxygen concentrations, water temperature and carbon flux. Charts and tables summarising the correlation between modern foraminifera and a number of these factors are presented to assist in paleoenvironmental assessments. Post-mortem faunal changes, such as test breakdown, dissolution, winnowing, bed-load transport and reworking, can modify the composition of foraminiferal faunas and affect paleoenvironmental assessments. These changes may be recognised by study of the preservational state and test size distribution and composition of the benthic foraminifera and be useful in refining the paleoenvironmental assessment. A method for rapid paleoenvironmental assessment of individual fossil faunas is outlined, based largely on an estimate of the planktic percentage and identification of the dominant benthic taxa or faunal association. Keywords. Foraminifera; shallow water; brackish environments; shelf environments; systematics; species frequency; species duration; dispersal mechanisms; biogeography; benthic foraminiferal associations; ecologic distribution; paleoenvironmental assessment; New Zealand; Cavalli Islands; Helena Bay; Waitemata Harbour; Great Barrier Island; Pauatahanui Inlet; Wanganui Bight; Queen Charlotte Sound; Oparara Inlet; Purakanui Inlet; Port Pegasus
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Elphidiidae is a family of mostly shallow-water benthic foraminifera that occur throughout the world at present and in sedimentary rocks of Cenozoic age. Two subfamilies (Elphidiinae and Notorotaliinae) and four genera (Elphidium, Cristatavultatus, Parrellina, Notorotalia) occur in the South-west Pacific region today and two further genera (Cribrorotalia, Discorotalia) are present in the New Zealand fossil record. The paper describes the systematics, ecology, biogeography and biostratigraphy of recent Elphidiidae.
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The purpose of this study was to assess the oceanic seasonal evolution and spatial distribution of photosynthetic carbon fixation. Computation of primary production from the upper ocean chlorophyll-like pigment concentrations were made from monthly global maps from the coastal zone color scanner data archive. Relative contributions of various oceans and zonal belts were identified. Depending on the ratio used for active pigments to total pigments, the calculated global annual production ranges from 36.5 and 45.6 G tons (metric) carbon per year. These values are among the highest estimates proposed to date; although the absolute values may be somewhat questionable, the relative contribution of the various zonal belts and oceans are considered to have a high degree of accuracy. 33 refs., 4 figs., 2 tabs.
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We present a 5.3-Myr stack (the "LR04" stack) of benthic δ 18 O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm. This is the first benthic δ 18 O stack comprised of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene. We also present a new LR04 age model for the Plio-Pleistocene derived from tuning the δ 18 O stack to a simple ice model based on June 21 insolation at 65 • N. Stacked sedimentation rates provide additional age model constraints to prevent overtuning. Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 5.3 Myr and in the precession band for more than half of the record. The LR04 stack contains significantly more variance in benthic δ 18 O than previously published stacks of the late Pleistocene as the result of higher resolution records, a better alignment technique, and a greater percentage of records from the Atlantic. Finally, the relative phases of the stack's 41-and 23-kyr components suggest that the precession component of δ 18 O from 2.7–1.6 Ma is primarily a deep-water temperature signal and that the phase of δ 18 O precession response changed suddenly at 1.6 Ma.
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"Larger benthic foraminifera" are large, single celled organisms living under similar conditions as zooxanthellate corals, in shallow tropical seas. Just like other reef associated taxa the diversity of larger benthic foraminfera is highest in the border region between the Pacific and Indian Ocean, the Indo-West Pacific (IWP). Since foraminifera have calcareous tests and occur in huge numbers, they fossilise easily. Other taxa on which stratigraphical schemes have been built, e.g., planktonic foraminifera and nannoplankton, are not as abundant in tropical shallow marine carbonates and in these settings larger foraminfera have been used for stratigraphical purposes. The Recent distribution of larger foraminifera has mainly been studied in pristine areas with a deep photic zone. Distribution of larger foraminfera in such areas probably differs from those on mesotrophic carbonate shelfs. The latter are also more likely to preserve and dominate carbonate production during the Cenozoic in tropical southeast Asia (Wilson, 2002). The present thesis aims at: - Describing the Recent distribution over various reefs and carbonate platform. - Identifying the most important parameters that determine the occurence of species of larger benthic foraminifera. - Determining whether the distribution of empty tests of larger benthic foraminifera reflects the distribution of the living protists, and determining whether the occurrence of larger benthic foraminifera can be used for palaeoenvironmental analysis. - Use these models to interpret the fossil record.
Article
According to the micropaleontological assemblages related to the features of these cores, three sedimentary facies can be recognized, ie continental, transitional between marine-continent (five subfacies) and offshore facies. Based on the distribution, diversity and ecological characteristics of the fossil foraminifera in the sections of the bore holes, there existed at least three transgressive layers in the Tianjin Plain, hence three corresponding transgressions can be confirmed. The first and second transgressive layer are off-shore shallow water deposits distributed in the southeastern part of the area. The third transgressive layer are marine-continental transitional one with weak marine features. Its intensity increased gradually with its maximum occurred the mid-Holocene. -from English summary
Article
Two hundred and thirty-six benthonic species and six planktonic species are identified among Formainifera present in Holocene sediment of Exmouth Gulf, in a water depth of 5-30 m. The benthonic microfauna comprises 20 agglutinated species (including 9 Lituolida, 1 Trochamminida, and 10 Textulariida), 74 porcellaneous species (Miliolida), and 142 hyaline species (including 4 Spirillinida, 27 Lagenida, 37 Buliminida, and 75 Rotaliida). Abundant species, at least at one site, include Ammotium australiensis, Textularia foliacea, Textularia lateralis, and Textularia oceanica among the agglutinated types; Parahauerinoides fragilissimus, Peneroplis pertusus, Planispirinella exigua, Pseudomassilina australis, Quinqueloculina arenta, Q. philippinensis, Q. sp 8, Sigmoihauerina involuta, Sorites marginalis, Triloculina tricarinata among the porcellaneous species; and Ammonia parkinsoniana, Amphistegina lessonii, A. sp cf. A. Papillosa, A. radiata, Asterorotalia gaimardi, Cibicides sp cf C. refulgens, Discorbinoides patelliformis, Elphidium sp cf E. advenum, E. crispum, E. sp 1, Heterostegina depressa, Operculina ammonoides, Pararotalia nipponica, and Rosalina cosymbosella among the hyaline (Rotaliida) species.
Article
[1] We present a 5.3- Myr stack ( the " LR04'' stack) of benthic delta(18)O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm. This is the first benthic delta(18)O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene. We also present a new LR04 age model for the Pliocene- Pleistocene derived from tuning the delta(18)O stack to a simple ice model based on 21 June insolation at 65degreesN. Stacked sedimentation rates provide additional age model constraints to prevent overtuning. Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 5.3 Myr and in the precession band for more than half of the record. The LR04 stack contains significantly more variance in benthic delta(18) O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic. Finally, the relative phases of the stack's 41- and 23- kyr components suggest that the precession component of delta(18)O from 2.7 - 1.6 Ma is primarily a deep- water temperature signal and that the phase of delta(18)O precession response changed suddenly at 1.6 Ma.
Article
In this 2006 volume John Murray investigates the ecological processes that control the distribution, abundance and species diversity of benthic foraminifera in environments ranging from marsh to the deepest ocean. To interpret the fossil record it is necessary to have an understanding of the ecology of modern foraminifera and the processes operating after death leading to burial and fossilisation. This book presents the ecological background required to explain how fossil forms are used in dating rocks and reconstructing past environmental features including changes of sea level. It demonstrates how living foraminifera can be used to monitor modern-day environmental change. Ecology and Applications of Benthic Foraminifera presents a comprehensive and global coverage of the subject using all the available literature. It is supported by a website hosting a large database of additional ecological information (www.cambridge.org/0521828392) and will form an important reference for academic researchers and graduate students in Earth and Environmental Sciences. © Cambridge University Press, 2009 and John Murray 2006. All rights reserved.