![IODP Site U1463 downhole wireline log data plotted by age. (a) Thoriumpotassium ratio (Th/K*10-4 ), compared to an austral eccentricity-tilt-precession composite. Intervals with significant correlation between both records (p<0.01; 500-kyr windows) are indicated by rectangles (red: positive correlation; blue: negative correlation). Negative correlation indicates enhanced summer precipitation (high %K, low Th/K) at times of relatively high summer insolation (high ETP). (b) Uranium (Uppm) and (c) potassium (%K); lines are 15-pt moving average. Note reversed y-axis in (b). (d) Mg/Ca-derived temperature records from nearby Site 763A [Karas et al., 2011b] are shown for comparison along with (e)](https://www.researchgate.net/profile/Cecilia-Mchugh/publication/317841864/figure/fig1/AS:509929792053248@1498588144446/ODP-Site-U1463-downhole-wireline-log-data-plotted-by-age-a-Thoriumpotassium-ratio_Q320.jpg)
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Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene
Geophysical Research Letters
Abstract and Figures
Late Miocene to mid-Pleistocene sedimentary proxy records reveal that northwest Australia underwent an abrupt transition from dry to humid climate conditions at 5.5 million years (Ma), likely receiving year-round rainfall, but after ~3.3 Ma, climate shifted towards an increasingly seasonal precipitation regime. The progressive constriction of the Indonesian Throughflow likely decreased continental humidity and transferred control of northwest Australian climate from the Pacific to the Indian Ocean, leading to drier conditions punctuated by monsoonal precipitation. The northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by ~2.4 Ma, well after the intensification of northern hemisphere glaciation. The transition from humid to arid conditions was driven by changes in Pacific and Indian Ocean circulation and regional atmospheric moisture transport, influenced by the emerging Maritime Continent. We conclude that the Maritime Continent is the switchboard modulating teleconnections between tropical and high-latitude climate systems.
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... On the north-western margin of Australia, Paleogene to Neogene records of climate variability are influenced by global trends . Regional climate conditions also appear to be influenced by progressive oceanographic changes driving shifts in precipitation and changes between dry and humid climate conditions (Christensen et al., 2017;Groeneveld et al., 2017). Uplift of the Indonesian Archipelago to the north of Australia, from 10 to 4.4 Ma changed regional oceanographic conditions by trapping warm waters in the central Pacific, forming the Indo-Pacific Warm Pool north of Papua New Guinea. ...
... On the north-western margin of Australia, Paleogene to Neogene records of climate variability are influenced by global trends . Regional climate conditions also appear to be influenced by progressive oceanographic changes driving shifts in precipitation and changes between dry and humid climate conditions (Christensen et al., 2017;Groeneveld et al., 2017). Uplift of the Indonesian Archipelago to the north of Australia, from 10 to 4.4 Ma changed regional oceanographic conditions by trapping warm waters in the central Pacific, forming the Indo-Pacific Warm Pool north of Papua New Guinea. ...
... The age framework for IODP Site U1464 is determined by diagnostic planktic foraminifera (PF), calcareous nannofossils (CN), and larger benthic foraminifera (LBF) ( Table 2; Gallagher et al., 2017b;Groeneveld et al., 2017Groeneveld et al., , 2021. The oldest datum at IODP Site U1464 is the first occurrence of the LBF Nephrolepidina ferreroi, dated at ~16 Ma (Groeneveld et al., 2017). ...
The tropical North West Shelf of Australia hosts a diverse range of modern reefs. Six shelf edge isolated atolls are present north of 18◦S including: Ashmore Reef, Scott Reef and Seringapatam Reef, and three Rowley Shoals. The Ningaloo Reef is a fringing reef around the North West Cape at 22◦S. All of these reefs are the remnants of a vast 2000 km long barrier reef that drowned during the Late Miocene (~10 Ma). Despite extensive hydrocarbon exploration in the region, the history of these isolated reefs is not well known. Seismic analyses combined with
stratigraphic analyses of International Ocean Discovery Site U1464 near the Rowley Shoals has revealed that these modern isolated atolls have a complex evolution related to climate and tectonism as they managed to survive on their Miocene barrier reef foundation.
The first Miocene reefs (~17 Ma) near the Rowley Shoals were isolated small, mound-shaped features. These evolved into a barrier reef by the Middle Miocene (~16 Ma). However, by the Late Miocene (~10 Ma) this
barrier reef backstepped landward, evolved into isolated mounds/atolls and drowned prior to the Miocene-Pliocene boundary (~6 Ma) largely due regional tectonic subsidence. Early Pliocene reef expansion (~4.6
Ma) led to the growth of four isolated atolls (the Rowley Shoals) related to local faulting and Early Pliocene warmth. Subsequently a second Pliocene reef growth phase occurred from ~3.5 to 3 Ma when eastern Indian Ocean sea surface temperatures cooled by ~4 ◦C due to Indonesian Gateway constriction and a reduced Leeuwin Current. By the Pleistocene (~2.4 Ma) one the four Rowley Shoals had drowned. Strong sea level variability, together with Indonesian Throughflow constriction and reduction in intensity of the Leeuwin Current after 2.4 Ma may have led to enhanced cooling and regional upwelling. These factors may have been sufficient to cause local drowning of the southerly fourth Rowley Shoal while the more northerly three Shoals survived until present.
... There is a strong correlation between length and mass (r = 0.88) throughout the studied (Bell et al., 2015), monsoon intensification (Y. G. , high productivity warm intervals in East Antarctica (Cook et al., 2013), transition from humid to arid conditions (Christensen et al., 2017), and the later part of the late Miocene to early Pliocene biogenic bloom event (gray bar). Intervals I to IV (green dotted line and text) refer to the intervals discussed in the text. ...
... (Bell et al., 2015), monsoon intensification (Y. G. , high productivity warm intervals in East Antarctica (Cook et al., 2013), transition from humid to arid conditions (Christensen et al., 2017), and the later part of the late Miocene to early Pliocene biogenic bloom event (gray bar). Intervals I to IV (green dotted line and text) refer to the intervals discussed in the text. ...
... Significant paleoceanographic events are indicated: Central American Seaway shoaling (Bell et al., 2015), monsoon intensification (Y. G. , high productivity warm intervals in East Antarctica (Cook et al., 2013), transition from humid to arid conditions (Christensen et al., 2017), and the later part of the late Miocene to early Pliocene biogenic bloom event (gray bar). Intervals I to IV (green dotted line and text) refer to the intervals discussed in the text. ...
The Pliocene epoch emerges as a pivotal juncture in Earth's climatic evolution, characterized by pronounced warmth and elevated atmospheric carbon dioxide compared to contemporary levels. While the broader climatic context of the Pliocene has garnered attention, there remains an outstanding gap in detailed paleoclimate reconstructions of the early Pliocene, a new potential target for data‐model intercomparison. Addressing this, we investigate the drivers of the early Pliocene “Biogenic Bloom” and implications for nutrient dynamics and climate. By analyzing high‐resolution biotic assemblage and geochemical records from the Agulhas Plateau, southwestern Indian Ocean (International Ocean Discovery Program, IODP Site U1475), we aim to elucidate the forcing and feedback mechanisms driving the early Pliocene marine ecosystems. We identify a distinct shift in coccolithophore assemblages at ∼4.6 million years ago, characterized by a notable change in dominance between the larger and smaller Reticulofenestra and high abundances of Noelaerhabdaceae < 5 µm. Our findings confirm the adaptive strategies of coccolithophore communities to prevailing environmental conditions, underscoring their evolutionary resilience by producing smaller coccoliths while increasing their abundances in a nutrient‐replete ocean. Surface water dynamics, particularly the subtropical front migration and expansion of Southern Ocean waters, in combination with the southern African monsoon variability, emerge as key drivers of phytoplankton productivity during the early Pliocene. We posit that a weakened biological carbon pump, due to increased phytoplankton production driven by intense ocean circulation and mixing during the early Pliocene, served as a potential precursor to the subsequent middle Pliocene abrupt climate extremes.
... The abundance of surface and near-surface uranium deposits in Northwest Australia (Geoscience Australia 2015) provides additional support for linking U and dust fluxes . While uranium can also be related to the organic matter in specific carbonatedominated sedimentary environments (see Auer et al. 2016Auer et al. , 2021, a strong co-variation of both U and Th in marine archives can generally be considered indicative of variability in dust/riverine flux (Hesselbo 1996;Hladil et al. 2006;Christensen et al. 2017). The application of various NGR records provided both long-term and orbital trends of monsoonal variability and precipitation along the western shelf of Australia over the Neogene and Quaternary Groeneveld et al. 2017;De Vleeschouwer et al. 2018). ...
... The age model for ODP Site 762B log (Fe/Ca) core XRF data (Stuut et al. 2019) is revised by Auer et al. (2020). The data from 5.5 to 2 Ma are compared with records from ODP Hole 763A (Karas et al. 2009;revised by O'Brien et al. 2014), as well as terrigenous influx data from Site U1463 Christensen et al. 2017) with K% data updated to the most recent age model of Auer et al. (2019); The % C4 plants from ODP Site 763 is from Andrae et al. 2018; The LR04 isotope stack (Lisiecki and Raymo 2005). ...
... Elemental records from Sites U1463 and U1464 in combination with the recovery of sabkha-like sediments at IODP Site U1464 showed that northwest Australia was very arid throughout the year from the middle to the late Miocene Petrick et al. 2019). Near the Miocene-Pliocene transition, a rapid shift in the elemental records, supported by a change in sedimentation, indicates an abrupt transition to much wetter conditions, defined as the Humid Interval at ~5.5 Ma ( Fig. 11; Christensen et al. 2017;Groeneveld et al. 2017;Karatsolis et al. 2020). The deposition of the massive, siliciclastic Bare Formation on the northwest shelf illustrates the change to increased river input related to wetter climate (Tagliaro et al. 2021). ...
The Australian monsoon is part of the global monsoon and often included as a component of the Asian Monsoon
system although they operate out of phase. Due to their hemispheric positions, the dry (wet) Australian winter
(summer) monsoon coincides with the wet summer Asian monsoon and vice versa. The Australian monsoon
controls rainfall distribution in northern tropical Australia where over 80% of the median annular rainfall occurs
from December to March, the summer wet season. Three types of the Australian monsoon are distinguished based
on distinct atmospheric circulation and heating patterns: a northwest Pseudo-Monsoon, a northeast Quasi-Monsoon
and an Australian Monsoon (sensu stricto) north of Australia. While the modern climatology of the Australian monsoon
has been extensively documented, its paleohistory is poorly constrained, especially in Australia’s continental
interior where harsh arid climatic conditions have degraded almost all physical evidence of monsoonal activity.
However, reassessment of northern and central Australian terrestrial and marine sequences reveals a fairly robust
Cenozoic history of this monsoon, especially for the Neogene, which we synthesize for the first time here. Evidence
for a Paleogene Australian paleomonsoon is equivocal due to the small number of sites, their limited age control,
and the poor preservation of flora with ambiguous affinities. Modeling and tectonic evidence suggest the northern
part of the Australian Plate migrated to the (sub)tropical region (north of 30°S) creating “modern” boundary conditions
for monsoonal onset by ~10 Ma. Cores off northwest Australia reveal arid late Miocene and humid Pliocene
conditions were followed by the Pseudo-Monsoon at ~3.5 Ma when northern hemisphere glacial expansion “forced”
the ITCZ (Inter Tropical Convergent Zone) south. Subsequently, variable humid and arid periods typify Quaternary
high-amplitude glacio-eustatic cycles until ~1 Ma, when arid conditions expanded across Australia. Glacial/interglacial
cyclicity and obliquity/precession insolation during terminations modulated Pseudo-Monsoon intensity when the ITCZ
migrated northward (during glacial) and southward (during interglacial periods) from ~1 Ma to present. From ~1.6
to 1 Ma, precession paced Pseudo-Monsoon variability. Mega-lake expansion in central Australia and fluvial intensification
generally correspond to wetter interglacial periods. Lake Eyre monsoonal shorelines may have been influenced
by abrupt millennial events. Monsoonal conditions re-established near the base of Holocene as the ITCZ migrated
across northern Australia. The Australian Monsoon (sensu stricto) and Quasi-Monsoon (a) initiated from 12.5 to 11 ka;
(b) intensifying from 9 to 2 ka; then (c) weakened, possibly due to the onset of ENSO intensification. The Pseudo-Monsoon
was established at ~14.5 ka off northwest Australia intensifying from 11.5 to 7 ka. It weakened after ~7 ka north
of 15°S and ~5 ka to the south. In the absence of a topographic influence, insolation (precession/obliquity), abrupt
millennial events and/or ITCZ variability across northern Australia were important controls on Quaternary Australian
monsoon intensity. Further investigations of deeper time pre-Quaternary records off northwest and northeast Australia
will reveal the paleohistory of this important domain of the Global Monsoon.
... Red star marks International Ocean Discovery Program (IODP) Site U1464 (this study). Core sites discussed in this study are indicated with black circles: IODP Site U1482 (Chen et al., 2022), IODP Site U1463 (Christensen et al., 2017), Ocean Drilling Program Site 762 (Stuut et al., 2019), and Deep Sea Drilling Project Site 593 (McClymont et al., 2016). Detailed drainage basins (number 1-16) in the black rectangle are shown in Figure S1 in Supporting Information S1. ...
... Of the available high-resolution records, most tend to be focused on the last glacial cycle (the last ∼130 kyr), when the effects of millennial-scale climate variability and/or the last deglaciation obfuscate the primary response of the Australian monsoon and Northwest Australian dust flux to direct orbital forcing (Bayon et al., 2017;Denniston et al., 2017;Fu et al., 2017;Miller et al., 2018). A few longer records (>1 Myr) do exist, but their interpretations typically emphasize long-term trends (Christensen et al., 2017;Stuut et al., 2019). For example, proxy records of past dust flux based on sedimentary Th/K at International Ocean Discovery Program (IODP) Site U1463 (Christensen et al., 2017) and Log (Zr/Fe) at Ocean Drilling Program (ODP) Site 762 (Stuut et al., 2019) reveal increasing aridity variance from the Pliocene to the Pleistocene. ...
... A few longer records (>1 Myr) do exist, but their interpretations typically emphasize long-term trends (Christensen et al., 2017;Stuut et al., 2019). For example, proxy records of past dust flux based on sedimentary Th/K at International Ocean Discovery Program (IODP) Site U1463 (Christensen et al., 2017) and Log (Zr/Fe) at Ocean Drilling Program (ODP) Site 762 (Stuut et al., 2019) reveal increasing aridity variance from the Pliocene to the Pleistocene. ...
Paleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations.
... During Miocene, tectonic activities in the presentday Indo-Australian archipelago (IAA) caused significant alterations in oceanic circulation. The Indo-Australian plate moved northwards, thereby restricting deep-water trade-off and changing the current patterns from a warm South Pacific to a colder North Pacific flow on its passage (Christensen et al., 2017). Additionally, the projection of the Himalayas also began around such time and influenced the intensification of the East Asian monsoons (Clift & Webb, 2019). ...
Carangidae is an economically important fish family comprised of 32 genera with more than 140 circumglobally distributed species. Its members exhibit vast differences in morphology and lifestyle, thus making them compelling subjects for evolutionary studies. Recently, more works on carangids have detected the presence of cryptic lineages through molecular and/or non-molecular techniques. Credited for its inherent amplification efficiency, mitophylogenomics became effective in opening avenues to further understand higher-level interrelationships in many fish groups. However, the mitophylogenomic approach has not yet been widely applied to infer evolutionary history at the lower-level interrelationships, especially on cryptic representatives. In this study, we evaluated the diagnostic applicability of mitogenomes in detecting population-level divergences within Carangidae. Using the mitogenomes, we detected intraspecific divergences on some taxa, namely Caranx melampygus, Selaroides leptolepis, Seriola lalandi, Decapterus maruadsi, and Trachurus trachurus, with divergences highly correspondent to that of their geographic origins. Additionally, a widespread Pacific arrangement was also detected for S. rivoliana. Our discoveries were highly corroborative with findings from other Carangidae studies which utilized different diagnostic markers (e.g., SNPs, microsatellites, morphometrics, parasites). Dated phylogeny also suggested that intraspecific diversifications occurred during the Late Neogene. Likewise, we characterized two mitogenomes from different cryptic lineages of Selaroides leptolepis and revealed that the two mitogenomes were K2P pairwise = 5.58% different from each other. Its genetic compositions included 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a control region. These findings paved way for future evolutionary insights into the divergence histories of other fish populations.
... In addition, the aridification of inland Australia and East Africa was also closely related to the IPWP. The changes in the IPWP caused by the constriction of tropical seaways suppressed precipitation in Australia and thus promoted the formation of deserts [57]. Such a drying effect could also be observed in East Africa because the closure of the Indonesian seaway decreased SSTs in the Indian Ocean, leading to reduced precipitation over eastern Africa [15]. ...
... Despite the utility of these near-recent simulations in enhancing our understanding of ITF dynamics, on a geological timescale the Indonesian Gateway cannot be considered in terms of an open and closed gateway, but rather the interaction between (a) the source of the water (South versus North Pacific), (b) the location of the main outlet, and (c) variable sill depths and locations through time (Kuhnt et al. 2004. Furthermore, ITF restriction is controlled by two mechanisms: (a) sea level-related restriction causing shelf emergence and restricting ITF flow to the deep marine troughs during glacial phases (Zuraida et al. 2009, Holbourn et al. 2011, DiNezio et al. 2016, De Vleeschouwer et al. 2018) and (b) spatial reorganization of the Indonesian Gateway system due to tectonism caused by the northward movement of the Australian Plate and its collision with the Eurasian Plate (Cane & Molnar 2001, Kuhnt et al. 2004, Molnar & Cronin 2015, Christensen et al. 2017, Karas et al. 2017. ...
The tectonically complex Indonesian Gateway is part of the global thermohaline circulation and exerts a major control on climate. Waters from the Pacific flow through the Indonesian Archipelago into the Indian Ocean via the Indonesian Throughflow. Much progress has been made toward understanding the near-modern history of the Indonesian Gateway. However, the longer-term climate and ocean consequences of Australia's progressive collision with the Eurasian Plate that created it are less known. The gateway initiated ∼23 Ma, when Australia collided with Southeast Asia. By ∼10 Ma the gateway was sufficiently restricted to create a proto–warm pool. During the Pliocene it alternated between more or less restricted conditions, until modern oceanic conditions were established by 2.7 Ma. Despite its tectonic complexity, climate modeling and Indian and Pacific scientific ocean drilling research continue to yield insights into the gateway's deep history. ▪ The Indonesian Gateway is a key branch of global thermohaline oceanic circulation, exerting a major control on Earth's climate over the last the 25 Myr. ▪ We find that a complex interplay of tectonics and sea level has controlled Indonesian Gateway restriction since 12 Myr, resulting in La Niña– and El Niño–like states in the equatorial Pacific ▪ Long term Indonesian Gateway history is best determined from ocean drilling cores on the Indian and Pacific sides of the Indonesian Gateway, as records from within it are typically disrupted by tectonics. ▪ Model simulations show the global impact of the Indonesian Gateway. Further modeling with ocean drilling/tectonic research will enhance our understanding of Cenozoic Indonesian Gateway history.
Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Scientific drilling provides extended records of continental environmental conditions during the Neogene in Asia and northern Australia. Spectral data allows reconstruction of the environment using abundances of hematite and goethite. Hematite formation is favoured by dry or seasonal conditions. Hemipelagic sites show the most regular records. Monsoon strengthening started in the Early Miocene and peaked at 17–20 Ma in the Bay of Bengal and at 10–15 Ma in southern China before weakening after ~12 Ma and ~10 Ma respectively. The Indus dried after ~8 Ma and again after 3 Ma, while eolian sediment sources to the Sea of Japan show increased aridity after 5 Ma and 3 Ma. The Mekong indicates increasing aridity after 6 Ma, similar to Eastern Australia. In contrast, NW Australia shows a trend towards wetter conditions after 8 Ma, a humid period at 4–6 Ma, followed by drying. There is a link between drying and vegetation in the Mekong and Pearl River basins, as well as Eastern Australia. Monsoon strengthening is linked to topographic uplift in the Himalaya, together with Tethyan gateway closure. Long term drying is likely driven by global cooling since the Middle Miocene.
Global climate underwent a major reorganization when the Antarctic ice sheet expanded ~14 million years ago (Ma) (1). This event affected global atmospheric circulation, including the strength and position of the westerlies and the Intertropical Convergence Zone (ITCZ), and, therefore, precipitation patterns (2–5). We present new
shallow-marine sediment records from the continental shelf of Australia (International Ocean Discovery Program Sites U1459 and U1464) providing the first empirical evidence linking high-latitude cooling around Antarctica to climate change in the (sub)tropics during the Miocene. We show that Western Australia was arid during most of the Middle Miocene. Southwest Australia became wetter during the Late Miocene, creating a climate gradient with the arid interior, whereas northwest Australia remained arid throughout. Precipitation
and river runoff in southwest Australia gradually increased from 12 to 8 Ma, which we relate to a northward migration or intensification of the westerlies possibly due to increased sea ice in the Southern Ocean (5). Abrupt aridification indicates that the westerlies shifted back to a position south of Australia after 8 Ma. Our midlatitude Southern Hemisphere data are consistent with the inference that expansion of sea ice around Antarctica resulted in a northward movement of the westerlies. In turn, this may have pushed tropical atmospheric circulation and the ITCZ northward, shifting the main precipitation belt over large parts of Southeast Asia (4).
Global climate underwent a major reorganization when the Antarctic ice sheet expanded ~14 million years ago (Ma) (1). This event affected global atmospheric circulation, including the strength and position of the westerlies and the Intertropical Convergence Zone (ITCZ), and, therefore, precipitation patterns (2–5). We present new shallow-marine sediment records from the continental shelf of Australia (International Ocean Discovery Program Sites U1459 and U1464) providing the first empirical evidence linking high-latitude cooling around Antarctica to climate change in the (sub)tropics during the Miocene. We show that Western Australia was arid during most of the Middle Miocene. Southwest Australia became wetter during the Late Miocene, creating a climate gradient with the arid interior, whereas northwest Australia remained arid throughout. Precipitation and river runoff in southwest Australia gradually increased from 12 to 8 Ma, which we relate to a northward migration or intensification of the westerlies possibly due to increased sea ice in the Southern Ocean (5). Abrupt aridification indicates that the westerlies shifted back to a position south of Australia after 8 Ma. Our midlatitude Southern Hemisphere data are consistent with the inference that expansion of sea ice around Antarctica resulted in a northward movement of the westerlies. In turn, this may have pushed tropical atmospheric circulation and the ITCZ northward, shifting the main precipitation belt over large parts of Southeast Asia (4).
During the late Miocene epoch, about seven million years ago, large areas of the continents experienced drying, enhanced seasonality, and a restructuring of terrestrial plant and animal communities. These changes are seen throughout the subtropics, but have typically been attributed to regional tectonic forcing. Here we present a set of globally distributed sea surface temperature records spanning the past 12 million years based on the alkenone unsaturation method. We find that a sustained late Miocene cooling occurred synchronously in both hemispheres, and culminated with ocean temperatures dipping to near-modern values between about 7 and 5.4 million years ago. The period of maximum cooling coincides with evidence for transient glaciations in the Northern Hemisphere and with a steepening of the pole-to-equator temperature gradient, as well. We thus infer that late Miocene aridity and terrestrial ecosystem changes occurred in a global context of increasing meridional temperature gradients. We conclude that a global forcing mechanism, such as the previously hypothesized decline in atmospheric CO2 levels between eight and six million years ago, is required to explain the late Miocene changes in temperature, climate and ecosystems.
During International Ocean Discovery Program (IODP) expeditions, shipboard-generated data provide the first insights into the cored sequences. The natural gamma radiation (NGR) of the recovered material, for example, is routinely measured on the ocean drilling research vessel DV JOIDES Resolution. At present, only total NGR counts are readily available as shipboard data, although full NGR spectra (counts as a function of gamma-ray energy level) are produced and archived. These spectra contain unexploited information, as one can estimate the sedimentary contents of potassium (K), thorium (Th), and uranium (U) from the characteristic gamma-ray energies of isotopes in the 40K, 232Th, and 238U radioactive decay series. Dunlea et al. [2013] quantified K, Th and U contents in sediment from the South Pacific Gyre by integrating counts over specific energy levels of the NGR spectrum. However, the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons. Here, we present a new MATLAB algorithm for the quantification of NGR spectra that is transparent and accessible to future NGR users. We demonstrate the algorithm's performance by comparing its results to shore-based inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-emission spectrometry (ICP-ES), and quantitative wavelength-dispersive X-ray fluorescence (XRF) analyses. Samples for these comparisons come from eleven sites (U1341, U1343, U1366-U1369, U1414, U1428-U1430, U1463) cored in two oceans during five expeditions. In short, our algorithm rapidly produces detailed high-quality information on sediment properties during IODP expeditions at no extra cost. This article is protected by copyright. All rights reserved.
A comprehensive review of dryland climates and their relationship to the physical environment, hydrology, and inhabitants. Chapters are divided into four major sections on background meteorology and climatology; the nature of dryland climates in relation to precipitation and hydrology; the climatology and climate dynamics of the major dryland regions on each continent; and an extensive review of long-term climate variability in the world's drylands. It includes key topics such as vegetation, geomorphology, desertification, micro-habitats, and adaptation to dryland environments. This interdisciplinary volume provides an extensive review of the primary literature (covering over 2500 references) and the conventional and satellite datasets that form key research tools for dryland climatology. Illustrated with over 100 photographs, it presents a unique view of dryland climates for a broad spectrum of researchers, environmental professionals and advanced students in climatology, meteorology, geography, environment science, earth system science, ecology, hydrology and geomorphology.
