Article

Holocene sedimentary record from Lake Tutira: A template for upland watershed erosion proximal to the Waipaoa Sedimentary System, northeastern New Zealand

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Abstract

A Holocene lake record from northeastern New Zealand provides a detailed record of environmental controls on upper watershed sedimentation, and is proximal to the Waipaoa MARGINS Source-to-Sink focus site. In that context, Lake Tutira in Hawke's Bay was cored in 2003 to recover a complete sedimentary record since the lake's formation ca 7.2 ka. The 27.14 m-long core contains alternating lithotypes that are sedimentary responses to lacustrine organic accumulation, normal to severe rainfalls, earthquakes and volcanism. A diatom allochthonous ranking scheme, pollen counts, and C and N percentages were used to identify intra-lake and watershed-derived storm deposits and modes of lithotype deposition. The lithotypes and depositional modes are: tephras (volcanic airfall); organic-rich mud (algal-rich lake sedimentation); massive to weakly graded, brown silty clay beds (homogenites and redeposited lake sediments); grey, graded sandy mud beds (intense storm-delivered sediment); and, thin yellow clay layers (run-off from small storms). Using 12 tephras and 3 radiocarbon ages to provide a chronology, the long-term sedimentation rate is ca 3.3 mm/year, which increases to > 10 mm/year following European colonisation.

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... For the onshore portion of the WSS, and fundamental to interpreting landscape response to tectonic and climate drivers, and sediment flux to offshore depo-centres since the Last Glacial Coldest Period (LGCP) c. 30 cal ka BP, is an understanding of the dynamics and temporal evolution of fluvially eroded landscapes (Phillips et al. 2007). In this small mountainous setting seismic events generate and transport sediment by triggering subaerial landslides to create lake environments that record climatic and tectonic events until landslide dams are breached (Pere 2003;Orpin et al. 2010;Carrasco 2012;Kuehl et al. 2016). Thus, landscape evolution and lake studies have the potential to provide clear and detailed records of changes in both sediment production and event frequency (Kuehl et al. 2016). ...
... Stratigraphic variations in magnetic susceptibility (CHI), percent total organic matter (LOI 550°C), and percent total carbonate (LOI 950°C) were not consistent between Redpath 3 and 1A (values exhibit different patterns) and offered little insight as to the correlation of the two sections. Nevertheless, low readings of magnetic susceptibility for lacustrine sediments comprising typically thin dark coloured, laminated, organic-rich, silty clay are in keeping with that recorded at Lake Tutira where depositional patterns and composition are not dissimilar (Orpin et al. 2010). Similarly, and particularly at Redpath 3, the thick mantel of iron-rich Waimihia and Taupo macroscopic tephra derived from the TVZ (Figure 1) together with iron pans and iron-rich alluvial gravels produced the highest values (Appendix A3 and A4). ...
... Lake Tutira is a natural lake formed behind a landslide dam on a landscape of Tertiary sedimentary bedrock in the onshore Hikurangi forearc, ∼120 km southwest of the Redpath site (see Kuehl et al. 2016 and references therein) (Figure 1, inset B). The laminated silt and clay at Redpath is very similar to the Type 5 lithology at Lake Tutira which is considered the product of settling of silt and clay in following small storms based on the thickness of the resulting sediment runoff layers (Page et al. 2009;Orpin et al. 2010). The ∼1-10 cm thick beds of fine to very fine sand in the Redpath sections are akin to Type 4 Lake Tutira beds interpreted by Orpin et al. (2010) as deposited by storms with the intensity of Cyclone Bola. ...
Article
A recently discovered upland paleolake (Redpath Lake) provides evidence of the expansion of lowland podocarp temperate forest to higher elevations within the tectonically active Waipaoa Sedimentary System (WSS), eastern North Island, New Zealand, during the Last Glacial-Holocene Transition. Interpreted as a localised landslide-dammed lake, lithofacies analyses indicate deposition and preservation in a low energy, sub-aqueous, lacustrine environment. Robust Bayesian-derived age-depth models constrained by key tephra fall beds and independent 14 C dating (n = 7) indicate storm-bed frequency of c. 226 yrs on average. The absence of extensive soft-sediment deformation or lake-bed tilting implies that seismic shaking was insignificant during the Lake's c. 12 ka yr (17.3-5.5 cal ka BP) existence. Pollen spectra extracted from lacustrine deposits include a mix of montane shrubland and lowland podocarp species spanning a well-dated c. 2200-year (c. 16.3-14.1 cal ka BP) period coeval with a phase of significant climate amelioration (late NZCe-5/NZce-4 mild episode), based on biotic proxies during the latter part of the climatically variable Last Glacial-Interglacial Transition (LGIT) (c. 18.2-11.8 cal ka BP). These pollen spectra represent the first New Zealand record of replacement of montane shrublands in terrestrial uplands of the WSS were replaced by lowland podocarp forest. ARTICLE HISTORY
... Lake core data provide evidence of a background rate of sedimentation. After removing the effects of airfall tephra, the long-term rate of sedimentation in Lake Tutira was 3.3 mm/year, comprising 27% from storm surges (five events in the 20 th Century were classed as storm surges, Orpin et al. 2010) and a 73% background sedimentation rate, caused by slope wash, active gully erosion and shallow landslides caused by smaller rainfall events. So, although they look dramatic, events such as Cyclone Bola in 1988 are not the major drivers of sediment in the long-term, although these large events do result in the deposition of large amounts of sediment in water courses that are a source of downstream sedimentation for decades following the events. ...
... Livestock numbers reached a peak shortly after the Livestock Incentive Scheme of 1977. The result is seen in the Tutira core samples: 90% of the catchment was pasture in 1986 (Wilmshurst 1995) and the background, or non-storm, level of sedimentation over these three decades remained at the same high post-European settlement rate of approximately 10 mm/year (Orpin et al. 2010) After Cyclone Bola there was a renewed interest in planting poplar and willow poles to reduce storm erosion and some land was totally retired. More importantly, this period coincided with a huge focus on farming efficiently. ...
... Our bush has been degraded by introduced pests and so almost certainly has a higher rate of soil loss than in prehuman times. Taking these factors into account it seems highly likely that the rate of soil loss from pasture today is well below the 200% above the pre-human base rate calculated from data (Orpin et al. 2010) for European farming prior to 1990. ...
Article
For many hill-country farms sediment will be a bigger regulatory issue than nitrates over the next decade. A dense, resilient pasture can reduce the risk of insidious sediment loss. Any ecosystem that relies on a few species is fragile. Sowing a single species leads to repeated re-sowing and increasing bare ground to remove competition, increasing the risk of sediment flows. An important issue during regulatory consultation will be establishing a natural, pre-human baseline for forest cover and documenting more recent changes in sediment flows. Hill country cropping and pasture renewal is incompatible with resilient pasture. This is a farmer’s perspective on a diverse and persisting hill country pasture-based system that can make a good return on capital without re-grassing or fodder cropping. Funding of independent research on pasture and fodder systems is essential if farmers are to make good decisions.
... Subducting seamounts on the Pacific Plate have destabilized the frontal wedge of the margin creating large arcuate slope failures (Pedley et al., 2010) including the Poverty indentation/embayment ( Fig. 1), which serves as a major canyon-fed slope depocenter ultimately linking the Hikurangi Trough to Poverty Canyon (Figs. 1,2). Seismic events also generate and transport sediment via subaerial and submarine landslides, with the former creating lake environments that record climatic and tectonic events until landslide dams are breached (Carrasco, 2012;Pere, 2003;Orpin et al., 2010) and the latter creating seismogenic turbidite records in slope basins (Pouderoux et al., 2012b). ...
... Given the close proximity of sediment sources and vigorous maritime climate, sediment deposits resulting from storms occur continuously throughout the lake record, intercalated with the other sediment types. Page et al. (2010) investigated the relationship between frequency and magnitude for 1400 storms identified in the Tutira sediment record, and hindcast from layers of 0.05-20 + cm thickness that correlate linearly to historical rainfall intensity (Eden and Page, 1998;Orpin et al., 2010). Here, the average frequency of all storm layers is 1-in-5 years with a standard deviation of 14 years. ...
... But for storm layers ≥1.0 cm thick, the average frequency is every 53 years, with a considerably larger standard deviation of 75 years, testament to the variability of large rainfall events . The historical record was used by Orpin et al. (2010) to hindcast over the 7.1 ky pre-historic period using the relationship of storm-bed thickness and rain intensity, which indicates that~53 storms occurred similar in magnitude to an event like Cyclone Bola that produced a 21.5-cm-thick storm deposit. A further 7 similarly large pre-historic storm beds (N10 cm thickness) are inferred to reflect extreme, catastrophic rainfall events. ...
Article
A fundamental goal of the Earth Science community is to understand how perturbations on Earth's surface are preserved in the stratigraphic record. Recent Source to Sink (S2S) studies of the Waipaoa Sedimentary System (WSS), New Zealand, are synthesized herein to provide a holistic perspective of the processes that generate, transport and preserve sedimentary strata and organic carbon on the Waipaoa margin in the late Quaternary. Rapid uplift associated with subduction processes and weak sedimentary units have conspired to generate rapid rates of incision and erosion in the Waipaoa catchment since the Last Glacial Maximum (LGM). We show that although much of the sediment exported offshore during this time interval originated from valley excavation, a substantial portion emanated from hillslopes, mostly through deep-seated landslide and earthflow processes that were vigorous during periods of rapid fluvial incision just prior to the Pleistocene–Holocene transition. Lacustrine sediments deposited in naturally-dammed 7-ky-old Lake Tutira provide a record of Holocene environmental controls on upper catchment sedimentation in the WSS, with 1400 storms identified. Storm frequency is modulated by the waxing and waning of atmospheric teleconnections between the tropics and Antarctica. Furthermore, clear long-term changes in sediment yield are evident from the Lake Tutira record following human settlement as conversion to pasture is accompanied by a 3-fold increase in the long-term lake sediment accumulation rate.
... Turbidites are also found in lake sediments, and turbidite palaeoseismology has become a useful tool to reconstruct earthquake chronologies from lakes in close proximity to crustal and subduction zone faults. The time span represented by these records is variable, but frequently surpasses 10 000 yr. Lacustrine turbidite palaeoseismology has been used to reconstruct earthquake chronologies around the world, including Switzerland (Schnellman et al., 2002;Arnaud et al., 2006;Strasser et al., 2006), Chile, (Arnaud et al., 2006;Moernaut et al., 2007;Bertrand et al., 2008;Charlet et al., 2008), Argentina (Waldmann et al., 2008), Venezuela (Carrillo et al., 2008), France (Chapron et al., 1999;Arnaud et al., 2002;Guyard et al., 2007;Beck, 2009), Kyrghyzstan (Bowman et al., 2004), Japan, (Shiki et al., 2000a), Russia (Nelson et al., 1995), Canada (Doig, 1986(Doig, , 1990(Doig, , 1991, New Zealand (Orpin et al., 2010;Howarth et al., 2012), California (Smoot et al., 2000;Seitz and Kent, 2005;Kent et al., 2005;Brothers et al., 2009), Arizona (Twitchell et al., 2005), as well as in the vicinity of the CSZ at Lake Washington, USA (Karlin et al., 2004;Abella, 1992, 1996). In favourable settings, reconstructions can reach 50 000 yr (late-Pleistocene Lake Lisan, palaeo-Dead Sea; Marco et al., 1996). ...
... Homogenites and turbidites are typically visible, thick, basin-wide deposits and are best suited for large-scale palaeoseismology (e.g. Orpin et al., 2010;Strasser et al., 2007;Karlin et al., 2004;Seitz and Kent, 2005;Strasser et al., 2006). As with marine turbidite palaeoseismology, turbidite characteristics have been correlated within lake basins and fjords to establish stratigraphic continuity and suggest earthquake triggering (Karlin et al., 2004;Seitz and Kent, 2005;Guyard et al., 2007;Waldman et al., 2008). ...
... There are no definitive tests that can positively identify an earthquake source mechanism, though arguments for internal or external sources of sediment to the lake have been made on the basis of grading characteristics, chemistry, and diatom assemblages (e.g. Orpin et al., 2010). Here we review event triggers other than earthquakes to explain the presence of rapidly deposited terrigenous layers in lake sediments. ...
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Article
Here we investigate sedimentary records from four small inland lakes located in the southern Cascadia forearc region for evidence of earthquakes. Three of these lakes are in the Klamath Mountains near the Oregon-California border, and one is in the central Oregon Coast range. The sedimentary sequences recovered from these lakes are composed of normal lake sediment interbedded with disturbance event layers. The thickest of these layers are graded, and appear to be turbidites or linked debrites (turbidites with a basal debris-flow deposit), suggesting rapid deposition. Variations in particle size and organic content of these layers are reflected in the density and magnetic susceptibility data. The frequency and timing of these events, based on radiocarbon ages from detrital organics, is similar to the offshore seismogenic turbidite record from trench and slope basin cores along the Cascadia margin. Stratigraphic correlation of these anomalous deposits based on radiocarbon ages, down-core density, and magnetic susceptibility data between lake and offshore records suggest synchronous triggering. The areal extent and multiple depositional environments over which these events appear to correlate suggest that these deposits were most likely caused by shaking during great Cascadia earthquakes.
... In this paper we extend the hypothesis that ENSO and SAM interact to influence storm activity over northeastern New Zealand, by examining published, high-resolution paleoclimate records from the west-central region of the North Island and southern South America. First, we use the signature of large rainfall events preserved in Lake Tutira core LT24 (Orpin et al., 2010; Page et al., 2010; Figure 1 ), in conjunction with the sediment record from Poverty Shelf core MD972122 (Gomez et al., 2004aGomez et al., , 2007; Figure 1), to contextualize the regional response erosion processes had to variations in eastern North Island rainfall that were a product of interactions between ENSO and the SAM in middle and late Holocene. Then we consider variations in Holocene rainfall across the North Island, by comparing the Lake Tutira record with the master speleothem carbon isotope (δ 13 C) record from caves in the Waitomo district of the west-central North Island (Williams et al., 2004; Figure 1). ...
... Conversely, the teleconnection weakens when the climate modes are out of phase. Terrigenous sediment layers in core LT24 from Lake Tutira (39.22°S, 176.89°E; Figure 1 ) provide an uncensored and sensitive record of upland storm-driven erosional activity that initiated surface and channel erosion and shallow landslides on hillslopes in the surrounding 32 km 2 catchment (Orpin et al., 2010; Page et al., 2010 ). Layer thickness and lithotype are positively correlated with storm rainfall, and an assemblage of 397 clay layers and sand-silt-clay graded beds records variations in the South Pacific atmospheric circulation linked to ENSO and the SAM, that combined to influence the frequency of the largest magnitude rainstorms (event rainfall ≥300 mm) during the middle and late Holocene (). ...
... Macklin et al. (2012) confirmed that the Lake Tutira storm sediment record consistently captures extreme hydrological events preserved in the New Zealand Holocene fluvial sedimentary record as a whole. Our own analysis shows that extreme events in the >100 yr long modern rainfall record typically occur in years when annual rainfall exceeds the mean, and months with storms account for up to 39% of the annual rainfall (Orpin et al., 2010). The number of extreme rainfall events in the Lake Tutira archive varies over decadal to centennial timescales, and major periods of storm activity correlate with other Southern Hemisphere proxy climate data (Page et al., 2010). ...
Article
Intercorrelated terrestrial and marine records from New Zealand, Chile and Argentina provide the first evidence of a coherent pan-Pacific response to the growing influence that El Niño-Southern Oscillation (ENSO) and multicentury variations in the interaction between ENSO and the Southern Annular Mode (SAM) exerted on rainfall in the Southern Hemisphere mid-latitudes during the middle and late Holocene. Rainfall is also strongly influenced by moisture originating from the prevailing southern westerly winds (SWW), and we find that the variations in rainfall forced by the interaction of ENSO and the SAM are superimposed on an underlying long-term trend induced by a temporal strengthening of the westerly circulation. We conclude that the evolution of rainfall across the South Pacific reflects the influence seasonal insolation exerts on: (1) ENSO/SAM interactions; and (2) the strength of the SWW.
... Lake Tutira (39.223°S, 176.890°E) was formed by a coseismic landslide at ~7200 cal. yr BP (Orpin et al., 2010 ), and podocarpbroadleaved forest originally covered the 32 km 2 catchment surrounding the lake (McGlone, 2002). Humans used fire to destroy the native forests from ~500 cal. ...
... Piston core LT24 contains >1400 clay layers and sand-silt-clay graded beds ≥0.5 mm thick that provide an uninterrupted ~7000 yr long record of storm-driven erosional activity on hillslopes in the Lake Tutira catchment (Orpin et al., 2010; Page et al., 2010). LT24 was obtained ≤10 m from the location of core LT15, which has been the focus of efforts to evaluate paleostorm magnitude (Eden and Page, 1998; Page et al., 1994). ...
... LT24 was obtained ≤10 m from the location of core LT15, which has been the focus of efforts to evaluate paleostorm magnitude (Eden and Page, 1998; Page et al., 1994). Core chronologies rely on linear interpolation between well-established tephra dates supplemented by radiocarbon ages with uncertainties of ±100 yr (Eden and Page, 1998; Orpin et al., 2010). The event stratigraphy in the historic period is contingent on observed rainfall. ...
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Article
A new chronology of large magnitude rainfall events derived from the continuous high-resolution Lake Tutira storm sediment record covers the last 6800 years and provides the first insight into changes in El Niño-Southern Oscillation (ENSO) teleconnections to the higher southern latitudes to be obtained from New Zealand. Synthesis with independent paleoclimate records from the tropical Pacific and Antarctica also reveals a millennial-scale waxing and waning of the teleconnections that were not visible in the narrow historical window previously used to view interactions between ENSO and the Southern Annular Mode (SAM). Consistent with modern ENSO behaviour, we find teleconnections to the Southwest Pacific varied throughout the middle and late Holocene, depending on the strength and phase of ENSO and the phase of the SAM. We suggest that precession-driven changes in the seasonal cycle of solar radiation exert a first-order control on the interaction between the two climate modes. Consequently, their present status may neither be indicative of conditions that prevailed earlier in the Holocene, nor of those that might be associated with future climate changes in the Southern Hemisphere extratropics.
... Here, we used HydroTrend (Kettner and Syvitski, 2008a), a climate driven hydrological model, along with best estimates of climate variation through time to interpret environmental factors such as vegetation cover and unravel the important drivers of sediment delivery from the Waipaoa River mouth since the LGM. Using a sediment core from Lake Tutira to reconstruct the trend in regional rainfall (Orpin et al., 2010; Page et al., 1994, 2010) and a reconstruction of shoreline progradation across the Poverty Bay Flats (Wolinsky et al., 2010) we extend the 3000 year model of Kettner et al. (2007) back to the mid Holocene (5.5 cal ka, note that all ages used in this manuscript are calibrated ). We also use terrestrial and marine paleoenvironmental indicators in conjunction with a simulated model of northeast New Zealand's climate at the LGM (Drost et al., 2007) to tune a lower resolution version of the model and extend the simulation back to 22 ka, at the Last Glacial Maximum (LGM). ...
... In the historic record the $1:100 yr March, 1988 Cyclone Bola storm caused wide-spread landsliding and intensified gully erosion in the catchment and generated $36 million tonnes of suspended sediment in a 3 day period (Hicks et al., 2004). A hind-cast relationship based on the storm sediment record from Lake Tutira suggests that there may have been $53 pre-historic storms with a magnitude similar to the Cyclone Bola event in the past $7 ka, and perhaps 7 even larger catastrophic storm events (Orpin et al., 2010). Although under modern pastoral land use events of low and intermediate magnitude dominate suspended sediment yield (Hicks et al., 2000, 2004), these largemagnitude events dominated in the period prior to human arrival (40.5 ka), when the indigenous vegetation substantially decreased landscape sensitivity (Gomez et al., 2007a; Trustrum et al., 1999). ...
... We attempted to estimate erosion conditions within the Waipaoa catchment at the LGM. Lack of significant forest cover in the catchment at LGM is expected to have led to increased sediment loads (Orpin et al., 2010; Page and Trustrum, 1997; Page et al., 2010). Unlike today, the dominant ground cover was tussocks and native grasses with some shrublands. ...
... Situated 85 km west of Mahia Peninsula and 30 km above the subduction interface is Lake Tutira (Fig. 9). A 37 m-long lake sediment core archives a continuous record of mass-transport deposits, tephra and autochthonous muds that spans the last~7000 years (Orpin et al., 2010). 119 'homogenites' composed of fining upwards, largely autochthonous, silty clays are inferred to be formed by earthquake triggered subaqueous mass-wasting (Orpin et al., 2010;Gomez et al., 2015). ...
... A 37 m-long lake sediment core archives a continuous record of mass-transport deposits, tephra and autochthonous muds that spans the last~7000 years (Orpin et al., 2010). 119 'homogenites' composed of fining upwards, largely autochthonous, silty clays are inferred to be formed by earthquake triggered subaqueous mass-wasting (Orpin et al., 2010;Gomez et al., 2015). Triggering earthquakes are inferred to generate shaking of Modified Mercalli Intensity (MMI) VII or greater at the lake site. ...
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Article
The Hikurangi subduction margin, New Zealand, has not produced large subduction earthquakes within the short written historic period (~180 years) and the potential of the plate interface to host large (M > 7) to great (M > 8) earthquakes and tsunamis is poorly constrained. The geological record of past subduction earthquakes offers a method for assessing the location, frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments. We review evidence of Holocene coseismic coastal deformation and tsunamis at 22 locations along the margin. A consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake. To identify possible subduction earthquakes, we use temporal correlation of earthquakes, combined with the type of earthquake evidence, likely primary fault source and the earthquake certainty ranking. We identify 10 past possible subduction earthquakes over the past 7000 years along the Hikurangi margin. The last subduction earthquake occurred at 520–470 years BP in the southern Hikurangi margin and the strongest evidence for a full margin rupture is at 870–815 years BP. There are no apparent persistent rupture patches, suggesting segmentation of the margin is not strong. In the southern margin, the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved. The pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes, demonstrating different modes of slip behaviour occur on the central Hikurangi margin. Evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record. Large uncertainties remain in regard to evidence of past subduction earthquakes on the Hikurangi margin, with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages, and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes. However, areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future.
... Broad paleoclimatic conditions in the Waipaoa sedimentary system can be inferred from a number of paleoclimate studies using proxy data such as pollen assemblages, changes in sedimentation, and stable isotope ratios from sites around the North Island East Coast and the North Island in general (Fig. 1). Holocene records include speleothems from the Hawke Bay region (Lorrey et al., 2008), sediment cores from Lake Tutira Orpin et al., 2010;Gomez et al., 2011), and a sediment core from Repongaere Swamp within the Waipaoa catchment (Wilmshurst et al., 1999). Latest Pleistocene to Holocene paleoclimate proxy data from around the East Coast are derived from sediments from Kaipo Bog (Hajdas et al., 2006;Newnham and Lowe, 2000;Lowe et al., 1999) 2014 2004). ...
... Our observations are consistent with theories for threshold hillslopes where vertical river incision into bedrock oversteepens hillslopes to gradients near threshold angles, leading to increasing relief until gravitational stress exceeds mountain-scale material strength, and deepseated bedrock landsliding ensues (e.g., Pettinga, 1980;Pettinga and Bell, 1992;Schmidt and Montgomery, 1995;Burbank et al., 1996;Montgomery, 2001;Montgomery and Brandon, 2002;Binnie et al., 2007;Larsen and Montgomery, 2012). Deep-seated landslides in the Waipaoa sedimentary system may have been triggered by intense or long-duration precipitation events common to the Waipaoa sedimentary system Gomez et al., 2013) or by seismic events (Litchfi eld et al., 2009;Orpin et al., 2010), but the underlying causes for the observed widespread landsliding are river incision and low bedrock mass strength. ...
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Article
Quantifying how hillslopes respond to river incision and climate change is fundamental to understanding the evolution of uplifting landscapes during glacial-interglacial cycles. We investigated the interplay among uplift, river incision, and hillslope response in the nonglacial Waipaoa River catchment located in the exhumed inner forearc of an active subduction margin on the East Coast of the North Island of New Zealand. New high-resolution topographic data sets (light detection and ranging [lidar] and photogrammetry) combined with field mapping and tephrochronology indicate that hillslopes adjusted to rapid latest Pleistocene and Holocene river incision through the initiation and reactivation of deep-seated landslides. In the erodible marine sedimentary rocks of the Waipaoa sedimentary system, postincision deep-seated landslides can occupy over 30% of the surface area. The ages of tephra cover beds identified by electron microprobe analysis on 80 tephra samples from 173 soil test pits and 64 soil auger sites show that 4000-5000 yr after the initiation of river incision, widespread hillslope adjustment started between the deposition of the ca. 14,000 cal. yr B.P. Waiohau Tephra and the ca. 9420 cal. yr B.P. Rotoma Tephra. Tephrochronology and geomorphic mapping analysis indicate that river incision and deep-seated landslide slope adjustment were synchronous between main-stem rivers and headwater tributaries. Hillslope response in the catchment can include the entire slope, measured from river to ridgeline, and, in some cases, the interfluves between incising subcatchments have been dramatically modified through ridgeline retreat and/or lowering. Using the results of our landform tephrochronology and geomorphic mapping, we derive a conceptual time series of hillslope response to uplift and climate change-induced river incision over the last glacial-interglacial cycle.
... The continental shelves occupy an area of 27.5 × 10 6 km 2 , where a large amount of sediment is trapped (Petley, 2010). Although the interpretation of these records is more complicated than for other deposits, such sedimentary records should not be neglected (Orpin et al., 2010). Coastal and shelf sedimentary systems are sensitive to sea level changes. ...
... Thus, in situ measurements were carried out extensively to obtain information on the dynamic and sediment parameters (e.g., tidal currents, suspend sediment concentrations, setting velocity, near-bed shear stress, and flocculation) (Sternberg, 1967;Sternberg et al., 1973Sternberg et al., , 1986Evans and Collins, 1975;Collins et al., 1981;Downing et al, 1981). The intensity and spatial distributions of sediment transport was used then to explain the deposition rate and sequence distribution, as revealed by 210 Pb analysis and seismic surveycores (Orpin et al., 2010). Recently, numerical modeling, taking into account the various processes, has been adopted to predict the formation of sedimentary strata. ...
... (2) If each silt package was initiated by an extreme storm, then this implies only 22 such events occurred in the period from A.D. 800 to 6000 B.C. This is a low frequency compared with other New Zealand storm records (e.g., Griffi ths and McSaveney, 1983;Orpin et al., 2010;Page et al., 2010). ...
... They tend to have an irregular pattern, with an esti- mated average of 3-5 silt beds (millimeter-to centimeter-scale) per century, a rate more com- patible with an extreme storm record (cf. Lake Tutira record, Page et al., 2010). ...
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In southern and central South Island, New Zealand, the Alpine fault is the principal component of the weakly partitioned plate boundary, and it carries 70-75% of the total relative motion between the Australian and Pacific plates. At the Hokuri Creek site on the southernmost on-land section of the fault, recurrent surface rupture for a period of c. 7000 years has resulted in the temporary blockage of Hokuri Creek with consequent changes in environmental conditions in the adjacent alluvial sequence. Pale silt-dominated units are interpreted as clastic alluvial sediment and the dark coloured organic silts and peats are interpreted as units with a much higher component of locally-derived sediment (Clark et al., this meeting). The changes from ``peat'' to ``silt'' are interpreted to be event horizons of Alpine Fault rupture. At least eighteen couplets of ``silt and peat'' occur in the interval between about 1000 cal BP and 8000 cal BP. At Haast, about 100 km northeast of Hokuri Creek, the last three surface faulting events are recorded in trench stratigraphy. The youngest event at Hokuri Creek and the oldest event at Haast are coincident, and thus our composite record covers the last 20+ surface rupturing events on the Alpine Fault. Event ages have been derived from the larger radiocarbon age dataset (Biasi et al., this meeting), and indicate variable fault rupture recurrence behaviour. But the recurrence is not highly variable from event-to-event, with few intervals that are greater than 1.5 times the average of 390 years. However, in the c. 3000 year period between 5800 and 3000 years ago, and between the three most recent events, the recurrence intervals were consistently longer than average. The three most-recent events from Haast show that recurrence interval has been close to 500 years. It is possible that the long term average dextral slip rate of 25 mm/yr can be maintained during these periods of longer recurrence by larger displacements (requires about 12 m of slip per event for a 500 year recurrence interval). However, this is not borne out by events in the last 1000 years when the three dextral displacements were all in the range of 8±1 m. Another possibility is that there could be accelerated activity on other elements of the partitioned plate boundary when the Alpine fault is in its long recurrence mode.
... Auckland Volcanic Field-derived basaltic tephras 'AVF#' are given their centre names where the correlation is classified as 'Confidence Level 1 or 2' in Hopkins et al. (2017). Lakes Rotomanuka and Maratoto (composite core) after Green and Lowe (1985) and Lowe (1988aLowe ( , 2019; Kaipo bog from Lowe et al. (1999;Lowe et al. 2013); Lake Tutira from Eden et al. (1993) and Orpin et al. (2010); MD97-2121 marine core from Carter et al. (2002) and Taiapa (2016), '?' indicates a suggested correlation; ODP 181 sites 1123, 1124, and 1125 combined from Alloway et al. (2005), Allan et al. (2008), and Stevens (2010). Core source for each tephra is noted. ...
Article
Tephra deposits in Aotearoa New Zealand (ANZ) have been studied for >180 years. The now-global discipline of tephrochronology, which has some developmental roots in ANZ, forms the basis of a powerful chronostratigraphic correlational tool and age-equivalent dating method for geological, volcanological, palaeoenvironmental, and archaeological research in ANZ. Its utility is founded on the key principle that tephras or cryptotephras provide widespread isochrons in many different environments. In the first part of this article, we summarise the history of tephra studies in ANZ and then describe how tephras have been mapped, characterised, and correlated using field and laboratory-based methods. We document advances in geochemical fingerprinting of glass; tephra/cryptotephra detection and correlation by sediment-core scanning methods (e.g. X-radiography, CT imaging, XRF elemental analysis, magnetic susceptibility); statistical correlation methods; and dating of tephras/cryptotephras. We discuss the advent of ANZ cryptotephra studies (from mid-1970s) and their more-recent growth. The second part comprises examples of applications of tephrochronology in ANZ: climate-event stratigraphy (NZ-INTIMATE project); eruptive-event stratigraphy in the Auckland Volcanic Field; developments in the marine tephra record; advances in identifying, correlating, and dating old (pre-50 ka) tephras and weathered-tephra deposits; forming soils/paleosols on tephras; tephras and archaeology; Kopouatai bog tephrostratigraphy and palaeoenvironments; and volcanic-hazard assessments.
... These values are more than triple (linear) and double (mass) the mean rates measured at Kalilani Bay (Fig. 6). We interpret these data as spatially integrated evidence in support of the hypothesis that deforestation increases sediment accumulation rates in Lake Tanganyika, as has been observed in other lakes with drainage areas characterized by human land use modifications (e.g., Plater et al., 2006;Orpin et al., 2010;Chen et al., 2015;Poraj-Gorska et al., 2017). Our data detect sediment pollution in the sub-littoral zone offshore from a $15 km stretch of shoreline in the co-management area. ...
Article
Climate warming coupled with local disturbances within lakes are an accelerating global problem. This issue is acute at Lake Tanganyika (eastern Africa), where warming and overfishing have resulted in declining rates of pelagic fish catches and structural damage to diverse littoral cichlid communities. This deteriorating has fueled demand for alternative livelihoods, and thus conversion of shoreline-adjacent forests to agricultural fields and oil palm orchards, which in turn heightens the threat of siltation on nearshore benthic habitats. The spatial variability of sediment pollution is unknown, however, posing a barrier to effective conservation. This paper assesses the spatial patterns of nearshore sediment accumulation within the Tuungane Project co-managed area of Lake Tanganyika in Tanzania. Analysis of lead-210 data show that the mean nearshore mass-based sediment accumulation rate is 0.06 grams * centimeters⁻²* year⁻¹(g cm⁻² yr.-1) across six sites adjacent to deforested watersheds, double the mean rate (0.03 g cm⁻² yr.⁻¹) at a comparable but undisturbed control site. Spatial variance among rates is best explained by distance to deltaic point sources and bathymetric gradients. Data documenting carbon flux demonstrate that organic matter burial is higher in surface sediments offshore from deforested watersheds, consistent with onshore land use changes that promote erosion. Knowledge of sediment pollution patterns, coupled with maps of rocky benthic habitats, provide the necessary framework for effective conservation planning of fisheries in the present era of accelerated human interactions with the lake and its watershed. Findings provide a model for improved integrated management practices in large tropical artisanal fisheries in other parts of Africa.
... E-mail: hg_jinan@163.com Chen, 1993;Hori et al., 2002;Petley, 2010;Orpin et al., 2010;Gao, 2013), deep sea areas (Berger, 2013), ice (Davies et al., 2012), and coral reefs (Yu et al., 2006) contain indicators, which may be useful for paleoclimate or paleoenvironmental analysis. The coastal inner shelf has many advantages for studying environmental evolution based on the sedimentological record, especially during the Holocene, due to the vast quantities of terrestrial sediment transportation and subsequent high sedimentation rates. ...
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Article
Large amounts of sediments originating from the Changjiang (Yangtze) River are deposited in the subaqueous delta and in the adjacent muddy area off the mouth and on the inner shelf of the East China Sea. The terrestrial sediments deposited in these areas not only contain information about the composition and environment of the source area, but they also record changes in anthropogenic activities. A sediment piston core (CJ0702) was extracted from the Changjiang subaqueous depocenter (31.00°N, 122.67°E) in a water depth of 22.0 m. The core was subsampled at 1–2 cm intervals and analyzed for grain size, clay mineralogy, and major element geochemistry. Results indicate a relatively high sediment accumulation rate of approximately 3.11 cmyr−1. These parameters exhibited only minor cyclical fluctuations in the core, which resulted from many factors. During the past 120 years, the Changjiang River-derived sediment is the primary source of sediment in the offshore mud area without evidence for the Yellow River-derived sediment increasing. After the trunk stream shifted from the North Branch to South Branch, the variations of proxies are controlled by the periodic fluctuation possibly linked to El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). In addition, anthropogenic heavy metal concentrations can be divided into three stages, which coincide well with economic development and environmental protection policies.
... Kelling and Mullin 1975;Allen 1982;Johnson 1989;Donnelly et al. 2001;Ito et al. 2001;Pochat et al. 2005;Woodruff et al. 2008;Dezileau et al. 2011;Otvos 2011;Phantuwongraj et al. 2013;Li et al. 2014). Impact of storms is relatively less observed on sedimentary succession of non-marine basins such as lacustrine basins and is much less mentioned in geologic records (Greenwood and Sherman 1986;Hamblin 1992;Basilici 1997;Weidong et al. 1997;Eden and Page 1998;Houser and Greenwood 2005;Li et al. 2007;Orpin et al. 2010;Page et al. 2010;Liu et al. 2012;Li et al. 2014;Wang et al. 2015;Nutz et al. 2017Nutz et al. , 2018. ...
Article
Coastal environments are exposed to frequent and intense storm events which are one of the most important elements of sedimentation dynamics in nearshore environments. However, lacustrine storm deposits are rare Late Quaternary sediments of the Lake Van Basin, Turkey, which allow to analyse that kind of storm deposits in a closed lacustrine basin. The storm-induced sedimentary structures evaluated in these deposits reflect erosional and depositional storm processes and encompass erosional surfaces, graded bedding, wave-ripple crossbeds, parallel bedding, shell beds and biogenetic escape structures. They are present in both marginal and relatively deeper lacustrine facies. Evaluations of sedimentological and palaeontological features of storm deposits together with modern storm records of the Lake Van indicate intense storm effect on sedimentation.
... A more detailed and quantitative documentation of processes, rates, and spatial distribution of sedimentation does not necessarily equate to a better understanding of linkages between system segments. Better preserved and potentially more complete records in proximal storage areas, such as lakes, might allow more detailed records to be captured up system, but the localized nature might not reflect broader system functioning (e.g., Orpin et al., 2010). Combining observations from multiple localities will be essential to defining robust regional or global signals (e.g., Noren et al., 2002). ...
Preprint
Review of concepts of environmental signal (climate, tectonics, anthropogenic, etc.) propagation in sedimentary systems from source to sink.
... Previous work using Holocene macrotephra in Lake Pupuke indicates infrequent recurrence of tephra fall events in Auckland (one per 1500 years on average in the last 10 200 years; Horrocks et al., 2005;Molloy et al., 2009), although numerous tephra are known from this period at other distal locations (e.g. Lowe, 1988;Eden and Froggatt, 1996;Gehrels et al., 2006;Orpin et al., 2010). Five macrotephra (subalkalic and alkalic basaltic Rangitoto, and rhyolitic Taupo, Whakaipo and Tuhua) and 18 cryptotephra were identified in core Pup 6_06 (Table 1) with correlation confidence ranging from low to very high (Table 2). ...
Article
Post-depositional reworking of volcanic glass shards is a common problem in tephrochronological studies. Distinguishing between primary and reworked tephra is challenging, particularly in cryptotephra investigations that depend on identifying peaks of glass shard concentrations in sediment sequences rather than discrete macroscopic tephra layers. Here, we investigated macro- and cryptotephra in sediments of Lake Pupuke, New Zealand, to identify primary from reworked tephra and thus refine the record of tephra-fall events in the region over the last ca. 9 cal ka. Geochemical fingerprinting, stratigraphic correlation, 14C ages and X-ray fluorescence and magnetic susceptibility core scanning were employed to filter out reworked tephra and thus establish a new Holocene tephrochronological framework for the region. Five primary macrotephra layers and 18 primary cryptotephra were identified. Confidence levels are attached to the newly identified cryptotephra, and geochemical characterization of well-dated rhyolite tephra was used to establish an associated age model. Our results suggest that Holocene tephra fall from both local and distal volcanoes affected Auckland more frequently than previously documented, with a possible average frequency of at least once every 424 years. Furthermore, the study demonstrates the importance of identifying the extent of post-depositional reworking to establish the veracity of the cryptotephra record.
... The marine geologic record is incomplete, complicating interpretation of seabed observations (e.g. Sadler, 1981;Orpin et al., 2010). Flood deposits, for instance, comprise significant components of the geologic record on river-dominated margins, but are often reworked by physical and biological processes following initial emplacement (e.g. ...
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Article
The formation of the geologic record offshore of small mountainous rivers is event-driven and, more so than many other environments, can result in relatively complete sequences. One such river, the Waipaoa in New Zealand, has been studied from its terrestrial source to its oceanic sink over timescales spanning storms, seasons, and the Holocene. This study focused on the formation of riverine deposits on the Waipaoa Shelf during episodic flood and wave events, contrasting deposition during short-lived events to accumulation patterns created over thirteen months. Sediment fluxes and fate were estimated using the numerical hydrodynamic and sediment transport model ROMS, the Regional Ocean Modeling System, using CSTMS, the Community Sediment Transport Modeling System. During the study period (January 2010-February 2011), the model indicated that initial flood deposition generally occurred near the river mouth and along the coast in water shallower than 40. m, and that deposition during any one event was sensitive to variations in shelf currents and wave energy. Also, the sedimentation due to plume settling and suspended transport during these relatively short flood and wave events were not aligned with longer time-scale accumulation patterns (months or greater) previously reported for the Waipaoa shelf. In the days to months following a flood pulse, waves episodically reworked this initial deposit, resuspending centimeter-scale layers of sediment during energetic periods. Frequent and intense resuspension occurred in shallow areas where bed stresses were high. This encouraged redistribution of material toward deeper areas having lower near-bed wave stresses, including continental shelf depocenters and offshore areas. While fast settling material was preferentially retained near the river mouth, currents dispersed slower settling sediment farther before deposition. Overall, accumulation depended on characteristics of oceanographic transport (wave energy, current velocities), not just source characteristics (flood size, sediment size distribution).
... A number of these records are documented across the Northern Hemisphere (Mann et al. 2008;Ojala et al. 2012), but there remains a need to develop highresolution paleoclimate reconstructions from the Southern Hemisphere (Neukom and Gergis 2012). New Zealand is one of only few landmasses that lie in the core of the climatically important Southern Hemisphere westerly wind belt but few high-resolution terrestrial paleoclimate records have been recovered from the North and South Islands (Page et al. 1994Cook et al. 2002Cook et al. , 2006Lorrey et al. 2008;Orpin et al. 2010;Augustinus et al. 2011;Fowler et al. 2012;Striewski et al. 2013). Sediment cores collected from distal end of Lake Ohau, South Island, New Zealand ( Fig. 1) contain clastic varves, providing an opportunity to produce a high-resolution paleoclimate record from this important mid-latitude region (Roop et al. 2015). ...
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Article
Annually laminated sediments collected from Lake Ohau, New Zealand offer an opportunity to generate a high-resolution paleoclimate record for the Southern Hemisphere mid-latitudes. Correlation between regional precipitation and synoptic climate indices like the Southern Annular Mode, paired with a correlation between Ohau catchment precipitation, lake inflow and suspended sediment yield suggest that the Lake Ohau varves are a potentially powerful tool for estimating the amplitude, timing and interdependence of different climate modes operating in the Southern Hemisphere mid-latitudes over time. A robust chronology and sound climate-proxy model are fundamental requirements for all high-resolution paleoenvironmental records. Here we present a chronology derived from layer counts, and 137Cs and 210Pb ages for the top 60 cm of sediments from the distal basin of Lake Ohau that confirm the varved natured of the sedimentary sequence. Sedimentary facies of different varve motifs are used to develop a hydroclimate-proxy model which links stratigraphy to seasonal hydrology. To establish this relationship we use a model accuracy statistic, which shows a quantitative difference between the annual hydrographs associated with each of three primary varve motifs. Distribution of above average inflow events points to summer and autumn hydrologic regimes as the primary control on the deposition of different motifs. This relationship between varve characteristics and hydrology will serve as a tool to reconstruct lake inflow, and by extension precipitation, on an annual basis throughout the late-Holocene for the South Island of New Zealand.
... A more detailed and quantitative documentation of processes, rates, and spatial distribution of sedimentation does not necessarily equate to a better understanding of linkages between system segments. Better preserved and potentially more complete records in proximal storage areas, such as lakes, might allow more detailed records to be captured up system, but the localized nature might not reflect broader system functioning (e.g., Orpin et al., 2010). Combining observations from multiple localities will be essential to defining robust regional or global signals (e.g., Noren et al., 2002). ...
... Studies attempting to explore these issues have used sediment cores from lakes, bogs, estuaries and harbours throughout the country (Goff 1997;McGlone & Wilmshurst 1999;Wilmshurst et al. 1999;Nichol et al. 2007). However, some of the most comprehensive and -23-numerous studies have been conducted using cores from Lake Tutira, Hawke"s Bay (Turner 1997;Wilmshurst 1997;Eden & Page 1998;Page et al. 2004;Orpin et al. 2010). This relatively small, deep lake with a small catchment is located in an area subject to various natural phenomena such as subtropical storms which erode the surrounding soft rock, volcanic ashfall, and earthquakes. ...
... About 10 years after the initiation of research into modern marine storm facies, the terrigenous aspect of such deposits was also investigated (e.g., Kelling and Mullin, 1975;Kreisa, 1981). More recently, Page et al. (2010) and Orpin et al. (2010) identified several vast Holocene storms in New Zealand and their response in local lacustrine strata records. Modern lacustrine turbidite deposits in mountain areas of the Alps were studied by Fanetti et al. (2008), but he apparently omitted vast storms as trigger mechanisms for these deposits. ...
Article
A Late Cretaceous tempestite in the northern Songliao Basin, China, was studied based on thin-section and granularity analyses of borehole samples. The results indicated that the local tempestite can be categorized into several clastic constituent types, which include bottom erosion structures, graded beds, hummocky cross stratification (HCS), parallel beds, wave marks, and bioturbation structures. Based on these sedimentary characteristics and vertical sequence combinations, four tempestite sedimentary models were developed: (I) an autochthonous tempestite facies, (II) an allochthonous tempestite fades (the proximal subfacies), (III) a second allochthonous tempestite facies (the distal subfacies), and (IV) a turbidite facies. (C) 2012 Published by Elsevier Ltd.
... Unfortunately, there are not many areas of the Southern Hemisphere where annual or near-annual sedimentary records currently meet these requirements and the data are publically available (Black et al., 2007;Boës and Fagel, 2008;Rein, 2007;von Gunten et al., 2009). While a small number of 'high resolution' (decadal to centennial) sedimentary records covering the last 1000 years are available from South America (Conroy et al., 2008;Haberzettl et al., 2007;Lamy et al., 2001;Mohtadi et al., 2007;Moreno et al., 2009;Moy et al., 2002Moy et al., , 2009Piovano et al., 2009), Africa (Garcin et al., 2007;Johnson et al., 2001;Russell and Johnson, 2007;Stager et al., 1997;Verschuren et al., 2000), Indonesia (Langton et al., 2008;Oppo et al., 2009;Van Der Kaars et al., 2010), New Zealand (Eden and Page, 1998;Orpin et al., 2010;Page et al., 2010), Australia (Mooney, 1997;Moros et al., 2009;Skilbeck et al., 2005) and Antarctica (Verleyen et al., 2011), in practice they are better for independent decadal verification to preserve the chronological accuracy of the (still relatively small) absolutely dated network of high annual palaeoclimate records currently available from the Southern Hemisphere. There is great potential to use these lower resolution records to examine decadal-multidecadal low frequency climate variability alongside high resolution records as has been done for a handful of multiproxy studies (Mann et al., 2008(Mann et al., , 2009Moberg et al., 2005). ...
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Article
This study presents a comprehensive assessment of high-resolution Southern Hemisphere (SH) paleoarchives covering the last 2000 years. We identified 174 monthly to annually resolved climate proxy (tree ring, coral, ice core, documentary, speleothem and sedimentary) records from the Hemisphere. We assess the interannual and decadal sensitivity of each proxy record to large-scale circulation indices from the Pacific, Indian and Southern Ocean regions over the twentieth century. We then analyse the potential of this newly expanded palaeoclimate network to collectively represent predictands (sea surface temperature, sea level pressure, surface air temperature and precipitation) commonly used in climate reconstructions. The key dynamical centres-of-action of the equatorial Indo-Pacific are well captured by the palaeoclimate network, indicating that there is considerable reconstruction potential in this region, particularly in the post AD 1600 period when a number of long coral records are available. Current spatiotemporal gaps in data coverage and regions where significant potential for future proxy collection exists are discussed. We then highlight the need for new and extended records from key dynamical regions of the Southern Hemisphere. Although large-scale climate field reconstructions for the SH are in their infancy, we report that excellent progress in the development of regional proxies now makes plausible estimates of continental- to hemispheric-scale climate variations possible.
... The marine geologic record is incomplete, complicating interpretation of seabed observations (e.g. Sadler, 1981; Orpin et al., 2010). Flood deposits, for instance, comprise significant components of the geologic record on river-dominated margins, but are often reworked by physical and biological processes following initial emplacement (e.g. ...
Presentation
Small mountainous rivers transport over half of the global sediment flux from terrestrial to marine environments. Over 9 billion tons per year of sediment and associated nutrients and contaminants, including organic carbon, are transported from these rivers'floodplains to continental margins, primarily during flood events. The fate of such sediments is controlled by the sediment load, river discharge, waves, wind-driven currents, and larger scale currents. The study focused on the Umpqua River, OR because of its low sediment load and simple bathymetry. Seasonal variances in waves, river and sediment discharge, and wind-forced currents and their effect on sediment transport and deposition were analyzed using a version of the ECOMSED model on the continental shelf offshore of the Umpqua River, Oregon. This model is a three-dimensional hydrodynamic model with 9 vertical sigma layers and a horizontal resolution of 200 to 500 m that accounts for sediment transport, including gravity flows. Ten years of hourly data were averaged to obtain input parameters describing waves, winds, and sediment and water discharge for an average December flood (2.6x108 kg) and an average April/May flood (0.4x108 kg). Model results showed that seasonal variations in input parameters significantly affected sediment budgets. December deposits (6.9x107 kg) reached as far as 110 m depth, but April/May deposits (0.3x107 kg) occurred at depths shallower than 100 m. Additionally, the December deposit was over 20 times thicker and occupied an area 3 times larger than the size of the April/May deposit. 41.3% and 50.7% of sediment escaped the shelf during December and April/May storms, primarily to the Northwest. Differences in sediment budgets occurred because December flood events are characterized by stronger waves, larger sediment loads and stronger converging currents near the river mouth than April/May flood events. In December, these conditions initiated gravity flows, despite the small sediment load. These initial deposits underwent subsequent resuspension and gravity flows, resulting in a seasonal seaward shift in depocenter location. In contrast, in April/May, flood characteristics could not initiate gravity flows and almost all sediment was transported buoyantly. As a result of the increased residence time of sediments in the water column, the freshwater plume and smaller waves confined sediments to shallower depths. Overall, gravity flows and buoyant transport were the dominant means of sediment transportation in December and April/May, respectively.
... Cook et al., 2002). Cyclic climatic variability over this period is also observed in sediment records from Lake Tutira, eastern North Island ( Orpin et al., 2010;Page et al., 2010). ...
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Article
Our review of paleoclimate information for New Zealand pertaining to the past 30,000 years has identified a general sequence of climatic events, spanning the onset of cold conditions marking the final phase of the Last Glaciation, through to the emergence to full interglacial conditions in the early Holocene. In order to facilitate more detailed assessments of climate variability and any leads or lags in the timing of climate changes across the region, a composite stratotype is proposed for New Zealand. The stratotype is based on terrestrial stratigraphic records and is intended to provide a standard reference for the intercomparison and evaluation of climate proxy records. We nominate a specific stratigraphic type record for each climatic event, using either natural exposure or drill core stratigraphic sections. Type records were selected on thebasis of having very good numerical age control and a clear proxy record. In all cases the main proxy of the type record is subfossil pollen. The type record for the period from ca 30 to ca 18 calendar kiloyears BP (cal. ka BP) is designated in lake-bed sediments from a small morainic kettle lake (Galway tarn) in western South Island. The Galway tarn type record spans a period of full glacial conditions (Last Glacial Coldest Period, LGCP) within the Otira Glaciation, and includes three cold stadials separated by two cool interstadials. The type record for the emergence from glacial conditions following the termination of the Last Glaciation (post-Termination amelioration) is in a core of lake sediments from a maar (Pukaki volcanic crater) in Auckland, northern North Island, and spans from ca 18 to 15.64±0.41 cal. ka BP. The type record for the Lateglacial period is an exposure of interbedded peat and mud at montane Kaipo bog, eastern North Island. In this high-resolution type record, an initial mild period was succeeded at 13.74±0.13 cal. ka BP by a cooler period, which after 12.55±0.14 cal. ka BP gave way to a progressive ascent to full interglacial conditions that were achieved by 11.88±0.18 cal. ka BP. Although a type section is not formally designated for the Holocene Interglacial (11.88±0.18 cal. ka BP to the present day), the sedimentary record of Lake Maratoto on the Waikato lowlands, northwestern North Island, is identified as a prospective type section pending the integration and updating of existing stratigraphic and proxy datasets, and age models. The type records are interconnected by one or more dated tephra layers, the ages of which are derived from Bayesian depositional modelling and OxCal-based calibrations using the IntCal09 dataset. Along with the type sections and the Lake Maratoto record, important, well-dated terrestrial reference records are provided for each climate event. Climate proxies from these reference records include pollen flora, stable isotopes from speleothems, beetle and chironomid fauna, and glacier moraines. The regional composite stratotype provides a benchmark against which to compare other records and proxies. Based on the composite stratotype, we provide an updated climate event stratigraphic classification for the New Zealand region.
... (2) If each silt package was initiated by an extreme storm, then this implies only 22 such events occurred in the period from A.D. 800 to 6000 B.C. This is a low frequency compared with other New Zealand storm records (e.g., Griffi ths and McSaveney, 1983;Orpin et al., 2010;Page et al., 2010). ...
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Article
A sedimentary sequence that was highly sensitive to fault rupture-driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the Alpine fault, the fastest-slipping fault in New Zealand. At Hokuri Creek, in South Westland, an 18 m thickness of Holocene sediments accumulated against the Alpine fault scarp from ca. A.D. 800 to 6000 B.C. We used geomorphological mapping, sedimentology, and paleoenvironmental reconstruction to investigate the relationship between these sediments and Alpine fault rupture. We found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence. Climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment. Other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow-water environment for 6800yr. Our detailed documentation of this near-fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites-the continuity of sedimentation, abundance of dateable material, and pristine preservation of older events.
Article
A recently discovered upland paleolake (Redpath Lake) provides evidence of the expansion of lowland podocarp temperate forest to higher elevations within the tectonically active Waipaoa Sedimentary System (WSS), eastern North Island, New Zealand, during the Last Glacial-Holocene Transition. Interpreted as a localised landslide-dammed lake, lithofacies analyses indicate deposition and preservation in a low energy, sub-aqueous, lacustrine environment. Robust Bayesian-derived age-depth models constrained by key tephra fall beds and independent ¹⁴C dating (n = 7) indicate storm-bed frequency of c. 226 yrs on average. The absence of extensive soft-sediment deformation or lake-bed tilting implies that seismic shaking was insignificant during the Lake’s c. 12 ka yr (17.3–5.5 cal ka BP) existence. Pollen spectra extracted from lacustrine deposits include a mix of montane shrubland and lowland podocarp species spanning a well-dated c. 2200-year (c. 16.3–14.1 cal ka BP) period coeval with a phase of significant climate amelioration (late NZCe–5/NZce-4 mild episode), based on biotic proxies during the latter part of the climatically variable Last Glacial-Interglacial Transition (LGIT) (c. 18.2–11.8 cal ka BP). These pollen spectra represent the first New Zealand record of replacement of montane shrublands in terrestrial uplands of the WSS were replaced by lowland podocarp forest.
Article
Climate change is one of the biggest challenges facing humankind. Higher temperatures and changes in precipitation will lead to greater frequency of drought, wildfire, and intense storms that will threaten systems already vulnerable to climate and anthropogenic change. These threats will transform carbon delivery across the terrestrial–aquatic interface. This study investigated how anthropogenic activities and climate influence organic carbon delivery using Englebright Lake, a reservoir in California, as a model system. Organic carbon accumulation in three depositional settings (bottomset, foreset, topset) was analyzed using fatty acid, sterol and lignin biomarkers and compared to records of watershed events to determine responses to dam construction, mining impacts and flood events. Concentrations of long chain saturated fatty acids, plant sterols, epi-brassicasterol/brassicasterol and lignin biomarkers increased by an order of magnitude in foreset deposits in response to flood events (p < 0.007 for each biomarker). Hydraulic mining for gold was recorded as near-zero concentrations of terrigenous biomarkers in topset deposits, whereas decreases in diacids coincident with increases in aquatic sterols in bottomset deposits reflected the response to dam construction (p < 0.007 for each biomarker). Organic carbon accumulation was controlled by event magnitude and duration, and climate-driven event signals were up to an order of magnitude larger than anthropogenic-driven event signals. These data demonstrate the importance of understanding the depositional environment because the ability to characterize three different depositional settings in Englebright Lake enabled us to identify the smaller anthropogenic signals that would have been obscured by the much larger response to climate events.
Article
Sediment cores retrieved from landslide-dammed Loon Lake recorded events back to the 5th century AD in a forested, mountainous catchment, thereby providing an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of an early period in the cores, floods, fires, and earthquakes. High-resolution multi-parameter (grain size, %TC, %TN, and magnetic susceptibility) data allowed the core stratigraphy to be classified as background sedimentation and events. 137Cs and radiocarbon dating, as well as a varved record in the last 75 years provided age control. Mean mass accumulation rate from 1939 to 1978 AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation, was 0.79 (0.74-0.92, 95% C.L.) g cm-2 y-1, significantly higher than mean rates of both the more recent contemporary period (coincident with the passing of the legislation that regulated harvesting practices in the region), 1979-2012 AD, at 0.58 (0.48-0.70) and the entire early period, 0.44 (0.41-0.46). Several event deposits are coeval with independently estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700 AD Mw 9.0 event. These deposits are predominantly formed by hyperpycnal flows, as are the known event deposits in the contemporary period. The high mass accumulation rate and greater frequency of thick event deposits during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods.
Article
The dramatic changes that occurred to the post-glacial landscape in the headwaters of the Waipaoa River basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision. At times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it, the channel bed rises at the rate of tectonic uplift. Once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted, streams reestablish contact with bedrock and recuperate the time lost to fluvial incision. The first major perturbation occurred during the final phase of the last glaciation (ca. 33-17.5. cal.ka), when aggradation was driven by a climate-forced variation in the relative supplies of sediment and water. We suggest that the subsequent transformation of channels in the headwaters of the Waipaoa River basin, from alluvial to bedrock, occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca. 12. cal.ka. A second major perturbation that continues to the present began ca. 1910-1912. CE, when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture. The processes of terrace creation and incision are inherently unsteady, and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing. Events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid, storm-driven infilling of the Poverty Bay Flats. Tectonic subsidence dictates the course of the Waipaoa River across Poverty Bay Flats which, because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration, has remained virtually unchanged for the past 100 years. During this time the channel assumed a narrower, deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime.
Book
The evolution of high-crowned teeth, hypsodonty, is a defining characteristic of many terrestrial herbivores. To date, the most prominent focus in the study of the teeth of grazing herbivores has been co-evolution with grasses and grasslands. This book develops the idea further and looks at the myriad ways that soil can enter the diet. Madden then expands this analysis to examine the earth surface processes that mobilize sediment in the environment. The text delivers a global perspective on tooth wear and soil erosion, with examples from the islands of New Zealand to the South American Andes, highlighting how similar geological processes worldwide result in convergent evolution. The final chapter includes a review of elodonty in the fossil record and its environmental consequences. Offering new insights into geomorphology and adaptive and evolutionary morphology, this text will be of value to any researcher interested in the evolution of tooth size and shape.
Article
Based on core observation and grain analysis, the lacustrine storm deposits in Huangshanjie Formation in northern Tarim Basin were studied. The results show that they are mainly composed of middle-fine sandstone and siltstone, being short of coarse sandy conglomerate with bounder clay locally developed. Several typical storm sedimentary structures are recognized, including surface of scour, hommocky cross stratification, graded bedding, wave-ripple bedding, wavy bedding, deformation structures, as well as life-escaping structures. Grain-size probability curves show obvious two-section pattern, with saltation population mainly developed. The ideal storm sequence of this area is a Bouma-like sequence, and from bottom to top consists five segments, namely graded bedding (Sa), parallel bedding (Sb), hummocky cross stratification (Sc), wave-ripple or wavy bedding (Sd), mudstone segment (Se), with Sabde, Sace, Scde and Sde sequences commonly developed. There are two provenances for storm deposits in this area, of which one comes from northwestern Kalpin Uplift, and the other comes from northeastern Kuruketage Uplift. Judging from the sedimentary features and its relationship with provenances, the tempestites of this area are transtional or distal tempestite.
Article
Determining the earthquake segmentation of plate-boundary transform faults remains a scientific challenge because paleoseismic data sets rarely resolve the end points of past ruptures. In this study, we test whether lacustrine paleoseismology can be used to assess rupture end points and the earthquake segmentation of the Alpine fault, one of the longest and fastest-slipping plate-boundary transform faults on Earth. Sediment cores from Lake Ellery record eight episodes of high-intensity shaking (modified Mercalli intensity [MM] IX) from Alpine fault earthquakes as event sequences of a turbidite produced by coseismic subaqueous mass wasting, overlain by deposits representing sediment flux from co-and postseismic landsliding in the fluvial catchment. Age-depth modeling constrains the timing of shaking events at a decadal resolution, facilitating correlation with two previously published lake records to reconstruct the spatial distribution of MM IX shaking along ~150 km of the Alpine fault. When resolved with existing on-and near-fault paleoseismic records, the lake data set demonstrates that independent ruptures of the South Westland and Central segments occurred in A.D. 845- 775 and A.D. 739-646, and A.D. 646-592 and A.D. 416-370, respectively. Lakes adjacent to the Alpine fault provide paleoseismic records with sufficient spatial and temporal resolution to define along-strike differences in the pattern of rupture capable of distinguishing rupture termination at a geometric segment boundary. This multilake study suggests that locating the end points of ruptures using lacustrine paleoseismology will be most applicable in midlatitude convergent plate-boundary settings where along-strike topography and Quaternary glaciation have resulted in the widespread distribution of suitable lakes.
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Robust regional seismic-hazard assessments require millennialscale paleoseismic histories that extend far beyond the range of historical nd instrumental data. However, it is difficult to resolve the probability density functions for earthquake recurrence from the limited number of major to great earthquakes most paleoseismic records contain. Lake sediment records are repositories of information about paleoearthquake recurrence, with a sensitivity and fidelity over millennial time scales that suggest that they have the potential to yield reliable estimates of the recurrence distribution. We present a 7000 yr paleoseismic record from Lake Tutira (North Island, New Zealand) that ranks among the most detailed Holocene paleoearthquake chronologies available worldwide, and use it to empirically constrain the recurrence distribution of earthquakes with a minimum groundshaking intensity of MMI 7 in one of New Zealand's most seismically active areas. Our analysis confirms that a Poisson process describes the waiting times of single moderate to major and/or great paleoearthquakes in the Hawke's Bay region.
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Records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer-term context than is available from gauged river-flow and historical records. Recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high-magnitude floods over these longer timescales. Abyssal lake sediments can record past floods in the form of coarser-grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake. This paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment, outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection. The processes of sediment movement from watershed to lake bed are complex, meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear. Stratigraphical palaeoflood records are all affected to some degree by catchment conditioning, fluvial connectivity, sequencing of high flows, delta dynamics as well as within-lake processes including river plume dispersal, sediment focussing, re-suspension and trapping efficiency. With regard to analytical techniques, the potential for direct (e.g., laser granulometry) and indirect (e.g., geochemical elemental ratios) measurements of particle size to reflect variations in river discharge is confirmed. We recommend care when interpreting fine-resolution geochemical data acquired via micro-scale X-ray fluorescence (μXRF) core scanning due to variable down-core water and organic matter content altering X-ray attenuation. We also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and/or geochemistry with stream power. Where these processes are considered and suitable dating control is obtained, discrete historical floods can be identified and characterised using palaeolimnological evidence. We outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting, sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records. We also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers. To demonstrate their utility, we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions; these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records. These were achieved by consistently applying site-validated direct and proxy grain-size measurements; well-established chronologies; validation of the proxy-process interpretation; and calibration of the palaeoflood record against instrumental or historical records.
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Lacustrine sediments have been used successfully over the past few decades to develop earthquake chronologies and rupture assessments in a variety of locations and settings, from large lakes in Japan and Chile to Alpine lakes in central Europe. Although inland lakes in the Pacific Northwest have been used extensively for fire and vegetation reconstructions, they have been largely ignored with respect to their tectonic setting. Strong shaking from great earthquakes at subduction zones is known to produce significant environmental disturbance and can result in lake deposits that are distinctive and datable records of these events. Cascadia paleoseismic studies, including those at Lake Washington, Bradley Lake, and Effingham and Saanich Inlets, provide direct evidence that records of Cascadia great earthquakes are preserved in a variety of sedimentary archives. The field of marine turbidite paleoseismology has resulted in advancements which we have now begun to apply to inland lacustrine sediments using the records at Sanger and Bolan Lakes (both spring-fed, alpine cirque lakes), and Upper Squaw Lake (a stream-fed, landslide-dammed lake) located 45-100 km inland from the coast near the California/Oregon border. Inorganic terrigenous layers are visible in these sediments, and physical property data (via CT scans, magnetic susceptibility and gamma density) show characteristics that correlate between lakes, and more surprisingly, correlate great distances to seismogenic offshore turbidite deposits. The highest resolution site is Upper Squaw Lake, a 7.2 ha landslide-dammed lake which drains a 40 km2 watershed. A 10 m core spanning the past 2,000 years was extracted from this site, and is comprised of silty gyttja interbedded with inorganic turbidite deposits. Six major events are observed this core, similar to the number of events in the marine turbidite record in the same time period, with supporting age control. The characteristics of the physical property data are remarkably similar to those found at the Smith Apron offshore site approximately 160 km away. Striking correlation examples include a multiple peaked event or events at ~1500 years before present (ybp), a single peak fining upward with a small excursion near the top of the sequence at ~1000 ybp, and a large single peak for an event poorly constrained at ~500 ybp. The number of observed events is also comparable to those found at the Oregon coastal site Bradley Lake which records tsunami inundation. The great distance and multiple depositional environments over which these events correlate suggests these are earthquake-generated deposits and supports the hypothesis that gravity-driven seismogenic sediment deposits may record a crude primary signal of shaking which we call a "paleoseismogram". We hope to expand this investigation, by increasing the number of inland sites to be used in conjunction with marine and coastal records, to refine Cascadia paleo-rupture models by improving estimates of along-strike segmentation and the down-dip extent of the locked zone.
Article
The Waipaoa River Sedimentary System in New Zealand, a focus site of the MARGINS Source-to-Sink program, contains both a terrestrial and marine component. Poverty Bay serves as the interface between the fluvial and oceanic portions of this dispersal system. This study used a three-dimensional hydrodynamic and sediment-transport numerical model, the Regional Ocean Modeling System (ROMS), coupled to the Simulated WAves Nearshore (SWAN) wave model to investigate sediment-transport dynamics within Poverty Bay and the mechanisms by which sediment travels from the Waipaoa River to the continental shelf. Two sets of model calculations were analyzed; the first represented a winter storm season, January–September, 2006; and the second an approximately 40 year recurrence interval storm that occurred on 21–23 October 2005. Model results indicated that hydrodynamics and sediment-transport pathways within Poverty Bay differed during wet storms that included river runoff and locally generated waves, compared to dry storms driven by oceanic swell. During wet storms the model estimated significant deposition within Poverty Bay, although much of the discharged sediment was exported from the Bay during the discharge pulse. Later resuspension events generated by Southern Ocean swell reworked and modified the initial deposit, providing subsequent pulses of sediment from the Bay to the continental shelf. In this manner, transit through Poverty Bay modified the input fluvial signal, so that the sediment characteristics and timing of export to the continental shelf differed from the Waipaoa River discharge. Sensitivity studies showed that feedback mechanisms between sediment-transport, currents, and waves were important within the model calculations.
Article
Diverse terrestrial palynomorph assemblages of Pleistocene to Recent age have been recovered from mainly marine sediment cores along the eastern New Zealand margin. These assemblages record a range of environmental changes including climate, deforestation, reforestation, rates of erosion, sediment provenance and age, volcanic activity, Polynesian and European settlement, strength and direction of ocean currents, astronomical cyclicity, and other major events many of which can be correlated with shorter onshore terrestrial sequences. As such, pollen yields valuable information on the dynamic New Zealand landscape, which is of particular relevance to a source-to-sink approach. This paper provides an integrated summary of published and unpublished late Pleistocene palynological studies off eastern North Island, New Zealand that gives context for an analysis of cores within and marginal to the Waipaoa Sedimentary System. Pollen assemblages faithfully reflect the last glacial vegetation dominated by grass- and shrub-land species together with elevated Tertiary pollen from enhanced erosion of the regolith. The glacial termination and Holocene were marked by establishment of podocarp forest, a mid-Holocene disappearance of sediment-trapping mangroves, and introduction of distal pollen with establishment of coastal current systems under rising sea level. These natural signals are overprinted by abrupt changes in pollen species caused by volcanic eruptions. Finally, endemic forest and shrub pollen were markedly reduced with human colonisation, associated land use changes and introduction of exotic species.
Article
Recent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific–Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidites deposited since c. 18 ka in the Poverty, Ruatoria and Matakaoa re-entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity. Here, alternating hemipelagite, turbidite, debrite and tephra layers reflect distinctive depositional modes of marine sedimentation, turbidity current, debris flow and volcanic eruption, respectively. Turbidites dominate the record, ranging in lithofacies from muddy to sandy turbidites, and include some basal-reverse graded turbidites inferred to be derived from hyperpycnal flows. Stacked turbidites are common and indicate multiple gravity-flows over short time periods. The chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra, which facilitate sedimentation rate calculation and identification of the origin of turbidites. Sedimentation rates range from 285 cm/ka during late glacial time (18.5–17 ka) to 15 to 109 cm/ka during postglacial time (17–0 ka). Turbidite deposition is controlled by: (1) the emplacement of slope avalanches reorganising sediment pathways; (2) the postglacial marine transgression leading to a five-fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge, and (3) the Holocene/Pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain-size. Flood-induced turbidites are scarce: nine hyperpycnites are recognised since 18 ka and the youngest is correlated to the largest ENSO-related storm event recorded onland (Lake Tutira). Other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c. 7 ka. They yield a shorter return time (270–430 years) than the published coastal records for large earthquakes (c. 670 years), but the offshore record is likely to be more complete. The deep-sea sedimentation along the New Zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation. Climate warming and glacio-eustatic fluctuations are well recorded at a millennial timescale (18 ka), while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale (270–430 years).
Article
A mid to late Holocene record of storm events is preserved in the sediments of Lake Tutira, located on the eastern North Island of New Zealand. Previous studies of a 6 m sediment core established a storm chronology for the last 2250 years (Eden, D.N., Page, M.J., 1998. Palaeoclimatic implications of a storm erosion record from late Holocene lake sediments, North Island, New Zealand. Palaeogeogr. Palaeoclimatol. Palaeoecol. 139, 37–58). Here we extend the record, using a 27 m sediment core, to lake formation ∼ 7200 cal. yr ago. Outside the last ∼ 500 yr of human influence, the core records landscape response to natural climate variability and to tectonism/volcanism associated with the active collisional plate boundary setting.
Article
The joint US–NZ Source-to-Sink initiative aims to unravel the tectonic, climatic and other processes that shape the landscape from the mountains to deep ocean. Of two focus areas chosen world-wide, the Waipaoa Sedimentary System (WSS) of north-eastern New Zealand was identified as an example of a mid-latitude, high sediment input system. It resides within the westerly wind belt and extends across the convergence zone of the Australian and Pacific plates. Accordingly, the tectonic and climatic drivers are prominent and their influences on the WSS are decipherable as is documented in the suite of Source-to-Sink studies presented in this special issue of Marine Geology.
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No comprehensive scheme yet exists to describe the depositional products of submarine sediment failures at the scale of piston cores, resulting in misinterpretation of failure deposits and overuse of the genetic term ‘debris flow’. Ninety-nine sediment cores (0·5 to 20 m in length), from offshore eastern Canada and the Gulf of Mexico, are used to propose a descriptive sedimentary facies scheme with genetic implications for mass-transport deposits. Seven facies are distinguished: (i) allochthonous stratified sediment; (ii) distorted stratified sediment; (iii) clast-supported hard-mud-clast conglomerate; (iv) matrix-supported mud-clast conglomerate; (v) thin mud-clast conglomerate (<0·8 m thick); (vi) diamicton; and (vii) sorted sand-gravel deposits (≥0·05 m thick).
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Tephras of late Quaternary age are found interbedded with local laharic and fluvial deposits, and with distal rhyolitic tephras from Taupo and Okataina Volcanic Centres. Tephras are identified from their field characteristics and stratigraphic positions relative to dated rhyolitic tephra marker beds. The radiocarbon ages of these rhyolitic tephras proivde a chronology for the andesitic tephras, dating back to 22 500 yr BP. All tephras erupted from Tongariro Volcanic Centre are grouped into two subgroups: the Tongariro Subgroup (redefined) and the newly defined Tukino Subgroup. Tephras identified on the southeastern Mt Ruapehu ring plain are grouped into seven formations on the basis of lithology. -from Authors
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Widespread destruction of lowland podocarp/hardwood forests in Hawke's Bay followed permanent Maori settlement of the region. Forests cleared by fires were rapidly replaced with a bracken fern-scrubland which remained the predominant vegetation until European settlers cleared it away for pasture production in the late 1870s. Deforestation began about 500 calendar years B.P., but proceeded faster in the drier lowlands than in the wetter hill country. When the catchments were covered with either forest or fern-scrubland, soil erosion was minimal because the soil structure was maintained by the network of roots and protected from raindrop impact by a dense canopy. The main effect of storms before European settlement was to transport pulses of mostly riverbank sediment into the lakes. However, after European settlement, soil erosion increased markedly. Removal of soil stabilising vegetation and its replacement with pasture has left soft-rock hill country soils vulnerable to erosion and landslides.
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In tectonically active mountain belts, earthquake-triggered landslides deliver large amounts of sediment to rivers. We quantify the geomorphic impact of the 1999 Mw 7.6 Chi-Chi earthquake in Taiwan, which triggered >20,000 landslides. Coseismic weakening of substrate material caused increased landsliding during subsequent typhoons. Most coseismic landslides remained confined to hillslopes. Downslope transport of sediment into the channel network occurred during later storms. The sequential processes have led to a factor-of-four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean. Four years after the earthquake, rates of hillslope mass wasting remain elevated in the epicentral area.
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Rivers draining the tectonically active island of Taiwan commonly discharge suspended sediment to the ocean at hyperpycnal concentrations (>40 kg m−3), typically during typhoon-driven floods. During the period 1970–1999, between 99 and 115 Mt yr−1 of sediment was discharged at hyperpycnal sediment concentrations from Taiwan to the sea. This amount represents 30–42% of the total sediment discharge from Taiwan to the ocean. The spatial distribution of hyperpycnal discharge broadly mirrors the pattern of total sediment discharge, and rivers draining catchments having recent earthquakes and weak rocks, such as the Choshui and Erhjen, discharge up to 50–70% of their sediment at hyperpycnal concentrations. Following the Chi-Chi earthquake, the frequency of hyperpycnal flows increased, because of an earthquake-driven increase in sediment supply. Landslides triggered by the Chi-Chi earthquake have resulted in an increase in the concentration of suspended sediment in rivers for a given water discharge. In turn, the threshold flood discharge required to generate hyperpycnal flow has decreased, and so hyperpycnal flows are occurring more frequently. Our findings suggest that if hyperpycnal plumes evolve into bottom-hugging gravity currents descending to and ultimately debouching in the deep sea, earthquakes may be recorded as bundles of turbidites.
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A late Holocene (from c. 5500 yr B.P.) record of vegetation change is presented for the Gisborne region, based on pollen, charcoal, and tephra analyses of a terrestrial and a marine core. Up until the time of anthropogenic deforestation about 650 yr B.P., well drained lowland areas were covered with a Prumnopitys taxifolia, and Dacrydium cupressinum‐dominated podocarp/hardwood forest. The poorly drained Dacrycarpus dacrydioides‐dominated alluvial swamp forests were not as vulnerable to fire, and remained on the Gisborne Plains until European drainage and clearance began in the 19th century. In the last 5500 yr B.P., the lowland forests have been disturbed by at least five ashfalls originating from volcanic eruptions in the Central Volcanic Region. Where the terrestrial and marine cores overlap, comparisons of the pollen records show the vegetation changes and taxa present to be comparable. The fire record was not clear in the marine record, as the charcoal curve was diluted with high background levels of reworked charcoal. Sedimentation rates from the marine core indicate tha erosion in the Waipaoa catchment has increased significantly since European clearance of soil‐protecting remnant forest and fern/scrubland and its replacement with pasture.
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Palaeoecological investigations of sediment cores from two lake basins in the Tutira and Putere districts of Hawke's Bay demonstrate the impact of volcanic activity, fires, and storms on the vegetation and soil stability before human settlement and deforestation. A “disturbance curve” derived from the classification and ordination of pollen records, and correlated with charcoal and sediment records, illustrates relative forest disturbance over time. Before anthropogenic forest clearance in Hawke's Bay, forest composition fluctuated frequently as a result of disturbance from fires, droughts, and a major volcanic eruption. Each natural disturbance, indicated by short-term increases of seral taxa, was followed by complete forest redevelopment. Cyclonic storms were not a major cause of disturbance to lowland podocarp/hardwood forests in the region, nor to the bracken-scrubland vegetation that replaced the forest after clearance. However, storms scoured and rapidly transported riverbank sediments into the lake basins. Compared with the preceding natural disturbances, deforestation by early Maori settlers represents a type and magnitude of disturbance previously unrecorded in the cores.
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The boundary between the Pacific and Australian tectonic plates at the Hikurangi Subduction Zone, offshore of New Zealand's east coast, has not ruptured in a large earthquake in historical times. Therefore paleoseismological studies are required to elucidate the nature and history of subduction interface rupture. Multi-proxy reconstructions of paleoenvironments at two coastal sites arcward of the Hikurangi Trough provide evidence for significant Holocene subsidence. Radiocarbon dating, tephrochronology, stratigraphy and analysis of foraminiferal, diatom, spore and pollen assemblages enable assessment of vertical movement of the coastal plain relative to sea-level. Sequences outline a 9500-year history of coastal aggradation and progressive isolation from the sea. However the position of paleo-sea-level indicators almost 6 m below present mean sea level implies that subsidence has taken place since 7200 cal. years BP. A proportion of this subsidence appears to have happened suddenly in association with high-energy marine influx events and rapid infilling of newly created accommodation space. Two inferred coseismic subsidence events at c. 7100 and 5500 cal. years BP can be correlated with previously identified coseismic subsidence and tsunami inundation at a site 10 km away along the coast. Forward elastic dislocation models indicate the observed vertical deformation could occur in Mw 7.9 earthquakes on the subduction interface. However subsidence has not been recovered interseismically at these localities, and flights of raised marine terraces further trenchward suggest a large amount of permanent deformation is occurring along the margin. Reconstruction of earthquake records at additional sites is required to investigate the interplay of rupture on upper plate faults versus the subduction interface.
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Most humans live on and utilize the continental margin, the surface of which changes continually in response to environmental perturbations such as weather, climate change, tectonism, earthquakes, volcanism, sea level, and human settlement and land use. Part of the margin is above sea level and the rest is submarine, but these land and seascape components are contiguous, and material transport from source to sink occurs as a seamless cascade. The margin responds to environmental perturbations by changing the nature and magnitude of a variety of important functions, including the distribution of soil formation and erosion; biogeochemical functioning (especially the storage and release of water, limiting nutrients and contaminants); and the form and behavior of geomorphic components from hill slopes and floodplains through the coastal zone to the continental rise. While some areas of the margin are eroding-for example, hill slopes-others accumulate sediment, such as tectonic basins and continental slope and rise. These areas record the history of surface changes. A major goal of the Earth science community is to provide quantitative explanations and predictions of the effects of environmental perturbations on surface changes and preserved sedimentary strata of continental margins. In past decades, margins have been investigated piecemeal by researchers who have tended to focus on a particular segment from one disciplinary perspective while eschewing the broader perspective of the margin as an interconnected whole. Recognizing this shortcoming, the U.S. National Science Foundation (NSF) has initiated the MARGINS Source-to-Sink (S2S) program, which, for the first time, will attempt to understand the functioning of entire margin systems through dedicated observational and community modeling studies. Following input from the Earth science community, the Waipaoa Sedimentary System (WSS) of the North Island, New Zealand, was chosen as one of the focus sites for possible study (see MARGINS Source-to-Sink science plan for selection criteria and rationale: http://www.ldeo.columbia.edu/margins/S2S/S2Ssciplan02.html).
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A new research program focusing on sediment dispersal across the active margin of the New Zealand east coast has provided the foundation for a holistic understanding of the transport and fate of terrestrial materials in the coastal ocean. Field studies began in January 2005 with two acoustic mapping and shallow seabed sampling expeditions to the shelf and slope off the Waipaoa River (Figure 1), and in February 2006, the specially designed French research vessel (R/V) Marion Dufresne II collected seven long (up to 25 meters) piston cores from the study area for stratigraphic control. Both the 2005 and 2006 expeditions are part of the U.S. National Science Foundation (NSF) MARGINS Source-to-Sink (S2S) initiative.
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Marine core P69 (115 km off the southeastern North Island) has already yielded a 26 000 yr record of carbonate and silica influx, δO18 stratigraphy, foraminifera, and sea‐surface temperatures. A pollen analysis of the core is presented here. The full‐glacial (25 000–15 000 yr BP) pollen assemblages reflect a southern North Island landscape largely covered with scrub and grassland, but only limited areas of cool‐temperate forest. Abundant reworked Tertiary pollen types indicate increased erosion at this time. Rapid spread of podocarp‐dominant forest occurred between 15 000 and 11 500 yr BP, an event that relates only in a general way to increasing sea‐surface temperatures, but coincides exactly with a sharp reduction of wind‐induced upwelling and terrestrially sourced quartz. The abrupt movement southwards of the glacially expanded zone of strong westerlies at c. 15 000 yr BP, rather than warming, appears to be the main factor controlling postglacial reafforestation.
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Lake Brienz is a 14 km long and 261 m deep oligotrophic valley lake which lies in the front ranges of the Swiss Alps. Sedimentation is entirely clastic and is dominated by two rivers which enter the lake at opposite ends. The sediment load is transported and deposited in the lake by overflows, interflows and underflows (low- and high-density turbidity currents) depending on the density difference between river and lake water. Whereas high-density turbidity currents, which deposit up to 150 cm-thick graded sand layers, occur only once or twice per century after catastrophic flooding, low-density turbidity currents occur annually during periods of high discharge and deposit centimetre-thick faintly graded sand layers.Fine-grained sediment supplied by overflows and interflows rains down continuously during summer thermal stratification to form the dark-grey summer half-couplet of a varve; at turnover in the autumn the remaining sediment trapped at the thermocline settles out and forms the light-grey winter layer.Turbidites grade distally into thin dark-grey layers indistinguishable from the dark-grey summer half-couplet. Turbidites on the basin plain can be correlated with varves on the slopes. Therefore, in Lake Brienz the formation of varves and turbidites is genetically related and depends on the existence of over-and interflows, turbidity currents and seasonal thermal stratification.
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a b s t r a c t a r t i c l e i n f o Available online xxxx Keywords: Waipaoa River continental margin shelf sedimentation 210 Pb geochronology 239,240 Pu geochronology sediment budget The combination of high sediment yields and the prevalence of tectonically controlled accommodation on collision margins such as that adjacent to the Waipaoa River, NZ, create the potential for these areas to contain high-resolution records of natural and anthropogenic signals. This study describes modern (100-yr) sedimentation patterns off the Waipaoa and quantifies a sediment budget for the continental shelf, which is compared to long-term Holocene trends. 210 Pb and 239,240 Pu geochronologies reveal three main shelf depocenters. Two of these depocenters are located in subsiding synclinal basins on the mid-shelf, landward of the actively deforming Ariel and Lachlan anticlines. The depocenters exhibit accumulation rates ranging from 0.75 to 1.5 cm yr − 1 and display both steady-state and non-steady-state 210 Pb activity profiles. Textural characteristics of the non-steady-state cores indicate the possible preservation of flood event layers. The third depocenter is located near the shelf break and has accumulation rates as high as 1.0 cm yr − 1 . The inner shelf and central mid-shelf are characterized by low, uniform 210 Pb activity profiles and low accumulation rates, indicating that sediment is bypassing the inner shelf region and being deposited on the mid-to outer shelf. The modern sedimentation patterns seen in this study are similar to those for the Holocene, suggesting that regional tectonics are the major influence on Poverty shelf sedimentation. A modern, bulk sediment budget estimates that 3.6 ± 0.9 × 10 6 t yr − 1 of sediments remains on the shelf, amounting to only ~25% of the 15 Mt of sediments discharged from the river per year. This indicates massive export of sediments from the study area to the adjacent slope or along the shelf. In contrast, studies of the Mid-Late Holocene sediment budget in the same area indicate that the sediment input and shelf trapping have been roughly in balance. When compared with the modern budget, this suggests an extraordinarily rapid shift from shelf trapping to shelf bypassing, most likely driven by increasing sediment discharge in response to deforestation.
Article
This paper highlights some of the main developments to the radiocarbon calibration program, OxCal. In addition to many cosmetic changes, the latest version of OxCal uses some different algorithms for the treatment of multiple phases. The theoretical framework behind these is discussed and some model calculations demonstrated. Significant changes have also been made to the sampling algorithms used which improve the convergence of the Bayesian analysis. The convergence itself is also reported in a more comprehensive way so that problems can be traced to specific parts of the model. The use of convergence data, and other techniques for testing the implications of particular models, are described.
Article
Late Holocene lake sediments were used to determine the erosion response of a steepland catchment to land use change. Sediment cores were obtained from Lakes Tutira and Waikopiro, located in a landslide-prone area on the east coast of the North Island, New Zealand. Land use changes were identified in the cores by pollen and diatom analysis, and dated using a sedimentation chronology constructed from tephra layers and historical evidence. During the last 2000 years the catchment has undergone fire-induced changes from indigenous forest to fern/scrub following Polynesian settlement (c. 560 yr B.P.), and then to pasture following European settlement (A.D. 1878). Sedimentation rates under pastoral land use (A.D. 1878-1985) are between 5-6 times the rate under fern/scrub (c.560 yr B.P.-A.D. 1878) and 8-17 times the rate under indigenous forest (1850-c. 560 yr B.P.). Comparison is made with sedimentation rates from other lakes in the region. Well defined storm sediment pulses are present throughout the lake sediments and are responsible for the rapid increase in sedimentation rate under pastoral land use. The presence of these storm sediment pulses, together with a sediment budget for a large cyclonic storm, have identified the role that storms play in erosion and sedimentation processes, and also the influence that land use/vegetation change has had on this role.
Article
Magnitude-frequency analysis provides an approach to assess the effectiveness of rare events for generating and transporting sediment in the 32 km2 Tutira catchment and the 2205 km2 Waipaoa River basin, located in the erodible softrock hill country of the eastern portion of New Zealand's North Island. Shallow landsliding, triggered by high-intensity storms, is an important erosion process throughout out the region. The depositional record of Lake Tutira reveals the relationship between event magnitude and sediment yield of the Tutira catchment during the last 100 years, and illustrates the extent to which climate and land use change have affected the amount of sediment generated by landsliding over the past 2250 years. Magnitude-frequency relationships for hillslope erosion and for sediment deposition are closely related in the Tutira catchment, and large-magnitude, low-frequency landsliding events have been responsible for much of the deposition in Lake Tutira since European settlement. In the Waipaoa River basin, processes that affect sediment output are examined using a sediment budget approach. There, large storms appear to play a lesser role compared with the cumulative influence of more frequent, lower magnitude events. The difference in the effectiveness of large magnitude storms is probably attributable to the lower relative contribution of landsliding to catchment sediment yields, compared with other erosion processes such as gully and stream bank erosion where sediment can be generated by more frequent, lower-magnitude storms. Furthermore, the depositional response of large-magnitude storms may be buffered by transport lags, temporary storage, and a general diffusion of the magnitudes and frequencies of sediment contributions from the spatially variable distribution of erosion processes within the various tributaries. Certainly, the long-term record of sedimentation in Lake Tutira suggests that the magnitude and frequency of the erosional response varies with land use, vegetation type and climatic regime.
Article
A new study has been made of the Waimihia and Hatepe pumice deposits. Grainsize variation used in conjunction with isopach maps reveals that both deposits came from a vent or vents within the present Lake Taupo, probably situated in the Horomatangi Reef area; for the Waimihia pumice the isopach map alone is inadequate to give the vent position since there is a roughly uniform maximum thickness along 30 km of dispersal axis. The upper half of the Waimihia pumice contains streaky mix pumice and some mafic scoria, and it was dispersed in a slightly different direction from the lower rhyolitic part. Various indicators show that the dispersive power, and hence eruptive column height, in the Waimihia eruption was only slightly less than in the Taupo ultraplinian eruption; in the Hatepe eruption, an “average” plinian event, they were much less. In magnitude, the Waimihia eruption is one of the biggest plinian events yet studied. Application of a crystal concentration method yields volumes of 29 km and 6 km respectively for the Waimihia and Hatepe deposits, significantly higher than in previous estimates, and some 60% of these volumes is dispersed outside the mapped area. The whole-deposit grainsize populations have also been calculated; they are quite similar to the population of the Taupo plinian deposit in containing about 80% of sub-millimetre material, an unexpectedly high value in view of the coarseness of accessible parts of the deposits.
Article
Because turbidite beds aggrade progressively beneath a moving current, the vertical grain-size profile of a bed is generally an indication of the longitudinal velocity structure of the flow, and longitudinal gradients in suspended sediment concentration ("density"). A current is more likely to show a simple waning flow history farther from its source; this is because faster-moving parts of the flow overtake slower moving parts, and the flow organizes itself over time so that the fastest parts are at the front. Thus distal (e.g., basin plain) turbidites commonly show simple, normally graded profiles, whereas more proximal turbidites often show complex vertical sequences within a bed, related to unsteadiness. A turbidity current may deposit a structureless, poorly sorted bed where the capacity of the current is exceeded, i.e., where there is insufficient turbulent kinetic energy to maintain the entire suspended mass. Capacity-driven deposition may occur where the flow decelerates. Where flow nonuniformity is the cause of capacity-driven deposition, a massive interval will form the lowest part of the bed, and will have a flat base. Where flow unsteadiness is the cause, a normally graded massive interval may overlie erosional features or traction structures at the base of the bed. Based on the assumption of longitudinal gradients in velocity, density, and grain-size distribution, the longitudinal density structure of a current may induce a switch, at any given point, from capacity-driven deposition to either (1) bypass and resuspension, (2) bypass with traction, or (3) competence-driven deposition, each resulting in a characteristic upward change in deposit character. The temporal evolution of the flow at a point varies systematically in a streamwise sense. Taking account of these longitudinal variations permits predictions of complex vertical sequences within beds, and of their downstream relations.
Article
Late twentieth-century trends in New Zealand precipitation are examined using observations and re- analysis data for the period 1979-2006. One of the aims of this study is to investigate the link between these trends and recent changes in the large-scale atmospheric circulation in the Southern Hemisphere. The contributions from changes in Southern Hemisphere climate modes, particularly the El Niño-Southern Oscillation (ENSO) and the southern annular mode (SAM), are quantified for the austral summer season, December-February (DJF). Increasingly drier conditions over much of New Zealand can be partially explained by the SAM and ENSO. Especially over wide parts of the North Island and western regions of the South Island, the SAM potentially contributes up to 80% and 20%-50% to the overall decline in DJF precipitation, respectively. Over the North Island, the contribution of the SAM and ENSO to precipitation trends is of the same sign. In contrast, over the southwest of the South Island the two climate modes act in the opposite sense, though the effect of the SAM seems to dominate there during austral summer. The leading modes of variability in summertime precipitation over New Zealand are linked to the large-scale atmospheric circulation. The two dominant modes, explaining 64% and 9% of the overall DJF precipitation variability respectively, can be understood as local manifestations of the large-scale climate variability associated with the SAM and ENSO.
Article
Interannual extremes in New Zealand rainfall and their modulation by modes of Southern Hemisphere climate variability are examined in observations and a coupled climate model. North Island extreme dry (wet) years are characterized by locally increased (reduced) sea level pressure (SLP), cold (warm) sea surface temperature (SST) anomalies in the southern Tasman Sea and to the north of the island, and coinciding reduced (enhanced) evaporation upstream of the mean southwesterly airflow. During extreme dry (wet) years in South Island precipitation, an enhanced (reduced) meridional SLP gradient occurs, with circumpolar strengthened (weakened) subpolar westerlies and an easterly (westerly) anomaly in zonal wind in the subtropics. As a result, via Ekman transport, anomalously cold (warm) SST appears under the subpolar westerlies, while anomalies of the opposite sign occur farther north. The phase and magnitude of the resulting SST and evaporation anomalies cannot account for the rainfall extremes over the South Island, suggesting a purely atmospheric mode of variability as the driving factor, in this case the Southern Annular Mode (SAM). New Zealand rainfall variability is predominantly modulated by two Southern Hemisphere climate modes, namely, the El Niño-Southern Oscillation (ENSO) and the SAM, with a latitudinal grada- tion in influence of the respective phenomena, and a notable interaction with orographic features. While this heterogeneity is apparent both latitudinally and as a result of orographic effects, climate modes can force local rainfall anomalies with considerable variations across both islands. North Island precipitation is for the most part regulated by both local air-sea heat fluxes and circulation changes associated with the tropical ENSO mode. In contrast, for the South Island the influence of the large-scale general atmospheric circulation dominates, especially via the strength and position of the subpolar westerlies, which are modu- lated by the extratropical SAM.
Article
The Waipaoa sedimentary system spans ∼100 km from terrestrial upland to continental rise. Alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system, and hinterland-to-margin transport is accomplished rapidly. Because of this synergy, the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland, and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record. Manifested as variations in sediment properties, these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2.4 k.y. The signals represent the landscape response to vegetation and land-use change, short-term fluctuations in climate that affect surface properties and processes, and extreme storms and subduction-thrust earthquakes. Extreme storms are the minimum geomorphologically effective event preserved in the sediment records. Lower-magnitude storms that are integral components of the prevailing hydrometeorological regime create high-frequency fluctuations in sediment properties and collectively contribute to event sequences of >100 yr duration. Events and event sequences comprise a hierarchy of temporally sensitive phenomena, the impacts of which are conditioned by frequency and magnitude. By contrast, vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion. For this reason, the Taupo eruption of 1.718 ka and the piecemeal vegetation changes that occurred after the arrival of Polynesian settlers also generated strong depositional signals. After European colonization, deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude-frequency spectrum of events, regulating sediment delivery to and transport in stream channels. No other perturbation had such a profound impact on the Late Holocene depositional record.
Article
Eleven small lakes were formed by landslides caused by the 1929 Buller earthquake; four others were formed by other historic earthquakes in New Zealand. At least nine other New Zealand lakes are also dammed by landslides and were probably formed by prehistoric earthquakes. When recognized by morphology, synchronous age, and areal distribution, earthquake-dammed lakes could provide an estimate of paleoseismicity for the past few hundred or thousand years.
Article
Mahia Peninsula is a prominent coastal landmark in eastern North Island and is the closest point of land in the North Island to the Hikurangi Trough, where the Pacific plate plunges beneath the subduction complex at the eastern margin of the Australian plate. Uplifted Holocene marine deposits of both estuarine and open beach affinities are found in many parts of the peninsula and provide the basis of Holocene tectonic characterization. Estuarine deposits record the later part of the postglacial transgression that culminated about 6500 years B.P. in New Zealand. The deposits have been differentially uplifted since that time at a rate of 2.5+/-0.3 mm/yr in the central north coast area, decreasing to 0.7+/-0.2 mm/yr about 6 km to the west. The coastal plain is characterized in many places by a stepped sequence of emergent shore platforms overlain by fossiliferous beach deposits. Extensive radiocarbon dating of samples from beach deposits shows that terraces in widespread parts of the peninsula are of five distinct ages. Each of the terraces is inferred to have formed in conjunction with a large prehistoric earthquake because of the stepped terrace morphology, clustering of ages on each terrace, differential uplift of terraces across the peninsula, and historic coseismic uplift events in this tectonic setting. Paleoseismic events of MW 7.5-8.0 are estimated to have occurred approximately 250, ~1600, ~1900, ~3500, and ~4500 years B.P. Uplift distribution of the Holocene and late Pleistocene marine terraces shows that the peninsula lies on the west (gentle) flank of the active Lachlan anticline, which is cored by a major west dipping reverse fault (the Lachlan fault). Holocene active deformation at Mahia Peninsula and other coastal areas of eastern North Island is a continuation of structures developed in Pleistocene time in the landward part of the subduction complex adjacent to the Hikurangi subduction zone.
Article
New Zealand's complex orography gives distinct regional responses to variations in atmospheric circulation. By using rotated principal components, three spatially coherent temperature, and eight rainfall regions are defined for describing climate variations and trends for the period 1930-1994.Two main circulation changes have occurred in the New Zealand area over the record examined, around 1950 and 1975, making it convenient to analyse the data in three periods: 1930-1950, 1951-1975 and 1976-1994. From 1930 to 1950 more south to southwest anomalous flow occurred, relative to later years. All three temperature regions recorded lower temperatures, and wetter years occurred in the northeast of the South Island, with drier years in the north and west of the South Island. Airflow from the east and northeast increased during the period 1951-1975. This was accompanied by increases in mean temperature in all regions, with wetter conditions in the north of the North Island, and drier conditions in the southeast of the South Island. In the final period analysed (1976-1994) more prevalent west to southwest airflows occurred accompanying the higher incidence of El Niño events. Annual rainfall decreased in the north of the North Island, and increased in the north, west, south and southeast of the South Island. However, in spite of more southerly flow, regional temperatures showed little change from the 1951-1975 period.These results demonstrate that variations and trends in New Zealand regional temperature and rainfall respond significantly to circulation changes in the southwest Pacific.
Article
Taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite-dominated central portion of the Taupo Volcanic Zone in the North Island of New Zealand. Taupo has an average magma output rate of 0.2 m3 s-1 over the past 65 000 years, and is one of the most frequently active and productive rhyolite volcanoes known. The structure of the modern "inverse' volcano was formed largely by caldera collapse associated with the voluminous 22 600 14C years BP Oruanui eruption, and has been little modified since except for collapse following the 1850 14C years BP eruption. The products of 28 eruptions all of which post-date the Oruanui eruption, are defined and described here. The post-Oruanui activity at Taupo represents "noise' superimposed on the more uniform, longer term activity in the central Taupo Volcanic Zone, where large (greater than 100 km3) eruptions, such as the Oruanui, occur at more evenly spaced intervals of one per 40-60 000 years. -from Author
Article
A synchronous textural variation in intercorrelated, high-resolution sediment records from floodplain, continental-shelf, and continental-slope settings of the eastern North Island, New Zealand, provides evidence of increased storminess after ca. 4 ka. An upcore change in sediment texture reflects the transition to landsliding, which supplanted fluvial incision as the dominant mode of sediment production in the middle Holocene. This signal, which appears in all three records, indicates a regional response to external forcing and records the impact of an intensified atmospheric circulation marking the establishment of the contemporary climate that is strongly influenced by the El Niño Southern Oscillation. The change in climate was a hemispheric event, and in the Southern Hemisphere its timing is confirmed by independent proxy records from elsewhere in New Zealand and the circum South Pacific region.
Article
A database of tropical cyclone best track and intensity information for the southwest Pacific Ocean basin is used to construct a 28-year climatology for tropical cyclones that move into middle latitudes. Of the nine or so tropical cyclones that form each year, an average of about three can be expected to migrate south of 35degreesS, with the greatest fraction in March. Storms entering the Tasman Sea west of New Zealand (NZ) move almost due south on average and retain greater intensity than those to the east of NZ, where storms decay quickly while moving rapidly away to the southeast. Storms east of NZ are embedded in a stronger, more zonal flow than those to the west, which move poleward ahead of a larger-amplitude trough. During El Nino years, tropical cyclones that move into middle latitudes exhibit stronger zonal motion and occur over a wider range of longitudes than during La Nina years. Storm intensity is only weakly correlated with concurrent SST anomalies, suggesting that atmospheric circulation is the dominant influence on storm properties. Average structure changes during extratropical transition (ET) are identified using the NCEP-NCAR reanalysis dataset, for a subset of 33 transitioning storms during 1980-97. Composites are used to construct a three-dimensional conceptual model of the transformation from a mature hurricane to an asymmetric baroclinic midlatitude cyclone. Southwest Pacific tropical cyclones encounter the baroclinic westerlies early in their lives, accounting for their average eastward (and poleward) motion. At maximum average intensity near 20degreesS, baroclinic effects are already important, with warm frontogenesis appearing in the southeast quadrant and outflow aloft into a downstream subtropical wind maximum that moves poleward with the storm. By 25degreesS, the average TC has lost the characteristic symmetric anticyclonic outflow aloft and acquired the characteristics of a baroclinic midlatitude storm, including regions of warm and cold frontogenesis, a vertical motion dipole and a westward tilt with height. From about 30degreesS poleward, a second upper-tropospheric wind maximum appears west of the storm, with strengthening cyclonic vorticity advection aloft. Below about 400 hPa, the storm retains the vertical, warm cyclonic core as it migrates poleward.
Article
Modern sediment dispersal and accumulation on the Poverty Shelf off the Waipaoa River, New Zealand, is investigated using X-radiographic, radio-isotopic and physical property analyses of nearly 200 box and Kasten cores collected in January 2005 aboard the R/V Kilo Moana. The high-yield, small mountainous Waipaoa River empties onto a tectonically active, narrow margin and represents an important analog for shelf sedimentation in similar environments worldwide. X-radiographs and bulk-density measurements from a multi-sensor core logger show three distinct facies on the shelf where physical and/or biological factors dominate strata formation. Spatial distribution of these facies delineates a radial pattern with distance from the river mouth, from areas dominated by stratified layers on the inner shelf to mottled muds on the outer shelf, demonstrating a continuum of controls from wave reworking to episodic and extreme wet event sedimentation, despite a tectonic framework that supports rapid accumulation in two recently identified shelf depocenters. Analysis of short-lived 7Be (t1/2=53days) reveals a broad spatial distribution across- and along-shelf in surface sediments, suggesting rapid transport from the Waipaoa source. However, beryllium-7 inventories are consistent with centennial-scale trends observed by other researchers using longer-lived 210Pb analyses, with highest inventories in the shelf depocenters. Box core bulk-density analyses show lower than average bulk densities within these depocenters, and higher than average bulk densities on the inner shelf and between the depocenters. These observations confirm rapid deposition of low-density muds in the depocenters, with higher bulk-density, possibly physically reworked sediments, remaining off the mouth of Poverty Bay and between the depocenters. Based on this single observational period, there appears to be no fundamental difference between seasonal and longer-term accumulation patterns on the Poverty Shelf.
Article
Landsliding is the dominant mass-wasting process in humid-temperate uplands and an important regulator of sediment yield from steep-land drainage basins. Information about the magnitude and frequency distribution of landslides has been derived from aerial photography, but it has proved difficult to set limits on the long-term scaling behavior of landsliding because the requirements of spatial and temporal coherence and the large number of observations necessary to undertake magnitude versus frequency analyses are not easy to fulfill. We use a 2250-yr-long record of hillslope erosion associated with extreme hydrologic events preserved in sediments from Lake Tutira, New Zealand, to investigate scaling in landslide deposits. Both the magnitude versus frequency distribution of sediment layers attributed to landsliding and the distribution of time intervals between landsliding events take the form of power laws, the former with an exponent b = 2.06 and the latter with an exponent b = 1.4. These results suggest that the erosional events originate from a self-organized critical process, and are in agreement with observations of scaling in turbidite deposits and grain flows in controlled laboratory experiments. The implications are that the aggregate behavior of landsliding at the catchment scale is orderly and that the stratigraphic record preserves a unique, long-term perspective on a fundamental geomorphic process and the extreme hydrologic events that trigger it.
Article
An unusual stratigraphic unit (nicknamed 'homogenite') fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the W Mediterranean Ridge and the Calabrian Ridge. On near-bottom 4-kHz seismic-reflection profiles, this unit is an acoustically transparent, near-surface, flat-lying layer, whereas in cores, it is a homogeneous gray marl as much as 7m thick. Grain size decreases upcore within the unit, implying that it was deposited in a single event controlled by gravitational settling. The stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr B.P. The source of the homogenite is inferred to be the nearby basin walls and a Santorini tsunami mechanism is discussed.-Authors
Article
A core drilled in a swamp at the northern end of Lake Tutira, northern Hawke's Bay, New Zealand, as part of a programme to determine the erosion history of the Lake Tutira catchment, contains 14 tephra layers (10 rhyolitic and 4 andesitic). The mineralogy of each layer was determined, together with electron microprobe chemistry of glass shards, and of hornblendes from two of the andesitic tephras. The rhyolitic layers are identified from their stratigraphic position, mineralogy, and glass/mineral chemistry as: Taupo (1850 conventional radiocarbon years old), Mapara (2160 yr), Whakaipo (2685 yr), Waimihia (3280 yr), Hinemaiaia (4510 yr), Whakatane (4830 yr), and Motutere (5430 yr), but three additional rhyolitic layers (aged c. 3700, 4100, and 4300 yr) could not be correlated with known tephras. Two are possibly reworked layers, but one (c. 4300 yr) may represent a new tephra which has not been previously recognised. The mineralogy of three of the andesitic tephras (aged c. 3100, 4900, and 6000 yr) indicates that they were probably derived from Egmont Volcanic Centre, and tentative correlations are suggested for them. The fourth andesitic tephra (c. 5400 yr) is probably derived from Tongariro Volcanic Centre.Nine radiocarbon ages were obtained from the core and two of these, 6530 ± 110 yr B.P and 6330 ± 70 yr B.P located near the base of the core, indicate that Lake Tutira formed c. 6500 years ago.