High-resolution Sediment Cores Research Articles

Clustered slumping in the northern South China Sea: Implications for chronology and geohazards

Seismic facies analysis is the most widely used method to identify event deposits from subaqueous environments. However, the internal structures of a chaotic or transparent seismic unit that represent event deposits are usually poorly imaged. This is primarily due to the limited resolution (usually <10 m) of commonly available multi-channel seismic reflection data. As a consequence, potential (sub)meter-thick, interbedded background sediments that may divide the chaotic layer cannot be discerned on such a seismic profile. The result of this, is that a complex of multiple moderate-thickness event layers can be misinterpreted as a single, thick event layer and this can greatly impact age-depth model reconstruction and geohazard assessment. One approach to resolve the problem is to correlate seismic data with high-resolution sediment core analysis. To address the problem in the South China Sea, we combine multiple methods to identify event deposits in the IODP holes U1499A and U1432C. Our dataset reveals that: (1) the previously interpreted ~50 m-thick slumping unit in the region is a complex of multiple moderately sized units; (2) the slumping events are clustered between 0.6 and 0.4 Ma. Using our new understanding of event emplacement, we define event-free age models for mass wasting on the margin of the South China Sea, improving our understanding of local geohazards. Our methods here represent a sedimentological approach which could be used in other subaqueous environments to reconstruct event-free age models and geohazard histories.

High-resolution sea-level fluctuations during the Mid-Holocene in the Ningshao Coastal Plain region, eastern China

Sea level changes during the Mid-Holocene directly influenced the Neolithic culture in the Yangtze River Delta region (YRD). However, the high-resolution sea level change characteristics for this period remain unclear. In this study, we performed a high-resolution palynological analysis, including pollen, Dinoflagellate cysts, and Foraminiferal organic linings, using a high-resolution sediment core from Shanglin Lake, in the North of Ningshao Plain (the south of Hangzhou Bay). 11 accelerator mass spectrometry 14C(AMS) datings indicate the age of the sediments range from 8 cal ka B.P. to 5.6 cal ka B.P. The results show that during the Mid-Holocene, Shanglin Lake evolved from an estuary – subtidal lagoon – semi-enclosed bay – semi-enclosed lagoon – semi-enclosed bay – enclosed lagoon to a modern freshwater lake. There was a period of no, or minimal, eustatic sea-level rise between 7733 and 7585 cal yr B.P. The Mid-Holocene high sea level comes in 7253–7082 cal yr BP. Between 7000 cal yr BP and 5502 cal yr BP, the sea level is close to modern value. The sea level change during this period had a significant impact on the local Neolithic human activity.

Hydroclimate response of spring ecosystems to a two-stage Younger Dryas event in western North America

The Younger Dryas (YD) climate event is the preeminent example of abrupt climate change in the recent geologic past. Climate conditions during the YD were spatially complex, and high-resolution sediment cores in the North Atlantic, western Europe, and East Asia have revealed it unfolded in two distinct stages, including an initial stable climatic period between ~ 12.9 and 12.2 ka associated with a weakened Atlantic Meridional Overturning Circulation (AMOC) and a second phase characterized by variable conditions until 11.7 ka as the AMOC recovered. Decades of investigations into the climate of western North America during the YD have failed to identify this stepped phenomenon. Here we present hydroclimate data from paleospring deposits in Death Valley National Park (California, USA) that demonstrate unequivocal evidence of two-stage partitioning within the YD event. High groundwater levels supported persistent and long-lived spring ecosystems between ~ 13.0 and 12.2 ka, which were immediately replaced by alternating wet and dry environments until ~ 11.8 ka. These results establish the mid-YD climate transition extended into western North America at approximately the same time it was recorded by hydrologic systems elsewhere in the Northern Hemisphere and show that even short-lived changes in the AMOC can have profound consequences for ecosystems worldwide.

Trace metals enrichment and potential ecological risk in sediments of the Sepetiba Bay (Rio de Janeiro, SE Brazil)

The Sepetiba Bay (SB; SE Brazil) has been severely affected by growing of urbanization and industrial activity. This work aims to analyze the evolution of contamination by metals of sediments in SB. The results show a marked increasing trend in the concentrations of potentially toxic elements (PTEs), which is consistent with the rapid populational and industrial growth, mostly since 1970 CE. The remobilization and redistribution of sediments by currents have contributed to the dispersion of metals from the main source of pollutants to relatively distant regions. “Moderately to strongly polluted” sediments are also recorded in some sites in deeper sedimentary layers (namely in preindustrial periods), probably due to lithologic sources of the sediments. The concentrations of PTEs in SB are relatively high when compared with those found globally and in other Brazilian water bodies. Samples of high-resolution sediment cores confirmed that potential ecological risk to the coastal system is influenced not only through human actions but also by natural causes.

Geochemical baseline establishment and pollution assessment of heavy metals in the largest coastal lagoon (Pinqing Lagoon) in China mainland

Establishing geochemical baselines and assessment of heavy metal pollution in lagoon sediments are critical for providing guidance to coastal zone environmental management. We analyzed heavy metals in high-resolution sediment cores from Pinqing Lagoon in South China, and defined the baselines of common pollution elements with a significant anthropogenic contribution. With these baselines, a spatiotemporal pollution assessment revealed Cu and Cd as the predominant pollution metals in both core and surface sediments, although the ecological risk level in the interior lagoon remained low during the past ~170 years. Surface sediment pollution status indicate a significant spatial difference. The findings from this typical coastal lagoon evidence a strong self-clean capacity attributable to the frequent water-mass-energy exchange between the lagoon and the sea. Furthermore, despite the significant impact by the sea, the geochemical baselines are close to the catchment soil backgrounds that can be defined using a paleolimnological approach.

Phytolith reconstruction of early to mid-Holocene vegetation and climatic changes in the Lower Yangtze Valley

The Holocene variability of Poaceae (grasses) and their response to climate changes has not yet been investigated, despite their prevalence and biodiversity in the Lower Yangtze Valley. In this study, we analysed phytolith assemblages in a high-resolution sediment core from the Lower Yangtze Valley to reconstruct the past vegetation and climate of the early to mid-Holocene (ca. 9000–7200 cal a BP). The sediment core chronology was based on 11 radiocarbon dates of terrestrial plant macro-remains or char, which sufficiently captured regional centennial-scale vegetation and climatic variability of the early to mid-Holocene. We identified and classified phytoliths into 30 morphotypes covering seven taxonomic groups: Panicoideae, Pooideae, Bambusoideae, Chloridoideae, Oryzoideae, Arecaceae (palms), and broad-leaved trees. The downcore phytolith assemblage indicated a significant increase in palms, bamboo forests, and other evergreen broad-leaved trees after 8200 cal a BP. Both Panicoideae and Pooideae, which are indicative of dry or cold climates, decreased from 9000 to 7200 cal a BP, indicating a transition to a warmer and wetter climate during that period. Due to the coastal environment of the Lower Yangtze, both the strengthening East Asian summer monsoon (EASM) and rising sea-level likely influenced the early to mid-Holocene climate transition. The general climatic warming was interrupted by several centennial-scale intervals at 8800, 8200, 7700, and 7300 cal a BP, coinciding with weaker precipitation or lower temperature inferred from other high-resolution records; these changes were likely forced by meltwater input from the Laurentide ice sheet and solar activity. Our study provides a reliable reconstruction of climatic changes in the Lower Yangtze Valley. Moreover, the phytolith record provided a more detailed reconstruction of Holocene plant communities compared with a pollen-based record from the same core. We therefore recommend the use of phytoliths for plant reconstructions (mainly grasses) in evergreen and deciduous broad-leaved mixed forests.

Late Glacial Marine Transgression and Ecosystem Response in the Landlocked Elefsis Bay (Northern Saronikos Gulf, Greece)

Coastal landscapes are sensitive to changes due to the interplay between surface and submarine geological processes, climate variability, and relative sea level fluctuations. The sedimentary archives of such marginal areas record in detail the complex evolution of the paleoenvironment and the diachronic biota response. The Elefsis Bay is nowadays a landlocked shallow marine basin with restricted communication to the open Saronikos Gulf. A multi-proxy investigation of a high-resolution sediment core recovered from the deepest part of the basin offered a unique opportunity to record the paleoenvironmental and aquatic ecosystem response to climate and glacioeustatic sea level changes since the Late Glacial marine transgression. The retrieved sedimentary deposits, subjected to thorough palynological (pollen, non-pollen palynomorphs, dinoflagellates), micropaleontological (benthic foraminifera, calcareous nannoplankton, ostracods), and mollusc analyses, indicates isolation of the Elefsis Bay from the Saronikos Gulf and the occurrence of a shallow freshwater paleolake since at least 13,500 cal BP, while after 11,350 cal BP the transition towards lagoon conditions is evidenced. The marine transgression in the Elefsis Bay is dated at 7500 cal BP, marking the establishment of the modern marine realm.

A 450-year lacustrine record of recurrent seismic activities around the Fuyun fault, Altay Mountains, Northwest China

Seismic hazards and risks around an individual fault can be assessed from complementary paleoseismic data. A high-resolution sediment core recovered from the Yileimu Lake revealed 11 potential paleoearthquakes around the Fuyun fault in northern Xinjiang. Among them, three events recorded by ductile deformation and turbidites or coseismic subsidence were possibly correlated with Ms ≥ 7.0 earthquakes, and the others characterized by turbidites or coarse deposits were likely related to Ms ≥ 5.8 or Ms ≥ 5.5 earthquakes. Shaking intensities of 8.60 and 5.51 MMI were required to cause extensive landslides and turbidites, respectively; while 6.89, 6.35 and 5.34 MMI were likely to be required to cause coseismic subsidence, ductile deformation and coarse deposits related to landscape shattering in the catchment area, respectively. Absolute radiocarbon dating and historical earthquake-event markers disclosed a recurrence interval of 20–60 years for Ms ≥ 5.5 earthquakes, and a potential interval of 100 years for Ms ≥ 7.0 earthquakes during the last 450 years. A seismic quiescence of 89 years since the 1931/08/11 Ms8.0 Fuyun earthquake might have significantly increased the potential of a strong earthquake related to the fault in the near future.

Characteristics of palaeosalinity and palaeoredox records in sediment from Dali Lake: Climate change in North China from 0 to 2100 cal BP

Abstract To understand the salinity, redox characteristics, and climatology of Dali Lake during the late Holocene, we analysed trace element records from a high-resolution sediment core (DL-1), including Al, Mn, Zn, Mo, Pb, Fe, Sr, and Ba. The core was dated to 2100 cal BP based on accelerator mass spectrometry (AMS) 14C dating combined with the constant rate of supply (CRS) model. We identified five palaeoclimatic stages based on the down-core trace elemental characteristics. From ca. 2100 to 1650 cal BP (Stage Ⅰ), Mn-MAR (mass accumulation rates) and Fe-MAR showed no correlations with Mo-MAR, suggesting that anaerobic conditions limited the adsorption of Mo onto Mn–Fe oxides. From ca. 1650 to 1050 cal BP (Stage Ⅱ), we identified a weakened aerobic environment, coinciding with the Dark Ages Cold Period due to a decrease in the organic matter (OM), nutrients, Fe-MAR, and Zn-MAR, which inhibited Mo deposition. Salinity (Sr/Ba) did not influence the trace elemental fluxes, OM, or nutrients throughout Stages I and II. We identified aerobic conditions during Stage Ⅲ (between ca. 1050 and 650 cal BP), coinciding with the Medieval Warm Period, with observed lower salinity that facilitated Al-MAR, Mn-MAR, and Pb-MAR deposition. During the Little Ice Age (between ca. 650 and 30 cal BP; Stage Ⅳ), Mn-MAR, Zn-MAR, and Fe-MAR showed no correlation with Mo-MAR, implying anaerobic conditions. We also identified high salinity and OM concentrations that facilitated trace element deposition. Over the past 95 years (Stage V), high salinity levels have produced the deposition of Al-MAR, Mn-MAR, Zn-MAR, and Fe-MAR. However, the redox conditions in the lake sediment are difficult to interpret due to anthropogenic influences on trace elemental fluxes. We identified a salinity periodicity (Sr/Ba) of 100–150 years and a redox periodicity (Mo-MAR) of 100–260 years using the wavelet power spectrum. Our results indicate a gradual weakening of the East Asian summer monsoon, which may be controlled by insolation in the Dali Lake basin.

Contrasting the ecological effects of decreasing ice cover versus accelerated glacial melt on the High Arctic's largest lake.

Lake Hazen, the High Arctic's largest lake, has received an approximately 10-fold increase in glacial meltwater since its catchment glaciers shifted from net mass gain to net mass loss in 2007 common era (CE), concurrent with recent warming. Increased glacial meltwater can alter the ecological functioning of recipient aquatic ecosystems via changes to nutrient budgets, turbidity and thermal regimes. Here, we examine a rare set of five high-resolution sediment cores collected in Lake Hazen between 1990 and 2017 CE to investigate the influence of increased glacial meltwater versus alterations to lake ice phenology on ecological change. Subfossil diatom assemblages in all cores show two major shifts over the past approximately 200 years including: (i) a proliferation of pioneering, benthic taxa at approximately 1900 CE from previously depauperate populations; and (ii) a rise in planktonic taxa beginning at approximately 1980 CE to present-day dominance. The topmost intervals from each sequentially collected core provide exact dates and demonstrate that diatom regime shifts occurred decades prior to accelerated glacial inputs. These data show that diatom assemblages in Lake Hazen are responding primarily to intrinsic lake factors linked to decreasing duration of lake ice and snow cover rather than to limnological impacts associated with increased glacial runoff.

Sea Surface Temperature Variability on the SE‐Greenland Shelf (1796–2013 CE) and Its Influence on Thrym Glacier in Nørre Skjoldungesund

AbstractHeat transport via ocean currents can affect the melting of marine‐terminating glaciers in Greenland. Studying past changes of marine‐terminating glaciers allows assessing the regional sensitivity of the Greenland Ice Sheet to ocean temperature changes in the context of a warming ocean. Here, we present a high‐resolution multiproxy marine sediment core study from Skjoldungen Fjord, close to the marine‐terminating Thrym Glacier. Grain‐size data are obtained to reconstruct the calving activity of Thrym Glacier; sortable silt is used as a proxy for fjord water circulation, and sea surface temperatures (SSTs) are reconstructed from alkenone paleothermometry (Uk'37). Measurements of 210Pb, 137Cs, and 14C indicate that the core covers the past 220 years (1796–2013 CE). Comparisons with modeled SST data (Hadley Centre Sea Ice and SST) and instrumental temperatures (International Council for the Exploration of the Sea) suggest that the SST proxy record reflects temperature variability of the surface waters over the shelf and that alkenones are advected into the fjord. Additionally, average temperatures and the amplitude of fluctuations are influenced by alkenones advected from upstream the Irminger Current. We find that the SST record compares well with other alkenone‐based reconstructions from SE‐Greenland and thus features regional shelf water variability. The calving activity as well as the terminus position of Thrym Glacier did not seem to respond to the SST variability. Limited ice‐ocean interactions owing to the specific setting of the glacier would explain this. Instead, the fjord circulation may have been influenced by enhanced meltwater production as well as to larger scale changes in the Atlantic Meridional Overturning Circulation.

Spatiotemporal patterns of carbon sequestration in a large shallow lake, Chaohu Lake: Evidence from multiple-core records

Lake sediment can sequestrate large amounts of carbon and this issue has become a research hotspot. However, most of research on carbon burial in lakes is based on a single (or a few) sediment core records and so may underestimate the variability of carbon burial features within a single lake. In this study, therefore, Chaohu Lake, a typical large shallow lake in the middle and lower reaches of the Yangtze River, was selected to conduct multiple, high resolution sediment core studies to elucidate that variability. Overall 18 sediment cores are analyzed according to paleolimnological proxies (including 210Pb/137Cs for 3 master cores); sediment accumulation rate, total organic carbon, grain size and loss of ignition is measured or estimated for most cores. The spatiotemporal variations of organic carbon burial rate (OCBR), carbon storage and their driving factors were examined. Results show: 1) There was a clear temporal difference in carbon burial during the past 150 years, with OCBR varying from 1.1 g C/m2/y to 25.6 g C/m2/y (mean 9.8 g C/m2/y). OCBR began to increase after around 1900, a rapid increase followed after 1950s and a downward trend after 1970s. Total carbon burial amount (OCBA) in the lake since the 1850s is 1.11 x 1010 g. 2) The average OCBR of six sediment cores in the northwest lake area is 13.4 g C/m2/y, significantly higher than that for sediment cores in other areas (9.6 g C/m2/y). 3) TOC, OCBR, OCBA in all 18 cores exhibited similar temporal patterns (i.e. marked increase since 1950s in most of the cores) but with significant differences in several lake locations. 4) During the last 150 years, carbon burial in Chaohu Lake appears to be greatly affected by changes in regional temperature and population size, according to their significant correlations. OCBR also has a significant correlation with the average lake level in the past 50 years, indicating human activity (notably dam building). This has imposed an important impact on OCBR in Chaohu Lake. This multi-sediment core study reveals the spatiotemporal characteristics of carbon burial in the lake and provides an important basis for increasing the accuracy of calculating carbon storage in large shallow lakes.

A Paleoenvironmental Study Tracking Eutrophication, Mining Pollution, and Climate Change in Niven Lake, the First Sewage Lagoon of Yellowknife (Northwest Territories) + Supplementary Appendix 1 (See Article Tools)

Niven Lake was the first wastewater disposal site for the City of Yellowknife (Northwest Territories, Canada), receiving domestic sewage for more than 30 years. Here, we used a high-resolution sediment core to track past sewage inputs to Niven Lake by comparing changes in sedimentary sterols and three diagnostic ratios for human fecal contamination, as well as biological assemblages and overall lake production, with the known history of sewage inputs to the lake from 1948 to 1981. Coprostanol, often considered the best indicator of human fecal contamination, increased by ~8% between depths of 7.5 cm and 5 cm (~1950 to 1981) and was more reliable in tracking sewage contamination than diagnostic sterol ratios. Muted responses in subfossil diatom and chironomid assemblages were noted during the time of sewage inputs, and similar responses have been reported in other eutrophic Arctic sites, as well as in many macrophyte-dominated shallow lakes in general. More marked shifts in diatoms and chironomids occurred a decade after the end of sewage inputs, in the 1990s, a time that closely aligned with the warmest years on record for Yellowknife. This post–sewage era response was indicative of anoxia and possibly of positive feedback from internal phosphorus loading. The response may have been facilitated by recent climate warming, resulting in a lagging recovery from eutrophication. Changes in the diatoms and chironomids of Niven Lake were also indicative of metal pollution, suggesting that the lake has experienced the compounding effects of arsenic contamination from nearby gold mining.

Towards a refined understanding of the use of coastal zones in the Mesolithic: New investigations on human–environment interactions in Telemark, southeastern Norway

The study of the effects of human presence on vegetation in the Mesolithic has been controversial. It is often assumed that hunter-gatherers did not change or affect their environment in a way that can be detected by means of pollen analysis. In this paper, we explore potential human impact on the vegetation during the Mesolithic by comparing pollen data from a high-resolution sediment core from Lake Skogstjern with archaeological data obtained through extensive excavation and survey in Bamble, in the county of Telemark, southeastern Norway. The aim of this interdisciplinary approach is to reach a better understanding of the development and use of Mesolithic woodlands with regard to the availability of different resources, but also to put the question of human impact on Mesolithic vegetation on the agenda. Mesolithic settlement in southeastern Norway was to a very large degree shore bound, and the pollen analysis from Lake Skogstjern, situated in the coastal hinterland, allows for new perspectives on and interpretations of the use of the coastal wider landscape.

Deglacial variability in Okhotsk Sea Intermediate Water ventilation and biogeochemistry: Implications for North Pacific nutrient supply and productivity

The modern North Pacific plays a critical role in marine biogeochemical cycles, as an oceanic sink of CO2 and by bearing some of the most productive and least oxygenated waters of the World Ocean. The capacity to sequester CO2 is limited by efficient nutrient supply to the mixed layer, particularly from deeper water masses in the Pacific's subarctic and marginal seas. The region is in addition only weakly ventilated by North Pacific Intermediate Water (NPIW), which receives its characteristics from Okhotsk Sea Intermediate Water (OSIW). Here, we present reconstructions of intermediate water ventilation and productivity variations in the Okhotsk Sea that cover the last glacial termination between eight and 18 ka, based on a set of high-resolution sediment cores from sites directly downstream of OSIW formation. In a multi-proxy approach, we use total organic carbon (TOC), chlorin, biogenic opal, and CaCO3 concentrations as indicators for biological productivity. C/N ratios and XRF scanning-derived elemental ratios (Si/K and Fe/K), as well as chlorophycean algae counts document changes in Amur freshwater and sediment discharge that condition the OSIW. Stable carbon isotopes of epi- and shallow endobenthic foraminifera, in combination with 14C analyses of benthic and planktic foraminifera imply decreases in OSIW oxygenation during deglacial warm phases from c. 14.7 to 13 ka (Bølling-Allerød) and c. 11.4 to 9 ka (Preboreal). No concomitant decreases in Okhotsk Sea benthic-planktic ventilation ages are observed, in contrast to nearby, but southerly locations on the Japan continental margin. We attribute Okhotsk Sea mid-depth oxygenation decreases in times of enhanced organic matter supply to maxima in remineralization within OSIW, in line with multi-proxy evidence for maxima in primary productivity and supply of organic matter. Sedimentary C/N and Fe/K ratios indicate more effective entrainment of nutrients into OSIW and thus an increased nutrient load of OSIW during deglacial warm periods. Correlation of palynological and sedimentological evidence from our sites with hinterland reference records suggests that millennial-scale changes in OSIW oxygen and nutrient concentrations were largely influenced by fluvial freshwater runoff maxima from the Amur, caused by a deglacial northeastward propagation of the East Asian Summer Monsoon that increased precipitation and temperatures, in conjunction with melting of permafrost in the Amur catchment area. We suggest that OSIW ventilation minima and the high lateral supply of nutrients and organic matter during the Allerød and Preboreal are mechanistically linked to concurrent maxima in nutrient utilization and biological productivity in the subpolar Northwest Pacific. In this scenario, increased export of nutrients from the Okhotsk Sea during deglacial warm phases supported subarctic Pacific shifts from generally Fe-limiting conditions to transient nutrient-replete regimes through enhanced advection of mid-depth nutrient- and Fe-rich OSIW into the upper ocean. This mechanism may have moderated the role of the subarctic Pacific in the deglacial CO2 rise on millennial timescales by combining the upwelling of old carbon-rich waters with a transient delivery of mid-depth-derived bio-available Fe and silicate.

A push corer developed for retrieving high-resolution sediment cores from shallow waters

Shallow water environments are often difficult ones from which to recover undisturbed sediment cores, lending themselves to neither deep water sampling, nor techniques employed for wetland areas. The most simple and obvious way to obtain a core in water depths of less than 2 m is to drive a core tube directly into the sediments using some form of push rod or a percussion (hammer) device. A core driven by percussive methods, however, may be difficult to recover and sealing the tube may be problematic for retention of the sample. Here we describe a simple coring device designed for shallow water operation. The design contains elements of both deeper water gravity and directly driven push rod coring equipment. The device can recover cores up to about 1 m in length in water depths up to about 3–4 m deep. The sampling device has been tested over a number of years from diverse limnological settings (high and mid-Arctic lakes, temperate lakes) with consistently satisfactory results.

Holocene sea subsurface and surface water masses in the Fram Strait – Comparisons of temperature and sea-ice reconstructions

Two high-resolution sediment cores from eastern Fram Strait have been investigated for sea subsurface and surface temperature variability during the Holocene (the past ca 12,000 years). The transfer function developed by Husum and Hald (2012) has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period. Additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions, and to conclude on the Holocene climate and oceanographic variability on the West Spitsbergen continental margin . Results consistently reveal warm sea surface to subsurface temperatures of up to 6 °C until ca 5 cal ka BP, with maximum seawater temperatures around 10 cal ka BP, likely related to maximum July insolation occurring at that time. Maximum Atlantic Water (AW) advection occurred at surface and subsurface between 10.6 and 8.5 cal ka BP based on both foraminiferal and dinocyst temperature reconstructions. Probably, a less-stratified, ice-free, nutrient-rich surface ocean with strong AW advection prevailed in the eastern Fram Strait between 10 and 9 cal ka BP. Weakened AW contribution is found after ca 5 cal ka BP when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka BP. Cold late Holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high δ 18 O values of the subpolar planktic foraminifer species Turborotalita quinqueloba . While IP 25 -associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea-ice increase since about 7 cal ka BP in surface waters, planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface AW influx since ca 3 cal ka BP. The observed decoupling of surface and subsurface waters during the later Holocene is most likely attributed to a strong pycnocline layer separating cold sea-ice fed surface waters from enhanced subsurface AW advection. This may be related to changes in North Atlantic subpolar versus subtropical gyre activity. • Holocene sea subsurface temperatures after Husum & Hald (2012) estimated from planktic foraminifer fauna in E Fram Strait. • Biomarkers and IP25-derived indices (including DIP25) indicate surface water variability. • Delayed onset of early Holocene conditions in subsurface (∼10.6 ka) compared to surface (∼11.7 ka) water conditions. • Warm Atlantic layer likely occupied uppermost 200 m in eastern Fram Strait between 10 and 9 ka. • Diverging late Holocene trends in surface and subsurface conditions linked to presence of strong pycnocline/stratification.

Preliminary identification of palaeofloods with the alkane ratio C31/C17 and their potential link to global climate changes.

A major challenge in palaeohydrology is the extraction of continuous palaeoflood information from geophysical records. A high-resolution sediment core off the Minjiang estuary area in the Taiwan Strait, SE China, records the sedimentation history from approximately 1660 to the present. The alkane ratio C31/C17, a classic organic geochemical indicator of terrestrial/aquatic matter, peaks in the layers dating as 1876-1878 and 1968-1970, suggesting the large terrestrial input to the Minjiang estuary area by huge flood transporting during the each peak interval. Historical archives are consistent with this interpretations and record catastrophic floods in the Minjiang River during both intervals. Furthermore between 1876-1878 there were floods in southern China and droughts in northern China, as well as throughout Asia, Africa, Australia, and the Americas. The 1876-1878 catastrophic flood of the Minjiang River may therefore has been the local response to global climate anomalies during that time interval.

Temporal relationship between Holocene human occupation and vegetation change along the northwestern margin of the Central African rainforest

This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area.

Evaluating highly branched isoprenoid (HBI) biomarkers as a novel Antarctic sea-ice proxy in deep ocean glacial age sediments

Antarctic sea-ice plays a primary role in the climate system, potentially modulating interhemispheric millennial-scale climate change and deglacial warming. Recently, microfossil proxy data have provided important insights into this potential forcing. However, additional proxies for glacial sea-ice reconstructions are required, to support the microfossil data and to control for potential preservation issues. We considered highly branched isoprenoids (HBIs) as a sea-ice proxy, building on earlier studies in the Arctic and Antarctic. This study focused on measuring HBIs in glacial deposits in Southern Ocean deep ocean sediment cores. These deep ocean sites provided a study location away from the local sea-ice complexities associated with coastal and shallow water sites and allowed the comparison of HBIs during several phases of glacial sea-ice variability inferred from microfossils. Down-core profiles of di- and tri-unsaturated HBI isomers diene II and triene III were compared with diatom-based reconstructions of Antarctic sea-ice derived in three high resolution sediment cores recovered from a transect across the Scotia Sea, Southwest Atlantic. High quality chronological control was achieved through a combination of abundance stratigraphy, relative geomagnetic palaeointensity data, and down-core magnetic susceptibility/ice core dust correlation. Significant positive correlations, observed between HBI diene II and sea-ice presence, and between HBI triene III and open waters in the Marginal Ice Zone indicated that the two HBIs are both closely related to sea-ice and sea-ice edge dynamics, respectively. Highly significant down-core correlations between the HBIs indicate coeval sedimentation related to the summer breakdown of sea-ice melt-induced stratification. Combined, the two HBIs and diatoms demonstrated their potential as proxies for permanent sea-ice cover and sea-ice seasonality, two parameters poorly resolved in current climate models. The sea-ice reconstructions presented have developed our knowledge regarding HBIs and their relationship with the surface ocean environment and further highlight their potential as an important proxy for glacial Antarctic sea-ice and sea-ice dynamics back to at least ∼60 ka.