Sediment, isotopic and geochemical record during Marine Isotope Stages 29 to 34 of IODP Site 339-U1387

Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558 m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stage (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic d18O signal follows obliquity with the exception of an additional, smaller d18O peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3. A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065-1091 ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (< 12°C) SST that in their climatic impact were comparable to the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes.

Meiofauna densities, nematode biomass, nematode genus diversity, sediment grain size, organic matter, and pigments for the surface layers of two sites in summer (November 2009) and winter (august 2010)

The meiobenthic community of Potter Cove (King George Island, west Antarctic Peninsula) was investigated, focusing on responses to summer/winter conditions in two study sites contrasting in terms of organic matter inputs. Meiofaunal densities were found to be higher in summer and lower in winter, although this result was not significantly related to the in situ availability of organic matter in each season. The combination of food quality and competition for food amongst higher trophic levels may have played a role in determining the standing stocks at the two sites. Meiobenthic winter abundances were sufficiently high to infer that energy sources were not limiting during winter, supporting observations from other studies for both shallow water and continental shelf Antarctic ecosystems. Recruitment within meiofaunal communities was coupled to the seasonal input of fresh detritus for harpacticoid copepods but not for nematodes, suggesting that species-specific life history or trophic features form an important element of the responses observed.

Organic geochemistry of Cretaceous black shales

Organic-carbon-rich 'black shales' and adjacent organic-carbon-poor rocks from three different Cretaceous settings encountered during ODP Leg 103 have been studied by organic geochemical methods. Rock-Eval analysis, carbon isotope data, and lipid biomarkers show organic matter to contain varying proportions of marine and continental materials. In Hauterivian-Barremian organic-carbon-rich marlstone turbidites, large amounts of land-derived organic matter are found. Aptian-Albian black-colored shales are interspersed within green claystones, from which they differ by containing more marine organic matter. An abbreviated layer of black shale from the Cenomanian/Turonian boundary is dominated by well-preserved marine organic matter. Downslope transport and rapid reburial within a predominantly oxygenated deep-water setting created most of these examples of black shales, except for the Cenomanian-Turonian deposits in which deep-water anoxia may have been involved.

Biomarker records of DSDP Hole 24-231 and terrestrial sediments

ntegrated terrestrial and marine records of northeast African vegetation are needed to provide long high resolution records of environmental variability with established links to specific terrestrial environments. In this study, we compare records of terrestrial vegetation preserved in marine sediments in the Gulf of Aden [Deep Sea Drilling Project (DSDP) Site 231] and an outcrop of lacustrine sediments in the Turkana Basin, Kenya, part of the East African Rift System. We analyzed higher plant biomarkers in sediments from both deposits of known equivalent age, corresponding to a ca. 50-100 ka humid interval prior to the b-Tulu Bor eruption ca. 3.40 Ma, when the Lokochot Lake occupied part of the Turkana Basin. Molecular abundance distributions indicate that long chain n-alkanoic acids in marine sediments are the most reliable proxy for terrestrial vegetation (Carbon Preference Index, CPI = 4.5), with more cautious interpretation needed for n-alkanes and lacustrine archives. Marine sediments record carbon isotopic variability in terrestrial biomarkers of 2-3 per mil, roughly equivalent to 20% variability in the C3/C4 vegetation contribution. The proportion of C4 vegetation apparently increased at times of low terrigenous dust input. Terrestrial sediments reveal much larger (2-10 per mil) shifts in n-alkanoic acid delta13C values. However, molecular abundance and isotopic composition suggest that microbial sources may also contribute fatty acids, contaminating the lacustrine sedimentary record of terrestrial vegetation.

High resolution study of sediment core GeoB3606-1

Based on a high-resolution analysis of the diatom signal and biogenic bulk components at site GeoB3606-1 (25°S, off Namibia), we describe rapid palaeoceanographic changes in the Benguela Upwelling System (BUS) from early MIS 3 through to the early Holocene (55 000 to 7 000 14C yr BP). Coastal upwelling strongly varied at 25°S from MIS 3 through to MIS 2. The abrupt decrease in the accumulation rate of biogenic silica and diatoms from MIS 3 into MIS 2 records rapid oceanographic changes in the BUS off Namibia. During MIS 3, leakage of excess H4SiO4 acid from the Southern Ocean into low-latitude surface waters, as indicated by the occurrence of Antarctic diatoms, enhanced the production of spores of Chaetoceros at the expense of calcareous phytoplankton. Furthermore, shallower Antarctic Intermediate Water (AAIW) would have enriched the thermocline off Namibia with silicate transported from the Southern Ocean. The strong decrease of the siliceous signal throughout MIS 2 represents a decrease in the nutrient input to the BUS, even though the diatom assemblage is still dominated by spores of the upwelling-associated diatom genus Chaetoceros. Depletion of silicate in the thermocline from the onset of MIS 2 through to the early Holocene reflects the shutdown of AAIW injection from the Southern Ocean into the BUS, causing upwelled waters to become reduced in silicate, hence less favourable for diatom production. The deglaciation and early Holocene are characterised by the replacement of the upwelling-associated flora by a non-upwelling-related diatom community, reflecting weakened upwelling, retraction of the seaward extension of the chlorophyll filament off Lüderitz, and dominance of warmer waters.

Radiocarbon datings and temperature reconstructions of sediment core GeoB10038-4 off SW Sumatra

Surface and thermocline conditions of the eastern tropical Indian Ocean were reconstructed through the past glacial-interglacial cycle by using Mg/Ca and alkenone-paleothermometry, stable oxygen isotopes of calcite and seawater, and terrigenous fraction performed on sediment core GeoB 10038-4 off SW Sumatra (~6°S, 103°E, 1819 m water depth). Results show that annual mean surface and thermocline temperatures varied differently and independently, and suggest that surface temperatures have been responding to southern high-latitude climate, whereas the more variable thermocline temperatures were remotely controlled by changes in the thermocline temperatures of the North Indian Ocean. Except for glacial terminations, salinity proxies indicate that changing intensities of the boreal summer monsoon did not considerably affect annual mean conditions off Sumatra during the past 133,000 years. Our results do not show a glacial-interglacial pattern in the thermocline conditions and reject a linear response of the tropical Indian Ocean thermocline to mid- and high-latitude climate change. Alkenone-based surface temperature estimates varied in line with the terrigenous fraction of the sediment and the East Asian winter monsoon proxy records at the precession band suggestive of monsoon (sea level) to be the dominant control on alkenone temperatures in the eastern tropical Indian Ocean on sub-orbital (glacial-interglacial) timescales.

Sediment composition and stable isotopic ratio of Neogloboquadrina pachyderma from DSDP Site 94-609_Site, North Altlantic

Digitized records of optical desnity in many North Atlantic cores exihibt rapid changes from lighter to darker extrems, typically within less than 200 years, at the 5d/5e, 5b/5c and 4/5 boundaries. In cores from DSDP site 609 the changes from lighter to darker color coincide with increasing in relative abundance of Neogloboquadrina pachyderma (l.c.), with increases in abundances of lithic grains and with decreasing in carbonate content. The rapid changes to dark color, therefore, are climate-driven and correspond to a lowering of seas surface temperatures and to increases in amounts of ice rafted debris relative to biogenic carbonate. At the 5d&4c boundary, delta18O in N. pachyderma (l.c.) increases abruptly with the change to darker sediments as expected for cooler sea surface temperatures. At the 4/5 boundary, however, delta18O decreases with the change to darker sediment and cooler sea surface temperatures, suggesting that a layer of fresh surface water was present in the North Atlantic at that time.

Recent ostracods in surface sediment samples from Admiralty Bay, King George Island, West Antarctica

Ostracods from Admiralty Bay on King George Island (South Shetland Islands) represent 29 podocopid species, belonging to 19 genera, one cladocopid and six myodocopid species. They were recovered from Recent marine and/or glacio-marine sediment samples from water depths of up to 520 m. These ostracods constitute a variable assemblage, which is overall typical for the Antarctic environment. Shallow-water assemblages tend to be more variable in terms of frequencies and species richness than deep-water assemblages. The later are low in numbers and remain relatively high diversities. Overall, no linear relation between ostracod assemblage-composition and environmental features analyzed was recognized.

High-resolution IP25 of three sediment cores in the western North Pacific and Bering Sea

Due to its strong influence on heat and moisture exchange between the ocean and the atmosphere, sea ice is an essential component of the global climate system. In the context of its alarming decrease in terms of concentration, thickness and duration, understanding the processes controlling sea-ice variability and reconstructing paleo-sea-ice extent in polar regions have become of great interest for the scientific community. In this study, for the first time, IP25, a recently developed biomarker sea-ice proxy, was used for a high-resolution reconstruction of the sea-ice extent and its variability in the western North Pacific and western Bering Sea during the past 18,000 years. To identify mechanisms controlling the sea-ice variability, IP25 data were associated with published sea-surface temperature as well as diatom and biogenic opal data. The results indicate that a seasonal sea-ice cover existed during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas during warmer intervals (Bølling-Allerød and Holocene) reduced sea ice or ice-free conditions prevailed in the study area. The variability in sea-ice extent seems to be linked to climate anomalies and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea, especially the Alaskan Stream injection though the Aleutian passes.

Stable hydrogen isotopic composition (dD) and stable carbon isotopic composition (d13C) of sediment core GeoB9508-5 off Senegal

To reconstruct variability of the West African monsoon and associated vegetation changes on precessional and millennial time scales, we analyzed a marine sediment core from the continental slope off Senegal spanning the past 44,000 years (44 ka). We used the stable hydrogen isotopic composition (dD) of individual terrestrial plant wax n-alkanes as a proxy for past rainfall variability. The abundance and stable carbon isotopic composition (d13C) of the same compounds were analyzed to assess changes in vegetation composition (C3/C4 plants) and density. The dD record reveals two wet periods that coincide with local maximum summer insolation from 38 to 28 ka and 15 to 4 ka and that are separated by a less wet period during minimum summer insolation. Our data indicate that rainfall intensity during the rainy season throughout both wet humid periods was similar, whereas the length of the rainy season was presumably shorter during the last glacial than during the Holocene. Additional dry intervals are identified that coincide with North Atlantic Heinrich stadials and the Younger Dryas interval, indicating that the West African monsoon over tropical northwest Africa is linked to both insolation forcing and high-latitude climate variability. The d13C record indicates that vegetation of the western Sahel was consistently dominated by C4 plants during the past 44 ka, whereas C3-type vegetation increased during the Holocene. Moreover, we observe a gradual ending of the Holocene humid period together with unchanging ratio of C3 to C4 plants, indicating that an abrupt aridification due to vegetation feedbacks is not a general characteristic of this time interval.

n-Alkane, fatty acid and hopanoic acid concentrations of ODP Site 190-1178 samples

Ocean Drilling Program (ODP) Leg 190 was programmed to investigate deformational, diagenetic, and hydrologic processes and their interactions in the Nankai Trough accretionary prism. Site 1178 is the northernmost site in the Muroto Transect. Slope sediments and the underlying landward-dipping reflector zone were successfully cored. Temperature measurements and Cl concentrations in pore water indirectly indicate the presence of gas hydrate between 120 and 400 meters below seafloor (mbsf) at Site 1178, with the highest concentrations between 150 and 200 mbsf (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.190.109.2001). Sedimentary structures show a broad range of deformation structures rich in fractures, suggesting active fluid circulation in the Nankai Trough prism. One of the objectives of Leg 190 was to clarify the interplay of various fundamental processes taking place in the Nankai Trough accretionary prism. Bacteria or prokaryotes in deep subsurface sediment play an important role for material transformation and circulation in an accretionary prism. Significant amounts of bacteria are detected in many of the samples examined (Shipboard Scientific Party, 2001, doi:10.2973/odp.proc.ir.190.109.2001). The type of organic matter in sediments is an important factor related to bacterial activity. To assist investigations on material circulation in deep subsurface sediments, the samples from Site 1178 were analyzed for geolipids (extractable organic matter). The basic data set is preliminarily compiled in the present report to show the types of organic matter and their concentrations in sediments from Site 1178.

Diatom, ice rafted debris and Neogloboquadrina pachyderma (sinistral) abundance in sediment core OCE326-GGC14

A high-resolution diatom census coupled with other proxy data from Laurentian Fan (LF) provides a detailed description of the last deglaciation, bringing new insight to that period by revealing directly the timing of sea-ice formation and melting. Cold events Heinrich Event 1 (H1) and the Younger Dryas (YD) were multiphase events. H1 (~16.8-15.7 cal kyr BP) was defined by a two-pulse release of icebergs promoting sea-ice formation. Melting of sea-ice after H1 corresponds to a cold and fresh anomaly that may have kept the Bølling colder than the Allerød. At ~13.6 cal kyr BP, a cooling trend culminated with sea-ice formation, marking the YD onset (~12.8 cal kyr BP). The decrease in sea-ice (~12.2 cal kyr BP) led to a YD second phase characterized by very cold winters. However, the contribution of warm water diatoms tends to increase at the same time and the YD gradual end (~11.6 cal kyr BP) contrasts with its abrupt end in Greenland ice cores. The YD cannot be regarded as an event triggered by a fresh water input through the Laurentian Channel since only one weak brief input nearly 1000 yrs after its onset is recorded. Very cold and cool conditions without ice mark the following Preboreal. A northward heat flux between 10.8 and 10.2 cal kyr BP was interrupted by the increased influence of coastal waters likely fed by inland melting. There was no further development of sea-ice or ice-drift then.