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.

Data on multidisciplinary research in the Tajura Rift (Gulf of Aden) during Cruise 7 of R/V Akademik Mstislav Keldysh in winter 1983-1984

In the collective monograph results of geological and geophysical studies in the Tadjura Rift carried out by conventional outboard instruments and from deep/sea manned submersibles "Pisces" in winter 1983-1984 are reported. Main features of rift tectonics, geology, petrology, and geochemistry of basalts from the rift are under consideration. An emphasis is made on lithology, stratigraphy, and geochemistry of bottom sediments. Roles of terrigenous, edafogenic, biogenic, and hydrothermal components in formation of bottom sediments from the rift zone are shown.

Sea ice diatoms from Late Quaternary sediments in the Scotia Sea

Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4x10**6 km**2 to a maximum of 19x10**6 km**2 during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately 61°S to 52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ab. 30 ka and 22 ka that extended to ab. 59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.

Geochemical and palynological measurements from the ODP Leg 189 at Site 1172 on the East Tasman Plateau

A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of 13C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate Apectodinium. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX86, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are >10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX86 proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant Apectodinium confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 103 - 104 years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf.

Mineralogical, sedimentological and paleontological analyses of ODP Hole 127-797B upper Quarternary sediments

Nearly continuous cores of Quaternary fine-grained sediments with distinct dark-light colored cycles were recovered from Sites 794, 795, and 797 in the basinal parts of the Japan Sea during Leg 127. A comparison of gray value (darkness) profiles supplemented by visual inspection of core photographs between sites indicated that most of the dark and light layers were correlatable between sites, and that two of the dark layers lie close to adjacent marker ash layers. These observations indicate that deposition of dark and light layers resulted from basin-wide synchronous events. In order to understand the origin of these dark-light cycles, petrographical, mineralogical, compositional, and paleontological studies were carried out on closely spaced samples from the upper Quaternary sediments recovered from Site 797. Age model was constructed based on comparison between variation in diatom abundance and the standard oxygen isotope curve of Imbrie et al. (1984), the latter was interpolated between the five age controlled levels established at Site 797. The two curves show similar patterns which enabled us to "tune" the sediment ages to the oxygen isotope stages. We have to use variation in diatom abundance as a substitute for oxygen isotope curve since oxygen isotopic data are not available at the studied sites. Bottom water oxygenation conditions were estimated based on two criteria: (1) the degree of lamina preservation and (2) the ratio of Corg to Stot. The surface water productivity was deduced from the Corg and biogenic silica content. Results suggest that the bottom water oxygenation level and the surface water productivity varied significantly in response to the glacial-interglacial cycles. Glacio-eustatic sea-level changes and subsequent changes in water circulation in the Japan Sea appear to have been responsible for these variations and consequent changes in sediment composition throughout the Quaternary.

Characterization of insoluble organic matter in sediments at DSDP Site 87-582

Lipids, humic acids, and kerogens were isolated from Site 582 sediment cores. The amount of each organic fraction in the samples taken from 5.6 to 694 m sub-bottom is almost unrelated to depth of the sample. A study of the oxidation of organic matter by the alkaline KMnO4 method reveals that distribution of polymethylene chain lengths of the kerogens and humic acids in the marine sediments differ from those in lacustrine sediments. The order of abundance of these chains in the sediments is: kerogens, 52-66% of total methylene chains; humic acids, 25-33%; and lipids, 8-16%. The results suggest that polyunsaturated fatty acids (>=4 double bonds) may be important in the formation of polymethylene chains of kerogens and humic acids in marine sediments.

Miocene through Pleistocene dinoflagellates from ODP Site 170-1039

Palynological data from offshore Costa Rica, allow us to investigate the relationship between dinoflagellate cyst assemblages and changes in regional oceanic primary productivity. From Miocene to Pleistocene, productivity at ODP Site 1039 was influenced by tectonic drift, as Site 1039 approached the continent, from the Equator to its current position at ~10°N. In addition, dinoflagellate abundance is modulated by regional productivity events, which modified primary productivity, as also indicated by available data on calcareous nannofossils, diatoms, TOC, and CaCO3 content. Five palynomorph intervals are defined. The early-late Miocene one, dominated by Batiacasphaera, represents relatively stable, productive oceanic conditions before the closure of the Indonesian and Panama Seaways. The late Miocene decrease in palynomorph recovery is related to the Carbonate Crash Event. The high abundance and diversity of the assemblages at the end of the late Miocene to early Pliocene indicate increased productivity related to the Global Biogenic Bloom, and a change in dominance from Batiacasphaera to Impagidinium to Nematosphaeropsis. The low abundance of the late Pliocene interval is related to El Niño-like conditions, and there is another change related to the disappearance of Batiacasphaera and dominance of Impagidinium, Nematosphaeropsis, and Operculodinium. The abundant Pleistocene assemblages represent increased marine productivity, and a high influx of continental palynomorphs and bissacate pollen, associated with the proximity of the Costa Rica Dome. Pleistocene dinoflagellates are characterized by Spiniferites and Selenopemphix, together with rare Impagidinium and Nematosphaeropsis.

Microbiological investigations of the Canadian tundra

Microbial communities were analyzed at 17 sites visited during the expedition Tundra Northwest 1999 (TNW-99) by microscopic analyses (epifluorescence microscopy and image analyses). The data were used to describe the communities of bacteria, fungi and algae in detail by number, biovolume and biomass. Great variability was found, which could be related to organic matter content of soils and features of vegetation patterns. The amounts (numbers and abundance) of organisms and data on microbial biomass are discussed in relation to other polar environments of the Northern and Southern Hemispheres.

Abundance and of mesozooplanktopn in the Gulf of Lion during MOOGLI 1 and 3 in 1998 and 1999

The MOOGLI dataset contains mesozooplankton data collected in 1998-1999 in the Gulf of Lion (North Western Mediterranean Sea). Zooplankton taxonomy-related abundance per unit volume of the water column.

Water chemistry and diatom occurrences in sediments of Terrasovoje, Radok and Beaver Lake, Amery Oasis, East Antarctica

The diatom flora of three lakes in the ice-free Amery Oasis, East Antarctica, was studied. Two of the lakes are meltwater reservoirs, Terrasovoje Lake (31 m depth) and Radok Lake (362 m depth), while Beaver Lake (>435 m depth) is an epishelf lake. The lakes can be characterized as cold, ultra-oligotrophic and alkaline, displaying moderate (Radok and Terrasovoje lakes) to high (Beaver Lake) conductivities. There was no diatom phytoplankton present in any of the three lakes. While 34 benthic diatom taxa were identified from modern and Holocene sediments of Terrasovoje and Radok lakes, a 30-cm long sediment core recovered in Beaver Lake was barren. Five species (Luticola muticopsis, Muelleria peraustralis, Pinnularia cymatopleura, Psammothidium metakryophilum, P. stauroneioides) are endemic to the Antarctic region. All identified taxa are photographically documented and brief notes on their taxonomy, biogeography and ecology are provided. The most abundant diatom taxa are Amphora veneta, Craticula cf. molesta, Diadesmis spp, M. peraustralis and Stauroneis anceps. This is the first report on the diatom flora in lakes of the Amery Oasis.

Geological, geochemical and biogeochemical data on boundary zones of the Atlantic Ocean

Results of studies in two biogeochemically active zones of the Atlantic Ocean (the Benguela upwelling waters and the region influenced by the Congo River run-off) are reported in the book. A multidisciplinary approach included studies of the major elements of the ocean ecosystem: sea water, plankton, suspended matter, bottom sediments, interstitial waters, aerosols, as well as a wide complex of oceanographic studies carried out under a common program. Such an approach, as well as a use of new methodical solutions led to obtaining principally new information on different aspects of oceanology.

Diatom and hydrocarbon analysis of sediment core NBP00-03-JPC38

In this study, we present a unique high-resolution Holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the Vega Drift, eastern Antarctic Peninsula (EAP). These data add to the climate framework already established by high-resolution marine sedimentary records from the Palmer Deep, western Antarctic Peninsula (WAP). Heavy sea ice conditions and reduced primary productivity were observed prior to 7.4 ka B.P. in relation with the proximity of the glacial ice melt and calving. Subsequent Holocene oceanographic conditions were controlled by the interactions between the Westerlies-Antarctic Circumpolar Current (ACC)-Weddell Gyre dynamics. A warm period characterized by short seasonal sea ice duration associated with a southern shift of both ACC and Westerlies field persisted until 5 ka B.P. This warm episode was then followed by climate deterioration during the middle-to-late Holocene (5 to 1.9 ka B.P.) with a gradual increase in annual sea ice duration triggered by the expansion of the Weddell Gyre and a strong oceanic connection from the EAP to the WAP. Increase of benthic diatom species during this period was indicative of more summer/autumn storms, which was consistent with changes in synoptic atmospheric circulation and the establishment of low- to high-latitude teleconnections. Finally, the multicentennial scale variability of the Weddell Gyre intensity and storm frequency during the late Holocene appeared to be associated with the increased El Niño-Southern Oscillation frequency.

Organic geochemistry and sedimentology of lower to mid-Cretaceous at DSDP Leg 77 Holes

Analyses of 40 carbonate core samples - 27 from Site 535, 12 from Site 540, and 1 from Site 538A - have confirmed many of the findings of the Shipboard Scientific Party. The samples, all but one Early to mid-Cretaceous in age (Berriasian to Cenomanian), reflect sequences of cyclically anoxic and oxic depositional environments. They are moderately to very dark colored, dominantly planar-parallel, laminated lime mudstones. Most show the effects of intense mechanical compaction. Visual kerogen characteristics and conventional Rock-Eval parameters indicate that these deep basinal carbonates contain varying mixtures of thermally immature kerogen derived from both marine and terrigenous precursors. However, variations in kerogen chemistry are evident upon analysis of the pyrolysis mass spectral data in conjunction with the other geochemical analyses. Particularly diagnostic is the reduction index, Rl, a measure of H2S produced during pyrolysis. Total organic carbon, TOC, ranges from 0.6 to 6.6%, with an overall average of 2.4%. Average TOCs for these fine-grained mudstones are: late Eocene 2.5% (1 sample), Cenomanian 2.2% (6), Albian 2.0% (10), Aptian 1.3% (1), Barremian-Hauterivian 2.8% (11), late Valanginian 4.8% (3), Berriasian-early Valanginian 1.6% (7). Most of the carbonates have source-potential ratings of fair to very good of predominantly oil-prone to mixed kerogen, with only a few gas-prone samples. The ratings correlate well with the inferred depositional environments, i.e., whether oxic or anoxic. Several new organic-geochemical parameters, especially Rl, based on pyrolysis mass spectrometry of powdered whole-rock samples, support this view. Tar from fractures in laminated to bioturbated limestones of Unit IV (late Valanginian) at 535-58-4, 19-20 cm (530 m sub-bottom) appears to be mature, biodegraded, and of migrated rather than on site indigenous origin.

Results of biogeochemical studies in the Russian Arctic seas: isotope and radioisotope data

Comprehensive biogeochemical studies including determination of isotopic composition of organic carbon in both suspended matter and surface layer (0-1 cm) bottom sediments (more than 260 determinations of d13C-Corg) were carried out for five Arctic shelf seas: White, Barents, Kara, East Siberian, and Chukchi Seas. The aim of this study is to elucidate causes that change isotopic composition of particulate organic carbon at the water-sediment boundary. It is shown that isotopic composition of organic carbon in sediments from seas with high river run-off (White, Kara, and East Siberian Seas) does not inherit isotopic composition of organic carbon in particles precipitating from the water column, but is enriched in 13C. Seas with low river run-off (Barents and Chukchi Seas) show insignificant difference between d13C-Corg values in both suspended load and sediments because of low content of isotopically light allochthonous organic matter in suspended matter. Biogeochemical studies with radioisotope tracers (14CO2, 35S, and 14CH4) revealed existence of specific microbial filter formed from heterotrophic and autotrophic organisms at the water-sediment boundary. This filter prevents mass influx of products of organic matter decomposition into the water column, as well as reduces influx of OM contained in suspended matter from water into sediments.

Bacterioplankton and bacteriobenthos in surface layer waters and sediments between the Sakhalin Island and the Eastern Asia in June 2006

This work presents results of a study of plankton and benthic microbiocenoses of the Amur River estuary. It is shown that distribution of total abundance and indicator groups of bacteriobenthos are characterized by stronger heterogeneity compared with bacterioplankton and that it depends on the Amur River runoff and bottom type. The river runoff helps by increasing overall bacterioplankton abundance in the near-mouth part of the estuary. Microorganisms utilizing low concentrations of organic matter (OM) play major role in processes of OM utilization in water and bottom sediments. Saprophytic bacteria play a significant role in OM utilization only in water at certain sampling sites in the Tatarsky Strait and Sakhalin Bay and in bottom sediments sampled in the mouth part of the estuary. Some parts of the estuary subjected to organic contamination are found according to microbiological characteristics. It is shown that fluctuation of salinity leads to change of the role of bacteria with different food demands in the microbial community.