Distribution of euphausiids (Crustacea) at the Great Meteor seamount, Atlantic Ocean

In the course of the voyages 9a and 9c (1967) and 19 (1970) of the RV "Meteor" samples of plankton and neuston have been taken in the area of the Great Meteor Seamount. The euphausiids of this material have been examined quantitatively as well as qualitatively in order to study the influence of the Great and Small Meteor Seamount on a vertically migrating group of plankton. 20 species could be identified. All stem from the surrounding deep water and belong to the tropical and subtropical fauna. On the plateau of the Great Meteor Seamount no indigenous species have been encountered and also the typical neritic species from the west coast off Africa are lacking. As for the euphausiids no relationships exist between the Great Meteor Seamount and the shelf area of West Africa. The dominant species around the Meteor Seamount were Euphausia brevii, Stylocheiron suhmii, E. hemigibba, S. longicorne and Thysanopoda subaequalis. Using the index of diversity (Simpson) distinct differences in the composition of species could be shown to exist between the plateau area of the Meteor Seamount and the surrounding sea. On the plateau of the Great Meteor Seamount the number of species was only 7, E. brevis and S. suhmii dominated. None of the species occurred in great numbers and none is adapted to the specific environmental conditions of the plateau of the Meteor Seamount. The fauna of the plateau is a depauperate one as compared with that of the surrounding sea. This can be explained by the fact that adult euphausiids require for their existence greater water depths than are found above the plateau of the Meteor Seamount.

Neodymium isotope record of late Paleocene to eraly Eocene fish teeth

High-resolution, fish tooth Nd isotopic records for eight Deep Sea Drilling Project and Ocean Drilling Program sites were used to reconstruct the nature of late Paleocene-early Eocene deep-water circulation. The goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4-5°C warming of deep and bottom waters at the Paleocene/Eocene boundary - the Paleocene-Eocene thermal maximum (PETM) event. The combined set of records indicates a deep-water mass common to the North and South Atlantic, Southern and Indian oceans characterized by mean epsilon-Nd values of ~-8.7, and different water masses found in the central Pacific Ocean (epsilon-Nd ~-4.3) and Caribbean Sea (epsilon-Nd ~1.2). The geographic pattern of Nd isotopic values before and during the PETM suggests a Southern Ocean deep-water formation site for deep and bottom waters in the Atlantic and Indian ocean basins. The Nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the PETM. This finding is consistent with the pattern of warming established by recently published stable isotope records, suggesting that deep- and bottom-water warming during the PETM was gradual and the consequence of surface-water warming in regions of downwelling.

Sedimentology of ODP sites in the Cape Basin, southeast Atlantic Ocean

Middle/late Miocene to early Pliocene sedimentary sequences along the continental margin of southwest Africa have changes that correspond to the carbonate crash (12-9 Ma) and biogenic bloom events (~7-4 Ma) described in the equatorial Pacific by Farrell et al. (1995, doi:10.2973/odp.proc.sr.138.143.1995). To explore the origins of these changes, we analyzed the carbon and coarse fraction contents of sediments from ODP Sites 1085, 1086, and 1087 at a time resolution of 5 to 30 kyr. Several major drops in CaCO3 concentration between 12 and 9 Ma are caused by dilution from major increases in clastic input from the Oranje River during global sea level regressions. Abundant pyrite crystals and good preservation of fish debris reflect low oxygenation of bottom/pore waters. Regional productivity was enhanced during the time equivalent to the carbonate crash period. Higher benthic/planktic foraminiferal ratios indicate that CaCO3 dissolution at Site 1085 peaked between 9 to 7 Ma, which was after the global carbonate crash. This period of enhanced dissolution suggests that Site 1085 was located within a low-oxygen water mass that dissolved CaCO3 more easily than North Atlantic Deep Water, which began to bathe this site at 7 Ma. At 7 to 6 Ma, the onset of the biogenic bloom, increases and variations in total organic carbon and benthic foraminiferal accumulation rates show that paleoproductivity increased significantly above values observed during the carbonate crash period and fluctuated widely. We attribute the late Miocene paleoproductivity increase off southwest Africa to ocean-wide increases in nutrient supply and delivery.

Transient Holocene experiments under orbital forcing using the comprehensive global climate model CCSM3 (Community Climate System Model 3)

The Southern Hemisphere Westerly Winds (SWW) have been suggested to exert a critical influence on global climate through wind-driven upwelling of deep water in the Southern Ocean and the potentially resulting atmospheric CO2 variations. The investigation of the temporal and spatial evolution of the SWW along with forcings and feedbacks remains a significant challenge in climate research. In this study, the evolution of the SWW under orbital forcing from the early Holocene (9 kyr BP) to pre-industrial modern times is examined with transient experiments using the comprehensive coupled global climate model CCSM3. Analyses of the model results suggest that the annual and seasonal mean SWW were subject to an overall strengthening and poleward shifting trend during the course of the early-to-late Holocene under the influence of orbital forcing, except for the austral spring season, where the SWW exhibited an opposite trend of shifting towards the equator.

(Table 1) Estimated e-Nd(0) input calculated using the relative fraction of ODP Hole 105-647A amphibole grains originated from different provinces of the North America

Many marine radiogenic isotope records show both spatial and temporal variations, reflecting both the degree of mixing of distinct sources in the oceans and changes in the distribution of chemical weathering on the continents. However, changes in weathering and transport processes may themselves affect the composition of radiogenic isotopes released into seawater. The provenance of physically weathered material in the Labrador Sea, constrained through the use of Ar-Ar ages of individual detrital minerals, has been used to estimate the relative contributions of chemically weathered terranes releasing radiogenic isotopes into the Labrador Sea. A simple box-model approach for balancing observed Nd-isotope variations has been used to constrain the relative importance of localised input in the Labrador Sea, and the subsequent mixing of Labrador Sea Water into North Atlantic Deep-Water. The long-term pattern of erosion and deep-water formation around the North Atlantic seems to have been a relatively stable feature since 1.5 Ma, although there has been a dramatic shift in the nature of physical and chemical weathering affecting the release of Hf and Pb isotopes. The modelled Nd isotopes imply a relative decrease in water mass advection into the Labrador Sea between 2.4 and 1.5 Ma, accompanied by a decrease in the rate of overturning, possibly caused by an increased freshwater input into the Labrador Sea.

Oxygen and carbon isotopic composition in Eocene and Oligocene planktonic and benthic foraminifera from DSDP sediments

Oxygen and carbon isotope ratios in Eocene and Oligocene planktonic and benthic foraminifera have been investigated from Atlantic, Indian, and Pacific Ocean locations. The major changes in Eocene-Oligocene benthic foraminiferal oxygen isotopes were enrichment of up to 1 per mil in 18O associated with the middle/late Eocene boundary and the Eocene/Oligocene boundary at locations which range from 1- to 4-km paleodepth. Although the synchronous Eocene-Oligocene 18O enrichment began in the latest Eocene, most of the change occurred in the earliest Oligocene. The earliest Oligocene enrichment in 18O is always larger in benthic foraminifera than in surface-dwelling planktonic foraminifera, a condition that indicates a combination of deep-water cooling and increased ice volume. Planktonic foraminiferal d18O does not increase across the middle/late Eocene boundary at our one site with the most complete record (Deep Sea Drilling Project Site 363, Walvis Ridge). This pattern suggests that benthic foraminiferal d18O increased 40 m.y. ago because of increased density of deep waters, probably as a result of cooling, although glaciation cannot be ruled out without more data. Stable isotope data are averaged for late Eocene and earliest Oligocene time intervals to evaluate paleoceanographic change. Average d18O of benthic foraminifera increased by 0.64 per mil from the late Eocene to the early Oligocene d18O maximum, whereas the average increase for planktonic foraminifera was 0.52 per mil. This similarity suggests that the Eocene/Oligocene boundary d18O increase was caused primarily by increased continental glaciation, coupled with deep sea cooling by as much as 2°C at some sites. Average d18O of surface-dwelling planktonic foraminifera from 14 upper Eocene and 17 lower Oligocene locations, when plotted versus paleo-latitude, reveals no change in the latitudinal d18O gradient. The Oligocene data are offset by ~0.45 per mil, also believed to reflect increased continental glaciation. At present, there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from Eocene to Oligocene time using oxygen isotopes.

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.

Occurrence and isotopic composition (d18O, d13C) of benthic foraminifera in sediments from DSDP Leg 72

Changes in the vertical water mass structure of the Vema Channel during the Pliocene have been inferred from benthic foraminiferal assemblages and stable isotopic analyses from three sites of DSDP Leg 72 (South Atlantic). Faunal and isotopic results from Sites 516A and 518 suggest that a major change occurred in deep-water circulation patterns in the late Pliocene near 3.2 Ma. Benthic oxygen isotopic records from Sites 516A and 518 show a characteristic increase in d18O values near 3.2 Ma. This has been documented in numerous Pliocene isotopic records. The magnitude of the oxygen isotopic enrichment near 3.2 Ma appears to increase with water depth from an average enrichment of 0.34 per mil in Site 516A (1313 m) to an average enrichment of 0.58 per mil in Site 518 (3944 m). We suggest that this enrichment resulted partly from a change in deep-water circulation patterns which included a decrease in bottom-water temperatures. Planktonic d18O values near 3.2 Ma show no evidence of an enrichment which would be indicative of an increase in global ice volume. On the contrary, d18O values in Sites 517 and 518 become more depleted near 3.2 Ma, indicating a surface-water warming perhaps due to a change in the strength and/or position of the Brazil Current. An increase in the relative abundance of the benthic foraminifer Nuttalides umbonifera, which is associated with Antarctic Bottom Water (AABW) in the modern ocean, coincides with the benthic 18O enrichment in Site 518. At 3.2 Ma, oxygen and carbon isotopic gradients between Sites 518 (3944 m) and 516A (1313 m) show a marked increase such that Site 518 becomes enriched in 18O and depleted in 13C relative to Site 516A. This enrichment in d18O is interpreted as partly representing a temperature decrease at Site 518; the depletion in d13C indicates a corrosive water mass which is high in metabolic CO2. We suggest that benthic foraminiferal and stable isotopic changes in Site 518 resulted from a pulse-like increase in the formation of AABW near 3.2 Ma. The cause of this circulation event may have been linked to global cooling and/or the final closure of the Central American Seaway.

Abundance, biomass, ingestion rates and daily ratios of Salpa thompsoni individuals sampled during POLARSTERN cruise ANT-XVIII/5b to the Eastern Belingshausen Sea

Distribution, density, and feeding dynamics of the pelagic tunicate Salpa thompsoni have been investigated during the expedition ANTARKTIS XVIII/5b to the Eastern Bellingshausen Sea on board RV Polarstern in April 2001. This expedition was the German contribution to the field campaign of the Southern Ocean Global Ocean Ecosystems Dynamics Study (SO-GLOBEC). Salps were found at 31% of all RMT-8 and Bongo stations. Their densities in the RMT-8 samples were low and did not exceed 4.8 ind/m**2 and 7.4 mg C/m**2. However, maximum salp densities sampled with the Bongo net reached 56 ind/m**2 and 341 mg C/m**2. A bimodal salp length frequency distribution was recorded over the shelf, and suggested two recent budding events. This was also confirmed by the developmental stage composition of solitary forms. Ingestion rates of aggregate forms increased from 2.8 to 13.9 µg (pig)/ind/day or from 0.25 to 2.38 mg C/ind/day in salps from 10 to 40 mm oral-atrial length, accounting for 25-75% of body carbon per day. Faecal pellet production rates were on average 0.08 pellet/ind/h with a pronounced diel pattern. Daily individual egestion rates in 13 and 30 mm aggregates ranged from 0.6 to 4.8 µg (pig)/day or from 164 to 239 µg C/day. Assimilation efficiency ranged from 73 to 90% and from 65 to 76% in 13 and 30 mm aggregates, respectively. S. thompsoni exhibited similar ingestion and egestion rates previously estimated for low Antarctic (~50°S) habitats. It has been suggested that the salp population was able to develop in the Eastern Bellingshausen Sea due to an intrusion into the area of the warm Upper Circumpolar Deep Water

Oxygen and carbon isotopes from benthic and planktonic foraminifers at DSDP Leg 74 Holes

Oxygen and carbon isotope measurements have been made in picked planktonic and benthonic foraminifers from the five sites drilled on Leg 74, covering the whole Cenozoic. For the Neogene, the coverage gives good information on the development of the vertical temperature structure of Atlantic deep water. For the Paleogene, vertical gradients were weak and it is possible to combine data from different sites to obtain a very detailed record of both the temperature and carbon isotope history of Atlantic deep waters.