Stable carbon and hydrogen isotope record of n-Alkanoic acids of sediment core SO189/2_144KL

The Indo-Pacific Warm Pool (IPWP) is a key site for the global hydrologic cycle, and modern observations indicate that both the Indian Ocean Zonal Mode (IOZM) and the El Niño Southern Oscillation exert strong influence on its regional hydrologic characteristics. Detailed insight into the natural range of IPWP dynamics and underlying climate mechanisms is, however, limited by the spatial and temporal coverage of climate data. In particular, long-term (multimillennial) precipitation patterns of the western IPWP, a key location for IOZM dynamics, are poorly understood. To help rectify this, we have reconstructed rainfall changes over Northwest Sumatra (western IPWP, Indian Ocean) throughout the past 24,000 y based on the stable hydrogen and carbon isotopic compositions (dD and d13C, respectively) of terrestrial plant waxes. As a general feature of western IPWP hydrology, our data suggest similar rainfall amounts during the Last Glacial Maximum and the Holocene, contradicting previous claims that precipitation increased across the IPWP in response to deglacial changes in sea level and/or the position of the Intertropical Convergence Zone. We attribute this discrepancy to regional differences in topography and different responses to glacioeustatically forced changes in coastline position within the continental IPWP. During the Holocene, our data indicate considerable variations in rainfall amount. Comparison of our isotope time series to paleoclimate records from the Indian Ocean realm reveals previously unrecognized fluctuations of the Indian Ocean precipitation dipole during the Holocene, indicating that oscillations of the IOZM mean state have been a constituent of western IPWP rainfall over the past ten thousand years.

Dinoflagellate and other palynomorph abundance in sediments from ODP Leg 189 sites

At Ocean Drilling Program (ODP) Leg 189 Sites 1170-1172, the climatologically critical Eocene-Oligocene (E-O) transition is barren of any calcareous microfossils but contains rich marine organic walled dinoflagellate cyst (dinocyst) and diatom assemblages, suitable for detailed biostratigraphic and paleoenvironmental analysis. The resulting first-ever integrated dinocyst/diatom magnetostratigraphy allows confident correlation of the E-O interval between all Leg 189 sites, including Site 1168. Our correlations indicate that the (deep) opening of the Tasmanian Gateway occurred quasi-synchronously throughout the Tasmanian region, starting at ~35.5 Ma. At Sites 1170-1172, quantitatively, three distinct dinocyst assemblages may be distinguished that reflect the relatively rapid and pronounced stepwise environmental changes associated with the E-O transition in the Tasmanian region, from a pro-deltaic setting to a deep marine pelagic setting. Moreover, synchronous with the deepening of the gateway, at the southern and eastern Sites 1170-1172, typical endemic Antarctic assemblages were replaced by more cosmopolitan dinocyst communities. In marked contrast, at Site 1168 off western Tasmania, endemic Antarctic taxa are virtually absent during the E-O transition. At Sites 1170-1172, the endemic Antarctic dinocyst assemblage (Transantarctic Flora) drastically changes into a more cosmopolitan assemblage at ~35.5 Ma, with a more offshore character, reflecting the arrival of different oceanographic and environmental conditions associated with the deepening of the Tasmanian Gateway. In turn, this assemblage grades at ~34 Ma into one more typical for even more offshore and/or upwelling conditions at Site 1172. In slightly younger deposits at all sites, organic microfossils are virtually absent, reflecting winnowing and oxidation, indicative of a next step of oceanographic development. This phase may be dated as close to the Oceanic Anoxic (Oi)-1 18O (Antarctic glaciation) event (~33.3 Ma). In a single productive sample from the earliest Oligocene the northern Site 1172, a relatively warm-water cosmopolitan assemblage has been recovered. This aspect contrasts findings from coeval deposits from the Ross Sea, where endemic Antarctic species remain dominant. Somewhere between the paleogeographic positions of Site 1172 and the Ross Sea, a strong differentiation of surface waters occurred in the earliest Oligocene, possibly reflecting the onset of the Antarctic Circumpolar Current.

Distribution of benthic and planktic foraminifera in surface sediments of the Indian and Pakistan continental margin, Arabian Sea

During the Indian Ocean Expedition of the German research vessel "Meteor" and the following cruise with the Pakistani fishing vessel "Machhera" in February and March 1965, sediments were sampled from the shelf, continental slope and the Arabian Basin off Pakistan and India. The biostratigraphic studies are based on sedimentary material from 24 sediment cores up to 480 cm long and 100 grab samples. The faunal residues of the > 160 µ fraction (chiefly foraminifera and pteropods) were determined and counted in order to get an idea of the climatic conditions during the Late Quaternary of this region. Biostratigraphic correlations of these Late Quaternary deposits are only possible if the thanatocoenosis of the surface sediments are well known. The analysis of the benthonic foraminiferal populations resulted in the definition of several foraminiferal facies. The following sequence of forarniniferal facies, named after their most characteristic members, can be distinguished from the shelf to the deep-sea: 1. Ammonia-Florilus facies ; 2. Ammonia-Cancris facies; 3. Cassidulina-Cibicides facies; 4. Uvigerina-Cassidulina facies ; 5. Buliminacea facies ; 6. deepwater facies, partly with Bulimina aculeata or with Nonionidae. On the upper continental slope there is a zone extremely poor in benthonic foraminifera. In this water depth the oxygen minimum layer (0.05-0.02 ml/l) of the water column reaches the slope. Almost no connection can be observed between the living and the dead foraminiferal population of the same sample. The regional distribution of the planktonic foraminifera from plankton tows as well as from the surface sediments shows marked differences in the species composition of faunas from different regions within the area of investigation. That depends on oceanographic conditions such as upwelling, dissolution of carbonate at great depths etc. Based on the results of faunal analysis of samples from the recent sea-floor, a biostratigraphic subdivision of the sediments in the cores was established. The following biostratigraphically defined sections could be distinguished from the top of the sediment cores downwards : 1. Relatively cool climatic conditions are reflected by the foraminifera of the uppermost core sections. 2. The next section is characterized by much warmer conditions (Holocene climatic optimum). The C-14 ages of this interval range from 4000 to 10 000 years B.P. according to different authors. C-14 dates on the material investigated do not give reliable clues. 3. Foraminiferal populations adapted to much colder conditions can be observed in the underlying core section. The boundary between the warm climate reflected by the foraminifera of section 2 and the cold climate (section 3) is relatively sharp. It can be correlated from core to core over the whole area investigated. The cold climate sediments of section 3 are underlain by different cool-, warm- and cold-climate sediments which can only be correlated over very short distances. Since it appears certain that the last really cold conditions ended earlier in the Arabian Sea and its vicinity than in Europe it is recommended not to use the European stratigraphic terms for the Quaternary. Because of the lack of reliable absolute sediment ages for the cores no exact sedimentation rates can be given. According to rough estimates, however, the rates are 1-2 cm/1000 years in the deep basin and up to 40 cm/1000 years on the upper continental slope. Sedimentation rates are always larger near the mouth of the Indus-River than off South India at stations of about the same water depth. Planktonic gastropods (mainly pteropods) cannot be used for biostratigraphic purposes in the region under consideration. All of them seem to be displaced from the shelf. Their distribution there is given in.

Nannoplankton of multi-net samples, sediment surface and sediment core samples from the northern Arabian Sea

Recent nannoplankton from the "Meteor"-stations M 242, M 243 and M 245 in the northern Arabian Sea were studied by means of the light and electron microscope, and 19 species were found. The nannoplankton assemblage of the northern Arabian Sea is compared with those of the eastern and western Mediterranean Sea and the Atlantic Ocean. Gephyrocapsa oceanica (Kamptner), Cyclococcolithus leptoporus (Murray & Blackman), Emiliania huxleyi (Lohmann), Helicopontospbaera kamptneri (Hay & Mohler), and Umbilicosphaera mirabilis (Lohmann) are the most common species in the northern Arabian Sea. Reworked nannoplankton and nannoplankton species agglutinated by tintinnids are discussed.

Eocene-Oligocene calcareous nannofossil events of ODP Sites from the Southern Ocean

The evolution of the Southern Ocean climate during the late Eocene-late Oligocene interval is examined through highresolution, quantitative calcareous nannofossil analyses on samples from the Southern Ocean sections on Maud Rise and Kerguelen Plateau. We determined the abundance patterns of the counted species to clarify the biostratigraphy, which we correlated with high-resolution magnetostratigraphy [Roberts, A.P., Bicknell, S.J., Byatt, J., Bohaty, S.M., Florindo, F., Harwood, D.M., 2003a. Magnetostratigraphic calibration of Southern Ocean diatom datums from the Eocene-Oligocene of Kerguelen Plateau (Ocean Drilling Program Sites 744 and 748). In: Florindo, F., Cooper, A.K., O'Brien, P.A. (Eds.), Antarctic Cenozoic Palaeoenvironments: Geologic Record and Models. Palaeogeogr., Palaeoclimatol., Palaeoecol. 198 145-168; Florindo, F., Roberts, A.P., in press. Eocene-Oligocene magnetobiochronology of ODP Sites 689 and 690, Maud Rise, Weddell Sea, Antarctica. Geol. Soc. Am. Bull.], and used this data to interpret paleoceanographic changes through the late Eocene to late Oligocene. Percentage plots of the individual species, compared with R-mode principal component and cluster analysis results, allowed us to divide the assemblages into three groups: temperate-water taxa, cool-water taxa, and no temperature-affinity taxa. We attempt correlations between these paleoecological groups and the major sea-surface temperature (SST) variations with tectonic and paleoceanographic changes in the Southern Ocean. During the late Eocene, the nannofossil assemblage data reveal that there were several minor SST decreases (coolings) from 36 to 34 Ma, before the Eocene/Oligocene (E/O) boundary. A sharp cooling event, dated at 33.54 Ma (earliest Oligocene), occurred about 160 kyr after the E/O boundary, which is dated at 33.7 Ma. Relatively stable, cool conditions are interpreted to persist until the latest Oligocene, when an increase in abundance of temperate-water taxa, which corresponds to an antithetical decrease in abundance of cool-water indicators, is recorded. On the basis of our dating, the opening of the Drake Passage, allowing shallow-water circulation, began by 33.54 Ma at the latest, while the establishment of deep-water connections through the Tasmanian Gateway occurred at 33 Ma, as suggested by Exon et al. [Proc. ODP, Init. Rep. 189 (2001) 1].

ATP, chlorophyll "a", and size structure of phytolpankton in seawater at stations in the Atlantic sector of the Southern Ocean

Chlorophyll "a" and adenozine triphosphate (ATP) concentrations together with size structure of microplankton were investigated in January-April 1989 in the Indian Ocean and in the Weddell Sea. ATP values varied from 11 to 92 ng/l, and chlorophyll "a" concentrations varied from 0.04 to 0.27 µg/l in the Indian Ocean, with prevailing nanoplankton and picoplankton fractions. Both ATP and chlorophyll "a" concentrations increased 2 times to the south of 40°S; in the Weddell Sea they exceeded 400 ng/l and 0.6 µg/l, respectively. Cells of nanophytoplankton and microphytoplankton (mainly diatoms) prevailed in size spectra. Spatial variabilities of the parameters were within one order of magnitude; their values decreased 3-4 times during 1 month. Size structure changed due to increased portion of nanoplankton and picolankton. ATP concentrations in the photic layer (0-200 m) varied from 31.96 mg/m**2 in February to 8.02 mg/m**2 in March to April. ATP concentrations were 61.5 and 98.8 mg/m**2 at depths of 4200 and 4700 m, respectively.

Abundance of thecosomatous pteropods in the Arabian Sea and Persian Gulf (Table 2)

This paper deals with the presence and distribution of Thecosomatous Pteropods in the Indian Ocean. 122 plankton-samples, taken by R.V. "Meteor" during the International Indian Ocean Expedition (IIOE) in 1964-65 were investigated. They contain a total number of about 45000 Thecosomata, belonging to 22 species and 5 families. Some species (e.g. Creseis acicula and Limacina inflata) are common in the entire area, others (e.g. Creseis chierchiae and Desmopterus gardinieri) show a quite distinct distribution. From several species only one single specimen was captured, others are completely lacking in the collection though they have been reported frequently from the same area by other expeditions. This may be due to seasonal variations and to the fact that no bathial tows were taken. In spite of these restrictions the extensive material from a relatively small area offers the possibility to compare specific and nonspecific features in related species and to question their taxonomic value.

Stable oxygen isotope and Mg/Ca ratios of planktonic foraminifera from the Holocene and the Last Glacial Maximum

We measured oxygen isotopes and Mg/Ca ratios in the surface-dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to investigate upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka), and the late Holocene (0-2 ka). Our records from 24 stations in the South China Sea, Timor Sea, Indonesian seas, and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. During the early Holocene, sea surface temperatures increased by ~3°C over the entire region, indicating intensification of the IPWP. However, in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow (ITF). Increased surface salinity in the South China Sea during the Holocene appears related to northward displacement of the monsoonal rain belt over the Asian continent together with enhanced influx of saltier Pacific surface water through the Luzon Strait and freshwater export through the Java Sea. Opening of the freshwater portal through the Java Sea in the early Holocene led to a change in the vertical structure of the ITF from surface- to thermocline-dominated flow and to substantial freshening of Timor Sea thermocline waters.

Lipids in ocean particulate matter and bottom sediments

Lipid contents both in particulate matter and bottom sediments decreases with passage from the shelf toward the open ocean. Lipid concentration in particulate matter collected by a separator (Ls) decreases by a factor of 7 (from 7.05 to 0.95 % of dry matter), while in particulate matter collected on filters (Lf) it decreases by a factor of 13 (from 78 to 6 µg/l) in the vicinity of the Limpopo River and by a factor of 6 (from 74 to 13 µg/l) in the vicinity of the Zambezi River. Concentration of Lf also decreased with depth. In the upper sediment layers lipid concentration was 0.0028-0.039% of dry matter; all mud samples were richer in lipids, than sand samples. During sedimentogenesis there is an increase in proportion of lipids relative to other classes of organic matter, proportion of low-polarity compounds increases among the lipids, and proportion of hydrocarbons rises among these compounds. Sediments inherit composition of particulate matter to the greatest degree in the vicinity of river mouths.