Environmental Sciences

C37-C39 long-chain unsaturated ketones (alkenones) and alkenes were identified in samples of particulate organic matter obtained from surface waters spanning the temperature range -0.7-12.2?C in the Southern Ocean south of Australia. The carbon number distribution indicates that these compounds are derived from the prymnesiophyte alga Emiliania huxleyi which is the predominant coccolithophorid in these waters.

A high-resolution (~1-2 kyr) multiproxy record from the Timor Sea in the easternmost Indian Ocean (International Marine Global Change (IMAGES) Program Core MD01-2378, latitude 13?04.95'S, longitude 121?47.27'E, 1783 m water depth) closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the Indonesian Throughflow. Spectral analysis of five different flux-based productivity proxies indicates spectral power concentrated in the 100 kyr (glacial-interglacial) and the 23 kyr and 19 kyr (precessional) periods.

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (black shales) were found to have significantly lower delta15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have delta15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools.

Coastal zones of the Humboldt Current Upwelling System (HCUS) are composed both of rocky and sandy beaches inhabited by macrozoobenthic communities. These show oscillating changes in the dominance of species; the abundance of the sand crab Emerita analoga is linked to phases of the El Ni?o Southern Oscillation (ENSO). The biogenic surfaces of these crabs serve as substrate for opportunistic colonizers. This study is the first record of an epibiosis between E. analoga and the rock mussel Semimytilus algosus, detected at a southern Peruvian sandy beach.

Two techniques for estimating past variations in sea surface temperature (SST) have been used to investigate climatic change in Biogeochemical Oceanic Flux Study (BOFS) core 31K (19?N, 20?W) from the eastern subtropical Atlantic. High-resolution SST records for the last 28 kyr have been produced using planktonic foraminiferal assemblages, based on the Imbrie-Kipp transfer function technique, and the UK' 37 index derived from abundances of C37 alkenones biosynthesized by prymnesiophyte algae.

Palaeomagnetic investigations of two sediment cores recovered from RV Polarstern near the eastern slope of the Yermak Plateau (sites PS1533 and PS2212) reveal convincing evidence for four polarity events of the Earth's magnetic field during the last 170 Ka. A comprehensive rock magnetic study of the sediments proved that fine-grained magnetite is the principal carrier of the remanent magnetization. No changes in magneto-mineralogy across the polarity transitions in the sediments investigated were found.

The intensification of Northern Hemisphere Glaciation (iNHG) is one of the critical climate thresholds in the Cenozoic. This study focuses on marine sediments recovered from Marine Isotope Stages 101/100 at the Ocean Drilling Program Site 1083 to assesses the impact of the iNHG on continental southern African vegetation through n-alkane (straight-chain hydrocarbon) abundance and delta13C values. The n-alkane abundance data yield a convoluted signal due to the number of controlling factors such as the source area, transportation routes and vegetation type.

Metamorphosed oceanic gabbros provide a record of the cooling history of the lower crust near mid-ocean ridges, but the temperature range, rate, and location of subsolidus events are poorly known. We combine hornblende-plagioclase thermometry, statistical analysis, and thermal models to estimate precisely the temperature, time, distance from axis, and duration of metamorphism in East Pacific Rise gabbros from Hess Deep, ODP Hole 894G.

We have determined the boron content and isotopic composition of bulk carbonates and associated pore waters from Ocean Drilling Program Site 851. The delta11B of the carbonates range from 23? to as low as -5.5?, greatly extending the range of reported carbonate delta11B values. In contrast, pore fluid isotopic compositions are relatively constant. Based on the correlation of delta11B and 1/B (r = 0.99) we conclude that the bulk carbonate at this site is a mixture of a biogenic component (~7 ppm with delta11B of 23?) and a recrystallized component (~2.5 ppm with delta11B of -5.5?).

Sediment cores retrieved in the Benguela coastal upwelling system off Namibia show very distinct enrichments of solid phase barium at the sulfate/methane transition (SMT). These barium peaks represent diagenetic barite (BaSO4) fronts which form by the reaction of upwardly diffusing barium with interstitial sulfate. Calculated times needed to produce these barium enrichments indicate a formation time of about 14,000 yr. Barium spikes a few meters below the SMT were observed at one of the investigated sites (GeoB 8455).