(Table 2) Annual mass fluxes, 230Th composition and organic geochemistry of sediment trap samples in the South Altantic

The scavenging of 231Pa and 230Th was investigated in the Atlantic Sector of the Southern Ocean by combining results from sediment trap and in situ filtration studies. We present the first high-resolution profile of dissolved 230Th and 231Pa in surface waters across the ACC, showing a dramatic southward increase of both radionuclides around the southern ACC Front at 533S. High dissolved 231Pa/230Th ratios combined with low 230Th/231Pa fractionation factors (F) in these surface waters result in extremely high 231Pa94/230Th94 ratios of material collected in the shallow traps. Particulate 231Pa94/230Th94 ratios in a shallow trap near Bouvet Island increase continuously during the productive period in austral summer, and drop back in the low flux period. This behavior, following the Rayleigh fractionation principle, is interpreted to be due to an increase in the dissolved 231Pa/230Th ratio in the euphotic zone resulting from preferential scavenging of 230Th relative to 231Pa, even in opal-dominated regions. In the post-bloom stage, the depleted radionuclide concentrations are replenished by upwelling of Circumpolar Deep Water. The high particulate 231Pa94/230Th94 signal is weakened during downward transport of the bloom particles in the water column by incorporation of deep suspended particles, which have a lower 231Pa94/230Th94 ratio. It is shown that under the special hydrographic conditions in the Southern Ocean scavenging from the upper water column significantly influences the budgets of 230Th and 231Pa in the sediment. Nevertheless, the budgets are still made up primarily by scavenging from the large standing stock of deep suspended particles.

Composition of bottom sediments from the Gulf of California

Abundances of globules, micronodules and their aggregates composed of iron sulfides from bottom sediments of the Gulf of California have been determined together with studies of chemical composition of these sediments.

Comparison of TEX86 and UK'37 temperature proxies in sinking particles in the Cariaco Basin

The Cariaco Basin, a silled, permanently anoxic basin on the continental shelf of Venezuela with a dynamic chemocline (-240-350 m), has been subject of > 20 years of oceanographic observation and sediment trap studies. We evaluated UK'37 and the TEX86 temperature proxies using sinking particles collected in shallow sediment trap samples at 275 m (Trap A) and 455 m (Trap B) (within and below the chemocline). The organic geochemical temperature proxies, UK'37. (based on coccolithophorid alkenone lipids) and TEX86 (based on archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids), use observed relationships between the ratio of specific lipids and measured sea surface temperature to hindcast past sea surface temperatures. In this study, both UK'37 and TEX86 temperature proxies record seasonal temperature variations, including the cooling associated with upwelling events. UK'37-based temperatures are colder than measured sea surface temperatures, and better correlated temperature at the chlorophyll maximum. In sediment trap material collected below the chemocline (Trap B), UK'37 values are higher than those in Trap A. Warmer subchemocline UK'37 based temperatures may be related to autooxidation of sinking particles, either by small amounts of available oxygen or by alternate electron acceptors concentrated in the biologically dynamic chemocline (e.g. intermediate sulfur compounds). The absolute flux weighted TEX86 temperature values measured in sinking particles from Trap A match the measured SST well. The differences in the TEX86 values between Traps A and B are small and reflect less impact of degradation. Overall, the TEX86 temperatures in sinking particles in the Cariaco Basin reflect annual SST.

Geochemistry, SiO2 minerals and isotopes at DSDP Hole 72-516F

Cherts recovered during DSDP Leg 72 from Rio Grande Rise sediments (Site 516) consist of both cristobalite and quartz, and contain ghosts of foraminifers and (more rare) radiolarians. Porcelanite made of disordered cristobalite is found in most old enclosing sediments. Local dissolution of siliceous microfossils during diagenesis is the most likely source of the silica required for the chert formation. As sediment age increases, the proportion of biogenic silica decreases and authigenic silica increases.

Particle flux studies of sediment traps from the northern and equatorial Indian Ocean

The Asian monsoon system governs seasonality and fundamental environmental characteristics in the study area from which two distinct peculiarities are most notable: upwelling and convective mixing in the Arabian Sea and low surface salinity and stratification in the Bay of Bengal due to high riverine input and monsoonal precipitation. The respective oceanography sets the framework for nutrient availability and productivity. Upwelling ensures high nitrate concentration with temporal/spatial Si limitation; freshwater-induced stratification leads to reduced nitrogen input from the subsurface but Si enrichment in surface waters. Ultimately, both environments support high abundance of diatoms, which play a central role in the export of organic matter. It is speculated that, additional to eddy pumping, nitrogen fixation is a source of N in stratified waters and contributes to the low-d15N signal in sinking particles formed under riverine impact. Organic carbon fluxes are best correlated to opal but not to carbonate, which is explained by low foraminiferal carbonate fluxes within the river-impacted systems. This observation points to the necessity of differentiating between carbonate sources for carbon flux modeling. As evident from a compilation of previously published and new data on labile organic matter composition (amino acids and carbohydrates), organic matter fluxes are mainly driven by direct input from marine production, except the site off Pakistan where sedimentary input of (marine) organic matter is dominant during the NE monsoon. The explanation of apparently different organic carbon export efficiency calls for further investigations of, for example, food web structure and water column processes.

Results of bulk sediment X-ray diffraction analysis and quantification of mineral phases based on the RockJock and on the QUAX quantitative analysis

We have performed quantitative X-ray diffraction (qXRD) analysis of 157 grab or core-top samples from the western Nordic Seas between (WNS) ~57°-75°N and 5° to 45° W. The RockJock Vs6 analysis includes non-clay (20) and clay (10) mineral species in the <2 mm size fraction that sum to 100 weight %. The data matrix was reduced to 9 and 6 variables respectively by excluding minerals with low weight% and by grouping into larger groups, such as the alkali and plagioclase feldspars. Because of its potential dual origins calcite was placed outside of the sum. We initially hypothesized that a combination of regional bedrock outcrops and transport associated with drift-ice, meltwater plumes, and bottom currents would result in 6 clusters defined by "similar" mineral compositions. The hypothesis was tested by use of a fuzzy k-mean clustering algorithm and key minerals were identified by step-wise Discriminant Function Analysis. Key minerals in defining the clusters include quartz, pyroxene, muscovite, and amphibole. With 5 clusters, 87.5% of the observations are correctly classified. The geographic distributions of the five k-mean clusters compares reasonably well with the original hypothesis. The close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable at both the WNS-scale and at a more local scale in NE Greenland.

Interstitial water and sediment chemistry at DSDP Sites 87-582 and 87-584

Two trenches off Japan were explored during DSDP Leg 87. One is the Nankai Trough and the other is the Japan Trench; Site 582 is located on the floor of the former and Site 584 is situated on the deep-sea terrace of the latter. Cores from Site 582 and 584 consist mainly of hemipelagic sediments and diatomaceous silts and mudstone, respectively. In this report we analyze the chemistry of the interstitial water and sediments, as well as the sediment mineralogy. Sulfate reduction is accompanied by the production of secondary pyrite, which is rich in the sediment at both sites. Dissolved Ca concentration is relatively low and changes only slightly at both sites, probably because of the formation of carbonate with high alkalinity. Concentrations of dissolved Mg decrease with depth at Site 584. The dissolved Mg depletion probably results from the formation of Mg-rich carbonate and/or ion exchange and reaction between interstitial water and clay minerals. Higher Si/Al values are due to biogenic opal in the sediments and roughly correlate with higher values of interstitial water SiO2. Increases in dissolved Li concentrations may be related to its release from clay minerals, to advection that results from dewatering, and/or to fluid transport.

High resolution paleoceanography of the Guaymas Basin, Gulf of California, during the past 15000 yeras

Deep Sea Drilling Project Site 480 (27°54.10'N, 111°39.34'W; 655 m water depth) contains a high resolution record of paleoceanographic change of the past 15000 years for the Guaymas Basin, a region of very high diatom productivity within the central Gulf of California. Analyses of diatoms and silicoflagellates were completed on samples spaced every 40-50 yr, whereas ICP-AES geochemical analyses were completed on alternate samples (sample spacing 80-100 yr). The Bolling-Allerod interval (14.6-12.9 ka) (note, ka refers to 1000 calendar years BP throughout this report) is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals, suggesting conditions somewhat similar to those of today. The Younger Dryas event (12.9-11.6 ka) is marked by a major drop in biogenic silica and an increase in calcium carbonate. Increasing relative percentage contributions of Azpeitia nodulifera and Dictyocha perlaevis (a tropical diatom and silicoflagellate, respectively) and reduced numbers of the silicoflagellate Octactis pulchra are supportive of reduced upwelling of nutrient-rich waters. Between 10.6 and 10.0 ka, calcium carbonate and A. nodulifera abruptly decline at DSDP 480, while Roperia tesselata, a diatom indicative of winter upwelling in the modern-day Gulf, increases sharply in numbers. A nearly coincident increase in the silicoflagellate Dictyocha stapedia suggests that waters above DSDP 480 were more similar to the cooler and slightly more saline waters of the northern Gulf during much of the early and middle parts of the Holocene (~10 to 3.2 ka). At about 6.2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom A. nodulifera marks a major change in oceanographic conditions in the Gulf. A winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions (El Nino-driven?) of the North Equatorial Countercurrent during the summer. Beginning between 2.8 and 2.4 ka, the amplitude of biogenic silica and wt% Fe, Al, and Ti (proxies of terrigenous input) increase, possibly reflecting intensification of ENSO cycles and the establishment of modern oceanographic conditions in the Gulf. Increased numbers of O. pulchra after 2.8 ka suggest enhanced spring upwelling.