Pliocene to Pleistocene calcium carbonate and organic carbon record of ODP Hole 117-722B

Site 722 provides high resolution records of percent CaCO3, magnetic susceptibility, d18O, organic carbon, and coarse fraction for the past 3.4 m.y. from the crest of the Owen Ridge, northwestern Arabian Sea. Within this time interval, most of the carbonate percent variations can be attributed to terrigenous dilution and do not reflect changes in the carbonate system. From the late Pliocene to Present, the average rate of calcium carbonate accumulation increases from 1 to 3 g/cm**2/k.y. and the average accumulation of organic carbon decreases from 75 to 30 mg/cm**2/k.y. The carbonate component is more dissolved in the older interval. The long-term variations in carbonate accumulation may reflect a greater input of organic matter in the late Pliocene, which decomposes to produce CO2 and dissolve carbonate. Magnetic susceptibility and % noncarbonate (100 - CaCO3%) reflect changes in the amount of the lithogenic component in the sediments. The period of variation of lithogenic material is the same period as the original forcing of the regional summer monsoon, however, the timing matches global aridity patterns and global ice volume (sea level) changes. This preliminary analysis suggests that the high frequency variation of lithogenic material persists for at least the last 3.4 m.y. Within the last million years, calcium carbonate accumulation has a large amplitude signal that covaries with major changes in ice volume. Both calcium carbonate and noncarbonate (mostly terrigenous) accumulation are greatest during glacial stages. Interglacial intervals are characterized by low mass accumulation rates, increased foraminifer fragmentation, and increased opal concentration. The accumulation of organic carbon matches the high frequency changes in sedimentation rates. We attribute this high correlation to enhanced preservation of organic carbon by increased sedimentation rate. Of the three major biological components studied, only opal exhibits the variations expected for a biological productivity system forced by monsoonal upwelling driven by changes in northern hemisphere summer radiation.

Millenial variability of dust in South Atlantic sediment records

Fluxes of lithogenicmaterial and fluxes of three palaeo productivity proxies (organic carbon, biogenic opal and alkenones) over the past 100,000 years were determined using the 230Th-normalization method in three sediment cores from the Subantarctic South Atlantic Ocean. Features in the lithogenic flux record of each core correspond to similar features in the record of dust deposition in the EPICA Dome C ice core. Biogenic fluxes correlate with lithogenic fluxes in each sediment core. Our preferred interpretation is that South American dust, most probably from Patagonia, constitutes a major source of lithogenic material in Subantarctic South Atlantic sediments, and that past biological productivity in this region responded to variability in the supply of dust, probably due to biologically available iron carried by the dust. Greater nutrient supply as well as greater nutrient utilization (stimulated by dust) contributed to Subantarctic productivity during cold periods, in contrast to the region south of the Antarctic Polar Front (APF), where reduced nutrient supply during cold periods was the principal factor limiting productivity. The anti-phased patterns of productivity on opposite sides of the APF point to shifts in the physical supply of nutrients and to dust as cofactors regulating productivity in the Southern Ocean.

Investigation of time series stations along a productivity gradient north of the Canary Islands

Three stations along a productivity gradient north of the Canary Islands were investigated for surface-water properties, particle flux, and composition (biogenic and lithogenic components, and stable nitrogen isotope composition, delta15N) and export production. Investigation sites along the east-west transect off the NW African upwelling margin included the European Station for Time-Series in the Ocean, Canary Islands (ESTOC), one location contiguous to the NW African upwelling zone in the Eastern Boundary Current (EBC) and one station north of the island La Palma (LP). The seasonality of surface-water properties along the transect was mainly influenced by the winter cooling and simultaneous phytoplankton maximum and, in addition at EBC, by nearby upwelling. Accordingly, particle flux and composition along the transect were closely linked to the winter bloom sedimentation and upwelling related enhanced plankton biomass stemming from the primary upwelling and the Cape Yubi filament at EBC. During all seasons, particle flux was highest at EBC and had the highest contribution of biogenic opal and lithogenic components, and the lowest delta15N compared to the offshore stations. But contrary to what would be expected from the productivity gradient, particle flux did not decrease from ESTOC to LP. Below the upper several hundred meters, particle flux was enhanced by additional particle input along the entire transect, manifested by an increase of flux with depth and lower delta15N values. We offer a scenario in which intermediate nepheloid layers originating from the primary upwelling as well as particle dispersion from upwelling filaments, mainly the Cape Ghir filament, impact on the trap stations as far as 700 km into the open ocean. This study contributes to our understanding of the poorly resolved biogeochemical transition between the productive shelf and subtropical gyre provinces.

Susupended particulate matter from the Franz Victoria Trough and its composition

In this paper authors present and discuss data on distribution and mineral composition of suspended particulate matter (SPM) in the Franz Victoria Trough, collected during Cruise 14 of scientific icebreaker Akademik Fedorov in the northern Barents Sea in October 1998. Higher total SPM concentrations (0.4-1.8 mg/l) were measured in the near-bottom layer of the Franz Victoria Strait and central part of the trough. Potential source of mineral particles in SPM is fine fractions of Barents Sea bottom sediments. They form the nepheloid layer, which spreads on the continental slope along the trough together with Barents Sea waters at 350-400 m depth.