Age models of sediment cores from the Southern Ocean

Recent geochemical models invoke ocean alkalinity changes, particularly in the surface Southern Ocean, to explain glacial age pCO2 reduction. In such models, alkalinity increases in glacial periods are driven by reductions in North Atlantic Deep Water (NADW) supply, which lead to increases in deep-water nutrients and dissolution of carbonate sediments, and to increased alkalinity of Circumpolar Deep Water upwelling in the surface Southern Ocean. We use cores from the Southeast Indian Ridge and from the deep Cape Basin in the South Atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by Circumpolar Deep Water. This suggests that deep Southern Ocean carbonate ion concentrations were lower in glacial stages than in interglacials, rather than higher as suggested by the polar alkalinity model [Broecker and Peng, 1989, doi:10.1029/GB001i001p00015]. Our observations show that changes in Southern Ocean CaCO3 preservation are coherent with changes in the relative flux of NADW, suggesting that Southern Ocean carbonate chemistry is closely linked to changes in deepwater circulation. The pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient-depleted water (NADW) to the Southern Ocean and with an increase of nutrients in deep water masses. Carbonate mass accumulation rates on the Southeast Indian Ridge (3200-3800 m), and in relatively shallow cores (<3000 m) from the Kerguelen Plateau and the South Pacific were significantly reduced during glacial stages, by about 50%. The reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in CaCO3:Corg flux ratios, acting as another mechanism which would raise the alkalinity of Southern Ocean surface waters. The polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant. Even if overall productivity in the Southern Ocean were held constant, a decrease in the CaCO3:Corg ratio would result in increased alkalinity and reduced pCO2 in Southern Ocean surface waters during glacials. This ecologically driven surface alkalinity change may enhance deepwater-mediated changes in alkalinity, and amplify rapid changes in pCO2.

(Table 1) 137Cs and 90Sr concentrations, salinity, and temperature in waters of the southeastern Baltic Sea on October 16, 2001

An analysis of variations in 137Cs and 90Sr concentrations in Baltic Sea surface waters after the accident at the Chernobyl nuclear power plant was performed. Instability of 137Cs concentrations during the short-term observations was found, when they differed 2- to 3-fold. Concentrations of 90Sr appeared to be more stable; meanwhile, their deviations sometimes exceeded ranges of experimental errors. By variations in the monthly average values of radionuclide concentrations in surface waters of the Baltic Sea in 1989-1995, no trend of water self-purification was observed. Theoretical results obtained confirmed a potential of formation and propagation of patches with increased concentrations of 137Cs in the southeastern Baltic Sea. The most reliable factor that controlled the process of self-purification of Baltic Sea water appeared to be the mean annual value of radionuclide concentration. Pronounced divergences were obtained between the measured and calculated mean annual concentrations of 137Cs and 90Sr in surface waters of the Baltic Sea in 1989-2001. These divergences are explained by potential influence of waters from the Gulf of Bothnia and by other additional supplies of radionuclides to marine environment, which were not included into mathematical models.