Evidence for lower productivity in the Antarctic Ocean during the last glaciation

Modelled glacial and non-glacial HCO3−, Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO2 concentrations and a potential proxy of continental chemical erosion, the marine Ge/Si ratio

“…No significant change in Si flux between the present day and the LGM is contrary to previous suggestions that Si fluxes were double at the LGM (Froelich et al, 1992). This proposed doubling of non-glacial Si flux was calculated from Ge/Si ratios derived from ocean cores (Mortlock et al, 1991). The modelled riverine Ge/Si ratio at the LGM (Fig.…”

“…Little variation in the terrestrial Si flux is found, and the glacial contribution to the total flux is minimal. It is possible to perturb the riverine Ge:Si ratio significantly, on the assumption that the glacial Ge:Si ratio is high, but the Ge flux calculated is a factor of about 5 too small to give rise to the observed increase in marine opals (Froelich et al, 1992;Mortlock et al, 1991). It may well be the case that the next generation of ocean carbon cycle models will be able to explore in greater detail the change in dissolved inorganic carbon species at depth that arise from changes in ocean circulation (Broecker, 1995;Dokken and Jansen, 1999).…”

“…Ge/Si ratios within opals derived from deep ocean cores (Mortlock et al, 1991) vary on glacial to interglacial time scales. Froelich et al (1992) and Bareille et al (1998) have shown that these ratios within the opal faithfully record those of the ocean at the time they were formed.…”

CO2 sensitivity of Southern Ocean phytoplankton

“…To the extent that we can extrapolate our bottle incubation experiments to the open ocean, we suggest that the low CO 2 concentrations of the glacial Southern Ocean may have restricted the growth of larger, chain-forming diatoms despite higher iron inputs, instead favoring smaller, more weakly silicified taxa that are seldom preserved in the sediments. This effect could lead to the apparent decrease in total opal fluxes that has been reported for some glacial Antarctic sediments [Mortlock et al, 1991;De La Rocha et al, 1998]. Many authors have suggested that changes in Southern Ocean phytoplankton productivity could explain part of the observed glacial atmospheric CO 2 drawdown [Sigman and Boyle, 2000].…”

Variations in the particulate flux of Th-230 and Pa-231 and paleoceanograhpic applications of the Pa-231/Th-231 ratio

“…This is consistent in all the observations in the Southern Ocean around today's Polar Front (DeMaster, 1979;Kumar et al, 1993;Yu, et al, 1990;Chapter 5 154 in this thesis). High siliceous productivity and opal burial rate is associated clearly with the Polar Front in the Antarctic (DeMaster, 1979;Burckle and Cirilli, 1987;Charles et al, 1991;Mortlock et al, 1991; Chapter 5 in this thesis); however, north of the front, the siliceous production and burial rates drop greatly.…”