Dissolution and Preservation of Antarctic Diatoms and the Effect on Sediment Thanatocoenoses

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Abstract
Comparison of Southern Ocean diatom populations from (i) surface ocean production, (ii) underlying Antarctic sediments, and (iii) laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in Southern Ocean sediments. Increasing dissolution causes relative depletions in N. kerguelensis (K), enrichments in T. lentiginosa (L), and slight enrichments in E. antarctica (A). This reflects the relative susceptibility to dissolution of the three species that dominate Antarctic sediments. We have devised a preservation index for the Southern Ocean based on the ratio K/(K + L) to estimate relative extents of dissolution and applied it to natural assemblages. Holocene Southern Ocean sediments display increasing opal preservation toward higher latitudes, but south of the Antarctic Polar Front preservation decreases in the order: well preserved = SE Indian > S. Atlantic ∼ SW Indian > SE Pacific = poorly preserved. Dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum (LGM) sediments of the Indian and Pacific sectors, but in the Atlantic, increased E. antarctica abundances at LGM must have resulted from an increase in surface ocean production of this species. Holocene and LGM diatoms in Atlantic and Pacific sector sediments are equally well preserved, but in the Indian sectors, Holocene sediments are better preserved than those of LGM age. Paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution.