Southern Ocean contributions to glacial-interglacial changes of atmospheric pCO(2): An assessment of carbon isotope records in diatoms

Eleven new Antarctic records of diatom-bound delta(13)C(org) show significa ntly lighter values during the Last Glacial Maximum than during the Holocen e with a general trend of increasing depletions southward of the modern Ant arctic Polar Front (MAPF). In contrast, glacial diatoms from cores farther north of the MAPF show delta(13)C(org) values which are similar to 1 parts per thousand heavier than during the Holocene. Likely causes for the law gl acial delta(13)C(org) in Antarctic diatoms higher [CO2](aq), lower growth r ates, and changes in diatom abundance or size. Taken at face value, the gla cial depletions of delta(13)C(org) suggest that Antarctic surface waters so uth of the MAPF might have been a source of atmospheric pCO(2) during the g lacial period. Alternatively, the glacial depletions might have been caused by either a relatively small decrease in growth rates or changes in the ab undance of the two dominant diatom species or their average cell size. Inte rpretations of the Subantarctic records are complicated by similar uncertai nties.