Southern Ocean contributions to glacial-interglacial changes of atmospheric pCO2:: An assessment of carbon isotope records in diatoms

Eleven new Antarctic records of diatom-bound delta(13)C(org) show significantly lighter values during the Last Glacial Maximum than during the Holocene with a general trend of increasing depletions southward of the modern Antarctic 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 glacial delta(13)C(org) in Antarctic diatoms higher [CO2](aq), lower growth rates, and changes in diatom abundance or size. Taken at face value, the glacial depletions of delta(13)C(org) suggest that Antarctic surface waters south of the MAPF might have been a source of atmospheric pCO(2) during the glacial period. Alternatively, the glacial depletions might have been caused by either a relatively small decrease in growth rates or changes in the abundance of the two dominant diatom species or their average cell size. Interpretations of the Subantarctic records are complicated by similar uncertainties.