Regional differences in Quaternary subantarctic nutrient cycling: Link to intermediate and deep water ventilation

Abstract

Several fundamental issues regarding carbon cycling in the glacial oceans rest on the development of reliable descriptions of high southern latitude surface waters. Here we compare new Subantarctic planktonic foraminiferal δ13C records with previously published records to demonstrate two distinct regional patterns over glacial cycles: (1) a low‐amplitude signal (∼0.7‰), previously observed in the Indian (primarily in Globigerina bulloides), that also dominates the Pacific, and (2) a higher‐amplitude signal, previously observed in Neogloboquadrina Pachyderma, that is confined to the Atlantic and western Indian sectors. The new observations from the Southeast Pacific, a primary region of Antarctic Intermediate Water (AAIW) formation, strengthen the suggestion that intermediate water acted as a conduit for transferring δ13C variability to low latitudes, because the timing and amplitude of the Indo‐Pacific low‐amplitude δ13C changes are similar to those observed in planktonic records from the tropical Pacific and Atlantic. A new benthic foraminiferal δ13C record from intermediate depths in the South Atlantic is also similar to the Southeast Pacific surface water records, further demonstrating that this link between high‐ and low‐latitude surface waters might be maintained. The widespread Indo‐Pacific Subantarctic surface water signal is obscured in records from the Atlantic sector by the large glacial‐interglacial δ13C signal (>1.0‰) that is most likely the result of nutrient changes related to variable North Atlantic Deep Water (NADW) production. We find that the large change found uniformly in Atlantic N. pachyderma δ13C records is not matched in a new G. bulloides δ13C record. The confined regional extent of the high‐amplitude signal and the discrepancy between the two species suggest that most of the excess nutrients in the glacial Atlantic (inferred from δ13C) may be removed seasonally by increased production in the Subantarctic.