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Consistent Changes in Nitrate Consumption in Two Sectors of the Antarctic Zone Through the Last Glacial Cycle

par Ai, Xuyuan;Studer, Anja S.;Sigman, Daniel M;Martínez-García, Alfredo;Fripiat, François ;Michele, E;Thöle, L;Moretti, Simone;Jaccard, Sam;Haug, G. H.
Référence AGU Fall Meeting (2019: San Francisco)
Publication Publié, 2019-12-09

Poster de conférence

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Résumé :

We present new diatom-bound N isotope (δ15Ndb) records and complementary data from two sediment cores in the Indian sector of the Southern Ocean, with age models that benefit from correlation of TEX86 to Antarctic ice-core temperature. An unprecedented degree of consistency is observed between these two δ15Ndb records and with a previously published δ15Ndb record from the Pacific sector of the Southern Ocean. Even modest δ15Ndb excursions within the progression toward the LGM (e.g., one centered on MIS 5a at ~85 ka) are found to apply in both the Indian and Pacific sectors of the Antarctic. That such similar changes in δ15Ndb are measured on nearly opposite sides of the Antarctic continent argues that they represent the overall history of δ15Ndb in the open Antarctic Zone. In general, across the last glacial cycle, δ15Ndb is found to be strongly correlated with Antarctic climate and atmospheric CO2 , with higher δ15Ndb (and thus the inference of more complete nitrate consumption) during Antarctic cold intervals. The low opal and biogenic barium export previously documented for the glacial Antarctic Zone is observed in the Indian sector cores as well. Thus, the data comport with the interpretation of reduced nitrate supply during glacial periods. In one Indian sector core with appropriate sedimentation rate, sampling density and age constraints, minima in δ15Ndb are observed during Marine Isotope Stage (MIS) 3 that appear to reflect the Antarctic Isotope Maxima (warm) events, indicating that the same processes producing glacial/interglacial changes in nitrate supply also operate at smaller amplitude and on shorter timescales against the glacial background state. We suggest that this and other findings from the data are best explained by a westerly wind-driven mechanism for the glacial/interglacial changes in nitrate supply. Finally, there are characteristic δ15Ndb histories shared by all records during the Holocene and previous interglacial MIS 5e, which have implications for the climate/CO2 relationships that have been reconstructed for these interglacials.