Sara Jean Reinelt

The Southern Ocean is a primary location where CO₂ is exchanged with the atmosphere via interactions between ocean circulation and atmospheric dynamics. Previous work has established that the ocean’s overturning circulation changed in the Last Glacial Maximum (LGM), with the shallowing of North Atlantic Deep Water (NADW) to Glacial North Atlantic Intermediate Water (GNAIW) fundamentally altering the Global Overturning Circulation (GOC). This was accompanied by an atmospherically driven northward shift of the Antarctic Circumpolar Current (ACC) in the Southern Ocean that together enhanced the sequestration of CO₂ in the deep ocean.

Although past conditions in the Atlantic and Pacific sectors of the Southern Ocean are better constrained, information from the Indian sector is scarce. Surface δ¹³C enrichment indicates carbon uptake and depletion indicates release, making δ¹³C a useful tracer for CO₂ ventilation. Here we compare high-resolution down-core records of surface-dwelling Globigerina bulloides δ¹³C in three cores from the Indian sector of the Southern Ocean to construct a latitudinal transect of surface conditions for the LGM and deglaciation.

During the LGM, surface δ¹³C was depleted relative to modern values, likely indicating a northward shift of the ACC that placed the cores in the Southern Ocean. Early in the deglaciation, the northern most core of this study became rapidly depleted in δ¹³C coincided with a rapid increase in atmospheric CO₂. Maximum depletion in the two other cores followed within 1kyr, as atmospheric CO₂ continued to increase. This sequence indicates a southward shift of the ACC early in the deglaciation, placing our cores in the axis of upwelling favorable winds at the locus of CO₂ release to the atmosphere. The timing suggests the release of CO₂ at our cores’ locations occurred before GNAIW deepened and NADW reappeared, indicating Southern Ocean dynamics were responsible for CO₂ release in the first half of the deglaciation leading the resumption of the deep GOC.

Presented orally and via poster at the Rutgers RIOS REU Poster Presentation and Session (2021) and orally at the Ocean Sciences Meeting (2022). (Poster)