What role does the N. Atlantic subtropical cell play in warming the shallow underwater of the Caribbean Sea on decadal to centennial time scales? Constraints from radiocarbon records across the tropical Atlantic

Abstract:

Coral and sclerosponge skeletons provide long time-series of ocean DIC D¹⁴C values, a tracer of oceanic circulation, effectively extending the observational record back in time. Here, we present new coral and sclerosponge D¹⁴C records from the Atlantic that provide useful constraints on the dynamics of the subtropical cells (STCs). The STCs are shallow meridional wind-driven circulations that transport heat and water masses from the subtropics to the tropics. We use a coral from the Cape Verde Islands and a sclerosponge from the Bahamas to investigate the circulation patterns of the off-equatorial upwelling regions of STCs, which are not well understood. We find an abrupt change in bomb curve of the Cape Verde record that is related to ventilation rate of the STC, and we use these data to show that the strength of the northern STC was likely constant through the latter half of the 20^th century. Finally, we present the first ¹⁴C record of equatorial upwelling in the Atlantic using a coral from Principe Island in the Gulf of Guinea. We find that the water that upwells in the equator has a ¹⁴C signature that is markedly different than the water that is brought to the surface in the off-equatorial sites, suggesting that the northern and southern STCs interior pathways are not well connected in the Atlantic.