Meeting Documents

Annual Coral Δ¹⁴C from Tobago Reveals a Possible Shift in Surface Water Circulation in the Tropical North Atlantic Since the Early 2000s

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is a large network of warm surface and cool deep ocean currents mainly responsible for the mass poleward transport and redistribution of heat and salt. AMOC plays a vital role in ocean circulation and changes to its flow or transport can significantly impact global climate on decadal to millennial timescales. Since the 1990s, concerns of a possible AMOC slowdown due to increasing temperatures brought about by greenhouse gas emissions are rising. However, direct measurements of North Atlantic Deep Water (NADW) formation informing us of thermohaline circulation strength have only been made since 2004. Massive, long-lived scleractinian corals are natural recorders of environmental conditions, allowing for the extraction of high-resolution climate signals beyond instrumental records. Here, we present a 57-year record of annual radiocarbon (Δ¹⁴C) generated from a Siderastrea siderea coral from Tobago (1960-2017), as a proxy for surface water volume transport and ocean circulation. The coral Δ¹⁴C record was detrended and normalized from 1973-2017 to remove the long-term production trend following the input of anthropogenic bomb 14C. Preliminary results indicate coral Δ¹⁴C is sensitive to both the North Brazil Current (NBC) and the Florida Current (FC) volume transport changes, albeit during different time periods. From 2003-2016, coral Δ¹⁴C tracks FC transport anomalies (p<0.05), however, prior to 2003 (1992-2002), coral Δ¹⁴C positively correlates to NBC transport anomalies (p<0.05). The observed shift in the coral Δ¹⁴C coincides with a change in the Atlantic Multidecadal Oscillation from a negative to a positive phase, resulting in higher sea surface temperatures beginning in the late 1990s-early 2000s, and coincides with a shift to higher sea surface height anomalies (ORAS5 SSHa) along western boundary currents (WBCs) at both Florida and Tobago, which may be indicative of surface water changes and current volume transport in the north Atlantic basin. The relationship between coral Δ¹⁴C and surface water circulation changes and its potential link to MOC variability will be further examined using an estimate of the MOC strength calculated from ECCOv4r4 along the OSNAP array.