Southward Displacement of the North Atlantic Subtropical Gyre Circulation System During North Atlantic Cold Spells

• Published in: Paleoceanography and paleoclimatology 2019-05, Vol.34 (5), p.866-885
• Main Authors: Reißig, S., Nürnberg, D., Bahr, A., Poggemann, D.‐W., Hoffmann, J.
• Format: Article
• Language: English
• Subjects: Atlantic Meridional Overturning Circulation; Atlantic Meridional Overturning Circulation (AMOC); Brazil Current; Calcium; Climate change; Cold spells; Downwelling; Foraminifera; foraminiferal Mg/Ca; Holocene; Magnesium; Ocean currents; Perturbations; Salinity; Salinity effects; Salinity gradients; Storage; subsurface warming; Subtropical circulation; subtropical gyre; Teleconnections; Temperature gradients; Thermocline; Trade winds; Tropical circulation; Tropical climate; Tropical climates; tropical west Atlantic; Younger Dryas
• ISSN: 2572-4517; 2572-4525
• DOI: 10.1029/2018PA003376

During times of deglacial Atlantic Meridional Overturning Circulation (AMOC) perturbations, the tropical Atlantic experienced considerable warming at subsurface levels. Coupled ocean‐atmosphere simulations corroborate the tight teleconnection between the tropical Atlantic and climate change at high northern latitudes but still underestimate the relevance of the subsurface North Atlantic subtropical gyre (STG) for heat and salt storage and its sensitivity to rapid climatic change. We here reconstruct vertical and lateral temperature and salinity gradients in the tropical west Atlantic and the Caribbean over the last 30 kyr, based on planktic deep and shallow dwelling foraminiferal Mg/Ca and δ18O records. The rapid and large‐amplitude subsurface changes illustrate a dynamic STG associated with abrupt shifts of North Atlantic hydrographic and atmospheric regimes. During full glacial conditions, the STG has been shifted southward while intensified Ekman downwelling associated to strengthened trade winds fostered the formation of warm and saline salinity maximum water (SMW). The southward propagation of SMW was facilitated by the glacially eastward deflected North Brazil Current. During periods of significant AMOC perturbations (Heinrich Stadials 1 and the Younger Dryas), extreme subsurface warming by ~6 °C led to diminished lateral subsurface temperature gradients. Coevally, a deep thermocline suggests that SMW fully occupied the subsurface tropical west Atlantic and that the STG reached its southernmost position. During the Holocene, modern‐like conditions gradually developed with the northward retreat of SMW and the development of a strong thermocline ridge between the Subtropical Gyre and the tropical west Atlantic. Key Points Rapid subsurface oceanographic change in the tropical west Atlantic reflects shifting subtropical gyre Subsurface warming responds to deglacial AMOC perturbations (Heinrich Stadials 2 and 1, and the Younger Dryas) Southward propagation of salinity maximum water during Northern Hemisphere cold spells shifts the mixing zone of tropical and subtropical waters