Low-latitude control of interhemispheric sea-surface temperature contrast in the tropical Atlantic over the past 21�kyears: the possible role of SE trade winds

Abstract

To stimulate a discussion on the role of tropical atmospheric circulation versus thermohaline circulation changes for tropical Atlantic sea-surface temperature (SST) variations, we present a record of the SST contrast (ΔSST) between the tropical northwest and southeast Atlantic from the Last Glacial Maximum to the Late Holocene. The ΔSST was calculated from two alkenone-derived SST records; one from the Caribbean Sea and the other from the Angola Basin. Changes in the cross-equatorial ΔSST were then compared with an abundance record of Florisphaera profunda from the equatorial Atlantic, which is indicative of SE trade-wind induced variations in thermocline depth in the equatorial divergence zone. This comparison implies that the Last Glacial Maximum, the Younger Dryas, and the Mid to Late Holocene were periods of strong SE trade winds, which led to an intense upwelling-related cooling in the southeast Atlantic and concurrently enhanced advection of warm tropical South Atlantic waters into the western tropical Atlantic. Accordingly, a coupled ocean-atmospheric process has probably created a dipole-like SST distribution pattern in the tropical Atlantic during these three distinct climatic periods. In contrast, Heinrich Event 1, the Bolling-Allerod, and the Early Holocene were intervals of weakened SE trade winds, causing a warming in the southeast Atlantic. However, synchronous warming in both regions during Heinrich Event 1 can be partially attributed to a weakening of thermohaline overturning which caused a reduced northward heat transport from the low-latitude to the high-latitude North Atlantic.