Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana basin) and high latitude climate signals over the last 140 000 years

Abstract

Abstract. Sea surface temperatures (SST) in the Guiana basin over the last 140 ka were obtained by measuring the C37 alkenone unsaturation index U37'k in sediment core MD03-2616 (7° N, 53° W). The resulting dataset is unique for this period in the western tropical Atlantic region. SSTs range from 25.1 to 28.9 °C, i.e. glacial-to-interglacial amplitude of 3.8 °C, which is common in tropical areas. During the last two interglacials (MIS1 and MIS5e) and warm long interstadials (MIS5d-a), the sediments studied trace rapid transmission of the climate variability from arctic-to-tropical latitudes and vice-versa. During these periods, MD03-2616 SSTs showed a remarkable parallelism with temperature changes observed in Greenland and SST records of North Atlantic cores. The last deglaciation in Guiana is particularly revealing. MIS2 stands out as the coldest period of the interval analysed, with SSTs reaching as low as 25.1 °C. It contains reminders of northern latitude events such as the Bølling-Allerød warming and the Younger Dryas cooling which ensued. These oscillations were previously documented in the δ18O of the Sajama tropical ice core and are present in Guiana with rates of ca. 6 °C ka−1 and changes of over 2 °C. During the glacial interval, significant abrupt variability is observed; e.g. oscillations of 0.5–1.2 °C during MIS3, i.e. about 30% of the maximum glacial–interglacial SST change. Nevertheless, in the MD03-2616 record it is hard to identify unambiguously either the Dansgaard–Oeschger type of oscillations described in northern latitudes or the SST drops associated with the Heinrich events characterising North Atlantic records. Although these specific events form the background of the climate variability observed, what truly shapes SSTs in Guiana is a long-term tropical response to precessional changes, which is modulated in the opposite way to polar variability. This lack of synchrony is consistent with other tropical records in locations to the north or south of Guiana and evidences an arctic-to-tropical decoupling when a substantial reduction in the Atlantic meridional overturning circulation (AMOC) takes place.