TEX86H proxy and BIT index of sediment core GeoB9528-3 and reconstructed temperature data from NW Africa surface sediments

Changes in the strength of Atlantic meridional overturning circulation (AMOC) are known to have profound impacts on global climate. Coupled modelling studies have suggested that, on annual to multi-decadal time scales, a slowdown of AMOC causes a deepening of the thermocline in the tropical Atlantic. However, this process has been poorly constrained by sedimentary geochemical records. Here, we reconstruct surface (UK'37 Index) and thermocline (TEX86H) water temperatures from the Guinea Plateau Margin (Eastern tropical Atlantic) over the last two glacial-interglacial cycles (~ 192 kyr). These paleotemperature records show that periods of reduced AMOC, as indicated by the d13 C benthic foraminiferal record from the same core, coincide with a reduction in the near-surface vertical temperature gradient, demonstrating for the first time that AMOC-induced tropical Atlantic thermocline adjustment exists on longer, millennial time scales. Modelling results support the interpretation of the geochemical records and show that thermocline adjustment is particularly pronounced in the eastern tropical Atlantic. Thus, variations in AMOC strength appear to be an important driver of the thermocline structure in the tropical Atlantic from annual to multi-millennial time scales.

Bulk sediment parameter of surface sediment samples (Table 3)

Comparison of rates of accumulation of organic carbon in surface marine sediments from the central North Pacific, the continental margins off northwest Africa, northwest and southwest America, the Argentine Basin, and the western Baltic Sea with primary production rates suggests that the fraction of primary produced organic carbon preserved in the sediments is universally related to the bulk sedimentation rate. Accordingly, less than 0.01% of the primary production becomes fossilized in slowly accumulating pelagic sediments [(2 to 6 mm (1000 y)**-1] of the Central Pacific, 0.1 to 2% in moderately rapidly accumulating [2 to 13 cm (1000 y)**-1] hemipelagic sediments off northwest Africa, northwest America (Oregon) and southeast America (Argentina), and 11 to 18% in rapidly accumulating [66 to 140 cm (1000 y)**-1] hemipelagic sediments off southwest America (Peru) and in the Baltic Sea. The emiprical expression: %Org-C = (0.0030*R*S**0.30)/(ps(1-Theta)) implies that the sedimentary organic carbon content (% Org-C) doubles with each 10-fold increase in sedimentation rate (S), assuming that other factors remain constant; i.e., primary production (R), porosity and sediment density (ps). This expression also predicts the sedimentary organic carbon content from the primary production rate, sedimentation rate, dry density of solids, and their porosity; it may be used to estimate paleoproductivity as well. Applying this relationship to a sediment core from the continental rise off northwest Africa (Spanish Sahara) suggests that productivity there during interglacial oxygen isotope stages 1 and 5 was about the same as today but was higher by a factor of 2 to 3 during glacial stages 2, 3, and 6.