Multicentennial Agulhas leakage variability and links to North Atlantic climate during the past 80,000 years

Abstract

New high-resolution sea surface temperature (SST) and sea surface salinity (SSS) estimates are presented from the Agulhas Bank slope in the Atlantic sector of the Agulhas Corridor using planktic foraminiferal (Globigerinoides ruber) δ 18 O and Mg/Ca-derived SST. By focusing on the last 80,000 years, this is the first fine-scale Agulhas leakage record that overlaps in time with much of the Greenland ice core record of abrupt climate changes in the North Atlantic region. The multicentennial profiles indicate instances of warm SST and/or increased SSS coincident with Northern Hemisphere cool periods, followed by Northern Hemisphere warming. These periods of enhanced SST and SSS in the Agulhas Corridor occur at the last glacial termination (T1) and during North Atlantic cold episodes associated with Heinrich (H) meltwater events. To a first-order approximation, the timing of maximal salinity events in relation to periods of North Atlantic freshwater perturbation is consistent with the concept suggested by climate models that enhanced Agulhas leakage provides for buoyancy compensation and can potentially trigger increased convective activity in the North Atlantic, thereby restoring Atlantic overturning circulation after relatively weak states.

Global Core Top Calibration of δ18O in Planktic Foraminifera to Sea Surface Temperature

“…Such residual patterns could reflect advection of foraminifera shells which calcified along the colder side of these boundaries (Martínez‐Méndez et al, ). However, sediment trap studies suggest that the rapid settling rate of foraminifera shells is unlikely to result in a strong advection bias (e.g., King & Howard, ), and differences in habitat related to water masses may be strongly dependent on species (e.g., Dyez et al, ). An alternate explanation is that sharp hydrological gradients in these frontal regions may bias the estimation of from limited measurements (LeGrande & Schmidt, ; Waelbroeck et al, ).…”

Dinocyst assemblage constraints on oceanographic and atmospheric processes in the eastern equatorial Atlantic over the last 44 kyr

“…The final residue was mounted between slide and coverslip with glycerine jelly coloured with fuchsin. When the recommended number of 300 dinocysts could not be reached, a minimum of 100 specimens was counted on each sample (Fatela and Taborda, 2002), using a Leica DM 2500 microscope at ×630 magnification. Fifteen samples, containing less than 100 specimens, were excluded from dinocyst results.…”

South African Climates (Agulhas LGM Density Profile)

“…The vigorous Agulhas Current and its variability can cause sediment redistribution because meanders and eddies frequently reach the seafloor. However, a number of published studies and emerging work demonstrate that paleoceanographic records of excellent quality are in fact achievable for reconstructing both surface and deep-water variability in the region (e.g., Rau et al, 2002Rau et al, , 2006Peeters et al, 2004;Dickson et al, 2010;Martínez-Méndez et al, 2010;Caley et al, 2011Caley et al, , 2012Caley et al, , 2014Marino et al, 2013;Dyez et al, 2014;Petrick et al, 2015).…”