Description: The Southern Westerly Winds (SWW) exert a crucial influence over the world ocean and climate. Nevertheless, a comprehensive understanding of the Holocene temporal and spatial evolution of the SWW remains a significant challenge due to the sparsity of high-resolution marine archives and appropriate SWW proxies. Here, we present a north-south transect of high-resolution planktonic foraminiferal oxygen isotope records from the western South Atlantic. Our proxy records reveal Holocene migrations of the Brazil- Malvinas Confluence (BMC), a highly sensitive feature for changes in the position and strength of the northern portion of the SWW. Through the tight coupling of the BMC position to the large-scale wind field, the records allow a quantitative reconstruction of Holocene latitudinal displacements of the SWW across the South Atlantic. Our data reveal a gradual poleward movement of the SWW by about 1-1.5° from the early to the mid-Holocene. Afterwards variability in the SWW is dominated by millennial-scale displacements in the order of 1° in latitude with no recognizable longer-term trend. These findings are confronted with results from a state-of-the-art transient Holocene climate simulation using a comprehensive coupled atmosphere-ocean general circulation model. Proxy-inferred and modeled SWW shifts compare qualitatively, but the model underestimates both orbitally forced multi-millennial and internal millennial SWW variability by almost an order of magnitude. The underestimated natural variability implies a substantial uncertainty in model projections of future SWW shifts.

Description: The deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), is a major component of the global oceanic circulation. It has been suggested that the deep Atlantic water mass structure changed significantly during the last glacial/interglacial cycle. However, deep SCW source-proximal records remain sparse. Here we present three coherent deep SCW paleo-current records from the deep Argentine continental margin shedding light on deep-water circulation and SCW flow strength in the Southwest Atlantic since the Last Glacial Maximum (LGM). Based on coherently increased sortable silt values, we propose enhanced deep SCW flow strength from 14 to 10 cal ka BP relative to the early deglacial/LGM and the Holocene. We propose a direct influence of deep northern component water (NCW) on deep SCW flow strength due to vertical narrowing of deep SCW spreading concurrent with a migration of the high-energetic LCDW/AABW interface occupying our core sites. We suggest a shoaled NCW until 13 cal ka BP, thereby providing space for deep SCW spreading that resulted in reduced carbonate preservation at our core sites. Only from 13 cal ka BP on, increased carbonate content indicates that NCW expanded vertically leading to a deeper NCW-SCW interface. This NCW expansion changed deep-water properties in the deep Southwest Atlantic causing enhanced carbonate preservation at our core sites. We further show that southern-sourced terrigenous sediment-supply to our core sites was uninterrupted since the LGM due to a persistent deep SCW flow leading to contourite drifts at the Argentine continental margin.

Description: The Mar del Plata Canyon is located at the continental margin off northern Argentina in a key intermediate and deep-water oceanographic setting. In this region, strong contour currents shape the continental margin by eroding, transporting and depositing sediments. These currents generate various depositional and erosive features which together are described as a Contourite Depositional System (CDS). The Mar del Plata Canyon intersects the CDS, and does not have any obvious connection to the shelf or to an onshore sediment source. Here we present the sedimentary processes that act in the canyon and show that continuous Holocene sedimentation is related to intermediate-water current activity. The Holocene deposits in the canyon are strongly bioturbated and consist mainly of the terrigenous "sortable silt" fraction (10-63 µm) without primary structures, similarly to drift deposits. We propose that the Mar del Plata Canyon interacts with an intermediate-depth nepheloid layer generated by the northward-flowing Antarctic Intermediate Water (AAIW). This interaction results in rapid and continuous deposition of coarse silt sediments inside the canyon with an average sedimentation rate of 160 cm/kyr during the Holocene. We conclude that the presence of the Mar del Plata Canyon decreases the transport capacity of AAIW, in particular of its deepest portion that is associated with the nepheloid layer, which in turn generates a change in the contourite deposition pattern around the canyon. Since sedimentation processes in the Mar del Plata Canyon indicate a response to changes of AAIW contour-current strength related to Late Glacial/Holocene variability, the sediments deposited within the canyon are a great climate archive for paleoceanographic reconstructions. Moreover, an additional involvement of (hemi) pelagic sediments indicates episodic productivity events in response to changes in upper ocean circulation possibly associated with Holocene changes in intensity of El Niño/Southern Oscillation.

Description: Negative stable carbon isotopic excursions have been observed throughout most of the mid-depth (~1000-3000m) Atlantic Ocean during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Although there is agreement that these mid-depth excursions were in some way associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), there is still no consensus on the precise mechanism(s). Here, we present benthic stable carbon and oxygen isotopic (d13C and d18O) records from five cores from the western equatorial Atlantic (WEA). Together with published benthic isotopic records from nearby cores, we produced a WEA depth transect (~800-2500m). We compare HS1 and YD data from this transect with data from previously published North- and South Atlantic cores and demonstrate that the largest negative d13C excursions occurred in the WEA during these times. Moreover, our benthic d18O records require the presence of two water masses flowing from the Southern Ocean, bisected by a Northern Component Water (NCW). Given that d18O is a conservative water mass tracer, we suggest that d13C was decoupled from water mass composition and do not correspond to simple alternations between northern and southern sourced waters. Instead, d13C behaved non-conservatively during HS1 and the YD. Consistently with our new 231Pa/230Th record from the WEA transect, that allowed the reconstruction of AMOC strength, we hypothesize that the negative d13C excursions reflect an increase in the residence time of NCW in response to a weakened AMOC, allowing for a marked accumulation of 13C-depleted respired carbon at the mid-depth WEA.