Southwest Atlantic intermediate and deep water circulation : 20,000 years of water mass re-organization and current strength variability

As one of the major players of the Atlantic meridional overturning circulation, the deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), ventilates the deep waters and influences global climate. However, detailed information about deep SCW strength are lacking, due to its corrosivity resulting in a lack of appropriate paleoceanographic archives. In order to improve the accuracy of ocean circulation variability, detailed deep SCW reconstructions require additional efforts from many branches of climate research. In the frame of this thesis, seven radiocarbon-dated Sediment cores from the Argentine continental margin (i.e. from contourite deposits, the Mar del Plata Canyon and the deep slope) were investigated. The core sites provide the opportunity to investigate the intermediate and deep water mass circulation, e.g. deep SCW flow strength variations, of the deep Southwest Atlantic during the last 20 ka. Furthermore, part of these sediment cores were used to analyze the influence of intermediate and deep ocean currents on sedimentary processes within a blind canyon system

Die Zwischen- und Tiefenwasserzirkulation des Südwestatlantiks : 20.000 Jahre der Wassermassenumorganisierung und Strömungsstärkenvariabilität

As one of the major players of the Atlantic meridional overturning circulation, the deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), ventilates the deep waters and influences global climate. However, detailed information about deep SCW strength are lacking, due to its corrosivity resulting in a lack of appropriate paleoceanographic archives. In order to improve the accuracy of ocean circulation variability, detailed deep SCW reconstructions require additional efforts from many branches of climate research. In the frame of this thesis, seven radiocarbon-dated Sediment cores from the Argentine continental margin (i.e. from contourite deposits, the Mar del Plata Canyon and the deep slope) were investigated. The core sites provide the opportunity to investigate the intermediate and deep water mass circulation, e.g. deep SCW flow strength variations, of the deep Southwest Atlantic during the last 20 ka. Furthermore, part of these sediment cores were used to analyze the influence of intermediate and deep ocean currents on sedimentary processes within a blind canyon system

Deglacial changes in the strength of deep southern component water and sediment supply at the Argentine continental margin

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 paleocurrent records from the deep Argentine continental margin shedding light on deep water circulation and deep SCW flow strength in the Southwest Atlantic since the Last Glacial Maximum (LGM). Based on increased sortable silt values, we propose enhanced deep SCW flow strength from 14 to 10 cal ka B.P. 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 B.P., thereby providing space for deep SCW spreading that resulted in reduced carbonate preservation at our core sites. Increased carbonate content from 13 cal ka B.P. indicates that the NCW expanded changing deep water properties at our core sites in the deep Southwest Atlantic. However, southern sourced terrigenous sediments continued to be deposited at our core sites, suggesting that deep SCW flow was uninterrupted along the Argentine continental margin since the LGM

Different analysis of sediment core GeoB13823-2, GeoB13824-1 and GeoB13861-1 from the Argentine continental margin

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