334-year coral record of surface temperature and salinity variability in the greater Agulhas Current region

• Main Authors: Zinke, Jens, Rühs, Siren, Pfeiffer, Miriam, Watanabe, Takaaki K., Grab, Stefan, Garbe-Schönberg, Dieter, Biastoch, Arne
• Format: Text
• Language: English
• Published: 2021
• Subjects: Indian; Pacific; South Atlantic Ocean
• Online Access: https://doi.org/10.5194/cp-2021-120; https://cp.copernicus.org/preprints/cp-2021-120/

The Agulhas Current (AC) off the southern tip of Africa is one of the strongest western boundary currents and a crucial chokepoint of inter-ocean heat and salt exchange between the Indian and the South Atlantic Ocean. However, large uncertainties remain concerning the sea surface temperature and salinity variability in the AC region and their driving mechanisms over longer time scales, due to short observational datasets and the highly dynamic nature of the region. Here, we present an annual coral skeletal Sr/Ca composite record paired with an established composite oxygen isotope record from Ifaty and Tulear reefs in southwestern Madagascar to obtain a 334 year-long (1661–1995) reconstruction ofδ 18 O seawater changes related to surface salinity variability in the wider Agulhas Current region. Our new annual δ 18 O seawater composite record from Ifaty traces surface salinity of the southern Mozambique Channel and AC core region from the SODA reanalysis since 1958. δ 18 O seawater appears mainly driven by large-scale wind forcing in the southern Indian Ocean on interannual to decadal time scales. The δ 18 O seawater and SST at Ifaty show characteristic interannual variability of between 2 to 4 years, typical for ENSO. Lagged correlations with the Multivariate ENSO index reveals a 1–2 year lag of δ 18 O seawater and salinity at Ifaty and the AC region, suggesting that propagation of anomalies by ocean Rossby waves may contribute to salinity changes in the wider southwestern Indian Ocean. The δ 18 O seawater and SST reconstructions at Ifaty reveal the highest interannual variability during the Little Ice Age, especially around 1700, which is in agreement with other Indo-Pacific coral studies. Our study demonstrates the huge potential to unlock past interannual and decadal changes in surface ocean hydrology and ocean transport dynamics from coral δ 18 O seawater beyond the short instrumental record.