Beschreibung:
<jats:p>Abstract. The Agulhas Current (AC) off the southern tip of Africa is one of the
strongest western boundary currents and a crucial choke point of inter-ocean
heat and salt exchange between the Indian Ocean and the southern Atlantic Ocean.
However, large uncertainties remain concerning the sea surface temperature
(SST) and salinity (SSS) variability in the AC region and their driving
mechanisms over longer timescales, due to only short observational datasets being available 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 (1661–1995) reconstruction of δ18Oseawater changes related to surface salinity variability in
the wider Agulhas Current region. Our new annual δ18Oseawater composite record from Ifaty traces surface salinity
of the southern Mozambique Channel and AC core region from the SODA
reanalysis between 1958 and 1995. δ18Oseawater appears to be
mainly driven by large-scale wind forcing in the southern Indian Ocean on
interannual to decadal timescales. The δ18Oseawater and SST at Ifaty show characteristic interannual variability of between 2 and 4 years and interdecadal variability of 8 to 16 years, coherent with El
Niño–Southern Oscillation (ENSO) records. Lagged correlations with the
multivariate ENSO index reveals a 1–2-year lag of δ18Oseawater 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 δ18Oseawater and SST reconstructions at Ifaty reveal the highest
interannual variability during the Little Ice Age, especially around 1700 CE, 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
δ18Oseawater beyond the short instrumental record.
</jats:p>