Preprints
https://doi.org/10.5194/cp-2021-120
https://doi.org/10.5194/cp-2021-120

  22 Sep 2021

22 Sep 2021

Review status: this preprint is currently under review for the journal CP.

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

Jens Zinke1,2,3,4, Siren Rühs5, Miriam Pfeiffer6, Takaaki K. Watanabe6,7, Stefan Grab4, Dieter Garbe-Schönberg6, and Arne Biastoch5 Jens Zinke et al.
  • 1School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, United Kingdom
  • 2Molecular and Life Sciences, Curtin University, Perth, WA 6102, Australia
  • 3Australian Institute of Marine Science, Townville, QLD 4810, Australia
  • 4School of Geography, Archaeology and Environmental Studies, University of Witwatersrand, Witwatersrand, South Africa
  • 5GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24105, Germany
  • 6Institute for Geosciences, University of Kiel, Kiel, 24118, Germany
  • 7KIKAI Institute for Coral Reef Sciences, Kikai Town, Kagoshima 891-6151, Japan

Abstract. 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 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 since 1958. δ18Oseawater appears mainly driven by large-scale wind forcing in the southern Indian Ocean on interannual to decadal time scales. The δ18Oseawater 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 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, 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.

Jens Zinke et al.

Status: open (until 17 Nov 2021)

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Jens Zinke et al.

Jens Zinke et al.

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Short summary
Salinity is an important and integrative measure of changes to the water cycle steered by changes to the balance between rainfall and evaporation and by vertical and horizontal movements of water parcels by ocean currents. However, salinity measurements in our oceans are extremely sparse. To fill this gap, we have developed a 334 year coral record of seawater oxygen isotopes that reflects salinity changes in the globally important Agulhas Current system revealing it's main oceanic drivers.