Reconstruction of Caribbean Sea Surface Temperatures Using the Skeletal Elemental Composition of the Coral Siderastrea Siderea

Abstract:

Anthropogenic climate change has resulted in an increase in sea surface temperature (SST) of 0.1^oC per decade from 1971-2010. Satellite data reveals that Southern Belize has experienced greater temperature increases of up to 0.9^oC from 1982 to 2009. Recent investigations have demonstrated that this warming has had a negative impact on coral calcification [1,2]. Instrumental temperature records in this region prior to 2002 are sparse, and the coarse spatial resolution of the satellite temperature data from 1982 to 2009 present problems when comparing changes in SST to rates of coral calcification. This makes it necessary to reconstruct past ocean temperatures indirectly to more accurately assess the impact of SST changes on coral calcification.

The trace element composition of coral skeletons has been widely used in palaeothermometery, based on the assumption that the incorporation of trace elements such as Li, Mg and Sr (expressed as a ratio to Ca) is temperature dependent. In this study, we investigate the elemental composition of two samples sets (i) Siderastrea siderea coral samples cultured at controlled temperatures and pH, and (ii) annual and monthly resolved field samples of S. siderea measured across three major reef zones.

To explore the optimum method for SST reconstruction in this species, the widely used Sr/Ca temperature proxy is compared with the more recently described Li/Mg proxy [3,4]. We demonstrate that Li/Mg appears to be the most reliable temperature proxy, with a well-defined correlation with temperature such that it is able to provide more precise temperature reconstructions than the traditional Sr/Ca approach. The results of this study pave the way to using Li/Mg in S. siderea as a reliable palaeothermometer to further our understanding of the response of Caribbean reef systems to climate change.

[1] Castillo et al., 2011. PLoS One, 6(2): e14615. [2] Castillo et al., 2012. Nature Climate Change, 2: 756-760 2. [3] Hathorne et al., 2013. Paleocenography, 28: 143-152. [4] Montagna et al., 2014. Geochimica et Cosmochimica Acta, 132: 288–310.