The geochemistry of deep-sea corals (DSCs) provides unique paleoceanographic insights into the carbon content and temperature of sub-surface waters. However, before robust proxy information can be attained species-specific “vital effects” must be quantified using modern environmental calibrations. Stylasterids are a diverse and cosmopolitan family of DSC that accrete their carbonate skeleton using either calcite or aragonite. Despite their wide spatial and bathymetric distribution, stylasterid calcification mechanisms and potential as paleoceanographic archives remains largely unexplored. Here, the proxy potential of stylasterids as recorders of seawater temperature and pH is assessed using a global distribution of wild specimens (both aragonitic and calcitic) from a range of hydrographic conditions (spanning 17oC and 0.35 pH units). New bulk trace metal, δ18O and δ11B data are used to test the applicability of current temperature (Sr/Ca, Li/Mg and δ18O) and pH (δ11B) proxies while also introducing the possibility of a novel Mg/Na-temperature proxy. Results support the use of Li/Mg and δ18O as robust proxies for temperature in aragonitic stylasterids. Li/Mg ratios are shown to be consistent across aragonitic marine calcifiers and a new global biogenic aragonite Li/Mg calibration is presented (5.26(±0.04)e–0.0486(±0.0005)T). Previous δ18O measurements in stylasterids have shown significantly less internal variation than DSC Scleractinia. Here, this is hypothesised to result from a lack of fractionation of their internal calcifying fluid during biomineralisation (evident from δ11B). Boron isotope data also suggest that stylasterids do not strongly modify pH at the site of calcification (c.f. pH-upregulation in Scleractinia), the first aragonitic Cnidaria known to show no ability to regulate their internal carbonate parameters. As such, stylasterid biocalcification is fundamentally different to Scleractinia and leaves these organisms potentially at high risk from future ocean acidification.
|Date of Award||1 Oct 2019|
- The University of Bristol
|Supervisor||Laura F Robinson (Supervisor)|