Abstract
Abstract. The increasing pCO2 in seawater is a serious threat for marine calcifiers and alters the biogeochemistry of the ocean. Therefore, the reconstruction of past-seawater properties and their impact on marine ecosystems is an important way to investigate the underlying mechanisms and to better constrain the effects of possible changes in the future ocean. Cold-water coral (CWC) ecosystems are biodiversity hotspots. Living close to aragonite undersaturation, these corals serve as living laboratories as well as archives to reconstruct the boundary conditions of their calcification under the carbonate system of the ocean. We investigated the reef-building CWC Lophelia pertusa as a recorder of intermediate ocean seawater pH. This species-specific field calibration is based on a unique sample set of live in situ collected L. pertusa and corresponding seawater samples. These data demonstrate that uranium speciation and skeletal incorporation for azooxanthellate scleractinian CWCs is pH dependent and can be reconstructed with an uncertainty of ±0.15. Our Lophelia U / Ca–pH calibration appears to be controlled by the high pH values and thus highlighting the need for future coral and seawater sampling to refine this relationship. However, this study recommends L. pertusa as a new archive for the reconstruction of intermediate water mass pH and hence may help to constrain tipping points for ecosystem dynamics and evolutionary characteristics in a changing ocean.
Highlights
Natural and anthropogenic changes in atmospheric pCO2 strongly influence global climate
We investigated the reef-building Cold-water coral (CWC) Lophelia pertusa as a recorder of intermediate ocean seawater pH
Analysed samples were processed according to Rüggeberg et al (2008) by using a Dremel tool averaging several growth bands of the theca wall avoiding the centre of calcification (COC)
Summary
Natural and anthropogenic changes in atmospheric pCO2 strongly influence global climate. Anagnostou et al, 2012; Form and Riebesell, 2012; Maier et al, 2009; McCulloch et al, 2012) This implies that they may have developed adaptive strategies to thrive in cool waters and to survive under low carbonate saturations states. Biocalcification models suggest that, similar to zooxanthellate tropical corals, scleractinian azooxanthellate CWCs have physiological mechanisms to elevate the aragonite saturation in the extracellular calcifying fluid (ECF; Adkins et al, 2003; Blamart et al, 2007; McConnaughey, 1989). This potentially complicates seawater pH reconstructions and needs to be explored further with different tracers. We investigate the influence of seawater pH on U / Ca ratios in the scleractinian CWC L. pertusa and evaluate the potential to serve as a pH proxy for intermediate water masses
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