The influence of skeletal micro-structures on potential proxy records in a bamboo coral

Abstract

Assessing the physicochemical variability of the deeper ocean is currently hampered by limited instrumental time series and proxy records. Bamboo corals (lsididae) form a cosmopolitan family of calcitic deep sea corals that could fill this information gap via geochemical information recorded in their skeletons. Here we evaluate the suitability of high-resolution chemical imaging of bamboo coral skeletons for temperature and nutrient reconstruction. The applied elemental mapping techniques allow to verify the suitability of the chosen transect on the sample section for paleo-reconstructions and enhance the statistical precision of the reconstruction. We measured Mg/Ca via electron microprobe at 111m resolution and Ba/Ca via laser ablation ICP-MS at 35 11m resolution in a historic specimen of Keratoisis grayi from the Blake Plateau off Eastern Florida. Long-term growth temperatures of 7.1 ± 3.4 oc (± 2 SD) that are in agreement with recent ambient temperature range can be reconstructed from Mg/Ca ratios provided that anomalously Mg-enriched structural features around the central axis and isolated features related to tissue attachment are avoided for reconstruction. Skeletal Ba/Ca measurements reflect mean seawater barium [Ba] 5 w concentrations ([Ba] 5 w =51± 24 nmol kg-1 (± 2 SD)), in agreement with instrumental data (47 nmol kg-1). We show for the first time that Ba/Ca forms concentric structures in a bamboo coral skeleton section. Our investigations suggest that, while bamboo coral skeletons do record environmental parameters in their mean chemical composition, the magnitude of environmental variability reconstructed from high-resolution chemical maps exceeds that expected from instrumental time series. This necessitates additional investigation of the factors driving bamboo coral skeletal composition.

Elemental systematics of the calcitic skeleton of Corallium rubrum and implications for the Mg/Ca temperature proxy

“…9B). The potential for Mg/Ca compositions of calcitic corals to serve as a temperature proxy has been suggested by others (Thresher et al, 2004;Thresher et al, 2007;Sherwood et al, 2005;Thresher et al, 2010), and more recent studies of bamboo corals (Thresher et al, 2016;Flöter et al, 2019) have shown that the innermost juvenile layers have significantly higher Mg/Ca compositions than the skeletal bands precipitated during adult growth stages. These observations are analogous to the increased Mg/Ca ratios of the medullar zone in juvenile C. rubrum (Figs.…”

Apparent Periodic and Long‐Term Changes in AAIW and UCDW Properties at Fixed Depths in the Southwest Pacific, With Indications of a Regime Shift in the 1930s

“…We inferred the environmental conditions experienced by the corals during their lifetimes from metal:calcium proxies measured along the radial axes of their skeletons using laser ablation ICP‐MS (for analytic details, see Strzepek et al., 2014, and supporting information). Magnesium:calcium ratios (Mg/Ca) were measured as a proxy for ambient temperature (Thresher et al., 2010, 2016; Weinbauer et al., 2000; see, however, Flöter et al., 2019) (Figure ), barium:calcium ratios (Ba/Ca) as a proxy for ambient barium and by inference silicate, and U/Ca as a possible proxy for pH/carbonate ion concentrations. Isidid skeletal Ba/Ca has been suggested as an indirect proxy for silicates on the basis of generally covarying ambient concentrations of it and barium in seawater (Geyman et al., 2019; LaVigne et al., 2011; Thresher et al., 2016).…”

Glacial-aged development of the Tunisian Coral Mound Province controlled by glacio-eustatic oscillations and changes in surface productivity

“…In CWCs the Ba/Ca ratios are linked to seawater Ba concentrations (Ba SW ; Anagnostou et al, 2011;Flöter et al, 2019;Spooner et al, 2018), similarly to foraminifera and tropical corals (e.g. Boyle, 1989, 1990;Lea and Spero, 1994;Sinclair, 2005;De Nooijer et al, 2017).…”