Refining C. wuellerstorfi and H. elegans Mg/Ca temperature calibrations

Abstract

We present core top Mg/Ca, Sr/Ca and  18 O measurements for Cibicidoides wuellerstorfi and Hoeglundina elegans from the Timor Sea and the Makassar Strait, which span a bottom water temperature (BWT) range from 2 to 18 °C. In both species Mg/Ca ratios are positively and significantly correlated with BWT, while  18 O measurements are significantly anti-correlated with BWT. Comparison of calcification temperatures derived from Mg/Ca ratios and  18 O measurements yield comparable results and closely match CTD-measured temperatures. We integrate our results with previously published data sets from the Atlantic, Indian and Pacific Oceans and provide temperature calibration equations over the temperature range from 2 to 12 °C for H. elegans and from 0 to 10 °C for C. wuellerstorfi. We found geographical differences in the relation of benthic Mg/Ca ratios to BWT: C. wuellerstorfi shows Mg/Ca sensitivity to BWT of 19% increase in Mg/Ca per °C for the Atlantic Ocean and of 15% per °C for the Indian and Pacific Oceans. Hoeglundina elegans shows Mg/Ca sensitivity to BWT of 16% increase in Mg/Ca per °C for the Atlantic Ocean and of 14% per °C for the Indian and Pacific Oceans. Cibicidoides wuellerstorfi Sr/Ca variability appears to be driven by carbonate ion saturation, whereas H. elegans Sr/Ca variability is closely linked to BWT in the compiled data sets from the Atlantic, Indian and Pacific Oceans. 2.1. Introduction The recognition that substitution of magnesium for calcium in both planktonic and benthic foraminiferal tests occurs as a temperature-controlled process [Savin and Douglas, 1973; Bender at al., 1975] led to the development of Mg/Ca ratios as a proxy for paleotemperature reconstructions [e.g.:

Controls on planktonic foraminifera apparent calcification depths for the northern equatorial Indian Ocean

“…See Table 7 for species-specific equation references which are also indicated by a * below. (Planktonic references a: [59], b: [60]*, c: [61], d: [62], e: [63], f: [64], g: [65], h: [13]*, i: [66], j: [67], k: [68], l: [69]*, m: [70]; Benthic references n: [71], o: [52], p: [72], q: [73], r: [74], s: [53], t: [75], u: [76]*, v: [77]. See S2 Table for more information regarding each equation.…”

A Saltier Glacial Mediterranean Outflow

“…Theoretically, high MOW salinity would be expected to also increase foraminiferal Mg/Ca (Lea et al, ; Nürnberg et al, ). Some culture and core‐top evidence exists for a reduction in Mg incorporation in waters highly oversaturated in carbonate ion concentration (Lo Giudice Cappelli et al, ; Russell et al, ). However, other studies indicate that the impact of saturation state on Mg‐incorporation is very small or absent (Dueñas‐Bohórquez et al, , ; Raitzsch et al, ).…”

Deep Thermohaline Circulation Across the Closure of the Central American Seaway

“…To better understand the dynamics of bottom‐water masses, well‐preserved benthic foraminifers from bottom sediments are analyzed as archives of paleoceanography and paleoclimate. In the last two decades, a growing number of projects have focused on Mg/Ca‐derived bottom‐water temperature (BWT) estimates from benthic foraminifers (e.g., Billups & Schrag, 2003; Elmore et al, 2015; Hasenfratz et al, 2017; Lo Giudice Cappelli et al, 2015; Raitzsch et al, 2008; Tisserand et al, 2013) to complement Mg/Ca‐derived sea surface temperature (SST) estimates from planktic foraminifers (Barker et al, 2005; Eggins et al, 2003; Nürnberg et al, 1996). In this context, epibenthic C ibicidoides wuellerstorfi are analyzed due to their ubiquitous abundance in the main ocean basins during the Neogene and Quaternary (Billups & Schrag, 2002; Elderfield et al, 2006; Healey et al, 2008; Lear et al, 2002; Raitzsch et al, 2008; Repschläger et al, 2015; Tisserand et al, 2013; Yu & Elderfield, 2008) but have so far not been investigated from the Caribbean Sea.…”