Strontium, magnesium, and barium incorporation in aragonitic shells of juvenile Arctica islandica: Insights from temperature controlled experiments

Abstract

In order to constrain spatial and temporal temperatures and environmental conditions in the North Atlantic Ocean during the Holocene, high-resolution (seasonal to annual) marine proxies with excellent chronological constraints are needed. The long-lived ocean quahog, Arctica islandica, which has the potential to provide a precise annually-dated record, via crossdating techniques, is a fairly well-developed and tested marine proxy archive. In particular, oxygen isotopes derived from A. islandica shell carbonate have provided a wealth of information on marine climate and ocean circulation dynamics, however, shell-derived oxygen isotopes are influenced by both the isotopic source water signature (covarying with salinity) and seawater temperature. If seawater isotopic signature is not known, temperature reconstructions become challenging. Thus, an independent technique to estimate past seawater temperatures is highly desired, however based on previous studies on adult and juvenile clams, the utility of elemental ratios in A. islandica shell material as environmental proxies remains questionable. To further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization, A. islandica shells were grown at constant temperatures under two regimes during a 16-week period from March 27 to July 21, 2011 at the Darling Marine Center in Walpole, Maine. Individual juvenile clams were stained with calcein and cultured at 10.30 ± 0.30 °C for six weeks. After this, the clams were again stained with calcein and cultured at 15.00 ± 0.40 °C for an additional 9.5 weeks. Average salinity values were 30.20 ± 0.70 and 30.70 ± 0.70 in the first and second phases of the experiment, respectively. Continuous sampling within and across the temperature conditions (from 10.30 °C to 15.00 °C) coupled with the calcein markings provided the ability to place each sample into a precise temporal framework and to establish exact average growth rates for the shells sampled. After accounting for changes in the isotopic composition of seawater, oxygen isotopes from one sampled shell effectively recorded seawater temperatures during the study and also gave confidence to the temporal fit of the data. Elemental ratios (Sr/Ca, Mg/Ca, Ba/Ca) from five aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry. Sr/ Ca and Mg/Ca data showed little coherence with temperature during the culture experiment, including the rapid 5 °C increase in seawater temperature. However, Ba/Ca ratios showed an inverse relationship with seawater temperatures although this relationship was noisy. Additionally, salinity interactions were present during the 15.00 °C treatment, further highlighting complex incorporation of elements during biomineralization. Incorporation of Sr, Mg, and Ba were strongly and variably impacted by growth rates. Combined, the results from these culture experiments demonstrate that Sr/Ca, Mg/Ca, Ba/Ca ratios in juvenile A. islandica shell material are dominated by phys...

Environmental and biological factors influencing trace elemental and microstructural properties of Arctica islandica shells

“…Specifically, the pathways of elements from the water and food into the shell needs further study. Our study, however, supports the conclusion of Wanamaker and Gillikin (2018) that at present, there is not yet enough and consistent information that would allow to use trace element-to-calcium ratios of A. islandica shells as reliable environmental proxies.…”

“…In many organisms, Sr/Ca and Mg/Ca ratios serve as useful paleo-temperature proxies (e.g., foraminifera, Nürnberg et al, 1996;corals, Goodkin et al, 2007;sclerosponges, Rosenheim et al, 2004;bivalves, Zhao et al, 2017b). As shown by several studies, in the bivalve A. islandica vital effects have an important effect on the incorporation of these two trace elements into the shell (Toland et al, 2000;Foster et al, 2008Foster et al, , 2009Schöne et al, 2011Schöne et al, , 2013Marali et al, 2017a;Wanamaker and Gillikin, 2018). Most of these studies, which are based on small samples sizes (3-8 specimens vs. 73 this study), concluded that it is unclear whether these metal-tocalcium ratios in the shells of A. islandica can be used as temperature proxies.…”

“…Moreover, multiple regression analysis showed that shell growth rate explained 23 % of the Mg/Ca variability, and identified the effect of temperature as being negligible in our data set (Table 4). Thus, it appears that the Sr/Ca and Mg /Ca ratios of A. islandica shells to a large proportion reflect physiological processes and do not exclusively reflect water temperature (Gillikin et al, 2005;Freitas et al, 2006;Elliot et al, 2009;Foster et al, 2008Foster et al, , 2009Wanamaker et al, 2008;Geeza et al, 2018;Wanamaker and Gillikin, 2018).…”

“…However, Sr/Ca and Mg/Ca ratios are still difficult to interpret because the incorporation of trace and minor impurities in the shell carbonate is partly physiologically controlled (e.g., Urey et al, 1951;Purton et al, 1999;Lorrain et al, 2005;Freitas et al, 2005Freitas et al, , 2006Schöne et al, 2010Schöne et al, , 2013Marali et al, 2017a;Geeza et al, 2018). Published results on the relationship between the Sr/Ca and Mg/Ca ratios of bivalve shells and temperature are highly ambiguous; previous studies have reported a positive relationship (Stecher et al, 1996;Hart and Blusztajn, 1998;Toland et al, 2000), negative relationship (Dodd, 1965;Stecher et al, 1996;Surge and Walker, 2006;Schöne et al, 2011), and no relationship (Gillikin et al, 2005;Strasser et al, 2008;Izumida et al, 2011;Wanamaker and Gillikin, 2018). The variation on the type of relationship (positive, negative, or neutral) have been identified as species-specific and can even change depending on the season of the year (e.g., Gillikin et al, 2005;Freitas et al, 2006).…”

“…Under laboratory conditions, A. islandica individuals from the same population were reared at different temperatures and food concentrations. Several studies have used controlled laboratory experiments to determine the relationship between the elemental composition of bivalve shells and variable environmental parameters (Lorens and Bender, 1980;Strasser et al, 2008;Wanamaker et al, 2008;Poulain et al, 2015;Wanamaker and Gillikin, 2018). However, fewer studies have tested the effect of the environment on the shell microstructure.…”