Abstract
Shells of the bivalve Arctica islandica are used to reconstruct paleo-environmental conditions (e.g. temperature) via biogeochemical proxies, i.e. biogenic components that are related closely to environmental parameters at the time of shell formation. Several studies have shown that proxies like element and isotope-ratios can be affected by shell growth and microstructure. Thus it is essential to evaluate the impact of changing environmental parameters such as high pCO2 and consequent changes in carbonate chemistry on shell properties to validate these biogeochemical proxies for a wider range of environmental conditions. Growth experiments with Arctica islandica from the Western Baltic Sea kept under different pCO2 levels (from 380 to 1120 µatm) indicate no affect of elevated pCO2 on shell growth or crystal microstructure, indicating that A. islandica shows an adaptation to a wider range of pCO2 levels than reported for other species. Accordingly, proxy information derived from A. islandica shells of this region contains no pCO2 related bias.
Highlights
Marine biogenic carbonates such as bivalve shells represent complex composites of organic and inorganic phases [1,2,3]
The aim of this study is to investigate the impact of pCO2 on the shell microstructure of A. islandica from the Kiel Bight, in order to evaluate the possible impact such changes would have on shell based proxies
Within most shells the calcein mark did not appear along the whole shell margin but only in the fastest growing segments (Figure 2). This indicates asynchronous shell growth of Arctica islandica during short time periods (4K h calcein immersion)
Summary
Marine biogenic carbonates such as bivalve shells represent complex composites of organic and inorganic phases [1,2,3]. Bivalve shells provide information on environmental conditions at times of shell formation in the form of structural and biogeochemical properties [8,9,10]. In bivalve shells, some of the ‘‘classic’’ proxy systems (e.g. trace elements) developed for paleo-temperature, salinity and food availability have been shown to be affected by growth patterns, crystal fabric structure [11], the organic and the mineral phase of the biogenic carbonate (calcite, the more soluble aragonite or both) [11,12,13]. Raising atmospheric CO2 and the corresponding decrease in ocean pH represents a challenge for marine calcifiers on a global scale (e.g. [22])
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