Potential of Greenland cockles (Serripes groenlandicus) as high resolution Arctic climate archive [Potential der Grönlandherzmuschel (Serripes groenlandicus) als hochauflösendes Klimaarchiv der Arktis]

Juergen.Laudien [ at ] awi.de


In order to predict the climatic future of the earth, knowledge about the past is indispensable. Climate models which predict possible developments of future climate change are based on data of past environmental conditions. The precision of these climate models depends on quality and quantity of those data. Since recent measurements are limited, climate archives are used to reconstruct past conditions. Archives indirectly provide information about the surrounding environmental conditions at the time of their formation. Once the relationship between a representative parameter recorded by an archive and an environmental parameter is known this could function as a so called proxy. Bivalves are possible archives recording ambient seawater parameter incrementally as a variation of growth rates or shell calcium carbonate (CaCO3) composition. A potential temperature proxy is the ratio of 18O/16O (δ18O) recoded in the shell carbonate of some Bivalves. The equilibrium between recoded and measured δ18O of the seawater is determined by temperature and salinity. In order to use this recording of δ18O in shell carbonate it is necessary calibrating δ18O of the seawater with measurements of surrounding seawater parameters to exclude the possibility of metabolic influences on this equilibrium. The Greenland cockle Serripes groenlandicus (Bruguiere, 1789), a bivalve occurring circumpolar has already been a subject to stable oxygen and carbon isotopes analyses. However, a calibration have not been provided yet. This study investigated whether the equilibrium between δ18O measured subsequently in shell carbonate of S. groenlandicus and the ambient seawater is influenced by metabolic processes. Therefor the shells of 37 specimens, were collected from a population located in Kongsfjorden (Spitsbergen). Three of them were used to subsequently measure δ18O values of shell carbonate and compared to predicted δ18O shell values. The predicted δ18O values of the shell were calculated from temperature and salinity measurements of the ambient seawater. Growth line deposition and growth rate were examined in specimens of the same population in order to prove that the three individuals chosen for stable isotope analysis are representative for this population regarding their growth pattern. Additionally the structure of shell carbonate was analyzed using a Confocal Raman microscope and a scatter electron microscope. Results prove, that the individuals chosen for stable isotopes analyses were representative individuals of the population regarding their growth rate. The evaluation of growth line deposition examined in all collected shells showed a deposition in late summer up to fall. It was also proven that the crystalline structure of the shell carbonate was aragonite. However, embedding shells in Araldite showed the occurrence of a porous structures in the outer shell layer. Stable oxygen isotope analysis and comparison with ambient conditions during shell formation prove a strong similarity between predicted and measured δ18O values of the shell where an alignment was possible. However, the minimum of predicted δ18O values was not recoded in the shell carbonate, indicating that the growth of S. groenlandicus is limited by either high temperature or low salinity. The total range of δ18Oshell values was 3.53‰. From these findings it was concluded, that the equilibrium between shell stable oxygen isotope ratios is not influence by metabolic processes. It was furthermore noted that a high resolution sampling (68 μm) of shell carbonate of S. groenlandicus by manual milling possible.

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Merk, V. (2015): Potential of Greenland cockles (Serripes groenlandicus) as high resolution Arctic climate archive [Potential der Grönlandherzmuschel (Serripes groenlandicus) als hochauflösendes Klimaarchiv der Arktis] , Master thesis, Uni Rostock, AWI.

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