Geochemistry of the brachiopod Hemithiris psittacea from the Canadian Arctic: Implications for high latitude palaeoclimate studies

Abstract Fossil shell material from high palaeo-latitudes is increasingly studied for environmental forcings specific to these latitudes and as sensitive archives of climate change. However, more detailed studies of modern analogues are necessary for putting findings into global and high latitude perspectives. Here we present δ 13 C and δ 18 O values, as well as Mg, Sr, Na, Mn and Fe contents for the rhynchonellide brachiopod Hemithiris psittacea from Friday Harbor, U.S.A. and twenty-five sites from Canada ranging in latitude from 48° to 71°N. Median Mn/Ca ratios are below 0.1 mmol/mol and Fe/Ca ratios are below 0.3 mmol/mol, with no strong correlation between ratios and no apparent geographical relationship. Mg/Ca and Sr/Ca ratios vary within relatively narrow limits and yield median ratios of 3.7 mmol/mol and 1.13 mmol/mol. Na/Ca ratios vary widely amongst the sites with median values ranging from 9 to 20 mmol/mol. Relatively uniform median δ 13 C values of + 1.8 ± 0.6‰ (2 sd, n = 25) are observed for the Canadian sites, whereas at Friday Harbor the signature of 13 C depletion in local DIC is imprinted in the shell calcite. Median δ 18 O values of − 0.5 to + 2.7‰ are more variable than carbon isotope signatures and point to precipitation of shell material in seawater diluted by variable amounts of freshwater and affected by seasonal sea ice. Our results imply that robust elemental patterns and carbon isotope signatures of high latitude brachiopod fossils can be expected for most palaeogeographic situations. In contrast, δ 18 O signatures of shell material from high latitude marginal seas, particularly during glacial periods, would yield unreasonably high seawater temperature estimates unless the oxygen isotopic composition of the ambient water is accurately accounted for in palaeotemperature calculations.