Sea surface water temperatures over the period 1884–1983 reconstructed from oxygen isotope ratios of a bivalve mollusk shell (Arctica islandica, southern North Sea)

Although climate system modeling cannot be imagined without long sea surface temperature (SST) records, observational data is spatiotemporally incomplete and inhomogeneous prior to about 1950. Moreover, almost no high-resolution SST proxies exist from temperate and boreal marine settings. Here, we present a temporally equidistant, high-resolution SST proxy record of the southern North Sea during the period 1884–1983 calculated from oxygen isotope ratios (δ18Oaragonite) of Arctica islandica (L.), a bivalve mollusk shell. Arctica islandica produces daily growth increments, which enable precise intraannual dating. The growing season of specimens from about 25 m water depth (upper well-mixed layer of the ocean) started in February and ended in September. Observational (COADS, etc.) and δ18Oaragonite-derived SST data during February through September compare well to each other, especially after 1950. Apart from similar overall SST trends, we found North Atlantic Oscillation-type cycles of 7–9 years in our proxy SST record and in various different instrumentally determined SST chronologies. No vital effects exist, so that δ18Oaragonite ratios determined across the shell (i.e., throughout lifetime) of the studied specimen reflect ambient water temperatures that occurred during shell growth. Results of our study demonstrate that A. islandica provides long, independent and high-resolution SST proxy chronologies from higher latitudes. Such records can complement and further validate observational SST data and help improving climate system models.