Oceanographic control on shell growth of Arctica islandica (Bivalvia) in surface waters of Northeast Iceland — Implications for paleoclimate reconstructions

Abstract

Absolutely dated, annually resolved sea surface temperature records from middle to higher latitudes covering long time intervals are crucial to better understand the climate system. Such data can potentially be obtained from variations in shell growth of long-lived bivalves such as Arctica islandica. This study presents the first statistically robust 178-yr long composite chronology (covering 1835–2012) based on sixteen live-collected and subfossil specimens of A. islandica from unpolluted, shallow waters of Northeast Iceland. Between 1875 and 1996, up to 43% of the variation in annual shell growth was explained by SST during February to September. Faster growth occurred when temperatures were warmer and food supply was elevated. However, the correlation was subject to strong temporal variations. Likewise, the inter-series correlation (synchrony among time series) was intermittently stronger and weaker. If more uniform environmental conditions prevailed over a longer time interval and the habitat was solely influenced by one of the major currents in this region – the warm, nutrient-rich Irminger Current or the cold, nutrient-poor East Iceland Current – the agreement between growth records of contemporaneous specimens broke down and the correlation between shell growth and SST was at minimum. However, when the habitat was under the alternating influence of both currents, the inter-annual variability of shell growth and synchrony in growth among the specimens were at maximum, and the correlation between SST and shell growth strengthened. As demonstrated here, the relationship between shell growth of A. islandica and environmental variables is highly complex and depends on oceanographic parameters. These findings should be taken into account in subsequent studies in order to reliably reconstruct SST and other environmental variables from shells of this species.