Sea Ice Variations Influence Benthic Community Growth Rates over Decadal Scales: Evidence from Bivalve Population near the Barents Sea Polar Front

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We examined growth of the Arctic bivalve Clinocardium ciliatum from 1977-2006 in the Barents Sea to evaluate the effect of different water masses on growth and to assess the influence of climatic forcing on ecological processes over decadal scales. Analysis of annually-deposited growth lines in shells of 22 individuals from 3 stations allowed us to assess growth conditions for up to 30 years, thus encompassing both warmer and colder climatic phases of the last century. Growth rates of specimens at younger ages (6-13 years) were highest in Atlantic water, resulting in an average size 20% greater compared to similarly aged individuals from Arctic water or at the Polar Front, reflecting warmer sea temperatures and/or presumably greater food supplies in the Atlantic-dominated regions of the Barents Sea. Despite different absolute growth rates, temporal patterns of ontogenetically-adjusted growth (i.e. Standard Growth Index = SGI) had similar features, with below-average but increasing SGI throughout the 1980s and culminating in 1994 or 1995 with the highest SGI. An abrupt decline starting in 1996 led to below-average growth rates for most of the years from the turn of the century to the end of the record in 2006. The decline in growth coincides with abrupt phase shifts in two hemispheric oscillatory indices: the North Atlantic Oscillation (NAO) and the Arctic Climate Regime Index (ACRI). The strongest statistical relationships were found between growth and the ACRI, and its local manifestations through precipitation