Obtaining High Resolution Environmental Archives from Fish Otoliths

Geochemical signatures in bivalves and corals have frequently been used to reconstruct past climates at high temporal resolution and over long time periods, but similar approaches have not yet been widely applied to otoliths. Here, we use features of otoliths (periodicity of growth increments, incorporation of trace elements from environment) to demonstrate how high resolution environmental archives can be obtained. Geochemical profiles (element:Ca) across the otoliths were obtained via laser ablation inductively coupled plasma-mass spectrometry and related to growth increments on a monthly or seasonal time scale. A series of mixed effects models were used to investigate intrinsic (within individual) and extrinsic (environmental) factors influencing seasonal variation in otolith geochemical profiles. Results demonstrate that multidecadal seasonal geochronologies can be created from otoliths for a range of element:Ca ratios and fish species. In addition, several geochemical profiles were correlated with environmental data (upwelling, salinity) suggesting that fish otoliths can reconstruct past environmental conditions including from past centuries. Such geochronologies provide not only long-term environmental information, which in the southern hemisphere is lacking, but also unprecedented information on drivers of geochemical profiles that will allow a range of ecological questions to be addressed.