Inter- and intra-annual growth increments of bivalve mollusks of the North and Baltic Seas will be used for the reconstruction of Holocene climate and environmental history. We focus on the past few centuries. Variations in growth rates and geochemical properties of the growth increments reflect seasonal and inter-annual variations of the physio-chemical conditions during growth (temperature, food; ageing, reproduction).
Currently, we are establishing multi-species master chronologies (compound chronologies) using annual, fortnightly, and daily growth increments of long- and short-lived bivalves: Arctica islandica, Spisula solida, Astarte sp., etc. Ontogenetic growth trends are removed by detrending methods explored by dendrochronologists. Detrended growth increment time-series of indivudals with overlapping life spans are linked together in order to produce long master chronologies. Live collected specimens anchor the time-series at known points. Later, dead collected specimens will be incorporated into this time-series. The end result will be a master chronology many generations in duration providing information on low- and high frequency environmental variations and trends, both inter-annual and seasonal. In addtion to variations in relative growth rates, we are synthesizing geochemical and meterological data in order to provide a multi-proxy archive of environmental variation.
High-temporal-resolution proxies of environmental change are not widely distributed in the mid-latitudes. Our results will enable the calibration of climate models and resolve variations like the flux of North Atlantic water masses into the North Sea, the North Atlantic Oscillation, etc.
One major goal of our research is to construct master chronologies of bivalve mollusks form the North Atlantic and North Pacific sectors. Inter-annual and seasonal variations in growth rates will be used to infer environmental and climate conditions during the most recent period of the Holocene. Furthermore, we measure delta18O- und delta13C ratios in the growth increments. These measurements help us interpret the relationship between environmental variables and growth rates. Geochemical data also provide an independent measure of environmental conditions.
Past climate and environmental conditions provide the basis for modeling future ecological trends. In the mid latitudes, modelers have frequently relied on tree-ring data. (e.g., Becker et al. 1991, Briffa et al. 1990, 1998, Scuderi 1993, Jones et al., 2001). Unfortunately, tree rings only vaguely record seasonal environmental variations and interpretations from such data cannot be accurately extended to marine settings. Direct measurements from marine settings are limited in time (maximum 200 years). Our project on bivalve mollusk sclerochronologies ("clam"-ring chronologies) will quantitatively assess environmental conditions beyond the limits of direct measurements. In addition, we are studying the life history traits of other bivalve mollusks in the North and Baltic Seas and their and suitability for environmental reconstructions. It is foremost importance to identify the growing season of each species in its preferred habitat. We plan to apply the results achieved through the present investigation to fossil environments, e.g., to interpret seasonal environmental variability in the contect of global catastrophic events. (Schöne 1999).
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