Bivalve Shells—Unique High-Resolution Archives of the Environmental Past - Towards an Interdisciplinary Approach in Earth System Science - page 161

with increasing frequency, providing environmental information on daily to multi-
centennial time-scales (Sch ne et al. 2005b ; Hallmann et al. 2009 ; Butler et al.

2010 ). For this purpose, analyses of the anatomical-morphological features of the
skeletal hard parts

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are commonly
combined with geochemical analyses (e.g., stable isotopes, trace elements). Due to
its wide distribution throughout the North Atlantic (Dahlgren et al. 2000 ) and its
longevity (500 years and more, Butler et al. 2013 ), the bivalve Arctica islandica
represents an exceptional bio-archive for northern temperate regions.
A. islandica forms annual growth rings (increments), which can be measured and
used as a calendar (Jones 1980 ). However, when working with fossil specimens, the
state of preservation is an essential aspect to consider prior to any kind of geo-
chemical analysis (e.g., stable oxygen isotopes (

— such as growth patterns and crystal structures —

18 O) as a proxy for water tem-
perature and salinity). Confocal Raman microscopy (CRM) is a non-destructive
method, which allows a test for diagenetic alteration on the same sample that will
later be used for the geochemical measurement.
The annual growth rate of bivalves mainly depends on ambient water temper-
ature and food quality and availability (e.g., Witbaard et al. 1997 ) which vary on a
regional scale, but may be affected by large-scale ocean-atmosphere phenomena,
too (Sch

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ne et al. 2003a ), like the North Atlantic Oscillation (NAO). The frequency
analysis of the growth record of just a single A. islandica shell can identify such
decadal signals (several years to decades) in a time window corresponding to the
animal s lifetime.

For demonstration purposes we combine the results from modern and fossil shell
material to emphasise the unique character of the bio-archive A. islandica.We
demonstrate its outstanding potential in terms of intra-annual (stable oxygen iso-
topes) as well as decadal (frequency analysis) climatic and environmental recon-
structions and show how these can be combined to inform our understanding of
climate in the past (Fig. 1 ).

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2 Methods

2.1 Shell Origin and Laboratory Work

We use three A. islandica specimens of different geological age (see Table 1 for
details) to demonstrate how sclerochronological analyses at intra-annual and dec-
adal scale fit together. The CRM approach has been applied on Pliocene specimen

AI-TjBe-01, which was removed from the biostratigraphically dated Tj rnes Bed

formation, Iceland. Specimen AI-EgLo-02 has been found dead in beach deposits at
the Lofoten, Norway, and used for the frequency analysis. Further, specimen

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