Bivalve Shells—Unique High-Resolution Archives of the Environmental Past - Towards an Interdisciplinary Approach in Earth System Science - page 164

information on water temperatures (e.g., Sch ö ne et al. 2005 c) and salinity (e.g.,

Sch ed

temperature equation by Dettman et al. ( 1999 ) is used for A. islandica, which is
based on the empirically determined relationship between temperature and

ö ne et al. 2003b ) at the moment of shell formation. In general, the modi

18 O for

δ

aragonite by Grossman and Ku ( 1986 ).
Carbonate samples were milled by hand (Dettman and Lohmann 1995 ) using a
700 m drill bit (Komet/Gebr. Brasseler GmbH & Co. KG) mounted onto an

industrial high precision drill (Minimo C121, Minitor Co., Ltd.) and attached to a
binocular microscope. Measurements were performed on a Thermo Finnigan MAT
253 isotope ratio mass spectrometer and calibrated against a NBS-19 standard with
a precision error of 0.08

μ

for oxygen. Shell-derived water temperatures have been
compared to SST measurements reported online ( http://www.seatemperature.org/
europe/norway/tromso.htm ).

‰

3 Results

3.1 State of Preservation

From the Raman scan it can be seen that the area of the fossil A. islandica shell
(shell ID: AI-TjBe-01) marked in Fig. 3 a consisted of both aragonite and calcite. An
area scan of 520

m (Fig. 3 b), partly covering the potentially recrystallized
shell portion, indicates the distribution of (pristine) aragonite and (recrystallized)
calcite within the shell carbonate. Both polymorphs share carbonate-speci

× 500 μ

c peaks

at 155 and 1085 cm − 1 in their Raman spectra (Fig. 3 c). The aragonite-speci

c peak

206 cm − 1 280 cm − 1

at (blue line in Fig. 3 c) is shifted towards in (recrystal-

* *

lized) calcite (red line in Fig. 3 c).

(a) (b) (c)

Fig. 3 State of preservation tested by confocal Raman microscopy. a Schematic illustration of a
(fossil) A. islandica specimen. Light grey colour exemplary indicates area of potential
recrystallization. b Areal CRM scan in specimen AI-TjBe-01 close to the altered shell portion
and as indicated in a. Two different materials have been identified. c Raman spectra for two
different polymorphs of calcium carbonate explaining colour coding in B. Intensity differences in
liberation modes (peaks at

280 cm − 1 for calcite) in single spot
Raman spectra identify pristine aragonite (blue) and recrystallized calcite (red)

206 cm − 1

for aragonite and

* *