Understanding environmental proxies stored in biogenic carbonates has become a major task and a multidisciplinary endeavour. The CALMARs project (CALcareous MARine Skeletons as recorders of global climate changes) involved reading these records stored in biogenic carbonates and aimed at validating the skeletons of sclerosponges, bivalves and echinoderms as environmental proxies. The first aim was to determine the growth rates of two hyper calcified sponges: Ceratoporella nicholsoni and Petrobiona massiliana. Accumulative data for all specimens of C. nicholsoni collected and measured showed the mean average growth rate to be 198.25μm/yr (9 specimens: n=557, σ=15.23 μm/yr). The mean growth rate of Petrobiona massiliana was 242.76 μm/yr (13 specimens, n=189, σ=161.42 μm/yr). However, the growth rate of this species shows much variation between and within specimens, but falls within the range observed in other hyper calcified sponges. Secondly, we investigated the uptake route of elements into the tissues of Petrobiona massiliana. Transmission Electron Microscopy (TEM) observations showed uptake and accumulation of particles inside endocytic vesicles of specific cell types. Bacteria marked with strontium were also accumulated within phagosomes of the same cells and retained their strontium after incorporation. Incubations with the dissolved elements (up to 10 mM) did not allow the location of elements to be determined within the sponge tissue. However, supersaturated incubations (providing particulate ions) allowed element hotspots to be discovered using Scanning Electron Microscopy (SEM) + Energy Dispersive X-ray analysis (EDX). Focused Ion Beam-cut sections from the element hotspots enabled positive analysis using the Scanning TEM + EDX, but the exact cellular locations are still to be determined at the ultrastructural level. Thirdly, lead profiles from several sclerosponge skeletons were investigated. Nine lead profiles covering more than 130 years from eight sclerosponges of two different species, Ceratoporella nicholsoni and Stromatospongia vermicola, collected off Jamaica, Acklins Island and Turks and Caicos Island are compared. All the profiles display i) the rise in lead around 1950 linked with the atmospheric pollution due to the increasing use of leaded gasoline, and ii) the decrease in lead content during the eighties following the introduction of unleaded gasoline. It is demonstrated that lead curves from sclerosponges are reproducible within single specimens as well as between different specimens from similar locations. In addition, the study reveals information on the physiological functioning of sclerosponges and suggests non-linearity of the lead partitioning coefficient. Bivalve shells offer a great potential as environmental proxies, since they have a wide geographical range and are well represented in the fossil record since the Cretaceous. Nevertheless, they are much less studied than corals and foraminifera and are largely limited to isotopic studies. The general aim of this project was to increase our knowledge of δ18O, δ13C, Sr/Ca, Mg/Ca, U/Ca, Ba/Ca, and Pb/Ca in bivalve aragonite and calcite. The most well studied proxy of sea surface temperature (SST) in bivalve carbonate is δ18O, and it is well known that in addition to SST, the δ18O of the water dictates the δ18O value of the shell. This study clearly demonstrates that unknown δ18O of the water can cause severe errors when calculating SST from estuarine bivalve shells; with the example presented here providing calculated SSTs 1.7 to 6.4 °C warmer than measured. Therefore, a salinity independent or salinity proxy would greatly benefit SST reconstructions. In estuaries, shell δ13C has long been regarded as a potential salinity indicator. However, this study highlights the problems associated with the incorporation of light metabolic CO2 in the shell. Therefore, interpreting δ13C values in bivalve carbonate should be done with caution. In addition to δ13C, Ba/Ca ratios were investigated as a salinity proxy as well. In the calcite shells of M. edulis a strong linear relationship between shell ‘background’ Ba/Ca and water Ba/Ca was found in both the laboratory and field. Although each estuary will have different relationships between salinity and water Ba/Ca, shell Ba/Ca can be used as an indicator of salinity within one estuary. Similar patterns of relatively stable background levels interrupted with sharp episodic peaks were also found in the aragonite shells of S. giganteus, and appear nearly ubiquitous to all bivalves. However, there was an ontogenic decrease in S. giganteus background Ba/Ca ratios, illustrating that these proxies can be species specific. The ratios of Sr/Ca, Mg/Ca and U/Ca were investigated as salinity independent SST proxies, but none were correlated to SST in the two aragonitic and one calcitic bivalve studied. Finally, the use of bivalve shells as recorders of pollution was also assessed. There was both large inter- and intra-specimen variability in Pb/Ca ratios of M. mercenaria shells, but when enough shells were averaged, the typical anthropogenic Pb profile from 1949 to 2003 was evident. Biomineralization is obviously a biological process, and therefore, understanding the pathway of elemental incorporation is vital to understanding proxy incorporation under different temperature and salinity regimes. Results for the mussel, Mytilus edulis, showed uptake of Ca, Cd, Co, Cu and Hg displayed saturation kinetics. Because steady-state was observed at all the different metal exposure levels, it was unlikely that either internal metal binding sites or membrane transporters were saturated under those conditions. Our results indicate that uptake of trace elements and further processing in mussels involves different combinations of the general pathways including those intended for homeostasis of major ions such as Ca and Mg. There was no clear distinction between uptakes of essential and non- essential metals. Through uptake of trace elements is dependent mainly on free ion activity in the exposure water, our results have shown that there are cases when other chemical species may also be important predominantly taken up via the dietary route. Also the effect of temperature and salinity clearly shows deviations from the free ion activity model indicative for physiological regulation. Echinoderms are abundant in a wide geographical range from equatorial to Polar Regions and several species are rather long-lived (60 to 100y). In the present study, we investigated the effects of temperature on the incorporation of minor and trace elements and on the δ18O and δ13C in the skeleton of the wide-ranged temperate starfish Asterias rubens and in closely related sea urchin species collected from boreal to tropical latitudes. A highly significant temperature effect on the Mg incorporation in the skeleton in both experimental and field conditions was evidenced and matches the relation obtained in benthic foraminifera. This effect was independent of growth rate, contrary to previous statements. The slope of relative δ18O versus temperature in skeletons of starfish is also highly significant and neatly matches slopes measured in corals or molluscs. The Mg/Ca ratios of museum specimens are below those of present day specimens indicating a general warming trend.