Seawater carbonate chemistry and biological processes of Mytilus edulis during experiments, 2010

Marine organisms are exposed to increasingly acidic oceans, as a result of equilibration of surface ocean water with rising atmospheric CO2 concentrations. In this study, we examined the physiological response of Mytilus edulis from the Baltic Sea, grown for 2 months at 4 seawater pCO2 levels (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm). Shell and somatic growth, calcification, oxygen consumption and excretion rates were measured in order to test the hypothesis whether exposure to elevated seawater pCO2 is causally related to metabolic depression. During the experimental period, mussel shell mass and shell-free dry mass (SFDM) increased at least by a factor of two and three, respectively. However, shell length and shell mass growth decreased linearly with increasing pCO2 by 6-20 and 10-34%, while SFDM growth was not significantly affected by hypercapnia. We observed a parabolic change in routine metabolic rates with increasing pCO2 and the highest rates (+60%) at 243 Pa. excretion rose linearly with increasing pCO2. Decreased O:N ratios at the highest seawater pCO2 indicate enhanced protein metabolism which may contribute to intracellular pH regulation. We suggest that reduced shell growth under severe acidification is not caused by (global) metabolic depression but is potentially due to synergistic effects of increased cellular energy demand and nitrogen loss.

Physical oceanography and hydrochemistry from the Laptev Sea, Arctic Ocean

Combined d18O/salinity data reveal a distinctive water mass generated during winter sea ice formation which is found predominantly in the coastal polynya region of the southern Laptev Sea. Export of the brine-enriched bottom water shows interannual variability in correlation with atmospheric conditions. Summer anticyclonic circulation is favoring an offshore transport of river water at the surface as well as a pronounced signal of brine-enriched waters at about 50 m water depth at the shelf break. Summer cyclonic atmospheric circulation favors onshore or an eastward, alongshore water transport, and at the shelf break the river water fraction is reduced and the pronounced brine signal is missing, while on the middle Laptev Sea shelf, brine-enriched waters are found in high proportions. Residence times of bottom and subsurface waters on the shelf may thereby vary considerably: an export of shelf waters to the Arctic Ocean halocline might be shut down or strongly reduced during "onshore" cyclonic atmospheric circulation, while with "offshore" anticyclonic atmospheric circulation, brine waters are exported and residence times may be as short as 1 year only.