Dissolution rate spectra data of calcite single crystal and micrite material

The large discrepancy between field and laboratory measurements of mineral reaction rates is a long-standing problem in earth sciences, often attributed to factors extrinsic to the mineral itself. Nevertheless, differences in reaction rate are also observed within laboratory measurements, raising the possibility of intrinsic variations as well. Critical insight is available from analysis of the relationship between the reaction rate and its distribution over the mineral surface. This analysis recognizes the fundamental variance of the rate. The resulting anisotropic rate distributions are completely obscured by the common practice of surface area normalization. In a simple experiment using a single crystal and its polycrystalline counterpart, we demonstrate the sensitivity of dissolution rate to grain size, results that undermine the use of "classical" rate constants. Comparison of selected published crystal surface step retreat velocities (Jordan and Rammensee, 1998) as well as large single crystal dissolution data (Busenberg and Plummer, 1986) provide further evidence of this fundamental variability. Our key finding highlights the unsubstantiated use of a single-valued "mean" rate or rate constant as a function of environmental conditions. Reactivity predictions and long-term reservoir stability calculations based on laboratory measurements are thus not directly applicable to natural settings without a probabilistic approach. Such a probabilistic approach must incorporate both the variation of surface energy as a general range (intrinsic variation) as well as constraints to this variation owing to the heterogeneity of complex material (e.g., density of domain borders). We suggest the introduction of surface energy spectra (or the resulting rate spectra) containing information about the probability of existing rate ranges and the critical modes of surface energy.

Impact of ocean acidification and warming on respiration, heart rate and acid-base status of Mytilus edulis from the North Sea

Anthropogenic climate change confronts marine organisms with rapid trends of concomitant warming and CO2 induced ocean acidification. The survival and distribution of species partly depend on their ability to exploit their physiological plasticity during acclimatization. Therefore, in laboratory studies the effects of simulated future ocean acidification on thermal tolerance, energy metabolism and acid-base regulation capacity of the North Sea population of the blue mussel Mytilus edulis were examined. Following one month of pre-acclimation to 10 °C and control CO2 levels, mussels were exposed for two weeks to control and projected oceanic CO2 levels (390, 750 and 1120 µatm) before being subjected to a stepwise warming protocol between 10 °C and 31 °C (+ 3 °C each night). Oxygen consumption and heart rates, anaerobic metabolite levels and haemolymph acid-base status were determined at each temperature. CO2 exposure left oxygen consumption rate unchanged at acclimation temperature but caused a somewhat stronger increase during acute warming and thus mildly higher Q10-values than seen in controls. Interestingly, the thermally induced limitation of oxygen consumption rate set in earlier in normocapnic than in hypercapnic (1120 µatm CO2) mussels (25.2 °C vs. 28.8 °C), likely due to an onset of metabolic depression in the control group following warming. However, the temperature induced increase in heart rate became limited above 25 °C in both groups indicating an unchanged pejus temperature regardless of CO2 treatment. An upper critical temperature was reached above 28 °C in both treatments indicated by the accumulation of anaerobic metabolites in the mantle tissue, paralleled by a strong increase in haemolymph PCO2 at 31 °C. Ocean acidification caused a decrease in haemolymph pH. The extracellular acidosis remained largely uncompensated despite some bicarbonate accumulation. In all treatments animals developed a progressive warming-induced extracellular acidosis. A stronger pH drop at around 25 °C was followed by stagnating heart rates. However, normocapnic mussels enhanced bicarbonate accumulation at the critical limit, a strategy no longer available to hypercapnic mussels. In conclusion, CO2 has small effects on the response patterns of mussels to warming, leaving thermal thresholds largely unaffected. High resilience of adult North Sea mussels to future ocean acidification indicates that sensitivity to thermal stress is more relevant in shaping the response to future climate change.

Using the critical salinity (Scrit) concept to predict invasion potential of the anemone Diadumene lineata in the Baltic Sea

It is widely assumed that the ability of an introduced species to acclimate to local environmental conditions determines its invasion success. The sea anemone Diadumene lineata is a cosmopolitan invader and shows extreme physiological tolerances. It was recently discovered in Kiel Fjord (Western Baltic Sea), although the brackish conditions in this area are physiologically challenging for most marine organisms. This study investigated salinity tolerance in D. lineata specimens from Kiel Fjord in order to assess potential geographical range expansion of the species in the Baltic Sea. In laboratory growth assays, we quantified biomass change and asexual reproduction rates under various salinity regimes (34: North Sea, 24: Kattegat, 14: Kiel Fjord, 7: Baltic Proper). Furthermore, we used 1H-NMR-based metabolomics to analyse intracellular osmolyte dynamics. Within 4 weeks D. lineata exhibited a 5-fold population growth through asexual reproduction at high salinities (34 and 24). Biomass increase under these conditions was significantly higher (69%) than at a salinity of 14. At a salinity of 7, anemones ceased to reproduce asexually, their biomass decreased and metabolic depression was observed. Five main intracellular osmolytes were identified to be regulated in response to salinity change, with osmolyte depletion at a salinity of 7. We postulate that depletion of intracellular osmolytes defines a critical salinity (Scrit) that determines loss of fitness. Our results indicate that D. lineata has the potential to invade the Kattegat and Skagerrak regions with salinity >10. However, salinities of the Baltic Proper (salinity <8) currently seem to constitute a physiological limit for the species.

Critical bed shear stress and threshold of motion of maërl biogenic gravel

Critical bed shear stress for incipient motion has been determined for biogenic free-living coralline algae known as maërl. Maërl from three different sedimentary environments (beach, intertidal, and open marine) in Galway Bay, west of Ireland have been analysed in a rotating annular flume and linear flume. Velocity profile measurements of the benthic boundary layer, using an Acoustic Doppler Velocimeter, have been obtained in four different velocity experiments. The bed shear stress has been determined using three methods: Law of the Wall, Turbulent Kinetic Energy and Reynolds Stress. The critical Shields parameter has been estimated as a non-dimensional mobility number and the results have been compared with the Shields curve for natural sand. Maërl particles fall below this curve because its greater angularity allows grains to be mobilised easier than hydraulically equivalent particles. From previous work, the relationship between grain shape and the settling velocity of maërl suggests that the roughness is greatest for intertidal maërl particles. During critical shear stress determinations, beds of such rough particles exhibited the greatest critical shear stress probably because the particle thalli interlocked and resisted entrainment. The Turbulent Kinetic Energy methodology gives the most consistent results, agreeing with previous comparative studies. Rarely-documented maërl megaripples were observed in the rotating annular flume and are hypothesised to form at velocities ~10 cm s-1 higher than the critical threshold velocity, where tidal currents, oscillatory flow or combined-wave current interaction results in the preferential transport of maërl. A determination of the critical bed shear stress of maërl allows its mobility and rate of erosion and deposition to be evaluated spatially in subsequent applications to biological conservation management.