Mechanisms and rate of anthropogenic CO2 uptake in Canadian coastal waters and the response of shallow and deep-ocean carbonate sediments to ocean acidification.

点击翻译按钮获取中文摘要

Over the next funding period, my research program will focus on the mechanisms by which Canadian coastal waters (Canadian Arctic and St. Lawrence system) are being acidified by anthropogenic CO2. We will determine how fast the saturation depths with respect to aragonite and calcite will rise in the water column, and how, where, and when the global ocean will respond to or mitigate this environmental stress through dissolution of CaCO3-rich sediments.**** The ocean is the largest reservoir of CO2 on Earth and, thus, will absorb much of the anthropogenic CO2 emitted to the atmosphere. CaCO3-rich sediments will ultimately neutralize most of the anthropogenic CO2 delivered to the ocean. The time required to neutralize this CO2 is predicated on the rate of transfer of CO2 from the surface ocean to the deep ocean as well as the dissolution kinetics of benthic CaCO3. To predict the timescale over which dissolution takes place, we need to know the dissolution kinetics accurately. We have determined experimentally that the dissolution rate of calcite-rich sediments varies linearly with the degree of undersaturation of the overlying bottom water. This finding challenges the current paradigm that the calcite dissolution rate follows higher order kinetics (3 to 4). To extend our work to in-situ conditions, we have designed a rotating-disk reactor that will allow us to accurately simulate the range of shear stresses encountered at the seafloor. We will investigate the effects of environmental (temperature, pressure) and lithological (porosity) variables as well as various carbonate mineralogies (aragonite, Mg-calcites) and biogenic materials on carbonate dissolution kinetics. Given the dissolution kinetics we have documented (water-side diffusion-controlled) and the relationships we will elucidate between dissolution rate, saturation state, carbonate sediment content, and hydrodynamics at the sediment-water interface, we will be able to develop a global model to predict where and how fast the deep-ocean will respond to the invasion of anthropogenic CO2 under various emission scenarios. Finally, we will compare our results with the mineralogy and geochemistry of ancient carbonate deposits that experienced past greenhouse periods/events. The latter study should reveal if the present ocean is responding to acidification as it did in the past, how fast it did so, and how long it took to fully recover from these events.**** In combination with other stresses, such as global warming and eutrophication, ocean acidification affects the ecology of carbonate-secreting organisms (e.g., coccolithophores, pteropods, bivalves, corals), as well as non-calcifiers. This is because pH plays a critical role in mediating physiological processes such as growth, recruitment, and predation. Ongoing ocean acidification may impact the structure of the marine ecosystem, the marine food chain, and threaten our own food security.*********