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

在下一个资助期内，我的研究项目将集中在加拿大沿海水域（加拿大北极和圣劳伦斯系统）被人为二氧化碳酸化的机制上。我们将确定文石和方解石在水柱中的饱和深度将以多快的速度上升，以及全球海洋将如何、在何处、何时通过富含caco3的沉积物的溶解来应对或减轻这种环境压力。****海洋是地球上最大的二氧化碳储存库，因此，海洋将吸收大部分人为排放到大气中的二氧化碳。富含caco3的沉积物最终将中和大部分人为排放到海洋中的二氧化碳。中和这些二氧化碳所需的时间取决于二氧化碳从海洋表层向深海转移的速率以及底栖CaCO3的溶解动力学。为了预测溶解发生的时间尺度，我们需要准确地知道溶解动力学。我们通过实验确定，富方解石沉积物的溶解速率与上覆底部水的欠饱和程度呈线性变化。这一发现挑战了目前方解石溶解速率遵循高阶动力学（3到4）的范式。为了将我们的工作扩展到现场条件，我们设计了一个旋转盘反应器，使我们能够准确地模拟海底遇到的剪切应力范围。我们将研究环境（温度，压力）和岩性（孔隙度）变量以及各种碳酸盐矿物学（文石，镁方解石）和生物物质对碳酸盐溶解动力学的影响。考虑到我们已经记录的溶解动力学（水侧扩散控制）以及我们将阐明的溶解速率、饱和状态、碳酸盐沉积物含量和沉积物-水界面流体动力学之间的关系，我们将能够开发一个全球模型来预测在各种排放情景下深海对人为二氧化碳入侵的响应位置和速度。最后，我们将把我们的结果与经历过温室时期/事件的古代碳酸盐矿床的矿物学和地球化学进行比较。后一项研究将揭示目前的海洋是否像过去那样对酸化做出反应，酸化的速度有多快，以及从这些事件中完全恢复需要多长时间。****与全球变暖和富营养化等其他压力相结合，海洋酸化影响碳酸盐分泌生物（例如，球石藻、翼足类、双壳类、珊瑚）以及非钙化生物的生态。这是因为pH在调节生理过程中起着关键作用，如生长、招募和捕食。持续的海洋酸化可能会影响海洋生态系统的结构，海洋食物链，并威胁到我们自己的粮食安全。*********

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.*********