MEL Seminar｜CO2 Dynamics, Anthropogenic Carbon Accumulation, and Ocean Acidification Along the North American Ocean Margins

报告摘要：

Since 2007, carbonate chemistry along three North American ocean margins (West Coast, East Coast, and Gulf of Mexico Coast) have been consistently studied under the auspices of National Oceanic and Atmospheric Administration (NOAA)’s Ocean Acidification Program (OAP). Based on underway and water column data collected from these cruises and others, I will provide an overview of the sea surface CO₂ distribution, water column carbonate chemistry features, and anthropogenic carbon accumulation rates on the North American margins with the focus on the Mid and South Atlantic Bight (MAB and SAB) along the east coast.

Along the Atlantic and Gulf coasts the meridional distributions of sea surface dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and pCO₂ do not exhibit a simple spatial pattern and are seriously influenced by local physical and biological processes which impede equilibrium with the atmosphere. In the water column, however, water mass characteristics play a critical role in controlling the distribution of pH and Ω. Along the West Coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values.

In the MAB with data back to 1996, our work shows that the offshore slope waters have anthropogenic CO₂ uptake rates or C_anthro consistent with water mass properties and atmospheric CO₂ history. The ΔC_anthro is highest in the top 200 m (the Gulf Stream), lowest ΔC_anthro in the water between 200 m to 500 m (the Antarctica Intermediate Water), and is intermediate below 600 m in the upper branch of the North Atlantic Deep Water. From offshore to nearshore, a conservative decreasing of ΔC_anthro with salinity in the subsurface indicates a nearly zero river-estuarine-wetland export of C_anthro to the shelf. In the West Coast, the ΔC_anthro is also highest in surface waters. The rates gradually decrease with depths. Corresponding rates of pH and Ω decreases resulting from the ΔC_anthro are also estimated and discussed in the context of buffer factors of the various water masses.

个人介绍：

Dr. Wei-Jun Cai obtained his B.S. in Oceanography in 1982 from Xiamen University, Xiamen, China, M.S. in Marine Chemistry in 1985 from the Shandong College of Oceanography (now Ocean University of China), Qingdao, China, and Ph.D. in Oceanography in 1992 from the Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, USA. He was a professor in the Department of Marine Sciences, University of Georgia from 1994 to 2012 and is currently Mary A. S. Lighthipe Chair Professor of Earth, Ocean and Environment at the University of Delaware. He is an author of over 250 peer-reviewed publications (H index = 80; https://scholar.google.com/citations?user=7i0r93YAAAAJ&hl=en). For his distinguished academic accomplishment, Dr. Cai was elected Fellow of the American Association for the Advancement of Science (AAAS) in 2021, the American Geophysical Union (AGU) in 2017, Geochemical Society (GS) and European Association of Geochemistry (EAG) in 2021, and the Association for the Sciences of Limnology and Oceanography (ASLO) in 2017.

Dr. Wei-Jun Cai has worked in the field of marine and estuarine carbon cycle and biogeochemistry for over 30 years and is a leading scientist in coastal ocean acidification research. His research areas include, in the early days, CaCO₃ dissolution and sediment diagenesis in sea floor sediments using microelectrodes (O₂, pH and pCO₂) and, since late-1990s, air-sea exchange of CO₂ and carbon cycle in coastal and the polar oceans. More recently, his research focuses on the responses of coastal ocean carbon cycle and ecosystem to a changing terrestrial export of carbon and nutrients and interactions between ocean acidification and other environmental stressors. He has also accomplished technical and methodological development in measuring inorganic carbon concentration and stable isotope in aquatic and environmental sciences.