05 Nov 2019

Seminar Title: Controls on Surface Water Carbonate Chemistry in North American Ocean Margins

Speaker: Prof. CAI Wei-Jun , School of Marine Science and Policy, University of Delaware, Newark, USA

Date: 5 November, 2019 (Tuesday)
Time: 2:00 pm – 4:00 pm
Venue: Room 2408 (Lift no. 17/18), HKUST, Clear Water Bay, Kowloon

While spatial patterns of carbonate system properties and their variability have been a focus of studies in the global ocean, such large-scale syntheses are lacking for the coastal oceans. Our ability to plan for the impacts of ocean acidification especially in more dynamic coastal domains is still quite limited. Here, we show that in the Atlantic and Gulf coasts total dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are largely controlled by partial gas equilibrium with the atmosphere resulting in low DIC to total alkalinity (TA) ratios and high Ω in warm southern waters and the opposite in cold northern waters, making the latter more vulnerable to acidification. However, pH and the partial pressure of carbon dioxide (pCO2) have no simple spatial pattern. This is because that acid-base equilibrium is not sensitive to temperature changes for DIC and Ω, rendering the control of their meridional distributions to be regulated by the temperature sensitive CO2 solubility. By contrast, the two temperature effects cancel each other out for pH and pCO2, and lead to no simple pattern in their meridional distributions. Within the California Current System in the Pacific coast, however, upwelling brings subsurface waters with high DIC and low temperature, Ω, and pH, while biological CO2 removal works to counteract these patterns. This results in waters with high pH but low Ω, confounding general carbonate system relationships found in open ocean waters and challenging our ability to readily anticipate biological responses to future acidification. Perturbation of the carbonate chemistry from equilibrium with the atmosphere by coastal ocean processes may strongly amplify ocean acidification signals. Finally, I will also discuss changes in the CO2 chemistry seasonal variability patterns in the US eastern ocean margins over the past few decades.

(Host faculty: Prof. GAN Jianping)

All Are Welcome!