INTERDISCIPLINARY APPROACH

The study of air-sea gas exchange is multifaceted and challenging due to the range of time and space scales over which the dominant processes occur. Interfacial and bubble-mediated gas exchange are dependent on both the sea-state and air-sea concentration gradient, which can be highly variable and often relates to ocean temperature and local biochemistry.

My research objectives are: 1) further quantify the roles of interfacial and bubble-mediated gas flux as they relate to both the sea-state and seasonal/mesoscale biological dependencies; 2) investigate processes by which mesoscale ocean variability impacts surface-to-deep ocean carbon sequestration.

This approach requires an interdisciplinary understanding of topics ranging the mechanics of wave breaking and energy dissipation at the wavy air-sea interface to carbon fixation by phytoplankton and export production. The cartoon to the right highlights these efforts.

 

RESEARCH SIGNIFICANCE AND MOTIVATION

Covering over 70% of the Earth's surface, the oceans are a major player in the global carbon budget. Over decadal time scales the oceans act as a significant sink of both natural and anthropogenic atmospheric carbon dioxide (CO2).

For centuries prior to the industrial age (1000 - 1750) the atmospheric concentration of CO2 was relatively stable with values between 275 and 285 parts per million (ppm) however, between 1750 and 2005, the concentration of atmospheric CO2 has jumped by 36% to around 380 ppm (Forster et al., 2007). The increase in atmospheric CO2 is due primarily to anthropogenic activity (IPCC, 2007). With the human-induced increase in atmospheric CO2, the surface ocean will slowly equilibrate resulting in an average net, oceanic uptake. This result is already playing-out as over the past 200 years 48% of anthropogenic CO2 produced was deposited into the oceans (Millero, 1996) and estimates from 2000 indicate that the ocean's were capable of extracting 1.8 PgC from the atmosphere, representing 20% of the anthropogenic emissions produced in that year (Metzl, 2008). Recent estimates suggest atmospheric CO2 concentrations could be as high as 450 ppm if the anthropogenic sources were not mitigated by oceanic uptake (Sabine et al., 2004; Doney et al., 2009). The top figure on the right shows how atmospheric CO2 concentrations have been increasing (red), resulting in an increase in seawater partial pressure of carbon dioxide (pCO2) and a decrease in seawater pH.

Given the recent anthropogeic inceases in CO2, a full understanding of air-sea gas transfer and carbon sequestration as they relate to the physical and biological environment has become a pressing and time-sensitive issue.

The Southern Ocean (SO) is an ideal region to study gas exchange processes as the dominant drivers are seasonally out of phase and the pCO2 gradient is large. The bottom figure on the right shows the 2001-2012 seasonal climatologies of cholorphyll concentrations (mg/m3) as observed from MODIS on the NASA/Aqua platform (Top Row) and the 2001-2011 seasonal climatologies of the 10 meter wind speed, U10, (m/s) from NOAA/GFS Re-Analysis data (Bottom Row). Left Column: SO summer months(DJF). Right Column: SO winter months (JJA). The expectation is for the CO2 flux to be dominated by physical processes in the SO winter while mesoscale variability resulting in physical-biological interactions, along the a seasonal increase in solar irradiance, likely play a larger role during DJF.

   
RESEARCH TOPICS