Summary:
Overview
Dr. Wei-Jun Cai at the University of Delaware and Dr. Xinping Hu at Texas A&M Corpus Christi were awarded an RFP-II grant at $443,377 to conduct the RFP-II project entitled “Dynamics of Dissolved Inorganic Carbon and Dissolved Oxygen Following Natural or Manmade Petroleum Carbon Release into Marine Environments”. The project consisted of 4 institutions and 5 research team members.
During this study, the following research questions were addressed:
- Can we still observe lingering effects of oil leak in the northern Gulf of Mexico continental shelf?
- How do dissolved inorganic carbon (DIC) and Dissolved Oxygen (DO) covary during controlled oil spill, and what group of organic compounds will be remineralized?
- As a product, a standard protocol will be constructed in terms of evaluating the degradation of petroleum carbon and associated oxygen dynamics, i.e., DIC can be used as a constraint in addition to oxygen measurement.
- Whether there is a detectable basin-wide change in DO and DIC ratio, as a result of the 2010 oil spill.
- Finally, do natural oil and gas seepages modify the chemical evolutions of DIC and oxygen in the Gulf of Mexico? In other words, whether the DO consumption to DIC generation ratio in the Gulf of Mexico is clearly different from other U.S. Atlantic ocean margins.
Research Highlights
Dr. Cai’s and Dr. Hu’s research, which included 9 outreach products and activities, resulted in 8 peer-reviewed publications and 4 datasets being submitting to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be available to the public. Dr. Cai and Dr. Hu engaged 3 PhD and 5 Masters students over the award period. Significant outcomes of his research according to GoMRI Research Theme are highlighted below.
Theme 2:
- Finished synthesizing multiple years of data (hydrographic, nutrients, total dissolved oxygen or DO, total dissolved inorganic carbon or DIC and total alkalinity or TA) using an improved extended optimum multi-parameter (OMP) analysis. Dr. Jianhong Xue was the main person working on this effort, and regular teleconferences were made between her and Cai, Hu and Huang to discuss the progress. The main purposes of this effort were to constrain the relative rates of respiration and biogeochemical patterns and elemental ratios in bottom waters from spring to summer. Dr. Cai’s team found that the DIC, released from bottom water through organic carbon remineralization via aerobic respiration and denitrification, increased steadily from April to July, peaked in August, and dropped slightly in September. This temporal pattern reflects an increase of organic carbon (OC) supply from the plume and the subsequent DIC release through OC respiration. They also found that Corg/N/P/-O2 remineralization ratios generally followed the Redfield ratio of
106/16/1/138. This paper has been published in the journal – Journal of Geophysical Research – Oceans. - Partially funded by the GOMRI funding, Hu’s group analyzed long-term carbonate chemistry in northwestern Gulf of Mexico estuaries and adjacent coastal water. In this study, the team concluded that these estuaries are undergoing gradual acidification. This manuscript was published in the journal – Environmental Science and Technology and the finding was featured in two news reports in Houston Chronicle and Galveston County Daily News, respectively. Hu was also interviewed by NPR Corpus Christi affiliate KEDT radio.
- The JGR-Ocean paper (Huang et al. 2015) led by postdoc, Wei-Jen Huang, summarizes the spatial and season patterns of surface water pCO2 and water-air CO2 flux in the northern Gulf of Mexico. This is the first such comprehensive report in this region. Results from this study showed that the river plume was a strong CO2 sink due to intensive primary production and that the entire nGOM was a weak sink of CO2. Seasonal and temporal signals were variable, switching from being a strong CO2 sink during spring and early summer to a source during the fall and winter when the water column is mixed.
- Another paper also led by postdoc Wei-Jen Huang, Continental Shelf Research (2015), analyzed the water column biochemistry patterns of dissolved inorganic carbon (DIC) and Alkalinity. In particular, it illustrated the response of inorganic carbon distributions and dynamics to upwelling-favorable winds on the northern Gulf of Mexico during summer.
- A paper led Dr. Hu and included Cai, Rabalais, and Xue has been published in a special issue of Deep-Sea Research II (2014) to examine the dynamics of oxygen and carbon in the past seven years (2006-2013) in the northern Gulf of Mexico shelf.
