NGOMEX (2009-2014) - Mechanisms Controlling Hypoxia: Integrated Causal Modeling

The physical and biogeochemical processes that control and maintain the hypoxic zone in the northern Gulf of Mexico are complex and their relative strengths are known to vary temporally and spatially at many scales. Although close to the Mississippi River Delta, the mechanisms that maintain and sustain the hypoxia are mostly driven by biological processes, further downstream the dominant controlling processes are mostly physical as currents and winds combine to break down the vertical stratification necessary to sustain the low dissolved oxygen. Because the eastern region of the shelf, between 91°W and 89°W, is almost always hypoxic in mid-summer, it is variability of the western region, between 91°W, the Texas border and west, that largely controls the total size of the hypoxic area in a given year. Investigations of water quality data from coastal Texas have shown that hypoxic conditions frequently occur there and with variable driving factors. Therefore, understanding the interactions of the physical, biological, and geochemical processes and their variability throughout the shelf is critical for a comprehensive description of the mechanisms that control hypoxia.

A comprehensive, integrated, and multidisciplinary study of the Texas-Louisiana Shelf is proposed that includes multidisciplinary moored time-series observations, two seasonal interdisciplinary process cruises near the mooring locations, two summertime shelf-wide surveys using a undulating towed sensor (to determine spatial extent of hypoxia), and remote sensing observations. The field component is designed to complement, and provide rates and other parameters necessary for the initiation, control, and skill assessment of a realistic coupled three-dimensional hydrodyamic-biological-geochemical-sediment numerical modeling and statistical (multivariate) modeling elements. A diagenetic model of the upper seabed, sediment resuspension, and surface gravity waves will be coupled to this model as previous studies have indicated that seabed processes can impact oxygen consumption and contribute to the variability of the hypoxic area.

The principal scientific objective of this study is to build upon a previously funded (2003- 2009) and proven realistic coupled hydrodyamic-biological-geochemical-sediment numerical model of the northern Gulf of Mexico that is capable of resolving the dominant oceanographic processes that control the timing, duration, and severity of hypoxia of the region. Observations and modeling activities will be coordinated with relevant and existing federal and state funded operational and regional efforts and other regional investigators through active data exchange and participation and sample collection on appropriate and available cruises of opportunity.

PIs:

Dr. Steven F. DiMarco (Lead-PI, TAMU), Dr. Thomas S. Bianchi, Dr. Piers Chapman, Dr. Michael Dagg (LUMCON), Dr. Katja Fennel (Dalhousie), Dr. David Forrest (VIMS), Dr. Norman L. Guinasso, Jr., Dr. Courtney Harris (VIMS), Dr. Robert Hetland, Dr. Matthew K. Howard, Dr. Heath Mills, Dr. Antonietta Quigg (TAMUG), Dr. Nan Walker (LSU), Dr. Kehui (Kevin) Xu (Coastal Carolina Univ.).