Recurrence of extensive hypoxia on the Louisiana shelf during the summer has strong impacts to the marine life and ecosystems. The formation of hypoxia depends on the photosynthesis, chemolithotrophic production and metabolism in the water and sediment. It also depends on the physical processes of transport, mixing and air-sea exchanges. All those processes are spatially and temporally dependent. A high resolution 3D hypoxia model, therefore, is desirable for realistic simulation to better understand the processes of hypoxia formation at the region. To do so, an 1D model developed by the EPA for hypoxia simulation (Eldridge and Roelke, 2010) has been extended to 3D and integrated with a circulation model on 2-km horizontal grids and 20 vertical layers on the shelf that covers the Louisiana shelf. The circulation model is forced with real-time wind, air pressure, heating/cooling, salinity flux and tides. The open boundary conditions are derived from a regional model that covers the Gulf of Mexico (IASNFS: Ko et al., 2003). The important river runoffs from 95 rivers and streams based on USGS and Army Corp of Engineers daily measurement are included in the model. The hypoxia model consists of a plankton food web model that has 6 phytoplankton groups and 1 zooplankton group and a multi-element diagenetic model that traces oxygen, nitrogen, phosphate, carbon and various organic matters.

Multi-year model simulation has been conducted, initialized with NODC monthly DO, DIN and DIP climatology. The monthly climatology is also used for the open boundary conditions. Preliminary result demonstrates summer occurrence of hypoxia on the shelf as observed but it also shows high temporal variation on the hypoxia intensity and extent often associated with rapid wind change, particularly, during a hurricane. The implications of the strengths and limitations of the model for simulating hypoxia will be discussed.

References:

Eldridge, P.M, and D.L. Roelke, 2010: Origins and scales of hypoxia on the Louisiana shelf: importance of seasonal plankton dynamics and river nutrients and discharge, Ecological Modeling, 221, 1028-1042.

Ko, D.S., R.H. Preller, and P.J. Martin, 2003: An experimental real-time Intra-Americas Sea Ocean Nowcast/Forecast System for coastal prediction, Proceedings, AMS 5th Conference on Coastal Atmospheric and Oceanic Prediction and Processes, 97-100.