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Circulation, biogeochemistry and carbon cycling in ocean margins
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Towards predicting the largest Louisiana hypoxic area: an analysis of a coupled physical-biogeochemistry model results from 1985-2009
Monday 7th @ 1010-1030, Concert Hall
Yang Feng* , South China Sea Institute of Oceanography &
NASA Jet Propulsion Laboratory
Steven F. DiMarco, Texas A&M University, College Station
Karthik Balaguru, Marine Sciences Laboratory, Pacific Northwest Laboratory, Sequim, Washington, USA
Huijie Xue, Dalhousie University
Presenter Email: yfeng1982@126.com |
| The extent of hypoxic area on the Louisiana shelf has been measured once per year during July since 1985. The measured area was presumed to be the seasonal maximum in different years and was used to derive a relationship with the Mississippi-Atchafalaya riverine nitrogen loading and to make management strategies. However, the measured hypoxic area may or may not be the largest of the year, which complicated the nutrient-hypoxia relationship. In this study, we analysed 25 years of simulations from a coupled physical-biogeochemical numerical circulation model. An EOF analysis on the model-derived hypoxic fields reveals that the dominant pattern is east-west, with strong seasonality in June, July and August. A single linear regression model was performed to examine the explained power of nutrients to hypoxia. It shows that nutrients can explain about 30%-45% measured hypoxia, less than 50%-70% maximum hypoxia. The recent Gulf of Mexico Hypoxia Task Force set a goal to reduce the 5-yr moving average size of the Gulf hypoxic zone to less than 5000 km2 by 2035 and suggested that a 20% reduction in nitrogen loading by 2025 to reach that goal. Our result suggested that the 20% reduction might need a re-estimation once the real largest hypoxic area could be known. A further cross-correlation analysis suggested that potential predictors for largest hypoxia are: 3-months lagged Mississippi River discharge; 2-months lagged shelf-wide surface chlorophyll maximum; 1-month lagged wind direction; 0-month lagged wind intensity; 0-month lagged surface salinity, all of which are readily available from satellite observations. |
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