PARENT SESSION
Contributed Oral Session 27: Marine Populations Under Harvest
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal

Gulf of Mexico hypoxia: A declining threshold.

Stow, Craig^*,1, Qian, Song², Craig, Kevin², ¹ Department of Environmental Health Sciences, Columbia, SC, USA² Nicholas School of the Environment and Earth Sciences, Durham, NC, USA

ABSTRACT- We examined 21 years of data (1982-2002), collected and provided by the NOAA National Marine Fisheries Service Pascagoula laboratory from their annual Southeast Area Monitoring and Assessment Program (SEAMAP) summer survey in the hypoxic region of the Gulf of Mexico. Our analysis indicates that the top:bottom salinity difference is an important predictor of hypoxia, exhibiting a threshold, where the probability of hypoxia increases rapidly, at approximately 4.1 ppt. At salinity differences less than 4.1 ppt the mean DO concentration was 5.5 mg/L and the probability of hypoxia 7.1%, while above 4.1 ppt the mean DO concentration was 3.3 mg/L and the probability of hypoxia 32.6%. Using a Bayesian change-point model we show that this stratification threshold decreased from 1982-2002, indicating the degree of stratification needed to induce hypoxia has gone down. Though this declining threshold does not link hypoxia and nutrient loading it does implicate a long-term factor transcending yearly flow-induced stratification differences. Concurrently, our analysis indicates that over this period surface temperature increased, while surface dissolved oxygen levels decreased, suggesting that factors in addition to nutrient inputs may be influencing the incidence of hypoxia in the bottom water.

Key words: coastal hypoxia, gulf of mexico, threshold, bayesian