Examination of the relationship of river water to occurrences of bottom water with reduced oxygen concentrations in the northern Gulf of Mexico

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Title: Examination of the relationship of river water to occurrences of bottom water with reduced oxygen concentrations in the northern Gulf of Mexico
Author: Belabbassi, Leila
Abstract: Six years of comprehensive data sets collected over the northern continental shelf and upper slope of the Gulf of Mexico during the LATEX -A and NEGOM -COH programs showed that low -oxygen waters ( <2 .4 mL ? ? ? ?L -1 ) are found only in spring and summer and only in water depths between 10 and 60 m . Four regions in the northern Gulf show considerable differences in the occurrence of low -oxygen waters . Lowoxygen waters are observed almost exclusively in regions subject to large riverine influences : the Louisiana and Mississippi -Alabama shelves . Hypoxic waters (oxygen concentrations <1 .4 mL ? ? ? ?L -1 ) are found only over the Louisiana shelf . No low -oxygen water is found over the Florida shelf which has minimum riverine influence . Lowoxygen water is found at only one station on the Texas shelf ; this is during spring when the volume of low -salinity water is at maximum . The distributions of low -salinity water influenced the different distributions of low -oxygen and hypoxic waters in the four regions . Low -oxygen occurrences are clearly related to vertical stratification . Lowoxygen occurred only in stable water columns with maximum Brunt -V ? ? ? ?is ? ? ? ?l ? ? ? ? frequency (Nmax ) greater than 40 cycles ? ? ? ?h -1 . When Nmax exceeded 100 cycles ? ? ? ?h -1 in summer over the Louisiana shelf , oxygen concentrations dropped below 1 .4 mL ? ? ? ?L -1 , and the bottom waters became hypoxic . Salinity is more important than temperature in controlling vertical stratification . Locations where temperature influence was larger were found in summer in water depth greater than 20 m over the Louisiana shelf , along the near shore areas of the Mississippi -Alabama shelf west of 87 ? ? ? ?W , and in the inner shelf waters of the Texas shelf . The extent of oxygen removal at the bottom of these stable water columns is reflected in the amount of remineralized silicate . Silicate concentrations are highest closest to the Mississippi River Delta and decrease east and west of the Delta . EOF analyses show that more than 65 % of the oxygen variance is explained by the first mode . The amplitude functions of the first EOF modes of bottom oxygen , water column Brunt - V ? ? ? ?is ? ? ? ?l ? ? ? ? maxima , and bottom silicate are well correlated , indicating that much of the variance in bottom oxygen is explained by water column stratification and bottom remineralization .
URI: http : / /hdl .handle .net /1969 .1 /5018
Date: 2007-04-25

Citation

Examination of the relationship of river water to occurrences of bottom water with reduced oxygen concentrations in the northern Gulf of Mexico. Available electronically from http : / /hdl .handle .net /1969 .1 /5018 .

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