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-Väisälä 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 87úW, 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-
Väisälä 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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/5018 |
| Date | 25 April 2007 |
| Creators | Belabbassi, Leila |
| Contributors | Nowlin, Worth |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 4810104 bytes, electronic, application/pdf, born digital |
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