Abstract
Hypoxic conditions in the coastal waters off Texas (USA) were observed since the late 1970s, but little is known about the causes of stratification that contribute to hypoxia formation. Typically, this hypoxia is attributed to downcoast (southwestward) advection of waters from the Mississippi–Atchafalaya River system. Here, we present evidence for a hypoxic event on the inner shelf of Texas coincident with the presence of freshwater linked to high flow of the Brazos River in Texas. These conclusions are based on hydrographic observations and isotopic measurements of waters on the inner shelf near the Brazos River mouth. These data characterize the development, breakdown, and dispersal of a hypoxic event lasting from June through September 2007 off the Texas coast. Oxygen isotope compositions of shelf water indicate that (1) discharge from the Brazos River was the principal source of freshwater and water column stratification during the 2007 event, and (2) during low Brazos River discharge in 2008, freshwater on the Texas shelf was derived mainly from the Mississippi–Atchafalaya River System. Based on these findings, we conclude that the Mississippi–Atchafalaya River System is not the sole cause of hypoxia in the northern Gulf of Mexico; however, more data are needed to determine the relative influence of the Texas versus Mississippi rivers during normal and low flow conditions of Texas rivers.
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Acknowledgments
This research was supported by a Rapid Response Award by Texas Sea Grant College Program (No. 404538). Partial funding was through a grant to S. DiMarco (NOAA-CSCOR NA06NOS4780198), contribution number NGOMEX-132, and the TAMU Department of Oceanography. Support for the stable isotope analyses was provided by a grant from Texas’ Norman Hackerman Advanced Research Program (No. 010366-0053-2007). The authors thank the dedication of Drs. Matthew Howard, Timothy Dellapena, GERG Marine Technicians, high school students, Scott Hall, Nathaniel Weidner, Josh Andrews, and the cohort of TAMU and TAMUG graduate students for their fortitude and dedication during the August 7, 2007 small boat armada to collect the ocean samples. The authors also thank T. S. Bianchi (TAMU), N. Walker (LSU), A. Quigg (TAMUG), R. Smith (Yale), and M. Fisher (Texas Parks and Wildlife Division) for useful discussions related to this work. The thoughtful comments of four reviewers greatly helped to focus this manuscript. This work is dedicated to the memory of our friend and colleague Professor John W. Morse (Mackenzie et al. 2011).
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DiMarco, S.F., Strauss, J., May, N. et al. Texas Coastal Hypoxia Linked to Brazos River Discharge as Revealed by Oxygen Isotopes. Aquat Geochem 18, 159–181 (2012). https://doi.org/10.1007/s10498-011-9156-x
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DOI: https://doi.org/10.1007/s10498-011-9156-x