☆ 4.5 Article

Stable isotope characterization of hypoxia-susceptible waters on the Louisiana shelf: Tracing freshwater discharge and benthic respiration

CONTINENTAL SHELF RESEARCH (2012)

期刊

CONTINENTAL SHELF RESEARCH

卷 47, 期 -, 页码 7-15

出版社

PERGAMON-ELSEVIER SCIENCE LTD

DOI: 10.1016/j.csr.2012.07.020

关键词

Stable isotopes; Hypoxia; Gulf of Mexico; Coastal processes; Dissolved inorganic carbon

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Oceanography

资金

NOAA/CSCOR [NA06NOS4780198]
Norman Hackerman Advanced Research Program of the Texas Higher Education Coordinating Board [010366-0053-2007]

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摘要

To examine the sources of freshwater and carbon cycling associated with Louisiana shelf hypoxia, we measured delta O-18 and delta D of water, delta C-13 of dissolved inorganic carbon (DIC), salinity and dissolved oxygen (DO) in waters from 37 stations during April and July of 2008. Seafloor delta O-18 values resemble typical Gulf of Mexico seawater (approximate to 1.1%) while surface waters values are substantially lower (e.g., < -2.0%) due to mixing with river-sourced freshwater. Salinity-delta O-18 regressions for 2008 surface waters show the delta O-18 of discharge to average -6.8% in April and -5.1% in July. Salinity-delta D regressions show the delta D of discharge to be -38% in April and -28% in July. Together these regressions suggest Mississippi discharge was the dominant freshwater source in the study area in April followed by a shift to nearly total Atchafalaya discharge during July, a trend that coincides with summer coastal current reversals. The delta C-13(DIC) of July surface water varies from -5.0 to 1.2% and correlates with salinity indicating mixing of seawater and river water. April surface water shows no relationship with salinity because of the influence of primary productivity, which enriches certain waters in delta C-13(DIC) and DO. The delta C-13(DIC) of subpycnocline water ranges from -2.3 to 0.3%, with lower values reflecting increased respiration. The inshore (10 m depth) delta C-13(DIC)-DO relationship yields a lower y-intercept relative to offshore (20 m depth) bottom waters, possibly indicating a terrestrial source of OC being respired. Mass balance estimations of respired OC do not have the accuracy to quantify any difference between nearshore and offshore locations. Regardless, the delta C-13(DIC)-DO relationships suggest that the delta C-13 of biogenic carbonates may provide a valuable tool for paleo-redox studies in this region. (c) 2012 Elsevier Ltd. All rights reserved.

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Satellite prediction of coastal hypoxia in the northern Gulf of Mexico

Yingjie Li, Samuel V. J. Robinson, Lan H. Nguyen, Jianguo Liu

Summary: The increasing frequency and severity of coastal hypoxia pose a significant threat to marine ecosystems and human well-being. It is crucial to implement continuous and comprehensive monitoring using advanced tools to track spatial and temporal changes in coastal hypoxia. This study utilized satellite imagery and statistical modeling techniques to estimate the spatiotemporal dynamics of hypoxia in the Gulf of Mexico. The results revealed the influence of surface water processes on bottom water hypoxia, highlighting the need for considering time lags in hypoxia studies. Additionally, the study demonstrated the potential of satellite remote sensing for accurate and real-time hypoxia mapping.

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