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Ocean Deoxygenation and Coastal Hypoxia in a Changing World GESAMP 39 18 April 2012 Nancy N. Rabalais et al. Louisiana Universities Marine Consortium nrabalais@lumcon.edu http://www.gulfhypoxia.net

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Goolsby et al. 1999, Rabalais 2002 Point Source 10% Nonpoint Source 90%

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http://water.usgs.gov/nawqa/sparrow/gulf_findings/Alexander et al. 2008 & Nutrient Yields from the Mississippi Basin

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Effects are more far reaching than suspended sediment plume, esp. N & somewhat P New Orleans dominant wind direction Mississippi River Atchafalaya River Hypoxic Area Mississippi River Gulf of Mexico Ecosystem Continuum Source: N. Rabalais

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up to 22,000 km 2 4 - 5 m nearshore to 35 - 45 m offshore 0.5 km nearshore to 100 + km offshore widespread and severe in Jun Sep Source: N. Rabalais, LUMCON Extensive, Severe Low Oxygen Waters

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April 29 rain June 18 rain

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2011 2010 maximum average minimum Mississippi River Discharge Hydrographs Tarbert Landing, MS (1930-2011) Cubic feet per second x 1000 * Trans C&F Shelfwide * Heterosigma bloom

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Station:C6C, approx 15 miles south of LUMCON (29 o 52.12 N / 90 o 29.42 W) Date: March 21, 2011 Bottom Depth: 19.5 m Bloom Color: Greenish-brown Salinity: 28.7 psu Chlorophyll: 117 ug/L Oxygen: 204% oxygen saturation DO: 16-17 mg/L Heterosigma akashiwo

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Predicting Hypoxia in summer (nitrate-N flux in May, year) Turner et al. 2006

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LA TXMSAL Mississippi River Atchafalaya River Distribution of bottom-water dissolved oxygen July 18-21 (east of the Mississippi River delta) and July 24-30 (west of the Mississippi River delta), 2011. Data source: NN Rabalais, Louisiana Universities Marine Consortium, and RE Turner, Louisiana State University. Funding source: National Oceanic and Atmospheric Administration, Center for Sponsored Coastal Ocean Research. http://www.gulfhypoxia.net

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June 18, 2011 rain

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Anthropogenic activities Vertical carbon flux Nutrient-enhanced productivity Physical environment (Stratification +) (Oxygen saturation -) (Current shifts) (Tropical storms) Nutrient loads (+) (-) Hydrologic cycle (+) (-) Water temperature (mostly +) Bottom-water hypoxia Climate variability climate change Sedimentary carbon and nutrient pools Sea level rise (+) Harmful & noxious algal blooms Winds Reactive N (mostly +) Biological responses (Metabolic rates mostly +) (Primary production +) (Respiration +) Rabalais et al. 2009, 2010

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(modified by N. Rabalais; Galloway and Cowling 2002; Boesch 2002) Developing Countries Developed Countries They are increasing

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The Future Climate Change Biofuels Increased Population Increased Agribusiness Increased Atmospheric Deposition