HYPOXIA Definition: ~63 µm; 2 mg l -1 ; 1.4 ml l -1 ; 30 %

Transcription

1 HYPOXIA Definition: ~63 µm; 2 mg l -1 ; 1.4 ml l -1 ; 30 % Consequences of hypoxia Reduce habitat for living resources Change biogeochemical processes P released from sediments Denitrification reduced It is a vicious circle helping to sustain eutrophication (Vahtera et al. 2007)

2 Box plot showing the distributions of oxygen thresholds among taxa for (A) LC50 (mg O2/liter), (B) SCL50 (mg O2/liter), and (C) LT50 (h) < 4 days Menhaden kill (Narragansett Bay) Vaquer-Sunyer R., Duarte C. M. PNAS 2008;105:

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5 Hypoxia is a growing global problem Source: Diáz & Rosenberg (2008)

6 Many places oxygen concentrations decline, consequences are known but attribution is often unclear Attribution: Local physical processes (altered hydrodynamics) Local biological processes (eutrophication) Remotely controlled (global change) Natural variability

7 US West Coast: Oregon

8 Chen et al Hypoxia in the East China Sea: One of the largest coastal low-oxygen areas in the world Greater than 12,000 km 2 (or 432 km 3 volume) Seasonal pycnocline Marine Environmental Research Volume 64: Li et al.l, 2010 Large nutrient inputs and phytoplankton seem to contribute to hypoxia in the Changjiang estuary. Journal of Coastal Research 27: 52 62

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10 Figure 5. Vertical distribution of nitrate and nitrite and phosphate concentrations from the central Baltic Sea (monitoring station BY15, eastern Gotland basin) in relation to oxygen conditions (black contours, 0 2 ml O2 L 1). Values are 90-day averages. Vahtera el al., AMBIO 2007

11 The Rowe and Chapman hypotheses describing the physical and biochemical processes that initiate and sustain hypoxia on the Texas-Louisiana Shelf, (Rowe and Chapman, 2002)

12 GU SP TE 400 km 2 1/2 depth < 20 % O2 Saturation Signoret et al., 2006 ECSS

13 BAHIAS-2 Cruise in June 2009 RV ANTEA - IRD 54 stations CTD-OFT Hydrobiology 8 stations Benthic Metabolism (red dots)

14 M03 M01 M02 Tem perature S alin ity O 2 (m g l -1 ) M M M02 M01 M

15 Salinity 30 km 15 km 450 km 'N 8 40'N 8 20'N Bottom O 2 (mg/l) Ciudad Del Carmen Laguna de Terminos Bottom Oxygen 93 00'W 92 40'W 92 20'W 92 00'W 91 40'W 91 20'W > < 1.25

16 SOC In situ and Lab measurements Oxygen concentration (µm) Sonde 1 Sonde 2 Sonde 3 Depth mm) O2 concentration Time

17 Oxygen Content (µm) M M M Oxygen Content (% Sat) 0 M01 M02 M03 M04 M05 M06 M07 M08 0 M01 M02 M03 M04 M05 M06 M07 M Sediment Oxygen Demand (µmol.m -2.h -1 ) Ammonium fluxes (µmol.m -2.h -1 ) M01 M02 M03 M04 M05 M06 M07 M08 0 M01 M02 M03 M04 M05 M06 M07 M08 Depth above bottom (m) M01 M02 M Days SOC explains hypoxia in less than 2 weeks (1/3 water column) even 1 month (1/2 water column)

18 HYPOMEX HYPOMEX research questions What are the onset, expansion and duration of hypoxia in S-GOM? What are the main drivers that lead to and maintain hypoxia? What are the impacts on pelagic and benthic communities and biogeochemical processes? Are there differences between sites (low versus high latitude)? Can we separate anthropogenic from climate forcing? Numerical tools to manage and mitigate hypoxia? (scenarios related to global change)

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20 Usamacinta Grijalva Rivers (10) Rhône river Outflow km 3 y m 3 s * (18 400)** 1710 Length km Bassin area km (3.270 M)** Relief m *ENSO - La Nina summer precipitation **Mississippi River

21 Moyenne mensuelle des Précipitations ENE FEB MAR ABR MAY JUN JUL AGO SEP OCT NOV DIC Fig. 3. Circulation pattern and sea surface height (cm) in the Bay of Campeche, modified from TOPEX (from University of Colorado, Center for Astrodynamic Research: Moorings CTD & P. Processes Benthos Fluxes 2 Cruises J-J 3 weeks 10 miles RV Justo Sierra GU SP TE 18 40

22 TASK 1 Hydrodynamic and biogeochemical characterization of the inputs Sub Task 1.1: Fluxes and offshore distribution of river inputs Sub Task 1.1.a. Freshwater river discharge Sub Task 1.1.b. Fluxes, temporal variability and offshore distribution of materialdischarged by the rivers Sub Task 1.1.c. Long term variations of water and nutrient discharge and model scenarios. SubTask 1.2: Hydrodynamics SubTask 2.1.a.: Temporal measurements SubTask 2.1.b.: Spatial survey SubTask 2.1.c.: Atmospheric forcing TASK 2 Role of the GU plume ecosystem in transforming and transferring particulate and dissolved organic and inorganic riverine input to the benthic system. Field and laboratory experiments SubTask 2.1 : Nutrient fixation and assimilation, downward flux of organic matter and the role of the microbial loop (field campaigns) SubTask 2.2: Effects of simulated changes in nutrients and terrestrial organic matter discharge upon microbial communities (Microcosm experiments). TASK 3 Benthic remineralization of terrestrial and marine organic matter and its temporal variation Sub Task 3.1: The Organic matter elemental composition (C:N:S) and stable isotopic signature Sub Task 3.2 : Quantification of organic matter export, recycling and burial using sediment profiles and core incubations Sub task : Relation of organic matter input to benthic infaunal structure and function Sub task 3.4 : Diagenetic Modelling - TASK 4 Hydrodynamic and coupled biogeochemica circulation Models l SubTask 4.1. : Hydrodynamic modeling SubTask 4.2. : Development of a coupled physical biogeochemical model SubTask 4.3. : Calibration and validation of the coupled models SubTask 4.4. : Diagnostic and prognostic simulations related to hypoxic events and carbon cycling in the context of global change ICMyL C. C. Atm Minéralisation pélagique? MOD CDOM?

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