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Slide 1 - Center for Coastal Physical Oceanography


									                             Dissolved Oxygen in U. S. East Coast Continental Shelf Waters (Paper #OS25G-24)
                                                                       John E. Siewert, Department of Meteorology, The Pennsylvania State University, University Park, PA 16802, email:
                                            Raymond G. Najjar, Department of Meteorology and Geosciences, The Pennsylvania State University, University Park, PA 16802, email:

1. Motivation                                                                                                                                                                                        4. Results
• The US ECoS team is developing the Regional Ocean Modeling System (ROMS                                                                                                                            • The oxygen anomaly has a distinct seasonality in all bins but the nearshore surface
  v2.0) to study the role of continental shelves on the carbon cycle                                                                                                                                 water in the MAB (Fig. 3)
• Dissolved oxygen is used in ROMS v2.0 for the following reasons                                                                                                                                    • The oxygen anomaly also has a distinct seasonality in the SAB (Fig. 4) but has a
  • Oxygen is an excellent tracer of carbon cycling                                                             0-30 m
                                                                                                                                                                                                     smaller amplitude when compared to the MAB
                                                                                                                                                                30-60 m
  • There are numerous measurements of oxygen in the study region                                                                                                                                    • There is a distinct seasonality in air-sea flux of oxygen in both the MAB and the SAB
                                                                                                                                                                                                     (Fig. 5)
     • U. S. is one of the most highly sampled oceanographic regions
                                                                                                                                                                                                     • The air-sea flux of oxygen is larger in the SAB than in the MAB
  • Oxygen can become depleted in the shelf region
     • Can affect water quality                                                                                                                                                                      5. Conclusions
     • Can increase denitrification                                                                                                                                                                  • In the MAB, away from shore, oxygen is supersaturated near the surface in the spring
                                                                                                                                                                                                     and summer, and undersaturated in fall and winter
     • Can change processing of detrital matter in the water column
                                                                                                                                                                                                     • At depth in the MAB, oxygen is less undersaturated in spring and summer than in fall
                                                                                                                                                                                                     and winter
                                            Inner        Mid       Outer           Slope
                                                                                                            60-100 m                                       100-200 m                                 • The nearshore surface water in the MAB looks to be net heterotrophic
                                                               B                                                                                                                                     • The SAB has a similar cycle to the MAB near the surface
                                                                                                                                                                                                     • At depth the SAB data are a little noisier, probably due to lack of data
                                                                               D             Figure 3. Oxygen anomaly in the inner shelf (upper left), mid-shelf (upper right), outer shelf (lower
                                                                                             left), and slope (lower right) waters in the MAB. Colors correspond to bins as defined in Figure 2.     • The deepest layer (60-500 m) in the SAB is very undersaturated throughout the year,
                      MAB                                                                                                                                                                            which is possibly due to Antarctic Intermediate Water
                                               A          B        C       D

                                      MAB    30 m       60 m   100 m 200 m                                                                                                                           • The MAB seems to have an overall net outgassing of oxygen throughout the year
                                                                                                                                                                                                     away from shore, but near the shore, there is an overall net ingassing
                                      SAB    20 m       40 m   60 m    500 m
                                                                                                                                                                                                     • Oxygen in the SAB outgasses during spring and summer and ingasses in the fall and
                                                                                                                  0-20 m
                                                                                                                                                                   20-40 m                           • The noise in air-sea flux is likely due to lack of data in the 0-10 m layer in either region
                                      Figure 2. Schematic of binning process. Lettered
                                      points show isobaths that correspond to distances                                                                                                              6. Future Work
Figure 1. U. S. ECoS study region.    away from the coast. Table shows these isobaths for
                                      the MAB and SAB color coded as in Figure 1.                                                                                                                    • Include data from other databases (HydroBase, MEDS)
                                                                                                                                                                                                     • Do quality control and error estimation on the data
                                                                                                                                                                                                     • Separate the MAB and the SAB into subareas
2. Data and Study Region
                                                                                                                                                                                                     • Evaluate the ROMS v2.0 model
• Study region is Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) (Fig. 1)
                                                                                                                                                                                                     • Use ROMS v2.0 to study periods of oxygen depletion along the East Coast shelf
   • MAB from Cape Cod to Cape Hatteras
                                                                                                                                                                                                        • Look at historical cases and recreate them using the model (e.g. Falkowski et al.
                                                                                                                                                                             60-500 m
   • SAB from Cape Hatteras to southeast Florida                                                              40-60 m                                                                                   1980; Stoddard et al. 1986; Rabalais and Turner 2001; Buzzelli et al. 2002)
• Temperature, salinity, and oxygen concentration data from World Ocean Database                                                                                                                        • Use the model to try to predict future cases of hypoxia and anoxia
2001 (NODC)
                                                                                                                                                                                                     7. References
• ETOPO2 bathymetry data (NGDC)
                                                                                                                                                                                                     • Buzzelli, C. P., R. A. Luettich, S. P. Powers, C. H. Peterson, J. E. McNinch, J. L. Pinckney, and H. W. Paerl, 2002:
• NCEP monthly average wind reanalysis                                                       Figure 4. Oxygen anomaly in the inner shelf (upper left), mid-shelf (upper right), outer shelf (lower   Estimating the spatial extent of bottom-water hypoxia and habitat degradation in a shallow estuary. Mar. Ecol.: Prog.
                                                                                             left), and slope (lower right) waters in the SAB. Colors correspond to bins as defined in Figure 2.     Ser., 230, 103-112.

3. Methods                                                                                                                                                                                           • Falkowski, P. G., T. S. Hopkins, and J. J. Walsh, 1980: An analysis of factors affecting oxygen depletion in the New
                                                                                                                                                                                                     York Bight. J. Mar. Res., 38, 479-506.

• Bin data by depth and distance from coast (Fig. 2)                                                                                                                                                 • Garcia, H. E., and L. I. Gordon, 1992: Oxygen solubility in seawater: Better fitting equations. Limnol. Oceanogr.,
                                                                                                                                                                                                     37, 1307-1312.
• Calculate oxygen saturation concentration by the method of Garcia and Gordon (1992)                                                                                                                • Keeling, R. F., B. B. Stephens, R. G. Najjar, S. C. Doney, D. Archer, and M. Heimann, 1998: Seasonal variations in

• Oxygen anomaly calculated using O2   O2   O2 sat
                                                                                                                                                                                                     the atmospheric O2/N2 ratio in relation to the kinetics of air-sea gas exchange. Global Biogeochem. Cycles, 12, 141-

 Monthly average of temperature, salinity, oxygen concentration, oxygen saturation                                                                                                                   • Najjar, R. G. and R. F. Keeling, 2000: Mean annual cycle of the air-sea oxygen flux: A global view. Global
                                                                                                                                                                                                     Geochemical Cycles, 14, 573-584.
concentration, and oxygen anomaly calculated                                                                                                                     Slope    Outer Shelf
                                                                                                                Inner Shelf                                                                          • Rabalais, N. N., and R. E. Turner, 2001: Hypoxia in the northern Gulf of Mexico: Description, causes, and change.
• Transfer velocity calculated using the Wanninkhof (1992) relation and the Schmidt                                              Mid-Shelf                                                           Pages 1-36 in Rabalais, N. N., Turner, R. E., eds., Coastal Hypoxia: Consequences for Living Resources and
number in Keeling et al. (1998)                                                                                                                                                                      Ecosystems, Coastal and Estuarine Studies No. 58, American Geophysical Union, Washington, DC.
                                                                                                                                                                                                     • Stoddard, A., J. E. O’Reilly, T. E. Whitledge, T. C. Malone, and J. F. Hebard, 1986: The application and
• Oxygen anomaly converted from μmol/kg to mol/m3 using constant seawater density of                                                                                                                 development of a compatible historical data base for the analysis of water quality management issues in the New
1025 kg/m3                                                                                                                                                                                           York Bight. Oceans ’86, 3, 1030-1035, IEEE Press, Piscataway, NJ.
                                                                                             Figure 5. Air-sea flux of oxygen in the 0-10 m layer of the MAB (left) and the SAB (right). Colors      • Wanninkhof, R., 1992: Relationship between wind speed and gas exchange over the ocean. J. Geophys. Res., 97,
• Air-sea flux calculated as in Najjar and Keeling (2000)                                    correspond to distance from the coast as defined by Figure 2.                                           7373-7382.

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