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: firstname.lastname@example.org Raymond G. Najjar, Department of Meteorology and Geosciences, The Pennsylvania State University, University Park, PA 16802, email: email@example.com 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 A B • The SAB has a similar cycle to the MAB near the surface C • 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 SAB winter 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- 164. 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.