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: jes448@psu.edu
Raymond G. Najjar, Department of Meteorology and Geosciences, The Pennsylvania State University, University Park, PA 16802, email: najjar@meteo.psu.edu
1. Motivation
4. Results
• The US ECoS team is developing the Regional Ocean Modeling System (ROMS
v2.0) to study the role of continental shelves on the carbon cycle
• The oxygen anomaly has a distinct seasonality in all bins but the nearshore surface
• 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
smaller amplitude when compared to the MAB
• Oxygen is an excellent tracer of carbon cycling
water in the MAB (Fig. 3)
0-30 m
30-60 m
• There is a distinct seasonality in air-sea flux of oxygen in both the MAB and the SAB
(Fig. 5)
• There are numerous measurements of oxygen in the study region
• 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
• Can change processing of detrital matter in the water column
and summer, and undersaturated in fall and winter
Inner
Mid
• At depth in the MAB, oxygen is less undersaturated in spring and summer than in fall
and winter
Slope
Outer
A
B
• The nearshore surface water in the MAB looks to be net heterotrophic
100-200 m
60-100 m
• 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
MAB
A
B
C
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.
D
MAB
30 m
60 m
100 m 200 m
SAB
20 m
40 m
60 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
500 m
• Oxygen in the SAB outgasses during spring and summer and ingasses in the fall and
winter
SAB
0-20 m
Figure 1. U. S. ECoS study region.
• The deepest layer (60-500 m) in the SAB is very undersaturated throughout the year,
which is possibly due to Antarctic Intermediate Water
• The noise in air-sea flux is likely due to lack of data in the 0-10 m layer in either region
20-40 m
Figure 2. Schematic of binning process. Lettered
points show isobaths that correspond to distances
away from the coast. Table shows these isobaths for
the MAB and SAB color coded as in Figure 1.
6. Future Work
• 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
• SAB from Cape Hatteras to southeast Florida
60-500 m
40-60 m
• Temperature, salinity, and oxygen concentration data from World Ocean Database
2001 (NODC)
• Use the model to try to predict future cases of hypoxia and anoxia
7. References
• ETOPO2 bathymetry data (NGDC)
• NCEP monthly average wind reanalysis
• Look at historical cases and recreate them using the model (e.g. Falkowski et al.
1980; Stoddard et al. 1986; Rabalais and Turner 2001; Buzzelli et al. 2002)
Figure 4. Oxygen anomaly in the inner shelf (upper left), mid-shelf (upper right), outer shelf (lower
left), and slope (lower right) waters in the SAB. Colors correspond to bins as defined in Figure 2.
• Buzzelli, C. P., R. A. Luettich, S. P. Powers, C. H. Peterson, J. E. McNinch, J. L. Pinckney, and H. W. Paerl, 2002:
Estimating the spatial extent of bottom-water hypoxia and habitat degradation in a shallow estuary. Mar. Ecol.: Prog.
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)
• Oxygen anomaly calculated using O2   O2   O2 sat
• Keeling, R. F., B. B. Stephens, R. G. Najjar, S. C. Doney, D. Archer, and M. Heimann, 1998: Seasonal variations in
the atmospheric O2/N2 ratio in relation to the kinetics of air-sea gas exchange. Global Biogeochem. Cycles, 12, 141164.
Monthly average of temperature, salinity, oxygen concentration, oxygen saturation
concentration, and oxygen anomaly calculated
• 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.
• Transfer velocity calculated using the Wanninkhof (1992) relation and the Schmidt
number in Keeling et al. (1998)
Slope
Outer Shelf
Inner Shelf
Mid-Shelf
• Stoddard, A., J. E. O’Reilly, T. E. Whitledge, T. C. Malone, and J. F. Hebard, 1986: The application and
development of a compatible historical data base for the analysis of water quality management issues in the New
York Bight. Oceans ’86, 3, 1030-1035, IEEE Press, Piscataway, NJ.
• Oxygen anomaly converted from μmol/kg to mol/m3 using constant seawater density of
1025 kg/m3
• Air-sea flux calculated as in Najjar and Keeling (2000)
• Rabalais, N. N., and R. E. Turner, 2001: Hypoxia in the northern Gulf of Mexico: Description, causes, and change.
Pages 1-36 in Rabalais, N. N., Turner, R. E., eds., Coastal Hypoxia: Consequences for Living Resources and
Ecosystems, Coastal and Estuarine Studies No. 58, American Geophysical Union, Washington, DC.
Figure 5. Air-sea flux of oxygen in the 0-10 m layer of the MAB (left) and the SAB (right). Colors
correspond to distance from the coast as defined by Figure 2.
• Wanninkhof, R., 1992: Relationship between wind speed and gas exchange over the ocean. J. Geophys. Res., 97,
7373-7382.