3. Methods

1
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_at_psu.edu Raymond G. Najjar, Department of
Meteorology and Geosciences, The Pennsylvania
State University, University Park, PA 16802,
email najjar_at_meteo.psu.edu

• Motivation
• 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
• Dissolved oxygen is used in ROMS v2.0 for the
  following reasons
• Oxygen is an excellent tracer of carbon cycling
• There are numerous measurements of oxygen in the
  study region
• U. S. is one of the most highly sampled
  oceanographic regions
• Oxygen can become depleted in the shelf region
• Can affect water quality
• Can increase denitrification
• Can change processing of detrital matter in the
  water column

• 4. Results
• The oxygen anomaly has a distinct seasonality in
  all bins but the nearshore surface water in the
  MAB (Fig. 3)
• The oxygen anomaly also has a distinct
  seasonality in the SAB (Fig. 4) but has a smaller
  amplitude when compared to the MAB
• There is a distinct seasonality in air-sea flux
  of oxygen in both the MAB and the SAB (Fig. 5)
• The air-sea flux of oxygen is larger in the SAB
  than in the MAB

• 5. Conclusions
• In the MAB, away from shore, oxygen is
  supersaturated near the surface in the spring and
  summer, and undersaturated in fall and winter
• At depth in the MAB, oxygen is less
  undersaturated in spring and summer than in fall
  and winter
• The nearshore surface water in the MAB looks to
  be net heterotrophic
• 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
• The deepest layer (60-500 m) in the SAB is very
  undersaturated throughout the year, which is
  possibly due to Antarctic Intermediate Water
• 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
• Oxygen in the SAB outgasses during spring and
  summer and ingasses in the fall and winter
• The noise in air-sea flux is likely due to lack
  of data in the 0-10 m layer in either region

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.
A B C D
MAB 30 m 60 m 100 m 200 m
SAB 20 m 40 m 60 m 500 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
• Evaluate the ROMS v2.0 model
• Use ROMS v2.0 to study periods of oxygen
  depletion along the East Coast shelf
• 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)
• Use the model to try to predict future cases of
  hypoxia and anoxia

Figure 1. U. S. ECoS study region.

• 2. Data and Study Region
• Study region is Mid-Atlantic Bight (MAB) and
  South Atlantic Bight (SAB) (Fig. 1)
• MAB from Cape Cod to Cape Hatteras
• SAB from Cape Hatteras to southeast Florida
• Temperature, salinity, and oxygen concentration
  data from World Ocean Database 2001 (NODC)
• ETOPO2 bathymetry data (NGDC)
• NCEP monthly average wind reanalysis

• 7. References
• 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.
• 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.
• Garcia, H. E., and L. I. Gordon, 1992 Oxygen
  solubility in seawater Better fitting equations.
  Limnol. Oceanogr., 37, 1307-1312.
• 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, 141-164.
• 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.
• 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.
• Stoddard, A., J. E. OReilly, 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.
• Wanninkhof, R., 1992 Relationship between wind
  speed and gas exchange over the ocean. J.
  Geophys. Res., 97, 7373-7382.

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.

• 3. Methods
• Bin data by depth and distance from coast (Fig.
  2)
• Calculate oxygen saturation concentration by the
  method of Garcia and Gordon (1992)
• Oxygen anomaly calculated using
• Monthly average of temperature, salinity, oxygen
  concentration, oxygen saturation concentration,
  and oxygen anomaly calculated
• Transfer velocity calculated using the
  Wanninkhof (1992) relation and the Schmidt number
  in Keeling et al. (1998)
• 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)

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.