In the early 1980's, interest developed in the circulation in canyons. This interest was the result of a study in a narrow canyon near Vancouver Island, British Columbia (Freeland and Denman, J. Marine Res., 40, 1,069--1,093, 1982), which showed that the canyon acted as a conduit moving water, which was originally deep and offshore, onto the shelf. The vertical and horizontal distances over which this upwelling occurred were much greater than those observed in classical wind-driven upwelling systems. Other observational studies (Hotchkiss and Wunsch, Deep Sea Res., 29, 415--442, 1982) indicated that deep circulation in canyons responded rapidly to changes in surface wind stress. Later observations were less clear about the effect of these canyons on the alongshore flow; in some cases, the coastal flow crossed the canyons apparently oblivious to their presence, while in other cases the alongshore flow was disrupted by pools of dense water that appeared on the shelf near the head of the canyons. This exchange between shelf and offshore waters has important implications for biological and chemical processes of continental shelf systems.
A consensus has formed among the cognoscenti on the dynamical processes responsible for the circulation within submarine canyons. The critical factor is that submarine canyons are narrow, in general, being 5 to 15 km in width, relative to the internal radius of deformation, which is a natural scale for horizontal gradients in rotating, stratified fluids. For canyons that are narrower than this scale (nearly always true), the influence of the Coriolis force is reduced and the flow converts from a geostrophic to a pressure-driven circulation. That is, as the system becomes narrow, the flow tends to be down the pressure gradient instead of transverse to the pressure gradient.
The remaining piece to the puzzle is the origin of the coastal pressure gradient. Almost all continental shelves have a large-scale flow parallel to the coast, which is driven by buoyancy flux from rivers or by large-scale winds. Since this flow is geostrophically balanced, there is a pressure gradient across the shelf, which is aligned, generally, with the axis of the canyons and can drive circulation in the canyons.
There have been several observational studies, based on current meters and hydrography, that have shown a correlation between flow on the shelf and circulation along the axis of a canyon. As is the case in oceanography, the correlations are not perfect, which indicates that other processes are at work. So, this description of the pressure-driven flow is, thus far, a general framework rather than a final answer.
JOHN KLINCK'S (associate professor of CCPO) interest in the dynamics of circulation in submarine canyons began with these observations, which indicated a multi-level circulation pattern. Current work on circulation dynamics uses 3-D numerical models to look at the interaction of alongshelf flow with an idealized canyon. The shape of the canyon is gaussian and the geometry (width, length, and depth) is appropriate for conditions on the eastern coast of the U.S. A series of numerical experiments considered several different choices of initial stratification and direction of coastal flow. The simulations were started from rest and the alongshore flow was built up over a period of six days. Simulations lasted up to 100 days, but the basic circulation pattern around the canyon developed by about 10 days.
The simulations show that the direction of the alongshore flow, and hence the direction of the cross-shelf pressure gradient, has the most important effect on the resulting circulation. When the pressure gradient drives offshore flow in the canyon, there is mild downwelling in the canyon but only a very weak exchange between the shelf and the deep ocean. However, when the pressure gradient drives onshore flow, there is strong upwelling and a persistent flux of deeper water up onto the shelf.
These simulations are useful in revealing processes associated with flow in submarine canyons, but additional dynamics and forcing remain to be added to the circulation model. Future work will focus on transient coastal flow, wind forcing, and other influences on circulation in and near submarine canyons.
CCPO successes have been documented in this publication for the past year, and they continue as more exciting projects are started and more faculty, students, and staff are brought onboard. But what are the ``challenges,'' and what are the ``interesting times''? They are the fact that the Commonwealth of Virginia, who asked us for a self-sufficiency plan that would take effect when funding ended in 1996, reduced our funding unexpectedly in the 1994-95 budget. Luckily the plan was well along, so we could start it earlier than anticipated. Old Dominion University has been very supportive of the plan and has developed new policy to allow our research center and others yet to be formed to prosper. The policy involves the creation of self-supporting research positions and other changes in resource allocation. The research positions are critical to CCPO's long-term success, and we have already established three positions.
I believe that CCPO and other research centers at Old Dominion University will thrive in this environment, and the University is to be complimented for its forward thinking during rough budget times.
Larry P. Atkinson Director, Center for Coastal Physical Oceanography
Soon after Lou's arrival to CCPO, he left for Singapore to join the T. G. Thompson as chief scientist for the first leg of the NSF-funded JGOFS Arabian Sea process study, and he will participate in two additional Thompson cruises in the Arabian Sea during 1995. Lou will be able to continue his studies of the Arctic Ocean with support from the Office of Naval Research and will continue to assist and advise ONR on the Arctic Nuclear Waste program that he has managed for the last two years. He also participates in a bi-lateral research program between the National Institute of Oceanography in India and the United States.
Lou has many research interests, but his interest in the global nitrogen cycle and how it interacts with climate change is at the core of many of them. He has published papers and reports on coastal oceanography, paleoceanography, nitrogen cycling, carbon cycling, the oceanography of the Arctic Ocean, and instrument development. Lou has also served the oceanographic community in administrative capacities and as a member of advisory committees, such as the WOCE/DOE carbon dioxide science team and advisory committees for NSF's Arctic System Science Program. He also has interests in public education and in developing environmental courses for undergraduate non-majors.
Tidally-forced flow beneath the existing trestle of the CBBT causes significant distortion of the ambient density field in the immediate vicinity of the trestle due to flow over the scour zone around the pilings. Effects are minimal a short distance away from the trestle. Estimates of piling-induced destratification based on direct observations of temperature, salinity, and currents near the pilings indicate that piling effects are less than naturally occurring destratification due to bottom and wind stresses. Loss of stratification during times of strongest flow past the pilings is a few percent.
If you think you know the mystery photo, please e-mail your response to carole@ccpo.odu.edu, or fax to Carole Blett, editor, CCPO Circulation, at (804) 683-5550. We are eager to hear everyone's responses, and we will publish the results when the mystery photo is revealed in the fall issue of CCPO Circulation, due to be published mid-November.
Ana's dissertation work is entitled, ``Winter Variability of CZCS Derived Winter Distributions on the Southeastern U.S. Continental Shelf.'' This study uses available CZCS data to obtain a description of the near-surface pigment distributions of the South Atlantic Bight (SAB) in terms of regional variability and dominant space and time scales. It will also provide parameter values that can be used to optimize atmospheric correction and pigment retrieval of CZCS and SeaWiFS imagery in the SAB.
After graduation, Ana plans to return to her home in Portugal, where she will return to her faculty position at the University of the Azores and continue her research.
YVETTE HERBERT SPITZ received a License in Physics and a License in Oceanology from Liege University, Belgium. Yvette worked as a research assistant at Liege University and then at the Management Unit for the Mathematical Models of the North Sea and Scheldt Estuary (MUMM). She moved to the United States in 1987, where she received her M.S. in physical oceanography from Florida State University, and then started Old Dominion University, where she is currently pursuing her Ph.D. in physical oceanography under the direction of John M. Klinck.
Yvette's dissertation is entitled, ``A Feasibility Study of Dynamic Assimilation of Tide Gauge Data in the Chesapeake Bay.'' In this study, the recovery of the circulation in the Chesapeake Bay is investigated by using a variational method, and tide gauge observations are assimilated into a vertically integrated 2-D shallow water model. The surface wind stress and bottom drag coefficients are adjusted to improve agreement with data.
Yvette hopes to obtain a university position in the United States. She is interested in continuing research using numerical modeling and data assimilation techniques and in mathematical modeling of ecosystems.
E. E. HOFMANN, D. A. SMITH, B. L. LIPPHARDT, JR. and R. A. Locarnini of Texas A&M University, and R. C. Smith of the University of California, Santa Barbara, ``Circulation West of the Antarctic Peninsula.''
J. M. KLINCK and R. C. Smith of the University of California, Santa Barbara, ``Heat Budgets and Implications for Circulation on the Continental Shelf West of the Antarctic Peninsula.''
D. A. SMITH, E. E. HOFMANN, J. M. KLINCK, B. L. LIPPHARDT, JR., and R. A. Locarnini of Texas A&M University, and R. C. Smith of the University of California, Santa Barbara, ``Hydrography in the Region West of the Antarctic Peninsula.''
C. M. LASCARA, E. E. HOFMANN, J. M. KLINCK, and R. M. Ross and L. B. Quetin, both of the University of California, Santa Barbara, ``Seasonal and Geographic Variability in the Distribution of Antarctic Krill, Euphausia superba, West of the Antarctic Peninsula.''
L. B. Quetin and R. M. Ross, both of the University of California, Santa Barbara, and C. M. LASCARA, ``Fine-scale Distribution of Antarctic Krill, Euphausia superba, Within Coastal Waters Near Palmer Station off the Antarctic Peninsula.''
E. E. HOFMANN, C. M. LASCARA, B. L. LIPPHARDT, JR., J. M. KLINCK, D. A. SMITH, and R. A. Locarnini of Texas A&M University and R. C. Smith of the University of California, Santa Barbara, ``Seasonal Changes in the Hydrographic Structure of the Upper 100 m of the Water Column.''
For the last five years, Dr. Ivanov has collaborated with CCPO scientists, principally A. D. Kirwan, Jr., on assimilation of Lagrangian data into numerical models and on the distribution in the Black Sea of radioactive tracers released by the Chernobyl incident. Two papers resulting from this collaboration were recently published in the Journal of Geophysical Research, Vol. 97(C6), 9,733--9,742 and 9,743--9,753, 1992. Also, one paper has been accepted for publication in the Journal of Environmental Radioactivity on the fate of radioactive from Chernobyl in the Black Sea. Drs. Ivanov and Kirwan have also been studying methods for assessing the predictive capability of numerical models of ocean circulation.
This past visit to CCPO was Dr. Ivanov's third visit to the U. S. and to CCPO, and Dr. Kirwan has also made three visits to the Ukraine for ongoing collaboration with Dr. Ivanov.
Ph.D.: SUNNY YU WU, dissertation title, ``On the Low-Frequency Current and Temperature Fluctuations Along the Shelf Break in the South Atlantic Bight,'' August 1994, Advisor: Larry P. Atkinson. Dr. Wu has a position at the Horn Point Environmental Laboratory, University of Maryland, Cambridge, MD.
A. D. KIRWAN, JR., ``Ocean Eddies: The Inside Story,'' presented to the Department of Physics, College of William and Mary, Williamsburg, VA, May 17, 1994.
A. D. KIRWAN, JR., J. J. Holdzkom, II, C. E. Grosch, and M. Zubair and N. Kausar of the Computer Science Department, ``Particle in Cell Simulations of Oceanic Flow,'' The International Conference on Nonlinear Dynamics and Pattern Formation in the Natural Environment (ICPF), Noordwijkerout, The Netherlands, July 3-8, 1994.
A. D. KIRWAN, JR., B. L. Lipphardt, Jr., and R. P. Mied of the Naval Research Laboratory, Washington, DC, ``The Dynamics of Steady, Rotating Baroclinic Multipole Vortex Systems,'' The International Conference on Nonlinear Dynamics and Pattern Formation in the Natural Environment (ICPF), Noordwijkerout, The Netherlands, July 3-8, 1994.
E. N. Powell, E. E. Hofmann, J. M. Klinck, and M. M. DEKSHENIEKS, ``Perkinsus Marinus: Triggering Mechanisms for Epizootics,'' The 1994 Chesapeake Research Conference, Norfolk, VA, June 1-3, 1994.
Y. H. SPITZ and J. M. Klinck, ``Recovery of Circulation and Forcing in the Chesapeake Bay by Assimilation of Tide Gauge Observations,'' The 1994 Chesapeake Research Conference, Norfolk, VA, June 1-3, 1994.
A. VALLE-LEVINSON, ``Water Exchange in the Lower Chesapeake Bay,'' The 1994 Chesapeake Research Conference, Norfolk, VA, June 1-3, 1994.
G. H. WHELESS, ``Estuary/Shelf Exchange Variability Due to Synoptic Scale Wind Events and Freshwater Runoff: Implications for Biological Recruitment,'' The 1994 Chesapeake Research Conference, Norfolk, VA, June 1-3, 1994.
C. P. MULLEN, National Research Council Research Associateship Fellowship Award, as Resident Research Associate at National Oceanic and Atmospheric Administration (NOAA/NESDIS), Washington, DC.
C. E. GROSCH, ``Reacting Compressible Mixing Layers: Structure and Stability,'' Combustion in High-Speed Flows, pp 131-190, J. Buckmaster, et al. (eds), 1994 Kluwer Academic Publishers, The Netherlands.
E. N. Powell of Texas AM University, J. M. KLINCK and E. E. HOFMANN, and S. M. Ray of Texas AM University, ``Modeling Oyster Populations. IV: Rates of Mortality, Population Crashes, and Management,'' Fishery Bulletin, Vol. 92, 347-373, 1994.
M. TONER and A. D. KIRWAN, JR., ``Periodic and Homoclinic Orbits in a Toy Climate Model,'' Nonlinear Processes in Geophysics, Vol. 1(1), 31-40, May 1994.
C. P. MULLEN and A. D. KIRWAN, JR., ``Surface Flow Structure of the Gulf Stream from Composite Imagery and Satellite-Tracked Drifters,'' Nonlinear Processes in Geophysics, Vol. 1(1), 64-71, May 1994.
A. VALLE-LEVINSON and R. E. Wilson of State University of New York at Stony Brook, ``Effects of Sill Processes and Tidal Forcing on Exchange in Eastern Long Island Sound,'' J. Geophy. Res., Vol. 99(C6), 12,667--12,681, June 1994.
CCPO CIRCULATION is published quarterly.
Contact Carole E. Blett, editor, for more information, (804) 683-4945.
Editor ........................Carole E. Blett Technical Editor ..............Julie R. Morgan Design Editor .................Karal L. Gregory Distribution Manager ..........Beverly S. Mitchell