Eileen E. Hofmann

Effect of upwelling on phytoplankton productivity of the outer southeastern United States continental shelf

Abstract Gulf Stream frontal disturbances cause nutrient-rich waters to frequently upwell and intrude onto the southeastern United States continental shelf between Cape Canaveral, Florida and Cape Hatteras, North Carolina. Phytoplankton response in upwelled waters was determined with three interdisciplinary studies conducted during April 1979 and 1980, and in summer 1978. The results show that when shelf waters are not stratified, upwelling causes productive phytoplankton (diatom) blooms on the outer shelf. Phytoplankton production averages about 2 g C m −2 d −1 during upwelling events, and ‘new’ production is 50% or more of the total. When shelf waters are stratified, upwelled waters penetrate well onto the shelf as a subsurface intrusion in which phytoplankton production averages about fives times higher than the nutrient-depleted overlying mixed layer. Phytoplankton within the intrusion deplete upwelled NO 3 in about 7 to 10 days, at which point no further net increase in phytoplankton biomass occurs. Current meter records show that upwelling occurs roughly 50% of the time on the outer shelf during November to April (shelf not stratified), and we estimate that seasonal primary production in upwelled waters is 175 g C m −2 6 months −1 of which at least 50% is ‘new’ production. More than 90% of outer shelf primary and ‘new’ production occurs during upwelling and thus upwelling is the dominant process affecting primary productivity of the outer shelf. Our seasonal estimates of outer shelf primary and ‘new’ production are, respectively, three and ten times higher than previous estimates that did not account for upwelling.

A bottom water intrusion in Onslow Bay, North Carolina

Abstract During the period 20 July to 8 August 1976, a bottom intrusion of Gulf Stream water was observed in hydrographic data and data from moored current meters from Onslow Bay, North Carolina. The event was the result of southerly winds (upwelling favorable) and Gulf Stream meandering. Offshore (easterly) movement of the Gulf Stream causes an upward movement of isotherms which presents cold, saline water at the shelf break. Once this water is present at the shelf break, some other mechanism, such as southerly winds, is necessary for it to upwell into Onslow Bay. The extent of the upwelling is determined by the intensity and duration of the wind event.

A time-dependent model of nutrient distribution in continental shelf waters

Abstract A time dependent, vertical plane mathematical model of nitrate distribution in Onslow Bay, North Carolina, is developed using similarity theory and conventional numerical techniques. Inputs of nitrate into Onslow Bay are the result of Gulf Stream intrusions (Atkinson et al., 1980) and this forcing is included as a boundary condition for this system. Advective and diffusive processes provide the mechanisms for transport of nitrate in Onslow Bay. The time dependence of the resulting nitrate fields is determined by the rate of phytoplankton removal of nitrate. Nondimensional numbers, arising from model formulation, indicate the relative importance of various processes included in the model. Two nondimensional numbers, H and P , and the nondimensional ratio, P / H , indicate interactions of physical processes. Importance of the biological terms is determined by a third nondimensional number, A . Model results are compared to nitrate data collected in Onslow Bay, North Carolina during an intrusion.

Predicting the Influence of Seed and Commercial Oyster Fisheries on Metapopulation Genetic Connectivity Using Model Simulations

s of Technical Papers, Presented at the 104th Annual Meeting, National Shellfisheries Association, Seattle, Washington, March 24–29, 2012 National Shellfisheries Association Follow this and additional works at: https://scholarworks.wm.edu/vimsarticles Part of the Aquaculture and Fisheries Commons Recommended Citation National Shellfisheries Association, Abstracts of Technical Papers, Presented at the 104th Annual Meeting, National Shellfisheries Association, Seattle, Washington, March 24–29, 2012 (2012). VIMS Articles. 524. https://scholarworks.wm.edu/vimsarticles/524 This Article is brought to you for free and open access by W&M ScholarWorks. It has been accepted for inclusion in VIMS Articles by an authorized administrator of W&M ScholarWorks. For more information, please contact scholarworks@wm.edu. ABSTRACTS OF TECHNICAL PAPERSS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATION

How Do Marine Protected Area Strategies Influence Metapopulation Genetic Connectivity? A Modeling Study with Oysters

s of Technical Papers, Presented at the 104th Annual Meeting, National Shellfisheries Association, Seattle, Washington, March 24–29, 2012 National Shellfisheries Association Follow this and additional works at: https://scholarworks.wm.edu/vimsarticles Part of the Aquaculture and Fisheries Commons Recommended Citation National Shellfisheries Association, Abstracts of Technical Papers, Presented at the 104th Annual Meeting, National Shellfisheries Association, Seattle, Washington, March 24–29, 2012 (2012). VIMS Articles. 524. https://scholarworks.wm.edu/vimsarticles/524 This Article is brought to you for free and open access by W&M ScholarWorks. It has been accepted for inclusion in VIMS Articles by an authorized administrator of W&M ScholarWorks. For more information, please contact scholarworks@wm.edu. ABSTRACTS OF TECHNICAL PAPERSS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATION

Mathematical model of nutrient distribution in coastal waters

An approach to biological modelling involving the use of separation transformation theory has been developed. By use of the theory, it is possible to reduce the number of independent variables in the system. The original four dimensional system (x, y, z, t) can be reduced to a vertical plane conceptual model by assuming along isobath homogeneity in the flow field as a partial function of the baroclinic flow field. Both temporally dependent and independent nitrate concentration equations are then obtained and solved by conventional approximation methods. This technique has applicability to ecological modelling and results obtained by its use show good agreement with field data. Parameterization of the physical processes shows horizontal diffusion and advection to be the important forces in the system. Scaling of biological dynamics show nutrient uptake by phytoplankton and detrital decomposition to be the most important biological factors in the system. This technique permits the testing of various hypotheses with a minimum amount of computer time. Applications in studies on the continental shelf processes affecting the oceanography of the South Atlantic Bight, with emphasis on nitrogen cycling in coastal waters of Onslow Bay, North Carolina, are described.