O'Donnell
James
O'Donnell
James
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ArticleWater masses and nutrient sources to the Gulf of Maine(Sears Foundation for Marine Research, 2015-05-01) Townsend, David W. ; Pettigrew, Neal R. ; Thomas, Maura A. ; Neary, Mark G. ; McGillicuddy, Dennis J. ; O'Donnell, JamesThe Gulf of Maine, a semienclosed basin on the continental shelf of the northwest Atlantic Ocean, is fed by surface and deep water flows from outside the gulf: Scotian Shelf Water (SSW) from the Nova Scotian shelf that enters the gulf at the surface and slope water that enters at depth and along the bottom through the Northeast Channel. There are two distinct types of slope water, Labrador Slope Water (LSW) and Warm Slope Water (WSW); it is these deep water masses that are the major source of dissolved inorganic nutrients to the gulf. It has been known for some time that the volume inflow of slope waters of either type to the Gulf of Maine is variable, that it covaries with the magnitude of inflowing SSW, and that periods of greater inflows of SSW have become more frequent in recent years, accompanied by reduced slope water inflows. We present here analyses of a 10-year record of data collected by moored sensors in Jordan Basin in the interior Gulf of Maine, and in the Northeast Channel, along with recent and historical hydrographic and nutrient data that help reveal the nature of SSW and slope water inflows. We show that proportional inflows of nutrient-rich slope waters and nutrient-poor SSWs alternate episodically with one another on timescales of months to several years, creating a variable nutrient field on which the biological productivities of the Gulf of Maine and Georges Bank depend. Unlike decades past, more recent inflows of slope waters of either type do not appear to be correlated with the North Atlantic Oscillation (NAO), which had been shown earlier to influence the relative proportions of the two types of slope waters that enter the gulf, WSW and LSW. We suggest that of greater importance than the NAO in recent years are recent increases in freshwater fluxes to the Labrador Sea, which may intensify the volume transport of the inshore, continental shelf limb of the Labrador Current and its continuation as the Nova Scotia Current. The result is more frequent, episodic influxes of colder, fresher, less dense, and low-nutrient SSW into the Gulf of Maine and concomitant reductions in the inflow of deep, nutrient-rich slope waters. We also discuss evidence that modified Gulf Stream ring water may have penetrated to Jordan Basin in the summer of 2013.
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ArticleExploring the role of wave-driven turbulence at the air-sea interface through measurements of TKE dissipation rates across the air-sea interface(American Geophysical Union, 2024-08-16) Cifuentes-Lorenzen, Alejandro ; Zappa, Christopher J. ; Edson, James B. ; O’Donnell, James ; Ullman, David S.This work serves as an observation-based exploration into the role of wave-driven turbulence at the air-sea interface by measuring Turbulent Kinetic Energy (TKE) dissipation rates above and below the sea surface. Subsurface ocean measurements confirm a TKE dissipation rate enhancement relative to the predicted law-of-the-wall (εobs > εp), which appears to be fully supported by wave breaking highlighting the role of the transport terms in balancing the subsurface TKE budget. Simultaneous measurements of TKE dissipation rates on the atmospheric side capture a deficit relative to the law-of-the-wall (εobs < εp). This deficit is explained in terms of wave-induced perturbations, with observed convergence to the law-of-the-wall at 14 m above mean sea level. The deficit on the atmospheric side provides an estimate of the energy flux divergence in the wave boundary layer. An exponential function is used to integrate in the vertical and provide novel estimates of the amount of energy going into the wave field. These estimates correlate well with classic spectral input parameterizations and can be used to derive an effective wave-scale, capturing wind-wave coupling purely from atmospheric observations intimately tied to wave-induced perturbations of the air-flow. These atmospheric and oceanic observations corroborate the commonly assumed input-dissipation balance for waves at wind speeds in the 8-14 ms−1 range in the presence of developed to young seas. At wind speeds above 14 ms−1 under young seas (U10/cp > 1.2)observations suggest a deviation from the TKE input-dissipation balance in the wave field.
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ArticleProgress and challenges in coupled hydrodynamic-ecological estuarine modeling(Springer, 2015-07-07) Ganju, Neil K. ; Brush, Mark J. ; Rashleigh, Brenda ; Aretxabaleta, Alfredo L. ; del Barrio, Pilar ; Grear, Jason S. ; Harris, Lora A. ; Lake, Samuel J. ; McCardell, Grant ; O’Donnell, James ; Ralston, David K. ; Signell, Richard P. ; Testa, Jeremy M. ; Vaudrey, Jamie M. P.Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review, we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy.