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Thomas N. Lee

Bio: Thomas N. Lee is an academic researcher from University of Miami. The author has contributed to research in topics: Gulf Stream & Continental shelf. The author has an hindex of 42, co-authored 88 publications receiving 6002 citations.


Papers
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Journal ArticleDOI
TL;DR: Independent data from the Gulf of Mexico are used to develop and test the hypothesis that the same sequence of physical and ecological events each year allows the toxic dinoflagellate Karenia brevis to become dominant in a global response to both desertification and eutrophication.
Abstract: [1] Independent data from the Gulf of Mexico are used to develop and test the hypothesis that the same sequence of physical and ecological events each year allows the toxic dinoflagellate Karenia brevis to become dominant. A phosphorus-rich nutrient supply initiates phytoplankton succession, once deposition events of Saharan iron-rich dust allow Trichodesmium blooms to utilize ubiquitous dissolved nitrogen gas within otherwise nitrogen-poor sea water. They and the co-occurring K. brevis are positioned within the bottom Ekman layers, as a consequence of their similar diel vertical migration patterns on the middle shelf. Upon onshore upwelling of these near-bottom seed populations to CDOM-rich surface waters of coastal regions, light-inhibition of the small red tide of ∼1 ug chl l−1 of ichthytoxic K. brevis is alleviated. Thence, dead fish serve as a supplementary nutrient source, yielding large, self-shaded red tides of ∼10 ug chl l−1.The source of phosphorus is mainly of fossil origin off west Florida, where past nutrient additions from the eutrophied Lake Okeechobee had minimal impact. In contrast, the P-sources are of mainly anthropogenic origin off Texas, since both the nutrient loadings of Mississippi River and the spatial extent of the downstream red tides have increased over the last 100 years. During the past century and particularly within the last decade, previously cryptic Karenia spp. have caused toxic red tides in similar coastal habitats of other western boundary currents off Japan, China, New Zealand, Australia, and South Africa, downstream of the Gobi, Simpson, Great Western, and Kalahari Deserts, in a global response to both desertification and eutrophication.

372 citations

Journal ArticleDOI
TL;DR: In this article, the authors study the development and evolution of buoyant river plumes on the continental shelf and propose a plume classification scheme based on a bulk Richardson number, which expresses the relative magnitude of the buoyancy-induced stratification versus the available mixing.
Abstract: We study the development and evolution of buoyant river plumes on the continental shelf. Our calculations are based on three-dimensional numerical simulations, where the river runoff is introduced as a volume of zero salinity water in the continuity equation and mixing is provided by the model's turbulence closure scheme and wind forcing. In the absence of wind forcing, the modeled river plumes typically consist of an offshore bulge and a coastal current in the direction of Kelvin wave propagation. We propose a plume classification scheme based on a bulk Richardson number, which expresses the relative magnitude of the buoyancy-induced stratification versus the available mixing. When the ratio of the discharge and shear velocities is greater (less) than 1, the plume is categorized as supercritical (subcritical); that is, the width of the bulge is greater (less) than the width of the coastal current. Supercritical plumes are often characterized by a meandering pattern along the coastal current, caused by a baroclinic instability process. For a given discharge, subcritical plumes are produced by large mixing and/or shallow water depths. In the presence of wind forcing, the favorable conditions for offshore removal of coastal low-salinity waters include high river runoff and strong upwelling-favorable wind stress. When the rivers are treated as individual sources of freshwater (“point source” behavior), the wind-driven flow may exhibit substantial spatial variability. Under the above removal conditions, strong offshore transport takes place in “jetlike” flow regions within the river plume, in contrast to the downwind acceleration of adjacent waters. When the rivers are treated as a long “line source” of freshwater, the plume region resembles a coastal low-salinity band, and the above removal conditions trigger offshore transport that is most pronounced at the “head” of the source.

296 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report results from a 1-year moored current meter array spanning the continental margin off French Guiana near 8° N in the western tropical Atlantic, where current profiles were recorded at three sites: at the shelf break, over the mid-continental slope, and at the base of the continental rise.
Abstract: We report results from a 1-year (September 1987 to September 1988) moored current meter array spanning the continental margin off French Guiana near 8° N in the western tropical Atlantic. Current profiles were recorded at three sites: at the shelf break, over the mid-continental slope, and at the base of the continental rise. Upper level mean currents showed a northwestward flowing North Brazil Current (NBC) and offshore retroflection of this flow into the North Equatorial Countercurrent from late summer through about January. Generally weak upper level mean flows were observed during the spring (February–June). Persistent northwestward mean flow was observed at 900 m depth over the continental slope, indicating northward transport of Antarctic Intermediate Waters in a subsurface boundary flow at speeds of 10–15 cm s−1. Deep currents over the continental rise showed a strong southeastward Deep Western Boundary Current (DWBC) extending from 2500 m to the bottom, with mean core speeds of nearly 30 cm s−1 at 4300 m depth. Transport estimates based on these data and a few geostrophic sections suggest a DWBC transport of 20–40 × 106 m3 s−1 at this location. Low-frequency current fluctuations were dominated by a well-defined 40- to 60-day oscillation with peak-to-peak meridional velocity amplitudes of > 1 m s−1 during the fall. Analysis of historical coastal zone color scanner imagery suggests that these oscillations are related to quasi-periodic generation and subsequent westward movement of ≈ 400 km diameter eddies from the NBC retroflection. These results contrast sharply with earlier indications of a quasi-permanent “Demerara Eddy” in this region, and suggest that this commonly observed feature is in fact a transient phenomenon associated with the time-dependent behavior of the NBC retroflection.

280 citations

Journal ArticleDOI
TL;DR: In this paper, current meter observations from an array of three subsurface moorings located on the Brazil continental slope near 4°N are used to describe the annual cycle and low-frequency variability of the North Brazil Current (NBC).
Abstract: Current meter observations from an array of three subsurface moorings located on the Brazil continental slope near 4°N are used to describe the annual cycle and low-frequency variability of the North Brazil Current (NBC). The moored array was deployed from September 1989 to January 1991, with further extension of the shallowest mooring, located over the 500-m isobath near the axis of the NBC, through September 1991. Moored current measurements were also obtained over the adjacent shelf for a limited time between February and May 1990. The NBC has a large annual cycle at this latitude, ranging from a maximum transport of 36 Sv (Sv ≡ 106 m3 s−1) in July–August to a minimum of 13 Sv in April–May, with an annual mean transport of approximately 26 Sv. The mean transport is dominated by flow in the upper 150 m, and the seasonal cycle is contained almost entirely in the top 300 m. Transport over the continental shelf is 3–5 Sv and appears to be fairly constant throughout the year, based on the available...

248 citations

Journal ArticleDOI
01 Apr 1981
TL;DR: In this paper, the effect of Gulf Stream frontal disturbances on low-frequency current and temperature variability, water exchange, and nutrient flux in the outer region of the Georgia shelf was analyzed using satellite, hydrographic and data from moored current meters.
Abstract: Satellite, hydrographic, and data from moored current meters are used to show the effect of Gulf Stream frontal disturbances on low-frequency current and temperature variability, water exchange, and nutrient flux in the outer region of the Georgia shelf. Perturbations of the Gulf Stream cyclonic front are commonly observed as folded wave patterns in routine satellite-derived analyses of the western boundary of the Gulf Stream between Cape Hatteras and Miami. The disturbances consist of southward-flowing warm filaments or streamers of near-surface Gulf Stream water, 15 to 20 m deep, which can extend 35 to 40 km over the outer shelf around a cold upwelled core. Downstream dimensions of the filaments reach 100 to 200 km in the region from Jupiter, Florida, to Charleston, South Carolina, 10 to 50 km south of Jupiter, and 200 to 300 km between Charleston and Cape Hatteras. The features are defined as cyclonic, cold-core frontal eddies due to their flow and water mass properties. They appear to form from amplified waves in the Gulf Stream cyclonic front on an annual average of one every two weeks but with considerable monthly variability. They can persist up to three weeks and travel to the north with the same phase speed as the waves, approx. 40 cm s−1. The cyclonic circulation in frontal eddies provides a means for rapid shelf-Gulf Stream water exchange. The eddies appear to control the residence time of the outer shelf waters, defined as the mean separation time between eddy events, or approx. two weeks. Upwelling in the cold core extended into the euphotic zone (45 m) and shoreward (35 to 40 km) beneath the southward-flowing warm filament in a bottom intrusion layer 20 m thick. The annual nitrogen input to the shelf waters by this process is estimated as 55,000 tons each year, about twice all other estimated nitrogen sources combined; it can support an annual carbon production by phytoplankton of 32 to 64 g C m−2y−1 with no nitrogen recycling.

245 citations


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TL;DR: Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed and a full understanding of population connectivity has important applications for management and conservation.
Abstract: Connectivity, or the exchange of individuals among marine populations, is a central topic in marine ecology. For most benthic marine species with complex life cycles, this exchange occurs primarily during the pelagic larval stage. The small size of larvae coupled with the vast and complex fluid environment they occupy hamper our ability to quantify dispersal and connectivity. Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed. Understanding the biophysical processes that contribute to observed dispersal patterns requires integrated interdisciplinary approaches that incorporate high-resolution biophysical modeling and empirical data. Further, differential postsettlement survival of larvae may add complexity to measurements of connectivity. The degree to which populations self recruit or receive subsidy from other populations has consequences for a number of fundamental ecological processes that affect population regulation and persistence. Finally, a full understanding of population connectivity has important applications for management and conservation.

1,640 citations

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TL;DR: In this paper, an improved estimation of mesoscale surface ocean circulation was obtained by merging TOPEX/Poseidon (T/P) and ERS-1 and -2 altimeter measurements between October 1992 and May 1998.
Abstract: This study focuses on the improved estimation of mesoscale surface ocean circulation obtained by merging TOPEX/Poseidon (T/P) and ERS-1 and -2 altimeter measurements between October 1992 and May 1998. Once carefully intercalibrated and homogenized, these data are merged through an advanced global objective analysis method that allows us to correct for residual long wavelength errors and uses realistic correlation scales of ocean dynamics. The high-resolution (0.25°×0.25°) merged T/P+ERS-1 and -2 sea level anomaly maps provide more homogeneous and reduced mapping errors than either individual data set and more realistic sea level and geostrophic velocity statistics than T/P data alone. Furthermore, the merged T/P+ERS-1 and -2 maps yield eddy kinetic energy (EKE) levels 30% higher than maps of T/P alone. They also permit realistic global estimates of east and north components of EKE and their seasonal variations, to study EKE sources better. A comparison of velocity statistics with World Ocean Circulation Experiment surface drifters in the North Atlantic shows very good agreement. Comparison with contemporary current meter data in various oceanic regimes also produces comparable levels of energy and similar ratios of northward and eastward energy, showing that the maps are suitable to studying anisotropy. The T/P + ERS zonal and meridional components of the mapped currents usually present comparable rms variability, even though the variability in the Atlantic is more isotropic than that in the Pacific, which exhibits strong zonal changes. The EKE map presents a very detailed description, presumably never before achieved at a global scale. Pronounced seasonal changes of the EKE are found in many regions, notably the northeastern Pacific, the northeastern and northwestern Atlantic, the tropical oceans, and the zonally extended bands centered near 20°S in the Indian and western Pacific Oceans and at 20°N in the northwestern Pacific.

1,575 citations

Journal ArticleDOI
TL;DR: In this article, the authors review observations, theory and model results on the monsoon circulation of the Indian Ocean and discuss possible physical mechanisms behind seasonal variability of the meridional overturning streamfunction and heat flux.

1,437 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe carbon system formulation and simulation characteristics of two new global coupled carbon-climate Earth System Models (ESM), ESM2M and ESM 2G).
Abstract: The authors describe carbon system formulation and simulation characteristics of two new global coupled carbon–climate Earth System Models (ESM), ESM2M and ESM2G. These models demonstrate good climate fidelity as described in part I of this study while incorporating explicit and consistent carbon dynamics. The two models differ almost exclusively in the physical ocean component; ESM2M uses the Modular Ocean Model version 4.1 with vertical pressure layers, whereas ESM2G uses generalized ocean layer dynamics with a bulk mixed layer and interior isopycnal layers. On land, both ESMs include a revised land model to simulate competitive vegetation distributions and functioning, including carbon cycling among vegetation, soil, and atmosphere. In the ocean, both models include new biogeochemical algorithms including phytoplankton functional group dynamics with flexible stoichiometry. Preindustrial simulations are spun up to give stable, realistic carbon cycle means and variability. Significant differences...

1,214 citations