J. O. Blanton

Bio: J. O. Blanton is an academic researcher from Skidaway Institute of Oceanography. The author has contributed to research in topics: Continental shelf & Upwelling. The author has an hindex of 20, co-authored 34 publications receiving 1550 citations.

Interactions between behaviour and physical forcing in the control of horizontal transport of decapod crustacean larvae.

Abstract: We summarize what is known of the biophysical interactions that control vertical migration and dispersal of decapod larvae, asking the following main questions: How common is vertical migration in decapod crustacean larvae? What is the vertical extent of the migrations? What are the behavioural mechanisms that control vertical migrations? How does vertical migration interact with the physics of the ocean to control the dispersal of larvae? These questions are analysed by first giving a synopsis of the physical processes that are believed to significantly affect horizontal transport, and then by describing migration patterns according to taxon, to ecological category based on the habitat of adults and larvae, and to stage within the larval series. Some kind of vertical migration has been found in larval stages of virtually all species that have been investigated, irrespective of taxonomic or ecological category. Most vertical migration schedules have a cyclic nature that is related to a major environmental cyclic factor. Tidal (ebb or flood) migration and daily (nocturnal and twilight) migration are the two types of cyclic migration that have been identified. In general, all species show some type of daily migration, with nocturnal migration being the most common, whereas tidal migrations have only been identified in species that use estuaries during part of their life cycle. Moreover, there are several examples indicating that the phasing and extent of migration both change throughout ontogeny. Reported ranges of vertical displacement vary between a few metres in estuaries and several tens of metres (sometimes more than 100 m) in shelf and oceanic waters. Vertical movements are controlled by behavioural responses to the main factors of the marine environment. The most important factors in this respect are light, pressure and gravity, but salinity, temperature, turbulence, current and other factors, also influence behaviour. Many of these factors change cyclically, and the larvae respond with cyclic behaviours. The type of response may be endogenous and regulated by an internal clock, as in the case of some tidally synchronised migrations, but in most cases it is a direct response to a change in an environmental variable, as in diel migration. The reaction of the larvae to exogenous cues depends both on the rate of change of the variable and on the absolute amount of change. A series of dispersal types, involving different spatial and temporal scales, have been identified in decapod larvae: retention of the larval series within estuaries; export from estuarine habitats, dispersal over the shelf, and reinvasion of estuaries by the last stage; hatching in shelf waters and immigration to estuaries by late larvae or postlarvae; complete development on the shelf; and hatching in shelf waters, long-range dispersal in the ocean, and return to the shelf by late stages. In all of these cases, vertical migration behaviour and changes of behaviour during the course of larval development have been related to particular physical processes, resulting in conceptual mechanisms that explain dispersal and recruitment. Most decapod larvae are capable of crossing the vertical temperature differences normally found across thermoclines in natural systems. This ability may have significant consequences for horizontal transport within shelf waters, because amplitude and phase differences of the tidal currents across the thermocline may be reflected in different trajectories of the migrating larvae.

The Relationship of Upwelling to Mussel Production in the Rias on the Western Coast of Spain

Abstract: We have calculated an upwelling index for each month over a 17-year period (1969-1985) for a point off the western coast of Spain. We interpret April through September values of the index to indicate the flux of nitrate-rich water into the Spanish Rias. The index representing the 6-month upwelling series has been correlated with an index representing the conditions of mussels grown during that season on rafts in Ria de Arosa. Two seasons represent extreme upwelling conditions over the 17-year sampling period: 1977 when the upwelling index was the highest, and 1983 when it was the lowest. A comparison of the condition of mussels during these years showed that meat content was double in 1977. We suggest, by this study, that long range forecasts of synoptic scale weather patterns could be used to predict the potential nutritional value of mussels harvested in the rias of Spain.

Wind‐driven upwelling in the vicinity of Cape Finisterre, Spain

Abstract: Observations and numerical simulations of the evolution of upswelling and the resultant coastal circulation in response to two wind events occurring along the Galician coast of Spain during the April 18-26, 1982 period are presented. In situ measurements include shipboard determinations of hydrographic and biological parameters, and wind stress estimates obtained from the ship winds and from surface pressure charts. Sea surface temperature information was derived from NOAA 7 satellite images, and pigment concentration information was acquired from the Nimbus 7 coastal zone color scanner. The indication from the simulations that the greatest upswelling will occur either at Cape Finisterre or along the northern coast was confirmed by observations, and it is suggested that wave disturbances propagate northward along the coast at a speed of 120-160 km/day, and that organic material formed north of Cape Finisterre is advected out to sea northwest of the cape.

The intrusion of Gulf Stream water across the continental shelf due to topographically-induced upwelling

Abstract: Summer bottom temperatures along the continental shelf between Cape Hatteras and Cape Canaveral are abnormally low in regions where isobaths diverge. The regions are north of capes and shoals, which force the flow of shelf water to change vorticity and induce upwelling. Gulf Stream Water intrudes across the bottom during summer to replace the upwelled water, and accounts for the colder and more stratified water over the northern Florida and the North Carolina shelves.

Transport and fate of river discharge on the continental shelf of the southeastern United States

Abstract: The authors analyzed 8 years of wind and salinity data from a frontal zone in a region of the inner continental shelf off the southeastern United States. The changes in low-salinity water stored in the frontal zone have been parameterized by analyzing the monthly rate of change in freshwater content. When the rate of change in freshwater content was negative, this was interpreted as a loss of low-salinity water from the frontal zone. When this parameter was compared with seasonally averaged alongshore wind stress, the rate of loss was independent of the alongshore wind stress magnitude until threshold of about 0.1 dyne cm/sup -2/ was reached. Above the threshold there was a clear relationship between northward alongshore wind stress and rate of loss of freshwater from the inner shelf. Experimental evidence suggests that horizontal currents in the inner-shelf frontal zone have cyclonic shear with increasing depth. When wind stress is northward and offshore, near-surface low-salinity water is transported offshore by Ekman transport while near-bottom high-salinity water is transported shoreward. 9 figures, 2 tables.

Large groundwater inputs to coastal waters revealed by 226 Ra enrichments

Abstract: THE flow of ground water directly into the coastal ocean has been studied previously by in situ measurements, seep meters and diffusion gradient models1. Although these techniques provide ample evidence that such flows occur, they do not provide a means of quantifying the groundwater flux on a regional scale. Here I report large enrichments of 226Ra in coastal waters of the South Atlantic Bight, and demonstrate that groundwater discharge is the main source of the 226Ra surplus. Using 226Ra data for brackish ground waters with estimates of residence times of nearshore waters, I conclude that the groundwater flux to these coastal waters must be about 40% of the river-water flux during the study period. Besides Ra, other metals, nutrients and organic compounds are expected to be enriched in brackish ground waters, so these findings require an upward revision of terrestrial fluxes of dissolved materials to these coastal waters, and perhaps a re-evaluation of such fluxes to the global ocean. These fluxes may be sensitive to hydrological factors, groundwater usage, dredging and sea-level change.

Estuarine and Coastal Ocean Carbon Paradox: CO2 Sinks or Sites of Terrestrial Carbon Incineration?

Abstract: Estuaries are a major boundary in the land-ocean interaction zone where organic carbon (OC) and nutrients are being processed, resulting in a high water-to-air carbon dioxide (CO2) flux (approximately 0.25 Pg C y(-1)). The continental shelves, however, take up CO2 (approximately 0.25 Pg C y(-1)) from the atmosphere, accounting for approximately 17% of open ocean CO2 uptake (1.5 Pg Cy(-1)). It is demonstrated here that CO2 release in estuaries is largely supported by microbial decomposition of highly productive intertidal marsh biomass. It appears that riverine OC, however, would bypass the estuarine zone, because of short river-transit times, and contribute to carbon cycling in the ocean margins and interiors. Low-latitude ocean margins release CO2 because they receive two-thirds of the terrestrial OC. Because of recent CO2 increase in the atmosphere, CO2 releases from low latitudes have become weaker and CO2 uptake by mid- and high-latitude shelves has become stronger, thus leading to more dissolved inorganic carbon export to the ocean.

Oceanic Bacterial Production

Abstract: There has been an explosion of research on marine microbial foodweb processes in the past decade. Today it is widely accepted that about 50% of the primary production in marine and fresh water is processed by bacteria each day (Williams, 1981; Cole et al., 1988). This striking finding was stimulated, as others have noted, by the introduction of convenient methods for the estimation of microbial biomass and activities in natural waters. Hobbie et al. (1977) and Watson et al. (1977) demonstrated conclusively that bacterial populations in the sea were large. By 1980, in addition to the pioneering and prescient work by Sorokin (e.g., Sorokin, 1971, 1973), reports of bacterial production measurements had begun to emerge (Sieburth et al., 1977; Karl, 1979; Larsson and Hagstrom, 1979; Fuhrman and Azam, 1980). Brock (1971) and Sieburth (1977) wrote early reviews on the subject, and Pomeroy (1974) introduced the importance of marine microbial processes to a large audience. In this chapter we review recent research on bacterial production in the ocean. The emphasis is on the open sea, but we will also discuss other marine habitats, partly because there are still few comprehensive studies of oceanic bacterial production. There is an equally large and rapidly growing literature on bacterial production in fresh waters (Cole et al., 1988; Currie, 1990) which deserves a review of its own, as well as comparison with the marine findings (Hobbie, 1988). We will not review related work in sediments, nor for the most part, related work on bacteriovores.

Between Coastal Marshes and Coastal Waters — A Review of Twenty Years of Speculation and Research on the Role of Salt Marshes in Estuarine Productivity and Water Chemistry

Abstract: It has been almost 20 years since John Teal (1962) published his well-known paper synthesizing a variety of independent studies of production, respiration, and animal abundances in the salt marsh ecosystem of Sapelo Island, Georgia. Teal’s work brought out a number of interesting points, but I think the reason the paper is most often cited is because of its last sentence. After discussing various trophic relationships in the marsh, the paper ended with the conclusion that “...the tides remove 45% of the production before the marsh consumers have a chance to use it and in so doing permit the estuaries to support an abundance of animals.”