James J. Singer

Bio: James J. Singer is an academic researcher from Skidaway Institute of Oceanography. The author has contributed to research in topics: Bay & Gulf Stream. The author has an hindex of 4, co-authored 5 publications receiving 125 citations.

Variability of surface pigment concentrations in the South Atlantic Bight

Abstract: A time sequence of surface pigment images of the South Atlantic Bight (SAB), derived from the Nimbus 7 CZCS for the period between November 1978 and October 1979, was correlated with in situ observations of hydrographic parameters, fresh-water discharge, sea level, coastal winds, and currents in order to couple physical processes and the spatial and temporal variability of the surface pigment fields. A definite seasonal modulation of the surface pigment fields was found, with the concentrations in the Georgia Bight being highest in summer, and those north of Cape Romain highest in winter. This phase difference was found to be the result of variations in wind fields, Gulf Stream-shelf interactions, and fresh-water discharge patterns. At some locations (e.g., near Charleston) the alongshore band of high pigment concentrations increased in width throughout the year; at other locations (near Jacksonville), the alongsore band exhibited a minimum width in the summer and a maximum width in the fall of 1979.

Cape Romain and the Charleston Bump: Historical and recent hydrographic observations

Abstract: A review and analysis of historical and new hydrographic data are presented for the Charleston Bump region. An area of doming isotherms is identified primarily between 31.5/sup 0/ and 34.5/sup 0/N and the 200 and 400 m isobaths. The highest incidences of doming are found off Long Bay (86%). Cape Fear (38%), and Cape Romain (25%). Evidence suggests that low salinity shelf water collects in the doming area off Long Bay in July and that seasonal fluctuations in the depth of the main thermocline layer in this area are linked to Gulf Stream transport and local winds. At times there is a gradual offshore-onshore movement of the Gulf Stream opposite Long Bay roughly following the 400 m isobath and at other times an abrupt eastward movement near 32/sup 0/N. Much of the time there appears to be a direct seasonal relationship between historical seasonal velocity fields and offshore deflection with higher (lower) velocities corresponding to greater (lesser) deflection.

Volume of summer subsurface intrusions into Onslow Bay, North Carolina

Abstract: Onslow Bay, North Carolina is a continental shelf area bounded alongshore by extensive shoals and offshore by the Gulf Stream. Motions of the Gulf Stream often cause the intrusion of deeper, cold Gulf Stream water into the bay, especially during summer. Observations in 1975 and 1976 gave a range of intrusion volumes from 11 to 36%, averaging 20% (84 km3) of the bay volume. The minimum and maximum lifetimes for these intrusions were 14 and 60 days. The intrusions moved through the bay from south to north.

Hydrography of Onslow Bay, North Carolina: September 1975 (OBIS II)

Abstract: Data collected during studies of Onslow Bay, off the North Carolina coast during cruises during September, 1975, are reported. Current meters and thermography were placed at depths of 10 and 22 m along the 28 m isobath in the northeastern and southwestern sectors of the Bay. Data are included on wind turbulence and velocity; seawater salinity and temperature at various depths; the content of nitrates, phosphates, silicate, oxygen, chlorophyll, and phytoplankton biomass at various depths. Hydrographic and meteorologic conditions during the cruises are included. (CH)

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.

Gulf Stream frontal eddy influence on productivity of the southeast U.S. continental shelf

Abstract: Weekly period meanders and eddies are persistent features of Gulf Stream frontal dynamics from Miami, Florida, to Cape Hatteras, North Carolina. Satellite imagery and moored current and temperature records reveal a spatial pattern of preferred regions for growth and decay of frontal disturbances. Growth regions occur off Miami, Cape Canaveral, and Cape Fear due to baroclinic instability, and decay occurs in the confines of the Straits of Florida between Miami and Palm Beach, between 30° and 32°N where the stream approaches the topographic feature known as the Charleston bump and between 33°N and Cape Hatteras. Eddy decay regions are associated with elongation of frontal features, offshore transport of momentum and heat, and onshore transport of nutrients. Onshore transport of new nitrogen from the nutrient-bearing strata beneath the Gulf Stream indicates that frontal eddies serve as a “nutrient pump” for the shelf. New nitrogen flux to the shelf due to Gulf Stream input could support new production of 7.4×1012 g C yr−1 or about 8 million tons carbon per year if all nitrate were utilized. Calculations indicate that approximately 70% of this potential new production is realized, yielding an annual new production for the outer shelf of 4.3×1012 g C.

Benthic flux of biogenic elements on the Southeastern US continental shelf: influence of pore water advective transport and benthic microalgae

Abstract: In situ, paired light and dark benthic flux chamber incubations were used to estimate the exchange of nutrients, oxygen and inorganic carbon across the sediment – water interface of the South Atlantic Bight (SAB) continental shelf. The results indicate that physically forced non-diffusive pore water transport and benthic primary production (BPP) by sea floor microalgae exert a major influence on benthic exchange rates on the mid- and outer-continental shelf (depths of 14–40 m). Light fluxes to the sea floor and sediment photosynthetic pigment distributions determined on two, widely spaced cross-shelf transects suggest that BPP may occur over 84% of the SAB continental shelf area. Microalgal gross BPP rates at all study sites averaged 400±260 mg C m−2 d−1 between May and September 1996 while water column primary productivity averaged 682±176 mg C m−2 d−1, implying a total primary productivity for this region of approximately 1100 mg C m−2 d−1 (1.6 times the water column productivity alone). The results are also consistent with the advective transport of pore waters. Benthic flux chambers appear to retard this exchange, affecting the accuracy of derived net fluxes. Given our inability to relate pore water gradients to fluxes in non-diffusive regimes and to mimic natural advective transport in intact core incubations, traditional techniques such as pore water gradient diffusion calculations or shipboard core incubations also may not provide accurate flux estimates. Because of these limitations, fundamental questions remain concerning the processes that control nutrient inventories in pore waters and the magnitude of the net benthic flux of nutrients on the sandy SAB shelf.

Low‐frequency current and temperature variability from Gulf Stream frontal eddies and atmospheric forcing along the southeast U.S. outer continental shelf

Abstract: Low-frequency current and temperature time series from the outer shelf between Cape Canaveral, Florida, and Cape Romain, South Carolina, are compared with shipboard hydrographic data, satellite VHRR, coastal and buoy winds, and coastal sea level during the period from February to June 1980. Low-frequency current and temperature variability along the shelf break was primarily produced by cyclonic, cold core Gulf Stream frontal eddies. These disturbances traveled to the north at speeds of 50 to 70 cm s−1 with periods of 5 to 9 days throughout the experiment and produced cold cyclonic perturbations of the northward mean flow and temperature fields over an along-shelf coherence scale of 100 km. Frontal eddies appear to be an important mechanism in the observed eastward transport of northward momentum and heat along the shelf edge. They also appear to play a key role in the transfer of eddy kinetic and potential energy back to the mean flow, which suggests an upstream formation region and shear-induced dissipation. Upwelling velocities of about 10−2 cm s−1 in the cold core provide the major source of new nutrients to the outer shelf. Subtidal flow variability at the 40-m isobath was a mixed response to Gulf Stream and wind forcing. Barotropic along-shelf current oscillations were coherent with the local winds and coastal sea level at periods of 3–4 and 10–12 days over along-shelf scales of 400 km with small phase lags, suggesting a nearly simultaneous frictional equilibrium response to coherent wind-induced sea level slopes.