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.

Short-term fluctuations south of Japan and their relationship with the Kuroshio path: 8- to 36-day fluctuations

“…Frontal waves of similar frequencies have been reported in other coastal areas in Japan: in the East China Sea (Sugimoto et al 1988;Qiu et al 1990;James et al 1999), in the Tokara Strait (Qiu et al 1990;Maeda et al 1993;Feng et al 2000), south of Shikoku (Awaji et al 1991), near the separation point of the Kuroshio to the Kuroshio Extension (Itoh and Sugimoto 2008), and in the Kuroshio Extension (Tracey et al 2012). Frontal wave disturbances have been also found in the Gulf Stream (Lee and Atkinson 1983;Tracey and Watts 1986;Oey 1988;Savidge 2004). Itoh and Sugimoto (2008) successfully applied the analytical model of baroclinic instability by Pedlosky (1987) to the variability of the Kuroshio near the separation point from the western boundary, and they also discussed similar fluctuations in other regions of the Kuroshio.…”

The effect of the Leeuwin Current on phytoplankton biomass and production off Southwestern Australia

“…[43] A similar mechanism has been described for several western boundary currents, where eddies and meanders over the continental slope ''pump'' nutrients onto the continental shelf and thereby promote a significant proportion of the shelf productivity off the southeast USA [Yoder et al, 1981;Lee and Atkinson, 1983;Lee et al, 1989Lee et al, , 1991, Brazil [Campos et al, 2000], Japan [Kimura et al, 1997], and eastern Australia [Tranter et al, 1986;Harris et al, 1987]. The western boundary currents are often notably low in nutrients, yet the eddy and meander structures promote shelf productivity through eddy-induced upwelling along the shelf break, because the nitricline is lifted upward toward the continental shelf.…”

“…Meanders and eddies spin up during the autumnwinter period and often continue to evolve through winter, to be either reabsorbed or shed into the interior of the eastern Indian Ocean and drift westward Fang and Morrow, 2003]. Western boundary current eddies and meanders have been shown to contribute significantly to the productivity of the continental shelves off the southeastern USA [Yoder et al, 1981;Lee and Atkinson, 1983;Lee et al, 1989Lee et al, , 1991, Brazil [Campos et al, 2000], Japan [Kimura et al, 1997], and eastern Australia [Tranter et al, 1986;Harris et al, 1987], but the impact of eddies off the coast of Western Australia on shelf productivity has not been previously examined.…”

Flux of larval fish around Cape Hatteras

“…(MAB and SAB) responds to oceanographic and meteorological forcing (Lee and Atkinson 1983;. Dynamic forcing results in various scenarios of mixing, offshore flow, or penetration of water from one bight into the other (Gawarkiewicz et al 1992;Flagg et al 1994;.…”