Mesoscale eddies in the Fram Strait marginal ice zone during the 1983 and 1984 Marginal Ice Zone Experiments

Abstract

During the summer Marginal Ice Zone Experiment in Fram Strait in 1983 and 1984, fourteen mesoscale eddies, in both deep and shallow water, were studied between 78 ø and 81øN. Sampling combined satellite and aircraft remote sensing observations, conductivity-temperature-depth observations, drift of surface and subsurface floats and current meter measurements. Typical scales of these eddies were 20-40 km. Rotation was mainly cyclonic with a maximum speed, in several cases subsurface of up to 40 cm s-• Observations further suggest that the eddy lifetime was at least 20 to 30 days. Five generation sources are suggested for these eddies. Several of the eddies were topographically trapped, while others, primarily formed by combined baroclinic and barotropic instability, moved as much as 10-15 km d -• with the mean current. The vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear. In the most completely observed eddy south of 79øN the available potential energy exceeded the kinetic energy by a factor of 2. Quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1-2 km d-• !. INTRODUCTION The marginal ice zone (MIZ) is the transition region from open ocean to pack ice. Here strong mesoscale air-ice-ocean interactive processes occur which control the advance and retreat of the ice margin. To gain better understanding of these processes, the 1984 Marginal Ice Zone Experiment (MIZEX '84) was carried out in Fram Strait between Greenland and Svalbard from May 18 to July 30, !984, following a preliminary summer experiment in 1983 I-MIZEX Group, 1986]. One of the central objectives of MIZEX is to understand the physics of mesoscale eddies and their importance in the various exchange processes of mass, heat, and momentum which affect the position of the ice edge. Major investigations of mid-ocean eddies started in 1973 with the Mid-Ocean Dynamics Experiment (MODE) 1 program [Robinson, 1983]. Although it is now well established that eddies are present in all the world oceans with important implications for physical, biological, chemical, and geological oceanography and acoustics [Robinson, 1983; Maqaard et al., 1983], eddy features have not been extensively investigated in the MIZ. To qualitatively demonstrate the effect of eddies in the MIZ, a unique aerial photograph obtained on June 30, 1984 is shown in Plate 1, where the ice traces the cyclonic orbital motion of an eddy at the ice edge. (Plate 1 is shown here in black and white. The color version can be found in the separate color section in this issue.) Such motion advects large amounts of ice, Polar Water (PW), and Atlantic Water (AW) into closer contact, causing enhanced floe breakup and ice melting. While Plate 1 shows one ice edge eddy in detail, the National Oceanic and Atmospheric Administration (NOAA) satellite image from July 1, 1984 (Plate 2) establishes that eddies and meanders are the dominant features along the ice edge under moderate wind con...

Ice–ocean coupled computations for sea-ice prediction to support ice navigation in Arctic sea routes

“…The first reason is mesoscale eddy-resolving capability. Johannessen et al (1987) and Li et al (2013) discussed the important of iceÁeddy interaction process in the Arctic Ocean. As shown in Fig.…”

Seasonal Cycle of Mesoscale Instability of the West Spitsbergen Current

“…The mesoscale eddy field in Fram Strait has been studied in the 1980s as part of the Marginal Ice Zone Experiment (Johannessen et al 1983(Johannessen et al , 1987. Long-lived eddies were observed then as well as large features (compared to the Rossby radius of deformation) such as a cyclonic circulation seemingly associated with the f/H (where f is the Coriolis parameter and H is the depth) contours of the Molloy Hole (Manley et al 1987;Quadfasel et al 1987).…”

Warming of Atlantic Water in two west Spitsbergen fjords over the last century (1912–2009)

“…The EGC transports the major part of the drifting sea-ice from the Arctic Basin (Vinje 2001;Kwok 2009). In central Fram Strait, between the EGC and the WSC, there is a complex circulation pattern with high mesoscale activity and a recirculation (Johannessen et al 1987). …”