On the excitation of resonant double Kelvin waves in the Barents Sea Opening

In the northern Barents Sea Opening (BSO) the K1 tidal energy is predominant in the diurnal tidal frequency band, suggesting the generation of a topographic wave with the K1 tidal frequency. Tidal energy of the K1 component becomes strong where bottom topography undulates in the BSO and the scale of the undulation is close to the wavelength of the K1 wave. An analytical model is developed to investigate the energy enhancement mechanism of the tidally induced topographic wave due to a resonance between tidal current, a topographic wave and periodic topography. The wave excited by the resonance is identified as a resonant double Kelvin wave (DKW) and the significant K1 energy in the BSO could be due to the excitation of the resonant DKW

North Atlantic Water in the Barents Sea Opening, 1997 to 1999

North Atlantic Water (NAW) is an important source of heat and salt to the Nordic seas and the Arctic Ocean. To measure the transport and variability of one branch of NAW entering the Arctic, a transect across the entrance to the Barents Sea was occupied 13 times between July 1997 and November 1999, and hydrography and currents were measured. There is large variability between the cruises, but the mean currents and the hydrography show that the main inflow takes place in Bjørnøyrenna, with a transport of 1.6 Sv of NAW into the Barents Sea. Combining the flow field with measurements of temperature and salinity, this results in mean heat and salt transports by NAW into the Barents Sea of 3.9×1013 W and 5.7×107 kg s?1, respectively. The NAW core increased in temperature and salinity by 0.7 °C yr?1 and 0.04 yr?1, respectively, over the observation period. Variations in the transports of heat and salt are, however, dominated by the flow field, which did not exhibit a significant change

Fish migration in oscillating stratified water masses

Abstract Time series records from data storage tag (DST) attached on Northeast Arctic cod (Gadus morhua L.) and Greenland halibut (Reinhardtius hippoglossoides) are investigated in connection with hydrodynamic and hydrographic features at specific locations to obtain spatial and temporal variation on fish migration patterns, which may change the availability of fish to survey gears. From spring to autumn, some Greenland halibut, at 500-800 m depth, were exposed to a persistent diurnal fluctuation of temperature between subzero and 5.5±C. Tidally induced topographic trapped waves with diurnal (K1) frequency were indicated in some region along the Barents Sea escarpment, where the transition zone between warm Atlantic water (AW) and cold Norwegian Sea Arctic Intermediate Water (NAIW) is at 500-700 m. An asymmetry in the temperature diurnal pattern showed a gradual increase followed by a rapid drop. This event may be related to the displacement mechanism of stratified water masses together with the fish diurnal migration pattern in synchrony with tidal motion. The pattern indicates that fish migrated seawards off the slope and was pelagic part of the day, thus unavailable to bottom trawl. Up to three weeks in April, some tagged cod had low vertical activity at a depth exposed to semidiurnal tidal fluctuations of the transition layer between 100-200 m, where cold coastal waters flow on top of warm Atlantic waters. Along the southern coast of the Barents Sea, strong semidiurnal tides can generate baroclinic coastal Kelvin waves causing vertical motion of the pycnocline, thus semidiurnal fluctuation of temperature was observed. Keywords: bottom trapped waves, data storage tag, diurnal vertical migration, Kelvin waves, NE Artic cod, NE Arctic Greenland halibut, spawning activity, temperature gradient

Physical oceanography from the TRACTOR project

Primary Objectives - Describe and quantify the present strength and variability of the circulation and oceanic processes of the Nordic Seas regions using primarily observations of the long term spread of a tracer purposefully released into the Greenland Sea Gyre in 1996. - Improve our understanding of ocean processes critical to the thermaholine circulation in the Nordic Seas regions so as to be able to predict how this region may respond to climate change. - Assess the role of mixing and ageing of water masses on the carbon transport and the role of the thermohaline circulation in carbon storage using water transports and mixing coefficients derived from the tracer distribution. Specific Objectives Perform annual hydrographic, chemical and SF6 tracer surveys into the Nordic regions in order to: - Measure lateral and diapycnal mixing rates in the Greenland Sea Gyre and in the surrounding regions. - Document the depth and rates of convective mixing in the Greenland Sea using the SF6 and the water masses characteristics. - Measure the transit time and transport of water from the Greenland Sea to surrounding seas and outflows. Document processes of water mass transformation and entrainment occurring to water emanating from the central Greenland Sea. - Measure diapycnal mixing rates in the bottom and margins of the Greenland Sea basin using the SF6 signal observed there. Quantify the potential role of bottom boundary-layer mixing in the ventilation of the Greenland Sea Deep Water in absence of deep convection. Monitor the variability of the entrainment of water from the Greenland Sea using time series auto-sampler moorings at strategic positions i.e., sill of the Denmark Strait, Labrador Sea, Jan Mayen fracture zone and Fram Strait. Relate the observed variability of the tracer signal in the outflows to convection events in the Greenland Sea and local wind stress events. Obtain a better description of deepwater overflow and entrainment processes in the Denmark Strait and Faeroe Bank Channel overflows and use these to improve modelling of deepwater overflows. Monitor the tracer invasion into the North Atlantic using opportunistic SF6 measurements from other cruises: we anticipate that a number of oceanographic cruises will take place in the north-east Atlantic and the Labrador Sea. It should be possible to get samples from some cruises for SF6 measurements. Use process models to describe the spread of the tracer to achieve better parameterisation for three-dimensional models. One reason that these are so resistant to prediction is that our best ocean models are as yet some distance from being good enough, to predict climate and climate change