Interannual Variability of the Labrador Current Transport

The Labrador Current flows mainly along the shelf-edge and upper continental slope off Atlantic Canada. It carriesi cold and less saline water of the Arctic origin, as part of the coastal currents associated with the subpolar gyre of the North Atlantic. Its variability can have significant impacts on physical, chemical, and biological features and fisheries on the Atlantic Canadian coastal and shelf seas, and may be indicative of the large-scale oceanic and atmospheric variability and climate change. We have combined satellite altimetry with ocean modelling to generate proxy indices of the Labrador Current volume transport.

For officially released results, see Labrador Current Volume Transport Index

For recently updated indices, click Track191 and Track226_48. Data are available upon request.

For the index at the Seal Island transect, click Seal Island Transect.

FVCOM Modeling and Applications

Finite-volume coastal ocean model (FVCOM) is being developed for the Newfoundland coastal seas and embayments for applications to ocean climate, ecosystem sciences, habitat, aquaculture, and marine safety. The project is supported by the DFO Centre for Ocean Model Development and Application, Canadian Space Agency, the ArcticNet, and is in collaboration with Memorial University.

Model surface circulation and temperature (degree Celcius) fields at (a) April-19-18:00 and (b) June-15-0:00, 1999 (Figure 1).In the April case, the lower temperature water spread westward along the coast. The northerly winds pushed the cold water along the east coast into the inner Bay and the cold water flowed further to the west coast following the cyclonic circulation. In contrast, in the June case, the southwesterly winds pumped the low temperature water from deeper layer onto surface along west coast instead of the warmer incoming water from the east coast. The offshore transport of low temperature water was most notable near 47N where a pool of low temperature water is observed. The model temperature patterns are supported by concurrent satellite observations.

Northwest Atlantic Surface Circulation

Multi-satellite data are used to create daily and weekly surface current maps from satellite altimetry, scatterometer and ocean models. The circulation include wind- and density-driven currents and Stokes drift for ocean monitoring, ecosystem sciences, and marine safety. The project is mainly supported by Canadian Space Agency.

Weekly surface circulation centred on December 22, 2004 (Figure 1). The thick arrows are estimates based on satellite-tracked buoys.

Scotian Shelf/Slope Sea Level and Impacts of Large-scale Circulation

The mean sea surface topography (MSST) relative to the T/P ellipsoid (z6_fig1058) is derived from the altimeter data for the period from 1992 to 2002.

The long-term seasonal-mean anomalies (seasons) relative to the MSST indicate the coastal sea level is highest in fall and lowest in spring. We define winter, spring, summer and fall as Jan-Mar, Apr-Jun, Jul-Sep, and Oct-Dec, respectively. Over the open shelf the sea level is highest in late summer and lowest in early spring. The seasonal variability enhances over the continental slope, presumably associated with meandering of the Gulf Stream and rings pinched off from it. The range varies from 10 cm near the coast to 20 cm over the lower slope.

The seasonal anomalies by year and season (1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002) from the TOPEX/Poseidon data had significant seasonal variations with a range of ~10 cm over the shelf and ~20 cm over the lower continental slope. Sea level was higher in summer/fall and lower in winter/spring. There was substantial interannual variability in the 1990s. The sea level over the Scotian Shelf was lower in 1994 and higher in 1997. In contrast, the fluctuation over the slope was nearly out of phase. Comparison with tide-gauge data at North Sydney, Halifax and Yarmouth shows fair agreement at seasonal (z6_fig1006) and inter annual (z6_fig1008) scales.

The interannual sea level variability seems to be controlled by the interplay between the Gulf Stream north-south movement (Fig7a.jpg) and the strength of the Labrador Current (Figure 2). The coastal sea level rose when the Gulf Stream position (the solid curve in the upper panel of Fig7a) shifted from north to south after 1995/1996 and fell with the intendifcation and on-shelf intrusion of shelf-edge current (the extension of the Labrador Current) in 1997/1998.

Finite-element Ocean Circulation Models

A suite of the state-of-the-art finite-element ocean circulation models have been developed for the Newfoundland and Labrador Shelf and Slope. The model solutions for the first time provided three-dimensional high-resolution monthly-mean observationally based and dynamically consistent ocean currents, temperature, salinity, and turbulence fields. They were validated against historical current meter data, vessel mounted ADCP data and satellite-tracked drift data. The model circulation at the 20-m depth (Figure 1) indicates significant seasonal, along-shelf and cross-shelf variations and prominent cross-shelf and cross-slope exchanges. The velocity distribution (Figure 2) at the four AZMP transects (depicted as dashed lines in Fig. 1) show strong deep currents asscoiated with the nearshore and shelf-edge Labrador Currents.

MITACS Unstructured Grid Modelling Network

Ocean Currents and Eddies From Space Observations

The major circulation features over the Scotian Slope off Nova Scotia consists of the southwestward shelf-edge current carrying fresher and colder water and the northeastward slope current transporting warmer and more saline water north of the Gulf Stream. The variability of physical and biological features over the Scotian Slope is strongly influenced by Gulf Stream meanders and clockwise warm-core rings (WCR). Both the shelf/slope front (separating the colder shelf water and warmer slope water) and the Gulf Stream northern boundary (separating the slope water from the warm Gulf Stream water) fluctuate on various time and space scales, including the seasonal (Figure 1)and inetrannual (Figure 2) variability. The SeaWiFs sea surface temperature data for May 1-15, 2002 clearly identify the existence of a WCR with a diameter of about 200 km (Figure 3). Associated with the WCR is the low chlorophyll concentration (in mg/m**(-3)) as evident in the concurrent SeaWiFs ocean color data (Figure 4). The rotational speed of the WCR is about 1 m/s, as revealed by TOPEX/Poseidon satellite altimetry derived currents (white arrows) on May 8, 2002. Both moored measurements (black arrows) and satellite-derived currents indicate the shelf-edge Labrador Current extension was completely reversed during this period as a result of the close proximity of the WCR and the shelf/slope front to the Scotian Shelf edge (Figure 1). The SeaWiFs data are obtained from DFO/BIO Biology Group, and the TOPEX/Poseidon data from the NASA Jet Propulsion Lab.

Fisheries Oceanography

The temporal and spatial distribution and development of fish eggs and larvae are related to adult spawning location and timing and to environmental conditions. Here we examine potential Atlantic cod egg drift with climatological monthly-mean model circulation (Han and Wang, 2006) in the Placentia Bay in May. Eggs are uniformly distributed at the 20-m depth and tracked with the circulation fields from May 1st for 30 days.

Northern Bay Release Southern Bay Release

Acoustic surveys identified Perch Rock and Bar Haven are major spawning locations of Atlantic cod in 1997. The following movies show possible surface egg drift under the climatological monthly-mean circulation in May. The model results show some consistency with field drift experiments (Bradbury et al., 2000).

Perch Rock Release Bar Haven Release