Labrador Shelf Research Articles

Habitat selection by hooded seals (Cystophora cristata) in the Northwest Atlantic Ocean

Abstract Andersen, J. M., Wiersma, Y. F., Stenson, G. B., Hammill, M. O., Rosing-Asvid, A., and Skern-Maurizen, M. 2013. Habitat selection by hooded seals (Cystophora cristata) in the Northwest Atlantic Ocean. – ICES Journal of Marine Science, 70:173–185. We examined annual habitat use for 65 hooded seals (32 adult females, 17 adult males, and 16 juveniles) equipped with satellite relay data loggers (SRDLs) in spring or summer during five field seasons (2004–2008). A combined approach using first passage time (FPT) analysis and a generalized additive model (GAM) was applied to test for habitat selection, with a focus on environmental parameters of depth, slope, ice, sea surface temperature (SST), and chlorophyll. The models were run on adult males, adult females, and juveniles separately, and the results identified SST, depth, and chlorophyll as the most important factors influencing habitat selection across all categories. Furthermore, males and females preferred similar habitat conditions, but were separated geographically, and by depth, at various times of the year. Males appeared to be more localized in their habitat use patterns, focusing their search effort in areas of complex seabed relief such as Baffin Bay, Davis Strait, and the Flemish cap, while females concentrated their search effort along shelf areas (e.g. the Labrador shelf). These findings support our hypothesis that hooded seals prefer areas where topography and oceanographic processes create favourable foraging conditions.

The circulation of eastern Canadian seas

The eastern Canadian seas including Baffin Bay, the Labrador Sea and shelf, the N.E. Newfoundland Shelf, the Scotian Shelf and the Gulf of St. Lawrence form an integrated hydro-dynamical system. The circulation is investigated using current meter data and a high resolution three dimensional coupled ice-ocean circulation model, CECOM (Canadian East Coast Ocean Model) covering the entire area. The model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008. Many features of the model current fields are similar to those from the previous regional circulation models for the shelves. New findings from CECOM include seasonal differences of the circulation around Davis Strait, the detailed structure of the Labrador Current re-circulation, two cross-shelf currents on the Scotian Shelf, and strong currents in Halibut Channel which connects the waters of the western Grand Banks and Scotian Shelf. The annual variation of the circulation is investigated. Both the model and data show the Labrador Current is strong in fall and weak in spring. The outflow from the Gulf of St. Lawrence through Cabot Strait and the currents on the inner Scotian Shelf are strong in winter and fall and weak in spring, and are in phase with the Labrador Current. The model currents are compared to observations using a qualitative method of visual comparison, and a quantitative method based on statistical analysis. The comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model. The quantitative analysis indicates that the model currents are in reasonable agreement with the observations. Specifically, a good agreement is found in the Labrador shelf, Newfoundland Shelf and Flemish Pass, a fair agreement is found in Davis Strait, the inner Scotian Shelf and Sable Bank. However, the agreement for Cabot Strait and the Scotian Shelf break is less satisfactory. An analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field. The regions with low spatial variability generally have good agreements. The volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data.

Lake Agassiz outburst age and routing by Labrador Current and the 8.2 cal ka cold event

Catastrophic drainage of glacial Lake Agassiz, impounded by the Laurentide Ice Sheet (LIS), into Hudson Bay and Strait is widely thought to have caused the 8.2 cal ka cold event, though the path of its drainage in the North Atlantic is poorly known. Analysis and compilation of 10 sediment cores from 8 sites distributed on the eastern Canadian continental shelf and upper slope south of Hudson Strait revealed distinct beds with elevated detrital carbonate (DC) concentrations, known by their distinct composition to originate from erosion of carbonate bedrock and carbonate-rich glacial sediments in the Hudson Bay-Hudson Strait region. At all but one site, radiocarbon ages, bracketing and within the thickest and most widespread of these beds, are coeval with the age constraints for the Agassiz floods in Hudson Strait and southeastern Hudson Bay. The DC distribution and concentration of this bed are consistent with southward transport in the Labrador Current. Transfer function analysis of dinoflagellate assemblage data from cores on the central Labrador Shelf, in Hudson Bay, and on the Northeast Newfoundland Shelf reveal that early Holocene seasonal ice cover was 5–6 months longer than at present, requiring the application of a 200-year reduction to the radiocarbon age constraints on the Lake Agassiz outburst floods. The age of the floods is reduced to about 8.33 cal ka (7.5 14C ka) from the previous determination of 8.47 cal ka (7.7 14C ka), with a similar reduction in their error ranges to 8.04–8.49 cal ka from 8.16–8.74 cal ka. Based on present current routing, the Agassiz floodwaters and icebergs are inferred to have travelled south in the Labrador Current, and to have possibly become incorporated into the North Atlantic Current, and transported to the Nordic seas. There the freshwater additions would have lessened deepwater production with a concomitant reduction in northward heat transport in the upper limb of the Atlantic meridional overturning circulation, thereby contributing to the 8.2 cal ka cold event. Variation in the calcite and dolomite content of the Agassiz DC bed, two salinity reductions during Agassiz bed deposition, and low-level shorelines of lakes Agassiz and Ojibway suggest that more than one outburst was delivered during the final Agassiz drainage. The 8.2 cal ka cold event registered in Greenland was coeval with a second or later flood, which possibly accompanied the final collapse of the LIS in Hudson Bay.

Overlapping size ranges of Calanus spp. off the Canadian Arctic and Atlantic Coasts: impact on species' abundances

In the North Atlantic, Calanus finmarchicus, C. glacialis and C. hyperboreus are identified based on subtle morphological traits, which is fastidious, or based on their allegedly non-overlapping prosome length ranges. We reappraised the prosome length-based diagnosis for the copepodite stage V stage by coupling prosome length and molecular identifications (mtDNA, 16S gene) for 1159 individuals collected over 2 years from 15 stations off the Canadian coast from the Arctic to the Atlantic. We observed spatial but no intra-annual variation in species’ average prosome length. At sympatric coastal sites, prosome length overlap was frequent between C. finmarchicus and C. glacialis and restricted to the Estuary/Gulf of St. Lawrence between C. glacialis and C. hyperboreus. We used discriminant analyses to redefine prosome length criteria to minimize errors in species identification. Species abundances were corrected and this affected mostly C. glacialis. In the St. Lawrence Estuary and on the Labrador shelf, abundance of C. glacialis was underestimated by 19 and 35%, respectively, with important interannual variations since 2000. This increase in abundance could enhance estimation of the role of C. glacialis in the food web and potentially alter our view of the long-term changes along the eastern Canadian coast.

Atmospheric forcing on the Canadian Arctic Archipelago freshwater outflow and implications for the Labrador Sea variability

The variability of the freshwater export through the Canadian Arctic Archipelago (CAA) is analyzed using a hindcast simulation forced by surface atmospheric forcing from the ERA40 reanalysis (1958-2001). Although the two channels representing the archipelago in the model are both sensitive to the along-channel sea surface height (SSH) gradient, they appear to have very distinct behaviors. The outflow to Lancaster Sound is shown to be largely controlled by the magnitude of the upstream SSH gradient across McClure Strait. The gradient shows a close link to the wind stress curl in the western Arctic but also to a large-scale SSH anomaly pattern which has a strong signal over the shelf to the south of McClure Strait. The latter has, however, little statistical connection to the SSH variability in the Beaufort Gyre. By contrast, the outflow through Nares Strait responds preferentially to SSH variations in the northern Baffin Bay which are remotely forced by air-sea heat exchanges in the Labrador Sea. The variability is largely coherent between the two outflows and is controlled by a dipolar atmospheric pattern reminiscent of the North Atlantic/Arctic Oscillation. When entering the subpolar gyre, the CAA freshwater outflow remains confined to the Labrador shelf with little impact on the salinity of the interior Labrador Sea and potentially on the convection. The latter is represented by a distinct mode of salinity variability in the western subpolar gyre which is rather influenced by the variability of the sea ice export through Fram Strait.

What is the fate of the river waters of Hudson Bay?

We examine the freshwater balance of Hudson and James bays, two shallow and fresh seas that annually receive 12% of the pan-Arctic river runoff. The analyses use the results from a 3-D sea ice-ocean coupled model with realistic forcing for tides, rivers, ocean boundaries, precipitation, and winds. The model simulations show that the annual freshwater balance is essentially between the river input and a large outflow toward the Labrador shelf. River waters are seasonally exchanged from the nearshore region to the interior of the basin, and the volumes exchanged are substantial (of the same order of magnitude as the annual river input). This lateral exchange is mostly caused by Ekman transport, and its magnitude and variability are controlled by the curl of the stress at the surface of the basin. The average transit time of the river waters is 3.0 years, meaning that the outflow is a complex mixture of the runoff from the three preceding years.

Seasonal patterns in zooplankton community structure on the Newfoundland and Labrador Shelf

We report on the patterns in zooplankton community structure on the Newfoundland and Labrador Shelf from seasonal collections along oceanographic sections during 2000–2007. We use a combination of constrained and unconstrained multivariate methods to assess latitudinal and cross shelf patterns in community structure. Both physical and biological features of the region are dominated by the cross-shelf gradient in water mass characteristics although there is evidence of a latitudinal gradient that may be a reflection of the influence of freshwater outflow from the Arctic. All analyses reveal a strong and consistent pattern in species composition among water masses that extends across spring, summer and autumn, although there are some variations that occur among seasons that reflect differences in development state of certain taxa. The strong association between community structure and water mass characteristics in the region may be the result of the Newfoundland and Labrador Shelf being at the intersection of several major oceanographic domains, bounded by strong Labrador and Gulf Stream currents, that allows the formation and persistence of well defined zooplankton communities. Our findings have implications for the region’s potential as a monitoring location for long term changes in ocean state.

Simulation of three-dimensional circulation and hydrography over the Grand Banks of Newfoundland

There are few ocean models that both adequately resolve the cross-shelf structure of the Labrador Current and have been sufficiently evaluated against in situ observations at tidal, synoptic and seasonal scales. We present a three-dimensional, high-resolution, prognostic, nonlinear circulation model for the Newfoundland offshore based on the finite volume coastal ocean model (FVCOM). The FVCOM uses unstructured grid in the horizontal and thus allows efficient and effective use of grid resolution to resolve coastal- and shelf-scale features. The model results are evaluated against current meter measurements, vessel-mounted acoustic Doppler current profiler (ADCP) data, and tide-gauge observations. The FVCOM climatological monthly-mean currents over the shelf and slope show good agreement with observations and substantial improvement over those from an earlier finite-element model. The simulated tidal elevations agree well (4 cm of the root-sum-square absolute error for the total tidal height) with observations, and show improvement over previous tidal models over the Labrador Shelf. The hindcasts for the spring to fall of 1999 show reasonable skill in reproducing temperature, salinity and currents. At station 27 the observed temperature and salinity have seasonal ranges of 14 °C and 1.5 psu near the surface from April to November; while the root-mean-square (RMS) differences are 2.1 °C and 0.3 psu between the model and observations. On the Flemish Cap transect the observed temperature and salinity range from −1.5 to 13.1 °C and from 31.3 to 34.9 psu on July 17–20, 1999; while the RMS differences are 1.0 °C and 0.2 psu. The model-observation velocity difference ratio is 0.53 on this transect on July 17–18, 1999.

Observations of fresh, anticyclonic eddies in the Hudson Strait outflow

The waters that flow out through Hudson Strait, a coastal system that connects Hudson Bay with the Labrador Sea, constitute the third largest freshwater contribution to the northern North Atlantic. Recent studies have documented the mean structure and transport of the outflow, as well as highlighting significant variability on synoptic scales (days–week). This study examines the outflow's variability on these synoptic scales through the use of observations collected by a mooring array from 2005 to 2006. We focus on the mechanisms that cause the freshwater export to be concentrated in a series of discrete pulses during the fall/winter season. We find that the pulses occur once every 4.4 days on average and are associated with anticyclonic, surface-trapped eddies propagated through the strait by the mean outflow. Their occurrence is related to the passage of storms across Hudson Bay, although local instability processes also play a role in their formation. The eddies are responsible for approximately 40% of the mean volume transport and 50% of the mean freshwater transport out of the strait. We discuss the implications of this freshwater release mechanism on the delivery of nutrient-rich and highly stratified waters to the Labrador shelf, a productive region south of Hudson Strait.

Interannual to decadal variability of outflow from the Labrador Sea

A decade of weak convection in the Labrador Sea associated with decreasing water mass transformation, in combination with advective and eddy fluxes into the convection area, caused significant warming of the deep waters in both the central Labrador Sea and boundary current system along the Labrador shelf break. The connection to the export of Deep Water was studied based on moored current meter stations between 1997 and 2009 at the exit of the Labrador Sea, near the shelf break at 53°N. More than 100 year‐long current meter records spanning the full water column have been analyzed with respect to high frequency variability, decaying from the surface to the bottom layer, and for the annual mean flow, showing intra‐ to interannual variability but no detectable decadal trend in the strength of the deep and near‐bottom flow out of the Labrador Sea.

Calcium carbonate saturation states in the waters of the Canadian Arctic Archipelago and the Labrador Sea

Ocean acidification is predicted to occur first in polar oceans. We investigated the saturation state of waters with respect to calcite (Ωcal) and aragonite (Ωarg) in six sections along an Arctic outflow pathway through the Canadian Arctic Archipelago (CAA) and into the northwestern Atlantic using dissolved inorganic carbon and total alkalinity measurements from 2003 to 2005. The study area, a key region connecting the Arctic and the North Atlantic, includes Smith Sound, Barrow Strait, Baffin Bay, Davis Strait, Hudson Strait, and the Labrador Sea. The average Ωarg in the Arctic outflow was 1.18 ± 0.17 in Barrow Strait and 1.31 ± 0.14 in Smith Sound, with areas where Ωarg < 1. The Arctic outflow through the CAA has a high content of Pacific waters, which have a low saturation state. These waters can be traced along the western Baffin Bay to Davis Strait. South of Davis Strait, this outflow is modified by mixing with slope and offshore waters of Atlantic origin and with the outflow from Hudson Strait. Despite the mixing, low saturation state water can still be identified on the southern Labrador Shelf. The aragonite saturation horizon is found at ∼150 m in Barrow Strait; at 200 m in Baffin Bay, Davis Strait, and Hudson Strait; and at 2300 m in the Labrador Sea. This study provides baseline data of the saturation states for the waters of the CAA and the northwest Atlantic. It also illustrates the downstream evolution of low saturation state Arctic outflow in the northwest Atlantic.

Physical controls and interannual variability of the Labrador Sea spring phytoplankton bloom in distinct regions

We investigated the variability of the spring phytoplankton bloom in the Labrador Sea, dividing into distinct biogeographical zones, then analyzing the relationship between the bloom and physical forcings. The spring phytoplankton bloom in the north Labrador Sea varied in intensity by a factor of 4 and in timing of onset by 3 weeks over the 11-year record from SeaWiFS satellite ocean chlorophyll, 1998–2008. This north bloom (north of 60 °N and west of the Labrador shelves) is earliest and most intense, owing in part to the offshore-directed freshwater stratification from the West Greenland Current. On interannual timescales, significant correlations were found between the north bloom intensity and ocean processes, namely offshore advection, eddy activity and runoff from Greenland. In contrast, the central Labrador Sea is later and weaker, and only a correlation between the bloom timing and irradiance was found. As the subpolar gyre shifts in strength and shape, freshwater outflow from the Arctic and Greenland changes, we may expect further changes in the biological response as indicated by these relationships.

Movement Patterns of Hooded Seals (Cystophora cristata) in the Northwest Atlantic Ocean During the Post-Moult and Pre-Breed Seasons

Movement patterns of hooded seals (Cystophora cristata) in the Northwest Atlantic in the period following moulting and prior to breeding are not well known. Here, we describe in detail the movement patterns of 21 seals for this period based on information gathered from satellite linked time depth recorders (SLTDRs). This study provides important baseline information necessary to understand the ecological requirements and patterns in habitat selection for the species. Adult and sub-adult hooded seals were tagged with SLTDRs directly after moulting in SE Greenland during July 2004, 2005 and 2007. Due to variation in tag date and arrival date to the breeding grounds, data between 1 Aug–28 Feb were used which gave all seals a track duration of 211 days (212 in 2005) except for one juvenile where the tag lasted for only 154 days. The tags yielded 36 107 location fixes (SD = 410.64, mean = 1 719.38). Although there was individual variation between seal trajectories during migration, the population shared a similar overall pattern. After moulting in July individuals travelled along the continental shelf area up to Davis Strait and Baffin Bay, thereafter moving southwards along the Labrador shelf until they arrived at the breeding grounds by March. Females tended to cut across the Labrador Sea and arrived at the Labrador shelf before heading up to the Baffin Bay area, while males tended to move straight there. The majority of the seals ended up at the Front (off Newfoundland and Southern Labrador) by March although a few of the tagged seals may have belonged to the Davis Strait breeding population and one male belonged to the Gulf of St. Lawrence breeding population. Seven seals displayed an eastward migratory pull and might have overlapped with the Northeast Atlantic population. This would support the theory of a panmitic population structure.

Long-term seasonal and spatial patterns in mortality and survival of Calanus finmarchicus across the Atlantic Zone Monitoring Programme region, Northwest Atlantic

Abstract Plourde, S., Pepin, P., and Head, E. J. H. 2009. Long-term seasonal and spatial patterns in mortality and survival of Calanus finmarchicus across the Atlantic Zone Monitoring Programme region, Northwest Atlantic. – ICES Journal of Marine Science, 66: 1942–1958. The vertical life table method was used to estimate stage-specific daily mortality rates and survival from 1999 to 2006 for Calanus finmarchicus sampled in the Canadian Atlantic Zone Monitoring Programme, which covers the Newfoundland–Labrador Shelf (NLS), Gulf of St Lawrence (GSL), and Scotian Shelf (SS). Stage-specific mortality rates and survival showed significant regional and seasonal differences, with the largest signal associated with variations in temperature. Density-dependent mortality, associated with the abundance of C6 females, was the main factor influencing mortality in the egg–C1 transition during the period of population growth in spring on the SS, and in summer in the GSL and on the NLS. In autumn, mortality in egg–C1 was positively related to temperature and negatively related to phytoplankton biomass, with particularly high mortality rates on the SS. The integration of our results into stage-specific recruitment rates from egg to C5 revealed that C. finmarchicus populations experience their greatest loss (mortality) during the egg–C1 transition. Loss during development to C1 was greater in the GSL than in the other regions during the period of population growth, resulting in lower recruitment success in the GSL. In autumn, C. finmarchicus showed low stage-specific daily recruitment rates on the SS at high temperatures, and low phytoplankton biomass compared with those in the GSL and on the NLS. Our findings reinforce the necessity of describing regional and seasonal patterns in mortality and survival to understand factors controlling the population dynamics of C. finmarchicus.

Rapid warming of Large Marine Ecosystems

The need to understand local effects of global climate change is most urgent in the Large Marine Ecosystems (LMEs) since marine ecosystem-based management requires information on the LME scale. Reported here is a study of sea surface temperature (SST) change in the World Ocean LMEs in 1957–2006 that revealed strong regional variations in the rate of SST change. The rapid warming in 1982–2006 was confined to the Subarctic Gyre, European Seas, and East Asian Seas. These LMEs warmed at rates 2–4 times the global mean rate. The most rapid warming was observed in the land-locked or semi-enclosed European and East Asian Seas (Baltic Sea, North Sea, Black Sea, Japan Sea/East Sea, and East China Sea) and also over the Newfoundland–Labrador Shelf. The Indian Ocean LMEs’ warming was slow, while two major upwelling areas – California and Humboldt Currents – experienced a slight cooling. The Subarctic Gyre warming was likely caused by natural variability related to the North Atlantic Oscillation. The extremely rapid surface warming in the enclosed and semi-enclosed European and East Asian Seas surrounded by major industrial/population agglomerations may have resulted from the observed terrestrial warming directly affecting the adjacent coastal seas. Regions of freshwater influence in the European and East Asian Seas seem to play a special role in modulating and exacerbating global warming effects on the regional scale.

Fronts in Large Marine Ecosystems

Oceanic fronts shape marine ecosystems; therefore front mapping and characterization are among the most important aspects of physical oceanography. Here we report on the first global remote sensing survey of fronts in the Large Marine Ecosystems (LME). This survey is based on a unique frontal data archive assembled at the University of Rhode Island. Thermal fronts were automatically derived with the edge detection algorithm of Cayula and Cornillon (1992, 1995, 1996) from 12 years of twice-daily, global, 9-km resolution satellite sea surface temperature (SST) fields to produce synoptic (nearly instantaneous) frontal maps, and to compute the long-term mean frequency of occurrence of SST fronts and their gradients. These synoptic and long-term maps were used to identify major quasi-stationary fronts and to derive provisional frontal distribution maps for all LMEs. Since SST fronts are typically collocated with fronts in other water properties such as salinity, density and chlorophyll, digital frontal paths from SST frontal maps can be used in studies of physical–biological correlations at fronts. Frontal patterns in several exemplary LMEs are described and compared, including those for: the East and West Bering Sea LMEs, Sea of Okhotsk LME, East China Sea LME, Yellow Sea LME, North Sea LME, East and West Greenland Shelf LMEs, Newfoundland–Labrador Shelf LME, Northeast and Southeast US Continental Shelf LMEs, Gulf of Mexico LME, and Patagonian Shelf LME. Seasonal evolution of frontal patterns in major upwelling zones reveals an order-of-magnitude growth of frontal scales from summer to winter. A classification of LMEs with regard to the origin and physics of their respective dominant fronts is presented. The proposed classification lends itself to comparative studies of frontal ecosystems.

Seasonal variability of the Labrador Current and shelf circulation off Newfoundland

Three‐dimensional finite element models were established for the Newfoundland and Labrador Shelf to investigate climatological monthly mean wind‐ and density‐driven circulation. The model was forced using wind stresses from the National Center for Environmental Prediction‐National Center for Atmospheric Research reanalysis data prescribed at the sea surface, large‐scale remote forcing determined from a North Atlantic model, monthly mean temperature and salinity climatology, and M2 tide on the open boundary. The model results were examined against various in situ observations (moored current meter, tide gauge, and vessel‐mounted acoustic Doppler current profiler data) and satellite drift measurements and discussed together with literature information. The seasonal mean circulation solutions were investigated in terms of relative importance of wind to density forcing for the Labrador Current. The model results indicate significant seasonal and spatial variations, consistent generally with previous study results and in approximate agreement with observations for the major currents. The region is dominated by the equatorward flowing Labrador Current along the shelf edge and along the Labrador and Newfoundland coasts. The Labrador Current is strong in the fall/winter and weak in the spring/summer. The mean transport of the shelf edge Labrador Current is 7.5 Sv at the Seal Island transect and 5.5 Sv through the Flemish Pass. The seasonal ranges are 4.5 and 5.2 Sv at the two sections, respectively. Density‐ and wind‐driven components are both important in the inshore Labrador Current. The density‐driven component dominates the mean component of the shelf edge Labrador Current while the large‐scale wind‐forcing contributes significantly to its seasonal variability.

Phytoplankton growth and regulation in the Labrador Sea: light and nutrient limitation

The importance of light and nutrients in regulating phytoplankton growth in the Labrador Sea was evaluating using climatological data, 12 years of measurements made as part of the Labrador Sea Monitoring Program (LSMP) and physiological information from the literature. Light limits primary production and phytoplankton growth much of the year, even during summer when surface irradiance is at its seasonal peak. Nutrients, nitrogen (nitrate) and silicate, are reduced to low levels in surface waters in summer/autumn and can limit phytoplankton production and growth at this time of year. Nitrate appears to be the nutrient in shortest supply on the Labrador Shelf while silicate is in shortest supply in the central Labrador Basin. Multiyear trends in regional hydrography (increases in water temperatures, decreases in mixed layer depth) and changes in nitrate and silicate supply over the past decade (i.e. increases in nitrate and decreases in silicate) may be linked to changes in phytoplankton community composition and structure (i.e. decreases in large forms such as diatoms and increases in small picoplankton and nanoplankton forms).

Variations in overwintering depth distributions of Calanus finmarchicus in the slope waters of the NW Atlantic continental shelf and the Labrador Sea

Vertical depth distributions of Calanus finmarchicus were examined in autumn and winter (2001–2003) for the slope and offshore waters of the Canadian Atlantic continental shelf from the south Labrador Shelf in the north to the southwestern tip of the Scotian Shelf in the south as well as along sections across the Labrador Sea and in Cabot Strait. A total of 324 samples were collected at 53 stations that ranged over ~19 degrees of latitude and ~17 degrees of longitude. Calanus finmarchicus populations in the subsurface layers (depths >100 or 200 m) were dominated (>90%) by CV copepodites off the western Scotian Shelf, in Cabot Strait, the central Newfoundland slope waters and the Labrador Sea. Along the slope between Flemish Pass and the eastern Scotian Shelf CVs made up 60–80% of the population in autumn and 80–86% in winter, with accompanying CIVs being replaced by CVs and adults between autumn and winter. CVs were deepest off the Greenland Shelf (70% below 1 000 m) and shallowest in Cabot Strait (80% in the 100–300 m interval; bottom depth ~450 m). Overwintering depth intervals were generally broad and covered large ranges of temperature and salinity. There were relatively high concentrations (>15 m-3) of late stage (CIV–CVI) C. finmarchicus in the surface layers in the Cabot Strait region in autumn (2003) and in the slope waters off St. Pierre Bank (south Newfoundland Shelf) in winter (2003). These were probably the result of late seasonal production in the Gulf of St. Lawrence and Cabot Strait region, or on the Newfoundland Shelf where vertical ring net tows indicated high numbers (>10 000 m-2) of C. finmarchicus at stations upstream of the St. Pierre Bank sampling area. The vertical distribution data from winter 2003 suggest that transport of overwintering animals around the Tail of the Grand Bank where water depths are >1 000 m and southwestwards along the Scotian shelf break was limited, and that populations along the slope between the NW Grand Bank and the eastern Scotian Shelf had important local sources. There was also evidence of northeasterly transport of overwintering CVs from the western Scotian Shelf to the central Scotian Shelf slope waters between October and December 2003.

Paleoenvironments along the Eastern Laurentide Ice Sheet Margin and Timing of the Last Ice Maximum and Retreat

Palynological and isotopic analysis in a few deep-sea cores from the Labrador Sea reveals strong environmental changes related to the Late Pleistocene glacial fluctuations over eastern Canada. On the whole, the Labrador Sea was characterized by strong exchanges between North Atlantic water masses, Arctic outflows, and meltwater discharges from Laurentide, Greenland and lnuitian ice sheets. The penetration of temperate Atlantic waters persisted throughout most of the Late Pleistocene, with a brief interruption during the Late Wisconsinan. During this glacial substage, a slight but continuous meltwater runoff from the Laurentide ice margins grounded on the northern Labrador Shelf is indicated by relatively low 18O values and low-salinity (< 30‰) dinocyst assemblages. The calving of the ice margin, the melwater outflow and the subsequent dilution of surface waters offshore Labrador probably contributed to the dispersal of floating ice and, consequently, to a southward displacement of the polar front restraining the penetration of North Atlantic waters into the Labrador Sea. The advection of southern air masses along the Laurentide ice margins, shown by pollen assemblages, was favourable to abundant precipitation and therefore, high ice accumulation rates, especially over northern Labrador during the Late Wisconsinan. The déglaciation is marked by a brief, but significant, melting event of northern Laurentide ice shortly after 17 ka. The main glacial retreat occurred after ca. 11 ka. It allowed restoration of WSW-ENE atmospheric trajectories, increased phytoplanktonic productivity, and penetration of North Atlantic water masses into the Labrador Sea.