Labrador Shelf Research Articles

Community size spectra provide indicators of ecosystem recovery on the Newfoundland and Labrador shelf

Species- and size-selective overexploitation often have ecosystem-wide impacts that are evident in community size spectra. To both derive potential ecosystem targets for community rebuilding and assess contemporary indicators relative to these targets, we constructed theoretical size spectra to predict pristine biomass densities using a combination of species- and size-specific nitrogen stable isotope signatures and a range of trophic efficiencies and primary productivity estimates within and among 3 sub-regions of the Newfoundland and Labrador shelf. Theoretical size spectra were compared to empirically derived size spectra using trawl survey data. The descending slopes of the empirically determined size spectra were between 1.25 and 2.42 times steeper than the theoretical slopes. The percentage of the theoretical distribution represented by the empirical size structure ranged between 1.1 and 29.4%, with the closest and furthest estimates associated with the smallest- and largest-sized fishes, respectively, and strongly influenced by estimates of trophic efficiency and primary productivity. Regional variation was also observed, with southern regions reaching 1.3-32.3% of the theoretical biomass density and the northernmost region reaching only 0-8.3%. Importantly, the descending slopes varied depending on fish size, with biomass density of larger sizes decreasing faster than that of smaller sizes. Variations among sub-regions and fish guilds were also observed. These analyses provide a means to derive potential ecosystem targets and indicators through which recovery of fish communities can be monitored and assessed.

North Atlantic right whale (Eubalaena glacialis) and its food: (II) interannual variations in biomass of Calanus spp. on western North Atlantic shelves

AbstractThe North Atlantic right whale (NARW), Eubalaena glacialis, feeds on zooplankton, particularly copepods of the genus Calanus. We quantified interannual variation in anomalies of abundance and biomass of Calanus spp. and near-surface and near-bottom ocean temperature and salinity from 19 subregions spanning the Gulf of Maine–Georges Bank (GoM–GBK), Scotian Shelf (SS), Gulf of St. Lawrence (GSL) and Newfoundland and Labrador Shelves. We analyzed time series from 1977 to 2016 in GoM–GBK, 1982 to 2016 in southwest GSL and 1999 to 2016 in remaining areas. Calanus finmarchicus dominated abundance and biomass, except in the GSL where Calanus hyperboreus was abundant. The biomass of Calanus spp. declined in many subregions over years 1999–2016 and was negatively correlated with sea surface temperature in GoM–GBK and on the SS. We detected ``regime shifts” to lower biomass of Calanus spp. in the GoM–GBK in 2010 and on the SS in 2011. In the GoM–GBK, shifts to lower biomass of C. finmarchicus coincided with shifts to warmer ocean temperature and with published reports of changes in spatial distribution and reduced calving rate of NARW. We hypothesize that warming has negatively impacted population levels of Calanus spp. near their southern range limit, reducing the availability of prey to NARW.

Geology and Oil and Gas Bearing Potential of the East Canadian Continental Margin

Within the East Canadian continental margin, three oil and gas bearing regions have been identified from north to south: the Labrador Sea shelf, the margin of the Grand Banks of Newfoundland, and the Nova Scotia continental margin. In each of these regions, a number of sedimentary basins are distinguished and completely submerged. The following large sedimentary basins are distinguished on the Labrador Sea shelf: the Saglek, Hopdale, and Havke; on the margin of the Grand Banks of Newfoundland, the following basins are known: the Jeanne d’Arc, Flemish Pass, and Orphan. The Scotian Shelf distinguishes the Nova Scotia and Sable basins. It is noteworthy that at high latitudes, such as the Labrador Sea region, the age of productive sediments begins with more ancient rocks (since the Paleozoic) than in the basins to the low latitude (since the Mesozoic), due to which the stratigraphic range of oil and gas bearing in the high latitude basins is much wider. The oil and gas bearing potential in the entire region is mainly related to the continental slopes and turbidite deposits occurring within them. Late Jurassic and Early Cretaceous reservoirs will be the target sediments during deep drilling. Widespread Late Cretaceous and Early Tertiary formations with oil and gas potential are quite realistic, since they do not lie at deep horizons. The oil and gas bearing potential on the margins of basins is associated with Late Cretaceous and Tertiary sediments, alluvial fan deposits, and salt diapirs.

Generating higher resolution regional seafloor maps from crowd-sourced bathymetry.

Seafloor mapping can offer important insights for marine management, spatial planning, and research in marine geology, ecology, and oceanography. Here, we present a method for generating regional bathymetry and geomorphometry maps from crowd-sourced depth soundings (Olex AS) for a small fraction of the cost of multibeam data collection over the same area. Empirical Bayesian Kriging was used to generate a continuous bathymetric surface from incomplete and, in some areas, sparse Olex coverage on the Newfoundland and Labrador shelves of eastern Canada. The result is a 75m bathymetric grid that provides over 100x finer spatial resolution than previously available for the majority of the 672,900 km2 study area. The interpolated bathymetry was tested for accuracy against independent depth data provided by Fisheries and Oceans Canada (Spearman correlation = 0.99, p<0.001). Quantitative terrain attributes were generated to better understand seascape characteristics at multiple spatial scales, including slope, rugosity, aspect, and bathymetric position index. Landform classification was carried out using the geomorphons algorithm and a novel method for the identification of previously unmapped tributary canyons at the continental shelf edge are also presented to illustrate some of many potential benefits of crowd-sourced regional seafloor mapping.

Chromosomal inversions in the Atlantic cod genome: Implications for management of Canada’s Northern cod stock

Following stock collapse and over twenty years of moratoria, the state of Canada’s Northern Atlantic cod (Gadus morhua) remains precarious. To test if recent stock growth was of endogenous or exogenous origin, we performed a whole genome scan (ddRAD) on 135 adults captured in 2015 at three offshore spawning locations spanning the range of the offshore stock along the northeastern Newfoundland and Labrador shelf (Hawke Channel, Notre Dame Channel and Bonavista Corridor), with an additional 105 adults from three more southern locations (St. Anns Bank, Browns Bank and Bay of Fundy). Population structure analysis using 5,077 single nucleotide polymorphisms (SNPs) detected a distinct genetic break off the coast of Nova Scotia near 45 °N. Gene flow between groups north and south of this divide appears to be limited despite the presence of several northern-type and admixed individuals present in the southern area. North of the genetic divide, allele frequencies of neutral loci were indicative of a panmictic population. Several outlier SNPs were found to be associated with ecologically relevant physical characteristics (visual pigments, fin development, response to hypoxia, and various metabolic processes), which may be indicative of different ecological niches.

REE distribution and Nd isotope composition of estuarine waters and bulk sediment leachates tracing lithogenic inputs in eastern Canada

The rare earth element (REE) concentrations and the neodymium (Nd) and strontium (Sr) isotope compositions of the detrital fraction and authigenic FeMn oxyhydroxide coatings of marine sediments may provide valuable information for better understanding the pathways of weathering inputs and estuarine and coastal exchange processes on different time scales. Here, we present the REE concentrations and 143Nd/144Nd (expressed in epsilon units, εNd) and 87Sr/86Sr ratios of detrital and authigenic (leached FeMn oxyhydroxides) fractions from sediment core-top samples and of estuarine water samples collected in the Estuary and Gulf of St. Lawrence (EGSL) and continental shelf off southeastern Canada. The REE distribution patterns, εNd values, and 87Sr/86Sr isotopic values from the detrital fraction allow for the discrimination of sediment from continental sources in the EGSL. Sediments in the Baie des Chaleurs and on the continental shelf, which have εNd values ranging from −14.3 to −16, 87Sr/86Sr values ranging from 0.72708 to 0.71475, and low La/Yb and Gd/Yb ratios, are mainly supplied by the early Paleozoic Appalachian Mountains. In contrast, sediments in the Laurentian and Esquiman channels (εNd = −18.7 to −21.8, 87Sr/86Sr = 0.72068 to 0.72607, and high La/Yb and Gd/Yb ratios) come from the Grenvillian metamorphic rocks in the Canadian Shield, and surface sediments on the southern Labrador Shelf (εNd = −28.7, 87Sr/86Sr = 0.73062, and high La/Yb and Gd/Yb ratios) mainly originate from the Hudson Strait and Baffin Bay. The εNd values obtained from estuarine water samples and bulk sediment leachates are unradiogenic, with values ranging between −18.9 and − 21.7 and between −16.1 and − 27.2, respectively. Based on these results and the dissolved REE concentrations, we speculate that salt-induced coagulation of colloidal matter, dissolution of lithogenic sediments from the adjacent continents (notably from the erosion of the Grenville Province on the North Shore), bottom scavenging within the nepheloid layer, and brine rejection during sea ice formation significantly influence the distribution of REEs and the authigenic εNd signal throughout the water column in the EGSL. Overall, our results both underscore the fact that caution must be exercised when interpreting authigenic εNd records due to bottom water-mass mixing in estuarine and coastal marine environments and highlight the potential of REE and NdSr isotope compositions in investigating changes in sediment sources and transport pathways in the EGSL.

Holocene water mass changes in the Labrador Current

The Labrador Current is part of the anticlockwise subpolar gyre and plays a major role in the formation of North Atlantic Deep Water. It is influenced by the West Greenland and Baffin currents supplying warmer Atlantic and cold polar waters, respectively. During the early Holocene, at the final stage of the last deglaciation, meltwater and iceberg discharge caused highly variable conditions in the Labrador Current. In order to assess its sensitivity to such freshening, this study provides a well-resolved Holocene paleoclimatic record from the Labrador Shelf. Based on benthic foraminiferal faunal and alkenone biomarker analyses, we differentiated four distinct climatic periods in the western Labrador Sea. From 8.9 to 8.6 ka BP, the Labrador Shelf was dominated by polar water outflow from Baffin Bay and covered by perennial sea ice. Between 8.6 and 7.4 ka BP, a strong subsurface inflow of warmer Atlantic water masses is ascribed to an intensification and redirection of the West Greenland Current. At 7.4 ka BP, the decreased influence of Atlantic water masses on the Labrador Shelf marks the establishment of winter convection leading to the formation of Labrador Sea Water in the central basin. Concurrently, an intensified polar water outflow through the Canadian Gateways strengthened the inner Labrador Current, and higher primary productivity suggests longer spring blooms because of a shorter sea-ice season during the Holocene Thermal Maximum. In the late Holocene after 3 ka BP, periodic fluctuations of primary productivity may tentatively be correlated with stronger and weaker northwesterly winds.

Assessing connectivity patterns among management units of the Newfoundland and Labrador shrimp population

AbstractThe Eastern Canadian northern shrimp population, representing one of the most important fisheries in the region, decreased dramatically since the mid‐2000s to a historical low in 2017, but changes were not spatially uniform. Applying a biophysical model within Newfoundland and Labrador (NL) management areas, we investigated connectivity processes during the long pelagic larval phase (2–3 months) of Pandalus borealis and key drivers of larval dispersal in different environmental conditions. We selected 3 years representative of contrasting North Atlantic Oscillation (NAO) phases to assess potential larval dispersal patterns of the northern shrimp population in NL, and hierarchically assessed the impact of the timing of release (yearly and daily), release location, and vertical migration behaviour on shrimp larval dispersal. Overall, we found that populations located on the northern Newfoundland and Labrador shelf supplied potential settlers to southern populations because of the dominant Labrador Current. Ocean circulation and current velocities during the NAO positive year differed from other years, generating contrasting settlement spatial patterns. Larval release location and vertical migration behaviour were the two most important influences on the strength of larval supply and settlement patterns. Inclusion of diel and ontogenic swimming behaviour increased settlement success of larvae released from inshore areas, regardless of study years. Our study improves understanding of northern shrimp stock‐recruitment relationships, their sensitivity to changing environmental conditions, and spatially non‐homogeneous population decline for bentho‐pelagic species with a long larval phase, which could potentially help improve management strategies.

Seasonal vessel activity risk to seabirds in waters off Baffin Island, Canada

Millions of seabirds use the waters off Baffin Island. Considering current and future vessel activity in this region, it is important to understand where vulnerability to anthropogenic threats is highest to enable sound wildlife management and regulatory decisions. Using kernel density analysis on at-sea survey data spanning 1970 to 1983 and 2007 to 2016, we identified marine areas of high density for five of the most abundant species sighted: Dovekie Alle alle, Thick-billed Murre Uria lomvia, Black-legged Kittiwake Rissa tridactyla, Northern Fulmar Fulmarus glacialis and Black Guillemot Cepphus grylle, in summer (June–August) and fall (September–November). We quantified the level of vessel activity from vessel traffic data spanning 2011 to 2015. Overlapping these data layers, we identified regions where high vessel activity posed the highest risk to these species. Navy Board Inlet, Eclipse Sound, Frobisher Bay, Hudson Strait and the northern Labrador Shelf were consistently identified as areas of highest risk to multiple species of seabirds in summer and autumn. These waters not only encompass important summer foraging areas near colonies and post-breeding/migratory habitat but are also frequently navigated by vessels servicing busy communities. The level of vessel activity we found for the study area is relatively low compared to waters where many Arctic species overwinter (e.g., Thick-billed Murres off Newfoundland and Labrador). However, identifying current high-risk areas in Arctic waters is important for the conservation and management of Arctic seabirds as industrial and commercial development in this region expands and leads to higher levels of vessel activity.

Long-lived coralline alga records multidecadal variability in Labrador Sea carbon isotopes

While the recent decline in the δ13C composition of oceanic dissolved inorganic carbon (DIC) can be attributed to increasing anthropogenic CO2 emissions (13C Suess effect), the causes of natural variability in the δ13C of oceanic DIC (δ13CDIC) are far less understood. Unfortunately, instrumental oceanic DIC measurements are not available prior to the 1970s, prohibiting the observation and study of long-term variability in oceanic carbon isotope dynamics. Thus, in order to identify the main driving forces of changes in oceanic δ13CDIC, multicentury carbon isotope time series that extend from the present into the preindustrial period are required. Such time series may be extracted from the carbonate skeletons of long-lived marine organisms, which have been shown to be robust recorders of fluctuations and trends in oceanic δ13CDIC. In this study, we use an annually-banded coralline alga live-collected from the Labrador shelf to generate a 266-year time series of δ13CDIC changes in the Labrador Sea. Our results indicate that from the 1960s onwards, the rate of δ13CDIC decline in the Labrador Sea slightly exceeds the rate of δ13C decline in the atmosphere, providing support for the enhanced CO2 uptake ability of the Labrador Sea. In addition, the detrended algal δ13C time series displays multidecadal variability with typical Atlantic Multidecadal Oscillation (AMO) frequencies. We show that prior to the late 1980s, algal δ13C compositions significantly correlate with regional sea ice cover (SIC) variability, post-1850 instrumental, reconstructed AMO indices, and solar variability. We speculate that these low-frequency oscillations in δ13C reflect changes in marine primary productivity modulated by a mechanism involving solar changes, the AMO and SIC variability. Our algal carbon isotope time series suggests that while the anthropogenic Suess effect has influenced Labrador Sea δ13CDIC since the 1960s, its influence may have been obscured by the effects of natural climatic variability up until the late 1980s.

Ekman and Eddy Exchange of Freshwater and Oxygen across the Labrador Shelf Break

AbstractTransport of freshwater from the Labrador Shelf into the interior Labrador Sea has the potential to impact deep convection via its influence on the salinity of surface waters. To examine this transport, the authors deployed two underwater gliders on a mission to traverse the continental shelf break multiple times between 5 July and 22 August 2014, the period when Arctic meltwater has historically peaked in transport down the Labrador Shelf. The field campaign yielded a unique dataset of temperature, salinity, and oxygen across the shelf break to a depth of 1000 m at unprecedented spatial resolution. Two mechanisms of cross-shelf transport were examined: Ekman transport and transport due to mesoscale eddies. Ekman transport is quantified using satellite wind stress and near-surface hydrographic properties, and eddy-induced transport is scaled using a parameterized eddy diffusivity and thickness gradients of layers of uniform potential density, as well as the tracer gradients along those isopycnals. Both the Ekman and eddy terms transport high-oxygen and low-salinity water from the shelf to the Labrador Sea during the field campaign. The influence of the eddy-driven oxygen flux from the shelf to the Labrador Sea on oxygen budgets depends strongly on the size of the region over which this eddy flux converges. The deduced offshore transport of freshwater (4 ± 6 mSv; 1 mSv = 103 m3 s−1) from both Ekman and eddy mechanisms, which is likely at a seasonal maximum during this summertime survey, represents about 3% of the annual-mean freshwater flowing through Hudson and Davis Straits but may be an important component of the total freshwater budget of the interior Labrador Sea.

Climate Change on Newfoundland and Labrador Shelves: Results From a Regional Downscaled Ocean and Sea-Ice Model Under an A1B Forcing Scenario 2011–2069

ABSTRACTClimate change may affect ocean and ice conditions in coastal oceans and thus have significant impacts on coastal infrastructure, marine navigation, and marine ecosystems. In this study a three-dimensional ice–ocean model is developed to examine likely changes of ocean and ice conditions over the Newfoundland and Labrador Shelves in response to climate change. The model is configured with a horizontal grid of approximately 7 km and a vertical grid of 46 levels and is run from 1979 to 2069. The projection period is 2011 to 2069 under a median emission scenario A1B used by the Intergovernmental Panel on Climate Change. For the projection period, the surface atmospheric forcing fields used are from the Canadian Regional Climate Model over the North Atlantic. The open boundary conditions come from the Canadian Global Climate Model, Version 3 (CGCM3), adjusted for the 1981–2010 mean of the Simple Ocean Data Assimilation model output. The simulated fields over the 1981–2010 period have patterns consistent with observations. Over the Newfoundland and Labrador Shelves during the projection period, the model shows general trends of warming, freshening, and decreasing ice. From 2011 to 2069, the model projects that under A1B sea surface temperature will increase by 1.4°C; bottom temperature will increase by 1.6°C; sea surface salinity will decrease by 0.7; bottom salinity will decrease by 0.3; and sea-ice extent will decrease by 70%. The sea level will rise by 0.11 m at the St. John's tide-gauge station because of oceanographic change, and the freshwater transport of the Labrador Current will double as a result of freshening. The regional ice–ocean model reproduces more realistic present climate conditions and projects considerably different future climate conditions than CGCM3.

Sources, cycling and transfer of mercury in the Labrador Sea (Geotraces-Geovide cruise)

Abstract The Labrador Sea links the Arctic and North Atlantic oceans and constitutes one of the main entrances of atmospheric inputs into the Ocean's interior. We report here the first high-resolution Hg distribution pattern along a transect from Greenland to Labrador coasts sampled after the 2014 winter convection. Total Hg concentrations in unfiltered (HgT UNF ) samples ranged from 0.25 pmol L − 1 to 0.67 pmol L − 1 averaging 0.44 ± 0.10 pmol L − 1 (n = 113, 1σ). Concentrations in filtered samples (HgT F , UNF and exhibited a similar distribution. High HgT UNF concentrations were found (i) in the waters of the Labrador Current, which receive desalted waters from the Canadian Arctic Archipelago, and (ii) in the waters over the Labrador shelf and rise. In the Labrador Sea Waters formed during the 2014 winter convection, HgT UNF concentrations were low (0.38 ± 0.05 pmol L − 1 , n = 23), and increased gradually with depth (up to > 0.5 pmol L − 1 ) in the Northeast Atlantic Deep Waters. HgT F correlates with apparent oxygen utilization implying that atmospheric deposition, biological uptake, and microbial respiration control the Hg distribution in the Labrador Sea. Subtracting the amount of Hg released during organic matter remineralization allows us to identify a Hg and organic matter enriched fraction, which originates from fluvial sources in the Canadian Arctic Archipelago waters. This fraction is transferred southward, in surface waters with the Labrador Current, and at depth with the lower limb of the Atlantic Meridional Overturning Circulation. Climate warming, which will increase the mobilization of Hg from thawing permafrost, would consequently increase the Arctic export of Hg initially associated with organic matter.

From interannual to decadal: 17 years of boundary current transports at the exit of the Labrador Sea

AbstractOver the past 17 years, the western boundary current system of the Labrador Sea has been closely observed by maintaining the 53°N observatory (moorings and shipboard station data) measuring the top‐to‐bottom flow field offshore from the Labrador shelf break. Volume transports for the North Atlantic Deep Water (NADW) components were calculated using different methods, including gap filling procedures for deployment periods with suboptimal instrument coverage. On average the Deep Western Boundary Current (DWBC) carries 30.2 ± 6.6 Sv of NADW southward, which are almost equally partitioned between Labrador Sea Water (LSW, 14.9 ± 3.9 Sv) and Lower North Atlantic Deep Water (LNADW, 15.3 ± 3.8 Sv). The transport variability ranges from days to decades, with the most prominent multiyear fluctuations at interannual to near decadal time scales (±5 Sv) in the LNADW overflow water mass. These long‐term fluctuations appear to be in phase with the NAO‐modulated wind fluctuations. The boundary current system off Labrador occurs as a conglomerate of nearly independent components, namely, the shallow Labrador Current, the weakly sheared LSW range, and the deep baroclinic, bottom‐intensified current core of the LNADW, all of which are part of the cyclonic Labrador Sea circulation. This structure is relatively stable over time, and the 120 km wide boundary current is constrained seaward by a weak counterflow which reduces the deep water export by 10–15%.

A 10Be chronology of early Holocene local glacier moraines in central West Greenland

New cosmogenic 10Be exposure ages constrain Greenland Ice Sheet (GrIS) deglaciation and the culmination of a local glacier advance on the southern shore of Nuussuaq (peninsula) in central West Greenland. Mean ages of GrIS deglaciation and local glacier moraine deposition are 10.5±0.1 ka (n = 2) and 10.4±0.2 ka (n = 5), respectively. The similar ages suggest an advance/stillstand of local glaciers soon after the local retreat of the GrIS. The moraines dated in this study may be correlative to the nearby Disko Stade moraines. Moraine chronologies for both GrIS moraines and our local glacier moraines in central West Greenland correspond to detrital carbonate peaks in a Labrador shelf marine sediment core that records Laurentide Ice Sheet (LIS) discharge from Hudson Strait. Large freshwater discharge events into the North Atlantic sub‐polar gyre have been linked to abrupt cooling events in the Northern Hemisphere during the early Holocene. We propose LIS freshwater input to the sub‐polar gyre and associated regional cooling as the main driver for advance/stillstand of both local glaciers and the GrIS in central West Greenland during the early Holocene.

Composition of freshwater in the spring of 2014 on the southern Labrador shelf and slope

The Labrador Current is an important conduit of freshwater from the Arctic to the interior North Atlantic subpolar gyre. Here we investigate the spatial variability of the freshwater sources over the southern Labrador shelf and slope during May–June 2014. Using measurements of seawater properties such as temperature, salinity, nutrients, and oxygen isotopic composition, we estimate the respective contributions of saline water of Atlantic and Pacific origins, of brines released during sea ice formation, and of freshwater from sea ice melt and meteoric water origins. On the southern Labrador shelf, we find a large brine signal and Pacific water influence indicating a large contribution of water from the Canadian Arctic. The brine signal implies that more than 4 m of sea ice formed upstream, either in the Arctic or in Baffin Bay and the northern Labrador Sea. Over the midshelf and slope at 52°N, we find a stronger influence of slope water from the West Greenland Current with a smaller contribution of Pacific water and no brine signal. Thus, there is advection of water from the slope region to the midshelf between 55°N and 52°N. Very freshwater with high meteoric content is found close to the coast in June 2014. Observations from 1995 and 2008 suggest a higher fraction of brine and Pacific water on the shelf compared to that observed in 2014.

Ocean migration of pop-up satellite archival tagged Atlantic salmon from the Miramichi River in Canada

The ocean migration of 16 post-spawned adult Atlantic salmon [Salmo salar L.] from the Miramichi River, Canada, tagged concurrently with pop-up satellite archival tags and acoustic transmitters was reconstructed using a Hidden Markov Model. Individuals exclusively utilized areas within the Gulf of St Lawrence and the Labrador Sea, and showed little overlap with known distributions of European stocks. During the migration, individuals were generally associated with surface waters and spent &amp;gt;67% of the time in the upper 10 m of the water column. The Atlantic salmon occupied greater depths and showed more diving activity during the day than during the night, with a few exceptions. Although residing in the Gulf of St Lawrence, individuals used different geographical areas and displayed frequent dives to shallow depths (10–30 m). All fish that entered the Labrador Sea (n = 8) migrated through the Strait of Belle Isle (767 km from the river mouth), after spending 41–60 d in the Gulf of St Lawrence. After exiting the Gulf of St Lawrence, individuals utilized different areas in the Labrador Sea, and overlaps in spatial distributions among the individuals were largely limited to the Labrador Coast. This variation in area use was accompanied by individual differences in diving behaviour, with maximum depths recorded for individuals ranging from 32 to 909 m. Dives to depths exceeding 150 m were only performed by four individuals and mainly restricted to the central Labrador Sea (areas with water depths &amp;gt;1000 m). Vertical movements were shallower and resembled those in the Gulf of St Lawrence when fish migrated through shallower coastal areas along the Labrador Shelf. In conclusion, the large overall variation in migration routes suggests that post-spawners from the Miramichi River encounter different habitats during their ocean migration and that the growth and survival of adults may depend on ecological conditions in multiple regions, both in the Gulf of St Lawrence and in the Labrador Sea.

Meltwater pathways from marine terminating glaciers of the Greenland ice sheet

AbstractThe Greenland ice sheet (GrIS) stores the largest amount of freshwater in the Northern Hemisphere and has been recently losing mass at an increasing rate. An eddy‐permitting ocean general circulation model is forced with realistic estimates of freshwater flux from the GrIS. Two approaches are used to track the meltwater and its trajectory in the ocean. We show that freshwater from western and eastern GrIS have markedly different fates, on a decadal time scale. Freshwater from west Greenland predominantly accumulates in Baffin Bay before being exported south down the Labrador shelf. Meanwhile, GrIS freshwater entering the interior of the Labrador Sea, where deep convection occurs, comes predominantly (∼80%) from east Greenland. Therefore, hosing experiments, which generally assume a uniform freshwater flux spatially, will not capture the true hydrographic response and regional impacts. In addition, narrow boundary currents are important for freshwater transport and distribution, requiring simulations with eddy‐resolving resolution.

Surface and bottom temperature and salinity climatology along the continental shelf off the Canadian and U.S. East Coasts

A new hydrographic climatology has been created for the continental shelf region, extending from the Labrador shelf to the Mid-Atlantic Bight. The 0.2-degree climatology combines all available observations of surface and bottom temperature and salinity collected between 1950 and 2010 along with the location, depth and date of these measurements. While climatological studies of surface and bottom temperature and salinity have been presented previously for various regions along the Canadian and U.S. shelves, studies also suggest that all these regions are part of one coherent system. This study focuses on the coherent structure of the mean seasonal cycle of surface and bottom temperature and salinity and its variation along the shelf and upper slope. The seasonal cycle of surface temperature is mainly driven by the surface heat flux and exhibits strong dependency on latitude (r≈−0.9). The amplitude of the seasonal cycle of bottom temperature is rather dependent on the depth, while the spatial distribution of bottom temperature is correlated with latitude. The seasonal cycle of surface salinity is influenced by several components, such as sea-ice on the northern shelves and river discharge in the Gulf of St. Lawrence. The bottom salinity exhibits no clear seasonal cycle, but its spatial distribution is highly correlated with bathymetry, thus Slope Water and its intrusion on the shelf can be identified by its relatively high salinity compared to shallow, fresher shelf water. Two different regimes can be identified, especially on the shelf, separated by the Laurentian Channel: advection influences the phasing of the seasonal cycle of surface salinity and bottom temperature to the north, while in the southern region, river runoff and air-sea heat flux forcing are dominant, especially over the shallower bathymetry.

Variability of sea ice melt and meteoric water input in the surface Labrador Current off Newfoundland

AbstractThe respective contributions of saline (Atlantic and Pacific water) and freshwater (sea ice melt, meteoric water) components in the surface Labrador Current are quantified using salinity, δ18O, and nutrient data collected between 2012 and 2015 east of Newfoundland to investigate the seasonal variability of salinity in relation with the different freshwater contributions. Nutrient data indicate that the surface saline water is composed on average over 2012–2015 of roughly 62% Atlantic Water and 38% Pacific Water. A large salinity seasonal cycle of ≈ 1.5 peak‐to‐peak amplitude is found over the middle continental shelf, which is explained by the freshwater input seasonal variability: 2/3 of the amplitude of the salinity seasonal cycle can be explained by meteoric water input and 1/3 by the sea ice melt. A smaller seasonal salinity cycle (≈1.3) is observed over the inner shelf compared to the middle shelf, because of smaller variability in the large meteoric water inputs. Furthermore, the data reveal that sea ice melt (SIM) input was particularly important during July 2014, following a larger extension of sea ice over the Labrador shelf during the 2013/2014 winter season, compared to both previous winter seasons. Some patches of large SIM contribution observed during July 2014 and April 2015 were located on the continental slope or further offshore. The comparison of 2012–2015 data with data collected in 1994–1995 shows that the surface water over the Newfoundland shelf and slope is strongly affected by sea ice processes in both periods and suggests a larger contribution of brines over the slope during 1994–1995.