Northern Labrador Sea Research Articles

Sex Change and Population Fluctuations in Pandalid Shrimp

Sex Change and Population Fluctuations in Pandalid Shrimp

Seismic stratigraphy of late Cenozoic sediments in the northern Labrador Sea: a history of bottom circulation and glaciation

The seismicstratigraphy of the upper 1 km of sediment in the northern Labrador Sea has been determined from the examination of about 26 000 line kilometres of seismic profiles. Four key reflectors (A to D) have been correlated with Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) holes and range in age from mid-Pliocene to approximately mid-Pleistocene. Ten seismic facies have been distinguished and are interpreted as resulting from slope progradation, turbidite deposition in channels and on the basin floor, and widespread contourite deposition.Tertiary sediments are predominantly hemipelagic or contourite, but in the mid-Pliocene, turbidite deposition began in the northeast Labrador Basin, which might reflect either Greenland glaciation or lowering of sea level. At the same time, widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom-water circulation, probably reflecting high-latitude cooling. This was followed by a return to less dynamic conditions as increased sea-ice cover reduced bottom-water generation in high-latitude seas. A turbidite deep-sea fan developed off Hudson Strait in the Early Pleistocene. In the mid- and late Quaternary, there was a major increase in the supply of turbidites from the Labrador margin, accompanied by the development of an extensive channel system on the continental margin. This was a consequence of glacial ice sheets extending to the top of the continental slope and discharging sediment directly to deep water.

Upper Cenozoic history of the Labrador Sea, Baffin Bay, and the Arctic Ocean: A paleoclimatic and paleoceanographic summary

Foraminifera, palynomorphs, and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern Labrador Sea, southern Baffin Bay, and the Alpha Ridge region of the central Arctic Ocean. Foraminifera in cores from the Labrador Sea and southern Baffin Bay show glacial‐interglacial δ18O values similar to those reported from the Norwegian and Greenland seas. In contrast to the eastern North Atlantic Ocean, however, peaks of Subarctic foraminifera and dinoflagellates in the western North Atlantic cores show that relatively warm Atlantic surface water continued to flow into the northern Labrador Sea during the early glaciation growth phases of isotopic stages 2, 4, 6, and 8. Boreal and Subarctic pollen suggest that warm Atlantic air flowed into the northern Labrador Sea and Baffin Bay during the ice sheet growth phases. The advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the Laurentide, Innuitian, and Greenland ice sheets. Isotopic and microfossil records in Arctic cores can also be tentatively correlated with major high latitude north Atlantic glacial‐interglacial events. Magnetostratigraphic, palynological and amino acid dating, however, shows that sedimentation on the Alpha Ridge has been very slow during the past 0.73 m.y.; therefore, events of less than 20,000 years duration cannot be clearly discerned. Interpretation of pre‐Pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils.

Influence of sediment source and type on the magnetic susceptibility of fiord and shelf deposits, Baffin Island and Baffin Bay, N.W.T.

Volume and mass magnetic susceptibility are measured on Recent and late Quaternary sediments from the fiords and shelf of eastern Baffin Island, Baffin Bay, and the northern Labrador Sea. Major changes in hinterland bedrock geology are associated with order of magnitude changes in magnetic susceptibility. The fiords that head into the Proterozoic Foxe Fold Belt have mass magnetic susceptibilities (MS) of ~ 2–4 × 10−7 m3/kg, compared with 25–60 × 10−7 m3/kg in sediments derived from Archean gneisses and granites. Another low-MS region is the middle reach of Frobisher Bay. MS studies in Cambridge, McBeth, and Itirbilung fiords included analyses of surface samples and samples from Lehigh (< 3 m) and piston (< 11 m) cores. Lehigh cores had higher MS values on average than the piston cores, suggesting a coarsening in texture or an increase in the flux of magnetic minerals during the last 0.3–3 ka. An analysis of the MS logs of 17 piston cores indicated that six broad patterns of MS can be recognized based on a combination of the MS trend with depth and the number of MS modes in the frequency distribution. Specific comparison of lithofacies logs and the MS signal indicates that variations in MS are frequently associated with changes in texture, but in some cases significant changes are independent of texture and represent major fluctuations in source materials.

Late Quaternary marine sediment accumulation in fiord-shelf-deep-sea transects, Baffin Island to Baffin Bay

Piston cores from fiords, shelf troughs, and the deep-sea off eastern Baffin Island, N.W.T., Canada, have been sampled for texture and detrital carbonate in the <2 mm fraction. The sediments consist primarily of silty clays usually containing <5% sand. Estimates are made for sediment accumulation (kg/m 2 ka) over the last ca. 10 ka. Three sets, of two cores each, lie on a fiord-shelf transect and thus define variations in sediment accumulation gradients. These continental margin data are compared with cruder estimates of Holocene sediment accumulation at three sites farther offshore in Baffin Bay, Davis Strait and the northern Labrador Sea. Minimum accumulation in a 2 ka interval was 200 kg/m 2 with a maximum estimate of 8,800 kg/m 2. Detrital carbonate accumulation varies between 0 and 1,300 kg/m 2. Median accumulation for a typical fiord-shelf-deep-sea transect over the last 10 ka have been 10,340, 3493 and 820 kg/m 2. At DSDP Leg, site 645 in central Baffin Bay, the sedimentation rate ranged between 40 and 130 m/Ma (ca. 400 and 1200 kg/m 2 2ka); that is, comparable with the Late Quaternary input into Baffin Bay.

Late Quaternary stratigraphy and paleoecology of northwest Labrador Sea

Sedimentological study of 20 piston cores from the northwestern Labrador Sea shows that thin bedded distal turbidites are important constituents of the Quaternary strata on the continental slope and rise. Sedimentation on the outer shelf (ca. 500–900 m) is dominated by ice-rafting and hemipelagic deposition. Detailed study of two outer shelf cores reveals a stratigraphic record extending to oxygen isotopic stage 9. Studies of foraminifera and dinoflagellates show that subarctic surface waters penetrated into the northern Labrador Sea during the early-middle glacial stages and pollen data indicate that northward advection of warm air masses occurred at the same time. Microfossil data indicate that late glacial stages were characterized by year around sea-ice cover and arctic surface water, and by the dominance of cold, dry Arctic air masses. Transitions from glacial to interglacial stages are marked by the presence of low salinity melt water. These data support models which postulate that open water in the Labrador Sea played an important role in supplying moisture to Laurentide and Greenland ice-sheets.

Origin of the marine magnetic quiet zones in the Labrador and Greenland Seas

The central part of the northern Labrador Sea is a magnetic quiet zone, and is flanked by regions exhibiting well developed linear magnetic anomalies older than anomaly 24. The quiet zone dies out progressively to the south, where it becomes possible to correlate anomalies between adjacent profiles. A 45 degree change in spreading direction at anomaly 25 time was accompanied by a major jump in ridge position and orientation. As a consequence of this reorganisation, spreading in the northern Labrador Sea next occurred within a rift that was oriented at 45 degrees to the spreading direction, while to the south spreading occurred within in a rift that was orientated at 90 degrees to the spreading direction. Obliquity of spreading changed, between these limits, progressively along the ridge. The quiet zone may be present to the north because the oblique northern geometry resulted in a fragmented ridge composed of many small-offset transform faults joining many short spreading ridge segments. Each magnetic source block produced by magnetisation of sea floor at these small ridge segments will be surrounded by similar small blocks that have opposite polarity, so that none can be resolved at the sea surface. Supporting evidence comes from multi-channel seismic profiles across the Labrador Sea, which show that the basement is more textured within the quiet zone than outside, suggesting the presence of numerous small fracture zones in the quiet zone.

Dynamics and Community Structure of Zooplankton in the Davis Strait and Northern Labrador Sea

The dynamics and community structure of zooplankton in the Davis Strait and the northern Labrador Sea were studied over an annual cycle (23 April 1977 - 16 May 1978). Biological spring, defined as the time of year which includes the annual phytoplankton increase and subsequent increases in zooplankton abundance, proceeds in a counterclockwise sense around the region. It is first observed in April near the southern Greenland coast, from where it proceeds north in the Davis Strait, then moves southward in the Baffin Current and along the retreating ice edge before reaching the Hudson Strait in September and October. Recurrent group analysis was used to identify communities of zooplankton in the region. Distributions of these groups were closely related to the hydrography. The West Greenland Drift is characterized by abundant populations of Calanus finmarchicus , C. hyperboreus , Oithona similis , Conchoecia obtusata , Metridia longa and Microcalanus pygmaeus. The colder, less saline water of the Baffin Current and the Hudson Strait arctic outflow are characterized by populations of Calanus glacialis and the early developmental stages of Pseudocalanus minutus. The breeding cycles of the three species of Calanus tend to be separated both spatially and temporally. Key words: Davis Strait, Labrador Sea, Zooplankton, Zoogeography, arctic, recurrent group analysis, Calanus

The Autumn Migration of Thick-billed Murres near Southern Baffin Island and Northern Labrador

Aerial surveys were used to assess the timing and route of the swimming migration of Thick-billed Murres (Uria lomvia) near southern Baffin Island and northern Labrador in the autumn of 1977, 1978 and 1979. Several hundred thousand adults and chicks from six southern Baffin area colonies departed east through Hudson Strait, in the direction of surface currents, in the latter half of August. Most murres from three eastern Hudson Strait colonies were in offshore waters in early September, arrived in the northern Labrador Sea within a few days, and were followed later in September by murres from three western Hudson Strait colonies. From the Labrador Sea, murres go to marine wintering sites around Newfoundland. Murres from a large colony on southeast Baffin Island apparently did not migrate to the Labrador Sea through western Davis Strait; instead, they either migrated through central Davis Strait en route to Newfoundland, or east to west Greenland, which was also the probable destination of many adult murres which flew by a drillship in southwest Davis Strait.Key words: Thick-billed Murre (Uria lomvia), migration, Baffin Island, Davis Strait, Labrador Sea, eastern Canada, colonial seabird

Iceberg-Seabed Interaction (Northern Labrador Sea)

Large-scale furrows occurring in unconsolidated Quaternary sediments on the Labrador Shelf are considered to be gouge marks of bottom-dragging icebergs. Side-scan sonograph mosaics from the northern Labrador Shelf were constructed for two bathymetric interbank areas. They reveal that both relict ice bottom gouging and modern iceberg scouring have taken place at water depths greater than 180 m. The recent scours are linear to curvilinear to crater-like in form, with average widths of 30 m at a mean scour depth of 5 m and lengths in excess of 3 km. The dominant scour trend is north-south, reflecting the Labrador Current.Impedance of icebergs by bottom interaction is primarily a function of the gross iceberg size and shape, sediment encountered by the keel, and prevailing current. For modern scouring, frequencies of detectable impact decrease exponentially with increasing scour depth, and scour depth is inversely proportional to the sediment shear and compressive strengths.

Aspects of Cenozoic stratigraphy and paleoceanography of the labrador sea and baffin bay

Paleogeographic reconstruction show significant opening of the southern Labrador Sea in Campanian/Maestrichtian to Eocene time and of the northern Labrador Sea in Paleocene/Eocene time. Baffin Bay opened in Eocene time, but motion there probably was largely translational. Micropaleontological studies of Labrador Shelf wells show that the latest Cretaceous—Eocene widespread transgression coincides with the opening phase of the Labrador Sea. Deepest (bathyal) conditions occurred in the Eocene. A broad shelf regresion occurred in the Oligocene, probably accentuated by eustatic sea-level lowering. Shelf sedimentation rates were generally high, in excess of 10 cm/1000 yr, since Maestrichtian time, except locally in the mid-Tertiary, when little or no sedimentation took place. The Labrador Shelf region and adjacent land has undergone renewed tectonic activity in (late) Neogene time. It is likely that a sea strait linking the Atlantic and Arctic Oceans became established as early as Campanian—Maestrichtian time, with surface circulation toward the Arctic. Principal incursions of warm-temperature watermass planktonic foraminifers took place in Maestrichtian and Early—Middle Eocene times. The latter correlates with apostulated Early—Middle Eocene North Atlantic Ocean climatic optimum, and with the findings of Early—Middle Eocene warm-temperature invertebrate and vertebrate remains in the Canadian Arctic. Reversal of surface circulation from the Arctic to the Atlantic occurred in the Late Miocene—Middle Pliocene, when the cold Labrador current became established along the Canadian Atlantic margin.

Evolution of the Labrador Sea and its bearing on the early evolution of the North Atlantic

Geophysical data collected from 1972 to 1975 during a systematic mapping program of the Labrador Sea have been analysed to investigate its geological history and evolution. The data have been used to establish the location of the ridge axis, the age of the ocean floor, and the direction of movement of Greenland relative to North America. Different poles of rotation for the Eurasian and Greenland plate relative to the North American plate in the Late Cretaceous have been derived in order to fit together satisfactorily the plate boundaries defined by the magnetic anomalies in the Labrador Sea and the North Atlantic. The analysis shows that active seafloor spreading commenced in the southern Labrador Sea during the Campanian (anomaly 32) and in the northern Labrador Sea during the Maastrichtian (anomaly 28), with little or no spreading in the Baffin Bay region during this period. With the commencement of active seafloor spreading in the Norwegian Sea during the lower Paleocene (anomaly 24), the direction of seafloor spreading changed in the Labrador Sea and spreading commenced in Baffin Bay. The spreading ceased in the Labrador Sea and Baffin Bay during the lower Oligocene (pre-anomaly 13) when Greenland started to move with the North American plate. Paleogeographic reconstruction of the three plates shows that Greenland moved north relative to North America during the first phase of opening of the Labrador Sea (75–60 Myr), giving rise to compressive forces between northern Greenland and the Canadian Arctic Islands. During the second phase of opening of the Labrador Sea (60–40 Myr) Greenland moved past Ellesmere Island in the left lateral sense along Nares Strait. Some compression is also inferred from these constructions between the margins of northeast Greenland and Svalbard. The poles of rotation obtained for the three plates show a different set of events which may have been responsible for the separation of Rockall Plateau from the British Isles during the early evolution of the North Atlantic.

Seasonal Variations of Sea Ice Extent in the Davis Strait-Labrador Sea Area and Relationships with Synoptic-Scale Atmospheric Circulation

Using published data sources for south-eastern Baffin Island, Ungava Bay and the northern Labrador Sea area, a study of the general patterns of sea ice growth and decay has been made for the years 1964 to 1974. From a comparison of individual years an "early" and a "late" pattern of both ice advance and ice retreat are recognized. Mean daily sea level pressure patterns for June - July and for October - mid-November are examined and a relationship is established between the type of ice advance or retreat pattern and the synoptic circulation over the area. In the years of early ice retreat there is an increased frequency of southerly airflow over the region. Strong winds and the advection of warm air leads to the more rapid removal of the ice compared to years of late ice retreat. Similarly for the years of early ice advance there is an increased frequency of northerly and westerly flow, bringing lower temperatures and an influx of second-year and multi-year ice into the area.

Influences of Norwegian Sea overflow water on sedimentation in the northern North Atlantic and Labrador Sea

Reflection profiles and hydrographic data indicate that sedimentation in parts of the northernmost Atlantic and in the Labrador basin has been largely governed by the movement of bottom water derived from the Norwegian Sea. Three areas are considered in detail. The first is the channel separating Rockall bank from the Irish continental shelf, where a ridge, nearly 600 km long, composed of sediment deposited on a gently dipping reflector of early Tertiary age, has been found. Hydrographic observations suggest that the feature, for which the name Feni ridge is proposed, is the result of deposition close to the boundary of a component of the Iceland-Scotland overflow water from the Norwegian Sea, which enters the channel from the north and in flowing southward is constrained by Coriolis force to the Rockall scarp. Farther north, reflection profiles show a marked asymmetry of sediment distribution across the volcanic Faeroe-Iceland ridge, the sediment cover being much thicker and more continuous on the north-facing slope than on the crest and southern flank. This difference is attributed to fast bottom currents in the south, caused by sinking of the Norwegian Sea overflow, and the persistence of tranquil bottom conditions in the north. Seismic profiles from the Labrador basin reveal a well-defined body of thick sediments trending NNW on a portion of the continental rise of southern Greenland where turbidity currents cannot reach. The thick sediments lie in a region in which the flow of deep water is weak and in which rapid deposition from sediment-laden bottom waters is allowed. Appreciably stronger bottom currents associated with the counterclockwise circulation of dense water derived from the Norwegian Sea appear to have greatly inhibited deposition of pelagic material in the area surrounding the sediment body. Sedimentation under the influence of bottom currents in this region, in the Rockall area, and on the Blake-Bahama outer ridge took place throughout a large part of Tertiary time but did not occur in the Upper Cretaceous. This is attributed to a major alteration in the circulation pattern of the North Atlantic caused by continental drift, polar wandering, and climatic deterioration between late Cretaceous and late Eocene times.

The Northwest Atlantic Mid-Ocean Canyon

The Northwest Atlantic Mid-Ocean Canyon is a depositional–erosional linear feature which extends southward from the northern Labrador Sea to the Sohm Abyssal Plain. Analysis of the data accumulated over the past 20 yr allows us to conclude: (1) The canyon does not have any major tributaries; (2) it is Quaternary in age; and (3) it is not a tectonic feature. However, neither the source nor the sedimentary process which constructed the canyon can as yet be established.

Geologic and Geophysical Observations in the Northern Labrador Sea

Reports and discusses the results of a 3500 mi magnetic, bathymetric and seismic reflection reconnaissance survey concentrated in the area 61 - 64 N in Aug-Sept 1967 by the USCGC Mariposa in cooperation with the US Naval Oceanographic Office and the Univ of Wisconsin. The continental shelf off West Greenland is ~100 fathoms shallower than that off the east coast; the continental slope is precipitous and the continental rise poorly developed and irregular. The origin of the marginal trench at the base of the slope seaward of Godthaab is either tectonism, bottom current erosion or a combination. Depths of the Labrador continental shelf break range 250-300 f; its slope gradients are 1:20-1:40 and there is a well developed continental rise. A number of canyons are noted in the sea floor of the area, and Northwest Atlantic Mid-Ocean Canyon is the dominent feature as far as 60 N. Seismic data suggest a continuous buried ridge near the geographic axis of the basin, the Mid-Labrador Sea Ridge, traced to the Davis Strait sill. It is suggested that this ridge is a relic of Mid-Oceanic Ridge which, as it developed, separated the continental blocks of Greenland and Canada. The bottom conditions of the sea indicate major sculpting by bottom currents.