Convection in the Labrador Sea

1997 ◽  
Author(s):  
Russ E. Davis
Keyword(s):  
Labrador Sea

40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea

1999 ◽  
pp. 19-29 ◽  
Author(s):  
Lotte Melchior Larsen ◽  
David C. Rex ◽  
W. Stuart Watt ◽  
Philip G. Guise
Keyword(s):  
Alkali Basalt ◽  
Dyke Swarm ◽  
Labrador Sea ◽  
Precambrian Basement ◽  
Stress Regime ◽  
Southwest Coast ◽  
Eastern Margin ◽  
Step Heating ◽  
Igneous Activity ◽  
Break Up

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Melchior Larsen, L., Rex, D. C., Watt, W. S., & Guise, P. G. (1999). 40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea. Geology of Greenland Survey Bulletin, 184, 19-29. https://doi.org/10.34194/ggub.v184.5227 _______________ A 380 km long coast-parallel alkali basalt dyke swarm cutting the Precambrian basement in south-western Greenland has generally been regarded as one of the earliest manifestations of rifting during continental stretching prior to break-up in the Labrador Sea. Therefore, the age of this swarm has been used in models for the evolution of the Labrador Sea, although it has been uncertain due to earlier discrepant K–Ar dates. Two dykes from this swarm situated 200 km apart have now been dated by the 40Ar–39Ar step-heating method. Separated biotites yield plateau ages of 133.3 ± 0.7 Ma and 138.6 ± 0.7 Ma, respectively. One of the dykes has excess argon. Plagioclase separates confirm the biotite ages but yield less precise results. The age 133– 138 Ma is earliest Cretaceous, Berriasian to Valanginian, and the dyke swarm is near-coeval with the oldest igneous rocks (the Alexis Formation) on the Labrador shelf. A small swarm of alkali basalt dykes in the Sukkertoppen (Maniitsoq) region of southern West Greenland was also dated. Two separated kaersutites from one sample yield an average plateau age of 55.2 ± 1.2 Ma. This is the Paleocene–Eocene boundary. The swarm represents the only known rocks of that age within several hundred kilometres and may be related to changes in the stress regime during reorganisation of plate movements at 55 Ma when break-up between Greenland and Europe took place.

Late Quaternary palaeo-oceanography of the Denmark Strait overflow pathway, South-East Greenland margin

1998 ◽  
Vol 180 ◽  
pp. 163-167
Author(s):  
Antoon Kuijpers ◽  
Jørn Bo Jensen ◽  
Simon R . Troelstra ◽  
And shipboard scientific party of RV Professor Logachev and RV Dana
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Deep Convection ◽  
Conveyor Belt ◽  
Water Masses ◽  
Labrador Sea ◽  
Greenland Sea ◽  
The North ◽  
Denmark Strait ◽  
The North Atlantic

Direct interaction between the atmosphere and the deep ocean basins takes place today only in the Southern Ocean near the Antarctic continent and in the northern extremity of the North Atlantic Ocean, notably in the Norwegian–Greenland Sea and Labrador Sea. Cooling and evaporation cause surface waters in the latter region to become dense and sink. At depth, further mixing occurs with Arctic water masses from adjacent polar shelves. Export of these water masses from the Norwegian–Greenland Sea (Norwegian Sea Overflow Water) to the North Atlantic basin occurs via two major gateways, the Denmark Strait system and the Faeroe– Shetland Channel and Faeroe Bank Channel system (e.g. Dickson et al. 1990; Fig.1). Deep convection in the Labrador Sea produces intermediate waters (Labrador Sea Water), which spreads across the North Atlantic. Deep waters thus formed in the North Atlantic (North Atlantic Deep Water) constitute an essential component of a global ‘conveyor’ belt extending from the North Atlantic via the Southern and Indian Oceans to the Pacific. Water masses return as a (warm) surface water flow. In the North Atlantic this is the Gulf Stream and the relatively warm and saline North Atlantic Current. Numerous palaeo-oceanographic studies have indicated that climatic changes in the North Atlantic region are closely related to changes in surface circulation and in the production of North Atlantic Deep Water. Abrupt shut-down of the ocean-overturning and subsequently of the conveyor belt is believed to represent a potential explanation for rapid climate deterioration at high latitudes, such as those that caused the Quaternary ice ages. Here it should be noted, that significant changes in deep convection in Greenland waters have also recently occurred. While in the Greenland Sea deep water formation over the last decade has drastically decreased, a strong increase of deep convection has simultaneously been observed in the Labrador Sea (Sy et al. 1997).

Early basin insights and AVO supported leads from new long offset 2D seismic data, Labrador Sea, Canada

2013 ◽  
Author(s):  
Richard Wright ◽  
James Carter ◽  
Deric Cameron ◽  
Tom Neugebauer ◽  
Jerry Witney ◽  
...  
Keyword(s):  
Seismic Data ◽  
Labrador Sea ◽  
Long Offset

The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

2019 ◽  
Vol 60 (10) ◽  
pp. 1991-2024 ◽  
Author(s):  
M G Kopylova ◽  
E Tso ◽  
F Ma ◽  
J Liu ◽  
D G Pearson
Keyword(s):  
North Atlantic ◽  
Thermal State ◽  
Mineral Chemistry ◽  
Mantle Metasomatism ◽  
Labrador Sea ◽  
The North ◽  
Rock Types ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

scholarly journals A sea change in our view of overturning in the subpolar North Atlantic

Science ◽  
2019 ◽  
Vol 363 (6426) ◽  
pp. 516-521 ◽  
Author(s):  
M. S. Lozier ◽  
F. Li ◽  
S. Bacon ◽  
F. Bahr ◽  
A. S. Bower ◽  
...  
Keyword(s):  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Climate Change Projections ◽  
Overturning Circulation ◽  
Intergovernmental Panel ◽  
Freshwater Transport ◽  
Deep Waters ◽  
Meridional Overturning ◽  
Prevailing View

To provide an observational basis for the Intergovernmental Panel on Climate Change projections of a slowing Atlantic meridional overturning circulation (MOC) in the 21st century, the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system was launched in the summer of 2014. The first 21-month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the OSNAP line. In a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate MOC variability, these results suggest that the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins is largely responsible for overturning and its variability in the subpolar basin.

scholarly journals Atmospheric Conditions Associated with Labrador Sea Deep Convection: New Insights from a Case Study of the 2006/07 and 2007/08 Winters

2016 ◽  
Vol 29 (14) ◽  
pp. 5281-5297 ◽  
Author(s):  
Who M. Kim ◽  
Stephen Yeager ◽  
Ping Chang ◽  
Gokhan Danabasoglu
Keyword(s):  
North America ◽  
North Atlantic ◽  
Large Scale ◽  
Initial Conditions ◽  
Deep Convection ◽  
La Niña ◽  
Labrador Sea ◽  
Atmospheric Conditions ◽  
Circulation Anomaly ◽  
La Nina

Abstract Deep convection in the Labrador Sea (LS) resumed in the winter of 2007/08 under a moderately positive North Atlantic Oscillation (NAO) state. This is in sharp contrast with the previous winter with weak convection, despite a similar positive NAO state. This disparity is explored here by analyzing reanalysis data and forced-ocean simulations. It is found that the difference in deep convection is primarily due to differences in large-scale atmospheric conditions that are not accounted for by the conventional NAO definition. Specifically, the 2007/08 winter was characterized by an atmospheric circulation anomaly centered in the western North Atlantic, rather than the eastern North Atlantic that the conventional NAO emphasizes. This anomalous circulation was also accompanied by anomalously cold conditions over northern North America. The controlling influence of these atmospheric conditions on LS deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and/or initial conditions are modified. An extended analysis for the 1949–2009 period shows that about half of the winters with strong heat losses in the LS are associated with such a west-centered circulation anomaly and cold conditions over northern North America. These are found to be accompanied by La Niña–like conditions in the tropical Pacific, suggesting that the atmospheric response to La Niña may have a strong influence on LS deep convection.

Predation on marine-phase Atlantic salmon (Salmo salar) by gannets (Morus bassanus) in the Northwest Atlantic

2002 ◽  
Vol 59 (4) ◽  
pp. 602-612 ◽  
Author(s):  
W A Montevecchi ◽  
D K Cairns ◽  
R A Myers
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Labrador Sea ◽  
Atlantic Salmon Salmo Salar ◽  
Limited Sampling ◽  
Large Colony ◽  
Pelagic Food Webs ◽  
Migratory Routes ◽  
Pass Through ◽  
Foraging Ranges

Predation on Atlantic salmon (Salmo salar) has been recorded in rivers and estuaries, but there is little documentation of predation at sea. Prey landed by gannets (Morus bassanus) over 24 years in a large colony off northeast Newfoundland included small proportions of post-smolt Atlantic salmon. Before 1990, when shifts in oceanographic conditions and pelagic food webs occurred in the Labrador Sea, post-smolts, on average, made up 0.29% of estimated intake by gannets during August 1977–1989. In contrast, during the 1990s, this estimate increased to 2.53%, peaking at 6.37% in 1993. Model estimates with wide error margins projected that gannets consumed a mean of 1.6 t and 19.2 t of post-smolts during August 1977–1989 and 1990–2000, respectively, making up 0.22% and 2.70% of estimated North American post-smolt biomass during these periods. The migratory routes of post-smolt Atlantic salmon pass through the foraging ranges of gannet colonies, but limited sampling at colonies other than Funk has not revealed salmon in gannet diets. Sampling seabird diets is an economic, biological means of investigating the ecology and natural mortality of Atlantic salmon. Spatial and temporal expansion of this sampling would enhance its oceanographic context and reduce uncertainty associated with estimates of predation by seabirds.

Autumn Stranding of a Northern Bottlenose Whale (Hyperoodon ampullatus) in the Bay of Fundy, Nova Scotia

1975 ◽  
Vol 32 (7) ◽  
pp. 1019-1040 ◽  
Author(s):  
Edward Mitchell ◽  
V. Michael Kozicki
Keyword(s):  
Nova Scotia ◽  
Rhode Island ◽  
Growth Curve ◽  
North American ◽  
Labrador Sea ◽  
Bay Of Fundy ◽  
Winter Migration ◽  
Hyperoodon Ampullatus

A 615-cm male northern bottlenose whale (Hyperoodon ampullatus) stranded in Cobequid Bay, Bay of Fundy, in early October 1969. The skull, mandible, tympano-periotics, and teeth are described and illustrated. Five growth layers in the lower teeth place the animal below a growth curve based on samples from the Labrador Sea taken in May and June. A summary of nine other North American occurrences of 12 individuals, mainly south of Sable Island, indicates a winter migration to waters offshore of Massachusetts and Rhode Island.

Postsmolt Atlantic Salmon (Salmo salar) in the Labrador Sea

1991 ◽  
Vol 48 (1) ◽  
pp. 2-6 ◽  
Author(s):  
D. G. Reddin ◽  
P. B. Short
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Age Distribution ◽  
Labrador Sea ◽  
Scale Reading ◽  
Gill Nets ◽  
Atlantic Salmon Salmo Salar ◽  
Catch Rates ◽  
Abundance And Distribution ◽  
High Catch

In order to learn more about the existence, abundance, and distribution of postsmolt Atlantic salmon (Salmo salar) in the Labrador Sea, exploratory fishing was done with surface-set gill nets in early autumn of 1987 and 1988. In total, there were 468 salmon of various sea ages captured, of which 207 were postsmolts. The high catch rates compared with catch rates from Greenland suggest that the population of postsmolts in the Labrador Sea may be large. Postsmolts from rivers in Maine to Labrador were caught in the Labrador Sea, as indicated by Carlin tags and river age distribution from scale reading. The highest catch rates of postsmolts occurred in the Labrador Sea between 56° and 58°N latitude.

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