799 research outputs found

    Evolution of Labrador Sea–Baffin Bay: Plate or Plume Processes?

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    Breakup between Greenland and Canada resulted in oceanic spreading in the Labrador Sea and Baffin Bay. These ocean basins are connected through the Davis Strait, a bathymetric high comprising primarily continental lithosphere, and the focus of the West Greenland Tertiary volcanic province. It has been suggested that a mantle plume facilitated this breakup and generated the associated magmatism. Plume-driven breakup predicts that the earliest, most extensive rifting, magmatism and initial seafloor spreading starts in the same locality, where the postulated plume impinged. Observations from the Labrador Sea–Baffin Bay area do not accord with these predictions. Thus, the plume hypothesis is not confirmed at this locality unless major ad hoc variants are accepted. A model that fits the observations better involves a thick continental lithospheric keel of orogenic origin beneath the Davis Strait that blocked the northward-propagating Labrador Sea rift resulting in locally enhanced magmatism. The Davis Strait lithosphere was thicker and more resilient to rifting because the adjacent Paleoproterozoic Nagssugtoqidian and Torngat orogenic belts contain structures unfavourably orientated with respect to the extensional stress field at the time

    The crustal structure in the Northwest Atlantic region from receiver function inversion – Implications for basin dynamics and magmatism

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    The Labrador Sea and Baffin Bay form an extinct Palaeogene oceanic spreading system, divided by a major continental transform, the Davis Strait, with the whole region defined as the Northwest Atlantic. The Davis Strait hosts the Ungava Fault Zone and is the central structural element of the Davis Strait Large Igneous Province (DSIP) that formed broadly coeval with continental breakup to its north and south. While constraints on the crustal structure in this region primarily exist in the offshore, crustal models are limited onshore, which makes an interpretation of regional structures as well as the extent, and therefore origin of the DSIP extremely difficult to ascertain. Here, we have collected all available teleseismic data from the Northwest Atlantic margins and applied a receiver function inversion to retrieve station-wise velocity models of the crust and uppermost mantle. We integrate the outcomes with published controlled-source seismic data and regional crustal models to make inferences about the crustal structure and evolution of the Northwest Atlantic. In particular, we focused on constraining the spatial extent and origin of high velocity lower crust (HVLC), and determining whether it is generically related to the Davis Strait Igneous Province, syn-rift exhumed and serpentinised mantle, or pre-existing lower crustal bodies such as metamorphosed lower crust or older serpentinised mantle rocks. The new results allow us to better spatially constrain the DSIP and show the possible spatial extent of igneous-type HVLC across Southwest Greenland, Northwest Greenland and Southeast Baffin Bay. Similarly, we are able to relate some HVLC bodies to possible fossil collision/subduction zones/terrane boundaries, and in some instances to exhumed and serpentinised mantle.publishedVersio

    Radiogenic isotopes on marine sediments from the Baffin Bay : implications for the sediment supply during the last deglaciation

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    The Baffin Bay is a marginal sea of the Atlantic Ocean, a semi-enclosed basin, situated between Greenland, Baffin Island and the Canadian Arctic Archipelago (CAA). It is an important link in the Northern Hemisphere circulation and is connected to the Arctic Ocean and to the Labrador Sea. During the Last Glacial Maximum (LGM) the Baffin Bay was flanked by three North American Ice sheets: Laurentide, Innuitian and Greenland. Ice sheet dynamics is still poorly understood but highly valuable in the frame of recent Greenland ice sheet mass loss and recent climate change data. Understanding the mechanisms and interplay between ice sheets, ocean circulation and climate is a key to more accurate climate prediction models. Thus the deglaciation history of the Baffin Bay is a matter of interest for the research community and has been a topic for many projects in the last decades. There is a gap, however, in a thorough provenance study, which would contribute to the information on sediment supply in the Baffin Bay. Knowing the main sediment sources can further improve the research on ice sheet dynamics and paleocirculation. For this project three cores were investigated: one in the central (PC 16) and two in the southern Baffin Bay, along both eastern (SL 170) and western (SL 174) coasts. The location of these cores allows to characterize sediment provenance in the Baffin Bay as well as to reproduce transport mechanisms, in particular, water masses. The major research goal of the Ph.D project, therefore, is to perform a sediment provenance study in the Baffin Bay based on radiogenic isotope analyses (Sr, Nd, Pb) on the detrital fraction of the sediment cores and to connect these results with the information on sediment delivery mechanisms and ice sheet extent/retreat. We were able to determine major sediment sources for the core SL 170: central West Greenland (Nagssugtoqidian Mobile Belt) and southern West Greenland (Archean Block) terrains. Moreover, we observed the shift in all three radiogenic isotope records at 12 ka and attributed it to the change in the relative importance of the terrains: probably, at 12 ka the deglaciation of the central West Greenland ice sheet margin intensified or started, increasing the material supply to the location of the SL 170 core. The provenance of SL 174 and PC 16 cores was much more difficult to distinguish due to the influence of the minerals with a specific isotope composition (micas, feldspars). However, the Precambrian sources seem to prevail in their sediments. Additionally, Northern Baffin Bay Proterozoic or Paleozoic carbonate terrains could be an extra source for the PC 16 sediments. Paleocirculation study was initially the second aim of the project. Information on the water masses movement in the Baffin Bay should have been derived from the leachates fraction - 15 - of the same sediment cores. Leachates are thought to be dominated by the iron-manganese (Fe-Mn) oxyhydroxides, which are formed on the sediment grain and incorporate rare earth and trace elements reflecting the composition of the bottom seawater. However, the extraction of the true seawater signal from the Baffin Bay sediment leachates is complicated due to detrital dolomite material, which has been extracted during the leaching procedure as well. Moreover, after a brief mineralogical and chemical investigation we discovered no Fe-Mn coatings on the sediment grains or in the leachates samples. One of the potential origins of the detrital dolomite in the Baffin Bay samples was determined as the Borden Basin in Nunavut (Baffin Island, Canada). Pb isotopes appear to have a potential to trace chemical weathering and freshwater routing regime. The comparison between Baffin Bay and North Atlantic cores demonstrated, that by the end of the Baffin Bay Detrital Event 0 (around 11 ka), the modern-like circulation commenced to being established. The present-day water circulation in the Baffin Bay was possibly achieved by 9-8 ka. Overall, this PhD thesis showed that radiogenic isotopes indeed can be used for reconstructing sediment supply from the nearby land masses, and their variations can be explained in the light of changing provenance, circulation, weathering regime and ice sheet history. However, we emphasize here, that a profound chemical and mineralogical investigation is absolutely necessary along the traditional leaching procedures, in order to have a better control on the method and results and to be able to present strong arguments for the interpretation

    Atlantic water inflow to Labrador Sea and its interaction with ice sheet dynamics during the Holocene

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    The hydrodynamics of the Labrador Sea, controlled by the complex interplay of oceanographic, atmospheric and ice-sheet processes, play a crucial role for the Atlantic Meridional Overturning Circulation (AMOC). An improved understanding of the hydrodynamics and its forcing in the past could therefore hold a key to understanding its future behaviour. At present, there is a remarkable temporal mismatch, in that the largely microfossil-based reconstructions of Holocene Atlantic-water inflow/influence in the Labrador Sea and Baffin Bay appear to lag grain size-based current strength reconstructions from the adjacent North Atlantic by > 2ka. Here, we present the first current strength record from the West Greenland shelf off Nuuk to reconstruct Atlantic Water (AW)-inflow to the Labrador Sea via the West Greenland Current. Our data show that the Holocene AW-inflow into Labrador Sea is well aligned with the Holocene Speed Maximum documented in the North Atlantic (McCave and Andrews, 2019; Quat. Sci. Rev. 223), suggesting a close coupling with the AMOC. The observed lag between the microfossil-based records and the Holocene Speed Maximum can be explained when considering the presence of an extended meltwater lens that prevented the shoaling of the inflowing Atlantic waters. Once the meltwater discharge waned after the cessation of large-scale melting of the surrounding ice sheets, the AW could influence the surface waters, independently of the strength of its inflow. Only then was an effective ocean-atmosphere heat transfer enabled, triggering the comparably late onset of the regional Holocene Thermal Maximum. Furthermore, sediment geochemical analyses show that short term cooling events, such as the 8.2 ka event related to the final drainage of glacial Lake Agassiz, lead to glacier advances of the Greenland Ice Sheet. Since the grain size data show that these events had no influence on the AW-inflow to the north eastern Labrador Sea, these advances must have been caused by atmospheric cooling. Consequently, we argue that (i) in this region, surface water-based proxies register AW influence rather than inflow (ii) the AW inflow into the Labrador Sea is controlled by the AMOC, but (iii) its impact on an effective ocean-atmosphere heat transfer was hindered by a prevailing meltwater lens in the early Holocene, i.e. until the cessation of large-scale melting of the surrounding ice sheets

    Improving the paleoceanographic proxy tool kit – On the biogeography and ecology of the sea ice-associated species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica in the northern North Atlantic

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    A long-term perspective is essential for understanding environmental change. To be able to access the past, environmental archives such as marine and lake sediments that store information in the form of diverse proxy records are used. Whilst many analytical techniques exist to extract the information stored in these proxy records, the critical assessment and refinement of current methods in addition to developing new methods is crucial to improving our understanding. This study aims to improve our knowledge on diatom species used for reconstructing ocean surface conditions, especially temperature and sea ice variability over time. We define the distribution and the relationship to sea surface temperature (SST) and sea ice concentrations (SIC) of the species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica using diatom training sets from the northern North Atlantic. We further assess the effect of separating these species compared to grouping them under F. oceanica, as has been done in the past. Our results suggest that while these three species share similarities such as the preference for stratified waters induced by sea ice or glacier meltwater, they also exhibit heterogeneous distributions across the northern North Atlantic, with individual optima for SST and SIC. This also affects quantitative reconstructions based on our data, resulting in lower SST and higher SIC estimates when the species are separated in the surface sediment and down-core diatom assemblages.Peer reviewe

    Evolution of the Laurentide and Innuitian ice sheets prior to the Last Glacial Maximum (115 ka to 25 ka)

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    The Laurentide Ice Sheet was the largest global ice mass to grow and decay during the last glacial cycle (~115 ka to ~10 ka). Despite its importance for driving major changes in global mean sea level, long-term landscape evolution, and atmospheric circulation patterns, the history of the Laurentide (and neighbouring Innuitian) Ice Sheet is poorly constrained owing to sporadic preservation of stratigraphic records prior to the Last Glacial Maximum (LGM; ~25 ka) and a case-study approach to the dating of available evidence. Here, we synthesize available geochronological data from the glaciated region, together with published stratigraphic and geomorphological data, as well as numerical modelling output, to derive 19 hypothesised reconstructions of the Laurentide and Innuitian ice sheets from 115 ka to 25 ka at 5-kyr intervals, with uncertainties quantified to include best, minimum, and maximum ice extent estimates at each time-step. Our work suggests that, between 115 ka and 25 ka, some areas of North America experienced multiple cycles of rapid ice sheet growth and decay, while others remained largely ice-free, and others were continuously glaciated. Key findings include: (i) the growth and recession of the Laurentide Ice Sheet from 115 ka through 80 ka; (ii) significant build-up of ice to almost LGM extent at ~60 ka; (iii) a potentially dramatic reduction in North American ice at ~45 ka; (iv) a rapid expansion of the Labrador Dome at ~38 ka; and (v) gradual growth toward the LGM starting at ~35 ka. Some reconstructions are only loosely constrained and are therefore speculative (especially prior to 45 ka). Nevertheless, this work represents our most up-to-date understanding of the build-up of the Laurentide and Innuitian ice sheets during the last glacial cycle to the LGM based on the available evidence. We consider these ice configurations as a series of testable hypotheses for future work to address and refine. These results are important for use across a range of disciplines including ice sheet modelling, palaeoclimatology and archaeology and are available digitally

    “Late Quaternary ice sheet dynamics and palaeoceanography in the Baffin Bay region”

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    There remains a lack of data surrounding the timings and dynamics of the initial retreat of the Greenland ice sheet (GIS) from its maximum extent at the end of the last glacial maximum (LGM), with poor chronostratigraphic constraint also present on the timings of major Baffin Bay detrital carbonate events (BBDC) during the last deglaciation. This study presents new high-resolution data from two cores extracted from the deep abyssal plain of central Baffin Bay. Two separate radiocarbon dates have been extracted using foraminifera which have been used in the development of an age-depth model; estimating the base of the longer gravity core ‘GC01’ to be approximately 22 ka in age. Samples adequate for radiocarbon dating are few and far between due to intense dissolution of biogenic carbonate in both cores. Measurements of elemental concentrations indicate that significant changes in sediment provenance occurred in central Baffin Bay over the last 22Ka. Substantial amounts of sediment influx from western Greenland occurred during the LGM until approximately 15.8 ka BP when the GIS began its initial stages of retreat as the marine area of Baffin Bay increased. Thereafter the use of sedimentological, geochemical and biological markers alongside radiocarbon dating has captured two separate periods of ice sheet instability associated with the BBDC 1 and BBDC 0 estimated to have occurred between 14.1-13.6 ka BP and 12.7-11.4 ka BP respectively. Further analysis of elemental concentrations attributes these two BBDC events to both be associated with large amounts of sediment influx from northern Baffin Bay i.e. the break-up of the Laurentide (LIS) and the Innuitian Ice Sheets (IIS). When plotted as a timeseries against GISP2 and NGRIP ice core records and regional records of marine palaeoenvironmental, change it is clear that BBDC 1 and BBDC 0 occur out-of-phase with Heinrich event 1 or Heinrich event 0. Instead, BBDC 1 appears to start during the later stages of the Bþlling Interstadial and continue into the Allerþd Interstadial, peaking during the Older Dryas Stadial. BBDC 0 is generally coeval with the Younger Dryas Stadial although likely ends before the start of Heinrich event 0 in the North Atlantic. Due to BBDC events occurring during both interstadials and stadials periods this would also suggest that the initial trigger for the start of BBDC events are not necessarily linked to temperatures changes on Greenland, supporting Jackson et al., 2017. Therefore, indicating that the LIS and IIS were likely decoupled from the North Atlantic climate mode during the last deglaciation

    The biogeography and ecology of common diatom species in the northern North Atlantic, and their implications for paleoceanographic reconstructions

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    Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiants, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.Peer reviewe

    lsotopic and Palynological Records of the Late Pleistocene in Eastern Canada and Adjacent Ocean Basins

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    Correlations of isotopic and palynological records from deep sea cores in Baffin Bay and Labrador Sea with terrestrial palynological sequences, supported by a few Th/U chronological controls, allow the establishment of a regional climatostratigraphic scheme for the Late Pleistocene climatic fluctuations in eastern Canada. During the climatic optimum of isotopic substage 5e, warmer conditions than present prevailed both on land and in oceanic surface water masses. The 5e/5d transition is marked by an abrupt shift in 818O values in Baffin Bay and Labrador Sea as a consequence of ice growth over circumpolar areas of northeastern Canada. From substage 5d to substage 5a, the Baffin Bay border lands experienced glacial conditions while subarctic to cool-temperate and humid climates persisted over Labrador Sea and Atlantic Canada. A short (<104yrs) stage 4 is recorded in deep sea cores with high 8'8O values. It corresponds to the Early Wisconsinan southward extension of the Laurentide Ice Sheet dated at ca. 80,000 yrs in the central St. Lawrence Lowland. There is no clear evidence of full glacial conditions in the Atlantic Provinces during this episode. Stage 3 (Middle Wisconsinan) corresponds in the isotopic records to large oscillations in 818O values suggesting meltwater transits in both Baffin Bay and Labrador Sea. The ice cover remained relatively extensive over eastern Canada, although some areas experienced ice-marginal conditions : in the Atlantic Provinces, notably on Cape Breton Island, hemiarctic to subarctic climate is inferred from palynological records; in the Appalachian foothills of Québec glacial Lake Gayhurst developed some 46,000 yrs ago. During isotopic stage 2 (Late Wisconsinan), the Laurentide Ice Sheet reached its maximum extent while satellitic ice-caps developed over the Atlantic Provinces. In deep sea cores, high 818O values mark the full glacial conditions of isotopic stage 2, although slightly lower values in western Labrador Sea indicate discrete but continuous meltwater influxes. An early melting phase of the northeastern margin of the Laurentide Ice Sheet is recorded shortly after 16,700BP. The full ice-retreat is observed after ca. 11,000BP. At that time, southeastern Canada was already largely ice-free. Finally, the optimum climatic conditions of isotopic stage 1 settled diachronously in the adjacent basins of eastern Canada.La comparaison des enregistrements isotopiques et palynologiques des mers de Baffin et du Labrador avec ceux que fournissent la palynologie et la chronologie U/Th de séquences continentales, autorise l'établissement d'un schéma climatostratigraphique régional représentatif des fluctuations climatiques du Pleistocene supérieur dans l'est du Canada. Pendant l'optimum climatique du stade isotopique 5e, des conditions plus chaudes que celles de l'Actuel ont caractérisé les milieux océanique et continental. La transition 5e 5d est marquée par une augmentation brutale des teneurs en 180 des foraminifÚres dans les mers de Baffin et du Labrador, en réponse à la formation de calottes glaciaires dans les milieux circumpolaires du nord-est du Canada. Pendant les stades 5d à 5a, le secteur arctique connut des conditions glaciaires, alors que dans la mer du Labrador et les provinces atlantiques des conditions subarctiques à tempérées fraßches persistÚrent. Un bref (<104ans) stade 4 se distingue par une augmentation notable des teneurs en 180 dans les séquences océaniques: il correspondrait au développement méridional de l'Inlandsis laurentidien pendant le Wisconsinien inférieur, par ailleurs daté d'environ 80,000 ans dans les basses terres du Saint-Laurent. Rien ne permet cependant de démontrer que des conditions pleinement glaciaires existaient aussi dans les provinces atlantiques. Le stade 3 (Wisconsinien moyen) est caractérisé par des fluctuations des teneurs en 180 des foraminifÚres indiquant des transits épisodiques d'eau de fonte dans les mers du Labrador et de Baffin. En dépit d'un important volume de glace s'étendant sur l'est du Canada, certaines régions connurent des conditions de marge glaciaire: dans les provinces atlantiques, en particulier à l'ßle du Cap-Breton. Ia palynostratigraphie révÚle l'existence d'un climat subarctique à hémiarctique; au pied des Appalaches au Québec, le lac proglaciaire Gayhurst s'est formé vers 46,000 ans avant l'Actuel. Au cours du stade 2 (Wisconsinien supérieur), l'inlandsis laurentidien a atteint son volume maximal alors que des calottes satellites se sont formées dans les provinces atlantiques. Dans les carottes océaniques, des fortes teneurs en 180 témoignent des conditions pléniglaciaires du stade 2, bien que des valeurs relativement faibles dans le secteur ouest de la mer du Labrador indiquent des apports d'eau de fonte discrets mais quasi continus. Une phase précoce de fonte glaciaire de la marge nord-est de l'inlandsis se traduit par une baisse des teneurs en 180 peu aprÚs 16,700BP. Le retrait final des glaces laurentidiennes le long de la facade océanique du Labrador s'est effectué vers 11,000 BP, alors que les glaces avaient déjà disparu du sud-est du Canada. Le rétablissement de conditions interglaciaires fut apparemment diachronique dans les bassins adjacents de l'est du Canada

    The outflow from Hudson Strait and its contribution to the Labrador Current

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    Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 55 (2008): 926-946, doi:10.1016/j.dsr.2008.03.012.Hudson Strait delivers a large amount of fresh water to the subpolar North Atlantic due to a large riverine input into the upstream Hudson Bay System and to the rerouting of Arctic Ocean waters. The fresh waters flowing out of Hudson Strait feed the Labrador Current, a current that has a significant impact on the climate and ecosystem of the entire northeastern seaboard. The lack of measurements from the strait have, until recently, made it difficult to determine the relative contribution of Hudson Strait to the properties and variability of the Labrador Current compared to other sources. This study describes the first year round observations of the outflow as obtained from a moored array deployed midstrait from August 2004 to 2005, and from a highresolution hydrographic section conducted in September of 2005. The outflow from Hudson Strait has the structure of a buoyant boundary current spread across the sloping topography of its southern edge. The variability in the flow is dominated by the extreme semidiurnal tides and by vigorous, mostly barotropic, fluctuations over several days. The fresh water export is seasonally concentrated between June and March with a peak in NovemberDecember, consistent with the seasonal riverine input and seaice melt. It is highly variable on weekly timescales due to synchronous salinity and velocity variations. The estimated volume and liquid fresh water transports during 20042005 are respectively of 11.2 Sv and 7888 (2829) mSv relative to a salinity of 34.8 (33). This implies that the Hudson Strait outflow accounts for approximately 15% of the volume and 50% of the fresh water transports of the Labrador Current. This larger than previously estimated contribution is partially due to the recycling, within the Hudson Bay System, of relatively fresh waters that flow into Hudson Strait, along its northern edge. It is speculated that the source of this inflow is the outflow from Davis Strait.Straneo acknowledges support from the Woods Hole Oceanographic Institution's Ocean and Climate Change Institute and the Comer Foundation, in particular, as well as support for NSF OCE0629411. Support to FJS from NSERC Research Grant and the Canadian Program on Energy Research and Development
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