The 62 million year old lava flows of Baffin Island and West Greenland represent the earliest phase of magmatism in the North Atlantic Igneous Province (NAIP). These picritic lavas are characterised by high magnesium contents owing to their high proportion of olivine crystals. The parental magmas for the picrites are likely to have accumulated olivine crystals on their transit through the lithosphere and crust. Debate over the origin of accumulated crystals in the lavas results in uncertainty in the temperature and composition of the parental magmas for the early NAIP. The magnesium-rich olivine crystals (up to Fo93) in the picrites of this study are shown not to have a xenocrystic origin. The samples, therefore, support the inference of high potential temperatures for the Baffin Island-West Greenland magmas, ~200oC above ambient mantle. The picrites of Baffin Island and West Greenland display the highest terrestrial magmatic 3He/4He (up to 50 Ra, where Ra is the atmospheric value 1.39 x 10-6), values that are considerably higher than the highest 3He/4He in contemporary ocean island basalts, which reach a maximum of ~30 Ra. High 3He/4He in Baffin Island and West Greenland are associated with a wide range of incompatible trace element and lithophile radiogenic isotopic compositions, not dissimilar to the range of compositions displayed by lavas at mid-ocean ridges, and overlapping the range displayed by most northern hemisphere ocean island basalts. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks are mixed with depleted parents cannot account for the compositional trends displayed by the picrites. Major and trace element compositions were determined on melt inclusions in high- 3He/4He picrites that span a wide range of whole-rock incompatible trace element and radiogenic isotopic compositions. The melt inclusions support the findings from the whole-rock study since melt inclusion compositions reflect the composition of their associated whole-rock, with no anomalous compositions present. In addition, there is no evidence for a contribution of a proportion of depleted melts to the source of the relatively enriched whole-rock samples. Therefore, since all melt inclusions were contained within high-3He/4He samples, it is shown that high 3He/4He is a feature of both depleted and relatively enriched melt compositions. The wide range in whole-rock compositions of the Baffin Island and West Greenland picrites represents that of the sub-lithospheric mantle source region and is inconsistent with derivation of the picrites from residues of ancient mantle depletion. The apparent decoupling of helium from trace elements and radiogenic isotopes is hard to reconcile with simple mixing of a high-helium concentration, high-3He/4He reservoir with various depleted and enriched helium-poor mantle reservoirs. It is possible that primordial helium has diffused into a reservoir with a composition similar to that of the convecting upper mantle. However, this must have occurred after the development of existing mantle heterogeneity. The high-3He/4He picrites require the existence of a deep, primordial helium-rich reservoir. Whether this reservoir is present in the upper or deep mantle, or even the core, remains uncertain.

No description available.

Approved for public release; distribution is unlimited / During the month of July 1987 an acoustical experiment was conducted by the United States Naval Research Laboratory (NRL) in the East Greenland Sea Marginal Ice Zone (MIZ) . Ambient noise "hot spots" or concentrated areas of relatively high noise levels were found along the ice edge using a towed array. Ambient noise levels were obtained on 27 and 28 July using AN/SSQ-57A and AN/SSQ-57XN5 calibrated sonobuoys . The temperature structure of the area was determined using XBT (ship) and AXBT (P3C aircraft) buoys placed inside and outside the ice edge. The ice edge was determined from coincident satellite photos, 90 GHz microwave imagery and P3 radar ice edge maps. Weather data (sea state and wind speed and direction) were recorded on the ship. The data seem to indicate a correlation between the high ambient noise levels of the hot spots and the presence of a large topographically controlled mesoscale eddy located at the southeastern extent of the MIZ. / http://archive.org/details/spatialvariabili00bigg / Lieutenant, United States Navy

Near-surface air temperature (SAT) over Greenland has important effects on mass balance of the ice sheet, but it is unclear which SAT datasets are reliable in the region. Here extensive in-situ SAT measurements are used to assess monthly mean SAT from seven global reanalysis datasets, four gridded SAT analyses, one satellite retrieval and two dynamically downscaled reanalyses. Strengths and weaknesses of these products are identified, and their biases are found to vary by season and glaciological regime. MERRA2 reanalysis overall performs best with mean absolute error less than 2 °C in all months. Ice sheet-average annual mean SAT from different datasets are highly correlated in recent decades, but their 1901–2000 trends differ in sign. Compared with the MERRA2 climatology combined with gridded SAT analysis anomalies, thirty-one earth system model historical runs from the CMIP5 archive reach ~5 °C for the 1901–2000 average bias and have opposite trends for a number of sub-periods.

This work aims to study the behavior of the western margin of the Greenland Ice Sheet during a period of pronounced ice retreat roughly 10,000 years ago, after the end of the last glacial period. It explores the efficiency of subglacial erosion, the spatial dynamics of ice retreat, and the rates of ice retreat. To address these questions, I use the radionuclides 10Be and 26Al, which form in rocks due to the bombardment of cosmic rays, only after the rocks have been exposed from underneath retreating ice. These nuclides can be used as a geologic dating technique to explore exposure history. Before applying this dating technique to address geological questions, it was critical to first perform methodological development. My work in the University of Vermont‘s new Cosmogenic Nuclide Laboratory served to improve the precision and efficiency of the pre-existing laboratory methods. New methodological advances ensured that samples from Greenland, which contained only low concentrations of 10Be and 26Al, could be used to yield meaningful results about ice behavior. Cosmogenic nuclide dating was applied at two sites along the ice sheet margin in central-western Greenland. At both of these sites, I collected paired bedrock and boulder samples in a transect normal to and outside of the present-day ice sheet margin. Samples were collected from a variety of elevations at numerous locations along the transects, thus providing three-dimensional coverage of the field area. After isolating the mineral quartz from the rocks, and isolating the elements Be and Al from the quartz, isotopic analysis was performed using accelerator mass spectrometry to quantify the relative abundances of the radionuclides against their respective stable isotopes. The southern study site, Ilulissat, is located on the western coast of Greenland at a latitude of 69N. Much previous work has been conducted here due to the presence of one of the largest ice streams in the northern hemisphere, Jakobshavn Isbræ. My work in Ilulissat demonstrated that subglacial erosion rates were high during previous glacial periods, efficiently sculpting and eroding the landscape. Ice retreat across the land surface began around 10,300 years ago, and the ice sheet retreated behind its present-day margin about 7,600 years ago. Ice retreat occurred at a rate of about 100 meters per year. My work in this area suggests that retreat in the large ice stream set the pace and timing for retreat of the neighboring ice sheet margin. The northern site, Upernavik, is located on the western coast of Greenland at a latitude of 73N. Little research has been conducted here in the past. Unlike in Ilulissat, my work here shows that the ice sheet did not efficiently erode the landscape, especially at high elevations, during previous glacial periods. This is likely because the ice was thinner, and therefore had a colder base, than the ice in Ilulissat. My work suggests that ice cover was lost from this area very rapidly, likely at rates of about 170 meters per year, in a single episode around 11,300 years ago. Comparison between the two study sites reveals that ice characteristics can vary appreciably over relatively small distances.

Meltwater accumulated on the Greenland Ice Sheet drains to glacier beds, discharging into fjords hundreds of meters below sea level. The injection of meltwater at depth generates an upwelling plume that entrains warm ocean water as it rises along the terminus, increasing submarine melt and driving a fjord-scale exchange flow. However, due to sparse ocean-glacier observations, we lack a process understanding of how plumes control fjord circulation and submarine melt. Combining numerical modeling, theory, and observations, this dissertation investigates near-glacier plume dynamics, the influence of glacier depth on plume structure and submarine melt, and the role of fjord-glacier geometry on circulation in tidewater glacier fjords. In Chapter II, I use buoyant plume theory and a nonhydrostatic, three-dimensional ocean–ice model to investigate the sensitivity of plume dynamics to subglacial discharge, turbulent diffusivity, and conduit geometry. Large discharges result in plumes with positive temperature and salinity anomalies in the upper water column. Fjord circulation is sensitive to conduit geometry; distributed subglacial discharge results in a stronger return flow of warm water toward the terminus. In Chapter III, I use buoyant plume theory, initialized with realistic ranges of subglacial discharge, glacier depth, and ocean stratification, to investigate how plume structure and submarine melt vary during summer months in 12 Greenland fjords. Grounding line depth is a primary control on plume-induced submarine melt: deep glaciers produce warm, salty subsurface plumes that undercut termini, and shallow glaciers produce cold, fresh surface-confined plumes that can overcut. Finally, in Chapter IV, I use regional-scale numerical ocean simulations to systematically evaluate how fjord circulation forced by subglacial plumes, tides, and wind stress depends on fjord width, glacier depth, and sill height. Glaciers grounded below sill depth can draw shelf waters over a shallow sill and into fjord basins with seasonal subglacial discharge; this process is independent of external shelf forcing. These results underscore the first-order effect that subglacial discharge and fjord-glacier geometry have in controlling fjord circulation and, thus, ocean heat flux to the ice. This dissertation includes previously published and co-authored material.

Opaque phases from carbonatites of the Grønnedal-Íka alkaline complex (1299±17 Ma) of Southwest Greenland were analyzed in terms of their mineralogy and microstructure. The analysis demonstrates that a later intrusion by a 55 m wide dolerite dyke of unknown age has prompted the mineralization of magnetite by activating hydrothermal fluid convection. The fluid has interacted with the carbonatite, replacing siderite and ankerite by magnetite, which at places constitutes over half of the rock volume. Magnetite is shown to have become partly replaced by hematite at a later stage. A paragenetic sequence is suggested for the opaque phases that com- prise major magnetite and hematite, accessory pyrite and trace amounts of sphalerite, chalcopyrite and galena. / Low-temperature geologic sequestration of carbon by ikaite formation

The emergence and radiation of metazoan body plans around the Precambrian/Cambrian boundary, some 500-600 million years ago, seems to be concordant with the appearance and diversification of preservable hard parts. Several Precambrian soft-bodied, multicellular organisms most likely represent stem-group bilaterians, but their fossil record is rather sparse.  In contrast, the Cambrian fossil record is comparably rich – comprising hard part, trace fossil and delicate soft tissue preservation – and most animal phyla that we know of today had evolved by the end of the Cambrian. Consequently, this time represents an important period in the early evolution of metazoan life forms. Most skeletal remnants of invertebrate organisms from this period are preserved in incomplete, disarticulated sclerite assemblages, and the true architecture of the original skeletal structure, the scleritome, may therefore be hard to discern. Many scleritomous taxa have been suggested to be members of the lophotrochozoan clade, while their exact position within this group remains unclear. Such taxa are often referred to as Problematica. This thesis deals with some problematic scleritomous early Cambrian lophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions. In the first part, completely disarticulated calcareous sclerites from the lower Cambrian of North Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstruction alternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack of articulated material obscures any satisfactory conclusions regarding phylogenetic affinities and the original morphology of the organism. The other part of the thesis focuses on some minute, organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestone successions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – their scleritome architecture and their phylogenetic relationship with paterinid brachiopods. The oldest brachiopod from South Australia, Askepasma saproconcha, and the slightly younger Askepasma toddense are also described and discussed. Based on articulated specimens, recently described partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shell ultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with a tubular/conical scleritome. The morphological similarities with Paterimitra point in the same direction for the slightly older Kulparina.

This thesis examines and analyzes the extant archaeological, historical, and literary evidence for the beliefs and practices of the Greenland Norse, their influences, and their evolution over time. By critically examining previously held assumptions about the cultural, climatic, and religious conditions of Greenland during this time the available data is placed in its proper context and reveals the geoconceptual world of the Greenlanders and their place in it. This interdisciplinary approach illustrates the extent to which the physical environment and location of Greenland played a role in the transition from a collective of enterprising colonists to an established Christian community over the course of almost 500 years. Specific questions addressed within include: 1 ­ How does archaeology challenge, support, or augment the historical and literary narrative of Greenland’s transition into a Christian place?; 2 – What are the physical correlates of the Greenlanders’ beliefs and practices, and how have they been interpreted? This thesis finds that the development of Christianity was driven by the Greenlanders’ increasing perception of their place in the world as one of marginality and spiritual danger.

Despite their central importance to the Earth system, nowhere within the literatures of Polar Studies or the Humanities does there exist a comprehensive cultural and scientific history of ice sheets that takes into consideration both Greenland and Antarctica, or that is not constrained to a particular exploratory, technological, or geopolitical period or framing. My thesis addresses this lacunae by contributing a bi-polar, empirical history and analysis of the different scientific and cultural processes, transformations, and discontinuities through which ice sheets have been transformed from unexplored realms of the imagination, into tangible, material objects of investigation and meaning. Its scope extends from early Greek mapping to 1970. Within this timeframe, it identifies three broad phases in the perception of ice sheets. The first, preceding their earliest physical exploration, corresponds to the perception of ice sheets as one-dimensional realms defined and bounded by the human imagination. The second phase, associated with their early surface exploration between 1870 and 1930, corresponds to the perception of ice sheets as undifferentiated, two-dimensional 'topographies of absence', best characterized by their horizontal desolation. The third phase, triggered by the deployment of new technologies of sub-surface investigation such as seismic sounding, radio echo sounding (RES), and the practice of ice coring, corresponds to the perception of ice sheets as three-dimensional, super-massive, and interdependent objects of internal and material complexity. Although primarily rooted in archival research and the study of first hand textual and visual materials, my arguments and observations also draw on secondary literatures from the history of science and technology, geopolitics, visual culture, and the geography of space and place. These literatures allow me to contextualize and substantiate my analysis of historical processes within broader perspectives, notably Humboldtian science, Romanticism, visual abstraction, scientific imagery, and the Cold War.