Eddies in the Marginal Ice Zone of Fram Strait and Svalbard from Spaceborne SAR Observations in Winter

Here we investigate the intensity of eddy generation and their properties in the marginal ice zone (MIZ) regions of Fram Strait and around Svalbard using spaceborne synthetic aperture radar (SAR) data from Envisat ASAR and Sentinel-1 in winter 2007 and 2018. Analysis of 2039 SAR images allowed identifying 4619 eddy signatures. The number of eddies detected per image per kilometer of MIZ length is similar for both years. Submesoscale and small mesoscale eddies dominate with cyclones detected twice more frequently than anticyclones. Eddy diameters range from 1 to 68 km with mean values of 6 km and 12 km over shallow and deep water, respectively. Mean eddy size grows with increasing ice concentration in the MIZ, yet most eddies are detected at the ice edge and where the ice concentration is below 20%. The fraction of sea ice trapped in cyclones (53%) is slightly higher than that in anticyclones (48%). The amount of sea ice trapped by a single ‘mean’ eddy is about 40 km2, while the average horizontal retreat of the ice edge due to eddy-induced ice melt is about 0.2–0.5 km·d–1 ± 0.02 km·d–1. Relation of eddy occurrence to background currents and winds is also discussed.

Variations in Atmospheric Energy Transport across the Arctic Circle

<p>Understanding the variability of energy transport and its components, and the mechanisms involved, is critical to improve our understanding of the Arctic amplification. Large amounts of energy are transported from the equator to the poles by the large-scale atmospheric circulation. At the Arctic Circle, this represents an annual average net transport of about two PW. The energy transport can be divided into latent and dry static components which, when increasing, indirectly contribute to the Arctic amplification. While the enhanced dry static energy transport favors sea ice melt and changes the lapse rate, the enhanced influx of latent energy affects the water vapor content and cloud formation, and thus also the lapse rate and sea ice melt via radiative effects.</p> <p>In this study, 40 years (1979-2018) of 6-hourly ERA-Interim reanalysis data are used to calculate the energy transport and its components. Inconsistencies due to spurious mass-flux are accounted for by barotropic wind field correction before the calculation. The first and last decade of the ERA-Interim period differ in terms of sea ice cover, sea surface temperature, and greenhouse gas concentrations, all of which affect the atmospheric circulation.</p> <p>The comparison between these periods shows significant changes in monthly and annual vertically integrated energy transport across the Arctic Circle. On an annual average, energy transport significantly increases in the late period for both total energy and its components, whereas the transport of dry static energy decreases in the winter season. The analysis of the atmospheric circulation reveals variations in the frequency of occurrence of preferred circulation regimes and the associated anomalies in energy transport as a potential cause for the observed changes.</p> <p>The hemispheric-scale and climatological view provides an expanded overall picture in terms of poleward energy transport to atmospheric events as cold air outbreaks and atmospheric rivers. This is demonstrated using the example of the atmospheric river which occurred over Svalbard on 6<sup>th</sup> & 7<sup>th</sup> June 2017.</p>

Signature of ice melt over the Greenland derived from MSMR (OCEANSAT-1) data

In order to monitor the impact of global warming phenomena over the Polar Regions, it is necessary to monitor snow/ice melt on the Greenland and the Antarctic ice sheets. Using MSMR data, it is possible to differentiate sea ice at different concentration levels. On the basis of microwave emissivities of continental ice and sea ice, useful information on the formation and melting of the ice can be derived. The paper discusses different strategies to derive a melt signal from the MSMR observations for the continental ice sheets in Greenland. The Polarization Difference (PD) for 21 GHz, available from MSMR data, is studied and an appropriate threshold is selected to detect the presence of melt signal. The results of the present study have bearing on climate changes.

Sediment Load Concentration and Resultant Channel Planform in the Lower Gandak Plain

Erosion, transportation and deposition by running water are closely related and these works are performed in association and not in isolation. One cannot be performed without others. These works are determined on other factors like topography, geology, structure and composition of rocks, slope, amount of water availability and its characteristics, climate etc. Huge catchment area of the Gandak River is lying in the Himalayan mountainous region. This region is receiving good amount of rainfall concentrated in four months of monsoonal period June to September (JJAS). This period has also high temperatures leading to large amount of glacial ice melt. Hence, enormous water is drained off the mountain steep slope. The Himalaya is very young and has fragile rocks and ecosystem. Anthropogenic activities in those areas are primary cause, apart from natural weathering, for generation of more and more shattered materials which are brought by running water downstream much easily. Therefore, highly sediment concentrated water brings large quantity of loads. It is deposited in suitable conditions along its paths in the plain and with flood water. It results the formation of flood plain. According to the erosion and deposition, different types of major and minor features are formed. In other words, water and sediment determine the layout of the plain appearance. In this background, it is attempted to (i) study sediment concentration in discharged water and (ii) illustrate the channel planform of the Gandak River in the plain. To achieve these aims, secondary data has been collected and analyzed. It is expected that this study will help in executing an integrated development plan for the flood affected area of Lower Gandak River Plain. Keywords: sediment load, channel bars, channel planform, meandering, braiding, slope/gradient and channel cutoff.

Aerodynamic roughness length of crevassed tidewater glaciers from UAV mapping

The aerodynamic roughness length (z0) is an important parameter in the bulk approach for calculating turbulent fluxes and their contribution to ice melt. However, z0 estimates for heavily crevassed tidewater glaciers are rare or only generalised. This study used uncrewed aerial vehicles (UAVs) to map inaccessible tidewater glacier front areas. The high-resolution images were utilised in a structure-from-motion photogrammetry approach to build digital elevation models (DEMs). These DEMs were applied to five models (split across transect and raster methods) to estimate z0 values of the mapped area. The results point out that the range of z0 values across a crevassed glacier is large, by up to 3 orders of magnitude. The division of the mapped area into sub-grids (50 m × 50 m), each producing one z0 value, accounts for the high spatial variability in z0 across the glacier. The z0 estimates from the transect method are in general greater (up to 1 order of magnitude) than the raster method estimates. Furthermore, wind direction (values parallel to the ice flow direction are greater than perpendicular values) and the chosen sub-grid size turned out to have a large impact on the z0 values, again presenting a range of up to 1 order of magnitude each. On average, z0 values between 0.08 and 0.88 m for a down-glacier wind direction were found. The UAV approach proved to be an ideal tool to provide distributed z0 estimates of crevassed glaciers, which can be incorporated by models to improve the prediction of turbulent heat fluxes and ice melt rates.

The migration law of magnesium ions during freezing and melting processes

To explore the migration law of magnesium ions (Mg2+) during freezing and melting processes, laboratory simulation experiments involving freezing and melting were carried out to investigate the influence of ice thickness, freezing temperature, initial concentration, and initial pH on the distribution of Mg2+ in the ice-water system. The distribution coefficient “K” (the ratio of the Mg2+ concentration in the ice layer to the Mg2+ concentration in the water layer under ice) was used to characterize the migration ability of Mg2+. The results showed that during the freezing process, the concentration distribution of Mg2+ in the ice and water two-phase system was as follows: ice layer < water before freezing < water layer under ice; in other words, it migrated from ice layer to the water layer under ice. “K” decreased with increasing ice thickness, freezing temperature, initial concentration, and initial pH; the higher the ice thickness, freezing temperature, initial concentration, and initial pH were, the higher the migration efficiency of Mg2+ into the water layer under ice was. During the melting process, Mg2+ was released in large amounts (50–60%) at the initial stage (0–25%) and in small amounts (25–100%) uniformly in the middle and later periods. According to the change of Mg2+ concentration in ice melt water, an exponential model was established to predict Mg2+ concentration in ice melt period. The migration law of Mg2+during the freezing and melting process was explained by using first principles.

Methane emissions from northern lakes under climate change: a review

Northern lakes are important sources of CH4 in the atmosphere under the background of permafrost thaw and winter warming. We synthesize studies on thermokarst lakes, including various carbon sources for CH4 emission and the influence of thermokarst drainage on carbon emission, to show the evasion potential of ancient carbon that stored in the permafrost and CH4 emission dynamics along with thermokarst lake evolution. Besides, we discuss the lake CH4 dynamics in seasonally ice-covered lakes, especially for under-ice CH4 accumulation and emission during spring ice melt and the possible influential factors for CH4 emission in ice-melt period. We summarize the latest findings and point out that further research should be conducted to investigate the possibility of abundant ancient carbon emission from thermokarst lakes under climate warming and quantify the contribution of ice-melt CH4 emission from northern lakes on a large scale.

Reconstructing Neogene Climate and Glacial History of Southern McMurdo Sound, Antarctica

<p>Understanding the glacial changes that have occurred in southern McMurdo Sound throughout the Neogene makes an important contribution to reconstructing Antarctic ice volume changes during past periods of climatic warmth, and provides insight into future possible response of the ice sheet. Fossiliferous glacimarine deposits previously identified throughout McMurdo Sound have provided inferences on past changes in ice volume and the implications for global sea level. This study investigates new stratigraphic sections comprising fossiliferous glacimarine sediments from two locations on the flanks of Mount Discovery and one on Brown Peninsula at ~150m above present day sea-level. The aim of this thesis is to undertake a sedimentological, facies and glacimarine sequence stratigraphic analysis together with a quantitative assessment of the constituent micro and macrofossils in order to determine depositional processes, changes in environment and implications for glacial variability in the southern McMurdo Sound. Up to four distinct sedimentary cycles are evident in the Mt Discovery sections with each cycle consisting of: 1. A basal glacial surface of erosion (GSE) or its correlative conformity (CC) seaward of the grounding line, displaying an abrupt transition from a more distal facies to a more proximal facies. 2. A sharp-based massive diamictite displaying physical intermixing of subjacent lithologies, intra formational clasts, soft sediment deformation features, clast rotation features, and a lack of bioturbation, interpreted as subglacial, or in very close proximity to a marine grounding line. In some cases stratified diamictites overly correlative conformities displaying clast alignment, graded beds, and weak decimeter scale parallel bedding in the matrix, interpreted as grounding-line proximal sediment gravity flows or rain-out from ice melt. 3. In some cases, the diamictite passes gradationally-upwards or is sharply overlain by a conglomerate representing appearance of glacimarine fluvio-deltaic deposition or debris flows as the glacier grounding line begins to retreat. 4. Conglomerates are overlain, often sharply, by hemipelagic laminated or massive mudstone and represent the most ice distal and marine part of the sequence at the interglacial minima. 5. A proglacial facies succession is sometimes preserved below the GSE or correlative conformity marking the top of the sequence and usually consists of a transition from mudstone facies into grounding zone proximal conglomerates during re-advance of the grounding line. Lithofacies analysis supported by sediment grainsize, the results of a foraminiferal census and macrofaunal identifications conducted on each facies imply deposition on the continental shelf in depths of up to 400 m, during oscillations in the proximity of a marine grounding line. Radiocarbon dating of constituent macrofauna (barnacle plates) reported only background ¹⁴C implying an age of deposition older than the Last Glacial Maximum. The present day elevation of the site and a model developed here using glacio-iostatic loading and unloading implies that the Mt Discovery sites have been above sea-level for approximately the last ~2.7Ma. Given their inferred association with Scallop Hill Formation and faunal similarity to sequences in the nearby ANDRILL drill cores, a Pliocene age is considered most likely. This finding is consistent with previous investigations that indicate a dynamic, sub-polar marine-terminating ice sheet margin in Southern McMurdo Sound during the Pliocene, with periods of open ice shelf free conditions potentially associated with more frequent regional collapse and retreat events of a marine-based ice sheet in the Ross Sea embayment.</p>

Reconstructing Neogene Climate and Glacial History of Southern McMurdo Sound, Antarctica

<p>Understanding the glacial changes that have occurred in southern McMurdo Sound throughout the Neogene makes an important contribution to reconstructing Antarctic ice volume changes during past periods of climatic warmth, and provides insight into future possible response of the ice sheet. Fossiliferous glacimarine deposits previously identified throughout McMurdo Sound have provided inferences on past changes in ice volume and the implications for global sea level. This study investigates new stratigraphic sections comprising fossiliferous glacimarine sediments from two locations on the flanks of Mount Discovery and one on Brown Peninsula at ~150m above present day sea-level. The aim of this thesis is to undertake a sedimentological, facies and glacimarine sequence stratigraphic analysis together with a quantitative assessment of the constituent micro and macrofossils in order to determine depositional processes, changes in environment and implications for glacial variability in the southern McMurdo Sound. Up to four distinct sedimentary cycles are evident in the Mt Discovery sections with each cycle consisting of: 1. A basal glacial surface of erosion (GSE) or its correlative conformity (CC) seaward of the grounding line, displaying an abrupt transition from a more distal facies to a more proximal facies. 2. A sharp-based massive diamictite displaying physical intermixing of subjacent lithologies, intra formational clasts, soft sediment deformation features, clast rotation features, and a lack of bioturbation, interpreted as subglacial, or in very close proximity to a marine grounding line. In some cases stratified diamictites overly correlative conformities displaying clast alignment, graded beds, and weak decimeter scale parallel bedding in the matrix, interpreted as grounding-line proximal sediment gravity flows or rain-out from ice melt. 3. In some cases, the diamictite passes gradationally-upwards or is sharply overlain by a conglomerate representing appearance of glacimarine fluvio-deltaic deposition or debris flows as the glacier grounding line begins to retreat. 4. Conglomerates are overlain, often sharply, by hemipelagic laminated or massive mudstone and represent the most ice distal and marine part of the sequence at the interglacial minima. 5. A proglacial facies succession is sometimes preserved below the GSE or correlative conformity marking the top of the sequence and usually consists of a transition from mudstone facies into grounding zone proximal conglomerates during re-advance of the grounding line. Lithofacies analysis supported by sediment grainsize, the results of a foraminiferal census and macrofaunal identifications conducted on each facies imply deposition on the continental shelf in depths of up to 400 m, during oscillations in the proximity of a marine grounding line. Radiocarbon dating of constituent macrofauna (barnacle plates) reported only background ¹⁴C implying an age of deposition older than the Last Glacial Maximum. The present day elevation of the site and a model developed here using glacio-iostatic loading and unloading implies that the Mt Discovery sites have been above sea-level for approximately the last ~2.7Ma. Given their inferred association with Scallop Hill Formation and faunal similarity to sequences in the nearby ANDRILL drill cores, a Pliocene age is considered most likely. This finding is consistent with previous investigations that indicate a dynamic, sub-polar marine-terminating ice sheet margin in Southern McMurdo Sound during the Pliocene, with periods of open ice shelf free conditions potentially associated with more frequent regional collapse and retreat events of a marine-based ice sheet in the Ross Sea embayment.</p>