Hydrography and circulation in the Filchner Depression, Weddell Sea, Antarctica

Cold and dense Ice Shelf Water (ISW) emerging from the Filchner-Ronne Ice Shelf cavity in the southwestern Weddell Sea flows northward through the Filchner Depression to eventually descend the continental slope and contribute to the formation of bottom water. New ship-born observations of hydrography and currents from Filchner Depression in January 2013 suggest that the northward flow of ISW takes place in a mid-depth jet along the eastern flank of the depression, thus questioning the traditional view with outflow along the western flank. This interpretation of the data is supported by results from a regional numerical model, which shows that ISW flowing northward along the eastern coast of Berkner Island turns eastward and crosses the depression to its eastern side upon reaching the Filchner ice front. The ice front represents a sudden change in the thickness of the water column and thus a potential vorticity barrier. Transport estimates of northward ISW flux based on observations ranges from 0.2-1.0 Sv

Measurements of Ice Shelf Water beneath the front of the Ross Ice Shelf using gliders

Measurements made by an underwater glider deployed near the Ross Ice Shelf were used to identify the presence of Ice Shelf Water (ISW), which is defined as seawater with its potential temperature lower than its surface freezing point temperature. Properties logged by the glider included in situ temperature, electrical conductivity, pressure, GPS location at surfacings and time. For most of the first 30 recorded dives of its deployment, evidence suggests the glider was prevented from surfacing due to being under the ice shelf. For dives under the ice shelf, farthest from the ice shelf front, ISW layers of varying thicknesses and depth locations were observed; between 2 m thick (centred at 231 m depth) to >93 m thick (centred at >360 m). For dives under the ice shelf, close to the ice shelf front, either no ISW was observed or ISW layers were centred at shallower depths (116–127 m). Thicker ISW layers (e.g. up to 250 m thickness centred at 421 m) were observed for some glider dives in open water in front of the Ross Ice Shelf. No in situ supercooling (water colder than the pressure-dependent freezing point temperature) was observed

Energetic plumes over the western Ross Sea continental slope

Rapid descent of dense Drygalski Trough (western Ross Sea, Antarctica) shelf water over the continental slope, within 100 to 250 m thick benthic plumes, is described. Speeds of up to 1.0 m/s are recorded flowing at an average angle of 35° to the isobaths, entraining ambient Lower Circumpolar Deep Water en route. This process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor Antarctic Bottom Water. Nonetheless, a 4-hour duration pulse of undiluted shelf water was observed at depth (1407 m) directly north of the Drygalski Trough, moving at around 90 degrees to isobaths, and at a speed of 1.4 m/s. Thus the export of Ross Sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths, punctuated by rapid downhill cascades

Machine learning for property valuation : an empirical study of how property price predictions can improve property tax estimations in Norway

This thesis investigates whether machine learning methods can improve property price predictions, leading to more accurate property tax estimations in Norway. This study is important to ensure fair and trustworthy taxation for Norwegian taxpayers. The current method for predicting property values is a hedonic pricing model, developed by Statistics Norway using multiple linear regression. This model shows that 25% of all predicted property prices deviate by more than 20% of their observed price. These predictions are further used to estimate property tax, and the deviation in the current model suggests there is potential for improvement. The use of machine learning to improve property price predictions has yet to be explored by Statistics Norway. Consequently, this thesis investigates the predictive performance of more advanced machine learning methods on transacted properties, covering three districts in Oslo, from 2005 to 2020. These methodologies include decision trees, Random Forest, gradient boosting, and neural networks. All methodologies, except decision trees, performed better than multiple linear regression. Gradient boosting produced the best results, with an RMSE of 0.1140 compared to an RMSE of 0.2132 from the multiple linear regression. The total percentage of predictions deviating more than 20% of observed values were 6.4% using the gradient boosting approach, providing an improvement of 74% to the current method. The main conclusion drawn from this research confirms the superiority of machine learning methods for property valuation, capable of improving the current methods for estimating property tax in Norway. Additionally, the use of Local Interpretable Model-agnostic Explanations (LIME) can make the results transparent and compliant with current GDPR legislation for automated decisions. This thesis recommends the implementation of gradient boosting as the new method for property valuation in Norway. Keywords – Property tax, machine learning, LIME, GDPR, gradient boostingnhhma

Icebergs in the North Atlantic: Modelling circulation changes and glacio-marine deposition

In order to investigate meltwater events in the North Atlantic, a simple iceberg generation, drift, and melting routine was implemented in a high-resolution OGCM. Starting from the modelled last glacial state, every 25th day cylindrical model icebergs 300 meters high were released at 32 specific points along the coasts. Icebergs launched at the Barents Shelf margin spread a light meltwater lid over the Norwegian and Greenland Seas, shutting down the deep convection and the anti-clockwise circulation in this area. Due to the constraining ocean circulation, the icebergs produce a tongue of relatively cold and fresh water extending eastward from Hudson Strait that must develop at this location, regardless of iceberg origin. From the total amount of freshwater inferred by the icebergs, the thickness of the deposited IRD could be calculated in dependance of iceberg sediment concentration. In this way, typical extent and thickness of Heinrich layers could be reproduced, running the model for 250 years of steady state with constant iceberg meltwater inflow

Optimal timing of return migration in Atlantic salmon

In many populations of Atlantic salmon, individuals return to rivers months or even a year prior to spawning. This premature arrival in fresh water by far exceeds the time needed for upstream migrations to spawning areas. Leaving the ocean early means forgoing substantial growth and incurring high metabolic costs of fasting in freshwater. Differences in timing of return migration has been shown to have a genetic basis, and different sea age classes return to rivers at different times. Previously suggested explanations regarding the cause for this behaviour have included both environmental factors and life history trade-offs, but these hypotheses have not been tested. Here, we combine data on marine growth and mortality of Atlantic salmon with the calculations of energetic expenditures of fasting in freshwater to explore how timing of river entry affects the probability of survival and energy recourses available for spawning. Our results show that to maximize the product of survival until spawning and energy available at spawning, multi sea winter fish in general must enter rivers earlier than one sea winter fish. And that for a large range of sea survival rates, the optimum river entry date for multi sea winter fish is as early as possible. This strongly suggests that the phenomena of premature arrival in Atlantic salmon is adaptive behaviour. Atlantic salmon, energy, migration, premature migration, run timing, sea survivalpublishedVersio

Last glacial benthic foraminiferal d18O anomalies in the polar North Atlantic: A modern analogue evaluation

Modern processes are evaluated to understand the possible mechanisms behind last glacial benthic foraminiferal δ18O anomalies that occurred concurrent with meltwater events in the polar North Atlantic; such anomalies in the Nordic seas were recently interpreted to be caused by brine formation. Despite intensive sea-ice production on circumarctic shelves, modern data show that brines ejected from sea-ice formation containing low δ18O water do not significantly contribute to deep waters in the Arctic Ocean today. Assuming that this process was, nevertheless, responsible for δ18O anomalies in Nordic seas deep water during the last glaciation, a broad, shallow shelf area adjacent to the Nordic seas, such as the Barents Sea, had to be seasonally free of sea-ice in order to serve as an area for brine formation. Another process which may explain δ18O-depleted water at depth is found in the Weddell Sea today, where a low δ18O signal in deep waters originates from ice shelf interactions. If temperature were considered the main mechanism for the low benthic δ18O values, an increase of 4°C must have occurred in the deep water. An analogous situation with a reversed water temperature pattern due to a subsurface inflow of warm Atlantic water is found today in the eastern Arctic Ocean, and deep water warming is observed in the Greenland Gyre in the absence of deep convection. Because paleoproxy data also indicate an Atlantic water inflow into the Nordic seas during such benthic δ18O anomalies, temperature as a principal mechanism of changing δ18O cannot be excluded

Acute toxicity testing of the tire rubber-derived chemical 6PPD-quinone on Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Recent identification of 6PPD-quinone as the chemical causing acute toxicity in coho salmon has led to substantial concern regarding toxicity of this contaminant for other aquatic species. Environmental occurrence of 6PPD-quinone is probably high as it is an oxidation product of a common tire rubber additive. Research on 6PPD-quinone toxicity in fish has revealed a rather unusual pattern, with closely related species exhibiting responses ranging from extreme sensitivity to no effect. Of eleven previously studied fish species, 6PPD-quinone was toxic to four. The species-specific toxicity of 6PPD-quinone complicates urgently needed environmental risk assessment. We investigated acute toxicity of 6PPD-quinone in Atlantic salmon and brown trout alevins (sac fry). These species have previously not been tested for sensitivity to 6PPD-quinone. The fish were exposed in static conditions in eight treatments with initial concentrations ranging from 0.095–12.16 µg/L. Fish were observed for 48 h and changes in concentrations of 6PPD-quinone were monitored throughout the experiment. No mortalities or substantial changes in behaviour were recorded in either Atlantic salmon or brown trout. This provides an important first step in assessing effects of 6PPD-quinone on these highly economically and culturally important species.acceptedVersio