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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Plio-Pleistocene Environments In The Western Arctic Ocean Based On Sediment Records From The Northwind Ridge

Dipre, Geoffrey R. January 2019 (has links)
No description available.
232

Multi-year Arctic Sea Ice Classification Using QuikSCAT

Swan, Aaron M. 10 June 2011 (has links) (PDF)
Long term trends in Arctic sea ice are of particular interest with regard to global temperature, climate change, and industry. This thesis uses microwave scatterometer data from QuikSCAT and radiometer data to analyze intra- and interannual trends in first-year and multi-year Arctic sea ice. It develops a sea ice type classification method. The backscatter of first-year and multi-year sea ice are clearly identifiable and are observed to vary seasonally. Using an average of the annual backscatter trends obtained from QuikSCAT, a classification of multi-year ice is obtained which is dependent on the day of the year (DOY). Validation of the classification method is done using regional ice charts from the Canadian Ice Service. Differences in ice classification are found to be less than 6% during the winters of 06-07, 07-08, and the end of 2008. Anomalies in the distribution of sea ice backscatter from year to year suggest a reduction in multi-year ice cover between 2003 and 2009 and an approximately equivalent increase in first-year ice cover.
233

Mitigation of Sea Ice Contamination in QuikSCAT Wind Retrieval

Hullinger, Weston Jay 12 March 2012 (has links) (PDF)
Satellite borne radar scatterometers provide frequent estimates of near surface wind vectors over the Earth's oceans. However in the polar oceans, the presence of sea ice in or near the measurement footprint can adversely a ect scatterometer measurements resulting in inaccurate wind estimates. Currently, such ice contamination is mitigated by discarding measurements within 50 km of detected sea ice. This approach is imperfect and causes loss of coverage. This thesis presents a new algorithm which detects ice-contaminated measurements based on a metric called the Ice Contribution Ratio (ICR) which measures the spatial ice contribution for each measurement. The ICR calculation is made for each measurement using a spatial ice probability map which is determined using Bayesian probability theory. Determined by simulation, the ICR processing thresholds the ICR for each measurement depending on local wind, ice backscatter, and cross-track location. ICR processing retrieves winds at a distance of 22.5 km from the ice edge on average, while ensuring wind accuracy. Retrieved wind distributions using ICR processing more closely resembles uncontaminated wind distributions than winds retrieved using previous methods. The algorithm is applied to QuikSCAT in this thesis but could be applied to other scatterometers such as the Oceansat-2 scatterometer.
234

Sea Ice Mapping Using Enhanced Resolution Advanced Scatterometer Images

Reeves, Steven Joseph 18 April 2012 (has links) (PDF)
Sea ice is of great interest due to its effect on the global climate, the Earth's ecosystem, and human activities. Microwave remote sensing has proven to be an effective way to measure many of the characteristics of sea ice. In particular, several algorithms map the daily sea ice extent using a variety of instruments. Enhanced resolution images generated from the Scatterometer Image Reconstruction (SIR) algorithm can be used to generate a high resolution ice extent map. Previous algorithms using SIR images were developed for scatterometers which are no longer operational. The Advanced Scatterometer (ASCAT) is a newer scatterometer which has different characteristics from the earlier scatterometers. The previous algorithms do not perform as well when applied to ASCAT. This thesis presents a new algorithm for ASCAT developed to discriminate sea ice from the open ocean and create daily maps of the ice extent. It is developed from previous algorithms used on earlier scatterometers. The algorithm uses an iterative Bayes decision rule to classify pixels as sea ice or ocean. Digital image processing techniques are used to reduce misclassifications. The ice maps from the new algorithm are compared with the NASA Team sea ice concentration maps from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E). The comparisons include: difference in area, distance between ice edges, number of missed and false detections. The new ice maps are also compared with the Remund-Long algorithm for the QuikSCAT satellite using the same metrics. The ice edge is verified with high resolution Synthetic Aperture Radar (SAR) data. The new ice maps perform similarly to previous ice mapping algorithms for scatterometers.
235

Analysis of Ship Traffic and Ship Accidents in the Canadian and Global Arctic

Nicoll, Adrian 31 March 2023 (has links)
In the Canadian Arctic, ship traffic has been increasing at the same time as sea ice has been declining over the past decade-plus. The decrease in sea ice has been associated with trends in warm weather and atmospheric conditions in the summer seasons, which are expected to continue. Thus, it is anticipated that ship traffic will also continue to grow, as areas in the Arctic, including the Northwest Passage (NWP) and Northern Sea Route (NSR) experience less and less sea ice. The appeal of the opening of these major Arctic shipping routes, is that these routes are shorter in distance for commercial ships on international voyages in comparison to traditional routes that travel through the Panama and Suez Canals. Assuming safe and smooth sailing a shorter route can be beneficial monetarily for commercial shipping companies and as a result for other economic sectors reliant on the efficient shipment of goods. However, a major concern associated with the anticipated increase in Arctic ship traffic is the potential for an increase in the number and severity of maritime navigational related accidents. Thus, the overall aim of this thesis is to quantify recent historic links between ship traffic, sea ice, ship accidents, and accident rates within the Canadian Arctic as well as the global Arctic. There are three specific objectives including to: 1. Conduct a comparative statistical analysis between two ship traffic databases (NORDREG and AIS) within the Canadian Arctic to evaluate datasets strengths and weaknesses; 2. Use the best available data (see objective 1) to examine the statistical associations and trends for ship traffic, ship accidents, accident rates, and sea-ice extent within the Canadian Arctic during the shipping-season from 1990 to 2019; and 3. Derive and compare recent ship traffic accident rates to determine if statistical trends from 2012 to 2019 exist for ships across the global Arctic. Results of the study show that both NORDREG and AIS data is useful in understanding shipping traffic trends in Arctic Canada over time and that each dataset is effective depending on the temporal period of interest (Objective 1). NORDREG data is most effective for identifying ship positioning before 2012 (+106,811 more nm sailed per matched unique vessels and +9 overall unique vessels from NORDREG) and from 2012 onwards AIS is more accurate, highlighted by the year of 2018 (+84,149 more nm sailed and +169 unique vessels from AIS). Using available data sources from 1990 to 2019, it was revealed that although commercial and non-commercial ship traffic is increasing across in Arctic Canada, the total number of accidents and overall accident rate for commercial vessels has declined, whereas they have increased for non-commercial ships (Objective 2). There are significant positive trends in overall ship traffic for all ship types (+9,275 nm yr⁻¹), commercial ships (+5,011 nm yr⁻¹) and non-commercial ships (+4,658 nm yr⁻¹). Whereas there have been significant negative trends in ship accidents for commercial ships (-0.06 accidents yr⁻¹), ship accident rates, for all ship types (-6.31E-07 accidents/nm yr⁻¹). Sea ice extent at the monthly level during the shipping season has been significantly decreasing (-3,193 km² mo⁻¹). Results also indicate that there are significant negative correlations between monthly ship traffic and sea ice extent, for all ship types (-0.50), commercial ships (-0.49), and non-commercial ships (-0.48). At the global scale, ship traffic is increasing while ship accident rates are decreasing (Objective 3). For the global Arctic there are positive statistically significant trends for all ship traffic (+2.655 million nm yr⁻¹), commercial ships (+1.598 million nm yr⁻¹), and non-commercial ships (+1.446 million nm yr⁻¹); where there are statistically significant annual decreases in ship accident rates for all ships (-3.64E-07 ship accidents/nm yr⁻¹), commercial ships (-9.39E-07 ship accidents/nm yr⁻¹), and non-commercial ships (-1.19E-07 ship accidents/nm yr⁻¹). At the country level, ship traffic associated to Russia, Norway, and Iceland contributes the most to global increase for both commercial and non-commercial ships. Norway has the largest statistically significant negative trend for all ship and commercial ship accident rates. Future research should focus around expanding on the analytical approach taken for objective 3, as more years of AIS data become available, as currently, the focus is on a shorter time-period (2012 to 2019). Given that incident rates are low globally, for high impacts (i.e., large spills), working with a long time series allows for considering more incidents. It would also be beneficial to perform an analysis that determines if there are statistical associations between yearly accident rates and sea ice extent in the global Arctic, as well as for each country within the Arctic. This information can help to answer questions around ship safety in the global Arctic, specifically: (a) Has the shipping become safer (e.g., less accidents per distance sailed) for the global Arctic and the countries within the Arctic? (b) Are there statistical associations between sea ice extent and accident rates within the global Arctic and the countries within the Arctic? (c) Are there countries associated with a higher incident rate compared to others? This information would help target measures to specific country ships that may be less safe for navigation.
236

Diatoms as Recorders of Sea Ice in the Bering and Chukchi Seas: Proxy Development and Application

Caisse, Beth A. 01 May 2012 (has links)
The recent, rapid decline in Arctic summer sea ice extent has prompted questions as to the rates and magnitude of previous sea ice decline and the affect of this physical change on icerelated ecosystems. However, satellite data of sea ice only extends back to 1978, and mapped observations of sea ice prior to the 1970s are sparse at best. Inventories of boreal ecosystems are likewise hampered by a paucity of investigations spanning more than the past few decades. Paleoclimate records of sea ice and related primary productivity are thus integral to understanding how sea ice responds to a changing climate. Here I examine modern sedimentation, decadal-scale climate change in the recent past, and centennial- to millennial-scale changes of the past 400 ka using both qualitative and quantitative diatom data in concert with sedimentology and organic geochemistry. Diatom taxonomy and corresponding ecological affinities are compiled in this study and updated for the Bering Sea region and then used as recorders of past climate changes. In recent decades, the Pacific Decadal Oscillation and the strength of the Aleutian Low are reflected by subtle changes in sediment diatom assemblages at the Bering Sea shelf-slope break. Farther back in time, the super-interglacial, marine isotope stage (MIS) 11 (428-390ka), began in Beringia with extreme productivity due to flooding of the Bering Land Bridge. A moisture-driven advance of Beringian glaciers occurred while eustatic sea level was high, and insolation and seasonality both decreased at the global peak of MIS 11. Atlantic/Pacific teleconnections during MIS 11 include a reversal in Bering Strait throughflow at 410 ka and a relationship between North Atlantic Deep Water Formation and Bering Sea productivity. Finally, concentrations of the biomarker-based sea ice proxy, IP25, are compared to sea ice concentration across the Bering and Chukchi seas. Changes in the concentration of IP25 in the sediments may be driven by the length of time that the epontic diatom bloom lasts. When combined with a sediment-based proxy for sea surface temperatures, IP25 can be used to reconstruct spring ice concentration.
237

Using Traditional Inuit Knowledge and Scientific Methods to Characterize Historical Climate Change Impacts to Sea Ice in Resolute Bay, Nunavut

Forsythe, Alexandra 27 November 2023 (has links)
One of the most visible impacts of climate change in Arctic environments is declining sea ice. Due to an absence of spatially coarse quantitative data, there is a lack of understanding on declining sea ice on a community scale. This study seeks to document historical trends in air temperature, sea ice thickness (SIT), break-up dates (BUDs) and freeze-up dates (FUDs), correlate sea ice behaviour to air temperatures, and document the socio-economic impacts of sea ice change in Resolute Bay Nunavut, using traditional Inuit knowledge (TIK) and scientific methods. During the scientific portion of this study linear regression, statistical significance, anomaly analysis, and change point detection were used on time series of sea ice concentration (SIC), SIT, and air temperature. Two SIC datasets were accessed to characterize BUDs and FUDs, Canadian Ice Services archived sea ice charts from 1982-2022 and Copernicus Climate Change Services (C3S) gridded satellite derived SIC from 1979-2015. The BUD was defined when SIC fell and stayed below 20%, and the FUD was when SIC returned and stayed above 50%. By applying a statistically significant linear regression to both datasets, the BUD was shown to occur 37.5 days earlier and the FUD occurred 23.4 days later in 2022 than in 1979. This study accessed two SIT datasets, Environment and Climate Change Canada fast ice measurements from 1947-2022 and C3S satellite derived sea ice freeboard measurements from 2002-2020 at four locations in the Barrow Strait. After applying change point detection algorithms, this study found annual maximum fast ice thicknesses increased 32.5 cm from 1948-1981 and decreased 33.2 cm from 1981-2021. Fast ice decreased most substantially in the months of April and May. Sea ice freeboard decreased by 260.8 cm on average from 2002-2020 in the Barrow Strait. Freezing degree days (FDDs) were used to correlate sea ice behaviour to air temperature. As FDDs decrease, sea ice freeboard was the most rapidly changing sea ice parameter and fast ice thickness was most strongly correlated to FDDs. Both these results indicate that air temperature has a greater effect on SIT than the BUD and FUD. During the TIK investigation of this study, seventeen community members from Resolute Bay, Nunavut, ranging from age 19-81 were interviewed about their perception of changes in SIT, BUD, FUD, and seasonal weather patterns. Participants were interviewed about the socio-economic impacts of sea ice change, traditional Inuit methods of determining thickness, and asked to indicate typical areas of thin and thick ice, areas that break-up and freeze-up first, and hunting and travel routes on printed maps. The interviewees described a decline in sea ice thickness, areas of thin ice in the Barrow Strait, north of Cornwallis Island, and between Bathurst and Devon Island, less frequent use of the sea ice, less traditional food available in the community, increased vessel traffic, a decrease in seal population, new species and birds in the area, and detailed traditional methods of determining ice thickness through observation of color and use of the harpoon. Agreement between traditional knowledge and the scientific data was present in typical break-up and freeze-up patterns, and annual maximum thickness decreasing over time. While most respondents indicated FUD was later and BUD earlier, more participants responded there have been changes to the FUD than the BUD, whereas the scientific data showed more severe changes to the BUD than FUD. During interviews, there was consensus that summer temperatures are getting warmer but there was variability in responses when asked about winter temperatures. The scientific results showed less warming in the summer (Jun-Aug) than winter months (Jan-Mar) with the most warming in the fall (Sept-Nov). The lack of agreement between these results could be attributed to local perceived changes to winter weather referring to storminess rather than strictly temperature. TIK provided small scale information about the sea ice that the current state of scientific observation can not. In conclusion, a more holistic understanding of sea ice behaviour can be achieved by including Inuit traditional knowledge in partnership with scientific methods.
238

Benthic foraminifera as paleo-sea-ice indicators in the western Arctic Ocean

Lazar, Kelly Best January 2014 (has links)
No description available.
239

A Synoptic Climatological Assessment of the Relationship between Arctic Sea Ice Variability and Climate Anomalies over North America

Ballinger, Thomas J. 09 April 2015 (has links)
No description available.
240

A Historic Record of Sea Ice Extents from Scatterometer Data

Otosaka, Inès January 2017 (has links)
Sea ice is a vital component of the cryosphere and does not only influence the polar regions but has a more global influence. Indeed, sea ice plays a major role in the regulation of the global climate system as the sea ice cover reflects the sun radiation back to the atmosphere keeping the polar regions cool. The shrinkage of the sea ice cover entails the warming up of the oceans and as a consequence, a further amplification of the melting of sea ice. Therefore, the polar regions are sensitive to climate change and monitoring the sea ice cover is very important. To assess sea ice change in the polar regions, satellite active microwave sensors, scatterometers, are used to observe the evolution of sea ice extent and sea ice types. Thus, this research aims at creating a historic record of daily global Arctic and Antarctic sea ice extents and analysing the change in sea ice types with scatterometer data. A Bayesian sea ice detection algorithm, developed for the Advanced scatterometer (ASCAT), is applied and tuned to the configurations of the scatterometers on board the European Remote Sensing satellites, ERS\textendash 1 and ERS\textendash 2. The sea ice geophysical model functions (GMFs) of ERS and ASCAT are studied together to validate the use of ASCAT sea ice GMF extrapolated to the lower incidence angles of ERS. The main adaptations from the initial algorithm aim at compensating for the lower observation densities afforded by ERS with a refined spatial filter and time\textendash variable detection thresholds. To further analyse the backscatter response from sea ice and derive information on the different sea ice types, a new model of sea ice backscattering at C\textendash band is proposed in this study. This model has been derived using ERS and ASCAT backscatter data and describes the variation of sea ice backscatter with incidence angle as a function of sea ice type. The improvement of the sea ice detection algorithm for ERS\textendash 1 and ERS\textendash 2, operating between 1992 and 2001, leads to the extension of the existing records of daily global sea ice extents from the Quick scatterometer (QuikSCAT) which operated from 1999 to 2009 and ASCAT operating from 2007 onwards. The sea ice extents from ERS, QuikSCAT and ASCAT show excellent agreement during the overlapping periods, attesting to the consistency and homogeneity of the long\textendash term scatterometer sea ice record. The new climate record is compared against passive microwave derived sea ice extents, revealing consistent differences between spring and summer which are attributed to the lower sensitivity of the passive microwave technique to melting sea ice. The climate record shows that the minimum Arctic summer sea ice extent has been declining, reaching the lowest record of sea ice extent in 2012. The new model for sea ice backscatter is used on ERS and ASCAT backscatter data and provides a more precise normalization of sea ice backscatter than was previously available. An application of this model in sea ice change analysis is performed by classifying sea ice types based on their normalized backscatter values. This analysis reveals that the extent of multi\textendash year Arctic sea ice has been declining remarkably over the period covered by scatterometer observations.

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