| 1. |
- Holmes, Felicity Alice, 1995-
(författare)
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Glacier-Ocean Interactions in the Arctic : Contemporary calving and frontal melt from field observations, remote sensing, and numerical modelling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Globally, glaciers are losing mass as a result of the changing climate, with this mass loss having a considerable societal impact through rising sea levels. Glaciers which terminate in the oceans are particularly vulnerable to changing external conditions as a result of high sensitivity at their marine margins. Both changing meteorological patterns as well as changing ocean heat content and transport have been previously identified as potential drivers for contemporary rapid glacier retreat and acceleration. However, uncertainties remain and provide motivation for studies which improve our process understanding. Here, we use a combination of field data, remotely sensed data, and targeted numerical modelling experiments to investigate marine terminating glacier response to external changes. This is done in order to address uncertainties around mass loss at the inaccessible glacier-ocean interface. In particular, focus is paid to the processes of submarine melt and calving, together referred to as frontal ablation. Submarine melt is the melting of glacier termini by warm ocean waters below the waterline, whilst calving is the breaking off of icebergs from glacier termini. The two processes are interlinked, with submarine melting undercutting the glacier terminus and contributing to calving, whilst calving events can expose larger areas of the glacier margin to submarine melt. To look for relationships between frontal ablation and external forcings, four glacier-fjord systems were studied to varying extents; two grounded glaciers in Svalbard (Kronebreen and Tunabreen) and two glaciers with floating ice tongues in Greenland (Ryder glacier and Petermann glacier). Both submarine melt and calving were examined at various different scales, both temporally and spatially. Specifically, analysis was carried out from the scale of individual calving events up to decadal long time series of glacier margin change. Much of the data used focused on specific glaciological variables such as satellite-derived velocities, margin positions, model simulations, and time-lapse photography of calving events. However, as glaciers and their adjacent fjord or ocean environments impact on each other, data such as water temperatures were also collected from glacier proximal fjord environments. The results from both the observational data and model experiments suggest that ocean temperatures are of great importance for the frontal ablation of glaciers in the Arctic, but that the relationship is complex. Heterogeneous glacier response to external forcings highlights how site specific factors such as bathymetry and fjord geometry can add an additional layer of complexity and make it challenging to scale up results from one glacier to an entire region. However, there are some strong indications that it is the presence of warm air temperatures in conjunction with warm ocean temperatures that is most important for driving frontal ablation - highlighting the need to situate glacier behaviour within a wider environmental context.
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| 2. |
- Larsson, Simon A., 1990-
(författare)
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Ashes to ashes : Applications of tephrochronology in Scandinavia
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The project presented in this thesis provides two examples of applications of tephrochronology in Scandinavia. The usage of tephra deposits preserved in sediments—i.e. horizons of volcanic ashes, detected either as visible layers or as low-concentration “cryptotephras”—is demonstrated to be a strong and versatile tool for chronological control of individual sediment sequences and for correlation between study sites on both local and wider-regional scales.Fieldwork was done at a number of study sites in southernmost Sweden and mid-Norway to sample sediments formed in lakes and peatlands during the Last Glacial–Interglacial Transition, i.e. c. 16,000–8,000 years ago. Labwork was then performed to analyse the sediments by methods to estimate organic matter, organic and carbonate carbon, and elemental contents as well as to find datable macrofossils and to detect tephra occurrences. Among the detected tephras between the different study sites, identifications were made of the Fosen Tephra, the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. These were used for the purposes of either application in the project; (1) a palaeoclimate reconstruction at Körslättamossen, with new proxy analyses and correlations to a previous study of the same site as well as to other studies in Europe via linkages established by the tephras, and (2) a palaeoglaciological reconstruction on the Fosen peninsula, based on correlations between study sites using the detected tephras to assess the timing of glacial retreat in the area.The palaeoclimate reconstruction at Körslättamossen and correlation to previous studies provides new information about the climatic development in Europe after the end of the last ice age, specifically regarding the timing of the cold stage known as the Younger Dryas. Detailed knowledge of such events, spatially and temporally, is necessary to understand the behaviour of the climate system in the past and, thereby, its behaviour in the present and the future. This is one of several studies demonstrating the usefulness of tephrochronology for such research questions.The palaeoglaciological reconstruction on the Fosen peninsula, also relating to the Younger Dryas, is one of a few recent studies which demonstrate the strengths of tephra investigations in providing evidence for the timing of events on more local scales than the wider spatial perspective more often utilised in tephrochronological applications. Other than resulting in a significantly revised chronology for the retreat of the Scandinavian Ice Sheet in the study area, this study should also encourage new, similar tephra studies in future Quaternary research.In addition to the direct results of either study (mainly presented in the related scientific papers) and the addition of new reference data for later tephra studies, the thesis also discusses further implications of the results and observations made with emphasis on considerations and study design issues in Quaternary research at large and for the tephrochronologist in particular.
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| 3. |
- Nyangoko, Baraka, 1989-
(författare)
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Managing Mangrove Ecosystem Services for Local Livelihoods and Adaptations in Tanzania
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recognizing the importance of ecosystem services (ES) for peoples' livelihoods and well-being is important for decision-making processes on conservation. Mangrove ecosystems in Tanzania are protected by law, but they continue to be exposed to degradation and loss, and there is still limited information about the awareness, preferences, status and trends of the ES they provide. This thesis aims to explore the link between mangrove ecosystem services (MES) and community livelihoods, changes in MES and associated drivers of change, adaptation options and their management in Tanzania, using the Rufiji Delta and Pangani Estuary as case studies. A mixed framework of methods including focus group discussions, key informant interviews, household surveys, direct observations, and literature reviews was used to gather data. Provisioning services were the most commonly identified MES, and they were more often reported to be deteriorating than regulating, cultural, and supporting services. Proximity to mangrove forest and residence time were positively associated with communities' awareness of all identified MES. Poles for building, firewood for cooking, coastal protection, and fisheries habitats were perceived as the most important MES for sustaining local livelihoods, though perceptions varied between sites. Reliance on mangrove resources was significantly predicted by household residence time, household main occupation, household size, and the cost of alternative resources to substitute mangrove wood as a source of domestic fuel. Illegal harvesting of mangrove poles, rice cultivation, climate change and inadequate governance and conservation measures were identified as the most critical drivers of mangrove degradation, but differed significantly from place to place. Fishing was perceived as the most impacted livelihood occupation compared to the other groups of occupations. Potential ways to adapt to environmental changes in the study areas included reliance on MES for ecosystem-based adaptation (EbA), switching of occupation, diversifying crops, offshore fishing, and migrating to other areas. This thesis argues that the linkage between MES and human well-being is site-specific, and drivers impacting on mangroves and their associated services vary spatially and is greatly accelerated by anthropogenic disturbances. Raising more awareness about the multifunctionality of mangroves and committing to participatory forest management that involves local people, as well as reforming the current forest policy by incorporating clear legal mechanisms for engaging communities around mangrove management and diversifying livelihood options are re-emphasized as appropriate ways to improve mangrove conservation. Furthermore, investment by providing adequate funding for conservation in long run rather than relying on short-term international donor-funded projects are recommended to government institutions as a basis for sustainable management of mangrove forests in Tanzania.
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