Browsing by Subject "sea ice"
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(2023)Climate change and temperature rise in the Arctic is resulting in a decrease in sea ice extent and changes in sea ice variability. The impact of climate change on sea ice variability can be better understood when studying past events of climate change and sea ice extent change. Past environmental change can be reconstructed using bioindicators such as chrysophyte cysts, siliceous resting stages of chrysophyte algae. Archaeomonas spp., a genus of chrysophyte cyst, is often found preserved in Marginal Ice Zone sediments in the Arctic and its relationship with sea ice extent is explored here, to further understand its potential as a sea ice proxy. Diatom slides from three cores in the North Atlantic (Melville Bay, the North Water Polynya and Placentia Bay) were used to evaluate relationships between Archaeomonas spp. and known sea ice diatom species like Fragilariopsis reginae-jahniae. The Melville Bay core spans the last 8000 years, the North Water Polynya core spans the last 4000 years, and the Placentia Bay core spans the last 5800 years, providing a broad account of Archaeomonas spp. and diatom species abundances over the Holocene. It was concluded that Archaeomonas spp. was not directly correlated with known sea ice diatom species like F. reginae-jahniae at any of the three study sites. Archaeomonas spp. did display some similar relationships with cold water species like Thalassiosira hyalina, Thalassiothrix longissima, Thalassiosira nordenskioeldii and Fragilariopsis oceanica, and pack ice species like Actinocyclus curvatulus and Melosira arctica. Archaeomonas spp. can form in a range of conditions but prefers colder conditions where sea ice may form or drift to, as opposed to warmer, open water conditions. However, it is not directly linked to sea ice. Further research should focus on understanding whether Archaeomonas spp. forms in sea ice or not. There were some suggestions made to identifying Archaeomonas spp. at species level, but further research should be conducted on Archaeomonas spp.’s morphology to advance identification.
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(2023)The coastal Baltic Sea hosts a very special ecosystem due to its brackish water and high seasonality. However, there is little research on the seasonality of the ecosystem and organic matter (OM) cycling, as many studies are conducted during summer or in areas without ice cover. This study is based on material collected continously over one year (Oct 2012-Oct 2013) by a sequencing sediment trap at 7-56 day intervals. It will provide knowledge of the seasonal variability in the vertical flux of organic material (TOC) and its sources (C:N, δ13C, δ15N) as well as dinoflagellate resting stages (dinocysts). Dinoflagellates are important primary producers in the Baltic Sea, some of which produce well-preserving resting stages (cysts). The seasonal changes in the fluxes and source of OM and dinoflagellate species' seasonal succession are not only ecologically interesting, but as both are used as sediment paleo proxies, provide more information for reliable reconstruction models for the Baltic Sea in the past. The seasonal sedimentation of the coastal Baltic Sea was strongly impacted by seasonality, with strong primary production causing high OM sedimentation rate during spring bloom and lack of primary production causing very small sediment flux in winter. During the fall resuspension played a big role in sedimentation. Only three species of dinocysts were present in the trap samples and most of the dinocyst flux of the whole year was formed by Biecheleria baltica. Most important drivers of B. baltica abundance and encystment were likely temperature signals for encystment at 6 °C and a small bloom under ice that got B. baltica a head start for competition in the spring bloom. Changes in terrestrial material input were not clearly visible in the sedimenting material, but primary production had an enriching influence on the OM stable isotopic composition and elevated the C:N ratio due to reaching limiting conditions of N. During winter long sea-ice cover and cold-water temperature created anomaly depleted isotopic composition similar to those in Arctic ecosystems. Even with long time-series of phytoplankton spring blooms, more knowledge is needed of links to environmental characteristics to better understand how climate change and eutrophication will impact the spring bloom in the Baltic Sea. Especially more information of under ice conditions are needed for a better understanding of the past, present and future of the Baltic Sea.
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