ALBERT

Description: An 8,000-year lacustrine sediment record from Lake Motosu (Fuji Five Lakes) records several eruptions, including potentially unreported events, of the active Mt. Fuji volcano, which receives approximately 47 million annual visitors. A high-fidelity age model is constructed from tephra ages and high-density radiocarbon dating of terrestrial macrofossil and bulk organic matter. Variability in lake reservoir age is constrained by modern lake water radiocarbon measurement and reverse calibration of tephra calendar ages. We present more accurate ages for known eruptions, detect a wider distribution of ejecta for the most recent summit eruption, and potentially identify previously undetected flank eruptions. There are closely spaced scoria-fall layers that may be difficult to differentiate as separate events in land-based surveys. These results demonstrate the utility of lacustrine sediments as powerful tools for understanding characteristics of volcanic eruptions.

Description: With increasing pressure on the oceans from environmental change, there has been a global call for improved protection of marine ecosystems through the implementation of marine protected areas (MPAs). Here, we used species distribution modelling (SDM) of tracking data from 14 seabird species to identify key marine areas in the southwest Atlantic Ocean, valuing areas based on seabird species occurrence, seasonality and extinction risk. We also compared overlaps between the outputs generated by the SDM and layers representing important human threats (fishing intensity, ship density, plastic and oil pollution, ocean acidification), and calculated loss in conservation value using fishing and ship density as cost layers. The key marine areas were located on the southern Patagonian Shelf, overlapping extensively with areas of high fishing activity, and did not change seasonally, while seasonal areas were located off south and southeast Brazil and overlapped with areas of high plastic pollution and ocean acidification. Non-seasonal key areas were located off northeast Brazil on an area of high biodiversity, and with relatively low human impacts. We found support for the use of seasonal areas depending on the seabird assemblage used, because there was a loss in conservation value for the seasonal compared to the non-seasonal approach when using 'cost' layers. Our approach, accounting for seasonal changes in seabird assemblages and their risk of extinction, identified additional candidate areas for incorporation in the network of pelagic MPAs.

Description: The global climate change has an unprecedented impact on the Arctic Ocean, resulting in warming of the Arctic surface air at much faster rates than the global average. The warming temperatures lead to constantly declining Arctic sea ice cover, which reached in September 2018 the sixth lowest summertime minimum extent in the satellite record (since the late 1970s). Shrinking sea ice has a strong impact on the entire Arctic marine ecosystem, through alterations of the primary production, grazers communities, and subsequently the biological carbon pump. Current predictions of entirely sea-ice free summers in the Arctic Ocean already in the second half of this century urges the need to understand the ongoing oceanographic and biological processes in order to predict how the Arctic ecosystem will respond to further environmental changes. The differentiation between natural temporal ecosystem variability and anthropogenically-induced impact of the climate change requires long-term observations. The Ocean Observing System FRAM (FRontiers in Arctic marine Monitoring), which was established in 2014, is an Arctic long-term observatory for investigating the impact of changing ocean properties and sea ice conditions of the Arctic Ocean on its marine ecosystem. The starting point for the FRAM project was the already existing long-term observatory HAUSGARTEN, situated in the main gateway between the Arctic and the Atlantic Oceans - the Fram Strait. To date, despite their importance for the biogeochemical cycling, very little is known regarding the diversity and function of microbial communities in the Arctic Ocean in general, and specifically in the Fram Strait. In the framework of FRAM, a Molecular Observatory was established, for conducting standardized molecular-based high-resolution observations of the Arctic microbial communities. This thesis was conducted as part of the FRAM Molecular Observatory, and as part of the establishment process of the observatory it contributes to the methodological and procedural standardization required for long-term microbial observations. This thesis provides a first comprehensive overview of currently existing long-term microbial observatories around the world, it provides guidelines for initial steps towards establishing a community network between them, and stresses the urgent need in community efforts towards methods standardization. Furthermore, as part of the methods standardization for long-term microbial observations, this thesis includes a performance comparison between two, broadly used in microbial oceanography, 16S rRNA gene primer sets. The main focus of the thesis is on the ecology of pelagic bacterial and archaeal communities in the Fram Strait. Its overall objective was to investigate the distribution of these communities in the Fram Strait, and to identify environmental drivers of their diversity. The observations of this thesis reveal that sea ice has a strong impact on the development of the seasonal phytoplankton bloom during the summer. As a result, sea ice conditions are affecting the bacterial diversity in surface water, and are leading to a distinct community in sea-ice free and sea-ice covered regions of the Fram Strait. However, the impact of the sea ice is not limited to the surface ocean, as it also heavily affects the vertical export of aggregated organic matter to the deep ocean. The results of this thesis also show that aggregates formed under the sea ice sink faster, and by that provide a stronger vector for transport of bacterial and archaeal taxa to the deep ocean, compared to ice-free waters. Altogether, this thesis contributes to the baseline knowledge needed for further long-term observations of pelagic microbial communities in the Arctic marine ecosystem. Furthermore, it provides an important insight into the strong impact of the sea ice on bacterial and archaeal communities throughout the entire water column, underlining the potential impact of further environmental changes on the Arctic Ocean in the light of prevalent global warming and climate change.