ALBERT

Description: The anthropogenic emissions of CO2 and other climate-active gases lead to a steep increase of global temperatures. Global climate change is particularly amplified in the Arctic (e.g., Serreze et al., 2009; Serreze and Barry, 2011). Increasing temperatures and the rapid sea ice decline have shown profound effects on life in the Arctic ecosystem (Wassmann et al., 2011). Climate model predictions suggest a seasonally sea ice-free Arctic well before the first half of this century (Overland and Wang, 2013; Docquier and Koenigk, 2021). The composition, structure and function of the Arctic microbiome will be altered with distinct effects on the marine system, on primary productivity, carbon fluxes and food web structures. Changes in the composition and structure of primary producers were already observed in Fram Strait (Nöthig et al., 2015), the boundary and highly dynamic zone between the Atlantic and the Arctic Ocean. These changes were reflected in the export flux of particulate organic matter (Lalande et al., 2013), also observable in the benthic communities (Jacob, 2014). Thus, understanding how the microbial communities changed over time under different environmental conditions is a scientific task needed to assess future changes in the Arctic ecosystem. This thesis aimed to understand the composition, distribution and function of bacteria, archaea and eukaryotic communities in Fram Strait across different spatial and temporal scales and their relationship with environmental variables. The overall objective was to identify signature groups and key factors of change, to provide a baseline to the effects of climate change and sea ice retreat. It provides a comprehensive overview of the Arctic microbiome by the incorporation of seawater, sinking particles and sea ice samples to identify key microbial indicators of change and environmental drivers in these communities. Samples were obtained in the frame work of the Long-Term Ecological Research (LTER) site HAUSGARTEN and the FRontiers in Marine Monitoring (FRAM) program. The results of Chapter I and Chapter II highlight the usage of methods free of compositional- bias and meta’omics approaches necessary to understand the role of microbial communities. The observations in Chapter I revealed that different water masses characterized by different physicochemical conditions harboured different active microbial communities. A late phytoplankton bloom dominated by diatoms in the surface waters of the eastern Fram Strait was identified, where members of the Bacteroidetes, Alteromonadales, Oceanospirillales and Rhodobacterales were significantly active. Abundant transcripts of transporters and fundamental cellular functions supported the degradation of organic matter. The deeper waters of Atlantic origin were marked by strong chemolithotrophic activities by members of Thaumarchaeota. In Chapter II I analysed bacterial and archaeal groups in deep-sea waters that benefitted from a phytoplankton bloom at the surface. Chapter III studied the development of microbial composition of sinking particles using a 12-year time-series study. The presence of sea ice and the passing warm anomaly were the drivers of change in these communities. In Chapter IV, microcosm experiments revealed bacterial taxa that responded to eukaryotes and substrates sourced from the sea ice during sea ice melt in seawater. Altogether, the results of this thesis provide baseline knowledge to better assess the effects of climate change on the Arctic microbiome and the consequences for ecosystem functioning and carbon cycling.

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.

Description: In the race against time, the European Union must move swiftly to navigate the green transition. This imperative isn't just about staying ahead in the global green technology competition; it is about securing the future of Europe's economy while combating climate change. Ahead of the EU elections looming, the urgency of this dual challenge cannot be overstated. With a new pro-EU Polish government in place, the Weimar Triangle - a trilateral forum that brings together Poland, France and Germany - could provide the ideal place to offer a new bold industrial policy leadership in Europe.

Description: The Mekong River drains a catchment of over 800,000 km2 and is the world's 12th longest river (4800 km), the 8th largest water discharge (470 × 106 m3/year), and the 10th largest sediment load (160 × 106 tons/year). The Mekong starts on the Qinghai–Tibet Plateau with a maximal elevation of 5220 m, flows through six countries (China with 16% of its basin, Myanmar with 5% of its basin, Laos with 35% of its basin, Thailand with 18% of its basin, Cambodia with 18% of its basin, and Vietnam with 11% its basin), and empties into the Vietnam East Sea (South China Sea). The Mekong River basin (MRB) has the world's most diverse river ecosystem. It is the world's largest inland fishery. Its biodiversity is fundamental to agricultural production and the food security of 90 million people in the Lower Mekong basin, including about 18 million people in the Vietnamese Mekong delta.

Description: Biodiversity generally increases productivity in ecosystems; however, this is mediated by the specific functional traits that come with biodiversity loss or gain and how these traits interact with environmental conditions. Most biodiversity studies evaluate the effects of species richness alone, despite our increasing understanding that intraspecific diversity can have equally strong impacts. Here, we manipulate both species richness and intraspecific richness (i.e., number of distinct strains) in marine diatom communities to explicitly test the relative importance of species and strain richness for biomass and trait diversity in six distinct temperature/nutrient environments. We show that species and strain richness both have significant effects on biomass and growth rates, but more importantly, they interact with each other, indicating that cross-species diversity effects depend on within-species diversity and vice versa. This intertwined relationship thus calls for more integrative approaches quantifying the relative importance of distinct biodiversity components and environmental context on ecosystem functioning.