Description: The trace metal iron is considered to be the nutrient that limits marine primary production in one third of the global surface ocean (Martin, 1990; Boyd et al., 2007; Moore et al., 2013). It is also the nutrient that maintains future ocean fertility due to its irreplaceable role in the process of nitrogen fixation, which adds “new” nitrogen (another nutrient for phytoplankton) to the surface ocean (Raven, 1988; Kustka et al., 2003b; Zehr and Capone, 2020). Due to iron’s importance, it is not surprising that the demand for incorporating iron into global biogeochemical models is high. However, including iron in an earth system model has been shown to have no clear benefits with respect to model misfit against observational data (Nickelsen et al., 2015) . How smart is it then to introduce iron models into global biogeochemical models, when the benefits are not clearly identifiable? Especially, when the iron models perform poorly at reproducing observed iron patterns in the ocean (Tagliabue et al., 2016). The poor performance of iron models, coupled with their failure to improve biogeochemical tracer representation of the ocean, inspired this additional effort to identify the advantages of including iron in a global biogeochemical model, both for the preindustrial state and under conditions of a changing climate. The working hypothesis was that the relatively poor performance of iron models might come from inadequate model calibration. A first sensitivity study on biogeochemical model parameter values was conducted in order to identify key parameters for model calibration. It was found that while some of the parameters influence simulated nitrogen, phosphorus, and oxygen concentrations, few parameters influence simulated iron concentrations. This suggests that our modelling skill of the iron cycle is still limited and/or that the observational data base is insufficient for comprehensive model calibration so far. Thus it was decided not to include iron data in further model calibration. A model calibration framework (Kriest et al., 2017) was next applied to a hierarchy of global models with different implementations of iron; one without iron, one with prescribed iron concentrations, and another one with a dynamic iron cycle. Using calibration against global data sets of nitrogen, phosphorus, and oxygen, the misfit of each model was pushed to its minimum. It was found that under an assumed preindustrial steady state, the calibrated model with a full dynamic iron cycle has the lowest model misfit against observations (thus confirming the working hypothesis). It was also found that the calibrated model with a fully dynamic iron cycle has 50% less net primary production (which is closer to empirical estimations) compared to the calibrated model without iron. Finally, transient simulations for all calibrated models were integrated from their pre- industrial state until the end of the 21st century using an atmospheric CO2 concentration pathway consistent with a ’business-as-usual’ CO2 emission scenario. It was found that nitrogen fixation trends diverge among models. This divergence is caused by whether iron limits the productivity of the upwelling regions, e.g. in the eastern tropical Pacific. The export production in the eastern tropical Pacific (and other tropical upwelling regions) reacts differently to warming, depending on whether iron is a limiting nutrient. These different responses trigger a divergent chain of downstream responses that affect nitrogen fixation across the tropical oligotrophic regions in the model. Through the comparison between calibrated models, this thesis quantifies the advantages of including iron in a global biogeochemistry model and reveals how important iron is for future nitrogen fixation trends. It furthermore illustrates the interconnection between tropical upwelling and oligotrophic regions.

Description: To limit global warming to 1.5°C, vast amounts of CO2 will have to be removed from the atmos‐ phere via Carbon Dioxide Removal (CDR). Enhancing the CO2 sequestration of ecosystems will require not just one approach but a portfolio of CDR options, including so‐called nature‐based approaches alongside CDR options that are perceived as more technical. Creating a CDR “supply curve” would however imply that all carbon removals are considered to be perfect substitutes. The various co‐benefits of nature‐based CDR approaches militate against this. We discuss this aspect of nature‐based solutions in connection with the enhancement of blue carbon ecosys‐ tems (BCE) such as mangrove or seagrass habitats. Enhancing BCEs can indeed contribute to CO 2 sequestration, but the value of their carbon storage is low compared to the overall contri‐ bution of their ecosystem services to wealth. Furthermore, their property rights are often un‐ clear, i.e. not comprehensively defined or not enforced. Hence, payment schemes that only compensate BCE carbon sequestration could create tradeoffs at the expense of other im‐ portant, often local, ecosystem services and might not result in socially optimal outcomes. Ac‐ cordingly, one chance for preserving and restoring BCEs lies in the consideration of all services in potential compensation schemes for local communities. Also, local contexts, management structures, and benefit‐sharing rules are crucial factors to be considered when setting up inter‐ national payment schemes to support the use of BCEs and other nature‐ or ecosystem‐based CDR. However, regarding these options as the only hope of achieving more CDR will very prob‐ ably not bring about the desired outcome, either for climate mitigation or for ecosystem preser‐ vation. Unhalted degradation, in turn, will make matters worse due to the large amounts of stored carbon that would be released. Hence, countries committed to climate mitigation in line with the Paris targets should not hide behind vague pledges to enhance natural sinks for re‐ moving atmospheric CO2 but commit to scaling up engineered CDR.

Description: SIPRI’s Environment of Peace initiative focuses on managing the risks that are created by two interwoven crises: the darkening security horizon and the immense pressures being placed on the natural world and the systems that support life on earth. The Environment of Peace research report is an in-depth look at the evidence base and analysis of the policy report Environment of Peace: Security in a New Era of Risk, including many real-world case studies. The report is the result of two years’ work by more than 30 researchers, led and guided by some of the leading voices in the fields of environment and security. Accessibly designed, the new research report is available to download in four parts: Elements of a Planetary Emergency (part 1); Security Risks of Environmental Crises (part 2); Navigating a Just and Peaceful Transition (part 3); and Enabling an Environment of Peace (part 4). This part—Security Risks of Environmental Crises (part 2)—shows how combinations of environmental and security phenomena are generating complex risks. Through a theoretical framework informed by the literature, Cedric de Coning, Research Professor at the Norwegian Institute of International Affairs (NUPI), and his team explore different pathways from environmental stress to conflict and how the darkening security horizon and environmental crises are interacting to generate different types of risk: compound, cascading, emergent, systemic and existential. The analysis is supported by numerous case studies, spanning a variety of social-ecological systems and different types of risks. Part 2 also discusses options for responding to these complex risks.

Description: The publication provides a summary on the state of the climate indicators in 2021 including global temperatures trends and its distribution around the globe; most recent finding on Green House Gases concentration, Ocean indicators; Cryosphere with a particular emphasis on Arctic and Antarctic sea ice, greenland ice sheet and glaciers and snow cover; Stratospheric Ozone; analysis of major drivers of inter-annual climate variability during the year including the El Niño Souther Oscillation and other Ocean and Atmshperic indices; global precipitation distribution over land; extreme events including those related to tropical cyclones and wind storms; flooding, drought and extreme heat and cold events. The publication also provides most recent finding on climate related risks and impacts including on food security, humanitarian and population displacement aspects and impact on ecosystems.

Description: The sentence “every second breath you take comes from the Ocean” is commonly used in Ocean Literacy and science communication to highlight the importance of Ocean oxygen. However, despite its widespread use, it is often not phrased correctly. In contrast, awareness about the threat of the global oxygen loss in the Ocean, called deoxygenation, is low, particularly in comparison with other important stressors, such as Ocean acidification or increasing seawater temperatures. Deoxygenation is increasing in the coastal and open Ocean, primarily due to human-induced global warming and nutrient run-off from land, and projections show that the Ocean will continue losing oxygen as global warming continues. The consequences of oxygen loss in the Ocean are extensive and include decreased biodiversity, shifts in species distributions, displacement or reduction in fisheries resources, changes in biogeochemical cycling and mass mortalities. Low oxygen conditions also drive other chemical processes which produce greenhouse gases, toxic compounds and further degrade water quality. Degraded water quality directly affects marine ecosystems, but also indirectly impacts ecosystem services supporting local communities, regional economies and tourism. Although there are still gaps in our knowledge, we know enough to be very concerned about the consequences: the impacts might even be larger than from Ocean acidification or heat waves, and three out of the five global mass extinctions were linked to Ocean deoxygenation. The sense of urgency to improve Ocean health is reflected in the UN Decade of Ocean Science for Sustainable Development and the EU Mission: Restore our Ocean and Waters, and tackling the loss of oxygen in the Ocean is critical to achieving the aims of these two initiatives.

Description: In an era of biodiversity loss caused by anthropogenic impacts, it appears essential to improve our understanding of how ecological filters interact with regional species pools, in order to obtain valuable information on the process of community assembly as well as for biodiversity conservation. Especially in the Baltic Sea, which is characterized by strong environmental gradients and far reaching human-mediated pressures, baseline information provided by monitoring approaches are needed to disentangle community shifts from natural background variability. In the frame of this doctoral thesis, the role of ecological filters on the richness and community structure of hard-bottom assemblages in the southwestern Baltic Sea was investigated and the variability of important environmental drivers described. In the southwestern Baltic Sea, hard-bottom communities are mainly found on boulders and stones left by the last glaciation. The characteristics of these substrates are thought as an important driver of the benthic assemblages living in these boulder fields. Thus, the relationship between geological and biological diversity was examined at the local and regional scale. In a multidisciplinary approach, geological seafloor mappings were combined with biological samplings of hard-bottom communities. At the local scale, the size of boulders was found to positively correlate with taxonomic and functional richness, and negatively correlate with the β diversity of the communities. At the regional scale, differences in taxonomic community composition and β diversity were suggested to be the result of site-specific factors like boulder densities and sediment distribution. Whether of natural or anthropogenic origin, the shallow waters of the Baltic Sea are subject to strong environmental fluctuations, sometimes within short timeframes. Temporally highly resolved in-situ measurements of important water parameters can therefore help to understand the environmental dynamics biological communities are facing in coastal waters. Thus, a monitoring network along the southwestern Baltic coast was established, to measure temperature, salinity and oxygen concentration at 10 min interval as well as nutrient concentrations twice a month. The obtained recordings revealed strong temporal and spatial variabilities, highlighting the need to consider such fluctuations in experimental scenarios, as predictors of biodiversity patterns or within environmental assessments. Long-term records of community composition are crucial to distinguish directional regime shifts from random fluctuations. The monitoring of hard-bottom communities established on standardized settlement panels over a period of 11 years showed regional differences in community development. Multivariate analyses revealed the decline of the foundational species Mytilus sp. to be responsible for the observed community changes over time. In a modeling approach, the decline was explained by changes in sea surface temperature, current speed and chlorophyll a content. Moreover, since the mussels recovered only in stations of Lübeck Bight, regional factors like limitations in dispersal and population connectivity were suggested as significant driving forces. To summarize, this doctoral project demonstrated the effects and variabilities of ecological filters in hard-bottom communities of the southwestern Baltic Sea. In all studies, monitoring approaches were of central importance to detect the presented patterns, underlining the strategic need of these efforts in order to improve our understanding of community assembly and persistence, in times when biodiversity management is more vital than ever.