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    Arctic Deltas: Carbon and nitrogen rich deposits in a dynamic permafrost landscape

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    Arctic river deltas are sensitive polar landscapes at the land-ocean interface. In contrast to lower latitude deltas, Arctic deltas are characterized by low temperatures, a strong seasonality and the presence of permafrost. Seasonal freezing conditions and underlying permafrost hinders runoff for most of the year and leads to typical land forms such as ice wedge polygons, frost mounds and thermokarst lakes. However, compared to other permafrost dominated landscapes, Arctic deltas are more dynamic. The surface morphology is changing constantly due to river ice break up and subsequent spring flooding, coastal and shoreline erosion, thaw slumping, and degradation of ice rich deposits. Deltaic sediments also tend to be highly susceptible to ground-ice aggradation, making them more ice-rich than adjacent nondeltaic landscapes. In addition, Arctic deltas will be severely affected by global climate change through sea level rise, lengthened thaw season, changing river discharge, storm surge flooding and thawing permafrost. We are therefore at risk, to face reactivation of millennia-old soil carbon and nitrogen deposits by the degradation of previously permanently frozen river delta deposits. However, there is a lack of studies on Arctic deltas and only very coarse estimates on Arctic delta carbon and nitrogen stocks exist. Here we present a new data-set of 140 soil cores, including more than 1400 samples from 17 different deltas spread across the Arctic. We combine new and legacy soil core data to estimate for the first time pan-Arctic deltaic carbon and nitrogen stocks and close a knowledge gap for deep permafrost stock estimations. We found that Arctic deltas present a significant pool for organic carbon and nitrogen, thus their change poses risks far beyond the Arctic. Permafrost thaw in such dynamic landscapes will increase nutrient transport from land to ocean with implications on Arctic near-shore zones (e.g. affecting foodwebs and biogeochemical processes) as well as increased greenhouse gas release due to large amounts of carbon and nitrogen becoming available from previously frozen ground. Our study highlights the need to better understand dynamic processes in Arctic deltas, since these vulnerable carbon and nitrogen rich deposits will be severely affected by the effects of global climate change

    The AWI Climate Model: response to increased resolution in dynamically active regions

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    State-of-the-art climate models do still exhibit pronounced deviations from the measured climate. Those deviations are often common between those models. The challenging problems in the Northern hemisphere include warming and salinization of the deep ocean being most pronounced in the northern North Atlantic, reduced deep water formation in the Labrador Sea which is sometimes accomplished by the sporadic ice coverage of the whole Labrador Sea, and an extensive ice presence in the Barents Sea. All these biases are often attributed in literature to the lack of oceanic resolution. The multi-resolution approach used in the ocean component of the AWI climate model (ECHAM6-FESOM) allows to use enhanced horizontal resolution in dynamical active regions while keeping a coarse-resolution setup everywhere else. In this study we develop strategies for improving the climate model biases by means of increasing resolution in the ocean. The current computations have been performed on multi-centennial time scales using refinement in the different parts of the global ocean. Benefits from the local refinement have been analyzed. It is found that already with moderate refinement of the unstructured ocean grid, AWI-CM performs as well as some of the most sophisticated climate models participating in CMIP5

    The Arctic Jellies (ARJEL) project: Investigating the impact of gelatinous zooplankton communities on changing Arctic ecosystems

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    Gelatinous zooplankton are known to be major drivers of ecosystem changes. Increases in jelly biomass, referred to as “jellification”, have been observed in several marine ecosystems, causing, amongst others, the collapse of major fisheries. For the Arctic region, abundance data on jellies are virtually non-existent, impeding our ability to detect changes of a similar magnitude. To better understand the role of jellies in the Arctic seas, the Helmholtz Young Investigator project ARJEL (2019-2025), will combine the most recent technologies in optics, acoustics, and environmental DNA analyses. Integrative field surveys will allow us to link distributional patterns of jellies to sea-ice and oceanographic features. Furthermore, we will apply species distribution models to a broader set of archived data to understand observed species patterns and to predict changes under future scenarios. The role of jellies in the Arctic food web, their importance for higher trophic levels and their link to the sea-ice trophic pathway will be elucidated with metabarcoding and biomarker studies. Physiological and transcriptomic studies serve to predict range expansions, and consequences of expansion will be predicted based on food web models. An overview of the goals and methods planned will be given with scope for collaborations

    On the representation of Southern Ocean mass variability in GRACE-derived ocean bottom pressure anomalies

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    The Gravity Recovery and Climate Experiment provides monthly estimates of the Earths gravity field. Temporal changes in the gravitational field are associated with mass movement. Over the ocean these fluctuations are primarily due to changes in atmosphere and ocean circulation associated with ocean bottom pressure (OBP). In this study the ability of GRACE to observe circulation variability in the Southern Ocean is investigated
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