Arndt Stefanie

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Influence of ice thickness and surface properties on light transmission through Arctic sea ice

2015-09-04 , Katlein, Christian , Arndt, Stefanie , Nicolaus, Marcel , Perovich, Donald K. , Jakuba, Michael V. , Suman, Stefano , Elliott, Stephen M. , Whitcomb, Louis L. , McFarland, Christopher J. , Gerdes, Rudiger , Boetius, Antje , German, Christopher R.

The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea-ice-melt and under-ice primary production. Recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance using the new Nereid Under-Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely piloted and autonomous surveys underneath land-fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance during summer. Our results show that surface properties such as melt ponds dominate the spatial distribution of the under-ice light field on small scales (<1000 m2), while sea ice-thickness is the most important predictor for light transmission on larger scales. In addition, we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.

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Reviews and syntheses: a framework to observe, understand and project ecosystem response to environmental change in the East Antarctic Southern Ocean

2022-11-23 , Gutt, Julian , Arndt, Stefanie , Barnes, David Keith Alan , Bornemann, Horst , Brey, Thomas , Eisen, Olaf , Institute, Hauke , Griffiths, Huw , Institute, Christian , Hain, Stefan , Hattermann, Tore , Held, Christoph , Hoppema, Mario , Isla, Enrique , Janout, Markus , Le Bohec, Céline , Link, Heike , Mark, Felix Christopher , Moreau, Sebastien , Trimborn, Scarlett , Van Opzeeland, Ilse , Pörtner, Hans-Otto , Schaafsma, Fokje , Teschke, Katharina , Tippenhauer, Sana , Van De Putte, Anton , Wege, Mia , Zitterbart, Daniel , Piepenburg, Dieter

Systematic long-term studies on ecosystem dynamics are largely lacking from the East Antarctic Southern Ocean, although it is well recognized that they are indispensable to identify the ecological impacts and risks of environmental change. Here, we present a framework for establishing a long-term cross-disciplinary study on decadal timescales. We argue that the eastern Weddell Sea and the adjacent sea to the east, off Dronning Maud Land, is a particularly well suited area for such a study, since it is based on findings from previous expeditions to this region. Moreover, since climate and environmental change have so far been comparatively muted in this area, as in the eastern Antarctic in general, a systematic long-term study of its environmental and ecological state can provide a baseline of the current situation, which will be important for an assessment of future changes from their very onset, with consistent and comparable time series data underpinning and testing models and their projections. By establishing an Integrated East Antarctic Marine Research (IEAMaR) observatory, long-term changes in ocean dynamics, geochemistry, biodiversity, and ecosystem functions and services will be systematically explored and mapped through regular autonomous and ship-based synoptic surveys. An associated long-term ecological research (LTER) programme, including experimental and modelling work, will allow for studying climate-driven ecosystem changes and interactions with impacts arising from other anthropogenic activities. This integrative approach will provide a level of long-term data availability and ecosystem understanding that are imperative to determine, understand, and project the consequences of climate change and support a sound science-informed management of future conservation efforts in the Southern Ocean.