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PreprintUpstream sources of the Denmark Strait Overflow : observations from a high-resolution mooring array( 2016-02-19) Harden, Benjamin E. ; Pickart, Robert S. ; Valdimarsson, Héðinn ; Våge, Kjetil ; de Steur, Laura ; Richards, Clark G. ; Bahr, Frank B. ; Torres, Daniel J. ; Børve, Eli ; Jonsson, Steingrimur ; Macrander, Andreas ; Østerhus, Svein ; Håvik, Lisbeth ; Hattermann, ToreWe present the first results from a densely instrumented mooring array upstream of the Denmark Strait sill, extending from the Iceland shelfbreak to the Greenland shelf. The array was deployed from September 2011 to July 2012, and captured the vast majority of overflow water denser than 27.8 kgm-3 approaching the sill. The mean transport of overflow water over the length of the deployment was 3.54 ± 0.16 Sv. Of this, 0.58 Sv originated from below sill depth, revealing that aspiration takes place in Denmark Strait. We confirm the presence of two main sources of overflow water: one approaching the sill in the East Greenland Current and the other via the North Icelandic Jet. Using an objective technique based on the hydrographic properties of the water, the transports of these two sources are found to be 2.54 ± 0.17 Sv and 1.00 ± 0.17 Sv, respectively. We further partition the East Greenland Current source into that carried by the shelfbreak jet (1.50 ± 0.16 Sv) versus that transported by a separated branch of the current on the Iceland slope (1.04 ± 0.15 Sv). Over the course of the year the total overflow transport is more consistent than the transport in either branch; compensation takes place among the pathways that maintains a stable total overflow transport. This is especially true for the two East Greenland Current branches whose transports vary out of phase with each other on weekly and longer time scales. We argue that wind forcing plays a role in this partitioning.
ArticleFRIS revisited in 2018: on the circulation and water masses at the Filchner and Ronne Ice Shelves in the Southern Weddell Sea(American Geophysical Union, 2021-05-18) Janout, Markus A. ; Hellmer, Hartmut H. ; Hattermann, Tore ; Huhn, Oliver ; Sultenfuß, Jurgen ; Østerhus, Svein ; Stulic, Lukrecia ; Ryan, Svenja ; Schröder, Michael ; Kanzow, TorstenThe Filchner-Ronne Ice Shelf (FRIS) is characterized by moderate basal melt rates due to the near-freezing waters that dominate the wide southern Weddell Sea continental shelf. We revisited the region in austral summer 2018 with detailed hydrographic and noble gas surveys along FRIS. The FRIS front was characterized by High Salinity Shelf Water (HSSW) in Ronne Depression, Ice Shelf Water (ISW) on its eastern flank, and an inflow of modified Warm Deep Water (mWDW) entering through Central Trough. Filchner Trough was dominated by Ronne HSSW-sourced ISW, likely forced by a recently intensified circulation beneath FRIS due to enhanced sea ice production in the Ronne polynya since 2015. Glacial meltwater fractions and tracer-based water mass dating indicate two separate ISW outflow cores, one hugging the Berkner slope after a two-year travel time, and the other located in the central Filchner Trough following a ∼six year-long transit through the FRIS cavity. Historical measurements indicate the presence of two distinct modes, in which water masses in Filchner Trough were dominated by either Ronne HSSW-derived ISW (Ronne-mode) or more locally derived Berkner-HSSW (Berkner-mode). While the dominance of these modes has alternated on interannual time scales, ocean densities in Filchner Trough have remained remarkably stable since the first surveys in 1980. Indeed, geostrophic velocities indicated outflowing ISW-cores along the trough's western flank and onto Berkner Bank, which suggests that Ronne-ISW preconditions Berkner-HSSW production. The negligible density difference between Berkner- and Ronne-mode waters indicates that each contributes cold dense shelf waters to protect FRIS against inflowing mWDW.
ArticleReviews and syntheses: a framework to observe, understand and project ecosystem response to environmental change in the East Antarctic Southern Ocean(European Geosciences Union, 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, DieterSystematic 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.