Description: Die sechste Ausgabe des „World Ocean Review“ (WOR) widmet sich der Arktis und Antarktis, diesen zwei extremen und ausgesprochen gegensätzlichen Regionen der Erde. Mit profunden Informationen zur Entstehungs- und Entdeckungsgeschichte bietet der WOR 6 ein tiefes Verständnis der Bedeutung der Pole für das Leben auf unserer Erde. Er zeigt zudem die zu beobachtenden Veränderungen in der Tier-und Pflanzenwelt und analysiert die zum Teil schon dramatischen Folgen, die der Klimawandel in diesen äußerst gefährdeten Regionen bewirkt.

Description: This sixth World Ocean Review (WOR) focuses on the Arctic and the Antarctic – two regions which are, in a very real sense, polar opposites, with some of the world’s most extreme conditions. Besides presenting a wealth of facts and figures about the history and exploration of the polar regions, WOR 6 builds a deeper awareness of their key role for life on our planet. It highlights the changes that can be observed in their flora and fauna and analyses the already dramatic impacts of global warming on these extremely fragile regions.

Description: Mass loss around the Antarctic Ice Sheet is driven by basal melting and iceberg calving,which constitute the two dominant paths of freshwater flux into the Southern Ocean. Although of similarmagnitude, icebergs play an important and still not fully understood role in the balance of heat andfreshwater around Antarctica. This lack of understanding is partly due to operational difficulties inlarge-scale monitoring in polar regions, despite observational and remote sensing efforts. In this study, anovel machine learning approach, augmented by visual inspection, was applied to three SyntheticAperture Radar (SAR) mosaics of the whole Antarctic continent and its adjacent coastal zone. Althoughoriginally intended for a mapping of the Antarctic continent, the SAR mosaics allow us to document theevolution and distribution of the size (and mass) of icebergs in the pan-Antarctic near-coastal zone for theyears 1997, 2000, and 2008. Our novel algorithm identified 7,649 icebergs in 1997, 13,712 icebergs in 2000,and 7,246 icebergs in 2008 with surface areas between 0.1 and 4,567.82 km2and total masses of 4,641.53,6,862.81, and 5,263.69 Gt, respectively. Large regional variability was observed, although a zonal patterndistribution is present. This has implications for future climate modeling studies that try to estimate thefreshwater flux from melting icebergs, which demands a realistic representation of the interannuallyvarying near-coastal iceberg pattern to initialize the simulations.

Description: Antarctic ice sheet mass loss and thus part of global sea-level rise is related to enhanced ice stream discharge to the fringing ice shelves. The transfer of ice into the ocean occurs via iceberg calving and ice shelf basal melting. For decades the balance of both terms was assumed to be in favor of the calving, but recent results, based on remote sensing, revealed that basal melting seems to be at least of similar importance. A recent model study indicates that future atmospheric conditions in the southern Weddell Sea may switch the continental shelf, formerly dominated by the formation of cold saline waters, to one influenced by warm open ocean waters with consequences for the basal mass flux and ice shelf/ice sheet dynamics. Here, we continue the simulations showing a warming of the Filchner-Ronne Ice Shelf cavity, applying 20th-century atmospheric and basal mass flux forcing at different future points in time. Our numerical study indicates that once the system reaches the 'warm phase', a positive meltwater feedback stabilizes the shelf circulation such that only a reduction to 20th century basal mass flux can stop warm water from penetrating onto the continental shelf and into the sub-ice cavity. This has implications for the future of the Antarctic Ice Sheet, since a major decrease of basal melting only can be achieved by a significant disintegration of the floating portion of the ice sheet.

Description: A general ocean circulation model is coupled with a 3D-thermodynamical ice-sheet/shelf model to simulate the response of the Filchner–Ronne Ice Shelf (FRIS, Antarctica) and coastal parts of its catchment basin to a postulated inflow of Warm Deep Water into the ice-shelf cavity on a 1000-yr timescale. Prescribed ocean warming (based on climate projections) enters the ice-shelf cavity in the up to 1500 m deep Filchner Trough and penetrates deep into the sub-ice cavity. Increasing basal melt rates induce geometry changes of the cavity, which in turn have an impact on the ocean circulation and therefore the modelled melt rates. Highest melt rates of about 20 m yr−1 follow the (up to 180 km) retreating grounding line. Basal mass loss reaches about 250 km3 yr−1, doubling the present-day value. The most vulnerable areas below the FRIS are the Bailey Ice Stream and the area between the Institute and Moeller Ice Streams, where the increased melting accounts for about 80 km of the modelled grounding line retreat on the backward sloping bedrock. The potential additional contribution to the eustatic sea level rise due to the grounded-ice loss, simulated in an ensemble approach against a transient control experiment, is about 0.05 mm yr−1 during the first 500 yr and about 0.17 mm yr−1 thereafter.

Description: Der Westantarktische Eisschild hat aufgrund seiner unter dem Meeresspiegel gegründeten Basis einen besonderen Einfluss auf den globalen Meereisspiegelanstieg. Änderungen in der Ozeantemperatur oder im Zustrom warmer Wassermassen auf den Kontinentalschelf und in die Schelfeiskavernen hinein führen zu einem vermehrten Ausdünnen der Schelfeisgebiete, die eine rückstauende Wirkung auf den Abfluss von Eismassen aus dem Inland ausüben. Für viele Regionen der Westantarktis kommt hinzu, dass sich der Meeresboden landeinwärts neigt. Dies stellt eine instabile Position für die Gründungszone der Schelfeise dar und einmal in Bewegung gebracht, führt es zu einem fortschreitenden Rückzug und einem vermehrten Eisabfluss. Simulationen mit eisdynamischen Modellen unter der Annahme einer zukünftigen Klimaerwärmung prognostizieren einen verstärkten Beitrag insbesondere der Westantarktis zum globalen Meeresspiegel. Für die nächsten hundert bis tausend Jahre kann dieser bis zu einem halben Meter betragen. Es ist sogar mit einem teilweisen Kollaps des Westantarktischen Eisschild zu rechnen, der den globalen Meeresspiegel um mehrere Meter ansteigen lassen würde. The West Antarctic Ice Sheet has a particular influence on global sea-level rise owing to its base being below sea level. Changes in ocean temperature or in the inflow of warm water masses onto the continental shelf and into the ice-shelf cavities lead to increased thinning of the ice shelves which exert a buttressing effect on the outflow of ice from the ice sheet. For widespread regions of West Antarctica, in addition the seabed slopes downward inland. This causes possible instabilities of the grounding-line position of the ice shelves and once set in motion, might cause an irreversible retreat of the grounding line and an increased ice loss. Simulations with thermomechanical ice-sheet models, based on future climate-change scenarios, predict an increasing contribution in particular of West Antarctica to global sea-level rise. For the next few hundred to a thousand years, this contribution can be up to half a meter. Even a partial collapse of the West Antarctic Ice Sheet is possible, which would raise the global sea level by several meters.

Description: The Filchner-Ronne Ice Shelf (FRIS), fringing the southern Weddell Sea, plays a key role in the formation of Weddell Sea Deep and Bottom Water, which are precursors of world ocean’s AABW. At present, a large continental shelf covered with cold and dense water protects FRIS from intense basal melting. Model studies, however, have suggested the potential for enhanced flow of Modified Warm Deep Water (MWDW) toward and under FRIS via the Filchner Trough, causing a substantial increase in basal melt rates by the end of this century. Mooring time series spanning 2014 to 2016 at 76 ◦ S revealed a distinct seasonal cycle in hydrography along the eastern flank of the Filchner Trough with warm inflow occurring only during summer, while winter is dominated by a weakly stratified water column at the surface freezing point. The seasonality is driven by seasonal evolution of the shelf break thermocline in combination with local buoyancy forcing. The mooring time series was extended to 2018 and while the general pattern of the described seasonal cycle is reaffirmed, an unprecedented strong warm inflow with temperatures being about 0.5 ◦ C above the previously observed inflow, was observed in 2017. Additionally, bottom temperatures above −1.5 ◦ C persisted throughout the whole winter together with a fresh anomaly in salinity. A warm signal was also measured by a LoTUS buoy deployed at 77 ◦ C during 2017. Weaker than average along-coast wind stress was present in the upstream region from summer through winter 2017 and likely lead to a stronger shoaling of the shelf break thermocline upstream of Brunt Shelf Ice causing the observed inflow. Likely, MWDW also entered the Brunt Ice Shelf cavity, which lead to enhanced basal melting that, in turn, could explain the observed fresh water anomaly. The inflow event affected the continental shelf hydrography in a favourable way for an earlier onset of warm inflow in the following summer.

Description: Germany intends to present the Working Group on Ecosystem Monitoring and Management (WG EMM) the background document that provides the scientific basis for the evaluation of a marine protected area (MPA) in the Weddell Sea planning area. The contents and structure of the whole document reflect its main objectives, i.e. to set out the general context of the establishment of MPAs and to provide the background information on the Weddell Sea MPA (WSMPA) planning area (Part A); to inform on the data retrieval process (Part B) and to describe the results of the scientific analyses and the MPA scenario development with the directly science-based aspects of the WSMPA proposal, i.e. the objectives and the boundaries and zones of the MPA (Part C). Here, the authors intend to update WG EMM on the current state of Part A of the document that has been presented at the meeting of the CCAMLR Scientific Committee in 2014. The Scientific Committee had welcomed and endorsed the scientific background document (SC-CAMLR-XXXIII/BG/02) as a foundation reference for the Weddell Sea MPA planning (SC-CAMLR-XXXIII, § 5.21). Part A contains (i) a synopsis in terms of the establishment of MPAs (chapter 1); (ii) a description of the boundaries of the WSMPA planning area (chapter 2); (iii) a comprehensive, yet succinct, general description of the Weddell Sea ecosystem (chapter 3); (iv) and finally a guidance regarding the future work beyond the development of the scientific basis for the evaluation of a WSMPA (chapter 4). Please note that the current state of Part A of the document presents a comprehensive yet incomplete version concerning chapters that have to be (further) developed or revised.