Seasonal and interannual variability of landfast sea ice in Atka Bay, Weddell Sea, Antarctica

Abstract

Abstract. Landfast sea ice (fast ice), attached to Antarctic coastal and near-coastal elements, is a critical element of the local physical and ecological systems. Through its direct coupling with the atmosphere and ocean, fast ice and its snow cover are also potential indicators of processes related to climate change. However, in-situ fast-ice observations in Antarctica are extremely sparse because of logistical challenges. Since 2010, a monitoring program, which is part of the Antarctic Fast Ice Network (AFIN), has been conducted on the seasonal evolution of fast ice of Atka Bay. The bay is located on the north-eastern edge of Ekström Ice Shelf in the eastern Weddell Sea, close to the German wintering station Neumayer Station III. A number of sampling sites have been regularly revisited between annual ice formation and breakup each year to obtain a continuous record of snow depth, freeboard, sea-ice- and sub-ice platelet layer thickness across the bay. Here, we present the time series of these measurements over the last nine years. Combining them with observations from the nearby meteorological observatory at Neumayer Station as well as satellite images allows to relate the seasonal and interannual fast-ice cycle to the factors that influence its evolution. On average, the annual consolidated fast-ice thickness at the end of the growth season is about two meters, with a loose platelet layer accumulation of four meters beneath and 0.70 meters snow on top. Results highlight the predominately seasonal character of the fast-ice regime in Atka Bay without a significant trend in any of the observed variables over the nine-year observation period. Also, no changes are evident when comparing with measurements in the 1980s. However, strong easterly winds in the area govern the year-round snow redistribution and also trigger the breakup event in the bay during summer months. Due to the substantial snow accumulation on the ice, a characteristic feature is frequent negative freeboard, associated flooding of the snow/ice interface and subsequent formation of snow ice. The buoyant platelet-ice layer beneath negates the snow weight to some extent, but snow thermodynamics is identified as the main driver of the energy and mass budgets for the fast-ice cover in Atka Bay. An enhanced knowledge on the seasonal and interannual variability of the fast-ice properties will improve our understanding of interactions between atmosphere, fast ice, ocean and ice shelves in one of the key regions of Antarctica.

Detailed Seismic Bathymetry Beneath Ekström Ice Shelf, Antarctica: Implications for Glacial History and Ice‐Ocean Interaction

“…Locally, our observed seafloor bathymetry suggests a separation of different circulation regimes beneath the ice shelf. While the central part of the cavity seems to be dominated by the trough system; the eastern portion of the ice shelf, adjacent to Atka Bay, comprises a relatively shallow water column (Figures 3a and 3c, C–C') that is likely subject to intense tidal mixing and may be responsible for the vigorous accretion of marine ice in the area (Arndt et al, 2020). The two successive temperature profiles from the EIS‐4 site confirm the existence of a tidally mixed zone in this region.…”

Dynamics of Large Pelagic Ice Crystals in an Antarctic Ice Shelf Water Plume Flowing Beneath Land-Fast Sea Ice

“…This supercool water drives sea ice growth by absorbing heat into the stratified upper ocean and facilitates the generation and growth of ice crystals (Robinson et al, 2014;McPhee et al, 2016;Hoppmann et al, 2020).…”

“…A decade-long sequence of sea ice camps in the McMurdo Sound region (Robinson et al, 2020) have revealed that these platelets form a coherent layer on the underside of sea ice (a sub-ice platelet layer, SIPL Hunkeler et al, 2015;Wongpan et al, 2015;Hoppmann et al, 2020) into which they are eventually incorporated (Smith et al, 2001;Langhorne et al, 2015). The McMurdo Ice Shelf, a small ice shelf that sits between the Ross Ice Shelf (the largest ice shelf on the planet by area) and McMurdo Sound.…”

“…This, in itself, is evidence of supercool oceanic conditions. Hoppmann et al (2020) review our present understanding of Antarctic platelet ice and makes it 75 clear the topic is still in a discovery phasepartly due to the challenges of making comprehensive observations. At the same time, modelling approaches have needed to advancecreating a tension.…”

“…It remains highly likely at grounding line zones where a confluence of ice shelf water outflow, glacially-driven sediment supply, tidal and subglacial resuspension and supercooling-induced re-freezing all likely 400 combine. Furthermore, substantial platelet ice layers exist in many ice shelf influenced locations where there is no obvious sediment source (Langhorne et al, 2015;Hoppmann et al, 2020). The intriguing speculation that follows from this iswhat role might sediment play in crystal nucleation near ice shelf grounding-lines and would we be able to tell if this influences marine ice formation (e.g.…”