Sea ice refers to ice that forms from the freezing of saline ocean water in polar regions. The majority of this sea ice is pack ice – freely drifting ice that moves with oceanic and atmospheric circulation. However, along the (ice shelf) coasts of the Antarctic continent and around icebergs, there are also areas where sea ice is attached to the land – this is known as fast ice. Fast ice, which is relatively flat, typically breaks up annually and reforms in the same cycle.
Fast ice provides a stable habitat for microorganisms and ice algae, as well as a secure breeding ground for larger animals such as emperor penguins and seals. As such, it plays a particularly important role in the local ecosystem.
Platelet ice is a layer of delicate ice crystals that can reach several meters in thickness beneath the sea ice. The cycle of platelet ice begins when relatively warm, salt-rich water flows beneath the ice shelf, slowly melting its underside. As a result, the fresh meltwater mixes with the saline seawater at the base of the ice shelf. Due to the high water pressure at these depths, this water mixture remains liquid but has a lower density than the surrounding seawater, causing it to slowly rise along the underside of the ice shelf. As the water pressure decreases and a critical depth is reached, tiny ice crystals form in situ. These crystals gradually grow into thin platelets, ranging from coin-sized to hand-sized, which then accumulate directly beneath the sea ice as platelet ice.
The Antarctic Fast Ice Network (AFIN) was initiated during the International Polar Year (IPY) to develop an international network of fast ice measurements along the Antarctic coastline. To date, numerous international collaboration partners have joined this project and established routine measurement programs at or near their Antarctic research stations. Standard parameters recorded within AFIN include snow and ice thickness, freeboard, as well as the timing of fast ice formation and its (interim and final) breakup.
Since 2010, the sea ice section at AWI has been actively contributing to AFIN with sea ice measurements in the Atka Bay near our German overwintering base Neumayer III. Routine measurements are conducted by the overwintering team from spring until the bay's breakup in summer. These measurements include snow, fast ice, and platelet ice thickness along a standardized transect across the entire Atka Bay. AWI stands out in the international network due to the continuity of its measurements and the long-term time series it provides.
Monthly manual drillings to determine the thickness of snow, fast ice, and platelet ice at six fixed measurement points distributed across Atka Bay (ATKA03-24).
Electromagnetic (EM) induction sounding surveys are conducted by towing an EM sensor behind a snowmobile along (fixed) transect lines across Atka Bay. This non-invasive method provides data on the total thickness (sea ice thickness plus snow depth) and the sub-ice platelet layer thickness.
Deployment of autonomous ice-tethered platforms to derive continuous time series of sea ice and snow thickness throughout the seasonal cycle.
At the end of the ice growth season, ice cores are collected across the bay during summer to analyze and understand the ice growth processes.
To describe the water mass properties in the vertical water column, a Conductivity-Temperature-Depth (CTD) sensor suit is lowered from the ice bottom down to the ocean floor.
Prof. Dr. Stefanie Arndt
(coordination of AFIN program at Neumayer Station)
Prof. Dr. Christian Haas
(aircraft campaigns)
Mara Neudert
(sea ice and platelet layer thickness retrievals)
Jan Rohde
(technical development)
Dr. Markus Janout
(oceanography)
Dr. Mario Hoppmann
(oceanography)
This project aims to qualitatively assess seasonal dynamics of Antarctic fast ice, emphasizing local sea ice, ice shelf, and ocean interactions, and their future changes (Project within the AWI INSPIRES call).
Project duration: 2025 to 2028
PI (AWI): Prof. Dr. Stefanie Arndt
The overall goal of this project was to improve our understanding of formation processes and properties of Antarctic sea ice and how these are influenced by snow cover and platelet ice (Project within the DFG SPP 1158).
Project duration: 2011 to 2015
PI (AWI): Dr. Marcel Nicolaus
Involved scientist (AWI):
Dr. Mario Hoppmann (PhD thesis)
Neudert, M., Arndt, S., Hendricks, S., Hoppmann, M., Schulze, M., and Haas, C.: Improved sub-ice platelet layer mapping with multi-frequency EM induction sounding, Journal of Applied Geophysics, 230, 105540, 10.1016/j.jappgeo.2024.105540, 2024.
Arndt, S., Hoppmann, M., Schmithüsen, H., Fraser, A. D., and Nicolaus, M.: Seasonal and interannual variability of landfast sea ice in Atka Bay, Weddell Sea, Antarctica, The Cryosphere, 14, 2775-2793, 10.5194/tc-14-2775-2020, 2020.
Hoppmann, M., Richter, M. E., Smith, I. J., Jendersie, S., Langhorne, P., Thomas, D., and Dieckmann, G.: Platelet ice, the Southern Ocean’s hidden ice: a review, Annals of Glaciology, 61(82), 10.1017/aog.2020.54, 2020.
Hunkeler, P. A., Hoppmann, M., Hendricks, S., Kalscheuer, T., and Gerdes, R.: A glimpse beneath Antarctic sea ice: Platelet layer volume from multifrequency electromagnetic induction sounding, Geophysical Research Letters, 43, 222-231, 10.1002/2015GL065074, 2016.
Hoppmann, M., Nicolaus, M., Hunkeler, P. A., Heil, P., Behrens, L. K., Konig-Langlo, G., and Gerdes, R.: Seasonal evolution of an ice-shelf influenced fast-ice regime, derived from an autonomous thermistor chain, Journal of Geophysical Research: Oceans, 120, 1703-1724, 10.1002/2014jc010327, 2015.
Hoppmann, M., Nicolaus, M., Paul, S., Hunkeler, P. A., Heinemann, G., Willmes, S., Timmermann, R., Boebel, O., Schmidt, T., Kuhnel, M., Konig-Langlo, G., and Gerdes, R.: Ice platelets below Weddell Sea landfast sea ice, Annals of Glaciology, 56, 175-190, 10.3189/2015AoG69A678, 2015.
Hunkeler, P. A., Hendricks, S., Hoppmann, M., Paul, S., and Gerdes, R.: Towards an estimation of sub-sea-ice platelet-layer volume with multi-frequency electromagnetic induction sounding, Annals of Glaciology, 56, 137-146, 10.3189/2015AoG69A705, 2015.
Paul, S., Willmes, S., Hoppmann, M., Hunkeler, P. A., Wesche, C., Nicolaus, M., Heinemann, G., and Timmermann, R.: The impact of early-summer snow properties on Antarctic landfast sea-ice X-band backscatter, Annals of Glaciology, 56, 263-273, 10.3189/2015AoG69A715, 2015.
