Platelet Ice Under Arctic Pack Ice in Winter

Katlein, Christian; Mohrholz, Volker; Sheikin, Igor; Itkin, Polona; Divine, Dmitry; Stroeve, Julienne; Jutila, Arttu; Krampe, Daniela; Shimanchuk, Egor; Raphael, Ian; Rabe, Benjamin; Kuznetsov, Ivan; Mallet, Maria; Liu, Hailong; Hoppmann, Mario; Fang, Ying-Chih; Dumitrascu, Adela; Arndt, Stefanie; Anhaus, Philipp; Nicolaus, Marcel; Matero, Ilkka; Oggier, Marc; Eicken, Hajo; Haas, Christian

doi:10.1029/2020gl088898

Cited by 26 publications

(17 citation statements)

References 47 publications

(68 reference statements)

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“…First results with a focus on snow and sea ice conditions have been published, for example, on the history of the ice drift prior to the MOSAiC expedition , on the ice conditions from satellite observation along the drift track in previous years (Krumpen et al, 2021), on the representativeness of the selected ice floe (Belter et al, 2021), on the linkages to the general atmospheric circulation (Dethloff et al, 2021), on sea ice RS methods (Munoz-Martin et al, 2020;Stroeve et al, 2020;Semmling et al, 2021), and on the platelet ice accumulation in winter (Katlein et al, 2020).…”

Section: Methods and Approachmentioning

confidence: 99%

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Overview of the MOSAiC expedition: Snow and sea ice

et al. 2022

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Year-round observations of the physical snow and ice properties and processes that govern the ice pack evolution and its interaction with the atmosphere and the ocean were conducted during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition of the research vessel Polarstern in the Arctic Ocean from October 2019 to September 2020. This work was embedded into the interdisciplinary design of the 5 MOSAiC teams, studying the atmosphere, the sea ice, the ocean, the ecosystem, and biogeochemical processes. The overall aim of the snow and sea ice observations during MOSAiC was to characterize the physical properties of the snow and ice cover comprehensively in the central Arctic over an entire annual cycle. This objective was achieved by detailed observations of physical properties and of energy and mass balance of snow and ice. By studying snow and sea ice dynamics over nested spatial scales from centimeters to tens of kilometers, the variability across scales can be considered. On-ice observations of in situ and remote sensing properties of the different surface types over all seasons will help to improve numerical process and climate models and to establish and validate novel satellite remote sensing methods; the linkages to accompanying airborne measurements, satellite observations, and results of numerical models are discussed. We found large spatial variabilities of snow metamorphism and thermal regimes impacting sea ice growth. We conclude that the highly variable snow cover needs to be considered in more detail (in observations, remote sensing, and models) to better understand snow-related feedback processes. The ice pack revealed rapid transformations and motions along the drift in all seasons. The number of coupled ice–ocean interface processes observed in detail are expected to guide upcoming research with respect to the changing Arctic sea ice.

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Section: Methods and Approachmentioning

confidence: 99%

“…The novel observation of platelet ice under winter sea ice in the Arctic showed that platelet ice contributed to bottom ice growth during winter (Katlein et al, 2020). Over time, the ice pack became strongly deformed.…”

Section: Sea Ice and Snow Mass Balancementioning

confidence: 99%

Overview of the MOSAiC expedition: Snow and sea ice

et al. 2022

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“…Supercooled water, that is, water with a temperature below a reference freezing point temperature, has been observed in the polar oceans of the Arctic (e.g., Drucker et al., 2003; Katlein et al., 2020; Skogseth et al., 2009) and Antarctic (e.g., Brett et al., 2020; Countryman, 1970; Lewis & Perkin, 1986). Seawater may be supercooled relative to the local freezing point, making it “in situ” supercooled (Ushio & Wakatsuchi, 1993), or the surface ocean freezing point, making it “potentially” supercooled (Shcherbina et al., 2004).…”

Section: Introductionmentioning

confidence: 99%

“…Potential supercooling could also result from downward mixing of frazil ice by strong winds (Matsumura & Ohshima, 2015). Additionally, supercooling is observed in the Arctic under a closed sea‐ice cover and calm conditions (Katlein et al., 2020; Peterson, 2018) and is potentially related to the rejection of cold brine from sea ice. Prior to the present study, there had been no evidence of widespread sea ice‐induced supercooling or the occurrence of supercooled waters away from the continental shelf in the Southern Ocean.…”

Section: Introductionmentioning

confidence: 99%

Supercooled Southern Ocean Waters

Haumann

Moorman

Riser

et al. 2020

Geophysical Research Letters

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In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice-covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55°S, we find temperatures below the surface freezing point ("potential" supercooling), and half of these have temperatures below the local freezing point ("in situ" supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal-ocean supercooling to melting of Antarctic ice shelves and surface-induced supercooling in the seasonal sea-ice region to wintertime sea-ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes-an important mechanism for vertical tracer transport and water-mass structure in the polar ocean. Plain Language Summary Ocean water, which contains about 34 grams of salt per kilogram of seawater, generally freezes around −1.85°C. However, seawater can be cooled to even lower temperatures without turning into ice. This phenomenon is called supercooling. Supercooled water is found in the polar oceans, typically in regions where the ocean is in contact with ice, as is the case for the enormous seasonal sea-ice region around Antarctica. But collecting measurements in this region under the thick ice cover during the dark and cold Antarctic winter is challenging. Here, we supplement rather sparse traditional ship-based observations with data collected by autonomous floats and instrumented marine mammals to detect and analyze where, when, and how supercooled seawater forms in the Southern Ocean. We find widespread supercooling related to melting floating glaciers (ice shelves) along the Antarctic coast and sea-ice formation. Our analysis enables us to detect sinking supercooled plumes from sea-ice formation, which may be important for cooling the deep ocean and transporting constituents such as carbon, nutrients, or oxygen from the ocean's surface to deeper layers.

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“…Subice platelet layers can be separated from frazil ice in such way that the geometric size of the platelet ice crystals is on the order of 1-10 cm. Frazil ice describes the crystal habit resulting from the initial stages of sea ice growth, when small disk and needle-like crystals smaller than 1 cm appear suspended in the upper water column or at the ocean surface (Hoppmann et al, 2020;Weeks & Ackley, 1986;Zubov, 1963). Subice platelet layers exhibit a rather random orientation of crystal axes.…”

Section: Introductionmentioning

confidence: 99%

Platelet Ice under Arctic Pack Ice in Winter

Katlein

Mohrholz

Sheikin

et al. 2020

Preprint

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The formation of platelet ice is well known to occur under Antarctic sea ice, where subice platelet layers form from supercooled ice shelf water. In the Arctic, however, platelet ice formation has not been extensively observed, and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long-term in situ observations of a decimeter thick subice platelet layer under free-drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth. Plain Language Summary Platelet ice is a particular type of ice that consists of decimeter sized thin ice plates that grow and collect on the underside of sea ice. It is most often related to Antarctic ice shelves and forms from supercooled water with a temperature below the local freezing point. Here we present the first comprehensive observation of platelet ice formation in freely drifting pack ice in the Arctic in winter during the international drift expedition MOSAiC. We investigate its occurrence under the ice with a remotely controlled underice diving robot. Measurements of water temperature from automatic measurement devices distributed around the central MOSAiC ice floe show that supercooled water and thus platelet ice occur widely in the winter Arctic. This way of ice formation in the Arctic has been overlooked during the last century, as direct observations under winter sea ice were not available and contrary to typical Antarctic observations; manifestation of platelet ice in Arctic ice core stratigraphy has been more challenging to identify.

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Platelet Ice Under Arctic Pack Ice in Winter

Cited by 26 publications

References 47 publications

Overview of the MOSAiC expedition: Snow and sea ice

Overview of the MOSAiC expedition: Snow and sea ice

Supercooled Southern Ocean Waters

Platelet Ice under Arctic Pack Ice in Winter

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