Ice platelets below Weddell Sea landfast sea ice

Abstract

ABSTRACT. Basal melt of ice shelves may lead to an accumulation of disc-shaped ice platelets underneath nearby sea ice, to form a sub-ice platelet layer. Here we present the seasonal cycle of sea ice attached to the Ekström Ice Shelf, Antarctica, and the underlying platelet layer in 2012. Ice platelets emerged from the cavity and interacted with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout winter and spring led to an average platelet-layer thickness of 4 m by December 2012, with local maxima of up to 10 m. The additional buoyancy partly prevented surface flooding and snow-ice formation, despite a thick snow cover. Subsequent thinning of the platelet layer from December onwards was associated with an inflow of warm surface water. The combination of model studies with observed fast-ice thickness revealed an average ice-volume fraction in the platelet layer of 0.25 � 0.1. We found that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice was equivalent to more than one-fifth of the annual basal melt volume under the Ekström Ice Shelf.

Multiphase Reactive Transport and Platelet Ice Accretion in the Sea Ice of McMurdo Sound, Antarctica

“…These floating crystals modify the ice‐ocean interface, creating a highly porous layer of platelet ice with notably different crystal geometry and texture than the typical granular or columnar ice produced by the direct freezing of ocean water onto the sea ice‐ocean interface (Dempsey et al, ; Dempsey & Langhorne, ). The addition of platelet ice crystals to the sea ice layer can modify the thermal and mechanical properties of the ice as well as contribute meters of consolidated platelets to the overall ice thickness (with maximums near ice shelf fronts reaching ∼10 m; Eicken & Lange, ; Hellmer, ; Hoppmann et al, ; Hunkeler et al, ). Quantifying this interaction between sea ice and ice shelves and incorporating it into numerical simulations of platelet‐affected ice would improve the fidelity and predictions of such models, increasing our understanding of polar ice‐ocean interactions.…”

The Inferred Formation of a Subice Platelet Layer Below the Multiyear Landfast Sea Ice in the Wandel Sea (NE Greenland) Induced by Meltwater Drainage

“…The phenomenon of platelet ice crystals forming a porous matrix (hereafter referred to as a platelet layer) under an existing ice cover has been observed in many coastal regions around Antarctica (e.g., Eicken & Lange, 1989;Hoppmann et al, 2015a;Langhorne et al, 2015;Price et al, 2014). In Antarctic waters, the formation of a platelet layer is related to the so-called ice-pumping process (Lewis & Perkin, 1986) in which cool, fresh water from the basal melt of an ice-shelf becomes supercooled as it rises, due to increasing buoyancy, and leads to the formation of platelet crystals (Foldvik & Kvinge, 1974).…”

Turbulent heat transfer as a control of platelet ice growth in supercooled under-ice ocean boundary layers

“…They suggested that variable currents were responsible for the episodic nature of the crystal growth. The appearance of these supercooling-induced crystals is not limited to the western margin of the Ross Ice Shelf, with observations made in other cold-cavity systems sampled to date (Dieckmann et al, 1986;Craven et al, 2014;Hoppmann et al, 2015;Langhorne et al, 2015).…”

“…There is a growing awareness of the ubiquity of such downward heat flux conditions in the vicinity of ice shelves (Robinson et al, 2014;Craven et al, 2015;Hoppmann et al, 2015). The resistance then imposed by a stationary ice cover influenced by such crystal growth on underlying boundary layer flow depends on the undersurface hydraulic roughness, z 0 .…”

“…1) under ice shelves is difficult to observe directly (Craven et al, 2005), but similar effects are readily observed beneath nearby sea ice where it is called platelet ice (e.g. Robinson et al, 2014;Hughes et al, 2014;Hoppmann et al, 2015;Langhorne et al, 2015). For example in McMurdo Sound, Antarctica, sea ice crystals that have formed in supercooled water have been observed and reported since the British National Antarctic (Discovery) Expedition of 1901-1904(Hodgson, 1907 and the British Antarctic (Terra Nova) Expedition of 1910-1913(Wright and Priestley, 1922.…”