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Christof König Beatty and David M. Holland

1. Introduction Landfast ice is sea ice that forms and remains fixed along a coast, where it is either attached to the shore or held between shoals or grounded icebergs. It covers Arctic shelves during large portions of the year, normally starting to form in October and reaching its widest extent during April and May ( Volkov et al. 2002 ; Barber and Hanesiak 2004 ; Divine et al. 2005 ). Because of its lack of mobility, landfast ice fundamentally modifies the momentum exchange between

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Alexander V. Wilchinsky and Daniel L. Feltham

1. Introduction Sea ice forms from the freezing of polar waters and covers a significant fraction, up to almost 10%, of the earth’s oceans. Sea ice is well recognized as an important component of the earth’s climate system and, as a result, sea ice models are routinely incorporated into global climate models (GCMs). Although sea ice affects polar and global climate through its impact on the thermohaline budget (e.g., through its high albedo compared to seawater), its insulating effect on polar

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R. C. Frew, D. L. Feltham, P. R. Holland, and A. A. Petty

1. Introduction Satellite observations have shown Antarctic sea ice to be expanding over the past four decades ( Parkinson and Cavalieri 2012 ). Although this increasing trend is modest, it is in stark contrast to the well-documented rapid Arctic sea ice decline. The small net increase is the result of stronger, opposing regional and seasonal trends ( Holland 2014 ), though a rapid decline in Antarctic sea ice was observed in 2016/17 ( Stuecker et al. 2017 ; Turner et al. 2017 ). There is no

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Jinlun Zhang, Rebecca Woodgate, and Richard Moritz

1. Introduction The Bering Sea supports one of the world’s most productive and valuable fisheries, immense populations of marine birds and mammals, and the subsistence activities of native communities ( ARCUS 2004 ). This great biological productivity takes place in a dynamic ocean with substantial seasonal ice cover. Significant changes in the Bering ecosystem have been measured in recent decades. Observations indicate that large-scale ecological “regime shifts” occurred in the Bering Sea

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Harold D. B. S. Heorton, Nikhil Radia, and Daniel L. Feltham

1. Background Leads and polynyas are ice-free areas within the sea ice cover in which the ocean is in contact with the cold atmosphere in winter. They can form due to warm-water upwelling (sensible heat polynya), katabatic winds or ocean currents that drive newly formed ice away (latent heat polynyas), or when the ice breaks due to internal stresses (leads). Leads are typically long thin features 10 m to 1 km wide and up to 100 km long ( Wilchinsky et al. 2015 ), whereas polynyas are defined as

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L-B. Tremblay and M. Hakakian

1. Introduction The advection of sea ice by surface wind and ocean stresses is a fundamental process affecting the concentration and thickness distribution of sea ice at high latitudes. These two factors in turn control the surface albedo, mediate the heat and freshwater fluxes between the atmosphere and ocean (and between different ocean basins), and through multiple feedbacks have a large influence on the high-latitude climate. For instance, projections of future climate change have often

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Yoshihiro Nakayama, Kay I. Ohshima, and Yasushi Fukamachi

1. Introduction Sea ice drift is determined as a result of wind forcing and ice–ocean interaction. Studies on sea ice drift can be traced back to Nansen (1902) , who found that sea ice drifts with a speed of about 2% of the surface wind and about 25° to the right of the wind in the Northern Hemisphere. Recently, sea ice drift has been studied using drifting-buoy and satellite-microwave data in the entire polar sea ice regions (e.g., Thorndike and Colony 1982 ; Emery et al. 1997 ; Heil and

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Annie P. S. Wong and Stephen C. Riser

1. Introduction Each year, from early autumn to late spring, the heat lost from the sea surface around Antarctica leads to the development of a seasonal sea ice cover whose extent, at its maximum, essentially doubles the surface area of the continent. The presence of sea ice has a direct influence on the physical and biological processes in the ocean in the region. For example, the melting of sea ice in summer results in a stable and shallow surface mixed layer into which solar radiation can

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Benjamin I. Barton, Yueng-Djern Lenn, and Camille Lique

1. Introduction The Arctic has been predicted to be free of sea ice in summer by the middle of the twenty-first century ( Wang and Overland 2012 ; Snape 2013 ; Notz and Stroeve 2016 ). This follows an Arctic-wide decline in sea ice extent over recent decades ( Screen and Simmonds 2010 ). The Barents Sea alone has seen a 50% reduction in annual sea ice area between 1998 and 2008 ( Årthun et al. 2012 ), associated with a strong sea ice decline in all seasons including winter ( Onarheim and

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Yueng-Djern Lenn, Tom P. Rippeth, Chris P. Old, Sheldon Bacon, Igor Polyakov, Vladimir Ivanov, and Jens Hölemann

et al. 1981 ). Consequently, Arctic halocline formation theories have focused on mechanisms for diapycnal and lateral mixing of the shelf and oceanic waters (e.g., Rudels et al. 2000 ; Woodgate et al. 2005 ; Shimada et al. 2005 ; Itoh et al. 2007 ). These halocline formation and maintenance mechanisms are critical to Arctic upper-ocean stratification that in turn influences Arctic circulation, sea ice, and climate. Mixing between the different water masses during halocline formation is

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