The Arctic sea ice cover of 2016 was highly noteworthy, as it featured recordlow monthly sea ice extents at the start of the year but a summer (September)extent that was higher than expected by most seasonal forecasts.Here we explore the 2016 Arctic sea ice state interms of its monthly sea ice cover, placing this in the context of the seaice conditions observed since 2000. We demonstrate the sensitivity of monthlyArctic sea ice extent and area estimates, in terms of their magnitude andannual rankings, to the ice concentration input data (using two widely useddatasets) and to the averaging methodology used to convert concentration toextent (daily or monthly extent calculations). We use estimates of sea icearea over sea ice extent to analyse the relative "compactness" of theArctic sea ice cover, highlighting anomalously low compactness in the summerof 2016 which contributed to the higher-than-expected September ice extent.Two cyclones that entered the Arctic Ocean during August appear to havedriven this low-concentration/compactness ice cover but were not sufficientto cause more widespread melt-out and a new record-low September ice extent.We use concentration budgets to explore the regions and processes(thermodynamics/dynamics) contributing to the monthly 2016 extent/areaestimates highlighting, amongst other things, rapid ice intensificationacross the central eastern Arctic through September. Two different productsshow significant early melt onset across the Arctic Ocean in 2016, includingrecord-early melt onset in the North Atlantic sector of the Arctic. Ourresults also show record-late 2016 freeze-up in the central Arctic, NorthAtlantic and the Alaskan Arctic sector in particular, associated with strongsea surface temperature anomalies that appeared shortly after the 2016minimum (October onwards). We explore the implications of this low summer icecompactness for seasonal forecasting, suggesting that sea ice area could be amore reliable metric to forecast in this more seasonal, "New Arctic", seaice regime.
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