Effects of Greenland Anticyclone Magnitude and Persistence on Spring Sea Ice Melt in the North Atlantic

Rapid environmental changes are occurring in the Arctic Ocean connected to warming temperatures across the high latitudes. Observed changes in the marine environment include widespread transitioning from multi-year to first-year sea ice cover and lengthening of the melt season due to earlier spring melt onset (MO) and later autumn ice formation. Melt season changes are especially notable around Greenland as Baffin Bay-Davis Strait-Labrador Sea (BDL) MO has occurred ~8 days/decade earlier from 1979-2015. Several years since the mid-1990s are characterized by anomalously early MO (of at least one standard deviation below the 1981-2010 mean melt date) coincident with increased high pressure, blocking conditions across Greenland and the surrounding North Atlantic. In this study, we investigate atmospheric and oceanic factors over the freeze period that subsequently influence BDL sea ice MO variability and extremes. Particular emphasis is placed on the early melt extreme that transpired in spring of 2013, which was nearly 8 weeks earlier than the 1981-2010 melt climatology. Analyses of daily reanalysis fields and a recently developed Greenland Blocking Index (GBI) reveal a persistent, strong 500 hPa anticyclone over the BDL region across the 40-day period prior to the 2013 MO anomaly. During this timeframe, >75% of days possessed a GBI value exceeding one standard deviation from the 1951-2000 index mean. The consistent presence of the anticyclonic circulation pattern resulted in abundant transfer of warm air from lower latitudes onto the thin, first-year sea ice leading to a much earlier than normal melt. The GBI is shown to be an important metric for understanding the timing of sea ice melt over the North Atlantic Ocean.