Monitoring Ice Variability and Change through an Ice Reduction Date

Average ice conditions at the end of the melt season exhibit an annual loss of ice at the perimeter of the Arctic Ocean and throughout many of the surrounding bays and seas. Recent years have displayed record minimums in both Arctic ice concentration and extent when measured with average values at the end of the melt season (September). These recent extremes may be indicators of Arctic climate change, or feedbacks from atmospheric variability (i.e., the Arctic Oscillation, a dominant mode of Arctic atmospheric variability). Many studies have involved autumn ice conditions, whereas this study investigates the initial loss of ice by monitoring spring and summer decreases in remotely sensed ice concentration.

In order to evaluate changes in ice characteristics during the spring and summer months, an ice reduction date is defined as the first day in which a median-filtered Bootstrap Method ice concentration drops below 80%. A mean ice reduction date is calculated over the full period of available data (1979-2003) for the perimeter of the Arctic Ocean and adjacent areas that frequently experience a seasonal loss of ice. Ice reduction date anomalies are linked to dynamic and thermodynamic forcing. Long term trends in ice reduction dates are examined, with statistically significant and earlier trends located in portions of the Chukchi and Beaufort Seas, as well as western Hudson and northern Baffin Bay.