Drivers of variability in Arctic sea‐ice drift speed

Abstract

We explore the main drivers of seasonal and long-term variations in basin-scale Arctic sea-ice drift speed. To do so, we examine the relationship between the observed time-varying area-mean ice drift speed in the central Arctic and observed thickness and concentration as well as surface wind stress. Drift speeds are calculated from the positions of drifting buoys, thickness is based on submarine observations, concentration on satellite observations, and the wind stress comes from a global reanalysis. We find that seasonal changes in drift speed are correlated primarily with changes in concentration when concentration is low and with changes in thickness otherwise. The correlation between drift speed and concentration occurs because changing concentration changes how readily the ice responds to the synoptic-scale forcing of the atmosphere. Drift speed is correlated with neither concentration nor thickness in April and May. We show this behavior to be correlated with a decrease in the localization of deformation. This indicates that the increase in drift speed is caused by newly formed fractures not refreezing, leading to an overall reduced ice-cover strength without a detectable change in ice concentration. We show that a strong long-term trend exists in months of relatively low ice concentration. Using our analysis of the seasonal cycle, we show that the trend in concentration drives a significant portion of the drift-speed trend, possibly reinforced by a trend in cyclone activity. Hence, the trend in drift speed in this period is primarily caused by increased synoptic-scale movement of the ice pack.

Anthropogenic influence on recent circulation‐driven Antarctic sea ice changes

“…Consequently, we show that the finding by Haumann [] and Holland and Kwok [] that ice drift changes (Figure e) are induced by wind changes (Figure c), is also evident over the period 1979 to 2011. Potential inconsistencies in the drift trend [ Fowler et al , ; Olason and Notz , ] do not affect these results qualitatively (Figure S1 in the supporting information). The increased northward drift in the Ross Sea causes a higher sea ice production at the coast, a higher northward advection, thus an expansion and concentration increase at the ice edge.…”

neXtSIM: a new Lagrangian sea ice model

“…This is highest in summer, decreasing steadily from August to January, when it plateaus until April and then starts increasing again. Ólason and Notz (2014) found that over the 33 years they considered, the observed drift speed depends on concentration when concentration is low, thickness when concentration is high, and is related to an increased number of active fractures in AprilMay. It is not clear how well our model captures this relationship since the results for only 1 year can be heavily influenced by the timing and intensity of storms passing through the region.…”

Loitering of the retreating sea ice edge in the Arctic Seas

“…An analysis of such observations for the years 1979-2001 found summer speeds generally less than or equal to $5 cm s 21 [Martin and Gerdes, 2007]. However, more recent studies indicate a rapid acceleration of arctic sea ice floes [Rampal et al, 2009] to values closer to $12 cm s 21 at the end of summer [Spreen et al, 2011] or 8 km/d in winter [Olason and Notz, 2014].…”