Spatial and temporal characterization of sea-ice deformation

Abstract

In late March 2007 an array of GPS ice drifters was deployed in the Beaufort Sea as part of the Sea Ice Experiment: Dynamic Nature of the Arctic (SEDNA). The drifters were deployed in an array designed to resolve four, nested spatial scales of sea-ice deformation, from 10 to 140 km, with the arrays maintaining appropriate shape for strain-rate calculation until mid-June. In this paper, we test whether sea-ice deformation displays fractal properties in the vicinity of SEDNA. We identify that deformation time series have different spectral properties depending on the spatial scale. At the scales around 100 km, deformation is a red-noise process, indicating the importance of the ice-pack surface forcing in determining the deformation rate of sea ice at this scale. At smaller scales, the deformation becomes an increasingly whiter process (it has pink noise properties), which suggests an increasing role of dissipative processes at smaller scales. At spatial scales of 10-100 km, and sub-daily scales, there is no deformation coherence across scales; coherence only becomes apparent at longer scales greater than 100 km. The lack of coherence at small scales aids in understanding previous observations where correlation between 10 km regions adjacent to each other varied widely, with correlation coefficients between -0.3 and 1. This suggests it is not appropriate to think of sea ice as having a decorrelation length scale for deformation. We find that lead scale observations of deformation are required when estimating ice growth in leads and ridging time series. For the two SEDNA arrays, we find coherence between 140 and 20 km scale deformation up to periods of 16 days. This suggests sea-ice deformation displays coherent deformation between 100 km scale and the scale of the Beaufort Sea (of order 1000 km), over synoptic time periods (daily to weekly timescales). Organization of leads at synoptic and larger scales is an emergent feature of the deformation field that is caused by the smooth variation of surface forcing (wind) on the ice pack.

Method to characterize directional changes in Arctic sea ice drift and associated deformation due to synoptic atmospheric variations using Lagrangian dispersion statistics

“…The role of forcing (wind stress) and coastline geometry in establishing coherence in lead patterns/fractures in the ice cover captured by sea ice deformation has also been explored in past studies (Overland et al, 1995;Hutchings et al, 2005Hutchings et al, , 2011. Overland et al (1995) demonstrated that in the Beaufort Sea for spatial scales: (i) exceeding 100 km the sea ice cover moves as an aggregate; (ii) less than 100 km the ice cover moves as an aggregate or discrete entity; and (iii) on the order of 1 km the ice cover is characterized by floe (ice-ice) interactions.…”

“…Previous studies have examined sea ice drift and deformation response to atmospheric forcing and coastline geometry on varying timescales (Overland et al, 1995;Richter-Menge et al, 2002;Geiger and Perovich, 2008;Hutchings et al, 2011). In an assessment of springtime sea ice drift in a region to the west of the Antarctic Peninsula, Geiger and Perovich (2008) identified low-frequency motion in response to atmospheric forcing and coastal geometry associated with regional-scale transport and higher-frequency near-inertial oscillatory motion associated with mixing.…”

“…Overland et al (1995) demonstrated that in the Beaufort Sea for spatial scales: (i) exceeding 100 km the sea ice cover moves as an aggregate; (ii) less than 100 km the ice cover moves as an aggregate or discrete entity; and (iii) on the order of 1 km the ice cover is characterized by floe (ice-ice) interactions. Through analysis of a nested beacon configuration and array with spatial scales ranging from 10 to 140 km as part of the late-winter (April) 2007 Sea Ice Experiment: Dynamic Nature of the Arctic (SEDNA) campaign in the Beaufort Sea, Hutchings et al (2011) demonstrated coherence between 140 and 20 km divergence arrays for time periods of up to 16 days in March. Over shorter (sub-synoptic) timescales from May 2007 onward, nested buoy arrays captured the loss of connectivity in the sea ice cover associated with the winter-to-summer transition during a substantial iceloss year (Stroeve et al, 2008).…”

Lagrangian analysis of sea-ice dynamics in the Arctic Ocean

“…Increased drift and deformation rates from 1979 to 2009 were found in the central Arctic and have been attributed to sea-ice kinematics and accompanying reduction in ice cover strength (Rampal et al 2009). Hutchings et al (2011) demonstrated coherence in deformation over length scales exceeding 100 km on daily to weekly timescales. Hutchings & Rigor (2012) further demonstrated a transition to a younger, thinner ice cover in the Beaufort Sea region associated with a change in ice-drift regimes in the western Arctic and Beaufort Sea since 1998.…”

“…Recent Lagrangian analyses have also used buoy trajectories to quantify sea-ice drift and deformation (Rampal et al 2008;Rampal et al 2009;Hutchings et al 2011;Weiss 2013). Spatial and temporal scaling laws illustrated coupling in space and time in sea-ice deformation processes (Rampal et al 2008).…”