Sea-Ice Wintertime Lead Frequencies and Regional Characteristics in the Arctic, 2003–2015

Sascha Willmes,Günther Heinemann

doi:10.3390/rs8010004

Abstract

The presence of sea-ice leads represents a key feature of the Arctic sea ice cover. Leads promote the flux of sensible and latent heat from the ocean to the cold winter atmosphere and are thereby crucial for air-sea-ice-ocean interactions. We here apply a binary segmentation procedure to identify leads from MODIS thermal infrared imagery on a daily time scale. The method separates identified leads into two uncertainty categories, with the high uncertainty being attributed to artifacts that arise from warm signatures of unrecognized clouds. Based on the obtained lead detections, we compute quasi-daily pan-Arctic lead maps for the months of January to April, 2003–2015. Our results highlight the marginal ice zone in the Fram Strait and Barents Sea as the primary region for lead activity. The spatial distribution of the average pan-Arctic lead frequencies reveals, moreover, distinct patterns of predominant fracture zones in the Beaufort Sea and along the shelf-breaks, mainly in the Siberian sector of the Arctic Ocean as well as the well-known polynya and fast-ice locations. Additionally, a substantial inter-annual variability of lead occurrences in the Arctic is indicated.

Highlights

Almost the entire the Arctic Ocean is covered by sea ice during wintertime and spring
The comparison is meant to provide only a qualitative measure since changes in the reflective signature of leads do not necessarily need to be congruent with changes in their thermal signature, i.e., a lead covered with thin ice and snow can still exhibit a substantial warm temperature anomaly while its reflectance may already approach a characteristic value for thick sea ice
All three subsets indicate that the FCAF captures the most significant leads, i.e., dark regions in left column, very well and achieves a reasonable separation from warm surface features that are not associated with real leads

Summary

Introduction

Almost the entire the Arctic Ocean is covered by sea ice during wintertime and spring. Leads promote a very strong exchange of heat and moisture between the relatively warm ocean and the cold winter atmosphere (e.g., [1,2]). The recurrence of leads and their spatial distribution are valuable diagnostic parameters for the sea-ice drift [4] and changes in the sea-ice stability [5] and represent an essential habitat for marine mammals and birds [6]. Especially in light of the observed trends in Arctic sea-ice extent ([7,8,9]), and with respect to the projected future changes in the Arctic climate system, the structure and dynamics of leads represent essential information for global change monitoring, e.g., [10]. The sub-grid lead fraction in global and regional sea-ice/ocean models is mainly parameterized [11]. As leads have a strong impact on the atmospheric boundary layer (e.g., [12,13])

Results

Discussion

Conclusion