Comment on tc-2021-135

doi:10.5194/tc-2021-135-rc2

Abstract

Abstract. In the Arctic, multi-year sea ice is being rapidly replaced by seasonal sea ice. Baffin Bay, situated between Greenland and Canada, is part of the seasonal ice zone. In this study, we present a long-term multi-mission assessment (2003â2020) of spring sea ice thickness in Baffin Bay from satellite altimetry and sea ice charts. Sea ice thickness within Baffin Bay is calculated from Envisat, ICESat, CryoSat-2, and ICESat-2 freeboard estimates, alongside a proxy from the ice chart stage of development that closely matches the altimetry data. We study the sensitivity of sea ice thickness results estimated from an array of different snow depth and snow density products and methods for redistributing low-resolution snow data onto along-track altimetry freeboards. The snow depth products that are applied include a reference estimated from the Warren climatology, a passive microwave snow depth product, and the dynamic snow scheme SnowModel-LG. We find that applying snow depth redistribution to represent small-scale snow variability has a considerable impact on ice thickness calculations from laser freeboards but was unnecessary for radar freeboards. Decisions on which snow loading product to use and whether to apply snow redistribution can lead to different conclusions on trends and physical mechanisms. For instance, we find an uncertainty envelope around the March mean sea ice thickness of 13â% for different snow depth/density products and redistribution methods. Consequently, trends in March sea ice thickness from 2003â2020 range from â23 to 17âcm per decade, depending on which snow depth/density product and redistribution method is applied. Over a longer timescale, since 1996, the proxy ice chart thickness product has demonstrated statistically significant thinning within Baffin Bay of 7âcm per decade. Our study provides further evidence for long-term asymmetrical trends in Baffin Bay sea ice thickness (with â17.6âcm per decade thinning in the west and 10.8âcm per decade thickening in the east of the bay) since 2003. This asymmetrical thinning is consistent for all combinations of snow product and processing method, but it is unclear what may have driven these changes.

Highlights

We aim to reconcile the spring sea ice thickness derived from multiple satellite altimetry sensors and sea ice charts in Baffin Bay and produce a robust long-term record (2003–2020)
We investigate the impact of different snow depth and density products and redistribution methods on retrieved sea ice thickness from satellite altimetry along-track sea ice freeboard data
As there are few in situ observations of snow depth or sea ice thickness available within Baffin Bay, it is not possible to determine unambiguously which of the snow depth products and redistribution methods give the most accurate estimation of sea ice thickness from satellite altimetry

Summary

Introduction

Arctic sea ice concentration and thickness has reduced significantly in recent decades (Kwok, 2018; Stroeve and Notz, 2018). With a > 50 % decrease in multi-year ice (MYI) cover since the turn of the century, the Arctic is increasingly becoming dominated by seasonal ice (Kwok, 2018). The Arctic winter area coverage of seasonal ice has surpassed that of MYI, making the understanding of processes over firstyear ice (FYI) as important as those over MYI (Jeffries et al, 2013). Glissenaar et al.: Impacts of snow data and processing methods

Objectives

Methods

Results

Conclusion