Variability of light transmission through Arctic land-fast sea ice during spring

M. A. Granskog,M. Nicolaus,C. Petrich,S. R. Hudson

doi:10.5194/tc-7-977-2013

Abstract

Abstract. The amount of solar radiation transmitted through Arctic sea ice is determined by the thickness and physical properties of snow and sea ice. Light transmittance is highly variable in space and time since thickness and physical properties of snow and sea ice are highly heterogeneous on variable time and length scales. We present field measurements of under-ice irradiance along transects under undeformed land-fast sea ice at Barrow, Alaska (March, May, and June 2010). The measurements were performed with a spectral radiometer mounted on a floating under-ice sled. The objective was to quantify the spatial variability of light transmittance through snow and sea ice, and to compare this variability along its seasonal evolution. Along with optical measurements, snow depth, sea ice thickness, and freeboard were recorded, and ice cores were analyzed for chlorophyll a and particulate matter. Our results show that snow cover variability prior to onset of snow melt causes as much relative spatial variability of light transmittance as the contrast of ponded and white ice during summer. Both before and after melt onset, measured transmittances fell in a range from one third to three times the mean value. In addition, we found a twentyfold increase of light transmittance as a result of partial snowmelt, showing the seasonal evolution of transmittance through sea ice far exceeds the spatial variability. However, prior melt onset, light transmittance was time invariant and differences in under-ice irradiance were directly related to the spatial variability of the snow cover.

Highlights

Physical properties and the thickness of sea ice and snow cover play a key role for the Arctic climate and ecosystems
Wavelength-integrated albedo is reasonably well quantified for different surface types, and the seasonal evolution is described in several ways for multi-year sea ice (Nicolaus et al, 2010a; Perovich et al, 2002a) and seasonal land-fast sea ice (Perovich and Polashenski, 2012; Perovich et al, 1998, 2012)
Changes in snow depth and snow properties can be seen in the photographs of surface conditions in Fig. 2, showing a visibly lower albedo and wet snow in June

Summary

Introduction

Physical properties and the thickness of sea ice and snow cover play a key role for the Arctic climate and ecosystems. The role of surface optical properties has been investigated extensively from in situ observations (Grenfell and Perovich, 2004; Perovich et al, 1998, 2002b), numerical simulations (Gardner and Sharp, 2010; Grenfell, 1991; Light et al, 2003), laboratory experiments (Perovich and Grenfell, 1981), airborne measurements (Hanesiak et al, 2001; Perovich et al, 2002a), and remote sensing (Comiso and Kwok, 1996; Hall et al, 2004; Hall and Martinec, 1985; Tschudi et al, 2001) From these studies, wavelength-integrated (total or broadband) albedo is reasonably well quantified for different surface types, and the seasonal evolution is described in several ways for multi-year sea ice (Nicolaus et al, 2010a; Perovich et al, 2002a) and seasonal land-fast sea ice (Perovich and Polashenski, 2012; Perovich et al, 1998, 2012).

Objectives

Methods

Results

Conclusion