Variability in Arctic sea ice optical properties

Abstract

Abstract. The optical properties of sea ice exhibit considerable spatial, temporal, and spectral variability. During a field experiment at Barrow, Alaska, we examined the horizontal variability of spectral albedo and transmittance as well as the vertical variability of in-ice radiance. Temporal changes were monitored under cold conditions in April and during the onset of melt in June. Physical properties, including ice structure and concentrations of particulate and dissolved material, were measured to provide a context for understanding the observed temporal, horizontal, vertical, and spectral variability in optical properties. For snow-covered first-year ice in April, wavelength-integrated (300-3000 nm) albedos were high (0.8) and spabally uniform, but there was considerable variability in transmittance. Transmittance at 440 nm ranged by more than a factor of 2 over horizontal distances of only 25 m, owing primarily to differences in snow depth, although spectral variations in transmittance indicate that absorbing organic materials in the ice column contribute significantly to the horizontal variability. Peak values of transmittance in April were 1% near 500 nm, decreasing at both longer and shorter wavelengths. At the onset of melt in June, the ice surface rapidly evolved into a variegated mixture of melting snow, bare ice, and melt ponds. Albedos were much lower and exhibited considerable spatial variability, ranging from 0.2 to 0.5 over distances of a few meters concomitant with the variation in surface characteristics. Transmission increased over the spring transition as surface characteristics evolved to decrease albedo and as inice structure was altered by heating to reduce attenuation within the ice. The exception to this trend occurred over a period of a few days when an algal bloom developed on the underside of the ice and transmission was significantly reduced. Variability in the in-ice spectral radiance values was observed between nearby sites in both first-year and multiyear ice. While the radiance measurements are strongly dependent on the incident solar radiance, under similar solar conditions there was an observed shift in the peak of the maximum in the spectral radiance from 460 nm in clean ice to between 500 and 550 nm in ice that contained particulates in the surface layer. More impressive spectral shifts were found in an old melt pond that had accumulated particles at its base.

First-year sea ice melt pond fraction estimation from dual-polarisation C-band SAR – Part 2: Scaling in situ to Radarsat-2

“…Coupling between the physical and thermodynamic properties of seasonally evolving snow-covered sea ice, and SAR backscatter, is already well established from detailed in situ characterisations of ice electromagnetic properties and microwave interactions (e.g. Livingstone et al, 1987;Drinkwater, 1989;Barber, 2005;Perovich et al, 1998). Past studies focused mainly on backscatter measured at C-band frequency from SARs ERS-1 and 2 (European Remote Sensing) (VV) and Radarsat-1 (HH).…”

Changes in snow distribution and surface topography following a snowstorm on Antarctic sea ice

“…In winter, the snow cover can limit the thermodynamic growth of the ice [e.g., Maykut and Untersteiner, 1971;Ledley, 1993;Powell et al, 2005], especially in the Antarctic where deep snow accumulations and high ocean heat flux can lead to basal melting [e.g., Jeffries et al, 1998;Lewis et al, 2011]. In the Artic, the spatial distribution of snow has been shown to influence the evolution of melt ponds [Petrich et al, 2012;Polashenski et al, 2012], which in consequence affects the surface albedo [Perovich et al, 1998. Similarly, snow accumulation can lead to isostatic adjustment allowing flooding of sea ice surfaces with ocean water, which enhances the formation of snow ice [e.g., Eicken et al, 1995;Jeffries et al, 1998;Maksym and Markus, 2008].events are often accompanied by strong winds, and direct measurement of snowfall amounts and separation of snowfall as opposed to blowing snow have proven to be difficult.…”

Mesoscale Distribution of Springtime Waters and Nutrients near the Continental Shelf Break, Beaufort Sea, Alaska~!2010-05-13~!2010-06-25~!2010-09-08~!

“…From the oceanographic water bottle, 50 ml of seawater were drained into a previously acid-cleaned and thoroughly dry polyethylene sample bottle. From this, 20 ml were pipetted into a clean glass scintillation bottle with polyseal lid, for later measurement of the 18 O/ 16 O ratio of the seawater. The remainder in the polyethylene bottle, about 20 ml, was frozen for later nutrient determinations.…”

“…Similarly, ammonium concentrations were less than 1.40 µM and averaged 0.25 µM, so this nutrient also was not considered here. The 18 O/ 16 O isotopic ratios of the seawater samples (δ 18 O, [39]) were determined at the Stable Isotope Mass Spectrometer Facility at the University of Maine Orono. The average precision of the mass-spectrometer determinations was reported to be +/-0.013‰ for 205 determinations.…”

“…The 1-m decrease in ice thickness reported by Rothrock et al [16] would increase light intensity below the ice by 25%. In cases where ice was completely removed in summer, the light level would increase over 10-100 fold in the upper water column [17,18], which could increase the depth of the euphotic zone to over 50 m.…”