Articles | Volume 11, issue 6
The Cryosphere, 11, 2611–2632, 2017
The Cryosphere, 11, 2611–2632, 2017

Research article 17 Nov 2017

Research article | 17 Nov 2017

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

Joseph M. Cook1,2, Andrew J. Hodson1,3, Alex S. Gardner4, Mark Flanner5, Andrew J. Tedstone6, Christopher Williamson6, Tristram D. L. Irvine-Fynn7, Johan Nilsson4, Robert Bryant1, and Martyn Tranter6 Joseph M. Cook et al.
  • 1Department of Geography, University of Sheffield, Winter Street, Sheffield, UK
  • 2College of Life and Natural Sciences, University of Derby, Kedleston Road, Derby, UK
  • 3University Centre in Svalbard (UNIS), Svalbard, Norway
  • 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
  • 5Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48105, USA
  • 6Centre for Glaciology, University of Bristol, Bristol, UK
  • 7Centre for Glaciology, Aberystwyth University, Aberystwyth, Wales, UK

Abstract. The darkening effects of biological impurities on ice and snow have been recognised as a control on the surface energy balance of terrestrial snow, sea ice, glaciers and ice sheets. With a heightened interest in understanding the impacts of a changing climate on snow and ice processes, quantifying the impact of biological impurities on ice and snow albedo (bioalbedo) and its evolution through time is a rapidly growing field of research. However, rigorous quantification of bioalbedo has remained elusive because of difficulties in isolating the biological contribution to ice albedo from that of inorganic impurities and the variable optical properties of the ice itself. For this reason, isolation of the biological signature in reflectance data obtained from aerial/orbital platforms has not been achieved, even when ground-based biological measurements have been available. This paper provides the cell-specific optical properties that are required to model the spectral signatures and broadband darkening of ice. Applying radiative transfer theory, these properties provide the physical basis needed to link biological and glaciological ground measurements with remotely sensed reflectance data. Using these new capabilities we confirm that biological impurities can influence ice albedo, then we identify 10 challenges to the measurement of bioalbedo in the field with the aim of improving future experimental designs to better quantify bioalbedo feedbacks. These challenges are (1) ambiguity in terminology, (2) characterising snow or ice optical properties, (3) characterising solar irradiance, (4) determining optical properties of cells, (5) measuring biomass, (6) characterising vertical distribution of cells, (7) characterising abiotic impurities, (8) surface anisotropy, (9) measuring indirect albedo feedbacks, and (10) measurement and instrument configurations. This paper aims to provide a broad audience of glaciologists and biologists with an overview of radiative transfer and albedo that could support future experimental design.

Short summary
Biological growth darkens snow and ice, causing it to melt faster. This is often referred to as bioalbedo. Quantifying bioalbedo has not been achieved because of difficulties in isolating the biological contribution from the optical properties of ice and snow, and from inorganic impurities in field studies. In this paper, we provide a physical model that enables bioalbedo to be quantified from first principles and we use it to guide future field studies.