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Bonnie Light

Chair, Polar Science Center & Senior Principal Physicist

Affiliate Associate Professor, Atmospheric Sciences





Department Affiliation

Polar Science Center


B.S. Engineering, Cornell University, 1986

M.S. Electrical Engineering, University of Maryland - College Park, 1990

M.S. Atmospheric Sciences, University of Washington - Seattle, 1995

Ph.D. Atmospheric Sciences, University of Washington - Seattle, 2000


Earth's Frozen Oceans: Properties and Importance of Sea Ice

Bonnie Light and Maddie Smith present a webinar for the National Ocean Science Bowl (NOSB) Professional Development Program. The NOSB is an academic competition for high school students. This webinar by Light and Smith provides subject matter expertise to NOSB coaches, organizers, and student competitors on the 2021 theme: Plunging Into Our Polar Oceans.

22 Jan 2021

MOSAiC: Multidisciplinary drifting Observatory for the Study of Arctic Climate

Bonnie Light's video tutorial on Sunlight and Arctic Sea Ice, made for the MOSAiC "Frozen in the Ice: Exploring the Arctic" series.

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19 Mar 2020

The goal of the MOSAiC expedition is to take the closest look ever at the Arctic as the epicenter of global warming and to gain insights that are key to understanding global climate change. Hundreds of researchers from 20 countries will work from the icebreaker Polarstern as it is frozen into and drifts with the sea ice for 1 year, 2019–2020. Bonnie Light joins the 5th leg of the expedition during summer 2020 to study the optical properties of melting sea ice.

Extreme Summer Melt: Assessing the Habitability and Physical Structure of Rotting First-year Arctic Sea Ice

Sea ice cover in the Arctic during summer is shrinking and thinning. The melt season is lengthening and the prevalence of "rotten" sea ice is increasing.

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30 Jul 2015

A multidisciplinary team of researchers is making a series of three monthly (May, June, and July) expeditions to Barrow, AK. They are measuring the summertime melt processes that transform the physical properties of sea ice, which in turn transform the biological and chemical properties of the ice habitat.

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2000-present and while at APL-UW

Evolution of the microstructure and reflectance of the surface scattering layer on melting, level Arctic sea ice

Macfarlane, A.R., R. Dadic, M.M. Smith, B. Light, M. Nicolaus, H. Henna-Reetta, M. Webster, F. Linhardt, S. Hammerle, and M. Schneebeli, "Evolution of the microstructure and reflectance of the surface scattering layer on melting, level Arctic sea ice," Elem. Sci. Anth., 11, doi:10.1525/elementa.2022.00103, 2024.

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6 Apr 2024

The microstructure of the uppermost portions of a melting Arctic sea ice cover has a disproportionately large influence on how incident sunlight is reflected and absorbed in the ice/ocean system. The surface scattering layer (SSL) effectively backscatters solar radiation and keeps the surface albedo of melting ice relatively high compared to ice with the SSL manually removed. Measurements of albedo provide information on how incoming shortwave radiation is partitioned by the SSL and have been pivotal to improving climate model parameterizations. However, the relationship between the physical and optical properties of the SSL is still poorly constrained. Until now, radiative transfer models have been the only way to infer the microstructure of the SSL. During the MOSAiC expedition of 2019–2020, we took samples and, for the first time, directly measured the microstructure of the SSL on bare sea ice using X-ray micro-computed tomography. We show that the SSL has a highly anisotropic, coarse, and porous structure, with a small optical diameter and density at the surface, increasing with depth. As the melting surface ablates, the SSL regenerates, maintaining some aspects of its microstructure throughout the melt season. We used the microstructure measurements with a radiative transfer model to improve our understanding of the relationship between physical properties and optical properties at 850 nm wavelength. When the microstructure is used as model input, we see a 10–15% overestimation of the reflectance at 850 nm. This comparison suggests that either a) spatial variability at the meter scale is important for the two in situ optical measurements and therefore a larger sample size is needed to represent the microstructure or b) future work should investigate either i) using a ray-tracing approach instead of explicitly solving the radiative transfer equation or ii) using a more appropriate radiative transfer model.

Effects of increasing the category resolution of the sea ice thickness distribution in a coupled climate model on Arctic and Antarctic sea ice mean state

Smith, M.M., M.M. Holland, A.A. Petty, B.Light, and D.A. Bailey, "Effects of increasing the category resolution of the sea ice thickness distribution in a coupled climate model on Arctic and Antarctic sea ice mean state," J. Geophys. Res., 127, doi:10.1029/2022JC019044, 2022.

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1 Oct 2022

Many modern sea ice models used in global climate models represent the subgrid-scale heterogeneity in sea ice thickness with an ice thickness distribution (ITD), which improves model realism by representing the significant impact of the high spatial heterogeneity of sea ice thickness on thermodynamic and dynamic processes. Most models default to five thickness categories. However, little has been done to explore the effects of the resolution of this distribution (number of categories) on sea-ice feedbacks in a coupled model framework and resulting representation of the sea ice mean state. Here, we explore this using sensitivity experiments in CESM2 with the standard 5 ice thickness categories and 15 ice thickness categories. Increasing the resolution of the ITD in a run with preindustrial climate forcing results in substantially thicker Arctic sea ice year-round. Analyses show that this is a result of the ITD influence on ice strength. With 15 ITD categories, weaker ice occurs for the same average thickness, resulting in a higher fraction of ridged sea ice. In contrast, the higher resolution of thin ice categories results in enhanced heat conduction and bottom growth and leads to only somewhat increased winter Antarctic sea ice volume. The spatial resolution of the ICESat-2 satellite mission provides a new opportunity to compare model outputs with observations of seasonal evolution of the ITD in the Arctic (ICESat-2; 2018–2021). Comparisons highlight significant differences from the ITD modeled with both runs over this period, likely pointing to underlying issues contributing to the representation of average thickness.

Arctic sea ice albedo: Spectral composition, spatial heterogeneity, and temporal evolution observed during the MOSAiC drift

Light, B., M.M. Smith, D.K. Perovich, M.A. Webster, M.M. Holland, F. Linhardt, I.A. Raphael, D. Clemens-Sewall, A.R. Macfarlane, P. Anhaus, and D.A. Bailey, "Arctic sea ice albedo: Spectral composition, spatial heterogeneity, and temporal evolution observed during the MOSAiC drift," Elem. Sci. Anth., 10, doi:10.1525/elementa.2021.000103, 2022.

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4 Aug 2022

The magnitude, spectral composition, and variability of the Arctic sea ice surface albedo are key to understanding and numerically simulating Earth’s shortwave energy budget. Spectral and broadband albedos of Arctic sea ice were spatially and temporally sampled by on-ice observers along individual survey lines throughout the sunlit season (April–September, 2020) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The seasonal evolution of albedo for the MOSAiC year was constructed from spatially averaged broadband albedo values for each line. Specific locations were identified as representative of individual ice surface types, including accumulated dry snow, melting snow, bare and melting ice, melting and refreezing ponded ice, and sediment-laden ice. The area-averaged seasonal progression of total albedo recorded during MOSAiC showed remarkable similarity to that recorded 22 years prior on multiyear sea ice during the Surface Heat Budget of the Arctic Ocean (SHEBA) expedition. In accord with these and other previous field efforts, the spectral albedo of relatively thick, snow-free, melting sea ice shows invariance across location, decade, and ice type. In particular, the albedo of snow-free, melting seasonal ice was indistinguishable from that of snow-free, melting second-year ice, suggesting that the highly scattering surface layer that forms on sea ice during the summer is robust and stabilizing. In contrast, the albedo of ponded ice was observed to be highly variable at visible wavelengths. Notable temporal changes in albedo were documented during melt and freeze onset, formation and deepening of melt ponds, and during melt evolution of sediment-laden ice. While model simulations show considerable agreement with the observed seasonal albedo progression, disparities suggest the need to improve how the albedo of both ponded ice and thin, melting ice are simulated.

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In The News

Freezer Lab Work Reveals Sea Ice Properties of MOSAiC Ice Cores

Sea Ice Portal — Alfred Wegener Institut

A group of scientists from four international partner institutions and a filmmaker have come to Bremerhaven to process and analyze sea-ice cores samples from the MOSAiC (2019–2020) expedition. The researchers aim to better understand the growth history of the sea ice and its internal optical properties. This will help them better understand the seasonal changes of the ice cover over its lifetime.

27 Jan 2023

Fact check: Cherry-picked data behind misleading claim that Arctic sea ice hasn't declined since 1989

USA Today, Kate S. Petersen

Arctic sea ice minimum extent — its size at the end of the summer melt — has declined 13% per decade since the late 1970s, according to the National Snow & Ice Data Center and NASA data. However, some social media posts use images from the National Snow & Ice Data Center's public online data tool, Sea Ice Index, to suggest that Arctic sea ice extent has not meaningfully changed in decades.

30 May 2022

Fact check: NASA did not deny warming or say polar ice has increased since 1979

USA Today, Kate Petersen

NASA researchers have documented the loss of trillions of tons of ice from Earth's poles due to human-driven climate change. Citing published reports from the Polar Science Center and other sources, popular social media memes claiming an increase in polar ice since 1979 are swatted down.

21 Jan 2022

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