Seasonal Evolution of Light Transmission Distributions Through Arctic Sea Ice

Abstract

Light transmission through sea ice is a critical process for energy partitioning at the polar atmosphere‐ice‐ocean boundary. Transmission of sunlight strongly impacts sea ice melting by absorption, as well as heat deposition, and primary productivity in the upper ocean. While earlier observations relied on a limited number of point observations, the recent years have seen an increase in spatially distributed light measurements underneath sea ice using remotely operated vehicles covering a wide range of ice conditions. These measurements allow us to reconstruct the seasonal evolution of the spatial variability in light transmission. Here we present measurements of sea ice light transmittance distributions from 6 years of Arctic under‐ice remotely operated vehicle operations. The data set covers the entire melt period of Central Arctic sea ice. Data are combined into a pseudo time series describing the seasonal evolution of the spatial variability of sea ice optical properties from spring to autumn freezeup. In spring, snowmelt increases light transmission continuously, until a secondary mode originating from translucent melt ponds appears in the histograms of light transmittance. This secondary mode persists long into autumn, before snowfall reduces overall light levels again. Comparison to several autonomous time series measurements from single locations confirms the detected general patterns of the seasonal evolution of light transmittance variability. This also includes characteristic spectral features caused by biological processes at the ice underside. The results allow for the evaluation of three different light transmittance parameterizations, implying that light transmission in current ice‐ocean models may not be accurately represented on large scales throughout all seasons while ice thickness alone is a poor predictor of light transmittance.

Environmental drivers of under-ice phytoplankton bloom dynamics in the Arctic Ocean

“…Since 1979, the summer sea-ice extent has declined by >40%, with first-year ice replacing the once prevalent multiyear ice pack (AMAP, 2017). Sea-ice melt is beginning earlier in the year while freeze-up is delayed; consequently, more solar radiation is reaching the upper ocean now than it has in the past (Nicolaus et al, 2012;Arndt and Nicolaus, 2014;Katlein et al, 2019). Such modifications result in a substantially thinner sea-ice cover that is more prone to deformation…”

Spatial Heterogeneity as a Key Variable Influencing Spring-Summer Progression in UVR and PAR Transmission Through Arctic Sea Ice

“…From the melt pond onset on 15 June, wet patches on the ice surface increased, which led to a rapid increase inT(PAR) until maximum transmittance values were reached during the largest spread of surface melt water on 22 June. Another study by Katlein et al (2019) of the seasonal evolution of light transmission through mobile Arctic sea ice observed a similar increase of integratedT(320-900nm) from 0.01 through melting snow-covered ice in June to 0.25 through ponded ice in August. Katlein et al (2019) also note that spatial variability ofT(320-900nm) was highest after the melt pond onset.…”

“…Another study by Katlein et al (2019) of the seasonal evolution of light transmission through mobile Arctic sea ice observed a similar increase of integratedT(320-900nm) from 0.01 through melting snow-covered ice in June to 0.25 through ponded ice in August. Katlein et al (2019) also note that spatial variability ofT(320-900nm) was highest after the melt pond onset. This widespread ponding in stage II due to the disappearance of snow matches as hypothesized the start of the ice ablation season described elsewhere (Eicken et al, 2002;Polashenski et al, 2012;Landy et al, 2014).…”

“…To capture regional variability of light transmission through sea ice and the underlying water column, remotely operated vehicles (ROVs) equipped with different sensor arrays are more frequently used. ROVs were deployed to perform large-scale irradiance measurements beneath landfast sea ice and moving pack ice in the Arctic Ocean (Nicolaus and Katlein, 2013;Katlein et al, 2015Katlein et al, , 2019, West Greenlandic fjord (Lund-Hansen et al, 2018), and in the Weddell Sea (Arndt et al, 2017). The minimized disturbance caused by ROV-based measurements compared to traditional core-based point-sampling methods also enables repeated operations within the same area throughout the melt season (Nicolaus et al, 2012).…”

Interannual variability in Transpolar Drift ice thickness and potential impact of Atlantification

“…The importance of continuous measurements of Arctic SIT change is demonstrated by the implications these changes have on the Arctic summer sea ice energy and mass balance. Changing optical properties and thinning of sea ice allow increased penetration of solar energy into the ocean (Nicolaus et al, 2012;Katlein et al, 2019), with implications for ocean heat deposition (Perovich et al, 2007;Pinker et al, 2014) and primary productivity (Assmy et al, 2017). Intensified melt and thinning of Arctic sea ice also impact the pathways of sea ice from the major source regions on the Russian shelves.…”