Under-Ice Light Field in the Western Arctic Ocean During Late Summer

Frontiers in Earth Science

Lovro Valcic¹  Alia L. Khan²  Indea Rogers³  Marcel Nicolaus⁴  Giulia Castellani⁴  Gaëlle Veyssière⁵  Jeremy Wilkinson⁵  Eun-Jin Yang⁶  Joo-Hong Kim⁶  Jinyoung Jung⁶  Julienne C. Stroeve⁸  Frank Kauker⁹  Michael Karcher⁹  Alexander Hayward^1,10 

[1] 0Bruncin, Zagreb, Croatia;1Western Washington University, Department of Environmental Sciences, Bellingham, WA, United States;2The George Washington University, Washington, WA, United States;Alfred Wegener Institute, Bremerhaven, Germany;British Antarctic Survey, Cambridge, United Kingdom;Korea Polar Research Institute, Yeonsu-gu, Incheon, SouthKorea;National Institute of Water and Atmospheric Research, Wellington, New Zealand;National Snow and Ice Data Center, University of Colorado, CO, Boulder, United States;O.A.Sys-Ocean Atmosphere Systems GmbH, Hamburg, Germany;The University of Otago, Dunedin, New Zealand;University College London, Earth Science Department, London, United Kingdom;University of Manitoba, Centre for Earth Observation Science, Winnipeg, MB, Canada;

关键词: transmittance;    arctic;    late summer;    first-year ice;    ice extinction coefficient;    under-ice irradiance;   

DOI  :  10.3389/feart.2021.643737

来源: DOAJ

【 摘 要 】

The Arctic is no longer a region dominated by thick multi-year ice (MYI), but by thinner, more dynamic, first-year-ice (FYI). This shift towards a seasonal ice cover has consequences for the under-ice light field, as sea-ice and its snow cover are a major factor influencing radiative transfer and thus, biological activity within- and under the ice. This work describes in situ measurements of light transmission through different types of sea-ice (MYI and FYI) performed during two expeditions to the Chukchi sea in August 2018 and 2019, as well as a simple characterisation of the biological state of the ice microbial system. Our analysis shows that, in late summer, two different states of FYI exist in this region: 1) FYI in an enhanced state of decay, and 2) robust FYI, more likely to survive the melt season. The two FYI types have different average ice thicknesses: 0.74 ± 0.07 m (N = 9) and 0.93 ± 0.11 m (N = 9), different average values of transmittance: 0.15 ± 0.04 compared to 0.09 ± 0.02, and different ice extinction coefficients: 1.49 ± 0.28 and 1.12 ± 0.19 m−1. The measurements performed over MYI present different characteristics with a higher average ice thickness of 1.56 ± 0.12 m, lower transmittance (0.05 ± 0.01) with ice extinction coefficients of 1.24 ± 0.26 m−1 (N = 12). All ice types show consistently low salinity, chlorophyll a concentrations and nutrients, which may be linked to the timing of the measurements and the flushing of melt-water through the ice. With continued Arctic warming, the summer ice will continue to retreat, and the decayed variant of FYI, with a higher scattering of light, but a reduced thickness, leading to an overall higher light transmittance, may become a more relevant ice type. Our results suggest that in this scenario, more light would reach the ice interior and the upper-ocean.

【 授权许可】

Unknown