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Windows in Arctic sea ice: Light transmission and ice algae in a refrozen lead
Author(s) -
Kauko Hanna M.,
Taskjelle Torbjørn,
Assmy Philipp,
Pavlov Alexey K.,
Mundy C. J.,
Duarte Pedro,
FernándezMéndez Mar,
Olsen Lasse M.,
Hudson Stephen R.,
Johnsen Geir,
Elliott Ashley,
Wang Feiyue,
Granskog Mats A.
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003626
Subject(s) - sea ice , arctic ice pack , melt pond , antarctic sea ice , oceanography , environmental science , cryosphere , colored dissolved organic matter , lead (geology) , atmospheric sciences , geology , chemistry , phytoplankton , geomorphology , nutrient , organic chemistry
The Arctic Ocean is rapidly changing from thicker multiyear to thinner first‐year ice cover, with significant consequences for radiative transfer through the ice pack and light availability for algal growth. A thinner, more dynamic ice cover will possibly result in more frequent leads, covered by newly formed ice with little snow cover. We studied a refrozen lead (≤0.27 m ice) in drifting pack ice north of Svalbard (80.5–81.8°N) in May–June 2015 during the Norwegian young sea ICE expedition (N‐ICE2015). We measured downwelling incident and ice‐transmitted spectral irradiance, and colored dissolved organic matter (CDOM), particle absorption, ultraviolet (UV)‐protecting mycosporine‐like amino acids (MAAs), and chlorophyll a (Chl a ) in melted sea ice samples. We found occasionally very high MAA concentrations (up to 39 mg m −3 , mean 4.5 ± 7.8 mg m −3 ) and MAA to Chl a ratios (up to 6.3, mean 1.2 ± 1.3). Disagreement in modeled and observed transmittance in the UV range let us conclude that MAA signatures in CDOM absorption spectra may be artifacts due to osmotic shock during ice melting. Although observed PAR (photosynthetically active radiation) transmittance through the thin ice was significantly higher than that of the adjacent thicker ice with deep snow cover, ice algal standing stocks were low (≤2.31 mg Chl a m −2 ) and similar to the adjacent ice. Ice algal accumulation in the lead was possibly delayed by the low inoculum and the time needed for photoacclimation to the high‐light environment. However, leads are important for phytoplankton growth by acting like windows into the water column.