Characteristics of late summer Arctic brash sea ice and its melting effect on the surface-water biogeochemistry of the Chukchi Shelf and Canada Basin
Author:
Akino Ryota1, Nomura Daiki123, Sahashi Reishi1, Tozawa Manami1, Hatta Mariko4, Matsuno Kohei13, Endo Wakana1, Shiozaki Takuhei5, Kawakami Tatsuya1, Ito Masato6, Murata Akihiko4, Fujiwara Amane4
Affiliation:
1. 1Graduate School/Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan 2. 2Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Hokkaido, Japan 3. 3Arctic Research Center, Hokkaido University, Sapporo, Hokkaido, Japan 4. 4Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan 5. 5Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan 6. 6National Institute of Polar Research, Tachikawa, Tokyo, Japan
Abstract
To understand the impact of the melting of late summer Arctic brash ice on the surface waters of the Chukchi Sea, we collected sea-ice samples during 2021. Floating sea ice was collected by a wire mesh pallet cage from the side of the R/V Mirai. We measured physical and biogeochemical parameters such as salinity, oxygen stable isotopic ratios, turbidity, and concentrations of chlorophyll-a and nutrients. The samples of brash ice were multiyear ice based on satellite back-trajectory analysis. Comparison of nutrient concentrations in brash ice with those of seawater samples from the temperature minimum layer similar to the water in the sea ice originated suggested that the characteristics of the brash ice were greatly affected by biogeochemical processes such as remineralization. The extremely high turbidity and concentrations of chlorophyll-a observed in the brown/green ice samples reflected the impact of sediment as well as the influence of biological activities. The N:P ratios were less than 1 because of the high phosphate concentrations, even though the ammonium concentrations were high. We hypothesized that this low N:P ratio reflected the combined effects of the accumulation of nutrients due to remineralization in the biofilm and differences of remineralization rate and adsorption features of nitrogen and phosphorus. Based on the high nitrate and ammonium concentrations in the sea-ice samples, we postulated a marked impact of sea-ice meltwater on the nitrogen cycle in the nitrate-depleted surface waters of the Chukchi Sea during late summer. We estimated that meltwater nitrogen could support 0.3%–2.6% of primary production in the northern Chukchi Sea. Our results suggest that high-turbidity ice will play an important role as a source of nutrients to the ocean during melting of sea ice, and understanding its distribution, amount, and geochemical characteristics is vital.
Publisher
University of California Press
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