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Nutrient distributions associated with snow and sediment-laden layers in sea ice of the southern Sea of Okhotsk

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Title: Nutrient distributions associated with snow and sediment-laden layers in sea ice of the southern Sea of Okhotsk
Authors: Nomura, Daiki Browse this author →KAKEN DB
Nishioka, Jun Browse this author →KAKEN DB
Granskog, Mats A. Browse this author
Krell, Andreas Browse this author
Matoba, Sumito Browse this author →KAKEN DB
Toyota, Takenobu Browse this author →KAKEN DB
Hattori, Hiroshi Browse this author →KAKEN DB
Shirasawa, Kunio Browse this author →KAKEN DB
Keywords: Sea ice
Sea of Okhotsk
Issue Date: 20-Apr-2010
Publisher: Elsevier B.V.
Journal Title: Marine Chemistry
Volume: 119
Issue: 1-4
Start Page: 1
End Page: 8
Publisher DOI: 10.1016/j.marchem.2009.11.005
Abstract: Samples of first-year sea ice, snow and under-ice water were collected in the southern Sea of Okhotsk in mid-February 2007 and 2008 to elucidate the processes controlling nutrient concentrations in sea ice. Temperature, salinity, oxygen isotopic ratio (δ18O) and inorganic nutrient concentrations (NO3, NH4, NO2, PO4 and SiO2) were measured. Sea ice was categorized into four types; snow-ice, frazil ice, columnar ice and a mixture of granular and columnar ice, based on δ18O composition and ice texture. Frazil ice dominated the total ice thickness (52.8%), and columnar ice was sandwiched between frazil ice layers, indicating dynamic ice-growth processes such as rafting and ridging. Furthermore, the ice was banded by layers of particulate materials (sediment layers), which were frequently encountered during cruises. High NO3 and NH4 concentrations were found in snow and snow-ice implying that these were supplied from the atmosphere with snowfall and incorporated into the sea ice through snow-ice formation. In the sediment-laden layers, which were categorized as frazil ice, NO2, PO4 and SiO2 concentrations were highest of all the ice types and considerably enriched compared to parent seawater, suggesting the remineralization of the particulate organic matter. On the other hand, NO3 concentrations in sediment layers were low (depleted), leading to extremely low N (NO3 + NH4 + NO2): P ratios in sediment layers, from 0.2 to 0.8, with respect to that of under-ice water or Redfield ratio. These results suggest that in part of sediment-laden layers fixed-nitrogen was removed partially as molecular nitrogen (N2) from the sea ice environment by anaerobic nitrate reduction processes (denitrification) by denitrifying bacteria while adding phosphate from associated remineralization of organic phosphorus. The effect of melting of snow and sea ice is dilution for salinity, NO3 and SiO2, no change in NO2 and PO4, and a minor enrichment for NH4 in the mixed layer in spring and early summer. This suggests that snow/ice meltwater with different nutrient ratios than in under-ice water/Redfield ratio is supplied to under-ice water during melt season in April/May in southern Sea of Okhotsk. However, the impact of sediment-laden sea ice cannot be assessed at this point.
Type: article (author version)
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 白澤 邦男

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