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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 8
Biogeosciences, 13, 2563-2578, 2016
https://doi.org/10.5194/bg-13-2563-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Catastrophic reduction of sea ice in the Arctic Ocean...

Biogeosciences, 13, 2563-2578, 2016
https://doi.org/10.5194/bg-13-2563-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 29 Apr 2016

Research article | 29 Apr 2016

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

Shigeto Nishino1, Takashi Kikuchi1, Amane Fujiwara1, Toru Hirawake2, and Michio Aoyama3,4 Shigeto Nishino et al.
  • 1Institute of Arctic Climate and Environment Research, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
  • 2Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
  • 3Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
  • 4Institute of Environmental Radioactivity, Fukushima University, Fukushima, Japan

Abstract. We analysed mooring and ship-based hydrographic and biogeochemical data obtained from a Hope Valley biological hotspot in the southern Chukchi Sea. The moorings were deployed from 16 July 2012 to 19 July 2014, and data were captured during spring and autumn blooms with high chlorophyll a concentrations. Turbidity increased and dissolved oxygen decreased in the bottom water at the mooring site before the autumn bloom, suggesting an accumulation of particulate organic matter and its decomposition (nutrient regeneration) at the bottom. This event may have been a trigger for the autumn bloom at this site. The bloom was maintained for 1 month in 2012 and for 2 months in 2013. The maintenance mechanism for the autumn bloom was also studied by hydrographic and biogeochemical surveys in late summer to autumn 2012 and 2013. Nutrient-rich water from the Bering Sea supplied nutrients to Hope Valley, although a reduction in nutrients occurred in 2012 by the influence of lower-nutrient water that would have remained on the Chukchi Sea shelf. In addition, nutrient regeneration at the bottom of Hope Valley could have increased nutrient concentrations and explained 60% of its nutrient content in the bottom water in the autumn of 2012. The high nutrient content with the dome-like structure of the bottom water may have maintained the high primary productivity via the vertical nutrient supply from the bottom water, which was likely caused by wind-induced mixing during the autumn bloom. Primary productivity was 0.3gCm−2d−1 in September 2012 and 1.6gCm−2d−1 in September 2013. The lower productivity in 2012 was related to strong stratification caused by the high fraction of surface sea ice meltwater.

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We analysed mooring and ship-based data obtained from a biological hotspot in the southern Chukchi Sea. Mooring data were collected for the first time in this site and were captured during spring and autumn blooms with high chlorophyll a concentrations. The data suggest that a dome-like structure of the bottom water and nutrient regeneration at the bottom play important roles in maintaining the autumn bloom of the biological hotspot.
We analysed mooring and ship-based data obtained from a biological hotspot in the southern...
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