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

Nishino, Shigeto; Kikuchi, Takashi; Fujiwara, Amane; Hirawake, Toru; Aoyama, Michio

doi:10.5194/bg-13-2563-2016

Cited by 54 publications

(33 citation statements)

References 53 publications

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“…rPWW in summertime is overlain by fresher and warmer water from sea ice melt, thus isolated from the surface by a density barrier (Gong & Pickart, 2015;Woodgate et al, 2005). The shelf is highly productive in spring through summer, at which time nutrients are drawn down in the surface layer and regenerated in the subsurface, with a commensurate consumption of oxygen ( Figure 4; Lowry et al, 2015;Nishino et al, 2016). rPWW thus accumulates nutrients and AOU in summer ( Figure 4).…”

Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

“…Conversely, in winter, salinization from sea ice formation results in an isohaline water column with the salinity and temperature characteristics of PWW (Figure 4; Woodgate et al, 2005). Although sea ice cover substantially curtails gas exchange with the atmosphere (Butterworth & Miller, 2016), a few published data indicate that O 2 concentrations on the Chukchi shelf in winter are at~90% of saturation (Nishino et al, 2016), suggesting sufficient exchange to counter any substantial O 2 consumption by respiration. The O 2 concentrations in wintertime shelf PWW are thus not sufficiently low to explain its depletion in PWW downstream.…”

Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

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On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

et al. 2018

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Nitrogen is a limiting nutrient for primary production in the western Arctic Ocean. Measurements of the nitrogen (15N/14N) and oxygen (18O/16O) isotope ratios of nitrate in the southeastern Beaufort Sea provide insight into biogeochemical cycling of nitrogen in the western Arctic Ocean. Nitrate O isotope ratios in the Pacific halocline evidence a highly regenerated reservoir. Coincident peaks in nutrient concentrations and reduced dissolved oxygen concentrations suggest that nitrate accrues from organic matter remineralization in bottom waters of the Chukchi shelf and that these ventilate the basin predominantly in summer, when isolated from the atmosphere. Preformed nitrate in Pacific Winter Water lacks 18O/16O elevation from nitrate assimilation, contrasting with preformed nitrate in other ocean regions. A reactive N deficit and elevated nitrate N isotope ratios in the Pacific halocline further indicate substantial N loss to coupled nitrification‐denitrification in shelf sediments upstream. In the Atlantic Water below, nitrate isotope ratios identify two distinct waters entering the Arctic at Fram Strait, from (1) the surface West Spitsbergen Current, bearing isotopic signatures akin to North Atlantic waters, and (2) deeper inflows of waters ventilated in the Nordic Seas, transporting nitrate O isotope ratios indicative of regenerated nitrate. Poorly ventilated Canada Basin Deep Water shows evidence of nominal accrual of remineralized products, and nitrate isotope ratios suggest an influence of slow benthic denitrification on the sea floor. The observations reveal that shelf processes have a disproportionate influence on tracer properties of the Pacific halocline, while those in Atlantic Water are dominated by processes in the Nordic Seas.

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Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

et al. 2018

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“…According to Nishino et al (2016), a temperature of 4°C was set as thresholds for the ACW, the BSW, and the AW in this study. Water masses with a temperature higher than 4°C, including the ACW, were defined as warm water in this study.…”

Section: Definition Of Water Mass With Temperature and Salinitymentioning

confidence: 99%

Characterization of the Water Masses in the Shelf Region of the Bering and Chukchi Seas With Fluorescent Organic Matter

et al. 2019

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Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOM H ) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOM H as a third parameter of water mass analysis. The levels of FOM H were different among specific water masses in the region, and FOM H seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOM H implies that FOM H estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOM H levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations. Plain Language Summary The continental shelves of the northern Bering Sea and the ChukchiSea are known to be the area characterized by a high abundance of organisms from phytoplankton to marine mammals and seabirds. Such a high density of marine organisms is sustained by intensive primary production induced by inputs of enough nutrients. The inputs of nutrients to the region are possibly sensitive to climate change. To project future changes in nutrient supply to the region, the present mechanism of nutrient supply should be quantitatively understood. To date, however, the mechanism is poorly determined because the origin and modification of water masses that convey nutrients have not been well understood. This study measured humic-like fluorescent organic matter, products during the decay and transformation of biogenic remains, in addition to temperature and salinity by in situ sensors to characterize the water masses in the shelf region of the Bering and Chukchi Seas during the early summer of 2013. The levels were clearly different among water masses defined by temperature and salinity and characterized by different concentrations of nutrients, indicating that humic-like fluorescent organic matter is useful to refine the water masses in the region for quantitative understanding of the mechanism of nutrient supply.

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“…Total alkalinity of the water was measured using a spectrophotometric system (NIPPON ANS, Inc.) and the scheme of Yao and Byrne (1998). We calculated the fraction of freshwater contents (i.e., the sea ice meltwater, f SIM , and other freshwater, f OF , carried by the water of Pacific origin) from the values of total alkalinity and salinity following the method of Yamamoto-Kawai et al (2005), and the endmembers of salinity and total alkalinity were obtained from Nishino et al (2016). We conducted the measurement of vertical profile of PAR using a PRR-800 spectroradioimeter with a freefall profiler (Biospherical Inc.).…”

Section: Cruise Summary and Water Samplingmentioning

confidence: 99%

Changes in phytoplankton community structure during wind-induced fall bloom on the central Chukchi shelf

et al. 2018

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The recent increasing of atmospheric turbulence has had considerable impact on the oceanic environment and ecosystems of the Arctic. To understand its effect on phytoplankton community structure, a Eulerian fixed-point observation (FPO) was conducted on the Chukchi shelf in fall 2013. Temporal and vertical distributions of the phytoplankton community were inferred from algal pigment signatures. A strong wind event (SWE) occurred during the observation term, and significant convection supplied nutrients from the bottom layer to the surface. Before the SWE, pigment composition in the warmer, less saline, and nutrient-poor surface waters was diverse with low concentration of chlorophyll-a (chla). Vertical mixing induced by the SWE weakened the stratification and brought sufficient nutrients to enhance diatom-derived pigment concentrations (e.g., fucoxanthin and chlc3), suggesting increases in diatoms. We also developed a model to predict the distribution of major phytoplankton pigment/chla ratios using a profiling multi-wavelength fluorometer (Multi-Exciter) with higher spatio-temporal resolution. The Multi-Exciter also captured changes in pigment composition with environmental changes at the FPO site and at four observation sites 16 km from the location of the FPO. Furthermore, we investigated the change in grazing rates of the major Arctic copepod Calanus glacialis copepodid stage five to assess the interaction between primary and secondary producers during the fall bloom. Increased diatom biomass caused a significant increase in the grazing rate on microphytoplankton (> 20 µm) and a decrease on nanophytoplankton (2-20 µm), indicative of a strong cascade effect because of the reduction of microzooplankton due to the grazing from C. glacialis. We conclude that SWEs during fall might affect food webs via the alternation of seasonal succession of phytoplankton community structure.

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

Abstract: 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

Cited by 54 publications

References 53 publications

On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

Characterization of the Water Masses in the Shelf Region of the Bering and Chukchi Seas With Fluorescent Organic Matter

Changes in phytoplankton community structure during wind-induced fall bloom on the central Chukchi shelf

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