Shigeto Nishino

Japan Agency for Marine-Earth Science Technology | JAMSTEC

The recent influx of microplastics into the Arctic Ocean may increase environmental stress on the western Arctic marine ecosystem, which is experiencing significant sea-ice loss due to global warming. Quantitative data on microplastics in the western Arctic Ocean are very limited, and the microplastic budget of the water column is completely unknow...

Nitrogen fixation is the major source of reactive nitrogen in the ocean and has been considered to occur specifically in low-latitude oligotrophic oceans. Recent studies have shown that nitrogen fixation also occurs in the polar regions and thus is a global process, although the physiological and ecological characteristics of polar diazotrophs are...

We measured dissolved radiocesium (¹³⁴Cs and ¹³⁷Cs) in surface seawater collected in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020. The radiocesium released from the accident of the Fukushima Dai-ichi nuclear power plant (FNPP1) in 2011 was still observed in these areas (∼2 Bq m⁻³ decay-correct...

Phytoplankton production in the Arctic Ocean is increasing due to global warming‐induced sea ice loss, which is generally assessed through satellite observations of surface chlorophyll. Here we show that a diatom bloom can occur near the seafloor rather than at the surface in the open Arctic Ocean. Light can reach the seafloor underlying nutrient‐r...

The Chukchi Sea is an increasing CO2 sink driven by rapid climate changes. Understanding the seasonal variation of air‐sea CO2 exchange and the underlying mechanisms of biogeochemical dynamics is important for predicting impacts of climate change on and feedbacks by the ocean. Here, we present a unique data set of underway sea surface partial press...

The Arctic Ocean is now facing dramatic environmental and ecosystem changes. In this context, an international multiship survey project was undertaken in 2020 to obtain current baseline data. For the first time, extremely low dissolved oxygen and acidified water were found in a fishable area of the western Arctic Ocean. The data suggested that the...

Rapid sea-ice retreat in the Arctic Ocean can promote the release of methane (CH4) from microbe and from sediment on the continental shelf. The released methane can be the cause or effect of strong climate feedback. Nevertheless, few observations have been reported of temporal changes of dissolved CH4 in the Arctic Ocean, especially in western coas...

Light condition, day length, and amount of incident sunlight vary widely with season in the Arctic. Absorption-based primary production (PP) models incorporate light absorption coefficients and photosynthetically active radiation (PAR); however, algorithm sensitivity to such parameters has not been investigated in the Arctic Ocean. Therefore, we as...

The Arctic Ocean has turned from a perennial ice-covered ocean into a seasonally ice-free ocean in recent decades. Such a shift in the air-ice-sea interface has resulted in substantial changes in the Arctic carbon cycle and related biogeochemical processes. To quantitatively evaluate how the oceanic CO2 sink responds to rapid sea ice loss and to pr...

Urea sinks are mainly associated with assimilation by phytoplankton. However, recent studies have shown that there is a process by which nitrifiers convert urea‐derived nitrogen (urea‐N) into nitrate. We examined these two processes in the shelf and off‐shelf regions of the Arctic Ocean. Urea concentration was high near the bottom in the shelf regi...

We review recent trends and projected future physical and chemical changes under climate change in transition zones between Arctic and Subarctic regions with a focus on the two major inflow gateways to the Arctic, one in the Pacific (i.e. Bering Sea, Bering Strait, and the Chukchi Sea) and the other in the Atlantic (i.e. Fram Strait and the Barents...

We studied time‐series fluxes of radiolarian particles collected by two sediment traps deployed at the eastern (Sta. NAP12t) and western (Sta. CAP12t) sides of the Chukchi Borderland in the Chukchi Sea from 04 October 2012 to 18 September 2013. In order to elucidate the contribution of radiolarian skeletons to the biogenic silica flux, a three‐dime...

Ocean–atmosphere gas exchange in the Arctic Ocean is sensitive to global warming because the decrease of sea‐ice covered area enhances the exchange. Melting sea ice affects the vertical transport of dissolved gases. Few reports of Arctic Ocean studies have described observations of dissolved N2O or temporal variation of sea‐to‐atmosphere N2O flux....

Ocean observation research theme under ArCS project, “Theme 4: Observational research on Arctic Ocean environmental changes”, aimed to elucidate the status and trends of ongoing Arctic Ocean environmental changes and to evaluate their impacts on Arctic marine ecosystem and the global climate system. For these purposes, we conducted field observatio...

Anadyr Strait, located at the northernmost reaches of the Bering Sea, influences pan‐Arctic climate through processes occurring in the strait as the Siberian Coastal Current carries water from the subpolar North Pacific Ocean into the western Arctic Ocean. A sharp sea surface temperature front near the Anadyr Strait segregates a tongue‐shaped mass...

The long‐distance migrations by marine fishes are difficult to track by field observation. Here, we propose a new method to track such migrations using stable nitrogen isotopic composition at the base of the food web (δ¹⁵NBase), which can be estimated by using compound‐specific isotope analysis. δ¹⁵NBase exclusively reflects the δ¹⁵N of nitrate in...

In general, strong wind events can enhance ocean turbulent mixing, followed by episodic nutrient supply to the euphotic zone and phytoplankton blooms. However, it is unclear whether such responses to strong winds occur in the ice‐free Canada Basin, where the seasonal pycnocline is strong and the nutricline is deep. In the present study, we monitore...

The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better underst...

The shallow Chukchi Sea is a gateway to the Arctic Ocean for Pacific‐origin waters. While a substantial portion of the Pacific‐origin waters flows through Barrow Canyon in the northeast corner of the Chukchi Sea, little is known on the hydrography of the surrounding regions in winter. We present profiles of wintertime hydrography on the Chukchi slo...

A coordinated effort involving trailblazing science—and icebreaking ships—from many nations is needed to fill gaps in our understanding of the Arctic Ocean and how it’s changing.

Nitrification is susceptible to changes in light and pH and, thus, could be influenced by recent sea ice reductions and acidification in the Arctic Ocean. We investigated the sensitivity of nitrification to light, pH, and substrate availability in a natural nitrifier community of the Arctic Ocean. Nitrification was active near the bottom of the she...

Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can exceed 100 cm s-1. Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the...

A drastic sea-ice reduction has been observed in the Pacific sector of the Arctic Ocean during the last few decades. However, it is still poorly understood how the future reduction in sea-ice cover will impact the microzooplankton communities within the Arctic marine ecosystems. To elucidate the relationship between hydrographic conditions and the...

Twenty-four repeat hydrographic transects occupied across Barrow Canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from July–October as well as the occurrence of upwelling. The mean sections revealed that the Alaskan coastal water is mainly confined to the eastern flank of the canyon, corresponding to a...

I concentrations were measured in surface waters and for two depth profiles in the Chukchi Borderland (74.5°N 162.0°W) and the southern Canada Basin (72.5°N 155.4°W) during the R/V Mirai cruises in 2014 and 2015. The ¹²⁹ I concentrations in the surface waters of the North Pacific Ocean and the Bering and Chukchi seas in 2014 and 2015 were 1.35 ± 0....

In the oligotrophic Arctic Ocean, previous studies have implied positive impacts of eddies on phytoplankton biomass. However, direct observations for estimating vertical nutrient fluxes in various parts of eddies are still lacking; these could explain the mechanism of high phytoplankton biomass associated with eddies compared to their surroundings....

We measured dissolved radiocesium (¹³⁴Cs and ¹³⁷Cs) in seawater collected in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2015 and 2017. The radiocesium released from the accident of the Fukushima Dai-ichi nuclear power plant (FNPP1) in March 2011 was still observed in the surface seawater of the western su...

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 communi...

Solar heating in summer in the Chukchi Sea was estimated using satellite-derived sea-ice concentration data and reanalysis shortwave radiation data. The shortwave radiation was validated by in-situ data obtained by the R/V Mirai and NCEP-CFSR/CFSv2 was found to reproduce in-situ data accurately compared with NCEP/NCAR Reanalysis 1 and ERA-Interim....

Recent Arctic warming and decreasing sea-ice can promote the release of methane (CH4), a greenhouse gas, from the Arctic Ocean, thereby providing a strong climate feedback. However, the dynamics of dissolved CH4 in the Arctic Ocean remain uncertain, especially in western areas. This report describes the horizontal and vertical distributions of conc...

In September 2013, we observed an expanse of surface water with low CO2 partial pressure (pCO2sea) (< 200 µatm) in the Chukchi Sea of the western Arctic Ocean. The large undersaturation of CO2 in this region was the result of massive primary production after the sea-ice retreat in June and July. In the surface of the Canada Basin, salinity was low...

The eastern Bering Sea has a vast continental shelf, which contains various endangered marine mammals and large fishery resources. Recently, high numbers of toxic A. tamarense resting cysts were found in the bottom sediment surface of the eastern Bering Sea shelf, suggesting that the blooms have recently occurred. However, little is known about the...

Winter subsurface transport of the Pacific-origin warm water toward the Arctic Chukchi Borderland located west of the Canada Basin was investigated by mooring measurements and modeling analyses. In mid-winter or spring of 2011-2014, subsurface warming signals under sea ice were detected by the multi-year bottom-tethered mooring data in the Chukchi...

In September 2013, we observed an expanse of surface water with low CO2 partial pressure (pCO2sea) (2 in this region was the result of massive primary production after the sea-ice retreat in June and July. In the surface of the Canada Basin, salinity was low (pCO2sea was closer to the air–sea CO2 equilibrium (~ 360 μatm). From the relationships bet...

Species distributions are changing with various rates and directions in response to recent global warming. The velocity of sea surface temperature (SST) has been used to predict species migration and persistence as an expectation of how species track their thermal niches; however, several studies have found that evidence for species shifts has devi...

We measured radiocesium (¹³⁴Cs and ¹³⁷Cs) in seawater from the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2013 and 2014. Fukushima-derived ¹³⁴Cs in surface seawater was observed in the western subarctic area and Bering Sea but not in the Arctic Ocean. Vertical profile of ¹³⁴Cs in the Canada Basin of the Arcti...

A high abundance of resting cysts of the toxic dinoflagellate Alexandrium tamarense was recently reported in the vast continental shelf of the Chukchi Sea in the Arctic Ocean, suggesting that the species is widespread in the shelf. Nevertheless, little is known about the occurrence of A. tamarense vegetative cells in the water column of the arctic....

Heterotrophic bacterial abundance and production, dissolved free amino acid (DFAA) and dissolved combined amino acid (DCAA) concentrations, and other microbial parameters were determined for seawater samples collected at a fixed station (maximum water depth, 56 m) deployed on the Chukchi Sea Shelf, in the western Arctic Ocean, during a 16-day perio...

Distribution of calcium carbonate saturation state (Ω) was observed in the Chukchi Sea in autumn 2012 and early summer 2013. Ω in bottom water ranged from 0.3 to 2.0 for aragonite and from 0.5 to 3.2 for calcite in 2012. In 2013, Ω in bottom water was 1.1–2.8 for aragonite and 1.7–4.4 for calcite. Aragonite and calcite undersaturation was found in...

Distributions of trace metals (Mn, Fe, Ni, Zn and Cd) in the western Arctic Ocean (Chukchi Sea and Canada Basin) in September 2012 were investigated to elucidate the mechanisms behind the transport of these metals from the Chukchi Shelf to the Canada Basin. Filtered (< 0.22 μm) and unfiltered seawater samples were analyzed to determine dissolved (D...

Simultaneous observations of atmospheric potential oxygen (APO=O2+1.1×CO2) and air-sea O2 flux, derived from dissolved oxygen in surface seawater, were carried out onboard the research vessel MIRAI in the northern North Pacific and the Arctic Ocean in the autumns of 2012-2014. A simulation of the APO was also carried out using a three-dimensional a...

The Arctic Ocean is known to be quiescent in terms of turbulent kinetic energy (TKE) associated with internal waves. To investigate the current state of TKE in the seasonally ice-free Chukchi Plateau, Arctic Ocean, this study performed a 3-week, fixed-point observation (FPO) using repeated microstructure, hydrographic, and current measurements in S...

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 decr...

We produced 204 monthly maps of the air–sea CO2 flux in the Arctic north of 60°N, including the Arctic Ocean and its adjacent seas, from January 1997 to December 2013 by using a self-organizing map technique. The partial pressure of CO2 (pCO2) in surface water data were obtained by shipboard underway measurements or calculated from alkalinity and t...

Distribution of calcium carbonate saturation state (Ω) was observed in bottom waters of the Chukchi Sea in autumn 2012 and early summer 2013. Aragonite and calcite undersaturation were found in high productivity regions in autumn 2012 but not in early summer 2013. Comparison with other parameters has indicated that biological processes -respiration...

Spatial and temporal variations in major phytoplankton populations such as diatoms in the changing Arctic Ocean have been well studied, whereas only a few monitoring studies have been conducted on minor siliceous flagellates. To discern the relationship between hydrographic conditions and the spatio-temporal distribution of silicoflagellates, ebrid...

Increased understanding on how marine species shift their distribution is required for effective conservation of fishery resources under climate change. Previous studies have often predicted distributional shifts of fish using satellite derived sea surface temperature (SST). However, SST may not fully represent the changes in species distribution t...

Most of anthropogenic 129I in marine environment are due to discharge from the nuclear fuel reprocessing facilities at Sellafield (U.K.) and La Hague (France) for past few decades. The discharge raised 129I concentration in seawaters in the North Atlantic and Arctic Oceans to more than 109 atoms L-1, which is two orders of magnitude higher than tha...

This report describes surface water temperature measurements obtained by an autonomous observing instrument “UpTempO” as a part of RV Mirai Arctic cruise in 2014, MR14-05. The UpTempO is a drifting buoy consisting of an underwater thermistor chain, carrying 16 thermistors and 3 pressure sensors, and a surface floating unit for Iridium satellite com...

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 fall blooms with high chlorophyll a concentrations. Turbidity increased and dissolved oxygen decrea...

In summer 2012, we measured activity concentration of radiocesium in surface seawater collected in the Arctic Ocean, Bering Sea, western Pacific Ocean, and Antarctic Ocean. The radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011 was found in the Bering Sea and western North Pacific between 25°N and 63°N, which...

A table list of our radiocesium data is attached as an electric supplementary file

The future conditions of Arctic sea ice and marine ecosystems are of interest not only to climate scientists, but also to economic and governmental bodies. However, the lack of widespread, year-long biogeochemical observations remains an obstacle to understanding the complicated variability of the Arctic marine biological pump. Here we show an earl...

Timing of sea ice retreat (TSR) as well as cell size of primary producers (i.e., phytoplankton) plays crucial roles in seasonally ice-covered marine ecosystem. Thus, it is important to monitor the temporal and spatial distribution of phytoplankton community size structure. Prior to this study, an ocean color algorithm has been developed to derive p...

We conducted a shipboard observation over the Chukchi Sea and the Canada Basin in the western Arctic Ocean in September and October 2012 to obtain vertical distributions of four volatile organic iodine compounds (VOIs) in seawater. VOIs are believed to play a role in ozone destruction in the troposphere and lower stratosphere. The VOIs observed in...

The species composition of Arctic zooplankton differs greatly from that of the zooplankton of the North Pacific and Bering Sea. Particularly with greater warming from sea-ice retreat, the reproduction of North Pacific species transported into the Chukchi Sea and beyond may lead to changes in the Arctic pelagic ecosystem. We report the egg productio...

Transparent exopolymer particles (TEP), particulate organic carbon (POC), and particles (size range: 5.2–119 μm) as determined by laser in situ scattering and transmissometry (LISST) were measured in the water column from the Chukchi Sea to the Canada Basin in the western Arctic Ocean, during the late summer of 2012. In general, the percentages of...

To evaluate the effect of atmospheric turbulence on a marine ecosystem, high-frequency samplings (two to four times per day) of a mesozooplankton community and the gut pigment of dominant copepods were performed at a fixed station in the Chukchi Sea from 10 to 25 September 2013. During the study period, a strong wind event (SWE) was observed on 18...

An increase in atmospheric turbulence in the Chukchi Sea due to the recent drastic sea-ice reduction during summer months has been reported. The importance of the effects of this atmospheric turbulence on the marine ecosystem in this region, however, is not fully understood. To evaluate the effects of atmospheric turbulence on the marine ecosystem,...

Isoprene (C5H8) and three volatile organic iodine compounds (VOIs: CH3I, C2H5I, and CH2ClI) in surface seawater were measured in the western Arctic, Northwest Pacific, Indian, and Southern Oceans during the period 2008–2012. These compounds are believed to play an important role in the marine atmospheric chemistry after their emission. The measurem...

Over the past few decades, sea ice retreat during summer has been enhanced in the Pacific sector of the Arctic basin, likely due in part to increasing summertime heat flux of Pacific-origin water from the Bering Strait. Barrow Canyon, in the northeast Chukchi Sea, is a major conduit through which the Pacific-origin water enters the Arctic basin. Th...

Phytoplankton production measurements were conducted in the northeast Chukchi Sea and western Canada Basin in the summer season, from 20 July to 10 August 2010, using a 13C–15N dual tracer technique. The daily carbon uptake rate in the northeast Chukchi Sea in 2010 was extremely low, with a mean of 29.8 mg C m−2 d−1 (SD=17.6 mg C m−2 d−1). Regional...

To evaluate the effect of atmospheric turbulence on a marine ecosystem, high-frequency samplings (two to four times per day) of a mesozooplankton community and the gut pigment of dominant copepods were performed at a fixed station in the Chukchi Sea from 10 to 25 September 2013. During the study period, a strong wind event (SWE) was observed on 18...