Motoyo Itoh's research while affiliated with Japan Agency for Marine-Earth Science Technology and other places
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Publications (73)
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...
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...
The anti-cyclonic Beaufort Gyre is the dominant circulation of the Canada Basin and the largest freshwater reservoir in the Arctic Ocean. Using an extensive historical hydrographic dataset together with updated satellite dynamic ocean topography data, we find that the Beaufort Gyre has transitioned to a new state in which the increase in sea surfac...
The processes of seafloor sediment transport from the Chukchi shelf to the western Arctic basin were investigated using a pan‐Arctic sea ice‐ocean model and sediment‐trap measurements at four mooring stations: North of Barrow Canyon, North of Hanna Canyon, Northwind Abyssal Plain, and Chukchi Abyssal Plain. The available sediment‐trap data verified...
Using long‐term moorings data together with wind and sea ice measurements, we document the characteristics and variations of upwelling in Barrow Canyon and investigate the upwelled Atlantic Water (AW) on the Chukchi Sea shelf and how it impacts the ice cover. Driven by strong northeasterly winds, upwelling occurs more often in the cold months, and...
Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well a...
Time series monitoring of hydrography and marine settling particles supplies a large amount of information regarding the marine lower‐trophic ecosystem with respect to the changing Arctic Ocean. To investigate the interannual relationship between the settling particles and hydrographic conditions of the western Arctic Ocean, bottom‐tethered sedimen...
A composite dataset of 27 moorings across the Chukchi Sea and Bering Strait in 2013-14, along with satellite sea ice concentration data, weather station data, and atmospheric reanalysis fields, are used to explore the relationship between the circulation, ice cover, and wind forcing. We find a clear relationship between northeasterly winds along th...
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...
We investigated the transport and heat loss of the Pacific Summer Water (PSW) along the Chukchi Sea northern slope using the temperature, salinity, and velocity data of the mooring time series obtained in 2003–2005 (Period 1) and 2015–2019 (Period 2). The PSW at Stations HSN/NHC on the Chukchi Sea northern slope was warmer and fresher in Period 2 t...
From late‐summer 2013 to late‐summer 2014, a total of 20 moorings were maintained on the eastern Chukchi Sea shelf as part of five independent field programs. This provided the opportunity to analyze an extensive set of timeseries to obtain a broad view of the mean and seasonally varying hydrography and circulation over the course of the year. Year...
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...
In this study, intra-annual variation of near-inertial internal wave (NIW) in the Arctic Ocean is examined using year-round mooring in the Northwind Abyssal Plain. Our emphasis is on dynamical responses of NIW to local sea-ice variables such as concentration, draft, and drift. We obtained those using a coupling system of ice profiling sonar (IPS) a...
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...
A high-resolution regional ocean model together with moored hydrographic and velocity measurements is used to identify the pathways and mechanisms by which Pacific water, modified over the Chukchi shelf, crosses the shelf break into the Canada Basin. Most of the Pacific water flowing into the Arctic Ocean through Bering Strait enters the Canada Bas...
Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter W...
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....
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...
Surface absorption and fluorescence measurements of Dissolved Organic Matter (DOM) were conducted along with hydrographic parameters in the Amerasian and Makarov Basins. Parallel factor analysis of DOM fluorescence identified four humic-like and one protein-like component in all 107 surface samples. Based on strong negative trends observed between...
Surface absorption and fluorescence measurements of Dissolved Organic Matter (DOM) were conducted along with hydrographic parameters in the Amerasian and Makarov Basins. Parallel factor analysis of DOM fluorescence identified four humic-like and one protein-like component in all 107 surface samples. Based on strong negative trends observed between...
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...
The Bering and Chukchi/Beaufort shelf-breaks form the beginning and end of the dramatic sea-level and wind-forced flow of Pacific Ocean water across the Bering and Chukchi continental shelves between the Pacific and Arctic Oceans. Recent model results suggest that the on-shelf flow in the Bering is distributed along the shelf-break, wind-dependant,...
Barrow Canyon, in the northeast Chukchi Sea, is a major conduit for
Pacific Water to enter the interior Arctic basins. Assemblies of annual
(September 2000 to August 2008) temperature, salinity, and velocity data
acquired from a mooring array in the mouth of Barrow Canyon and
high-resolution hydrographic and velocity transects along the mooring
arr...
The concentration of dissolved iron (DFe) and suspended leachable particulate iron (LPFe) in the water column of the western Beaufort Sea were investigated during the late summer of 2010. Elevated concentrations of surface DFe (0.49–1.42 nM) were similar to those reported in resent studies, likely reflecting input from melting sea ice and river dis...
[1] The water mass changes in the Makarov Basin and adjacent areas associated with the recent loss of Arctic sea ice had not been studied in detail. We combined data obtained from multiple cruises in these regions and used chemical tracers to investigate the spatial and temporal changes in water masses. Our data show that a previously present tempe...
This paper presents a detailed hydrographic survey of a large anticyclone eddy (referred to as MO-eddy) that was found in early September 2010 during a Mirai Arctic cruise along the east flank of the Northwind Ridge in the southwest corner of the Canada Basin. It is ∼60–70km in diameter, which is even larger than those found in previous studies. Mo...
We examined the interannual variability of Pacific Winter Water (PWW), both upstream in the northeastern Chukchi Sea and Barrow Canyon using mooring observations from 2000 to 2006, and downstream in the Canada Basin using hydrographic data acquired in 2002–2006. The interannual variation of PWW salinity is governed by two factors: (1) variability i...
Recent freshening of the Arctic Ocean due to melting of sea ice and enhanced Ekman pumping has deepened the nutricline over the Canada Basin and reduced nutrient concentrations in the euphotic zone. Cold-core eddies frequently transport nutrient-rich shelf water to the Canada Basin, but the eddies are much deeper than the euphotic zone. Because war...
1] Winter water formation is examined in the Chukchi Sea for the winters of 1992–2006 using a primitive equation ocean model forced by NCEP wind and surface salinity flux derived from SSM/I thin ice thickness estimates. The model is also forced by an external inflow of 0.8 Sv through the Bering Strait. The model successfully reproduces the oceanic...
The biological pump is a central process in the ocean carbon cycle, and is a key factor controlling atmospheric carbon dioxide (CO2). However, whether the Arctic biological pump is enhanced or reduced by the recent loss of sea ice is still unclear. We examined if the effect was dependent on ocean circulation. Melting of sea ice can both enhance and...
Sea-ice melting processes were inferred from in situ sea-ice and ocean condition data obtained in the Arctic in summer 2006 and 2007. The relationship between ice concentration observed by on-board ice watches and water temperature showed negative correlations. This implies that as ice concentration decreases, the upper ocean becomes warmer due to...
The R/V Mirai conducted hydrographic surveys in the western Arctic Ocean during summer 2004 (Mirai04) over wide east-west
ranges from Alaska to eastern Siberia, where sea-ice cover has been greatly reduced in recent summers. The obtained data reveal
differences in silicate profiles between shelf slope areas east and west of the Chukchi Plateau, the...
The 1990-1991 influx of Atlantic water, both anomalously warm and in greater volume than in the past, enveloped the Chukchi Borderland in the western Canada Basin by 2002 and spread across the southeastern Canada Basin by 2007. Warmer, younger (more ventilated), and less dense Fram Strait Branch waters have replaced colder, older, and denser waters...
We investigate basin-scale mechanisms regulating anomalies in freshwater content (FWC) in the Beaufort Gyre (BG) of the Arctic Ocean using historical observations and data collected in 2003-2007. Specifically, the mean annual cycle and interannual and decadal FWC variability are explored. The major cause of the large FWC in the BG is the process of...
The R/V Mirai conducted hydrographic surveys in the western Arctic Ocean during summer 2004 across a front between cold Arctic water and warm water from the Pacific Ocean where sea ice cover has been largely reduced in recent summers. The hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline s...
As part of the global hydrological cycle, freshwater in the form of water vapour inexorably moves from warm regions of evaporation to cold regions of precipitation and freshwater in the form of sea ice and dilute seawater inexorably moves from cold regions of freezing and net precipitation to warm regions of melting and net evaporation. The global...
Intensive CTD observations that resolve the mean and tidal components were done with a total of 129 casts in summer of 2001 at Bussol’ Strait. Based on these data and all the available historical data, we have revealed the outflow from Bussol’ Strait to the Pacific and the significant diapycnal mixing in the strait. In the range 27.0−27.3σ
θ
, the...
1] We identify the source region and spreading pattern of cold, oxygen-rich water observed in the halocline of the northern Canada Basin using both Joint Western Arctic Climate Studies 2002 – 2005 and other data. This water originates in the winter mixed-layer in the Nansen Basin and, because of its convective origin, can be traced by its cold, oxy...
Okhotsk Sea Intermediate Water (OSIW), the source water for ventilation of North Pacific Intermediate Water, exhibits a multidecadal
warming trend. Historical data show that OSIW temperatures increased by 0.28, 0.57, 0.31 and 0.10°C during 1955 to 2003 at
potential densities of 26.8, 27.0, 27.2 and 27.4σ
θ
, at depths of approximately 250, 500, 700...
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L08605, doi:10.1029/2005GL025624. The spatial pattern of recent ice reduction in the Arctic Ocean is sim...
The contribution of nutrient regeneration in summer to the nutrient maximum associated with Bering Sea Winter Water (BSWW) is estimated from the ammonium data, which was obtained in the outer shelf region of the Chukchi Sea for the first time by the R/V Mirai in 2002. The contribution rate reaches 20-30%, which is larger than the rate studied earli...
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 32 (2005): L03605, doi:10.1029/2004GL021358. We examine the varieties and spatial distributions of Pacific and East...
Physical and geochemical data collected in 2002 during a multi-disciplinary expedition across the southern Canada Basin are interpreted here to provide context for the biological program that included observations from the entire water column. The mixed layer was shallow (15–20m) and depleted of nitrate, indicating it was the limiting nutrient. Bel...
![Figure 4. Velocities at 250 m depth [yellow color] and topographic...](profile/Eddy-Carmack-3/publication/43294636/figure/fig4/AS:668909858467860@1536491946900/Velocities-at-250-m-depth-yellow-color-and-topographic-vectors-as-described-by-dh-dy_Q320.jpg)
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L20301, doi:10.1029/2004GL020860. Penetration of the 1990s warm temperature anomaly (WTA) of the Fram St...
An outflow from the Sea of Okhotsk to the North Pacific was measured at the Bussol' Strait, the largest strait connecting these basins, from 31 August to 11 September 2001. Yo-yo casts of a lowered acoustic Doppler current profiler were performed at 13 stations across the narrowest part of the strait. Time series covering more than approximately 24...
Hydrographic observations under sea ice were conducted in the southwestern part of the Sea of Okhotsk for 4 years from 1996 to 1999. Every year a cold mixed layer with near-freezing temperature was distributed from the sea surface to a depth of 150–300m near the shelf break under sea ice. The thicknesses of the mixed layer and sea ice were largest...
It is proposed that the cyclonic gyre over the northern half-basin of the Okhotsk Sea is driven by the wind stress curl and that a major part of the East Sakhalin Current (ESC) can be regarded as its western boundary current. Both from the high-resolution ECMWF and Comprehensive Ocean-Atmosphere Dataset (COADS) data, the annual mean wind stress cur...
In order to clarify the distribution and formation of Okhotsk Sea Intermediate Water (OSIW) an isopycnal climatological data set based on all of the available historical observations is developed and examined. The isopycnal maps clearly show that there are two direct ventilation sources for OSIW: Dense Shelf Water (DSW) with cold and fresh properti...
Direct current measurements were made at the largest strait (depth about 2400m) in the Kuril Islands that separate the Sea of Okhotsk and the North Pacific. The narrowest part (roughly 80 km wide) of the strait is covered by 13 stations and more than 140 casts of an lowered acoustic Doppler current profiler and a CTD were performed. The tidal flow...
In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a
depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this...
A new grid data set for the southwestern part of the Okhotsk Sea was compiled by using all the available hydrographic data from the Japan Oceanographic Data Center, World Ocean Atlas 1994 and the other additional data sources with the resolution of about 10 km. We examine the seasonal variations of areas and volumes of Soya Warm Current Water (SWCW...
