Itoh
Motoyo
Itoh
Motoyo
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ArticlePacific Ocean inflow : influence on catastrophic reduction of sea ice cover in the Arctic Ocean(American Geophysical Union, 2006-04-21) Shimada, Koji ; Kamoshida, Takashi ; Itoh, Motoyo ; Nishino, Shigeto ; Carmack, Eddy C. ; McLaughlin, Fiona A. ; Zimmermann, Sarah ; Proshutinsky, AndreyThe spatial pattern of recent ice reduction in the Arctic Ocean is similar to the distribution of warm Pacific Summer Water (PSW) that interflows the upper portion of halocline in the southern Canada Basin. Increases in PSW temperature in the basin are also well-correlated with the onset of sea-ice reduction that began in the late 1990s. However, increases in PSW temperature in the basin do not correlate with the temperature of upstream source water in the northeastern Bering Sea, suggesting that there is another mechanism which controls these concurrent changes in ice cover and upper ocean temperature. We propose a feedback mechanism whereby the delayed sea-ice formation in early winter, which began in 1997/1998, reduced internal ice stresses and thus allowed a more efficient coupling of anticyclonic wind forcing to the upper ocean. This, in turn, increased the flux of warm PSW into the basin and caused the catastrophic changes.
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ArticleMean and seasonal circulation of the eastern Chukchi Sea from moored timeseries in 2013-2014(American Geophysical Union, 2021-04-30) Tian, Fei ; Pickart, Robert S. ; Lin, Peigen ; Pacini, Astrid ; Moore, G. W. K. ; Stabeno, Phyllis J. ; Weingartner, Thomas J. ; Itoh, Motoyo ; Kikuchi, Takashi ; Dobbins, Elizabeth ; Bell, Shaun ; Woodgate, Rebecca ; Danielson, Seth L. ; Wang, ZhaominFrom 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-long mean bottom temperatures reflected the presence of the strong coastal circulation pathway, while mean bottom salinities were influenced by polynya/lead activity along the coast. The timing of the warm water appearance in spring/summer is linked to advection along the various flow pathways. The timing of the cold water appearance in fall/winter was not reflective of advection nor related to the time of freeze-up. Near the latitude of Barrow Canyon, the cold water was accompanied by freshening. A one-dimensional mixed-layer model demonstrates that wind mixing, due to synoptic storms, overturns the water column resulting in the appearance of the cold water. The loitering pack ice in the region, together with warm southerly winds, melted ice and provided an intermittent source of fresh water that was mixed to depth according to the model. Farther north, the ambient stratification prohibits wind-driven overturning, hence the cold water arrives from the south. The circulation during the warm and cold months of the year is different in both strength and pattern. Our study highlights the multitude of factors involved in setting the seasonal cycle of hydrography and circulation on the Chukchi shelf.
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ArticlePenetration of the 1990s warm temperature anomaly of Atlantic Water in the Canada Basin(American Geophysical Union, 2004-10-16) Shimada, Koji ; McLaughlin, Fiona A. ; Carmack, Eddy C. ; Proshutinsky, Andrey ; Nishino, Shigeto ; Itoh, MotoyoPenetration of the 1990s warm temperature anomaly (WTA) of the Fram Strait branch of Atlantic Water (FSBW) in the Canada Basin is described using available temperature, salinity, and velocity data. The core temperatures of FSBW show distinct pathways. Over the Chukchi Borderland advective velocities of the FSBW are well-correlated with bottom topography. The resulting multifarious pathways over the Chukchi Borderland act to modulate and substantially increase the time scale of WTA spreading and advancement. Further downstream two WTA tongues are observed. One tongue followed the Beaufort Slope and, along this pathway, the core temperatures of FSBW decreased rapidly. The depth integrated value of heat content remained near constant however, suggesting enhanced vertical mixing. The second tongue debouched from the northern tip of the Northwind Ridge and spread eastward into the deep Canada Basin, suggesting a complex recirculation structure within the Beaufort Gyre.
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ArticleMonitoring Alaskan Arctic shelf ecosystems through collaborative observation networks(Oceanography Society, 2022-04-28) Danielson, Seth L. ; Grebmeier, Jacqueline M. ; Iken, Katrin ; Berchok, Catherine L. ; Britt, Lyle ; Dunton, Kenneth ; Eisner, Lisa B. ; Farley, Edward V. ; Fujiwara, Amane ; Hauser, Donna D.W. ; Itoh, Motoyo ; Kikuchi, Takashi ; Kotwicki, Stan ; Kuletz, Kathy J. ; Mordy, Calvin W. ; Nishino, Shigeto ; Peralta-Ferriz, Cecilia ; Pickart, Robert S. ; Stabeno, Phyllis J. ; Stafford, Kathleen M. ; Whiting, Alex V. ; Woodgate, RebeccaOngoing 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 as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.
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ArticleBeaufort Gyre freshwater reservoir : state and variability from observations(American Geophysical Union, 2009-06-24) Proshutinsky, Andrey ; Krishfield, Richard A. ; Timmermans, Mary-Louise ; Toole, John M. ; Carmack, Eddy C. ; McLaughlin, Fiona A. ; Williams, William J. ; Zimmermann, Sarah ; Itoh, Motoyo ; Shimada, KojiWe 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 Ekman pumping (EP) due to the Arctic High anticyclonic circulation centered in the BG. The mean seasonal cycle of liquid FWC is a result of interplay between the mechanical (EP) and thermal (ice transformations) factors and has two peaks. One peak occurs around June–July when the sea ice thickness reaches its minimum (maximum ice melt). The second maximum is observed in November–January when wind curl is strongest (maximum EP) and the salt input from the growing ice has not yet reached its maximum. Interannual changes in FWC during 2003–2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a−1 in the center of EP influenced region. Decadal FWC variability in the period 1950–2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change. The center of maximum FWC shifted to the southeast and appeared to contract in area relative to the pre-1990s climatology. In spite of the areal reduction, the spatially integrated FWC increased by over 1000 km3 relative to climatology.
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ArticleWater properties, heat and volume fluxes of Pacific water in Barrow Canyon during summer 2010(Elsevier, 2015-04-25) Itoh, Motoyo ; Pickart, Robert S. ; Kikuchi, Takashi ; Fukamachi, Yasushi ; Ohshima, Kay I. ; Simizu, Daisuke ; Arrigo, Kevin R. ; Vagle, Svein ; He, Jianfeng ; Ashjian, Carin J. ; Mathis, Jeremy T. ; Nishino, Shigeto ; Nobre, CarolinaOver 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. This paper presents results from 6 repeat high-resolution shipboard hydrographic/velocity sections occupied across Barrow Canyon in summer 2010. The different Pacific water masses feeding the canyon – Alaskan coastal water (ACW), summer Bering Sea water (BSW), and Pacific winter water (PWW) – all displayed significant intra-seasonal variability. Net volume transports through the canyon were between 0.96 and 1.70 Sv poleward, consisting of 0.41–0.98 Sv of warm Pacific water (ACW and BSW) and 0.28–0.65 Sv of PWW. The poleward heat flux also varied strongly, ranging from 8.56 TW to 24.56 TW, mainly due to the change in temperature of the warm Pacific water. Using supplemental mooring data from the core of the warm water, along with wind data from the Pt. Barrow weather station, we derive and assess a proxy for estimating heat flux in the canyon for the summer time period, which is when most of the heat passes northward towards the basin. The average heat flux for 2010 was estimated to be 3.34 TW, which is as large as the previous record maximum in 2007. This amount of heat could melt 315,000 km2 of 1-meter thick ice, which likely contributed to significant summer sea ice retreat in the Pacific sector of the Arctic Ocean.
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ArticleHalocline structure in the Canada Basin of the Arctic Ocean(American Geophysical Union, 2005-02-05) Shimada, Koji ; Itoh, Motoyo ; Nishino, Shigeto ; McLaughlin, Fiona A. ; Carmack, Eddy C. ; Proshutinsky, AndreyWe examine the varieties and spatial distributions of Pacific and Eastern Arctic origin halocline waters in the Canada Basin using 2002–2003 hydrographic data. The halocline structure in the Canada Basin is different from the Eastern Arctic halocline because it includes fresher Pacific Winter Waters that form a “cold halostad” which lies above the Eastern Arctic origin lower halocline waters. The structure of the halostad in the Canada Basin, however, is not spatially uniform, and depends on the pathway and history of the source water. Pacific Winter Water entering through the Bering Strait becomes salty due to sea ice formation and this, in turn, is dependent on the occurrence and distribution of polynyas. In particular, saline water from the eastern Chukchi Sea forms thick halostad and causes depression of the isohalines in the southern Canada Basin. This depression influences thermohaline structure of the oceanic Beaufort Gyre.
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ArticleTransport of Pacific water into the Canada Basin and the formation of the Chukchi Slope Current(John Wiley & Sons, 2018-10-22) Spall, Michael A. ; Pickart, Robert S. ; Li, Min ; Itoh, Motoyo ; Lin, Peigen ; Kikuchi, Takashi ; Qi, YiquanA 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 Basin through Barrow Canyon. Strong advection allows the water to cross the shelf break and exit the shelf. Wind forcing plays little role in this process. Some of the outflowing water from Barrow Canyon flows to the east into the Beaufort Sea; however, approximately 0.4 to 0.5 Sv turns to the west forming the newly identified Chukchi Slope Current. This transport occurs at all times of year, channeling both summer and winter waters from the shelf to the Canada Basin. The model indicates that approximately 75% of this water was exposed to the mixed layer within the Chukchi Sea, while the remaining 25% was able to cross the shelf during the stratified summer before convection commences in late fall. We view the Ό(0.5) Sv of the Chukchi Slope Current as replacing Beaufort Gyre water that would have come from the east in the absence of the cross-topography flow in Barrow Canyon. The weak eastward flow on the Beaufort slope is also consistent with the local disruption of the Beaufort Gyre by the Barrow Canyon outflow.
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ArticleUpwelling of Atlantic Water in Barrow Canyon, Chukchi Sea(American Geophysical Union, 2022-02-26) Li, Shutong ; Lin, Peigen ; Dou, Tingfeng ; Xiao, Cunde ; Itoh, Motoyo ; Kikuchi, Takashi ; Qin, DaheUsing 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 the occurrence tends to increase interannually since 2001. Over the 12-year mooring record at the mouth of Barrow Canyon, roughly 10% of the upwelling events can drive AW onto the Chukchi Sea shelf. Both AW and non-AW upwelling events have more occurrence and stronger strength in the cold months, but do not present a significant interannual trend. These variations are associated with the northeasterly winds. Comparing to the non-AW upwelling, the AW upwelling is generally characterized by more vertical displacement of the AW layer at the mouth of Barrow Canyon, and stronger up-canyon volume and heat transport. In the ice-covered period, these two types of upwelling have different consequences for forming polynyas on the shelf. Under similar wind forcing, the ice reduction appears confined in the coastal region in the non-AW upwelling events, while during AW upwelling events, the sea ice declines dramatically in the shelf interior with 15% more ice loss. It elucidates that the heat carried by the upwelled AW plays a considerable role in modulating the ice cover in the shelf interior.
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ArticleAnalysis of the Beaufort Gyre freshwater content in 2003-2018(American Geophysical Union, 2019-12-11) Proshutinsky, Andrey ; Krishfield, Richard A. ; Toole, John M. ; Timmermans, Mary-Louise ; Williams, William J. ; Zimmermann, Sarah ; Yamamoto-Kawai, Michiyo ; Armitage, Thomas ; Dukhovskoy, Dmitry S. ; Golubeva, Elena ; Manucharyan, Georgy E. ; Platov, Gennady A. ; Watanabe, Eiji ; Kikuchi, Takashi ; Nishino, Shigeto ; Itoh, Motoyo ; Kang, Sung-Ho ; Cho, Kyoung-Ho ; Tateyama, Kazutaka ; Zhao, JingHydrographic data collected from research cruises, bottom‐anchored moorings, drifting Ice‐Tethered Profilers, and satellite altimetry in the Beaufort Gyre region of the Arctic Ocean document an increase of more than 6,400 km3 of liquid freshwater content from 2003 to 2018: a 40% growth relative to the climatology of the 1970s. This fresh water accumulation is shown to result from persistent anticyclonic atmospheric wind forcing (1997–2018) accompanied by sea ice melt, a wind‐forced redirection of Mackenzie River discharge from predominantly eastward to westward flow, and a contribution of low salinity waters of Pacific Ocean origin via Bering Strait. Despite significant uncertainties in the different observations, this study has demonstrated the synergistic value of having multiple diverse datasets to obtain a more comprehensive understanding of Beaufort Gyre freshwater content variability. For example, Beaufort Gyre Observational System (BGOS) surveys clearly show the interannual increase in freshwater content, but without satellite or Ice‐Tethered Profiler measurements, it is not possible to resolve the seasonal cycle of freshwater content, which in fact is larger than the year‐to‐year variability, or the more subtle interannual variations.
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ArticleThe Pacific water flow branches in the eastern Chukchi Sea(Elsevier, 2023-11-10) Pickart, Robert S. ; Lin, Peigen ; Bahr, Frank B. ; McRaven, Leah T. ; Huang, Jie ; Pacini, Astrid ; Arrigo, Kevin Robert ; Ashjian, Carin J. ; Berchok, Catherine L. ; Baumgartner, Mark F. ; Cho, Kyoungho ; Cooper, Lee W. ; Danielson, Seth L. ; Dasher, Doug H. ; Fuiwara, Amane ; Gann, Jeanette C. ; Grebmeier, Jacqueline M. ; He, Jiangfeng ; Hirawake, Toru ; Itoh, Motoyo ; Juranek, Laurie ; Kikuchi, Takashi ; Moore, G. W. Kent ; Napp, Jeffrey M. ; John Nelson, R. ; Nishino, Shigeto ; Statscewich, Hank ; Stabeno, Phyllis J. ; Stafford, Kathleen M. ; Ueno, Hiromichi ; Vagle, Svein ; Weingartner, Thomas J. ; Williams, Bill ; Zimmermann, Sarah L.The flow of Pacific-origin water across the Chukchi Sea shelf impacts the regional ecosystem in profound ways, yet the two current branches on the eastern shelf that carry the water from Bering Strait to Barrow Canyon – the Alaskan Coastal Current (ACC) and Central Channel (CC) Branch – have not been clearly distinguished or quantified. In this study we use an extensive collection of repeat hydrographic sections occupied at three locations on the Chukchi shelf, together with data from a climatology of shipboard velocity data, to accomplish this. The data were collected predominantly between 2010 and 2020 during the warm months of the year as part of the Distributed Biological Observatory and Arctic Observing Network. The mean sections show that mass is balanced for both currents at the three locations: Bering Strait, Point Hope, and Barrow Canyon. The overall mean ACC transport is 0.34 ± 0.04 Sv, and that of the CC Branch is 0.86 ± 0.11 Sv. The dominant hydrographic variability at Bering Strait is seasonal, but this becomes less evident to the north. At Barrow Canyon, the dominant hydrographic signal is associated with year-to-year variations in sea-ice melt. Farther south there is pronounced mesoscale variability: an empirical orthogonal function analysis at Bering Strait and Point Hope reveals a distinct ACC mode and CC Branch mode in hydrography and baroclinic transport, where the former is wind-driven. Finally, the northward evolution in properties of the two currents is investigated. The poleward increase in salinity of the ACC can be explained by lateral mixing alone, but solar heating together with wind mixing play a large role in the temperature evolution. This same atmospheric forcing also impacts the northward evolution of the CC Branch.