Yamamoto-Kawai Michiyo

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Yamamoto-Kawai
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Michiyo
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  • Article
    Variations in rates of biological production in the Beaufort Gyre as the arctic changes: Rates from 2011 to 2016
    (American Geophysical Union, 2019-04-30) Ji, Brenda Y. ; Sandwith, Zoe O. ; Williams, William J. ; Diaconescu, Oana ; Ji, Rubao ; Li, Yun ; Van Scoy, Emma ; Yamamoto-Kawai, Michiyo ; Zimmermann, Sarah ; Stanley, Rachel H. R.
    The Arctic Ocean is experiencing profound environmental changes as the climate warms. Understanding how these changes will affect Arctic biological productivity is key for predicting future Arctic ecosystems and the global CO2 balance. Here we use in situ gas measurements to quantify rates of gross oxygen production (GOP, total photosynthesis) and net community production (NCP, net CO2 drawdown by the biological pump) in the mixed layer in summer or fall from 2011 to 2016 in the Beaufort Gyre. NCP and GOP show spatial and temporal variations with higher values linked with lower concentrations of sea ice and increased upper ocean stratification. Mean rates of GOP range from 8 ± 1 to 54 ± 9 mmol O2·m−2·d−1 with the highest mean rates occurring in summer of 2012. Mean rates of NCP ranged from 1.3 ± 0.2 to 2.9 ± 0.5 mmol O2·m−2·d−1. The mean ratio of NCP/GOP, a measure of how efficiently the ecosystem is recycling its nutrients, ranged from 0.04 to 0.17, similar to ratios observed at lower latitudes. Additionally, a large increase in total photosynthesis that occurred in 2012, a year of historically low sea ice coverage, persisted for many years. Taken together, these data provide one of the most complete characterizations of interannual variations of biological productivity in this climatically important region, can serve as a baseline for future changes in rates of production, and give an intriguing glimpse of how this region of the Arctic may respond to future lack of sea ice.
  • Article
    The rapid response of the Canada Basin to climate forcing : from bellwether to alarm bells
    (Oceanography Society, 2011-09) McLaughlin, Fiona A. ; Carmack, Eddy C. ; Proshutinsky, Andrey ; Krishfield, Richard A. ; Guay, Christopher K. ; Yamamoto-Kawai, Michiyo ; Jackson, Jennifer M. ; Williams, William J.
    Sea ice extent in the Arctic Ocean diminished significantly during the first decade of the 2000s, most particularly in the Canada Basin where the loss of both multiyear and first-year ice was greater than in the other three subbasins. Using data collected during basin-wide surveys conducted from 2003–2010 together with data collected during the 1990s and 2000s at one station in the southern Canada Basin, we investigate the response of the Canada Basin water column to this significant decrease in ice cover. Changes were evident from the surface down to the Atlantic layer: some changes were the result of Beaufort Gyre forcing on regional processes, others were the result of Arctic Ocean atmospheric forcing on a hemispheric scale and large-scale advection. These changes have troubling consequences for the ecosystem.
  • Article
    Freshwater and its role in the Arctic Marine System : sources, disposition, storage, export, and physical and biogeochemical consequences in the Arctic and global oceans
    (John Wiley & Sons, 2016-03-30) Carmack, Edward C. ; Yamamoto-Kawai, Michiyo ; Haine, Thomas W. N. ; Bacon, Sheldon ; Bluhm, Bodil A. ; Lique, Camille ; Melling, Humfrey ; Polyakov, Igor V. ; Straneo, Fiamma ; Timmermans, Mary-Louise ; Williams, William J.
    The Arctic Ocean is a fundamental node in the global hydrological cycle and the ocean's thermohaline circulation. We here assess the system's key functions and processes: (1) the delivery of fresh and low-salinity waters to the Arctic Ocean by river inflow, net precipitation, distillation during the freeze/thaw cycle, and Pacific Ocean inflows; (2) the disposition (e.g., sources, pathways, and storage) of freshwater components within the Arctic Ocean; and (3) the release and export of freshwater components into the bordering convective domains of the North Atlantic. We then examine physical, chemical, or biological processes which are influenced or constrained by the local quantities and geochemical qualities of freshwater; these include stratification and vertical mixing, ocean heat flux, nutrient supply, primary production, ocean acidification, and biogeochemical cycling. Internal to the Arctic the joint effects of sea ice decline and hydrological cycle intensification have strengthened coupling between the ocean and the atmosphere (e.g., wind and ice drift stresses, solar radiation, and heat and moisture exchange), the bordering drainage basins (e.g., river discharge, sediment transport, and erosion), and terrestrial ecosystems (e.g., Arctic greening, dissolved and particulate carbon loading, and altered phenology of biotic components). External to the Arctic freshwater export acts as both a constraint to and a necessary ingredient for deep convection in the bordering subarctic gyres and thus affects the global thermohaline circulation. Geochemical fingerprints attained within the Arctic Ocean are likewise exported into the neighboring subarctic systems and beyond. Finally, we discuss observed and modeled functions and changes in this system on seasonal, annual, and decadal time scales and discuss mechanisms that link the marine system to atmospheric, terrestrial, and cryospheric systems.
  • Article
    Sources of dissolved inorganic carbon to the Canada Basin halocline : a multitracer study
    (John Wiley & Sons, 2016-05-04) Brown, Kristina A. ; McLaughlin, Fiona A. ; Tortell, Philippe D. ; Yamamoto-Kawai, Michiyo ; Francois, Roger
    We examine the dissolved inorganic carbon maximum in the Canada Basin halocline using a suite of geochemical tracers to gain insight into the factors that contribute to the persistence of this feature. Hydrographic and geochemical samples were collected in the upper 500 m of the southwestern Canada Basin water column in the summer of 2008 and fall of 2009. These observations were used to identify conservative and nonconservative processes that contribute dissolved inorganic carbon to halocline source waters, including shelf sediment organic matter remineralization, air-sea gas exchange, and sea-ice brine export. Our results indicate that the remineralization of organic matter that occurs along the Bering and Chukchi Sea shelves is the overwhelming contributor of dissolved inorganic carbon to Pacific Winter Water that occupies the middle halocline in the southwestern Canada Basin. Nonconservative contributions from air-sea exchange and sea-ice brine are not significant. The broad salinity range associated with the DIC maximum, compared to the narrow salinity range of the nutrient maximum, is due to mixing between Pacific and Atlantic water and not abiotic addition of DIC.
  • Article
    Analysis 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, Jing
    Hydrographic 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.