Publications by authors named "Yutaka W Watanabe"

With the accelerating mass loss of Antarctic ice sheets, the freshening of the Southern Ocean coastal oceans (SOc, seas around Antarctica) is gradually intensifying, which will reduce the formation of bottom water and weaken the meridional overturning circulation, thus having a significant negative impact on the ocean's role in regulating global climate. Due to the extreme environment of the Southern Ocean and the limitations of observational techniques, our understanding of the glacier-derived freshening of SOc is still vague. We developed a method that first provided us with an expansive understanding of glacier-derived freshening progress over the SOc.

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Accidental leakage of radionuclides from the Fukushima Nuclear Power Plant (FNPP1) took place in the aftermath of the catastrophic tsunamis associated with the Great East Japan Earthquake that occurred on March 11, 2011. Significant amount of radionuclides released into the atmosphere were reportedly transported and deposited on land located near FNPP1. The Niida River, Fukushima, Japan, has been recognized as a terrestrial source of highly contaminated suspended radiocesium adhering to sediment particles in the ocean through the river mouth as a result of hydrological processes.

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This study examines long-term ocean pH data to evaluate ocean acidification (OA) trends at two coastal research institutions located on the Sea of Japan and the Pacific Ocean. These laboratories are located away from the influences of large rivers and major industrial activity. Measurements were performed daily for the past 30 years (1980s-2010s).

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Article Synopsis
  • Researchers measured sediment cesium-137 concentrations near the Fukushima Daiichi Nuclear Power Plant from 2011 to 2017, noting high levels initially but a decrease in seven stations over time.
  • They identified 25 radioactive cesium-bearing microparticles (CsMPs), with their contribution to sediment samples varying significantly, particularly lower in the southern part of the plant compared to the northern part.
  • The study suggests that while many small CsMPs in the south dispersed shortly after the accident, larger, more persistent CsMPs likely accumulated in the northern region due to the sediment's characteristics.
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The oceanic external nitrogen (N) deposition to the global ocean is expected to rise significantly owing to human activities. The Southern Ocean (SO) is an important pathway, which brings external influences into the ocean interior. It touches the borders of several developing countries that emit a large amount of anthropogenic nitrogen.

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Article Synopsis
  • A study investigated radioactive cesium concentrations in suspended matter of coastal waters near the Fukushima Daiichi Nuclear Power Plant from January 2014 to August 2015, revealing much higher cesium levels compared to sediments.
  • Highly radioactive cesium particles were identified in the suspended matter, with a maximum radioactivity of 0.6 Bq and an average of 0.2 Bq.
  • These particles significantly contributed to cesium levels in the suspended matter, affecting about 36% on average and potentially delaying the removal of radioactive cesium from bottom-dwelling organisms.
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Dimethyl sulfide (DMS) derived from marine biological activity affects radiative forcing of the climate. The general analytical technique for DMS in seawater (purge and trap analytical method, P&T) is complex onboard ship. Thus it is difficult to obtain sufficient data for a comprehensive understanding of the spatiotemporal variability of DMS in the sea surface layer.

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