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A Fukushima tracer perspective on four years of North Pacific mode water evolution
Deep Sea Research Part I: Oceanographic Research Papers ( IF 2.4 ) Pub Date : 2020-09-02 , DOI: 10.1016/j.dsr.2020.103379
Alison M. Macdonald , Sachiko Yoshida , Steven M. Pike , Ken O. Buesseler , Irina I. Rypina , Steven R. Jayne , Vincent Rossi , Jennifer Kenyon , Jessica A. Drysdale

We present the results of a multi-platform investigation that utilizes tracer information provided by the 2011 release of radioisotopes from the Fukushima Dai-ichi Nuclear Power Plant to better understand the pathways, mixing and transport of mode waters formed in the North Pacific Ocean. The focus is on transition region mode waters and radiocesium (137Cs and 134Cs) observations obtained from the May–June 2015 GO-SHIP occupation of the 152°W line in the Northeast Pacific. Samples include profiles from the surface to 1000 m and surface/subsurface pairs that provide an average 1° of latitude spacing along 152°W. We find a clear Fukushima (134Cs) signal from the surface to 400 m. The core signal (134Cs ∼10 Bq m-3, 137Cs ∼12 Bq m-3) at 41°-43°N lies at 30–220 m where mode waters formed through deep winter mixing in 2011 outcropped in the western North Pacific. The strongest 2015 152°W Fukushima-source radiocesium signal is associated with Dense-Central Mode Waters consistent with the densest variety of these mode waters being formed off the coast of Japan 4 years earlier. The radionuclide signal transited the basin along subsurface mode water isopycnals mainly on the northern side of the subtropical gyre before outcropping at and to the east of the 152°W line. In 2015, the densest 152°W waters with 134Cs lie at ∼435 m in the bottom range of Dense-Central Mode Water at 40°N. There is a weak, but detectable, signal in the boundary current off both Kodiak and Sitka. The deepest detectable 137Cs (weapon's testing background) are found at and to the north of 45°N at 900–1000 m. With the exception of a single subsurface sample near Hawaii, as of spring 2015, the southernmost 134Cs was found above 200 m at 30°N. A total date-corrected 134Cs inventory of 11–16 PBq is estimated. Qualitative comparison to model output suggests good consistency in terms of general location, latitudinal breadth, and predicted depth of penetration, allowing discussion of the bigger picture. However, the model's 2015 152°W radiocesium signal is quantitatively weaker and the core is offset in latitude, potentially due to the lack of consideration of atmospheric deposition.



中文翻译:

福岛示踪者对北太平洋模式水演化四年的看法

我们介绍了利用2011年福岛第一核电站放射性同位素释放所提供的示踪剂信息进行的多平台调查结果,以更好地了解北太平洋形成的模式水的路径,混合和运输。重点是从2015年5月至6月GO-SHIP占领东北太平洋152°W线获得的过渡区模式水和放射性铯(137 Cs和134 Cs)观测值。样本包括从地表到1000 m的剖面,以及沿152°W的平均纬度间隔为1°的地表/次表对。我们发现从表面到400 m的清晰的福岛(134 Cs)信号。核心信号(134 Cs 〜10 Bq m -3,在41°-43°N处137 Cs〜12 Bq m -3)位于30-220 m处,北太平洋西部地区在2011年通过冬季深层混合形成的模态水露头。2015年最强的152°W福岛源放射性铯信号与密集中部模式水有关,这与4年前日本沿海形成的这些模式水中最稠密的一致。放射性核素信号主要在亚热带回旋的北侧沿地下模式水等渗物穿过盆地,然后在152°W线以东露头。2015年,最稠密的152°W水域有134个在40°N的稠密中央模式水的底部范围内,Cs位于约435 m。Kodiak和Sitka的边界电流中都有一个微弱但可检测的信号。在45°N及其以北900-1000 m处发现了可探测到的最深137 Cs(武器的测试背景)。到2015年春季,除了夏威夷附近的一个地下样品外,在30°N处200 m以上发现了最南端的134 Cs。校正日期总计134估计11-16 PBq的CS库存。对模型输出的定性比较表明,在一般位置,纬度宽度和预测的穿透深度方面具有良好的一致性,从而可以讨论更大的图景。但是,该模型的2015年152°W放射性铯信号在数量上较弱,并且岩心在纬度上有偏移,这可能是由于缺乏对大气沉积的考虑。

更新日期:2020-09-02
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