A plume of volcanic 3He observed in the Shallow North Pacific

IF 4.8 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
W.J. Jenkins , T.M. Joyce , G.C. Johnson , D.A. Hansell
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Abstract

In April 1994, we observed a ∼100 m thick plume of volcanic 3He at 140 m depth, extending approximately 700 km meridionally, and centered at 18°N along 110°W in the Pacific. It was not present in two subsequent occupations. The plume had a significant dissolved helium excess, with a 3He/4He ratio 7.4 ± 0.6 times atmospheric, consistent with an upper mantle volcanic source. It resulted from a series of eruptions that occurred at 250 m depth on the flank of nearby Socorro Island from January 1993 that continued to the end of 1995. Using plume rise height, we estimate an initial heat flux of 6.7 ± 3.3 GW, with a total output of 0.2 - 4 × 1017 Joules. Numerical simulations show that the estimated 3He inventory released is a function of persistence, ocean velocity, and horizontal eddy mixing rates, allowing us to constrain the total release of 3He to 24 – 28 mol, about 5 – 6 % of the annual global oceanic hydrothermal 3He flux. The 3He:heat ratio was 0.06 – 2 fmol J-1, about 3 to 100 times larger than the ratio of helium to heat produced by U and Th decay, and much greater than “typical” mid-ocean ridge hydrothermal systems. By entraining deeper, nutrient-rich water, including iron, the buoyant plume from such venting may spur bursts of new biological activity in otherwise low-productivity waters, which may locally enhance export of particulate matter to the deep sea and significantly alter shallow inventories of dissolved organic carbon.
他在北太平洋浅层观察到的火山羽流
1994年4月,我们在140米深度观测到一个~ 100米厚的3He火山羽流,经向延伸约700公里,中心位于18°N,沿110°W在太平洋。它在随后的两次占领中都没有出现。该地幔柱具有明显的溶解氦过剩,3He/4He比值为大气的7.4±0.6倍,与上地幔火山源一致。它是由1993年1月至1995年年底在附近索科罗岛侧面250米深处发生的一系列喷发造成的。利用羽流上升高度,我们估计初始热流密度为6.7±3.3 GW,总输出为0.2 - 4 × 1017焦耳。数值模拟表明,估计的3He释放量是持久性、海洋速度和水平涡混合率的函数,使我们能够将3He的总释放量限制在24 - 28 mol,约占全球海洋热液3He年通量的5 - 6%。3He:热比为0.06 - 2 fmol J-1,约为U和Th衰变产生的氦热比的3 - 100倍,远远大于“典型的”洋中脊热液系统。通过携带更深的富含营养的水,包括铁,这种喷口产生的浮力羽流可能会在其他低生产力的水域刺激新的生物活动爆发,这可能会在局部增加颗粒物向深海的出口,并显著改变浅层溶解有机碳的库存。
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来源期刊
Earth and Planetary Science Letters
Earth and Planetary Science Letters 地学-地球化学与地球物理
CiteScore
10.30
自引率
5.70%
发文量
475
审稿时长
2.8 months
期刊介绍: Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.
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