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首页> 外文期刊>Marine Chemistry >Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge
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Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge

机译：夏威夷边缘的短命镭同位素：通过普纳山脊的大量流体通量的证据

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We measured significant activities of short-lived radium isotopes, ~(223)Ra (half-life=11 days) and ~(224)Ra (half-life=3.7 days), around the margins of the Hawaiian Islands to water depths of 3500 m. These measurements suggest fluid inputs from the basalt to the surrounding ocean. In general ~(223)Ra activities were considerably greater than ~(224)Ra in spite of the expected higher production rate of ~(224)Ra activity in basalt. The ~(223)Ra was not supported by dissolved ~(227)Ac. The highest enrichments of ~(223)Ra were measured over the Puna Ridge (2100 m depth) east of Hawaii. Here ~(223)Ra activities reached 19 dpm/m~3, similar to activities measured near sites of active submarine groundwater discharge in the South Atlantic Bight. To explain the high activities of ~(223)Ra unaccompanied by ~(224)Ra, we postulate that thermally-driven circulation of seawater through the Puna Ridge deposits ~(231)Pa on basalt surfaces. With time the ~(231)Pa produces ~(227)Ac and ~(223)Ra; and ~(223)Ra desorbs into the circulating fluids. These fluids then transport ~(223)Ra into the overlying ocean. Based on the inventory of ~(223)Ra above the Puna Ridge, we estimate the flow of fluids through the ridge to be on the order of 20-60 cm~3 cm~(-2) day~(-1). In less than 1000 years the incoming seawater could provide enough ~(231)Pa to basalt surfaces to balance the inventory of ~(223)Ra above the ridge if only 8% of the ~(223)Ra was transported to the overlying water. These observations on the flanks of a volcanically-active ocean island have significant implications for quantifying fluid fluxes from the flanks of the mid-ocean ridge system. By mapping ~(223)Ra inventories in the ocean above ridge flanks and measuring the activity of ~(223)Ra in the emerging fluids, the fluid flux can be obtained.
机译：我们测量了短寿命镭同位素的重要活动，其附近夏威夷群岛的边缘到水深为〜（223）Ra（半衰期= 11天）和〜（224）Ra（半衰期= 3.7天）。 3500米这些测量表明从玄武岩到周围海洋的流体输入。通常，尽管玄武岩中〜（224）Ra活性的预期生产率更高，但〜（223）Ra活性仍显着大于〜（224）Ra。 〜（223）Ra不受溶解的〜（227）Ac的支持。在夏威夷以东的Puna Ridge（深度2100 m）上测得〜（223）Ra的最高富集量。在这里，〜（223）Ra活性达到19 dpm / m〜3，类似于在南大西洋海岸线活跃的海底地下水排放场所附近测得的活动。为了解释〜（223）Ra未被〜（224）Ra伴有的高活性，我们假设海水通过热驱动的循环流经玄武岩表面上的Puna Ridge沉积物〜（231）Pa。随着时间的流逝，〜（231）Pa产生〜（227）Ac和〜（223）Ra； 〜（223）Ra解吸到循环流体中。这些流体然后将〜（223）Ra运到上覆海洋中。根据普纳山脊上方〜（223）Ra的存量，我们估计流经山脊的流体流量约为20-60 cm〜3 cm〜（-2）天〜（-1）。在不到1000年的时间里，如果仅将〜（223）Ra的8％输送到上覆水中，则海水可以为玄武岩表面提供足够的〜（231）Pa，以平衡山脊上的〜（223）Ra的存量。这些对具有火山活动性的海洋岛屿的侧翼的观测对于量化来自中洋脊系统侧翼的流体通量具有重要意义。通过绘制海脊侧面上方的〜（223）Ra清单并测量新兴流体中的〜（223）Ra活度，可以获得流体通量。

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