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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Dissolved and particulate ~(231)pa and ~(230)Th in the Atlantic Ocean: constraints on intermediate/deep water age, boundary scavenging, and ~(231)Pa/~(230)Th fractionation
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Dissolved and particulate ~(231)pa and ~(230)Th in the Atlantic Ocean: constraints on intermediate/deep water age, boundary scavenging, and ~(231)Pa/~(230)Th fractionation

机译：大西洋中溶解的和颗粒状的〜（231）pa和〜（230）Th：对中/深水年龄，边界清除和〜（231）Pa /〜（230）Th分馏的约束

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~(231)pa and ~(230)Th concentrations were determined in filtered seawater and suspended particulate matter collected from the Labrador Sea and the Equatorial and South Atlantic to constrain their application as tracers of intermediate/deep water age and Atlantic thermohaline circulation. Distributions of total ~(231)Pa and ~(230)Th indicate the influence of recently formed North Atlantic Deep Water, as evidenced by nearly invariant concentrations below ～1000 m in the Labrador Sea and increasing ~(231)Pa and ~(230)th concentrations as deep waters progress southward from northern source regions. Application of a scavenging-mixing model to both tracer distributions indicates an intermediate/deep water age of 12 yr in the Labrador Sea and a ～30-140 yr transit time to the low-latitude stations. We attribute a striking increase in total ~(230)Th in the Labrador Sea from 1993 to 1999 to aging of intermediate waters as a consequence of the cessation of deep convection in the Labrador Sea since 1993. The temporal change in the ~(23)Th age of these waters is consistent with the 6 yr time interval between the observations. The average particulate ~(231)Pa/~(230)Th activity ratio in the Labrador Sea and low-latitude deep waters is 0.057 ± 0.003, significantly below the ~(231)Pa/~(230)Th production ratio (0.093) and in agreement with excess ~(231)Pa/~(230)Th ratios in Holocene sediments (0.060 ± 0.004) and sediment trap material (0.034 ± 0.012) from the Atlantic and model simulations. This observation is consistent with the southward transport of deep water strongly attenuating boundary scavenging in the Atlantic. A latitudinal dependence in particle fractionation of these tracers is also evident, with elevated fractionation factors (F_(Th/Pa)) observed near the Equator and South Atlantic gyre (～11) compared to low values in the Labrador Sea (～3) and Southern Ocean (～2). There also exists a depth dependence in F_(Th/Pa), characterized by low values in surface waters, a broad mid-depth maximum, and decreasing values towards the sea-floor. The latitudinal and depth variations in F_(Th/Pa) are suggested to reflect differences in the chemical composition of marine particles.
机译：测定了从拉布拉多海，赤道和南大西洋收集的过滤海水和悬浮颗粒物中的〜（231）pa和〜（230）Th浓度，从而限制了它们在中/深水时代和大西洋热盐循环中的示踪作用。总〜（231）Pa和〜（230）Th的分布表明了最近形成的北大西洋深水的影响，这在拉布拉多海的〜1000 m以下几乎恒定的浓度和〜（231）Pa和〜（230）的增加中得到了证明。随着深水从北部水源区向南发展在两种示踪剂分布上应用清除混合模型表明，拉布拉多海的中/深水年龄为12年，到低纬度站的过渡时间约为30-140年。我们将1993年至1999年拉布拉多海的〜230总水位显着增加归因于1993年以来拉布拉多海停止深对流的结果，中间水域的老化。〜（23）的时间变化这些水的年龄与两次观测之间的6年时间间隔一致。拉布拉多海和低纬深水区的平均〜（231）Pa /〜（230）Th活度比为0.057±0.003，大大低于〜（231）Pa /〜（230）Th的产水率（0.093）并与大西洋和模型模拟得出的全新世沉积物（0.060±0.004）和沉积物捕集材料（0.034±0.012）中的〜（231）Pa /〜（230）Th比率过高相符。这一观察结果与深水向南的输送强烈减弱了大西洋边界清扫的现象是一致的。这些示踪剂在颗粒分级中的纬度依赖性也很明显，在赤道和南大西洋回旋处（〜11）附近观察到分级因子（F_（Th / Pa））升高，而在拉布拉多海（〜3）和南洋（〜2）。 F_（Th / Pa）也存在深度相关性，其特征在于地表水中的值较低，中深度最大值较宽，而朝向海底的值则减小。 F_（Th / Pa）的纬度和深度变化建议反映海洋颗粒化学成分的差异。

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