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首页> 外文期刊>Marine Chemistry >Short-lived radium isotopes on the Scotian Shelf: Unique distribution and tracers of cross-shelf CO_2 and nutrient transport
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Short-lived radium isotopes on the Scotian Shelf: Unique distribution and tracers of cross-shelf CO_2 and nutrient transport

机译：斯科特陆架上的短命镭同位素：跨架CO_2和养分转运的独特分布和示踪剂

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摘要

Radium (Ra) isotopes have become an established tool for investigating mixing rates on continental shelves, and more recently have been used to quantify the release of dissolved compounds enriched in pore-waters into the water column. We present results from Ra sampling of the Scotian Shelf region of the Canadian northwestern Atlantic Ocean, which reveal cross-shelf Ra distributions that are unique compared to other coastal regions. We explain the observations of lower ~(224)Ra activities near the coast, relatively high activities at large distances offshore (＞100 km), and gradients in both offshore and onshore directions by referring to regional geomorphology, as well as shelf bathymetry and circulation patterns. Vertical mixing above shallow offshore banks allows for Ra enrichments in offshore surface waters, while horizontal dispersion of this bottom-generated signal can transport Ra off the shelf break in surface waters, and towards the shore beneath the surface mixed layer. On the Scotian Shelf, estimating horizontal diffusivity (K_x) using a 1-D Ra diffusion model is limited by the presence of two distinct Ra sources (land and sediment), by three dimensional shelf topography, as well as by complex hydrodynamic conditions. Here, a numerical 2-D diffusion model reproduces Ra distributions on the shelf using both coastal and benthic sources. Horizontal and vertical mixing coefficients are then calculated by minimizing deviations between model output and observations. Onshore gradients in CO_2 and nutrient species combined with model-derived K_x values can yield onshore carbon and nutrient fluxes in subsurface waters, which in turn supply the CO_2 outgassing from the Scotian Shelf. Our results thus provide constraints for cross-shelf transports of carbon and nutrients on the Scotian Shelf in order to guide mass balance or model based budget approaches in future studies.
机译：镭（Ra）同位素已成为研究大陆架上混合速率的既定工具，最近已用于量化富集孔隙水的溶解化合物向水柱的释放。我们介绍了加拿大西北大西洋斯科特陆架地区的Ra采样结果，该结果揭示了与其他沿海地区相比独特的跨架Ra分布。通过参考区域地貌学，架子测深和环流，我们解释了在海岸附近〜（224）Ra较低的活动，在远距离（＞ 100 km）相对较高的活动以及近海和陆上方向的梯度观测结果模式。浅层近海堤岸上方的垂直混合可以使Ra富集在近海地表水中，而这种底部生成信号的水平扩散可以将Ra从地表水的现成断层运到地表混合层之下的海岸。在斯科托陆架上，使用一维Ra扩散模型估算水平扩散率（K_x）受到两个不同Ra源（土地和沉积物）的存在，三维架子地形以及复杂水动力条件的限制。在这里，一个二维二维扩散模型使用沿海和底栖资源再现了货架上的Ra分布。然后通过最小化模型输出和观测值之间的偏差来计算水平和垂直混合系数。陆上CO_2和养分种类的梯度与模型推导的K_x值相结合可以在地下水中产生陆上碳和养分通量，进而提供了从陆架上释放出CO_2的作用。因此，我们的结果为在斯科蒂货架上跨架运输碳和营养提供了限制，以指导质量平衡或在未来研究中基于模型的预算方法。

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