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首页> 外文期刊>Paleoceanography >Correcting for the influence of ice-rafted detritus on grain size-based paleocurrent speed estimates
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Correcting for the influence of ice-rafted detritus on grain size-based paleocurrent speed estimates

机译：校正浮冰碎屑对基于粒度的古流速度估计的影响

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The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modeling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electrosensing and laser diffraction techniques, despite issues previously raised on the low precision of electrosensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modeling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction, the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modeling meaningful current speed reconstructions can be obtained from mixed sediments.
机译：深海沉积物的颗粒大小显然是当前速度的简单替代。但是，当粒度分布反映了过程的组合时，基于粒度的代理可能是模棱两可的，当前仅对其中一个进行排序。尤其是，这种沉积物的混合阻碍了与冰河北大西洋漂流事件相关的深度循环变化的重建，因为可变的浮冰碎屑（IRD）输入可能会错误地暗示当前的速度变化。已经提出了逆建模作为克服该问题的方法。但是，这种方法需要高精度的尺寸测量，这些尺寸记录了尺寸分布的微小变化。在这里，我们显示出可以使用电感应和激光衍射技术获得此类数据，尽管先前在电感应方法的低精度和对激光衍射的潜在晶粒形状影响方面引发了一些问题。从北大西洋的沉积岩心获得的岩心尺寸下降模式对于这两种技术都是相似的，这进一步证明了两种技术都能产生可比结果的结论。但是，IRD输入会导致粗化，这可能会暗示更快的电流速度。我们表明，只要考虑宽尺寸光谱，就可以使用逆向建模说明这种IRD影响。这会产生与其他代理一致的当前速度变化。因此，我们的实验表明，对于当前速度重建，仪器的选择要服从对确定尺寸分布的各种过程的正确认识，而通过使用逆模型，可以从混合沉积物中获得有意义的当前速度重建。

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