Biota, fractures, and thresholds: Emergent self-organization in landscape evolution?

这项建议是我们正在进行的工作的延续，在地球形状第一阶段，我们调查的生物控制切割和河流泥沙运输。我们的研究重点是流量变化和侵蚀阈值对河流下切的综合影响。在第一阶段，我们利用地球形状的气候和植被梯度来破译生物签名的流量变化和侵蚀效率。然而，第一阶段的结果也表明，河流沉积物的大小（侵蚀阈值）和风化层厚度的巨大空间变异性都沿着和跨越EarthShape梯度。在个别EarthShape研究站点内，观察到的风化层厚度的空间梯度似乎遵循断裂密度的梯度。因此，我们假设，生物群，通过其对化学风化的影响，也可能会影响沉积物粒度，但这种影响可能是有限的断裂密度。此外，EarthShape场址的剥蚀率很低（约10米/百万年）。这意味着我们所研究的景观是在数百万年的时间内形成的，当时的条件可能与现在不同。要解开化学风化，沉积物的大小，因此侵蚀阈值的生物影响，并避免虚假的相关性，我们承认潜在的重要影响的断裂密度和景观演变的时间依赖性。在这里，我们建议（1）定量断裂间距，风化层厚度和沉积物大小之间的关系，（2）确定子流域尺度的空间和时间变化的山坡剥蚀率，和（3）联合收割机结合景观演化模型中的这些观察，以量化生物区系对河流切割的影响。为此，我们将广泛利用第一阶段从所有项目收集的数据和观测结果，并将这些数据和观测结果与新的实地测量结果结合起来，采用一种新的建模方法，明确考虑水文和地形对化学风化和沉积物粒度的影响。我们的研究结果将提供地球形状网站的可比性的关键限制，我们的建模方法将提供一个新的接口，有助于整合不同的科学方法在地球形状计划。

This proposal is a continuation of our ongoing work in EarthShape phase 1, in which we investigate the biotic controls on incision and sediment transport by rivers. Our research focuses on the combined effect of discharge variability and erosion thresholds on river incision. During phase 1, we exploit the EarthShape climate and vegetation gradient to decipher the biotic signature in discharge variability and erosional efficiency. However, results from phase 1 also indicate enormous spatial variability in river sediment size (erosion thresholds) and regolith thickness both along and across the EarthShape gradient. Within individual EarthShape study sites, observed spatial gradients in regolith thickness appear to follow gradients in fracture density. We thus hypothesize that biota, through its influence on chemical weathering, may also affect sediment grain sizes, but that this influence may be limited by fracture density. Furthermore, denudation rates in the EarthShape sites are low (~10 m/Myr). This means that the landscapes we study have been formed over time periods of up to several million years, during conditions that were likely different from the present. To unravel the biotic influence on chemical weathering, sediment size, and hence erosion thresholds, and to avoid spurious correlations, we acknowledge the potentially important influence of fracture density and the time-dependent nature of landscape evolution. Here, we propose to (1) quantify the relationship between fracture spacing, regolith thickness, and sediment size, (2) determine the sub-basin scale spatial and temporal variability in hillslope denudation rates, and (3) combine these observations in landscape evolution modeling to quantify the influence of biota on river incision. To do so, we will make extensive use of data and observations collected from all projects during phase 1 and combine these with new field measurements in a new modeling approach in which we explicitly account for hydrologic and topographic effects on chemical weathering and sediment size. Our results will provide key constraints on the comparability of the EarthShape sites, and our modeling approach will provide a new interface that helps integrating the diverse scientific approaches in the EarthShape program.