Cosmogenic nuclide and solute flux data from central Cuban rivers emphasize the importance of both physical and chemical mass loss from tropical landscapes
Cosmogenic nuclide and solute flux data from central Cuban rivers emphasize the importance of both physical and chemical mass loss from tropical landscapes
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DOI：
10.5194/gchron-4-435-2022
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发表时间：
2022-07
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通讯作者：
M. K. Campbell;P. Bierman;A. Schmidt;Rita Y. Sibello Hernández;Alejandro García-Moya;L. Corbett;A. Hidy;Hector A. Cartas Aguila;Aniel Guillén Arruebarrena;G. Balco;D. Dethier;Marc Caffee
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作者：
M. K. Campbell;P. Bierman;A. Schmidt;Rita Y. Sibello Hernández;Alejandro García-Moya;L. Corbett;A. Hidy;Hector A. Cartas Aguila;Aniel Guillén Arruebarrena;G. Balco;D. Dethier;Marc Caffee
抽象的。我们使用25个新的测量原位产生的宇宙成因的26铝和10铍在河砂，与估计溶解负荷通量在河水中，表征古巴中部的景观变化的过程和步伐。从古巴中部河砂中提取的石英中的10 Be浓度推断出的长期侵蚀速率范围为3.4-189 Mg km−2 yr−1（平均值为59，中位数为45）。根据河流溶质浓度和模拟径流计算的溶解负荷（10-176 Mg km−2 yr−1;平均值92，中位数97）在23个盆地中的18个中超过了测得的宇宙成因10 Be侵蚀速率。这种差异要求在这种环境下宇宙成因核素测量不能完全代表宇宙尺度的质量损失。24个样品中有16个样品的26 Al/10 Be比值低于稳态暴露或侵蚀的预期值。凹陷的26铝/10铍比发生在许多盆地之间的溶解负荷（高）和侵蚀速率推断宇宙成因核素浓度（低）的最大差距。凹陷的26铝/10铍比是一致的存在下，深，混合，风化层提供延长存储时间的斜坡和/或埋葬和延长存储在河流运输。河水化学分析表明，许多盆地的低26铝/10 Be的比率和高10 Be浓度的基础上，至少有一部分是快速溶解的镁铝榴辉岩。我们的数据表明，在评估潮湿的热带景观质量损失时，考虑到岩石溶解在深度的贡献是特别重要的。在这种温暖潮湿的气候中，矿物溶解可以发生在地表以下数米处，超过大多数宇宙射线的穿透深度，从而产生大多数宇宙成因核素。我们的数据表明，重要的是估计溶质通量和测量成对的宇宙成因核素，以更好地了解在流域尺度的传质过程和速率。
Abstract. We use 25 new measurements of in situ produced cosmogenic 26Al and 10Be in river sand, paired with estimates of dissolved load flux in river water, to characterize the processes and pace of landscape change in central Cuba. Long-term erosion rates inferred from 10Be concentrations in quartz extracted from central Cuban river sand range from 3.4–189 Mg km−2 yr−1 (mean 59, median 45). Dissolved loads (10–176 Mg km−2 yr−1; mean 92, median 97), calculated from stream solute concentrations and modeled runoff, exceed measured cosmogenic-10Be-derived erosion rates in 18 of 23 basins. This disparity mandates that in this environment landscape-scale mass loss is not fully represented by the cosmogenic nuclide measurements. The 26Al / 10Be ratios are lower than expected for steady-state exposure or erosion in 16 of 24 samples. Depressed 26Al / 10Be ratios occur in many of the basins that have the greatest disparity between dissolved loads (high) and erosion rates inferred from cosmogenic nuclide concentrations (low). Depressed 26Al / 10Be ratios are consistent with the presence of a deep, mixed, regolith layer providing extended storage times on slopes and/or burial and extended storage during fluvial transport. River water chemical analyses indicate that many basins with lower 26Al / 10Be ratios and high 10Be concentrations are underlain at least in part by evaporitic rocks that rapidly dissolve. Our data show that when assessing mass loss in humid tropical landscapes, accounting for the contribution of rock dissolution at depth is particularly important. In such warm, wet climates, mineral dissolution can occur many meters below the surface, beyond the penetration depth of most cosmic rays and thus the production of most cosmogenic nuclides. Our data suggest the importance of estimating solute fluxes and measuring paired cosmogenic nuclides to better understand the processes and rates of mass transfer at a basin scale.