Leaky Sinks: Should (Paleo)erosion Rates and Floodplain Sedimentation Rates Covary?
Abstract
Sediments in floodplain are the only available terrestrial record of past environmental conditions in some settings. The information gleaned from these floodplain sediments - specifically rates of sedimentation - are often used as indirect indicators of past erosion rates. Ultimately, erosion and the deposition rates must match to satisfy mass balance. However, over short-timescales storage creates unsteadiness in this balance, and over long-timescales floodplains act as `leaky sinks.' A global compilation of Holocene floodplain accumulation rates suggests rates measured over the last 100 years are faster than those averaged over 1000 years, which in turn are faster than those for the last 10000 years. The apparent acceleration in sedimentation rates appears globally synchronous, despite diachronous human and land use histories and can pre-date significant human land use. The pattern of rate increase in sedimentation over time (inverse power law) and rates of erosion that match over short and long timescales point to the rate increase indicating infilling behavior of all floodplains and not specifically tied to the supply of (anthropogenic) sediment. The apparent synchrony of accelerating floodplain accumulation is consistent with a model that could include but does not require increased anthropogenic erosion or more, recent flooding episodes. In this presentation, we will present our progress and prospects of developing a new technique to quantify paleoerosion rates in floodplain sediments along the Rio Fajardo in eastern Puerto Rico. We use meteoric cosmogenic 10Be concentrations to observe changed in erosion rate at multiple radiocarbon-dated intervals. Due to sea level rise providing accommodation space, this floodplain sedimentation record spans the last 20,000 years. During this time, sedimentation rates and potentially El Nino hurricane-forced erosion have fluctuated in concert with meteoric 10Be concentrations. This work was supported by the U.S. National Science Foundation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP12A..05W
- Keywords:
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- 1165 Sedimentary geochronology;
- GEOCHRONOLOGYDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 3002 Continental shelf and slope processes;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4558 Sediment transport;
- OCEANOGRAPHY: PHYSICAL