LONG-TERM RECORDS OF LANDSCAPE DYNAMICS PRESERVED IN MARINE AND LACUSTRINE SEDIMENTARY CARBON

Erosional processes in upland areas result in transfer of organic carbon (OC) to downstream sites of storage such as continental margins and lakes and thus are important components of the long-term carbon cycle. Conversely, OC in marine and lacustrine sedimentary deposits potentially records changes in the relative roles of various geomorphic processes over time. Shallow erosion processes such as sheetwash, for example, mobilize OC fractions that are relatively young and labile, whereas deeper erosion by mass wasting may deliver older, more refractory material from soils and rocks to fluvial networks and beyond. A number of different techniques can be applied to estimating the contributions of these distinctive pools of OC to sedimentary archives, with potential for reconstructing long-term records of upland response to environmental perturbations.

On the continental shelf off northeastern New Zealand, radiocarbon analysis indicates that storage times for charcoal, plant fragments, and mineral-bound organic carbon in the Waipaoa River catchment have varied substantially over the Holocene. Accumulation of above-average-aged material on the shelf during the middle Holocene and again in the past 700 years is interpreted to record activation of deep seated landslides and/or gullies during first a mid-Holocene wet climate phase and then a period of anthropogenic deforestation. In the Upper Quinault River catchment, Washington, we have further developed criteria for recognizing OC mobilization via shallow and deep-seated landslides with a focus on the potential impacts of large earthquakes on the steep terrain. Results highlight the utility of Rock Eval pyrolysis for estimating the relative contributions of carbon from recent plant biomass, soil, and rocks to sedimentary deposits and thereby for decoding a long-term record of climate and seismicity buried in Lake Quinault.