Temporal Constraints on the Delivery of Terrestrial Organic Carbon to Marine Sediments

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ABSTRACTOCE-0137005In this project, researchers at the Woods Hole Oceanographic Institution will attempt to quantify the residence times of terrestrial vascular plant biomarkers between their synthesis on land and deposition in marine sediments. The approach will involve ultra-high resolution sampling of anoxic, annually laminated sediments and compound-specific AMS 14 C dating of leaf waxes and lignin phenols. Above-ground nuclear weapons testing peaked in 1963, creating a large and abrupt peak in atmospheric 14C concentration that is discernable well above the uncertainty in compound- specific AMS 14 C measurements. The radiocarbon "bomb spike" individual biomarker compounds (or compound classes) will be identified with near-annual sampling resolution. The calendar age of the 14 C peak identified in the biomarker compounds will be compared to the known 1963 age layer in annually laminated sediments from four different marine sites to derive biomarker residence and transport times with precision as high as 1-2 years.A modeling approach will be used to examine the characteristics of the bomb spike curve, in order to distinguish between eolian and riverine transport pathways, as well as periods of storage in reservoirs (e.g., forest litter, soils, river beds, floodplains and lakes). In addition to timing of the bomb spike, the high-resolution sampling will permit identification of details of the magnitude and shape of the curves, key diagnostics for reservoir storage time as well as contamination with ancient organic compounds. The study locations will encompass a transect of climatic zones from the tropical Cariaco Basin (Venezuela), across the temperate United States (Pettaquamscutt River, RI; Santa Barbara Basin, CA; Eel River basin, CA), up to the boreal Saanich Inlet (British Columbia, Canada). These study sites vary according to drainage basin (area, topography), climate (mean annual temperature, precipitation), vegetation cover (tropical rainforest, semi-arid scrubland, temperate deciduous forest, boreal evergreen forest), and degree of human land-use impact. This proposed work should provide insights into a wide range of environmental and anthropogenic impacts on the residence times of terrestrial organic carbon, allowing results to be scaled globally. In addition, accurately quantifying terrestrial biomarker residence times will contribute greatly to the development of these compounds as geochronological and paleoclimatic proxies.