Marine organic matter is one of Earth's largest actively cycling reservoirs of organic carbon and nitrogen. The processes controlling organic matter production and removal are important for carbon and nitrogen biogeochemical cycles, which regulate climate. However, the many possible cycling mechanisms have hindered our ability to quantify marine organic matter transformation, degradation and turnover rates. Here we analyse existing and new measurements of the carbon:nitrogen ratio and radiocarbon age of organic matter spanning sizes from large particulate organic matter to small dissolved organic molecules. We find that organic matter size is negatively correlated with radiocarbon age and carbon:nitrogen ratios in coastal, surface and deep waters of the Pacific Ocean. Our measurements suggest that organic matter is increasingly chemically degraded as it decreases in size, and that small particles and molecules persist in the ocean longer than their larger counterparts. Based on these correlations, we estimate the production rates of small, biologically recalcitrant dissolved organic matter molecules at 0.11-0.14 Gt of carbon and about 0.005 Gt of nitrogen per year in the deep ocean. Our results suggest that the preferential remineralization of large over small particles and molecules is a key process governing organic matter cycling and deep ocean carbon storage.
University of California, Irvine, Department of Earth System Science, 2212 Croul Hall, Irvine, California, United States; Stony Brook University, School of Marine and Atmospheric Sciences, CH123, Stony Brook, New York, United States; University of California, Santa Cruz, Department of Ocean Science, 1156 High Street, Santa Cruz, California, United States; Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry (CAMS), LLNL-L397, 7000 East Avenue, Livermore, California, United States
Recommended Citation:
Walker B.D.,Beaupré S.R.,Guilderson T.P.,et al. Pacific carbon cycling constrained by organic matter size, age and composition relationships[J]. Nature Geoscience,2016-01-01,9(12)