Department of Earth System Science

Particulate organic carbon (POC) in the ocean often exhibits more depleted radiocarbon contents (lower Δ ¹⁴C values) than expected if its sole source were POC recently synthesized by primary production and export from the overlying surface waters. An examination of available Δ¹⁴C data sets for sinking POC show that this phenomenon is both common and globally widespread. Also, a strong correlation is found to exist between Δ¹⁴C values of organic carbon and aluminum content in sinking particles that is consistent over a range of oceanic settings. Together, these findings imply that aged organic carbon associated with lithogenic material from sediment resuspension is responsible for the observed low Δ ¹⁴C values as opposed to other processes such as incorporation of dissolved inorganic carbon or dissolved organic carbon into POC at depth. An estimate based on POC flux-weighted Δ¹⁴C values shows that about 35% of sinking POC at the locations studied is derived from resuspended sediment. Our results suggest that resuspension of sediment and its subsequent lateral transport is an important component of the oceanic carbon cycle and should be considered in models of oceanic carbon export and burial.