Abstract
Continental margins play a fundamental role in the carbon cycle as primary oceanic locations of organic carbon (OC) burial. However, gaps remain in our understanding of factors controlling the distribution and preservation of organic matter (OM) in these heterogeneous and dynamic systems. In particular, the impact of hydrodynamic processes on the age, abundance, and stable isotopic composition of sedimentary OC is poorly constrained. Here, we characterize the OC present in bulk and grain-size sediment fractions from seven continental margin settings. Our results reveal that hydrodynamic particle sorting processes exert a ubiquitous influence on the radiocarbon age of OC. Both, hydrodynamic characteristics of mineral particles and the nature of their interactions with OM influence sedimentary OC content, whereas no significant influence of either effect is manifested in corresponding δ13C values. Since OC preferentially resides within the fine silt fraction (2-8 μm), and this fraction accounts for a substantial fraction of the bulk sediment mass, translocation and subsequent re-deposition of distant fine silt has the greatest potential to distort local OC signatures relative to those associated with clay or coarse silt fractions. We suggest that the magnitude of differences in 14C-age and OC content among grain-size fractions, determined by the interplay of hydrodynamic sorting and other site-specific processes, allow three different categories of depositional environment to be defined: initial, stable, and mature. Each domain is characterized by different degrees of vertical and lateral OC supply that reflect influences of local biological productivity and carbon export from overlying surface waters and physical forcing that drive hydrodynamic processes. This generic framework may serve as a guide to refine assessment of OC burial and to constrain the magnitude of potential aliasing among co-eval proxy signals in continental margin sedimentary sequences.
Highlights
Continental margins account for only 10-20% of the global ocean floor, these regions store ca. 90% of the organic carbon (OC) preserved in marine sediments (Hedges and Keil, 1995; Premuzic et al, 1982), and play a key role in the global carbon cycle as major OC sinks
Continental margins are characterized by rapid sediment accumulation, and organic signatures preserved in marine sediment sequences retrieved from these spatially heterogeneous and highly dynamic regions are of strategic value in studies of continent-ocean interactions and pa
Sediment cores were sectioned on-board every 1 cm, and sealed and stored in glass or plastic containers at −20 ◦C until they were further processed for analyses
Summary
Continental margins account for only 10-20% of the global ocean floor, these regions store ca. 90% of the organic carbon (OC) preserved in marine sediments (Hedges and Keil, 1995; Premuzic et al, 1982), and play a key role in the global carbon cycle as major OC sinks. Continental margins account for only 10-20% of the global ocean floor, these regions store ca. 90% of the organic carbon (OC) preserved in marine sediments (Hedges and Keil, 1995; Premuzic et al, 1982), and play a key role in the global carbon cycle as major OC sinks. Continental margins are characterized by rapid sediment accumulation, and organic signatures preserved in marine sediment sequences retrieved from these spatially heterogeneous and highly dynamic regions are of strategic value in studies of continent-ocean interactions and pa-. The observation that OC content is broadly correlated with mineral-specific surface area of continental margin sediments led Mayer (1993) to propose OM sorption on mineral surfaces as a mechanism for its long-term physical protection.
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