G02_P09

Tracing bomb radiocarbon in sinking particulate organic carbon in the deep Sargasso Sea

Schnepper C¹,  Pedrosa-Pamies R², Conte M², Gruber N¹, Haghipour N¹, Eglinton T¹

¹Geological Institute, ETH , Zürich, Switzerland, ² Marine Biological Laboratory, WHOI, Woods Hole, USA

The imprint of bomb radiocarbon on sinking particulate organic carbon (PO¹⁴C) intercepted by sediment traps, together with flux and compositional data, provides information about the origin and dynamics of oceanic particles (Hwang et al., 2010). Of particular interest is the question of whether the intercepted POC in the deep ocean stems from overlying primary production, i.e., as part of the “extrinsic“ biological pump, or whether the POC additionally originates from advection and subsequent aggregation of resuspended sedimentary carbon originating from continental margins and other far-away sources (“intrinsic” flux). Measurements by Kim et al. (2020) revealed significant variability in PO¹⁴C, however the processes driving this variability remain poorly understood. To quantify the intra- and inter-annual variability in PO¹⁴C, an in-depth study was initiated at the Ocean Flux Program site in the Sargasso Sea. This sediment trap time-series has generated (bi-)weekly samples and resulting information on particle fluxes and flux compositions at three water depths (500, 1500, 3200 m) since 1978. Preliminary data reveal intra-annual variations in PO¹⁴C with an amplitude of ca. 100 ‰. Seasonal Δ¹⁴C variations are paralleled by shifts in the POC/Lithogenic ratio. This supports the notion that POC with high Δ¹⁴C values, high POC/Lithogenic ratio and POC flux reflects supply of particles that originate via the “extrinsic“ biological pump, while lower Δ¹⁴C values and POC/Lithogenic ratios may reflect the “intrinsic” flux including resuspended sediments with higher lithogenic content emanating from continental margins. A nascent global PO¹⁴C database will allow to assess the broader relevance of our findings.