A Decadal Record of Elemental Composition of the Particle Flux in the Deep Sargasso Sea

The production, flux and depth of remineralization of biogenic particles controls, in part, the oceanic distributions of many elements. Additionally, details of particle composition provide rich information on atmospheric deposition, surface productivity, ocean circulation and processes such as zooplankton feeding, aggregation/disaggregation and chemical scavenging that control particle cycling processes within the ocean interior. Even so, there have been relatively few studies of the elemental composition of the deep ocean flux. Here we present a decadal time-series of particulate elemental fluxes (Mg, Al, Si, P, Ca, Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Ba, and Pb) at the Oceanic Flux Program (OFP) time-series site located near Bermuda. A distinct seasonality is clearly apparent in the elemental composition of the flux at all three trap depths (500, 1500 and 3200m depths), which reflects variations in the relative magnitude of inputs from overlying surface water production ("extrinsic" flux) and scavenging/aggregation processes within the ocean interior ("intrinsic" flux). With increasing depth, the sinking flux becomes depleted in nutrient elements (P, Cd and Zn) due to organic matter remineralization and enriched in lithogenic and redox-sensitive elements, reflecting scavenging of suspended lithogenic particles advected from continental margins and authigenic precipitation of Mn-Fe oxides. Interannual variability in elemental fluxes and particle composition is also clearly apparent in the record as well as multi-year trends, underscoring the close linkage between ocean variability and deep flux composition.