Award: OCE-1234294

This grant supported the Oceanic Flux Program (OFP), a four-decade long time series of particle flux in the deep Sargasso Sea and the longest time-series of its kind. Understanding the ocean?s particle flux is important because it is a key process regulating many aspects of ocean biogeochemistry and global element cycles. For example, generation of large particles in surface waters, fueled by primary productivity, and the transfer of these particles to ocean depths via the sinking flux provides the food source that support most life in the ocean?s interior and controls, in part, the ocean?s ability to absorb atmospheric carbon dioxide. The depth profile at which particles are degraded and dissolved, coined the "length scale of remineralization", affects how elements and nutrients are redistributed by ocean currents and, in turn, geographic patterns of productivity. New particle formation at depth by the feeding activities of deep-water biota and sorption of dissolved materials cleanses the ocean by aggregating small, suspended particles (e.g. continentally-sourced clays, pollutants, and authigenic minerals precipitated in-situ) and transferring them to the seafloor, to form the underlying sedimentary record. Over its nearly 40 year history, the OFP time-series has transformed our understanding of the oceanic particle flux and how the flux magnitude and composition varies in direct response to changes in the upper ocean environment and processes operating within the water column. OFP results provided the first direct observation of seasonality in the deep ocean, and evidence of the tight linkage between the surface and deep ocean environments via the particle flux. The synergy between the OFP and other Bermuda time-series programs has provided unprecedented new knowledge about the coupling between ocean physics, biology and chemistry and particle flux generation, composition and reprocessing within the ocean interior. Additionally, the OFP has been central in the development of numerous paleo-proxies that are used in reconstructions of past ocean history by studies of the ocean sedimentary record. The OFP time-series is now becoming long enough to reveal how the deep ocean environment is affected on longer time-scales by basin-scale climatic forcing such as the North Atlantic Oscillation and is ideally suited to provide valuable insights into how changing climate scenarios will affect the particle cycle and the deep ocean environment. During this grant cycle, we completed a decadal analysis of the detailed elemental composition of the particle flux, which expanded our knowledge of seasonality and upper ocean controls on elemental fluxes. With depth, the sinking flux becomes depleted in nutrient elements (P, Cd and Zn) due to organic matter remineralization and more enriched in lithogenic and authigenic elements due to suspended particle scavenging and oxide and hydroxide mineral formation. Flux elemental composition exhibits a clear signal of seasonal variations in the relative magnitude of inputs from overlying surface water production and from scavenging processes within the ocean interior. A related study of the carrier phases of the phosphorus flux found that as organic materials are degraded the importance of inorganic carrier phases increases, with a trend towards increasing importance of Mn-Fe (oxy)hydroxides and opal carriers in deeper waters. Last Modified: 02/16/2017 Submitted by: Maureen Conte