Award: OCE-2414704

Oceanic Flux Program (OFP): Time Series Particle Flux Measurements in the Sargasso Sea

This award supported the Oceanic Flux Program (OFP), the long-term time series of deep-ocean particle flux in the Sargasso Sea that has continuously operated since 1978. The OFP is the longest running deep-ocean sediment trap program providing a unique record of the magnitude, composition, and variability of particle flux in the Sargasso Sea (North Atlantic).

Particle flux plays a central role in ocean biogeochemistry by capturing organic carbon and other elements produced in surface waters and transporting them to the deep ocean. Sinking particles carry carbon, nutrients, and trace elements to the deep ocean, providing the primary food source for most organisms living below the sunlit zone and contributing to long-term sequestration at depth. The depth at which these particles are degraded controls both the redistribution of elements by ocean circulation and the residence time of carbon in the ocean interior. Particle cycling processes also aggregate and relocate suspended materials from seawater, including lithogenic particles, authigenic minerals, and anthropogenic contaminants, transferring them to the seafloor where they become part of the sedimentary record.

During this grant period, the Oceanic Flux Program continued measurements of particle flux at 500 m, 1500 m, and 3200 m depths, extending the time series while preserving its long-term continuity and high data quality. The grant supported maintenance of the OFP mooring equipment and cruise operations, as well as laboratory processing and physical archiving of recovered flux material, measurements of mass flux, in depth analyses of its biological and chemical composition, and continued development of a quantitative image archive began in 2004 that documents and virtually preserves fragile particle types (such as fecal pellets and aggregates) not preserved intact during the processing for  long-term dry storage. Research conducted by the OFP team and collaborating scientists and students using these data and samples has yielded new insights into the dynamic processes controlling particle flux variability over time scales from weeks to decades and into particle cycling mechanisms within the ocean interior.

A major outcome of this award was the publication of a four-decade (1978–2022) climatology of deep particle flux. This synthesis provides the first comprehensive view of seasonal and interannual variability in the deep ocean particle flux and establishes a baseline for evaluating future environmental change. The results show strong seasonality in flux magnitude and composition, large interannual variability, especially in winter and spring, and decreasing variability with depth. Analyses also demonstrate that a substantial fraction of deep particle flux is generated within the ocean interior through aggregation and scavenging processes, rather than originating solely from direct export out of the surface ocean.

The OFP record further shows that deep carbon flux is temporally coherent throughout the water column and closely linked to surface ocean productivity, with a characteristic lag of approximately one month. Quantification of the fraction of surface production and export that reaches bathypelagic depths provides important constraints on the efficiency of the ocean's biological pump and its role in long-term carbon sequestration.

The OFP also continued to document the effects of extreme events on the biological pump. Expanded analyses of hurricane impacts show that the magnitude of enhanced carbon export to the deep ocean depends on storm characteristics and upper ocean conditions. In addition, OFP observations revealed episodic transport of shallow-water carbonate platform sediments to deep ocean during the passage of two hurricanes impacting Bermuda, with implications for deep-ocean alkalinity, trace element cycling, and sediment composition.

Beyond scientific outcomes, the OFP continues to function as a shared research resource for the oceanographic community. The project supported graduate and undergraduate research, provided shipboard and laboratory training opportunities, and engaged high school students as laboratory assistants. OFP samples, data, and infrastructure were used by numerous collaborators across a wide range of disciplines, amplifying the scientific impact of the program.

The OFP time series continues to provide an essential reference for understanding how the ocean's biological pump responds to natural variability and long-term environmental change.

 

Last Modified: 01/14/2026
Modified by: Rut Pedrosa Pamies