Award: OCE-1829885

Even the clearest ocean water is full of particles, which range in size from macromolecular colloids to centimeter-long mucous aggregates of smaller particles. These particles exist in a dynamic balance between the myriad processes that generate, recycle and destroy particles as they sink through the water column. This gravitational transfer of particulate material from the surface through the interior, the particle flux, plays a fundamental role in the transport of energy and materials through the ocean. The particle flux transfers photosynthetic energy in the form of reduced carbon compounds from the surface photosynthetic zone to depth, providing the main food source that fuels life in the vast ocean interior. The depths at which sinking materials eventually degrade to release their contents back into the water column controls the redistribution of nutrient elements by ocean currents and, in turn, spatial patterns of ocean productivity. Chemical scavenging of dissolved elements and organic phases onto sinking particles and biological and chemical aggregation of suspended materials into larger, sinking particles controls the ocean cycling of many elements and also cleanses the ocean of accumulated debris. The particle flux is commonly referred to as the "biological pump" because it is so closely regulated by ecosystem processes. The particle flux also controls, in part, the ocean's ability to take up atmospheric carbon dioxide. Carbon transported to depths greater than the maximum wintertime mixing depth (typically 150-300 m) is isolated from the surface on time scales of decades to centuries, while carbon transported to greater than 1000 m depth is isolated from the surface on time-scales up to that of ocean turnover, approximately 1000 years. The small residual fraction that survives transit through the water column to become buried in deep ocean sediments retains a wealth of information about past ocean conditions that is used to reconstruct Earth history. In 1978 the NSF Chemical Oceanography Program first funded the Oceanic Flux Program (OFP) time-series in the deep Sargasso Sea off Bermuda. The OFP has since evolved to become the longest running deep ocean time series of its kind- an unsurpassed, continuous record of deep particle flux magnitude and composition over the last 44 years. This grant supported maintenance of the OFP mooring equipment and cruise operations to extend the OFP time-series, processing and archiving of the recovered flux material, and in depth analyses of its biological and chemical composition. OFP research, including studies by collaborating scientists and students, has led to numerous discoveries about the controls on particle flux variability over time-scales from weeks to decades, and particle cycling processes within the ocean interior. Two highlights of research findings during this grant are noted here. We found that hurricanes can have large impacts on the particle flux on short-time scales, via upwelling of nutrients to enhance surface ocean productivity and accelerated downward transport of particles, with the impact of a particular hurricane on the particle flux determined by its specific physical characteristics and translational speeds. Another research area focused on the decadal record. This research showed that the deep ocean carbon flux is directly linked to the basin-scale climate organization of the North Atlantic Ocean, a discovery only made possible by the continuous, uninterrupted NSF support of the OFP time-series. While many aspects of the myriad connections between climate, physical forcing and ocean biogeochemical processes and the particle flux remain to be discovered, OFP research findings have made it increasingly clear that the particle flux and even the deepest depths of the ocean will be not be immune to future human-induced alteration in climate patterns and ocean chemistry. Broader impacts: The OFP has been deemed a "community resource" in light its broad support to the oceanographic community. In addition to basic societal contributions that come from an improved understanding of the oceanic particle flux, the OFP also contributes to science education and public outreach. This grant provided seagoing research opportunities to both undergraduate and graduate students, supported several MS and PhD students who used OFP sample material and/or data in their thesis research, and supported and mentored high school assistants and summer undergraduate interns who gained invaluable science and chemistry skills working in the lab with the OFP team. Last Modified: 02/16/2023 Submitted by: Maureen Conte