Award: OCE-1659995

Despite the importance of marine particles in the cycling of carbon, major and trace nutrients and associated particle reactive elements, they remain difficult to collect in an unbiased manner. Most commonly, marine particles are sampled and classified by size (e.g. filtration) or sinking rate (e.g. sediment traps). The central focus of this project was an intercomparison of different direct, tracer, and optical based estimates of sinking particle flux in the upper ocean, an important parameter in larger scale global carbon and climate models. The main activity was our participation in a research cruise on the RRS Discovery (DY077), April 14-May 1, 2017, Southampton, UK to Weymouth, UK (Figure 1). On this cruise, we compared three different sediment trap designs used to collect sinking particles. Sediment traps, are something like a rain gauge that captures in a tube the sinking particles that are slowly settling through the water. These different estimates of sinking particle flux were also compared to optical methods and a technique that uses a naturally occurring element called thorium-234 that is slightly radioactive and decays with a precise 24.1 day half-life. This clock allows us to calculate very precisely the sinking flux of particles. The results (Figures 2a-c) showed some differences between the different trap designs and different elements measured on sinking particles, but generally similar amounts and types of material were collected. Due to an equipment failure of an older trap design on this cruise, we requested supplemental funding to conduct an additional test cruise in January 2017 off Bermuda, with a new float that is commercially available and can be adapted to form the main platform for our new neutrally-buoyant sediment traps (NBSTs). In addition to providing an intercomparison of existing trap designs, our new NBST design will be freely shared with the scientific community. As part of this project, two female PhD students were trained, one from US (WHOI), and one from the UK who visited WHOI for over 3 months. This is also an early career project for co-PI Margaret Estapa at Skidmore. Last Modified: 09/07/2018 Submitted by: Ken O Buesseler