Award: OCE-1736601

Intellectual Merit: We determined the concentration and chemical composition of marine particles in the ocean along a North-South track at 152W from Alaska to Tahiti in the Pacific Ocean (the U.S. GEOTRACES GP15 Pacific Meridional Transect). This includes the concentrations of the major particle components, which are particulate organic carbon (POC), the minerals calcium carbonate and opal, and lithogenic (suspended sediment) particles, and minor and trace elements. Marine particles play crucial roles in the chemical and biological cycling of most elements in the ocean, including how major elements such as carbon and trace elements such as lead are transformed and transported in the ocean. For example, the production, destruction, and sinking of particulate organic carbon in the ocean, termed the biological pump, are an important set of processes by which the ocean takes up carbon dioxide from the atmosphere. One of our papers from this project (Amaral et al., 2024) used the particulate organic carbon measured on this cruise to quantify the rates of these particle transformations across a range of environmental conditions. We found that particles tend to sink faster with depth, that the respiration (destruction) of organic carbon was not sensitive to temperature and oxygenic concentrations, as we had hypothesized, and that particles in productive regions were less sticky that in less productive regions. Another paper from this project (Lanning et al., 2023) showed that the biological pump processes modelled in Amaral et al. 2024 were responsible for efficiently transporting surface lead isotope signatures into the deep ocean through a process called reversible scavenging, in which lead atoms adsorb (stick) to the surface of marine particle of primarily biological origin in the surface ocean, but then desorb (unstick) from particles and back into the water phase as the particles sink, painting the surface signature of lead isotopes all the way down to the bottom of the ocean. Broader Impacts: this project supported an early career female research scientist, four PhD students, one of whom is a first generation Latinx student (and who received his PhD in 2023), and two of whom are women, and two undergraduate students at the University of California, Santa Cruz. One of the undergraduate students used some of the data that she helped to generate to design a high school curricular module to explain the biological carbon pump. She worked with local high school teachers, who provided feedback on materials and activities, one of whom is using the materials that she created in his classroom in the San Lorenzo Valley School District in Santa Cruz county. Last Modified: 02/18/2024 Submitted by: PhoebeJLam