Award: OCE-1657781

This project funded the management and implementation of the ?GP15 Pacific Meridional Transect?, a U.S. GEOTRACES research cruise that crossed over 5400 miles of the Pacific Ocean, from the Alaskan coast in the North Pacific at 56?N south to Tahiti in the South Pacific at 20?S along 152?W (Figure 1). The International GEOTRACES Programme (www.geotraces.org) is a coordinated global effort to measure the distribution of ?trace elements and their isotopes? (TEIs) in the global ocean. Trace elements are any element on the periodic table that is found in very small quantities. The trace elements measured by the GEOTRACES program include those that are essential nutrients for life in the ocean, such as iron, cobalt, and zinc, those that are contaminants and toxic, such as lead and mercury, and those that trace specific inputs, such as aluminum for inputs from land. Isotopes are variations of elements that differ in their atomic mass, and can be stable or radioactive. The stable isotopes (such as for nitrogen and iron) are useful for identifying sources and processes affecting that element. The radioactive isotopes (such as beryllium and thorium) provide a natural clock by which rates of important processes can be quantified. The distribution of these TEIs provide a fingerprint of key biological, chemical, physical, and geological processes that may be difficult or impossible to measure directly. The simultaneous measurement of a suite of over a dozen TEIs on every GEOTRACES cruise provides exquisite constraints on oceanographic processes. The GEOTRACES programme is thus providing us new insights about how the ocean works. The U.S. GEOTRACES GP15 Pacific Meridional Transect crossed many of the major oceanographic regimes on Earth, allowing us to apply our geochemical lens to understanding large swaths of the global ocean. Major research questions included the following: Are the volcanic rocks of coastal Alaska changing the chemistry of the North Pacific ocean, and what does this tell us about how rocks influence ocean chemistry? How do the TEI distributions differ between highly productive regions, such as the Gulf of Alaska and the Equatorial Pacific, and ocean deserts, such as the subtropical North and South Pacific, and how does this help us understand major biological, chemical, and physical processes in the ocean? Separate individual grants were submitted to NSF by 25 groups of scientists from across the United States to measure specific TEIs on samples from the GP15 cruise. The goal of the management team (this project) at sea was to coordinate and collect all water, sediment, and suspended particle samples needed by the 25 groups of scientists, and to collect and measure important oceanographic parameters such as temperature, salinity, nutrients, oxygen, and phytoplankton pigment concentrations required by most groups to provide the environmental context for their specific TEI measurements. Altogether, 37 scientists on board spent 67 days at sea (split into two legs) (Figure 2), sampled from 36 ?stations? spaced regularly throughout the transect (Figure 1), collected tens of thousands of liters of water for measurements of TEIs in seawater and filtered hundreds of thousands of liters of water for measurements of TEIs in marine particles. After the cruise, the goal of the management team was to facilitate the sharing of data and collaboration between the 25 groups of scientists to ensure that the entire cruise was more than the sum of its parts. Much of this data synthesis time occurred during COVID restrictions, so we organized regular virtual Zoom meetings to ensure that all groups could continue to learn from each other despite our physical isolation and were finally able to meet in person in March 2022 for a final data synthesis workshop. Papers are being published in highly regarded scientific journals by the participants of the cruise, and data from this project will be released to the public and made freely available. Early data from the GP15 cruise have already been released and are available at: https://www.geotraces.org/geotraces-intermediate-data-product-2021/. Last Modified: 12/29/2022 Submitted by: Phoebe J Lam