Award: OCE-1737152

DisclaimerThis Project Outcomes Report for the General Public is displayed verbatim as submitted by the PrincipalInvestigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed inthis Report are those of the PI and do not necessarily reflect the views of the National Science Foundation;NSF has not approved or endorsed its content. Award Title: Collaborative Research: US GEOTRACES PMT: Pb and CrisotopesFederal Award ID: 1736996Report Submission Period: 08/01/2021 to 07/31/2022 The goals of the project are:(1) to provide long-term intercalibration of Pb concentrations and Pb isotopes for US GEOTRACES(2) to obtain Pb isotope data from the southern section of the US GEOTRACES GP15 PMT section. The data will be used to evaluate the penetration of anthropogenic Pb into the Pacific Ocean and processesthat affect it, and to evaluate mechanisms that control Cr stable isotope distributions in the marineenvironment. The latter also extends to support for geological interpretations of Cr isotopes in sediments.We have analyzed 450 samples from US GEOTRACES GP15 Alaska to Tahiti ocean section for Pb isotopes(204,206,207,208). This is probably the most detailed ocean section for Pb isotopes. We also obtained ~60analyses for Pb concentrations from three stations. We also obtained Cr isotope data from a station nearTahiti.We are tracing the sources of anthropogenic (mainly) and natural Pb to the ocean, how they aretransported within the ocean, and how they are evolving with time.At the time of sampling (2018) The uppermost waters north of 10.5?S are dominated by Pb emitted byChina, which has a higher 208/206 ratio at a given 206/207 ratio. Much of the Chinese Pb is emitted fromcoal combustion. In the deep South Pacific, the Pb either comes dominantly from natural sources or SouthAmerican sources. In the deep North Pacific, Pb has evolved on a decadal-century scale as the dominantsources were initially US-Australian but now are US-Chinese, transported by sinking particles that arereversibly exchanged. Under high productivity "particle veils" at the equator and ~42?N, the shift fromnatural-U.S. Pb to Chinese Pb in the upper ocean is sufficiently strong that lateral ocean mixing is overcomeby the local flux from the surface. In the mid-depths (300-700m) of the South Pacific, there is a strongsignature of Australian-type Pb showing as a strong minimum in 206/207 (and maximum in 208/207) in thenorthward transport of Sub-Antarctic mode water formed in the South Pacific. This Pb may either come from atmospheric transport of Pb from Australian sources or from the Indian Ocean transported to the SouthPacific by the Antarctic Circumpolar Current.We have seen a snapshot of Pb evolution that a significant stage of the Pb evolution documenting significantU.S., Chinese, and Australian-type Pb sources. The Pb isotope distribution is sufficiently distinct in the deepwaters under the high-flux particle veils that we can see a Pb isotope anomaly that overcomes thehomogenizing influence of lateral ocean eddy mixing, quantitatively constrained. Last Modified: 08/16/2022Modified by: Edward A Boyle Last Modified: 04/27/2023 Submitted by: Robert D Rember