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Abstract Distributions of the natural radionuclide²¹⁰Po and its grandparent²¹⁰Pb along the GP15 Pacific Meridional Transect provide information on scavenging rates of reactive chemical species throughout the water column and fluxes of particulate organic carbon (POC) from the primary production zone (PPZ).²¹⁰Pb is in excess of its grandparent²²⁶Ra in the upper 400–700 m due to the atmospheric flux of²¹⁰Pb. Mid‐water²¹⁰Pb/²²⁶Ra activity ratios are close to radioactive equilibrium (1.0) north of ∼20°N, indicating slow scavenging, but deficiencies at stations near and south of the equator suggest more rapid scavenging associated with a “particle veil” located at the equator and hydrothermal processes at the East Pacific Rise. Scavenging of²¹⁰Pb and²¹⁰Po is evident in the bottom 500–1,000 m at most stations due to enhanced removal in the nepheloid layer. Deficits in the PPZ of²¹⁰Po (relative to²¹⁰Pb) and²¹⁰Pb (relative to²²⁶Ra decay and the²¹⁰Pb atmospheric flux), together with POC concentrations and particulate²¹⁰Po and²¹⁰Pb activities, are used to calculate export fluxes of POC from the PPZ.²¹⁰Po‐derived POC fluxes on large (>51 μm) particles range from 15.5 ± 1.3 mmol C/m²/d to 1.5 ± 0.2 mmol C/m²/d and are highest in the Subarctic North Pacific;²¹⁰Pb‐derived fluxes range from 6.7 ± 1.8 mmol C/m²/d to 0.2 ± 0.1 mmol C/m²/d. Both²¹⁰Po‐ and²¹⁰Pb‐derived POC fluxes are greater than those calculated using the²³⁴Th proxy, possibly due to different integration times of the radionuclides, considering their different radioactive mean‐lives and scavenging mean residence times. 

Abstract Deposition of aerosols to the surface ocean is an important factor affecting primary production in the surface ocean. However, the sources and fluxes of aerosols and associated trace elements remain poorly defined. Aerosol²¹⁰Pb,²¹⁰Po, and⁷Be data were collected on US GEOTRACES cruise GP15 (Pacific Meridional Transect, 152°W; 2018).²¹⁰Pb fluxes are low close to the Alaskan margin, increase to a maximum at ∼43°N, then decrease to lower values. There is good agreement between²¹⁰Pb fluxes and long‐term land‐based fluxes during the SEAREX program (1970–1980s), as well as between GP15 and GP16 (East Pacific Zonal Transect, 12°S; 2013) at adjacent stations. A normalized fractionf(⁷Be,²¹⁰Pb) is used to discern aerosols with upper (highf) versus lower (lowf) troposphere sources. Alaskan/North Pacific aerosols show significant continental influence while equatorial/South Pacific aerosols are supplied to the marine boundary layer from the upper troposphere. Lithogenic trace elements Al and Ti show inverse correlations withf(⁷Be,²¹⁰Pb), supporting a continental boundary layer provenance while anthropogenic Pb shows no clear relationship withf(⁷Be,²¹⁰Pb). All but four samples have²¹⁰Po/²¹⁰Pb activity ratios <0.2 suggesting short aerosol residence time. Among the four samples (²¹⁰Po/²¹⁰Pb = 0.42–0.88), two suggest an upper troposphere source and longer aerosol residence time while the remaining two cannot be explained by long aerosol residence time nor a significant component of dust. We hypothesize that enrichments of²¹⁰Po in them are linked to Po enrichments in the sea surface microlayer, possibly through Po speciation as a dissolved organic or dimethyl polonide species.