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Mangahas, Racquelle Sabrina

University of British Columbia

The long-range transport of aerosols originating from Asian deserts and megacities can have a significant impact on the biogeochemical cycling of metals, in the Fe-limited, high nutrient-low chlorophyll (HNLC) regions of the northeast (NE) subarctic Pacific Ocean. These atmospheric aerosols can deposit essential (e.g., Fe from desert dust) and possibly toxic (e.g., Cu from anthropogenic pollutants) metals to surface waters; thereby, affecting micronutrients’ bioavailability, and ultimately primary productivity in this region. To determine the spatiotemporal trends of Asian outflows into the NE Pacific Ocean, aerosols were collected along the Line P transect (GEOTRACES GPpr07; along coastal, intermediate, and open ocean stations), across three seasons: winter (February 2020), spring (March 2022, May 2021), and summer (August 2019, 2020, 2021). Lead isotopic compositions displayed distinctive geochemical signatures, with the winter and spring months being less radiogenic (high²⁰⁸ Pb/²⁰⁶Pb; low ²⁰⁶Pb/²⁰⁷Pb) than the summer months, signifying a greater anthropogenic Asian source in the former seasons. Furthermore, aerosol metal content further revealed seasonality. Aerosols collected in March 2022 (late winter/early spring) contained higher concentrations of the crustal metals Ti, Fe, Mn and Co, in comparison to those in the August 2021 aerosols (summer). The March 2022 aerosols also had the highest concentrations of the anthropogenic elements Cu, Cd and Pb, as well as the mixed elements Ni and V, among all 2021-2022 Line P aerosols. Though our calculations indicate that short-term deposition events (i.e., <10-day) will not significantly change the metal concentrations in the surface mixed layer at OSP, we estimated that the annual atmospheric flux of Fe accounted for ~25% of the total flux to the surface mixed layer (i.e., vertical mixing plus atmospheric flux), while that of Cu accounted for ~65%. This study provides the first insight into the seasonal patterns of long-range transported Asian aerosols along the Line P transect, and their geochemical characterizations. Anthropogenic human activities, such as rapid industrialization and desertification, as well as container ship traffic, will likely increase the input of aerosol-derived metals from distant Asian sources into the NE Pacific Ocean in the coming years, potentially influencing biogeochemical cycles in this Fe-limited oceanic region.

Text

2025-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84417

Oceanography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/