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1. The competition between anthropogenic aerosol and greenhouse gas climate forcing is revealed by North Pacific water-mass changes

   https://doi.org/10.1126/sciadv.adh7746  

   Shi, Jia-Rui ; Wijffels, Susan E. ; Kwon, Young-Oh ; Talley, Lynne D. ; Gille, Sarah T. ( September 2023 , Science Advances)

   Modeled water-mass changes in the North Pacific thermocline, both in the subsurface and at the surface, reveal the impact of the competition between anthropogenic aerosols (AAs) and greenhouse gases (GHGs) over the past 6 decades. The AA effect overwhelms the GHG effect during 1950–1985 in driving salinity changes on density surfaces, while after 1985 the GHG effect dominates. These subsurface water-mass changes are traced back to changes at the surface, of which ~70% stems from the migration of density surface outcrops, equatorward due to regional cooling by AAs and subsequent poleward due to warming by GHGs. Ocean subduction connects these surface outcrop changes to the main thermocline. Both observations and models reveal this transition in climate forcing around 1985 and highlight the important role of AA climate forcing on our oceans’ water masses.

    

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2. Subsurface Ocean Temperature Responses to the Anthropogenic Aerosol Forcing in the North Pacific

   https://doi.org/10.1029/2022GL101035  

   Shi, Jia‐Rui ; Kwon, Young‐Oh ; Wijffels, Susan E. ( January 2023 , Geophysical Research Letters)

   Separating the climate response to external forcing from internal climate variability is a key challenge. While most previous studies have focused on surface responses, here we examine zonal‐mean patterns of North Pacific subsurface temperature responses. In particular, the changes since 1950 driven by anthropogenic aerosol emissions are found by using a pattern recognition method. Based on the single‐forcing large‐ensemble simulations from two models, we show that aerosol forcing caused a nonmonotonic temporal response and a characteristic zonal‐mean pattern within North Pacific, which is distinct from the pattern associated with internal variability. The aerosol‐forced pattern with the nonmonotonic temporal feature shows a substantial temperature change in subpolar regions and a reversed change on the southern flank of the subtropical gyre. A similar characteristic pattern and nonmonotonic time evolution are extracted from the subsurface observations, which likely reflect the subsurface responses to the aerosol forcing, although differences exist with the simulated responses.

    

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3. Surface Ocean Biogeochemistry Regulates the Impact of Anthropogenic Aerosol Fe Deposition on the Cycling of Iron and Iron Isotopes in the North Pacific

   https://doi.org/10.1029/2022GL098016  

   König, D. ; Conway, T. M. ; Hamilton, D. S. ; Tagliabue, A. ( July 2022 , Geophysical Research Letters)

   Distinctively‐light isotopic signatures associated with Fe released from anthropogenic activity have been used to trace basin‐scale impacts. However, this approach is complicated by the way Fe cycle processes modulate oceanic dissolved Fe (dFe) signatures (δ⁵⁶Fe_diss) post deposition. Here we include dust, wildfire, and anthropogenic aerosol Fe deposition in a global ocean biogeochemical model with active Fe isotope cycling, to quantify how anthropogenic Fe impacts surface ocean dFe and δ⁵⁶Fe_diss. Using the North Pacific as a natural laboratory, the response of dFe, δ⁵⁶Fe_diss, and primary productivity are spatially and seasonally variable and do not simply follow the footprint of atmospheric deposition. Instead, the effect of anthropogenic Fe is regulated by the biogeochemical regime, specifically the degree of Fe limitation and rates of primary production. Overall, we find that while δ⁵⁶Fe_dissdoes trace anthropogenic input, the response is muted by fractionation during phytoplankton uptake, but amplified by other isotopically‐light Fe sources.

    

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4. Seaglider surveys at Ocean Station Papa: Circulation and water mass properties in a meander of the North Pacific Current: SEAGLIDERS AT STATION PAPA

   https://doi.org/10.1002/2016JC011920  

   Pelland, Noel A. ; Eriksen, Charles C. ; Cronin, Meghan F. ( September 2016 , Journal of Geophysical Research: Oceans)
5. Diel variability of bulk optical properties associated with the growth and division of small phytoplankton in the North Pacific Subtropical Gyre

   https://doi.org/10.1364/AO.394123  

   Henderikx Freitas, Fernanda ; Dugenne, Mathilde ; Ribalet, François ; Hynes, Annette ; Barone, Benedetto ; Karl, David M. ; White, Angelicque E. ( July 2020 , Applied Optics)

   Cross-platform observing systems are requisite to capturing the temporal and spatial dynamics of particles in the ocean. We present simultaneous observations of bulk optical properties, including the particulate beam attenuation (${\mathit{\text{c}}}_{\mathit{\text{p}}}$) and backscattering ($b_{\text{bp}}$) coefficients, and particle size distributions collected in the North Pacific Subtropical Gyre. Clear and coherent diel cycles are observed in all bulk and size-fractionated optical proxies for particle biomass. We show evidence linking diurnal increases in${\mathit{\text{c}}}_{\mathit{\text{p}}}$and${\mathit{\text{b}}}_{\text{bp}}$to daytime particle growth and division of cells, with particles$<<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$driving the daily cycle of particle production and loss within the mixed layer. Flow cytometry data reveal the nitrogen-fixing cyanobacteriumCrocosphaera($\sim <\#comment/>4-<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$) to be an important driver of${\mathit{\text{c}}}_{\mathit{\text{p}}}$at the time of sampling, whereasProchlorococcusdynamics ($\sim <\#comment/>0.5\text{µ<\#comment/>}\mathrm{m}$) were essential to reproducing temporal variability in${\mathit{\text{b}}}_{\text{bp}}$. This study is a step towards improved characterization of the particle size range represented byin situbulk optical properties and a better understanding of the mechanisms that drive variability in particle production in the oligotrophic open ocean.

    

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