Youhei Yamashita

The subarctic North Pacific, the terminus of the global deep overturning circulation, hosts silicate-rich waters that sustain diatom-driven primary production. However, the pathways linking deep silicic acid (dissolved Si; dSi) reservoirs to the surface ocean remain unresolved. Here, we identify a direct dSi pathway from the deep reservoir to the surface in the Aleutian Passes by quantifying turbulent dSi flux using in-situ observations of turbulence and bottle-sampled dSi. This pathway is driven by intense turbulence in the Aleutian Passes, yielding vertical dSi fluxes of 1.9–11 mmol m ^− 2 d ^− 1 and a total vertical transport of (1.5–8.2) × 10 ¹¹ mol yr ^− 1 from mid-depth dSi maxima at ~2000 m depth to the surface layer. This transport accounts for 1.3–7.3% of global biogenic silica export production. This pathway possibly enhances diatom productivity in the downstream Bering Sea and subarctic North Pacific, where the dissolution of sinking diatom particles replenishes the deep dSi reservoir.

Pyrogenic carbon (PyC) is a continuum of compounds generated during the incomplete combustion of biomass or fossil fuels. Water-soluble PyC (WSPyC), a PyC smaller than 0.7 µm, is transported to the ocean via rivers or atmospheric deposition and is considered a key component in the long-term regulation of the global carbon cycle. Compared to the riverine input flux, the atmospheric deposition flux of WSPyC may have large uncertainties due to limited observations. This study examines the factors influencing WSPyC concentration in atmospheric aerosols in Sapporo, Hokkaido, based on a year-round observation. The WSPyC concentration in the aerosols, determined with the benzene polycarboxylic acid method, ranged from 1.41 to 46.5 ng C m−3, with an average value of 13.7±10.6 ng C m−3. The average concentration was lower than previously observed near combustion sources. Positive Matrix Factorization (PMF) analysis revealed that 60 % of the WSPyC concentration was attributed to a K+-dominated combustion, which included the burning of biomass and biofuels. Meanwhile, 40 % of WSPyC was associated with factors related to the atmospheric aging of aerosols derived from fossil fuel combustion. The global WSPyC deposition flux to the ocean has previously been estimated based on the concentration ratio of WSPyC to elemental carbon (EC) or water-soluble organic carbon (WSOC). The results of this study suggested that these ratios vary due to the atmospheric aging processes, including photochemical production of WSPyC from soot, indicating the need for a reassessment of the global WSPyC deposition flux.

The Sea of Okhotsk is one of the most biologically productive regions, where primary production during spring phytoplankton blooms after sea ice melting/retreat has the potential to contribute to the sea-to-air emission flux of atmospheric organic aerosols (OAs). To elucidate the effect of oceanic biological activity during blooms on the formation process of OAs, aerosol samples and surface seawater were collected during the bloom period of April 2021. Organic matter (OM) was the dominant component of submicrometer aerosols during both the bloom (53 ± 16 %) and bloom-decay periods (44 ± 12 %), with OM being highly water-soluble during the bloom. Stable carbon isotope ratios of aerosol organic carbon (OC) showed that 73 %–82 % of the observed aerosols were of marine origin. Relations between water-soluble OC (WSOC) and molecular tracers suggested that aerosol WSOC of marine origin was likely affected by secondary formation from precursors such as α-pinene and DMS-relevant compounds rather than primary emissions of sea spray aerosols. The amounts of water-soluble organic nitrogen (WSON) in aerosol and dissolved organic nitrogen (DON) in seawater during the bloom were larger than those during bloom-decay period, suggesting the preferential formation of N-containing water-soluble OAs of marine origin during the bloom. The increase in the amount of DON during the bloom was likely associated with the predominant diatoms, Thalassiosira spp. and Fragilariopsis spp. This study highlights the significant contribution of the secondary formation of marine biogenic OAs with increased N-containing components during the bloom after sea ice melting/retreat in the subarctic ocean.

Pyrogenic carbon (PyC) is a continuum of compounds generated during the incomplete combustion of biomass or fossil fuels. Water-soluble PyC (WSPyC), a PyC smaller than 0.7 µm, is transported to the ocean via rivers or atmospheric deposition and is considered a key component in the long-term regulation of the global carbon cycle. Compared to the riverine input flux, the atmospheric deposition flux of WSPyC may have large uncertainties due to limited observations. This study examines the factors influencing WSPyC concentration in atmospheric aerosols in Sapporo, Hokkaido, based on a year-round observation. The WSPyC concentration in the aerosols, determined with the benzene polycarboxylic acid method, ranged from 1.41 to 46.5 ngC m⁻³, with an average value of 13.7±10.6 ngC m⁻³. The average concentration was lower than previously observed near combustion sources. Positive Matrix Factorization (PMF) analysis revealed that 60 % of the WSPyC concentration was attributed to a K⁺-dominated combustion, which included the burning of biomass and biofuels. Meanwhile, 40 % of WSPyC was associated with factors related to the atmospheric aging of aerosols derived from fossil fuel combustion. The global WSPyC deposition flux to the ocean has previously been estimated based on the concentration ratio of WSPyC to elemental carbon (EC) or water-soluble organic carbon (WSOC). The results of this study suggested that these ratios vary due to the atmospheric aging processes, including photochemical production of WSPyC from soot, indicating the need for a reassessment of the global WSPyC deposition flux.

Pyrogenic carbon (PyC) is a continuum of compounds generated during the incomplete combustion of biomass or fossil fuels. Water-soluble PyC (WSPyC), a PyC smaller than 0.7 µm, is transported to the ocean via rivers or atmospheric deposition and is considered a key component in the long-term regulation of the global carbon cycle. Compared to the riverine input flux, the atmospheric deposition flux of WSPyC may have large uncertainties due to limited observations. This study examines the factors influencing WSPyC concentration in atmospheric aerosols in Sapporo, Hokkaido, based on a year-round observation. The WSPyC concentration in the aerosols, determined with the benzene polycarboxylic acid method, ranged from 1.41 to 46.5 ngC m⁻³, with an average value of 13.7±10.6 ngC m⁻³. The average concentration was lower than previously observed near combustion sources. Positive Matrix Factorization (PMF) analysis revealed that 60 % of the WSPyC concentration was attributed to a K⁺-dominated combustion, which included the burning of biomass and biofuels. Meanwhile, 40 % of WSPyC was associated with factors related to the atmospheric aging of aerosols derived from fossil fuel combustion. The global WSPyC deposition flux to the ocean has previously been estimated based on the concentration ratio of WSPyC to elemental carbon (EC) or water-soluble organic carbon (WSOC). The results of this study suggested that these ratios vary due to the atmospheric aging processes, including photochemical production of WSPyC from soot, indicating the need for a reassessment of the global WSPyC deposition flux.

Pyrogenic carbon (PyC) is a continuum of compounds generated during the incomplete combustion of biomass or fossil fuels. Water-soluble PyC (WSPyC), a PyC smaller than 0.7 µm, is transported to the ocean via rivers or atmospheric deposition and is considered a key component in the long-term regulation of the global carbon cycle. Compared to the riverine input flux, the atmospheric deposition flux of WSPyC may have large uncertainties due to limited observations. This study examines the factors influencing WSPyC concentration in atmospheric aerosols in Sapporo, Hokkaido, based on a year-round observation. The WSPyC concentration in the aerosols, determined with the benzene polycarboxylic acid method, ranged from 1.41 to 46.5 ngC m⁻³, with an average value of 13.7±10.6 ngC m⁻³. The average concentration was lower than previously observed near combustion sources. Positive Matrix Factorization (PMF) analysis revealed that 60 % of the WSPyC concentration was attributed to a K⁺-dominated combustion, which included the burning of biomass and biofuels. Meanwhile, 40 % of WSPyC was associated with factors related to the atmospheric aging of aerosols derived from fossil fuel combustion. The global WSPyC deposition flux to the ocean has previously been estimated based on the concentration ratio of WSPyC to elemental carbon (EC) or water-soluble organic carbon (WSOC). The results of this study suggested that these ratios vary due to the atmospheric aging processes, including photochemical production of WSPyC from soot, indicating the need for a reassessment of the global WSPyC deposition flux.

The Sea of Okhotsk is one of the most biologically productive regions, where primary production during spring phytoplankton blooms after sea ice melting/retreat has the potential to contribute to the sea-to-air emission flux of atmospheric organic aerosols (OAs). To elucidate the effect of oceanic biological activity during blooms on the formation process of OAs, aerosol samples and surface seawater were collected during the bloom period of April 2021. Organic matter (OM) was the dominant component of submicrometer aerosols during both the bloom (53±16 %) and bloom-decay periods (44±12 %), with OM being highly water-soluble during the bloom. Stable carbon isotope ratios of aerosol organic carbon (OC) showed that 73–82 % of the observed aerosols were of marine origin. Relations between water-soluble OC (WSOC) and molecular tracers suggested that the majority of WSOC of marine origin was affected by secondary formation from precursors such as α-pinene and DMS-relevant compounds instead of primary emissions of sea spray aerosols. The amounts of water-soluble organic nitrogen (WSON) in aerosol and dissolved organic nitrogen (DON) in seawater during the bloom were larger than those during bloom-decay period, suggesting the preferential formation of N-containing water-soluble OAs of marine origin during the bloom. The increase in the amount of DON during the bloom was likely associated with the predominant diatoms, Thalassiosira spp. and Fragilariopsis spp. This study highlights the significant contribution of the secondary formation of marine biogenic OAs with increased N-containing components during the bloom after sea ice melting/retreat in the subarctic ocean.

The Sea of Okhotsk is one of the most biologically productive regions, where primary production during spring phytoplankton blooms after sea ice melting/retreat has the potential to contribute to the sea-to-air emission flux of atmospheric organic aerosols (OAs). To elucidate the effect of oceanic biological activity during blooms on the formation process of OAs, aerosol samples and surface seawater were collected during the bloom period of April 2021. Organic matter (OM) was the dominant component of submicrometer aerosols during both the bloom (53±16 %) and bloom-decay periods (44±12 %), with OM being highly water-soluble during the bloom. Stable carbon isotope ratios of aerosol organic carbon (OC) showed that 73–82 % of the observed aerosols were of marine origin. Relations between water-soluble OC (WSOC) and molecular tracers suggested that the majority of WSOC of marine origin was affected by secondary formation from precursors such as α-pinene and DMS-relevant compounds instead of primary emissions of sea spray aerosols. The amounts of water-soluble organic nitrogen (WSON) in aerosol and dissolved organic nitrogen (DON) in seawater during the bloom were larger than those during bloom-decay period, suggesting the preferential formation of N-containing water-soluble OAs of marine origin during the bloom. The increase in the amount of DON during the bloom was likely associated with the predominant diatoms, Thalassiosira spp. and Fragilariopsis spp. This study highlights the significant contribution of the secondary formation of marine biogenic OAs with increased N-containing components during the bloom after sea ice melting/retreat in the subarctic ocean.

The Sea of Okhotsk is one of the most biologically productive regions, where primary production during spring phytoplankton blooms after sea ice melting/retreat has the potential to contribute to the sea-to-air emission flux of atmospheric organic aerosols (OAs). To elucidate the effect of oceanic biological activity during blooms on the formation process of OAs, aerosol samples and surface seawater were collected during the bloom period of April 2021. Organic matter (OM) was the dominant component of submicrometer aerosols during both the bloom (53±16 %) and bloom-decay periods (44±12 %), with OM being highly water-soluble during the bloom. Stable carbon isotope ratios of aerosol organic carbon (OC) showed that 73–82 % of the observed aerosols were of marine origin. Relations between water-soluble OC (WSOC) and molecular tracers suggested that the majority of WSOC of marine origin was affected by secondary formation from precursors such as α-pinene and DMS-relevant compounds instead of primary emissions of sea spray aerosols. The amounts of water-soluble organic nitrogen (WSON) in aerosol and dissolved organic nitrogen (DON) in seawater during the bloom were larger than those during bloom-decay period, suggesting the preferential formation of N-containing water-soluble OAs of marine origin during the bloom. The increase in the amount of DON during the bloom was likely associated with the predominant diatoms, Thalassiosira spp. and Fragilariopsis spp. This study highlights the significant contribution of the secondary formation of marine biogenic OAs with increased N-containing components during the bloom after sea ice melting/retreat in the subarctic ocean.