5:15 PM - 6:30 PM
[ACG44-P02] Verification of the effect of aerosol deposition on surface chlorophyll in subtropical oligotrophic waters using JRAero reanalysis datasets
Keywords:depotision, aerosol
Introduction
Aerosols emitted from highly populated areas in East Asia contain inorganic nitrogen as a form of nitrate ion (NO3-) and ammonium ion (NH4+). Some of them deposit in the subtropical zone of the western North Pacific. This area is called “the desert of the ocean” due to its oligotrophy and low productivity. The aerosol deposition is supposed to be a valuable source of nutrients in this region. According to model calculations, significant increases in surface chlorophyll concentration and gross primary production are estimated in the western North Pacific due to the deposition [Taketani et al., 2018]. However, there are few examples of verifying the effect of the deposition on biochemical processes using observational data. In this study, the effects of the deposition on ocean biochemical parameters are examined by using the data obtained in research vessels and Japanese Reanalysis for Aerosol (JRAero) [Yumimoto et al., 2017].
Data
Hydrographic data obtained by research vessels “Ryofu-Maru” and “Keifu-Maru” which belong to Japan Meteorological Agency is used for our analysis. The study area and period are 20-30N, 130-165E, and winter (January, February, and March) from 2011 to 2017, respectively. Temperature, salinity, and chlorophyll data obtained from 10 m depth are used. Nitrate and ammonia are not recorded in JRAero although they supply inorganic nitrogen and stimulate biological activity in the ocean. Black carbon was used as a substitute index of nitrate and ammonia.
Results
The chlorophyll concentration in winter tended to be high as the temperature was low (see Figure). This is thought to be due to the vertical mixing and the entrainment of nitrates was promoted in cold water. On the other hand, the chlorophyll concentration was variable even at the same water temperature. This means chlorophyll concentration depended on factors other than the water temperature. In an incubation experiment onboard, chlorophyll concentration increases within 24-48 hours after the deposition [Zhang et al., 2019]. Therefore 24-hours accumulated amount of black carbon deposition was calculated. As a result, when the water temperature was about the same, the chlorophyll concentration tended to be higher when the amount of black carbon deposition was large.
In our study, the possibility that atmospheric deposition stimulates biological activity in the subtropical oligotrophic region is shown by actual observations. However, quantitative evaluation is difficult as the number of data is too small spatially and temporally. For more accurate verification, more detailed observations of both the atmosphere and the ocean are essential.
References
Taketani et al., Scientific Report, 2018.
Yumimoto et al., Geosci. Model Dev., 2017.
Zhang et al., Global Biogeochemical Cycles, 2019
Figure caption
Relationship between the water temperature and chlorophyll concentration at a depth of 10 m. The color shows the amount of black carbon deposition (dry + wet) in 24 hours before observation at the grid point of JRAERO closest to the observation point.
Aerosols emitted from highly populated areas in East Asia contain inorganic nitrogen as a form of nitrate ion (NO3-) and ammonium ion (NH4+). Some of them deposit in the subtropical zone of the western North Pacific. This area is called “the desert of the ocean” due to its oligotrophy and low productivity. The aerosol deposition is supposed to be a valuable source of nutrients in this region. According to model calculations, significant increases in surface chlorophyll concentration and gross primary production are estimated in the western North Pacific due to the deposition [Taketani et al., 2018]. However, there are few examples of verifying the effect of the deposition on biochemical processes using observational data. In this study, the effects of the deposition on ocean biochemical parameters are examined by using the data obtained in research vessels and Japanese Reanalysis for Aerosol (JRAero) [Yumimoto et al., 2017].
Data
Hydrographic data obtained by research vessels “Ryofu-Maru” and “Keifu-Maru” which belong to Japan Meteorological Agency is used for our analysis. The study area and period are 20-30N, 130-165E, and winter (January, February, and March) from 2011 to 2017, respectively. Temperature, salinity, and chlorophyll data obtained from 10 m depth are used. Nitrate and ammonia are not recorded in JRAero although they supply inorganic nitrogen and stimulate biological activity in the ocean. Black carbon was used as a substitute index of nitrate and ammonia.
Results
The chlorophyll concentration in winter tended to be high as the temperature was low (see Figure). This is thought to be due to the vertical mixing and the entrainment of nitrates was promoted in cold water. On the other hand, the chlorophyll concentration was variable even at the same water temperature. This means chlorophyll concentration depended on factors other than the water temperature. In an incubation experiment onboard, chlorophyll concentration increases within 24-48 hours after the deposition [Zhang et al., 2019]. Therefore 24-hours accumulated amount of black carbon deposition was calculated. As a result, when the water temperature was about the same, the chlorophyll concentration tended to be higher when the amount of black carbon deposition was large.
In our study, the possibility that atmospheric deposition stimulates biological activity in the subtropical oligotrophic region is shown by actual observations. However, quantitative evaluation is difficult as the number of data is too small spatially and temporally. For more accurate verification, more detailed observations of both the atmosphere and the ocean are essential.
References
Taketani et al., Scientific Report, 2018.
Yumimoto et al., Geosci. Model Dev., 2017.
Zhang et al., Global Biogeochemical Cycles, 2019
Figure caption
Relationship between the water temperature and chlorophyll concentration at a depth of 10 m. The color shows the amount of black carbon deposition (dry + wet) in 24 hours before observation at the grid point of JRAERO closest to the observation point.