5:15 PM - 6:45 PM
[AOS13-P05] Behavior of dissolved trace metals in the western Bering Sea
Keywords:biogeochemical cycle, nutrients, coastal area, Fe-limitation
Background
Trace metals play important roles in various biological processes of marine microorganisms. Generally, trace metals such as iron (Fe), manganese (Mn), cobalt (Co), and zinc (Zn) function as nutrients, while others like cadmium (Cd), lead (Pb) and copper (Cu) can inhibit phytoplankton growth at high concentrations. Therefore, understanding the behaviors of these trace metals is crucial for assessing environmental changes and their impacts on marine ecosystems. In this study, we elucidated the distributions of seven trace metals (Mn, Co, Ni, Cu, Zn, Pb, Cd) in the western Bering Sea. The Bering Sea is a high nutrient low chlorophyll region where primary productivity is controlled by trace metal availability.
Methods
Seawater samples were collected from the western Bering Sea onboard R/V Professor Multanovskiy during cruise Mu18 between August and October 2018. The samples were filtered using a 0.2 µm pore-size capsule filter, and then acidified to below pH 2 for preservation. Prior to analysis, ultraviolet light (400 W, 365 nm) was applied to break down organic ligands that form organic complexes with metal ions. Then, the pH of the samples was adjusted to 6.1±0.1. Solid phase extraction with NOBIAS Chelate PA-1 (Hitachi High-Tech) chelating resin was employed for the extraction of trace metals. The resin was first conditioned with 0.05 M ammonium acetate buffer before the seawater sample was passed through it. Residual salts were removed by rinsing the resin with the same buffer. Finally, the metal ions were eluted using 2 M HNO3. The trace metals were quantified using ICP-MS with Lu as the internal standard.
Results and Discussion
In the Bering Sea, the water masses can be categorized into: surface water (σθ < 26.9), intermediate water (27.0 < σθ < 27.4), and deep water (σθ > 27.4). The intermediate water is characterized by low dissolved oxygen concentration. In coastal areas, surface waters exhibited lower salinity, likely due to the inflow of river water.
Dissolved Mn concentrations in the surface waters ranged from 0.5 nM to 6.0 nM, while Ni concentrations varied between 5.5 nM and 7.2 nM. The highest concentrations of both metals were observed in the coastal areas, indicating river water inputs.
Dissolved Ni displayed a linear increase in concentration with depth, showing a nutrient-type distribution profile similar to those of dissolved Cd and Zn. Particularly, there is a strong positive correlation between Cd and phosphate (R2 = 0.82). The Cd/P ratio in the Bering Sea was 0.38±0.03, which agrees with those reported in previous studies in the North Pacific (e.g., Zheng et al., 2019). Zn also showed a strong correlation with silicate (R2 = 0.80). However, dissolved Zn concentration was slightly elevated compared to Si in the intermediate water, similar to the observations of Kim et al., (2017) in the subarctic Pacific.
Dissolved Cu and Co exhibited hybrid-type distribution profiles and their behaviors varied across different regions of the western Bering Sea. Dissolved Cu concentrations were generally in the range of 1.2 nM to 3.0 nM, while dissolved Co concentrations were between 0.03 nM and 0.11 nM.
Trace metals play important roles in various biological processes of marine microorganisms. Generally, trace metals such as iron (Fe), manganese (Mn), cobalt (Co), and zinc (Zn) function as nutrients, while others like cadmium (Cd), lead (Pb) and copper (Cu) can inhibit phytoplankton growth at high concentrations. Therefore, understanding the behaviors of these trace metals is crucial for assessing environmental changes and their impacts on marine ecosystems. In this study, we elucidated the distributions of seven trace metals (Mn, Co, Ni, Cu, Zn, Pb, Cd) in the western Bering Sea. The Bering Sea is a high nutrient low chlorophyll region where primary productivity is controlled by trace metal availability.
Methods
Seawater samples were collected from the western Bering Sea onboard R/V Professor Multanovskiy during cruise Mu18 between August and October 2018. The samples were filtered using a 0.2 µm pore-size capsule filter, and then acidified to below pH 2 for preservation. Prior to analysis, ultraviolet light (400 W, 365 nm) was applied to break down organic ligands that form organic complexes with metal ions. Then, the pH of the samples was adjusted to 6.1±0.1. Solid phase extraction with NOBIAS Chelate PA-1 (Hitachi High-Tech) chelating resin was employed for the extraction of trace metals. The resin was first conditioned with 0.05 M ammonium acetate buffer before the seawater sample was passed through it. Residual salts were removed by rinsing the resin with the same buffer. Finally, the metal ions were eluted using 2 M HNO3. The trace metals were quantified using ICP-MS with Lu as the internal standard.
Results and Discussion
In the Bering Sea, the water masses can be categorized into: surface water (σθ < 26.9), intermediate water (27.0 < σθ < 27.4), and deep water (σθ > 27.4). The intermediate water is characterized by low dissolved oxygen concentration. In coastal areas, surface waters exhibited lower salinity, likely due to the inflow of river water.
Dissolved Mn concentrations in the surface waters ranged from 0.5 nM to 6.0 nM, while Ni concentrations varied between 5.5 nM and 7.2 nM. The highest concentrations of both metals were observed in the coastal areas, indicating river water inputs.
Dissolved Ni displayed a linear increase in concentration with depth, showing a nutrient-type distribution profile similar to those of dissolved Cd and Zn. Particularly, there is a strong positive correlation between Cd and phosphate (R2 = 0.82). The Cd/P ratio in the Bering Sea was 0.38±0.03, which agrees with those reported in previous studies in the North Pacific (e.g., Zheng et al., 2019). Zn also showed a strong correlation with silicate (R2 = 0.80). However, dissolved Zn concentration was slightly elevated compared to Si in the intermediate water, similar to the observations of Kim et al., (2017) in the subarctic Pacific.
Dissolved Cu and Co exhibited hybrid-type distribution profiles and their behaviors varied across different regions of the western Bering Sea. Dissolved Cu concentrations were generally in the range of 1.2 nM to 3.0 nM, while dissolved Co concentrations were between 0.03 nM and 0.11 nM.