5:15 PM - 7:15 PM
[MZZ42-P09] Distributions and biogeochemical cycles of Fe, Mn, Cu, Zn in the Western North Pacific
Keywords:Trace metals, labile particulate Fe, subarctic Pacific Intermediate water
The distributions of trace metals (Fe, Mn, Cu and Zn) in the ocean are controlled by biological, physical, and chemical processes. Phytoplankton takes up some trace metals as essential micronutrients, along with the major nutrients such as nitrate, phosphate and silicate. The study area is the western North Pacific, one of the high-nutrient, low-chlorophyll (HNLC) regions. According to previous study (Nishioka and Obata, 2017), the formation mechanisms of HNLC regions in the subarctic North Pacific are affected by seasonal variations in the biogeochemical parameters, but also by remineralization of iron and phosphate and their uptake rate by phytoplankton. However, to understand their distribution by remineralization process, it is necessary to investigate not only the dissolved iron but also the chemical speciation that is bioavailable. Therefore, we investigated the distribution of dissolved and particulate trace metals in seawater in the western North Pacific. Marine phytoplankton primarily takes up the dissolved phase of trace metals (< 0.2 μm) in seawater. However, recently, not only dissolved but also particulate trace metals have been investigated because the particulate trace metals are partially bioavailable. The purpose of this study is to clarify the distributions of dissolved and total dissolvable trace metals in the western North Pacific and to understand their biogeochemical cycles.
In this study, seawater samples at three representative stations in the western North Pacific were used during the R.V. Hakuho-maru research cruises (KH-22-7 and KH-23-2) conducted in 2022 and 2023. Trace metals in seawater samples were preconcentrated by solid-phase extraction method using a chelating resin (Presep® Poly Chelate) and eluted from the resins with nitric acid. Their concentrations in the eluate were measured by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Both dissolved and total dissolvable trace metals were determined by the same method. The concentrations of labile particulate trace metals were obtained from the difference between the concentrations of total dissolvable trace metals and dissolved trace metals.
The results represented that the distribution of iron in the intermediate layer (200-1000 m) in the subarctic North Pacific, was different compared with that in the previous study (Zheng and Sohrin, 2019). To reveal the process that elevated the concentrations of dissolved iron, the dissolved Fe/total dissolvable Fe ratio was compared. The ratio in this study (0.23-0.52) was higher than those in the previous study (0.1-0.31). According to previous studies, apparent oxygen utilization (AOU) and dissolved iron had a positive correlation, suggesting that the regeneration process of biogenic particles affected the distribution of dissolved iron. However, the dissolved oxygen concentrations in this study were similar to those in the previous study. There are possibilities that other processes influenced the regeneration process of iron, such as complexation with organic ligands or disaggregation of suspended particles which can regulate solubility of dissolved iron.
In this study, seawater samples at three representative stations in the western North Pacific were used during the R.V. Hakuho-maru research cruises (KH-22-7 and KH-23-2) conducted in 2022 and 2023. Trace metals in seawater samples were preconcentrated by solid-phase extraction method using a chelating resin (Presep® Poly Chelate) and eluted from the resins with nitric acid. Their concentrations in the eluate were measured by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Both dissolved and total dissolvable trace metals were determined by the same method. The concentrations of labile particulate trace metals were obtained from the difference between the concentrations of total dissolvable trace metals and dissolved trace metals.
The results represented that the distribution of iron in the intermediate layer (200-1000 m) in the subarctic North Pacific, was different compared with that in the previous study (Zheng and Sohrin, 2019). To reveal the process that elevated the concentrations of dissolved iron, the dissolved Fe/total dissolvable Fe ratio was compared. The ratio in this study (0.23-0.52) was higher than those in the previous study (0.1-0.31). According to previous studies, apparent oxygen utilization (AOU) and dissolved iron had a positive correlation, suggesting that the regeneration process of biogenic particles affected the distribution of dissolved iron. However, the dissolved oxygen concentrations in this study were similar to those in the previous study. There are possibilities that other processes influenced the regeneration process of iron, such as complexation with organic ligands or disaggregation of suspended particles which can regulate solubility of dissolved iron.