The mystery of diiodo-methane observed in the ocean surface layer
Topic outline
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The mystery of the presence of photolyzed diiodo-methane in high concentrations in the ocean surface layer where the light is reflected
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Diiodo-methane (CH2I2) concentrations are increasing in surface seawater, as observed every year from May onwards in Funka Bay.
The underlying reason is a complete mystery.
The diiodo-methane concentration was also high near the seabed of the Arctic Ocean. Hence, assuming the presence of a source of the generation of diiodo-methane at the seabed, we collected marine sediments and measured iodine gas.
Results showed that only iodoethane (C2H5I) was present in high concentrations in the sediment, and the expected phenomenon of high diiodo-methane concentrations failed to materialize.
As observed with the vertical distribution of the seawater analysis at Funka Bay, diiodo-methane appears to be generated near the surface layer.
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Existence of diiodo-methane near the surface layer is also a complete mystery.
Diiodo-methane is easily decomposed by the blue-wavelength light of the sunlight. Hence, it is a mystery why diiodo-methane is constantly present in the ocean layer where light can reach.
It was initially believed that diiodo-methane accumulated in the subsurface layer where the light was weak and reached the surface layer via vertical mixing. Subsequently, it maintained the surface layer concentration.
Therefore, we decided to confirm this by simultaneously investigating three aspects: “turbulence measurements” evaluating vertical mixing in detail, “light observations” analyzing the depth of light penetration, and diiodo-methane measurements.
(We worked on this as an open call for participants for the establishment of marine mixing studies (representative: Professor Yasuda Ichiro) and cooperated with Professor Yasuda’s group and Professor Hirawake’s group)
Results showed that vertical mixing cannot maintain the diiodomethane concentration in the ocean surface layer. Hence, we formulated various hypotheses and begun verifying them. As shown below, currently we hypothesize that iodine is retained in the body of the phytoplankton (or the acidic polysaccharides on their surfaces), and we are attempting to verify this.
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Considering that diiodo-methane is generated from living phytoplankton, we started culturing dinoflagellates, which dominate Funka Bay in the summer.
（Under the guidance of Professor Matsuno of the School of Fisheries Sciences, the fourth-year student Kawanishi is attempting mass culturing. Good luck Kawanishi!）
（Kasai-kun, "For phytoplankton culture, it is important to properly direct light, let them rest at night (for cell division), control the temperature, add nutrients, vitamins, and sodium hydrogen carbonate properly so as not to let them be carbon rate-determining." You need to be careful during plankton culture. Note: these are used for gas measurements. Hence, the complete sealing results are obtained after carbon control）.
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