Hokkaido University · Earth and Planetary Sciences
Professor Daïki Nomura's research lab specializes in polar biogeochemistry, focusing on the exchange of greenhouse gases—particularly CO₂ and DMS—between sea ice, snow, and the atmosphere in Arctic and Antarctic regions. The lab investigates how physical and chemical processes during sea-ice formation, melt, and snow-ice interactions regulate carbon cycling and trace gas emissions. Key research directions include air-ice CO₂ flux dynamics, ikaite mineral formation in sea ice, and the role of meltwater layers and superimposed ice in modulating gas exchange. The lab employs field measurements, chamber techniques, and laboratory experiments to understand climate-relevant processes in ice-covered oceans.
Figures are computed from collected data and may differ slightly.
In order to clarify the CO2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO2 concentration above the sea-ice began to increase since the beginning of the sea-ice formation, and increased at larger rates with time and the decrease in air temperature. This increase of CO2 concentration in air was mainly caused by the increase in dissolved inorganic carbon concentration in the brine of the upper par
Abstract The air–sea-ice CO 2 flux was measured in the ice-covered Saroma-ko, a lagoon on the northeastern coast of Hokkaido, Japan, using a chamber technique. The air–sea-ice CO 2 flux ranged from −1.8 to +0.5 mg C m −2 h −1 (where negative values indicate a sink for atmospheric CO 2 ). The partial pressure of CO 2 (pCO 2 ) in the brine of sea ice was substantially lower than that of the atmosphere, primarily because of the influence of the under-ice plume from the Saromabetsu river located in
In this study, we present evidence that Antarctic and Arctic sea ice act as sink for atmospheric CO 2 during periods of snowmelt and surface flooding. The CO 2 flux measured directly at the flooded sea ice surface ( F flood ) constituted a net CO 2 sink of −1.1 ± 0.9 mmol C m −2 d −1 (mean ± 1 SD), which was an order of magnitude higher than the flux measured at the snow‐air surface ( F snow ) and bare ice surface ( F ice ). The F snow / F flood ratio decreased with increasing water equivalent o
Abstract We identified ikaite crystals (CaCO 3 · 6H 2 O) and examined their shape and size distribution in first-year Arctic pack ice, overlying snow and slush layers during the spring melt onset north of Svalbard. Additional measurements of total alkalinity (TA) were made for melted snow and sea-ice samples. Ikaite crystals were mainly found in the bottom of the snowpack, in slush and the surface layers of the sea ice where the temperature was generally lower and salinity higher than in the ice
We present the first direct measurements of dimethylsulfide (DMS) emissions from Antarctic sea ice to the atmosphere during the seasonal warming period obtained using a chamber technique. Estimated DMS fluxes measured over the snow and superimposed ice (ice formed by the freezing of snow meltwater) were from 0.1 to 0.3 μ mol m −2 d −1 . The DMS fluxes measured directly over the sea‐ice slush layer after removal of the snow and superimposed ice, ranged from 0.1 to 5.3 μ mol m −2 d −1 , were large
Leads play an important role in the exchange of heat, gases, vapour, and particles between seawater and the atmosphere in ice-covered polar oceans. In summer, these processes can be modified significantly by the formation of a meltwater layer at the surface, yet we know little about the dynamics of meltwater layer formation and persistence. During the drift campaign of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), we examined how variation in lead width, re
Abstract Cracks are common and natural features of sea ice formed in the polar oceans. In this study, a sea ice crack in flooded, multiyear, land‐fast Antarctic sea ice was examined to assess its influence on biological productivity and the transport of nutrients and microalgae into the upper layers of neighboring sea ice. The water inside the crack and the surrounding host ice were characterized by a strong discoloration (brown color), an indicator of a massive algal bloom. Salinity and oxygen
Saroma-ko Lagoon, located on the Okhotsk Sea coast of Hokkaido, is seasonally covered by flat, homogeneous, easily accessible and safe sea ice. As such, it proves a very useful experimental site for the study of sea ice processes, the inter-comparison of methods, the testing of equipment, and the training of researchers new to the Polar regions. In this contribution, we describe a physical, chemical, and ecosystem survey at Saroma-ko Lagoon, conducted over February 23-28, 2019 under the auspices
Abstract. Partial pressure of CO2 (pCO2) in surface water and vertical profiles of the carbonate system parameters were measured during austral summer in the Indian sector of the Southern Ocean (64–67° S, 32–58° E) in January 2006 to understand the CO2 dynamics of seawater in the seasonal ice zone. Surface-water pCO2 ranged from 275 to 400 μatm, and longitudinal variations reflected the dominant influence of water temperature and dilution by sea ice meltwater between 32 and 40° E and biological
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