The University of Tokyo · Earth and Planetary Sciences
Professor Akira Oka's research lab specializes in Earth system science, with a focus on paleoclimatology, ocean biogeochemistry, and climate modeling. The lab investigates the mechanisms of glacial-interglacial climate change, particularly the role of the biological carbon pump, iron fertilization, and ocean circulation dynamics in regulating atmospheric CO2 and deep-ocean oxygenation. Using coupled climate and biogeochemical models, the lab explores past climate states such as the Last Glacial Maximum to understand feedbacks involving the ocean, atmosphere, and carbon cycle. Their work bridges observational paleoclimate data with numerical simulations to improve understanding of long-term climate variability and carbon cycle dynamics.
Figures are computed from collected data and may differ slightly.
The HLA-Cw6 antigen has been associated with psoriasis vulgaris despite racial and ethnic differences. However, it remains unclear whether it is the HLA-Cw6 antigen itself or a closely linked, hitherto unidentified, locus that predisposes to the disease. Here, in order to map the susceptibility locus for psoriasis vulgaris precisely within the HLA class I region, 11 polymorphic microsatellite markers distributed throughout a 1060 kb segment surrounding the HLA-C locus were subjected to associati
Paleo proxy data suggest that the Atlantic meridional overturning circulation (AMOC) was shallower and weaker at the Last Glacial Maximum (LGM) than at present. In this study, we have identified the existence of a thermal threshold of the AMOC which may explain why many coupled climate models fail to simulate the weaker AMOC during the LGM. By using results obtained from a coupled climate model and conducting sensitivity simulations with an ocean general circulation model, we found that the sudd
Observed vertical profiles of rare earth elements (REEs) in the North Pacific Ocean show a systematic change from lighter to heavier REEs. Their source and sink consist of external fluxes coming from the surface and the bottom of the ocean and internal recycling within the ocean. In order to evaluate the role of each source and sink in controlling the vertical profiles of REEs, we conduct numerical simulations of REEs by using an ocean general circulation model. These simulations demonstrate tha
[1] Using a biogeochemical ocean model that includes the iron cycle, we carry out preindustrial (control, CTL) and glacial (Last Glacial Maximum, LGM) climate simulations focusing on changes in export production (EP). The model successfully reproduces general trends of a paleoclimate reconstruction of EP at the LGM except over the Atlantic Ocean. By conducting a series of sensitivity simulations, we investigate the mechanism controlling EP at the LGM in each basin. In the Southern Ocean, the mod
Abstract. Increased accumulation of respired carbon in the deep ocean associated with enhanced efficiency of the biological carbon pump is thought to be a key mechanism of glacial CO2 drawdown. Despite greater oxygen solubility due to seawater cooling, recent quantitative and qualitative proxy data show glacial deep-water deoxygenation, reflecting increased respired carbon accumulation. However, the mechanisms of deep-water deoxygenation and contribution from the biological pump to glacial CO2 d
The ballast parameterization separates sinking organic flux into two parts: the flux associated with ballast minerals and the flux independent of minerals. The ballast parameterization begins to be incorporated into global ocean biogeochemical models. However, parameters used in this parameterization such as those of calcium carbonate flux are not constrained enough and it has been difficult to evaluate quantitatively how much the ballast‐induced flux affects nutrient concentration in deep ocean
Abstract Abrupt climate warming events, known as Dansgaard-Oeschger events, occurred frequently during glacial periods, and are thought to be linked to changes in the Atlantic meridional overturning circulation. However, the mechanism responsible is not fully understood. Here, we present numerical simulations with a sea-ice coupled ocean general circulation model that systematically investigate the thermal threshold where deep water formation, and hence the overturning circulation, shift abruptl
Abstract The ocean stores 60 times as much carbon as the atmosphere, and the ocean carbon cycle has a critical role in controlling atmospheric CO 2 concentration. The concept of ocean carbon pump is widely used for describing the ocean carbon cycle, but the term “ocean carbon pump” is not necessarily strictly defined and has been differently referred in previous studies. Here, using three dimensional distributions of dissolved inorganic carbon concentration, total alkalinity, phosphate, and sali
Abstract In this study, we report our ocean general circulation model simulations of the global distribution of rare earth elements (REEs) in the ocean. As previously reported (Oka et al. in Glob Biogeochem Cycles 23:1–16, 2009), the vertical profiles of REEs in the North Pacific Ocean are strongly controlled by the reversible scavenging process, and the systematic differences between REEs can be reproduced in the model by selecting an appropriate model parameter which controls affinity to parti
Numerical experiments are conducted using a sea ice–coupled ocean general circulation model (OGCM) forced by two different freshwater flux datasets. These two datasets are the National Centers for Environmental Prediction– National Center for Atmospheric Research (NCEP–NCAR) reanalysis and the European Centre for Medium-Range Weather Forecasts (ECMWF)-based climatological datasets, which are widely used to force OGCMs. It is found that the strength of the simulated Atlantic deep circulation cons
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