気候システムセミナー

日時：金曜日 13:30-15:00
場所：東京大学柏キャンパス 総合研究棟270室
（＊変更の場合もありますので、詳細は下記の予定をご確認ください）

今後の予定

• Title: Studying climate through a spectral lens
• Time: 13:30 - 15:00 on May. 15, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Radiative transfer processes are intrinsically spectral dependent, yet this spectral dimension is not broadly utilized in physical climate studies. I will present three examples to illustrate the merit of spectral dimension in such studies, closely tied to relevant satellite observations. First, I will show how the longwave spectral flux derived from observations can be used in model diagnostics to reveal compensating biases that broadband diagnostics alone cannot tell in the radiative feedback analysis. Second, I will describe why two longwave processes, namely surface spectral emission and cloud longwave scattering, are missing in current climate models but should be included for a faithful simulation of polar climate. Third, I will briefly describe the implication of the most recent NASA solar spectral irradiance measurements from TSIS-1 on the International Space Station, especially the partition between visible and near-infrared, for high-latitude climate simulation.

• Title: Thoughts on CMIP and the future of climate science
• Time: 10:00 - 11:30 on Apr. 27, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: With the arrival of climate change, and the acceptance of the basic tenets of climate science, we are entering a new era. These changes are colored by an explosion of computational capacity, supporting machine learning and high-resolution simulation and increasing interest by the private sector. In this talk I share some thoughts on what these changes mean for how we structure our science, and in so doing present my ideas, and our activities, in relation to high-level international activities such as CMIP, Destination Earth, EVE, and the Berlin Summit.

• Title: TBD
• Time: 13:30 - 15:00 on Apr. 27, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: TBD

• Title: Use of trace gas measurements to quantify convective transport pathways toward developing a new transport diagnostic and metric
• Time: 13:30 - 15:00 on Apr. 6, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Convective transport from the marine boundary layer (MBL) to the upper troposphere (UT) is investigated using airborne in situ measurements of chemical tracers over the tropical western Pacific (TWP). Using 42 trace gas species with photochemical lifetimes ranging from shorter than a day to multiple decades, we developed a diagnostic called Transit Time Distribution, G(t) to characterize convective transport time scales associated with UT air parcels sampled over the convectively dominant TWP region. G(t) describes relative contributions of air masses transported from the MBL to the UT via all transport paths with different transit times (see the schematic illustration below). We further demonstrate that the tracer-derived transit time scale is broadly comparable to that estimated from convective mass flux and Lagrangian trajectory analysis. The observation-based Transit Time Distribution not only provides insights into convective transport pathways, but also has the potential to serve as an effective metric for evaluating the representation of convective transport in global models.

• Title: From High-Resolution to Global Storm Resolving Models: achievements and perspectives
• Time: 15:00 - 16:30 on Apr. 6, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Increasing available high-performance computing has enabled global coupled models to resolve some of the fundamental processes governing the climate system. More explicit representation of eddies in the ocean and of weather systems in the atmosphere impacts the general circulation and reduces inter-model disagreement. More realistic simulation of the global hydrological cycle at resolutions beyond 50km underpins more trustworthy projections of the availability of heat, carbon and water to land vs ocean ecosystems. Global “Weather-Resolving” models produce reliable global teleconnections that govern regional changes in weather and climate, including extremes (e.g. Tropical Cyclones). Resolving the ocean mesoscale produces “out of trajectory” future climates for Europe. Global Storm Resolving Models now operate in the resolution range of 1-10 km, removing some long-standing errors in the simulation of precipitation (location, organization, diurnal cycle, intensity/frequency). However, uncertainties remain with respect to the adequateness of key parametrisations at such scales, motivating research on global cloud-resolving capability.

• Title: Clouds and precipitation in two versions of the Energy Exascale Earth System Model (E3SM)
• Time: 13:00 - 14:30 on Apr. 4, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: As part of the US Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) project, two versions of climate models are currently being developed. The 100-km scale version 3 of the E3SM Atmosphere Model (EAMv3) and a 3.25km scale Simple Cloud Resolving E3SM Atmosphere Model (SCREAM). In this talk, I will present early results of clouds and precipitation in these two model configurations. Compared to earlier versions of the model, EAMv3 employs a new microphysics scheme (P3) and a range of new deep convection enhancements that help to represent the impacts of meso-scale convection, the impact of large-scale circulations on convection, and a more sophisticated convective cloud microphysics scheme that allows for aerosol effects. These new adjustments improve the tropical and diurnal variability in clouds and precipitation, while also maintaining the mean-state patterns of precipitation. Results from a pair of 30-year present-day and +4K warmed SST simulations will be discussed, regarding the impact of the new physics on cloud and precipitation responses.

• Title: Use of LES case studies for improving cloud physics in large-scale models
• Time: 14:30 - 16:00 on Apr. 4, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: The most recent Earth system model development cycle at NASA GISS relied heavily on side-by-side comparison of large-eddy simulation (LES) case studies with GISS-ModelE3 run in single-column model (SCM) mode. Introduction of a moist turbulence scheme was first tested against clear-sky boundary layer cases. Adding two-moment stratiform microphysics with prognostic precipitation was tested against stratocumulus, cumulus, transition, mixed-phase, cirrus and deep convection cases. A recently developed case of highly supercooled mixed-phase stratus observed over Antarctica during the DOE AWARE campaign is highlighted to demonstrate derivation of microphysical process parameter uncertainty ranges as input to a machine learning tuning process. New cases currently under development for use in the next round of GISS-ModelE3 development are being derived from several recent field campaigns (DOE COMBLE and TRACER, and NASA CAMP2Ex and SEAC4RS), including three general improvements. First, new cases are all taking a cloud-following Lagrangian approach, starting with cloud-free conditions and tracking cloud life cycle. Second, each case includes realistic aerosol size distributions based on observations, suitable to test prognostic droplet activation, primary ice formation, and aerosol wet scavenging. Third, several diverse cases of target regimes are being derived from each campaign, thus providing a stronger test of physics across varying conditions (e.g., range of cold-air outbreak index). The availability and development of well-constrained LES/SCM case studies has revealed several additional applications beyond the main objective of providing a benchmark for handling uncertain microphysical processes: namely, the LES/SCM case studies have proved useful for testing instrument simulators, evaluating satellite data products used for large-scale model tuning, and studying retrieval algorithms. For instance, development of a new ground-based radar-lidar forward simulator software (the Earth Model Column Collaboratory package) was tested against LES and SCM output for the AWARE case, enabling a confident interpretation of simulator and model performances against observed quantities, and a similar test of a satellite lidar simulator against the well-constrained SCM results led to substantial changes in evaluation conclusions. In addition, the process of seeking to well constrain multiple Lagrangian case studies revealed discrepancies in liquid water path retrieval products and a recommendation to revise product use for GISS-ModelE3 tuning using machine learning. Finally, past LES case studies with realistic aerosol and hydrometeor particle size distributions (using a size-resolved microphysics modeling approach) have been used to test detection of multimodal drop size distributions using multi-angle polarimeter measurements, suggesting an improved route versus use of idealized simulations (e.g., with fixed droplet number concentration). In closing, it is proposed that developing realistic aerosol-to-precipitation LES simulacra of cloud life cycles observed during field campaigns can offer a strong foundational activity for large-scale model physics improvement, providing a clearly actionable pathway to improve the representation of cloud processes, as well as retrievals and model evaluation tools.

• Title: A clearer view of cloudy skies: Understanding systematic cloud and radiation errors in the ECMWF global model
• Time: 13:30 - 15:00 on Mar. 22, 2023.
• Place: 270室(General Research Bldg. 2F room 270)
• Abstract: Global weather and climate models have significant regime-dependent systematic errors of clouds and their impacts on radiation, many of which are common across a range of different modelling systems. Here we describe how the systematic cloud and radiation errors in the ECMWF global numerical weather prediction (NWP) model have reduced over the last decade, how they change with increasing model resolution down to the kilometre scale, and how the use of observations and data assimilation has helped to understand the source of errors and implement improvements to the physical parametrizations, with impacts across prediction timescales from hours (data assimilation), to days (weather forecasts) to decades (climate). The focus is on top-of-atmosphere reflected shortwave radiation as it is a key quantity for model assessment: well-observed globally, fundamental for driving the atmospheric and ocean dynamics and is strongly affected by cloud.

• Title: 混相雲内での氷晶形成に関わるエアロゾル
• Time: 11:00 - 12:00 on Mar. 9, 2023.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: 約-36℃〜0℃の温度下では過冷却水滴と氷晶が混在する混相雲がしばしば発生する。混相雲内での微物理過程を考慮する上で、エアロゾル-雲相互作用は非常に重要な役割を果たしている。例えば、氷晶核粒子（INP: ice nucleating particle）として働くエアロゾルを介した氷晶形成は、混相雲の光学特性や寿命等に多大な影響をもたらすといわれている。今回のセミナーでは、INPに関する概説やこれまでの実大気中でのINP観測から得られてきている科学的知見などについて紹介する。

• Title: Global impact of recent Southern Ocean cooling
• Time: 15:30 - 16:30 on Feb. 2, 2023.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Since the beginning of the satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed Southern Ocean cooling has previously been reported to have minimal impact on the tropical Pacific, the efficiency of this teleconnection has recently shown to be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model inter-comparison of paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and the other with Southern Ocean SST anomalies constrained to follow observations. We reveal a global impact of observed Southern Ocean cooling in the model with stronger (and more realistic) cloud feedbacks, including Antarctic sea-ice expansion, southeastern tropical Pacific cooling, northward-shifted Hadley circulation, Aleutian Low weakening, and North Pacific warming. Our results therefore suggest that observed Southern Ocean SST cooling might have contributed to cooler conditions in the eastern tropical Pacific in recent decades. This remotely driven eastern tropical Pacific cooling is shown to halve the bias in global radiative feedback during the historical period in coupled simulations.

• Title: Ensemble Simulations of the climate and ice sheets of the Last Glacial Maximum with a climate-ice sheet coupled model
• Time: 10:00 - 11:00 on Jan. 10, 2023.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Simulating past climates and ice sheets that largely differ from today with climate-ice sheet models is essential to evaluate the their performance and to improve our confidence of future sea level projections. The Last Glacial Maximum is a good target period for this purpose as the global climate was colder by 6K and additional ice sheets of 120m sea level equivalent expanded over the northern continent. Here we performed ensemble simulations of the climate and ice sheets at the Last Glacial Maximum with a recently developed ice sheet-climate coupled model Famous-Bisicles. From these ensemble simulations, we aim to check whether the model reproduces the ice sheets reasonably well and to learn what parameters play a role in controlling the ice volume as well as the global climate. Roles of clouds, albedo and ice sheet basal drag parameters on the climate and ice sheets will be discussed.

• 場所: 270室＋Zoomによる開催（予定）

• Title: イギリス気象庁気候モデルの雲フィードバック過大評価の理解、改善へ向けて：中緯度の雲
• Time: 13:30 - 14:30 on Dec. 15, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: 雲フィードバックは長年気候感度のばらつきの最大不確定要素である。近年その理解のために地表気温、 安定度、700hPaおよび対流圏上層の相対湿度、および500hPaの鉛直流速度など雲に影響を与える大気要素 (cloud controlling factors: 以下c-factors)を使った解析が盛んに進められている。それらの研究の一つ、 Ceppi and Nowack (2021)はridge regression手法をCMIP5,CMIP6の大気海洋結合モデルの出力に適用し、 諸モデルの温暖化に伴う雲のフィードバックが、温暖化に伴う地表気温、安定度の変化、そして現在気候における 雲の放射効果のそれらの要素に対する感度を用いることで良く再現されることを示した。 同様の解析を最新のイギリス気象庁全球大気モデル(HadGEM3 GA8)のPerturbed Parameter Ensemble(PPE)に適用したところ、 中緯度海上の雲の放射効果がc-factorsに対し観測が示すよりも過敏であり、中層雲の感度が特にその傾向と合致することが分かった。 太平洋では雲は黒潮、親潮およびその境界領域に該当し、太平洋に領域を限定した雲の季節変化の基礎解析を行ったところ、 特に寒流である親潮領域の雲の季節変化がモデルで観測と大きくことなることが分かった。 今回の滞在中、GPM、CloudSatなどの観測データを用い、これらの領域の季節変化に伴うc-factorsの変化、雲の変化について 理解を深めようとしている。一方PPEの解析から、この領域の雲の放射効果のc-factorsへの感度に影響のある諸パラメター及び 観測の感度を得るためのパラメター値の範囲を見積もることができる。現在提案中のタスクについても紹介する。

• Title: Global multi-centennial coupled climate modelling towards 10km resolution
• Time: 13:30 - 15:00 on Nov. 21, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: There is increasing evidence of the importance of improved representation of both the ocean mesoscale and corresponding scales in the atmosphere in global climate models, in order to better understand future climate risk. The Met Office is developing a physical climate model aiming at 10km grid spacings in both atmosphere and ocean, with a view to simulating the full CMIP6 1850-2100 period. The work will build on the understanding gained from CMIP6 HighResMIP and from EU PRIMAVERA while also relaxing some of the constraints used there, such as short ocean spin-up and simplified aerosol forcing. New model components developed since CMIP6, such as a new atmosphere convection scheme, will also be incorporated to improve aspects of large-scale model biases and smaller scales such as cyclone intensities. Such models are increasingly challenging our standard methods of data output, storage, sharing and analysis, particularly given their improved capabilities to represent high impact weather and hence the need for high frequency output. The project is developing software tools to be run inline with the model simulations, in order to automate analyses such as storm and eddy tracking and frontal diagnosis, with the potential to reduce the storage footprint while speeding up scientific insight. This work is also engaged with the HighResMIP community and its evolving plans for new science questions and experimental protocols post-CMIP6. It is also a part of a new EU project EERIE (beginning in 2023) led by Thomas Jung, in which four European models will produce simulations at around 10km resolution, initially using the HighResMIP simulation design, to better understand the role of the ocean mesoscale on climate.

• Time: 10:00 - 12:00 on Oct. 19, 2022.
• Place: 270室(General Research Bldg. 2F room 270)
• Title and Abstract:
  ・Modelling the evolution of the Greenland ice sheet during the Last Intergl acial period (Dr. Marie Sicard)
  The Last Interglacial (129-116 ka BP; LIG) is one of the warmest periods in the last 800 ka at many locations with a maximum surface temperature increase in the high latitude of the Northern Hemisphere. This period provides a good testing ground to evaluate the ice sheet-climate interactions under warmer conditions than today. We conducted a transient simulation over the interval from 130 to 120 ka using the GRISLI ice sheet model forced by several snapshots run with the IPSL-CM5A2-VLR model. As a result of climate change over the Last Interglacial, the GRISLI ice sheet model simulates a Greenland ice loss of 10.7-57.1 %, corresponding to a GMSL rise of 0.83-4.35 m and a 0.2 C additional warming in the Arctic region. To better assess ice sheet-climate feedbacks in the Arctic, we therefore carried out a preliminary study using the icoLMDZOR model that includes the new dynamical core DYNAMICO developed at the Institut Pierre-Simon Laplace (IPSL). This study shows that the use of high-resolution atmospheric fields improves the calculation of the surface mass balance in Greenland.
  ・Last-Interglacial Arctic sea-ice simulated by the CMIP6/PMIP4 climate models - an overview (Dr. Marie Sicard)
  The 16 models that run the Last Interglacial (LIG) experiment as part of the CMIP6/PMIP4 exercise consistently produce a smaller Arctic summer sea-ice area at 127 ka BP relative to the pre-industrial period. However, they do not agree on the magnitude of this decrease. This large spread between climate models is partly explained by differences in representation of melt-ponds and cloud microphysics, which affects radiation fluxes over sea-ice. News investigations showed similar sea-ice distribution in the central Arctic between the LIG experiment and an idealized simulation of the near-future climate, but a different sea-ice loss pattern in the Atlantic sector. Climate models generally simulate more sea ice East of Greenland and less sea ice over the Barents Sea for the near-future compared to the LIG. East of Greenland, changes in sea ice are due to a strengthening of the northern winds. In the Barents Sea, the increased sea-ice melt is driven by a warming of the Atlantic Waters along their poleward pathway.
  ・The greenland icesheet during Pliocene (Dr. Gilles Ramstein)
  We first used Pliomip1 simulations using IPSL CM5 climate model and GRISLI in a one-way coupling and different sensitivity experiments (pCO2, insolation) to investigate the full glaciation of Greenland icesheet during late Pliocene (Contoux et. Al, EPSL 2015). We then used an asynchronous coupling method previously developped for Antarctica by Ladant et. Al Paleoceanography 2014 ou 2015), based on 56 sensitivity simulations that enable us to produce different transient simulations driven by different Pco2 scenarios and computed insolation from Laskar (2004). One of the results demonstrates that a CO2 threshold is necessary to build and melt part of the icesheets with insolation forcing. The second important result is to validate which pCO2 scenarios reconstructed from data is the most realistic (Tan et. Al 2019 ou 1017 Nature comm).
  ・Coupled ice sheet : climate simulations of the last two glacial terminations (Dr. Aurlien Quiquet)
  The deglaciation of the Quaternary offers an unique opportunity to understand the climate--ice-sheet interactions in a global warming context. To tackle this question, we use here an ice sheet model synchronously coupled to an Earth system model of intermediate complexity to simulate the last two deglaciations. For the last deglaciation, we show that our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions. Large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets even though the past abrupt sea level rises are underestimated, possibly because the climate model underestimates the millenial-scale temperature variability. In our model, Atlantic oceanic circulation is strongly sensitive to freshwater flux from ice sheet melting and abrupt warming phases in Greenland are linked to oceanic circulation recoveries. The penultimate deglaciation resembles the last deglaciation with a more rapid ice sheet collapse because of stronger insolation forcing. Our model produces a Greenland ice sheet contribution to sea level rise during the last interglacial of about 2 m of sea level equivalent, in agreement with most recent estimates.

• Title: A Super Best Track for Tropical Cyclone Forecasting & Research
• Time: 10:00 - 11:30 on Oct. 17, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Deterministic tropical cyclone (TC) track forecasts have become so accurate in the medium range (e.g., the mean 72-h position error of the global models is now below predictability 'limits') that I expect tropical cyclone (TC) forecasting to move in new directions that include: 1) a more explicit (and better) prediction of the surface wind field; and 2) 'completing the forecast' with predictions of genesis (and dissipation). Additionally, the availability of high-resolution/high-quality global reanalyses will allow more dynamical studies of long-term TC variability.
  Current best track data sets have several deficiencies that limit both research and forecasting since they lack:
  * position/intensity/structure data in the pre/potential TC (pTC) genesis stage
  * observational analyses of the surface wind field and precipitation
  * a ‘diagnostic file,’ with environmental and storm variables known to be related to intensity and structure change (e.g., vertical wind shear)
  The foundation of the super best track (BT++) is the 'final' best tracks ofthe two US operational forecast centers - the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center (NHC). The BT++ is thus global and unique in three important ways by including:
  * pTC tracks taken from a curated archive of all (both 'numbered' and INVEST or 9X systems) working best track data from JTWC/NHC since 2005
  * dynamical environmental variables (analysis and forecasts) come the latest ECMWF reanalysis - ERA5 - that uses a model with the same resolution as the NWP global models circa 2015
  * satellite precipitation and wind radii from surface wind analyses
  The initial version of the BT++ covers a 15-year period 2007-2021 and after a brief summary of BT++ properties, the talk gives one application example for TC genesis. In a preliminary BT++, using operational ECMWF analyses/forecasts, we examined the difference between developing and non-developing pTCs. While there was a clear signal of vertical wind shear decreasing 48-72 before genesis, a more surprising result was that the global model vortex also intensified in the developing cases.
  The paper concludes with a discussion of other potential science and forecasting applications.

• 場所: 270室＋Zoomによる開催

• Title: Atmospheric nonspherical particles: Toward advanced cloud-aerosol remote sensing
• Time: 13:30 - 15:00 on May. 26, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Spaceborne cloud-aerosol property retrievals have been widely used not only for climate studies and validations of numerical modeling capabilities but also nowadays process-oriented microphysics studies. However, these satellite-based cloud-aerosol products may involve systematic biases and/or uncertainties primarily due to inappropriate assumptions made in the retrieval algorithms. In particular, the particle shape models assumed in the retrieval algorithms are generally much simpler than those in nature that exhibit a variety of particle sizes and nonspherical shapes. In this presentation, I will first briefly review cloud-aerosol remote sensing and the importance of the relevant assumptions of atmospheric nonspherical particles in remote sensing. Next, I will introduce a recently developed comprehensive database for the single-scattering properties of irregular aerosol particles (the so-called TAMUdust2020 database) for mineral dust optical property models as an example. The new mineral dust optical property model assumes an ensemble of various irregular particle shapes that mimic realistic mineral dust particle shapes and their diversity and is developed with state-of-the-art light scattering computational capabilities. Furthermore, I will describe the potential applications of the new optical property model to multi-satellite-based remote sensing of dust aerosols, including spaceborne active and passive sensor observations. If time allows, I will describe an example of an active-passive combined remote sensing of cloud properties for cloud microphysics studies.
  References: Saito et al.,(2021) J. Atmos. Sci., 78, 2089-2111; Saito and Yang, (2021) Geophys. Res. Lett., 48, e2021G095121.

• Title: 海洋生態系・物質循環に対する人為起源の栄養塩流入の影響
• Time: 13:30 - 15:00 on Apr. 21, 2022.
• Place: 270室およびZoomによる開催
• 要旨：化石燃料の燃焼や農業用の化学肥料の利用などの人間活動は、大気と河川から海洋への栄養塩(窒素や鉄など)の流入を大幅に増加させている。このような富栄養化は基礎生産を増加させ、気候変動による減少を一部打ち消す可能性がある。また、海洋内部への有機物の輸送とその分解を増やすため、炭素の吸収を促進し、気候変動による海洋の脱酸素化を増幅させる。しかし、CMIP5の地球システムモデルなどでは人為起源の栄養塩流入の影響は考慮されていない。そのため、このような擾乱が海洋の生物地球化学循環に与える影響についての理解は、気候変動の影響の理解に比べ不十分である。特に、気候変動の影響と、人為起源の栄養塩流入の影響との定量的な関係は、ほとんど理解されていない。 本研究では、大気と河川からの人為起源の栄養塩流入を考慮したCMIP6モデルの一つ（MIROC-ES2L）によるヒストリカル実験を用いて、海洋基礎生産量、炭素吸収量、溶存酸素インベントリーの変化に対する人為起源の栄養塩流入の寄与が気候変動の寄与と同程度であることを示す。特に、 (1)富栄養化は、海洋の温暖化と成層化に伴う基礎生産の減少を打ち消す以上の効果がある、(2)気候変動に伴う海洋上層の貧酸素化を加速し、モデルと観測の不整合の一部を補う、という2つの注目すべき結果が得られた。これらの結果から、海洋の生物地球化学循環に対する人間活動の影響を評価するためには、栄養塩流入と気候変動の両方の影響を考慮することが重要であることがわかった。

• Title: Co-evolution of atmospheric oxygen level and marine biogeochemical cycles on early Earth
  初期地球の大気酸素濃度と海洋物質循環系の共進化についての理論的研究
• Time: 13:30 - 15:00 on Apr. 14, 2022.
• Place: 270室およびZoomによる開催
• 要旨：地球史初期の太古代（40-25億年前）の地球は大気酸素濃度は現在より6桁以上小さい無酸素条件下にあったと考えられている。一方、その後の原生代初期の約24-22億年前には大気酸素濃度が現在の数％程度まで一気に上昇する「大酸化イベント」が発生したと考えられている。この大酸化イベントを駆動するためには酸素を多量に放出できる酸素発生型光合成生物が海洋中に存在することが必要であるが、酸素発生型光合成生物はこの大酸化イベントから数億年以上先んじて登場していたのではないかということが、地質学的・系統学的に議論されている。私はそのような無酸素条件の太古代の酸素発生型光合成生物の登場後から原生代にかけての大気-海洋-生態系-気候の共進化について、これまで主に鉛直一次元大気光化学系モデルと海洋生物地球化学循環ボックスモデルを用いて理論的な検討を進めてきた。今回の発表ではその背景となる知識について紹介した上で、これらの成果について議論を行いたい。

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