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Dr. Takasumi Kurahashi-Nakamura

Phone: 

+49 421 218-65438

Fax:

+49 421 218-65438

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GEO, 5500
Takasumi Kurahashi-Nakamura

CUR­RENT RE­SEARCH (for PalMod WG2)

Un­der­stand­ing the role of mar­ine biogeo­chem­ical pro­cesses in the cli­mate changes dur­ing the gla­cial-in­ter­gla­cial cycles (with CESM)

  • Coupling of a sediment diagenesis model (MEDUSA) and an Earth system model (CESM1.2)
  • The mechanism for the low CO2 level during the LGM
  • The dynamics of marine carbon cycle in millennial-scale climate changes in MIS3

It is well known that car­bon di­ox­ide con­cen­tra­tion (CO2 level) in the at­mo­sphere has been in­creas­ing since the in­dus­trial re­volu­tion due to hu­man’s CO2 emis­sion. Our life in the fu­ture can suf­fer from cli­mate changes in­duced by the in­crease in the CO2 level and/​or from the CO2 in­crease it­self (e.g., ocean acid­i­fic­a­tion). To pro­ject the his­tory of the CO2 level in the fu­ture, it is es­sen­tial to un­der­stand the con­trolling mech­an­isms of the CO2 level in the cli­mate sys­tem. The gla­cial-in­ter­gla­cial cycles in the last 100 kys are con­sidered to be one of the most qual­i­fied re­search tar­gets for that pur­pose, be­cause they demon­strate his­tor­ical (nat­ural) cli­mate changes with large vari­ations in CO2 level.

It is widely con­sidered that the mar­ine car­bon cycle would have had a large in­flu­ence on the CO2-level vari­ations in the gla­cial-in­ter­glacial cycles. However, the dy­nam­ics are not well-un­der­stood yet. We will tackle this is­sue by fo­cus­ing on the budget of carbon and alkalinity in the ocean that crucially affects the chem­ical con­di­tion (i.e. pH) of the en­tire ocean, and thus the at­mo­spheric CO2 level.

(The official website of the project)

Schematic illustration for the coupling scheme between CESM and MEDUSA
Schematic illustration for the coupling scheme between CESM and MEDUSA

PRE­VI­OUS RE­SEARCH (for the former Cluster of Ex­cel­lence OC1)

Dynamical reconstruction of the global ocean state during the LGM (4D-VAR with MITgcm)

  • LGM ocean reconstruction with an adjoint-based data assimilation technique
  • Physics-based three-dimensional interpolation/extrapolation of existing paleoceanographic data
  • More stratified LGM ocean with a stronger but shallower AMOC

We reconstructed the global ocean state for the modern age and for the Last Glacial Maximum (LGM) with a sophisticated data assimilation technique. A substantial amount of data such as seawater temperature and the isotopic composition of oxygen and carbon were integrated into an ocean general circulation model with the help of the adjoint method or 4D-VAR, thereby the model was optimized to reproduce plausible continuous fields of tracers, overturning circulation and water mass distributions. The reconstructed sea-surface temperature for the LGM shows a global-mean cooling of 2.2 K compared to the modern state.

Schematic diagram of the state estimate with the adjoint method or 4D-VAR
Schematic diagram of the state estimate with the adjoint method or 4D-VAR

EDU­CA­TION

03/2004 Ph.D. "Evol­u­tion of the Sur­face En­vir­on­ment of Mars: Nu­mer­ical Stud­ies on the Cli­mate Sys­tem", De­part­ment of Earth and Plan­et­ary Sci­ence, Uni­versity of Tokyo.
03/2001 M.Sc. De­part­ment of Earth and Plan­et­ary Sci­ence, Uni­versity of Tokyo.
03/1999 B.Sc. De­part­ment of Geo­lo­gical Sci­ence, Uni­versity of Tokyo.

 

PRO­FES­SIONAL EX­PER­I­ENCE

05/​2015
-
09/​2016		 Postdoc­toral Fel­low, Jac­obs Uni­versity Bre­men.
01/​2010
-
present		 Re­searcher, MARUM, The university of Bre­men.
06/​2008 -
10/​2009		 Vis­it­ing Fel­low, School of Geo­graph­ical Sci­ences, Uni­versity of Bris­tol.
04/​2008 -
12/​2009		 Ja­pan So­ci­ety for the Pro­mo­tion of Sci­ence (JSPS) Re­search fel­low, Cen­ter fo Cli­mate Sys­tem Re­search, The Uni­versity of Tokyo.
04/​2004 -
03/​2008		 Postdoc­toral re­searcher, Fron­tier Re­search Cen­ter for Global Change, JAM­STEC.
04/​2001 -
03/​2004		 Ja­pan So­ci­ety for the Pro­mo­tion of Sci­ence (JSPS) Re­search fel­low, De­part­ment of Earth and Plan­et­ary Sci­ence, The Uni­versity of Tokyo.

 

GEN­ERAL IN­TEREST

Nu­mer­ical mod­el­ing is an informative method that helps to de­scribe, com­pre­hend, and pre­dict the be­ha­vi­ors of complex sys­tems in a quant­it­at­ive way. The con­sist­ent and gen­eral motive of my re­search is an in­terest in nu­mer­ical mod­el­ling of nat­ural phe­nom­ena, and of so­cial phe­nom­ena as well. 



In nat­ural sci­ence, my main fo­cus is on the cli­mate sta­bil­ity (or vari­ab­il­ity) and the hab­it­ab­il­ity of ter­restrial plan­ets, on the dy­nam­ics of the cli­mate sys­tem, and on how to com­bine know­ledge from nu­mer­ical mod­eling and that from ob­ser­va­tion. In particular, I have been always interested in the carbon cycle of planets because it has a crucial influence on the amount of CO2 in the at­mo­sphere that strongly affects the sur­face en­vir­on­ment of them through the global energy balance.



In the field of so­cial sci­ence, dy­nam­ics of people’s opin­ions in a so­ci­ety is a ma­jor con­cern, for ex­ample, from a polit­ical-sci­ence view­point because they govern how ma­jor­it­ies are formed, how many ma­jor­it­ies are cre­ated, and how stable they are. Ana­lyz­ing so­cial dy­nam­ics with a sim­pli­fied nu­mer­ical model will offer a beneficial insight to help our gen­eral un­der­stand­ing of phe­nom­ena based on plenty of well-con­trol­lable ex­per­i­ments. That will also provide fundamental ideas to design more real­istic models for the projection into the future.



Spe­cific re­search in­terests of mine in­cludes/ in­cluded:

  • Mechanisms to control the atmospheric CO2 level in the glacial-interglacial period
  • The role of marine carbon cycles in climate changes in the past and future
  • General understanding the behaviour of the climate system (e.g., intrinsic feedback mechanisms)
  • Regulating mechanisms of the long-timescale evolution of climate of Mars
  • Opnion dynamics with agent-based modelling

LIST OF PUB­LIC­A­TIONS FOR NAT­URAL SCI­ENCE

Kurahashi-Nakamura, Takasumi, A. Paul, U. Merkel, and M. Schulz, "Glacial state of the global carbon cycle: time-slice simulations for the last glacial maximum with an Earth-system model", Clim. Past, 18, 1997–2019, https://doi.org/10.5194/cp-18-1997-2022, 2022. 

Kurahashi-Nakamura, Takasumi, A. Paul, G. Mun­hoven, U. Merkel, and M. Schulz, "Coup­ling of a sed­i­ment dia­gen­esis model (ME­DUSA) and an Earth sys­tem model (CESM1.2): a con­tri­bu­tion to­ward en­hanced mar­ine biogeo­chem­ical mod­el­ling and long-term cli­mate sim­u­la­tions", Geosci. Model Dev., 13, 825–840, ht­tps://​doi.org/​10.5194/​gmd-13-825-2020, 2020.

Breit­kreuz, C., A. Paul, T. Kurahashi‐Nakamura, M. Losch, and M. Schulz, "A dy­nam­ical re­con­struc­tion of the global monthly‐mean oxy­gen iso­topic com­pos­i­tion of sea­wa­ter", J. Geo­phys. Res. Oceans, ht­tps://​doi.org/​10.1029/​2018JC014300, 2018.

Kurahashi-Nakamura, Takasumi, A. Paul, and M. Losch, "Dy­nam­ical re­con­struc­tion of the global ocean state dur­ing the Last Gla­cial Max­imum", Pa­leocean­o­graphy, 32, doi:10.1002/​2016PA003001, 2017.

Kurahashi-Nakamura, Takasumi, M. Losch, and A. Paul, "Can sparse proxy data con­strain the strength of the At­lantic me­ri­di­onal over­turn­ing cir­cu­la­tion?", Geosci. Model Dev., 7, 419-432, doi:10.5194/​gmd-7-419-2014, 2014.

Kurahashi-Nakamura, Takasumi, A. Abe-Ou­chi, and Y. Yaman­aka, “Ef­fects of phys­ical changes in the ocean on at­mo­spheric pCO2 dur­ing the last gla­cial max­imum", Clim. Dyn., DOI10.1007/​s00382-009-0609-5, 2010.

Kurahashi-Nakamura, Takasumi, A. Abe-Ou­chi, Y. Yaman­aka and K. Misumi, “Com­pound ef­fects of Ant­arc­tic sea ice on at­mo­spheric pCO2 change dur­ing gla­cial–in­ter­gla­cial cycle", Geo­phys. Res. Lett., 34, L20708, doi:10.1029/​2007GL030898, 2007.

Kurahashi-Nakamura, Takasumi, and E. Tajika, “At­mo­spheric col­lapse and trans­port of car­bon di­ox­ide into the sub­sur­face on early Mars”, Geo­phys. Res. Lett., 33, L18205, doi:10.1029/​2006GL027170, 2006.

Kurahashi-Nakamura, Takasumi, and E. Tajika, “Evol­u­tion of the Mar­tian cli­mate: ef­fects of the ice sheets”, Seppyo, Journal of the Ja­pan­ese So­ci­ety of Snow and Ice, Vol. 67, No. 2, pp.133-145, 2005 (in Ja­pan­ese).

Nakamura, Takasumi, and E. Tajika, “Cli­mate change of Mars-like plan­ets due to ob­liquity vari­ations: im­plic­a­tions for Mars”, Geo­phys. Res. Lett., 30, No. 13, 1685, doi:10.1029/​2002GL016725, 2003.

Nakamura, Takasumi, and E. Tajika, “Sta­bil­ity of the Mar­tian cli­mate sys­tem un­der the sea­sonal change con­di­tion of solar ra­di­ation”, Journal of Geo­phys­ical Re­search, vol.107, no.E11, 5094, doi:10.1029/​2001JE001561, 2002.

Nakamura, Takasumi, and E. Tajika, “The Mar­tian Cli­mate Sys­tem : Its Sta­bil­ity and Evol­u­tion”, Plan­et­ary People, Journal of the Ja­pan­ese So­ci­ety for Plan­et­ary Sci­ence, vol.10, no.4, pp.192-201, 2001 (in Ja­pan­ese).

Nakamura, Takasumi, and E. Tajika, “Sta­bil­ity and evol­u­tion of the cli­mate sys­tem of Mars”, Earth, Plan­ets, and Space, vol.53, pp.851-859, 2001.

LIST OF PUB­LIC­A­TIONS FOR SO­CIAL SCI­ENCE

Lorenz, Jan, T. Kurahashi-Nakamura, and S. Shi­k­ano, "Cycles of pub­lic policy mood through opin­ion dy­nam­ics un­der het­ero­gen­eous bounds of con­fid­ence" (in prep.).

Kurahashi-Nakamura, Takasumi, M. Mäs, and J. Lorenz, "Ro­bust clus­ter­ing in gen­er­al­ized bounded con­fid­ence mod­els", Journal of Ar­ti­fi­cial So­ci­et­ies and So­cial Sim­u­la­tion, 19, (4), 7, DOI:10.18564/​jasss.3220, 2016.