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SUMMARY:Carbon isotope modelling implications for changes in the Southern 
 Ocean carbon cycle during the last deglaciation - Hidetaka Kobayashi\, Uni
 versity of Toyama
DTSTART:20240424T130000Z
DTEND:20240424T140000Z
UID:TALK212395@talks.cam.ac.uk
CONTACT:Dr Birgit Rogalla
DESCRIPTION:Atmospheric carbon dioxide (pCO2) concentrations increased by 
 about 80 ppm from the Last Glacial Maximum (LGM) to the early Holocene\, r
 eflecting the climate system's response to gradual changes in insolation. 
 Previous models have suggested that this deglacial pCO2 increase was mainl
 y due to CO2 released from the ocean\, partly influenced by abrupt shifts 
 in the Atlantic Meridional Overturning Circulation (AMOC) and associated i
 nterhemispheric climate changes. However\, a comprehensive understanding o
 f how changes in ocean circulation and geochemical properties during the l
 ast deglaciation influenced atmospheric pCO2 remains elusive.This study na
 rrows the focus to the Southern Ocean and examines its role in changes in 
 the ocean carbon cycle during the last deglaciation (21 to 11 ka BP) using
  three-dimensional ocean fields from the MIROC 4m climate model\, which su
 ccessfully simulates abrupt AMOC shifts seen in reconstructions. We aim to
  improve our understanding by comparing modeled carbon isotope ratios with
  sediment core data\, identifying model biases and highlighting potentiall
 y underestimated processes. The simulation is in qualitative agreement wit
 h ice core records of atmospheric pCO2 fluctuations: an increase of 10.2 p
 pm during the Heinrich Stadial 1 (HS1)\, a decrease of 7.0 ppm during the 
 Bølling-Allerød (BA)\, and a subsequent increase of 6.8 ppm during the Y
 ounger Dryas (YD). Nevertheless\, the model underestimates pCO2 changes co
 mpared to ice core data\, suggesting that some ocean dynamics have been mi
 ssed in the simulations. A particular limitation of the model is its under
 estimation of the influence of the Southern Ocean\, especially during HS1.
  This suggests a misrepresentation of the complex interplay between activa
 ted deep ocean ventilation\, reduced biological carbon export efficiency\,
  and their cumulative effect on atmospheric pCO2. The decomposition of the
  drivers of ocean pCO2 changes highlights temperature and alkalinity as ke
 y drivers. Their interaction reveals the intricate link between AMOC shift
 s\, Southern Ocean carbon dynamics leading to changes in SST and geochemic
 al properties\, and the resulting atmospheric pCO2 variations during degla
 ciation. This study underscores the critical need for detailed modeling of
  Southern Ocean biogeochemical processes to refine our understanding of pa
 st and future climate dynamics.
LOCATION:BAS Seminar Room 1\; https://bas-ac-uk.zoom.us/j/98483093717
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