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SUMMARY:Contemporary Southern Ocean CO2 flux variability in the UKESM1 and
  ocean-only simulations. -  Andrea Rochner (University of Exeter)
DTSTART:20210407T130000Z
DTEND:20210407T140000Z
UID:TALK156286@talks.cam.ac.uk
CONTACT:100933
DESCRIPTION:The Southern Ocean is a strong contemporary sink for atmospher
 ic CO2 due to the interaction of various drivers\, including strong winds\
 , biological activity\, or the overturning of water masses and their carbo
 n content. A fundamental question is whether the Southern Ocean will conti
 nue taking up similar proportions of CO2 in the future. However\, future p
 rojections are hampered by the large uncertainty in contemporary CO2 fluxe
 s in Earth System Models (ESMs) and result from differences in individual 
 model set-ups and their representation of CO2 flux drivers\, historically 
 sparse observations\, and gaps in the understanding of the regional distri
 bution and natural variability of air-sea CO2 flux.\n \nIn this talk\, I w
 ill first introduce some of the open questions and challenges for both obs
 ervations and models with regard to the CO2 flux in the Southern Ocean. I 
 then explore the CO2 flux and its drivers in the Southern Ocean for the fu
 lly-coupled historical UK Earth System Model (UKESM1) simulation\, compare
 d to simulations using the UKESM1’s ocean component forced with reanalys
 is data. The comparison highlights several shortcomings in the UKESM1 simu
 lations. Differences in the phase of the seasonal cycle of net CO2 flux ap
 pear between the simulations: while the seasonal cycle is out of phase wit
 h observations in the UKESM1\, the ocean-only simulation is in phase. This
  phase change is related to differences in the underlying physical process
 es\, namely upper ocean stratification\, winter mixed layer depth in the s
 ub-Antarctic region\, and circulation\, which occur in response to the dif
 ferent atmospheric forcing. Disagreements in the timing of the seasonal cy
 cle are not uncommon for ESMs\, as are biases in the named physical proces
 ses. The results described here may therefore be valid for a larger group 
 of ESMs. However\, there are features of the CO2 flux which do not improve
  or even exacerbate despite improved physics representation in the ocean-o
 nly run\, such as the magnitude of the CO2 flux or the decadal variability
 . The results thus illustrate the complexity of simulating the Southern Oc
 ean CO2 flux\, current limitations and opportunities for future model deve
 lopments.\n
LOCATION:British Antarctic Survey\, Zoom
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