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SUMMARY:Challenges in Understanding Decadal Trends and Variability of Ocea
 nic Dissolved Oxygen: Perspectives from MPI-ESM's Large Ensemble Simulatio
 ns - Yohei Takano\, Max Planck Institute for Meteorology
DTSTART:20171123T110000Z
DTEND:20171123T120000Z
UID:TALK84021@talks.cam.ac.uk
CONTACT:Dr Peter Davis
DESCRIPTION:Ocean deoxygenation is known to be one of the major marine eco
 system stressors along with the warming and ocean acidification under futu
 re climate change [_Gruber_\, 2011]. The observational studies [e.g.\, _It
 o et al._\, (2017)\;_Schmidtko et al_.\, (2017)] indicate that the ocean d
 eoxygenation might already have started to emerge in the recent decades. H
 owever\, it is challenging to detect the emergence of ocean deoxygenation 
 from the observations because of the limited sample size in both space and
  time. The existence of internal/natural variability rise additional uncer
 tainties on interpreting the observed dissolved oxygen variability and tre
 nd along with future projections from the Earth System Models (ESMs).\n\nI
 n this talk\, I will address the potential role of the internal variabilit
 y in driving the observed decadal trend and variability of oceanic oxygen 
 in the upper 300m. To disentangle the internal variability and forced tren
 d (i.e. the long-term trend (response) rising from external forcing such a
 s greenhouse gases and volcanic eruptions)\, we use so-called "Large Ensem
 ble Simulations" from the Max-Planck Institute for Meteorology Earth Syste
 m Model (MPI- ESM). The Large Ensembles are powerful tool for quantifying 
 the internal variability of the climate system and are widely used in the 
 climate science community [e.g.\,_Deser et al._\, (2012)] We analysed the 
 globally compiled dissolved oxygen observations from the World Ocean Datab
 ase 2013 [_Boyer et al ._\, (2013)\; _Ito et al_.\, (2017)] within the con
 text of the MPI-ESM’s Large Ensemble Simulations and discuss the possibl
 e role of internal variability in driving the decadal trends.\n\nThe resul
 ts indicate that most of the decadal trends in global and regional oceanic
  oxygen are driven by internal variability. Internal variability could cha
 nge the decadal trends in a diverse way\, causing differences in magnitude
 s and even the sign of the decadal trends. The effect of ventilation and b
 iological consumption play a dominant role regulating the decadal trends r
 ather than the thermodynamically driven solubility effect for both observa
 tions and Large Ensembles. However\, the observed decadal trend is larger 
 than the range of internal variability simulated from Large Ensembles. It 
 is likely that both model limitations (in simulating unresolved features s
 uch as mesoscale eddies) and the nature of chaotic spatial patterns of int
 ernal variability of oceanic oxygen could both introduce major challenges 
 in the interpretation of the observations within the context of the Large 
 Ensembles. I will further discuss how limitations in both observations and
  modelling could cause additional uncertainties when interpreting the past
  observations and future projections.
LOCATION:British Antarctic Survey\, Innovation Centre\, Seminar Room 330b
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