Parameterising primary production and convection in a 3D model

Report
Parameterising Primary Production
and Convection in a 3D Model
Fabian Große1*, Johannes Pätsch2 and Jan O. Backhaus2
1
Research Group Scientific Computing, Department of Informatics, University of Hamburg
2 Institute of Oceanography, University of Hamburg
* Corresponding author: [email protected]
45th Liège Colloquium
May 13 – 17, 2013
Introduction: ARGO measurements
Source: Quadfasel (unpublished)
Source: Quadfasel (unpublished)
• convection as driving mechanism
(Backhaus et al., 1999)
Introduction: Phytoconvection
• mean spatial aspect ratio of
2.5:1 (horizontal vs. vertical
scale) (Kämpf & Backhaus, 1998)
• convective cycle takes 1-2
days (D’Asaro, 2008)
• same probability of residence
in the euphotic zone for each
phytoplankton particle
Source: Backhaus (2003)
2.5:1
Source: Janout (2003)
MLD
MLD
Phytoconvection in a 3D Model
• Phytoconvection = upward and downward displacement of phytoplankton within a convective cell
• hydrostatic approximation requires parameterisation
• Steele (1962):
PB … growth rate
• MLD-dependent sliding function between standard
and phytoconvection
Model Setup and Simulations
• 3D physical-biogeochemical model
ECOHAM4 (Lorkowski et. al., 2012)
• 20 km horizontal resolution
• 5-1000 m vertical resolution (24
layers)
• physics initialised from climatology
• initialisation for biochemistry from
standard simulation of 1995
• simulation period: 1996
• comparison of 2 simulations:
• Standard
• Phytoconvection
position of
1D analysis
MLDsim
• Standard run
• low winter concentrations
within mixed layer
• near-surface bloom in April
• high concentrations until
autumn within mixed layer
mg chl-a m-3
depth [m]
Results – Part I: 1D Analysis
chlorophyll-a
depth [m]
mg chl-a m-3
• Phytoconvection run
• high winter concentrations
within mixed layer
• deep maximum in April
• high concentrations until
autumn within mixed layer
chlorophyll-a
MLDsim
depth [m]
MLDsim
mg chl-a m-3
depth [m]
Results – Part I: 1D Analysis
MLDobs
depth [m]
mg chl-a m-3
chlorophyll-a
chlorophyll-a
chlorophyll a [mg m-3]
Data source: BODC
Results – Part I: 1D Analysis
• Standard run:
• significantly lower
concentrations throughout
whole water column
depth [m]
• Phytoconvection run:
• upper layer concentrations
in good agreement with
observations
• low chlorophyll-a below
mixed layer
MLD
MLDsim
sim
MLD
MLDobs
obs
• depth of chlorophyll-a
gradient ≠ MLD
chlorophyll a [mg m-3]
Data source: BODC
Results – Part II: 3D analysis
Chlorophyll-a (depth-integrated)
April - standard
April - standard
April - phytoconvection
mg chl-a m-2
g C m-2 month-1
Primary production
mg chl-a m-2
g C m-2 month-1
April - phytoconvection
Results – Part III: Carbon fluxes
mmol C m-2 month-1
Air-sea flux
mmol C m-2 month-1
Export (below 500m)
Summary & Conclusion
• parameterisation of phytoconvection:
• observed upper layer chlorophyll-a concentrations reproduced
• strong influence of convection on primary production and
carbon export production
• sliding function allows continuous transition from winter
to summer regime
• problems during decline of mixed layer in spring
• applied MLD criterion (Tsurf – T > 0.4K) not suitable to:
• detect haline stratification
• distinguish between convective and frictionional mixing
Outlook
• improvement of sliding function:
→ include turbulent mixing depth (Taylor & Ferrari, 2011)
• replace MLD criterion (Tsurf – T > 0.4K)
• apply parameterisation on model area with more
regions of deep winter convection for better data basis
• include results from tank experiments investigating
phytoplankton adaptation to different dark-light cycles
Titelmasterformat durch Klicken
Parametrisierung von Primärproduktion und
bearbeiten
winterlicher Konvektion
in einem 3D Modell
Thank you for your attention.
Vielen Dank für Ihre
Aufmerksamkeit.
[email protected]
45th Liège Colloquium
May 13 – 17, 2013
References
•
D’Asaro, Eric A.. Convection and the seeding of the North Atlantic bloom.
Journal of Marine Systems, 69:233–237, 2008.
•
Backhaus, J., Wehde, H., Hegseth, E., and Kämpf, J. ‘Phyto-convection’: the
role of oceanic convection in primary production. Marine Ecology.
Progress Series, 189:77–92, 1999.
•
Backhaus, J., Hegseth, E., Wehde, H., Irigoien, X., Hatten, K., and
Logemann, K. Convection and primary production in winter. Marine
Ecology Progress Series, 251:1–14, 2003.
•
Janout, M. Biological parameterization of convection in a mixed layer model.
Pages 1–87, 2003.
•
Lorkowski, I., Pätsch, J., Moll, A., and Kühn, W. Interannual variability of
carbon fluxes in the North Sea from 1970 to 2006 - Competing effects
of abiotic and biotic drivers on the gas-exchange of CO2. Estuarine,
Coastal and Shelf Science, 2012.
•
Taylor, J. and Ferrari, R. Shutdown of turbulent convection as a new criterion
for the onset of spring phytoplankton blooms. Limnology and
Oceanography, 56(6):2293, 2011.

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