critical turbulence revisited: the impact of submesoscale vertical transports on plankton patchiness...
Post on 21-Dec-2015
215 Views
Preview:
TRANSCRIPT
Critical turbulence revisited: The impact of submesoscale vertical transports on plankton patchiness
Anne Willem OmtaBas Kooijman
Theoretical Biology, Vrije Universiteit (Amsterdam)Henk Dijkstra
IMAU, Universiteit Utrecht
www.bio.vu.nl/thb
Grant No. 635.100.009 (Computational Life Sciences)
Project overview
• Organic carbon pump in meso-scale ocean flowsAim: determine effect of (sub)meso-scale flows on
phytoplanktonMethod: computer simulations and theory
developmentSupervisors: Kooijman, Dijkstra, SommeijerPhD’s: Bruggeman & OmtaPostdoc: Van RaaltePeriod: March 2004 – March 2009
My PhD
• Feedback mechanisms between climate and Redfield ratio (GRL 33, L14613, 2006)
• Impact of submesoscale eddies on organic carbon pump (JGR 112, C11006, 2007)
• Critical turbulence revisited (JMR 66, 61-85, 2008)
• How to interpret satellite chlorophyll observations (submitted to DSR)
Feedback mechanisms between climate and Redfield ratio
• With plankton physiological model, I investigated impact of mixed-layer depth and temperature on C:N ratio
• Increase of C:N ratio with decreasing mixed-layer depth and temperature: possible implications for glacial cycles
Impact of submesoscale eddies on organic carbon pump
• 3D-simulation of phytoplankton in baroclinically unstable submesoscale eddy
• Vertical transports lead to upward N transport and plankton bloom
• Effect on distribution and net transport of carbon very modest: enhanced upward transport of DIC, enhanced downward transport of organic carbon
How to interpret satellite chlorophyll observations
• Looked at seasonal Chl cycle in Mozambique Channel
• Tried to reproduce cycle with various plankton population models
• Modeled Chl/N ratio gave best correlation with observed Chl: suggests that cycle represents variation in Chl/N rather than in plankton
Critical turbulence
Huisman et al. (1999): if downward transport of plankton is faster than growth, then plankton goes extinct
Critical turbulence = 1-D concept: How does it work out in 3-D?
Ocean eddy field
Real 3-D ocean eddy
field very complicated: simulate one
single eddy for better
understanding
Flow model
• Non-hydrostatic 3-D model
• Domain 32 km * 32 km * 1 km
• Periodic boundary conditions
SU-based Internal Transformation Yield (SITY) model
- Three state variables (nutrient, algal biomass, detritus), only six parameters- Uptake according to SU-kinetics: organisms can be limited by light and nutrients- Detritus sinks
Initial conditions
• Biomass: – Sinking of organic
nutrient balanced by upward diffusion of inorganic nutrient
• Eddy radius ~8 km, no vertical velocity
Vertical velocity patterns
3.6 days
7.2 days
12 days
Plankton distributions at different light intensities
50 mol/(m2 d) 2 mol/(m2 d)
Two very distinct regimes!
2-D simulations
Again, two regimes show up!
D=0.01m2/sD=0.01m2/s D=1m2/s
Explanation of regimes
Eddy region optimal for
plankton (high nutrients)
Vertical exchange subcritical everywhere
Vertical exchange supercritical in eddy region
Adjacent regions optimal for plankton (relatively high nutrients and low vertical exchange)
1-D simulations consistent with explanation
- Vertical mixing + algal growth
Distinct plankton distributions
- Explanation: critical turbulence
Conclusions
More information: www.bio.vu.nl/thbOmta et al., J. Mar. Res. 66: 61-85 (2008)
top related