1' Introduction 2' Modeled changes in dissolved O2 3' A revised carbon budget 4' Large Scale Circula

1
The influence of mesoscale processes on the
dynamics of the upper ocean carbon cycle along
the U.S. West Coast G.-K. Plattner, H. Frenzel,
N. Gruber, A. Leinweber, P. Marchesiello, and J.
C. McWilliams - UCLA G. E. Friederich and
F. P. Chavez - MBARI


EPOC, September 2003
2
Eddy-induced enhancement of primary production?

• e.g. Oschlies and Garçon, Nature 1998, North
  Atlantic
• 30 of new production from nutrient supply by
• mesoscale eddy activity
• --gt moderate effect
• e.g. McGillicuddy et al., Nature 1998, Sargasso
  Sea
• 73 of primary production from nutrient supply
  by
• mesoscale eddy activity
• --gt dominant effect
• --gt What about the California Current System
  (CCS)?

3
Eddy Kinetic Energy increases largely withfiner
model resolution- spatial distribution in the CCS
ROMS 15km
ROMS 5km
Surface EKE (cm2 s-2)
4
Eddy Kinetic Energy increases largely withfiner
model resolution- mean and mesoscale variability
in the CCS
Surface EKE (cm2 s-2)
5 km
10 km
20 km
Time (years)
(Marchesiello et al., JPO 2003)
5
Surface Chl-a (mg m-3) ROMS vs. SeaWiFSAnnual
Mean
ROMS (155 km embedded)
SeaWiFS
Pt. Arena
Pt. Arena
San Francisco
San Francisco
Monterey Bay
Monterey Bay
ROMS setup Climatological forcing (COADS), NPDZ
ecosystem with carbon cycle
6
Surface Chl-a ROMS 15 km vs. 5 km Annual Mean
Pt. Arena
Pt. Arena
San Francisco
San Francisco
Monterey Bay
Monterey Bay
ROMS 15 km
ROMS 5 km
Chl-a (mg m-3)
7
Surface Chl-a ROMS 15 km vs. 5 kmSnapshot May
21
ROMS 15 km
ROMS 5 km
Chl-a (mg m-3)
8
NPP ROMS 15 km vs. 5 kmAnnual mean over the
euphotic zone (1 PAR)
ROMS 15km
ROMS 5km
NPP (mol C m-2 yr-1)
9
NPP ROMS 15 km vs. 5 kmSnapshot May 21
ROMS 15km
ROMS 5km
Surface layer NPP (mol C m-3 yr-1)
10
NPP offshore profile ROMS 15 km vs. 5 kmAnnual
mean over the euphotic zone
11
Conclusions

• Including mesoscale processes does not enhance
  NPP in the CCS region, however
• Spatial distribution of NPP (and other
  biogeochemical fluxes) is modified values closer
  to the coast are decreased with finer resolution,
  while offshore values are increased (filaments)
• Annual averages for different model resolutions
  of ROMS over a 500 km core region of the CCS are
  almost identical
• Thus mesoscale processes in ROMS affect the
  upper ocean carbon cycle in the CCS primarily on
  small spatial and short time scales, but do not
  significantly affect the overall budgets

12
Outlook

• Need for further sensitivity studies to improve
  our current model solutions
• From climatological forcing to synoptic
  forcing new wind forcing (blended product, Chao
  et al., GRL 2003)
• Improve the representation of ecosystem/biogeoche
  mical processes by including multiple nutrient
  limitation and multiple phytoplankton classes
  (see Moore et al., DSR II, 2002)