Primary production & DOM
OUTLINE:
What makes the PP levels too low?
1- run 760
- Boundary conditions not seen (nudging time)
- Phytoplankton parameter: 
- (Grazing: Gmax, Kphy)
- Background diffusivity: Kz_bak
Results and comparisons (Chla, semilabile DOC)
2- run 761
- Phytoplankton parameters: max
- KCDOM
Results and comparisons (Chla)
St. Augustine Cross-Shelf Transects of Chlorophyll, Nitrate, and PAR
GABEX-II In Situ
NENA 758 (1/=0)
NENA 760 (1/=20 d)
Primary production
 = initial slope of the PI curve
f(I)= I / sqrt(max 2+(I)2)
I (W.m-2)
max (d-1)
Thus  is in (W.m-2 )-1. d-1
Not in mg C.(mg Chl)-1.(W.m-2 )-1. d-1
as in the code.
Original value = 0.025 (W.m-2 )-1. d-1
Literature = 0.017-0.025-0.050-0.140 (W.m-2 )-1. d-1
Value chosen  = 0.050 (W.m-2 )-1. d-1
Original at 6 & 25 oC
Modified at 6 & 25 oC
Grazing
The balance between producers and grazers has been slightly modified
introducing a variable (and mostly lower) assimilation efficiency for
modeling the sloppy feeding:
Maximum grazing: Gmax
Original value = 0.6 d-1
Literature = 0.5-0.9-1.0-1.2 d-1
New value Gmax = 0.75 d-1
Half-saturation constant: Kphy
Original value = 2.0 (mmol N.m-3)2
Literature = 0.56-3.5 (mmol N.m-3)2
New value Kphy = 1.5 (mmol N.m-3)2
Primary production
Background diffusivity: Kz_bak
Original value = 10-6 m-2.s-1
Literature = 5. 10-6 m-2.s-1
(Mackinnon et al. 2005)
Since small scale processes
are not taken into account in
the 10 km grid, as well as
internal waves, the value
chosen is:
Kz_bak = 10-6 m-2.s-1
10-6 m-2.s-1
Station 1
10-5 m-2.s-1
Net vertical diffusion of DIN
10-6 m-2.s-1
Station 3
10-5 m-2.s-1
Primary production
What makes the PP levels too low…
Run 758
- Boundary conditions
- *2
-Kz_bak
Run 760
… in the North?
Chlorophyll JAN
-Too low in winter
North of Cape
Hatteras
-Especially GoM
FEB
ROMS
MAR
-Bloom occurs in
April North of
Cape Hatteras
APR
SeaWiFS
Chlorophyll MAY
-Modeled bloom
occurs in
May/June, thus
with a 4-6 weeks
delay
-Summer levels
are reasonable
JUN
ROMS
JUL
AUG
SeaWiFS
Chlorophyll SEP
-Lack of horizontal
gradient from the
coast towards offshore.
OCT
ROMS
NOV
-Too low values
again North of
Cape Hatteras.
DEC
SeaWiFS
TOTAL DOC MAY
JUN
ROMS
-FOCUS ON THE
MAB !
JUL
AUG
SeaWiFS
SAB (21 m depth)
MAB (44 m depth)
Denitrification - 2004
Carbon Excess Uptake - 2004
Carbon burial -2004
Burial Efficiency -2004
Export ratio on the shelf - 2004
Grazing - 2004
Primary production
What makes the PP levels too low…
SEASONAL TEMPERATURE (max)
SEASONAL SALINITY (KCDOM)
Run 760
…especially in the North?
Primary production
KCDOM = f(salinity)
-The CDOM traced here is terrestrial
since the marine fraction is implicitly
included in the KChl
-Formulation based on MARMAP data
located in the MAB with the hypothesis
that the Chl level is reasonable
-Leads to a permanent anomaly in the
northern part due to fresher waters
from the Labrador current with a priori
no terrestrial CDOM and due to the
lack of attenuation from the too low
Chl levels
-Test performed with a KCDOM set to a
low salinity formulation:
KCDOM =-0.02*Salt+0.6
Primary production
Is the maximum growth temperaturedependant?
-Temperature is not needed to reproduce the
phytoplankton seasonal cycle, species are
adapted to their environment.
-Brush et al. 2002 showed that the use of the
Eppley (1972) formulation leads to an
underestimation of the PP.
-They even recommend the use of an empirical
formulation independent of temperature, following
an observed consistent relationship between PP
and the photic depth, the chlorophyll content in
the photic zone and the surface irradiance.
- Test performed with a constant maximum
growth rate = 2.5 d-1
 = initial slope of the PI curve
Former value = 0.050
(W.m-2 )-1.
d-1
Value chosen  = 0.025 (W.m-2 )-1. d-1
Original at 6 & 25 oC
Modified at 6 & 25 oC
Winter Gulf of Maine
Result shown
Current test
= 0.020 (W.m-2 )-1. d-1
max = 2.2 d-1
Chlorophyll JAN
RUN 761
= 0.020 (W.m-2 )-1. d-1
max = 2.2 d-1
FEB
KCDOM=-0.02*Salt+0.6
ROMS
MAR
APR
SeaWiFS
Chlorophyll JAN
RUN 760
= 0.025 (W.m-2 )-1. d-1
max = Eppley (1972)
FEB
KCDOM= MARMAP
ROMS
MAR
APR
SeaWiFS
January-April Primary Production
Run 760
Run 761
Conclusion
• Primary production and chlorophyll levels are
about to be calibrated, some refinement might
be necessary.
• The specificities of phytoplankton dynamics are
well simulated in the SAB and MAB.
• Realistic DOC levels and distribution are shown
in summer.
• The primary production must be realistic for the
rest of the year to be able to simulate reasonably
the DOC.