Primary production & DOM

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)

GABEX-II In Situ NENA 758 (1/=0) NENA 760 (1/=20 d)

St. Augustine Cross-Shelf Transects of Chlorophyll, Nitrate, and PAR

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

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

Primary production 10-6 m-2.s-1

10-5 m-2.s-1

10-6 m-2.s-1

10-5 m-2.s-1

Station 1

Station 3

Net vertical diffusion of DIN

Primary production What makes the PP levels too low…

Run 758

Run 760

- Boundary conditions

- *2

-Kz_bak

… in the North?

ROMS SeaWiFS

Chlorophyll JAN

FEB

MAR

APR

-Too low in winter North of Cape Hatteras-Especially GoM

-Bloom occurs in April North of Cape Hatteras

ROMS SeaWiFS

Chlorophyll MAY

JUN

JUL

AUG

-Modeled bloom occurs in May/June, thus with a 4-6 weeks delay

-Summer levels are reasonable

ROMS SeaWiFS

Chlorophyll SEP

OCT

NOV

DEC

-Lack of horizontal gradient from the coast towards off-shore.

-Too low values again North of Cape Hatteras.

ROMS SeaWiFS

TOTAL DOC MAY

JUN

JUL

AUG

-FOCUS ON THE MAB !

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…

Run 760

…especially in the North?

SEASONAL TEMPERATURE (max)

SEASONAL SALINITY (KCDOM)

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 temperature-dependant?

-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

Primary production

Winter Gulf of Maine

Result shown

Current test= 0.020 (W.m-2 )-1. d-1

max = 2.2 d-1

ROMS SeaWiFS

Chlorophyll JAN

FEB

MAR

APR

RUN 761

= 0.020 (W.m-2 )-1. d-1

max = 2.2 d-1

KCDOM=-0.02*Salt+0.6

ROMS SeaWiFS

Chlorophyll JAN

FEB

MAR

APR

RUN 760

= 0.025 (W.m-2 )-1. d-1

max = Eppley (1972)

KCDOM= MARMAP

January-April Primary Production

Run 761Run 760

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.