Primary production & DOM OUTLINE: What makes the PP levels too low? 1- run Boundary conditions not seen (nudging time) - Phytoplankton parameter:  - (Grazing: G max, K phy ) - Background diffusivity: K z_bak Results and comparisons (Chla, semilabile DOC) 2- run Phytoplankton parameters:  max - K CDOM 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 = (W.m -2 ) -1. d -1 Literature = (W.m -2 ) -1. d -1 Value chosen  = (W.m -2 ) -1. d -1 Original at 6 & 25 o C Modified at 6 & 25 o C

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: G max Original value = 0.6 d -1 Literature = d -1 New value G max = 0.75 d -1 Half-saturation constant: K phy Original value = 2.0 (mmol N.m -3 ) 2 Literature = (mmol N.m -3 ) 2 New value K phy = 1.5 (mmol N.m -3 ) 2

Background diffusivity: K z_bak Original value = m -2.s -1 Literature = 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: K z_bak = m -2.s -1 Primary production m -2.s m -2.s m -2.s 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 Boundary conditions -  *2 -K z_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

Carbon Excess Uptake

Carbon burial -2004

Burial Efficiency -2004

Export ratio on the shelf

Grazing

Primary production What makes the PP levels too low… Run 760 …especially in the North? SEASONAL TEMPERATURE (  max ) SEASONAL SALINITY (K CDOM )

K CDOM = f(salinity) -The CDOM traced here is terrestrial since the marine fraction is implicitly included in the K Chl -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 K CDOM set to a low salinity formulation: K CDOM =-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 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 = (W.m -2 ) -1. d -1 Value chosen  = (W.m -2 ) -1. d -1 Original at 6 & 25 o C Modified at 6 & 25 o C Primary production Winter Gulf of Maine Result shown Current test  = (W.m -2 ) -1. d -1  max = 2.2 d -1

ROMS SeaWiFS Chlorophyll JAN FEB MAR APR RUN 761  = (W.m -2 ) -1. d -1  max = 2.2 d -1 K CDOM =-0.02*Salt+0.6

ROMS SeaWiFS Chlorophyll JAN FEB MAR APR RUN 760  = (W.m -2 ) -1. d -1  max = Eppley (1972) K CDOM = 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.