Our Conceptual Model

1 2 43 5 6 70

4

6

8

10

12

14

Nitrate (uM)

JUL- SEPT

Seasonal cycle of nutrients and temperature on the crest of Georges Bank

Pastuzak et al., 1982

Nutrient Recharge is Across the Flanks…

in Fall, not Winter

The “Donut” Hypothesis of Post-Bloom Nutrient Injections & Production

Presumed Greater Production on NE Peak…

CRITICAL DEPTH

Z=1.0 Zcr=1.4

[DIN]Seasonal Changein Critical Depth

SeasonalChange in

Position of Front

Ratio (R) =Mixing Depth

Critical Depth “Production Velocity”

Subsurface Chl. Max. Proportional to

Compensation Depth (notcritical depth)

And Production = f(Ratio, [N])

R = 1.4 R = 1.0

DIN PON

Sources of, and what happens to, dissolved inorganic nutrients that are brought onto Georges Bank

Ammonia Silicate

SmallPhytoplankton

LargePhytoplankton

SmallZooplankton

LargeZooplankton

DetritusNitrogen

DetritusSilica

PredationMortality

Remineralization

UptakingUptaking Uptaking

Dissolution

Fecal

Mortality

Grazing Grazing

Mortality

Mortality

Nitrate

GrazingMortality

Biological Model (Rubao Ji, UMass Dartmouth)

Proposed Modeling Experiments:Seasonal Cycle and Transects…

Divergent Upwelling onNE & SW Portions?

Another Interesting Angle…

Giving Two Phytoplankton Patches?

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(ug/L)0.0

1.6

3.2

4.8

6.4

8.0

9.6

11.2

12.8

14.4

16.0

1997 1998 1999

Jan

Feb

Mar

Apr

May

Jun

Surface Chlorophyll

All Data

What about interannual

variability intiming of the

spring bloom?

Evidence of NE & SW Patches?

Jan

Feb

Mar

Apr

May

Jun

1998 1999

Chl a ug/L

Available SeaWiFS Images:

Monthly Composites

False Start in 1998

Earlier Start in 1999…

Delta t /m

EL9905 SB911 CTD Casts (n=89)

Station Depth (m)

Dep

th (

m)

Calm sunny days led to atypical structure (shallow thermocline) during part of the frontal study

front

Shelf regions were therefore defined by T ( ºC) from 5 m to bottom: <1 = crest; 1-2 = front; >2 = strat.

Mean No. m-3 x 104

Dep

th (

m)

Copepodites

Nauplii

Mixed (n= 3 profiles) Front (n=8) Stratified (n=17)

0 100 200 300 400 500

C. finmarchicus

Centropages

Metridia

Oithona

Pseudocalanus

Temora

0 200 400 600 800 1000 1200 1400

C. finmarchicus

Centropages/Temora

Oithona

Pseudocalanus/Metridia

0 100 200 300 400 500

C. finmarchicus

Centropages

Metridia

Oithona

Pseudocalanus

Temora

0 200 400 600 800 1000 1200 1400

C. finmarchicus

Centropages/Temora

Oithona

Pseudocalanus/Metridia

0 100 200 300 400 500

C. finmarchicus

Centropages

Metridia

Oithona

Pseudocalanus

Temora

0 200 400 600 800 1000 1200 1400

C. finmarchicus

Centropages/Temora

Oithona

Pseudocalanus/Metridia

-5 5 15 25

1

2

3

4

5

6

7

Copepodites

Nauplii

Mixed (n= 3 profiles) Front (n=8) Stratified (n=17)

n = 14,254 identifications, 249 samples, 29 profiles; variances available but not plotted

Taxonomic Composition

Size Category

Leng

th (

mm

)

Size Bins Used for Copepod Lengths

0 5 10 15 20 25

1

2

3

4

5

6

7

0 5 10 15 20 25

1

2

3

4

5

6

7

0 5 10 15 20 25

1

2

3

4

5

6

7

0 5 10 15 20 25

1

2

3

4

5

6

7

0 5 10 15 20 25

1

2

3

4

5

6

7

0 5 10 15 20 25

1

2

3

4

5

6

7

Mixed (n= 3 profiles) Front (n=8) Stratified (n=17)

Mean No. m-3 x 103 at 15 – 20 m depth

Mean No. m-3 x 103 at 25 – 30 m depth

Particle size spectrum and abundance at two depth intervals

-5 5 15 25

1

2

3

4

5

6

7

Copepodites

Nauplii

Mean No. m-3 x 104

Dep

th (

m)

Copepodites

Nauplii

Mixed (n= 3 profiles) Front (n=8) Stratified (n=17)

Crest

Front

Middle ShelfDep

th (

m)

Proportion

Larval cod from 1 m MOC, May 1999, Greg Lough

Size (mm) No. m-2