Developing NPP algorithms for the Arctic

1. Empirical chlorophyll based algorithm

Chlorophyll (mg m-3)

0.001 0.01 0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.01

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

Chukchi Sea

ANCOVA H0 – means between light levels are equal

SourceSum-of-

Squaresdf Mean-Square F-ratio P

LIGHT_CH 170.6 5 34.1 15.1 0.000

DAILY_PP_CH 3052.7 1 3052.7 1354.8 0.000

Error 1428.6 634 2.3

1% 5% 15% 30% 50% 100%

1% 1.000

5% 0.000 1.000

15% 0.000 0.912 1.000

30% 0.000 0.921 1.000 1.000

50% 0.000 0.780 1.000 0.999 1.000

100% 0.000 0.931 1.000 1.0000 0.99 1.000

P < 0.00 , H0 is rejected

1% 5% 15% 30% 50% 100%

1% 1.000

5% 0.000 1.000

15% 0.000 0.912 1.000

30% 0.000 0.921 1.000 1.000

50% 0.000 0.780 1.000 0.999 1.000

100% 0.000 0.931 1.000 1.0000 0.99 1.000

1. Empirical chlorophyll based algorithm

Chlorophyll (mg m-3)

0.001 0.01 0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.01

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

Chlorophyll (mg m-3)

0.001 0.01 0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.01

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

Chukchi Sea

1. Empirical chlorophyll based algorithm

Resolute Bay

Chlorophyll (mg m-3)

0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

ANCOVA H0 – means between light levels are equal

Source Sum-of-Squares df Mean-Square F-ratio P

LIGHT_CH 1027.1 5 205.4 11.7 0.000

DAILY_PP_CH 8696.4 1 8696.4 495.6 0.000

Error 2913.1 166 17.5

P < 0.00 , H0 is rejected

1% 5% 15% 30% 50% 100%

1% 1.000

5% 0.000 1.000

15% 0.000 0.581 1.000

30% 0.000 0.322 0.998 1.000

50% 0.000 0.205 0.988 0.999 1.000

100% 0.000 0.502 1.000 1.0000 0.995 1.000

1. Empirical chlorophyll based algorithm

Chlorophyll (mg m-3)

0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

Resolute Bay

Chlorophyll (mg m-3)

0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

0.1

1

10

100

1000

10000

100% 50% 30% 15% 5% 1%

1. Empirical chlorophyll based algorithm

Barents Sea

Chlorophyll (mg m-3)

0.1 1 10 100

Dai

ly P

P (

mg

C m

-3 d

ay-1

)

1

10

100

1000

1. Empirical chlorophyll based algorithm

Log Chlorophyll (mg m-3)

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Lo

g D

aily

PP

(m

g C

m-3

da

y-1)

-2

-1

0

1

2

3

4

Resolute BayChukchi BayBarents

Combined dataset

ANCOVA H0 – means between regions are equal

Source Sum-of-Squares df Mean-Square F-ratio P

LIGHT_CH 2.28 2 1.14 18.55 0.000

DAILY_PP_CH 136.48 1 136.48 2220.18 0.000

Error 33.93 552 0.061

P < 0.00 , H0 is rejected

Resolute Bay

Chukchi Sea Barents Sea

Resolute Bay 1.000

Chukchi Sea 0.000 1.000

Barents Sea 0.361 0.000 1.000

Log Chlorophyll (mg m-3)

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Lo

g D

aily

PP

(m

g C

m-3

day

-1)

-2

-1

0

1

2

3

4

Resolute BayChukchi BayBarents

1. Empirical chlorophyll based algorithm

Combined dataset

ANCOVA

•Chl 0.8 – 32 mg m-3

•P < 0.01

Average Chlorophyll•Resolute Bay 8.1 mg m-3

•Barents Sea 4.2 mg m-3

•Chukchi Sea 1.2 mg m-3

Log PP = 1.36 + 1.0.Log Chl

1.1 Surface chlorophyll vs. Euphotic zone chlorophyll

Chlorophyll (mg m-3)

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Dep

th (

m)

0

20

40

60

80

100

Primary production P (mg C m-3 h-1)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Spring

2 4 6 8 10 120

20

40

60

80

1000.5 1.0 1.5 2.0

ChlorophyllProductivity

Summer

1.1 Surface chlorophyll vs. Euphotic zone PP

Surface Chlorophyll (mg m-3)

0.01 0.1 1 10 100

Eu

ph

oti

c zo

ne

intr

egra

ted

p

rim

ary

pro

du

ctiv

ity

(mg

C m

-2 d

-1)

1

10

100

1000

10000

Chukchi Sea Spring 2002 & 2004

Chukchi Sea Summer 2002 & 2004Resolute Bay

Chukchi Spring r2=0.51

Chukchi Summer r2=0.01

Resolute Bay r2=0.63

1.1 Rrs vs. Euphotic zone PP

Rrs 444>490>510/555

1 10

Wat

er c

olu

mn

in

teg

rate

d

pro

du

ctiv

ity

(mg

C m

-2)

0.01

0.1

1

10

100

SpringSummer

2. Model based on C:Chl ratios

Behrenfeld et al. (2005) developed a productivity model based on Chl:C ratios and chlorophyll concentrations derived from ocean color satellite observations.

1. Carbon (POC) is retrieved from backscatter2. Chlorophyll is retrieved from Rrs ratios (i.e OC4V4, OC3M or OC3Arc)

These are coupled with mixed layer light levels from surface PAR and K490 observations and growth rates estimated from the literature. The final equation is:

NPP = C . µ . Zeu . h(Io)

Where C is carbon, µ is growth rate, Zeu is the euphotic depth and h(Io) describes how changes in surface light influence the depth dependent profile of carbon fixation

2. Model based on C:Chl ratios

Chlorophyll vs Rrs n = 791

y = -3.229x + 0.4986

R2 = 0.7958

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Log Rrs (443>490>510/555)

Log

Chl

orop

hyll

(mg/

m3)

Lab00Lab97Lab96Res98Res96Res95Res94Goa97Ber96Ber95Arc00Arc02-1Arc02-2OC4v4Arc04-1Arc04-2allGreenland SeaLinear (all)

2. Model based on C:Chl ratios

Model Input

1. Carbon (POC) is retrieved from backscatter – Behrenfeld global relationship2. Chlorophyll is retrieved from Rrs ratios - OC3Arc3. Surface PAR – estimated from observations4. Mixed layer light levels – estimated from observations5. Growth rate – literature global, 0.5 – 2 divisions d-16. h(Io) taken from Behrenfeld and Falkowski (1997)

NPP = C . µ . Zeu . h(Io)

Model output

1. NPP euphotic zone integrated - g C m-2 day-1

2.1 Results

Measured euphotic zone daily productivity (g C m-2 d-1)

0.001 0.01 0.1 1 10

Mo

del

led

eu

ph

oti

c zo

ne

dai

ly

pro

du

ctiv

ity

(g C

m-2

d-1

)

0.001

0.01

0.1

1

10

Chukchi Sea SpringChukchi Sea Summer

Spring r2 =0.32Slope = 2.6P > 0.05

Summer r2 =0.00Slope = 0.02P > 0.1

Measured euphotic zone daily productivity (g C m-2 d-1)

0.001 0.01 0.1 1 10

Mo

del

led

eu

ph

oti

c zo

ne

dai

ly

pro

du

ctiv

ity

(g C

m-2

d-1

)

0.001

0.01

0.1

1

10

Chukchi Sea SpringChukchi Sea Summer

Spring r2 =0.32Slope = 2.6P > 0.05

Summer r2 =0.00Slope = 0.02P > 0.1

2.1 Results – adjusted model

Measured 1st optical depth daily productivity (g C m-2 d-1)

0.0001 0.001 0.01 0.1 1 10

Mo

de

lle

d 1

st o

pti

cal

de

pth

da

ily

pro

du

cti

vity

(g

C m

-2 d

-1)

0.0001

0.001

0.01

0.1

1

10Chukchi Sea SpringChukchi Sea Summer

Summer r2 =0.60Slope = 1.28P < 0.01

Spring r2 =0.81Slope = 0.82P < 0.01

Euphotic zone integrated 1st optical depth

Data Slope r2 P Slope r2 P

Chukchi Spring 0.36 0.61 < 0.01 0.82 0.81 < 0.01

Chukchi Summer 0.18 0.00 > 0.10 1.28 0.60 < 0.01

2.2 Sensitivity to model input

Measured euphotic zone daily

productivity (g C m-2 d-1)

0.01 0.1 1 10

Mo

del

led

eu

ph

oti

c zo

ne

dai

ly

pro

du

ctiv

ity

(g C

m-2

d-1

)

0.01

0.1

1

10

Mean Ig_0.8 Mean - 1stdev Ig_0.26 Mean + 1 stdev Ig_1.34

Sensitivity to changes in mixed layer light levels

2.2 Sensitivity to model input

Mixed layer light levels Surface PAR Growth rates

r2 Slope RMS r2 Slope r2 slope

Mean 0.75 0.36 0.76 0.75 0.36 0.75 0.49

- 1 stdev 0.75 0.22 0.69 0.75 0.29 0.75 0.33

+ 1 stdev 0.75 0.57 0.88 0.75 0.64 0.75 0.65

3.0 Comparison of both methods

Measured Surface NPP (g C m-3 d-1)

0.0001 0.001 0.01 0.1 1

Pre

dic

ted

Su

rfac

e N

PP

(g

C m

-3 d

-1)

Pre

dic

ted

1st

op

tica

l d

epth

NP

P (

g C

m-2

d-1

)

0.0001

0.001

0.01

0.1

1

Summer 2000 Summer 2000Summer 2004 Summer 2004

Chl based Behrenfeld Model

Measured 1st optical depth NPP (g C m-2 d-1)

Chl basedr20.76slope 0.6

Chl basedr20.46slope 0.62

Surface Chlorophyll - Spring

Surface Chlorophyll - Summer

Surface chlorophyll - Fall

Surface chlorophyll – Winter

Surface PP - Spring

Surface PP - Summer

Surface PP - Fall

Surface PP - Winter

Kd PAR – Spring + Summer