Phytoplankton and nutrient dynamics in a vortex off Western AustraliaPaterson, H. L.1, Waite, A. M.1,   Thompson, P. 2

1 The University of Western Australia, 2 CSIRO Marine Research

Introduction• Understand the role of meso-

scale eddies in transporting material offshore and modifying productivity.

• In May 2007 we investigated an eddy during its formation.

– Physical and chemical properties of the eddy

– Picoplankton distribution (Flow-cytometry, SYBR Green 1)

• Offshore, >90% of the phytoplankton in the <5µm fraction (Koslow et al. 2007)

Picture

113.4 Transect May 20 2006

MODIS SST MODIS chlorophyll image

Salinity and Temperature 113.4

35.2

35.3

35.4

35.5

35.6

35.7

35.8

35.9

31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8

300

250

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100

50

0

300

250

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50

0

22

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16

Dep

th (m

)

Latitude (S)

S alin

i ty

(PSU

)Te

mpe

ratu

re ̊C

Salinity maximum Central Indian Ocean Water

North side High current speed Leeuwin Current (Low salinity Warm)

South side Dissociation between high current speed and Leeuwin Current????

Dilution of the Leeuwin Current?

Centre Gradient across body of eddy

Isohaline Contour Line Salinity = 35.65

Water-mass - T/S?

Salinity (PSU)

35.2 35.4 35.6 35.8 36.0

Tem

pera

ture

o C

12

14

16

18

20

22

24

0-0.390.4-0.790.8-1.191.2 - 5.31.2 - 5.3 warm

Nitrate ML-1

Salinity maximum – Central Indian Ocean water

T/S plot does not clearly separatewater-masses

15

16

17

18

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23

24

35.2 35.3 35.4 35.5 35.6 35.7 35.8 35.9 36

Salinity

Tem

per

atu

re º

C

Centre

Leeuw in Current

Shelf Lancelin

ShelfTw o Rocks

Shelf north of Tw o Rocks

shelf Mandurah

Potential eddy water

T/S plot. Data 0 – 150 m four casts per region

112.5 113 113.5 114 114.5 115 115.5 116

-33.5

-33

-32.5

-32

-31.5

-31

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Longitude

Latit

ude

Nitr

ate

µM L

-1

112.5 113 113.5 114 114.5 115 115.5 116

-33.5

-33

-32.5

-32

-31.5

-31

1.5

2

2.5

3

3.5

4

4.5

Longitude

Latit

ude

Silic

ate

µM L

-1

Silicate M L-1

0 1 2 3 4 5

Nitr

ate

M L

-1

0

1

2

3

4

5200 - 100 m200 - 100 m 100 - 60 m 60 - 30 m 30 - 0 m

1:1

line

Longitude

112 113 114 115 116

Latit

ude

(S)

-34

-33

-32

-31 Nitrate richSilicate rich

Surface silicate

Surface nitrate

32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6

300

250

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50

1.2

2

2.8

3.6

4.4

31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8

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Latitude (S)

Dep

th (m

)

Nitr

ate

µmL-

1Si

licat

e µm

L

Isohaline Contour Line Salinity = 35.65

Silicate and nitrate 113.4

Eddies 2003

Anya’s chapter from the text book

Warm Core Eddy: Anomalous Large Diatom Population

Key Features:1. Atypical of open ocean2. V. Deep mixed layer (275 m)3. Low-light, low nutrient

Calculations estimate that >1 μM L-1 of nitrate was required during eddy formation to establish diatom population

>20 m fraction on GF/F

Synechococcus sp. Prochlorococcus sp.

112.5 113 113.5 114 114.5 115 115.5 116

-33.5

-33

-32.5

-32

-31.5

-31

0.0E+000

1.0E+012

2.0E+012

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6.0E+012

7.0E+012

8.0E+012

9.0E+012

1.0E+013

1.1E+013

1.2E+013

1.3E+013

1.4E+013

1.5E+013

1.6E+013

1.7E+013

1.8E+013

1.9E+013

2.0E+013

Latit

ude

(S)

Longitude (E)

Cells

m2

Synechococcus sp. Prochlorococcus sp.

112.5 113 113.5 114 114.5 115 115.5 116

-33.5

-33

-32.5

-32

-31.5

-31

0.0

1.0×1013

2.0×1013

3.0×1013

4.0×1013

L atit

ude

(S)

Longitude(E)

Cells

m

Synechococcus sp. Prochlorococcus sp.

1.0×1013

2.0×1013

3.0×1013

4.0×1013

5.0×1013

5.0×10

1 2

2.0×10

13

1.5×1 0

13

1 .0×10

1 3

0

0

Prochlorococcus sp

.

Synechococcus

112.5 113 113.5 114 114.5 115 115.5 116

-33.5

-33

-32.5

-32

-31.5

-31

Prochlorococcus sp. dominated

Synechococcus sp. dominated

Latit

ude

(S)

Longitud

Y=1.22X+2.0*1012

Transect 113.4S

ynec

hoco

ccus

sp.

Pro

chlo

roco

ccus

sp.

31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6

140

120

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80

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20

0

0

5 0 0 0

1 0 0 0 0

1 5 0 0 0

2 0 0 0 0

2 5 0 0 0

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3 5 0 0 0

31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8

0

0

1 0 0 0 0

2 0 0 0 0

3 0 0 0 0

4 0 0 0 0

5 0 0 0 0

6 0 0 0 0

7 0 0 0 0

Dep

th (m

)

Latitude (S)

140

120

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80

60

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20

Cells

mL-

1Ce

lls m

L

Prochloroccocus sp.

y = -7541.5Ln(x) + 6098.1

R2 = 0.6797

0

10000

20000

30000

40000

50000

60000

70000

0 0.5 1 1.5 2 2.5

Nitrate µM L-1

Pro

chlo

roco

ccu

s C

ells

mL-1 0.4 µM L-1

Transect 113.4

31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8

140

120

100

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60

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20

0

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

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3 5 0 0

4 0 0 0

Dep

th (m

)

Latitude (S)

Cells

mL-1

31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8

140

120

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80

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0

2 0 0 0 0

6 0 0 0 0

1 0 0 0 0 0

1 4 0 0 0 0

1 8 0 0 0 0

2 2 0 0 0 0

2 6 0 0 0 0

3 0 0 0 0 0

3 4 0 0 0 0

3 8 0 0 0 0

4 2 0 0 0 0

Cells

mL-1

Latitude (S)

Dep

th (m

)

Pic

o-eu

kary

otes

Het

erot

roph

ic B

acte

ria

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31.6 31.8 32 32.2 32.4 32.6 32.8 33 33.2 33.4 33.6 33.8300

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0

Chlo

r oph

yll a

µg

L-1

Latitude (S)

Dep

th (m

)Transect 113.4Fluorescence

Eddy formation, propagation and detachmentSST Blue Link Images (CSIRO)

Conceptual model of warm-core eddy

Cell cycle

• Growth of phytoplankton using cell cycle analysis

• Can be done using flow cytometry

Flow data

Gaussian 4 parameter curve

Synechococcus P<0.0001R2 = 0.59

Prochlorococcus P<0.0001R2 = 0.40

Conclusion or questions and acknowledgments

• Eddy water shelf origin.• Eddy - shelf water modified by Leeuwin Current

entrainment.– Modification of Leeuwin Current as it circles the eddy. Nitrate

and silicate concentrated by different mechanisms?

• Leeuwin Current is a source of Prochlorococcus sp.• Abundance of Prochlorococcus sp. related to nitrate

availability.• Synechococcus sp. Shelf/coastal origin.• Asymmetry of the eddy – Salinity, Nitrate,

Prochlorococcus sp.• Leeuwin Current modification enhances productivity?• Is the salinity maximum a physical barrier, what is its

contribution to the biology of the eddy?

Acknowledgments

• Waite et al., ARC discovery grant 2006 - 2008• Waite, Thompson and Twomey, SRFME

Collaborative Grant• Waite, Thompson and Beckley, Marine National

Facility Ship Time• Southern Surveyor MNF staff and crew• Ming Feng, CSIRO• Adele Pile• Kathy Heel-Miller and the Biomedical Imagine

Centre (UWA)