1

Melting glaciers help fuel productivity hotspots around Antarctica

Kevin R. ArrigoGert van Dijken

Stanford University

Areas of open water surrounded by sea ice

Can be identified with SSM/I satellite data

Based on days of open water Red = Max Blue = Min Polynyas are blue areas near coast

2

Antarctic polynyas

3

40 120 20016080

Hot spots of primary production (g C m-2 yr-1)

Antarctic polynyas

Hot spots of primary production (g C m-2 yr-1)

Can support high densities of marine mammals and birds

Ann

Annual production (mg C m-2 yr-1)

Mea

n co

lony

siz

e (1

000

pairs

)

Adelie Penguins vs. Polynya Productivity

R2 = 0.63

4

Arrigo and Van Dijken (2003)

Antarctic polynyas

Antarctic polynyas

Hot spots of primary production (g C m-2 yr-1)

Can support high densities of marine mammals and birds

Large sinks for anthropogenic CO2

Anthropogenic CO2 flux (g C m-2 yr-1)

5

Arrigo et al. (2008)

Ross Sea

Question:

What controls phytoplankton abundance in Antarctic coastal polynyas?

6

Photo:John Weller

Phaeocystis antarctica

Approach

7

SeaWiFS

AVHRR

SSM/IFor 1998-2012:Used satellite data to identify polynyas, track changes in sea ice, measure chlorophyll a concentration, and calculate primary production (Arrigo et al. 2008)

PacificOcean

IndianOcean

AtlanticOcean

ANTARCTICA

8

Polynya number

Chl

orop

hyll

a (m

g m

-3)

Pacific PacificIndianAtlantic

Annual mean phytoplankton abundance in 46 coastal polynyas

9

Polynya number

Pacific PacificIndianAtlantic

Annual mean phytoplankton abundance in 46 coastal polynyasNot controlled by light or temperature (p > 0.05)

10

Chl

orop

hyll

a (m

g m

-3)

Polynya number

Pacific PacificIndianAtlantic

She

lf w

idth

(km

)

Annual mean phytoplankton abundance in 46 coastal polynyasRelated to width of local continental shelf

11

Chl

orop

hyll

a (m

g m

-3)

Polynya number

Pacific PacificIndianAtlantic

She

lf w

idth

(km

)

Annual mean phytoplankton abundance in 46 coastal polynyasRelated to width of local continental shelf

R2 = 0.40p < 0.01

Chl

orop

hyll

a (m

g m

-3)

Shelf width (km)

12

Chl

orop

hyll

a (m

g m

-3)

Blue = Low iron concentrationOrange = High iron concentration visibleearth.nasa.gov 13

Why the relationship between phytoplankton abundance and continental shelf width?

• Highest seawater iron concentrations are on the shelf• Wider shelves have larger iron inventory and permit greater

entrainment of iron into surface waters (Bruland et al. 2005, Biller et al. 2013)

• More iron = higher phytoplankton biomass

Polynya number

Pacific PacificIndianAtlantic

14

What other factors control phytoplankton abundance in coastal polynyas?

Chl

orop

hyll

a (m

g m

-3)

Polynya number

Pacific PacificIndianAtlantic

15

What other factors control phytoplankton abundance in coastal polynyas?

• 37 of 46 coastal polynyas are adjacent to melting ice shelves

Chl

orop

hyll

a (m

g m

-3)

Polynya number

Pacific PacificIndianAtlantic

Bas

al m

elt

rate

(G

t yr

-1)

What other factors control phytoplankton abundance in coastal polynyas?

• 37 of 46 coastal polynyas are adjacent to melting ice shelves

• Basal melt rates are now available (Rignot et al. 2013)

16

Chl

orop

hyll

a (m

g m

-3)

Bas

al m

elt

rate

(G

t yr

-1)

Polynya number

Pacific PacificIndianAtlantic

R2 = 0.59p < 0.01

What other factors control phytoplankton abundance in coastal polynyas?

Chl

orop

hyll

a (m

g m

-3)

Basal melt rate (Gt yr-1)

17

Chl

orop

hyll

a (m

g m

-3)

Bas

al m

elt

rate

(G

t yr

-1)

Polynya number

Pacific PacificIndianAtlantic

Polynyas w/o ice shelf = 0.44±0.19 mg m-3

What about coastal polynyas not near ice shelves?

18

Chl

orop

hyll

a (m

g m

-3)

Bas

al m

elt

rate

(G

t yr

-1)

Polynya number

Pacific PacificIndianAtlantic

y-intercept = 0.40 mg m-3

Chl

orop

hyll

a (m

g m

-3)

Basal melt rate (Gt yr-1)

What about coastal polynyas not near ice shelves?

Polynyas w/o ice shelf = 0.44±0.19 mg m-3

19

Chl

orop

hyll

a (m

g m

-3)

Bas

al m

elt

rate

(G

t yr

-1)

Polynya number

Pacific PacificIndianAtlantic

y-intercept = 0.40 mg m-3

Chl

orop

hyll

a (m

g m

-3)

Basal melt rate (Gt yr-1)

What about coastal polynyas not near ice shelves?

Very productive polynyas require input of glacial meltwater

Polynyas w/o ice shelf = 0.44±0.19 mg m-3

20

Chl

orop

hyll

a (m

g m

-3)

Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves?

• Ice sheets grind up bedrock as they flow to sea• Particulate and dissolved iron is released into seawater• Facilitated by upwelling of warm CDW• Iron taken up by growing phytoplankton

(CDW)

Phytoplanktonbloom

21

Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves?

• Ice sheets grind up bedrock as they flow to sea• Particulate and dissolved iron is released into seawater• Facilitated by upwelling of warm CDW• Iron taken up by growing phytoplankton

22Modified from Gerringa et al. (2012)

0

100

200

300

De

pth

(m

)

Dissolved iron (nM)

0.8

0.6

0.4

0.2

0200250 150 100 50 0

Distance from Pine Island Glacier (km)

Chlorophyll > 5 mg m-3

Chlorophyll > 10 mg m-3

DynaLiFe Cruise

Even coastal Antarctic polynyas are iron limited

Together, basal melt rate and continental shelf width explain 70% of variance in phytoplankton abundance in coastal polynyas

Basal melt rate and shelf width are weakly correlated with each other (R2=0.19)

Antarctic polynyas are a 0.2 Pg C yr-1 sink for anthropogenic CO2

Larger than entire high latitude Southern Ocean

No interannual trends over 15 year time series

However, if the rate of ice sheet melting accelerates, polynyas could become even more productive in the future

23

CONCLUSIONS

24

THANK YOU!

Ocean Biology and Biogeochemistry

Cryosphere Science Program