Melting glaciers help fuel productivity
hotspots around Antarctica
Kevin R. Arrigo
Gert van Dijken
Stanford University
1
Antarctic polynyas
Areas of open water
surrounded by sea ice
Can be identified with
SSM/I satellite data
Based on days of
open water
Blue = Max
Red = Min
Polynyas are blue
areas near coast
2
Antarctic polynyas
40
80
120
160
200
Hot spots of primary
production (g C m-2 yr-1)
3
Antarctic polynyas
Can support high
densities of marine
mammals and birds
Adelie Penguins vs. Polynya Productivity
Mean colony size (1000 pairs)
Hot spots of primary
production (g C m-2 yr-1)
Ann
R2 = 0.63
Annual production (mg C m-2 yr-1)
Arrigo and Van Dijken (2003)
4
Antarctic polynyas
Can support high
densities of marine
mammals and birds
Seal Pups vs. Polynya Productivity
Weddell seal pups weaned
Hot spots of primary
production (g C m-2 yr-1)
Ann
R2 = 0.63
Annual production (mg C m-2 yr-1)
Arrigo and Rotella (submitted)
5
-10
-20
Antarctic polynyas
80
-30
40
-40
-50
0
Hot spots of primary
production (g C m-2 yr-1)
O2 (fraction of annual net primary production)
1.0
0.9
-2 yr-1)
Anthropogenic
CO
flux
(g
C
m
-2
-1
2
Anthropogenic FCO (g C m yr )
2
0
f
-10
0.8
-20
0.7
Can support high
densities of marine
mammals and birds
0.6
-30
0.5
-40
0.4
0.3
-50
Ross Sea
0.2
Large sinks for
170°E
180°
170°W
anthropogenic
CO160°W
2
-60
0.1
0
160°E
170°E
180°
170°W
160°W
-70
Arrigo et al. (2008)
Figure 1
6
Question:
What controls phytoplankton abundance in Antarctic
coastal polynyas?
Phaeocystis antarctica
Photo:
John Weller
7
Approach
SeaWiFS
For 1998-2012:
Used satellite data to identify
polynyas, track changes in
sea ice, measure chlorophyll
a concentration, and calculate
primary production (Arrigo et
AVHRR
al. 2008)
SSM/I
8
Atlantic
Ocean
17 18
1516
14
13
12
11
9
19 20
21
22
23
24
25
26
27
28
10
8
7
6
29
ANTARCTICA
30
5
4
3
Pacific
Ocean
2
1
45
46
44
43
42
41
40
31
32
33
34
35
36
37
38
39
Indian
Ocean
9
Annual mean phytoplankton abundance in 46 coastal polynyas
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
2.0
1.5
1.0
0.5
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
10
Annual mean phytoplankton abundance in 46 coastal polynyas
Not controlled by light or temperature (p > 0.05)
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
2.0
1.5
1.0
0.5
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
11
Annual mean phytoplankton abundance in 46 coastal polynyas
Related to width of local continental shelf
Pacific
Atlantic
Indian
Pacific
700
600
2.0
500
1.5
400
300
1.0
200
0.5
Shelf width (km)
Chlorophyll a (mg m-3)
2.5
100
0.0
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
12
2.0
Atlantic
2.5
R2 = 0.40
p < 0.01
2.0
1.5
Indian
1.0
700
0.5
600
0.0
500
0
1.5
Pacific
200
400
600
Shelf width (km)
400
300
1.0
200
0.5
Shelf width (km)
Chlorophyll a (mg m-3)
2.5
Pacific
Chlorophyll a (mg m-3)
Annual mean phytoplankton abundance in 46 coastal polynyas
Related to width of local continental shelf
100
0.0
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
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
Blue = Low iron concentration
Orange = High iron concentration
visibleearth.nasa.gov 14
What other factors control phytoplankton abundance in coastal
polynyas?
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
2.0
1.5
1.0
0.5
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
15
What other factors control phytoplankton abundance in coastal
polynyas?
• 39 of 46 coastal polynyas are adjacent to melting ice shelves
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
2.0
1.5
1.0
0.5
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
16
What other factors control phytoplankton abundance in coastal
polynyas?
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
180
160
140
2.0
120
1.5
100
80
1.0
60
40
20
0.5
0
Basal melt rate (Gt yr-1)
• 39 of 46 coastal polynyas are adjacent to melting ice shelves
• Basal melt rates are now available (Rignot et al. 2013)
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
17
2.0
1.5
Atlantic
2.5
R2 = 0.59
p < 0.01
2.0
1.5
Indian
Pacific
1.0
180
160
0.5
140
0.0
120
0
50
100
150
200
Basal melt rate (Gt yr-1)
100
80
1.0
60
40
20
0.5
0
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
2.5
Pacific
Chlorophyll a (mg m-3)
What other factors control phytoplankton abundance in coastal
polynyas?
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
18
Chlorophyll a (mg m-3)
2.5
Pacific
Atlantic
Indian
Pacific
180
160
140
2.0
120
1.5
1.0
100
Polynyas w/o ice shelf = 0.40±0.13 mg m-3
80
60
40
20
0.5
0
Basal melt rate (Gt yr-1)
What about coastal polynyas not near ice shelves?
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
19
2.0
Atlantic
y-intercept = 0.40 mg m-3
2.0
1.5
Indian
Polynyas w/o ice shelf =
Pacific
1.0
180
160
0.5
140
0.0
120
0
1.5
1.0
2.5
50
100
150
200
Basal melt rate (Gt yr-1)
0.40±0.13 mg m-3
100
80
60
40
20
0.5
0
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
2.5
Pacific
Chlorophyll a (mg m-3)
What about coastal polynyas not near ice shelves?
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
20
What about coastal polynyas not near ice shelves?
2.0
Atlantic
y-intercept = 0.40 mg m-3
2.0
1.5
Indian
Polynyas w/o ice shelf =
Pacific
1.0
180
160
0.5
140
0.0
120
0
1.5
1.0
2.5
50
100
150
200
Basal melt rate (Gt yr-1)
0.40±0.13 mg m-3
100
80
60
40
20
0.5
0
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
2.5
Pacific
Chlorophyll a (mg m-3)
Very productive polynyas receive input of glacial meltwater
0.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45
Polynya number
21
Why the relationship between phytoplankton abundance and
basal melt rate of nearby ice shelves?
• Particulate and dissolved iron is released into seawater
From ground up bedrock and Fe accumulated in ice
• Facilitated by upwelling of warm CDW
Phytoplankton
bloom
(CDW)
22
Why the relationship between phytoplankton abundance and
basal melt rate of nearby ice shelves?
• Particulate and dissolved iron is released into seawater
From ground up bedrock and Fe accumulated in ice
• Facilitated by upwelling of warm CDW
• Iron taken up by growing phytoplankton
DynaLiFe Cruise
Depth (m)
0
Dissolved iron (nM)
Chlorophyll > 10 mg m-3
0.8
Chlorophyll > 5 mg m-3
100
0.6
0.4
200
0.2
300
0
250
200
150
100
50
0
Distance from Pine Island Glacier (km)
Modified from Gerringa et al. (2012)
23
CONCLUSIONS
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
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THANK YOU!
Ocean Biology and
Biogeochemistry
Cryosphere Science
Program
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