Changes in Arctic Ocean Primary
Production from 1998-2008
Kevin R. Arrigo
G. L. van Dijken
Department of Environmental Earth System Science
Stanford University
Background
• Circulation influenced by both Atlantic and Pacific waters
• Atlantic (red):
Warm, salty, low
nutrient, deep
• Pacific (blue):
Cold, fresh, high
nutrient, shallow
• Cold halocline
layer restricts
influx of nutrients
from depth
Background
• Extensive continental
shelves (53% of area)
- Highly productive
• Large input of freshwater from rivers
• Relatively low surface
water nutrients
• High nutrients in deep
basins
Bathymetry (m)
Background
• Sea ice dynamics are important
Maximum ice extent
Minimum ice extent
Background
• Sea ice dynamics are important
• Decreasing trend in summer minimum ice cover
~20% drop
Background
Long term decline in sea ice attributed to:
• Increased advection of warm water into Arctic Ocean
(Steele and Boyd 1998, Dickson et al. 2000, Maslowski et al. 2001, Shimada et al. 2006)
• Atmospheric circulation favoring ice advection out of Arctic
(Rigor and Wallace 2005, Maslanik et al. 2007, Serreze et al. 2007)
• Increased Arctic temperatures due to greenhouse warming
(Rothrock and Zhang 2005, Lindsay and Zhang 2005)
• Above processes result in strong ice albedo feedback
(Perovich et al. 2007)
Given ongoing changes in
the Arctic Ocean…
How has primary production
changed in recent years?
Background
How primary production was calculated
• Algorithm modified
from Southern Ocean
(Arrigo et al. 2008,
Pabi et al. 2008)
• Based on remotely
sensed SST, Chl a,
and sea ice
• Forced with winds,
cloud cover, and solar
radiation
Background
How primary production was calculated
• Different Chl a algorithms and
sensors give different results
• Empirical OC3 and OC4v4
Chl a algorithms exhibit similar
interannual patterns
• Semi-analytical GSM algorithm,
which estimates Chl a, CDOM,
and backscattering, gives low
values
- Chl a not well validated
Background
How primary production was calculated
• Used “merged” Chl a product
from MODIS and SeaWiFS
• Validated primary productivity
algorithm using in situ Chl a
and primary production
Background
• How did primary production in the Arctic vary prior to 2007?
• 356-459 Tg C yr-1
from 1998-2006
(Pabi et al. 2008)
• Non-significant
increase in annual
primary production
• 1998 within 10% of
Sakshaug (2003):
329 Tg C yr-1
Pabi et al. (JGR, 2008)
Changes in Arctic Sea Ice Cover
Changes in Arctic Sea Ice Cover
Summer minimum sea ice cover dropped dramatically in
2007 and 2008
2007
2008
Changes in Arctic Sea Ice Cover
2006
2007
Difference (2006-2007)
• Large area of Arctic Ocean was exposed for first time
Approximately 1.3 x 106 km2 (area in red)
• New ice-free pelagic habitat
Arrigo et al. (GRL, 2008)
Changes in Arctic Productivity
How has Arctic primary production changed since 2006?
Annual
Primary
Production
2006
2007
2008
459 Tg C
544 Tg C
480 Tg C
• 2007 and 2008 are the most productive years on record
• Between 2006 and 2007, production increased by >15%
• Only 30% of this increase was due to
increased open water habitat in 2007
(Arrigo et al., GRL 2008)
Changes in Arctic Productivity
• 70% of 2007 increase in primary production related to longer
growing season
Changes in Arctic Productivity
Similar pattern in 2008, but not to same degree as in 2007
Changes in Arctic Productivity
QUESTION:
If interannual changes in
production are tied to
changes in sea ice cover,
why was annual primary
production in 2008 so
much less than in 2007?
• In 2008, the summer
minimum sea ice extent
was similar to that in 2007
• Shouldn’t annual
production be similar?
Changes in Arctic Productivity
• It turns out, summer minimum ice
cover is not a particularly good
predictor of annual primary
production
• Annual production is more highly
correlated with annual mean open
water area
• This metric is better because it
incorporates changes in length of
the open water season
Changes in Arctic Productivity
• Although the summer minimum ice
cover in 2007 and 2008 were
similar, the length of the open water
season was reduced in 2008
• Daily production was similar
between years
• More open water in 2007 all year
• As a result, annual production was
greater in 2007 than in 2008
Spatial Changes in Arctic Productivity
Annual production
Mean 2006-08
(Tg C yr-1)
23
36
41
48
63
26
Largest increase
In 2007-2008:
Beaufort, Chukchi,
East Siberian, Laptev
(25-75%)
127
136
Temporal Changes in Arctic Productivity
These 4 sectors
also exhibited
the largest
interannual
differences in
the timing of the
spring bloom
over the last 3
years
39 days
27 days
26 days
48 days
Temporal Changes in Arctic Productivity
Related to
changes in the
timing of
increase in open
water area
How will
organisms
respond to
changes in the
timing of the
spring bloom?
21 days
31 days
40 days
28 days
Changes in Arctic Productivity
• Annual primary production increased by 140 Tg C yr-1
between 1998 and 2008 (statistically significant trend)
• A 40% increase over the last decade
• Unexpected given
presumed nutrient
limitation
• Largest increases
on continental
shelf
Changes in Arctic Productivity
• If current trends in mean
annual open water area
continue, annual Arctic
primary productivity could
increase by 14 Tg C yr-1
each year
• Are continued increases in primary production sustainable?
• Would require additional nutrient input
Increased shelf-break upwellling? (Carmack and Chapman 2003)
Impacts of Changes in Arctic Productivity
• Increased flux of organic carbon
• Higher benthic-pelagic coupling?
• May depend on mechanism for
sea ice loss:
1) Atmospheric circulation
- Could reduce ice cover while
ocean was still cold
- Algae bloom in cold water
- Reduced grazing losses
2) Ocean warming
- Algae bloom in warm water
- Increased grazing losses
Impacts of Changes in Arctic Productivity
• Increased flux of organic carbon
Atlantic water
• More denitrification on Arctic
shelves?
Less nitrogen (more excess
phosphorus) entering N. Atlantic?
• Will nitrogen loss be compensated
for by greater N2-fixation in Atlantic?
• Is there enough Fe?
Yamamoto-Kawai et al. (2007)
Conclusions
Conclusions
• Changes in Arctic Ocean productivity related to changes in
sea ice cover
• Both the magnitude and timing of production are changing
• 40% increase in production over last decade represents a
weak negative feedback on atmospheric CO2 concentration
and greenhouse warming
• If further loss of sea ice is accompanied by processes that
increase upward flux of nutrients, Arctic productivity could
increase even more in the future
• Many ecological and biogeochemical ramifications