The Carbon Pump: higher carbon sink with global warming or not?
Predictions
Arctic will be a bigger carbon pump with climate warming
Causes
Sea ice melt --> more ice
Lower SST
--> higher CO2 solubility
--> higher photosynthetic rate
Arctic won't be a bigger carbon sink
Decrease in the CO2 uptake capacity in an ice-free arctic ocean basin (Cai et al. 2010)
Observations (Cai et al. 2010)
Assessment based on observations of (Cai et al. 2010)
Highly productive ocean margin
Ice covered basins before the major recent ice retreat
High CO2 concentration in sea surface across Canada-Basin > earlier observations
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Because
A lot of CO2 coming in
Low biological drawdown
Stops more CO2 from coming in (saturation / max partial pressure)
Premisses (Cai et al. 2010)
Ocean absorbs CO2 (30% since industrial revolution)
Ocean Acidification
More important in the Arctic
Arctic Ocean
Ratio (CO2 uptake) / Surface higher than average
Important continental shelves
Low temperature
Uncertainty because of few observations and climate changes
Survey in the Canada Basin (Western Arctic) in 2008
measure of pCO2
Substantial melt in this particular area
Salinity of 24 PSU < 26 PSU in 2008
pCO2 = 375 µatm < atmospheric values on average
lowest pCO2 (120-250 µatm) in marginal sea areas (less uptake)
ice free region of canada basin: 2008 pCO2 = 320-365 > 1998 pCO2 = 260 - 300 µatm > 1994 = < 260 µatm
Weissmann & Reigstad 2011
3 models of biogeochemical cycling and climate warming in the seasonal ice zone of the Arctic Ocean
Pelagic benthic coupling
Speculations
(a) Northern part of seasonal ice zone will expand to cover entire Arctic Ocean
(b) Southern part of seasonal ice zone will be exposed to more thermal stratification
(c) less variable 1ary production --> less average food concentration for pelagic heterotrophs
Possible changes in 1ary prod°
Increase in 1ary prd°
Decrease in 1ary prod°
Episodic nutrient availability (upwelling at shelf-breaks)
Increased light availability because of sea ice loss and reduced snow cover
Increase nutrient discharge from rivers (increased glaciers outflow)
Increased stratification
Increased denitrification on the shallow shelves of the pacific sector
More cloudy weather in the low-pressure belt --> less light
Increased turbidity in river discharge regions: glaciers melting, sediment displacements, permafrost melt, beach erosion --> less light
How will global warming change the timing in primary production in the ice-covered Arctic Ocean
Ice-algae bloom & phytoplankton (ice-free water) bloom
2 times of blooming
Ice-Algae: progressively as light increases
Phytoplankton: more suddenly as ice melts at the end of summer
Future: predictions = higher phytoplankton bloom as ice melts earlier and for a longer time
Future predictions = amount & time span of bloom decreases in the north and disappears in the south
Temporal Development in the
Seasonal Ice Zone and Pelagic-
Benthic Coupling in Times of
Global Warming: A Simple View
Now
Future
Ice gets thinner and breaks down quite rapidly at the end of spring --> brief and intense phytoplankton bloom
More 1ary prod° than heterotrophy --> depth at which nutrients are depleted increases --> net autotrophic carbon production
Ice-algae blooms end & heterotrophy takes over --> second contribution to carbon vertical migration
Ice algae & phytoplankton blooms start earlier & less suddenly (Kahru et al., 2011; Perrette et al., 2011)
Nutrients are consumed faster, and the period when heterotrophic processes dominate lasts longer.
Stratificat° caused by melting sea ice persists
Nutrient availability does not increase with the increase of PAR
Autotrophic carbon vertical export starts earlier & time span with more heterotrophic C production (regenerated prod°) lasts longer
Zooplankton will ascend earlier to reach food (Leu et al. 2011)
Food supply by ice algae less pulsed --> heterotroph feeding matches 1ary production --> less C vertically exported
Productive time window increase by 40%
heterotrophic pelagic organisms optimise their intake of ice & plankton alga --> less export to the benthos
Vertical export increase earlier in the season following low winter export
Longer productivity compensates for lower pulse heterotrophy --> annual sequestration of C may be the same, or more than today
If more heterotrophy --> less direct input of carbon from primary producers --> less food for benthic feeders (personal suggestion)
Collateral damage = ocean acidification
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Highest rate in Arctic ocean
High 1ary prod° in the Arctic
Low temperature = high CO2 solubility
Large ocean margins = upwelling
High ice melt areas
Low salinity
high SST--> 0-5°C