Biological pump
description
Transcript of Biological pump
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Biological pump• Low latitude versus high latitudes
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Low-latitude ecosystem• Productivity limited by nutrient
supply to the mixed layer
Mixed layer
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Mixed layer nutrient and Chl-a
• Chlorophyll is maximum at about 100m near Hawaii
• What causes this deep chlorophyll maximum?
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High latitude ecosystem• Stronger seasonality in solar radiation,
nutrients and productivity
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Seasonal cycle of mixed layer depth
Y. Takano
• Shallow mixed layer = More light
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Low vs high latitude ecosystem• Low-latitude, low-nutrient
condition• Small cell size• Efficient recycling of nutrient
• High-latitude, high-nutrient condition
• Large cell size• Efficient export of nutrient
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Surface nutrient vs chlorophyll
Chlorophyll-a
Nitrate
Sarmiento and Gruber (2006)
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NO3-Chl relationship
• HNLC (High-Nutrient Low-Chlorophyll)
• Southern Ocean• Equatorial Pacific• Subarctic North Pacific
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HNLC region and iron limitation• Southern Ocean nutrient problem
– Siegenthaler and Wenk (1984); Sarmiento and Toggweiler (1984); Knox and McEloy (1984)
– Utilization of excess nutrient in the Southern Ocean
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The iron hypothesis
• Phytoplankton needs trace amount of iron as a micro-nutrient
• Due to the remoteness of the Southern Ocean from the continents, phytoplankton growth is limited by the availability of iron (Martin, 1990)
• Macro-nutrient such as NO3 are not fully utilized in the Southern Ocean
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Atmospheric dust deposition in present climate
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Southern Ocean Iron Release Experiment (Boyd et al., 2000)
• Monitor two similar “patches” of surface waters in the Southern Ocean
• One patch is seeded with high-level of iron• The other patch is not seeded• Measure photosynthesis after the iron
addition and compare the two patches
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Satellite Images from
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Results from SOIREE
• Photosynthesis responded to the artificial addition of iron– Increased chlorophyll and primary production
• The seeded patch is mixed with the environment after a few weeks– Long-term effect is difficult to determine
• Carbon export to the deep ocean was not confirmed
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Implications
• Can we increase ocean CO2 uptake by adding iron to the Southern Ocean?
• Is there any geologic evidence for the past climate changes involving iron supply to the oceans?
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Polar ice core data
Petit et al., (1999)
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Glacial-interglacial CO2 problem
Antarctic ice coreLuthi et al., (2008)
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Last glacial cycle
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Since the last glacial maximum
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Timescale
• 100 ppmv– Fossil fuel CO2 in the present atmosphere– De-glacial increase in the atmospheric CO2
• Current rate of increase in atmospheric CO2 is about 100 times faster than that during the “abrupt” end of last glacial period.
• Industrial carbon emission: decades• De-glaciation CO2 increase: 5,000 years
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Theme II: Climate-Carbon relation
• The carbon cycle interacts with climate in fundamentally different ways between the two timescales
• Modern Ocean: the carbon cycle mediates climate warming (stabilizing feedback)
• Glacial Ocean: the carbon cycle enhanced climate cooling (de-stabilizing feedback)
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Last Glacial Maximum
• Cold and dry climate• Increased albedo due to the land ice sheets– Some land vegetation was replaced by ice
• Global mean temperature was about 5°C cooler
• Sea level was lower by about 120m– Salinity was higher
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Attribution of CO2 change
• Relatively well known effects– Land forest loss due to ice sheet– Solubility change due to temperature and salinity
Sigman and Boyle (2000)
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Dust deposition over the Southern Ocean during LGM
Petit et al., (1999)
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A simple theory• Theory predicts a strong
relationship between polar surface nutrient and atmospheric CO2
• About 50% consumption of current polar surface nutrient will lower atmospheric CO2 by 100 ppmv
Sarmiento and Toggweiler 1984
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Can the iron hypothesis be the solution for the glacial CO2 problem?
• Scientists included iron cycling into the ocean climate-carbon models and simulated LGM condition– Bopp et al., (2003), 15 ppmv decrease– Parekh et al., (2006), 8 ppmv decrease
• Model prediction is much smaller than the observed 100 ppmv change!
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Circulation and biology
• Dust deposition itself is unlikely the sole mechanism for glacial CO2 decrease
• Other mechanisms?– Circulation of the Southern Ocean– Sea ice and its impact on gas exchange in the Southern
Ocean– Silica and CaCO3 marine snow (silica leakage hypothesis)– More…