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Biological pump

Biological pump. Low latitude versus high latitudes. Low-latitude ecosystem. Productivity limited by nutrient supply to the mixed layer. Mixed layer. Mixed layer nutrient and Chl -a. C hlorophyll is maximum at about 100m near Hawaii What causes this deep chlorophyll maximum?.

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Biological pump

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  1. Biological pump • Low latitude versus high latitudes

  2. Low-latitude ecosystem • Productivity limited by nutrient supply to the mixed layer Mixed layer

  3. Mixed layer nutrient and Chl-a • Chlorophyll is maximum at about 100m near Hawaii • What causes this deep chlorophyll maximum?

  4. High latitude ecosystem • Stronger seasonality in solar radiation, nutrients and productivity

  5. Seasonal cycle of mixed layer depth • Shallow mixed layer = More light Y. Takano

  6. 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

  7. Surface nutrient vs chlorophyll Chlorophyll-a Nitrate Sarmiento and Gruber (2006)

  8. NO3-Chl relationship • HNLC (High-Nutrient Low-Chlorophyll) • Southern Ocean • Equatorial Pacific • Subarctic North Pacific

  9. 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

  10. 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

  11. Atmospheric dust deposition in present climate

  12. 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

  13. Satellite Images from

  14. 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

  15. 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?

  16. Polar ice core data Petit et al., (1999)

  17. Glacial-interglacial CO2 problem Antarctic ice core Luthi et al., (2008)

  18. Last glacial cycle

  19. Since the last glacial maximum

  20. 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

  21. 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)

  22. 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

  23. 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)

  24. Dust deposition over the Southern Ocean during LGM Petit et al., (1999)

  25. 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

  26. 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!

  27. 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…

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