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Impact of Freshwater Release in the North Atlantic

This study explores the impact of freshwater release in the North Atlantic under different climate conditions using an OAGCM. The findings provide insights into abrupt climate changes, monsoon changes, and ITCZ migration. The study also examines the climatic responses and mechanisms under various climate scenarios.

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Impact of Freshwater Release in the North Atlantic

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  1. Impact of freshwater release in the North Atlantic under different climate conditions in an OAGCM Didier Swingedouw, Masa Kageyama, Juliette Mignot, Pascale Braconnot, Eloi Mosquet, Charline Marzin, Ramdane Alkama, Olivier Marti LSCE-IPSL, France

  2. Abrupt climate changes during glacial period Cooling and iceberg surge • Origin? • Mechanisms for the teleconnections ? Monsoon changes (Wang et al. 2001) ITCZ migration(Peterson et al. 2000) Courstesy of M. Kageyama

  3. No Greenl. CTRL With Greenl. What about warm climates? • Reduction of the Greenland ice sheet during the Eemian • Potential collapse in the future AMOC • What are the freshwater inputs under different climate conditions? • Are the climatic responses and mechanisms similar under different climate conditions? Swingedouw et al. Clim. Dyn. 2007

  4. Experimental design Insolation at the top of the atmosphere PRE, FUT HOL-PRE 10 simulations using the IPSL-CM4 AOGCM of 250 years, with and without (computed) freshwater input • Last Interglacial (126 kyr BP, LIG) • Last Glacial Maximum (21 kyr BP LGM) • Holocene (6 kyr BP, HOL) • Preindustriel (PRE) : 0.1 Sv hosing following Stouffer et al. 2006) • Future (2xCO2, FUT) LGM-PRE LIG-PRE -126 kyr -21 kyr -6 kyr 2250 1860 FUT LGM HOL PRE LIG

  5. Atlantic Meridional Overturning Circulation (year 220-250) LIGc LIGh Freshwater input and AMOC response LGMc LGMh Freshwater is computed according to the heat flux budget over land-ice area in the model (except for PRE and LGM) HOLc HOLh Greenland melting after 250 years PREc PREh FUTc FUTh

  6. Climatic impact of « hosing » Temperature (year 220-250, hosing-CTRL) Precipitation LIG LGM LIG LGM HOL PRE HOL PRE FUT FUT

  7. SLP (year 220-250, hosing-CTRL) LIG LGM Sea level pressure response • Change in the mean state • Resembling the Aleutian Low-Icelandic Low seesaw (Honda et al. 2001) • Adjustment of the storm track to different temperature gradients HOL PRE FUT En TW

  8. Sea-ice cover and wind stress changes (year 220-250, hosing-CTRL) LIG LGM Explanation for the « slight warming » pattern • Changes in surface winds associated with large-scale SLP changes • Interaction with sea ice cover • Albedo feedback leads to the observed « slight warming » HOL PRE FUT En TW

  9. A complex energetic adjustment Net SW LW TOA AHT Atmosphere Atmosphere Land Sea ice OHT Ocean 25°N 90°N

  10. A complex energetic adjustment Net=+13 LW=+185 SW=-172 • Common mechanisms: • Oceanic heat transport decreases due to AMOC weakening • Partial compensation by the atmosphere • Differences: • AMOC changes • Radiative adjustment and changes in reservoirs (sea ice) TOA AHT=+99 Atmosphere Atm=-2 Glace=-91 OHT=-232 Oce=-17 25°N 90°N Hosing preind. (en TW)

  11. ITCZ migration amplitude Zonal precipitation changes over the Atlantic(year 220-250, hosing-CTRL) • The amplitude of the ITCZ shift depends on the experiment • What drives these changes? LIG LGM FUT HOL PRE

  12. SST and wind stress changes (year 220-250, hosing-CTRL) LIG LGM ITCZ migration mechanism • Fast signal • C-shape wind change in the tropics • Atmospheric bridge and oceanic tunnel • Wind-Evaporation-SST feedback (Chiang et al. 2008) HOL PRE FUT

  13. Linearity • Phase diagram of the response of different climate indicators (after 250 years) • Temperature changes in the NH linear with clear sky radiative changes (sea ice) • ITCZ changes linear with cooling (atmospheric bridge)

  14. Conclusions • The Greenland freshwater input amount computed during the Eemian is larger than a 2xCO2 (using a simple heat flux budget) after 250 years • In the IPSL-CM4, the climatic impact of a freshwater input shares similarities∀ the climate • Cooling of the Northern Hemisphere • Southward ITCZ migration, mainly in the Atlantic • Slight warming on the west coast of Greenland • Complex energetic adjustment: important role of the sea ice

  15. Thank youSwingedouw et al. Impact of freshwater release in the North Atlantic under different climate conditions in an OAGCM. Journal of Climate 22, 6377-6403, 2009

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