1 / 73

Nathan Bindoff, Kieran Helm and John Church CAWCR, ACECRC, IASOS, CSIRO University of Tasmania

Global changes of the hydrological cycle and ocean renewal inferred from ocean salinity, temperature and oxygen data. Nathan Bindoff, Kieran Helm and John Church CAWCR, ACECRC, IASOS, CSIRO University of Tasmania. IPCC AR4 Synthesis. Data Distributions. Methods Interpolated WOCE

derry
Download Presentation

Nathan Bindoff, Kieran Helm and John Church CAWCR, ACECRC, IASOS, CSIRO University of Tasmania

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Global changes of the hydrological cycle and ocean renewal inferred from ocean salinity, temperature and oxygen data Nathan Bindoff, Kieran Helm and John Church CAWCR, ACECRC, IASOS, CSIRO University of Tasmania

  2. IPCC AR4 Synthesis

  3. Data Distributions • Methods • Interpolated WOCE • Used adaptive • Blue water • Database • WOCE (Red) • Profiles (Blue) • ARGO (Green)

  4. Water Mass change Shallow salinity maximum Salinity Minimum

  5. Zonally averaged changes Salinity change on density surface displacement of density surfaces

  6. Apparent surface fluxes

  7. Apparent surface fluxes P-E Heat Volume

  8. Climate models, essential to hypothesis testing Observations 1980-2000 Mean Model 1980-2000

  9. Comparison with models IPCC models 1970-2000 Estimated P-E +16±6% in S. Ocean + 7±4% in N.H - 3±2% in S.T. gyres

  10. Excess P-E near Antarctica? Altimetry • Antarctica is loosing mass • 0.14 ± 0.41 mm yr-1 SLE, 1961-2003 • 0.21 ± 0.35 mm yr-1 SLE, 1991-2003 • ~0.4 ± 0.35 mm yr-1 SLE,2002-2007 • Wahr and Velicogna 2007. • Increasing evidence of melt • Jacobs 2001, Rintoul 2006, • Aoki et al 2005 • Melt of ice shelves? • <5% over 30 to get extra 50 mm.yr-1 • no sea-level rise • negligible gravity signal • consistent with ocean melt • 700 years at ~50mm.yr-1 Gravity

  11. Is ocean renewal changing? • Decrease • surf. Buoyancy • Changing • stratification • Carbon cycle

  12. Zonal oxygen changes Oxygen change on density surface Oxygen change from displacement of density surface • Global Scale • Not heave • 1970 to 1990’s

  13. Apparent surface fluxes Oxygen flux Heat flux • Decrease 1.8+-0.9 mmol.l-1 • Equivalent to ~1% decrease • Equivalent flux • 0.6+-0.3 1014 mol.yr-1 • 0.2 to 0.7 1014 mol.yr-1 in the literature (eg • Keeling and Garcia 2002) • Implications: • Reduce O2 exchange with atmosphere • Reduced water mass ventilation in the subduction

  14. Winds or buoyancy? 1 ∫ Bnet Sann = dt Tyrρ g h Qb

  15. High latitudes processes and symmetry • High Latitudes large impact on storage changes • Zonal averages similar in both hemispheres

  16. Conclusions • Changing freshwater fluxes • Plausibly attributable climate change • Evidence of increased melt of Antarctic ice shelves • Acceleration of hydrological cycle • Striking global scale oxygen changes • Evidenced for reduced ocean exchange • Weakening of the global overturning circulation?

  17. Interpretation

  18. Global Oxygen Changes • Decrease 1.8+-0.9 mmol.l-1 • Equivalent to ~1% decrease • Equivalent flux • 0.6+-0.3 1014 mol.yr-1 • 0.2 to 0.7 1014 mol.yr-1 • In the literature (eg • Keeling and Garcia 2002)

  19. More evidence Aoki et al, 2005 1960’s to 1990’s 30E to 180 HadCM3 1990's- 1960's Banks and Bindoff, 2003

  20. Climate Differences

  21. Winds or buoyancy? 1 ∫ Bnet Sann = dt Tyrρ g h Qb

  22. Consequence of ocean acidity and renewal change • Impacts on organisms that have calcareous shells (in particular aragonite) • Coral reefs • Changes in upwelling

  23. Observations (Gille) Model Warming of the Southern Ocean O’Farrell + Budd, in prep

  24. Antarctic Ice Mass Loss from GRACE East/West dividing line Rate of ice volume change: All Antarctica: -149 km3/yr West Antarctica: -115 km3/yr East Antarctica: -23 km3/yr Wahr and Velicogna, 2007

  25. Data Distribution: profile data Oxygen Temperature and salinity

  26. (See: Bindoff & McDougall, 1994, 2000) Changes on neutral surfaces new thermocline old thermocline new thermocline old thermocline ρ2 ρ2 Pot. Temperature (°C) Pot. Temperature (°C) ρ1 ρ1 Salinity Salinity Pure warming Pure freshening

  27. Comparison with HADCM3

  28. Comparison with CSIRO Mk3 Model 2090’s minus 1950’s Downes et al, inprep.

  29. More evidence Aoki et al, 2005 1960’s to 1990’s 30E to 180 HadCM3 1990's- 1960's Banks and Bindoff, 2003

  30. Decadal variability Mixed layer depths and section lines • Bryden et al., 2003, McDonagh et al. 2005

  31. Observations

  32. Zonally averaged differences on density surfaces

  33. Time series of zonal averages at sigmat=26.7

  34. Extremes of modelled mixed layer development Murray et al. 2007 Message: the water mass variations related Mixed layer thickness changes

  35. Climate Differences Mawson Harbour, Antarctica

  36. Data and method Convert Hydrobase2 from pressure to density levels Optimally interpolate 800,000 pre-1988 profiles to 40,000 post-1988 locations

  37. Data and method Convert Hydrobase2 from pressure to density levels Optimally interpolate 800,000 pre-1988 profiles to 40,000 post-1988 locations Directly compare 1970 with the early 1990s using a ‘snapshot’ approach Helm et al., inprep

  38. Regional T-S changes

  39. Salinity increases in thermocline water on isopycnals (γn=24.8)

  40. Freshening of intermediate water on isopycnals (γn=27.0)

  41. Zonal changes on density surfaces Salinification sub-tropics CDW IW Mode Cooler/Fresher Warmer/Saltier

  42. Deeping of isopynals in mid to high latitudes Salinification sub-tropics CDW IW Mode Shoalling Deepening

  43. Global oxygen decreases Salinification sub-tropics CDW IW Mode

  44. Key findings 1970’s to 1990’s • On neutral density surfaces: • Globally coherent temperature/salinity changes • Warming/increasing salinity of upper thermocline waters • Cooling/freshening of mode and intermediate waters • Oxygen decrease in upper thermocline, mode, intermediate waters and CDW • Largest changes occurred in the upper 1500m

  45. Summary

  46. Subduction Changes Processes • CSIRO Mk3 • 2090’s minus 1950’s • Diagnosed using MNW • Model diagnostics SAMW AAIW CDW

  47. Buoyancy Changes • CSIRO Mk3 • 2090’s minus 1950’s • Diagnosed using MNW • Model diagnostics CW SAMW AAIW CDW

  48. Schematic of changes… CSIRO MK3 model 2090’s to 1950’s Process that matter: • CW Increased subduction,decreased buoyancy • SAMW Decreased subduction, Decreased HF and FF • AAIW Decreased subduction, HF and FF • CDW Decreased entrainment, increased HF,FF

  49. Detection Parallel Climate Model Observations ACC Simulations Barnett et al. Science 2005

More Related