1. Deep circulation and meridional overturning Steve Rintoul and many others ….

2. CSIRO. OceanObs09 Venice September 2009 Outline Significance of the deep circulation and meridional overturning Progress in last decade Remaining challenges A strategy for observations of the deep ocean

3. CSIRO. OceanObs09 Venice September 2009 Meridional overturning circulation Lumpkin and Speer

4. CSIRO. OceanObs09 Venice September 2009 Meridional overturning circulation Speich (2009) adapted from Lumpkin (2007)

5. CSIRO. OceanObs09 Venice September 2009 Significance of the deep ocean and MOC The MOC is the primary mechanism responsible for transport and storage of heat, freshwater and carbon and the resupply of nutrients. Variations in the MOC are likely to have consequences for climate, both in present and future climates. The MOC is a three-dimensional circulation spanning the full- depth global oceans. Therefore our observations of the MOC must extend throughout the full-depth of the ocean. Changes in the deep ocean make a significant contribution to budgets of carbon, freshwater and heat (and hence sea-level rise). Changes in the overturning circulation will impact on ecosystems by changing the nutrient content and carbon saturation state of surface waters.

6. CSIRO. OceanObs09 Venice September 2009 Progress in the last decade First demonstration of sustained measurements of the MOC at 26.5N in the Atlantic. Provides evidence for substantial variability in MOC and deep ocean circulation. Documented changes in heat, freshwater and carbon throughout the full ocean depth: link between surface climate and the deep ocean is stronger than suspected. Showed that the deep ocean makes a significant contribution to changes in ocean heat content and sea-level rise. First direct velocity measurements of a number of deep outflow pathways. Deeper appreciation of role of the MOC in biogeochemical budgets (both sequestration and outgassing). Deeper appreciation of role of the MOC and deep circulation in low-frequency climate variability.

7. CSIRO. OceanObs09 Venice September 2009 Projected slowing of Atlantic MOC

8. CSIRO. OceanObs09 Venice September 2009 MOC variability at 26.5N

9. CSIRO. OceanObs09 Venice September 2009 Changes in deep temperature (western Atlantic) Johnson and Doney (2006)

10. CSIRO. OceanObs09 Venice September 2009 Changes in salinity of Antarctic Bottom Water

11. CSIRO. OceanObs09 Venice September 2009 Anthropogenic carbon storage in the deep ocean Wanninkhof et al. (2009)

12. CSIRO. OceanObs09 Venice September 2009 MOC influence on Atlantic SST Latif

13. CSIRO. OceanObs09 Venice September 2009 Observing the deep ocean and MOC Need to observe transport and inventory in the deep ocean. Transport strategy: Direct velocity measurements in boundary current (current meters, PIES, cables, pressure gauges) Ekman contribution calculated from winds (eg QuikScat) End-point monitoring of geostrophic flow Altimetry and gravity measurements Inventory strategy: Repeat deep hydrography (with tracers; ie GOSHIP) More rapid repeat hydro in overflows and main pathways Broad-scale, long-duration deep moorings with data transfer Deep floats

14. CSIRO. OceanObs09 Venice September 2009 Repeat hydrography

15. CSIRO. OceanObs09 Venice September 2009 Proposed AMOC observing system Add figure of RAPID array

16. CSIRO. OceanObs09 Venice September 2009 Global-scale deep observations Velocity measurements Deep water property moorings Deep carbon observations

17. CSIRO. OceanObs09 Venice September 2009 Measuring the southern limb of the deep overturning

18. CSIRO. OceanObs09 Venice September 2009 Data capsule for long-duration moorings

19. CSIRO. OceanObs09 Venice September 2009 Summary: need for deep ocean observations To determine the MOC, its variability and its influence on climate To close the planetary energy budget To determine rates and mechanisms of sea-level rise To determine the global budgets of carbon and nutrients and their sensitivity to change To constrain ocean state estimates (including errors) To understand the dynamics and nature of the global-scale ocean circulation, including response to forcing and modes of variability To test and develop models, proxies and satellite data (eg gravity)

20. CSIRO. OceanObs09 Venice September 2009 Summary: a strategy for deep ocean observations Build on established sites and technologies Moored arrays in deep boundary currents End-point monitoring for cost-effective measurements of basin- scale, full-depth flows Repeat full-depth hydrography with tracers (including enhanced measurements near dense water outflows) Broad-scale, inexpensive moorings for water properties Technology advances needed: Deep floats Data capsules for long duration moorings Biological and biogeochemical sensors

21. Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au Thank you CSIRO Marine and Atmospheric Research Wealth from Oceans Flagship Antarctic Climate and Ecosystems Cooperative Research Centre Steve Rintoul steve.rintoul@csiro.au