deep circulation and meridional overturning steve rintoul and many others …

Deep circulation and meridional overturning

Steve Rintoul and many others ….

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


Meridional overturning circulation

Lumpkin and Speer


Meridional overturning circulation

Speich (2009) adapted from Lumpkin (2007)


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.


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.


Projected slowing of Atlantic MOC


MOC variability at 26.5N


Changes in deep temperature (western Atlantic)

Johnson and Doney (2006)


Changes in salinity of Antarctic Bottom Water


Anthropogenic carbon storage in the deep ocean

Wanninkhof et al. (2009)


MOC influence on Atlantic SST

Latif


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


Repeat hydrography


Proposed AMOC observing system

Add figure of RAPID array


Global-scale deep observations

Velocity measurements

Deep water property moorings

Deep carbon observations


Measuring the southern limb of the deep overturning


Data capsule for long-duration moorings


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)


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

Contact UsPhone: 1300 363 400 or +61 3 9545 2176

Email: [email protected] Web: www.csiro.au

Thank you

CSIRO Marine and Atmospheric ResearchWealth from Oceans FlagshipAntarctic Climate and Ecosystems Cooperative Research Centre

Steve Rintoul

[email protected]

deep circulation and meridional overturning steve rintoul and many others …

Documents

deep circulation

deep oceanoceanobs09

deep ocean circulation

deep hydrography

deep oceanwanninkhof

wateroceanobs09 venice

speeroceanobs09 venice

2009oceanobs09 venice