Sea Surface Temperature, 4 - 9 November 2002

Nomenclature

• Meridional Overturning Circulation (MOC): Total northward/southward flow, over latitude and depth

• Thermohaline Circulation (THC): Part of MOC driven by heat & water exchange with atmosphere

• MOC is observable quantity; THC an interpretation

• Often used synonymously, but wind-driven MOC part must be considered separately

Meridional Overturning Circulation (MOC)

Jayne & M 2001

CO2-induced THC slowdown? Possibly leading to cooling?

• Current observations do not allow us to identify which model’s projection is correct (if any)

• MOC estimated through ship-based sections across ocean, usually >10 years apart

• Need continuous observation of MOC

• Cannot base strategy on repeat sections (not enough people or money)

Approach: Integrated

thermal wind(geostrophy)

• Ekman contribution to MOC included

• Surface layer Ekman transport assumed to return independent of depth (Jayne & M ‘01)

MOC, Jan. - July

Jayne & M 2001

“Ekman reconstruction”

Jan. - July

26.5°N MOC Monitoring Project

•PIs: Jochem Marotzke, Stuart Cunningham, Harry Bryden (SOC)

•Funded by NERC RAPID with £4.0M over 5 years

•Will support 2 Post-docs, 1 Research Assistant,

•Started 1 April 2003

•Expected first instrument deployment: January 2004

Why 26.5°N?

• Near Atlantic heat transport maximum – captures total heat transport convergence into North Atlantic

• South of area of intense heat loss from ocean to atmosphere over Gulf Stream extension

• MOC dominates heat transport (Hall & Bryden ‘82)

• Heat transport variability dominated by velocity fluctuations (Jayne & Marotzke, 2001)

• Florida Strait transport monitored for >20 years (now: Johns, Baringer & Beal, Miami, collaborators)

• 4 modern hydrographic occupations

The Future:

• Deployment of instruments likely to start Jan 2004

• 4 full years of measurements during RAPID

• Deliverable: Demonstration of how MOC can be monitored effectively and efficiently

• Measurements must continue beyond lifetime of RAPID, as part of an early warning system