Potential temperature(oC, Levitus 1994)

Surface

Global zonal mean

Salinity (psu, Levitus 1994)

Surface

Global zonal mean

Evaporation – precipitation

Density as function of temp, salinity and pressure

max densityfreezing point

ρ–1000 kg m–3

Potential density(-1000 kg m–3, Levitus 1994)

Surface

Global zonal mean

Mixed layer depth

Seasonal variation of mixed layer depth

World ocean currents Map shows vertically averaged currents around the world oceans

Western boundary currents: Gulf Stream

Benjamin Franklin’s map (Richardson,

Science1980)

SST satellite image, from U. Miami

RSMAS

Surface wind (NCEP, m/s)

January

July

Ekman spiral

Coastal upwelling due to Ekman transport

Observed asymmetry of gyres

what one might expect what one observes

westerlies

trades

Annual mean Ekman pumping (m/year)

Friction in western boundary current

World ocean overturning and heat transport

Results from a numerical model (Boccaletti et. al 2005)

mass flux (Sv)

heat flux (PW)

Eq 40N 80N40S80S

Atlantic salinity and flow

The Great Conveyor Belt

Ocean heat transport by basin

Lumpkin and Speer (2007)

The present perception of Southern Ocean

overturning: it makesthe globalglobal thermohaline circulation

possible

Speer et al., 2000; Sloyan and Rintoul, 2001ab

Warm sources have to be deeper than cold ones:The Sandström’s theorem

Mixing is crucial:A scenario with a surface buoyancy

forcing of NADW upwelling is problematic

NADWNADWFormation Formation

NADWNADWConsumption Consumption

Mixing Mixing

No THCNo THC Intense THCIntense THC

“[…] understanding the physics related to the spatial and temporal distribution of mixing is one of the most important research frontiers in

physical oceanography.” Huang (2004)

Mixing is crucial:Different scenarios for the NADW

upwelling

a) Pushing by deepwater formation

b) Pulling by deep mixing

c) Pulling by wind stress & surface waves

A simple model of the thermohaline circulation

= flow strength, proportional to density difference

, adim. constants

temperature difference

salinity difference

Multiple equilibria

Change in surface temperature 30 years after thermohaline shutdown

Tropical Pacific sea-surface temperature

Equatorial temperature cross section

Equatorial currents

Surface

Meridional cross section

Equatorial undercurrent

Driving the undercurrent

Water parcel trajectories