Great Ocean Conveyor Belt illustration of thermohaline circulation

Great Ocean Conveyor Belt

- illustration of thermohaline circulation

- shows link between surface and deep circulation

- demonstrates connectivity of the world ocean

- transport of energy and biogeochemical tracers

- significant link between ocean and climate (weather)

Geography 104 - “Physical Geography of the World’s Oceans”

• processes that change temperature (thermo) or salinity (haline) and thus density driven flow

• winter storms and rapid surface cooling

• freezing seawater and salt rejection

• sinking (vertical motion) of near-surface water

Thermohaline Circulation

• only very small density changes are needed

• vertical velocities are small (< 1 m/day)

• downward movement at one location must be compensated by upward movement (conservation of volume)

• resulting horizontal velocities small (< 1 cm/s)

• important for sea life – oxygen moved downward

– nutrients moved upward

Thermohaline Circulation

Water masses are defined by their T-S properties

Movement of seawater is along isopycnal surfaces

know there are a variety of water masses in the ocean……….

identifiable by their T-S properties,

with the densest waters being deepest.

Atlantic Deep Circulation

Global Conveyor Circulation

WinnipegLondon

50º

Climate differences: N. America vs. Northern Europe

WinnipegLondon

50º

Climate differences: N. America vs. Northern Europe

conveyor circulation drive:North Atlantic & Southern Ocean

conveyor circulation drive:North Atlantic & Southern Ocean

deep water formation regions

vapor export from North Atlantic

from Broecker (1997)

- arrows show water vapor transport in Sverdrups (x106 m3 s-1)- negative values show evaporation- ~15 cm of freshwater over entire Atlantic per year

North Atlantic surface salinity

North Atlantic deep water formation: North Atlantic Conveyor Drive

Curry and Mauritzen (Science, 309, 1772-1774 2005)

North Atlantic deep water formation: North Atlantic Conveyor Drive

Curry and Mauritzen (Science, 309, 1772-1774 2005)

water mass sinking

North Atlantic deep circulation

NADW

http://www-das.uwyo.edu/~geerts/cwx/notes/chap11/sea_ice.html

Antarctic sea ice formation: Southern Ocean Conveyor Drive

Antarctic bottom water formation: Southern Ocean Conveyor Drive

AABW

Southern Ocean deep circulation

AABW

Southern Ocean Conveyor Drive

S3

Salinity – Southern Ocean Conveyor Drive

AABW

NADW

AAIW

Pot. Temp. – Southern Ocean Conveyor Drive

AABW

NADW

AAIW

global Winds and PressureJuly

Westerlies

Antarctic Circumpolar Current

Ekman transport

Westerlies

Antarctic Circumpolar Current

Antarctic IntermediateWater formation

temperature-salinity of deep water masses

mixing in the Antarctic Circumpolar Current

NADW formation

AABW formationAAIW

formationfrom Broecker (1997)

mixing in the Antarctic Circumpolar Current

NADW

salinity at 2000 m

- NADW mixes rapidly in Antarctic Circumpolar Current

North Pacific water formation

19%

30%51%

North Pacific Deep Wateror Pacific and Indian Ocean Common Water

North Pacific Deep Water flow

North Pacific Deep Water Formation

salinity at 2000 m

to Indian

Ocean

to Pacific

Ocean

North Pacific Deep Water flow

SectionP18

equator 20° N 65° S

North Pacific Deep Water along 105° W

North Pacific Deep Water

Global Conveyor Circulation

Global Conveyor Circulation

choke points in surface return flow

Indonesian Throughflow

Readings (Surface and Deep Circulation):Text Chapter 9 (pgs 165 - 189)Reader pgs. 105 – 129 (Thermohaline Circulation)