Chapter 6: Global Fluxes and The Deep Circulation

Heat Budget

Conservation of Salt

Oceanic Water Masses

Oceanic Mixing Temperature - Salinity Diagrams

•The temperature and salinity of water in the ocean are determined while that water is at the surface.

•Temperature of surface water is determined by the relative sizes of the different terms in the oceanic heat budget equation.

•Salinity is determined by the balance between evaporation and precipitation and by the freezing and melting of ice.

NOTES

Qs + Qv = Qb + Qh + Qe + Qt

HEAT- Budget Equation

Qs = incoming short-wave radiation

Qv = heat advected into the region in currents

Qb = heat lost from the sea-surface by long-wave radiation

Qh = heat lost by conduction/convection

Qe = net amount of heat lost by evaporation

Qt = net amount of heat available to raise the temperature

Qs: Wm-2

The net radiation balance is largely controlled by variations in Qs

Net Radiation Balance (Qs – Qb)

Qb: depends on surface temperature, cloud cover and type, and water vapor content.

Generally (Qs – Qb > 0)

Qs + Qv = Qb + Qh + Qe + Qt

HEAT- Budget Equation

Qv = heat advected into the region in currents (includes vertical circulation (i.e. upwelling and downwelling currents)).

Qh, Qe

•depend upon the gradients of temperature and water content respectively, of the air above the sea-surface

•Generally represent a loss of heat from the sea

•Enhanced by increased atmospheric turbulence above the sea-surface.

•Difficult to estimate

•Qe is negative around the Grand Banks off Newfoundland where the cold Labrador Current promotes condensation of water vapour onto the sea-surface

SST: July and January

15oN – 15oS net heat gain

Net loss in winter hemisphere at higher latitudes

Qh greater role in NH winter cooling, cold dry continental air also enhances Qe

Sea ice reduces Qs but leaves Qb relatively unaffected so is maintained