Salinity

Major constituents (by mass)

Major Constituents Concentrations

Cl- 546mM

Na- 470mM

Mg- 53mM

SO4- 28mM

Ca- 10.2 mM

K- 10.2mM

HCO3- 2.4mM (variable)

• Na and Cl constant ratio with S for all seawater

• constant proportions between pools of major constituents for the past 500my, which coincides with formation of multicellular life

Principle of constant proportions

• regardless of salinity, major ion ratios are constant

• Na/Cl constant for all seawater

• Na/S also constant

Exceptions for principle of constant proportions

HCO3 - ±<20%

Ca2+ ±<1%

Sr2+ ±<2%

• all biologically active- variable incorporation depending on where we are in the ocean

Salinity measurement methods

direct measurement- weigh the dried salt (some dissolved ions volatilize at high temps, so inaccurate)

Refractometer- a refractometer measures the change of direction or bending of the light as it passes from air to water

• light moves slower in water than in air. the more salt in the water, the slower the light moves— not as precise (1 part in 70)

chemical- chlorinity (based on constant proportions)— titration with AgNO3 to precipitate AgCl, AgBr etc..

• the titration gives the grams of Cl equivalent in 1kg of seawater

physical- conductivity

• but need to correct for temperature simultaneously (Very precise; 1 part in 40,000)

Sea surface salinity patterns

• high in atlantic

• low at poles (particularly in artic)

• lower closer to land

• high at gyre centers

• low at equator

Evaporation and precipitation patterns

Atmospheric circulation controls evap/precip

Relationship between evap-precip and salinity

• it mirrors salinity patterns

What is the volume transport for water flux

• 10⁶ m³/s (=SV)

Global water cycle

• mid-latitude evaporation

• high and low latitudes have high precip

• dominance of water cycle is in the ocean with a minor role of the land

• complementary return flow in ocean

describe salinity and the water cycle

in temperate northern latitudes, there is a net loss from the Atlantic to Pacific totaling 0.32 SV

Salinity and the water cycle summary

• The majority of the water cycle is between the atmosphere and the ocean

• oceanic salinity is an excellent indicator of a changing water cycle

  • this makes it an important climate variable to monitor

• the general patterns of surface salinity reflect the workings of the global water cycle

correlation between warming and the water cycle

• 7% increase in vapor press. for each 1c increase in temp.

• in the future we could see more drought, flooding from rain, and more violent storms

Salinity profile at high latitude

• high latitude regions are dominated by precipitation and ice melt

• salinity is lowest at the surface and increases along the halocline

Salinity profile at North Atlantic subpolar gyre

• it is affected by inflow of a thick layer of saline, warm surface water from the subtropical gyre

• halocline typical of the subpolar pacific and subpolar southern hemisphere

• absent in most of the subpolar north atlantic

  PROFILE FROM HIGH LAT

  

Salinity profile for tropics

subtropical underwater is gyre water that has flowed equatorward

intermediate water (high latitudes) is coming from high latitudes

Salinity profile for the subtropics

• N. atlantic saltier because of NADW

• AABW in pacific and indian oceans

  

Salinity at 1500m

salinity at 3000m

temperature and salinity in atl vs pacif vertical structure

• in atl you can see water masses

Shipboard sampling strategies

• Profile CTD (conductivity, temperature, pressure)

• Rosette: profiling CTD, Niskin bottles

• supports numerous auxiliary sensors (dissolved oxygen, pH, turbidity, fluorescence, PAR (photosynthetically active radiation), altimeter)

• ARGO float