Sea water properties

Sea water properties

Density

increase in kinetic energy cause a decrease however this is more pronounced in liquid and gas phase - and increase the intermolecular distance

however it increase upon melting

the maximum density of purw water at 3.98 degrees.

due to dipole dipole bonds

- high boiling and freezing pionts

- high heat capacity , high latent heat

-high dissolving ability

Heat capacity

Water has very high specific heat

capacity 4.19 J g-1

K-1

and very high heat latent heat of

vaporisation 2261 J g-1

Paleothemometer

oxygen isoptopes indicate past tempretures

- atmospheric water - evaportaion

they are heavier then normal atoms = more energy for evaporation

precipitation shows less than seawater

- 15. drop cause a 1 mm decrease in oxygen isotope

there fore this water in ice cores shows past temperature change

dissolving ability

salts - involves cations and anions - held together by electrostatic forces

dipole - ion interactiosn - dissolved ions surronded by a layer of water - hydration shell

why is the ocean salty

sources

- weathering - dissolution ofcrustalrocks by acidic rainwater (K,Na,Ca,Mg,Si)

-volcanism - excess volatiles (Cl,S)

- Hydrothermal Vent activity - spreadin centres (K,Ca,Cl.S)

sinks

- Evaporite formation - salts left behind after evaporation of seawater

-Aerosol formation - seasalt injected into atmosphere = salt spray

- Adsorption - ions on particle surfaces

-Sedimentation/burial - biogenice and authigenic

- hydrothermal vent activity - vent fluid reactions

wether exsamples

constitutes of seawater

-dissloved salts - major ions - nuitrients and trace elements

-dissolved organics - DOM like DOC = carbon

-dissolved gases

- suspended particulates - dust,ash,sediments and live and dead organic matter

all components are important but MAJOR IONS SOMINATE MACROSCOPIC SEAWATER PROPERTIES

major and minor

the major ions are the 11 most dissolve ions that contribute to 99.99% of all that is contributed

nuitrients, trace element and organic acount for less then 0.01% however they are important for phytoplankton growth and global elements cycles

constant proportions

major elements in seawater exist in constant proportions to each other

this is a fundamental concept in oceanography - basis for all salinity determinations.

ocean mixing is rapid compare to that of major ions

conservative behaviour

- residence times of major ions in sea water are much longer than residence time of water = ions mix well

- oceans are in a steady staet with regard to major ions = eqaul sources and sinks

- no addition or removal by biological or chemical processes in seawater itself

-concentration changed due to addition or removal of wtaer , mixing of water masses

however the ratio remains consatnt between ions

Exceptions

-land-locked seas - large variation in riverine inputs

-low oxygen water - bacteria removes sulphate

- ice formation - ice disturb lattice - only partly dissolves ions are reatianed - also retains more sulpahte then chloride

- carbonate formation - removes carbon

- seawater - magma reactions - sulphate and magnesium lost

however most seawater shows conservative behaviour of major ions

salinity is expressed as a mass-mass ratio

salinity derived from conductivity measurements

salinity

highest salinitys are in the sub tropics

Affects:

freezing pionts decrease in salintiy - antartic bottom water is at -0.8 and - 2

-density also decrease rapidly - particularly important as it cause layering of different water masses and effects ocean circulation

processes affecting salinity

- evaporation

-precipitation

(together these are the nain for large scale patterns)

-river discharge - local important for estuaries and enclosde/coastal waters

- ice melt

- ice formation - brine rejection: major ions no incorportaed inot ice and increase salinity of surface waters

carbonate system

reflects seawater ph

affects:

air-sea gas exchange

photosynthesis

respirtaion

precipitation

dissolution

ocean acidification

ph predicted to drop this will effect calcareous organisms - phytoplankton and zooplankton and also may affect carbon cycle and sediment burial

Alkalinity

capacity of seawater to neutralise strong acids or the TA

they are buffers

carbonate ions and minor borate ions are used in this buffering

major anions do not contribute because they cannot neutralise hydrogen ions

it is define by the charge balance between major cations and anions

TA = carbonate alkaline + boraye alkaline + Ph balance ( which is the concentration of bases take acid)

CA can be determined by:

-alkalinity titration

-Ph measurement

-correction for non-carbonate alkalinity

allows calculations of carbonate/ carbon compound

important for geochemistry, carbon cycling and climate change studies.

processes

ocean acidification decrease the ph of sea water because it adds more hydrogen ions

calcium carbonate also increase as it adds more posititve calcium ions to the water also the reverse for formation

alkaline distribution pattern

-highest in subtropical gyre systems

-lowest in regions of high fresh water runoff and precipitation

why?

alkaline can also be defined as the difference the charge balance of positive and negative major ions.

carbonate and hydrogen carbonate ions make up this difference to ensure overall electroneutrality.