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Composition of seawater Processes controlling seawater composition - PowerPoint PPT Presentation

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This in an introduction to oceanography for 1st year students . In geochemistry, geology and misuse of the sea Resources are: Oceanography: An Illustrated Text C. P. Summerhayes, S. A. Thorpe John Wiley & Sons, May 1996 ISBN: 0470345373 or 0470235748 352 pages

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This in an introduction to oceanography for 1st year students. In geochemistry, geology and misuse of the sea

Resources are:

Oceanography: An Illustrated Text C. P. Summerhayes, S. A. Thorpe John Wiley & Sons, May 1996 ISBN: 0470345373 or 0470235748 352 pages

NASA visible Earth:

Essentials of Oceanography (7th Edition) (Paperback)by Harold V. Thurman, Alan P. Trujillo

A very good webpage can be found under:,7261,382992-,00.html

Composition of seawater students

Processes controlling seawater composition

Major drainage systems of rivers

Explain Rock weathering, vulcanic ashes, aerosols, hydrothermalism

Formation of sedimentary rocks

How does the salt get into the sea

Dominant ocean sediment types and locations

The biological pump (photosynthesis, settling etc)

The physical/solubility pump

Vertical profiles of chemical elements

Atlantic versus Pacific comparison

Explain the two box model

Oxygen in surface waters

The Marine Carbonate System

CO2 determination from ancient atmospheres

CO2 in surface waters

current atmospheric CO2 concentration

effect on global warming

CO2 saturation in seawater (name the different ions)

∑CO2 concentrations in oceans

Lysocline and Carbonate compensation depth

Ocean CO2 disposal option

Ocean resources


overfishing/clima effects

Oil/gas, Sand dredge, Manganese, Medicine, Biotechnology



Beach characteristics

Longshore current/drift

Erosional coasts

Depositional coasts

Barrier islands

Coastal protection

What you should know for the

Oceanography exam

Deployment of a CTD cast. This instrument is routinely used during oceanographic expeditions for in situ measurements of water temperature and salinity. CTD casts can also collect water samples from different depths, stored in the dark grey cylinders visible on the photograph, which can then be used for further chemical analyses on board.

Figure 2

: oceanography/f1f7.htm

Figure 3 during oceanographic expeditions for

Composition of seawater

Seawater is a solution of salts of nearly constant composition, dissolved in variable amounts of water. There are >70 elements dissolved in seawater but only 6 make up >99% of all the dissolved salts; all occur as ions - electrically charged atoms or groups of atoms: their concentrations are mostly conservative and only affected by physical processes

Oceanographers use salinity -- the amount (in grams) of total dissolved salts present in 1 kilogram of water -- to express the salt content of seawater. Normal seawater has a salinity of 35 grams/kilogram (or litre) of water -- also expressed as 35‰. Seawater from Wormly in southern England is used as the international standard for seawater composition.

As well as major elements, there are many trace elements in seawater - e.g., manganese (Mn), lead (Pb), gold (Au), iron (Fe), iodine (I). Most occur in parts per million (ppm) or parts per billion (ppb) concentrations. These minor constituets are mostly non-conservative and actively participate in chemical and biological processes that change their concentrations They are important to some biochemical reactions - both from positive and negative (toxicity) viewpoints.

River water during oceanographic expeditions for


Figure 18

Figure 6 during oceanographic expeditions for

precipitation during oceanographic expeditions for

Figure 7

Figure 8 during oceanographic expeditions for

Processes controlling seawater composition

Salts dissolved in seawater come from three main sources:

• volcanic eruptions

• chemical reactions between seawater and hot, newly formed volcanic rocks of spreading zones (mid-oceanic ridges)

• chemical weathering of rocks on the continents

Figure 4 3
FIGURE 4-3 during oceanographic expeditions for

Figure 4 4
FIGURE 4-4 during oceanographic expeditions for

Primary source for weathered during oceanographic expeditions for

material is crustal rock

Limestone, sandstone and

Shales are themselves sedimentary


Figure 2

Many salts in seawater originate from weathering of rocks on land. As rocks are weathered to form soils, they release soluble constituents like silica and elements like sodium, calcium, potassium and magnesium. River waters also carry bicarbonate (HCO3) - a by-product of weathering of silicate rocks or dissolution of limestone. Once they enter the oceans the dissolved salts remain, while the water continues to move through the hydrological cycle.

Figure 10

Figure 4 5
FIGURE 4-5 during oceanographic expeditions for

Figure 4 7
FIGURE 4-7 during oceanographic expeditions for

Vulcanic ashes during oceanographic expeditions for


hydrochlord acid

sulphur containimg gases

carbon dioxide

Figure 13

Volcanic eruptions produce large volumes of gases that eventually reach the oceans -- most important are sulphate and chloride. Submarine eruptions at spreading ridges inject gases directly into the oceans; gases from subaerial volcanoes are dissolved in rainfall.

Figure 4 6
FIGURE 4-6 during oceanographic expeditions for

Aerosols during oceanographic expeditions for

Aerosols are powders, or droplets, suspended in a gas, with a typical particle diameter of about one micrometer. they can act as a nucleus for the condensation of water to make a relatively large cloud droplet. Once formed, aerosol particles can collide and stick together, or they can grow by further condensation from the vapour phase.



Figure 14

October 13, 2001

Figure 9 during oceanographic expeditions for

Figure 4 18
FIGURE 4-18 during oceanographic expeditions for