• Guided by – Dr. Ajay yadav Professor M.sc Dept.

• Presented by – Abhishek giri M.Sc.-II/ Sem-III

* Chemical oceanography : Major & minor components of seawater

R.K.Talreja college, UNR-3

* contents

*Composition of major components of seawater.*Sources of major components of seawater.*Causes of major components not being conservative*Composition of minor components of seawater*Distribution of trace elements

* Components of seawater

*Solids*Gases*Colloids*Dissolved solutes

Solid doesn’t pass a 0.45 μM-filterColloids passes a 0.45 μM-filter but is not dissolved

* Introduction

The dissolved constituents of seawater can be divided into four broad categories :1. Major constituents.2. Minor constituents.3. Trace components.4. Gases.

Major elements 0.05 –750 μMMinor elements 0.05 –50 μMTrace elements 0.05 –50 nM

* Major constituents (99.7%)

A. Elements:1. Primary are Cl ⁻ (55.04 %) & Na (30.61 %) which make up 85.65 % of ⁺

all the dissolved constituents.2. Adding the next 4 most abundant (SO4² , Mg² , Ca² , and K ) brings ⁻ ⁺ ⁺ ⁺

the total to › 99% of the salts.3. Finally the last 5 (HCO3 ⁻, Br ⁻, H3BO3, Sr2 ⁺, F⁻) brings the total to ›

99.99% 4. Almost all of the rest of the 92 naturally occurring elements are found

in the ocean but they only total to 0.01% of the TDS.5. Although the other components are a very small % of the dissolved

materials, they are essential for life on earth.

* Composition of major components of seawater

The big 6 of major components of seawater

*Although ocean salinities vary from one part of the ocean to another, Forchhammer discovered that salt ions are always present in the same proportions.

*Thus, whether the salinity of a sample of seawater is 32‰ or 37‰, the chloride ion makes up 55.1% of the salt ions in the sample.

*This constant ratio is known as Forchhammer’s Principle, or the Principle of Constant Proportions.

* Seawater composition of 35 ‰ salinity

* Sources of major components of seawater

*Allothoneous1. Weathering2. Volcano eruption3. Anthropogenics*Autothoneous1. Advection2. Mixing/up welling3. Biodegradation4. Disolusi5. Underwater eruption6. Hydrothermal vent

*Conservative

*Non-reactive*The concentration is stable over time in the oceans*Remain in the ocean in long period (long

residence time)*Major components of seawater belong to

conservative element*Examples : Na, K, S, Cl, Br, Sr, B (conservative

major elements)

*Non-conservative

*Biologically &/OR chemically reactive.*There concentration varies over time.*Examples : C, P, Fe

* Conditions under which major elements may not be conservative

1. Estuaries & land-locked seas.*Examples : Black sea, Baltic Sea, Chesapeake Bay*These elements rations are much larger in river

water than in seawater.

*Runoff can be major effect for these ions

2. Anoxic basins* sulfate reduction:

3. Freezing * fractionates major ions* examples: Sea ice contains proportionally more

SO4²⁻ than Cl⁻

* Salinity

*Salinity is defined as the weight in grams of salt in a kilogram of seawater.*Since there are 1,000 grams in a kilogram, salinity

is expressed in parts per thousand, denoted ‰ or psu (practical salinity unit)*Salinities in the open ocean from 32 ‰ to 37‰

with an average level of 35‰.

* Salinities variations in open ocean

*Salinity is Red Sea = 40-42 ‰because there is little incoming fresh water and high evaporation*Gulf of Bothnia (off Finland) = 5 ‰because of just the

opposite situation*Completely isolated seas and lakes can reach as high

250 ‰if there is little influx of fresh water and lots of evaporation. For example, the salinity of the Dead Sea is about 240 ‰, and the salt is mainly MgCl2

*Evaporation and freezing cause salinity???*Precipitation causes salinity??*Where EVAPORATION > PRECIPITATION*seawater salinities are ??*Where PRECIPITATION > EVAPORATION *seawater salinities are??

* Composition of minor components of seawater

*Only 14 elements have concentration greater than 1 ppm (O, H, Cl, Na, Mg, S, Ca, K, Br, C, Sr, B, Si, and F). The remaining elements called minor element.*Many of these components are non-conservative.The ones which are involved in biological processes.Others which vary because of chemical processes

such as oxidation are also non-conservative.Usually called trace constituent if it occurs in amounts

< 1 ppm.

*Trace components

*Many minor and trace elements are essential for the survival of organisms, both in the sea and on land. *Some of these elements (Fe, Mn, Mo, Zn, Co, Cu,

and V) are so rare that their concentrations are commonly described in terms such as ppb. *The precise roles of many of these elements in

organism metabolism have not been established

*References

BOOKS*Nair N.B. and Thampi D.H., A textbook of marine ecology*R. Gordob Pirje, Oceanography. WEB-LINKS*http

://www.sce.lsu.edu/cego/documents/reviews/oceanography/salinity.pdf*www.marinebio.net/marinescience/02ocean/swcomp

osition.htm