NOTES
Links to summaries of key issues for each topic
VISUALS
Links to images employed in lectures on a topic-by-topic basis
TEXT
Link to chapter outlines at online learning center at McGraw Hill.
NOTES
Links to summaries of key issues for each topic
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The Chemistry of Seawater
|
Notes on Topic:
The notes represent summaries of key issues
for each topic
They emphasize the terminology used to describe
the various phenomena.
| 1. The Salts: |
| Learning Objectives: |
-
Understanding of the influences on ocean salinity and its salt content
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Recognition of the importance of specific salts, their origins and variability
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| Ocean Salinities: |
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Seawater is 3.5% salts, or 35â (per mil) salinity
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Surface salinity varies with latitude
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depends on precipitation and evaporation
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High salinities (>36â) occur in mid latitudes (c. 25°)
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they are also higher in evaporative basins
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Low salinities (>33â) reflect
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freshwater influx (rivers, meltwaters) or high precipitation.
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Seasonal changes in salinity occur in polar regions.
|
| Dissolved Salts: |
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Salts dissolve, form electrically charged particles called ions
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cations with positive charge (e.g. Na+)
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anions with negative charge (e.g. Cl¯);
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Major ions in seawater (6 total > 99%):
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Cl¯ (55.07%), Na+ (30.62%), SO42¯
(7.72%)
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Mg2+ (3.68%), Ca2+
(1.17%), K+ (1.10%)
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Average seawater is 3.5% salts, or 35â (per mil).
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Other elements are minor or trace constituents.
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Constituents of seawater:
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most are not added or removed by organisms: conservative constituents
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if affected by biological processes: non-conservative constituents.
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| Sources of Salt and Salt Balance: |
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Salt originally from Earth's interior
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introduced by dissolution of volcanic gases (e.g. H2S,
SO2, Cl)
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still emanating at ridge axes from hydrothermal vents
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river outflow no longer matches ocean constituents.
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Salt content of oceans constant for past 1.5Ga.
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Requires balancing of river inputs (and vents) by removal.
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Evaporites are salt deposits
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particles (mineral and biological) can adsorb ions and exchange them
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Fate of salt in marine sediments:
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uplift, erosion and continuation of cycling processes
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| Salts and Salinity: |
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Residence Times
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amount present/removal rate
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range of times for different elements and compounds
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Na long (260Ma), Al short (100a).
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Constant Proportions:
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seawater well mixed
-
ionic composition varies little
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contains elements in constant proportions except for organisms.
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Determining Salinity:
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measured by addition of AgNO3
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processes removes halogens, known as chlorinity.
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salinity (in â) = 1.80655 x chlorinity.
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measured electronically based on conductivity by salinometer
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Department
of Geological Sciences,
1001
E. Tenth Street, Bloomington, IN 47405-1403
Phone:
(812) 855-5582 Last updated: 15 October 2000
Comments:
simon@indiana.edu
Copyright
2000, The Trustees of Indiana University
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