defined as the amount of salt dissolved in a given volume of seawater.
Expressed as parts per thousand, or ppt.
For example, seawater with S = 35 is:
35 parts solids + 965 parts water = 1000 parts total
This is equivalent to 3.5 % salt solution
( 35 grams salt/1000grams total = 3.5/100)
Trace substances are measured in parts per million (ppm). For example 43 ppm = 43 mg/1000 g total
1 ppt = 1000 ppm
1ppm = .001 ppt
Salinity is often determined by the Conductivity of seawater. This is the ability of the seawater to conduct electricity.
defined as the ratio of the mass of a substance to the volume occupied by that substance. For example,
- fresh water density = 1.000 ( 1 gram/ cm3)
- warm seawater density = 1.015 (1.015 g/ cm3)
Density of seawater mainly determined by the temperature and salinity
Properties built into water mass at the surface, and
Property = 0
These are useful for untangling mixtures of water masses.
Two water masses, "X" and "Y" constitute water mass
JQ = JxFx + JyFy
F= fraction of each water mass
J = property
The number of water types identifiable in a mixture is equal to:
[number of properties + 1]
because the extra equation is
Sum of F = 1
examples: Temperature, Salinity
- conservative, in that
Change in the Property
/ change in time = 0 However, Change in input with time is also
Most elements change there composition as they are removed from the surface ocean. There are several processes responsible for this:
Biological processes (O2 produced, nutrients consumed, such as C, NO3, PO4.)
Scavenging reactions - trace metals removed upon sinking particles.
Radioactive Decay - some elements
are naturally radioactive, and dissappear with a known half-life (eg. 14C
t1/2 = 5720 yrs)
When particles sink, they may
dissolve, and re-release nutrients and metals. So there is a general transfer
of material from the surface to the deep. As many of these particles are
of biological origin (plankton) this process is called the "BIOLOGICAL
The ultimate sink for many elements introduced into the ocean.
Sediments consists of several components
Many sediments are mixtures of these components.
These components occur in variable amounts, depending on :
iii) geologic setting of the
(1) Terrigenous - land derived
coarse grained nearshore
fine grained farther offshore
- wind (eolian) deposit
In the deep sea, some areas on the seafloor are composed largely of terrigenous material. When this is the dominant component, the sediment is called RED CLAY. This is largely transported by wind.
ICE RAFTED material comes off calving glaciers. This contributes to GLACIAL MARINE sediments.
composed of shell fragments of minute, 1 celled plankton.
The distribution of this sediment component is affected by:
i) Production of plankton in the surface water
ii) Dissolution of the shells
iii) Dilution with other components
The 2 main components of these sediments are
SILICA and CaCO3.
CaCO3 dissolution increase with depth. It is more soluble with increased pressure and lower temperature. Therefore, in the deepest parts of the ocean, CaCO3 is absent.
SiO2 - dissolves everywhere. It is found in sediments only under zones of very high surface production of these plankton: Diatoms and Radiolarians.
This is a slowly accumulating component
It dominates only where there are no other major sediment sources.
It is formed when dissolved constituents of seawater are removed:
a) by scavenging upon sinking particles
b) by precipitating in seafloor minerals
- Mn nodules: accumulate only where sediment settles very slowly. Thus found in RED CLAY areas. They contain Cu, Ni, Co.
(4) METALLIFEROUS (HYDROTHERMAL)
The hydrothermal effluent from mid-ocean ridges form a distinctive type of sediment:
It is composed of 2 parts
1) The venting high temperature solutions have high concentrations of Fe and Mn, as well as some other metals such as Cu and Zn, which precipitate into the sediment.
2) In addition, precipitating Fe scavenges some dissolved seawater elements (P, V, As). This is similar to hydrogenous deposition.
In vent fluids, iron is dissolved in the Fe+2 state. When it hits the oxygenated bottom water,
Sedimentary Processes combine with Plate Motion
to yield the seafloor sedimentary
FACTORS CONTROLLING SEDIMENT DISTRIBUTION-----SUMMARY
I. Rain Rate and Preservation Rate
b) Terrigenous (Detrital)
c) Hydrogenous (Authigenic)
II. Time Transgressive Changes
Plate Motions a) Vertical
III. Synchronous Changes
a) Climatic events
b) Volcanic events
FACTORS INFLUENCING NUTRIENT GRADIENTS
IN THE DEEP SEA
Present mode of deep ocean ventilation, coupled with photosynthesis and respiration has a strong impact on nutrients and nutrient-related proprty distributions.
From the Atlantic to the
nitrate 14C/12C radiodecay, respiration
This pattern is imprinted upon deep-sea sediments:
1) The depth of the lysocline decreases along the deep water flow
CO2 + CO3-- + H2O yields 2HCO3--
yields Ca + CO3--
2) The abundances of benthic forams adopted to the low oxygen water increases along the path of the deep water flow.