The Ocean as a stratified body of water

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Emery Stevenson
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The Ocean as a stratified body of water Density = f (salt content, T, pressure) Γ 35,25,1 = 1.

1 The Ocean as a stratified body of water Density = f (salt content, T, pressure) Γ 35,25,1 = g cm -3 (= 1023 kg m -3 ) σ S,t,P = (Γ S,t,P -1) x 1000 σ 35,25,1 = g cm -3 (= kg m -3 )

2 The Ocean as a stratified body of water No means of measuring density in-situ with precision have yet been devised, the density must be computed from the coefficient of thermal expansion, salinity contraction, and isothermal compressibility for a given set of S, T and P (depth). On the other hand, what we really want to know is For simplicity, it is often assumed that the buoyancy of a parcel of seawater is unchanged relative to its surroundings when the hydrostatic pressure on both the parcel of water and its surroundings is changed by the same amount. Under the assumption that the density of seawater is determined by its salinity and temperature alone, the density of seawater is often expressed as: σ S,t,1 = σ t (sigma-tee) but in-situ temperature is a not a conservative property.

3 The Ocean as a stratified body of water Potential temperature: θ P=1 θ P=1 = T P δt T p = temperature at hydrostatic pressure δt = adiabatic temperature change due to decompression Lord Kelvin (~1850) δt = T e g δh/(f C p ) T = absolute temperature (K) e = coefficient of thermal expansion = f(s, T) g = acceleration due to gravity (9.8 m 2 sec -1 ) δh = vertical displacement (m) F = mechanical equivalent of heat C p = specific heat capacity of seawater at constant pressure = f(s, T) δt = ~0.132 C/1000 m = ~0.132 C/100 atm restores the stability of the water column.

4 The Ocean as a stratified body of water

5 The Ocean as a stratified body of water σ S,t,P = (Γ S,t,P -1) x 1000 σ S,t,1 = σ t (sigma-tee) Density = f (salt content, T, pressure) σ S,θ,1 = σ θ (sigma-theta) σ S,θ,P = σ 4 (sigma-four) Stable?

6 The Ocean as a stratified body of water (growth and decay of seasonal thermocline)

separated into two reservoirs, since they are

7 The Ocean as a stratified body of water (permanent thermocline) The existence of the permanent pycnocline is the reason why, for modelling purposes, the ocean is often separated into two reservoirs, since they are physically separated and limited exchange occurs between them.

8 01_09.jpg BIG BANG first proposed by G. Lemaitre (Ph.D. MIT) in 1927

10 27 K 10 10 K 10 10 15 K 9 K Protons and neutrons bind

9 10 27 K K K 9 K Protons and neutrons bind 3000K 18K 01_08c.jpg Sec. 3 min The expanding Universe

10 Nucleosynthesis neutron electron + proton = é + H + t 1/2 = 12 minutes H + + neutron Deuterium (D) 2 H + + neutrons Helium (He) 3 H + + neutrons Lithium (Li) From: W.S. Broecker (1985) How to build a habitable planet

11 Nebular clouds

12 Evolution of a star system

13 New 01_View.jpg born stars

14 Nucleosynthesis in burning stars Red Giants From: W.S. Broecker (1985) How to build a habitable planet

If larger, after collapsing, it will explode to form a supernova and leave behind a neutron star or even a

15 Death of a Star If a star is ~ 8 times mass of our sun, after evolving into a red giant it will collapse into a white dwarf. If larger, after collapsing, it will explode to form a supernova and leave behind a neutron star or even a black hole. Eta Carinae First observed in 2003 at 2 billion light years Crab Nebula First observed AD 1066 At 63,000 light years. Photographed as the explosion occurred a supernova caught in the act.

Evolution of the solar system Forming the solar system, according to the nebula hypothesis: A second- or thirdgeneration nebula forms from hydrogen and helium left over from the Big Bang, as well as

16 Evolution of the solar system Forming the solar system, according to the nebula hypothesis: A second- or thirdgeneration nebula forms from hydrogen and helium left over from the Big Bang, as well as from heavier elements that were produced by fusion reactions in stars or during the explosion of stars. The nebula condenses into a swirling disc, with a central ball surrounded by rings. 99.9% (99% H 2 and He) of the mass of the nebula was drawn into the central body the Sun.

18 The ball at the center grows dense and hot enough for fusion to begin (> 50 x10 6 o C). It becomes the Sun. Dust condenses in the rings. Evolution of the solar system Evolution of the solar system The nature of the condensed matter depends on temperature. At the distance of Earth from the Sun, temperature ~1500 o C. Iron (melting point 1538 o C) and olivine ((Fe,Mg) 2 SiO 4 ; melting point o C) condense. At the distance of Jupiter, water ice (melting point 0 o C) and ammonia (melting point -78 o C) condense, and at the distance of Neptune, methane (melting point -182 o C) condenses. Dust particles collide and stick together, forming planetesimals.

19 Evolution of the planetary system Planetesimals grow by continuous collisions. Gradually a protoplanet develops. Gravity reshapes the protoplanets into a sphere.

20 The Solar System Sun Mass =1.99 x kg Density = 1.41 g/cc Terrestrial planets Outer planets

Earth differentiation Early Earth heats up due to radioactive decay, compression, and

Over time the temperature of the planet interior rises beyond the melting point of iron.

Lighter materials, such as silicate minerals, migrate upwards in exchange.

21 Earth differentiation Early Earth heats up due to radioactive decay, compression, and impacts. Over time the temperature of the planet interior rises beyond the melting point of iron. The iron "drops" follow gravity and accumulate towards the core. Lighter materials, such as silicate minerals, migrate upwards in exchange. These silicate-rich materials may well have risen to the surface in molten form, giving rise to an initial magma ocean. From:

22 Formation of continents and oceans Soon after Earth formed (~4.4by), a small planet (Mars-sized) collided with it, blasting debris that formed a ring around the Earth A magma ocean!

continental subduction zones, volcanic island arcs and large shield volcanoes formed over hot

23 Formation of continents 4.4by zircon, found in Australian sandstone bed. According to one model, relatively buoyant (felsic and intermediate) rocks formed both at continental subduction zones, volcanic island arcs and large shield volcanoes formed over hot spots. Collisions sutured volcanic arcs and hot-spot volcanoes together, creating progressively larger blocks of protocontinents.

24 Classification of Igneous Rocks or felsic Viscosity Density Silica content

Partial melting Under the temperature and pressure conditions that occur in the Earth, only 2 to 30% of the rock melt to produce a magma partial melting

25 Partial melting Under the temperature and pressure conditions that occur in the Earth, only 2 to 30% of the rock melt to produce a magma partial melting Since felsic minerals melt at lower temperatures, magma formed from partial melting tend to be more felsic than the original rock from which they are derived.

26 The growth history of the continents

27 Evolution of the atmosphere During the hot, early stages of the Hadean Eon, rapid outgassing of the Earth s mantle took place. A magma ocean!

28 Evolution of the atmosphere H 2 O, CO 2,HCl, H 2 S, CH 4, NH 3, H 2 + traces of other gases Proterozoic Banded iron formation

29 The primordial atmosphere The primordial ocean (3.8 b.y.?)

30 Evolution of seawater composition Reaction of volatiles with fresh basalts (unaltered volcanic rocks) and the weathering and formation of subsequent sedimentary rocks. From: Lafon and Mackenzie (1974) Early evolution of the oceans. SEPM Special Publication No. 20

31 Evolution of seawater composition From: Lafon and Mackenzie (1974) Early evolution of the oceans. SEPM Special Publication No. 20

32 Evolution of seawater composition From: Lafon and Mackenzie (1974) Early evolution of the oceans. SEPM Special Publication No. 20

33 Evolution of seawater composition From: Lafon and Mackenzie (1974) Early evolution of the oceans. SEPM Special Publication No. 20

quantitatively: K-spar (KAlSi 3 O 8 ) illite kaolinite 5 KAlSi 3 O 8 + 4 H 2 CO 3 + 16 H 2 O KAl 4

34 Evolution of seawater composition In 1933, Victor M. Goldschmidt ( ) proposed: Igneous rock + volatiles seawater + sediments More quantitatively: K-spar (KAlSi 3 O 8 ) illite kaolinite 5 KAlSi 3 O H 2 CO H 2 O KAl 4 (OH) 4 AlSi 7 O H 4 SiO HCO K + 2 KAl 4 (OH) 4 AlSi 7 O H 2 CO H 2 O 5 Al 2 (OH) 4 Si 2 O H 4 SiO HCO K +

35 Evaporite deposits

The History of the Earth

The History of the Earth We have talked about how the universe and sun formed, but what about the planets and moons? Review: Origin of the Universe The universe began about 13.7 billion years ago The Big