The Hydrosphere

Question 1

What is the hydrosphere?

Answer 1

A collective name for forms of water on Earth:

Oceans, lakes, streams, snowpack, glaciers, polar ice caps, groundwater

70% of th Earth is covered by water

Question 2

What are the main properties of water?

Answer 2

H₂O is the only first row hydride that it a liquid

O is small, electronegative and has lone pairs

H₂O is extremely polar

H₂O dissolves polar and ionic material:

solvates ions and stabalises hem - both cations and anions:

Ammonium nitrates and carbonates

Question 3

What arethe thermal properties of water?

Answer 3

Oceans act as heat transfer - Gulf stream provides mild winters and summers - maritine climate

Water used tocool and heat:

cooling towers

As a heat source water won’t cause fire - evaporates away

Steam diven turbines

Question 4

What is the specific heat capacity of water?

Answer 4

Exceptionally high - 4.19 kJ kg^-1 K^-1

Slows down tempersture changes

Heat transported around the globe by ocean currents

Influences climate

Question 5

What is latent heat of fusion of water?

Answer 5

Exceedingly high - 333 kJ kg^-1

Stops the water temperature from changing rapidly when it is around 0°C due to the additional energy required to freeze or thaw the water

Question 6

What is heat of evaporation of water?

Answer 6

Highest of all substances - 2260 kJ kg^-1

Cuts down water and heat loss to the atmosphere

Question 7

What is the density of water?

Answer 7

103 kg m^-3

Increases with salinity

Ice floats, insulating the water below from cold atmosphere

Vertical circulation restricted in stratified bodies of water

Question 8

What is the surface tension of water?

Answer 8

Highest of all liquids - 73 nN m^-1

Controls the shape of raindrops, sea spray and capillary action between vapour and water (dry top soil is rehydrated by capillary action)

Question 9

What is the polarity/dissolving power of water?

Answer 9

Highest dielectric constant of any common liquid

Dissolving power exceptionally good - high polarity solvates and stabalises both cations and anions

Dissolves nutrients amd transports them to plants

Question 10

What is the transparency of water?

Answer 10

Relatively large

Absorbs/scatters UV and absorbs IR, but transmits the visible radiation required for photosynthesis

Question 11

What is the hydroglogical cycle driven by and what are the 4 types of water?

Answer 11

Driven by the sun [ energy required to evaporate water

$ types:

metoric: river, lakes, ice caps - fresh water from atmospheric condensation

Saline: oceans

Magmatic water trapped in earth as steam

Formation: water tied up in sediment

MAgmatic and Formation mostly removed from hydrological cycle

Question 12

How do we calculate the mean residence time in a resevoir?

Answer 12

Mean residence time = Amount in Resevoir / input or output

τ = A/δA / δt

A = amount in resevoir

Question 13

What is precipitation?

Answer 13

There are 14x10¹² tonnes of water in the atmosphere from evaporation of water, soil and transpiration

Droplets kept in suspension by rising air - coalensence = bigger droplets - gravitational settling ≈ 1mm

As warm, moist air is cooled, the amount if water ut can hold decreases - Cooling air beyond the point where relative humidity reaches 100% forces excess moisture to condense forming clouds

Further coolingh and condensation results in precipitation

Question 14

Which side of a mountain is most likely to get more rain?

Answer 14

The windward side

Air cools as it rises over mountain range - high precipitation on windward slopes

Descending air warms, evaporates water from soil - desert on leeward side

Question 15

What are Hadley cells?

Answer 15

Method by which there is circulation of the atmosphere

Transports heat from low to high latitudes

Moist air from equator rises dropping its moisture

The now dry air descends at 30° North and South producing deserts

Question 16

What is evaporation and transpiration?

Answer 16

Evap: transfer of water fromocean or land to the atmosphere - increases with temperature and decreases with humidity

Trans: water drawn from soil by plant roots evaporates through pores in leaf system - influenced by type of plant

Question 17

What water is accessible to humans?

Answer 17

Transpiration is essential to plants and therefore us - unavailable

Water is unavailable in the atmosphere

Actual rainfall - evapotranspiration = residual rainfall

Residual rainfall is the water that is accessible

This can vary substantially ≈ 20% of rainfall

Overcome through resevoirs - storing in times of plenty and water transport - pumping from areas of plenty

Question 18

What is groundwater?

Answer 18

Water found underground - 250 x moregroundwater than lakes - most too deep to tap

Some rocks store water

Rate of infiltration depends on permeability and porosity

Question 19

What are the ground water zones?

Answer 19

Water table is variable depending on the amount of water infiltrated

Question 20

What is permeability?

Answer 20

Hydraulic conductivity - rate at which water passes through geological rocks / sediment

Permeable - water flow > 1 m / day

Impermeable - >10^-8 m / day

Question 21

What is porosity?

Answer 21

What a rock can store

The proportion of the volume of the rock that consists of pores

Grain size / shape, degree of sorting, cementing of grains, amount of fracturing

rounded grains uniform size good sorting = high porosity

Angular grains, many grain sizes, poor sorting = very low porosity

Question 22

How do springs form?

Answer 22

Hill capped by a permeable rock underlain by impermeable rock

Water diverted laterally by the impermeable rock: spings results where the boundary between the permeable and impermeable rock intersects the ground surface

Question 23

Where does freshwater come from?

Answer 23

Comes from rainwater

Rainwater is dilute ocean water (spray and evaporation) but has different composition

Rain equilbrates with the atmosphere - contains O₂, N₂ and Ar

$th commonest gas is CO₂ - not inert, forms carbonic acid

Question 24

What are the most pure kinds of water?

Answer 24

Rain water is the most pure - 99.995% water

Seawater - 96.5%

Heavily polluted river - 99.3% water

Pure water should by pH 7.0

Rainwater is generally pH 5.0 - 5.5 from dissolved CO₂

Question 25

What are the major ions in river water?

Answer 25

Cations: Mg²⁺, Ca²⁺ , H⁺, Na⁺, K⁺, Fe³⁺

Anions: phosphates, nitrates, carbonates

Rivers are pH 7.5-8 due to calcium carbonate

H₂O + CO₃²⁺ <–> OH^- + HCO₃^-

Question 26

Which gases are commonly dissolved in water?

Answer 26

N₂ = 78.08%

O₂: 20.95%

Ar: 0.93%

All other gases: 0.04% - CO₂, N₂O, CH₄, O₃, H_2, He, Ne, Kr,Xe

Question 27

How are gases dissolved in water?

Answer 27

Gas molecules are continually transfering between the water surface and the atmosphere

For a gas at equilibrium between the atmosphere and in dissolved form in water: A_(g) <—-> A_(aq)

The concentration of a gas in water is related to the artial pressure of the gasin the atmosphere, P_A, by Henry’s law:

[A] = K_AP_A K_A = Henry’s constant

Question 28

What ae the four reactions to dissolve CO₂ in water?

Answer 28

Question 29

How do limestone caves form?

Answer 29

Solutional formation: limestone dissolves in water which contains H₂CO₃

Dissolution occurs along joints and faults and planes

Portions of a solutional cave that are below the water table will be flooded

Question 30

What affects the concentration of oxygen in rainwater?

Answer 30

Low temperature = more oxygen

High pressure = more oxgen

Dissolved salt = greater ionic strength = less oxygen

Turbulence - increases surface area with which can come to equilibrium, draws part of the atmosphere down into the water body

Contrast river with pond

Question 31

How is oxygen removed from freshwater bodies?

Answer 31

Animals require oxygen for metabolic processes?

Oxudative degredation of organic matter

Question 32

Describe aerobic respiration

Answer 32

Uses dissolved oxygen

(CH₂O) + O₂ —> CO₂ + H₂O + Energy

Other elements:

N —> NO₃^- - good in moderation

S —> SO₄^2-

P —> PO₄^3- - good in moderation

Question 33

Describe anaerobic respiration?

Answer 33

Doesn’t use oxidatio as energy source - use reduction

Stringest in O₂ defincient water

C —> CH₄

N —> NH₃

S —> H₂S

P —> PH₃

These are toxic and kill off organisms

Question 34

What is eutrophication?

Answer 34

If water is rich in nitrates and phosphates = rapid algal growth = phytoplankton bloom

During the day, high [O₂], water is saturated

Bloom reduces light penetration, inhibiting photosynthesis + groqwth pf rooted vegetation

Shirt lived - [O₂] decreases with decomposition

Anaerobic decomposition (odourous breakdown of products

Oxygen introduced again through turbulance, surface area and photosynthesis

Question 35

How does stratification of lakes change in March and July?

Answer 35

March - even temp ≈ 4.5°C

July - stratified - no mixing

• top layer (epilimnion) = hot ca 18-19°C

middle layer (thermocline) = warm

Bottom layer (hypolimnion) = cold ca 6-7°C - removed from the atmosphere, doesn’t equilibrate efficiently, aerobic + anearobic decomp form nutrients in cold area

Question 36

How does stratifocation of lakes change in november and january?

Answer 36

November - even temperature - 4.5°C - mixing = overturn = mixes nutrients to top layers

Jan - Epilimnion = ca. 0-1°C

Hypolimnion ≈ 5 m down ≈ 3-4°C

Ice provides thermal blanket

Question 37

What are the main characteristics of lakes?

Answer 37

Almost no current - pollutants persist

Organic broken down by oxidation

If all oxygen used up = reduction used to break down material - anearobic / anoxic water

Seasonal overturns

Question 38

What are global biogeochemical cycles?

Answer 38

Interactions between the geosphere, atmosphere and hydrosphere

The biosphere is intrinsically linked with this system while the cycles of matter are completed by tge alternatln snd / or uplift of sedimentary rocks

Question 39

What are the characteristics of the mixed ocean layer?

Answer 39

Surface ocean

uniform temperature and salinity

Strongly influenced by the atmosphere

Question 40

What are the characteristics of the thermocline in the ocean?

Answer 40

50-1000m depth

Preominent transition feature conditioning many physical, chemical, biological processes occurring in the oceanic upper layers

If the vertcle constraints of salinity are small also defines the pycnocline (pycno = density) i.e. warmer less dense surface waters overlying colder more dense deep waters

Question 41

What are the characteristics of deep water in the ocean?

Answer 41

Deep ocean water

interior isolated from the atmosphere

Question 42

What forces shallow and deep open dynamics

Answer 42

Shallow ocean dynamics forced by winds

Deep ocean dynamics forced by density variations

Question 43

What is the Coriolis effect?

Answer 43

Essential part of dynamics

In the northern hemisphere:

Wind generates a clockwise surface circulation - drives water downwards

Wind generates anticlockwise surface circulation - dirves water upwards

Resulting dynamic pressure variations can be read by satellites that measure sea-surface height relative to the geoid

Question 44

What is the general circulation of atmosphere?

Answer 44

GEnerally temperature is high at the equator and low at the poles

The inter-Tropical convergence zone is the pioint at which the trade winds converge, rainfall converges - This means freshwater is dropped in the Pacific not the Atlantic

This is shown in the salinity of the oceans - Atlantic high salinity whereas the tropics are fresher

Higher salinity makes the atlantic more dense

Question 45

What is Ekman pumping?

Answer 45

Upper 1mm of water is blown in the same direction of wind

Just below the surface the ocean deflects to the right and deflects more and more with depth eventually flowing in the opposite direction

Average flow of water due to wind = 90° to wind

This is to the right in the northern hemisphere and to the left in the southern hemsphere

This is called Ekman pumping

Question 46

How does wind affect surface ocean circulation?

Answer 46

Wind driven currents encircle large spinning gyres in subtropical oceans

Subtropical gyres - clockwise in N h/s, anticlockwise in S h/s

Dome of water in subtropics

Question 47

What is upwelling?

Answer 47

When the wind blows parallel to the coat the ocean surface layer is blown 90° to the direction of the wind (offshore) - Ekman transport

This means warmer waters are driven offshore and cooler waters upwell from below

At the equator trade winds cause warmer water to be driven towards the poles and cooler water upwells from below

This bring nutrients from below and so there is often lots of bio activity

Question 48

Describe the El Nino southern oscillation

Answer 48

Normal: surface winds blow stroingly from the east - Drives upwelling off south america - tilts thermocline towards the west - piles warmer water in a pool near indonesia with strong convection and rainfall above it - La Nina is extreme of this

Weak trade winds = less tilting of the thermocline - reversing upwelling/downwelling patterns - displacement of warm water pool to central Pacific = drought in Asia, torential rans in America and failure of Peruvoan fisheries

Question 49

What are major biological reactions?

Answer 49

Organic matter can be represented as CH₂O for fixed carbon and NH₃ for fixed nitrogen

CO_2(g) + H₂O <—> CH₂O_(s) + O_2(g)

NO₃^-_(aq) + H₂O + H⁺_(aq) <—> NH_3(s) + 2O_2(g)

These reaction lie to the right in photosynthesis and to the left in respiration

Question 50

What are the Redfield ratios?

Answer 50

Oceanic organic matter contains the elements C, N and P in nearly constant ratios - Redfield ratios

C : 106 N : 16 P: 1

Seawater contains N and P in exactly the same ratio

This imples: All N and P in shallow ocean comes from remineralisation of organic matter at depth so it is supplieed dto the cycle with Redfield ratio

Life has evolved to optimally utilise available nutrients leaving neither in significant excess

Question 51

What does the slight excess of PO₄ in the ocean tell us?

Answer 51

Excess comes from weathering input

Implies NO₃ is limitting but N₂ can befixed to NO₃ if Fe is present available - hence ideas about Fefertilisation of ocean and CO₂ sequestration

[PO₄] indicates where upwelling is providing nutrients and hence where primary productivity occurs in the ocean

These locations are where diatoms are makibg SiO₂shells that rain out to form siliceous sediments

Question 52

How is salinity measured?

Answer 52

Previously defined as Total amount of dissolved material in gams in one kg of seawater - this is a simple concept but impossible to meaure

Currently salinity is based on conductivity - dimentionless

easy and precise measurements found with conductib=vity meters

Question 53

How do we measure salinity and temperature?

Answer 53

We use a CTD - conductivity, temperature and depth

Actually measures conductivty, temperature and pressure

Depth is calculated from the pressure and density

The instrument can be deployed by itself on a wire or attached to a larger frame equipped with water sampling bottles

Question 54

How does temperature, salinity and pressure affect density?

Answer 54

Density is a function of temperature, salinity and pressure

Seawater density (ρ) quated in kg m^-3 - usually close to 1000

Often quoted as relative density (σ): σ = ρ -1000

Cold water is more dense than warm water - temp down, pressure up, σ up

Salt water is more dense than fresh water - salinity up, pressure up, σ up

Question 55

What is the thermohaline cycle?

Answer 55

traditionally thught of as the global deep water circulation of the oceans driven by differences in ocean density which is itself a function of both temperature and salinity

The overturning or internal mixing time

Question 56

What are the steps of the Gulf Stream?

Answer 56

Question 57

How can ocean bodies be identified?

Answer 57

By their temperature and salinity whih are properties or signatures

T and S a=properties are set at boundaries of ocean - exchange if heat and freshwater with atmosphere

In the ocean interior T and S are conservative propoerties of seawater - do not change unless mixed with waters of differing properties

As mixing is slow T and S can be used to trace movements of water masses - track deep ocean circulation

Question 58

Describe deep water circulation?

Answer 58

Very slow: driven by deep water formation and isopycnal flow

All southwards in the Atlantic Ocean, northwards in Indian and Pacific Oceans; steered western boundary of each ocean

Must be compensated by return flow in shallow ocean but this is small compared ti wind driven motions above thermocline

Question 59

what is the effect of the thermohaline circulation?

Answer 59

Transports large amounts of warm water into he North Atlantic and keeps Northern Europe warmer than it would otherwise be

Question 60

What was the Younger Dryas event?

Answer 60

Significant cooling in Northern hemisphere - shut down of the thermohaline circulation triggered by large melting of northern ice - introduce fresh water

Paleo-oceanographic evidence shows Younger dryas event was marked by a prolonged shut-down of the thermohaline circulation, which is likely to have triggered by the release of melt water

Question 61

What is the composition of sea water?

Answer 61

Particulates - > 0.2 μm :

sand, clay, detrital matter: excreta, molts, dead tissue, aggregates / marine snow - experience gravtational settling

Dissoled: gases: N_2, O₂, Ar, CO₂, N₂O, DMS, CH₂I₂

Major ions: Na⁺, Cl^-, Mg²⁺, SO₄^2-, Ca²⁺, HCO₃^-, Br^-

Minor ions: NO₃^-, NH₄⁺, PO₄^3-

Trace metals: Fe, Zn, Co, Cd, Mn, Pb

Organic compounds: amino acids, humic acids

Not impacted by gravity

Major constituents - major ionic - contribte to salinity significantly to salinity and are conservative or near conservative

Question 62

What determines how a constituentof the ocean behaves?

Answer 62

Depends on both chemical properties and physical properties that transport water and particles and lead to transfer of material from one part of the system to another

Question 63

How does diffusion affect transport?

Answer 63

Diffusion: Movement of constituents within the medium - In the presence of a concentration gradient net movement from high to low concentration

In non turbulnt medium diffusion coefficient ≈ 10^-5 - 10^-6 cm²s^-1

Turbulent diffusion (eddy diffusion) generally dominant - Oceanic vertical eddy diffusion coefficients typically 10⁵ times larger than molecular diffusion

Question 64

How does advection affect transport?

Answer 64

Flow of water (wind driven and density driven circulation of oceans)

In advection a dissolved constituent undergoes no change in concentration

Question 65

Why is the sea salty?

Answer 65

Oceans formed relatively early in Earth’s history - 4400 Ma

Water transport mainly riverine transfers material from continuents to oceans

Thousands of millions pf years of erosion transporting salts to the sea

Oceans are not saturated - (must be transport out)

Seawater doesn’t look like river water - transport must ne different for different continuents

Question 66

What is an MORT?

Answer 66

Mean ocean residence time

= amount in ocean / input or output

τ = A / δA/δt A = amount in resevoir

The MORT of a dissolved constituent is usually calculated with respect to the riverine input because this is usually the dominant input and it is the best qualified of all inputs or outputs from the ocean

We assume a well mixed ocean

Question 67

How do we use steady state assumption?

Answer 67

The concentration of a constituent is assumed to be constant over time

Evidence from the sedimentary record and evaporite deposits tell us that the broad characteristics of the ocean have been in steady state over the last 600 million years

Inputs amnd outputs may have been out of balance over certain periods but on long geological timescles they are balanced

Question 68

What is Geochemical reactivity?

Answer 68

Tells us the tendency of that cinstituet to change phase - how likely a dissolved constituent will change to a solid

These can be biologically mediated - e.g. incorporation of calcium carbonate into shells

Question 69

What are conservative elements?

Answer 69

Elements with low geochemical reactivity - B, Br, Cl, Cs, F, K, Li, Mg, Mo, Na, Rb, S, Tl, U

MORT_A > MORT_water (>10⁶ years)

Accumilate in ocean = conservative behaviour

MORT >> mixing time of the ocean = well mixed

Simple ions, inert gases - not biogeochemically active

Question 70

What are recycled elements?

Answer 70

e.g. C, Ca, N, P, Si, Zn

Biological uptake removes nutrient elements from surface seawater

Detrital material sinks, decomposing and releasing nutrients

Biological cycling involves transformations

Typically MORT_A ≈ 10⁴ - 10⁵ yr

Question 71

What are Scavenged elements?

Answer 71

e.g. Al, Bi, Ce, Co, Hg, Mn, Pb, Sn, Te, Th

If MORT < MORT_water (MORT ≤ 10³ years)

Depleted in oceans - particle reactive (adsorption, precipitation, biological uptake)

River inputs are lagely removed by estuarine processes - Atmosphere inputs to open ocean

A has been depleted in the oceans and has high geochemical recativity

Question 72

Why is the concentration of aluminium so much higher in the atlantic than the pacific?

Answer 72

Riverine inout is higher into the atlntic than the pacific

Deposits of sand from the sahara into the atlantic

Question 73

Why is the concentration of Zn and Silica higher in the Pacific than the atlantic?

Answer 73

Upwelling in the thermohaline cycle happens faster in the atlantic

In the Pacific nutrients have more time to dissolve

Question 74

What affects the solubility of gases in the oceans?

Answer 74

Temperature - colder water greater solubility

Salinity: higher salinity lower solubility

Other factors: atmospheric pressure, humidity, surface consition (wave action/bubblr bursting)

Solubility becomes non-linear as T and S increase

Accurate empirical equations have been derived to predict gas solubility as a functionof T and S

Question 75

What are conservative gases?

Answer 75

No significant changes in concentration occur other than by mixing with other water bodies with a different gas concentration - conservative behaviour

e.g. Ar, Xe, He

Excellent tracers

Question 76

What are non conservatuve gases?

Answer 76

If significant changes in concentration occur due to reactivity the gas shows non-conservatiuve behaviour

O₂ - used biologically

CO₂ - reacts with water

Question 77

How does the concentration of oxygen change in the oceans?

Answer 77

O₂ usually supersaturated in surface waters due to:

phytoplankton (photosynthesis)

Wzaveaction + bubble bursting

Question 78

How does oxygen concentration compare to nutrient concentration?

Answer 78

O₂ profiles generally mirroe those for nutrients

High in surface waters screasing t a minimum at 1000m as O₂ is consumed during recycling

Oxygen increases with depth below the oxygen minimum because it is supplied by relatuiveky young ventilated water

When productivity is very high or supply is cut off, deep waters may be cme anoxic

e.g. Black sea, Gulf of Mexico

Question 79

Why is CO₂ important?

Answer 79

Important greenhouse gas - control planetary climate

CO₂ is the raw material used to build organic matter

CO₂ controls pH of the oceans

Distribution of CO₂ species affects calcification and preservation of CaCO₃ on the sea floor

Question 80

What is the equation for total CO₂ in the oceans?

Answer 80

TCO₂ = CO₂* + HCO₃^- + CO₃^2-

Question 81

What are the equations and equilibrium constants for the dissolutions and dissociations of CO₂

Answer 81

Question 82

Why is the sea not acidic?

Answer 82

The sea contains anions of weak acids delivered by weathering processes

These associate with H+ ions and buffer seawater against incerase in pH

On short term the sea is buffered by its alkalinity

On long term the sea is buffered by balance between carbonate precipitation and amd dissolutions

Question 83

What is the equation for carbionate alkilinity?

Answer 83

Carbonate alkalinity (CA): total alkalinity can be converted to CA

CA = [HCO₃^-] + [2CO₃^2-]

Question 84

What is the dominant for of CO₂ at pH 8 (pH of seawater) and what affect does this have on the expression for TCO₂?

Answer 84

Speciation curve shows dominant species is HCO₃^-

TCO₂ = CO_2(aq) + H₂CO₃ + HCO₃^- + CO₃^2- = CO₂* + HCO₃^- + CO₃^2-

TCO₂ ≈ HCO₃^- + CO₃^2-

As pCO₂ increases: TCO₂ up, pH down, CO₂* up, HCO₃^- up, CO₃^2- down

Question 85

What affects how much atmospheric CO₂ is drawn into the ocean?

Answer 85

The solubility pump - combined influence of physical and chemical processes on ocean concentrations of dissolved CO₂ and air sea exchange

The biological pump - transport of carbon from the surface to the deep ocean by biological processes

Both pumps act to store carbon in the deep ocean

Question 86

Where and how is TCO₂ and CA consumed and released?

Answer 86

Surface ocean - photosynthesis and carbonate precipitation consume TCO₂ and CA

Deep ocean - recycling (respiration of C_organd dissoluton of CaCO₃) release CO₂ and CA

Question 87

What controlls the distribution of carbonate sediments on the ocean floor?

Answer 87

Source strength (production) and Degree of preservation (extent if dissolution)

Resuklts in sediment distribution which shows strong relationship with depth

Abyssal clays found in deep ocean basins

Calcaerous oozes abundant on ocean ridges and rises

Siliceous oozes aew found beneath areas of high biologic productivity

Question 88

What is K_SP and Ω

Answer 88

K_SP is the stochiometric solubility product for the equilibrium reaction: CaCO_3(s) ⇔ Ca²⁺ + CO₃^2-

K_SP = [Ca²⁺][CO₃^2-]

The precipitation and dissolution of calcium carbonate is controlled by the saturation state of seawater with repect to CaCO₃ (Ω)

Ω = [Ca²⁺]_SW[CO₃^2-]_SW / K_SP [Ca²⁺]_SW and[CO₃^2-]_SW are actual concs of calcium and carbonate ions in seawater

If Ω= 1 SW at equilibrim is saturated wrt CaCO₃

Question 89

What determines the degree of saturation of CaCO₃?

Answer 89

Determined by [CO₃^2-]

The saturation of carbonate ion concentration increases with depth because CaCO₃ is more soluble at T decreases and pressure increases

If [CO₃^2-] ions lie to the right of the saturation curve then CaCO₃ will not dissolve

The saturation curve for araonite lies to the right of that of calcite as it is less stable and dissolves more readily

Question 90

What is the CaCO₃ satyration horizon?

Answer 90

The depth at which Ω = 1

The point at which dissolution of CaCO₃ in sediment becomes significant is called the lysoclne (can be significantky below the horizon) - slow dissolution kinetics

The point at which CaCO₃ becomes a minor sediment component is called the carbonate compensation depth *(defined as where carbonate skeletal material falls below 20% of the total sediment)

Question 91

How does TCO₂ affect CaCO₃

Answer 91

Increased TCO₂:

Shift the carbomnate equilibria in favour of HCO₃^- and lower pH

Overall effect is to lower [CO₃^2-] and therefore the CaCO₃ compensagion depth and the hysocline will shoal

The high-CO₂ low pH Ocean: ocean pH is predicted to decrease by 0.3 units by 2100 - massive implications for ocean biology