The Hydrosphere Flashcards
What is the hydrosphere?
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
What are the main properties of water?
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
What arethe thermal properties of water?
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
What is the specific heat capacity of water?
Exceptionally high - 4.19 kJ kg-1 K-1
Slows down tempersture changes
Heat transported around the globe by ocean currents
Influences climate
What is latent heat of fusion of water?
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
What is heat of evaporation of water?
Highest of all substances - 2260 kJ kg-1
Cuts down water and heat loss to the atmosphere
What is the density of water?
103 kg m-3
Increases with salinity
Ice floats, insulating the water below from cold atmosphere
Vertical circulation restricted in stratified bodies of water
What is the surface tension of water?
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)
What is the polarity/dissolving power of water?
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
What is the transparency of water?
Relatively large
Absorbs/scatters UV and absorbs IR, but transmits the visible radiation required for photosynthesis
What is the hydroglogical cycle driven by and what are the 4 types of water?
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
How do we calculate the mean residence time in a resevoir?
Mean residence time = Amount in Resevoir / input or output
τ = A/δA / δt
A = amount in resevoir
What is precipitation?
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
Which side of a mountain is most likely to get more rain?
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
What are Hadley cells?
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
What is evaporation and transpiration?
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
What water is accessible to humans?
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
What is groundwater?
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
What are the ground water zones?
Water table is variable depending on the amount of water infiltrated
What is permeability?
Hydraulic conductivity - rate at which water passes through geological rocks / sediment
Permeable - water flow > 1 m / day
Impermeable - >10-8 m / day
What is porosity?
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
How do springs form?
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
Where does freshwater come from?
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
What are the most pure kinds of water?
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
What are the major ions in river water?
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-
Which gases are commonly dissolved in water?
N2 = 78.08%
O2: 20.95%
Ar: 0.93%
All other gases: 0.04% - CO2, N2O, CH4, O3, H2, He, Ne, Kr,Xe
How are gases dissolved in water?
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, PA, by Henry’s law:
[A] = KAPA KA = Henry’s constant
What ae the four reactions to dissolve CO2 in water?
How do limestone caves form?
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
What affects the concentration of oxygen in rainwater?
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
How is oxygen removed from freshwater bodies?
Animals require oxygen for metabolic processes?
Oxudative degredation of organic matter
Describe aerobic respiration
Uses dissolved oxygen
(CH2O) + O2 —> CO2 + H2O + Energy
Other elements:
N —> NO3- - good in moderation
S —> SO42-
P —> PO43- - good in moderation
Describe anaerobic respiration?
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
What is eutrophication?
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
How does stratification of lakes change in March and July?
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
How does stratifocation of lakes change in november and january?
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
What are the main characteristics of lakes?
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
What are global biogeochemical cycles?
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
What are the characteristics of the mixed ocean layer?
Surface ocean
uniform temperature and salinity
Strongly influenced by the atmosphere
What are the characteristics of the thermocline in the ocean?
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
What are the characteristics of deep water in the ocean?
Deep ocean water
interior isolated from the atmosphere
What forces shallow and deep open dynamics
Shallow ocean dynamics forced by winds
Deep ocean dynamics forced by density variations
What is the Coriolis effect?
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
What is the general circulation of atmosphere?
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
What is Ekman pumping?
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
How does wind affect surface ocean circulation?
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
What is upwelling?
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
Describe the El Nino southern oscillation
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
What are major biological reactions?
Organic matter can be represented as CH2O for fixed carbon and NH3 for fixed nitrogen
CO2(g) + H2O <—> CH2O(s) + O2(g)
NO3-(aq) + H2O + H+(aq) <—> NH3(s) + 2O2(g)
These reaction lie to the right in photosynthesis and to the left in respiration
What are the Redfield ratios?
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
What does the slight excess of PO4 in the ocean tell us?
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
How is salinity measured?
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
How do we measure salinity and temperature?
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
How does temperature, salinity and pressure affect density?
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
What is the thermohaline cycle?
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
What are the steps of the Gulf Stream?
How can ocean bodies be identified?
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
Describe deep water circulation?
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
what is the effect of the thermohaline circulation?
Transports large amounts of warm water into he North Atlantic and keeps Northern Europe warmer than it would otherwise be
What was the Younger Dryas event?
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
What is the composition of sea water?
Particulates - > 0.2 μm :
sand, clay, detrital matter: excreta, molts, dead tissue, aggregates / marine snow - experience gravtational settling
Dissoled: gases: N2, O2, Ar, CO2, N2O, DMS, CH2I2
Major ions: Na+, Cl-, Mg2+, SO42-, Ca2+, HCO3-, Br-
Minor ions: NO3-, NH4+, PO43-
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
What determines how a constituentof the ocean behaves?
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
How does diffusion affect transport?
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
How does advection affect transport?
Flow of water (wind driven and density driven circulation of oceans)
In advection a dissolved constituent undergoes no change in concentration
Why is the sea salty?
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
What is an MORT?
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
How do we use steady state assumption?
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
What is Geochemical reactivity?
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
What are conservative elements?
Elements with low geochemical reactivity - B, Br, Cl, Cs, F, K, Li, Mg, Mo, Na, Rb, S, Tl, U
MORTA > MORTwater (>106 years)
Accumilate in ocean = conservative behaviour
MORT >> mixing time of the ocean = well mixed
Simple ions, inert gases - not biogeochemically active
What are recycled elements?
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 MORTA ≈ 104 - 105 yr
What are Scavenged elements?
e.g. Al, Bi, Ce, Co, Hg, Mn, Pb, Sn, Te, Th
If MORT < MORTwater (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
Why is the concentration of aluminium so much higher in the atlantic than the pacific?
Riverine inout is higher into the atlntic than the pacific
Deposits of sand from the sahara into the atlantic
Why is the concentration of Zn and Silica higher in the Pacific than the atlantic?
Upwelling in the thermohaline cycle happens faster in the atlantic
In the Pacific nutrients have more time to dissolve
What affects the solubility of gases in the oceans?
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
What are conservative gases?
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
What are non conservatuve gases?
If significant changes in concentration occur due to reactivity the gas shows non-conservatiuve behaviour
O2 - used biologically
CO2 - reacts with water
How does the concentration of oxygen change in the oceans?
O2 usually supersaturated in surface waters due to:
phytoplankton (photosynthesis)
Wzaveaction + bubble bursting
How does oxygen concentration compare to nutrient concentration?
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
Why is CO2 important?
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
What is the equation for total CO2 in the oceans?
TCO2 = CO2* + HCO3- + CO32-
What are the equations and equilibrium constants for the dissolutions and dissociations of CO2
Why is the sea not acidic?
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
What is the equation for carbionate alkilinity?
Carbonate alkalinity (CA): total alkalinity can be converted to CA
CA = [HCO3-] + [2CO32-]
What is the dominant for of CO2 at pH 8 (pH of seawater) and what affect does this have on the expression for TCO2?
Speciation curve shows dominant species is HCO3-
TCO2 = CO2(aq) + H2CO3 + HCO3- + CO32- = CO2* + HCO3- + CO32-
TCO2 ≈ HCO3- + CO32-
As pCO2 increases: TCO2 up, pH down, CO2* up, HCO3- up, CO32- down
What affects how much atmospheric CO2 is drawn into the ocean?
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
Where and how is TCO2 and CA consumed and released?
Surface ocean - photosynthesis and carbonate precipitation consume TCO2 and CA
Deep ocean - recycling (respiration of Corgand dissoluton of CaCO3) release CO2 and CA
What controlls the distribution of carbonate sediments on the ocean floor?
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
What is KSP and Ω
KSP is the stochiometric solubility product for the equilibrium reaction: CaCO3(s) ⇔ Ca2+ + CO32-
KSP = [Ca2+][CO32-]
The precipitation and dissolution of calcium carbonate is controlled by the saturation state of seawater with repect to CaCO3 (Ω)
Ω = [Ca2+]SW[CO32-]SW / KSP [Ca2+]SW and[CO32-]SW are actual concs of calcium and carbonate ions in seawater
If Ω= 1 SW at equilibrim is saturated wrt CaCO3
What determines the degree of saturation of CaCO3?
Determined by [CO32-]
The saturation of carbonate ion concentration increases with depth because CaCO3 is more soluble at T decreases and pressure increases
If [CO32-] 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
What is the CaCO3 satyration horizon?
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)
How does TCO2 affect CaCO3
Increased TCO2:
Shift the carbomnate equilibria in favour of HCO3- and lower pH
Overall effect is to lower [CO32-] 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
