Intro SOES 1005 Flashcards
1
Q
What is biogeochemistry?
A
It is the interaction between animals and plants with their geological environment.
2
Q
Why is earth a Goldilocks planet?
A
Earth has an abundance of water which allows it to support life
3
Q
How did water come to Earth?
A
When the earth formed it captured its water from commits which migrated from the center of the earth to the surface which is held at the surface by gravity.
4
Q
Why is water a polar molecule?
A
Water is a polar molecule due to the sharing of electrons between slightly negatively charged oxygen atoms and slightly positively charged hydrogen atoms
5
Q
Water characteristics
A
*High boiling point
*High specific heat capacity
*Density decreases with freezing
*Good solvent
6
Q
Where does evaporation occur the most?
A
Evaporation occurs mainly in equatorial oceanic regions
7
Q
Where does precipitation mainly occur?
A
Precipitation occurs over high land masses
8
Q
What is the largest river?
A
Largest river is the Amazon it provides 20% of fresh water input into the oceans
9
Q
What are characteristics of the Brahmaputra river?
A
Brahmaputra river drains the Himalayas so contains a lot of particulate material as rivers are fast flowing due to steep gradient from high mountains.
10
Q
What are characteristics of arctic rivers?
A
Arctic rivers (Yensi and Lena) drain tundra. They a flat and slow moving so have lots of time to dissolve rocks so contain a lot more dissolved elements relative to particulate material.
11
Q
What is physical erosion?
A
Moving water grinds up rock carrying its material to oceans. Tiny particles of eroded rock is called suspended particulate material
12
Q
What is chemical erosion?
A
Rain water contains small quantities of carbon dioxide from the atmosphere, which dissolves into the rain water making it into a weakly acidic solution (carbonic acid) which can chemically break down rocks which the rain water falls on
13
Q
What is the Carbonic acid formation equation
A
2CO2 + 2H2O → 2H2CO3
14
Q
How does chemical weathering impact the global climate?
A
When Co2 which is dissolved in rainwater attacks the rock it is converted into hydrogen carbonate ions (2HCO3) which is a stable form of carbon. This helps to reduce the amount of greenhouse gases in the atmosphere helping to reduce global warming.
15
Q
What are other riverine material inputs?
A
*Windblown dust
*Hydrothermal vents
*Sediments
*Volcanic gases
*Ice
16
Q
What is a mole?
A
One mole is 6.02 x 10^23 atoms. The mass of one mole of atoms is the atomic mass
17
Q
How are plates moving?
A
Plates are slowly moving. Some are spreading apart while others are disappearing (they drop down at subduction zones into the earth). They are spreading at different rates across the world.
18
Q
Where do hydrothermal systems normally occour?
A
Hydrothermal systems normally occur where the midocean ridge is spreading apart.
19
Q
How does ocean crust form?
A
Hot magma towards the center of the earth flows up to fill the gap at the sea floor from moving plates, known as pillow lavas.
20
Q
What is hydrothermal circulation?
A
As the sea floor plate spread apart, pillow lavas form at the sea floor creating a crust that is permeable.
Due to a temperature gradient between the hot magma and cooler pillows, seawater is sucked down towards the magma chamber. It is heated and becomes buoyant so it rises back towards the sea floor.
21
Q
What are black smokers?
A
Hydrothermal vents at high temperatures (over 350’C) which erupt at high flow rates. Iron and other metals in the fluid precipitate as they mix with seawater, forming ‘black smoke”
22
Q
What are white smokers?
A
Hydrothermal vents at lower temperatures (below 200’C) which seep through small cracks. Lower metal concentrations and particles of anhydrite, barite, or talc forming “white smoke”
23
Q
What causes vent fauna and what are their characteristics?
A
Certain organisms use chemical compounds from hydrothermal fluids for energy when respiring allowing survival. Chemolithoautotrophic microbes are abundant around vents, they chemosynthesise reduced compounds (e.g. hydrogen sulphide and iron) for energy. There is low species diversity as organisms have to be well adapted
24
Q
What are conductivity measurements relative to KCL solutions?
A
Seawater contains both positively and negatively charged ions so a current can be zapped through to measure the conductivity against a known salinity of KCL.
25
What is salinity?
The total concentration of dissolved salts in seawater. It is the balance between precipitation and evaporation. It is temperature and pressure dependent.
26
Where is salinity the most unstable?
The most dramatic change in salt levels is at the ocean surface due to precipitation and evaporation
27
What is steady state?
What goes in balances what goes out.
28
What are salt inputs into the ocean?
*Rivers
*Volcanic gasses
*Dust
*Hydrothermal vent fluids
Major cations in seawater are derived from rock weathering, whereas the major anions have a volcanic source .
29
What is MORT?
Mean ocean residence time tells us how long between an element enters the ocean and then leaves the ocean.
30
What is the MORT equation
MORT=Ocean conc. x Ocean vol. / River conc. x River water flux
31
What elements are all organisms composed of?
All organisms are made of H, C, N, O, and P
32
What are nutrients?
Elements that limit primary production
33
Where does photosynthesis occour in the ocean?
Photosynthesis can only occur in the upper layers of the ocean as light can’t travel too far down.
34
What is the Photic zone??
Where sunlight penetrates the top of the ocean
35
What is the biological pump?
Combined biological processes which transfer organic matter and associated elements to depth. It is a pathway for rapid carbon sequestration.
36
How do particles cycle the ocean in the biological pump?
*Phytoplankton utilise dissolved carbon for photosynthesis
*Some phytoplankton is eaten by zooplankton and then excreted
*Most of this is decomposed by bacteria into dissolved organic carbon
*Some sinks as particles to the seafloor
*Death of zooplankton can also cause sinking particles, most are skeletal material as microbes can decompose soft tissue more easily.
37
What are the two main types of falling particles?
fecal pellets and marine ‘snow’. Marine snow is particles of biogenic debris in the upper water column. Some is soft tissue, so is sticky and can quickly grow in size increasing the rate of sinking to the sea floor.
38
What are the vertical distributions of the nutrients phosphate and nitrate?
*Crossing through 0 shows these are limiting nutrients
*At the top of the graphs, concentrations are low as they are being utilised by phytoplankton at the top of the ocean
*The thermocline in the ocean means as depth increases at the top recycling is rapid as there is a steep concentration however as we continue to go further in depth the rate of recycling slows due to colder temperatures
*Also as depth increases there is less phytoplankton due to lack of sunlight for photosynthesis so the nutrients are not being used by the phytoplankton so levels increase.
39
How does the distribution of silicon differ from phosphate and nitrate?
*Silicate increases more gradually with depth compared to other major nutrients (e.g. phosphate and nitrate)
*Weaker gradient due to phytoplankton not recycling so silicon has different mechanisms in comparison to phosphate and nitrate.
*It is used by diatoms to build their shells so has a low concentration at surface levels
*Levels rapidly increase as depth increases due to the dissolution of sinking particles.
40
What is thermohaline circulation dependent on?
Temperature (thermo) and salinity (hyaline)
41
What is the pycnocline?
Region of sharp change in density
42
How does salinity vary across the globe?
At a lower latitude salinity is higher at the surface due to evaporation drawing up only water and leaving behind salt. At higher latitudes precipitation and ice melt dilute the oceans decreasing the salinity. In the tropics temperatures are high increasing the rate of evaporation so salinity is high.
43
What is the ocean conveyor belt?
*The start of the ocean conveyor is in the North Atlantic and evaporation rates are high the surface level which sinks to great depth after cooling down, forming the North Atlantic Deep Water (NADW)
*The water flows south towards the equatorial pacific, where there is less evaporation, more rainfall entering the ocean and more time for the dissolution of particles to sink to lower depths, so the concentration of nutrients such as phosphate and nitrate is higher.
44
What is the Redfield ratio?
The Redfield ratio represents the constant proportion of major nutrients in seawater in global oceans.
C:N:P = 106:16:1
45
What is OILRIG?
Oxidation is loss of electrons. Reduction is gain of electrons.
46
What is the marine nitrogen cycle?
*Firstly, nitrogen from the atmosphere is fixed to form ammonia
*In oxic/aerobic environments nitrification occurs where ammonia (NH3) is oxidised into nitrite (NO2-). Nitrite can then be further oxidised into nitrate (NO3-)
*In anoxic/anaerobic environments nitrate is reduced to nitrite. Then denitrification occours and nitrites are converted to nitrogen. Sometimes it is fixed to ammonia.
*In both oxic and anoxic conditions assimilation can occur creating organic nitrogen.
47
What does the N* metric show?
It shows deviations of nitrogen concentration from average levels. We use nitrate and phosphate levels. Positive deviation (N*>0) there is an N-excess. Negative deviation (N*<0) there is an N-deficit
48
What are nitrogen inputs into the ocean?
*Rivers
*Upwelling
49
What are nitrogen outputs from the oceans?
*Falling particles
*Downwelling (small amount)
*Evaporation (small amount)
50
What process internally cycle nitrogen in the oceans?
*Assimilation (biological uptake)
*Remineralisation
*Nitrification
51
Why is denitrification a big nitrogen loss pathway?
Major remineralisation process in the oceans, as NO3- is thermodynamically the most favorable electron acceptor after O2.
NO3-, NO2-, N2O, N2
52
What is anammox and why is it a nitrogen loss pathway?
Anaerobic ammonium oxidation. One ammonium is combined with one nitrite molecule to form N2 gas and water. It produces quite a lot of energy. Occurs in low-oxygen water and sediments
53
Why is N2 fixation a major marine nitrogen input?
N2 is unusable for most organisms because the triple bonds linking the two nitrogen atoms is so strong it requires a lot of ATP to break down. Mediated by the enzyme nitrogenase, which needs Fe. Presumed to occur mainly in oligotrophic (low productivity) regions, e.g. subtropical gyres
54
How do humans impact nitrogen levels?
Anthropogenic (human) impacts have majorly increased the concentration of nitrogen inputs into the oceans. Causes include fossil fuel burning and fertilisers
55
what organisms is silicon needed by?
*diatoms
*silicoflagellates
*radiolarians
*some sponges
56
How do diatoms use silicon?
Silicon is a major nutrient for diatoms which are a major primary producer of phytoplankton in the ocean. They utilise silicon to create chains, reducing friction and sinking rate. They can also be used to create a protective shell.
57
what are the 5 forms of silicon?
silicon
silica/silicon dioxide
silicic acid
silicate
opal/biogenic silica
58
What are silicon inputs into the oceans?
Dominated by riverine inputs. River-dissolved Si comes from weathering of rocks by dilute carbonic acid in rain
59
What are silicon outputs from oceans?
Ultimate removal from ocean waters is to sediments
60
What is dissolution of silica in seawater?
The ocean is under-saturated with opal so opaline shells will dissolve to release dissolved silicon
The lower the concentration of dissolved silicon in surrounding waters, the more opal dissolves
61
What is the vertical distribution of silicate?
*Silicate increases more gradually with depth compared to other major nutrients (e.g. phosphate and nitrate)
*Weaker gradient due to phytoplankton not recycling so silicon has different mechanisms in comparison to phosphate and nitrate.
*It is used by diatoms to build their shells so has a low concentration at surface levels
*Levels rapidly increase as depth increases due to the dissolution of sinking particles.
62
what is the global distribution of silicon in the ocean?
Due to the ocean conveyor pacific deep water is richer in Si than Atlantic deep water because it is older.
63
What are siliceous oozes?
Deposits of falling particles on the sea floor containing more than 30% silicious materials
64
How do siliceous oozes form?
For them to form opal has to be rapidly transported to the seabed and there has to be reduced dissolution
65
What is the distribution of siliceous sediments in the ocean?
*They are common in high productivity belts such as equatorial and southern regions
*Rare in Atlantic as water is young
66
In what form is silicon found in the oceans at pH ~8?
Silicic acid, which is the main form of silicon in the oceans as ocean pH is approximately 8.1
67
How does the carbon cycle interact between the ocean and atmosphere?
*CO2 reacts with H20 forming carbonic acid
*Equilibration between atmosphere and ocean takes up to 1 year
68
What are the 4 forms of carbon?
*carbon dioxide (CO2)
*carbonic acid (H2CO3)
*bicarbonate ions (HCO3 -)
*carbonate ions (CO3 2-)
69
What is alkalinity?
The concentration of negative charge in a solution. pH <7 solution is acidic. pH >7 solution is alkaline
70
Why doesn't dissolution of CO2 in seawater effect alkalinity?
CO2 dissolves in water to form carbonic acid which is a weak acid not fully dissociated. Partial dissociation produces H+ ions which balances out the pH
71
What is total alkalinity (TA)?
The excess of proton acceptors over proton donors with respect to a zero level of protons
72
What are carbonate sediments formed from?
Composed principally of skeletal remains of calcite and aragonite secreting organisms.
73
What organisms produce calcite and aragonite?
*Foraminifera
*Pteropods
*Corals
74
What are the characteristics os calcite and aragonite?
Calcium carbonate has two polymorphs: calcite and aragonite
Calcite is a more stable form of calcium carbonate than aragonite
If aragonite is preserved in the sedimentary record it reverts to calcite over time. Corals and pteropods precipitate aragonite. Foraminifera produce calcite from their exoskeletons.
75
What is the distribution of carbonate sediments in the ocean?
The concentration of calcium carbonate is higher in the mid Atlantic ridge, due to the sea floor being more shallow so preservation is higher. In costal areas CaCO3 levels are diluted by freshwater river flux so deep water levels are higher,
76
How are carbonate sediments formed?
CaCO3 + H2O = 2HCO3
77
Why does CaCO3 solubility increase with depth?
Pressure is higher so total dissolved CO2 is higher so pH is lower
78
What is the saturation horizon of CaCO3?
The boundary between supersaturated conditions above this depth and undersaturated conditions below. Above CaCO3 will not dissolve but below it will.
79
What is the CCD?
The carbonate compensation depth. Which is the Depth where rate of dissolution just compensates the rate of deposition. It is the greatest depth where carbonate sediments are found
80
What is the distribution of CO2 in the oceans?
Higher concentrations in older waters such as south pacific due to continued input and decomposition of organic matter introducing more CO2
81
What is the distribution of CO3 2- (carbonate ions) in the oceans?
Addition of more CO2 along the conveyor causes the seawater to become slightly more acidic lowering CO3 2- levels. So levels are higher in young waters such as the Atlantic
82
What are the causes of increased atmospheric CO2?
*Fossil fuel combustion
*Cement manufacture
*Deforestation
*Agriculture
83
What are the consequences of increased atmospheric CO2
*Rising temperatures
*Reduced sea ice, sea level has risen
*Ocean acidification
84
What is the greenhouse effect?
Incoming radiation is adsorbed by the: Ocean and land (51%)
Atmospheric gases (19%). Some radiation is reflected from the Earth, long wavelenghts are re-absorbed by the atmosphere, only short wavelengths can escape.
85
What are some techniques for negative emissions?
*Reforestation
*Enhanced ocean productivity - adding iron and nitrogen to oceans to increase rate of photosynthesis in plankton
*Blue carbon habitat restoration
86
What do thermodynamic laws show us?
The thermodynamic laws show which chemical reactions are possible, but they do not tell us how quickly these reactions will occur
87
What is Gibbs free energy?
Gibbs free energy is a prediction about whether a reaction will occur spontaneously. If it can be spontaneous it is negatively charged.
88
What is the rate of reaction?
The rate of a reaction is the change in the concentration of product formed per unit of time, or the change in the concentration of reactant used per unit of time
rate = k × [reactant]^n
*K is the rate constant
*N is called the order of the reaction, only found experimentally
89
What is a first order reaction?
A first-order reaction is one in which the rate of reaction is proportional to the concentration of the reactant
Rate = K x [A]
*K is the rate constant
* [A] is the concentration
90
What is a second order reaction?
A second order reaction is one where the rate of reaction quadruples when the concentration of reactant doubles
Rate = K x [A]^2
*K is the rate constant
* [A] is the concentration
91
What is a zero order reaction?
A zero order reaction is one where a reactant has no effect on rate of reaction
92
What is half life?
The time taken for the concentration of a reactant to decrease by half
T1/2 = ln2/k
93
What is activation energy?
The Minimum amount of kinetic (movement) energy that two particles need for them to react
94
What factors affect rate of reaction in the ocean
*Concentration of reactants
*Temperature
*Presence of physical coating (inhibits collisions)
95
What is a trace metal?
Trace elements (TEs) are those elements whose abundance is < 10 mmol/kg. Trace metals essential to biota (enzymes), and low concentration may limit productivity however high concentrations may be harmful
96
What are trace metal inputs into the oceans?
*Rivers (but some elements lost in mixing processes between fresh and saltwater)
*Atmosphere
*Sediments
*Hydrothermal activity
97
What are trace metal outputs from the oceans?
*Sediments
*Biological uptake and recycling
98
What are nutrient type elements?
Higher concentrations at lower depth due to the thermocline (e.g. phosphate and silicon)
99
What are scavenged elements?
Higher concentrations at surface levels as mainly added to the ocean by the atmosphere
100
What are conservative elements?
Concentrations are constant due to high concentrations so no impact from the thermocline
101
What are hybrid elements?
Trace metals have distributions that are strongly influenced by both recycling and relatively intense scavenging processes (e.g.iron and copper)
102
What is a reductant?
Oxidised molecules are the reductant and are electron donors
103
What is an oxidant?
Reduced molecules are the oxidant and are electron acceptors
104
What is the most important oxidant in seawater?
Oxygen is the most important oxidant in seawater because of its relatively high concentration and use in cellular processes. It also generate as a lot of free energy.
105
What is the sequence of oxidising agents (electron acceptors)
O2 (oxygen)
NO3
Mn(IV)
Fe(III)
SO42-
CO2
106
What is AOU?
Apparent oxygen utilisation. It is the amount of oxygen consumed since a water mass was last at the ocean surface
AOU = NAEC - [O2]in situ
107
What are chemolithoautotrophs?
microorganisms can harness energy from different redox reactions to make their own organic matter
108
What are chemolithoautotrophs?
Microorganisms that can harness energy from different redox reactions to make their own organic matter
109
What are chemoorganoheterotrophs?
Microorganisms that can harness energy from different redox reactions to degrade organic matter
110
What are biomarkers?
Biomarkers are organic compounds with a distinct origin
111
Why are alkenones used as biomarkers in sediments?
*Resistant to degradation
*Can reconstruct past conditions
*Have a distinct origin
112
What are the characteristics of Fe3+?
Fe3+ is thermodynamically stable in the presence of oxygen and insoluble
113
What are the characteristics of Fe2+?
Fe2+ can be thermodynamically stable without any oxygen and is soluble
114
Why did the early atmosphere contain more FE2+?
The early atmosphere was CO2 rich and lacked free O2 so there were high concentrations of dissolved iron in the form of Fe2+ in the ocean
115
What basic biological processes is iron essential for?
*Photosynthesis
*Respiration
*Nitrogen assimilation
116
How did iron concentrations change over time from the early atmosphere?
CO2 became buried in sediments decreasing its atmospheric concentrations so O2 concentrations rose oxidising Fe2+ into Fe3+ and precipitates.
117
What do Banded iron formations (BIF) tell us?
The early ocean was rich in dissolved Fe however over time there was precipitation of Fe3+ into sediments
118
What is the process of BIF?
*Dissolved Fe(II) first entered water column from hydrothermal vents and became saturated by dissolved Si.
*. O2 at low concentrations (likely produced by the first cyanobacteria) reacted abiotically with dissolved Fe(II) to produce Fe(III)
*In an ocean with at least localised oxygen, microaerophilic Fe(II)-oxidising bacteria, took advantage of opposing oxygen-/Fe2+- gradients and precipitate cell–Fe(III)-mineral aggregates.
*In an anoxic water column, UV light could photo-oxidize Fe(II) and precipitate abiogenic Fe(III) (oxyhydr)oxides
*Anoxygenic Fe(II)-oxidising phototrophs directly oxidised Fe(II) to form cell–Fe(III)-mineral aggregates
119
What are inputs of iron into the oceans?
*Rivers
*atmospheric deposition
* hydrothermal inputs
120
What is the distribution of iron in the oceans?
More Fe in the pacific than the Atlantic due to the ocean conveyor belt and more time for inputs and dissolution
121
What is the iron hypothesis?
It suggests iron can help draw carbon into the ocean from the atmosphere by increasing plankton levels and productivity as iron is a limiting nutrient for photosynthesis. especially in HNLC regions.
122
What is Dalton's law of partial pressure?
Each type of gas in a mixture has its own independent pressure
These individual ‘partial pressures’ are additive to give the total pressure (Pa)
Pa = P1 + P2 + P3
123
What is Avogadro’s Law?
Equal volumes of different gases contain equal numbers of molecules at the same temperature and pressure. At 273 K (0 ˚C) and 1 atmosphere (101 kPa) (STP) 1 mole of gas occupies 22400 mL
124
What is the ideal gas equation?
Pressure, temperature and volume of a gas are related by the ideal gas equation
pV = nRT,
*p = pressure
*V = volume (m3)
*n = amount of gas in moles
R = the gas constant
T = temperature
125
What is Boule’s Law?
Volume of a fixed amount of gas is inversely proportional to its pressure at constant temperature. E.g. if you double the volume you will half the pressure and visa versa
126
What is Charles’ Law?
Volume of a fixed amount of gas is directly proportional to its absolute temperature at constant pressure
127
What is Henry’s Law?
Gas concentration in water is proportional to the partial pressure of gas above the water
[Aaq] = KH × PA
*[Aaq] = gas concentration in water (“aqueous activity”)
*KH is Henry’s constant
*PA is partial pressure
128
What factors affect gas solubility?
*Temperatures - colder water increases gas solubility
*Salinity - lower salinity increases gas solubility
*Atmospheric pressure
Surface conditions (e.g. oil slicks)
129
What is NAEC?
Normal Atmospheric Equilibrium Concentration. The equilibrium concentration of a gas can be thought of as the gas concentration that a water mass would attain if it were to equilibrate with the atmosphere at its in situ temperature and salinity
130
When is seawater saturated?
If the in situ concentration is equal to the NAEC, then the seawater is saturated
131
When is seawater supersaturated?
If the observed in situ gas concentration exceeds the NAEC, then the seawater is super-saturated with respect to the gas
132
When is seawater under-saturated
If the in situ gas concentration is less than that of the NAEC, the seawater is under-saturated
133
What is the % saturation equation?
% saturation = ( [A] in situ / NAEC fo A ) x 100
134
What is the vertical distribution of oxygen in the ocean?
High values at sea surface, actual value depends on T and S. Minimum levels at ~1 km depth corresponding to maximum re-cycling of particulate organic carbon from surface waters due to respiration. Deep water concentrations of water is controlled by the thermohaline conveyor. Concentration of oxygen highest in “young” water in the North Atlantic. Deep waters in pacific has lower oxygen as waters are old so oxygen has been consumed.
135
What is the horizontal distribution of oxygen in the oceans?
Highest concentrations occur in cold polar surface waters. There are higher oxygen concentrations in the poles due to colder temperature. Cold water increases gas solubility.
Lower surface concentrations occur at mid-latitudes
136
What factors affect the rate of gas exchange between the atmosphere and ocean?
*Sea state as waves can increase the surface area
*Chemical reactions, impacting the concentration gradient
*Organic films, such as hydrophobic matter concentrated near the surface
137
What are the 3 different ocean pumps?
*Soft tissue / POC (particulate organic carbon) pump
*Carbonate / PIC (particulate inorganic carbon) pump
*Solubility pump
138
What is the soft tissue pump?
Formation of organic carbon and sinking into the deep ocean. Remineralisation then releases CO2 at depth in the ocean. 𝚺CO2 increases with depth and along the conveyor. This reaction does NOT change alkalinity as there are no charges on the atoms.
139
What is the soft tissue pump?
Formation of organic carbon and sinking into the deep ocean. Remineralisation then releases CO2 at depth in the ocean. 𝚺CO2 increases with depth and along the conveyor. This reaction does NOT change alkalinity as there are no charges on the atoms. Also know as the POC pump.
140
What is the carbonate pump?
Biological formation of CaCO3 produces CO2. CaCO3 shells sink to deep water where they dissolve releasing carbon dioxide. This process pumps alkalinity from surface to deep water as HCO3 - is also produced which has a negative charge. Also known as the PIC pump.
141
What is the solubility pump?
The exchange of carbon dioxide between the atmosphere and ocean due to upwelling and downwelling. More CO2 is absorbed by colder waters as gases are more soluble.
142
What ocean pump has the biggest impact on CO2 levels?
The soft tissue pump has the biggest impact on CO2 levels
143
What are methods of removing CO2 from atmosphere/oceans?
*Carbon sequestration at point of combustion.
*Carbon sequestration from ambient air. However this is hard because the concentration of CO2 in the air is very low
*Reforestation
*Enhanced weathering
*Ocean fertilization (e.g. iron fertilisation)
*Biochar, organic material left over from burning materials which is can be buried and stored underground with agricultural waste.
*Alkalinity enhancement of the oceans, increasing the pH
*Direct air capture, separates ambient air into a concentrated CO2 stream and CO2-depleted air which is pumped back out.
144
What are feedback processes?
A process that responds to a stimulus to either counteract (negative feedback) or enhance (positive feedback) this stimulus. Negative feedback brings you back too optimal conditions however positive feedback brings you further always from optimum conditions. Iron dust inputs are an example of negative feedback. Higher temperatures increasing methane levels due the the dissociation of hydrate is an example of positive feedback as methane is a greenhouse gas.
145
What is the Gaia hypothesis?
A set of hypotheses that likens the Earth to a super organism with interrelated, mutually adjusting systems due to feedback loops. it was proposed by James Lovelock.
146
What is the Daisy world Gaia hypothesis?
Black daisies absorb sunlight and warm the planet. The black daisies prefer to grow in cooler conditions, so the steadily increasing temperature kills them off.
White daisies, which prefer warmer weather, start to proliferate. Since the white daisies reflect heat rather than absorb it, as they spread they cause the climate to cool. This leads to the fall of the white daisy and the resurgence of the black.
147
What is the rate of slow spreading ocean ridges?
1-2 cm yr-1
* The Mid-Atlantic Ridge is slow spreading
148
What is the rate of fast spreading ocean ridges?
6-8 cm yr-1
* The East Pacific Rise has fast spreading ridges
149
What is the process of fast spreading ridges?
*Mantle is permanently upwelling from below to fill the gap from ridges spreading apart.
*A magma lens also forms where molten lava forms just below the crest of the mid ocean ridge creating the dome.
150
What is the process of slow spreading ridges?
*Magma upwelling is a lot slower
*Magma tends to partially crystallise on ascent to seafloor, arriving in the crust as a mixture of crystals and liquid. Seismic studies indicate that below fast-spreading ridges there is usually a lens of magma a few hundreds of m thick, overlying a crystal mush zone. Slow spreading ridges have a narrower mush zone and usually lack a persistent magma body of any kind (ephermeral).
151
What is a volatile?
A substance that is easily evaporated
152
What are inputs of volatiles into the mantle?
*Helium-4 (4He) produced by radioactive decay of uranium and thorium in rocks
*Helium-3 (3He) mainly comes from the mantle- it was trapped there when the Earth first formed
153
What is the recharge zone?
The recharge zone is where seawater is just entering the ocean crust. It’s temperature when entering the crust is ~2 degrees and is then heated
154
What is the precipitation of anhydrite in recharge zones?
*At temperatures >150 °C, CaSO4 will precipitate from solution
*Since the Ca content of seawater is less than the SO4 content, Ca will be depleted to zero, SO4 will remain at lower levels
*We see this anhydrite in in situ ocean crust as a white mineral filling spaces is altered in rock
155
What is the uptake of Mg2+ in recharge zones?
*At temperatures >60 °C, Mg is removed into clays
*Other alkali earth metals e.g. Li+ and H+ are also incorporated into clays at temperatures < ~150 ˚C, but they are released at higher temperatures.
156
What process occurs in the reaction zone?
*The reaction zone is >300 ˚C.
*Dissolution of primary igneous sulphides releases metals to solution
*Input of H2S from sulphides and mantle
*Reduction of seawater sulphate
*Dissolution of silicate rocks release silicon and alkali earth metals
157
What is phase separation in hydrothermal systems?
*Hydrothermal fluids may pass through two-phase conditions in the sub-seafloor reaction path
*This generates a low-chlorinity vapour phase and a high-chlorinity brine phase
*The two phases have different physical properties leading to segregation and a wide range of chlorinities
158
What is the process of hydrothermal plumes?
As hot buoyant vent fluids erupt onto sea floor they rise and continually mix with sea water increasing the water concentration which forms the plume.
159
What is a steady state plume?
Steady state plumes are found all along MOR system above each vent site, they have been around for a long time steadily pumping out hydrothermal fluid. The temperature and release of material is steady creating a constant realise of smoke like plumes.
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What is a non-steady state plume?
Non-steady state plumes occur directly after magmatic input to seafloor. They are hotter, so are more bouyant and rise further.
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What are requirements of tracers for hydrothermal plumes?
*Highly enriched in hydrothermal fluids compared to background seawater
*conservative
*in situ measurement
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What tracers can be used for hydrothermal plumes?
*Fe oxide particles (smoke), measured by a nephelometer or a transmissometer
*Dissolved Mn2+ (oxidises slowly)
*Dissolved CH4 (also oxidises slowly)
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What are the dynamics of hydrothermal plumes?
*When the density within the plume equals the density of surrounding seawater it stops rising and begins to spread horizontally along the isopycnal. This is known as a neutrally bouyant plume and is approximately 200-440m above the ocean crust.
*Rising plumes are known as bouyant plumes and have a lower density than surrounding seawater.
*In bouyant plumes there is precipitation of Fe-sulphides in early stages of mixing; precipitation of Fe oxides tends to be slower
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What are the roles of microbes in hydrothermal plumes?
*Microbes catalyse oxidation of Fe and Mn
*Fe and Mn oxides produced are extremely reactive, removing phosphorous, vanadium, arsenic, chromium etc via scavenging and co-precipitation reactions from the seawater
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What are metalliferous sediments?
*Form from precipitation of Fe- and Mn-oxides from hydrothermal plume
*Found along MOR system
*Act as a repository for co-precipitated and scavenged elements
*They can be a source of REE (rare earth elements) which could be of ecomnomic benefit if mined.
