L6 & 7 - Glacier Hydrochemistry Flashcards
Give 5 reasons why chemistry is necessary
- Solute Sources
- Chemical Weathering Basics
- Chemical Weathering Reactions
- Simple Models
- Solute Acquisition Scheme
Why is studying the chemical weathering environment important?
For determining drainage system evolution
What has recently been discovered?
That glaciers can export as much solute as some of the worlds major rivers
What 2 things are needed for dissolution?
Rock and Water Sources
What is chemical weathering?
A process by which rocks and minerals undergo changes in their composition
Give 5 characteristics of glacial meltwater
- Low Temperatures
- Low Ionic Strength
- Dilute
- Freeze-Thaw Processes Occur
- High Suspended Sediment
Why are glaciers good at grinding up rock?
- Exposed Mineral Facies
2. High Surface Areas
What gives the potential for long rock:water contact times?
Bimodal Flow
What is used as a proxy for total dissolved solids ?
EC
What 5 things can chemistry tell you that EC cannot?
- What minerals are present
- Reaction kinetics
- Atmospheric contact
- Bed contact
- Any other processes?
Water splits into what 2 ions?
H+ and OH-
Rock splits into what?
Cations and anions
Chemical equations must what?
BALANCE!
Reaction speeds are controlled by what?
Physical conditions (wet and warm is favourable)
What are favourable reaction kinetics ?
Those that easily dissolve go into solution first
Which mineral is the easiest to dissolve?
Calcium Carbonate
No matter, which minerals are the most common in the bedrock which is always the major ion in the run off?
Bicarbonate
What is chemical balance and coupling of reactions?
One reaction changes the chemical conditions of water, which helps other reactions to proceed
Give 2 examples of coupling of reactions
- 2:1 ratios of Ca2+ + Mg2+ and SO4
2. Carbonate dissolution and Sulphide oxidation
What is hydrolysis?
The interaction between water and the mineral surface and almost always produces alkaline solutions
What is acid hydrolysis?
Similar to hydrolysis, but water interacts with another compound to produce an acid, whose H+ ions interact with the mineral surface
How does acid hydrolysis change the water conditions?
- pH increases
- PCO2 decreases
- Increased potential for CO2 adsorption
What enables silicate hydrolysis?
Acidic conditions from carbonate hydrolysis
What happens to water with regards to carbonate?
It becomes repaid saturated so that no more can dissolve
Where does sulphide oxidation occur and what does this man for carbonate dissolution?
Debris-Rich environments which lowers pH and allows for further carbonate dissolution
Why does silicate hydrolysis take longer than carbonate hydrolysis?
Requires longer rock contact time, solicit is more resistant to weathering and has slower reaction kinetics
Where were boreholes drilled that revealed 3 glacier modes?
Haut Glacier, d’Arolla
What does VPA show?
If there is water at the bed or if it has flowed out
What 2 things are needed to determine the drainage structure of the glacier?
- Borehole Data
2. Ions in Meltwater
What is the SO42- + HCO3-
Sulphate Mass Fraction - used to look at rock: water contact time
Which mode is furthest from the channel?
Mode 3
Which mode has low concentrations of all ions?
Mode 1
Which mode has carbonation of carbonates?
Mode 2
What is the most likely source of the excess sulphate?
Microbes!!!
What do microbes act as?
Catalysts to speed up reactions including the coupled Fe (III) reaction and to produce products that are used in reactions
What does microbial oxidation of organic carbon do?
Produces CO2 for carbonation of carbonates and silicates
What can microbial processes drive the bed towards?
Anoxia
What are psychrophiles?
Cold Specialists
What are psychrotolerant?
Cold Tolerant
What are autotrophs?
They make their own food/energy
What are heterotrophs?
Organisms that eat other organisms
What are chemolithoautotrophs?
Organisms that get their food from chemical reactions on the rocks
What can investigation subglacial microbes tell you?
The composition of meltwater and the properties of the weathering environment
Give 2 direct subglacial microbe measurements and how you can access this environment
- Sediment & Water Phases
- Genetic & Culturing Methods
Accessed via subglacial seeps and exposed basal debris
Give the 5 indirect indicators of microbes in the subglacial environment
- Major Ions (Nitrate and Sulphate)
- Gases (O2 and CH4)
- Nutrients (N, P and Fe) and Trace Elements
- Chemical Indicators (pH and CO2)
- Carbon
