MBIO 2230 - Topic 6 (Sulfur) 2

What did they find inside the trophosome?

1.) Symbioyic bacteria
2.) Elemental sulfur 

What did the symbiotic bacteria do in the trophosome

They oxidize sulfide as an energy source to reduce CO2, in order to form organic carbon, which can be used by the worm 

Where do the Candidatus Endoriftia persephone get the energy from

From oxidizing H2S, which is emitted from the Earth's interior

How do the Candidatus Endoriftia persephone get carbon?

They use the energy from the H2S oxidation to fix CO2 and form organic carbon

How do the worms get carbon?

They get it from the bacteria, which forms organic carbon by fixing CO2

Why does the worm not require a mouth?

It does not need to bring in solids, only dissolved gases, which reaches its targets in the worm via diffusion

Two isotopes of sulfur 

³²S and ³⁴S

Differentiation between S isotopes in the formation of evaporites

The precipitation of evaporites do not discriminate against either of the isoptopes, meaning it has no preference for either

Significance of the fact that evaporite formation do not discriminate against sulfur isotopes

The sedimentary records of evaporites can then be used to see the changes in the delta ³⁴S of seawater over time, since the isotope level of the evaporite will directly reflect the levels in the sea

The contemporary delta 34S of seawater is +21‰ --> Why is it positive

1.) The positive means there is a lot more heavy isotope in the sea
2.) This means that processes prefer the lighter isotope, which leaves behind the heavier isotope

Process that would prefer the lighter isotope of sulfur and would take it out of the seawater

Most likely dissimilatory sulfate reduction, as it forms H2S gas, which fluxes out of the sea and into the atmosphere

How were we able to determine when sulfate reduction was first seen?

It was first seen in looking at the delta ³⁴S of sedimentary rocks, which showed a depletion in ³⁴S

Why was there a depletion of ³⁴S in sedimentary rocks?

1.) Microbes performing sulfate reduction into H2S prefers the lighter isotope
2.) Therefore, when H2S forms pyrite, the pyrite also contains the lighter isotope, resulting in less ³⁴S

Sulfate <--> Sulfide cycle visualization

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A change in ___________ allows transformations of S to go ‘___ ____’ 

A change in environment allows transformations of S to go ‘full circle’ 

A change in environment allows transformations of S to go ‘full circle’ --> examples 

1.) Bulk flow may carry compounds out of their home environment
2.) The chemistry or redox potential of the environment changes overtime
3.) Gaseous products rise towards oxidizing environments

____ flow may carry compounds out of their ‘_____’ environment 

Bulk flow may carry compounds out of their ‘home’ environment 

Bulk flow may carry compounds out of their ‘home’ environment example

The mixing of water at hydrothermal vents brings reduced S species (H2S) into an environment favourable for their oxidation (i.e. to an oxic environment)

The chemistry of the local environment changing over time example 

1.) When nutrients feed algal blooms, they eventually die and form a dead zone with no O2
2.) This causes sulfate reduction to take over and form H2S, which then either goes into pyrite or forms solid elemental sulfur

Is elemental sulfur fully oxidized?

No

The redox potential of the local environment may changeing over time example

1.) The displacement of water causes oxygenated water to move in, changing the redox environment as a result
2.) Energy can now be harvested to oxidize reduced sulfur compounds 

Gaseous products rising toward oxidizing environments example 

Biogenic sulfide corrosion

Biogenic sulfide corrosion 

A process that contributes to the degredation of concrete sewer pipes

Concrete sewer pipes parts 

1.) Sewage (contains many microbes and elements, including reduced carbon)
2.) Air (above sewage)

What happens in the sewage part of the pipes

A combination of different reduction reactions, using reduced carbon as an energy source, and multiple possible terminal electron acceptors

Terminal electron acceptors used in biogenic sulfide corrosion (in sewage part)

1.) O2 by aerobic respirers
2.) Nitrate by nitrate reducers 
3.) Sulfur by sulfate reducers

What happens in the air part above the sewage

The H2S gas formed from sulfate reduction reactions in the sewage rises and reacts with O2, resulting in the production of sulfate and hydrogen ions 

Why is it called biogenic sulfide corrosion

Because the concrete pipe gets corroded by the hydrogen ions that are formed from the oxidation of the H2S gas, as it lowers the pH

Where does the sulfur comes from in the sewage?

They are remnants from household chemical products 

Where does corrosion occur in concrete sewer pipes

At the top

Winogradski columns  

A container containing mud, water, and nutrients that acts as a mesocosm that allows us to set the conditions to enrich for a particular microbe, such as sulfur bacteria

Using Winogradski columns to enrich for sulfur bacteria steps

1.) Collect mud from any aquatic environment
2.) Add in egg yolks as a sulfur source and eggshells (or newspaper) as a carbon source
3.) Put into a tall tube and add standing water on top
4.) Place near a window sill that has a lot of sunlight

Why put water on top of the mud mixture?

To limit the amount of O2 diffusion

How do the organisms (green and purple sulfur bacteria) above the mud mixture get access to S?

They get it from the H2S that is released from the microbes within the anaerobic environment

Do green and purple sulfur bacteria require oxygen?

No, they are photosynthetic anaerobes 

Why don't the green and purple bacteria grow at the bottom?

1.) The bottom is where high amounts of H2S are formed, causing it to be very concentrated
2.) H2S is toxic at high concentrations, so the sulfur bacteria grow slightly above it to avoid the toxic levels

"Why is the sulfur bacteria way at the top 
"

Too much egg yolks (sulfur) was likely added in the initial mud mixture, resulting in high toxic H2S levels

How do sulfides flux out of active cycling?

By the formation of metal sulfides, as it fluxes from the oceans into the sediments

Net release and consumption of sulfur in hydrothermal vents

There is more sulfur going into the vents then out, therefore there is a net consumption

Why is there a net consumption for hydrothermal sulfides instead of release

There are other metals going into the vents, which is able to reach with the sulfur to form metal sulfides

Processes that result in the flux of sulfur into the atmosphere and aquatic system

Atmosphere = Human mining + extraction
Aquatic = Natural weathering + erosion

Human mining + natural weathering that results in the release of sulfur

Acid rock drainage

Acid rock drainage

The outcome of crushing rocks that contain FeS2, a damaging form of environmental degredation, as it results in the release of stored sulfur

Acid rock drainage process

1.) Breaking rocks releases the S and exposes them to O2
2.) This allows them to be utilized by microbes

Pyrite is aka…

Fools gold

Microbe that oxidizes pyrite 

Acidithio-bacillus ferroxidans

Acidithio-bacillus ferroxidans name break down

Acido = Acidic conditions
Thio = To do with sulfur 
Bacillus = Its cell shape
Ferro = To do with iron
Oxidans = Oxidizing

Oxidation of pyrite reaction

FeS2 + H2O + O2 --> Fe2O3 + H⁺ + Sulfate

The ________ of pyrite is accelerated up to a ______-fold by ________

The oxidation of pyrite is accelerated up to a million-fold by enzymes

Oxidation of pyrite electron donor vs. acceptor

Electron donor = Ferrous iron (gets oxidized)
Electron acceptor = Oxygen (gets reduced)

Significance of the energy source in pyrite oxidation

It can be hard to access, especially by the ETC, which is why it is arranged in a way that is spans from the outer membrane to the inner membrane

Pyrite oxidation produces many __ ions, causing it to be very _____ 

Pyrite oxidation produces many H+ ions, causing it to be very acidic 

Impacts of acid rock drainage

1.) Produces very acidic water
2.) Leads to the deposition of iron oxides

Impacts of acid rock drainage producing acidic water

1.) Direct lethality to wildlife
2.) Causes damages when used as drinking water
3.) Can solubilize heavy metals

Impact of iron oxide deposits from acid rock drainage

1.) Changes the colour of the water, due to rust
2.) Thick deposits smother the bottom of the streams and lakes

What are the dominant movements of S on Earth caused by

It is primarily caused by human activity, specifically mining and extraction

Anthropogenic inputs of sulfur into the atmosphere is caused by…

The combustion of organic materials containing S, which produdes the chemically oxidized sulfur dioxide gas that can react with water in the atmosphere

SO2 is an air _________

Pollutant

SO2 reacting with water in the atmosphere can form _______ acid

Sulfuric acid

SO2 as a pollutant/toxicant

It irritates mucous membranes, making it a respiratory health hazard

Significance of sulfuric acid in the atmosphere

It is further broken down into hydrogen ions, which contributes to acid rain

PIR (acronym)

Pre-industrial revolution

Releases of sulfur to the atmosphere are __________ in North America 

Decreasing

Releases of sulfur to the atmosphere are decreasing in North America (how) 

This is thanks to the legislations that were made to reduce emissions, which have been successful

How sulfur emissions are being reduced

1.) Extract sulfur from fossil fuels prior to use
2.) Scrub from emissions (i.e. take it out as it is being used)

Extracting sulfur from fossil fuels prior to use

This involves removing sulfur from the petroleum before using it

Scrubbing emissions of sulfur

This involves trapping the sulfur from the exhaust flames before it is released 

Components required for scrubbing emissions 

1.) Water
2.) Base

Use of water and a base when scrubbing emissions of sulfur

Reacts with water to make sulfuric acid, which then reacts with the base to counteract the acidity

Significance of using water and base to scrub the emissions of sulfur

It is basically using the same reactions that naturally occur in the atmosphere

SO2 emissions aroudn the world

1.) Has decreased in North America
2.) Has increased in certain parts of Asia

Significance in the difference of SO2 emissions between North America and Asia

It does not mean that North America is not implicated, it just means the problem has been moved, but they are still benefiting from it

Is H2S volatile?

No, it is non-volatile

Biogenic sulfur _______ from ____ and ______ are an example of living things _________ the flux of S through the ___ phase

Biogenic sulfur volatiles from eggs and garlic are an example of living things increasing the flux of S through the gas phase

A biogenic sulfur volatile at globally relevant quantities example 

1.) Algae decomposes to form dimethyl sulfide gas
2.) It fluxes out of the ocean into the atmosphere, where it undergoes abiotic chemical oxidation to form sulfate

Is dimethyl sulfide a volatile sulfur compound?

Yes

Residence of sulfate in the trophosphere

It has a short RT of 5 days

Why sulfate has a short RT in the trophosphere

1.) Cylic salt
2.) Dry deposition
3.) Washing out
4.) Condensation nuclei

Why cyclic salt causes sulfate to have a short RT in the trophosphere

It refers to the rapid and local cycling of sulfate ions from the ocean into the air and back into the ocean

How dry deposition causes sulfate to have a short RT in the trophosphere

Sulfate aerosols bind to suspended particles, which eventually fall back into the ocean due to gravity

How washing out/condensation nuclei causes sulfate to have a short RT in the trophosphere

1.) Condensation nuclei is when the sulfate ions become the nuclei to water, as the water molecules interact with and surround the sulfate 
2.) This causes the sulfate to go back into the ocean when precipitation occurs

Residence time determining extent ot mixing

The residence time of a material in a large pool determines how well it is going to be mixed 

Residence time vs. extent of mixing relationship

1.) The longer the residence time, the more evenly mixed it is 
2.) The shorter the residence time, the less evenly mixed it is, with a higher degree of variation

High degree of variation = (evenly or non-evenly) mixed

Non-evenly

Example of an atmospheric molecule with a long RT that is homogenously mixed

Argon, a noble gas that has a residence time that is basically forever

Example of an atmospheric molecule that has a short RT and is non evenly mixed

SO2 

What's another reason why a molecule is not evenly distributed in the atmosphere, other than a short RT

Because it is being emitted from different places

What kinds of sulfur compounds released by volcanism? 

1.) SO2
2.) Hydrogen sulfide
3.) Carbonyl sulfide (OCS)

Residence time of carbonyl sulfide

~5 years

What is able to get sulfur above the tropopause

Volcanism

How volcanism gets sulfur above the tropopause

1.) Direct injection
2.) Long-lived forms of gaseous S (such as OCS)

Residence time of sulfate in the stratospheree

Roughly 1-3 years

Why is there a range in the RT of sulfate in the stratosphere

Because it depends on the amount of water present, such that the less water present, the longer the RT

Aerosol/particulate form of sulfur in the atmosphere 

Sulfate

Formation of sulfate in the atmosphere (how)

It forms from the photooxidation of sulfur gases, like sulfur dioxide and carbonyl sulfide, in the atmosphere

How sulfate affects the atmosphere 

1.) Acts as a nucleation site for droplets
2.) Facilitates cloud formation
3.) Has high albedo (reflection), which can help with global cooling

______ can sometimes be purposely put into the atmosphere, due to its ______ effects

Sulfate can sometimes be purposely put into the atmosphere, due to its cooling effects

Cooling effects of sulfate in the atmospher

It is able to effectively reflect insolation, therefore reducing the amount of heat that is retained by the atmosphere

Sulfate facilitating cloud formation

It increases cloud formation, since it acts as nucleiation sites for rain droplets

Sulfate effect on size and fall of water droplets

The amount of nucleation sites available affects the size of water droplets, such that the less sites there is are, the bigger the droplets, the faster it falls