Neoproterozoic Carbon Isotopes

What does the carbon isotope record during the NeoP look like

Large scale variations in isotopic value

What could be the source of the very light carbon throughout the neoP

• Methane oxidation

• Remineralized/oxidized organic carbon

What can result in the large CIE excursions below mantle values

Changing the d13c input into the system

Why is there a small positive rebound after a negative CIE

It is the environmental recovery since burial is proportional to mass in the system. When burial increases to offset the added carbon mass in the system which causes a faster light C drawdown than the input

What is the Rothman method of DOC oxidization

A DOC pool and DIC pool of reactive carbon exist in the carbon cycle model. Fluctuations in the size of the DOC pool can lead to major isotopic variations in carbonates.

In the Rothman method, how could the large CIEs in the neoP be form

The DOC pool had fluctuated in size throughout the NeoP until eventually depleted at the end due to enhanced biomineralization and fecal pellet evolution from early metazoans

What proxies could be used to determine if there was a NeoP oxidation event to oxidize the DIC pool

Trace metals, sulfur isotopes, organisms, iron speciation

What is the evidence of the NeoP oxidation event from sulfur isotopes

Apparent rise in oxidized S before the Shuram excursion, increased fractionation of S in the euxinic ocean suggests an addition of SO3 into the ocean leading to more pyrite burial (Rothman’s theory of pulsed O2 agrees)

What is the evidence of the NeoP oxidation event from Fe speciation

Proportions of different iron species can suggest what environment was present during their deposition

Anoxia: HR/T > 0.2

Ferruginous: HR/T > 0.2 and PY/HR < 0.8

Euxinic: PY/HR > 0.8

What’s the issue with the Fe speciation evidence from the Shuram excursion

There’s actually no obvious change in iron speciation throughout the NeoP

What is the evidence of the NeoP oxidation event from Redox sensitive trace elements

Can use concentrations of Mo and U in sediments to determine oxidation but once normalized, there’s no obvious event occurrence

What do I/Ca concentrations mean for ocean oxidation

Higher concentrations mean there’s more oxygen and lower concentrations mean nothing lol so cannot tell much

What are methane clathrates

Water ice that contain large amounts of methane in its crystal structure

How do methane clathrates form

When organic matter is remineralized by methanogenesis, forming CH4, within a narrow range of pressures and (cold) temperatures.

What promotes clathrate formation

Low SO4 and high organic matter export

What is a suggested method of exiting SBE

Methane clathrates causing destabilization of the earth’s climate by heating and increasing silicate weathering

If methane escape caused NeoP CIEs, what can be looked at

• global warming

• Ocean SO4 drawdown

• Ocean acidification

What alternatives explain the large variation in carbon isotopes during NeoP

• Diagenesis

• Local processes causing large scale variations that are assumed to align

• Authigenic carbonates with meteoric values