UV induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate

J. Savarino, A. Romero, J. Cole-Dai, S. Bekki, and M.H. Thiemens

Universität Heidelberg Institut für Umweltphysik

Content

• Some explanations/definitions

• Sulphur-Cycle

• Summary of the paper

• Questions

• Discussion

Universität Heidelberg Institut für Umweltphysik

What means and

= ( Rsample/Rstandard – 1) x 1000

R = [33S]/[32S]

33S = 33S – 1000 x [(1 + 34S/1000)0.515 – 1 ] 0

36S = 36S – 1000 x [(1 + 34S/1000)1.90 –1 ] 0

Universität Heidelberg Institut für Umweltphysik

Mass-dependent and mass- independent fraction

• Mass dependent: only the different mass is the cause of different fraction of the isotopes

• Mass independent: fractionation caused by something else as mass (example Photolyse in the case of SO2)

Universität Heidelberg Institut für Umweltphysik

Depth of penetration of solar radiation through the

atmosphere

Universität Heidelberg Institut für Umweltphysik

Sulphur-Cycle

Universität Heidelberg Institut für Umweltphysik

The sense behind it ?

• 1. determination of the degree of UV light affected S

oxidation in the atmosphere

Universität Heidelberg Institut für Umweltphysik

• 2. Determination of the stratospheric and tropospheric nature of volcanic eruptions -> reassess the climatic impact of past volcanic eruptions (?)

„sulfur isotopic analysis of ice core volcanic sulfate can be independent method to identify climatically

significant eruptions in the investigation of the climate volcanic connection“

Observation• Analysis of antarctic snow blocks, ice cores

and aerosol filter• For volcanic sulfate, the S - isotopes

demonstrate a significant range of variations• values 34S, 33S, 36S of aerosol and

background sulfate are all within small isotopic ranges

• mass-independent sulfur isotopes anomalies in the stratosphere appear to depend on the exposure of SO2 to UV radiation (experiments in the laboratory)

Universität Heidelberg Institut für Umweltphysik

Plot of 33S and 36S sulfur isotope anomalies of different

sulfate sources

Universität Heidelberg Institut für Umweltphysik

?

Plot of 33S versus 34S and Plot of 36S and 33S

Universität Heidelberg Institut für Umweltphysik

My Questions to the authors

• Did you inspect carefully into the graphics? C.f., why Cerro Hudson eruption is not included in the 36S plot?

• Why they show only this two examples of volcanic eruption, at least Tambora should have been a better examble than Cerro Hudson?

• .....?

Thanks for your

attention and tell

me - what do

you think...!!!

Plot of 33S values versus sample age

Universität Heidelberg Institut für Umweltphysik

Farquar, 2000