The possibility of obtaining ultra-low-δ18O signature of precipitation near equatorial latitudes during the Snowball Earth glaciation episodes

Abstract

Hydrothermally-altered rocks with ultra-low-δ18O and δD were discovered in Karelia, Russia, over 500km along the Belomorian Belt of the Baltic Shield. The ages of low δ18O and δD values are 2.41Ga and 2.29Ga, corresponding to the first and third Paleoproterozoic Snowball earth glacial episodes. Paleogeographic reconstruction suggests low latitudes for Baltica throughout Paleoproterozoic ice ages, requiring an effective distillation of water isotopes over short transport distances. Here we summarize how to use hydrothermally altered rocks to infer δ18O value of altering meteoric waters, then use an idealized General Circulation Model to test climate states with variable amount of ice cover and to check the hydrologic possibility of ultra-low-δ18O precipitation at low latitudes. Our model results suggest that the low δ18O values in precipitation is best achieved if the area of open water is quite narrow around the equator between latitudes 5°S and 5°N, or the Jormungand climate state. The δ18O of precipitation is high (>−15‰) over open water where high-δ18O vapor from ocean mixes with low-δ18O atmospheric water vapor. As such, a position of about 5–10° north or south of the equator is needed in order to achieve low δ18O of precipitation from an open water source. Our results suggest a slushball climate state with wide areas of open water is less likely to produce ultra-low-δ18O rocks for the low latitude position of Baltica.