Using ice cores to study solar influences on climate

A thin section of glacier ice under polarised light showing the bubbles in the ice and some of the crystal structure
A thin section of glacier ice under polarised light showing the bubbles in the ice and some of the crystal structure (Photo: Vin Morgan)

Aside from its direct effect on our climate by providing the heat input, questions remain about the ways in which the sun influences the climate system.

What effects result from its small variations in brightness? How do changes in cosmic ray bombardment that accompany changes in the sun's magnetic field influence the atmosphere? How does bombardment by solar particles themselves affect the atmosphere? 

This last question has had one contentious aspect in recent years. Some researchers have suggested that when the sun has an occasional outburst of protons, known as a solar proton event, this creates significant quantities of nitrate in the atmosphere which can be detected in ice cores. This finding has, however, been disputed by others.

If clear evidence or lack of evidence could be found for this connection, it would help resolve the dispute and advance understanding of nitrate chemistry - an area of atmospheric chemistry which is not well understood. 

Just such evidence comes from the Law Dome 'Dome Summit South' (DSS) core. With its very accurately dated record, nitrate from the DSS core has been compared to the dates of 17 known solar events from the late 19th to late 20th centuries.

The results showed that while not all nitrate spikes were associated with solar events and not all solar events produced nitrate spikes, there was a weak increase in nitrate on average following the solar events that was unlikely to be the result of chance.

This may help explain why different research groups have disagreed in the past, and raises questions about how important such factors as site location and snowfall rates might be in the detection of the solar effect.