Giant clams may be a good source of "paleoweather" data
If you're wondering what the weather was like several thousand years ago, well … there aren't going to be weather reports from back then that you can check. What there are, however, are fossilized giant clam shells, and a new study suggests that they could provide the answers.
Led by Prof. Yan Hong, scientists from the Chinese Academy of Sciences started by obtaining relatively recent non-fossilized shells of the Tridacna giant clam, which is found in the western Pacific Ocean. It was already known that the mollusks deposit clearly-defined growth bands in their shells – like the growth rings in a tree trunk – on a daily basis.
Upon analyzing these bands, the researchers were able to determine how the weather had varied throughout each individual day. For instance, on days when historical weather records showed that a cyclone had been approaching a clam's home area, the relatively short band for that day indicated that growth was slowed in response to the foul weather.
Additionally, because cyclones bring nutrient-rich water up from the depths to the surface, the growth bands for the stormy days correspondingly had a high iron/calcium ratio. And because that upwelling of nutrients also causes phytoplankton blooms, the bands additionally exhibited a strong fluorescence intensity.
It is now hoped that fossilized shells could be analyzed in the same fashion, in order to ascertain weather patterns dating back 65 million years or more.
A paper on the research was recently published in the journal PNAS.
Source: Chinese Academy of Sciences