Sharma researches ice age correlation

by Melana Yanos | 7/8/02 5:00am

Mukul Sharma, an assistant professor of earth science at Dartmouth, is one example of how some fresh insight into separate domains of knowledge, along with a bit of luck, can yield profound scientific results.

By utilizing information from previously published work, Sharma was able to recognize a significant correlation between the variation of the sun's magnetic activity and the variation of the earth's climate over the past 200,000 years.

Sharma first stumbled upon this discovery once he realized that the sun's magnetic activity has been varying in 100,000 year cycles " cycles which he later found out happened to correspond with the 100,000 year cycles of Earth's glacial and interglacial periods.

To calculate the sun's magnetic activity, Sharma turned to information about Beryllium-10 -- an isotope whose production increases when a large flux of cosmic rays enters Earth's atmosphere.

Sharma explained that essentially two factors -- the sun's magnetic field and the earth's magnetic field -- prevent the production of Beryllium-10 by deflecting away the galactic cosmic rays that promote its production.

"If you have high geomagnetic fields, the cosmic rays will not get in," said Sharma. He also explained that higher average magnetic fields created by the sun will decrease the flux of cosmic rays, and prevent it from reaching earth as well.

Sharma used data about the production of Beryllium-10 to make the appropriate calculations to determine the sun's solar activity for the past 200,000 years. He noticed that the solar activity varied in terms of 100,000 year cycles " a larger cycle than anyone had previously estimated.

Sharma consolidated this information regarding the sun's magnetic activity with data related to the Earth's climate changes, which had been derived from data of Oxygen isotopes extracted from various sites in the ocean.

"From my reading I realized that there's a cool way that I could use previously published data to estimate that variation," said Sharma, in regards to the calculations he had made for the sun's magnetic activity. "I recognized that variation in the oxygen isotopes of the ocean."

His discovery prompted further investigation, and eventually resulted in a full-fledged hypothesis that currently awaits ratification from other experts in the scientific community.

"So we find that the sun's activity seems to vary in a cyclical fashion; it has been close to zero and sometimes it is very high on a 1000-year time scale," Sharma explained.

"Therefore, when the sun is magnetically more active, there is a time of interglacials, which is when the earth's climate is relatively warm. When the solar activity is low, that is a time of glacial maximums."

Sharma cautioned that although the discovery appears compelling, it also has to be confirmed; particularly, the specific physical mechanisms that would explain why the sun is behaving in this cyclical manner have to be identified.

"People have identified mechanisms, the question is which one is actually working." said Sharma.

Additionally, Sharma's theory competes with the prominent Milankovitch theory, which attributes the Earth's climate cycles to the variation of Earth's eccentricity, or the distance from its position on the elliptical orbit to the sun..

The Earth orbits the sun in 100,000 year cycles, in which the Earth's orbital path fluctuates from becoming more circular to becoming more elliptical, and thus the consequent amount of radiation received from the sun varies as well.

Sharma pointed out that there is a major problem with the Milankovitch theory. "If you try to figure out how much radiation there would be from the eccentricity, you would find that it is very, very tiny; the sun's energy radiation is not sufficient enough."

He added, "if my hypothesis is right, that would imply that the 100,000 year cycles are caused by the solar activity and not by the orbital radiation and the eccentricity of the earth."

Sharma's compelling discovery did not begin with this end in mind; according to Sharma, the three-year project started as an avocation, with the purpose of studying the chemistry of the oceans.

"I went into it thinking I would learn something about transport of cosmic dust," he explained. "Cosmic dust contains a lot of Osmium, which falls into the oceans and changes the chemistry of the oceans."

Therefore, according to Sharma, the distribution of Osmium isotopes in the ocean can be used to figure out how much cosmic dust is falling into it.

Yet the implications of what started out as part-time research may now have the attention of an audience composed of scientists from many different areas of study.

Sharma noted that the verification of his hypothesis would bear a great deal of significance for researchers such as climatologists, who would have to adjust their predictions of future trends, and solar physicists, who would be able to more clearly understand the sun's behavior.