Zunli Lu, Syracuse
University: Ikaite Crystals Provide Climate Signal
March 27, 2012
first day of spring brought record high temperatures across the northern
part of the United States, while much of the Southwest was digging out
from a record-breaking spring snowstorm. The weather, it seems, has gone
topsy-turvy. Are the phenomena related? Are climate changes in one part
of the world felt half a world away?
To understand the present, scientists look for ways to unlock
information about past climate hidden in the fossil record. A team of
scientists led by Syracuse University geochemist Zunli Lu has found a
new key in the form of ikaite, a rare mineral that forms in cold waters.
Composed of calcium carbonate and water, ikaite crystals can be found
off the coasts of Antarctica and Greenland.
“Ikaite is an icy version of limestone,” say Lu, assistant professor of
earth sciences in SU’s College of Arts and Sciences. “The crystals are
only stable under cold conditions and actually melt at room
It turns out the water that holds the crystal structure together (called
the hydration water) traps information about temperatures present when
the crystals formed. This finding by Lu’s research team establishes, for
the first time, ikaite as a reliable proxy for studying past climate
conditions. The research was recently published online in the journal
Earth and Planetary Science Letters and will appear in print on April 1.
Lu conducted most of the experimental work for the study while a
post-doctoral researcher at Oxford University. Data interpretation was
done after he arrived at SU.
The scientists studied ikaite crystals from sediment cores drilled off
the coast of Antarctica. The sediment layers were deposited over 2,000
years. The scientists were particularly interested in crystals found in
layers deposited during the “Little Ice Age,” approximately 300 to 500
years ago, and during the “Medieval Warm Period,” approximately 500 to
1,000 years ago. Both climate events have been documented in Northern
Europe, but studies have been inconclusive as to whether the conditions
in Northern Europe extended to Antarctica.
crystals incorporate ocean bottom water into their structure as they
form. During cooling periods, when ice sheets are expanding, ocean
bottom water accumulates heavy oxygen isotopes (oxygen 18). When
glaciers melt, fresh water, enriched in light oxygen isotopes (oxygen
16), mixes with the bottom water. The scientists analyzed the ratio of
the oxygen isotopes in the hydration water and in the calcium carbonate.
They compared the results with climate conditions established in
Northern Europe across a 2,000-year time frame. They found a direct
correlation between the rise and fall of oxygen 18 in the crystals and
the documented warming and cooling periods.
“We showed that the Northern European climate events influenced climate
conditions in Antarctica,” Lu says. “More importantly, we are extremely
happy to figure out how to get a climate signal out of this peculiar
mineral. A new proxy is always welcome when studying past climate