Local community members met Tuesday at the Ames Public Library to hear a lecture on studying climate change through the use of bivalves, ice cores, speleothems and diatoms.
Alan Wanamaker, associate professor of geological and atmospheric sciences, and Beth Caissie, assistant professor of geological and atmospheric sciences, talked about the past of climate change to better understand the future.
The talk was the first of a three-part series that will continue April 26 and May 3. The event was hosted by Iowa State's department of geological and atmospheric sciences and the National Science Foundation.
The lecture focused on four methods in which climate change is studied. Wanamaker started the evening by saying he was going to “try to place what we see in the modern climate into context."
He also encouraged audience members to write down questions on slips of paper to later turn in so they can be answered in the third installment of the lecture series, “Behind the Science of Climate Change.”
Wanamaker first addressed what climate is as opposed to what weather is. Weather is variations of coldness, warmth, dryness and wetness from day to day.
“Climate is generally considered to be a 30-year average of weather condition,” Wanamaker said.
Environmental variables worth addressing when discussing climate include cloud cover, heat, temperature, humidity, pressure, winds and precipitation rate.
“Climate is not just temperature only," Wanamaker said. "It’s all those things combined."
Wanamaker prefaced his talk by introducing the audience to the word “paleo,” meaning ancient.
“Paleoclimate data can help place modern change into context," Wanamaker said. "It can also expand our understanding of natural climate variability over many time scales, and paleoclimate data can be used with instrumental data to better understand mechanisms that influence climate variability.”
One way Wanamaker sees climate change being studied is through proxy climate record. Proxy data is the data collected by paleoclimatologists from natural records of climate variability.
Wanamaker’s first example of studying seasonal to annual records of climate was through the age of clam shells.
Similarly to how trees are studied for their age, clams also have a “unique barcode” that can be studied to determine climate patterns. The thickness of the increments displayed on the shells are used to determine temperature. Variations of temperature are determined to help examine what caused climate changes through the years.
Wanamaker then discussed his time collecting clams in the Gulf of Maine, which he refers to as having “one fun day out in the field” of collecting clams followed by “months and months and months” of tedious work studying the clams in the laboratory.
Caissie then took the floor for the second example: ice cores.
Ice Cores are mostly extracted from places like Greenland and Antarctica through mechanical drilling.
In order to extract paleoclimate records from ice cores, little bubbles trapped within the ice are examined. These bubbles also referred to as “fossil air” are then studied because they have trapped methane or carbon dioxide in them.
“Carbon dioxide has been increasing over the entire industrial period, and today we’re up at about 410ppm,” Caissie said.
This type of information can be found through studying ice cores.
Similarly to determining age of clam shells and trees, ice cores have seasonal layers that help to tell their age. Marker horizons are also looked at for a pulse of atmospheric radioactivity, and volcanic eruptions. Flow modeling is also a method of determining age through making models showing how much the ice was moving and how much the ice has been compressed over time.
Stable isotopes from the ice are also looked at to determine the temperature of an ice core.
“This is one of the most amazing things that I think we’ve figured out through paleoclimate, which is using these ice cores and in this case we go from today back 800,000 years and we know what carbon dioxide concentration was like over that time period by looking at those bubbles and we can estimate what the temperature was by using that quantitative relationship,” Caissie said when referring to a specific graph on ice core data.
Wanamaker’s third example was speleothems. Speleothems are cave deposits with 10 to 10,000 years of climate data. Stalactites and stalagmites are types of speleothems made of CaCO3 that can be studied inside caves.
“The climate outside of the cave in fact makes its way into the cave," Wanamaker said. "The temperature in the cave mimics that of the mean annual temperature outside of the cave, and how much [speleothems] grow can be related to how much it rains and also the vegetation cover that is above the cave. When water flows through [vegetation], it interacts with it and the chemistry of the water going through that vegetation takes on a particular signal that gets recorded in that mineral."
The growth of these speleothems can be weakened or lengthened based on the rainfall.
Fine-scale sampling is used to determine the climate these stalagmites experiences from year to year.
Caissie focused on sediment cores for the final example of the lecture. The sediments cores are drilled from the seafloor and sliced open, similarly to how a book is opened, in order to study the characteristics seen within the core.
Diatom-based Sea Ice Proxy is one method for determining age of sediment cores. Under a microscope the cores are studied to determine the age of the sediment.
The second method for determining age is by picking out the little microorganisms found within the sediment core and looking at the chemistry in the shell of that organism. Patterns seen within the chemistry of these organisms helps to classify them as glacial or interglacial.
“If we take the paleoclimate data that we can come up with we can actually use that to extend our instrumental record of climate today so we can better understand the climate system and what’s driving it,” Caissie said.
The next installment in this lecture series will be at 7 p.m. April 26 in the Auditorium of the Ames Public Library. Modern and future climate estimates and projections will be discussed.