Sediments That Tell a Story: Patagonian Ice Field Sediment Cores Reveal Glacial Waxing and Waning Over Hundreds of Years
A picture of the Southern Patagonia Ice Field on February 13, 2014, taken from the International Space Station. (Expedition 38 crew member/ NASA)
A team of researchers began their journey around frigid Patagonia, moving through water channels to achieve the fjords, surrounded by ice and snow. They withstood freezing temperatures throughout their journey, all within the hope of extracting the proper sediment core: the important thing to glacial history within the Southern Patagonian Ice Field. Over the course of their research, which led to a study recently published in Quaternary Science Reviews, lead creator Matthias Troch of Ghent University and his colleagues geochemically analyzed a 12.2 meter-long sediment core from an area in Patagonia called the Wide Channel to find out when glaciers retreated and stabilized within the geological past. Their findings on glacial waxing and waning patterns may offer insights as to how the world’s glaciers may respond in the longer term as global temperatures increase.
Situated within the southernmost a part of South America, the Southern Patagonian Ice Field, where the team did its research, is one among two major ice fields within the Patagonian Andes. Ice fields are a series of interconnected ice caps and glaciers. Patagonia’s Northern and Southern Ice Fields are the most important within the Southern Hemisphere, other than those in Antarctica. They’re home to among the world’s fastest-flowing glaciers, and ice flow speeds vary between glaciers across the ice fields.
The Southern Patagonia Ice Field stretches north to south for 220 miles, and it’s drained by 53 principal outlet glaciers. The distant landscape is characterised by a cold, snowy climate with high mountain peaks and clouds that block most incoming sunlight. Westerly winds take up large amounts of moisture as they cross the Pacific, releasing as much as 160 inches of precipitation onto the peaks every year. The weather pose many challenges for researchers looking for to know the shrinking glaciers in the world; many are forced to spend weeks waiting for weather conducive to traveling, and researchers are sometimes stuck in tents for long periods while waiting for unfavorable weather to clear.
As ice flows through glaciers, it grinds up rock into superb particles because it passes over the bedrock. These superb particles are carried by streams that flow out of the glaciers, and the sediments are eventually deposited in oceans and glacier-fed lakes. As these sediments are deposited, they create distinct layers, each from a distinct time frame. Researchers then approach these sites with cylindrical tools, extracting long, cylindrical samples of sediment: these samples are sediment cores. Sediment cores, though fascinating in and of themselves, contain a record of past glacial activity.
Chilean Patagonia landscape (pxfuel).
The research team traveled through the Wide Channel alongside the ice fields, collecting samples from the fjord by boat. Sediment cores are composed of two principal sections: gray clay on the underside and alternating dark gray, light gray, and brown mud and clay layers on top. Since each layer of sediment represents a distinct time frame and draws on different portions of the underlying bedrock, the magnetic properties and grain sizes of the sediment particles vary. The study authors analyzed quite a few sediment core properties to find out what grain sizes, rock characteristics, chronology, and sediment composition reveal about glacial patterns over the past 10-15 thousand years.
The researchers analyzed quite a few properties, allowing them to find out exact periods of glacial stability and retreat dating back 15,000 years, providing priceless insights regarding environmental changes during those times. The findings indicate outlet glaciers fluctuated synchronously over many centuries throughout the Neoglacial period (which covers the last 5.8 thousand years). Two major glaciers within the Southern Ice Field, namely Penguin and Europa, remained relatively stable throughout the Holocene (11.2-5.8 thousand years ago), but they fluctuated considerably throughout the Neoglacial period. At times within the Neoglacial period, glaciers retreated further inland than the current day, providing insight into how these icecaps may respond in the longer term as CO2 emissions proceed to rise.
Bethan Davies, a senior lecturer at Newcastle University, makes a speciality of glaciology and glacial geology research. In an email interview with GlacierHub, Davies, who was not related to the paper, discussed the specifics of glacial sediment core research. She explains that when doing this type of research, “the final aim is twofold: to know a process, and to know the timing of the method.” In other words, sediment cores provide necessary insight regarding the processes of sediment formation, transport and deposition, the environment through which they occurred, and the timescale on which they occurred.
Sediment cores taken with a gravity corer on the Greenland continental slope, 2008.
Understanding the main points sediment cores provide requires “specialist skills,” like with the ability to discover what the sediment colours and composition say about the encompassing environment, in line with Davies.
Sediment cores have the power to recreate a geological landscape dating back hundreds of years. This is essential information, Davies says, for addressing the present climate crisis: “Glaciers are responding today to climate change, however the observational record could be very short. To be able to understand how they reply to extremes of climate change we’d like an extended data set.”
Analyzing sediment cores to find out periods of glacial waning allows scientists to check their findings with other resources, corresponding to ice cores, to see how the climate responds when glaciers melt and water levels rise. Much of the work on glaciers and climate has occurred within the Alps, Himalayas, and Alaska; recent glacier research in Patagonia, which is kind of distant from other research sites, may help determine the similarities and differences in regional patterns.
Many Patagonian glaciers have been shrinking for the reason that end of the Little Ice Age about 150 years ago, and increasing rates of melting in recent times have made the Patagonian Ice Sheets one among the most important contributors to sea level rise. Thus, understanding glacial waxing and waning patterns via sediment cores is becoming increasingly necessary in our ability to answer a changing climate.
GlacierHub is a climate communication initiative led by Ben Orlove, an anthropologist on the Columbia Climate School. Lots of GlacierHub’s writers are Climate School students or alumni.
