Young mountains versus CO2

Mountain view in Denali National Park, Alaska / Frank Kovalchek (Creative Commons Attribution 2.0 Generic license)
Mountain view in Denali National Park, Alaska / Frank Kovalchek (Creative Commons Attribution 2.0 Generic license)

Considering that the research site was a lake 62 miles north of the Arctic Circle in northeast Siberia, Russia, I didn’t think the topic would turn to mountains. Yet I’ve found a new love for mountains. Everything is interconnected.

Lake E project

Lake El-gygytgyn sits in a crater that formed 3.6 million years before present at the site of a massive meteorite impact. An international team of scientists from the United States, Russia, Germany and Austria converged on Lake E to extract a sediment core from the lake bed. The 1165 foot [355 meter] long paleoclimate record is an unprecedented achievement: the longest sediment core ever collected on land in the terrestrial Arctic, and it serves as a record indexing past climate change.

Paleoclimatology is the study of past climates. It helps inform our understanding of modern climate and climate change.

The Lake E project was part of the International Continental Drilling Program. The U.S. research team was led by Julie Brigham-Grette, professor of Quaternary Geology, Geosciences department, University of Massachusetts Amherst.

High levels of CO2 in Earth’s past

“One of the questions I always get is: If today’s carbon dioxide is 400 part per mil and it’s because of human intervention, why was the atmosphere in the 360 part per mil in the Pliocene?” Brigham-Grette told FrontierScientists. “From the time of the dinosaurs, back 65 million years ago, the earth’s carbon dioxide and greenhouse gases have been declining over time in steps and starts.”

Why? Most likely because of a natural process called “The rock weathering cycle, the rock weathering thermostat,” Brigham-Grette explained.

I’m grappling now with what I just learned about mountains– this earth process I’m surprised I wasn’t taught in school. There are so many parts of the Lake E project that leave me with a hundred tabs open as I read papers, research what terms mean, and click through further links, entranced. This is only one tiny piece of an immense and wondrous puzzle.

Brigham-Grette said “With mountain building we are actually bringing down, over millions of years, the levels of carbon dioxide.”

I’ve heard a lot lately about geoengineering and research into what mankind can do to quickly catch and store carbon to combat rising carbon dioxide levels. Mountains can’t match the pace of humankind’s fossil-fuel burning &c. alone, but they’ve been at this game for a long long time– long before anthropogenic (human caused) warming even began, earth processes have been regulating atmospheric carbon dioxide.

Chemical weathering

The chemical weathering process might be said to start in the clouds. While pure water (H2O) has a neutral pH of 7, rain water has a slightly acidic pH of 5 – 5.5 because airborne carbon dioxide (CO2) dissolves in water. Thus rain water contains carbonic acid (H2CO3). Being acidic, the carbonic acid can impact and react with most minerals. This reaction or chemical weathering is a slow process; the events I’m describing are commonly underway and the cycle takes place over millions of years.

Sandstone statue shows the effect of weathering, Dresden, Germany / (public domain)
Statue shows the effect of chemical weathering, Dresden, Germany / (public domain)

Rocks can be composed of minerals containing carbonates (i.e. limestone) and react swiftly, while other rocks are composed of silicate minerals (i.e. basalts) and react more slowly. Despite differences in how rocks react to being weathered by rainfall containing carbonic acid, on simple terms any of these reactions can release calcium (Ca) and bicarbonate (HCO3) into the hydrologic system. These are rock-forming elements in a number of ways. Dissolved in water, they flow through groundwater and creeks and rivers and, if not deposited somewhere and left behind, they eventually reach lakes and oceans.

Microorganisms living in aquatic systems use a product of those dissolved building blocks to create their hard shells, which they form from calcium carbonate (CaCO3). These organisms include plankton like coccoliths and planktonic foraminifera, corals, and even larger organisms like mollusks. When they die, their calcium carbonate shells fall through the water column to the ground, forming layers of sediment. They might eventually solidify into sedimentary rocks such as limestone, which traps the carbon in their calcium carbonate shells, locking it away from the atmosphere for long periods of time.

Rock weathering probably sequesters, or stores away, an estimated gigaton of atmospheric carbon dioxide annually, while the atmosphere holds around 720 gigatons. Something like 60 million gigatons of carbon are estimated to be stored away globally in sedimentary rocks. Pretty cool.

Toward a balance

Rock transportation along waterway, Crow Creek Pass, Alaska / Frank Kovalchek (Creative Commons Attribution 2.0 Generic license)
Rock transportation along waterway, Crow Creek Pass, Alaska / Frank Kovalchek (Creative Commons Attribution 2.0 Generic license)

Mountain building episodes, when the motion of earth’s tectonic plates causes uplift and rocks reach new heights, exposes rocks and their minerals to rainfall and therefore weathering. A cold and snowy mountain peak doesn’t meet the conditions well because very low temperatures prevent the flow of liquid water, but this process operates over million-year time scales. Given enough time, rockfalls, grinding glaciers, erosion and determined rivers can carry ground-up rocks to warmer, wetter, and more weathering-friendly locations.

You can imagine how the dependence on warm temperatures and rainfall helps to balance climate. Freezing temperatures inhibit the drawdown and storage of carbon dioxide through the chemical weathering process, while warm temperatures encourage it. Translation: during ice ages more carbon dioxide is left in the atmosphere to act as a greenhouse gas and retain warmth. During warm periods the opposite trend occurs.

Ice ages are divided by a series of glacial events, cold periods marked by the expansion of glaciers and ice sheets, which are interrupted by interglacial events, intermittent warm periods. We are currently experiencing an interglacial event which is part of an ice age that began 2.58 million years ago at at the start of the Pleistocene epoch. The Pleistocene was preceded by the Pliocene epoch (95.333 million – 2.58 million years before present) and followed by the Holocene Epoch (11,700 calendar years before present – modern day); these epochs are simply ways to subdivide, label and characterize geologic time scales.

We can learn to better predict our climate near-future by gaining a more clear understanding of climate-impacting forces in past time frames when conditions were similar.

Pliocene conditions

Brigham-Grette outlined high atmospheric carbon dioxide levels starting in the age of dinosaurs– “So at the time, coming from 2 or 3 thousand parts per mil, some very large number, we intersected some 400 parts per mil in the Pliocene, roughly.” This was said in 2013, and she was careful to note that the numbers were still approximate until there was official word from chemists reconstructing Pliocene-era CO2 levels in the Lake E sediment core. The rock weathering cycle is believed to be mainly responsible for lowering atmospheric carbon dioxide concentrations to roughly 400 parts per million during the Pliocene around the time of the meteorite strike 3.6 million years ago, when the Arctic supported a heavily forested ecosystem. Atmospheric carbon dioxide concentrations continued to lower incrementally, and some 2 – 3 million years before present the Arctic climate shifted toward a cold permafrost ecosystem.

That permafrost regime is now changing as permafrost thaws out in modern-day rising temperatures. Since the time of the Industrial Revolution, atmospheric carbon dioxide levels have increased swiftly.

Temperature change (blue) and carbon dioxide change (red) observed in ice core records / Courtesy NOAA
Temperature change (blue) and carbon dioxide change (red) observed in ice core records / Courtesy NOAA

Modern trends

Chemical weathering processes regulate the geologic carbon cycle over million-year time scales. Humans have radically changed Earth’s carbon balance over mere centuries.

“It looks like in fact the carbon dioxide at this time about 3.6 million years ago was close to 400 parts per mil– was basically what we just hit this year. So we’ve achieved that already in our own atmosphere in the modern world,” said Brigham-Grette. “What it means for us is, with a very small change in carbon dioxide which is really relatively small, we can basically be driving the earth’s system toward a forested Arctic, towards eliminating the major ice sheets.”



Work is ongoing, but you can already find two major Lake El’gygytgyn papers in Science.

2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia
Martin Melles, Julie Brigham-Grette, Pavel S. Minyuk, Norbert R. Nowaczyk, Volker Wennrich, Robert M. DeConto, Patricia M. Anderson, Andrei A. Andreev, Anthony Coletti, Timothy L. Cook, Eeva Haltia-Hovi, Maaret Kukkonen, Anatoli V. Lozhkin, Peter Rosén, Pavel Tarasov, Hendrik Vogel, and Bernd Wagner
Science 20 July 2012: 337 (6092), 315-320.Published online 21 June 2012 [DOI:10.1126/science.1222135] (abstract link)

Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia
Julie Brigham-Grette, Martin Melles, Pavel Minyuk, Andrei Andreev, Pavel Tarasov, Robert DeConto, Sebastian Koenig, Norbert Nowaczyk, Volker Wennrich, Peter Rosén, Eeva Haltia, Tim Cook, Catalina Gebhardt, Carsten Meyer-Jacob, Jeff Snyder, and Ulrike Herzschuh
Science 21 June 2013: 340 (6139), 1421-1427.Published online 9 May 2013 [DOI:10.1126/science.1233137] (abstract link)

Laura Nielsen

Frontier Scientists: presenting scientific discovery in the Arctic and beyond

Where is Lake El’gygytgyn? project