Atmospheric Chemistry Chemistry Climate Change Ocean Acidification thermodynamics

Does history repeat itself?: Investigating the Paleocene-Eocene Thermal Maximum

References: Haynes, Laura L..; Hönisch, Bärbel (2020). The seawater carbon inventory at the Paleocene-Eocene Thermal Maximum. Proc. Nat. Acad. Sci. U S A. 117, 24088-24095.

DOI: https://doi.org/10.1073/pnas.2003197117

Reading Time: 5 minutes

Picture this: 55.6 million years ago (otherwise written as 55.6 Mya). Earth’s geology and atmosphere was rapidly changing: volcanoes were erupting more often, global temperatures rose, oceans became more acidic, and large amounts of carbon-based molecules were released into the ocean. Furthermore, the diversity of species (otherwise known as biodiversity) fluctuated vigorously. This time period was known as the Paleocene-Eocene Thermal Maximum (PETM), as it was named after the spike in temperature on Earth. It must have been extremely stressful to live in these conditions, right? Well, we already know. For scientists, this time period has been studied to understand our world today. It is postulated that the PETM can mirror our current climate crisis, which really puts everything into perspective. So, if we want to understand today, we have to look past yesterday.

A team of scientists at Columbia University decided to undertake this task and investigate the ocean during the PETM. If you are reading this article, you have probably heard of the concept of Ocean Acidification. Well, the ocean also became more acidic during the PETM too, so the team wanted to see how we compare. The group decided to tackle this issue head on by calculating the amount of carbon molecules entering the ocean (and, by proxy, the ocean’s acidity) to refine our understanding of the PETM. What they found was very interesting!

What did they find? How much carbon entered the water?

Magma cooling when it reaches the Earth’s surface. Image Credit: NSF and NOAA

In totality, the group calculated that 14,900 petagrams or 32,848,877,065,547,000 pounds of carbon entered the ocean during the PETM! Interestingly, due to all of the geological activity (like volcanoes erupting) the land and subterranean sources of carbon on Earth lost about 10% of its amount to the ocean. Furthermore, their calculations tell us that a significant amount of the carbon released into the ocean came from magma. In addition, the release of thermogenic methane, which is a carbon-based molecule produced by very high heats and pressures under the ocean floor, was also a significantly high contributor to the amount of carbon in the ocean.

For more specific details, the amount of carbon in the ocean increased from ~21 parts per million (ppm) to 33ppm. For comparison, current ocean levels have about 25ppm of carbon. All of these findings simultaneously show the magnitude of climate change for both the PETM and now.

How did they do it?

An image of a planktic foraminifera. Image Credit: Hannes Grobe/AWI

Since the PETM was 55.6Mya, we cannot simply measure the conditions of the water. To overcome this issue, the group targeted organisms called planktic foraminifera which are microscopic plankton with hard shells that can be preserved as fossils. Their shells contain Boron and Calcium atoms, and their amounts in the shell are almost directly related to the acidity of the water. So, the group could mathematically relate measurements of the amount of Boron and Calcium in these shells to the acidity of the water, and therefore find the amount of dissolved carbon in the ocean. For clarity’s sake, the group studied the amount of dissolved inorganic carbon (DIC). These molecules include carbon dioxide, calcium carbonate, and others which all have an effect on the acidity of the water.

Why does it matter?

This study both informs our understanding of the PETM and enlightens us of our current climate crisis. By refining previous scientific work, we can better discern how our Earth has formed the way it has. The group indicates that currently modern society releases carbon at rates MUCH faster than what they calculated during the PETM. Not only does this inform us of the massive scale of our current climate issue, but it paints a scary story of what happens to species when this carbon release goes uncontrolled. This study matters because, to answer the titular question, yes history does repeat itself and we should learn from yesterday to create today.

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