The climate changes in the Atlantic Ocean seen in the shell of a clam

The valves of an ocean quahog
The valves of an ocean quahog

An article published in the journal “Nature Communications” describes a research on the climate changes in the last millennium in the north Atlantic Ocean studied by the shells of ocean quahog (photo ©Hans Hillewaert). This species, scientifically called Arctica islandica, is the longest-living animal in the world, therefore the growth rings of its shells can provide a lot of information on the environment in which they formed.

Ocean clams are widespread in the North Atlantic Ocean and are well known as they’re edible. They’re not to be confused with the quahog, also known as hard clam (Mercenaria mercenaria), another mollusk belonging to the clam family. Appreciated as food, for once the oceanic clam proved helpful due to its longevity as it can live for over 500 years and its shell forms growth rings, a bit like trees, which have chemical characteristics that can allow to reconstruct the history of ocean where the clam grew.

In particular, the analysis of the oxygen isotope content in the ocean quahog shell reflects certain environmental changes. In the past some studies were already carried out showing traces of the changes caused by the so-called Little Ice Age between the 16th and 19th centuries but also the great eruption of the volcano Tambora in 1815.

By examining the chemical changes occurring in the shell’s growth rings in specimens of ocean quahog and comparing them with recordings of events such as variability in solar activity, volcanic eruptions and temperatures in the atmosphere, the authors of this research led by experts of the universities of Cardiff and Bangor reconstructed a picture of the changes in the ocean and studied how they were linked to each other over time.

The result is that solar variability and volcanic eruptions have shown important roles in the changes that have occurred in the Atlantic Ocean last millennium. Marine variability proved to be important in driving the changes in the air temperature of the northern hemisphere in the pre-industrial era.

This trend isn’t seen in the industrial period, when the changes in temperature caused by human activities started. During this period, those changes occurred first on the mainland preceding the marine environment variability.

We started performing instrumental observations of the oceans only in the last century and reconstructions based on marine sediments provide approximate results. That made any research on the role played by the ocean in the broader climate system more difficult. Having more precise time references such as those recorded in the shells of ocean quahog can help to improve the research on very long periods.

Developing more accurate climate models may help us better understand the trends and predictions even in the short term. To obtain these results, the researchers use technological tools that are increasingly advanced but data collection can also be based on a humble mollusk such as the ocean quahog.

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