Thus the fjords regulate the Earth’s climate

The fjords are characteristic elements of the landscapes of the far north: deep and steep valleys, where the sea meets the land in a sinuous embrace. Their undoubted charm should not mislead, because far from being simple scenic attractions, the fjords are also, and above all, structures of crucial importance for the climate of our planet. In fact, they trap a huge amount of carbon on their seabed, away from the atmosphere where it would combine with oxygen to form tons of dangerous carbon dioxide. And as a new study published in Science Advances reveals, they thus contribute to regulating the Earth’s climate cycles, driving the alternation between glacial and interglacial periods.

For some years now, in fact, it has been discovered that these deep valleys carved out by glaciers represent one of the richest carbon sinks on the planet. The oceans are in fact the main deposit of organic sediments on Earth, and the fjords are one of the most active marine hot spots: although they constitute just 0.1% of the total marine surface of our planet, they trap about 12% of the carbon present in the seas and in the oceans of the globe. In fact, these are strategic drainage points, which collect the organic sediments transported by rainwater and rivers, and fix them in the sediment deposits that accumulate on their bottom. This, at least, in the so-called interglacial periods, i.e. in the phases of an glaciation in which the climate is milder (like the one we are currently in). When temperatures drop again, the situation could turn out to be very different: in fact, the glaciers once again cover the fjords, pushing the sediments accumulated on the seabed to the surface, thus exposing them once again to oxygen.

To understand what consequences the return of ice has for the carbon accumulated in the fjords, a team of international researchers coordinated by Brent Rosenheim, of the University of South Florida, studied how the sediments deposited in the fjords respond to heat, comparing their resistance temperature to that of sediments deposited on the ocean floor. Their experiments have shown that the ability of flowers to trap organic carbon is much more transient than that of the deepest parts of the oceans: once exposed to the sun and to the air by the movements of the glaciers, the sediments coming from the fjords tend to react with oxygen, again introducing large amounts of CO₂ in the earth’s atmosphere.

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In a normal climate cycle, fjords therefore act as a kind of thermostat for the planet: sequestering carbon during warm periods, thus helping to cool the atmosphere, and then reintroducing it in colder phases, helping the climate return, over time towards milder temperatures. However, with the arrival of the industrial age and the climate changes caused by our species, this delicate balance may no longer be the same. “Fiords occupy an overall limited space, but they play a significant role in modulating temperature changes between glacial and interglacial periods,” explains Rosenheim. ‘Human-induced global warming has disrupted this regular rhythm of glacial and interglacial cycles, making better understanding how fjords and other carbon-settled hot spots will react is increasingly critical.’