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A clue why the ice age became much longer

Enlarge / Wee foraminifera, whose shell holds chemical clues to past climates.If you have read about the "Ice Age" of Earth's latest history before you certainly learned that the cyclical rhythm of these climate changes is governed by several reliable cycles in the Earth's orbit. That relationship is quite clear, but there is also a fascinating and unresolved puzzle here. For about the last 700,000 years, glacial periods were each about 1 00,000 years long and revealed with a subtle cycle in the shape of the Earth's orbit around the sun. However, if you look at the 500,000 years before that, you will see shorter lakes that correspond to a 41,000-year cycle in the slope of the Earth's axis. Satisfactory explanations for this change in the Earth's time signature have proven to be painful. Of course there have been ideas. It may be that the ice sheet in North America and Europe reached a kind of critical mass that became too large to fail during the weaker 41,000 years of warming. The culprit can also lie in the sea, where the circulation changes or increases in the wind-blown dust that fertilizes plankton growth, could draw greenhouse gas out of the atmosphere, which makes the ice age older. A new study led by Adam Hasenfratz and Samuel Jaccard at the University of Bern may have found a piece of the puzzle bundle at the bottom of the sea around Antarctica. The passage of the gas The core of the seabed sediment…

 Wee foraminifera, whose should contain chemical clues to past climates.

Enlarge / Wee foraminifera, whose shell holds chemical clues to past climates.

If you have read about the “Ice Age” of Earth’s latest history before you certainly learned that the cyclical rhythm of these climate changes is governed by several reliable cycles in the Earth’s orbit. That relationship is quite clear, but there is also a fascinating and unresolved puzzle here. For about the last 700,000 years, glacial periods were each about 1

00,000 years long and revealed with a subtle cycle in the shape of the Earth’s orbit around the sun. However, if you look at the 500,000 years before that, you will see shorter lakes that correspond to a 41,000-year cycle in the slope of the Earth’s axis. Satisfactory explanations for this change in the Earth’s time signature have proven to be painful.

Of course there have been ideas. It may be that the ice sheet in North America and Europe reached a kind of critical mass that became too large to fail during the weaker 41,000 years of warming. The culprit can also lie in the sea, where the circulation changes or increases in the wind-blown dust that fertilizes plankton growth, could draw greenhouse gas out of the atmosphere, which makes the ice age older.

A new study led by Adam Hasenfratz and Samuel Jaccard at the University of Bern may have found a piece of the puzzle bundle at the bottom of the sea around Antarctica.

The passage of the gas

The core of the seabed sediment was gathered there – spanning 1.5 million years of history’s goal a place where surface water and deep water are mixed. Carbon dioxide accumulates in deep sea as water makes its long journey along the bottom. Where the water is mixed up against the surface in places like this, the gas has the ability to vent (perhaps complaining about how dark it is down there where it enters the atmosphere).

This emission of carbon dioxide is one of the keys to the ice age. The changes in the northern hemisphere summer sunlight caused by the Earth’s cycle cycles are weak enough to melt the continent, which spans ice lists a little, but not enough to explain the large temperature fluctuations. Therefore, you need other parts of the climate system to react and strengthen the orbital-controlled temperature change. The movement of CO 2 to and from the sea is a major part of this, reinforcing or weakening the earth’s greenhouse effect.

This means that everything that affects the exchange of CO 2 ] between the sea and the atmosphere can have a great impact on the dynamics of the ice lengths.

The researchers analyzed the shells of the small critics called forams, some of whom live as liquid plankton near the surface and some of them live down on the seabed. By measuring the isotopes of oxygen in their calcium carbonate scales, the researchers hoped to see how much mixture there was between deep and shallow water – and therefore how much CO waiting.

The more mixing takes place in this location, the more similar isotope is the signature of the seabed and the surface scales. If this mixture slows down the surface water to become less dense (and so less can descend), the isotope signature of the two shell types can remain separated. This is because the oxygen atoms in their shells partly come from the water around them. Mix the water together and the source material should be the same regardless of the depth. Draw from separate pools, and the shield chemistry will differ.

Review over the past hundred thousand years shows their data the shallow and deep water collectors with consistent patterns. But about 700,000 years ago – when the transition from 41,000 years of glacial periods to 100,000 years took place – there is a shift in data. The shallow and deep water shells diverged, which meant that deep water had a harder time mixing against the surface after that.

If significantly less CO 2 was vented from deep sea to atmosphere Light heating lamp from the 41,000-year cycle could not have been enough to kick off a full-blown global warming. Instead, atmospheric CO would have been low until the 100,000 year cycle forced it to rise.

One thing leads to another

How could it have happened? The researchers note that the shallow water is both less salty than deep water here, which should keep it from sinking, and a little colder, which would cause it to drop. Increased precipitation over the sea or increased meltwater from Antarctica would add more fresh water to the surface, making the shallow water even less salt. Reducing the salt content would reduce its density making it less willing to mix down. And less mixing would also give less salt up from the dips – further strengthen the stagnant fresher on the top layer as the stymie’s mix in the first place.

If this doesn’t feel like a satisfactory explanation for the change in ice age rhythm, it’s because it’s still part of a wider puzzle. The process envisaged here could strengthen the change, but it was probably not the initiator. Another factor-like ocean over-fertilization plankton growth – could have hit atmospheric CO levels down to a new low, with this shift from the Antarctic coast so that they could stay for the duration of a longer ice bike. Each of these things could have helped the ice sheet grow over the “critical mass” point, making the climate even harder.

The reason why the transition to longer ice age cycles has been difficult to explain is probably that there is no “big answer. The change in behavior can be the emerging result of complex interactions between many feedbacks in the Earth’s climate system. kind of thing we want to understand when we look at the future. After all, the ocean is currently increasing a significant part of our emissions, which would otherwise contribute to global warming.

Science 2019. 10.1126 / science.aat7067 (About DOIs).

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