The long-standing mystery of Earth's missing ice may have just been solved by scientists

 

North-east Greenland's Piedmont Glacier (Coen Hofstede/Institute of Alfred Wegener)

This ought to be easy. Massive quantities of water ice frozen in giant glaciers begin to thaw as temperatures on Earth get warm, dumping water into the oceans, and causing sea levels to rise. That's the tale of our lives.

In the other side, as global temperatures fall, which occur during ice ages, sea levels begin to decrease, as the water content retreats from the ocean, freezing once again in large inland ice sheets.

Since time immemorial, the changes from glacial to interglacial have occurred in this epic, continuing period of ice ebb and flow. But the problem is there.

Scientists tracking these cycles have proposed for years now that there is a "missing ice" problem: a mysterious difference between the very low levels of the sea approximately 20,000 years ago and the amount of ice deposited at the same time in glaciers.

The problem, at its heart, is this. Based on ancient coral sediment data, the sea level is believed to have been about 130 meters (427 ft.) lower than it is today at the peak of the last ice age of the Earth-the Last Glacial Maximum (LGM), which ended about 20,000 years ago.

But modeling shows that at this point in time, ice volume in glaciers wasn't great enough to justify such a low sea level. How do we explain the 'missing' ice, then?

Researchers seem to have found a solution in a recent study led by geophysicist Evan Gowan.

The researchers were able to model the evolution of global ice sheets well into the past with a new reconstruction called Paleo MIST 1.0, far further back than even the LGM.

As far back as 80,000 years, Gowan notes, it looks like we have found a new way to recreate the past.

The model results suggest that the anomaly in our data is not a case of lost ice, but rather erroneous inferences about how low the level of the sea actually dropped during the LGM.

The sea level fell no more than 116 meters below where the waves are lapping today, according to the ice physics model of Paleo MIST 1.0, with ice volume (which is entirely accounted for) clocking somewhere around 42.2 ⁇ 106 km3.

Therefore, as our LGM reconstruction is consistent with established sea-level constraints, the researchers clarify, we find no justification for the missing ice problem.

The misdirection of the missing ice claim, according to the team, stems from a variety of variables-first, over-reliance on far-field indicators (coral sediment data from locations elsewhere in the world), which, as we once believed they did, might not accurately reflect global average sea levels.

According to one of the team, geophysicist Paolo Stocchi, the isotope model has been commonly used for years to assess the amount of ice in glaciers up to millions of years prior to our period.

Our study now poses questions about this method's reliability.

Although the missing ice mystery seems to be solved, the researchers do not expect that the last word on this issue will be theirs.

After all, the incompatibility of their own solution with cycle-based reconstructions of oxygen isotope ratio has, in a way, produced a new missing ice problem, the team admits.

In future studies, whether and how the current complexity can be overcome is a question for another day, which could provide even clearer glimpses of the evolution of ice sheets in the distant past.