Around 14,650 years prior, the ocean levels rose 12 meters in only a couple of hundreds of years.
The fast rise of global temperature over the last decades is almost certainly novel in recent Earth history, but our current rate of sea-level rise has stiffer competition. About 14,650 years ago, as the melting of the last ice age began to hit its stride, sea level made an incredible jump of 12 meters or even more, in less than 400 years. This event is known to scientists as Meltwater Pulse 1A.
However, it isn’t an easy job figuring out where all that water came from. It was probably the result of melting glacial ice (and not some sort of biblical sky-flood), even if some models of past ice sheet changes haven’t quite added up.
A new study conducted by Jo Brendryen at the University of Bergen looked at the melting of the Eurasian Ice Sheet, which has largely been overlooked.
Looking for a date
As it appears, it about cell-based dating, estimating the measure of radioactive carbon-14 in something to figure its age by understanding its known rate of decay. Cell-based dating works a not quite the same as different sorts of radiometric dating, taking into account that carbon-14 is continually delivered by responses in Earth’s air. Anything that takes in carbon atoms, including living things, will have a comparable sum as the climate. Additionally, after it stops that take-up, carbon-14 will step by step decrease and transform into nitrogen-14. The more seasoned it gets, the less carbon-14 will be left in it.
One complication, however, is that the production rate of carbon-14 in the atmosphere fluctuates a little over time. Because this technique can only be used about 50,000 years or so into the past, however,
Scientists have been able to measure things with known ages using techniques like dendrochronology (the study of tree rings) to cross-check and calibrate carbon-14 concentrations to ages, even if this technique can only be used to provide accurate results from about 50,000 years or so into the past.
However, when it comes to the ocean, there’s a second complication because carbon-14 from the atmosphere gets into surface waters quite easily, leaving deep water isolated. So it could be hundreds of years since the carbon in deep water last saw the atmosphere. Moreover, if a small organism absorbs that carbon, it’s going to look hundreds of years older than it really is, in carbon-dating terms.
So just subtracting the right number when working with deep ocean samples isn’t always working as it should. The problem is that the “right number” relies on the ocean’s circulation in that place and at that time.
On ice
How about we investigate the ice sheets. During the last chilly time frame, an ice sheet once extended across Scandinavia and the Barents Sea. The record of its contracting depends on cell-based dating of ocean bottom dregs centers, pinpointing times that ice withdrew and life came back to an area. The recreations have demonstrated that the ice here had essentially dissolved before the beginning of Meltwater Pulse 1A, giving it an unmistakable reason. However, the cell-based dated ages accepted that the profound sea carbon-14 deferral in that district was steady after some time, coordinating the cutting edge design.
In this study, the researchers looked carefully at that assumption. They turned to a seemingly unlikely source, a cave in China because there is a pretty good connection between ocean circulation, the temperatures in the North Atlantic, and the Asian Monsoon rains, linked by a series of climatic dominoes. Also, cave records have excellent timelines, with annual layers and uranium radiometric dating.
By lining up the fluctuations in the cave record and Norwegian Sea sediment records, the researchers prevent having to guess the unknown deep ocean carbon-14 delay. Instead, they can calculate that delay and its changes, providing a new calibration for seafloor paleoclimate records in this region.
With that done, the reconstructed timing of Eurasian Ice Sheet melts shifts. Instead of showing that the local ice melted before Meltwater Pulse 1A even started, the researchers saw a major loss of ice during this event. Previous reconstructions gave the Eurasian Ice Sheet credit for perhaps one meter of the 12 or more meters of sea-level rise that occurred then. This study pushes that contribution up to about five meters, plus another meter or so in the century following.
There are hard challenges to working out which giant block of ice melted thousands of years ago, however, there are important clues. When an ice sheet melts, sea-level rise doesn’t rise equally all around the world, because the gravitational attraction of a massive ice sheet actually pulls seawater to it, raising more the sea levels near the sheet. As the ice sheet melts, its gravitational draw unwinds, so ocean level can really fall directly close to the ice sheet, even as it rises somewhere else. Furthermore, the records of ocean level change in different spots are really predictable with the Eurasian Ice Sheet being a major source: destinations around Norway and Finland show a drop in ocean level during this time of fast worldwide ocean level ascent.
Re-adjusting the Eurasian Ice Sheet history would make it fundamentally more obvious where 12 meters of ocean level originated from, yet it additionally brings up some fascinating issues. For instance, such an enormous progression of new water into the Norwegian Sea could be required to gum up the basically significant south-to-north transport line momentum in the Atlantic Ocean, yet records show it was very solid during this time. Also, how, precisely, did this part of the Eurasian Ice Sheet breakdown so rapidly?
That question about the past is important to our future. The bit of the Eurasian Ice Sheet being referred to rode topographic lows in contact with the sea, making it powerless against fast breakdown. The equivalent is valid for the West Antarctic Ice Sheet today—the greatest special case for future ocean level ascent. Each ice sheet is unique and the nearby subtleties matter, yet a similarly quick breakdown of ice in Antarctica would provide the biggest outcome imaginable.
