[ad_1]
Visualize the following: Earth's climate oscillates between cold ice ages and warm interglacial periods; the last ice age was about 20,000 years ago; the sea level was about 126 meters (413 feet) below modern sea level at that time; and the Holocene, which represents the last 12,000 years of climate change, is an interglacial period.
The last interglacial period, about 127,000 to 116,000 years ago, was the last time that sea level was as high or even higher than the current sea level. Understanding the change in sea level during the last interglacial period, a time when the earth was slightly warmer, is an important area of research to understand the future rise in sea level due to global warming.
The magnitude and trajectory of sea level change during the last interglacial, more specifically the marine isotope stage (MIS) 5th, are uncertain. To date, the consensus has been that sea level can be six to nine meters above sea level, with values requiring additional melting from Greenland and the Western Antarctic ice cap and one or more oscillations to reach several meters. .
However, scientists at the University of New Mexico (UNM) and the University of South Florida (USF) and their international team of collaborators are uncertain whether these sea level fluctuations are accurate. According to a new study published today in the journal Nature Geoscience titled A highly resolved record of the relative level of the sea in the western Mediterranean during the last interglacial period, these scientists present a relative record of sea level relative to MIS-5e of the island of Mallorca, in the western Mediterranean Sea, based on the presence of phreatic proliferations on the speleothems forming the sea level.
"On a global scale, the climate was warmer by 1 to 2 ° C during the last interglacial period known as Marine Isotope Stage 5e (MIS-5e) between 127,000 and 116,000 years ago" said Victor Polyak. Senior researcher and senior researcher in the Department of Earth Sciences and Planets of the UNM. "Although this period is well studied, we still do not know the exact sea level behavior during the MIS-5e. What we know for sure, is that the sea level was higher when the climate was 1 to 2 ° C warmer 120,000 years ago. For this reason, the history of sea level MIS-5e is important as an analogue of what will happen at the current level of the sea with the warming of the climate in the future.
Until now, the best markers of sea level were corals, as some species grow very close to sea level and corals can be dated using the uranium-thorium method. Significant reconstructions of sea level MIS-5e have been made from such coral studies. However, the scientific problem with coral is that no one can ever be certain of coral depths below sea level, and because they consist of biogenic calcium carbonate, they are slightly altered. regarding the accuracy of this method.
"The best MIS-5 sea level studies suggest that sea level during this period was 6 to 9 meters above sea level and that there were probably significant falls during the high seas MIS-5e, "said Polyak. "This is alarming because it suggests that if we warm our climate by 1 to 2 ° C, we could raise the sea level by 6 to 9 meters (20 to 30 feet). This could happen quickly, causing sea level instability. "
"The purpose of this research was to reconstruct precisely the sea-level position during the last warm period, between 127,000 and 116,000 years ago, using particular carbonate inlays precipitated into the coastal caves of the coast. Majorca, "says co-author and USF Bogdan School P. Onac, Geosciences karst geologist. "Most of the other known sea level studies for this period indicate altitudes between 6 and 9 m. So we wanted to better understand the magnitude, timing and stability of the sea level, as this information scenario of global warming of 2ºC.
Polyak, Onac and Professor Yemane Asmerom of the UNM have studied caves along the eastern coast of the Spanish island of Majorca in the western Mediterranean. They used unique cave formations called phreatic proliferations on speleothems (POS) that form naturally on the surface of the brackish cave water, which happens to be exactly equivalent to the sea level in these caves near on the side. The phreatic proliferations on speleothems are formed in the form of carbon dioxide outgassing from brackish creek waters that are hydrologically related to the Mediterranean Sea.
"The outlets are well preserved," said Mr. Polyak, "and as they can be dated, they provide very accurate elevations of sea level for the current and pre-existing sea level. They consist of inorganic calcium carbonate (calcite and aragonite) and are datable by the uranium-thorium method. Unlike corals, they are not subject to alteration and, therefore, uranium-thorium dates are accurate. Another advantage of the point of sale is that it will continue to grow as long as the sea level is stable at a given altitude. "
Polyak and Asmerom date from January 11 from eight different caves that have outlets located about 2 meters above sea level. Forty-five dates for uranium and thorium show that the relative level of the sea has remained stable. "This is the most accurate and best resolved sea level record for the MIS-5e of the last interglacial period," said Polyak. "It provides an exceptionally accurate calendar of sea level history during the aforementioned period and shows that it reached 6 meters above sea level 127,000 years ago, it would have dropped to 2 meters it 122,000 years ago. at that altitude, for the rest of the sea level, 116,000 years ago, "said Onac. "The results suggest that if the pre-industrial temperature is exceeded by 1.5 to 2 ° C, the sea level will respond and rise from 2 to 6 meters (7 to 20 feet) above the level of the current sea. "
Carling Hay, an assistant professor at Boston College University, corrected the sea level record for glacio isostatic adjustment using nine different ice isostatic models. Together, these models suggest that the sea level in Majorca reached its peak at the beginning of MIS-5e, then gradually decreased and stabilized 122,000 years ago, until the end high-end 116,000 years ago.
"One of the biggest unknowns of the future is the amount of global real estate we will lose to global warming and how fast that could happen," Asmerom said. "It's a pretty awesome science; it's a big thing, on a global scale. Beyond the rising sea level, we also need to know how fast it will go up.
"If you take the oldest data, in some cases the suggestion that the sea level rise by nine meters by simply heating two degrees would be catastrophic for our current configuration of cities and, in some cases, island countries. This work clearly shows the most important discoveries that sea level did not rise simply. You have had small changes in temperature and the sea level has remained fairly stable.
The research reported in this study is the result of an NSF collaborative project in which the USF is the main organization. Field activities (cave visits for sample collection and measurement of their elevation), mineralogical and crystallographic studies on mineral samples were performed by Onac at the USF.
"Although there are significant results, many aspects of sea level change require further exploration," said Polyak. "As a result, the UNM team and the University of South Florida received a new grant from the National Science Foundation to continue the work in the Mediterranean."
Source link
