After spending a month exploring and collecting samples from caves on the tiny South Pacific island of Niue, Paul Aharon, Hillary Sletten and Joe Lambert watched for two mornings as their work was sawed in half.
A Polish man named Henry operated the wet saw, whose diamond-tipped blade is typically used for splitting tile, carving up two stalagmites, rock formations formed by thousands of years of mineral-rich water dripping onto cave floors.
Led by Aharon, a University of Alabama geology professor, and funded by the National Science Foundation, the group, including Lambert, a geological research scientist at UA, and Sletten, a UA geology doctoral student, flew to Niue, 1,500 miles northeast of New Zealand.
The team was on a search for a “prize stalagmite” they hope will provide a rainfall record dating to up to 10,000 years into the past and illustrate the alternation between the El Nino and La Nina weather patterns, known in the scientific community as El Nino/La Nina-Southern Oscillation (ENSO), during that time period.
Aharon said without the ENSO pattern, without El Nino warming the surface temperature of the western Pacific Ocean and then La Nina cooling it, the movement of air in the atmosphere and the distribution of thermal energy across the planet, would not be possible.
After eight hours of sawing, the team was relieved to find the stalagmites they had pulled from Ulupaka Cave would prove to be suitable for their research.
Sletten said their stalagmites are good because they are without any voids or porous sections.
“If there are any voids in the sample, that’s missing data,” Sletten said.
But why is Niue, an island struggling to keep its own people from emigrating to nearby New Zealand, the best place to conduct this research? For one, it is riddled with caves to the point that Aharon compared it to Swiss cheese.
Second, Aharon is familiar with the island. This most recent expedition was his third visit to Niue, the last coming in 2002 to construct a prehistoric record of cyclones on the island by examining the coastal caves there.
In those two trips, Aharon befriended Sionetasi Pulehetoa, the director of the island’s meteorological office, and learned there existed a written rainfall record on the island dating all the way back to 1905.
“No other island has a record like that. Tuscaloosa and Birmingham don’t have records that date back that far,” Aharon said.
But the main reason Aharon is drawn to Niue is because the island is deeply affected by ENSO.
“Rainfall on Niue is engaged in the very gears of ENSO,” Aharon said. “During El Nino they have severe droughts and during La Nina they have excess rainfall.”
That means there is already a pretty extensive record of ENSO within the island’s written rainfall records. But to look several thousand years into the past, the stalagmites on Niue’s cave floors are the perfect telescopes.
Why? First, stalagmites are composed mainly of calcite, formed by a combination of calcium, carbon and oxygen. The oxygen comes from the slow-dripping water forming the stalagmites which pulls the carbon from the organic matter and caprock it seeps through when passing through the ground and into the cave.
The amount of carbon and oxygen in these stalagmites can be measured in ratios which are directly indicative of the amount of rainfall the island receives.
When there is heavy rainfall on the island, which occurs during La Nina, Aharon said the oxygen ratio is low. During El Nino and a drought, the oxygen ratio is high. Similarly, during a drought, the carbon ratio is high and during excess rainfall, it is low.
That means Aharon and his team can measure these oxygen and carbon ratios in the stalagmites and have a pretty good idea whether or not the island was going through El Nino or La Nina all those years ago.
And because they can check these measurements from the stalagmites against the island’s 106-year-old rainfall record they have a very strong control to move forward even further into the past.
Aharon and Sletten said they will also be checking the chemical composition of the stalagmites against rain collected from Niue over the next year as well as dripwater from Ulupaka Cave.
But before the team digs into the stalagmite, they first need to date it. The hope is to form a record extending back 10,000 years, but it would be difficult to do that using stalagmites that are only 1,000 years old.
Aharon and Sletten said samples of the stalagmites will be sent to the University of Melbourne in Australia to determine their age, however, Lambert said he is pretty confident that the five-foot-tall stalagmite the team returned with is at least 4,000 years old.
His estimate is based on the many curved lines the core of a stalagmite reveals. These lines are actually layers of calcite that are much like the rings in the trunk of a tree, Lambert said.
Just as each ring indicates a year in a tree’s life, a stalagmite’s layers, which vary in size but are usually just tenths of a millimeter, indicate a year of a stalagmite’s growth. By multiplying the average size of one of these layers by the five-foot length of one of the stalagmites the team pulled Niue, Lambert’s estimate is conservative.
“We’d like to look at the last 10,000 years but if we’re only able to look at even the past three or the past one, the size of this stalagmite will still allow Hillary to get very high resolution samples since the older these stalagmites get, the tighter packed their layers of growth can be,” Lambert said.
Aharon said much of this work will be done by Sletten over the next four years and will serve as her doctoral dissertation.
Lambert and Sletten said their work is simply to present the data, not make any predictions. In other words, they’ll work to figure out just how much rainfall Niue saw thousands of years into the past.
Any predictions or forecasts to be made from that data is for the climatologists to decide, Sletten said.
Source: Tuscaloosa News