Climate Change Could Diminish Drinking Water More Than Expected

 Researchers at Ohio State University have simulated how saltwater intrudes into fresh water supplies along coastlines, and found that mixed, or brackish, water, can extend much farther inland than previously thought. In this image from the simulation, saltwater is red and fresh water is dark blue. The colors in between represent brackish water with different amounts of salt. Image by Jun Mizuno, courtesy of Ohio State University.
Researchers at Ohio State University have simulated how saltwater intrudes into fresh water supplies along coastlines, and found that mixed, or brackish, water, can extend much farther inland than previously thought. In this image from the simulation, saltwater is red and fresh water is dark blue. The colors in between represent brackish water with different amounts of salt. Image by Jun Mizuno, courtesy of Ohio State University.

As sea levels rise, coastal communities could lose up to 50 percent more of their fresh water supplies than previously thought, according to a new study from Ohio State University.

Hydrologists here have simulated how saltwater will intrude into fresh water aquifers, given the sea level rise predicted by the Intergovernmental Panel on Climate Change (IPCC). The IPCC has concluded that within the next 100 years, sea level could rise as much as 23 inches, flooding coasts worldwide.

Scientists previously assumed that, as saltwater moved inland, it would penetrate underground only as far as it did above ground.

But this new research shows that when saltwater and fresh water meet, they mix in complex ways, depending on the texture of the sand along the coastline. In some cases, a zone of mixed, or brackish, water can extend 50 percent further inland underground than it does above ground.

Like saltwater, brackish water is not safe to drink because it causes dehydration. Water that contains less than 250 milligrams of salt per liter is considered fresh water and safe to drink.

Motomu Ibaraki, associate professor of earth sciences at Ohio State, led the study. Graduate student Jun Mizuno presented the results Tuesday, October 30, 2007, at the Geological Society of America meeting in Denver.

“Most people are probably aware of the damage that rising sea levels can do above ground, but not underground, which is where the fresh water is,” Ibaraki said. “Climate change is already diminishing fresh water resources, with changes in precipitation patterns and the melting of glaciers. With this work, we are pointing out another way that climate change can potentially reduce available drinking water. The coastlines that are vulnerable include some of the most densely populated regions of the world.”

In the United States, lands along the East Coast and the Gulf of Mexico — especially Florida and Louisiana — are most likely to be flooded as sea levels rise. Vulnerable areas worldwide include Southeast Asia, the Middle East, and northern Europe.

“Almost 40 percent of the world population lives in coastal areas, less than 60 kilometers from the shoreline,” Mizuno said. “These regions may face loss of freshwater resources more than we originally thought.”

Scientists have used the IPCC reports to draw maps of how the world’s coastlines will change as waters rise, and they have produced some of the most striking images of the potential consequences of climate change.

Ibaraki said that he would like to create similar maps that show how the water supply could be affected.

That’s not an easy task, since scientists don’t know exactly where all of the world’s fresh water is located, or how much is there. Nor do they know the details of the subterranean structure in many places.

One finding of this study is that saltwater will penetrate further into areas that have a complex underground structure.

Typically, coastlines are made of different sandy layers that have built up over time, Ibaraki explained. Some layers may contain coarse sand and others fine sand. Fine sand tends to block more water, while coarse sand lets more flow through.

The researchers simulated coastlines made entirely of coarse or fine sand, and different textures in between. They also simulated more realistic, layered underground structures.

The simulation showed that, the more layers a coastline has, the more the saltwater and fresh water mix. The mixing causes convection — similar to the currents that stir water in the open sea. Between the incoming saltwater and the inland fresh water, a pool of brackish water forms.

Further sea level rise increases the mixing even more.

Depending on how these two factors interact, underground brackish water can extend 10 to 50 percent further inland than the saltwater on the surface.

According to the United States Geological Survey, about half the country gets its drinking water from groundwater. Fresh water is also used nationwide for irrigating crops.

“In order to obtain cheap water for everybody, we need to use groundwater, river water, or lake water,” Ibaraki said. “But all those waters are disappearing due to several factors –including an increase in demand and climate change.”

One way to create more fresh water is to desalinate saltwater, but that’s expensive to do, he said.

“To desalinate, we need energy, so our water problem would become an energy problem in the future.”

Scientists help map Antarctic ice sheets

Newcastle University scientists are joining the race to discover how climate change is affecting Antarctic ice sheets.

Researcher David Barber will spend four months installing GPS signal receivers on two huge plateaus of ice that cover the sea, so that their movements can be monitored by satellite.

These measurements will enable other members of the project team in Newcastle, led by Dr Matt King (pictured), to calculate how much the ice sheets rise and fall with the tides. This will pave the way for much more accurate measurements of the thickness of the ice sheets, so that scientists will know whether and how fast the ice is melting.

David flies out to west Antarctica on 6 November and over the next few weeks will plant about 15 receivers on the vast Ronne ice shelf, which is about the same size as France.

He will then plant receivers on the smaller Larsen ice sheet, which featured in the opening scenes of the climate change disaster movie, The Day After Tomorrow, in which Hollywood special effects made it appear as if the ice sheet cracked as it was being drilled.

Matt said: ‘The Larsen sheet is quite famous because a couple of years ago, a chunk about half the size of Cumbria and a few hundred metres thick broke off in a matter of days – you could say that the real life scenario has exceeded Hollywood’s expectations!’

As a result, there was a very small increase in sea level, but scientists need to know the condition of the ice sheet across its whole expanse, said Matt.

‘Satellite measurements have helped us make great progress in mapping the entire ice sheet, but we still don’t actually know how quickly the ice sheets are melting, if at all, but it is important that we find out and monitor the situation so that we can anticipate any rise in sea level.

‘The tides are very large in this part of the world – perhaps eight to ten metres – and we need to know how this affects the ice sheets lying on top of the sea before we can measure their thickness.

The research project is being carried out by the School of Civil Engineering and Geosciences at Newcastle University and is being funded by the Natural Environment Research Council. Support for the project is being provided by the British Antarctic Survey and the Earth and Space Research organisation, Oregon, USA.

Once the effects of the tides have been taken into account, the picture will be much clearer. Upwards movement will mean a thickening of the ice and downwards thinning. Seasonal variations are normal but scientists will be looking for long-term changes.

David said: ‘Using satellites, we can now measure any movement on the Earth’s surface to an accuracy of a few millimetres. This is a very good way to measure small annual changes in the thickness of ice but you have to know about other movements, such as those caused by tides, first.’

David, who lives in North Shields, will fly out from RAF from Brize Norton in Oxfordshire to the Ascension Islands and then on to the Falklands. From there, he will fly to the British Antarctic Survey base at Rothera, in West Antarctica.

Staff from the Survey base will assist David on his project, which will involve flying to various points on the two ice shelves and installing the receivers, along with solar panels and wind turbine generators to power them.

David expects to be in the Antarctic until February. Because it will be the summer time, temperatures at the base are likely to be only a few degrees below freezing point, although temperatures as low as -20C are possible on the inner edge of the Ronne ice shelf. A few of the GPS receivers will be left for the winter to be retrieved the following Antarctic summer, experiencing temperatures perhaps as low as -40C in the winter.

Extinction Theory Falls From Favor

Doctoral student Catherine Powers traveled to fossil sites around the world, including this one in Greece, to study ancient bryozoan marine communities.
Doctoral student Catherine Powers traveled to fossil sites around the world, including this one in Greece, to study ancient bryozoan marine communities.

The greatest mass extinction in Earth’s history also may have been one of the slowest, according to a study that casts further doubt on the extinction-by-meteor theory.

Creeping environmental stress fueled by volcanic eruptions and global warming was the likely cause of the Great Dying 250 million years ago, said USC doctoral student Catherine Powers.

Writing in the November issue of the journal Geology, Powers and her adviser David Bottjer, professor of earth sciences at USC College, describe a slow decline in the diversity of some common marine organisms.

The decline began millions of years before the disappearance of 90 percent of Earth’s species at the end of the Permian era, Powers shows in her study.

More damaging to the meteor theory, the study finds that organisms in the deep ocean started dying first, followed by those on ocean shelves and reefs, and finally those living near shore.

“Something has to be coming from the deep ocean,” Powers said. “Something has to be coming up the water column and killing these organisms.”

That something probably was hydrogen sulfide, according to Powers, who cited studies from the University of Washington, Pennsylvania State University, the University of Arizona and the Bottjer laboratory at USC.

Those studies, combined with the new data from Powers and Bottjer, support a model that attributes the extinction to enormous volcanic eruptions that released carbon dioxide and methane, triggering rapid global warming.

The warmer ocean water would have lost some of its ability to retain oxygen, allowing water rich in hydrogen sulfide to well up from the deep (the gas comes from anaerobic bacteria at the bottom of the ocean).

If large amounts of hydrogen sulfide escaped into the atmosphere, the gas would have killed most forms of life and also damaged the ozone shield, increasing the level of harmful ultraviolet radiation reaching the planet’s surface.

Powers and others believe that the same deadly sequence repeated itself for another major extinction 200 million years ago, at the end of the Triassic era.

“There are very few people that hang on to the idea that it was a meteorite impact,” she said. Even if an impact did occur, she added, it could not have been the primary cause of an extinction already in progress.

In her study, Powers analyzed the distribution and diversity of bryozoans, a family of marine invertebrates.

Based on the types of rocks in which the fossils were found, Powers was able to classify the organisms according to age and approximate depth of their habitat.

She found that bryozoan diversity in the deep ocean started to decrease about 270 million years ago and fell sharply in the 10 million years before the mass extinction that marked the end of the Permian era.

But diversity at middle depths and near shore fell off later and gradually, with shoreline bryozoans being affected last, Powers said.

She observed the same pattern before the end-Triassic extinction, 50 million years after the end-Permian.

Powers’ work was funded by the Geological Society of America, the Paleontological Society, the American Museum of Natural History and the Yale Peabody Museum, and supplemented by a grant from USC’s Women in Science and Engineering program.

Geology is published by the Geological Society of America.

New Way To Measure Ancient Ocean Temperatures Refined

Spanish researcher Carme Huguet further refined the recently developed TEX86 paleothermometer during her doctoral research at the Royal Netherlands Institute for Sea Research (NIOZ). The thermometer measures seawater temperature dependent changes in the cell wall composition of archeabacteria.

Real thermometers have been available since the 17th century. For all periods before this, researchers depend on signs from nature. For such determinations, geochemists resort to molecules from microorganisms whose structure is well preserved in seabeds.

The TEX86 index has recently been developed at Royal Netherlands Institute for Sea Research (NIOZ). It is based on temperature-dependent changes in the lipid composition of the cell walls of certain types of archeabacteria. Their cell membranes are composed from special lipids of which the number of carbon rings in the molecule changes with the temperature of the surrounding seawater. These organisms therefore adjust the degree of fluidity of their membranes to the prevailing conditions. Carme Huguet studied several aspects of this in greater detail and made significant improvements to the determination.

With a new detection method the analytical reproducibility of the TEX86 paleothermometer was brought to ±0.3 °C and the deviation in the results measured was reduced to 5% of the average. The TEX86 values for organic material out of the water column and from the uppermost layer of the floor sediment best match the temperature of the uppermost 100 m of seawater.

However, the small cells of Crenarchaeota cannot sink to the floor by themselves; they are far too light for that. This is, however, achieved more rapidly if the cells of Crenarchaeota are eaten, for example, by crustaceous zooplankton. Fortunately, the time spent in the gastrointestinal tract of the crustaceans does not harm the molecules. Once they have landed on the sea floor, the preservation of the original fat molecules takes place best in anaerobic sediments.

In modern, anaerobic sediments from a side branch of the Oslo fjord, the measured TEX86 values accurately reflected the average spring-autumn air temperature in Oslo. Temperature estimations of the transition from the last ice age to the present interglacial period were made using two cores drilled from the Arabian Sea. The TEX86 temperatures were compared with values from a British index; the Uk37.

The index differences can be explained by differences in the growing season of the archeabacteria and algae that the Uk37 index is dependent on. The upwelling dynamic of the seawater in the Arabian Sea also exerts an influence. This dynamic is strongly dependent on the monsoon season in this area.

Carme Huguet’s research makes it clear that climate reconstructions should always be based on comparisons of several types of parallel measurements to prevent unexpected scientific blunders. Determining the surface seawater temperatures in oceans and coastal waters is essential for the reconstruction of historic climate changes and changes in ocean currents. This information is, in turn, vital for perfecting current climate models.

This research was funded by NWO.

Why Is The Ocean Salty?

Pacific Ocean at dawn. Today's ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff. (Credit: Michele Hogan)
Pacific Ocean at dawn. Today’s ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff. (Credit: Michele Hogan)

The saltiness of the sea comes from dissolved minerals, especially sodium, chlorine, sulfur, calcium, magnesium, and potassium, says Galen McKinley, a UW-Madison professor of atmospheric and oceanic sciences.

Today’s ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff.

Now, the ocean’s salinity is basically constant. “Ions aren’t being removed or supplied in an appreciable amount,” McKinley says. “The removal and sources that do exist are so small and the reservoir is so large that those ions just stay in the water.” For example, she says, “Each year, runoff from the land adds only 0.00005 percent of total ocean salts.”

In lakes, relatively rapid turnover of water and its dissolved salts keeps the water fresh – a water droplet and its ions will stay in Lake Superior for about 200 years, compared to roughly 100 to 200 million years in the ocean. “Even if you did have any accumulation of an ion in a lake, it would be washed out quickly,” McKinley explains.

Ocean salts, however, have no place to go. “The ions that were put there long ago have managed to stick around,” McKinley says. “There is geologic evidence that the saltiness of the water has been the way that it is for at least a billion years.”