The slow rise of The Andes

The Andes is the world’s longest continental mountain range and the highest outside Asia, with an average elevation of 4000 metres. The question of how quickly the mountains reached such heights has been a contentious one that University of Michigan paleoclimatologist Christopher Poulsen and graduate student Nadja Insel working with Todd Ehlers of the University of Tuebingen in Germany, believe they may now have settled with a new interpretation of isotopic data. Their work suggests that the rise of the Andes was a very gradual process.

Poulsen’s uplifting work suggests that previous interpretations of the evidence have misconstrued changes in oxygen isotope ratios as being due to a rapid rise of the mountain range whereas the more likely explanation is that the changes are due to shifts in ancient climate.

“In the modern climate, there is a well-known inverse relationship between oxygen isotopic values in rain and elevation,” Poulsen explains.
“As a rain cloud ascends a mountain range, it begins to precipitate.
Because atoms of oxygen-18 are more massive than those of oxygen-16, it is preferentially rained out. Thus, as you go up the mountain, the precipitation becomes more and more depleted in oxygen-18, and the ratio of oxygen-18 to oxygen-16 decreases.” Geologists use the ratio of these isotopes, preserved in rock, to infer past elevations and so the rate of rise of a mountain range.

“If the ratio decreases with time, as the samples get younger, the interpretation would typically be that there has been an increase in elevation at that location,” Poulsen adds. He points out that that is the precise conclusion drawn by a series of papers on the uplift history of The Andes published over the past four years. On the basis of oxygen isotope ratios determined by analysis of carbonate rocks, the authors of those papers suggested that the central Andes rose about 2500 to 3500 metres in a mere three million years, Other geologists had assumed that the rise to those heights took place over tens of millions of years.

Unfortunately, elevation is not the only thing to disturb oxygen isotope ratios in precipitation. “It can also be affected by where the vapour came from and how much it rained,” says Poulsen. “More intense rainfall also causes oxygen-18 to be preferentially precipitated.” He and his colleagues were skeptical of the rapid-rise scenario, and so performed climate modelling experiments to investigate whether something other than altitude might have given rise to the shift in ratio observed in carbonate deposits.

Andes: Credit to

“The key result in our modelling study is that we identified an elevation threshold for rainfall,” Poulsen says. “Once The Andes reached an elevation greater than 70 percent of the current elevation, the precipitation rate abruptly increased. In our model, the increased precipitation also caused the ratio of oxygen-18 to oxygen-16 to significantly decrease. Our conclusion, then, is that geologists have misinterpreted the isotopic records in the central Andes. The decrease in the ratio is not recording an abrupt increase in elevation; it is recording an abrupt increase in rainfall.”

This conclusion is backed up by geochemical and sedimentological data, Poulsen said. “There is evidence that the central Andes became less arid at the same time that the isotope records show a decrease in the ratio of oxygen-18 to oxygen-16.”


Christopher Poulsen

Science Express, 2010, online

Black gold

An estimated 513 billion barrels of “technically recoverable” heavy oil lie in Venezuela’s Orinoco Oil Belt, a 50,000 square kilometre region in the East Venezuela Basin Province.

Worldwide consumption of petroleum was 85.4 million barrels per day in 2008. The three largest consuming countries were United States with 19.5 million barrels per day, China with 7.9 million barrels per day, and Japan with 4.8 million barrels per day. So the Venezuelan heavy oil represents a potential supply that could last a decade at the current rate of consumption.

The United States Geological Survey (USGS) has carried out the first assessment that identifies how much oil might be technically recoverable using currently technology and standard industry practices. According to USGS Energy Resources Program Coordinator Brenda Pierce, this part of the world has one of the world’s largest recoverable oil accumulations. The USGS’s report is part of its program directed at estimating the technically recoverable oil and gas resources of priority petroleum basins worldwide. This is the largest accumulation ever assessed by the USGS.

“Knowing the potential for extractable resources from this tremendous oil accumulation, and others like it, is critical to our understanding of the global petroleum potential and informing policy and decision makers,” explains Pierce. “Accumulations like this one were previously very difficult to produce, but advances in technology and new understandings in geology allow us to assess how much is now technically recoverable.”

USGS team member and a co-author of the report, Christopher Schenk explains further: “Heavy oil is a type of oil that is very thick and therefore does not flow very easily. As a result, specialized production and refining processes are needed to generate petroleum products, but it is still oil and can generate many of the same products as other types of oil.”

The estimated petroleum resources in the Orinoco Oil Belt, range from 380 to 652 billion barrels of oil (at a 95 and 5 percent chance of occurrence, respectively). Schenk says that the estimates are based on a rate of oil recovery of between 40 and 45 percent.

Orinoco (Credit: USGS)
Credit: USGS


However, others are sceptical that these oil reserves are economically or environmentally viable. Venezuelan oil geologist Gustavo Coronel told the Associated Press that he doubted the recovery rate could be much higher than 25 percent given the nature of the crude oil. More intriguing is that the USGS announcement seems to have been timed to coincide with an international auction for drilling rights in the Orinoco Belt which took place on 28th January, with results to be announced on 10th February.

Moreover, there are no little energy and environmental costs to be considered in recovering heavy crude oil as it is not necessarily as easy to extract as conventional crude oil. Moreover, the existence of such reserves while perhaps saving us from short-term oil shortages does not address the issues of carbon emissions and potential climate change.


USGS Assessment

Energy Resources Program

Auction news

Crude claims

AP report

Climate change lifesaver

Adding lime to the oceans may help reverse the rise in atmospheric carbon dioxide, according to a report in the journal Chemistry & Industry. Petrochemicals giant Shell is pumping money into a feasibility study of the idea, which might one day reduce, if not reverse, the impact on climate change of fossil fuel use, the scheme’s proponents hope.

The theory, being developed as an open source concept under the name Cquestrate, suggests that adding lime (primarily calcium oxide) to seawater will increase its alkalinity and so boost the seawater’s ability to absorb carbon dioxide from the air. Moreover, it will reduce the water’s tendency to release the gas back into the air. However, until recently the idea was thought to be unworkable because of the expense of obtaining lime from limestone and the amount of carbon dioxide that would be released in the process. Additionally, there are issues associated with the macroscale chemical engineering that will be required to have a global effect.

Could pouring lime into the oceans be a climate change lifesaver? (Photo by David Bradley)

Could pouring lime into the oceans be a climate change lifesaver? (Photo by David Bradley)

We think it’s a promising idea, says Shell’s Gilles Bertherin, a coordinator on the project, There are potentially huge environmental benefits from addressing climate change – and adding calcium hydroxide to seawater will also mitigate the effects of ocean acidification, so it should have a positive impact on the marine environment.

Tim Kruger, a management consultant at London firm Corven, who previously worked for Shell, is the brains behind the plan to implement the lime process. He argues that it could be made workable by locating it in regions that have a combination of low-cost ‘stranded’ energy considered too remote to be economically viable to exploit – like flared natural gas or Solar energy in deserts – and that are rich in limestone, making it feasible for calcination to take place on site as it requires the strong heating of limestone.

Australia’s Nullarbor Plain visible as the smooth croissant shaped coastal region in this NASA satellite image (Credit Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

Australia’s Nullarbor Plain visible as the smooth croissant shaped coastal region in this NASA satellite image (Credit Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

Kruger says: There are many such places – for example, Australia’s Nullarbor Plain would be a prime location for this process, as it has 10000 cubic kilometres of limestone and soaks up roughly 20 megajoules per square metre of Solar irradiation every day. Kruger told Spotlight that to sequester several billion tonnes of carbon dioxide requires 1.5 cubic kilometres of limestone. Of course, the scheme ignores the environmental impact on pristine wilderness, such as the Nullarbor Plain.

Of course, the process of making lime generates carbon dioxide, but adding the lime to seawater absorbs almost twice as much carbon dioxide. The overall process is therefore carbon negative. This process has the potential to reverse the accumulation of carbon dioxide in the atmosphere, Kruger says. He believes it should be possible to reduce atmospheric carbon dioxide to pre-industrial levels. The oceans are already the world’s largest carbon sink, absorbing 2 billion tonnes of carbon every year. Increasing absorption ability by just a few percent could dramatically increase carbon dioxide uptake from the atmosphere. Klaus Lackner of Columbia University tentatively agrees, The theoretical carbon dioxide balance is roughly right…it is certainly worth thinking through carefully.

The fact that the concept is open source means that anyone with the will and the means could develop the required technology. However, it is likely to require vast tonnages of raw material, which must be mined and sourced and then spread into the oceans. So the question of it being carbon negative must be considered in detail taking into account the whole process lifecycle.

There are also issues of oceanic pH change in such a way as to interfere with the very ecosystems, including fragile coral reefs, that are already under threat from climate change. Researchers must investigate possible unforeseen outcomes with such a massive chemical experiment, especially, given the inconclusive and often negative results with other macro chemical engineering schemes, such as nitrogen control and iron seeding of the oceans.

With the hint of lime concept, a lot more theoretical work must be done before we plunge into a campaign to attempt to modify the oceans in this way. We’re looking at computer simulations of the process and will progress to small-scale laboratory tests first, Kruger told Spotlight, there’s certainly no intention to just dump lime into the oceans.

Further reading


Misguided Meddling


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