SERMILIK FJORD, GREENLAND (NYTIMES) - A few miles up this fjord in south-western Greenland, the water abruptly turned milky, a sign that it is loaded with suspended silt, sand and other sediment.
It is this material - carried here in a constant plume of meltwater from the Sermeq glacier at the head of the fjord - that Dr Mette Bendixen, a Danish scientist at the University of Colorado, has come to see. As their research boat moves farther through the murky water, she and several colleagues climb into a rubber dinghy to take samples.
Dr Bendixen, a geomorphologist, is here to investigate an idea, one that she initially ran by colleagues to make sure it was not crazy: Could this island, population 57,000, become a provider of sand to billions of people?
Sand for eroded beaches, potentially from the Rockaways to the Riviera. Sand to be used as bedding for pipes, cables and other underground infrastructure. Mostly, though, sand for concrete, to build the houses, highways and harbours of a growing world.
The world makes a lot of concrete, more than 10 billion tonnes a year, and is poised to make much more for a population that is forecast to grow by more than 25 per cent by 2050. That makes sand, which is about 40 per cent of concrete by weight, one of the most-used commodities in the world, and one that is becoming harder to come by in some regions.
But because of the erosive power of ice, there is a lot of sand in Greenland. And with climate change accelerating the melting of Greenland's 1.6km-thick ice sheet - a recent study found that melting has increased sixfold since the 1980s - there is going to be a lot more.
"It's not rocket science," Dr Bendixen said. "One part of the world has something that other parts of the world are lacking."
Dr Bendixen is planning a two-year study to answer basic questions about the idea, including its feasibility and the environmental effects of extracting and exporting large amounts of the material. The government of Greenland, a self-ruled territory of Denmark, is studying it as well.
It would be up to entrepreneurs, possibly with assistance from the government, to make the idea a reality. Given the potential cost of shipping sand around the world, its feasibility would depend on the price of sand rising.
Currently almost all sand is mined within 80km of where it is used, said Mr Jason C. Willett, a minerals commodity specialist with the US Geological Survey. "Once you move it any distance, it then costs too much," he said.
The idea also raises questions that go beyond science - about Greenland's economic future, about its potential independence from Denmark, and even about the appropriateness of capitalising on climate change.
The need to diversify the economy is a big issue in Greenland, where fishing accounts for about 90 per cent of exports and Denmark provides nearly half the government's budget through a block grant. A large sand-exporting industry could help reduce this subsidy, which would be critical to Greenland eventually becoming independent.
"The diversification discussion is very important," said Dr Birger Poppel, a political science professor at the University of Greenland. "This could fit into that discussion."
Mr Kuupik V. Kleist, Greenland's premier from 2009 to 2013, said that exploitation of mineral resources, including sand, were the obvious targets for greater economic growth.
"But in order to replace half of the government budget you would need a lot of profit from any new activity which might arise," he said. "How many projects it takes and how big, I'm not sure."
All told, Greenland's ice sheet delivers about 900 million tonnes of sediment to the waters surrounding the island each year, or about 10 per cent of all the sediment delivered to oceans worldwide. The glacier at Sermilik Fjord, about 80km south of the capital, Nuuk, delivers about a quarter of Greenland's total. That explains the vast delta of sand visible from the air as well as from a research boat as the tide begins to go out.
The delta, with muddy rivulets crisscrossing it, stretches to the glacier more than 8km away.
Dr Bendixen has made some hypothetical calculations. If just 15 per cent of the sediment pouring into Sermilik Fjord every year could be extracted, that amount of sand - 33 million tonnes - is twice the annual demand of San Diego county in California, one of the most populous in the United States.
Sermilik Fjord is only one of a number of places in Greenland with large amounts of sand. And the sand will keep coming as the world keeps warming and the ice sheet keeps melting. "It's like a tap pouring not only water, but sediment," she said.
It was Dr Bendixen's work on the effects of climate change on Greenland that sparked the idea. She had come across a trove of aerial photos of the island, taken by the US military during World War II. Comparing them with more recent satellite images, it was obvious that deltas like the one in Sermilik Fjord were growing as the planet warmed and more meltwater came out of the ice sheet.
Dr Bendixen noted that Greenlanders' contribution to global warming was very slight - their emissions are a tiny fraction of the global total. "They have a long list of negative consequences they have to deal with," she said, including rising sea levels and thawing permafrost. "If one of the consequences is actually positive, who are we to say that they cannot benefit from it?"
Worldwide, the demand for sand and gravel is relentless and increasing. Mining, usually from open pits or by dredging, is unregulated in many areas and often illegal. In India, for example, sand "mafias" have developed, with gangs stealing sand from a river bend or a beach overnight.
A United Nations report this year noted that extraction of sand around the world is exceeding the rates by which it is replenished. Sand removal along rivers and coastal regions often leads to greater erosion and harm to ecosystems, the report said.
In addition to better regulations, the report called for reducing the demand for sand and gravel through improved designs that cut the amount of concrete in buildings and infrastructure. Lighter designs would also help address a climate change problem: Manufacturing of cement, the reactive ingredient in concrete, is responsible for about 5 per cent of global emissions of carbon dioxide, the main greenhouse gas.
Concerns about the supply of sand seem far off in Nuuk, population 17,500, where it is possible to walk from one end of the city to another in less than an hour and where the Greenland government works out of an office building above a shopping centre.
But even Nuuk has its sights on expansion. There are plans to build thousands of homes and apartments to accommodate a population that is forecast to reach 30,000 by 2030. More immediately, work crews will soon begin lengthening the airport's sole runway to handle jets, which would help Greenland's nascent tourism industry.
Mr Nicolai Mogensen, who runs Nuuk's only concrete plant, is ready. This year, he stockpiled extra sand, anticipating the start of the runway project. He currently has about 15,000 cubic yards, a small gray mountain next to the plant. It comes from a nearby fjord, sucked from the bottom by a dredge.
Mr Mogensen, who has run concrete plants in Norway, Poland, Germany and Denmark, said he thought Dr Bendixen's idea was a good one. "All these countries are running out of sand," he said.