The icy mass sitting atop Greenland holds enough water to boost global sea levels by seven metres (23 feet), potentially drowning low-lying coastal cities and deltas around the world.

At present, the ocean watermark is rising at around three millimetres (0.12 inches) per year, a figure that compares with 1.8mm (0.07 inches) annually in the early 1960s.

But Greenland's contribution has more than doubled in the past decade, and scientists suspect climate change is largely to blame, although exactly how this is occurring is fiercely debated.

Some theories point to air temperatures, which are rising faster in far northern latitudes than the global average.

A rival idea is that shifting currents and subtropical ocean waters moving north are eroding the foundation of coastal glaciers, accelerating their slide into the sea, especially those inside Greenland's many fjords.

Until now, however, these studies have been mainly based on mathematical models rather than observation.

A team of scientists led by Fiammetta Straneo of Woods Hole Oceanographic Institution in Massachusetts set out to help fill that data void.

Working off of a ship in July and September 2008, the researchers took detailed measurements of the water properties in the Sermilik Fjord connecting Helheim Glacier in eastern Greenland with the ocean.

They found deep water streaming into the fjord was 3.0-4.0 degrees Celsius (37.4-39.2 degrees Fahrenheit), warm enough to cut into the base of the glaciers and hasten their plunge into the sea.

Moored instruments left in the fjord for eight months showed that winds aligned with the coastline played a crucial role in the influx of these warmer waters.

"Our findings support increased submarine melting as a trigger for the glacier acceleration, but indicated a combination of atmospheric and oceanic changes as the likely driver," the researchers say.

In a separate field study, Eric Rignot of the Jet Propulsion Laboratory in Pasadena, California and colleagues tried to calculate the relative share of the causes of glacier loss.

Investigating the western side of Greenland, they took ocean measurements in August 2008 in three fjords at the base of four glaciers breaking off into the sea, a process known as calving.

Ocean melting, they found, accounted for between 20 and 75 percent of ice loss from the glacier face, with calving from the part of the iceberg exposed to air accounting for the rest.

Meanwhile, a study also published in the journal Nature Geoscience warned that oceans could become more acidic faster than at any time over the last 65 million years.

Andy Ridgwell and Daniella Schmidt of the University of Bristol, western England compared past and future changes in ocean acidity using computer simulations.

They found that the surface of the ocean is set to acidify even faster than it did during a well-documented episode of greenhouse warming 55.5 million years ago.

Accelerating acidification has already begun to take a toll on numerous marine animals that play a vital role in ocean food chain and help draw off huge quantities of CO2 from the atmosphere.

The calcium carapace of microscopic animals called foraminifera living in the Southern Ocean, for example, have fallen in weight by a third.

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