February 16, 2010

Warming Ocean Melting Greenland Ice

According to studies released on Sunday, winds and currents that drive warmer water into fjords, where it carves out the base of coastal glaciers, are significantly eroding Greenland's ice sheet.

The icy mass holds enough water to boost global sea levels 23 feet, which could potentially drown low-lying coastal cities and deltas across the globe.

The ocean watermark is currently rising about 0.12 inches a year, which compares with 0.07 inches annually in the early 1960s.

However, Greenland's contribution has doubled in the past decade, and scientists believe climate change is mostly to blame.  However it is not well understood exactly how this is occurring.

Some theories say air temperatures are to blame, which are rising quicker and farther north than the global average.

Another idea is that shifting currents and subtropical ocean waters are helping to erode the foundation of coastal glaciers, which accelerate their slide into the sea. 

However, these studies have been mainly based on mathematical models rather than observation, until now.

Fiammetta Straneo of Woods Hole Oceanographic Institution in Massachusetts led a group of scientists that hoped to fill that data void.

The researchers took detailed measurements in July and September 2008 of the water properties in the Sermilik Fjord connecting Helheim Glacier in eastern Greenland with the ocean.

They discovered that deep water streaming into the fjord was 37.4 - 39.2 degrees Fahrenheit, which is warm enough to cut into the base of the glaciers and hasten their plunge into the sea.

Instruments were left anchored in the fjord for eight months.  They showed that winds aligned with the coastline, playing 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.

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

They took ocean measurements in August 2008 in three fjords at the base of four glaciers breaking off into the sea, which is known as calving.

They discovered that ocean melting 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 account for the rest.

One study, 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 in Western England compared past and future changes in ocean acidity using computer simulations.

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

The accelerating acidification has already started to take a toll on a bunch of marine animals that play an important 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 has fallen in weight by a third.


On the Net: