London: A part of the Antarctica coastline has been losing ice to the ocean for over four decades, far longer than had been expected, finds a new study of satellite images. The images of 2,000 km of west Antarctica's coastline showed a loss of about 1,000 km of ice, the researchers said. "We knew that ice had been retreating from this region recently but now, thanks to a wealth of freely available satellite data, we know this has been occurring pervasively along the coastline for almost half a century," said lead researcher Frazer Christie, doctoral student at the University of Edinburgh's School of GeoSciences in Britain. The findings showed that ice has been retreating consistently along almost the entire coastline of Antarctica's Bellingshausen Sea since satellite records began. Warmer ocean waters reaching Antarctica's coast, rather than rising air temperatures, are the reason behind the loss of ice, the scientists suggest. For the study, published in Geophysical Research Letters, the team analysed hundreds of satellite photographs of the ice margin captured by NASA, the United States Geological Survey (USGS) and the European Space Agency (ESA). The team also monitored ice thickness and thinning rates using data taken from satellites and the air. This showed that some of the largest changes, where ice has rapidly thinned and retreated several miles since 1975, correspond to where the ice front is deepest. "This study provides important context for our understanding of what is causing ice to retreat around the continent," said Robert Bingham from School of GeoSciences. The results will help improve estimates of global sea level rise caused by ice melt, the researchers noted adding that further satellite monitoring is needed to track progress of the ice sheet. "We now know change to West Antarctica has been longstanding, and the challenge ahead is to determine what has been causing these ice losses for so long," Bingham said.