The Slow Destruction of the Zachariae Isstrom Glacier Reading Answers

The Zachariae Isstrom glacier is the latest in a string of Greenland glaciers to undergo rapid change in the warming world. A new NASA study has found that Zachariae Isstrom has broken loose from a glaciologically stable position and entered a phase of accelerated retreat. It is expected that the consequences will be felt for decades to come.

The reason for these long-term effects is the size of the Zachariae Isstrom glacier. It drains ice from an area of 91,780 square kilometres, which is about 5 per cent of the Greenland Ice Sheet. All by itself, it holds enough water to raise global sea level by 46 centimetres if it were to melt completely. The Zachariae Isstrom glacier is currently crumbling, losing 5 billion tons of mass every year, which is disintegrating into the North Atlantic Ocean. Jeremy Close, one of the researchers on the NASA study, explains: "North Greenland glaciers are changing rapidly and especially the form and dynamics of Zachariae Isstrom have been transformed over the last few years. The melting glacier will now result in rising sea levels for decades to come."

The cause of the change in the Zachariae Isstrom glacier is solely due to warmer water temperatures. Greenland marine scientist Sophie Boldt explains the situation. "The warmer waters have caused the end of the glacier to float free from a ridge of bedrock below sea level on which it had rested until just recently. Without that natural brake, the glacier is now sliding more quickly and more icebergs are snapping off, adding a net five billion tonnes of ice a year to the oceans."

The NASA team used data from aerial surveys conducted by NASA and satellite-based observations acquired by multiple international space agencies coordinated by the Polar Space Task Group. The various tools used, including a highly sensitive radar sounder, gravimeter and laser profiling systems, coupled with radar and optical photographs from satellites, monitored and recorded changes in the shape, size and position of glacial ice over long time periods. This provided precise data on the state of Earth's polar regions.

The scientists determined the bottom of Zachariae Isstrom is being rapidly eroded by warmer ocean water mixed with growing amounts of melt water from the ice sheet surface. "Ocean warming has played a sole role in triggering the glacier's retreat," said section leader Joanna Morgan, "but we need more oceanographic observations in this critical sector of Greenland to determine the glacier's prognosis."

Adjacent to Zachariae Isstrom is another large glacier that is also melting rapidly, but is receding at a slower rate because it is protected by an inland hill. The two glaciers make up twelve per cent of the Greenland ice sheet and would boost global sea levels by more than ninety-nine centimetres if they fully collapsed. The sector where these two glaciers reside is one of three major marine-based basins in Greenland, along with Jakobshavn Isbrae in central west Greenland and the Petermann-Humboldt sector in central north Greenland. Glaciologist, Tom Ellis, explains that potential danger is imminent within the latter two areas.

"The Jakobshavn Isbrae and the Petermann-Humboldt basins hold enough water to raise global sea level by over half a metre each, and both are also undergoing significant changes related to warming at present. Even a small increase in sea levels can have devastating effects on shoreline habitats, and half a metre is not a small increase." As rising seawater reaches farther inland, it can cause destructive erosion, flooding of wetlands, contamination of aquifers and agricultural soils, and lost habitat for fish, birds, and plants. In addition, hundreds of millions of people live in areas that will become increasingly vulnerable to flooding. Higher sea levels would force them to abandon their homes and relocate. Low-lying islands could be submerged completely. One of the NASA study's authors, Paulina Weiler, summarises the study's conclusion. "It is likely that many of these Greenland glaciers will lose their ice shelves in coming years, further increasing Greenland's future contributions to global sea level rise. It is unlikely that world governments will take the necessary decisions to stop the melting and it is actually moot whether any action taken now would create the required changes in time."

The actual process of polar glacier iceberg calving into the sea is similar in most situations of glaciers that are situated next to the sea. First of all, the glacier must, of course, extend into the sea. This part has usually become rather thin, due to relatively warm circumpolar water that flows in from the deep and causes melting to the underside of the glacier. This water is cooled and then moves away from the sub-ice cavity in shallower water.

The warm water continues to erode the underside of the glacier, particularly at the grounding line, which is where the glacier comes into contact with glaciomarine muds, on which it rests. The weight of the thinning glacier as it extends into the sea causes crevasses to form on the top side and these will in turn snap off and calve the icebergs of the future. Higher up in the glacier, ice thinning is present and these fractures will eventually become the crevasses lower down.