Fresh water melting from glaciers in the Southern Hemisphere could make contributions to climate change, according to the recent study, “Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean,” by Neil F. Glasser and others in the journal Nature Scientific Reports. These findings are consistent with previous studies in North America and Europe.
It is not surprising to learn that climate change causes glaciers to melt, but perhaps counterintuitive to realize that glacial melting itself might intensify regional impacts of climate change, such as precipitation.
“The study is important because we are currently concerned about the volumes of fresh water entering the oceans from the melting ice sheets in Greenland and Antarctica and this gives us an indication of the likely effects,” Glasser said in an email to GlacierHub.
Deglaciation— the process of gradual glacier melting— has been found in North America and Europe to influence abrupt changes in climate. It works like this: the melting of vast volumes of ice can lead to the formation of large freshwater lakes, which can flow into the ocean; the freshwater from these lakes is less dense than the saltier waters of the ocean. An addition of such fresher, and less dense, waters can influence the structure of the ocean’s layers, which vary in their temperature, saltiness, and density. This structure also affects the currents within the ocean, which are driven largely by density (heavier water sinks, and lighter water rises) and the transfer of heat and water vapor between the ocean and the atmosphere.
The Younger Dryas (a sharp temperature decline in most of the Northern Hemisphere between 12,900 and 11,700 year ago), and other cooling events around 8000 years ago, are evidence of impact of the addition of freshwater into the oceans. There was no specific research in the Southern Hemisphere on this topic before this study; other researchers have known about past fluctuations, but not of the effects on oceans and climate. In order to clarify the principles in detail, the author and other researchers selected Patagonia as the target area. Patagonia, located at the southern end of South America, is an important area to test and interpret the records of environmental change because of its climatically sensitive location for its location near the core of westerly winds which greatly influence precipitation.
The research tried to establish the dates of three stages of rapid glacial lake drainage in the Pueyrredón basins of Patagonia using a group of methods called optically stimulated luminescence (OSL), which determines how long ago mineral grains were last exposed to sunlight and as a consequence can be used to estimate the date. In general, the lake drainage occurred between 13,000 and 8000 years ago. The water initially flowed eastward into the Atlantic, and then reorganized westward into the Pacific in new drainage routes formed as a result of deglaciation.
New geomorphological mapping and new OSL dates not only showed the glacial lake nature and evolution of the region, but also reconstructed the glacial lake system and associated drainage routes. By adopting coupled ocean-atmosphere model simulations, the understanding of ocean-climate interactions in the Southern Hemisphere has been significantly advanced. The study indicates that a great sea density change caused by salinity variance off the southern tip of South America could lead to significant impacts on the structure of coastal ocean layers, and thus the long-term regional climate and precipitation changes.
The research was also supported by the proxy data of the Andes and other eastern South Pacific data gathered from natural records of climate variability, such as tree rings and ice cores. Those proxy data indicated the relationship between the oceanic circulation and fresh water melting from glaciers during the deglaciation of the Patagonian Icefields, showing in particular a decrease in precipitation. These findings combine to further reinforce the fact that melting glaciers can affect the local climate. While previous studies were focused on the fact that the climate change has led to glacier melting, glacier melting can also influence the climatic system.