According to a combined technologies study, the incessant mountain rain, snow and melting glaciers pouring from thousands of mountain drainage channels into the Gulf of Alaska has disguised the total impact of the fresh water flow on the marine ecosystem of the Gulf of Alaska.
Total Impact
Satellite images combined with gravity and mass density estimates show that, if glacial melt and other freshwater runoff were to merge and flow as a single stream at one location into the Gulf of Alaska, such a merger would create the sixth largest river in the world, with a water flow one-and-a-half times that of the Mississippi, which drains a landmass of more than six times the area.
Magnitude and Importance
The University of Oregon’s six-year study of an average of precipitation, glacial melting and runoff from 2003 to 2009 allowed for a new perspective on what researchers describe as the clear “magnitude and importance of the runoff, which can affect everything from marine life to global sea level.” David Hill, lead author of the research and associate professor in the College of Engineering at Oregon State University (OSU), explains the broad impact this much fresh water can have on marine ecosystems by enumerating the interconnected systems that can be altered.
Freshwater runoff of this magnitude can influence marine biology, nearshore … temperature and salinity, ocean currents, sea level and other issues.
Volumes of Freshwater Runoff, Enough to Fill a River
The Gulf of Alaska, which is nestled in a small region of the southern Alaskan coast, is bounded by mountains that rise up to border the bay. In some places, accumulated precipitation is knocked down steep mountains, with runoff of more than 30 feet from precipitation and glacial melting in some locations but an average of six feet across the area.
This study is one of the first to document the volume of water being contributed to marine ecosystems by melting glaciers. In the Gulf of Alaska, melting glaciers contribute approximately 57 cubic kilometers of freshwater runoff. The combined runoff of 57 cubic kilometers from melting glaciers and approximately 792 cubic kilometers from annual precipitation results on a flood-stream of freshwater lager than the volumes of any of the world’s largest rivers, including, as the report specifies, the “Ganges, Nile, Volga, Niger, Columbia, Danube or Yellow River.”
What Is the Relevance of This?
The OSU study attained accuracy of and agreement between land-based observations and space-based images that show gravity and mass density variations. Specifically, the study results yield close agreement between NASA’s Gravity Recovery and Climate Experiment (GRACE satellites) and on-the-ground hydraulic, land-based measurements and modeling.
This accuracy and agreement relevant to glacier variations over time will be, as the report states, “important for better global understanding of water stored in [glaciers in] a high-altitude environment” because as the “glacial mass [density] decreases over time, the amount of melted water that was produced [during an interval] can be calculated.” Since the massive volume of fresh water entering marine ecosystems can have such significant effects on such a total range of systems, it will be beneficial to know what volumes of glacier melt are being added to precipitation runoff volumes.
Glacier Bay, Alaska, an Illustration
Hill notes that future trends in glacier melt runoff are not predicted because, although global warming is expected as a future climate factor, prediction of expected precipitation depends upon more variables than global warming alone. Glacial melt runoff is equally variable over time since glaciers in retreat may dwindle, slowing the volume of melt, then disappear. The OSU report notes also that Glacier Bay, Alaska, illustrates the processes at work in glacier melt and precipitation runoff.
The Bay also illustrates how melting glaciers can affect various species in the marine ecosystem. For instance, melting glaciers have been found to produce a loud bubbling noise, louder than ocean waves, as trapped air bubbles escape the glacier and pop back into their original shapes, as explained in “Popping bubbles from melting glaciers may hide seals from whales.” As the Glacier Bay glaciers have retreated to reach land, seals that populate the bay have dwindled in number. It is speculated that, with no glacier extension into the aquatic ecosystem, the seals vacate the area because the bubbling sound produced by the melting glaciers hide them from whale predators who can much more easily find them with no glacier noise cover. Based on this OSU study, the alteration to salinity in the bay resulting from the massive influx of fresh water from runoff may also be a significant factor in the retreat of the seals.
