Glaciers around the world are retreating at record speed: this is now known. Equally well known are the effects of this flash melting, from rising sea levels to alterations in ocean currents. Every now and then, however, something new is discovered on the subject, and it’s never good news.
The latest discovery, published on Nature Communicationsconcerns a relatively little explored issue so far: the loss of nutrients associated with the retreat of glaciers, which supply the oceans with fewer and fewer substances useful to marine ecosystems, and therefore put them at risk.
Ice nutrients. Even though they appear static to us humans, glaciers are always moving – very slowly, of course, and directed downward, pulled by gravity. By moving over the rocks on which they were formed, glaciers “grind up” enormous quantities of sediment, which then end up in the ocean, transported by the water that melts from the glaciers themselves. These sediments are often essential for marine ecosystems: they contain, for example, iron and manganese, which are fundamental metals for the growth of phytoplankton, but also more “classic” nutrients such as phosphorus.
The comparison. The University of Southern California study therefore investigated whether there are differences, in terms of nutrient supply to the ocean, between a glacier that is retreating rapidly and one that is stable. The two glaciers chosen for the study are two adjacent masses, both in Alaska, on the Kenai Peninsula: Aialik is the stable one of the two, and ends directly on the sea, while Northwestern has been retreating since the 1950s, and has since “returned” 15 km from the coast. The important detail is that both glaciers arise on the same rocks, so they have access to the same nutrients.
Metals. The analysis of the runoff water that reaches the sea from the glaciers has given very clear results: Aialik provides liquids that are richer in metals and other nutrients than those of Northwestern. To be precise, the bioavailable iron (i.e. the one already “ready for consumption” once it has arrived at the disposal of the phytoplankton) of Aialik was 18% of the total iron, while for manganese the percentage rose to 26%; Northwestern, however, had only 13% iron and 14% manganese.
The importance of being on the sea. But why are the waters coming from the retreating glacier less nutritious? According to the authors of the study, it is a matter of time: the metals that are captured by Aialik do not take long to arrive in the sea, where they are still “fresh” and more easily used by microorganisms.
The waters of Northwestern are instead “aged” and therefore its sediments are less reactive. In short: there is another reason why it is bad if glaciers retreat from the coast, and entire marine ecosystems could suffer the effects.
