Cordilleran Ice Sheet Retreat Caused Volcanic Eruptions, Deoxygenation Events 10,000 Years Ago
Ocean deoxygenation occurs when oxygen levels drop within the ocean, threatening marine animals and ecosystems that depend on small amounts of oxygen dissolved in water to survive. Known sources of deoxygenation include climate change, massive algae blooms, and nutrient pollution. In an try and higher understand these events, researchers in a recent study looked to the past for clues about triggers and causes of deoxygenation events and located a surprising source so as to add to the list: ice sheet retreat.
Understanding deoxygenation matters for aquatic ecosystems because oxygen, essential for the survival of nearly all animals including marine animals, is way harder to acquire in water than on land. Dissolved oxygen is the one form available to aquatic animals and microorganisms. Photosynthesizers like plants and marine algae can produce oxygen within the oceans but only near the surface where sunlight is abundant. Because of this, mid-level and deep water can develop into low oxygen zones. Nevertheless, an excessive amount of of thing can quickly develop into a foul thing. If photosynthetic algae grow too fast, they’ll quickly shade out sunlight, decompose, and create severely hypoxic regions called “dead zones” where nothing that needs oxygen can survive.
A satellite image of a green algae bloom within the Baltic Sea off the coast of Latvia and Lithuania. Photo: European Space Agency/Flickr
Scientists have been attempting to grasp the consequences of climate change on ocean deoxygenation events by taking a look at past events. Determining what caused deoxygenation events in past eras of swift climate change, reminiscent of the last major deglaciation period, could allow researchers to find out potential future sources of deoxygenation.
In a paper published within the journal Nature in November, geologists examined the potential relationship between ocean deoxygenation events and the top of the last ice age 17,000 to 10,000 years ago. Jianghui Du, a postdoctoral scholar on the Swiss Federal Institute of Technology in Zürich and lead creator of this study, recognized the urgency of understanding what processes can trigger deoxygenation. He selected to concentrate on the last deglaciation period when the Cordilleran ice sheet—a large ice sheet larger than Greenland that after covered the Pacific Northwest—shrank over the course of 1000’s of years.
A reconstructed image of the Laurentide and Cordilleran ice sheets. The Cordilleran ice sheet covered the northwest region of North America and merged with the larger Laurentide ice sheet near Montana. Photo: NPS Natural Resources/Flickr
To review ancient deoxygenation events like people who happened directly following the retreat of the Cordilleran ice sheet, Du and his colleagues used a wide range of methods. To reconstruct ocean oxygenation, they assessed mineral assemblages—the abundance and composite of various elements including rhenium, cadmium, and uranium. Since different elements accumulate in sediments under differing oxygen conditions, the abundance of specific elements can allow scientists to estimate oxygen levels from 1000’s of years ago based on geological records. This work, combined with assessments of volcanic inputs, measurements of radiogenic isotopes, and a compilation of volcanic eruption records, allowed the researchers to guage the potential predictors and triggers of the big deoxygenation events following the retreat of the Cordilleran ice sheet.
Through this research, Du told GlacierHub that he found the retreat of the Cordilleran ice sheet “drove explosive volcanism” within the northern Pacific 17,000 to 10,000 years ago. This volcanism caused a big input of ash within the ocean, which in response to Du, “fueled ocean productivity that triggered ocean deoxygenation.” While previous studies have hypothesized that ice sheet retreat might need induced volcanic eruptions, this study confirms that the deoxygenation events within the northern Pacific were a direct results of the volcanic eruptions brought on by the Cordilleran ice sheet retreat.
The Pavlof Volcano is one among Alaska’s most energetic volcanoes, erupting as recently as 2021. Photo: NASA Goddard Photo and Video/Flickr
Because the Cordilleran ice sheet retreated, a phenomenon called isostatic rebound occurred. This process occurs when land rises after the large weight of ice sheets is removed. Prior to retreat, the ice depresses the bottom, putting pressure on the mantle underneath the rock. When the ice retreats, the rebound and upward movement of the land makes it unsteady and allows magma to rise through cracks toward the surface, triggering volcanic eruptions, earthquakes, and other tectonic events.
Volcanic eruptions in turn can fuel deoxygenation events in the identical way that nutrient spills do. Volcanic ash accommodates high amounts of nutrients, including calcium, magnesium, and potassium, so large deposits of ash within the ocean quickly develop into areas where photosynthetic algae thrive. The resulting massive algae blooms can quickly cause water to develop into deoxygenated after the algae sink and die.
Because the ice coverage at present within the region is way smaller than the Cordilleran ice sheet was, current glacier and ice retreat isn’t more likely to cause widespread volcanism to the identical extent. Nevertheless, understanding past volcanism and deoxygenation events might help scientists evaluate potential triggers of future events and prepare for them.
The study has key implications on the prospect of ocean iron fertilization, a climate engineering tactic popularized within the early Nineties. Since aquatic algae can remove carbon dioxide from the atmosphere via photosynthesis, proposals exist to disperse nutrients which are often limited, like iron, into the ocean to fuel more photosynthesis and reduce the quantity of carbon in our atmosphere. Volcanic events like those studied by Du are examples of natural iron fertilization at a big scale. This study shows that while iron fertilization could indeed reduce the quantity of carbon within the atmosphere, it comes at the fee of enormous deoxygenation events and potential for ecosystem damage.
Du emphasizes that collaboration between a wide selection of scientists is required to grasp past volcanic events. He says that even “slight decreases of oxygen in [low oxygen zones] could have a disproportionately large impact on the ocean ecosystem,” making it vital to grasp and prepare for deoxygenation events. Understanding the triggers of past volcanic eruptions and resulting low oxygen zones might help scientists and resource managers predict and mitigate the consequences of such events in the longer term.
