10,000 years ago, retreat of the Cordillera ice sheet led to volcanic eruptions and deoxygenation events
Ocean deoxygenation occurs when oxygen levels in the ocean drop, threatening marine life and ecosystem Survive on a small amount of oxygen dissolved in water.Known sources of deoxygenation include climate change, massive algae bloomand nutrient pollute. To better understand these events, the researchers A recent study Looking back into the past for clues about the triggers and causes of deoxygenation events, we found a surprising source to add to the list: retreating ice sheets.
Understanding deoxygenation is important for aquatic ecosystems because oxygen, which is necessary for the survival of nearly all animals, including marine animals, is more difficult to obtain in water than on land. dissolved oxygen It is the only form available to aquatic animals and microorganisms. Photosynthesizers like plants and algae can produce oxygen in the ocean, but only near the sunny surface.Therefore, mid-level and deep water can become hypoxic zoneHowever, too much of a good thing can quickly turn into a bad thing. If photosynthetic algae grow too fast, they can quickly block sunlight, decompose and create areas of severe oxygen deficiency known as “dead zone“There, anything that needs oxygen can’t survive.
Satellite image of a green algae bloom in the Baltic Sea off the coast of Latvia and Lithuania. Photo: European Space Agency/Flickr
Scientists have been trying to understand the impact of climate change on ocean deoxygenation events by looking at past events. Understanding what caused deoxygenation events during past periods of rapid climate change, such as the last major glacier retreat, allows researchers to identify potential sources of future deoxygenation.
in a Paper published in a magazine nature In November, geologists examined the potential relationship between ocean deoxygenation events and the end of the last ice age between 17,000 and 10,000 years ago. Jianghui Du, a postdoctoral scholar at the Swiss Federal Institute of Technology in Zurich and lead author of the study, recognized the urgency of understanding which processes trigger deoxygenation.He chose to focus on the last deglaciation Cordille ice sheet— a gigantic ice sheet larger than Greenland that once covered the Pacific Northwest — has shrunk over thousands of years.
Reconstructed images of the Laurentide and Cordilleran ice sheets. The Cordillera Ice Sheet covers northwestern North America and merges with the larger Laurentide Ice Sheet near Montana. Photo: NPS Natural Resources/Flickr
To study ancient deoxygenation events like those that occurred directly after the retreat of the Cordillera ice sheet, Du and his colleagues used a variety of methods. To reconstruct ocean oxygenation, they assessed mineral assemblages — the abundance and combination of different elements including rhenium, cadmium and uranium. Because different elements accumulate in sediments under different oxygen conditions, the abundance of specific elements allows scientists to estimate oxygen levels thousands of years ago based on the geological record. This work, combined with assessments of volcanic input, measurements of radioisotopes, and compilation of volcanic eruption records, allowed the researchers to assess potential predictors and triggers of large deoxygenation events following receding Cordillera Ice Sheet.
Through the study, Du told GlacierHub he found that the retreat of the Cordillera ice sheet “triggered explosive volcanic activity” in the North Pacific between 17,000 and 10,000 years ago. This volcanic activity led to the creation of large amounts of volcanic ash in the ocean, which, according to Du, “drives ocean productivity and triggers ocean deoxygenation.” While previous research has hypothesized that retreating ice sheets may have triggered the eruptions, this study confirms that the deoxygenation event in the North Pacific was a direct result of eruptions caused by the retreating Cordillera ice sheet.
Pavlov Volcano is one of the most active volcanoes in Alaska, most recently erupting in 2021. Photo: NASA Goddard Photos and Videos/Flickr
As the Cordillera ice sheet recedes, a species called isostatic springback occur. This process occurs when the land rises after the enormous weight of the ice sheet is removed. The ice presses down on the ground before retreating, putting pressure on the mantle beneath the rock. As the ice retreats, the rebound and upward motion of the land destabilizes it and allows magma to rise through cracks to the surface, triggering volcanic eruptions, earthquakes and other tectonic events.
Volcanic eruptions, in turn, can exacerbate deoxygenation events in the same way as nutrient leaks. Volcanic ash contains high amounts of nutrients, including calcium, magnesium and potassium, so large deposits of volcanic ash in the ocean quickly became areas where photosynthetic algae thrived. The resulting massive algal blooms can quickly deoxygenate the water after the algae sink and die.
Since the current ice sheet in the region is much smaller than the Cordillera ice sheet, Current glaciers and ice retreat It is unlikely to cause the same level of widespread volcanic activity. However, understanding past volcanic activity and deoxygenation events can help scientists assess and prepare for potential triggers of future events.
The study has important implications for future prospects Marine Iron Fertilizerno, a climate engineering strategy that became popular in the early 1990s. Since aquatic algae can remove atmospheric carbon dioxide through photosynthesis, it has been proposed to disperse normally limited nutrients such as iron into the oceans to promote more photosynthesis and reduce atmospheric carbon. Volcanic events like those studied by Du are examples of large-scale natural iron fertilization. This study shows that while iron fertilization does reduce atmospheric carbon, it does so at the cost of large deoxygenation events and the potential for ecosystem damage.
Du emphasized that understanding past volcanic events requires extensive collaboration among scientists.Even with “a slight reduction in oxygen [low oxygen zones] may have a disproportionately large impact on marine ecosystems,” making it important to understand and prepare for deoxygenation events. Understanding the triggers of past volcanic eruptions and the resulting low-oxygen zones can help scientists and resource managers predict and mitigate such deoxygenation events in the future. impact of the event.
