Arctic Ocean Tipping Point

The loss of sea ice over the last two decades has triggered an irreversible chemical shift in the Arctic Ocean. By exposing shallow coastal waters to intense sunlight, the melting ice has accelerated a process that destroys nitrate, the foundational fertiliser required for marine life to survive.

This suggests the Arctic passed a critical ecological tipping point in 2009. The resulting nutrient famine is already affecting the whole Arctic food chain, threatening everything from microscopic plankton to commercial fish stocks, seabirds, and marine mammals.

20 years of oceanographic data collected from the Fram Strait where Arctic waters drain into the North Atlantic show that the extensive loss of sea ice has increased a process known as benthic denitrification on the shallow continental shelves that underlie nearly half of the Arctic Ocean. When ice disappears, increased sunlight triggers temporary algae blooms. As this organic matter dies and sinks to the shallow seafloor, it depletes oxygen in the sediment. In these oxygen-poor environments, marine microbes consume nitrate and convert it into inert nitrogen gas, removing it from the marine ecosystem entirely.

This shift to nitrate-limited conditions suggests the Arctic Ocean may only be able to support smaller, less nutritious species of plankton in the future, starving the upper tiers of the food chain. Because this shift is tied to systemic, ongoing ice loss, it is highly unlikely the Arctic Ocean will ever revert to its previous state.

Further research will need to explore the possible wider effects that changes in Arctic waters could have on marine populations in other parts of the world’s oceans, including commercial fishing in the North Atlantic.

SOURCE: based on Eva Cahill, https://oceanographicmagazine.com/news/arctic-ocean-passes-irreversible…;