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Over the past 1.2 million years, marine life has become extinct in the Dead Oxygen Dead Zone of the North Pacific.

Analysis of sedimentary cores from the Bering Sea reveals a recurring link between the warmer climate of the North Pacific sub-Arctic over the past 1.2 million years and the rapid eruption of low-oxygen “dead zones”.

The new study, led by researchers at the University of California, Santa Cruz, was published on June 2, 2021 Scientific progress. The results provide important information for understanding the causes of hypoxia or ‘hypoxia’ in the North Pacific and for predicting future hypoxia cases.

Waste samples from the Bering Sea have a history of oxygen depletion in the form of layered or “encapsulated” debris. Attribution: IODP

“It is important to understand whether climate change is leading the oceans to a rapid and severe hypoxic‘ tipping point ’that will destroy the ecosystems, food resources and economies of UCLA Earth Sciences, student and postgraduate degree.

The researchers based their findings on an analysis of deep sedimentary cores from a site in the Bering Sea. Over a long period of time, the debris is deposited and collected on the beach. The activities of the organisms living in the coastal wastes are usually disturbed and confused when they are collected, but if the hypoxia kills the organisms, a systematic classification is maintained. Therefore, scientists can find records of past hypoxic events in the form of layered or “lamellar” debris in cores excavated from sea level.

Scientists have long known episodes of widespread hypoxia in the North Pacific at the end of the last ice age, when ice sheets melted and freshwater flowed into the oceans in large numbers. The new study provides the first record of past low oxygen events, and recent events do not represent the majority of these events in mechanism or chronology.

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Anna Cristina Ravello, a professor of oceanography at the University of California, Santa Cruz, said: “There is no such thing as melting ice sheets. “Sudden hypoxic events are actually common in geographical records and are not usually associated with fragmentation. They always occur in warm snow, as we now experience. “

Hypoxia occurs after intense growth of phytoplankton (marine algae) on the surface of the water. When phytoplankton die, they sink deeper into the ocean and decompose, depleting oxygen and releasing carbon dioxide into the water below the surface. However, it is still unclear what caused the incident. Warming oceans, rising sea levels, and the availability of iron (a factor that limits phytoplankton growth) all play a role.

“Our study shows that sea level rise caused by hot, snowy weather is the cause of these anoxic events,” Knudson said. “As sea level rises, molten iron can be carried from the submerged continental shelf to the open ocean and promote the growth of phytoplankton that has evaporated in the surface water.”

Although sea level rise is a prerequisite in the background, it is not sufficient to cause anoxia on its own. Changes in ocean circulation may play an important role, including rising water to the surface and strong currents that can move iron from the intercontinental shelf to the open ocean to bring more nutrients to the surface, Nodson said.

Currently, local dead zones occur in coastal areas around the world due to the warmer climate and enrichment of coastal waters with nutrients from agricultural fertilizers. Even the huge dead area along the Mississippi River compared to the widespread hypoxia that occurred in the North Pacific at the end of the last ice age.

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The new study was based on debris from a single site, and researchers did not know the extent of the recorded inactive areas – whether they were confined to the Bering Sea or spread along the edge of the North Pacific Ocean, as in most other regions. . Recent events.

Joyds Resolution Research ship drills sediment core

Waste samples were mined off the coast of Beijing during a 2009 IODP expedition involving Christina Ravello, an oceanographer at the University of California, South Africa. Attribution: Carlos Alvarez Surrey, IODP / GUEST

“We do not know how widespread it was, but we do know that it was very severe and lasted much longer than the well – learned dismissal event,” said Ravello, co-chair of the Expedition 323 integrated marine drilling program. , Which re-established the Bering Sea Core in 2001. 2009.

The core has recorded multiple events during each interglacial period of the ice age, and rapid transitions occurred as laminated debris appeared and disappeared, Nudson said.

New findings raise concerns about whether climate change and ocean warming could lead to a major phase leading to widespread hypoxia in the North Pacific.

“The system is set up for this kind of event,” Ravello said. “We need to see how widespread this is, and we need to rethink how this event came about, because we now know it doesn’t need to be a big hurdle. This study sets the stage for a lot of follow-up work.

Reference: “Causes and timing of recurrent sub Arctic Pacific hypoxia” Carla B. Nudson, Anna Christina Ravello, Ivano W. Hi, Christina b. Nudson, Michelle K .; Scientific progress.
DOI: 10.1126 / sciadv.abg2906

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In addition to Nodson and Ravello, Ivano Illo and St. Christina Nodson of Moss Landing Marine Laboratories co-authored the paper. Thomas University of Minnesota, Michelle Drake of the University of California, Santa Cruz, and Tatusuhiko Sakamoto of Mi University, Japan.

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