Dead Zones Recurrently Forming in North Pacific During Warm Climates, Abrupt Episodes Happen Over the Last 1.2 Million Years

Recent analysis shows recurrent forming of dead zones in the North Pacific during warm climates. The new research, which researchers at UC Santa Cruz led, provides crucial information for understanding the reasons for the so-called "hypoxia" or low oxygen in the North Pacific. It also shows the reason for forecasting the incidence of hypoxic conditions in the future.

Specifically, a Phys.org report said, an analysis of sediment cores from the Bering Seas has shown a recurrent relationship association between warmer climates and sudden low-oxygen or dead zone episodes in the subarctic North Pacific Ocean over the last 1.2 million years.

According to first author Karl Knudson, who led the research as a graduate student in Earth sciences at UCSC, it is important to understand if climate change is pushing the ocean toward a tipping point for rapid and severe hypoxia would destroy food sources, ecosystems, and economies.

Sediment Cores from the Bering Sea

The study authors based their research on an assessment of deep sediment cores from an area in the Bering Sea.

For long periods, sediments are placed, and they build up on the seafloor. The activity of organisms that live in the seafloor sediments typically disrupts and mixes them as they build up, although if hypoxia has destroyed such organisms, a methodical pattern of layers is preserved.

Therefore, researchers can find a record of previous hypoxic occurrences in the form of these laminated or layered in cores drilled from the seafloor.

For a long time now, scientists had known about a major episode of prevalent hypoxia in the North Pacific at the end of the last ice age, when the ice sheets' melting sent a massive entry of freshwater into the ocean.

Hypoxia

This new study research, Causes and timing of recurring subarctic Pacific hypoxia published in Science Advances, provides the preliminary records of earlier dead zones and presents that the latest occurrence was not representative of most of these occurrences when it comes to timing or mechanisms.

According to UC Santa Cruz professor of ocean sciences Ana Christina Ravelo, also a corresponding author, it does not take a huge perturbation such as melting ice sheets for this to occur.

Such abrupt hypoxic occurrences, she added, are actually typical in the geologic record, and they are not usually linked to deglaciation. They nearly always occur during the warm interglacial eras, like the present time.

The hypoxia, according to the National Ocean Services, takes place following the intense growth of phytoplankton or marine algae on the waters' surface. When the marine algae die, they are sinking deeper into the ocean and decompose, which reduces the oxygen and releases carbon dioxide into the water underneath the surface.

What stimulates such events, nonetheless, remains unclear. Ocean warming, high sea levels and iron's availability all appear to play a vital role.

Lastly, explained Knudson, high sea levels which take place during warm interglacial climates, added to such hypoxic events.

During the high sea levels, elaborated the expert, dissolved iron from the flooded continental shelves can be delivered to the open ocean and stimulate the strong phytoplankton growth in surface waters.

Related information about hypoxia is shown on IUCN's YouTube video below:

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