Our planet’s oceans are crowded by life, with numerous creatures finding their homes underneath the waves.
However, not every place of the deep blue sea is favorable for life.
Over the past few years, scientists became particularly concerned about the so-called “dead-zones.”
According to Sciencealert, dead zones are places with hypoxic waters in the ocean where oxygen levels are on the low side, making the areas unhabitable.
Over the past few decades, dead zones have significantly expanded their reach and are no longer limited to the ocean, as oxygen loss in lakes is manifesting offshore too.
However, scientists believe that this is not particularly a new problem in the ocean.
A recent study shows that dead zones are a recurring problem of the Pacific Ocean for longer than anybody ever thought – More than 1.2 million years.
Analyzing fundamental ancient sediment extracted from the Bering Sea seabed of the North Pacific helped scientists identify 27 individual instances of dead zone, officially known as oxygen minimum zones (OMZs), over the past 1.2 million years, showing that repeat bouts of hypoxia were a common sight of the Pacific all the way through the Pleistocene.
Before that, it was known that the last ice age (approximately 12,000 years ago) overlapped with widespread hypoxia in the North Pacific, as considerable warming events provoked ice sheet melting that dislocated considerable amounts of fresh water right into the ocean.
Ana Christina Ravelo, an ocean scientist from the University of California, Santa Cruz, said that a significant perturbation like melting ice sheets isn’t necessarily needed for the phenomenon to happen.
“These abrupt hypoxic events are actually common in the geologic record, and they are not typically associated with deglaciation. They almost always happen during the warm interglacial periods, like the one we’re in now,” she added.