Analysis of deposits in the Bering Sea demonstrated the relationship between warming and the occurrence of the Pachantic “dead zones” with a catastrophically low oxygen content in subarctic regions of the Pachantic Ocean. The results of the study of scientists of the University of California are published in the journal Science Advances.
Experts studied cores extracted from the bottom of the sea containing rocks whose age covers the last 1.2 million years. An ordered pattern of layers is usually disturbed by the activities of living organisms, however, during hypoxia, marine creatures are dying. Thus, scientists can trace the events that led to the emergence of the “dead zones” in the past.
It is known that at the end of the last glacial period in the northern part of the Pacific Ocean, a large episode of large-scale hypoxia occurred as a result of the melting of ice shields and a mass flow of fresh water in the ocean. However, as the results of a new study showed, for the emergence of “zones of death” such catastrophic events are not required as the melting of ice shields. Typically, large-scale hypoxia occurs during warm membranes.
“Dead zones” occur after intensive reproduction of phytoplankton (seaweed) in surface waters. When phytoplankton dies, it is immersed deeper into the ocean and decomposes, depleting oxygen. Although the mechanism of communication between warming and phytoplankton is still unclear, the researchers believe that elevated temperature, high sea level and an increase in the availability of iron in the open ocean play the main role in this process.