A Decline in the Vertical Transport of Particulate Organic Carbon in the Global Open Ocean

Abstract

In recent years, as the ocean absorbs increasing amounts of atmospheric CO₂, ocean acidification has intensified. Simultaneously, global warming and enhanced ocean stratification have led to the continuous expansion of the oceanic oxygen minimum zone (OMZ). Under the combined effects of these processes, a key question arises: How will the transport of particulate organic carbon (POC) to the deep ocean (>1,000 m) be affected? Analysis of POC flux data from 547 stations, collected via global sediment traps since the 1980s, reveals that POC flux has increased only in the shallow ocean (<300 m) but has significantly decreased in the deep ocean. These findings suggest that the expansion of the OMZ has not led to more carbon being transported to the deep ocean. Instead, more POC is being retained in the mid-upper ocean (<1,000 m), where its degradation results in significant consumption of dissolved oxygen, contributing to the expansion of the OMZ.