Report: Ocean Dead Zones Tied To Abrupt Warming

The ocean is full of so-called dead zones — that is, areas where low oxygen levels resulted in a lack of marine life. A new study from the National Science Foundation points toward "abrupt ocean warming" and the formation of these dead zones, a clear tie between the two that has thus far been lacking. These historical warming periods happened about 14,700 and 11,500 years ago in the North Pacific, and raises concerns that warming ocean temperatures could cause dead zones to expand in the future.

The abrupt ocean warming periods that triggered the dead zones came at the end of the last ice age, according to the report, which was published last week in the journal Nature.

These dead zones are formally called "Oxygen Minimum Zones," and researchers have been tangled in debates about what causes these low-oxygen zones to expand. This time around, though, the study found "a clear connection" between the two aforementioned warming periods and the "sudden onset" of low-oxygen ocean zones.

Warmer water isn't enough to trigger these events, though it can cause a decrease in oxygen levels. However, the low-oxygen zones don't form until microscopic diatoms start blooming at a faster than average rate, dropping down to the seafloor.

Said the study's lead author Summer Praetorius, "Our study reveals a strong link between ocean warming, loss of oxygen and an ecological shift to favor diatom production. During each warming event, the transition to hypoxia occurred abruptly and persisted for about 1,000 years, suggesting a feedback that sustained or amplified hypoxia."

One big concern raised by the study is how quickly these changes can take place. As pointed out by the researchers, the effects of climate change are assumed to be slow and predictable. This study, though, hints that such an assumption could be wrong.

Said the paper's co-author Alan Mix, "This study shows that the ecological consequences of climate change can be massive and can occur pretty fast with little warning."

SOURCE: National Science Foundation