As the complex story of climate change unfolds, many of the endings are grim. But there are exceptions. Predictions that the lowest-oxygen environments in the ocean would get worse may not come to pass. Instead, University of Washington research shows climate change, as it weakens the trade winds, could shrink the size of these extreme low-oxygen waters.
"The tropics should actually get better oxygenated as the climate warms up," said Curtis Deutsch, a UW associate professor of oceanography. He is lead author of the study published Aug. 8 in Science.
Warmer water contains less gas, so climate change is expected to reduce oxygen levels worldwide. Observations show this is already taking place in many places. Declines during the past 20 years in the tropical low-oxygen zones, the lowest-oxygen waters on the planet, had led to a 2008 study proposing that these zones would also get worse over time.
Tropical regions are usually associated with an abundance of life, but they have some of the most inhospitable places for ocean dwellers. The oxygen minimum zones off Mexico and Peru have oxygen levels already too low to support most animals (so, unlike in other low-oxygen zones, here there's no risk of killing fish).
But when those levels drop even further, a particular group of bacteria, which can use nitrogen instead of oxygen as a source of energy, thrive. Nitrogen is an essential and very scarce nutrient for marine plants. When oxygen levels get low enough for that particular group of bacteria to take over, significant amounts of the ocean's fertilizer get deep-sixed to the bottom of the tropical ocean.
The new paper shows that water flowing into the tropics is indeed likely to get lower in oxygen, decreasing the initial oxygen supply. But demand will also shift under climate change. Specifically, as the trade winds weaken, the whole sequence of events that feeds this bacterial food chain will slow down, and the low-oxygen zone will
|Contact: Hannah Hickey|
University of Washington