An anonymous reader quotes a report from Oregon Live: Nearly two decades ago, fishers discovered an odd occurrence off the coast of Oregon. They were pulling up pots of dead or lethargic crabs. At first they suspected a chemical spill or a red tide. But instead, they learned, dangerously low levels of dissolved oxygen in the ocean water were to blame. The crabs had suffocated. These swaths of hypoxic areas have surfaced every summer on Pacific Northwest shores since it was first recorded in 2002. They are spurred by naturally occurring coastal upwellings and algae blooms, exacerbated by climate change, said Francis Chan, director of the Cooperative Institute for Marine Resources Studies at Oregon State University. Akin to fire season, hypoxia season arrived earlier this year -- the earliest start in 20 years, according to Chan. But unlike wildfire, or other visible climate emergencies, it's gone largely unrecognized. "It's kind of a silent problem happening out there," said Chan. "This year, I can look out and see trees with one side burnt because of the heat wave. As I'm driving on McKenzie highway, I can see Mount Jefferson has no snow on it. But when you drive out to the ocean, it looks exactly the same as last summer."
Typically, hypoxic conditions haven't arrived to the nearshore until mid-June or July. This year hypoxic conditions were reported in April with the upwelling season beginning in March. To get a sense of why an early beginning to the upwelling season is concerning, Chan compared it to the summer drought season. "Say we expected rainfall lasting until March but the rain stops in February. That's all the water we have. We have to last until next year." Similarly, if upwelling starts a month earlier than usual, the amount of oxygen, already low, has to last until the fall when storms promote mixing which adds oxygen back into the system. Chan said as of late September this year, upwelling is still occurring and low levels of oxygen are still persisting.
Climate change is playing a role in worsening oxygen levels. Simply put, warmer water holds less oxygen because the oxygen molecules are moving faster and are more likely to escape from the surface. A little more complicated, climate change is altering the structure of the oceans as the warmer upper layer is more buoyant than the cooler, deeper, already oxygen-poor ocean layer. The warmer upper layer keeps the deeper layer from "taking a breath," explained Chan. On a global scale, the oceans are already losing oxygen. Take this and add local factors like coastal upwelling and phytoplankton bloom decomposition off Washington and Oregon coasts, and you have a system with severely low oxygen levels. [...] There are no records of reoccurring low-oxygen levels like scientists have observed since 2002, despite over 50 years of oceanic monitoring.
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