Wednesday, June 5, 2024

Oxygen deprivation will accompany warming for Hawai'i oceans


The ocean waters around the Hawaiian Islands are likely to become less productive as climate warming reduces their ability to hold oxygen.

Some ocean species may be unable to survive the depleted oxygen levels. And yes, that could translate to less sashimi on Island platters.

It is a silent crisis, driven by two linked inevitabilities: Climate change is driving warmer temperature that is being absorbed by the seas; and warmer water loses its ability to hold oxygen.

We have already seen fish kills in areas with high temperature waters with low dissolved oxygen. 

And various other places are already seeing reduced oxygen levels in warming deep waters, like this example in the Sea of Japan

A wide range of changes is occurring in the oceans as a result of both warming and the increased uptake of carbon-dioxide from the atmosphere, which results in acidification of the seas. That’s another thing that’s not good for much marine life.

This paper reviews some of the changes that are already occurring or soon will. It is ponderously entitled “An Overview of Ocean Climate Change Indicators: Sea Surface Temperature, Ocean Heat Content, Ocean pH, Dissolved Oxygen Concentration, Arctic Sea Ice Extent, Thickness and Volume, Sea Level and Strength of the AMOC (Atlantic Meridional Overturning Circulation).” 

The upshot of this for us is that things in Hawai’i’s oceans are going to be different. The consequences of lower oxygen levels are far-reaching.

Big game fish like tuna and marlin, which require high levels of oxygen, are particularly vulnerable. They may be forced to move to waters away from the Hawaiian Islands where temperatures are cooler, or to shallower waters where oxygen levels are higher, making them more susceptible to overfishing. Neither is good for Hawai’i anglers and seafood eaters.

Creatures like jellyfish, which do better in low-oxygen conditions, may become more common.

This article reviews many of the ways climate change is impacting key habitats for marine life. 

“Driven by climate change, marine biodiversity is undergoing a phase of rapid change that has proven to be even faster than changes observed in terrestrial ecosystems,” the authors say.

Some species may be able to respond by moving toward the poles where water is cooler and has more oxygen. Some may be able to abandon oxygen-deprived deep waters and move to shallower waters. But some may completely lose core habitat, the paper says.

And as long as climate change keeps going, the problem keeps getting worse. “Our study highlights that the degree of range contraction and loss of suitable habitat will critically depend on the realized greenhouse gas emission pathway.”

© Jan TenBruggencate 2024

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