Squid invasions signal changes in the Pacific Ocean
In the Pacific, jumbo squid have moved to new waters, signaling changes in the ocean, scientists observe.
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Others have also noted a link among increased productivity, hypoxia, and squid abundance. Longtime fishermen in Mexico’s Sea of Cortez report that there were far fewer squid there in the past, says William Gilly, a professor of biology at Stanford University in Palo Alto, Calif. He suspects that agricultural development inland and the large quantities of fertilizer now dumped by rivers into the mostly enclosed sea have caused algal blooms, worsened hypoxia, and made the sea more inviting to the opportunist squid.
“The fertilizers and the oxygen minimum zone go in parallel, and then at some point the [numbers of] squid just explode,” he says.
The question remains, however, about what’s causing the hypoxic zone to expand not just locally but across the entire eastern Pacific. Whitney doubts that it’s higher productivity caused by fertilization.
“We see this hypoxia because the ocean and atmosphere are not exchanging oxygen as well as they used to,” he says.
He suspects that changing conditions in the sub-Arctic Pacific where deep water is created are at fault. In winter, oxygenated surface waters near Japan and Russia become cold and dense enough to sink. But intensified stratification, he thinks, has disrupted this process.
Rising temperatures have probably contributed, but Whitney also suspects a freshwater influx, a phenomenon observed in parts of the North Atlantic.
Low-density fresh water has probably capped the ocean, inhibiting the exchange of gases between ocean and atmosphere and impeding deep-water formation. Melting arctic ice and permafrost have probably increased freshwater flow into the north Pacific.
Rain could also be having an impact. Climate models predict that, in a warmer world, rainfall will increase at certain latitudes. More water evaporates from warmer tropical seas, and a warmer atmosphere holds more moisture. But eventually this water must fall from the sky somewhere. Some, Whitney suspects, falls at the higher latitudes of the sub-Arctic Pacific. “You keep doing that decade after decade, there’s going to be some impact,” he says.
Although natural cycles are probably behind some of the changes in the Pacific Ocean that scientists are observing, climate change seems to be pushing the ocean beyond the limits of natural variability. The jumbo squid invasion of California and beyond is one symptom of these larger oceanographic changes.
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