Sun, Aug 19, 2018 - Page 9 News List

Not just land heat waves: Oceans are in hot water, too
陸地遭熱浪襲擊 海洋升溫也發出警訊

A Sea lion bathes in the sun on Aug. 7 on the Pacific Ocean coast in La Jolla, San Diego, California, US.
一隻海獅在美國加州聖地牙哥面向太平洋的拉霍亞海灘上享受日光浴,照片攝於八月七日。

Photo: AFP
照片:法新社

Even the oceans are breaking temperature records in this summer of heat waves. Off the San Diego coast, scientists earlier this month recorded all-time high seawater temperatures since daily measurements began in 1916. “Just like we have heat waves on land, we also have heat waves in the ocean,” said Art Miller of the Scripps Institution of Oceanography.

Between 1982 and 2016, the number of “marine heat waves” roughly doubled, and likely will become more common and intense as the planet warms, a study released Wednesday found. Prolonged periods of extreme heat in the oceans can damage kelp forests and coral reefs, and harm fish and other marine life.

“This trend will only further accelerate with global warming,” said Thomas Frolicher, a climate scientist at the University of Bern in Switzerland, who led the research. His team defined marine heat waves as extreme events in which sea-surface temperatures exceeded the 99th percentile of measurements for a given location. Because oceans both absorb and release heat more slowly than air, most marine heat waves last for at least several days — and some for several weeks, said Frolicher.

Many sea critters have evolved to survive within a fairly narrow band of temperatures compared to creatures on land, and even incremental warming can be disruptive. Some free-swimming sea animals like bat rays or lobsters may shift their routines. But stationary organisms like coral reefs and kelp forests “are in real peril,” said Michael Burrows, an ecologist at the Scottish Marine Institute.

In 2016 and 2017, persistent high ocean temperatures off eastern Australia killed off as much as half of the shallow water corals of the Great Barrier Reef — with significant consequences for other creatures dependent upon the reef. “One in every four fish in the ocean lives in or around coral reefs,” said Ove Hoegh-Guldberg, a marine biologist at the University of Queensland. “So much of the ocean’s biodiversity depends upon a fairly small amount of the ocean floor.”

The latest study in Nature relied on satellite data and other records of sea-surface temperatures including from ships and buoys. It didn’t include the recent record-breaking measurements off Scripps Pier in San Diego — which reached 26.39°C on Aug. 9 — but Frolicher and Miller said the event was an example of a marine heat wave. Miller said he knew something was odd when he spotted a school of bat rays — which typically only congregate in pockets of warm water — swimming just off the pier earlier this month.

Changes in ocean circulation associated with warmer surface waters will likely mean decreased production of phytoplankton — the tiny organisms that form the basis of the marine food web, Miller said. Marine biologists nicknamed a patch of persistent high temperatures in the Pacific Ocean between 2013 and 2016 “the Blob.” During that period, decreased phytoplankton production led to a cascading lack of food for many species, causing thousands of California sea lion pups to starve, said Miller.

“We’ve repeatedly set new heat records. It’s not surprising, but it is shocking,” he added.(AP)

在今年夏天的多重熱浪襲擊下,連海洋溫度都不斷打破紀錄。本月初,科學家在聖地牙哥近岸處,記錄到自一九一六年以來開始進行每日測量後的空前海水高溫。斯克里普斯海洋研究所的阿特‧米勒表示:「正如同我們陸地上有熱浪,海洋也無法倖免。」

週三發表的研究發現,在一九八二年到二○一六年間,「海洋熱浪」發生的次數大概成長了一倍,並且很有可能隨著地球暖化變得更為常見且劇烈。海洋中極端高溫的時間一旦延長,就會對海藻森林與珊瑚礁造成破壞,進而傷害魚類和其他海洋生物。

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