世界の海の色に大きな変化、気候変動が原因か　米研究

【パリＡＦＰ＝時事】世界の海の色が過去２０年間で大きく変化したとする研究結果が１２日、英科学誌ネイチャーに発表された。（写真は植物プランクトンが発生し、海水の色が一分変化した様子。米アラスカ沿岸の海域で。米航空宇宙局〈ＮＡＳＡ〉の衛星画像より）
　論文によると世界の海洋面積の半分以上、すなわち地球の陸地面積よりも広い範囲で色の変化が確認された。熱帯に近づくほど緑がかっているという。
　研究チームは原因の解明にはさらなる研究が必要だとしながらも、生態系の変化、特に海洋食物網の中心であり、光合成によって大気の安定に重要な役割を果たしている植物プランクトンの変化によるものだと予想している。
　論文の主著者を務めた英国立海洋学センターのＢ・Ｂ・カエル氏はＡＦＰに「われわれが色の変化を気にするのは、色に生態系の状態が反映されるからだ。色の変化は生態系の変化を意味する」と語った。
　チームは２００２～２２年、地球観測衛星「アクア」に搭載されている「ＭＯＤＩＳ（中分解能撮像分光放射計）」が観測した、肉眼では判別しがたい海面の七つの色相についてデータを分析。通常の年ごとのばらつきを上回る変化を検出し、これをコンピューターによる気候変動予測モデルと比較したところ、実際の観測結果とほぼ一致した。
　米マサチューセッツ工科大学地球変動科学センター地球大気惑星科学部のステファニー・ドゥトゥキェビッチ氏は「海洋の変色のシミュレーションを何年も行ってきたが、実際の現象を目にするのは驚きというよりも恐ろしい。これらの変化は、人為的に引き起こされた気候変動と一致している」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2023/07/13-17:30）

Over the past 20 years huge swathes of the world's oceans have changed colour, displaying a subtle greening towards the tropics that researchers say points to the effect of climate change on life in the world's seas.
In the new research published on Wednesday, scientists said they had detected shifts in colours across more than half of the world's oceans -- an expanse bigger than Earth's total land area.
Authors of the study in Nature think that is down to changes in ecosystems, and particularly in tiny plankton, which are the centrepiece of the marine food web and play a crucial part in stabilising our atmosphere.
The reason we care about the colour changes is because the colour reflects the state of the ecosystem, so colour changes mean ecosystem changes, lead author B.B. Cael, of Britain's National Oceanography Centre, told AFP.
The colour of the seas when seen from space can paint a picture of what is going on in the upper layers of the water.
A deep blue would tell you that there is not much life, while if the water is greener it is likely to have more activity, specifically from the photosynthesising phytoplankton, which like plants contain the green pigment chlorophyll.
These produce a significant amount of the oxygen we breathe, are a crucial part of the global carbon cycle and are a foundational part of the ocean food web.
- Life colours -
Researchers are keen to develop ways of monitoring changes in ecosystems in order to track climate changes and enshrine protected areas.
But previous studies have suggested you would need three decades of ocean chlorophyll monitoring to detect a trend because of annual variations.
In the latest study, researchers broadened the colour spectrum, looking at seven hues of ocean colour monitored by the MODIS-Aqua satellite from 2002 to 2022.
These are too subtle for humans to see and would look largely blue to the naked eye.
The authors analysed the observational data to detect a trend above the year-to-year variability and then compared it to computer models of what would be expected with climate change.
They found that the real-world observations tallied closely with the changes predicted.
While the researchers said more work would be needed to find out what exactly those colour changes might mean, they said climate change was very likely to be the cause.
I've been running simulations that have been telling me for years that these changes in ocean colour are going to happen, said co-author Stephanie Dutkiewicz, of MIT's Department of Earth, Atmospheric and Planetary Sciences at the Center for Global Change Science.
To actually see it happening for real is not surprising, but frightening. And these changes are consistent with man-induced changes to our climate.