High concentration of radioactive carbon found in organisms in the deep sea, accumulated due to Cold War nuclear experiments

Recently CNN.co.jp reported the following:

超深海の生物から高濃度の放射性炭素、冷戦時代の核実験で蓄積

2019.05.14 Tue posted at 12:58 JST

  （ＣＮＮ） １９５０年代～６０年代にかけての冷戦時代に行われた核実験の影響で、超深海にすむ甲殻類の筋組織から高濃度の放射性炭素が検出されたという研究結果を、中国などの研究チームが発表した。

この研究は４月の学術誌に発表された。人間の汚染が海洋の食物連鎖に入り込み、深海に到達している状況が示されたと研究チームは指摘。中国科学院の研究者はＣＮＮに、「これほど高い濃度の炭素１４（放射性炭素）は予想していなかった」と話している。

冷戦時代の核実験では、大気中の放射性炭素が２倍に増え、爆弾によって放出された中性子が大気中の窒素と反応を起こして放射性炭素が生成された。

実験の終了に伴い放射性炭素の濃度は下がったが、大気から海面に落下した放射性炭素は、食物連鎖を通じて長年の間に海洋生物に取り込まれていた。

中国と米国の研究チームは、この「爆弾炭素」を使って、西太平洋の３つの海溝で深さ６０００～１１０００メートルの超深海にすむ甲殻類を調査した。深海の甲殻類は、海底に沈んだ有機物の死骸を餌にしている。

放射性炭素による年代測定を行った結果、超深海の甲殻類の筋組織からは、自然界よりも大幅に高い濃度の炭素１４が検出された。炭素１４は自然界のほぼ全ての生物に存在する。

普通であれば、海水の巡回によって爆弾炭素が深海に届くまでには１０００年ほどかかる。しかし海洋食物連鎖を通じて予想よりも早く放射性炭素が運ばれたと研究チームは推測する。

海溝にすむ甲殻類は、浅瀬にすむ種に比べて細胞が入れ替わるペースが遅く、寿命も大きさも４倍以上だった。このために体内に蓄積される放射性炭素の量が増えたと研究チームは解説している。

Translation

  (CNN) Research teams in China and other locations announced that high concentrations of radioactive carbon were detected in the muscle tissue of crustaceans in the deep sea due to the effect of nuclear tests conducted during the Cold War from the 1950s to the 1960s.

The study was published in a journal in April. The research team pointed out that human contamination had entered the food chain of the ocean and had reached the deep sea. Researchers at the Chinese Academy of Sciences told CNN that "We were not expecting such high a concentration of carbon-14 (radioactive carbon)."

In the Cold War-era nuclear tests, radioactive carbon in the atmosphere doubled, and neutrons emitted by the bomb reacted with nitrogen in the atmosphere to produce radioactive carbon.

Although the concentration of radioactive carbon decreased with the end of the experiment, radioactive carbon that dropped from the atmosphere to the surface of the sea were taken up by marine organisms for many years through the food chain.

Research teams from China and the United States had used these "bomb carbons" to investigate crustaceans that live in the deep ocean at a depth of 6000-11,000 meters in the three trenches of the western Pacific. Deep-sea crustaceans fed on corpses of organic matter that had sunk to the ocean floor.

As a result of dating by radioactive carbon, carbon 14 was detected in the muscle tissue of crustaceans in the deep sea at a much higher concentration than in the natural world. Carbon 14 was present in almost all living things in nature.

It usually took about 1000 years for the bomb carbon to reach the deep sea by the circulating seawater. But the research team speculated that radioactive carbon moved earlier than expected through the marine food chain.

The crustaceans living in the trench were slower in cells changing than those in the shallow water, and their life span were more than four times longer. The researchers commented that this would increase the amount of radioactive carbon accumulated in their bodies.

              So, the deep sea and the organisms living there are also affected by the senseless activities of human.