世界最大の氷山、ペンギンの繁殖地の手前で座礁か

【パリＡＦＰ＝時事】南極から移動していた世界最大かつ最古の氷山「Ａ２３ａ」が、英国領サウスジョージア島から約７０キロ手前で座礁した可能性があるとの観測結果を英国南極観測局（ＢＡＳ）が４日、発表した。南大西洋の重要な野生生物の繁殖地である同島への衝突は免れるとみられている。（写真は、南極海を移動する巨大氷山「Ａ２３ａ」）
　１９８６年に南極の棚氷から分離したＡ２３ａの面積は約３３６０平方キロで、英国の大都市圏グレーター・ロンドンの２倍以上に相当し、重量は１兆トン近い。２０２０年以降、南極からサウスジョージア島に向かってゆっくり北上していた。
　同島に衝突するか、周辺の浅い大陸棚で座礁すれば、餌場が物理的に遮られ、島で繁殖しているアザラシやペンギンに深刻な影響を与える可能性があると懸念されていた。
　しかしＢＡＳによると、Ａ２３ａの動きは３月１日以降、島から７３キロ手前で停滞。
　ＢＡＳの物理海洋学者アンドリュー・マイヤーズ氏は、「氷山が座礁したままであれば、サウスジョージア島の野生生物に大きな影響はないとみている」とし、「過去数十年の例では、南極海からこの進路をたどる多くの氷山はすぐに崩壊し、解けてしまう」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2025/03/05-16:43）

The world's biggest iceberg appears to have run aground roughly 70 kilometres from a remote Antarctic island, potentially sparing the crucial wildlife haven from being hit, a research organisation said Tuesday.
The colossal iceberg A23a -- which is more than twice the size of Greater London and weighs nearly one trillion tonnes -- has been drifting north from Antarctica towards South Georgia island since 2020.
This had raised fears it could collide with the island or run aground in shallower water near it, potentially disrupting the ability of penguins and seals to feed their young.
However, the gigantic wall of ice has been stuck 73 kilometres (45 miles) from the island since March 1, according to a statement from the British Antarctic Survey (BAS).
If the iceberg stays grounded, we don't expect it to significantly affect the local wildlife, BAS oceanographer Andrew Meijers said.
In the last few decades, the many icebergs that end up taking this route through the Southern Ocean soon break up, disperse and melt, added Meijers, who encountered A23a in late 2023 and has tracked its fate via satellite ever since.
Satellite images analysed by AFP showed that the closest edge of the roughly 3,300-square-kilometre iceberg had stopped more than 70 kilometres from the island in late February.
It remains unclear whether the iceberg is stuck for good.
It will be interesting to see what will happen now, Meijers added.
- Upside for wildlife? -
The world's biggest and oldest iceberg calved from the Antarctic shelf in 1986.
It remained stuck for over 30 years before finally breaking free in 2020, its lumbering journey north sometimes delayed by ocean forces that kept it spinning in place.
Satellite imagery had previously suggested it was not crumbling into smaller chunks along the familiar path that such icebergs take. However a 19-kilometre chunk broke off in January.
There had been concerns for wildlife on the crucial breeding ground of South Georgia if the iceberg parked too close.
This would have forced animals like penguins and seals to travel much farther to get around the colossal block of ice.
This could reduce the amount of food coming back to pups and chicks on the island, and so increase mortality, Meijers explained.
However in its current location, the iceberg could offer benefits to wildlife.
Nutrients stirred up by the grounding (of the berg) and from its melt may boost food availability for the whole regional ecosystem, including for charismatic penguins and seals, Meijers said.
Along with the nearby South Sandwich islands, South Georgia is home to around five million seals and 65 million breeding birds from 30 different species.
The island's seals and penguins have already had a bad season due to a bird flu outbreak, Meijers told AFP in January.
- What about climate change? -
The iceberg poses no threat to shipping. It is so huge that vessels can easily avoid it.
However, as it breaks up into smaller pieces, certain areas could become off limits to commercial fishing ships due to the number of smaller -- yet often more dangerous -- bergy bits, Meijers said.
There is no permanent human population on South Georgia, which the UK administers as a British overseas territory.
Argentina also claims the island -- along with the Falklands to the west which it calls Las Malvinas.
Icebergs of this size are rare but not unheard of. There have been two of similar sizes in the same area over the last five years, Meijers said.
Such huge icebergs are a completely normal part of the lifecycle of the Antarctic ice sheets, Meijers emphasised.
But ice shelves have lost 6,000 billion tonnes of mass since 2000, which is matched by accelerating ice loss attributed to climate change, he added.
Researchers warned last month that a rise in the planet's average temperature to between 1.5 and 2.0 degrees Celsius above pre-industrial levels could melt enough frozen water to lift oceans by a dozen metres -- and beyond the point of no return.
Last year -- which smashed previous heat records as the world was battered by fires, floods and storms -- was the first calendar year above 1.5C.