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Headline: Climate change resulting in 'megabergs' larger than London becoming more frequent
Caption: **VIDEO AVAILABLE: CONTACT INFO@COVERMG.COM TO RECEIVE** BY MARK WORGAN Climate change could lead to icebergs larger than Greater London becoming a regular occurrence, according to scientists. As some of the world’s largest and most famous icebergs fracture and melt in Antarctica, new research is shedding light on how they influence the ocean and its ecosystems. Giant icebergs are becoming more common due to accelerated warming in Antarctica. Rising atmospheric and ocean temperatures cause ice shelves - the floating ends to glaciers - to weaken, crack, and calve. This destabilisation increases the frequency of massive calving events, where icebergs exceeding 18 km in length break off into the Southern Ocean. A study led by scientists from the British Antarctic Survey (BAS) has compared the first water samples taken near two giant icebergs, A23a and A76a, as they drifted north through Antarctic waters. These so-called “megabergs” have captured global attention in recent years because of their vast scale, each more than twice the size of Greater London, and together they contain enough ice to supply the UK with freshwater for more than 250 years. The research found that nutrients locked within such icebergs can stimulate blooms of ocean life as the ice melts. However, at the time of sampling, only A76a appeared to release these beneficial nutrients into surrounding waters, while A23a showed no measurable impact. The findings are significant because giant icebergs are becoming more common. Some scientists had suggested this could bring a potential benefit, with more icebergs boosting ocean life that absorbs carbon dioxide. But the study suggests the reality is more complex. Giant icebergs can act as fertilisers for marine ecosystems by releasing nutrients as they melt. This supports the growth of phytoplankton - microscopic plant-like organisms that form the base of the marine food chain for animals such as penguins and whales. However, the study, published in Nature Communications Earth and Environment, shows that the scale of these blooms can vary dramatically, making their wider impact harder to predict. The scientists encountered the icebergs in a vast current known as “Iceberg Alley”, between the Weddell Sea and the sub-Antarctic island of South Georgia. By chance, both icebergs crossed paths with UK research vessels: A76a with the RRS Discovery in January 2023, and A23a with the RRS Sir David Attenborough in December the same year. This allowed researchers to collect seawater samples around them. Laura Taylor, a BAS biogeochemist who led the study, said: “Being so close to these icebergs is like standing next to a moving cliff face – walls of ice towering above you, stretching to the horizon in every direction. It makes you feel very small.” Samples were analysed in laboratories across the UK. By examining their chemical composition and freshwater content, scientists assessed how each iceberg influenced phytoplankton growth - with striking results. “We knew the icebergs could affect the waters around them differently, but the scale of that difference was a real shock,” explains Laura. “One was causing marine life to thrive; the other was having no detectable effect at all. It changes what we know about how icebergs interact with the ocean.” Although both icebergs originated from the same ice shelf and were studied less than a year apart, their histories differ markedly. A23a broke away from the Filchner–Ronne Ice Shelf in 1986, initially about the size of the UK county of Norfolk. It then remained grounded on the seabed in the Weddell Sea for more than 30 years before finally breaking free in 2020 and drifting north. Scientists believe this long period of stagnation helps explain its limited impact. “The story of each iceberg’s journey could explain our contrasting results,” explained Laura. “When A23a got stuck, it lost about a quarter of its total area from melting, and with it, potentially lots of the nutrients from its outer layers. By the time we came across it in Iceberg Alley, it may still have contained some of this ‘fertiliser’, but there wasn’t enough melting into the ocean to cause a phytoplankton bloom.” By contrast, A76a - which calved in May 2021 and quickly moved north - was found to be driving substantial phytoplankton growth. Researchers detected large blooms in surrounding waters, fuelled by nutrients released from the ice. They also identified another contributing process. Professor Kate Hendry, an ocean scientist at BAS, said: “Where giant icebergs meet deeper waters, the melting ice can cause water and nutrients to be drawn up along the iceberg’s edge in a processing known as upwelling. In the case of A76a, we think that this process pulled up other important nutrients, such as nitrogen, phosphorus and iron – which are more common in deeper Antarctic waters – to the surface, helping phytoplankton bloom to a level that would not be possible with only the nutrients melting from the iceberg.” The study challenges the assumption that all icebergs influence ocean ecosystems in the same way. It remains unclear how this will affect the cycling of carbon and nutrients in the Southern Ocean. However, researchers say the new findings represent an important step towards improving predictions of how Antarctic changes could shape the global climate.
Keywords: feature, video, photo, ice, iceberg, climate change, science
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