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The South Pacific subtropical gyre is one of the most isolated patches of water on Earth. Its surface chemistry was assumed to mostly reflect natural sources, but the new analysis suggests otherwise.<\/p>\n
Dr. Tal Ben Altabet is a postdoctoral researcher in geochemistry at the Swiss Federal Institute of Technology in Zurich (ETH Zurich<\/a>). He led a team that sampled floating particles and air across the open gyre.<\/p>\n The verdict on zinc: nearly all of it now traces back to factories, smelters, and power plants thousands of miles away.<\/p>\n Zinc travels long distances<\/p>\n Zinc enters the atmosphere from coal combustion, oil burning, and the smelting of nonferrous metals. The tiny zinc-laden particles, called atmospheric aerosols<\/a>, ride wind currents and travel.<\/p>\n It often travels thousands of miles. The aerosols cross continents and ocean basins, eventually settling onto the water. Industrial dust from Shanghai or Santiago can land on a wave near Tahiti.<\/p>\n Long-distance ocean transport was already well documented for lead and mercury, with contamination levels mapped globally in earlier research<\/a>. Zinc had been harder to track.<\/p>\n Zinc shows up naturally in seawater because phytoplankton<\/a> need it for photosynthesis. Untangling the industrial fraction from the natural one took a clever workaround.<\/p>\n Reading isotope clues<\/p>\n Every chemical element comes in slightly different weights \u2013 heavier or lighter versions of the same atom. The proportions form a kind of signature.<\/p>\n Natural seawater zinc carries a heavy fingerprint \u2013 dominated by the Zn-66 variant. Industrial zinc runs lighter, carrying more Zn-64. Two profiles, two stories.<\/p>\n For years, marine geochemists had been puzzled. Zinc in the upper ocean looked lighter than it should, given what they knew about natural sources. Two explanations competed.<\/p>\n One blamed a natural process \u2013 heavier zinc atoms sticking to particles and sinking out. The other suspected industrial fallout. Data to choose between them had been missing.<\/p>\n Sampling the gyre<\/p>\n Between February and April 2022, the team joined a research cruise crossing the South Pacific from Chile to New Caledonia. They collected seawater, particles, and air across more than 7,000 miles of ocean.<\/p>\n A novel twist: previous work had focused mainly on dissolved zinc. Dr. Altabet\u2019s team analyzed the zinc held inside tiny particles \u2013 ones aerosols had dropped, and ones living organisms produced.<\/p>\n Those particles preserve a record of whatever zinc landed in or settled through the water column. Their isotope ratios revealed where the zinc originally came from.<\/p>\n Similar work on the North Pacific recently traced iron contamination from coal-burning Asia in a different study<\/a>. Zinc, until now, had stayed elusive.<\/p>\n Lead confirms the pattern<\/p>\n To confirm the zinc story, the team layered a second tracer onto their results: lead. Lead pollution has been a workhorse for tracking industrial fallout, with a well-mapped signature.<\/p>\n In both aerosol samples and marine particles, lead signatures pointed to Australian ores, U.S. deposits, and a recent surge of Chinese emissions. Zinc followed the same pattern.<\/p>\n The result wasn\u2019t subtle. Zinc in upper-ocean particles was overwhelmingly industrial \u2013 some samples held 100 to 100,000 times more than natural rock and dust could account for.<\/p>\n \u201cThese results show that even elements previously thought to be unaffected by human activity are now dominated by industrial pollution, which has reached the most remote parts of the open ocean,\u201d said Dr. Altabet.<\/p>\n Phytoplankton need zinc<\/p>\n Why does the source of zinc make a difference? Because phytoplankton \u2013 microscopic plant-like organisms drifting near the ocean surface \u2013 build their cells with zinc and other trace metals<\/a>.<\/p>\n These tiny algae perform photosynthesis on a planetary scale, pulling carbon dioxide from the air and producing oxygen. They form the base of the marine food web, feeding everything from krill to whales.<\/p>\n Their growth depends on a careful balance of nutrients in seawater. Recent research has shown that zinc itself can limit phytoplankton growth in some regions paper<\/a>.<\/p>\n Whether human-delivered zinc \u2013 arriving in different amounts than the natural supply \u2013 will tip that balance is unclear. No one yet knows how phytoplankton will respond.<\/p>\n The outcome is uncertain<\/p>\n The big takeaway: even the most remote stretches of the open ocean carry a measurable signature of industrial pollution in a metal once thought to be governed mostly by natural processes. <\/p>\n That assumption is gone. What follows depends on how marine biology responds. <\/p>\n The ocean\u2019s nutrient balance has always involved trace metals working together. Iron, copper, and cadmium also show signs of human-driven accumulation, alongside zinc.<\/p>\n Phytoplankton communities evolved under a certain balance of metals in seawater. <\/p>\n As those proportions shift, their response could change as well \u2013 boosting growth, suppressing it, or reshaping which species dominate. Researchers still don\u2019t know what the outcome will be.<\/p>\n Researchers plan to repeat the analysis in other ocean basins, looking at iron and copper alongside zinc, to learn how widely the industrial fingerprint extends.<\/p>\n The study is published in the journal Communications Earth & Environment<\/a>.<\/p>\n \u2014\u2013
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