Guano Mercury Reveals 8,000 Years of Seabird History
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- Chuxian Li and colleagues at the Swedish University of Agricultural Sciences, University of Bern, and British Antarctic Survey analyzed peat cores from Bird Island, South Georgia, producing the first continuous 8,000-year record of seabird population change in the region.
- Published in PNAS, the study dates the first continuous seabird colonies on Bird Island to between 6,800 and 6,100 years ago—more than 1,000 years earlier than previously thought.
- Researchers identified four distinct periods of major seabird population growth, each coinciding with less intense Southern Hemisphere westerly winds, leading them to warn that the present-day intensification of those winds may drive further declines.
- The team developed a new method using mercury concentrations in peat layers—mercury bioaccumulates in seabirds and is deposited in guano washed into nesting-site peatlands—as a proxy for past colony sizes.
- Li cited globally monitored seabird populations declining by up to 70% since the 1950s as evidence that the new historical baseline is urgently needed to contextualize current and future climate impacts.
- The mercury-based proxy can be applied to peat and sediment archives worldwide, and combined with environmental DNA analysis to reconstruct historical ecosystems beyond seabirds.
Why it matters: The study provides the first long-term baseline showing that Southern Ocean seabird populations have repeatedly risen and fallen with westerly wind intensity over 8,000 years. Because those winds are intensifying today and global seabird populations have already dropped by up to 70% since the 1950s, the researchers say the new record gives a concrete historical yardstick for predicting where the next declines will hit hardest. The mercury-in-peat method also opens a replicable tool for reconstructing ecosystem history at nesting sites worldwide.
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