Multidecadal increase in microbial biomass and production along the western Antarctic Peninsula

Marine pelagic ecosystems around the world are changing in response to climate change. The marine pelagic ecosystem extending along the western Antarctic Peninsula (WAP) is a region of rapid warming and sea ice loss, and in response there have been conspicuous trends in the ecosystem ranging from phytoplankton to krill and penguins. Despite the many ecosystem responses observed globally for phytoplankton and other trophic levels, there have been only a few observations of trends in heterotrophic bacteria, the most numerically dominant organisms on the planet. Here we report on a sustained increase in bacterial biomass over 2003-2019 that occurred throughout a 140,000 km 2 area of the WAP. Concomitant with the rise in bacterial biomass, bacterial production, chlorophyll and primary production also increased throughout the region. The trends appear to be driven by the southward migration along the Peninsula of warm and moist conditions in the north into the cold and dry continental polar regime to the south. The extensive and sustained long-term increases in microbial biomass and activity are another sign of large changes in the WAP ecosystem. • Marine populations from phytoplankton to whales are affected by ocean warming • Few observations of bacteria, numerically dominant in the ocean, responding to warming • New observations show ocean bacteria have doubled in western Antarctica in past 16 yr • Bacterial and phytoplankton growth rates, and thus, DOM supply have also increased • Bacteria and phytoplankton growth respond to interannual variability in sea ice