A Growing Freshwater Lens in the Arctic Ocean with Sustained Climate Warming Disrupts Marine Ecosystem Function
Researchers from the University of California Irvine with collaborators from the National Center for Atmospheric Research examined the impacts of sustained climate warming on the marine ecosystem of the Arctic Ocean following the Representative Concentration Pathway 8.5 (RCP8.5) and its extension to the year 2300, in an Earth system model simulation. A growing freshwater lens in the Arctic Ocean overrides marine production gains associated with sea ice loss and strongly influences arctic marine food web dynamics.
Our analysis suggests that a growing freshwater lens continues to expand with sustained multi-century climate warming. This growing freshwater lens could increase nutrient stress, driving a community shift from diatom to small phytoplankton and shift bloom earlier. We estimate that export production is reduced by 53% in the Arctic Ocean by the year 2300.
Climate warming will increase rainfall and snowfall in northern regions, causing the Arctic Ocean to freshen. Using a global climate model, here we explore the long-term consequences of this freshening for the marine biosphere. As the Earth responds to a future scenario of “business-as-usual” fossil fuel emissions, an expanding freshwater lens will form a cap on the Arctic Ocean, limiting the upward mixing of nutrient-rich water from deeper ocean layers. This stunts the growth of phytoplankton, counteracting by 2100 gains in marine productivity from sea ice loss. After 2100, as the freshwater cap strengthens, small phytoplankton mostly replace diatoms in arctic ecosystems due to increasing nutrient stress. By 2300, export production, a measure of the flow of organic matter available to support zooplankton, fish, and marine mammals, declines by over 50%. At the same time, a shift in the timing of the peak phytoplankton bloom from July to May is likely to further disrupt arctic food webs. Our work shows that climate change impacts on the hydrological cycle in the far north will have long-lasting and far-reaching impacts on the Arctic marine biosphere, and highlights the importance of exploring the potential for ecological tipping points in deep future time.