A new ocean state after nuclear winter

Cheryl S Harrison, Louisiana State University, Baton Rouge, LA, United States, Tyler Rohr, Knauss/DOE, Washington, United States, Alice K DuVivier, NCAR, Boulder, United States, Elizabeth Maroon, University of Wisconsin Madison, Madison, WI, United States, Nicole S Lovenduski, University of Colorado, Department of Atmospheric and Oceanic Sciences, Boulder, CO, United States, Charles Bardeen, National Center for Atmospheric Research, Atmospheric Chemistry Observations and Modeling Laboratory, Boulder, United States, Samantha Stevenson, University of California Santa Barbara, Bren School of Environmental Science & Management, Santa Barbara, CA, United States, Alan Robock, Rutgers University, New Brunswick, United States, Owen B Toon, Univ Colorado Boulder, Boulder, CO, United States, Joshua Livingston Coupe, Rutgers University, Environmental Sciences, New Brunswick, NJ, United States, Jessica Stevens, University of Texas Rio Grande Valley, Port Isabel, TX, United States, Philipp Neubauer, Dragonfly Science, Wellington, New Zealand and Victor Rangel, Texas A&M University, College Station, United States
Abstract:
Nuclear war would likely result in firestorms that would loft smoke into the upper atmosphere, where it would persist for a decade. The resulting reduction of sunlight would lead to global cooling, triggering a suite of physical processes, with associated reduction in rainfall and energy available for photosynthesis. In a Community Earth System Model simulation, 150 Tg of black carbon was injected into the upper atmosphere to simulate atmospheric forcing from a nuclear war between Russia and the United States. As a result of this forcing, there is a global temperature reduction that peaks at 9oC of cooling in the first few years after the war. This rapid and sustained cooling drives a number of extreme ocean impacts, altering the ocean state, with multi-decadal and longer recovery times. Arctic sea ice extent expands rapidly, reaching latitudes south of Japan, and the Arctic sea ice volume is more than doubled thirty years after the war, likely a new stable state. Deep ocean vertical mixing is sustained throughout the summer at high latitudes for a number of years. This, combined with the reduction in sunlight and ice expansion, leads to a massive failure in ocean productivity, such that global net primary production in the ocean decreases by over 30% in the year after the war, with a complete shutdown in primary productivity for multiple years at high latitudes in the Northern Hemisphere. Deep mixing also causes multi-decadal changes in the ocean vertical stratification and biogeochemical profiles. The Atlantic meridional overturning circulation strengthens substantially due to weakened stratification and peaks at over 60 Sverdrups seven years after the war, over five times normal values. The North Pacific is ventilated, eroding oxygen minimum zones. Globally, the nutricline shoals, such that winter mixing brings up more nutrients, causing disrupted productivity patterns for decades. Together, this is likely an extinction level event for many marine species, especially fisheries in the North Atlantic and North Pacific, with long-term ocean ecosystem and biogeochemical impacts felt globally.
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