Industrial-era decline in subarctic Atlantic productivity.

Abstract

Marine phytoplankton have a crucial role in the modulation of marine-based food webs¹, fishery yields² and the global drawdown of atmospheric carbon dioxide³. However, owing to sparse measurements before satellite monitoring in the twenty-first century, the long-term response of planktonic stocks to climate forcing is unknown. Here, using a continuous, multi-century record of subarctic Atlantic marine productivity, we show that a marked 10 ± 7% decline in net primary productivity has occurred across this highly productive ocean basin over the past two centuries. We support this conclusion by the application of a marine-productivity proxy, established using the signal of the planktonic-derived aerosol methanesulfonic acid, which is commonly identified across an array of Greenlandic ice cores. Using contemporaneous satellite-era observations, we demonstrate the use of this signal as a robust and high-resolution proxy for past variations in spatially integrated marine productivity. We show that the initiation of declining subarctic Atlantic productivity broadly coincides with the onset of Arctic surface warming⁴, and that productivity strongly covaries with regional sea-surface temperatures and basin-wide gyre circulation strength over recent decades. Taken together, our results suggest that the decline in industrial-era productivity may be evidence of the predicted⁵ collapse of northern Atlantic planktonic stocks in response to a weakened Atlantic Meridional Overturning Circulation^6-8. Continued weakening of this Atlantic Meridional Overturning Circulation, as projected for the twenty-first century^9,10, may therefore result in further productivity declines across this globally relevant region.