Hjem

Geofysisk institutt

GFI/BCCR Seminar | Matt Osman: Recent reversal of a multicentury subarctic Atlantic productivity decline observed in Greenlandic ice

Matt Osman (Massachusetts Institute of Technology - Woods Hole Oceanographic Institution)

Recent reversal of a multicentury subarctic Atlantic productivity decline observed in Greenlandic ice

Abstract
Marine phytoplankton account for nearly 50% of primary production worldwide, and thus play a critical role in modulating marine-based food webs, fishery yields, and the global drawdown of atmospheric CO2. Yet, despite this importance, little is known about the long-term response of planktonic stocks to climatic forcing. Near-continuous, satellite-based observations of phytoplankton abundance extend back only as far as 1997 (though intermittently to 1979). This observational-paucity requires prior inferences to be drawn from spatiotemporally sparse sources, including ship-based ocean color observations (c. early 20th century to present), or marine proxy records. In this talk, I present new, annual-scale and spatially-integrated insights into marine-productivity trends occurring across the subarctic Atlantic – one of the most seasonally productive ocean basins in the world – detailing the last ~two and a half centuries. Using a unique signal of planktonic-derived organic aerosol commonly identified across twelve Greenlandic ice core sites, I provide evidence suggesting that recent, satellite-inferred increases in subarctic Atlantic planktonic biomass may be superimposed upon a much longer, multicentury productivity decline. Potential drivers, and implications, of this multicentury decline are hence discussed in the context of i) observed subarctic Atlantic ocean-atmosphere feedbacks (e.g., the North Atlantic Oscillation and Subpolar Gyre), ii) the congruent onset of 19th century Atlantic surface warming, and iii) the purported long-term decline in the vigor of North Atlantic thermohaline overturning.