How do ecosystems respond to climate change over long time scales?

North Atlantic marine productivity over the Industrial Era

Phytoplankton, the foundation of the marine food web, both respond directly to climate forcing and are critical components of the Earth’s climate system, due to their central role in global oxygen production and carbon sequestration. There are few observations, however, detailing past variability in marine primary productivity, particularly over multi-decadal to centennial timescales. This limits our understanding of the impact of climatic forcing on both past and future marine productivity.

In Osman et al. (2019), we develop high-resolution records of marine-biogenic aerosol emissions preserved in Greenland ice cores to reconstruct a ~250 year record of marine productivity across the North Atlantic, one of the most biologically productive and climatically sensitive regions on Earth. Our result have provided the most continuous reconstruction of basin-scale productivity to date, and strongly support sparse ship-derived data suggesting a 20th century declines in Atlantic planktonic biomass. Indeed, we reveal this decline to be part of a much longer, multicentury trend.

Our work provides the following major findings:

  • North Atlantic marine productivity has declined over the industrial-era, by as much as 5-20%;
  • The early 19th century onset of declining productivity coincides with the onset of North Atlantic warming, and covaries with regional ocean temperatures and ocean circulation strength;
  • There exists significant decadal- to centennial-scale covariation between northern Atlantic productivity variability and declining Atlantic Meridional Overturning Circulation (AMOC) strength, validating predictions by modeling studies.

Based on these results, we infer that continued atmospheric warming (predicted to contribute to accelerating glacier runoff, ocean freshening, and continued AMOC slowdown) may result in future productivity declines across the North Atlantic.

Figure 2 of Osman et al. (2019, Nature).

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  • Osman, M., Das, S., Trusel, L., Evans, M., Fischer, H., Grieman, M., Kipfstuhl, S., McConnell, J., Saltzman, E.: Industrial-era decline of subarctic Atlantic productivity, Nature, 569, 551–555, 2019.