08 Mar 2022
08 Mar 2022

Ecosystem impacts of marine heat waves in the Northeast Pacific

Abigale Wyatt1, Laure Resplandy1,2, and Adrian Marchetti3 Abigale Wyatt et al.
  • 1Department of Geosciences, Princeton University, Princeton, NJ, USA
  • 2High Meadow Environmental Institute, Princeton University, Princeton, NJ, USA
  • 3Earth, Marine and Environmental Sciences, University of North Carolina, Chapel Hill, NC, USA

Abstract. Marine heatwaves (MHWs) are a recurrent phenomenon in the Northeast Pacific that impact regional ecosystems and are expected to intensify in the future. These events, including the 2014–2015 “warm blob,” are associated with widespread surface nutrient declines across the subpolar Alaskan Gyre (AG) extending south into the North Pacific Transition Zone (NPTZ) with reduced chlorophyll concentrations confined to the NPTZ only. Here we explain the contrast between these two regions using a coupled global ocean-biogeochemical model (MOM6-COBALT) with Argo float and ship-based observations to investigate how the MHWs influence the productivity of the two primary phytoplankton size classes (large > 10 μm, small < 10 μm) and the subsequent ecosystem response. Differences in seasonal iron and nitrate limitations between the AG and NPTZ explain the differences in ecosystem response to MHWs between the two biomes. The reduced nutrient supply during MHWs most strongly influences large phytoplankton in the NPTZ (-13 % annually), whereas it has a limited impact on the climatologically iron-limited large phytoplankton population in the AG (-2 %). Contrastingly, we find that MHWs yield a springtime increase in small phytoplankton population in both regions due to shallow mixed layers and lower light limitation. These primary production anomalies modify the allometric phytoplankton distribution, resulting in a 2 % decrease in the ratio of large to small phytoplankton in both regions. This shift in the assemblage towards small phytoplankton production is associated with reduced secondary and export production especially in the NPTZ.

Abigale Wyatt et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-17', Anonymous Referee #1, 31 Mar 2022
    • AC1: 'Reply on RC1', Abigale Wyatt, 18 May 2022
  • RC2: 'Comment on egusphere-2022-17', Anonymous Referee #2, 11 Apr 2022
    • AC2: 'Reply on RC2', Abigale Wyatt, 18 May 2022

Abigale Wyatt et al.


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Short summary
Marine heatwaves (MHWs) are a frequent event in the Northeast Pacific with a large impact on the region's ecosystems. Large phytoplankton in the Northeast Pacific Transition Zone are greatly affected with less of an impact in the Alaskan Gyre. For small phytoplankton, we find MHWs increase the spring small phytoplankton population in both regions thanks to shallow mixed layers and lower light limitation. In both zones, this results in a 2 % decrease in the ratio of large to small phytoplankton.