FY 2022

Depth-resolved net primary production in the Northeast Pacific Ocean: A comparison of satellite and profiling float estimates in the context of two marine heatwaves

Long, J.S., A.J. Fassbender, and M.L. Estapa

Geophys. Res. Lett., 48(19), e2021GL093462, doi: 10.1029/2021GL093462, View online (open access) (2021)

Methods commonly used to estimate net primary production (NPP) from satellite observations are now being applied to biogeochemical (BGC) profiling float observations. Insights can be gained from regional differences in float and satellite NPP estimates that reveal gaps in our understanding and guide future NPP model development. We use 7 years of BGC profiling float data from the Northeast Pacific Ocean to quantify discrepancies between float and satellite NPP estimates and decompose them into contributions associated with the platform sensing method and depth resolution of observations. We find small, systematic seasonal discrepancies in the depth-integrated NPP (iNPP) but much larger (>±100%) discrepancies in depth-resolved NPP. Annual iNPP estimates from the two platforms are significantly, positively correlated, suggesting that they similarly track interannual variability in the study region. Using the long-term satellite iNPP record, we identify elevated annual iNPP during two recent marine heatwaves and gain insights about ecosystem functionality.

Plain Language Summary. Ocean net primary production is equal to gross photosynthesis minus respiration by primary producers, setting the maximum amount of carbon available for export from sunlit surface waters to depths where it can be sequestered from the atmosphere. Quantifying this important piece of the global carbon cycle puzzle is difficult due to the limited number of high-quality, ship-based observations of net primary production. Models have been developed to estimate net primary production from satellite observations; however, heavy cloud cover during winter and sun glint in high-latitude regions remain key challenges. Additionally, satellites observe just the top layer of the sunlit ocean, requiring assumptions to be made when extrapolating through depth. Biogeochemical profiling floats can help to fill remaining observing gaps and improve global net primary production estimates. We use 7 years of float and satellite data from the Northeast Pacific to evaluate how net primary production estimates are impacted by differences in platform detection method and vertical observing resolution. Such comparisons throughout the global ocean will clarify where and how we can leverage the long-term satellite record to study ecosystem events, such as marine heatwaves, and which gaps in our understanding persist.