Warm Events Induce Loss of Resilience in Organic Carbon Production in the Northeast Pacific Ocean

Abstract

Between 2013 and 2016, a series of warm events induced by ocean atmosphere oscillations negatively impacted productivity in the northeast Pacific Ocean. For two consecutive winters (2013–2014 and 2014–2015), suppressed wind stress and warm near‐surface ocean temperature anomalies restricted vertical mixing between the surface and underlying nutrient‐enriched waters. Here we assess historical data of sea surface temperature and sea level pressure, along with nearly a decade of biogeochemical float data to evaluate the impact of these warm events on organic carbon production. The first stratified winter experienced little apparent impact on the magnitude of net organic carbon production in the growing season relative to prior years, suggesting an immediate resilience from reduced new nutrients, apparently depending on recycled iron. However, the subsequent winter experienced virtually zero net production; a loss of resilience, perhaps due to net iron removal with export, was evident. We find that consistently enhanced winter stratification decreased carbon production much more so than a single warm winter. This study highlights the sensitivity of marine productivity to ocean atmosphere oscillations, reducing deep ocean carbon sequestration with prolonged ocean warming and stratification.

An operational overview of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) Northeast Pacific field deployment

“…These deeper fractional isolume depths reflect the lower Chl a concentrations observed during EXPORTS compared with typical Line P observations for the period from 2007 to 2017. Since 2008, a series of BGC profiling floats have collected data on the physical and biological properties of the water column in the vicinity of Station P (Figure 7; Bushinsky and Emerson, 2015;Plant et al, 2016;Yang et al, 2018;Bif et al, 2019;Haskell et al, 2020). Mixed layer temperatures change on average by 6 C to 9 C from winter to summer, with the EXPORTS cruise happening during the warmest time of the year.…”

Ecosystem impacts of marine heat waves in the Northeast Pacific

“…Float-based estimates of NCP (Appendix A) interpret nitrate changes sampled along the floats as 360 temporal changes, leading to a misattribution of this spatial variability in nitrate to seasonal biological drawdown. In Bif et al (2019b), NCP was calculated using the winter to summer difference in nitrate concentration measured by 6 Argo floats in the vicinity of OSP and the NPTZ between 2008 and 2018 (see details on method in SI, Fig. 10).…”

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

“…Float-based estimates of ANCP during the 2013-2016 MHW by Yang et al (2018) and Bif et al (2019), who used different chemical tracers, suggest reduced ANCP in different years of the warm event. Lower-than-average ANCP coupled with higher-than-average ANPP suggests that interannual variability in heterotrophic respiration may play an important role in regulating upper ocean carbon cycling and the efficiency of carbon export.…”

“…In the past decade, the NE Pacific has endured two marine heatwaves (MHWs;-2015-more than five consecutive days of sea surface temperature exceeding the 90th percentile of a 30year historical record (Bond et al, 2015;Hobday et al, 2016;Scannell et al, 2020). A number of studies have evaluated the ecosystem impacts associated with the earlier MHW, including two studies that used BGCfloat observations to estimate annual net community production (ANCP; Bif et al, 2019;Yang et al, 2018), which is equal to gross primary production minus community respiration (Laws, 1991). Here, we use a combination of satellite and float-estimated NPP to explore the ecosystem response to anomalous sea surface temperatures.…”