Abstract
El Niño Southern Oscillation (ENSO) influences multi-year variation in sea-surface temperature and the intensity of upwelling in many Pacific regions. However, it is currently unknown how El Niño conditions will affect the concentration and elemental ratios of particulate organic matter (POM). To test this, we have been quantifying POM weekly for six years (2012 to 2017) at the MICRO time-series station in the Southern California Bight. We found a strong influence of the 2015 El Niño on sea-surface temperature and phosphate concentration but to a lesser extent on nitrate availability. The 2015 El Niño also resulted in low POC and POP concentrations, whereas PON concentrations declined by 26% during the whole sampling period. The changes in POM concentrations led to high C:P and N:P ratios. Following the changes in PON, C:N continued to climb reaching ~9.4 at the end of the sampling. We suggest that an Eastern Pacific- vs. a Central Pacific-type El Niño as well as a switch in the Pacific Decadal Oscillation phase influenced the local response in POM concentrations and ratios.
Highlights
El Niño Southern Oscillation (ENSO) is a recurring climate cycle leading to multi-year variation in ocean environmental conditions (Dijkstra and Burges, 2002; McPhaden, 2015)
The Oceanographic El Niño Index (ONI) index data were significantly correlated with positive temperature anomalies at our MICRO site (Rpearson = 0.38, p < 1e-16) and more broadly in the SCB (Rpearson = 0.44, p < 1e-22)
Our time-series data suggest that the 2015 El Niño event impacted sea-surface temperature (SST), phosphate conditions, particulate organic matter (POM) concentrations, and stoichiometric ratios in our study region
Summary
El Niño Southern Oscillation (ENSO) is a recurring climate cycle leading to multi-year variation in ocean environmental conditions (Dijkstra and Burges, 2002; McPhaden, 2015). In the California Current System, ENSO regulates sea-surface temperature (SST), upwelling source and intensity, thermocline depth, and large-scale circulation patterns (Mcgowan et al, 1998; Chavez, 2002; Checkley and Barth, 2009). ENSO variability may have a negative effect on plankton growth and biomass accumulation, this link has been elusive (Kim et al, 2009). It is currently unclear how coastal plankton will respond to recent ENSO-driven changes in ocean conditions.
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