Future changes in coastal upwelling ecosystems with global warming: The case of the California Current System

Peng Xiu,Frederic S Castruccio,Fei Chai,Enrique N Curchitser

doi:10.1038/s41598-018-21247-7

Abstract

Coastal upwelling ecosystems are among the most productive ecosystems in the world, meaning that their response to climate change is of critical importance. Our understanding of climate change impacts on marine ecosystems is largely limited to the open ocean, mainly because coastal upwelling is poorly reproduced by current earth system models. Here, a high-resolution model is used to examine the response of nutrients and plankton dynamics to future climate change in the California Current System (CCS). The results show increased upwelling intensity associated with stronger alongshore winds in the coastal region, and enhanced upper-ocean stratification in both the CCS and open ocean. Warming of the open ocean forces isotherms downwards, where they make contact with water masses with higher nutrient concentrations, thereby enhancing the nutrient flux to the deep source waters of the CCS. Increased winds and eddy activity further facilitate upward nutrient transport to the euphotic zone. However, the plankton community exhibits a complex and nonlinear response to increased nutrient input, as the food web dynamics tend to interact differently. This analysis highlights the difficulty in understanding how the marine ecosystem responds to a future warming climate, given to range of relevant processes operating at different scales.

Highlights

Coastal upwelling ecosystems are among the most productive ecosystems in the world, meaning that their response to climate change is of critical importance
There is a mean bias of 0.58 °C between the modeled sea surface temperature (SST) and the extended reconstructed sea surface temperature (ERSST), which could be attributable to the under-representation of key processes in the coarse ERSST dataset
The above analysis indicates that both deep nutrients and upwelling are key factors in driving an upward nutrient flux to the euphotic zone in the California Current System (CCS)

Summary

Introduction

Coastal upwelling ecosystems are among the most productive ecosystems in the world, meaning that their response to climate change is of critical importance. The plankton community exhibits a complex and nonlinear response to increased nutrient input, as the food web dynamics tend to interact differently This analysis highlights the difficulty in understanding how the marine ecosystem responds to a future warming climate, given to range of relevant processes operating at different scales. Most observations and numerical models suggest that average phytoplankton biomass and primary productivity have declined over the past a few decades, and will to continue during the century[3,4,5,6] One explanation for this declining trend is that ocean surface warming increases upper-ocean stratification, which indirectly affects phytoplankton growth by limiting nutrient supply to the sunlit layer[3,7]. Considering that surface warming can otherwise increase upper-ocean stratification and decrease nutrient supply[19], exploring the response of ecosystems to intensified upwelling and ocean surface warming would require a more detailed modeling framework in which physical processes, and nutrient and plankton dynamics can be evaluated

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Conclusion