Oceanic Rossby waves drive inter-annual predictability of net primary production in the central tropical Pacific

Abstract

In the Pacific Ocean, off-equatorial Rossby waves (RWs), initiated by atmosphere-ocean interaction, modulate the inter-annual variability of the thermocline. In this study, we explore the resulting potential gain in predictability of central tropical Pacific primary production, which in this region strongly depends on the supply of macronutrients from below the thermocline. We use a decadal prediction system based on the Max Planck Institute Earth system model to demonstrate that for the time period 1998–2014 properly initialized RWs explain an increase in predictability of net primary productivity (NPP) in the off-equatorial central tropical Pacific. We show that, for up to 5 years in advance, predictability of NPP derived from the decadal prediction system is significantly larger than that derived from persistence alone, or an uninitialized historical simulation. The predicted signal can be explained by the following mechanism: off-equatorial RWs are initiated in the eastern Pacific and travel towards the central tropical Pacific on a time scale of 2–6 years. On their arrival the RWs modify the depths of both thermocline and nutricline, which is fundamental to the availability of nutrients in the euphotic layer. Local upwelling transports nutrients from below the nutricline into the euphotic zone, effectively transferring the RW signal to the near-surface ocean. While we show that skillful prediction of central off-equatorial tropical Pacific NPP is possible, we open the door for establishing predictive systems for food web and ecosystem services in that region.

Keywords

• decadal climate prediction
• net primary productivity
• oceanic Rossby waves
• ensemble Kalman filter
• MPI-ESM
• Pacific Ocean