Exploiting subsurface ocean dynamics for decadal predictability in the upwelling systems of the Eastern North Pacific

Abstract

Given the strong recent interest in the decadal timescale variability and the potential for its predictability, it is critical to identify dynamics that carry inherent decadal-scale predictability. This work enhances our understanding and prediction capability of the subsurface signature of the decadal variability in the eastern North Pacific upwelling systems using reanalysis products and a set of eddy-resolving ocean model simulations. We show that subsurface temperature anomalies propagated by mean advection along the North Pacific Current significantly contribute through mean upwelling to decadal changes of surface temperature in the Gulf of Alaska. We also show that this influence is comparable to the contribution associated with variations in atmospheric winds. We find that subsurface anomalies in the core of the North Pacific Current propagate temperature, salinity, and oxygen signals downstream into the coastal California Current upwelling system, following the path of the mean gyre circulation with a time scale of 10 years. We suggest these propagation dynamics lead to potential predictability of ocean tracers, specifically oxygen and nutrients. Using reanalysis products and a set of eddy-resolving ocean model simulations, we provide evidence that supports the proposed inherent decadal predictability associated with the propagation of subsurface anomalies. We quantify the predictability of impacts associated with the arrival of the subsurface anomalies in the California Current upwelling system. We find a region of strong deterministic, predictable variance in the core of the North Pacific Current and in the sub-polar gyre region. Finally, we propose a dynamical subsurface connection between the western and eastern boundary, with subsurface anomalies generating and propagating eastward from the Kuroshio-Oyashio Extension region in the Western Pacific all the way to the California Current region in the Eastern Pacific.