Mechanisms of interannual- to decadal-scale predictability for ocean physics and biogeochemistry in the California Current System

Project Summary: The California Current System (CCS) is a highly productive eastern boundary upwelling system, in which seasonal upwelling fuels primary production that supports a thriving marine ecosystem and socioeconomically valuable services including fisheries and tourism. The CCS and resources derived from it are strongly driven by changes in the physical and biogeochemical environment, both of which experience considerable variability on timescales ranging from days to centuries. Prognostic information on this variability is therefore highly desirable for marine resource users, for example managers of fisheries whose target populations are sensitive to variations in the climate system. With this motivation, a number of recent and ongoing efforts have begun to explore predictability and forecast skill in the CCS on seasonal timescales (~1-12 months), and to project long-term (~50-100 years) influences of climate change. However, near-term (2-20 year) predictions have received relatively little attention, at least in part because predictable signals are often obscured by intrinsic climate variability on these critical timescales.
Nonetheless, potential for skillful near-term forecasts of the physical and biogeochemical ocean state has been demonstrated for the CCS, and could in turn provide actionable information to marine resource managers. The overarching goal of this project is to quantify the predictability of the physical and biogeochemical CCS variability on interannual to decadal timescales, to understand the physical mechanisms that drive predictability, and to evaluate the ability of current decadal forecast systems to realize that predictability as forecast skill. Key elements of the proposed work plan are to (1) identify from historical data the physical mechanisms that drive interannual to decadal variability in CCS temperature, salinity, pH, oxygen, nutrient concentration, and marine productivity, (2) quantify the predictability and forecast skill of these quantities using the Community Earth System Model Decadal Prediction Large Ensemble (CESM-DPLE), and (3) identify sources of any differences between predictability and forecast skill in CESM-DPLE (i.e., potential forecast skill that is not being realized in modern decadal forecast systems). These tasks will be carried out using a suite of model and observational datasets including multi-decadal high-resolution ocean reanalyses, in situ ocean biogeochemical observations, and retrospective decadal forecasts from CESM-DPLE.
Relevance to the Competition and NOAA’s Long-Term Climate Goal: The proposed research will directly address the goal of the competition, to “identify state, mechanisms, and sources of predictability on the interannual to decadal timescale, which will help to lead to future improvements in skillful decadal prediction systems for climate (ocean and atmosphere)”. Key physical and biogeochemical variables identified in the proposal will be addressed, as will the physical mechanisms that govern their predictability on interannual to decadal timescales. Finally, comparison of this predictability with realized forecast skill in modern decadal predictions will allow us to identify key limitations on forecast skill and areas where predictability in the ecosystem can be exploited to improve it. The proposed project will also support NOAA’s long-term climate goals, particularly by advancing scientific understanding of variability and predictability in the North Pacific in a way that can support effective decision making about marine resources that are sensitive to that variability, thereby improving resilience of US ecosystems and economies.