Coastal SEES: developing new modeling tools to predict ocean acidification impacts on coastal ecosystems

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

An immediate consequence of the dissolution of CO2 in seawater is an increase in the acidity of the water, which has implications for organisms that rely on carbonate chemistry for vital functions. As the occurrence of lower pH and lower oxygen events along the U.S. west coast is likely to increase in frequency and worsen in magnitude over the next decades, it is paramount to carefully document present-day variability in water column pH and oxygen associated with seasonal and interannual changes in coastal upwelling, and produce reference pH and oxygen fields at the spatial (kilometers) and temporal (days) scales needed to assess their impact on ecosystem processes. To address this need, the proposed research uses a state-of-the art, data-assimilative, coupled physical-biogeochemical modeling framework to quantify the temporal variability of low pH and low oxygen intrusions along central California at the spatial scales relevant to coastal ecosystems. In addition, the modelling effort relies on an ensemble approach to identify the degree of certainty with which the frequency of occurrence and duration of low pH and low oxygen events can be predicted on daily to seasonal timescales, a critical component for improving future management strategies designed to mitigate the effects of ocean acidification on marine organisms. It is also anticipated that the results will apply to other eastern boundary current upwelling systems and improve broader knowledge of coastal upwelling impacts on biogeochemical processes (e.g., the long-term sign and magnitude of nearshore air-sea CO2 fluxes). The study will contribute to training a new generation of scientists versed in multidisciplinary ocean science and management concepts. Specifically, it will provide training for two post-doctoral researchers and one graduate student in (1) coupled physical-biogeochemical data assimilation, (2) regional-to-local downscaling of model simulations, (3) interpretation of complex numerical model solutions, and (4) creation of products targeted at improving resource management in the face of ocean acidification. In addition, the lead PI will give general audience lectures on the use of models and observations to study ocean acidification along the California coast. Because the significant amount of variability occurring over relatively short spatial (< 100 km) and temporal (days to weeks) scales presents a challenge for coastal ocean observing systems and monitoring programs, the routine use of data-assimilative physical-biogeochemical models would greatly enhance current capabilities for predicting the occurrence of low pH and low oxygen events off central California. In this regard, this research has the following short- and long-term benefits: (1) establish the connections between alongshore upwelling variability and the frequency, magnitude and duration of low pH and low oxygen conditions on the shelf, (2) examine the probability that certain pH and oxygen thresholds below which conditions become detrimental to key marine organisms are exceeded for extended periods, (3) guide the implementation of an efficient monitoring system network by identifying specific regions where pH and oxygen variability is expected to be largest, and (4) implement a modeling framework capable of predicting the occurrence of extreme low pH and low oxygen events off central California, and assess its usefulness for decision-making purposes. These developments contribute to Coastal SEES overarching objectives of advancing understanding of fundamental, interconnected processes in coastal systems on a variety of spatial and temporal scales, improving capabilities for predicting future coastal system states and impacts, and identifying pathways by which research results will be translated to policy and management domains and used to enhance coastal sustainability.