Background: Environmental variability on century and global scales has the potential to impact marine ecosystems at a variety of smaller scales. In a particularly striking example of how global climate change may be affecting ocean conditions on smaller scales, Andrew Bakun (in a 1990 Science paper) postulates that global warming will lead to increased coastal upwelling along eastern ocean boundaries. The effect on these ecosystems could be significant because of their highly productive nature and their potentially important role in the global CO2 budget.
Purpose of Activity/Goal of Project: Our objective was to examine the variability of coastal upwelling patterns during spring and summer in the CCS. Specifically, we test Bakun's hypothesis that a long-term global warming trend has led to increased equatorward wind stress along the west coast of North America, which has resulted in increased rates of coastal upwelling.
Description of Accomplishment and Significant Results: The results show that state-space statistical models clearly separate the seasonal signal from the nonlinear trend in long environmental time series. The utility of estimating seasonal patterns is demonstrated with the discovery of a systematic increase in equatorward stress and salinity, and decrease in SST and sea level during spring and summer, evidence that coastal upwelling has intensified. This evidence is strongest and most prevalent in areas where seasonal coastal upwelling is a dominant process (32º40°N). This pattern of increasing upwelling over time cannot be discerned in the monthly observations or trend model series, which overwhelm the seasonal tendency. A long-term warming trend masks seasonal cooling associated with increased upwelling during spring and summer, while the nonseasonal trend in wind stress implies an artificially large increase in seasonal upwelling-favorable stress. Evidence of increased upwelling found in fall-winter seasonal data.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic Plan Goals): The model results improve our understanding of the coastal ocean's response to long-term variations in atmospheric forcing, as well as the potential contribution of natural and anthropogenic signals, regional differences in these effects, and ultimately their impact on fishery stocks. The results demonstrate the importance of evaluating temporal and spatial variability over the entire spectrum, rather than simply at global climate scales, when examining long-term environmental fluctuations. They also demonstrate the importance of considering changes in seasonal patterns independently from changes in the long-term climate trend.
Problems: We wish to note that we provided JGR with a camera-ready copy that we typeset in-house, at a savings of about $2400 in printing charges
Key Contact: Frank Schwing (831-648-9034, fschwing@pfeg.noaa.gov)