Did Positive Feedback Play a Role in the Circulation of Elkhorn Slough (Monterey Bay, California) during the Last Three Decades of the 20th Century?

Breaker, L.C., 2025. Did positive feedback play a role in the circulation of Elkhorn Slough (Monterey Bay, California) during the last three decades of the 20th century? Journal of Coastal Research, 41(5), 907–916. Charlotte (North Carolina), ISSN 0749-0208. Elkhorn Slough (ES) has grown rapidly since the entrance to a harbor along Monterey Bay, California, was formed in 1946. To document this growth during the period from about 1970 to at least 2000, sufficient data were available to obtain reliable estimates of the increases in the rates of flow that occurred in ES. During this period, the speeds of the surface currents essentially doubled. Two forces, in particular, contributed: semidiurnal tides and frictional forcing along the lateral and bottom boundaries of the slough; additional factors included local winds, transfer of momentum, and most likely, positive feedback (PF). Momentum transfer can be predicted, but PF has the potential to increase beyond reasonable limits if negative feedback does not intervene. The results show that the rates of erosion along the banks and bottom of ES since the 1930s were accelerating, consistent with the idea that acceleration was a key factor that contributed to the overall increase in the surface circulation of ES. A numerical model is proposed where the residuals between the model and the observed data could be compared. Such a model would generates a set of proxy observations: the currents, for example, that would not contain the influence of PF but only the basic physics and numerical approximations that are required for such a model. By comparing the model-generated observations with real data acquired at the same location, such a comparison could be made. Providing a correct interpretation of these results is the challenge. The PF has the potential to unleash energy at levels that continue to increase in the absence of negative feedback; this could explain why ES continued to grow in the absence of sufficient negative feedback when other estuaries along the west coast that have been exposed to similar tidal and boundary forcing have not.