Abstract
The California Current System (CCS) is a highly productive region because of wind-driven upwelling, which supplies nutrients to the euphotic zone. Numerous studies of the relationship between phytoplankton productivity and wind patterns suggest that an intermediate wind speed yields the most productivity on the shelf. However, few studies have considered the productivity-wind relationship across the entire CCS, including the Northern CCS (north of 42˚N), an unusually productive region with highly variable upwelling- and downwelling-favorable winds. Using satellite chlorophyll concentration from GlobColour together with QuikSCAT and ASCAT winds, we examine the relationship between shelf (shallower than the 150 m isobath) chlorophyll concentration and wind patterns in the Central and Northern CCS. Results from this analysis suggest that while there is a dome-shaped relationship between mean chlorophyll concentration and wind stress for the whole system, the Central CCS and Northern CCS have significantly different relationships, which is evident in the separation between their mean chlorophyll concentration-wind stress curves. The Northern CCS also supports high chlorophyll concentration during downwelling-favorable winds. To understand this difference in chlorophyll concentration-wind stress relationships, results from particle tracking experiments using a ROMS model of the Northern CCS are used to map shelf retention times with respect to wind patterns. These results suggest that on the 1˚-latitude scale, the effect of wind intermittency on retention is minimal in the Northern CCS; however, this result does not disqualify the influence of more complex controls on retention like wind intermittency on smaller spatial scales. Lastly, we present a revised hypothesis to describe the relationship between chlorophyll concentration and wind stress in the CCS that includes the influence of non-upwelling-derived nutrients in the Northern CCS.
Highlights
Eastern Boundary Upwelling Systems like the California Current System (CCS) are highly productive regions due to the abundant nutrients largely supplied to the euphotic zone through coastal upwelling
Using chlorophyll concentration and wind stress derived from satellite observations, we analyze the relationship between chlorophyll concentration and wind patterns in the Central and Northern CCS to see if the domeshaped Botsford et al (2003) relationship applies to the CCS as a whole and whether the Northern CCS is comparable or exhibits different behavior
Data from the Central CCS, including from 37.5◦N, makes up the left side of the figure, while data from the Northern CCS, including from 47.5◦N, makes up the right side of the figure. This pattern shows the strong upwelling-favorable winds that are typical in the Central CCS, as well as the weaker upwelling-favorable winds that are typical in the Northern CCS
Summary
Eastern Boundary Upwelling Systems like the California Current System (CCS) are highly productive regions due to the abundant nutrients largely supplied to the euphotic zone through coastal upwelling. Despite the weak upwelling-favorable winds characteristic of the Northern CCS, it is an especially productive region This unusually high productivity has been speculatively attributed to a combination of wind patterns, geography, and freshwater inputs, all of which lead to abundant nutrients in the region (Hickey and Banas, 2008). Freshwater supply, outflow from the Salish Sea and, on a smaller scale, the Columbia River, brings additional nutrients to the region (Davis et al, 2014). These additional, non-upwelling-derived nutrient sources are essential for higher production with weaker wind speeds observed in this region but may complicate the relationship between phytoplankton biomass and wind
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