An Invisible Force of Nature
May 5, 2020
Located just off the coast of central California, the Farallon Islands rest within one of the most productive ecosystems on the globe: the California Current System (CCS). Perhaps the most influential force that contributes to the immense productivity of this region is wind. Over the last fifty years, biologists and interns stationed on Southeast Farallon Island have dutifully recorded the weather conditions every single day, which means we have a solid and comprehensive understanding of local wind conditions for every month of the year.
As shown in Figure 1, wind direction and speed is highly variable during the late fall and winter months, starting in October. During this time the island experiences more frequent southerly and easterly winds, bringing storms and much precipitation. As the days get longer and temperatures increase on the mainland, the predominance of winds from the northwest becomes apparent. This dramatic shift in wind direction occurs in early February and continues into the early fall, with the most intense forces felt in April and May. The northwest direction of these spring winds is crucial to the physical component of upwelling. For much of the California coast, northwest winds run parallel to the coastline, and along with the Coriolis Effect and Ekman Transport, coastal surface water is pushed offshore at a 90° angle. This process brings cold water up from below to replace wind-blown surface waters, completing a continuous upwelling cycle. This movement of deep, nutrient-rich water to the euphotic zone has profound ecological effects, as it fuels dramatic productivity experienced in the CCS. Diatoms explode to life, contributing to massive phytoplankton blooms that attract copepods, larval fish, and krill to the ocean’s surface. Fish such as sardine, anchovy, and juvenile rockfish arrive to feast upon the buffet of zooplankton, soon to be devoured by seabirds and marine mammals. Much of the life breeding on the Farallons utilize this magnificent bounty of food newly available within the waters surrounding the island, and thus are heavily dependent on the stability, endurance, and return of the northwest winds of spring and summer. The 2020 spring season is shaping up to be a highly productive one, as early egg laying dates for many of SEFIs breeding seabirds are indicative of plentiful food and, thus, excellent upwelling conditions.
By Amanda Spears