Abstract
Global increases in temperature are altering land-sea temperature gradients. Bakun (1990) hypothesized that changes within these gradients will directly affect atmospheric pressure cells associated with the development of winds and will consequently impact upwelling patterns within ecologically important Eastern Boundary Upwelling Systems (EBUS). In this study we used daily time series of NOAA Optimally Interpolated sea surface temperature (SST) and ERA 5 reanalysis wind products to calculate a series novel of metrics related to upwelling dynamics. We then use these to objectively describe upwelling signals in terms of their frequency, intensity and duration throughout the four EBUS during summer months over the last 37 years (1982–2019). We found that a decrease (increase) in SST is associated with an increase (decrease) in the number of upwelling “events,” a decrease (increase) in the intensity of upwelling, and an increase (decrease) in the cumulative intensity of upwelling, with differences between EBUS and regions within EBUS. The Humboldt Current is the only EBUS that shows a consistent response from north to south with a general intensification of upwelling. However, we could not provide clear evidence for associated changes in the wind dynamics hypothesized to drive the upwelling dynamics.
Highlights
Coastal upwelling is a major oceanic process driven by prominent currents, of which those within Eastern Boundary Upwelling Systems (EBUS) are most important globally (Bakun and Nelson, 1991; Messié et al, 2009; Gruber et al, 2011; Pegliasco et al, 2015; Varela et al, 2015, 2016, 2018; Bonino et al, 2019; Brady et al, 2019)
Our investigations of trends in upwelling metrics across individual time series for each of the EBUS currents revealed the presence of noticeable shifts in sea surface temperature (SST) patterns at each EBUS over the past 37 years (Figures 2A,B)
Number of upwelling signals per year Mean temperature anomaly during the upwelling signal Sum of the daily intensity anomalies over the duration of the signal differed across each EBUS
Summary
Coastal upwelling is a major oceanic process driven by prominent currents, of which those within Eastern Boundary Upwelling Systems (EBUS) are most important globally (Bakun and Nelson, 1991; Messié et al, 2009; Gruber et al, 2011; Pegliasco et al, 2015; Varela et al, 2015, 2016, 2018; Bonino et al, 2019; Brady et al, 2019). EBUS include the California (CCS), Humboldt (HCS), Canary (CnCS), and Benguela (BCS) current systems (Figure 1), with each of these significantly impacting their associated coastal ecosystems. These systems are present along the western shores of landmasses in the Pacific and Atlantic Oceans where they comprise vast regions of coastal ocean water (Bakun, 1990; Pauly and Christensen, 1995; Bakun et al, 2010, 2015; Santos et al, 2012b,a; Seabra et al, 2019). EBUS encompass a multitude of coastal regions stratified across several latitudes.
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