Twelve years of change in coastal upwelling along the central-northern coast of Chile: spatially heterogeneous responses to climatic variability

Abstract

We use time-series analyses to characterize the effects of recent climate variability upon the local physical conditions at 11 study sites along the northern-central coast of Chile (29-34°S). Environmental indices show that the 1° Bakun upwelling index in this coastal region has fluctuated in time, starting from a stable period around the 1980's, peaking during the mid 90s, decreasing during the next ten years and increasing at a steep rate since 2010. Upwelling intensity decreased with increasing latitude, showing also a negative correlation with climate patterns (El Niño3 sea surface temperature-SST anomalies and the Multivariate El Niño Index). We hypothesize that the impacts of climate variability on upwelling events seem to be spatially heterogeneous along the region. Non-sheltered locations and, particularly, sites on prominent headlands show an immediate (lag = 0) and negative correlation between local SST, upwelling events and wind stress. We suggest that near-shore thermal conditions are closely coupled to large-scale forcing of upwelling variability and that this influence is modulated through local topographic factors.

Figure 1. Study Area.

Sampling locations showing coastline exposure division (dotted line) between a more protected (from Temblador to Arrayan) and a more exposed coastline (from P. Talca to Matanzas), and upwelling locations (P. Talca, P. Curaumilla and Quintay) as described in the text.

Figure 2. Trends of time series upwelling (UI).

(A) UI anomalies time series (in grey) and trends using splines (black line) and (B) wavelet power spectrum (WPS) from 1980 to 2010 (including our time period span 1999–2010, dotted line). For the WSP, the area marked by the black lines indicates the cone of influence where edge effects become important (>95% confidence).

Figure 3. Spatio-temporal trends of sea surface temperature (SST).

Monthly mean SST time-series derived from satellite imagery and data loggers. The spatio-temporal trend in satellite evidences a clear seasonal patterns with cold (blue) and warm (red) periods in contrast with data loggers with predominance cold conditions (blue) in the exposed coastline (from P. Talca to Matanazas, dotted line). White spaces correspond to missing values.

Figure 4. Cross-correlations between MEI and UI.

Prewhitened cross-correlation functions (CCFs) between monthly time-series of the Multivariate EL Niño Index (MEI) and the Upwelling Index (UI) estimated for different latitude: 29° (ccf: −0.187; t: −2.151; p-value: 0.033), 30° (ccf: −0.194; t: −2.242; p-value: 0.003), 31° (ccf: −0.206; t: −2.378; p-value: 0.019), 32° (ccf: −0.216; t: −2.499; p-value: 0.014), 33° (ccf: −0.208; t: −2.402; p-value: 0.018) and 34°S (ccf: −0.182; t: −2.096; p-value: 0.038). Standard error limits are shown as dotted lines. The significant and inverse correlations are mostly observed at Lag = 0.

Figure 5. Cross-correlations between SST and UI.

Prewhitened cross-correlation functions (CCF) between monthly off- (satellite derived-SST) and near-shore (loggers-derived SST), and UI at all regular monitoring sites. Standard error limits are shown as dotted lines. The significant and inverse correlations are mostly observed at Lag = 0.

Figure 6. Cross-correlations between variables.

Summary of CCF (correlations values) obtained between the different physical variables (SST, upwelling index-UI, and wind-stress) considered along the northern-central Chilean coast. More significant CCFs were obtained in the more exposed coastline (from P. Talca to Matanzas) with highly significant values mainly observed towards southern locations.