Detecting Subtle Seasonal Transitions of Upwelling in North-Central Chile

Abstract

Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making it more difficult to identify an enhanced upwelling season. A two-phase linear regression model, which is typically used to detect subtle climate changes, is applied here to detect seasonal changes in CUI at Punta Lengua de Vaca. This method objectively finds distinct transitions for most years. The spring-to-summer transition is more readily detected and the slackening of the upwelling-favorable winds, warmer waters, and longer wind strengthening–relaxation cycles change the coastal upwelling ecosystem. While the spring-to-summer transition at Punta Lengua de Vaca could be influenced by large-scale circulations, the actual dates of transition are highly variable and do not show a clear relationship.

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

“…A possible mechanism driving the local variability observed at the southern section is the generation of local baroclinic instability and vorticity input from wind stress curl as observed for the Califor- nia system (Kelly et al, 1998). The southern section lies within the northeastern rim of the southeast Pacific anticyclone, and the peak in the seasonal DO eddy flux coincides with the reported intensity peak of the seasonal cycle of the Anticyclone, towards the end of the year (Rahn et al, 2015;Ancapichún and Garcés-Vargas, 2015). Therefore, the mesoscale activity in this region could be directly modulated by the winds.…”

Coastal biophysical processes and the biogeography of rocky intertidal species along the south‐eastern Pacific

“…Theoretically, the biogeographic structure of dispersal‐limited species should be influenced mainly by small‐scale processes, such as local adaptation, while species with broad dispersal capacities are likely influenced by regional‐scale processes such as geology, climate or oceanographic processes (Fenberg et al., ; Haye et al., ; Sanford & Kelly, ). The existence of a biogeographic break between 30°–32°S at the SEP has been shown by several studies (Camus, ; Thiel et al., ), and is associated with coastal circulation processes related the location of the South Pacific Anticyclone; upwelling‐favourable conditions prevail year‐round equatorward of around 30°S (Rahn, Rosenblüth, & Rutllant, ). Our analyses confirm the presence of a break around 30°S, only for lecithotrophic species, while the break for planktotrophic species is observed further south, around 34.5°S.…”

“…This break has also been described for other benthic invertebrates (Lancellotti & Vásquez, ), although based on data collected at coarse spatial scales (3° latitude). The transition area south of Punta Lengua de Vaca down to 35°S is an area of intense mesoscale variability (Aguirre, Pizarro, Strub, Garreaud, & Barth, ; Hormazabal, Shaffer, & Leth, ; Rahn et al., ), where eddies and plumes transport primary and secondary coastal productivity offshore (Correa‐Ramirez, Hormazabal, & Yuras, ; Morales et al., ). The well‐defined sectors of mesoscale and sub‐mesoscale biophysical coherence we observed along this transition region highlight the importance of larval strategies that minimize offshore advection around areas of intensified offshore transport.…”

Plasticity in organic composition maintains biomechanical performance in shells of juvenile scallops exposed to altered temperature and pH conditions

“…These two pH treatments were combined in a full factorial experimental design with two temperature treatments (14 °C and 18 °C). The scallops were exposed for 18 d, since one of the main focuses of our study was determine how scallops could respond to prolonged low temperature/low pH conditions, upon a scenario of extended exposure to upwelling condition , which typically last from 2 up to 8 days at present 12 , 62 . Over the experimental period, temperature, salinity, pH NBS and total alkalinity (AT) were monitored every 3 days to estimate the rest of carbonate system parameters (i.e., p CO 2 , calcite saturation state Ω) inside the experimental aquaria.…”