Seasonal climatology of hydrographic conditions in the upwelling region off northern Chile

Abstract

Abstract. Over 30 years of hydrographic data from the northern Chile (18øS-24øS) upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore. The data are interpolated to a grid with sufficient spatial resolution to preserve crossshelf gradients and then presented as means within four seasons: austral winter (JulySeptember), spring (October-December), summer (January-March), and fall (April-June). Climatological monthly wind forcing, surface temperature, and sea level from three coastal stations indicate equatorward (upwelling favorable) winds throughout the year, weakest in the north. Seasonal maximum alongshore wind stress is in late spring and summer (DecemberMarch). Major water masses of the region are identified in climatological T-S plots and their sources and implied circulation discussed. Surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year-round, strongest in summer and weakest in winter, bringing relatively fresh water to the surface nearshore. Surface geostrophic flow nearshore is equatorward throughout the year. During summer, an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields. Subsurface fields indicate generally poleward flow throughout the year, strongest in an undercurrent near the coast. This undercurrent is strongest in summer and most persistent and organized in the south (south of 21øS). A subsurface oxygen minimum, centered at ~250 m, is strongest at lower latitudes.Low-salinity subsurface water intrudes into the study area near 100 m, predominantly in offshore regions, strongest during summer and fall and in the southernmost portion of the region. The climatological fields are compared to features off Baja within the somewhat analogous California Current and to measurements from higher latitudes within the Chile-Peru Current system.

Coupled CO<sub>2</sub> and O<sub>2</sub>-driven compromises to marine life in summer along the Chilean sector of the Humboldt Current System

“…In general, the subsurface depth layer is affected by biocalcification and hypoxia, its thickness being maximum at low latitudes (200 to 400 m) and decreasing to nearly zero at high latitudes (Fig. 9), which is consistent with the increase of the ESSW thickness towards the Equator and in summer (Blanco et al, 2001). The habitat free of CO 2 -driven stresses was restricted to the upper mixed layer and to small water parcels at about 1000 m depth (Fig.…”

“…As a result of changes in upwelling most variability occurs in the upper 150 m, therefore, affecting STW and SAAW and, to a lesser degree, ESSW (Blanco et al, 2001;Antezana, 1978); deeper waters, such as AAIW, experience much more moderate seasonal changes, in any case, not directly linked to coastal upwelling. During summer, therefore, we expect there will major near-surface coastal changes associated to the onshore and upward transport of the oxygendeficient (the Oxygen Minimum Layer, OML) and strongly CO 2 supersaturated tropical and equatorial waters (in surface to reach 100 % near 23 • S and 200 % near 30 • S) (Torres et al, 2002).…”

Anthropogenic carbon distribution in the eastern South Pacific Ocean

“…The influence of Antarctic Intermediate Water (AAIW) can be seen at depths of around 500 to 700 m, typically south of 26 • S and with salinities <34.5 and temperatures <7 • C (Blanco et al, 2001;Zenk et al, 2005;Fiedler and Talley, 2006). The bottom water originates from the Lower Circumpolar Water (LCPW).…”

“…At intermediate water depths, the Eastern South Pacific Intermediate Water (ESPIW: Schneider et al, 2003), properties are those of the Subantarctic Water; it is relatively cool (∼12 • C) and fresh (S∼34.25) and it is bellow STSW offshore and above ESSW closer to the coast (Blanco et al, 2001). The influence of Antarctic Intermediate Water (AAIW) can be seen at depths of around 500 to 700 m, typically south of 26 • S and with salinities <34.5 and temperatures <7 • C (Blanco et al, 2001;Zenk et al, 2005;Fiedler and Talley, 2006).…”

Vertical segregation among pathways mediating nitrogen loss (N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O production) across the oxygen gradient in a coastal upwelling ecosystem

“…Blanco et al, 2001), which transports nutrient-rich, high-saline, and O 2 -depleted Equatorial Subsurface Waters -ESSWs (Strub et al, 1998). During austral spring-summer (SeptemberApril), a marked upwelling-favourable period driven by persistent southwesterly winds, ESSWs arrive at the coastal area off central Chile, impinging on one of the widest continental shelves in Chile (Sobarzo and Djurfeldt, 2004;Sobarzo et al, 2007).…”