Peru‐Chile upwelling dynamics under climate change

Abstract

The consequences of global warming on the Peru-Chile Current System (PCCS) ocean circulation are examined with a high-resolution, eddy-resolving regional oceanic model. We performed a dynamical downscaling of climate scenarios from the IPSL-CM4 Coupled General Circulation Model (CGCM), corresponding to various levels of CO 2 concentrations in the atmosphere. High-resolution atmospheric forcing for the regional ocean model are obtained from the IPSL atmospheric model run on a stretched grid with increased horizontal resolution in the PCCS region. When comparing future scenarios to preindustrial (PI) conditions, the circulation along the Peru and Chile coasts is strongly modified by changes in surface winds and increased stratification caused by the regional warming. While the coastal poleward undercurrent is intensified, the surface equatorial coastal jet shoals and the nearshore mesoscale activity are reinforced. Reduction in alongshore wind stress and nearshore wind stress curl drive a year-round reduction in upwelling intensity off Peru. Modifications in geostrophic circulation mitigate this upwelling decrease in late austral summer. The depth of the upwelling source waters becomes shallower in warmer conditions, which may have a major impact on the system's biological productivity.

The very strong coastal El Niño in 1925 in the far-eastern Pacific

“…Based on the individual ICOADS observations, the near-coastal pseudostress had a mean northerly component of 15.5 ± 4.7 m 2 /s 2 around the equator (1°S-1°N) in February-March 1925. Assuming an Ekman layer depth of H = 30 m (Oerder et al 2015), we calculate the equatorial southward current speeds as 18 ± 5 cm/s. This is a lower bound, since the high SST implies reduced atmospheric stability, i.e.…”

Changes in the partial pressure of carbon dioxide in the Mauritanian–Cap Vert upwelling region between 2005 and 2012

“…The variability of the Mauritanian-Cap Vert upwelling was analyzed in terms of the upwelling index (Nykjaer and Van Camp, 1994) (Fig. 2) using satellite wind data.…”

“…Moreover, evidence of increasing wind speed that would favor upwelling (Bakun, 1990;Demarcq, 2009;Oerder et al, 2015) supports the possibility of a change in the dynamics of these highly productive areas. Recently, eddyresolving regional ocean models have shown how upwelling intensification can cause a major impact on the system's biological productivity and CO 2 outgassing (Lachkar and Gruber, 2013;Oerder et al, 2015). Wind observations and reanalysis products are controversial regarding the Bakun intensification hypothesis (Bakun, 1990).…”

“…Automated instruments on volunteer observing ships (VOSs) serve to provide as many observations throughout the global ocean as possible. This is in addition to data collected on scientific cruises and at long-term moorings (i.e., Astor et al, 2005: Lüger et al, 2004Schuster et al, 2009;Ullman et al, 2009;Watson et al, 2009;Padin et al, 2010;Gruber et al, 2002;Dore et al, 2003;Santana-Casiano et al, 2007;Bates et al, 2014).…”

“…Several anthropogenic interactive effects strongly influence eastern boundary upwelling systems (EBUSs), including upper ocean warming, ocean acidification, and ocean deoxygenation (Gruber, 2011;Feely et al, 2008;Keeling et al, 2010). Moreover, evidence of increasing wind speed that would favor upwelling (Bakun, 1990;Demarcq, 2009;Oerder et al, 2015) supports the possibility of a change in the dynamics of these highly productive areas. Recently, eddyresolving regional ocean models have shown how upwelling intensification can cause a major impact on the system's biological productivity and CO 2 outgassing (Lachkar and Gruber, 2013;Oerder et al, 2015).…”