The future of coastal upwelling in the Humboldt current from model projections

Abstract

The Humboldt coastal upwelling system in the eastern South Pacific ocean is one of the most productive marine ecosystems in the world. A weakening of the upwelling activity could lead to severe ecological impacts. As coastal upwelling in eastern boundary systems is mainly driven by wind stress, most studies so far have analysed wind patterns change through the 20th and 21st Centuries in order to understand and project the phenomenon under specific forcing scenarios. Mixed results have been reported, and analyses from General Circulation Models have suggested even contradictory trends of wind stress for the Humboldt system. In this study, we analyse the ocean upwelling directly in 13 models contributing to phase 5 of the Coupled Model Intercomparison Project (CMIP5) in both the historical simulations and an extreme climate change scenario (RCP8.5). The upwelling is represented by the upward ocean mass flux, a newly-included variable that represents the vertical water transport. Additionally, wind stress, ocean stratification, Ekman layer depth and thermocline depth were also analysed to explore their interactions with coastal upwelling throughout the period studied. The seasonal cycle of coastal upwelling differs between the Northern and Southern Humboldt areas. At lower latitudes, the upwelling season spans most of the autumn, winter and spring. However, in the Southern Humboldt area the upwelling season takes place in spring and the summertime with downwelling activity in winter. This persists throughout the Historical and RCP8.5 simulations. For both the Northern and Southern Humboldt areas an increasing wind stress is projected. However, different trends of upwelling intensity are observed away from the sea surface. Whereas wind stress will continue controlling the decadal variability of coastal upwelling on the whole ocean column analysed (surface to 300 m depth), an increasing disconnect with upwelling intensity is projected below 100 m depth throughout the 21st Century. This relates to an intensification of ocean stratification under global warming as shown by the sea water temperature profiles. Additionally, a divergence between the Ekman layer and thermocline depths is also evidenced. Given the interaction of upwelled nutrients and microscopic organisms essential for fish growth, a potential decline of coastal upwelling at depth could lead to unknown ecological and socio-economical effects.

Oceanography of Harmful Algal Blooms on the Ecuadorian Coast (1997–2017): Integrating Remote Sensing and Biological Data

“…This study confirms that HAB dynamics in the Ecuadorian coastal zone seem to be constrained by the Humboldt upwelling system, high precipitation, and terrestrial nutrients from the Guayas Basin, aligning with other HAB studies in coastal ecosystems and upwelling zones (Kudela et al, 2005;Vila and Masó, 2005;Borbor-Cordova et al, 2006;Anderson et al, 2017;Oyarzún and Brierley, 2018). In addition, high sea surface temperature during ENSO and ocean heat waves seem to affect all the aforementioned drivers, along with the adaptive strategies of the phytoplankton species and their community assemblage (Masó and Garcés, 2006;Anderson, 2014;Anderson et al, 2017).…”

“…On the other hand, this study suggests that upwelling systems are related to HABs in the Gulf of Guayaquil. The Humboldt upwelling system is considered to be one of the most productive systems globally (Daneri et al, 2000;Taylor, 2008;Oyarzún and Brierley, 2018). Research groups, such as GEOHAB (Hallegraeff, 2004), have highlighted the potential impacts of HABs on upwelling systems in the context of climate change (Kudela et al, 2005;Edwards et al, 2006;Wei et al, 2008;Trainer et al, 2010;Díaz et al, 2016;Pitcher et al, 2017).…”

“…In the case of Ecuador and Peru, the Humboldt upwelling system is the foundation of both countries' fishery productivity and the economic benefits of the fishery industry, which can be impacted by emergent HABs (Pennington et al, 2006;Trainer et al, 2010). Considering that there are limited studies on the upwelling systems in the Gulf of Guayaquil region (Oyarzún and Brierley, 2018), understanding these dynamics is critical to assess the future impacts of a changing climate in this very productive ecosystem.…”

Spatio-Temporal Pattern of Dinoflagellates Along the Tropical Eastern Pacific Coast (Ecuador)

“…the world (Chavez et al, 2002;Pennington et al, 2006;Oyarzún and Brierley, 2018). In this study, highest concentrations of dinoflagellates were found in Manta (April 2017), La Libertad (March 2015), and Puerto Bolivar (May 2014 and May 2017), during wet season.…”

Variability of surface climate in simulations of past and future

“…However, a majority of models show suppressed IOD activity under the warming scenarios corresponding with the reduced temperature variability over the Arabian Sea upwelling (Fig. 2), which may be a response to the increased ocean stratification seen in the transient simulations (Oyarzún and Brierley, 2019). In the tropical Atlantic, weak but negative trends for the AMM (Fig.…”