Abstract
Abstract. The eastern boundary upwelling systems, located in the subtropics at the eastern boundary of the Atlantic and Pacific oceans and mainly driven by the trade winds, are the major coastal upwelling regions. Previous studies have suggested that the intensity of upwelling in these areas in the past centuries may have been influenced by the external radiative forcing, for instance by changes in solar irradiance, and it will also be influenced in the future by the increasing atmospheric greenhouse gases. Here, we analyse the impact of the external climate forcing on these upwelling systems in ensembles of simulations of two Earth system models. The ensembles contain three simulations for each period covering the past millennium (900–1849) and the 20th century (1850–2005). One of these Earth system models additionally includes the near future (2006–2100). Using a set of simulations, differing only in their initial conditions, enables us to test whether the observed variability and trends are driven by the external radiative forcing. Our analysis shows that the variability of the simulated upwelling is largely not affected by the external forcing and that, generally, there are no significant trends in the periods covering the past and future. Only in future simulations with the strongest increase of greenhouse gas concentrations the upwelling trends are significant and appear in all members of the ensemble.
Highlights
Eastern boundary upwelling systems (EBUSs, including the California, the Canary, the Benguela, and the Peru upwelling systems) are highly productive coastal ocean areas where nutrient-rich, cold water upwells by the action of favourable winds
Previous studies have suggested that the intensity of upwelling in these areas in the past centuries may have been influenced by the external radiative forcing, for instance by changes in solar irradiance, and it will be influenced in the future by the increasing atmospheric greenhouse gases
This task would be in any case not meaningful, since the main result of our study is that the external radiative forcing has not varied strongly enough over the past millennium, including the 20th century, to drive the upwelling variability over this period
Summary
Eastern boundary upwelling systems (EBUSs, including the California, the Canary, the Benguela, and the Peru upwelling systems) are highly productive coastal ocean areas where nutrient-rich, cold water upwells by the action of favourable winds. The main objective of the analysis is to test whether the external forcing prescribed in a set of ensembles of climate simulations is strong enough to drive upwelling in the four EBUSs, and whether, there are significant long-term trends in upwelling over the last millennium, the last 156 years, and the near future that appear common to all simulations. This is obviously closely related to Bakun’s hypothesis. We finalize the study with a discussion and conclusion section
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