Trends in coastal upwelling intensity during the late 20th century

Abstract

Abstract. This study presents linear trends of coastal upwelling intensity in the later part of the 20th century employing various indices of upwelling, derived from meridional wind stress and sea surface temperature. The analysis was conducted in the four major coastal upwelling regions in the world, which are off North-West Africa, Lüderitz, California and Peru. The trends in meridional wind stress showed a steady increase of intensity from 1960-2001, which was also reflected in the SST index calculated for the same time period. The steady cooling observed in the instrumental records of SST off California substantiated this observation further. It was also noted that the trends in meridional wind stress obtained from different datasets differ substantially from each other. Correlation analysis showed that basin-scale oscillations like the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) could not be directly linked to the observed increase of upwelling intensity off NW Africa and California respectively. The relationship of the North Atlantic Oscillation (NAO) with coastal upwelling off NW Africa turned out to be ambiguous due to a negative correlation between the NAO index and the meridional wind stress and a lack of correlation with the SST index. Our results give additional support to the hypothesis that the coastal upwelling intensity increases globally because of raising greenhouse gas concentrations in the atmosphere and an associated increase of the land-sea pressure gradient and meridional wind stress.

Under Pressure: Climate Change, Upwelling, and Eastern Boundary Upwelling Ecosystems

“…Those containing seemingly contradictory results (Demarcq, 2009;Dewitte et al, 2012) add uncertainty, but do not refute the findings of the metaanalysis, as they focus on local regions, use short time series and do not add uncertainty. Despite the fact that the meta-analysis by Sydeman et al generally supports Bakun's proposition, we still cannot attribute coastal wind intensification in EBUS to global warming because we cannot discount the role of multi-decadal climate variability in the observed trends (Chhak and Di Lorenzo, 2007;Narayan et al, 2010;Pérez et al, 2010;Macias et al, 2012;Santos et al, 2012;Cropper et al, 2014;Jacox et al, 2014), nor is it a test of the Bakun hypothesis mechanism.…”

The importance of external climate forcing for the variability and trends of coastal upwelling in past and future climate

“…Some observations over the 20th century (Narayan et al, 2010) and simulations of the 21st century (Wang et al, 2015) have been interpreted, according to this hypothesis, as indicative of upwelling intensification due to stronger external climate forcing in the recent past and future. Also, coastal sediment records covering the past millennium and indicative of upwelling (McGregor et al, 2007) have been interpreted as a response to past variations in the external climate forcing, mainly solar irradiance and volcanism, with weaker upwelling during the Little Ice Age (centuries around 1700 AD) and stronger upwelling during the Medieval Warm Period (around 1100 AD).…”

Response of O<sub>2</sub> and pH to ENSO in the California Current System in a high-resolution global climate model

“…Turi et al (2016) used a regional ocean model to demonstrate that a recent intensification of upwellingfavorable winds is linked to a drop in coastal pH and arag . It currently remains unclear whether these observed and modeled changes in the CalCS ocean biogeochemistry are ongoing signals of anthropogenic climate change, and thus could continue into the future, or whether they are driven by natural fluctuations in the climate system (e.g., Bakun, 1990;Narayan et al, 2010;Bakun et al, 2015;Rykaczewski et al, 2015;Wang et al, 2015).…”