External forcing mechanisms controlling the North Atlantic coastal upwelling regime during the mid-Holocene

Armand Hernández,José M Vaquero,Jürg Luterbacher,Ricardo M Trigo,Pedro Sousa,Maria C Freitas,Mário Cachão

doi:10.1130/g48112.1

Abstract

Abstract Nearshore upwelling along the eastern North Atlantic margin regulates regional marine ecosystem productivity and thus impacts blue economies. While most global circulation models show an increase in the intensity and duration of seasonal upwelling at high latitudes under future human-induced warmer conditions, projections for the North Atlantic are still ambiguous. Due to the low temporal resolution of coastal upwelling records, little is known about the impact of natural forcing mechanisms on upwelling variability. Here, we present a microfossil-based proxy record and modeling simulations for the warmest period of the Holocene (ca. 9–5 ka) to estimate the contribution of the natural variability in North Atlantic upwelling via atmospheric and oceanic dynamics. We found that more frequent high-pressure conditions in the eastern North Atlantic associated with solar activity and orbital parameters triggered upwelling variations at multidecadal and millennial time scales, respectively. Our new findings offer insights into the role of external forcing mechanisms in upwelling changes before the Anthropocene, which must be considered when producing future projections of midlatitude upwelling activity.

Highlights

Coastal upwelling regions are the most productive marine areas in the world
The seasonal nature of the upwelling system in the Iberian North Atlantic margin (INAM) indicates that F1 scores are a proxy for downwelling conditions in winter, whereas F2 scores can be considered a direct indicator of an enhanced summer upwelling regime (Fig. 2B)
Our results demonstrate the solar impact on the North Atlantic upwelling regime during the Holocene Climate Optimum (HCO) at different time scales

Summary

Introduction

Coastal upwelling regions are the most productive marine areas in the world. Current human-induced greenhouse warming influences the intensity of upwelling because it is strongly connected with the increase in land-sea temperature differences (Bakun et al, 2010). These background conditions (warm temperatures and high land-sea temperature differences) make the HCO a candidate period for evaluating the role of nonanthropogenic external forcing mechanisms in the upwelling regimes, comparable in some aspects to the impacts of future warming on ocean-atmosphere climate dynamics over the North Atlantic.

Results

Conclusion