Climate-induced variability in South Atlantic wave direction over the past three millennia

A P Silva,A F H Fetter-Filho,C Dalinghaus,F J Méndez,C J Hein,A H F Klein,M F Broggio

doi:10.1038/s41598-020-75265-5

Abstract

Through alteration of wave-generating atmospheric systems, global climate changes play a fundamental role in regional wave climate. However, long-term wave-climate cycles and their associated forcing mechanisms remain poorly constrained, in part due to a relative dearth of highly resolved archives. Here we use the morphology of former shorelines preserved in beach-foredune ridges (BFR) within a protected embayment to reconstruct changes in predominant wave directions in the Subtropical South Atlantic during the last ~ 3000 years. These analyses reveal multi-centennial cycles of oscillation in predominant wave direction in accordance with stronger (weaker) South Atlantic mid- to high-latitudes mean sea-level pressure gradient and zonal westerly winds, favouring wave generation zones in higher (lower) latitudes and consequent southerly (easterly) wave components. We identify the Southern Annular Mode as the primary climate driver responsible for these changes. Long-term variations in interhemispheric surface temperature anomalies coexist with oscillations in wave direction, which indicates the influence of temperature-driven atmospheric teleconnections on wave-generation cycles. These results provide a novel geomorphic proxy for paleoenvironmental reconstructions and present new insights into the role of global multi-decadal to multi-centennial climate variability in controlling coastal-ocean wave climate.

Highlights

Through alteration of wave-generating atmospheric systems, global climate changes play a fundamental role in regional wave climate
From 850 CE until present, we investigate the variability in wave direction in comparison to decadal means of mid- to high-latitudes mean sea-level pressure gradients (∆MSLP) and zonal westerly wind velocities estimated from the CESM1-CAM5 “Last Millennium Ensemble (LME)”[42]
The response of waves to climate-change-associated atmospheric variability differs across ocean basins[2,3], highlighting the need for studies of long-term changes in wave climate at the regional-scale; our new approach developed here, relying on wave-energy and wave-direction changes preserved in the paleo beach-foredune ridges (BFR) orientations, presents a tool for these reconstructions

Summary

Introduction

Through alteration of wave-generating atmospheric systems, global climate changes play a fundamental role in regional wave climate. Long-term variations in interhemispheric surface temperature anomalies coexist with oscillations in wave direction, which indicates the influence of temperature-driven atmospheric teleconnections on wave-generation cycles These results provide a novel geomorphic proxy for paleoenvironmental reconstructions and present new insights into the role of global multi-decadal to multi-centennial climate variability in controlling coastal-ocean wave climate. We explore connections between oscillations in the predominant wave direction and forcing mechanisms influencing the wave generation In this manner, we use this morphology-based paleoclimate proxy to better constrain Late Holocene wave-climate variability within the understudied South Atlantic, and to support paleoceanographic studies by refining the relationship between leading atmospheric variability and long-term beach morphodynamics, extending those to protected, highly embayed, headlanddominated coasts

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Results

Conclusion