Understanding the landscape evolution of El Mogote barrier spit, Baja California Sur, Mexico, using OSL dating, satellite images and a multivariate analysis

Abstract

Barrier spits are natural archives that provide information about coastal evolution and prevailing environmental conditions of the mainland. In this study, we analyze one of the largest barrier spits in Baja California Sur, Mexico, known as El Mogote bar, using a multi-method approach to unravel the coastal landscape evolution. We used (1) OSL dating to provide a robust geochronology and depositional rates of the emerged beach-dune ridges, (2) satellite imagery interpretation using the Digital Shoreline Analysis System (DSAS) software to assess shoreline changes on Landsat images from 1986 to 2014, and (3) the Principal Component Analysis (PCA) with climatic and geomorphologic parameters to elucidate the environmental conditions of the beach-dune ridges for the period comprised in the DSAS analysis. OSL results indicate that the emerged bars started to form ∼2 ka and were developed in three main building phases: (1) the Medieval Warm Period (MWP) and part of the Little Ice Age (LIA) with accretional rates of 1.13 m yr −1, (2) the ending of the LIA with 7.03 m yr −1 and (3) the post-LIA with 3.98 m yr −1. In this paper, we hypothesize two probable causes that led to the destruction of the former beach-dune ridges: (1) tsunami waves triggered by seismic events and (2) local sea level rise associated with local tectonic subsidence. Satellite images and DSAS analysis show that, in the barrier spit, accretion and erosion have been in dynamic equilibrium for at least three decades. PCA results indicate that dry and cold weather conditions, El Niño modes, and tropical cyclone occurrence with high accretional rates on the barrier spit are the main controls on the beach-dune ridges. We conclude that the multi-method approach used in this research is suitable to tease out the landscape evolution of a barrier spit from a climatic and geomorphological perspective, as we were able to identify that the accretional episodes of El Mogote bar are mainly related to rainfall during the coldest and driest environmental conditions that enhance sediment supply from continental areas to the coast.