Amazon Plume Salinity Response to Ocean Teleconnections

Pedro Tyaquiçã,Jacques Servain,Nathalie Lefèvre,Guy Caniaux,Doris Veleda,Thiago Silva,Moacyr Araujo,Carlos Noriega

doi:10.3389/fmars.2017.00250

Abstract

Pacific and Atlantic sea surface temperature (SST) variability strongly influences rainfall changes in the Amazon River basin, which impacts on the river discharge and consequently the sea surface salinity (SSS) in the Amazon plume. An Empirical Orthogonal Function (EOF) analysis was performed using 46 years of SST, rainfall, and SSS datasets, in order to establish the relationship between these variables. The first three modes of SST/rainfall explained 87.83% of the total covariance. Pacific and Atlantic SSTs led Amazon basin rainfall events by four months. The resultant SSS in the western tropical North Atlantic (WTNA) lagged behind basin rainfall by three months, with 75.04% of the total covariance corresponding to the first four EOF modes. The first EOF mode indicated a strong SSS pattern along the coast that was connected to negative rainfall anomalies covering the Amazon basin, linked to El Nino events. A second pattern also presented positive SSS anomalies, when the rainfall was predominantly over the northwestern part of the Amazon basin, with low rainfall around the Amazon River mouth. The pattern with negative SSS anomalies in the WTNA was associated with the fourth mode, when positive rainfall anomalies were concentrated in the northwest part of South America. The spatial rainfall structure of this fourth mode was associated with the spatial rainfall distribution found in the third EOF mode of SST vs rainfall, which was a response to La Nina Modoki events. A statistical analysis for the 46 year period and monthly anomaly composites for 2008 and 2009 indicated that La Nina Modoki events can be used for the prediction of low SSS patterns in the WNTA.

Highlights

Ocean salinity is an indicator of changes in the global hydrological cycle and large-scale climate variability (Du et al, 2015)
Based on the detection of the principal Empirical Orthogonal Function (EOF) analysis modes, this study identified the coupled modes of variability between sea surface temperature (SST) and rainfall over the Amazon basin, and between Amazon rainfall and sea surface salinity (SSS) over the Amazon plume in the western tropical North Atlantic (WTNA) to better understand the climate impacts on biogeochemical cycles in the WTNA
We used 46 years of ocean and atmospheric reanalysis data to show that interannual Pacific and Atlantic SST patterns can lead to different rainfall responses over the Amazon basin and, can drive different interannual patterns in the SSS over the WTNA

Summary

Introduction

Ocean salinity is an indicator of changes in the global hydrological cycle and large-scale climate variability (Du et al, 2015). The spatial distribution of sea surface salinity (SSS) in the global ocean reflects the pattern of air-sea freshwater fluxes, evaporation and precipitation, heat, momentum, solubility, and the biological pump (Geider et al, 2001; Yu et al, 2007; Schmitt, 2008; Du et al, 2015). Amazon Plume Salinity Answers Teleconnections in salinity patterns indicate where terrestrial and marine systems mix, which is where nutrients are distributed, and in turn impacts on the production of coastal and oceanic ecosystems (Smith and Demaster, 1996; Araujo et al, 2014). The low salinity Amazon plume creates a nearsurface barrier layer that inhibits mixing, increases the sea surface temperature (SST), and enhances salinity stratification; preventing vertical mixing between the upper warm mixed layer and the cold deep ocean (Ferry and Reverdin, 2004; Balaguru et al, 2012; Grodsky et al, 2012; Coles et al, 2013)

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