Atmospheric Forcing of the High and Low Extremes in the Sea Surface Temperature over the Red Sea and Associated Chlorophyll-a Concentration

Kamal A Alawad,Turki M Alraddadi,Mohammed A Alsaafani,Abdullah M Al-Subhi

doi:10.3390/rs12142227

Kamal A Alawad, Turki M Alraddadi + Show 2 more

Open Access

https://doi.org/10.3390/rs12142227

Copy DOI

Abstract

Taking advantage of 37-year-long (1982–2018) of high-quality satellite datasets, we examined the role of direct atmospheric forcing on the high and low sea surface temperature (SST) extremes over the Red Sea (RS). Considering the importance of SST in regulating ocean physics and biology, the associated impacts on chlorophyll (Chl-a) concentration were also explored, since a small change in SST can cause a significant impact in the ocean. After describing the climate features, we classified the top 5% of SST values (≥31.5 °C) as extreme high events (EHEs) during the boreal summer period and the lowest SST values (≤22.8 °C) as extreme low events (ELEs) during the boreal winter period. The spatiotemporal analysis showed that the EHEs (ELEs) were observed over the southern (northern) basin, with a significant warming trend of 0.027 (0.021) °C year−1, respectively. The EHEs were observed when there was widespread less than average sea level pressure (SLP) over southern Europe, northeast Africa, and Middle East, including in the RS, leading to the cold wind stress from Europe being relatively less than usual and the intrusion of stronger than usual relatively warm air mass from central Sudan throughout the Tokar Gap. Conversely, EHEs were observed when above average SLP prevailed over southern Europe and the Mediterranean Sea as a result of the Azores high and westward extension of the Siberian anticyclone, which led to above average transfer of cold and dry wind stress from higher latitudes. At the same time, notably less wind stress due to southerlies that transfer warm and humid air masses northward was observed. Furthermore, physical and biological responses related to extreme stress showed distinct ocean patterns associated with each event. It was found that the Chl-a concentration anomalies over the northern basin caused by vertical nutrient transport through deep upwelling processes are the manifestation of the superimposition of ELEs. The situation was the opposite for EHEs due to the stably stratified ocean boundary layer, which is a well-known consequence of global warming.

Highlights

An extreme sea surface temperature (SST) event is an important oceanographical phenomenon, which can have a serious impact on biodiversity and may result in consequences that are, as yet, unrecognized in marine ecosystems, especially under a climate change background
To obtain background information about the atmospheric circulation that influences the extreme SST in the Red Sea (RS), we present the climatology shown in the mean sea level pressure (SLP) and wind stress maps
We focused on the summer and winter months only, since extreme high events (EHEs) and extreme low events (ELEs) are likely to take place during the hottest and coldest seasons of the year

Summary

Introduction

An extreme sea surface temperature (SST) event is an important oceanographical phenomenon, which can have a serious impact on biodiversity and may result in consequences that are, as yet, unrecognized in marine ecosystems, especially under a climate change background. These events alter the frequency and intensity of blooms, reduce the deep-water nutrient flux to surface waters, and change the global food chain, which may create a suitable environment for pathogenic microbes [1,2,3,4]. The polar amplification property has meant that the SST and air temperature over the mid and high latitude of the northern hemisphere have been increasing faster than the tropical basins [13,14] while the shallow waters, such as semi-enclosed basins like the Red Sea (RS), may display larger variation compared with deep and/or open-water areas [15]

Objectives

Methods

Results

Conclusion