Temporal evolution of temperatures in the Red Sea and the Gulf of Aden based on in situ observations (1958–2017)

Abstract

Abstract. The Red Sea holds one of the most diverse marine ecosystems in the world, although fragile and vulnerable to ocean warming. Several studies have analysed the spatio-temporal evolution of temperature in the Red Sea using satellite data, thus focusing only on the surface layer and covering the last ∼30 years. To better understand the long-term variability and trends of temperature in the whole water column, we produce a 3-D gridded temperature product (TEMPERSEA) for the period 1958–2017, based on a large number of in situ observations, covering the Red Sea and the Gulf of Aden. After a specific quality control, a mapping algorithm based on optimal interpolation have been applied to homogenize the data. Also, an estimate of the uncertainties of the product has been generated. The calibration of the algorithm and the uncertainty computation has been done through sensitivity experiments based on synthetic data from a realistic numerical simulation. TEMPERSEA has been compared to satellite observations of sea surface temperature for the period 1981–2017, showing good agreement especially in those periods when a reasonable number of observations were available. Also, very good agreement has been found between air temperatures and reconstructed sea temperatures in the upper 100 m for the whole period 1958–2017, enhancing confidence in the quality of the product. The product has been used to characterize the spatio-temporal variability of the temperature field in the Red Sea and the Gulf of Aden at different timescales (seasonal, interannual and multidecadal). Clear differences have been found between the two regions suggesting that the Red Sea variability is mainly driven by air–sea interactions, while in the Gulf of Aden the lateral advection of water plays a relevant role. Regarding long-term evolution, our results show only positive trends above 40 m depth, with maximum trends of 0.045 + 0.016 ∘C decade−1 at 15 m, and the largest negative trends at 125 m (-0.072+0.011 ∘C decade−1). Multidecadal variations have a strong impact on the trend computation and restricting them to the last 30–40 years of data can bias high the trend estimates.

Deoxygenation in Marginal Seas of the Indian Ocean

“…Satellite remote-sensed SST data have revealed a warming trend with values ranging from 0.17 to 0.45 • C decade −1 across the Red Sea basin for the period 1982-2015 (Chaidez et al, 2017). However, the analysis of available water column data for the period 1958-2017 showed a more complex pattern -a steady decrease in SST from the 1960s up to the mid-1980s and an increasing trend thereafter (Agulles et al, 2020). It has been suggested that the long-term SST oscillations may be associated with the Atlantic Multidecadal Oscillation (AMO) and that the abovementioned high warming rates over the past three decades or so are probably a combined effect of global warming and a positive phase of natural SST oscillations (Krokos et al, 2019).…”

“…According to Krokos et al (2019) the cooling AMO phase may offset the global warming related SST increase in the Red Sea in the future. What is really intriguing is that the temporal trends in subsurface water temperatures appear to be decoupled to the SST trend, showing an overall cooling trend in deep waters during 1958-2017 (Agulles et al, 2020). The data compiled by Agulles et al (2020) show that since the time of the Sagar Kanya cruise the 100-500 m layer cooled up to mid 1990s and has been warming thereafter; the deeper waters showed a similar pattern, except that the minimum occurred a little later (in the late 1990s) and the subsequent warming has been more subdued.…”

“…What is really intriguing is that the temporal trends in subsurface water temperatures appear to be decoupled to the SST trend, showing an overall cooling trend in deep waters during 1958-2017 (Agulles et al, 2020). The data compiled by Agulles et al (2020) show that since the time of the Sagar Kanya cruise the 100-500 m layer cooled up to mid 1990s and has been warming thereafter; the deeper waters showed a similar pattern, except that the minimum occurred a little later (in the late 1990s) and the subsequent warming has been more subdued. It is hard to reconcile the observed deoxygenation in deep waters of the Red Sea with these temperature variations, but it is clear that the oxygen decrease cannot be simply attributed to decreased solubility in warmer water.…”

Flexibility in Red Sea Tridacna maxima‐Symbiodiniaceae associations supports environmental niche adaptation

“…The clams collected had an average length of 15.7 cm + − 0.8 (+-SD) which corresponds to sexually mature individuals (Manu & Sone, 1995 1a). In covering a wide range of latitudes along the Red Sea coast, the sampling sites also reflect distinct environmental settings with regard to temperature (Figure 1c) and salinity (Figure 1d), which display pronounced latitudinal gradients in the region that negatively covary (Agulles et al, 2020;Chaidez et al, 2017;Ngugi et al, 2012).…”

“…Pappas et al, investigated 207 samples, from nine sites, all located at 22°N at the eastern coast of the central Red Sea and within 28 km of the “Thuwal” site from this study (given their proximity to each other, these nine sites will hereafter be referred to as a single site, “Thuwal”), while Weber analyzed samples from a total of 20 clams, originating from four sites, of which two were located in the Gulf of Aqaba at 27° (Ras Nasrani) and 28°N (Dahab), and two off the Egyptian coast in the North‐western Red Sea at a latitude of 25° (El Qeseir) and 27° (Hurghada), respectively (Figure 1). Given the extraordinary latitudinal hydrographical gradients that exist in the Red Sea (Agulles et al., 2020; Arz et al., 2003; Berumen et al., 2019; Chaidez et al., 2017), the coverage thus far available provides a limited representation of the region. Here we build on these prior characterizations using the ITS2 marker and the SymPortal framework to conduct a fine‐scale characterization of Symbiodiniaceae associations in Red Sea T. maxima giant clams across the Red Sea's North‐South gradient (from the Gulf of Aqaba at a latitude of 29°N to the Farasan Banks at 18°N), covering 1,300 km of overwater distance, and environmental differences.…”