Temporal changes in the Red Sea circulation and associated water masses

Abstract

Long-term variability of the Red Sea deep water (RSDW) properties was investigated using hydrographic data stretching back to the beginning of the 19th century. The analysis of the potential temperature and salinity indicate that there is a signal of cooling and freshening trends between 1950 to 2011 in the RSDW by an average of 35.5 x10-4 ± 5.6x10-4 oC yr-1 and 13.8x10-4 ± 2.8x10-4 psu yr-1 respectively. Both trends of cooling and freshening are statistically significant with a confidence level of more than 95%. These cooling and freshening trends are consistent with the net heat loss trend in the three source regions for the deep water formation of the Red Sea by an average of -1.12 ± 0.49 Wm-2, -1.75 ± 0.49 Wm-2 and -1.58 ± 0.47 Wm-2 for the northern part of the Red Sea and the Gulfs of Suez and Aqaba respectively. The results suggest that the potential temperature and salinity seem to have decreased between 1950 and 2011 by as much as 0.12 oC and 0.13 psu respectively. These changes observed in the potential temperature and salinity in the RSDW are consistent throughout the Red Sea basin (subdivided into 2o grids) for the last three decades (1977-2011).
An inverse box model of the Red Sea is constructed using two hydrographic sections in the southern basin during August 2001 from research vessel (R/V) Maurice Ewing to provide quantification of the summer field fluxes (volume, heat and salt). The results show that the volume transport of the Red Sea outflow water (RSOW) to the Indian Ocean through the Strait of Bab el Mandeb is 0.11 ± 0.06 Sv (1 Sv = 106 m3 s-1). There is a heat loss by advection with a magnitude of 23.5 ± 5.7 W m-2 during a summer month (August) that fits well with the previous estimate by Patzert (1974b) with magnitude of 21.81 W m-2 and with magnitude of -22 Wm-2 based on data from i ii Sofianos et al. (2002). There is a salt loss by advection with a magnitude of 0.98 x109 kg s-1 this estimate is supported by the analysis of Tragou et al. (1999) which gives a magnitude of 0.8 x109 kg s-1.

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