Seasonal variability of hydrographical properties of the Syrian marine water
2011
Hussein, Mohammad | Courp, Thierry | Ibrahim, Amir | Benkhelil, Jean
The hydrographical properties of the Syrian marine water are described on the basis of three cruises performed during December 2006, March 2009 and October 2009. In all cruises a Conductivity-Temperature-Depth (CTD) instrument equipped with a fluorometer and oxygen sensor was used for casts that extended to a maximum depth of 480m. The hydrographic data reveal the presence of Levantine Surface Water (LSW) and Atlantic Water (AW) within the upper 90m layer, Levantine Intermediate Water (LIW) between 90 and 250m, and Deep Water (DW) further below. Stratification was clearer in October and December compared to March. Cyclonic and anticyclonic eddies were observed during the three cruises at different locations situated along the Syrian coast. The flow structure along the Syrian coast is controlled by the shape of the coastline and the bottom topography of the continental shelf. From March 2009 to October 2009 a dynamic height rise (within 6months) of about 3.7–9.8cm reflected the seasonal cycle of sea level due mainly to thermosteric expansion of the water column. This gave a rise rate in the range of 0.6–1.7cmmonth⁻¹. Dissolved oxygen was higher in March 2009 (214±4.8μM) than in December 2006 (202±11.5μM) or in October 2009 (188±18.9μM). During March 2009 the water column oxygen distribution was homogeneous. In December 2006 the oxygen distribution was homogeneous in the upper 125m where LSW was present and subsequently decreased in concentration due to bacterial oxidation of detritus. However, a shallow oxygen maximum (oversaturated) was present at 50–80m depth during October 2009. Oversaturation was attributed mainly to the biological and physical processes of rapid capping and trapping of oxygen in the AW mass. Chlorophyll-a concentration varied substantially depending on depth and season, having values of 0.05±0.01mgm⁻³ during December 2006, 0.08±0.01mgm⁻³ during March 2009 and 0.06±0.01mgm⁻³ during October 2009. The deep Chl-a maxima, of 0.08mgm⁻³ during December 2006, 0.1mgm⁻³ during March 2009 and 0.12mgm⁻³ during October 2009, were observed at 50–100m. These Chl-a maxima were associated with cyclonic and anticyclonic eddies at 40–75m and at 80–105m, during December 2006 and March 2009, respectively, and along all the stations sampled in October 2009. Comparisons of Chl-a estimates during December 2006 with the Sea-viewing Wide Field of view Sensor (SeaWiFS) and in situ measurements revealed a significant correlation of r²=0.82 and showed that the study region is the most oligotrophic in the Mediterranean sea.
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