Document Type : Original Article
Authors
1
Department of Nonliving Resources of Atmosphere and Ocean, Faculty of Marine Science and Technology, University of Hormozgan, Bandar Abbas, Iran
2
Associate Professor of Marine Physics, Department of Atmospheric and Oceanic Abiotic Sciences, Faculty of Marine Sciences and Arts, Hormozgan University, Bandar Abbas, Iran
10.30467/nivar.2024.444362.1283
Abstract
The Makran water basin includes the Gulf of Oman and part of the Arabian Sea, which is adjacent to the Indian Ocean.In this study, the surface temperature, salinity and density and vertical cross section of them related to a part of the Makran water basin(56.425-66.126°E;23.375-25.80°N)have been investigated.For this purpose, the World Ocean Atlas data set (2018) related to the National Oceanic and Atmospheric Organization of NOAA (abbreviated as WOA18) with the resolution of a quarter of a degree of latitude have been used as seasonal and annual averages.Using ArcGIS software, surface maps were plotted, and using Surfer software, cross-section maps were also illustrated, and vertical average profiles were plotted with the Grapher software as seasonally and annually averages. Sea Surface maps were contoured by spline interpolation. Cross-sectional maps were created from the surface to the depth of 2000 meters by the intervals of two degrees of latitude(four transects in total) and the distance between the grid station points was completed using IDW interpolation.The results show that density changes are largely dependent on salinity changes directly and temperature changes inversely.Seasonal and spatial changes of quantities are evident in Makran water basin. Also, the cross-sections show that the thermocline and halocline changes are dependent on each other and have a direct effect on the pycnocline changes. An increase in temperature causes a decrease in density, and an increase in salinity causes an increase in density, and as a result, the heavy layer falls down from the surface to a deeper part.Also, a significant difference in salinity can be seen in the west due to the presence of the Persian Gulf water mass (PGW) and in the east due to the river entrances and the occurrence of summer-time monsoon on this basin. Although the average annual sea surface density of Makran water basin is 24.5kg m-3, but its value decreases in the warm and rainy summer season. Moreover, the west of the Gulf of Oman is warmer and saltier than the east and shallow areas experience more temperature stress than the middle of the basin, which is deeper. In addition, the mixed layer (especially from the surface to a depth of 30 meters) is strongly affected by seasonal changes, and the difference between the warm summer season and the cool winter season can be seen well in the vertical profiles of the Makran water basin. The presence of the Persian Gulf water mass can be seen at a depth of 250 to 400 meters. In the deep layers with the depth of more than 1000 meters, the temperature has insignificant seasonal changes; but it decreases sharply and reaches a temperature of 4°C.The density also increases strongly and reaches more than 33 kg m-3.
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