Summer hydrographic characteristics in the northern ROPME Sea Area: Role of ocean circulation and water masses

Abstract

Spatial distributions of hydrographic variables, nutrients (nitrate, phosphate, and silicic acid), and chlorophyll-a in the surface layer of the northern Arabian/Persian Gulf (here after referred as northern ROPME Sea Area, NRSA) in summer are presented in this study. Water samples were obtained from 33 stations along six transects located between the State of Kuwait and Iran in the north, and the State of Qatar and Iran in the south. Multivariate analysis of the data sets displayed the presence of four discrete water masses with distinct hydrographic characteristics: Kuwait's Coastal Waters (KCW), Northern Gulf Waters (NGW), Central Arabian Coastal Waters (CACW), and Indian Ocean Surface Waters (IOSW). These water masses exhibited low phytoplankton concentrations (as indicated by chlorophyll-a, range: 0.1–1.5 μg l−1), and wide variability in nutrient distributions (nitrate: not detectable concentration (ND)-10.0 μM, phosphate: ND-3.5 μM, silicic acid: ND-10.8 μM). Each water mass was characterized by locally elevated nutrients, indicating the importance of local events and point sources influencing nutrient distribution patterns in the NRSA. The current patterns, which are characterized by inverse-estuarine circulation in the Gulf, spatially structured these water masses, indicating a significant role of hydrodynamics governing the nutrient and phytoplankton distribution in the NRSA. This study offers the first report in decades on spatial hydrographic characteristics including nutrients in the NRSA. Continuous collaborative sampling efforts by ROPME (Regional Organization for the Protection of the Marine Environment) member states would further enhance our understanding of the changing oceanographic conditions in this important yet scientifically poorly explored marginal sea in the northwestern Indian Ocean.