Biogeophysical setting of the Gulf

Abstract

The Gulf is a semi-enclosed sea (total area 240,000 km²) situated in the subtropical high-pressure-zone and thus characterized by low precipitation and high aridity, resulting in evaporation rates above 2000 mm yr⁻¹ (Barth 1998). It is a shallow sedimentary basin, about 1000 km long and between 200 and 330 km wide. The average depth is presently 35 m with a generally eastward dipping seafloor. The deepest areas are in front of the Iranian coast, reaching from 60 m to about 100 m at the entrance to the Strait of Hormuz. Thus, the whole Gulf lies within the photic zone. The shoreline at the Arabian side displays a gradual slope with a wide intertidal zone, compared to the steep and narrow shoreline at the Iranian side where the Zagros mountains rise more than 2000 m. As a consequence of the gradual topography and of the favourable environment to carbonate producing biota, the Gulf is a strongly sedimentary province with a dominating soft substrate benthos. Sediments of biogenic carbonates - mostly foraminifera - exist over much of the Gulf floor (Sheppard et al. 1992). Highest carbonate concentrations are to be found in the shallow waters of the western and southern Gulf (Fig. 1). Within a depositional setting along the southern Gulf coast the offshore bank is progressively extending (Kendall et al. 2002). Terrestrial sediments are limited to the northwest where the waterway of the Shatt al Arab discharges into the Gulf, and the eastern Iranian shoreline where terrestrial fluvial sediments from the Zagros mountains occasionally are accumulated in the nearshore region. Offshore, underlying salt domes have forced upwards numerous islands and banks of hard substrate which are now colonized by corals.