Oceanographic Variability in Sir Bu Nair Island (Arabian/Persian Gulf) based on In Situ Observations

Cavalcante, G.H.; Vieira, F.; Bento, R.; Bartholomew, A., and Burt, J.A., 2024. Oceanographic variability in Sir Bu Nair Island (Arabian/Persian Gulf) based on in situ observations. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 412-416. Charlotte (North Carolina), ISSN 0749-0208. In the past decade, research on climatological and seasonal circulation patterns in the Persian/Arabian Gulf has primarily relied on numerical models, with limited emphasis on in situ observations. Although these models capture large-scale circulation patterns, such as the cyclonic gyre along the Iranian coast and the influx of Indian Ocean Surface Waters through the Strait of Hormuz, our understanding of the Gulf's local and regional oceanographic conditions remains insufficient. This gap is particularly evident around Sir Bu Nair Island (SBNI) in the central Gulf, a crucial area for coral larvae source, dispersion, and settlement patterns in southern Gulf reef communities. This study addresses this gap by investigating hydrodynamic conditions and water temperature variability near SBNI through comprehensive in situ observations conducted from 19 May to 1 July 2021. Results indicate substantial temporal variability marked by abrupt shifts in temperature and current speed/direction. Recorded water temperatures ranged from approximately 27.5 °C on 20 May to a peak of about 33.5 °C on 26 June. The maximum daily temperature amplitude reached ∼4.0 °C, observed between 24 May at 06:00h (28.5 °C) and 24 May at 11:00h (32.5 °C). Near-bottom temperatures consistently rose by approximately 4.0 °C from 7 June (28.15 °C) to 16 June (32.2 °C). Water flow exhibited vertical variations, with an average near-surface current speed (∼0.8 m/s) about twice as fast as the combined near-bottom and mid-water speed (0.3 to 0.4 m/s). Predominantly, the current direction is aligned with tidal ebb/flood flow. Analysis reveals that hydrodynamic conditions in SBNI are influenced not only by tidal currents at diurnal (∼24 h) and semi-diurnal (12.5 h) periods but also by the M4 overtide driving the quarter-diurnal ebbing/flooding transport of “cold/warm” water, and to a lesser extent by “weather-band” periods (2-4 days).