The annual cycle of vertical mixing and restratification in the Northern Gulf of Eilat/Aqaba (Red Sea) based on high temporal and vertical resolution observations

Daniel F. Carlson, Erick Fredj, Hezi Gildor*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

The stratification in the Northern Gulf of Eilat/Aqaba follows a well-known annual cycle of well-mixed conditions in winter, surface warming in spring and summer, maximum vertical temperature gradient in late summer, and erosion of stratification in fall. The strength and structure of the stratification influences the diverse coral reef ecosystem and also affects the strength of the semi-diurnal tidal currents. Long-term (13 months) moored thermistor data, combined with high temporal and vertical resolution density profiles in deep water, show that transitions from summer to fall and winter to spring/summer occur in unpredictable, pulses and are not slow and gradual, as previously deduced from monthly hydrographic measurements and numerical simulations forced by monthly climatologies. The cooling and deepening of the surface layer in fall is marked by a transition to large amplitude, semi-diurnal isotherm displacements in the stratified intermediate layer. Stratification is rebuilt in spring and summer by intermittent pulses of warm, buoyant water that can increase the upper 100-150. m by 2. °C that force surface waters down 100-150. m over a matter of days. The stratification also varies in response to short-lived eddies and diurnal motions during winter. Thus, the variability in the stratification exhibits strong depth and seasonal dependence and occurs over range of timescales: from tidal to seasonal. We show that monthly or weekly single-cast hydrographic data under-samples the variability of the stratification in the Gulf and we estimate the error associated with single-cast assessments of the stratification.

Original languageAmerican English
Pages (from-to)1-17
Number of pages17
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume84
DOIs
StatePublished - Feb 2014

Bibliographical note

Funding Information:
The authors would like to thank the scientists, students, and staff of the InterUniversity Institute for Marine Sciences in Eilat for their assistance. Stephen G. Monismith and Amatzia Genin helped with the moored observations and provided helpful discussion. Alexander Ostrovskii, Volodya Soloviev, Dima Shvoev, and Andrei Tsybulsky provided critical assistance with the Aqualog moored profiling carrier. The Port Authority in Eilat kindly accommodates one of the HF radar sites and Air Span provides the wireless communication between antenna sites. This research was partially funded by the Ministry of Science and Technology . The long-term, fixed-depth moorings were part of NATO project SfP982220 and the short-term fixed-depth moorings were deployed as part of the Red Sea–Dead Sea Water Conveyance Study Program funded by the World Bank .

Keywords

  • Gulf of Eilat/Aqaba
  • Internal waves
  • Israel
  • Marginal Seas
  • Middle East
  • Mixing
  • Red Sea
  • Stratification

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