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

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 stratifica...

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Bibliographic Details
Published in:Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2014-02, Vol.84, p.1-17
Main Authors: Carlson, Daniel F., Fredj, Erick, Gildor, Hezi
Format: Article
Language:English
Subjects:
Aquatic ecosystems
Coastal oceanography, estuaries. Regional oceanography
Earth, ocean, space
Exact sciences and technology
External geophysics
Gulf of Eilat/Aqaba
Hydrography
Internal waves
Israel
Marginal Seas
Middle East
Mixing
Ocean currents
Oceanography
Physics of the oceans
Red Sea
Stratification
Stratigraphy
Temperature
Thermohaline structure and circulation. Turbulence and diffusion
Transitions
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Summary: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 100–150m by 2°C that force surface waters down 100–150m 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. •The majority of stratification variability occurs on timescales of 10 days or less.•Seasonal transitions are not gradual but marked by large temperature variability.•Large isotherm displacements are driven by internal tide and diurnal motions.•Spring advected heat pulses can displace surface waters and disrupt internal tide.
ISSN:0967-0637
1879-0119
DOI:10.1016/j.dsr.2013.10.004