Turbulence and Mixing in Stably Stratified Waters

104

In the Gulf of Aqaba, the northeasternmost segment of the Red Sea, phytoplankton blooms are more intense than in other oligotrophic regions (e.g., the Sargasso Sea). In this study, we use multiyear in situ (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) and Sea viewing Wide Field of View Sensor (SeaWiFS) (1999)(2000)(2001) chlorophyll a (Chl a) data to describe the dynamics of phytoplankton biomass throughout the Gulf of Aqaba. The temporal pattern of phytoplankton biomass in the Gulf of Aqaba includes a strong spring bloom and a somewhat weaker autumn bloom, the length, intensity, and timing of which vary from year to year. In addition, highly positive west-to-east (W to E) gradients in Chl a were found throughout the Gulf of Aqaba. A corresponding negative gradient in sea surface temperature (SST) obtained from MODerate resolution Imaging Spectroradiometer (MODIS) in 2001 indicates that the gradient of Chl a across the Gulf of Aqaba is an outcome of an Ekman-driven upwelling along the eastern side. Calculations of the upwelling and convective fluxes that are based on meteorological data from Eilat, Israel, indicate that upwelling is comparable to or exceeds convection during much of the year. We present a conceptual model demonstrating how upwelling and convection can either support or oppose each other, thereby jointly controlling mixed-layer depth and the development of phytoplankton blooms. Coastal upwelling plays a larger role in controlling phytoplankton dynamics than was previously thought, and it explains much of the observed spatial and temporal variability in phytoplankton distributions.

Section: Methodsmentioning

confidence: 99%

“…This relation assumes that 30% of the cooling flux results in mixing, a reasonable approximation for convective mixing (Sherman et al 1978).…”

Section: Methodsmentioning

confidence: 99%

The interplay between upwelling and deep convective mixing in determining the seasonal phytoplankton dynamics in the Gulf of Aqaba: Evidence from SeaWiFS and MODIS

Labiosa

Arrigo

Genin

et al. 2003

104

“…Surface layer dynamics are based on an integral turbulent kinetic energy model (Sherman et al 1978). The turbulent kinetic energy budget is partitioned into four discrete processes-wind stirring, convective overturn, interfacial shear production, and Kelvin-Helmholtz billowing.…”

Section: Lake Model With Artificial Destratificationmentioning

confidence: 99%

The physical response of temperate lakes to artificial destratification

Schladow

Fisher

1995

Prolonged periods of thermal stratification in a lake suppress convective motions capable of vertical Prolonged periods of thermal stratification in a lake suppress convective motions capable of vertical transport of dissolved oxygen and other dissolved and suspended matter. When this leads to anoxia in the transport of dissolved oxygen and other dissolved and suspended matter. When this leads to anoxia in the hypolimnion, it can give rise to profound water quality implications. Artificial destratification is one means hypolimnion, it can give rise to profound water quality implications. Artificial destratification is one means whereby low oxygen levels in the hypolimnion may be averted. The operating principles of bubble plume whereby low oxygen levels in the hypolimnion may be averted. The operating principles of bubble plume destratification and its effect on the physical transport and mixing that occurs in a lake are described. destratification and its effect on the physical transport and mixing that occurs in a lake are described. Monitoring of temperature and dissolved oxygen was conducted at Lake Nepean, Australia, prior to the Monitoring of temperature and dissolved oxygen was conducted at Lake Nepean, Australia, prior to the destratification, and then continued for two summers while the destratification system was operating. The destratification, and then continued for two summers while the destratification system was operating. The results showed that artificial destratification had an immediate effect on lake motions across a range of scales. results showed that artificial destratification had an immediate effect on lake motions across a range of scales. The actual process of destratification occurred by the erosion of the base of the thermocline. Deep-water The actual process of destratification occurred by the erosion of the base of the thermocline. Deep-water temperatures were elevated well above historical values, the heat storage in the lake increased, and the time temperatures were elevated well above historical values, the heat storage in the lake increased, and the time of turnover was brought forward 2.5 months. An integral plume model coupled with a one-dimensional lake of turnover was brought forward 2.5 months. An integral plume model coupled with a one-dimensional lake model is shown to predict the effect of the bubble plume entrainment and the subsequent redistribution of model is shown to predict the effect of the bubble plume entrainment and the subsequent redistribution of the entrained water throughout the lake.The natural stratification that exists in most temperate lakes for a large part of the year effectively cuts off the hypolimnetic water from contact with the atmosphere and, hence, from a major source of oxygen. When this is coupled with generally increasing levels of nutrient input and the resulting increase in primary productivity (OECD 1982) there is a growing tendency for hypolimnetic water to become anoxic for significant periods of time. Aside from the...

“…A parameterization of the entrainment that is valid in both the stirring or shear production regimes has been used to provide E in Eq. 4 (Sherman et al 1978). Dallimore et al (2004) coupled the underflow model described in Sherman et al (1978) with the 3D lake hydrodynamic Estuary Lake and Coastal Ocean Model (ELCOM) (Hodges et al 2000) and compared model results to field observations.…”

mentioning

confidence: 99%

Mixing of an interflow into the ambient water of Lake Iseo

Hogg

Marti

Huppert

et al. 2013

River water flowing as an interflow was investigated using field data, collected in Lake Iseo (Italy), and theory. A theory for the lateral falling mechanism of plunging was developed for inflows when the initial densimetric Froude number (Fr 0 ) is slightly larger than unity. The ratio of the river width to the offshore extent of the plunge region was equal to Fr 0 . The mixing ratio in the plunge region was 0.06. Theoretical results were quantitatively consistent with the length scale and mixing ratio of the observed plunge region. The progression of the inflow was interpreted as: initially a laterally falling plunge region with little mixing; followed by a steep underflow region with substantial mixing; and finally an intrusion. The intrusion was at first controlled dynamically by an inertiabuoyancy force balance. Further from the liftoff point, turbulent mixing effects dominated over those due to inertia. Ultimately, the intrusion diffused into the adjacent layers in such a way that the interflow fluid was effectively indistinguishable from the lake water.