scholarly journals Definitive evidence of the Mediterranean Outflow heterogeneity. Part 2: all along the Strait of Gibraltar

2017 ◽  
Author(s):  
Claude Millot
Keyword(s):  
Time Series ◽  
Direct Consequence ◽  
Major Effect ◽  
Similar Data ◽  
Density Range ◽  
Significant Information ◽  
Left Hand ◽  
Definitive Evidence ◽  
Mediterranean Outflow ◽  
The Mediterranean

Abstract. We have demonstrated in Part 1, with only a CTD transect across the Strait at 6°05' W, that the Mediterranean Outflow (MO) was definitely heterogeneous there. A yo-yo CTD time series has also provided astounding examples of both the marked layering that the Mediterranean Waters (MWs) display on the vertical at the Strait entrance (5°43' W), i.e. just upstream from the Camarinal sills (5°45' W), as well as the tremendous instability processes occurring in all layers. We focus herein on similar data collected within the Strait at both 5°50' W and 6°05' W (downstream from the Camarinal and Espartel sills, resp.) during five campaigns of the 1985–1986 GIBEX. We first show additional transects supporting the demonstration we made at 6°05' W, and we demonstrate that the marked heterogeneity of the MO within the Strait is clearly on the horizontal; as we expected, densest (resp. lightest) MWs flow on the bottom on its left-hand (resp. right-hand) side and all MWs are juxtaposed side by side. We also demonstrate that the density range within the MO in the western side of the Strait (6°05' W) is at least 0.5 kg m−3, which is the density range, in the vicinity of the Cape St Vincent (8°30' W), of the four veins formed by the MO splitting. We show that the lightest component of the MO has started to be split as soon as Camarinal sills and sink all along the Strait. The splitting of the MO into veins is thus mainly due to its intrinsic heterogeneity, which is a direct consequence of the Sea functioning and of the mixing, within the Strait itself, of the MO with this or that type of Atlantic Waters (AWs). Therefore, the bathymetry in the Strait, and even in the Strait exit surroundings (near 6°20' W), has no major effect on the MO characteristics in the whole Ocean. We also focus on a yo-yo CTD time series collected during ~24 h at 6°05' W which shows that markedly different MWs have been passing by, clearly demonstrating that the horizontally heterogeneous MO is significantly meandering within the Strait. Finally, we confirm one of our previous results that, provided the temporal variabilities of both the MWs and the AWs are not too large, significant relationships can possibly be established between the characteristics of the MWs at the Strait extremities, or at least that the slope of the mixing lines on a q-S diagram provides significant information. Parts 1 and 2 of our trilogy must be assimilated before reading Part 3.

scholarly journals Definitive evidence of the Mediterranean Outflow heterogeneity. Part 1: at the Strait of Gibraltar entrance

2017 ◽  
Author(s):  
Claude Millot
Keyword(s):  
Direct Consequence ◽  
Coriolis Effect ◽  
Strait Of Gibraltar ◽  
Hydrological Characteristics ◽  
Definitive Evidence ◽  
Mediterranean Outflow ◽  
The Mediterranean ◽  
Western Side ◽  
First Time ◽  
Theoretical Analyses

Abstract. All most recent papers about the Mediterranean Outflow (MO) assume that it is homogeneous at least in the western side of the Strait of Gibraltar and that its splitting into veins in the Atlantic Ocean is due to bathymetric effects at the Strait exit while we demonstrate that proofs about the MO heterogeneity within the whole Strait have been available since the mid 1980's at least. We focus herein on data collected at the Strait entrance in 1985 (Part 1), before analyzing 1985–1986 data within the Strait (Part 2) and data collected during the MO-2009 experiment at the Strait exit (Part 3). Having demonstrated that the MO is markedly heterogeneous from the Strait entrance to the Strait exit, our three papers demonstrate that the splitting into veins is essentially a direct consequence of the sea functioning. Indeed, veins have hydrological characteristics mainly dependent on those of the intermediate and deep Mediterranean Waters (MWs) formed in both the eastern and the western basins of the Sea, as well as on those of the Atlantic Waters (AWs) that mixed in the Strait with these MWs, the bathymetry at and downstream from the Strait exit playing a negligible role. Herein, we demonstrate that four-five MWs can be clearly identified at the Strait entrance, as we previously hypothesized, moreover forming relatively thick and homogeneous superimposed layers that are much more individualized than anywhere else in the Sea. For the first time ever, we provide numerous examples of density instabilities in all these layers that clearly illustrate the processes leading to such an increased stratification at the Strait entrance. So as to motivate theoretical analyses and numerical simulations that appear to be of dramatic interest, we hypothesize that the isopycnals slope (of a few %) across the Strait within the MO itself, that is a direct consequence of both the Coriolis effect and the different outflowing or overflowing velocities of the MWs, could be the main mechanism responsible for such a layering of the MO.

scholarly journals Definitive evidence of the Mediterranean Outflow heterogeneity. Part 3: at the Strait of Gibraltar exit

2017 ◽  
Author(s):  
Claude Millot ◽  
Mikhail Emelianov
Keyword(s):  
Time Series ◽  
Sampling Interval ◽  
Single Pair ◽  
Density Range ◽  
Mixing Processes ◽  
Data Set ◽  
The North ◽  
Mediterranean Outflow ◽  
The Mediterranean ◽  
Interface Layers

Abstract. We have pursued, in Parts 1 and 2, the re-analysis of the 1985–1986 GIBEX CTD data we initiated in the mid 2000's with a focus on the Mediterranean Outflow (MO) heterogeneity. At the Strait entrance (Part 1), a transect (5°40' W) and a yo-yo time series (5°43' W) show Mediterranean Waters (MWs) markedly stratified into relatively homogeneous layers where intense mixing processes occur, hence definitively showing that the MO there is composed of four-five different and essentially superimposed components. Within the Strait (Part 2), five north-south transects at both 5°50' W and 6°05' W, together with another yo-yo time series (6°05' W), show that the MO is markedly heterogeneous all along the Strait, but there on the horizontal, being composed of a set of different components juxtaposed side by side. All temperature-salinity diagrams from these transects are straight mixing lines between the Atlantic Waters (AWs) and each of the MWs, most of them evidence bottom homogeneous layers, the lightest of the MWs is split and starts sinking as soon as the Camarinal sills in the northern side of the Strait while the densest MWs are in its southern side, the MO has an overall density range > 0.5 kg m−3 and it is markedly meandering at 6°05' W, and the AWs' variability is much larger than that of the MWs, which prevents from accurately specifying the MO characteristics downstream. Herein (Part 3) we re-analyze the whole CTD data set from the MO-2009 Experiment that was conducted at the Strait exit (near 6°20' W) by the Institut de Ciències del Mar from Barcelona (Spain) in order to specify the downstream momentum and energy evolution of the MO and investigate the mechanisms leading to its structure. Even without the above-mentioned results and our previous hypotheses in mind, 418 CTD profiles combining regional surveys (over 30 × 30 km2), repeated tow-yo transects (over ~6 km) performed with a relatively low sampling interval (~1 km) in cross-MO and along-MO directions, and yo-yo time series, provide valuable information about the hydrological structure of the MO there. Four components, with the lightest (densest) in the north (south), clearly juxtaposed side by side and relatively isolated from each others, being often separated by marked interface layers, spread over a ~0.7 kg m−3 density range. Yo-yo time series confirm that short-term variability at a given place is essentially due to the MO meandering that allows evidencing locally two (up to three and even four) components, and density ranges up to 0.3 kg m−3 within a couple of hours, which demonstrates that the MO heterogeneity is mainly due to the Sea functioning and the AWs-MWs mixing, its splitting does not needing any bathymetric effect. The fact that any of the four components can be missed with profiles 1 km apart accounts for their relatively small wideness and we claim that a single pair of tow and tow-yo (at a few-hundred m interval) cross-Strait transects performed near 6°20' W with basic instrumentation will provide definite information about the MO heterogeneity.

scholarly journals About the seasonal and fortnightly variabilities of the Mediterranean outflow

2010 ◽  
Vol 7 (6) ◽  
pp. 2043-2058
Author(s):  
C. Millot ◽  
J. Garcia-Lafuente
Keyword(s):  
Time Series ◽  
Spatial Heterogeneity ◽  
Seasonal Variability ◽  
Internal Tide ◽  
Atlantic Water ◽  
Strait Of Gibraltar ◽  
Mediterranean Outflow ◽  
The Mediterranean

Abstract. CTD time series from the HYDRO-CHANGES programme and INGRES projects have been collected simultaneously (2004–2008) on the Moroccan shelf and at the Camarinal and Espartel Sills in the strait of Gibraltar. They provide information that supports results recently obtained from the analysis of the two former time series, as well as from a reanalysis of CTD GIBEX profiles (1985–1986). The outflow of Mediterranean Waters, which does not show a clear seasonal variability before entering the strait, strongly mixes within the strait, due mainly to the internal tide, with the seasonally variable inflow of Atlantic Water. The outflow thus gets marked seasonal and fortnightly variabilities within the strait. Furthermore, since the outflow entering the strait displays marked spatial heterogeneity and long-term temporal variabilities, predicting its characteristics when in the ocean appears almost impossible.

scholarly journals About the seasonal and fortnightly variabilities of the Mediterranean outflow

Ocean Science ◽  
2011 ◽  
Vol 7 (3) ◽  
pp. 421-428 ◽  
Author(s):  
C. Millot ◽  
J. Garcia-Lafuente
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Internal Tide ◽  
Atlantic Water ◽  
Strait Of Gibraltar ◽  
The North ◽  
Mediterranean Outflow ◽  
The Mediterranean

Abstract. CTD time series from the HYDRO-CHANGES programme and INGRES projects have been collected simultaneously (2004–2008) on the shelf of Morocco and at the sills of Camarinal and Espartel in the strait of Gibraltar. They provide information that supports results recently obtained from the analysis of the two former time series, as well as from a reanalysis of GIBEX CTD profiles (1985–1986). The outflow of Mediterranean Waters, which does not show a clear seasonal variability before entering the strait, strongly mixes within the strait, due mainly to the internal tide, with the seasonally variable inflow of Atlantic Water. The outflow thus gets marked seasonal and fortnightly variabilities within the strait. Furthermore, since the outflowing waters entering the strait display marked spatial heterogeneity and long-term temporal variabilities, accurately predicting the characteristics of the Mediterranean outflow into the North Atlantic Ocean appears almost impossible.

DEVELOPMENT OF STREAMFLOW DROUGHT INDICES IN THE MORAVA RIVER BASIN

2020 ◽  
Author(s):  
Ondrej Ledvinka ◽  
◽  
Pavel Coufal ◽  
Keyword(s):  
Time Series ◽  
Kendall Test ◽  
Drought Indices ◽  
Drought Period ◽  
Left Hand ◽  
Low Flows ◽  
Current Period ◽  
Catchment Size ◽  
Morava River ◽  
The Stability

The territory of Czechia currently suffers from a long-lasting drought period which has been a subject of many studies, including the hydrological ones. Previous works indicated that the basin of the Morava River, a left-hand tributary of the Danube, is very prone to the occurrence of dry spells. It also applies to the development of various hydrological time series that often show decreases in the amount of available water. The purpose of this contribution is to extend the results of studies performed earlier and, using the most updated daily time series of discharge, to look at the situation of the so-called streamflow drought within the basin. 46 water-gauging stations representing the rivers of diverse catchment size were selected where no or a very weak anthropogenic influences are expected and the stability and sensitivity of profiles allow for the proper measurement of low flows. The selected series had to cover the most current period 1981-2018 but they could be much longer, which was considered beneficial for the next determination of the development direction. Various series of drought indices were derived from the original discharge series. Specifically, 7-, 15- and 30-day low flows together with deficit volumes and their durations were tested for trends using the modifications of the Mann– Kendall test that account for short-term and long-term persistence. In order to better reflect the drivers of streamflow drought, the indices were considered for summer and winter seasons separately as well. The places with the situation critical to the future water resources management were highlighted where substantial changes in river regime occur probably due to climate factors. Finally, the current drought episode that started in 2014 was put into a wider context, making use of the information obtained by the analyses.

scholarly journals Latest Miocene restriction of the Mediterranean Outflow Water: a perspective from the Gulf of Cádiz

2021 ◽  
Vol 41 (2) ◽  
Author(s):  
Zhi Lin Ng ◽  
F. Javier Hernández-Molina ◽  
Débora Duarte ◽  
Francisco J. Sierro ◽  
Santiago Ledesma ◽  
...  
Keyword(s):  
Mass Exchange ◽  
Water Mass ◽  
Atlantic Water ◽  
Meridional Overturning Circulation ◽  
Gulf Of Cadiz ◽  
Mediterranean Outflow Water ◽  
Gulf Of Cádiz ◽  
Mediterranean Outflow ◽  
The Mediterranean ◽  
Water Mass Exchange

AbstractThe Mediterranean-Atlantic water mass exchange provides the ideal setting for deciphering the role of gateway evolution in ocean circulation. However, the dynamics of Mediterranean Outflow Water (MOW) during the closure of the Late Miocene Mediterranean-Atlantic gateways are poorly understood. Here, we define the sedimentary evolution of Neogene basins from the Gulf of Cádiz to the West Iberian margin to investigate MOW circulation during the latest Miocene. Seismic interpretation highlights a middle to upper Messinian seismic unit of transparent facies, whose base predates the onset of the Messinian salinity crisis (MSC). Its facies and distribution imply a predominantly hemipelagic environment along the Atlantic margins, suggesting an absence or intermittence of MOW preceding evaporite precipitation in the Mediterranean, simultaneous to progressive gateway restriction. The removal of MOW from the Mediterranean-Atlantic water mass exchange reorganized the Atlantic water masses and is correlated to a severe weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a period of further cooling in the North Atlantic during the latest Miocene.

scholarly journals Long-term monitoring programme of the hydrological variability in the Mediterranean Sea: a first overview of the HYDROCHANGES network

Ocean Science ◽  
2013 ◽  
Vol 9 (2) ◽  
pp. 301-324 ◽  
Author(s):  
K. Schroeder ◽  
C. Millot ◽  
L. Bengara ◽  
S. Ben Ismail ◽  
M. Bensi ◽  
...  
Keyword(s):  
Time Series ◽  
Mediterranean Sea ◽  
Sampling Interval ◽  
Global Changes ◽  
Hydrological Variability ◽  
Long Term Monitoring ◽  
The Mediterranean ◽  
Set Up ◽  
Term Monitoring

Abstract. The long-term monitoring of basic hydrological parameters (temperature and salinity), collected as time series with adequate temporal resolution (i.e. with a sampling interval allowing the resolution of all important timescales) in key places of the Mediterranean Sea (straits and channels, zones of dense water formation, deep parts of the basins), constitute a priority in the context of global changes. This led CIESM (The Mediterranean Science Commission) to support, since 2002, the HYDROCHANGES programme (http//www.ciesm.org/marine/programs/hydrochanges.htm), a network of autonomous conductivity, temperature, and depth (CTD) sensors, deployed on mainly short and easily manageable subsurface moorings, within the core of a certain water mass. The HYDROCHANGES strategy is twofold and develops on different scales. To get information about long-term changes of hydrological characteristics, long time series are needed. But before these series are long enough they allow the detection of links between them at shorter timescales that may provide extremely valuable information about the functioning of the Mediterranean Sea. The aim of this paper is to present the history of the programme and the current set-up of the network (monitored sites, involved groups) as well as to provide for the first time an overview of all the time series collected under the HYDROCHANGES umbrella, discussing the results obtained thanks to the programme.

scholarly journals The very first transformation of the Mediterranean outflow in the Strait of Gibraltar

2011 ◽  
Vol 116 (C7) ◽  
Author(s):  
Jesús García-Lafuente ◽  
Antonio Sánchez-Román ◽  
Cristina Naranjo ◽  
José C. Sánchez-Garrido
Keyword(s):  
Strait Of Gibraltar ◽  
Mediterranean Outflow ◽  
The Mediterranean
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