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 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 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.

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 Iterative land proxy based reconstruction of SST for the simulation of terrestrial Holocene climate

2012 ◽  
Vol 3 (1) ◽  
pp. 149-200
Author(s):  
K. Haberkorn ◽  
C. Lemmen ◽  
R. Blender ◽  
K. Fraedrich
Keyword(s):  
Time Series ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Climate Simulation ◽  
Data Set ◽  
Past Climate ◽  
The North ◽  
Main Driver ◽  
Simulated Climate

Abstract. Sea surface temperature (SST) is the main driver of simulated climate in coupled atmosphere-ocean general circulation models. A reliable reconstruction of past SST is necessary to simulate past climate realistically. We here present a novel method for reconstructing SST on the basis of terrestrial Holocene palaeothermometer data such that a climate model is able to represent the climate mean state in the land temperature time series. For our study, we use the Earth system model of intermediate complexity Planet Simulator (PlaSim). The land climate is represented by the high-resolution and long-term palaeothermometer time series from Lake Ammersee (Southern Germany), where the temperature is derived from the stable δ18O isotope in ostracod valves. To provide a climate simulation which reflects the proxy-derived climate during the Holocene, we (i) determine the sensitivities of the terrestrial PlaSim climate with respect to SST anomalies for present day conditions; (ii) define the inverse of these sensitivities to find the SST conditions necessary for representing past land proxy climate; and (iii) reapply the climate model to this newly reconstructed SST. We iterate over steps (ii) and (iii) until the mean model and proxy climate converge. We demonstrate the applicability of this new method to reconstruct past climate by comparing the simulated land temperatures to an independent (pollen derived) proxy data set of land temperatures for Europe. The implementation of a wider range of terrestrial palaeotemperature information from proxy archives analogous to our method will foreseeably yield better reconstructions of past SST. These can, for example, be used to overcome many models' difficulties with simulations extending to the time before 8500 yr before present, when the North American (Laurentide) ice sheet caused a no-analogue climate.

scholarly journals PALAEOCLIMATIC AND PALAEOCEANOGRAPHIC EVOLUTION OF THE MEDITERRANEAN SEA OVER THE LAST 18KA

2017 ◽  
Vol 43 (2) ◽  
pp. 1064
Author(s):  
K. Thomopoulos ◽  
M. Geraga ◽  
E. Fakiris ◽  
G. Papatheodorou ◽  
G. Ferentinos
Keyword(s):  
Mediterranean Sea ◽  
Marine Sediments ◽  
Mediterranean Region ◽  
Planktonic Foraminifera ◽  
Sampling Interval ◽  
Time Interval ◽  
Time Sampling ◽  
Data Set ◽  
The Mediterranean ◽  
Planktonic Species

he aim of the present study is the reconstruction of the palaeoclimatic and palaeoceanographic evaluation of the Mediterranean Sea over the last 18ka based on the distribution of the planktonic foraminifera species. Planktonic foraminifera species have been proven excellent indicators of the palaeoclimatic and palaeoceanographic variability. The data set of the present study consists of the variability in the abundances of planktonic foraminifera species as has been reported and published in previous studies, after the examination of marine sediments from cores selected all over the Mediterranean Sea. The evolution in the abundance of each planktonic species is examined on a time interval spacing of 1000years suggesting implications for the palaeoclimatic and palaeoceanographic evolution of the Mediterranean Sea for the same time sampling interval (1000yrs). The most pronounced results of this study suggest that: (i) the increase in surface temperature during the warm intervals always follow a decreasing trend from eastern to western areas, (ii) the eutrophication of the Mediterranean Sea in most of the time exhibits a decreasing trend from northern to southern areas, and (iii) during the Holocene two cool spells (at around 8ka and 4ka) seems that had affected the majority of the Mediterranean region.

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 Dissolution of calcium carbonate: observations and model results in the subpolar North Atlantic

2007 ◽  
Vol 4 (2) ◽  
pp. 205-213 ◽  
Author(s):  
K. Friis ◽  
R. G. Najjar ◽  
M. J. Follows ◽  
S. Dutkiewicz ◽  
A. Körtzinger ◽  
...  
Keyword(s):  
Calcium Carbonate ◽  
North Atlantic ◽  
Global Scale ◽  
Biogeochemical Model ◽  
Mixing Processes ◽  
Data Set ◽  
The North ◽  
Significant Process ◽  
Model Support

Abstract. We investigate the significance of in situ dissolution of calcium carbonate above its saturation horizons using observations from the open subpolar North Atlantic [sNA] and to a lesser extent a 3-D biogeochemical model. The sNA is particularly well suited for observation-based detections of in situ, i.e. shallow-depth CaCO3 dissolution [SDCCD] as it is a region of high CaCO3 production, deep CaCO3 saturation horizons, and precisely-defined pre-formed alkalinity. Based on the analysis of a comprehensive alkalinity data set we find that SDCCD does not appear to be a significant process in the open sNA. The results from the model support the observational findings by indicating that there is not a significant need of SDCCD to explain observed patterns of alkalinity in the North Atlantic. Instead our investigation points to the importance of mixing processes for the redistribution of alkalinity from dissolution of CaCO3 from below its saturation horizons. However, mixing has recently been neglected for a number of studies that called for SDCCD in the sNA and on global scale.

scholarly journals Dissolution of calcium carbonate: observations and model results in the North Atlantic

2006 ◽  
Vol 3 (5) ◽  
pp. 1715-1738 ◽  
Author(s):  
K. Friis ◽  
R. G. Najjar ◽  
M. J. Follows ◽  
S. Dutkiewicz ◽  
A. Körtzinger ◽  
...  
Keyword(s):  
Calcium Carbonate ◽  
North Atlantic ◽  
Global Scale ◽  
Biogeochemical Model ◽  
Mixing Processes ◽  
Data Set ◽  
The North ◽  
The North Atlantic ◽  
Model Support

Abstract. We investigate the significance of in situ dissolution of calcium carbonate above its saturation horizons. The study relies on observations from the open subpolar North Atlantic [sNA] and on a 3-D biogeochemical model. The sNA is particularly well suited for observation-based detections of in situ, i.e. shallow depth CaCO3 dissolution [SDCCD] as it is a region of high CaCO3 production, deep CaCO3 saturation horizons, and precisely-defined pre-formed alkalinity. Based on the analysis of a comprehensive alkalinity data set we find that SDCCD does not appear to be a significant process in the open sNA. The results from the model support the observational findings and do not indicate a significant need of SDCCD to explain observed patterns of alkalinity in the North Atlantic. Instead our investigation points to the importance of mixing processes for the redistribution of alkalinity from dissolution of CaCO3 from below its saturation horizons. However, mixing has recently been neglected for a number of studies that called for SDCCD in the sNA and on global scale.

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