Detailed studies of the candidate sites in the NESTOR region in the East Ionian Sea near Pylos have been carried out using side-scan sonar¹. The locations and the bathymetry of the candidate sites are shown in figure 1.1. The coordinates of the nearest point of the corresponding plateaus as well as the available sea bottom area at that depth are summarised in table 1.1. In figure 1.2 a typical detailed bathymetric map of the area NESTOR 4.5 (i.e. depth 4500m) is shown, with isobaths of 2m. Similar resolution charts are available for the whole NESTOR region. The sea bottom surface is flat and with very old sedimentation^2.

click on the image for a better map

 ¹ Hellenic Centre for Marine Research
 ² E. Trimonis et al, “Geomorphology and bottom sediments of the Pylos area”, Proceedings of the 2nd NESTOR International Workshop, page 321, L. K. Resvanis editor (1992);
 

click the image to enlarge

The weather data, collected during several years at the NESTOR site area were analysed. In particular, data gathered by the National Meteorological Service of Greece for wind speeds from 1.1.1956 to 31.8.2002, taken at the Methoni Meteorological Station; 36° 49.5'N, 21° 42.3E'. Wind speeds were recorded every 8 hours. In the following graph (figure 2.1), a “day” is defined as any time period of 3 consecutive 8 hour data readings. It is interesting to note that almost 50% of the time is covered with four consecutive days with wind force equal or less that 4 beaufort (i.e. less than wind speed of 15 knots or 7.9m/s).

Moreover, in 2007, the Hellenic Centre of Marine Research (HCMR) installed a Environmental Buoy of the program "POSEIDON" of HCMR, in the PYLOS area, at 36° 50.2N, 21° 36.7E, which records, stores and transmits in real time a collection of environmental data³ . In figure 2.2 the time percentage with wave height less or equal to 1m (equivalent to sea state 4 beaufort) are shown; here also a “day” is defined as any time period of 3 consecutive 8 hour data readings. Note that almost 35% of the time we have four consecutive days with wave height less or equal to 1m.
In Figure 2.3 the surface currents are presented.

Figure 2.3: Surface current at the NESTOR area, POSEIDON data

³ POSEIDON Oceanographic data management, Hellenic Centre of Marine Research,
www.poseidon.hcmr.gr.
 

• E.G. Anassontzis et al., “Water transparency measurements in the deep Ionian Sea”, Astroparticle Physics, Vol34, 187-197, 2010,
• E.G. Anassontzis et al.- “Light transmissivity in the NESTOR site”, Nuclear Instruments and Methods in Physics Research A 349(1994)242-246,
• S. A. Khanaev et al, “Measurements of Water transparency South-West of Greece”, Proceedings of the 2nd NESTOR International Workshop, page 253, L. K. Resvanis editor (1992),

Note the consistency of the results over twenty years.

Measurements of water mass circulation have been performed since 1990⁴. From February 2006 to September 2009, ten research cruises have been conducted in the NESTOR area in the Eastern margin of the Ionian Sea to the southwest of Peloponnese (Figure 3.1). In most of these cruises typical hydrographic work was carried out with collection of CTD (conductivity, temperature, and depth) profiles at the stations shown in Figure 3.2 in addition to long-term (3.5 year) tall mooring deployments at stations NESTOR 4.5 (i.e. depth 4500m) and NESTOR 5.2 (i.e. depth 5200m), figure 1.1. In February 2006 the moorings were deployed in the site NESTOR 4.5 and then at four levels of the water column of both sites NESTOR 4.5 and NESTOR 5.2. Current-meter mooring measurements at four levels at site NESTOR 4.5 were continued beyond September 2009. In the following, an overview of the hydrographic and current meter results for the period February 2006 to September 2009 are presented.
The techniques and instruments i.e. current meters and sediment traps used in similar measurements in the Capo Passero and Toulon areas are the same with those we have used in the Pylos area and therefore the results are directly comparable.
 

⁴ T. A. Demidova et al “Investigation of near bottom currents in mouse pit in the vicinity of NESTOR area”, Proceedings of the 2nd NESTOR International Workshop, page 284, L. K. Resvanis editor (1992)

Figure 3.3. Salinity (red), potential temperature (purple), density (black), water transparency (blue) and dissolved oxygen (green) profiles at site NESTOR 5.2 (i.e. depth 5200m) in May 2007

Deep circulation – currents

Figure 3.4 shows the deep dynamic height fields during October 2006, April 2008 and May 2009. The flow at the deep layer 3200-3850 m is cyclonic in October 2006 and April 2008, whereas it reverses into anticyclonic (clockwise) in May 2009. We note, however, that the mean flow field at depths greater than 4 km is cyclonic (counter-clockwise) during all of the 2006-2009 period, as is shown in the directly measured currents at sites NESTOR 4.5 (i.e. depth 4500m) and NESTOR 5.2 (i.e depth 5200m) in Figures 3.5 and 3.6. The basic feature observed on Figures 3.5 and 3.6 with respect to the site characterization for the installation of the deep neutrino telescope, is that the deep flow field at depths of 4.5 km and 5 km is characterized by extremely weak velocities with mean speeds near ~2 cm/sec. This is also shown on the histogram distributions of the current speeds in Figure 3.7.

Figure 3.4. Dynamic height field anomalies at 3200 m with reference at 3850 m during October 2006, April 2008 and May 2009 showing the corresponding circulation structure with black arrows for the layer 3200-3850 m.

Figure 3.5. Vector stick time-series of currents at various depths of site NESTOR 4.5 (i.e. depth 4500m) and basic statistics on current speeds and mean vectors obtained on the half-hourly unfiltered data

Figure 3.6 Vector stick time-series of currents at various depths of site NESTOR 5.2
(i.e. depth 5200m) and basic statistics on current speeds and mean vectors obtained on the half-hourly unfiltered data

Figure 3.7 Histogram distributions of current speeds of half-hourly/unfiltered current data at sites NESTOR 4.5 (i.e. depth 4500m) and NESTOR 5.2 (i.e. depth 5200m)

4a. Settling particle fluxes: results from time series sediment trap measurements at the NESTOR site
4b. LIMS: Sedimentation measurements on to Optical Modules; LIMS, the "Light Intensity Measuring System"
4c. Geomorphology and bottom sediments of the Pylos area
4d. Long Term effects of fouling on glass, metal and plastics

4a. Settling particle fluxes: results from time series sediment trap measurements
      at the NESTOR site ( February 18^th 2006 to October 15^th 2008)

In figure 4.1 we present the available mass data flux from ANTARES, NEMO and NESTOR (KM3NeT CDR p61, KM3NeT TDR pp.123-125) .

The total mass flux and the spatial variations at the NESTOR 4.5 and 5.2 sites have been thoroughly investigated. Two sediment trap lines were deployed in the area of NESTOR named NESTOR 5.2 (210 07.965E, 360 33.180N) and NESTOR 4.5 (210 28.925E, 360 32.955N) with one and five sets of trap (TECHNICUP, with 12 receiving cups and 1/8m2 collecting area) and current meter (AANDERAA RCM-11 and RCM-9) respectively (figure 4.2). In addition two Light Intensity Measuring Systems (LIMS) per line were also deployed. Dates, mooring positions, bottom depths of the mooring lines and the nominal depths of the instruments deployed in both sites are given in Table 4.1. The traps were synchronized to collect particles over 1 or 2-week periods. The experiment consisted of five individual deployments covering the period from February 18^th 2006 to October 15^th 2008. Data have also been collected in 2009 but the analysis is not completed yet. Further, measurements are continued to date.
The techniques and instruments i.e. current meters and sediment traps used in similar measurements in the Capo Passero and Toulon areas are the same with those we have used in the Pylos area and therefore the results are directly comparable.
 

Figure 4.1. Monthly mass flux variations from ANTARES, NEMO and NESTOR sites. The NESTOR fluxes are the mean month fluxes for the entire period of the experiment (KM3NeT CDR p61, KM3NeT TDR pp.123-125) .

Qualitative and quantitative results for the period June to October 2006 are given in table 4.3. The lithogenic component was the major constituent of settling particles as the content was always higher than 50% at all depths (table 4.3 and figure 4.3). Carbonates (mainly coccoliths, Emiliania Huxley) were the dominant biogenic factor. The analogous chemical composition particulate matter caught by all traps confirms the same origin of those particles. Fluxes of organic matter never exceed the 2 mg m^-2 d^-1 increasing from 1200m to 3200m and then decreasing down to 4300m. Chemical composition and fluxes at the near sea bed traps of NESTOR 4.5 (i.e. depth 4500m) and NESTOR 5.2 (i.e. depth 5200m) are almost alike.

Figure 4.3. Chemical composition of particulate matter (left plot) and fluxes of major constituents (right plot) during the summer deployment (3/6/06 – 7/10/06).

 In the South Ionian four different sediment trap experiments have measured particulate fluxes over the past ten years; in Capo Passero site, the ADIOS site, the SESAME site and the NESTOR sites. In ADIOS, SESAME and Capo Passero sites mass flux peaks similarly in April – May.
 

Figure 4.4. Locations of trap lines in S. Ionian Sea (up left). Mass flux temporal variations in Capo Passero site (up right), from ADIOS project 2001-2002 (down left plot) and SESAME project 2007-2008 (down right plot). The moorings of ADIOS and SESAME experiments were located at the same position. (Data from ADIOS and SESAME project are unpublished.)

In the NESTOR site the situation is more complicated, and the flux maxima occurred from March to August/September. Those periodical appearances of maxima, almost in all depths, probably due to periodical phenomena such as Aeolian transport and deposition of Sahara dust and the biological productivity. In February and October 2006 CTD measurements recorded benthic nepheloid layers detached from the shelf break that created intermediate nepheloid layers, while in June and October of 2006 a benthic nepheloid layer was observed in the NESTOR study area. That mechanism could transfer materials (mainly lithogenic particles) to the deep sea. Taking into account that the periods of high fluxes matches with the periods of low rainfall (figure 4.2), and the lack of remarkable riverine discharges from the adjacent land, that could transfer terrestrial material in the NESTOR site, means that the NESTOR site hardly receives any material directly from the mainland.

The similar ecological condition that prevails in the region can explain the similar seasonal dependence recorded at all sites in South Ionian Sea (figure 4.2 and 4.4). The slight decrease of mass flux with depth means that NESTOR shows an “oceanic flux pattern”, while in figure 4.5 the mean mass flux in the South Ionian Sea versus depth is shown. The mass flux measurements obtained from those experiments shown an eastward gradual decrease of total mass flux.

 

Figure 4.5. Mean mass flux in the S. Ionian Sea vs. depth.

Figure 4.6. Total mass flux temporal and spatial variations at NESTOR 4.5 and 5.2 sites as well as rainfall (see RHS axis). Note that the abnormal increase in sediment during the Summer of 2008 is caused by the extreme  forest fires in the Western Peloponnese and Messinia that Summer.
See also KM3NeT TDR p. 123

4b. LIMS: Sedimentation measurements on to Optical Modules; LIMS,
      the "Light Intensity Measuring System"

We have built a large number of autonomous systems, Light Intensity Measuring System (LIMS)⁹ , in order to measure the sedimentation which stays/stick on the optical modules and/or bio-fouling effect on the Optical Modules (OMs) by measuring light intensity variations on several positions on the glass spheres deployed in the deep-sea over long time periods; 6-15 months. In the course of over two years, May 2007 – Oct. 2009, 20 LIMS have been deployed in the sites NESTOR4.5 and NESTOR5.2; a total 260 LIMS-months.

A grid of photosensors is distributed inside a glass sphere (BENTHOS or VITROVEX) in the upper and lower hemisphere and measures the light intensity of two light sources located outside the glass sphere. The upper hemisphere is illuminated by the upper beacon, then it is switched off, and the lower hemisphere is illuminated by the lower beacon, and then switched off. This set of measurements is repeated every 3 hours.

The distribution of the photosensors inside the glass sphere is shown in Fig.4b.1 and a Light Intensity Measuring System (LIMS) figure, ready for deployment, is shown in Figure 4b.2.
 

Figure 4b.2: Light Intensity Measuring System (LIMS) ready for deployment.

Each of the two light sources consists of an LED at 472nm wavelength, coupled to a plexiglass casing with optical gel.
The photosensor (TAOS¹⁰, TSLB257), used inside the OM and inside the beacons, is a light-to-voltage optical converter, containing a photodiode and an operational-amplifier on a monolithic silicon IC.
The temperature in the sphere and the battery voltage are also monitored [1].

Typical LIMS raw data are shown in figure 4b.3.

⁹ E.G. Anassontzis et al., "A light intensity measuring system for sedimentation measurements on KM3NeT optical modules", Nuclear Instruments and Methods in Physics Research A 626-627(2011)111-114
¹⁰ Texas Advanced Optoelectronic Solutions, www.taosinc.com 

 

Fig. 4b.3. Typical LIMS raw data at various angles from Zenith and at Nadir of the glass sphere are shown; ( LIMS 210, site: NESTOR 4.5, depth: 3240m, data period: Oct.’07-Apr.’08).

The raw data of each photosensor is averaged every nine consecutive measurements, normalised by dividing with the average of the first five days since immersion and corrected for source luminosity variations by multiplying the normalised average of the corresponding reference photosensor.
Figure 4b.4a shows typical normalised averaged response of two photosensors.
In order to determine a photosensor’s variation response during the deployment period we compute the slope of the normalised averaged response in constant time intervals of 60 hours. Such slopes are shown in the histograms of figures 4b.4b and 4b.4c.
The Means of these histograms are plotted versus zenith angle in figure 4b.5 for a typical LIMS run of about 6 months duration.
 

Figure 4b.4. Typical normalised averaged response of two photosensors (a) and the histograms of their corresponding slopes, (b, c); (LIMS 210, 2 channels at 20 degrees from Zenith, site: NESTOR4.5, depth: 3240m, data period: Oct.’07-Apr.’08).

Figure 4b.5: The variation of the photosensors response is constant for the different positions on the glass sphere; (LIMS 210, site: NESTOR 4.5, depth: 3240m, data period: Oct.’07-Apr.’08).

The data for both the NESTOR 4.5 and 5.2 areas show that the probability that sediment will stick on the glass sphere does not depend on the zenith angle. A more detailed description of the instrument and the obtained results are published in E.G. Anassontzis et al., "A light intensity measuring system for sedimentation measurements on KM3NeT optical modules", Nuclear Instruments and Methods in Physics Research A 626-627(2011)111-114.
 

4c. Geomorphology and bottom sediments of the Pylos area

Figure 4c.2 Slides 15 and 19 from the presentation “New observations of life on the floor of the Ionian Sea” by Prof. I. Priede in the 2011 KM3NeT General meeting in Amsterdam (March 2011) with pictures of the seafloor surface at the NEMO and NESTOR 5.2 sites taken during the R/V METEOR expedition from 24 Jan to 6 Feb 2011

4d. Long Term effects of fouling on glass, metal and plastics .

We have not found any traces of fouling on the surfaces of the OMs, Ti-frames and the Al-cylinder of the LED capsule. One could see the presence of minor fouling on the surfaces of HARD-HATS (figure 4d.1). Thin traces of fouling could be seen on the polycarbonate dome of the main buoy flasher (figure 4d.2).

2. Mechanical structure of the detector.

The Recovery Buoy came to the surface in very good condition. The frame of the Recovery Buoy was ordinary steel, painted with ordinary primer and protected with Zn anode. The Zn-anodes protected the frame very well. The Al-housings of the LEDs does not show any trace of corrosion since it was also protected with Zn anodes.
The Ti-pipes of the arms did not have any corrosion. The welded joints look very well without any caverns, cracks, holes. There are no deformations along of arms. Some of the stainless steel washer used to hold together the hardhats of the glass spheres were corroded (figure 4d.1).

3. Optical modules.

We have recovered 15 glass spheres: Four OMs each with PMT inside (two were oriented with the photocathode looking down, figure 4d.3 and two with the photocathode looking up, figure 4d.4) and eleven floatation spheres. Note that the discolouring of the titanium frame is due to the pealing off of the ordinary black paint we used to cover the titanium frame. None of the glass spheres had any visual damage after being under 400 atm pressure for 2.5 years. One only sphere lost a visible piece glass chip (about 5 cm in diameter and 1 mm at the maximum thickness) from the external surface without any other structural damage. There was no sediment or growth or any other fouling on the glass.
 

The GISMA connectors on the OMs were opened easily. Neither water nor any other damage was found inside the connectors. For the OMs, marine grade bronze connectors were used. Their external surfaces had minimal corrosion. However, no corrosion was found on the Ti-connectors used.

Conclusions
The effect of sedimentation, fouling and marine growth was studied with three different ways (sediment traps, LIMS and long term exposure in the deep sea) and they were found minimal, if any at all.
 

5a. Bioluminescence bursts (see also KM3NeT TDR p.133)
5b. Bioluminescence

We have been measuring the bioluminescence burst activity that saturates the optical module readout electronics since 1996. We have been measuring consistently 1.1% dead time (see KM3NeT CDR pp59-60, S. Sotiriou PhD thesis University of Athens, 1998 p. 258) with autonomous strings as well as with the detector prototype that was deployed in 2003. Further details can be found in the following paper by G. Aggouras et al; "Operation and performance of the NESTOR test detector" Nucl.Instr. & Methods in Phys. Res. Sect. A, 2005, Vol.: 552, Issue: 3, pp. 420-439 (see p.437).

Compare our 1% dead time to the up to 40% dead time measured in one of the other two sites.

Further: We find it very instructive to reproduce Table 1 from the publication by Jessica Craig et al “Distribution of bioluminescent organisms in the Mediterranean Sea and predicted effects on a deep-sea neutrino telescope“ Nucl. Instr. & Methods in Phys. Res A 602 (2009) 224–226

Radiation activity in the NESTOR area has been investigated with water samples taken from various depths by the NESTOR Institute and were measured at the  DEMOKRITOS National Lab. No significant radioactivity was found in the water column of the NESTOR sites. No technical radionuclei were found either.