Scientific Research

Άγιος Νικόλαος Κρήτη 2001

Columnist: George Petrou

Photos: G. Vandoros, Chr. Bletsos, G. Petrou and other members of the expedition.

Lost deep in time, the legends wanted the Abyss of the Lagoon of Agios Nikolaos to be an Abyss, a bottomless lake around which countless stories were woven. This lake is in reality a doline formed by a precipitous drop.

• In 1945 it is said that the conquerors, while fleeing, threw all their light and heavy weapons into it so that it would not fall into the hands of the Cretans!!! That is what the elders say... and we trust them!
• In 1978, the legendary figure of Captain Cousteau comes to explore one of the most ambiguous marine areas of our homeland. His experienced divers dive, but the absolute darkness, the extreme cold, (and probably the absence of spectacular findings) keep them away from the secrets of the Lagoon. The period 22 - 30 September 2000 will be an important period for the history of the lagoon. A Greek Apostle carries out a series of dives with the aim of Exploring & Mapping the lake. HELLAS UNDERWATER EXPLORERS is one of the most specialized exploration groups with extensive experience in special forms of diving.

The team of 30 people is manned by Technical Diving Instructors, Cave Divers, Amateur & Technical Diving Scuba Divers, Photographers, Video Cameramen, Doctors, Oceanographers, Geologists, as well as surface support personnel. All of them guided by the organizer and Leader George Petrou.

Η υποστήριξη έγινε από το καταδυτικό κέντρο Buble Divers του Εκπαιδευτή Γιάννη Λίγκου. Σημαντική συνεισφορά στην οργάνωση και πραγματοποίηση της αποστολής από τους έμπειρους εκπαιδευτές Μιχάλη Τζενεβράκη, Στέλιο Κατσανεβάκη, Γιώργο Βανδώρο και Γιάννη Μικέλη που ανέλαβαν σαν αρχηγοί ο καθένας από έναν τομέα.

Special mention for their valuable contribution to the entire organization must go to Markella Giannatou, Stavros Oktapodas and Thanasis Nikolaopoulos. But who else can I mention without forgetting, Christos Bletsas, Kostas Tsiorvas, Manthos Marras, Alexia Grampa, Apostolos Pitsiotis...all of them were wonderful.

Να ευχαριστήσουμε ιδιαίτερα το Τμήμα Ωκεανογραφίας του Πανεπιστημίου Αθηνών και την Κα Αποστολοπούλου Μαρία. Να ευχαριστήσουμε τον Δήμο Αγίου Νικολάου, την FSS του Κο Κεφάλα, την Blue Star Ferries και όλους τους δημοσιογράφους, κανάλια, εφημερίδες και ΜΜΕ που κάλυψαν την όλη αποστολή, την Cressi Sub Αποστολίδης ΑΕΒΕ.

The diving begins with the whole world of Crete watching with great interest. The local authorities supported the project to the fullest extent possible. The interest of the media nationwide is enormous. Lost deep in time, these myths wanted the Abyss of the Lagoon of Agios Nikolaos to be an Abyss, a Lie, a bottomless lake around which countless stories were woven. In 1945, the conquerors, while fleeing, threw all their light and heavy weapons into it so that it would not fall into the hands of the Cretans. Weapons, tanks, radar!!! All the elders confirm the fact but no one believes them.

In 1953 the fish died suddenly, with a great stench emerging, and the waters acquiring a yellow color. It is connected to the Santorini volcano, many whispered. The lagoon is a great mystery that fascinates and provokes on a global level.

The period from 22 to 30 September 2000 will be an important period for the history of the lagoon. A Greek Expedition will carry out a series of dives with the aim of Exploring & Mapping the lake. HELLAS UNDERWATER EXPLORERS is one of the most specialized exploration groups with extensive experience in special forms of diving. The preparation began in 1998 as the expedition leader George Petrou informs us.

Οι καταδύσεις ξεκινάνε με όλο τον κόσμο της Κρήτης να παρακολουθεί με μεγάλο ενδιαφέρον. Οι τοπικές αρχές υποστήριξαν το εγχείρημα στο μέγιστο δυνατό. Το ενδιαφέρον των ΜΜΕ πανελληνίως είναι τεράστιο.

The diving begins. The research is carried out in very difficult and even extreme conditions. Up to 15 to 20 meters the water has an intense gray-green color and there is a lot of life, flora and fauna. The temperature is 26 degrees Celsius. Below that depth, even the slightest light is lost. The divers are immersed in darkness. For people on the surface, the wait is excruciating. Despite safety measures and excellent preparation, the dangers from unpredictable factors always threaten us.

The divers emerge and while everyone, outside the exploration team, believes that it will be difficult to find anything, a weapon and bullets from those thrown by the conquerors are triumphantly retrieved from a cliff on the sides of the lagoon, confirming what the elders said. If I remember correctly, Michalis Tzenevrakis and Yiannis Mikelis began the dance of discoveries. In the following days, after a series of many strenuous dives, other weapons reach the surface. And not only weapons. A German military motorcycle, bayonets and other bullets raise the interest.

From there on, as the days progress, the focus is on finally finding the bottom of the lake. A system of ropes with bars has been set up, from which the team will dive and in which they will then do the required decompression. Large lights will try to illuminate the path of the explorers, but once they fall into the terrible sediment, all they succeed in is forming a white curtain that limits visibility to 30 points!!! Powerful moments of eternity and suddenly at 51 meters we finally illuminate the first muddy and silent bottom of the lake.

Spreading our legs, we explore about 50 meters away from the bar, while one of the leaders of Apostoli, Michalis Tzenevrakis, records this new world for all of us with his video camera.

Our planned stay time has expired, and we return to the decompression bar for the ascent to the surface light. A long decompression time at depths of 12 to 3 meters that we are required to do before we emerge prolongs the anxiety of those waiting for us on the surface.

We all emerge, and our smiles, in addition to the very exciting dive that we did in complete safety, let them know that we had finally found the bottom. There is a bottom and it is initially located at a depth of 51 meters at the specific point where we dived. The team completed its work when its scientific members from the University of Athens carried out a series of investigations that brought to light important results.

The exploration team said goodbye to the always hospitable Crete and the warm residents of Agios Nikolaos who supported us so much, and already on the return trip we began planning our next exploration mission.

Scientific Work George Katsanevakis Oceanologist

I.Βυθομέτρηση

A sounding of the lagoon was carried out using a depth sounder from a fishing boat. The entire surface of the lake was scanned and the greatest depth recorded was 50m. The lake exhibits a strong bathymetric gradient and presents a deep oval-shaped plateau with an axis parallel to the major axis of the lake, with depths ranging from 41 to 50m.

II.Measurement of temperatures

Temperature measurements were taken at 7 different points in the lagoon throughout the water column. The measurements were made with a Hydro-Bios electrode from the surface to the bottom and every one meter. The diagram below shows all the measurements.

We observe the following:

The deepest point measured was at 46 meters, where the temperature was 16.4 oC, while the highest temperatures were measured at the surface and reached 26.8 oC. The temperature shows a small decrease from the surface to 10m (from 26.6 oC to 24.5 oC), while from 10m to 19m there is a strong thermocline and the temperature drops to 18 oC. From 19m and below the temperature continues to decrease but at a slower rate, reaching its minimum value at 46m. At one measuring station (ANS07) the temperature showed a very small increase after 30m which may be due to a slight downdraft. There is no differentiation between the measuring stations, with the sole exception of station ANS07 below 30 m. There is an obvious stratification of the water masses, caused at this time (warm months) by the limited recycling of the lake waters due to the narrow and shallow channel that connects it to the sea, the intense heating by the sun of the surface waters and the lack of intense waves due to the small surface area of the lake. That is, there are the surface warm masses that are slightly renewed through the channel and the deep cold masses that are not renewed and therefore not sufficiently oxygenated, as is evident from the measurements of dissolved oxygen.

III. Dissolved oxygen measurement

Water samples were taken from various depths (from 0 to 30m) and analyzed for dissolved oxygen concentration. The measurement of dissolved oxygen was done with a YSI electrode.

The results are shown in the diagram below.

We observe the following: In the first few meters due to contact with the atmosphere and the renewal of the waters from the sea through the channel we have supersaturation in dissolved oxygen. Gradually the concentration of dissolved oxygen decreases with depth. Below 12m the waters become hypoxic, as the concentration of dissolved oxygen drops below 2mg/lit, while from 16m it drops below 1mg/lit. The result of the hypoxic conditions is that aquatic life is dramatically limited below 12m and very few organisms survive. This observation was also made by the divers who did not encounter any obvious sign of life below 12m. On the contrary, in the first meters from the surface the lake has life (many and large fish, crustaceans, echinoderms, ascidians, mollusks, sponges, algae, etc.) In the sediment of the lake bottom at great depths, the conditions are anoxic. Due to the action of anaerobic bacteria, we have the production of H2S, CH4, etc., resulting in a strong stench but also toxicity for most aquatic organisms. The stench was strong and noticeable even to the scuba divers who descended to these depths. It should be noted that this situation prevails at the specific time when the research was carried out. In the winter months, the situation will most likely be completely different, as the thermocline will "break" and the richly oxygenated surface waters will descend to great depths, oxygenating the lake bottom. In order to determine the situation during the winter months, the measurements will have to be repeated. It should also be noted that the state of anoxia is most likely a normal process and is not linked to the pollution of the lake, although any form of pollution from organic materials certainly enhances the phenomenon.

IV. Hard and soft substrate sampling

The soft substrate sampling with a grab was not successful due to the steep slope of the bottom and the presence of many solid materials (stones, garbage, ropes, branches, etc.). The hard substrate sampling was successful and the samples will be further studied in the laboratory of the Zoology - Marine Biology Department of the University of Athens. A metal frame was placed on the surface of the substrate, with a suitable net at one end, and the entire surface it defined was scraped. Any material scraped was collected on the net and then placed in plastic containers and preserved with formalin. It should be noted that below 10m the rocks were completely bare and there was no material for sampling. Thus, the sampling was limited to 10m, 5m and the surface.

The Genesis of the Lake - Alexia Grampa Geologist

Crete presents a significant number of characteristic surface and underground Karst formations. The term karst describes areas that are structured by soluble carbonate rocks, such as limestone, with a characteristic relief, which is the result of the mechanical and chemical action of water. The dissolution of rocks by water causes the expansion of cavities within the rock, an increase in its permeability and the possibility of transferring large quantities of water through it. The presence of karst in Crete is due to the large surface spread of limestones, the intense tectonism of the island and the intense paleoclimatic changes that took place during the Early Cenozoic (the last 2 million years). The lake of Agios Nikolaos is also included in the Karst formations. It is a doline of precipices (Dermitzakis and Mariolakos, 1974). Sinkholes are closed depressions with a circular or elliptical shape, 10-1000m in diameter and 5-200m deep. Sedimentary sinkholes are formed by the collapse of the roof of an underground cavity or cave. If the cavity is filled with water or there is a subsequent rise in the water level (the case of Agios Nikolaos), sedimentary sinkholes form lakes of great depth, the bottom of which may be covered by sediment of a fairly large thickness.

Η εγκατακρήμνιση της οροφής του σπηλαίου του Αγ. Νικολάου τοποθετείται στο Ανωτ. Τεταρτογενές (πριν 70.000 χρόνια περίπου ) (Δερμιτζάκης και Μαριολάκος,1974).