Tuesday, February 2, 2016

Discovery of ‘river’ in the Bay of Bengal – vindicates the route of Ganges in the channel dug by Sagaras

A decade old research by NIO in collaboration with French scientists have found out that a river flows in the Bay of Bengal along the east coast starting from the estuary of Ganges up to the tip of South India. The waters poured into the Bay of Bengal by Ganges and Brahmaputra and the east flowing rivers such as Mahanadhi, Godavari and Krishna flow together for a width of 100 km down towards the south and to a depth of 40 meters from the surface. These rivers pour nearly 1100 cubic kilometres of fresh water from the monsoon rains into the Bay. Thus by the time the monsoon season gets over, this fresh water poured into the Bay by these rivers flow along the east coast and reach the tip of the South India and even circling Srilanka. The researchers have come up with this map of the flow of this river in the Bay.

Arrows showing the origin of the 'river in sea' in the Bay of Bengal all the way to the end. Locations from where fishermen collected water samples are named along the coast.
© Gopalakrishna, V. V. et al.

This discovery is a confirmation of what I have been repeatedly writing from 2008 onwards - on the presence of a channel bordering the east coastal line of South India, dug by the sons of King Sagara, the ancestor of Rama in which the river Ganges flowed down for the first time after the Gangotri melted to form the Ganges river. My detailed article in Tamil written in 2011 can be read here.

The digging ended at Setu in Rameswaram (read here). The Sagaras went on digging around Srilanka, circled it and ended up at Setu as that place (Setu) was hard to dig and had hot springs. The Ramayana description of Minaka Mountain encountered by Hanuman shows that there was volcanism or a vent in the mantle cover underneath that place. This is a fact, as studies done by the Geological Survey of India have found out hot springs of 60 to 70 degree Celsius along the Setu bund.  (Read here). (The sea near this place in Rameswaram is called as Agni Theertham even today). The heat of the springs had killed the Sagaras. Their ashes washed by the River Ganga could give them salvation. It was for this reason Bhagiratha, the descendant of Sagara, did penance to bring Ganga from the Himalayas.

What had actually happened was that the Gangotri glacier melted due to increasing heat at the end of Ice Age, sometime around 10,000 years BP and flowed down, initially as a lean stream. It flowed in the path dug by the Sagaras, according to Ramayana description. That path entered what is now Bay of Bengal. The Sagaras had dug along the east coast of India. The Ganges had entered that path and ended at Setu. As time went by Gangotri started melting more and more and the river Ganges started getting more water. But by then the water level at the Bay also had risen up and the shore lines had advanced towards land, sinking the channel of Sagaras underneath it. The location of this channel exists close to the shoreline as the land mass of India was slightly extended towards the Bay.

One can see the shoreline extended throughout the east and south of India.

The Bathometry analysis of the Bay of Bengal done by the researchers of NIO shows 4 strands parallel to the east coast at depths of 130, 80, 60 and 30 metres in this section. They consider it to be the marks of “sea level regressional phases” during the period between late Pleistocene and Holocene.  It must be remembered that at the start of Holocene (13,500 years ago), the ocean level was 120 metres lower than now. The Bay of Bengal being higher than the Indian Ocean must have had much lower water level. That means shore line existed until the outer most strand that was at a depth of 130 meters. The width of this extended shore line is not given by the researchers. But this area is enough for someone to make a tunnel. That is, this region offers scope to believe that the Sagaras dug along this patch of land along the shores.

This patch of land now under water is our focus of attention. It is here the river carrying the waters of Ganga and Brahmaputra are flowing along with the waters of Mahanadhi, Godavari and Krishna after picking up their water enroute. This water can be noticed from to the surface up to 40 meter depth in this length. And it flows to a width of 100 km. This is perfectly fine. But the question is why they should take a coastal route. Why didn’t the waters of these huge rivers just spread out in front of the estuaries?

In fact the bathymetry analysis of the Bay by NIO (here) says that the sedimentation brought by Ganga and Brahmaputra is so thick that it is 21 km thick at the apex of the Bengal Fan (near the estuary) and goes up to 7 degree South where it is a few hundreds of metres think. This has made the bottom of the Bay look plain and featureless. This also shows that the river water had spread straight into the Bay.

The above picture shows bathymetry of Indian Ocean along with the Bay of Bengal. One can see a light blue feature in the whole of Bay showing a more or less plain bottom. The arrow mark shows the Ninety East Ridge which is buried under the sediment as it nears the Indian land mass in the north.

It is logical to expect the waters of the rivers to spread in front their mouths. But why should they take a coastal route if not for the presence of a coastal channel that is at a higher level than the rest of the Bay?

The above picture shows the coastal band and the estuaries. Though water from the rivers had flushed into the Bay they had also taken coastal route throughout.

The coastal strands noted in the NIO study at depths of 40, 60, 80 and 130 meters may have a reason other than regressional coast line. Note the route of the coastal strands mapped by the NIO and compare with the recent discovery of the route of this river.

Route of the river mapped by NIO.

The route is the same as seen in the previous map.

What remains after the discovery of the coastal flow of the river water is the confirmation of  a verse by Valmiki in Ramayana that Sagar, the lord of the sea (in the Bay of Bengal) as it appeared to Rama (at Rameswaram) flowed down with the Ganga’s waters as the chief among the other river waters until that spot. “Ganga sindhu pradhanaabhir aapagaabhi” (Valmiki Ramayana, 6-22-22).

These waters were stopped by the Setu built by Rama’s Varana sena. Rama praises the Setu as “Paramam Pavithram, Maha Paathaka nashanam”  (Valmiki Ramayana 6-123-21). It is because water from the sacred rivers of Ganga, Brahmaputra, Mahanadhi, Godavari and Krishna are available together at Setu, enabling people take a dip at all the waters at one place. 

History of Rama shows that this combo river flowed down the channel dug by Sagara. Today’s researchers have found out that there is indeed a combo river flowing along this route. Future research is needed to show that this channel was facilitated by man-made action!

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Fishermen point scientists to ‘river in sea’

K. S. Jayaraman

Fishermen plying on the eastern coast of India have helped scientists discover a fresh water ‘river' that forms in the Bay of Bengal just after monsoon season1.

Arrows showing origin of the 'river in sea' n the Bay of Bengal all the way to the end. Locations from where fishermen collected water samples are named along the coast.© Gopalakrishna, V. V. et al.

The ‘river in the sea’ forms in northern Bay of Bengal at the end of the monsoon and ‘vanishes’ gradually after a while. About 100 kilometres wide, it flows southward hugging the eastern coast of India and reaching the southern tip after two and a half months. The seasonal river in the sea was discovered by salinity measurements of sea water samples collected by fishermen along the coast. 
The Bay of Bengal receives intense rainfall during the monsoon. This, and the run-offs from the rivers -- Ganges, Brahmaputra, Mahanadi, Godavari and Krishna -- bring around 1100 cubic kilometres of freshwater into the bay between July and September.

"This very intense freshwater flux into a relatively small and semi enclosed basin results in dilution of the salt in seawater," says one of the lead researchers V. V. Gopalakrishna, a scientist at the National Institute of Oceanography (NIO), Goa. The diluting effect gets concentrated in the upper 40 metres of the bay waters, resulting in a stark contrast between surface freshwater and saltier water below, he says. 

The presence of low salinity water (called stratification in oceanography parlance) over the Bay of Bengal prevents vertical mixing of sea water. This results in the accumulation of more heat in the near-surface layers, Gopalakrishna says. The sea surface temperature remains above 28.5°C, a necessary condition to maintain deep atmospheric convection and rainfall. Similarly, strong salinity stratification close to the coast would mean more intense tropical cyclones, he says. 

Earlier studies have shown that salinity plays a crucial role in influencing climate variability and cyclone activity. However, lack of in-situ observations in the bay hampered clarity on the temporal and spatial distribution of salinity near the coast. 

To fill this gap, the NIO engaged fishermen at eight specific stations along the east coast to collect seawater samples every five days in clean bottles. The bottles, marked with the date of collection, have been routinely brought back to NIO since 2005 for salinity measurements. 

The new dataset revealed a salinity drop of more than 10 grams per kilogram of water in the northern Bay of Bengal at the end of the summer monsoon. This relatively fresh water propagates southward as a narrow (100 km wide) strip along the eastern coast of India, according to the scientists. 

"Local fishermen have been a great help in developing this coastal network," Matthieu Lengaigne of the collaborating institute, French Institut de Recherche pour le Développement, told Nature India." 
This knowledge may help us validate models used to predict cyclones evolution in the Bay of Bengal," Lengaigne says. The study demonstrates the possibility of building a scientifically usable observational network at low cost by relying on local communities, he says. 

Following the success of the Indian programme, Sri Lankan oceanographers have initiated a similar network around Trincomalee and Colombo. 

While the scientists have so far focused on salinity measurements, they contend that the coastal seawater sampling programme could also be used for regular monitoring of other oceanic parameters such as phytoplankton or bacteria.

1. Chaitanya, A. V. S. et al. Salinity measurements collected by fishermen reveal a ‘river in the sea’ flowing along the east coast of India. Bull. Am. Meteorol Soc. (2014) doi: 10.1175/BAMS-D-12-00243.1



Fishermen discover river in Bay of Bengal


Continuous monitoring of salinity levels for nearly a decade confirmed the river’s presence. Photo: Special Arrangement

Movement of freshwater mass begins at the end of the summer monsoon
Fishermen have helped oceanographers discover a river in the sea that has been meandering its way along the eastern coast of the Bay of Bengal (BoB) after summer monsoon. A decade-long coastal salinity observations, carried out at eight collection points with local fishers from Paradeep downwards up to Colachel, allowed a detailed description of this uncommon oceanic feature.
The movement of the freshwater mass begins at the end of the summer monsoon and survives for nearly two-and-a half months. It also travels over 1000 km from the northern BoB to the southern most tip of India, say scientists.

A research paper on the formation of the “river in the sea flowing along the eastern coast of India” was recently published in the Bulletin of American Meteorological Society.

The presence of the river was confirmed through continuous monitoring of salinity levels for nearly a decade, said V. V. Gopala Krishna, Chief Scientist of the National Institute of Oceanography, Goa, the Principal Investigator of the project supported by the Ministry of Earth Sciences.

Sorbonne University and LOCEAN Laboratory, Paris, and the Indo-French Cell for Water Sciences, Goa, partnered in the research work.

The southwest monsoon roughly lasts from June to September. During this period, water vapour collected at the ocean surface by the powerful southwesterly winds is flushed over Indian continent and the BoB.

A large fraction of the monsoon shower reaches the ocean in the form of runoff and contributes to the freshwater flux into the BoB in equal proportion with rainfall over the ocean.

The large rivers — Ganges, Brahmaputra and the Irrawaddy, and three small others — Mahanadi, Godavari, and Krishna — together contribute approximately 1100 km of continental freshwater into the BoB between July and September.

This very intense freshwater flux into a relatively small and semi-enclosed basin results in an intense dilution of the salt contained in seawater, explained the paper.

The over 100 km-wide freshwater mass that is formed from river discharges and runoffs is transported down south by the East Indian Coastal Current, the western boundary current of the BoB. The freshwater signal generally becomes smaller and occurs later while progressing toward the southern tip of India, the paper said.

The salinity distribution in the BoB may impact cyclones and regional climate in the BoB. However, the paucity of salinity data prevented a thorough description of the coastal salinity evolution.

This lacuna was addressed by including fishermen in sea water sample collection process. Fishers collected seawater samples once in five days in knee-deep water at eight different coastal stations along the coastline. The samples were analysed at the modern lab of the institute and compared with open-ocean samples to obtain a picture of the salinity evolution, researchers said.
According to the research paper, the occurrence of this river in the sea along the eastern coast of India was probably not a generic feature that could be observed in many locations in the world.

The peculiar geography of the northern Indian Ocean that resulted in both a massive inflow of freshwater into the semi-enclosed northern BoB and the strong coastally trapped currents along the eastern coast of India were responsible for the formation of the river, the paper suggested.

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