What is a Himalayan geologist, typically acclimatized to working at altitudes in excess of 4000m, doing in the Bay of Bengal, bobbing around at sea level? Dr Yani Najman explains.
I’ve asked myself that question periodically (particularly when feeling seasick) during the past month I’ve spent working as part of the International Oceanographic Discovery Program (IODP) Expedition to the Bay of Bengal. The answer is that I hope that the sediment lying deep beneath the ocean floor will help reveal the secrets of the mountain range that is my life’s work.
I am part of an international group of 30 scientists and 100 crew aboard the Joides Resolution Research Vessel. We are drilling to the base of the Bengal Fan, a large sedimentary deposit of material eroded from the Himalayas over many millions of years and carried by rivers to be laid, layer upon layer, on the ocean floor. We hope to obtain a complete history of the erosion record of the Himalayas through time, and so understand how the mountain belt has influenced global climate since it started to form 50 million years ago.
To do this, we use a specially designed boat as we need to recover and analyse sediment from more than 1000m below the sea floor, in water depths of more than 3500m. The Joides Resolution has a 50m high derrick protruding from its rig floor, and custom made science labs on board.
For two months the routine is the same every day: work goes on 24/7 in two 12 hour shifts: the drillers drill and the scientists and technicians analyse the core that comes up. We wake up, we have a cross-over meeting with the outgoing shift and then we start working on the sediment that comes up every couple of hours in 9m cores. Twelve hours later we have another cross-over meeting with the incoming shift, we watch a movie or go to the gym, and then go to sleep.
Within this existence, small things take on unusual significance: seeing anything from ‘off’ the boat, be that a bird, or a fish, or another boat, is an event of note; a new food in the galley is a topic of discussion; someone sharing their ‘secret stash’ of goodies with you is a sign of true friendship indeed!
The highlight of each week is the BBQ on deck, and the highlight of the 2 months is the ‘Hump Day’ Party, to celebrate the half way mark. For us, that was last week, and we are now half way through our plan: to core five shallow holes so we get a spatial picture of the sediment record in this rapidly changing environment, and one deep hole (more than 1200m below the sea floor) to try to drill to the base of the Bengal Fan.
We’ve now started on the deep hole: it’s the part I’m most interested in, as we hope to recover the oldest Himalayan sediments ever cored, aged forty five million years old. It is also the most risky objective, as it's one of the deepest holes ever attempted by this ship in this type of difficult-to-drill sediment.
And sure enough, we’re having problems: we have drilled to 900m so far and the hole has already provided times of despondency and times of elation. Two days ago the drill got stuck in the sediments. It is really bad news when this happens: if we can’t release the drill our last resort is to blow the pipe with explosive to set ourselves free, losing the hole, and our objective, in the process. Tense hours followed as the chief driller worked with his team to release the drill and finally we were free and coring again.
Then, yesterday, the hole became too unstable and the drill too jammed to continue with a good chance of success, so coring was stopped for the day whilst attempts were made to clean the hole. Success, and onwards (and downwards) again.
And now… more tense moments…. no-one has drilled to the base of the fan before, so we only have seismic data to build up a picture of the subsurface deposit. We hope we are drilling at a place where the oldest sediments have been deposited, yet are near enough to the surface for our equipment to be able to reach them, but we can’t be sure.
The base of the fan, as estimated from the seismic information, is nearly upon us, and the sediments are only fifteen million years old; a far cry from the 45 million year ages we hoped for. Does this spell the end of our dream to retrieve the oldest Himalayan sediments? Maybe sedimentation happened much more slowly in the earlier time period, so the older sediments will appear before we reach the base of the fan? Perhaps the base of the fan occurs deeper than we thought: if so, can we drill still deeper? The next few hours will tell….. The Bengal Fan doesn’t give up her secrets lightly, it seems.
Whatever the result from this site, we’ll eventually move on and continue the transect of shallow holes in our efforts to understand Himalayan development and its relationship to the onset of the monsoon and change in global vegetation patterns 7 million years ago. Core will continue to come up at hourly intervals, the tannoy ‘core on deck’ will reverberate as usual throughout the ship, and it's action stations for all on shift - 12 hours on, 12 hours off - for another month to come.
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