3D Bathymetric Survey

We are now entering another phase of our expedition – high resolution imaging of the mid-Atlantic ridge, the place where tectonic plates are born! This is so exciting because we are imaging the ocean floor in a never seen before detail. The images come in near-real time as we sail north – south across the ridge.  The lab is always buzzing with people day and night who stop by simply to look and wander at the amazing structure of the oceanfloor. It is like having a closer look at an alien planet. The ocean is about 5000 meters deep, however, near the ridge it abruptly reduces to about 2000 meters. Some of the underwater mountains are as high as 3000 meters and the steepest walls are about 1800 – 2000 meters high!

The technology that enables us to image these features at a high resolution is based on the simple principle of echoes. An instrument called a multibeam echosounder, that is positioned at the bottom of the ship, emits a sound signal. This signal travels through the water, bouncing off objects and features on the seafloor and are recorded by the instrument. The time that a single beam of sound takes to travel from the ship to the bottom of the ocean and back is recorded. In a previous post we talked about measuring the sound velocity using an instrument called Sound Velocity Profiler. We use this sound velocity information convert the travel time of sound to depths. The longer an echo takes to arrive back, the deeper is the ocean! Using state-of-the-art tools, we process and visualize the oceanfloor in 3D. Here are some magnificient and breath-taking images of the mid-Atlantic ridge.

Follow our navigation live!

We are now sailing west, to the middle of the Atlantic Ocean to survey the Chain Fracture Zone. More on this in the next post. You can see our track live online on this website: http://mars.noc.ac.uk/missions/dy072. DY072 is the operation number for the current PILAB operations on the RRS Discovery. From the website you can see how much we have sailed so far and also read more about the expedition itself.

Another interesting read is the detailed blog of seismologist Prof. Mike Kendall from the University of Bristol. He is a great writer and also an amazing photographer, capturing great moments of people at work, of the ship and the beautiful sunrise and sunsets. Have a look at it yourself: http://jmkendall.blogs.ilrt.org

Third leg of our cruise

We have now recovered nearly 90% of our ocean-bottom instruments, a total of 68 out of 78 instruments! The last few days where the most intense, recovering about 8 instruments a day. These instruments were deployed at the mid – Atlantic ridge at about 50 – 100 km apart. The reason for this short distance between the stations is for us to be able to image the deep structure beneath the ridge at a high resolution. A little duck, brought on board the ship by Prof. Mike Kendall from the University of Bristol, helped us stay on track. The duck is a fieldtrip mascot for the geosciences department at the University of Bristol.

Life on board is more-or-less ‘normal’ albeit the ship being on high alert for pirates the last few days as we were few hundred kilometres from the African coast. The ship was on “lock down” for a couple of days – which meant no one could stay outside on deck unless an instrument was being picked up, all windows and portholes shut, and all external lights, except the navigation lights, were turned off. As we sail away from the African coast, preparations are underway for 4 days of surveying a section of the mid-Atlantic Ridge called the Chain Fracture Zone, which means research techs have a few days off!

A lost soul wandering to the bar!

The Royal Research Ship Discovery

It is indeed an honour to be on board the Royal Research Ship Discovery.

Few ships, if any, hold a name that has a long rich history in Earth science exploration. The history of the RRS Discovery stretches over 2 centuries. In total, 4 ships, including the current one, served the scientific community under this royal name.

While walking through the corridors on board this ship you come across various photos and memorabilia from the previous ships and the numerous expeditions she had been an integral part of. In these pictures, you can see how the ships have changed over time. The first ship was a wooden whaling ship that served as HMS Discovery in the Royal Navy in 1874 for the British Arctic expedition to the North Pole. The first ship to bear the RRS title was the last traditional wooden three-masted ship to be built in Britain, designed for Antarctic research and launched in 1901. It’s first mission was the British National Antarctic Expedition, famously captained by Robert Falcon Scott and Ernest Shackleton, which set sail on 6 August 1901 from the Isle of Wight and sighted the Antarctic coastline on 8 January 1902.

The current ship is the 4th Discovery to bear the RRS title and is one of the world’s most recent and technically advanced scientific research ship, commissioned by HRH The Princess Royal in 2013 in Southampton. There are more Royal Research Ships at present, however, only one holds the legacy of numerous discoveries – the RRS Discovery!

An interesting fact – NASA named one of its space shuttles, Discovery, to honour the legacy of this great ship!

Deep sea temperature and sound velocity

We would like to highlight another vital measurement that we take at each site, the sound velocity and temperature with depth profile. We use a special device that measures pressure, temperature and sound velocity as it is lowered down by a winch. We can literally reach the bottom of the ocean with a pretty long winch cable which is about 6.9 km long! The graph below shows the sound velocity and the temperature with depth down to 2000 metres. It is interesting to see how the temperature decreases rapidly to about 5 degrees Celsius at 700 metres depth and then decreases gradually to about 3 degrees Celsius at 2 km depth. The sound velocity also decreases rapidly from about 1540 metres per second at the surface down to about 1480 m/s at about 700 metres depth, however it starts to increase gradually with depth below 700 metres depth. The main reason for its increase is due to increase in pressure and density. The sound velocity profile is an important measure when imaging the topography of the ocean floor…. more on that in an upcoming post.

A Sound Velocity Profiler (SVP) is ready to get winched to 2000 metres.

Into the storm

So far we have been lucky with the weather, with calms seas and warm temperatures. Hard to believe that we are in such tranquillity in the middle of the Atlantic Ocean known for its bad temper. Murphy’s law lived up to its name! After we picked up the 17th station, we headed right into a storm. We weren’t alarmed by the sudden change as the mighty RRS Discovery is built to handle far tougher storms. Nonetheless, the scientific crew were a bit excited with many of us trying to capture some amazing pictures, while we get shelter inside. Rain or sunshine, the operations have to go on! But fortunately the storm had subsided by the time we reached our next station

Finally some science!

We reached station 18, working backwards from station 39, picking up more and more instruments along the way. We started looking at the recorded data from the stations with a special focus on the state of the instrument over its working cycle and the quality of the data. There is nothing more than a pristine clean seismogram that can make a seismologist happy. We are all overwhelmed by the high quality and richness of the dataset. This was somewhat expected because of the high-end, state-of-the art broadband seismometers that we used. However, one has to remember that these instruments operated exceptionally in a formidable environment, under 5 km of ocean water. To our delight the data recorded is good in comparison to some of the data recorded on dedicated seismic stations on land. This can only yield high quality research in the very near future!

Here we show a seismogram recorded on one of our stations for a teleseismic earthquake with a magnitude of 7.6 that struck Chile on Christmas Day 2016.

Party at sea – Happy Birthday Kate!

Amidst the hustle and bustle on the ship, today is a special day for the Principle Investigator of this research expedition. Today is Dr. Catherine Rychert’s birthday! Despite her efforts to closely watch our every move in the nerve center of operations – the main lab, we managed to prepare a small surprise for her. We designed a poster and a birthday card (pirate themed) at 4 am while recovery operations were underway! We gathered in the galley just before dinner at 17:15 hours, putting up a poster and setting the music system to play a birthday song. As we were approaching our next station, Kate couldn’t leave the main lab as she was on watch. This was perfect for us! We left one radio-on in the lab. At 17:30 hours Mike Kendall, the senior scientist, called Kate on the radio to urgently come up to the galley for a meeting. As Kate hurriedly came up to the galley, we started singing and played the birthday song and caught her by surprise. I guess she was totally embarrassed but thoroughly enjoyed it! Thanks chef Wally for a delicious chocolate cake.

Recovery in the darkness!

Early this morning, we were approaching site 30 to recover two more instruments from the bottom of the ocean. We generally prefer night-time recovery because the instruments have a beacon that starts flashing a bright white light as it reaches the surface. This is an extremely efficient way of spotting the instrument. The instruments also have a reflect flag to help spot it during the day. However, things can get a bit tricky and tense at night if the beacon fails. This is what exactly happened, or so we thought! The instrument was supposed to rise to the surface at 03:15 hours. Those awake were all out on the deck trying to spot a floating instrument. We were lucky to have a bright full moon to help us. A couple of us were on the bridge with binoculars and night vision scopes staring into the horizon. On the other end, the OBS group was using their acoustics system to continuously range the instrument and determine how far it is from the ship. This helped us steer the ship so that we get closer to the instrument. As we started approaching the instrument, it surfaced and the beacon started flashing! That probably was the tensest moment we had, knowing that the instrument was somewhere out there in the darkness and out of our sight. It turned out that the instrument had extra weight stuck to it and thus slowed its ascent to the surface. Everyone had a sigh of relief when the instrument was finally on deck and secured!

The entire operation lasted about 6.5 hours, followed by a short 140-minute transit to the next station. We are now recovering about 4 stations, i.e. 8 instruments a day, as we steadily sail from the mid-Atlantic ridge towards West Africa.

From the Galley to the Gym

We have been 10 days at sea already! Life on board is now getting into a routine, most times losing count of which day of the week it is. Having recovered 7 out of 39 stations, i.e. 14 instruments in total, the recovery procedure has now become pretty much “standard”. Everyone involved with recovery, from the bridge to the deck, works like a symphony. But life on the ship is not only about science and station recovery. We need to be fed good, healthy and delicious delicious food. The RSS Discovery is a big ship, and with such a ship comes a large, well-equipped kitchen. Two chefs, Peter and Wally, man the kitchen. A big ‘British-style’ breakfast is served at 7:30 am sharp. Lunch is between 11:30 – 12:20, and dinner is served between 17:30 and 18:30 hours. For those working on night shift, they can have their food served later. In addition to these strict meal times, there is always something to eat or nibble; salads, cold meat, fruits, and ice cream are available 24/7. Oh, and did we mention the desserts? They are ‘homemade’ and yes, they taste delicious!

Chefs Wally (left) and Peter (right) take a break for a picture

Such tasty pleasures come at a price. Yes, you got it right – painful workouts at the gym. The ship has a small but well equipped gym. The crew have a choice of treadmill, cycling, rowing, stepper, and weights. Surprisingly (or not), the gym is indeed a busy place and people use it throughout the day. Perhaps now is the time to go and burn some calories!!