The Thompson welcomed a visit from the 53rd Weather Reconnaissance Squadron on Sunday. This flight crew is stationed in the Keesler Airforce base in Biloxi Mississippi, where they keep an eye on Tropical Storms developing in the Atlantic. However, for the next 10 days or so they will be flying missions out of Colombo, sampling the atmosphere (temperature, pressure, winds and relative humidity) over very large-scales while flying from the Equatorial Indian Ocean up through the Bay of Bengal. On Sunday, they surveyed the Bay of Bengal taking a swing by the Thompson, where they launched a dropsonde (similar to the radiosondes– but dropped high-up with a parachute instead of launching from the surface with a balloon) and flew a calibration profile (the plane circles from 20’000 ft to 1000 ft sampling while underway) for comparison with the ship-based atmospheric measurements. The plane also left behind a few systems for the ocean: a wave buoy (measures surface waves), a surface drifter (measures upper ocean currents), and an Alamo float (profiles temperature and salinity over the upper ocean). These ocean measurements will continue after the Thompson heads back to port, expanding the footprint of our observations in time.
First images captured by our drone pilot S.K.
Evening clouds at the top of the humid marine atmospheric boundary layer, around 500-700 m high
R/V Thomas G. Thompson in the Bay of Bengal.
R/V Thomas G. Thompson in the Bay of Bengal.
An overview of the scientific instruments measuring the ocean and atmosphere during the summer monsoon in the central Bay of Bengal.
Black=hot. Note the hot exhaust plume, the warm water in the rectangular anti-roll tank forward of the bridge, the small hot lights on the mast and forward tower, the cold porthole windows into the air-conditioned interior, and the various hot and cold air vents over the structure.
What’s under the surface? Obviously more water, but how warm and salty is it at different depths? Finding the answer to that simple question is more difficult than you might expect, and crucial to understand the dynamics that create currents, transport heat, affect biology, and disperse pollutants.
One way to measure temperature and salinity (and thus density) along a vertical line is to stop the ship and lower a CTD rosette, (see previous post), which takes about 30 min to set-up, lower to 200 m, and retrieve.
Another way is to drop a streamlined instrument package to the same depth and reel it back up in under 3 minutes, while the ship moves at up to 4 knots, and then continuously repeat, getting the data in real-time while moving across the ocean.
The fastCTD system was developed at the Scripps Institution of Oceanography, and has been deployed on research vessels across the world’s oceans. With this automated instrument (one of 2 units currently operating) we observed the evolution of the Bay of Bengal’s upper ocean under the onset of the monsoon winds & rains. The profiler made over 6000 trips from the surface to 200 m depth and back! And for the first time, it recorded chlorophyl fluorescence and particulate backscatter along the profiles, offering new insights into the biological communities and their distributions.
Find out more at http://www.mod.ucsd.edu
The torpedo-like shape falls at around 5 meters per second.
While the instrument is automated, the winch and level-wind need to be monitored at all times.
Rain or shine.
Cameras and real-time data are monitored in the lab, an emergency stop-button ready in case something goes wrong.
Mechanical wear & tear can cause unexpected issues, always quickly fixed by the team.
Two days of data, showing a maximum of fluorescence below the surface layer, increasing in intensity during the day.
Big fish eat little fish, little fish (and big whales!) eat zooplankton (tiny shrimp-like creatures, small gelatinous animals, fish larvae…), and these zooplankton eat phytoplankton, the “plants” of the oceans. Floating in every single drop of water of the sunlit oceans, phytoplankton algae communities are at the base of the marine food web. How are these essential organisms affected by the different monsoon regimes?
To answer this question, we are collecting samples for biological and chemical analysis, in addition to the physical measurements acquired with the various instruments deployed.
Our versatile tool for this is called a CTD, measuring real-time Conductivity (from which we get salinity), Temperature, Depth, as well as other parameters like dissolved oxygen and phytoplankton fluorescence throughout the water column, with sampling bottles arranged in a rosette shape all around it. At the click of a button, we remotely close the bottles at particular depths, capturing water and bringing it back onboard. When the CTD rosette comes back on deck, the next step typically involves a few hours of water filtration and preservation! Transported with dry ice at -80°C back to our lab, we will sequence fragments of phytoplankton DNA and count cells. Our Indian collaborators from NIO Visakhapatnam will measure nutrients, pigments, organic carbon, and suspended matter in the water. These advanced techniques will offer a glimpse of the phytoplankton abundances and diversity at different depths and conditions, helping us understand distributions of these tiny yet vital organisms in the Bay of Bengal. C.P. & G.J.
C.P. starting up a Nitrate sensor right before the cast.
Launching the CTD rosette at 6am to catch the phytoplankton before they start photosynthesizing for the day.
From the surface to 200m depth
Monitoring the CTD cast in the computer lab, deciding which depths to sample.
J.L. collecting water for later chemical analysis.
C.P. collecting small amounts of water for preservation.
The water is filtered, extracting the phytoplankton along with other cells and particulate matter.
20 liters of water yields a thin yellow-greenish film of phytoplankton, for genomic analysis.
Drones are an up-and-coming data acquisition system, and the MISO-BOB expedition is an exciting opportunity to test the limits of what our existing platforms can achieve. We are using an infra-red camera to detect patterns of temperature in the sea surface, investigating the effects of flight altitude and sunlight reflections on these images. The goal is to make drones a valuable tool for physical oceanography, giving us novel insights into the workings of 7/10ths of our planet’s surface.
Stay tuned for some images from above!
The pilot is starting up the systems, as the drone fans watch in anticipation
>20kn winds make takeoffs and landings interesting. Especially under the watchful eye of the ship’s bridge, and in proximity to the many antennas and masts and instruments…
The IR-camera brings vision to nighttime operations, uncannily detecting warm shapes on the ship from far above.
Final landing for the night, impressive flying by S.K.
We typically take our measurements from the back of the ship. This keeps long lines away from the engine screws while moving (very good!!!), the downside is that the ship’s wake contaminates the upper 10 meters of the measurement, as it mixes up the surface waters. For this project, we really want to get undisturbed observations near the surface of the ocean… enter the bow chain!
This is a steel wire hanging over the side of the ship, pulled straight down by a 150 lb weight attached to its end. Along its length, we attach instruments, these then get dragged horizontally through the water as the ship moves. The bow chain measures temperature and salinity over the upper 10 meters of the ocean out in front of the ship’s wake.
In addition, to record water temperature right at the sea surface, we also have a “sea-snake” on the other side of the bow. This is basically a sensor in a garden hose that floats at about 5 cm below the sea surface, dragged along a few meters next to the ship.
We only have the bow chain in the water when the ship is moving slowly, so it has been recovered and deployed a few times now. Everyone enjoys the break from their typical jobs, so we often have a lot of hands out for this type of activity. The forward davit holds the line with the instruments. We use the aft davit to raise and lower a 150 lb. weight that keeps the instrument line vertical. E.S.
The top few thermistors (in yellow) are lifted out of the water as the boat heaves up. (GJ)
Two arms hold out a line of instruments with a weight hanging 10 m below the surface. (GJ)
Spray flies over the bow as the ship plunges into a wave. (AT)
A team pulls the line of instruments aboard while the weight is being lifted by crank. (AT)
A boathook steadies the bottom weight, about 150 lb. (AT)
Keep cranking at the winch! (AT)