On June 1st 2018, we will start expedition SO263 TONGARIFT on board the German research vessel “SONNE” in Suva, Fiji.
In total, 34 scientists from different institutes will be on board: from GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg (Chief Scientist: Prof. Dr. Karsten Haase), from Jacobs University Bremen, the University of Bremen, MARUM – Center for Marine Environmental Sciences at the University of Bremen, MPI Bremen, the University of Münster, from the University of Bayreuth, as well as international partners from the universities of Victoria and Ottawa, Canada and from the University of Hawaii. Additionally, a Tongan observer will join our expedition.
Our destination is a two-day trip away from Fiji, the Tonga arc, an island arc with dozens of active and inactive volcanoes at the bottom of the sea between 700 and 2000 meter water depth.
The focus of our expedition is the exploration and characterization of the geological and geochemical processes as well as the biological activity along the Tonga island arc, as these hydrothermal systems differ strongly compared to those at mid-ocean ridges.
MARUM-QUEST, the deep-sea remotely operated vehicle owned and operated by MARUM (University of Bremen) will be used to take samples directly at the source of the active hydrothermal vents. Apart from fluids, it will also sample rocks, ores and organisms such as mussels. A TV-grab will collect large amounts of rocks, while a water sampler, equipped with different online sensors, will take several liters of water from different water depths.
We will take water samples directly at the hydrothermal source as well as along the entire water column up to the surface. This is primarily done to characterize the less studied elemental fluxes of hydrothermal systems along the Tonga island arc and the understanding of their role for the global elemental budget of the ocean and for local chemical and biological processes in the water column and at the seafloor.
Here, the researchers report in a ship’s log about life and work on board.
June 19th: Trace metal supply to the ocean
In addition to the fluid chemists from University of Bremen, who are mainly interested in the gases in the fluids, the team of fluid geochemists aboard consists of Annika Moje, Charlotte Kleint and David Ernst from Jacobs University in Bremen, Britta Planner-Friedrich from University of Bayreuth, Ingo Meierhoff from Münster, Christian Peters from University of Münster, and Frederike Wilckens from MARUM – Center for Marine Environmental Sciences at the University of Bremen.
The fluid geochemists work with the fluids that are taken from the hydrothermal plumes collected by the water sampler and from the hot and diffuse hydrothermal fluids sampled by the MARUM-QUEST. One question of interest, for example, is how much arsenic and iron are released from the different vents and how far these elements can be "tracked" in the water column. Do these elements reach the top 200 meters of the water column, the photic zone, where bioproductivity is highest and most organisms live? Iron is an important but limited micro-nutrient for almost all marine organisms, whereas arsenic may have toxic effects. However, especially in the environment of hot vents, many microorganisms can at least tolerate arsenic or even use it to gain energy.
Some of the fluid parameters are already determined on board. Immediately after sampling, pH, oxygen, salinity and redox potential (Eh-value) of the fluids and plumes are measured. In addition, iron, sulfide, magnesium, calcium, and chlorine concentrations of the fluids are determined. Based on these initial results, we can estimate the quality of the sampling, i.e. the purity of the collected hydrothermal fluids. In addition, we can make first statements about the processes and sources that influenced the hydrothermal fluids.
However, the main work in the lab aboard is the sample preparation for transport and later analyses in the labs at home. As many fluid components are not stable under surface conditions, the sample preparation must be very fast. Thus, all fluid geochemists are already impatiently waiting as soon as the water sampler or the MARUM-QUEST come on deck to process the samples as quickly as possible. Depending on the later analysis, the fluids are filtered in various size fractions, partially acidified, cooled or frozen. In addition, the volatile components of the fluids are fixed, which is necessary for some of the methods to ensure accurate and precise results.
June 18th: MARUM-QUEST finds TV-Grab sampling location
During our dive today at a southern seamount in the Niuatahi Caldera, the MARUM-QUEST found the location that was sampled by the TV-grab the day before. The area is visible in the picture as the white hole.
Despite the size of the drag and the rather simple technology, it is shown that the TV-grab is able to take samples quite selectively, without leaving bigger damage at the seafloor.
The picture shows the different camera perspectives of MARUM-QUEST, which make detailed navigation and sampling with the ROV possible.
June 15th: Arriving in the third working area – Niuatahi Caldera
Today, we arrived in our third working area of SO263, the Niuatahi Caldera. During the first dive, we already reached a new temperature record, while successfully sampling two black smokers showing temperatures of 324°C and 334°C.
The petrologists and fluid chemists of the working group “Petrology of the Oceanic Crust” from the University of Bremen and MARUM – Center for Marine Environmental Sciences – Wolfgang Bach, Patrick Monien, Alexander Diehl and Stefan Sopke – take care of the sampling and first analysis of the emitted hydrothermal fluids from the black and white smokers.
Besides basic parameters, such as temperature and pH, alkalinity (the acid buffering capacity of water) as well as concentrations of hydrogen and methane are measured on-board immediately after a ROV dive ends.
Fluids are collected with isobaric gas-tight (IGT) samplers, which allow us to bring up the fluid while maintaining seafloor-pressure insight the sampler. Gases dissolved in the fluids at great pressures do hence not escape when the MARUM-QUEST comes up from the deep sea. In the lab, the fluid samples are drawn from the IGT-samplers into gastight syringes. Gas bubbles form inside the syringe when the pressure drops, similar to what happens when opening a bottle of sparkling water. Afterwards this gas is injected into a gas chromatograph and separated into its individual components, before two detectors simultaneously analyze the concentrations of methane and hydrogen. The concentration of hydrogen is a particularly crucial parameter in determining the subsurface environment as well as the occurring type of interaction between the hot fluids and the volcanic rocks.
This key parameter enables us, with the help of thermodynamic calculations, to better understand the chemical parameters that occur at the ocean floor, deep below the hydrothermal vents. Gas concentrations further play a major role for the fauna on the hydrothermal vents, as they represent the “fuel” for the chemosynthetic organisms.
To facilitate complete and detailed analyses of these precious fluids, all samples from the IGTs are split between the involved fluid chemists from the University of Bremen, the Jacobs University, the University of Münster as well the University of Bayreuth.
June 10th: “Mussel Mania” – Niua North
After we got several rocks and hydrothermal fluids (displaying temperatures above 300°C) in the 1200 meter deep working area Niua South, we are heading to our next working area, Niua North.
Niua North is located in only 700 meter water depth, and, as the name suggests, it lies approximately 10 kilometers north of Niua South.
The hydrothermalism is very different when compared to Niua South – instead of black smokers, it is rather apparent as white smokers. The fluids are very acidic (pH 1.8), sulphurous as well as gas-rich; the vent field is named Hellow Vents.
While we just found a single mussel in Niua South, there is a whole field of mussels in Niua North (Mussel Mania). The microbiologists Merle Ücker and Miguel Ángel González Porras from the Max Planck Institute for Marine Microbiology in Bremen are already excited about the first samples from this area.
The net, which is used by MARUM-QUEST to scoop the Bathymodiolus mussels, is securely stored in one of the drawers of the ROV. Once on deck, everything has to go fast: The mussels are quickly dissected in the labs of RV SONNE to minimize any sample alteration. The super-developed gills are their most interesting organ, as they contain the bacterial symbionts. These allow them to thrive “down there”, where it is dark and basically no organic matter present to feed on.
The bacterial symbionts are chemosynthetic, meaning that they are able to “digest” the reduced compounds that are released by the hydrothermal vents to produce organic matter, which is ultimately transferred to the hosts: The mussels.
Back in Bremen, the mussels’ gills will be studied in the laboratory. There, the microbiologists aim to understand how the symbionts and the mussel interact using a “molecular language”, how diverse the symbionts are, or how their population is determined by environmental parameters.
June 7th: Samples from the first working area – Niua South
After all labs are now fully equipped and all large equipment is ready for deployment, we are curious and happy to get first samples.
During the nights of the 3rd to 7th of June, four successful TV-grab deployments each night brought several kilograms of rocks from about 600 -1500 meter water depth aboard SONNE.
Amongst the rocks are not only pumices, frequently found in island arcs, but also basaltic samples, which are essential to understand the formation of the Niua South region. The range of recovered rock-types allows us to plan and adapt the upcoming TV-Grabs based on rocks and pictures from previous deployments to ensure an efficient sampling. Sawing, description and packing of the rocks for the transport back home is directly performed on board.
To detect possible plumes in the first working area Niua South, four additional profiles with the water sampler (so called tow-yos) were performed. To do so, the water sampler is towed behind the SONNE (which is moving along the selected profile with 1 knot), while online sensors continuously and live report parameters, such as depth, salinity, pressure and – most important for us – turbidity. A turbidity signal indicates that particles are present in the water column and is most likely a sign for a hydrothermal plume. In such depths, the bottles are closed by just pushing a button in the lab. Up to 24 bottles, 12 L volume each may be closed during each tow-yo. Back on deck, the scientists are waiting already to fill samples from the different bottles and respective water depths.
With the help of these profiles and later analysis of the samples, we are able to estimate the dimensions of the plume – lateral and vertical.
Our most important sampling device, the “MARUM-QUEST” dives already for the second time and delivers spectacular images and samples from the seafloor. After diving through the 1200 meter deep water column, it directly landed in an area with active and inactive hydrothermal vents. Therefore, the sampling could start right away.
Apart from rocks and ores, “QUEST” will also sample fluids, as well as biological samples, such as mussels, snails and tube worms.
The first processing and treatment of the samples starts directly in the labs of RV SONNE and will last into the night, while simultaneously the next device is already launched into the water to bring more samples aboard.
June 3rd: SO263 TongaRift started
In the morning of May 31st, all scientists embarked RV SONNE and moved into their cabins. As all containers and airfreight have arrived by that time, we left Suva, Fiji, towards Tonga around 9:00 am local time in the morning of June 1st. On board are geoscientists of several different disciplines, such as petrologists, geochemists, oceanographers, specialists for hydrothermalism and biologists. Some participants are still suffering from seasickness, due to strong winds and waves, however, the weather forecast is good and we are expecting better weather soon. As a full stomach is always good in case of seasickness, we are very thankful for the delicious food on board.
We use the two days of transit until we reach our first working area to fill and prepare the empty labs of RV SONNE. The setup reaches from a big rock saw to clean-labs for trace metal free work.
Additionally, the brought instruments, such as a gas chromatograph for the analysis of different gases or a photometer for the analysis of iron and sulfide are tested and set up. Work is not only carried out inside the ship, but also outside, where the bigger equipment, such as a water sampler, a TVgrab and of course the deep-sea robot ROV MARUM-QUEST are being prepared for their first deployment. The very helpful and skilled crew is supporting us with our preparations and also smaller issues are fixed immediately.
For June 3rd, the first sampling station is scheduled. During that station, we will use the water sampler to get water samples from different water depths. These samples are used for the analysis of background concentrations, but also to calibrate other devices. Following the water sampler, we will deploy the TV-grab at night, which will bring rocks from the sea floor on board SONNE. A first dive with MARUM-QUEST is scheduled for June 5th.
We are very excited and look forward to our first samples as well as to spectacular images of the hydrothermal systems.