October 05, 2021: Returning from Rainbow
Finally, we are approaching Emden Harbour after 5 weeks at sea and 20 intense days of sampling in the working area at the hydrothermally active vent site – called Rainbow - located at the Mid-Atlantic Ridge.
We experienced a different world underneath the sea surface and were very happy to observe the hydrothermal signal in many different ways. The first approach was the turbidity signal that we observed during the downcast of the TM clean CTD. This signal increases in the depth range of the plume due to the detection of particles derived from the hydrothermal source and decreases again below. So, we received information about the range of the plume and the intensity. Moreover and much more impressing was the downcast of the MUC, which is a device to collect sediment and porewater samples. This device was equipped with an underwater camera. The video signal was send to a control unit on board where we could watch it live and “dive” through the photic zone down to approx. 2500 m water depth passing dark clouds that that just recently were emitted from the hydrothermal field. This signal got weaker with more distance from the hydrothermal source since particles emitted from the hydrothermally active sites or that form during mixing with ambient cold seawater precipitate with more distance from the plume source. However, one could still see the signal of the plume on the filters that collected particulate matter > 0.2 µm from 3-9 L sample even though a signal in the turbidity and from the underwater camera was not detectable anymore.
We all are very happy about the successful sampling campaign and look forward to analyse and compile all the data from the participating groups to gain a detailed picture of the plume composition, fluxes of trace metals within in the plume and along the dispersion up to 60 km distance from its source.
What an impressive world we are living in although we cannot see it from the sea surface.
Sandra Pöhle, Vignesh Menon, Lukas Klose
October 04, 2021: Why to collect different size fractions of trace metals? - sequential filtration -
As any other day at a station, the day begins early with the trace metal clean CTD Rosette being lowered into the water to a depth of about 2500m, depending on the results of the bathymetry scan. All the scientists on board are eagerly waiting for their aliquot of water to be processed and analysed. Once the crew confirms the position of the frame at the maximum possible depth, the team leader responsible for that CTD cast extrapolates the depths of sampling based on the turbidity signal (which acts as a proxy for the plume) and closes the water sampler remotely from onboard the ship during upcast of the CTD. As soon as the CTD rosette frame is back on deck the Niskin bottles were carried into a special clean lab container and an unfiltered water sample was collected in a pre-cleaned and acid-washed 2L bottle, to ensure that the collected sample is as pristine and representative as possible. The water sample was then brought to a laboratory that we as Jacobs team can use. The water sample is then immediately processed by implementation of sequential filtration. Sequential filtration is implemented to obtain the different size fractionations of trace metals in a given sample. Within the scope of our research, we aim at obtaining size fractionation of 0.8 , 0.2 and 0.015 micrometer (10-6 m), respectively. For the same purpose, three filtration towers are used, one for each of the size fraction and the sample is processed through the three filters in the respective order sequentially, hence the term sequential filtration.
Initially, the filter tower is fit with the filter membrane with the largest pore size, 0.8 micrometer. For processing each of the unfiltered sample (volume of circa 1.5L), the filter tower is fed with 0.25L at a time and filtered through the respective membrane and the filtrate is collected. In order to facilitate this filtration process, we used nitrogen gas from a pressurized cylinder. Once the whole sample has passed through the membrane, the filter membrane itself and aliquots for different analytes e.g. platinum, which I will analyse within my Bachelor thesis are collected. The process is repeated with the remainder of the filtrate through a 0.2 micrometer filter membrane and then after a 0.015 micrometer filter membrane, with aliquots and filters collected after each of these steps. Some aliquots including the filters are frozen at -20°C and others are acidified to preserve the samples until they can be analyzed in the home lab.
One might be curious as to why go through all the effort to isolate size fractions in the orders of micro and nano meters. The open oceans in general have a low particle load in the water column, for all the larger particles are trapped within the estuarine and continental shelf regions, with exceptions such as the hydrothermal vents wherein there is a direct input of material from the oceanic crust and mantle. Once the hydrothermal fluid mixes with the water column above, the drastic change in the geochemical environment (pH, temperature, salinity) leads to a multitude of the elements in the mineral-rich fluid to precipitate out while the fluid rises to form a plume and spreads laterally in accordance with the water mass currents and buoyancy. The hydrothermal plume from the Rainbow vent field investigated in this expedition extends to north-northwest in ca. 2000 m water depth, which is about 200-300 m about the seafloor owing to the water characteristics of the Atlantic Ocean. To understand the fluxes and processes of various elements associated with the plume, the water samples collected are from below the plume, above the plume and within the plume itself.
This approach of measuring the concentration of elements in these three different size fractions will provide us information about possible processes in the plume that leads to a change in the fractionation of the respective element as the plume progresses. For instance, a decrease in the concentration of an element in a specific size class as we get farther from the plume could indicate removal of particles in this size class. Such an understanding would not only help in interpreting the various (bio)geochemical reactions involved, but also provide an idea on the source and sink (and thereby the flux) of the various elements within the hydrothermal plume and from the hydrothermal plume into the open ocean and thereby contributing to this GEOTRACES process study.
September 06, 2021: Rainbow Cruise
The Thursday morning began with a scrumptious breakfast in the Ship’s on-board restaurant. As we finished our breakfast, we headed onto our labs to start our day. We had to make final amendments to the lab to make it possible for us to carry out sample processing and handling in a trace metal clean environment. The three of us worked on covering up all the metal equipment in the lab to avoid contamination while sample handling. Then on, all the new filter towers and ultrafiltration equipment were unboxed carefully inside a flow bench (an experimental set-up that facilitates clean lab environment) and arranged for a blank test run of the filtration sequence. The following day, i.e., Friday, we were pleasantly surprised by a calm sea, which facilitated us to work in full efficiency in the respective laboratories, wherein we assembled the ultrafiltration setup and collected the respective blank. Nevertheless, the ship was on full steam to our destination, a bit southwest of the Azores with an E.T.A around Wednesday midnight.
Once at the Rainbow vent field region, we, the working from Jacobs under Prof. Dr. Koschinsky, are hoping to sample the Rainbow plume for various elements such as High Field Strength Elements (HFSE), Trace Metals, Pt, Cr and V, which would further on be analysed back in Jacobs University for concentration, ligands and speciation whenever applicable.
As a part of my Bachelor Thesis, I am aiming to analyse the concentrations of the element, Platinum, by implication of Voltametric methods. As a metal whose source, sink and the reaction processes thereof has been scarcely studied, such a study would provide an idea on the elemental distribution of Platinum in the Ocean in the close vicinity of the Rainbow vent field and acknowledge the plume as a source of platinum. Although it is known that the hydrothermal vents could be a potential source for Platinum (Pt) and Platinum group elements (PGE), there has been not much knowledge regarding the concentration of Pt in the hydrothermal vents and the associated plume, and this is the question I’d like to answer through this project.
Given that the expected concentration is in the range of pM (pico molar), extreme care needs to be taken while sampling, on board processing and storage of samples for further analysis. To facilitate such Trace Metal clean environment, numerous precautions and methods are implemented, viz., a Ti-frame CTD Rosette attached with Trace metal clean Niskin bottles from GEOMAR (which close at desired water depths on command) to sample the water column, a clean lab wherein the water samples are collected from the bottles to be transported to the respective working groups, Geo-traces clean (a protocol wherein the bottles go through a series of cleaning with acids and Distilled water) bottles for handling and storage of samples after processing, and finally acidifying or freezing the samples for further analysis once back on land. Apart from the total concentration in the water samples, the size fraction samples are also processed by sequential filtration (at 0.8 um, 0.2 um and 0.015um) and size fractionation of 10KDa by the ultrafiltration, both implemented to understand the size fractionation of the elements respectively.
If you are interested in the individual research questions of the cruise participants enjoy the cruise blog provided by the GEOMAR
September 01-02, 2021: First set-up of our lab equipment and the challenge of enough storage space
Our equipment arrived at RV Meteor 2 days before the three of us, Lukas Klose, Vignesh Menon and Sandra Pöhle, boarded the ship in Emden. Our three palettes stood on deck and we were glad that some boxes were already carried into our lab by our new family members – the scientific crew and the ship’s crew - for the next 5 weeks. Researchers from many different research institutions worldwide e.g GEOMAR, University of Hamburg, University of Marseille, University of Lausanne, Memorial University of Newfoundland participate in that cruise and are highly motivated to achieve their individual goals in a joint effort led by our chief scientist Eric Achterberg, GEOMAR.
At the very first day, when RV Meteor was still in the harbour of Emden, we stored almost all our equipment from 29 boxes into our lab. This is equipped with a long table, holders for gas cylinders, and much storage space in shelves and cupboards. We did not expect that all the pre-cleaned bottles, approx. 900, might find a place in the storage space waiting for their time to be filled with precious seawater – but we managed it.
Our cruise started Wednesday morning, 1st of September, towards the North Sea and we curiously observed the routines of leaving port and passing the flood gate of Emden. The Meteor steamed then on the River Ems north to enter the North Sea soon after. Although the weather is very good and the tide is low some of us suffered from seasickness at least during the first day of the cruise. But after that, we all got used to the movement of the ship and the waves and could enjoy the passage through the English Channel with the English coast to the starboard side and the French coastline to the port side. We already learned that the sea is usually much rougher here; so we are very happy, that we steam through calm waters these days and hope for good weather conditions for the next days.
The Corona pandemic affects also our research trip and we follow distinct hygiene rules that allows us to work safely together.
More information on that research cruise and on the research questions that participating scientist work on will be provided through a GEOMAR blog and we are looking forward to share that link with you soon.
Research cruise M176/2 to the Rainbow hydrothermal field: What happens in the underwater plume?
They form when hot solutions heated by igneous magma escape from the Earth's crust in the deep sea and encounter cold seawater: Hydrothermal plumes are enriched in many compounds, supplying the oceans with nutrients and metals. Researchers from Jacobs University Bremen want to investigate exactly which geochemical processes take place in them in a detailed study of the Rainbow Hydrothermal Field on the Mid-Atlantic Ridge, an area not far from the Azores.
The project at Jacobs University is led by Andrea Koschinsky, professor of geosciences. On the cruise led by GEOMAR Helmholtz Centre for Ocean Research Kiel, which will start in Emden on Sept. 1, 2021, and end there on Oct. 6, 2021, PhD student Lukas Klose, postdoctoral researcher Sandra Pöhle, and bachelor student Vignesh Menon will be on board the research vessel "Meteor" to take samples and blog about the cruise.