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Our wonderful cruise is now definitely coming to an end. We are nearly on our way back home, heading for one last station where we will cast a final CTD and send an ARGO float on its journey. These floats are part of a giant international project and basically drift with the water currents, all the while consistently measuring the salinity, temperature and pressure of different water layers. While writing these lines, there are about 4000 floats deployed in the world’s oceans. Tonight, it’ll be 4001. The floats are able to adjust themselves to maintain a certain depth and take measurement profiles along vertical transects. Every now and then (approximately every 10 days) they dive up to the surface and send the acquired data to a central data base. Being equipped with a SIM card, the communication between the ARGO on the sea surface and the data centre happens via satellite – this is the only stable and reliable way to transmit data, especially when being so far from land and away from any network reception. Once transferred, the raw data are processed and quality flagged automatically. This data freely and publicly available – if you are interested in the project and its data, you can visit the German hydrographic office website, who provide a platform for the ARGO program as well as regular updates on the whereabouts of active floats.
All of those measurements, data handover, and their publication happen within minutes to very few hours – hence anyone can observe the ocean parameters in near real-time. Scientists all over the world use these data to compute and predict currents, temperature variations, and weather and climate forecasts – they can even be used as tsunami early warning systems.
The life span of an ARGO float is about 4-5 years which is, compared to their small size (~ 2 x 0.3 m), a very long time – considering constant data recording, as well as large temperature and pressure variations, is battery intensive. When their expiry date has almost arrived, they travel to the surface one last time to send an EOL (end-of-life) message saying goodbye to the operators and then dive down to 1000 m to die. Unfortunately, there is no effective procedure yet for retrieval and re-use which is why all the ex-ARGOS gather in the water column at -1000m. However, efforts are being made to design a recovery method and involve recyclable material for the ARGO construction process. Once in a while, dead ARGO floats are being caught by accident. Last week, one was retrieved by a Portuguese fishing vessel – it is now on land and back in the hands of the operator. Its final words are not yet spoken and maybe it gets a chance to live a second life!
From my side, unfortunately these are the final words on this blog. It has been a true pleasure writing it and I would like to say thank you to you, dear readers. I hope you keep an eye on our iAtlantic homepage and on the Senckenberg website – our mission goes on and so does ocean research! At the end of an expedition, we scientists always have the ideas for the next one. The story will be continued…
The cruise is slowly coming to an end and we get a sense of home as we cross 54° N latitude. However, sniffing familiar air again doesn’t mean that there is no more work – on the contrary: we have reached the deep abyssal plains of the North Atlantic and start our measurements from 3500m down to 4500m water depth to get an idea about species distribution along a depth transect. Abyssal plains are the remote result of a spreading sea floor that is constantly being pulled sideways and stretched, meanwhile being covered in a fine grained sediment layer of silt and clay. Those plains make up almost 50% of the Earth’s surface – and they play a major role in the ecosystem.
To the untrained eye, there is not much to see: basically ‘only’ mud, wormholes, a fish every now and then, and countless numbers of sea cucumbers in all forms and sizes. For an expert however, the vast sediment desert and its residents are crucial to the fundamental carbon circle and, therefore, to the entire nutrition cycle. Anything that is washed into the oceans by rain, rivers, and organic matter from dead biomass eventually settles on the seafloor. Abyssal plains therefore act as carbon sinks, with carbon being held in the sediment until it is reworked by crucial fauna. The time taken for material to reach the seafloor can be incredibly slow, with sedimentation rates in the order of mm/1000 years.
This is also what life is like down in the deep: Unhurried and relaxed. Predators are opportunist feeders – waiting for prey to swim by rather than actively hunting it. Less so are the sea cucumbers or holothurians, who constantly devour the sediments and filter it for nutrients. Through their transparent bodies, this process is clearly visible and basically what goes in, comes out again, once particular organic matter has been digested. They leave (sea-cue-)cumbersome traces on the sediment as they gradually sweep over the seafloor– and sometimes, these trails end all of a sudden in the middle of nowhere, with no one in sight anywhere. This is when sea cucumbers decide to travel for a longer distance – they flood their body with water until they float and then go with the flow, wherever it may take them. Some specimens also have a sail that enables them to aim in a certain direction.
We leave the beautiful vent site behind us and head further south, riding on the storm and through heavy waves again. Time to take a look at what is going on in our onboard laboratories!
When samples are taken – geology or fauna from the ROV dives, EBS, plankton net, MUC, and box corer – they have to be observed and documented. Depending on the sample type, there are various methods to investigate the ‘prey’: sediment is being washed and sieved, water is being filtered to remove ‘pollution’ – larger bits that may misrepresent the actual sample – whereas bigger samples from the ROV or plankton net go directly into the labs to be examined under the microscope. Then comes the sorting. If you have ever wondered why biologists (maybe humans in general) have the tendency to create never-ending lists of various categories: groups, families, sub-families, genus, species and sub species … (to be continued) – here is why: things have to be put somewhere! Following ‘if you have a problem, give it a name’, taxonomy and generating categories are key to communicating about biodiversity and our understanding of how species distribute, behave and function together. This is why biologists sort all samples (in laborious, time-consuming fashion) under the binocular microscopes into groups: to find common features, similarities and differences across the collected species. The most frequent animals they find in the micro- to megafauna are: corals (anthrozoa), sponges (porifera), crustaceans (including decapods, amphipods and isopods), shells, molluscs (bivalvia and gastropoda), and the vast array of worms – the polychaetes. Each of them tells their own story about its habitat and the ecosystem it has been living in, as well as tales about its eating habits and travel patterns. For example, worms prefer soft sediment where they can dig a hole and either filter the water to feed or, in some cases, catch passing smaller animals. A rocky mid-ocean ridge is not a suitable environment for a soft sediment worm – hence it acts like a natural barrier and keeps the worm in place. All of those elements – fauna or ‘dead’ material like sand and stones – are interwoven in highly complex patterns, all interacting and forming unique and vulnerable habitats that react to even the smallest changes. We still have a long way to go and are far away from understanding this multifarious structure, but in very small steps we are getting there.
Depending on the field of interest, the next steps in the sample processing journal are fixing (preserving) the animal in either formol or ethanol, to allow us to investigate its morphology or genetics, respectively. The removal of animals from the seafloor is a very sensitive subject, and we strive to not take more specimens than we need to understand and describe the ecosystem efficiently.
But now for something completely different. It’s …. dark again at night time! After three weeks of 24h sun, which is stunning and beautiful but completely messes up the daily rhythm, a few dark hours are a gratefully-received gift for a much-needed sound sleep!
We found it! Our wish came true after about two hours of ROV diving in the dark on the legendary Reykjanes Ridge structure: The long desired hydrothermal vent field suddenly appeared in front of the cameras! Spewing out hot water up to 300°C, these little vents enable unique biodiversity in a peculiar looking environment. If I didn’t know we were about 700m under water, I’d probably think we had landed on the moon: standing on bizarrely-formed rocks and watching a chimney 1.5m high that pours hot fluid into the near-freezing cold water column is an extraordinary experience. Huge red fish, a giant halibut and numerous squids joined our dive through this dreamlike world. Unlike our former dive areas, where sediment and coral reefs prevailed, this one looks like as if giants had played cosmic marbles: the seafloor is covered in rocks (pillow lavas) that are almost perfect spheres, each about 0.5 – 1m in diameter. And what seems to be inhospitably rough environment is in fact full of life. A fundamental part is played by the large bacteria mats that spread in a smooth white layer over the rocks. They feed on the hydrothermal fluids and announce themselves by dispersing what look like big snowflakes in the water column. Hence each time we felt like flying through a cold winter night’s landscape, those bacteria mats couldn’t be far! And where they are, hydrothermal activity must be, thus they act as perfect signpost for our vent hunt. Many species rely on these mats, amongst them are a variety of anemones, crustaceans, corals and fish. They also enjoy the warmth of the vents and they vanish once the hydrothermal activity stops – that is why we passed over vast coral graveyards: similar to volcanoes on land, hydrothermal vents have an expiration date and cease to be when their time is up. The surrounding water that used to be lovely 20°C cools down to about 5°C which makes it uninhabitable for these corals. They die and leave behind fields of brittle bony pieces.
We’re in the middle of our transit to the Reykjanes Ridge region south of Iceland. This is a good time to talk about the bigger picture, why we chose Iceland as a research area and what it’s all about!
Iceland sits right on the northern Mid-Atlantic ridge, where the Eurasian and the North American plates are drifting apart. It is still active, meaning that the seafloor is spreading at the mid-ocean fracture zone and new crustal material is being produced from the uprising magma. All of these plate tectonic processes involve volcanic activity and the formation of hydrothermal fields, above as well as below the sea surface. Particularly in the case of the latter, the volcanic geology attracts numerous species that make up the delicate biodiversity of the North Atlantic benthos. Hydrothermal vent areas, where hot water escapes the earth’s mantle and meets the cold deep-sea waters, can be home to unique fauna that is rarely found anywhere else. Also, the topography on and around Iceland is exceptional: the island is surrounded by the deep Denmark strait channel on its western continental shelf, triggering a massive submarine waterfall about 600m high. On the island’s south-east side, ridge and sea mound structures prevail and cause a complex pattern of different water flows, from among which one of the most important is the north Atlantic overflow – a very strong and deep water current. The Norwegian Basin north of Iceland is the deep, ‘calm’ abyssal plain. Hence in terms of geomorphology, biodiversity and oceanography, the North Atlantic is a natural laboratory which holds the key to so much information about the formation and origin of life and our planet.
There have been numerous cruises to this area before and with IceAGE3. We are trying our best to fill data gaps and build upon a database of samples and models that has been existing for many years – aiming to find explanations for the distribution and population variations of species (and what could be a better indicator for that than isopods?), how and where they travel and how they react to a changing climate, and human impacts. So far it has been discovered that isopods wander from Norway to Iceland and then head down the Reykjanes Ridge – the part of the Mid-Atlantic ridge located just south of Iceland and is basically the extension of the faults on the island. This is where we are steaming to now, ETA tomorrow morning. We will spend the next three days in this area searching for hydrothermal vents and hunting gas bubbles that are emitted from their chimneys. Using hydroacoustics and imagery from ROV dives, we hope to discover more of this mystical under water world beauty.
Before beginning on the long transit to the ‘southern’ part of our voyage, we spend another two days sitting on Iceland’s continental shelf and doing ROV dives through the beautiful coral reef landscapes. Sadly, evidence of fishing pressures on these beautiful structures is visible. Corals need centuries to reach maturity, and on seafloor devastated by fishing activity they will probably never be able to grow again. Even in the bathymetry data we are able to see the footprint left behind by (most probably) the nephrops trawls – a fishing instrument used to skim over the seabed to catch lobster and langoustines. The positive side of this story is that the reefs were destroyed before people knew about their existence, and the reefs in the Lonsdjùp area were placed under protection in 2011. We aim to create more and more marine protected areas in the future.
Luckily, there are still some very vivid reefs and ocean inhabitants around us, as we can tell from the ROV dives. Thanks to incredibly good weather conditions – warm (well, as warm as it gets at 63° N, but t-shirt weather works!), sunny and calm sea – we can dive nearly every day.
Speaking of which – it is a unique experience to see R/V Sonne so far up north, as its usual area of operation is the Pacific and Indian Ocean. Although coronavirus is limiting a lot of travel, we now at least have the opportunity to do our research in the colder waters. Seeing this vessel in front of Iceland’s snow-covered summits is a very rare scene that we are able to enjoy, thanks to the gorgeous crew who took us on a Zodiac tour around our mother ship. Tomorrow it’s time to leave the continental shelf area and head for a region south of Iceland on the mid Atlantic ridge, where we hope to find hydrothermal vents.
We spend this day a little further north-east on the continental shelf sampling for all we are worth! In total, we have 20 stations (deployment of four CTDs, four box corers, four multi-corers, four epi-benthos sledges, and multibeam in between!) to be finished today before tonight’s transit back to the panoramic view on Iceland – a tough schedule but the weather is unbelievably nice, with sun shining and a dead calm sea! The day started again with another (or the same?) big school of pilot whales hanging around and watching us – life could be worse! Enjoy the photo show!
Yesterday morning we arrived on the continental shelf of Iceland – and a stunning panorama of glaciers, volcanoes and the rough cliffs of that beautiful island was awaiting us, immersed in bright sunlight. Not only was the view above the ocean surface great, but the ROV dive along the seafloor was once again a fascinating journey through all sorts of corals, lots of fish, fields of sponges, barnacles, and many more interesting beasties! There is a special interest in coral reefs as they are very important for both the food web and habitat complexity. Whilst to the untrained eye there is hardly any life on the sedimented seafloor, once solid substrate appears, life flourishes and complex ecosystems develop for all to see. Coral reefs can be vast in their extent and aid in the diversity of live in the surrounding area the improving habitat heterogeneity. Hence preserving coral reefs is a major concern for nature conservation and also for the fishing industry. Within the iAtlantic project, predicting such reef structures from bathymetry and its derivatives (slope, backscatter etc.) using spatial distribution models is an inherent part of our work. Depending on their accuracy, those models can be used to create habitat maps and locate coral reefs without having to conduct costly and time consuming (although really, really nice!) ROV dives. Also, highly accurate models can reduce the need for in-situ sampling, which is carried out more or less blind, though some ground truthing is of course inevitable to feed the models and to examine their performance. Laurence de Clippele from University of Edinburgh, UK, is working in the iAtlantic project and she is the one creating such models. She has provided us with her data that show maps of potential coral reef locations. We are now trying to verify those models by diving in target areas indicated by the models to confirm whether it is a coral reef or not.
As those vulnerable reef structures can become a victim of trawl net fishing, we hope to put those sophisticated complex organisms under protection against human impacts.
We have spent three spectacular days in a row in the deep! Today and yesterday, we dived down to the beginning of Aegir Ridge fracture zone with our ROV and witnessed, once again, the most stunning impressions of life on the unknown mysterious seafloor. Nothing can describe what we look at better than images and that’s why I will stop writing soon and let the photos speak! Just one more important thing to mention at this point: Yesterday (4.7.2020) was the 300th dive for the ROV Kiel 6000. This is a good opportunity to congratulate the excellent ROV team and thank them for making these unforgettable dives possible! It’s an honour to be part of this fantastic journey with such remarkable imagery of the flourishing life below the water surface.
Day 13: Friday 3 July 2020
A day full of mapping! We have put behind us 20 hours of transit to our next survey area, located just east off the Icelandic continental shelf, at the very beginning of Aegir Ridge. That’s where we expect to find reefs of cold water corals – the ‘Lophelia’. Corals are, as any other hard substrate on the seafloor, the solid base to most marine life. They build vast reef areas and are home to the most delicate biodiversity. Although being totally different in appearance and motion, medusae (or jellyfish) and corals have something in common: both animals belong to the group Cnidaria. They use nettles to capture their prey and to defend themselves against predators. However, unlike jellyfish, the corals’ harpoon-like nettles sit in cnidocytes and can be expelled whenever something is passing by.
Depending on the local water depth, corals can be seen in the multibeam bathymetry. Hence doing a careful map survey in advance to a ROV dive can save a lot of time as the location of the dive and where to take samples can be decided a lot more precisely. However, it’s also important to know the local water depth, which can usually be derived sufficiently enough from satellite altimetry (down to a resolution of about 1km, the seafloor topography can very roughly be obtained from satellite gravity measurement). In this special case however, at the beginning of Aegir Ridge, the difference in depth between the altimetry model and the true multibeam bathymetry was up to 1000m – and that makes a huge difference if the water depth is between 700 and 2600m!