oceanography – Seabed Habitats

How do marine heat waves affect cold-water corals in the deep-sea?

Ocean temperature plays an important role in governing the biophysical environment and in turn the realized ecological niche of benthic organisms and the distribution of marine habitats in the global ocean. As a result of anthropogenic-induced climate change Marine Heat Waves (MHWs) have resulted in widespread coral bleaching and mass mortality of tropical corals. Comparatively little is known about the impact of sub-surface MHWs on cold-water coral communities in the deep-sea, which lack the dependence on symbiotic zooxanthellae of their tropical cousins in surface waters. This study aims to address this deep-ocean knowledge gap utilising numerical modelling.

Previous studies have shown that prolonged and intense sub-surface MHWs and their cumulative intensity results in increasing thermal stress encountered by benthic organisms in depths down to 2000m. This study utilises hydrodynamic modelling outputs of reanalysis data to study impacts of sub-surface MHWs on cold-water corals. With intensification and duration of sub-surface MHWs predicted to rapidly increase in this century, it will increase the thermal stress experienced by cold-water corals and associated communities in the deep-sea.

It is hypothesized that through increased stratification and increased mixed layer depth due to increased storminess and deepening of the thermocline, cold-water coral distribution will be impacted physically (mechanically), however their mortality is more likely to be dependent on food availability and oxygen supply. Preliminary results support this hypothesis in the North Atlantic, indicating that although the cold-water corals may be resilient to thermal stress physiologically, the resulting physically dynamic environment will lead to secondary impacts at the local scale in the benthic boundary layer. Furthermore, oxygen saturation has been found to decrease with increasing temperature and is likely to have a secondary impact on cold-water coral health. This study demonstrates how numerical modelling can provide quantitative spatial and temporal information of biophysical interactions to inform marine habitat mapping studies and species distribution models of habitat suitability.

(Background: This is my research abstract made for the GeoHab 2024 conference – if you would like to learn more, my short oral presentation will be happening on Thursday 9th May 2024 at 1415 in Arendal, Norway. More information about the conference, including how to be a virtual participant, on the official conference website. An interesting program!) See also: https://www.marineheatwaves.org

New update: Marine Heat Waves Shiny App!!

Science

Guest Post by Damien Guihen of British Antarctic Survey

My name is Damien Guihen and I work for the British Antarctic Survey in Cambridge, UK. I am an oceanographer and study the interaction of physical processes with biological systems. At the moment I am part of a project called GENTOO, which stands for Gliders: Excellent New Tools for Observing the Ocean. The project is named after a species of penguin and is a partnership between the University of East Anglia (UEA), the British Antarctic Survey, Caltech in the US and the University of Cambridge. Together we are trying to use special robots that dive as deep as 1000 m underwater to learn more about how the ocean works in the Antarctic and particularly around the Antarctic Peninsula, that part of land that juts out of the frozen continent and stretches towards South America.

The robots being used are called ocean gliders. These gliders use changes in an oil bladder to sink or float and have short wings that move them forwards. We put the gliders in the water for periods as short as a day or as long as six months. They are very efficient and can take measurements for long periods using a range of sensors. A glider uses a satellite to call home every time it comes to the surface. It phones a computer in the UK and uploads its data. Then it asks for new instructions. This way, we can see the data very quickly and can control it from anywhere in the world.

Ocean Glider deployment map — Ocean glider deployment map shows the path taken by the ocean glider, west of the South Orkney Islands. The breaks between the red lines are when the glider is at the surface

The partners in the project are investigating different aspects of the ocean. UEA are using the high resolution temperature and salinity data from gliders to understand the different layers of water and how they interact. The Southern Ocean is very cold and dotted with countless icebergs, great and small. The cold causes water to sink and this sinking drives a lot of ocean flows. Using the glider allows UEA to take hundreds of thousands of measurements that help them to build a better picture of what is happening. Caltech are using the gliders, along with some floating instruments called drifters, to measure how the water in the southern ocean is mixing and moving. They have tracked some drifters for thousands of kilometres, from the Antarctic Peninsula to South Georgia. The University of Cambridge team are using the data collected to help build better mathematical models of how the water moves so that they can better describe and predict the mixing, particularly on slopes and near the icebergs.

At the British Antarctic Survey, we are using a special instrument that has been built into the glider. The instrument, called an echo sounder, sends little pings of sound. It then listens to the echo that comes back from small animals in the ocean. As the glider moves around, we collect a lot of data from the pings in different locations and at different depths. We can then use this data to build a picture of the distribution of these animals throughout the ocean. Using the data from the other groups, we can get a better idea how the ocean currents push the animals about and how a changing climate might effect the Antarctic marine ecosystem.

Working on a ship or a base in the Antarctic is always fascinating. Sometimes we have to crash our way through thick ice to get to where we need to go. We see a lot of ice bergs too and each one looks different. We often see large storms that keep us up at night as the ship rolls its way through big waves. We are fortunate too to see a lot of wildlife such an albatross, giant petrels, cape petrels, skuas, orca (killer) whales, elephant seals, crab-eater seals, Weddell seals, fur seals, and penguins such as gentoo, chinstrap, king, Adele and Magellanic. It’s a wonderful experience and each time I come back I count the days until I can go again.

A very big thank you goes out to Dr Damien Guihen of the British Antarctic Survey for sharing his experiences and photographs from the Antarctic with us the readers of this blog! The post has given a fascinating insight into the work of BAS in one of the most remote and undiscovered continents on the planet.

Technology

Benthic Lander Deployment

A benthic lander is a large three-legged frame with oceanographic instruments and sensors attached to it. These measure a range of parameters in-situ at the seabed; such as in this case, the current speed, temperature, salinity and turbulence. They are designed to operate in some cases 1000s of meters below the sea surface. Weights or ballasts are used to make the otherwise positively buoyant lander land down on the seafloor.

Here it was deployed from the Irish research vessel the Celtic Voyager in Galway Bay, West of Ireland, during a cruise by the National University of Ireland, Galway. The lander remains monitoring the conditions at the seabed for one month, in this case at depth of ~25m. Whilst out at sea during this period, it observes the impact of storm waves on the sediment transport. By making measurements at various heights above the seabed, it can obtain a profile of the benthic boundary layer and allow us to study how this changes during a storm.

By adding different sensors, you can also measure the chemical and biophysical properties of the water at the sediment-water interface. In-situ measurements allow us to study in the natural laboratory of the sea, without the need to remove anything. The measurements obtained by benthic landers are often used to verify as well as compliment laboratory results made under controlled situations.

It also has an acoustic positioning transponder which responds to the ship’s positioning call, to locate it for collection after its deployment. The weights or ballasts are released, with the buoyancy from the yellow floats allowing the lander to float back up to the surface.

Welcome

Welcome to Seabed Habitats- The newest blog about everything to do with marine habitats.The marine realm is such a dynamic system and is very much an “unexplored wilderness.” Being a relatively new science (with most sub-disciplines being only 50-120 years old), a lot of work is being done to gain a thorough understanding. With technological advances happening rapidly, there are always new methods to try out and new equipment to test. With research being so interdisciplinary in nature, spanning a range of areas such as marine ecology, marine geology, coastal processes, geophysics, oceanography, hydrography, remote sensing, surveying, GIS.. This blog attempts to keep you up to date on the latest developments in the field. From new research ideas to images to the latest technology- all can be discussed here.

Please feel free to send your suggestions by adding a comment or taking part in our poll below.