Good bye Croker!

After two weeks in the Irish Sea packed with action, our time has come to say good bye to the Croker Carbonate Slabs cSAC/SCI. We have had an amazingly productive survey and collected a huge amount of data, all ready to be analysed (see maps)!  In total we undertook 130 drop camera transects, visited 62 grab sample stations and deployed 176 grabs, we also travelled over 360 km collecting acoustic data. One of the really interesting components of this survey was seeing the variety of sampling techniques used coming together to give a detailed picture of what is happening at the Croker Carbonate Slabs cSAC/SCI both above and below the seabed.

Acoustic data collection (©JNCC/Cefas 2015)

Ground truth data collection (©JNCC/Cefas 2015)

The JNCC team wants to thank all the staff onboard the RV Cefas Endeavour, in particular the captain and crew, for all their hard work and another successful survey for the JNCC/Cefas partnership.

Until next time, bon voyage!

Good bye from the day shift (©Neil Golding/JNCC 2015)

Good bye from the night shift (©Neil Golding/JNCC 2015)

Sample O'Clock

With half of our time at the Croker Carbonate Slabs behind us, and a large quantity of acoustic and video data already under our belts, at the weekend we started collecting some samples!

Collecting samples for analysis in the marine environment is unfortunately not as simple as on land. However, there are a number of handy bits of equipment that we can use. On this survey we are mainly using the mini Hamon grab, and occasionally a Day grab.

The Hamon grab is deployed from the boat to the bottom of the seabed, where upon contact a mechanism in the device allows the jaws to shut, taking in a sample of the seabed which can be up to 8 litres. Two samples are taken from  each successful grab, one for a Particle Sediment Analysis (PSA) to determine the sediment type present and another to examine the fauna (sea creatures) which are living within and upon the sediment. The Day grab differs slightly in design from the Hamon grab as the sediment maintains an intact surface layer allowing a sediment profile to be taken. The Day grab is being used in a few locations to provide further detailed information on what microscopic creatures live within the top five centimetres of sediment (known as the meiofauna).

We will be collecting grab samples from across the survey area to cover the range of habitats we’ve found. Any samples of possible methane-derived authigenic carbonate (MDAC) will undergo carbon isotope analysis back on land in the laboratory.  This will tell us whether the carbonate rock is in fact methane-derived.

Collecting a sample from the mini Hamon grab. ©Neil Golding/JNCC 2015

Samples of ‘possible’ MDAC collected by the Hamon grab. ©JNCC\Cefas 2015

In addition to ‘possible’ MDAC in our grab samples, we have had a number of interesting critters, some of which we’ve seen on the video tows, including crabs, sand eels, anemones, feather stars, starfish and even a squat lobster!

The good weather conditions we’ve been experiencing have also allowed us to take water samples from a number of stations across the survey area. These will be analysed once back in the laboratory to look at the presence and concentration of gases.

Taking a water sample. ©Neil Golding/JNCC 2015

By Neil Golding and Chris Jenkins 

Life on (possible) MDAC

Interspersed with the collection of the acoustic data we previously posted about, we have also been taking videos of the seabed throughout the area in the hopes of finding possible MDAC. The drop camera (see picture below) is deployed over the side of the vessel and feeds real time video footage of the seafloor to us in the onboard lab. Another piece of equipment unique to this survey is a methane sensor that we attached to the camera frame. The ‘methane sniffer’ measures the concentration of methane in the water column and will help us to identify if there are any active methane seeps.

Drop camera frame. ©Neil Golding/JNCC 2015

A number of the video tows have shown images of what we believe to be MDAC throughout the survey area. This ‘possible’ MDAC comes in all shapes and sizes and there are often a number of interesting creatures either attached to it or hiding under MDAC ledges. 

 ‘Possible’ MDAC boulder on subtidal sand with dead man’s fingers (Alcyonium digitatum) and hydroid/bryozoan turf. ©JNCC\Cefas 2015

 ‘Possible’ MDAC boulder on subtidal sand with Sabellaria spinulosa crust, Dead man’s fingers (Alcyonium digitatum) and a long-clawed squat lobster (Munida rugosa). ©JNCC\Cefas 2015

‘Possible’ MDAC slab on coarse sediment with Sabellaria spinulosa crust, Dead man’s fingers (Alcyonium digitatum) and hydroid turf (Nemertesia antennina). ©Cefas/JNCC 2015

By Alice Cornthwaite and James Albrecht

To boom or not to boom?

Sunrise saw us arrive at the southern boundary of Croker Carbonate Slabs cSAC/SCI and we set to work! One of the interesting components of this survey is that we’ll be using a variety of specialised equipment to increase our understanding of the Methane-Derived Authigenic Carbonate (MDAC) feature for which the site is designated.

One of these is a type of sub-bottom profiler known as a ‘boomer’ that can be used to identify the presence of gas in the underlying geology below the seabed.  Identifying gas below the surface, especially areas where this gas may rise to the seabed, will help us to determine if MDAC is still actively forming.

Our on board geologist and MDAC specialist Alan Judd has been busy reviewing and interpreting the sub-bottom profile data we’ve been collecting. ©  Neil Golding/JNCC 2015

The boomer is towed underwater behind the vessel and works by emitting low frequency sound directed towards the seabed, typically at frequencies around 0.5-1.5 kHz.  On deck, it sounds like a loud clap. The sound that is reflected off the different layers beneath the seabed, is recorded onboard and provides us with a seabed profile of about 40m depth below the seabed surface.

  Profile generated by the boomer © Alice Cornthwaite & Alan Judd 2015. Bathymetry in upper image © Crown Copyright, 2012.

The use of the boomer introduces underwater noise into the surrounding water so we followed marine noise mitigation protocols (in line with JNCC seismic guidelines) to minimise any disturbance to marine mammals. We positioned a Marine Mammal Observer (MMO) on the bridge to carry out a pre-shooting search for whales and dolphins prior to the use of the boomer. On our first day of planned boomer operations, we were greeted by a pod of curious common dolphins that came and played in the ship's bow wave. As a result boomer operations were postponed. The next day, the pre-shooting watch was completed with no marine mammals in view and the MMO gave permission for the boomer to be used. The JNCC is currently reviewing the marine noise mitigation guidelines applicable to geophysical surveys to ensure they remain up to date and fit for purpose.

A processed side-scan image from a section of the seabed in the survey area ©JNCC/Cefas 2015

Another survey tool we regularly use on the RV Cefas Endeavour is the side-scan sonar, which is used to distinguish between hard substrata, such as rock, from the surrounding sandy sediment.  You can read more about this bit of equipment in our previous blog posts here.  Side-scan can be used to identify areas of potential MDAC on the seabed as well as the presence of gas seepage in the water column.

Full coverage multibeam echosounder data showing the seabed topography of the area had already been collected back in 2012 as part of another survey.  Using this existing data alongside the data collected on this survey helped guide the location of our underwater camera transects and decide where to take samples of the seabed.

By Alice Cornthwaite and James Albrecht 

Suited and Booted

With a full complement of scientists and crew on board, the RV Cefas Endeavour left Swansea docks beneath clear skies on Saturday 24th in the afternoon.  Prior to departure, a full safety briefing and drill was given by the ship’s crew which included the procedure for vessel evacuation in case of an emergency.  As an Endeavour ‘newbie’, James had the pleasure of squeezing into one of the flattering red survival suits – ideal attire if you need to leave the vessel in an emergency!

James ready to ‘abandon ship’. © Neil Golding/JNCC, 2015

As we started making our way around the coast of Wales and north up the Irish Sea, we were greeted by a small pod of common dolphins who made a beeline for the vessel, playing in the bow wave.

Common dolphins entertaining scientists on the MRV Cefas Endeavour. © Neil Golding/JNCC, 2015

We have used our transit time to prepare for the deluge of data that will shortly be coming our way, as well as tweaking the finer details of the survey plan, such as the order of sampling.

“Where shall we sample next?” © Neil Golding/JNCC, 2015

We interrupted our transit to do some critical equipment testing, especially as we’ll be using some new survey equipment unfamiliar to us such as the deep-tow boomer system.  This piece of acoustic equipment is towed underwater behind the vessel and works by emitting low frequency sound directed towards the seabed.  The reflected sound tells us about what is happening geologically beneath the surface of the seabed, and may give us clues as to the origins and formation of the feature we’re surveying: Methane-Derived Authigenic Carbonate or MDAC for short.

With a good weather forecast for the next few days, we’re set to arrive on site after breakfast on Sunday morning, ready to start collecting data!

By Neil Golding, JNCC Survey Lead.

Now we're in the Irish Sea, welcome to Croker Carbonate Slabs Site of Community Importance!

On the 23rd October 2015, JNCC, in partnership with the Centre for Environment, Fisheries and Aquaculture Science (Cefas), began a 14 day survey of Croker Carbonate Slabs Site of Community Importance aboard the Research Vessel (RV) Cefas Endeavour. Croker Carbonate Slabs is one of the 20 offshore candidate Special Areas of Conservation (cSAC) in UK offshore waters. The area is located in the Irish Sea, approximately 30km west of Anglesey. 

Map showing the distribution of Annex I habitat “Submarine structures made by leaking gases” within the cSAC/SCI boundary. View and download spatial data for this MPA on the JNCC UK MPA interactive mapper © JNCC, 2015.

The site is designated for Submarine structures made by leaking gases, specifically methane-derived authigenic carbonate (MDAC). These carbonate blocks and slabs form when methane rising from deep below the seabed is consumed by microbes in the seabed sediment.  The microbes create the carbonate, which acts as a cement, gluing sediment particles together to form a type of rock. The seabed habitats created by these MDAC structures support a diverse range of marine species that are absent from the surrounding seabed, which is characterised by coarse sediment.  Large carbonate blocks support a diverse range of soft corals, erect filter feeders, sponges, tube worms and anemones, whereas the flatter, pavement-like MDAC structures are colonised with scour-resistant animals such as hydroids and bryozoans.

During the survey, we will focus on gathering evidence to contribute to the development of a monitoring time-series for Croker Carbonate Slabs SCI from which the rate and direction of change in the condition of ‘submarine structures made by leaking gases’ can be inferred in the long term.

The survey aims to improve our knowledge of the distribution and spatial extent of MDAC, map the finer spatial extent of MDAC and gather further information on biological communities, including characterising the wider sediment areas found within the site.

By Alice Cornthwaite

Farewell to the Field, parting with the Plain

Hello once more from the Scotia, where our survey has drawn to a close and we have begun our 12 hour steam back to Aberdeen from East of Gannet and Montrose Field and Norwegian Boundary Sediment Plain Nature Conservation Marine Protected Areas (NCMPAs).

As the sun sets on the last day of the survey, the MRV Scotia heads back to Aberdeen © JNCC, 2015. 

So, what have we achieved in our 2 weeks out here in the middle of the North Sea?

Despite losing some time to bad weather, we have collected all of the data we originally set out to collect, as well as some additional camera sledge transects. Thanks to the persistent hard work of the crew and scientists aboard w,e now have a comprehensive dataset describing the animals and seabed habitats at both sites that will be used to help inform the monitoring work described in earlier posts.

In total, we have collected 276 Hamon grab samples (156 and 120 grab samples from East of Gannet and Montrose Field and Norwegian Boundary Sediment Plain respectively) and completed 57 camera sledge transects at East of Gannet and Montrose Field. The maps below show where the samples and transects have been collected.

Completed Hamon grab and camera sledge stations at East of Gannet and Montrose Field NCMPA (top), and Hamon grab station at Norwegian Boundary Sediment Plain NCMPA (bottom) © JNCC, 2015. 

It is with many thanks to the captain and crew of the MRV Scotia and our Marine Scotland Science colleagues for their efforts on this survey that this account closes. Please check back with us soon for more survey action, this time from Croker Carbonate Slabs Site of Community Importance (SCI) in the mid-Irish Sea!

Goodbye from the day shift (top) and the night shift (bottom) © JNCC, 2015.  

By Joey O'Connor