Monday, 14 January 2019

Our Historic Waters - Blog #4



Hello from Offshore Overfalls MCZ, where the team have been working hard to finish off collection of the multibeam data. Whilst collecting this data we have seen a few shipwrecks, which has added some excitement to the early hours of the morning for the night shift. I have written about how some of these ships came to be on the seafloor below. These shipwrecks were identified as being of interest before sailing, in collaboration with Historic England.

One of the wrecks we have seen is the SS Alaska, which sunk in 1939. The vessel sank in collision with a British cargo vessel SS Dotterel on 15th November 1939. Two men were sadly lost in the collision however the remaining crew were rescued by other vessels. The location of this vessel was not confirmed until recently as a number of different positions were given for this wreck although salvage operations directed at SS Alaska are recorded as having occurred between 1947 and 1951.

Wreck of the SS Alaska © Cefas/JNCC
HMS Implacable is an additional wreck that we have been keeping an eye out for on this survey. This vessel was scuttled by the Royal Navy in the English Channel in 1949, but it was built in Rochefort (France) 149 years earlier in 1800 as the 74-gun ship Daguay-Trouin. She saw action at Trafalgar in 1805 and was captured by the British in the battles aftermath and renamed HMS Implacable.

In the 1940s she was deemed too expensive to maintain and on 2nd December 1949 she was scuttled in the English Channel. The stern section and figurehead were removed beforehand and given to the National Maritime Museum, Greenwich where they can still be viewed today. Finding evidence of this wreck is very exciting as we were not sure how much of HMS Implacable's wooden structure would have survived 70 years on the seabed. 

Polandia is the third and final vessel that we have seen on this survey. Polandia was a steam-driven liner built in Germany in 1898 weighing 2,238 ton and original named Paul. She was captured by the British in 1914 and renamed Polandia only to be sunk claiming the lives of all 30 crew members after being attacked by a German U-boat on 10th or 11th March 1917.

These are just a few of the wrecks we have seen on the recent survey from the multibeam data out of the 50 wreck site records held for this area. Having completed the acoustic survey that we had planned for Offshore Overfalls, the team are now shifting focus to collection of photographs and videos of the seafloor within this MCZ. Steering clear of all known wrecks in this area to ensure our drop camera doesn’t join the many wrecks down at the bottom of the channel, the team are ready to get a closer view of what animal life can be found in this area.

The weekend weather is sadly looking to break the trend of calm seas we have been enjoying so far with the wind due to pick up and so the boat may be moving around a little more than previously. Fingers crossed my sea-legs have kicked in and the copious amounts of ginger biscuits at hand will keep the sea sickness at bay. 

For further updates before and during the survey - watch this space; follow JNCCCefas and the survey hashtag #CEND0119 on Twitter, or join us on Facebook.

Thursday, 10 January 2019

Sonar, So Good! - Blog #3


Since we last wrote, the team has been hard at work continuing to collect multibeam data at Offshore Overfalls MCZ.


JNCC and Cefas scientific crew monitoring the multibeam data acquisition. 
In addition to the protected seabed habitats at Offshore Overfalls MCZ, the site is also designated to protect the unique underwater landscape believed to have been created over 200,000 years ago. This was around the same time that the first humans (Homo sapiens) were thought to be alive in Africa.
A deep paleochannel (“paleo” – meaning ancient) runs through Offshore Overfalls MCZ. This channel has the shape of a river bed, which means that when the first humans were alive the English Channel would have been land, allowing people to walk from France to England.
This was all set to change at the end of the last ice age, when the melting glacier produced enough water to flood this river and the surrounding low-lying land to form the English Channel that we know today. This means the paleochannel at Offshore Overfalls MCZ is rather special as it is very similar to features you might see on land, such as those created by the large volumes of water that are produced as glaciers melt in the summer. 

Map showing multibeam data collected at Offshore Overfalls MCZ during the current survey (colour ramp), overlaid on existing lower resolution (singlebeam) data (greyscale). The Offshore Overfalls MCZ boundary is shown in purple. © JNCC/Cefas

Satellite image from Google maps showing channels created by the meltwaters of an Icelandic Glacier. Notice the similar features seen at Offshore Overfalls MCZ such as the tear-drop shaped islands. © JNCC/Cefas
 Another idea about how the paleochannel was formed is that a large lake existed in the area now known as the North Sea. This lake was made up of the water from melting glaciers and burst its bank to the south, in what has been referred to as a “catastrophic flood event”. Could this flood have created the paleochannel?
The higher resolution multibeam data has enabled us to see other seabed features. These include large “underwater dunes”, which have been created by strong currents that force the sediment to form these interesting features. The largest found so far measuring over a kilometre in length. It’s not clear whether these particular underwater dunes would have been created by a catastrophic flood event or by more recent tidal currents.

Underwater dunes seen at Offshore Overfalls MCZ © JNCC/Cefas
Multibeam alone won’t reveal all the secrets of these features, but later in the survey we will be collecting sediment using a grab sampler based on what we have found with the multibeam.

For further updates before and during the survey - watch this space; follow JNCCCefas and the survey hashtag #CEND0119 on Twitter, or join us on Facebook.


Monday, 7 January 2019

Arriving at Offshore Overfalls - Blog #2

And we’re off! The JNCC and Cefas crew have joined the RV Cefas Endeavour and set sail for Offshore Brighton and Offshore Overfalls Marine Conservation Zones (MCZs). After a transit hugging the coastline (which provided the team with plenty of phone signal!) in exceptionally flat calm seas for January, we have arrived at Offshore Overfalls MCZ.

Our first challenge on this survey is to produce a more detailed map of what the seabed looks like at Offshore Overfalls MCZ. To do this we will be using a Multibeam Echo Sounder. Multibeam uses sonar to tell us two things about the seabed; how deep it is, and how hard it is. This is worked out by measuring how long it takes for sound to travel from the ship to the seabed and back again (i.e. the longer it takes, the deeper the water is), and by measuring how strong the returning sound signal is (i.e. harder seabed like rock will reflect more sound energy than softer seabed like mud). Due to the large size of the area within the MCZ that we plan to map, we estimate that this element of the survey will require 7.5 days to complete!

Multibeam from Offshore Overfalls MCZ survey CEND0119 © JNCC/Cefas

Multibeam data collected for the site will be used to update the existing map of seabed habitats at Offshore Overfalls MCZ. This mapping will also help the team on the ship decide where to collect grab samples and drop-frame camera images later in the trip.

For further updates before and during the survey - watch this space; follow JNCC, Cefas and the survey hashtag #CEND0119 on Twitter, or join us on Facebook.


Survey Fun Fact

The multibeam uses sound waves to “see” through even the murkiest of waters, replacing the more traditional lead weight on a rope method to provide us with colourful bathymetric pictures of the seafloor. The term bathymetry comes from the Greek meanings “Deep”(Bathy) and “Measure”(metry) and is the measurement of the depth of water in oceans, seas, lakes, rivers, and canals.

Written by Jess Taylor