As many PhD students in physical geography will attest, the fieldwork is always the most exciting and fun part of the research process. So when I started my PhD on the Younger Dryas, and how it is recorded in marine and terrestrial records, I didn’t have high hopes for getting any marine-based fieldwork. While it is quite easy (and a lot of fun) to pop up the M5 to Scotland and take some cores, the money and preparation required to organise a cruising expedition in the North Atlantic requires a lot more resources.
So, when my supervisor David Thornalley mentioned that there were a couple of spaces on a cruise focussed on testing out a new piston coring system on the new research vessel Neil Armstrong, the opportunity was too good to miss! Chief scientist Lloyd Keigwin was very kind in allowing me, David and another PhD student from UCL – Jack – onboard.
The R/V Neil Armstrong is based at the Wood’s Hole Oceanographic Institute – the largest private oceanographic research institute in the world – located just south of Boston, on Cape Cod. The cruise was to last for 8 days, departing early on Monday the 2nd September so we needed to make sure we were all ready and onboard by Sunday evening.
After a 7 hour flight across the North Atlantic, with a couple of films and lots of food digesting, we were about ready to get down to the coast. We were staying for one night in Falmouth, a mid-sized town about 4 miles away from the Wood’s Hole docks, with an evening of great Mexican food, darts and pool planned before we went to Wood’s Hole the next day.
Getting our sea legs
Sunday saw us having lunch and a film (Toy Story 4 because why not) in Falmouth’s cinema pub before taking our stuff down to Wood’s Hole to see where home for the next week would be. We definitely weren’t disappointed! The ship itself can hold a scientific party of over 20 and has a full-time crew who operate the vessel on shifts – even in port the ship was bobbing about, invoking slight fears that the week might be spent being horrifically seasick (it was all ok in the end though).
A quick explore around the gorgeous Wood’s Hole beaches and shops led us to a tasty drink in the sun at the local favourite the Landfall, before we had one last meal on land. Back on the ship we explored a bit more and saw some of the coring kit before an early night was had by all.
We used three different coring instruments to obtain as full a record as possible from the seafloor – multicoring, gravity coring and piston coring. With both piston and gravity coring it is likely that the top ~20cm of mud is lost during the process, as the cores are plunged into the sediment, which has a very high water content. This is why multi-cores are also very valuable, especially when looking for records that cover the last ~1000 years or so, while piston cores are best for obtaining much longer term climate records.
Multi-cores are particularly useful for looking at recent changes recorded in ocean sediment. On this cruise they were extruded whole (to archive), cut into 1cm slabs for ease of sampling, and bagged in 1cm slabs to bring back to UCL and examine the foraminiferal changes over the last <1000 years. Of course, it is always difficult to estimate what the sedimentation rate is like at a new site, so small samples were taken from extra multi-cores to wash on ship and look for particular indicator forams like G. menardii, which are only seen in the North Atlantic in the Holocene after about 7 ka.
Gravity coring is fairly similar to multi-coring in that it is the weight at the top of the chamber that controls how deep the core will go into the seafloor. Gravity cores tend not to retrieve as much sediment as a piston core can, although they still reached ~7m on this cruise!
By far the most exciting, the piston cores were retrieved using the ships crane for the most part. The steel chamber is lined with PVC tubing and the piston itself weighed over 2 tonnes. This was placed on top of the chamber and lowered into the water before the trigger was primed. For the next stage it is really important to have an accurate estimate of the water depth, as the trigger must be released when the chamber is just above the sea floor – too shallow and the core will be filled with water, and too deep and some of the shallowest sediments won’t be captured. Once the trigger is released, the piston drives down and the head allowed the chamber to fill with mud as the core shoots down. For some of the deeper stations, it took almost half an hour to reach the seafloor, and almost 20m of sediment was retrieved.
Once collected, the core must be brought up into the boat and then the PVC cut into 1.5m sections and labelled carefully for splitting later. This is the part of the operation that required the most manpower, as the core was excruciatingly heavy and had to be cut by hand and carried to the fridge for storage.
Disruption from Dorian
After several days of getting into the swing of coring and extruding/slicing, it became apparent that this routine might be cut short. Hurricane Dorian was causing havoc in the Bahamas and all tracks (contrary to what the president suggested) had the R/V Neil Armstrong firmly in it’s path.
After several conversations between the Captain and the Navy, it was decided on the Wednesday that we would start to head back to port early, to avoid Dorian. This was sensible on several levels – as well as it being dangerous to stay and try to wait out Dorian, it was also likely that the swell that slightly precedes the main hurricane would have meant that we couldn’t have retrieved any more cores anyways. So, with heavy hearts we had to turn back several days early.
Once we had returned to port without too much swell, we buttoned down the hatches in the crew’s favourite pub – The Landfall – and got to know them a bit better. It was a very fitting end to a fantastic trip, filled with coring experts, incredible scientists and a lot of learning! We returned back to the UK with bags filled with mud and forams, ready to process.