Just off Spurn Point waiting to pick up our pilot. That’s me finished for a while now – no immediate plans to go on another cruise. I need to write another research proposal and get it funded! That could mean 2 or 3 years before heading off to sea again. But, we have a huge quantity of data to work through, some of which is likely to trigger new questions about how the ocean works.
We’re due to pick up the pilot off the Humber at 0800 tomorrow, so this is our last day at sea. Breakfast time saw us just entering the Dover Straits, at 51 degrees 2.4 minute N, 1 degree 35.5 minutes E. The weather was ok, about 10-15 knots, but it’s picked up now to 30 knots or so. Lots of grumbly waves about – probably the worst we’ve seen all trip. The really obvious contrast is in the seawater colour – from the azure, clear blue of the subtropics, to the plankton-filled soup of the coastal sea.
Just about everything is packed now, with the aft deck full of crates, boxes, cages and instrument cases. And, we’ve just spent a solid 3 hours cleaning, sweeping and mopping to get the labs back into a presentable state; i.e. presentable to the next bunch of scientists who’ll be joining probably in September to run back down the the Southern Ocean.
In the western English Channel now, at 49 degrees 31.9 minutes N, 3 degrees 58.1 minutes W. A quick look at the ship’s navigation shows about 25 ships around us – quite a bit busier than we are used to. The Channel is such a busy area generally that there are two lanes for shipping to keep westward and eastward traffic apart – as we are steaming eastward we’ll be on the French side of the Channel, turning across the traffic to head north once we are through the Dover Strait. Right now our position is just west of Guernsey.
Yesterday was the end-of-cruise party. The ship’s cooks and stewards put on a very impressive evening meal for us, and then it was an evening in the bar telling tall tales and, for Clement, listening to the Germany-France match. Other than packing up, the only plan for today is for 3 of us who have been working up some of the cruise data to give some short talks on what we think we have found (so far).
I’d spent this morning trying to lower the increasingly frenzied expectations of some of the scientists, who were expecting us to be tripping over dolphins when we got to the shelf edge. Sure enough though, right in the middle of the patch of water that has high amounts of plankton in it, some dolphins joined us. Initially a group of 10 started to surf on the ship’s bow wave. The we saw other groups ahead of us, swimming towrads the ship and turning quickly to catch the wave (just like any surfer would). There were probably about 40 or so eventually. After about 10 minutes they all suddenly disappered, to be spotted astern of us along with a group of diving seabirds – obviously a school of fish was more attractive than the bow wave.
The ocean started to get shallower this morning as we approach the edge of the continental shelf. At breakfast we were at 47 degrees 39 minutes N, 9 degrees 44.5 minutes W.
There’s a big change happening in the surface ocean as we cross the continental shelf edge. It’s an extreme example of the sorts of contrasts we were seeing over the ridge. The sloping seabed here causes lots of the under-sea waves as the tides flow up and down the slope. These waves cause lots of turbulence (like breaking surf at the beach, only underwater), which mixes nutrients up towards the sea surface. It’s really obvious looking at the sea now that it has turned a dull shade of blue/green as the phytoplankton are growing in response to the nutrients being mixed upward. We’ve done previous work in this area showing that not only do the phytoplankton grow more here, but the species of them changes as well – all the way along the edge of the continental shelf you tend to find larger phytoplankton, not the really small ones that we find out in the open ocean. Larger phytoplankton are good food for fish larvae, so this area turns out to be really important for breeding fish (mackerel, horse mackerel, whiting) which then attracts the predators (monkfish, dolphins, whales). The top predators are, of course, humans –
this is probably the most heavily fished part of all the seas around NW Europe. In the picture of the navigation plot below, all of the green triangles are other ships and all but one of them are fishing vessels. This area is a great example of how a physical process in the ocean can have really profound effects all the way up the food chain.
We are now at 45 degrees 24.0 minutes N, 15 degrees 4.1 minutes W, and so about level with the southern Bay of Biscay. Weather still fine, with 8-10 knot southerly winds. From the forecast it looks like there’s a nasty low pressure system chasing us in from the west, but we seem to be keeping ahead of it and should be into the English Channel by the time it crashes into the west of Ireland.
Packing began in earnest yesterday, with lots of aluminium boxes and wire cages brought up from the hold onto the aft deck. It’s hard to imagine where all that stuff was stored, though admittedly there’s a good deal of stuff on the deck that came up as parts of the moorings. Equipment is being broken down, checked, and then packed up. Lab instruments are gradually being packed as the samples are completed, and we’ll be cleaning out the labs in a couple of days. There will be 3 large lorries turning up at Immingham to take most of the gear back to the Marine Facilities base in Southampton.
I’ve been working through some of the turbulence data to see if what we hypothesised was really happening over the ridge. It looks like the turbulence over the ridge, at spring tides, was about 5 – 10 times greater than it was in the deeper water away from the ridge at spring tides. So, we were right! That’s something of a relief….
We are steaming along at about 250 nautical miles (460 km) per day, through a sea that continues to remain calm and blue. But we notice it is not as clear and blue now as when we were working over the ridge. We have left the warm, subtropical gyre and are now in water that is much more productive. It still looks clear, but there’s a definite shift in the hue of the sea surface that tells us there are more phytoplankton growing here. We are at 43 degrees 5.7 minutes N, 20 degrees 19.0 minutes W. That’s almost level with the north coast of Spain. Two days from now and we should be crossing onto the continental shelf SW of the UK.
We are having regular safety drills while heading back to the UK. In the past 3 days we have had one boat drill (muster station, lifejackets on, board the lifeboats and get strapped in, and learn about some of the gear in the lifeboats), a fire drill and just yesterday a man-overboard drill. The man-overboard drill was impressively fast. A lifebelt that we’d fished out of the sea a week ago was thrown back in, the man-overboard signal sounded, the ship stopped, the rescue boat launched, lifebelt recovered, and rescue boat brought back onto the ship all within 15 minutes. I remarked on the speed of the operation to George the bosun – his response was “well, we spend a lot of time in the Southern Ocean – if you fall in there you’ll be dead in less than 5 minutes, so this has to be quick”. The speed would have been quicker –
while the boat was in the water they took the opportunity to quickly drive round the ship checking the draught marks.