The twilight Zone…

by Mark Stinchcombe

For an Oceanographer, the twilight zone conjures up images of the dark and murky depths of the ocean, just under the sunlit surface waters with many marine ‘monsters’ living there. Fish with large eyes, mouth and teeth ready to eat anything they happen to come up against, squid of varying, sometimes terrifying, proportions, and bright red crustaceans trying to hide in the dark from all of the above.

On this cruise, however, the twilight zone can also be used to describe the time where you’ll find that most elusive of creature, the oceanographer on the night shift. Between the hours of 18:00 and 06:00 (or between dinner and breakfast) these members of the scientific party emerge, like zooplankton from the deep, to sample as much water as they can under the safety of darkness, then retiring to their cabins again before their light sensitive eyes are hurt by the sunlight that is emerging over the horizon.

The reality for us night shifters is not as bleak as all that. I am Mark Stinchcombe and I work within the Nutrients Group. As has been mentioned previously, the work we are doing on this cruise happens around the clock, and therefore the deck department (as Colin has already talked about in his post) and the science party also work around the clock. There are four groups who have member on the night shift, the physics, nutrients, carbon and CFC groups all have people working on shifts to cover every hour of the day. In the nutrients group this was decided by the drawing of lots, and as usually happens in these scenarios I draw the short straw, literally.

The nutrients group consists of Sinhue Torres (our leader, and on the 06:00 to 18:00, coincidence…??), Hannah Donald (PhD student on the 12:00 to 00:00) and Carolyn Graves (PhD student on the 00:00 to 12:00) and of course me (18:00 to 06:00). We are in charge of making inorganic and organic nutrient measurements, as well as dissolved oxygen measurements, from the water samples collected using the CTD rosette. The nutrients are analysed on an instrument called a Segmented Flow Autoanalyser, or ‘The Beast’ as we have affectionately named it. This has been analysing the water samples for silicate, phosphate, nitrate, nitrite, ammonia and total dissolved nitrogen. Nutrients play a very important role in the growth of phytoplankton, single-celled algae in the surface waters. If you think of your garden at home, if you want the best out of your tomato plants you need to add nutrients, in the form of fertilisers or compost, to the soil. The same is true at sea, although the nutrients at sea are mixed into the surface waters by vertical mixing of the water column during the winter, or close to land by run-off, and other processes. By analysing the water for these we can see how much is available for use, how much has already been used and whether these have changed with time by comparing against previous cruises to the same area.

The dissolved oxygen measurements are analysed using a method known as titration, where the volume of a chemical needed to complete a reaction is measured. In this case it is a specific method, called a Winkler titration. These are analysed to calibrate a sensor which is one of many on the underside of the CTD frame. Dissolved oxygen is a very good tracer of water masses, along with temperature and salinity. Different water masses will have different oxygen, temperature and salinity signatures and so can be identified and tracked along our cruise track, as Penny has already shown.

At midnight it is meal time. Paddy, the 2nd cook, is also on the night shift, so we usually all meet up for a chat around midnight over breakfast/lunch/dinner (depending on what part of the day it is for you). With some people coming off shift and some people coming on, it’s a busy period and is a good chance to get the latest news from the other groups or to talk to your own group about what’s been happening and what is likely to come up over the next part of the day.

By 06:00, when my shift has come to the end, I pass over to Sinhue. I give him all the information from the night before about what we’ve done and where we’re up to in terms of our analysis. I then wave goodbye to the other groups as I walk through the labs, away from the sunshine that I’m sure is getting brighter every day and is a hint that I should once again make a journey to the darkness of my cabin. Black-out blinds are a must for those of us sleeping during the day and give us the security of darkness. After reading a few pages of my book it’s time to go back to sleep, another night’s hard work is over.

Images: “the Beast” and oxygen titration equipment in the Main Lab, and the night shift sampling the CTD (Stefan, Mark, Carolyn, Gary, Claudia). Photos by Mark Stinchcombe.

Ensign flown at half mast yesterday

by Simon Evans, Chief Officer

All vessels working at sea are registered with a Flag (Country) and have a governing body that control the regulations and provide guidance for the vessel to operate. The RRS James Clark Ross is registered in Stanley, Falkland Islands and the governing body is the MCA (Maritime Coastguard Agency). The MCA produce lots of guidance and information to British Flagged ships. One Marine information note (MIN 475) that was published provided the following Information:

“Commemoration of the First World War Centenary

In line with a request from the Secretary – General of the International Maritime Organization and the United Nations Educational, Scientific and Cultural Organization (UNESCO), on 28 June 2014, all vessels at sea, if practical, are requested to fly flags and ensigns at half mast, to indicate mourning in remembrance of the Centenary of World War I.

Vessels moored in harbours are encouraged to use a remembrance sound signal on the same day as may be decided and permitted by the local port authorities, at 1700 h UTC (1900 h Middle European Time/MET), being the hour of the first shot fired in the conflict, to commemorate the Centenary.”

As the JCR was at sea we flew the ensign at half mast yesterday.

Images: Ensign at half mast (photo by Simon, 28 June 2014)

Working through the night and shrinking cups

By Stefan Gary

There are always people awake on the RRS James Clark Ross. Round-the-clock operations mean that even at night we need officers on the bridge, deck crew ready to get the CTD in the water, scientists to take and process samples, and a cook in the kitchen to prepare a midnight meal.

I am on the midnight to noon shift. Every morning, I wake up at about 11PM, shower, and then make my way to the main lab to catch up on what has happened since I fell asleep. I greet this moment with anticipation because I’m curious to see how much progress my colleagues have made “overevening.” Most days things have gone according to plan, but every once in a while there are important changes because instruments need repairing, or the sampling plan has altered. Last night, I found out that we were going to be able to put cups down to 3100 metres deep on CTD station 95.

Cups! The long-awaited polystyrene cup station is finally here! The intense pressure several thousand metres below the surface of the sea is capable of crushing a polystyrene cup into a nearly rock-solid mass. This is because they are made of plastic that has gas bubbles blown into it while it solidifies in a cup-shaped mold in the factory. The trapped bubbles provide insulation between your hand and your hot drink, but will be crushed by the weight of the water at the bottom of the sea.

What is particularly fun about pressure is that it acts evenly in all directions. This means that the whole cup is squashed evenly, and the result is a nearly identically shaped cup, except it’s been shrunk. Theoretically, anyway.

About an hour later, I have to figure out how to strap a menagerie of 20 creatively decorated polystyrene cups to the CTD frame without any chance of a cup getting caught in a sampling bottle when it closes, blocking an instrument, or falling off during the 2 hours it takes the CTD to go down and back up again. In the end, we put each cup in a sock and cable-tied the socks, in a single bouquet, to the CTD frame.

During the station, I was worried that we’d lose some cups, but they all made it back up, with some surprising results. The cups don’t always shrink perfectly. Some people tried to stuff paper inside the cups to help them keep their shape but we found out it is possible to overstuff, resulting in cups that now look very odd indeed.

Why did we wait so long before the cup station? It turns out that some types of polystyrene may have been created by blowing a type of chemical called a chlorofluorocarbon (CFC) through the foam to create the bubbles. There is a team of scientists aboard who are making extremely precise measurements of CFC in ocean waters (down to the picomole = 10-12 moles!). CFC from the polystyrene could spoil the samples they collect, but since no CFCs were being measured on this station we had the all clear to send down the cups.

After the station, I realised that folks on the day shift didn’t know about the cup-station in time to decorate their cups. So, on the next stations with no CFC sampling, more cups were strapped to the CTD.

Finally, although being on the night shift might seem arduous, now that I am accustomed to the new sleep pattern, it’s my favourite shift. It’s a little quieter than during the day and because we’re at high latitude, the nights are short and we can see sunrise and sunset.

Images: Sunset and sunrise (photos by Felicity Williams), Carolyn and Mark with their socks of cups (photo by Felicity Williams), socks tied to the CTD frame (photo by Stefan Gary), and some shrunken cups (photo by Jen Clarke)

Fighting a mid-cruise slump

By Penny Holliday

The cruise is nearing the half-way mark if you are counting the days at sea. This period can be tricky in a cruise that is 7 weeks long, because people get tired and it can feel like we have a long way to go still. The excitement of ice and Greenland is largely behind us (we may yet visit once more, but maybe not…. watch this space), and we have another hundred or so CTD stations to look forward too. Our days are long and repetitive, and it can be hard to find the joy in drawing water samples from another CTD in the rain.

The sheer number of stations that we still intend to do is particularly daunting for some of our chemists who have today looked at the map of planned stations and sighed. Each red dot on the map represents a lot of bottles full of cold clear water that need to be run through analysers or stored to bring home. As scientific leaders of the cruise, Brian and I have been in discussion with the chemistry team leaders today and have devised a good sampling plan that is achievable, less sigh-inducing, and fulfils the objectives of our experiment.

Drawing water from the CTD bottles is quite time consuming and is very repetitive. We quickly became skilled and efficient at rinsing and filling our bottles, and once that is achieved it’s easy for the mind to wander and tedium can set in. To help pass the time and make sampling more fun we have collectively created music playlists, and I bring my ipod and speakers down to the ‘”garage”. Our first playlist was compiled by a few songs from each person’s favourite music and turned out to be quite an odd, but enjoyable mix. With our diverse taste in music there are definitely some tracks that each of us wince at, but there is always someone singing as they sample (usually, it has to be said, me, Carolyn and Hannah). The biggest crowd pleaser, new to all of us except Ian who brought it to us, is Shanty Town by Mr Scruff, which seems very appropriate. Now we are on to CTD station numbers 90-100 we are, naturally, listening to a playlist of 90s music.

Over the coming days we will hopefully get a few hours break from CTDing and have a chance to wind down a little and recharge our batteries, ready for the rest of the cruise.

Images: Drawing water from the CTD bottles on the day shift.

Seals, snowy owls and testing my ideas

By Penny Holliday

Once again we’ve been lucky enough to have fine views of Greenland. The conditions yesterday were calm but grey, with flat light that made photos quite serene, but perhaps not quite as stunning as the sunny day ones from last week. The science party are not yet tired of this beautiful scenery, and throughout the afternoon and evening little clusters of cold, pink-cheeked scientists could be found on the aft deck, the fore deck and the monkey island. The monkey island is above the bridge and has the best views I think, although it can be a bit exposed if there is a fresh breeze. I have finally realised that wearing gloves keeps my hands warm, but have yet to remember to put on an extra pair of socks, and standing on a cold metal deck really chills your toes.

There has been little wildlife seen on this trip so far; a few instances of pilot whales, one sighting of a larger whale, and very few birds. But yesterday, in the thick ice surrounding our station closest to land, we were treated to a rare sight. Some lucky folk saw a snowy owl with her prey in her talons (see the photos by Ian Brown below). Sadly I missed that but I’m not too downhearted because I was lucky enough to see seals rolling off the ice and slipping into the water as we came upon them. This view, remarkably, was from my seat at dinner – as I finished off my cheese course I could see the dark mountains, the bright ice and a brief glimpse of fat, brown seals.

You might be wondering what keeps taking us out into deep water and then back to the Greenland coast again. We are doing four sections (lines of stations) at approximately right angles to Greenland, so that they cut across the main currents. The currents flow parallel to the main shape of the coast and they follow a curved path around the southern tip of Greenland (Cape Farewell). However the currents change as they progress along the path, so we are surveying them in four different places to establish what those changes are.

Some of my previous research has shown that about one-third of the water carried by these currents actually peels away from the main current at Cape Farewell and flows into the middle of the deep ocean basin (see the cartoon below, red dots are station positions). We want to know if that observation was a quirk of the data we collected earlier, or whether it is a long standing feature of the area. We have designed an experiment that will test my idea (a “hypothesis” in the language of science), and measure how much water stays in the main current, how much leaves it at Cape Farewell, and how much joins from the Labrador Sea. This will be an important contribution to OSNAP because it will help us understand what happens at between our two main sections (OSNAP West and OSNAP East).

You will notice from the cartoon that one of the sections (the line of stations shown as red dots) is short and incomplete. This is what happens when you are at sea; something comes along and your beautifully designed survey ends up looking rather different. When Brian (the Principal Scientist) and I made the cruise plans we developed an order of priority for the various parts of it, knowing that we may need to discard the lower priority elements if there was a delay. Delays can be caused by bad weather, thick ice, a problem with an instrument, or something else. In this case, the storm that caught up with us a couple of days ago was forecast to blow hard in that spot for a while. Between Brian, myself and the captain, we decided that it was better to give up on that section and steam to a place where we could continue working. The change of plan will still allow us to complete the experiment successfully (even though the station plot looks sadly unbalanced now), and we still have enough time to complete the rest of our high priority plans.

Images: Views of ice and Greenland (photos by Penny), the snowy owl (photos by Ian Brown), and a cartoon showing the branching currents of the area and the JR302 station positions (by Penny).

A guide to the deck department on JR302: part 2, a typical day on deck

By Colin Leggett, Bosun’s mate.

My day begins with an alarm call at 5 o’clock in the morning, a quick check of the email to see if its working well enough to get news from home, a shower, several cups of tea and even a coffee as I’ve finally come to like the taste of it. If we are on station or approaching a station (a science stop) then its a stare out of the window to decide on how many layers to put on or if the waterproofs are needed. Then its out on deck to take over from Martyn who is always smiling when it comes to knocking off time. Quick chat about what’s going on, update on the world cup scores from the day before, any scandalous gossip and then he’s off and we are in charge of the deck.

I normally fit in a quick chat with John O’ the Bosun to get any jobs that need doing for the day before he goes to bed. Depending on where the CTD is, either myself or Ken go off to do a job or two whilst the other one keeps an eye on the wire and the deck from the garage (the place where the CTD lives). Whilst in charge of the deck our main priority is to ensure that everyone is safe and no one is anywhere they shouldn’t be. When you have a lot of scientists onboard, and especially when some have never been to sea before, its very important that they are made aware of the dangers that are associated with the equipment. Areas that are roped off are done so for their protection and should not be entered.

We also keep a close eye on the wire and the gantry to make sure its all as it should be and no funny noises are coming from the gantry. We look to see whether the wire is being affected by a current and being swept to a dangerous angle. The ship is fitted with several CCTV cameras that assist the officer on the bridge in checking this, and their job is to keep the ship as close to the mark as possible whilst not having a dangerous lead on the wire.

Normally at our first stop of the day one of the scientists (Bita) appears to deploy her water sampler which involves us help her lower the sampler to the water so it just touches the surface and then recover it so she can collect the water. There is a photo earlier in the blog of her and Ken about to sample (see the post on 17 June).

Once the CTD has reached the required depth, everything stops and the first samples are taken. Just before the CTD is hauled back up from near the sea bed, we turn on an air dryer for the wire, to keep as much water off the storage drum and protect the wire as much as possible. When the CTD is around 200 metres from the surface the watch keeper joins us on deck to assist in stowing the CTD safely back in the garage to enable the scientists to sample whilst the ship is under way to the next stop.

Once the CTD is recovered and secured, it’s bacon sandwich time as long as the hungry hoards have left some for us, a quick cup of tea (I drink a lot of tea!!) and its on with the day’s jobs. My first call is the engine control room to read the gauges of the fresh water tanks. I record these figures on a wipe board in the engine room and on the bridge. There I have a quick nose at the chart to see where we are, ask the usual questions of what’s the weather doing, where is the ice and are we going into it. Then it’s down to the ships office to write the numbers in the logbook, a chat with the mate to see if there are any other jobs to do, a general chat about the ship and anything that’s coming up that needs to be done, and I’m off back downstairs and back out on deck. As we normally always are told when the ship is roughly due at the next station we plan our day around the science stops and what we can do and when we can do it.

This trip so far our jobs have mainly been having a good tidy up and a look around at the cargo lashing equipment we have. If any of it needs over hauling or replacing, the earlier we know about it the earlier it can be ordered and the more chance we have of getting it for when we need it. As bosun’s mate, cabin maintenance is also my job. So far this trip we’ve unblocked a couple of shower drains and fixed a book shelf – nothing to technical which is just as well given my DIY skills.

10 o’clock normally would mean smoko (a half hour break) but today the ship is coming onto station just before 10, so its a case of fitting in a quick cuppa as and when and back on deck to get ready for deployment. Once the CTD is deployed, Ken’s off to do a couple of jobs from the list and I am watching the wire and making a new canvas cover for the exhaust pipe of the ship’s cargo tender. The tender is used when we do base relief at the Antarctic bases where the ship is unable to get alongside. The tender sits just forward of the accommodation on the port side of the ship and if you look at the webcam, is directly at the bottom of the picture you see. The tender takes a far beating in bad weather so any protection we can give it from the elements is always a bonus.

Once the CTD is recovered back in the garage and the gantry is secured, its off to the next station and a chance for us to have an hour off to eat lunch. Then it’s a repeat on the CTD only this time its launch, recover and time to finish as we hand the reins over to the night gang for their 12 hours of CTD action. A quick chat to tell them what’s been happening and what they can expect to be doing and it’s boots off, eat dinner, shower, email, attempt to get on the internet, go to the gym. What an episode of true blood vampires, all very strange and then bed, ready for the alarm call at 0500 and a new day of sampling.

Watch a time lapse movie of Colin, Ken and Graham deploying, watching and recovering a CTD in ice:

http://youtu.be/9pfVtieOpKI

Images: Bringing the CTD safely back into the garage (photos by Colin). Ken, Colin (centre) and Graham bring the CTD back on board after a station in the ice (photo by Penny).

A guide to the deck department on JR302: part 1, who’s who and joining the ship

By Colin Leggett, Bosun’s Mate.

Before I give an insight into an average day for myself during a science cruise for those of you reading this who don’t know much about the way ships operate, I thought I’d start with a quick guide to the deck department which is always the hardest working department on the ship!!

The deck department is made up of the Captain who has overall charge of the ship, the chief officer, a second and a third mate. The rest of the deck department are the very important A.B’s ( able seaman) lead by our Bosun John O’, then myself as bosun’s mate, Martyn, Ken, Shaun, Les and Graham. We do have an additional member of the deck department, Cliff otherwise known as Mackum ( he’s from Sunderland) who is our Bosun Science Operations, and runs the science side of things on the ship and deals with the scientists and all their equipment.

The ship works shift patterns both when on science and when on passage to and from science deployments. The normal sea watches are 8-12 (3rd mate and Graham), 12-4 (2nd mate and Les), 4-8 (chief mate and Shaun). These watches continue when we are at sea, and when we encounter ice then the Captain spends a majority of his time on the bridge navigating us skillfully and safely through ice to where we need to be for the scientists to get their work done. When we are in the ice for long periods, or it is very thick and dangerous, the officers often change their shift patterns slightly so that they are doubled up on watches, with the Captain and Simon (Chief Officer) splitting the driving between them while the navigation is taken care of by the second and third mates.

While on science the rest of us are split into 12 hour shifts, so from 6 in the morning until 6 at night, Cliff the Science Bosun is in charge of driving the winches and equipment used to launch and recover the CTD machine, with myself and Ken on deck. Then at 6 p.m. John O’ takes over the winches and Martyn takes over on deck. Throughout the day we are assisted by the duty watch-keeping A.B. who comes down on deck for deploying and recovery of the equipment.

The ship is staffed by two teams who alternate their time on and off the ship. Our team joined the ship at the end of May after a period of leave. We flew out from the UK to join the ship in St Johns on three separate flights which was a bit unusual for us. Normally we all fly together so the usual hello’s, stories and chatter of things done on leave had to wait until we met up in the hotel the day before we joined the ship. This time was very different to a normal crew change as the ship was due to be in St Johns for 10 days which gave us a very unusually long period of time to get ready for the science cruise and re-familiarise ourselves with the ship. All the usual jobs were done, fresh food, water and fuel were all loaded. The longer stay in port enabled everyone to have a good look around the part of St Johns; a normal port call only lasts a few days and everyone is tearing around the place at break neck speed attempting to get everything loaded, set up and secured before the ship proceeds to sea.

On departure from St Johns we had a short steam to the first science site, so all the new guys on deck (unusually we had four new A.B’s this trip) were walked through the deployment of the CTD machine and all the jobs that they were expected to carry out whilst we were out at sea. The usual board of trade sports (fire drill and lifeboat drills) were carried out with everyone getting used to their roles and the equipment.

That’s a rough guide to us and the roles we fill on the ship. Tomorrow there will be a rough guide to an average day for me during this science deployment and a bit about what we do and have done since we joined the ship in St John’s.

Images: views of the ice and the CTD, by Colin Leggett.

The real subpolar North Atlantic and sacrifices for art

by Penny Holliday

Since the early hours of this morning we have been experiencing what feels to me like the real subpolar North Atlantic. The pressure dropped as we worked our way south of Greenland, and by breakfast time this morning the wind was up to 30 knots and the waves were building. We have to stop CTD work when these conditions take hold, because it becomes too dangerous to put the CTD in the water for a number of reasons. One is that it is difficult to hold the ship on station in strong winds, heavy seas and a strong surface current (we were in the West Greenland Current still). Another is that with each roll of the ship the drag and lift on the CTD package and the cable is dangles from, go from one extreme to the other and that will damage the wire and the winch or even cause the CTD to break off. And finally, it’s just too dangerous to be out on deck in that weather.

The winds picked up to 40 knots, and as the forecast suggested there might be better working conditions further south, the Principal Scientist and the Captain decided to break off work at that location and steam on to a different place. The ship turned and we took a course that had the waves coming towards our port stern. We stayed on that course for much of the day and it was reasonably comfortable even as the winds got up to 50 knots. Just before dinner we altered course to aim for our new station position, causing a huge roll as we turned and a few more since. Scientists had already been around the labs checking that every thing was lashed down and securely stowed; laptops, cups and small bottles can be especially vulnerable in this motion. After the first big roll we checked to see everyone was OK and they were.

Just now the pressure is rising, the wind is dropping and the optimists among us are sure the waves are reducing in size too. We are quite close to the new station so with any luck CTDs will recommence in a few hours. Meanwhile, we have made the most of the break to catch up with analysing samples and working on the data.

I’ve had another project to keep me busy today. On this cruise a small group of us are taking every opportunity to film the work and life on the ship, with the aim of making one or two short films for introducing people to the science we do. We are novice film-makers and I am the first to admit that it is still a skill that I need to work on. Today I have been trying to film the exciting weather, and it is proving to be harder (and colder and wetter) than I expected. I’ve been experimenting with using the tripod and using my sea legs to film the waves, but in either case they dont look nearly as dramatic on screen as in real life. I have managed to capture some reasonable clips but in the process got soaked by spray twice and now have sea salt all over my cameras. I have sacrificed my comfort (but not my safety) and a pair of pyjamas (soft cotton for cleaning the cameras) and I hope it is worth it in the end.

Images: ocean waves in 40 knot winds, including the moment I got soaked for the second time.

A view of Labrador Sea currents, and hello Greenland again

by Penny Holliday

We are here to measure the ocean currents in the Labrador Sea. The temperature and salinity data that we collect with the CTD will tell us about the strength of the currents through an indirect route; we calculate the gradient of density between stations, and high gradients mean strong currents. But we also have instruments that directly measure the currents below us. They make use of the presence of tiny biological particles being swept along in the water. The instruments (ADCPs) send a series of short bursts of sound, called “pings”, and wait for the sound reflected by the particles to return. The reflections have a different frequency to the pings, and that change tells us how fast the particles are moving. You might be familiar with this effect if you have heard a train whistle as it passes you; the change in the note of the whistle as it passes by is caused by the same phenomenon (called the Doppler effect).

The currents measured in this way are shown in the graphic below (made by Felicity Williams). The big arrows show the general location of the two main boundary currents of the Labrador Sea; the Labrador Current in the south west and the West Greenland Current in the north east. The latter is very fast, reaching a speed of about 1 m/s (or 2 knots); this is where we saw ice racing past us while we did a CTD station, and the ship had to steam gently forwards to stay in position. Between the two main currents there is a perfect eddy; a circulating ring of slightly warmer water. You might be able to see that there is quite a lot of to-ing and fro-ing in the currents, with arrows pointing in all directions, not just the main direction of the current. This is because water never flows in a straight line, but is always spinning and twirling, having been given energy by things like tides and winds.

Nice plots like this one make us scientists feel pleased with the way things are going, because they are simple illustrations of the progress we are making. But it’s not just data that make the ship’s company feel good. I dont think I should try to speak for everyone on board, but I know that another day in the presence of the dramatic Greenland coast certainly made me feel pretty good. It was less sunny than Thursday, but we were able to creep closer to the mountains and it was beautifully calm again. There was less ice, but the jagged triangular peaks were fantastic, and I could even see a glacier in the distance. Having taken another few hundred photos, it can be hard to drag yourself away from the views and back to the computer again. Right now however, we are heading back out into deeper water again. Our plans are to work back to the Greenland coast twice more before heading east across the open North Atlantic – I cant wait to see it again!

Images: surface currents of the Labrador Sea, and more views of Greenland and ice

Happy scientists: more ice and the first results from cruise JR302

by Penny Holliday, with some words by Sheldon Bacon

Today we are feeling a great sense of satisfaction for two reasons, firstly because we were treated to the most beautiful views of Greenland and the ice yesterday, and secondly because early in the afternoon we completed the final station of the section across the Labrador Sea. I don’t think that I have the words to properly describe the beauty of the views that day, so I will let my pictures tell the story. I’ve added some photos here but I also made a time-lapse movie of the view as we moved off the last station and away from Greenland through the ice. The movie is at http://youtu.be/HOI6q1VFQDA (try cutting and pasting if clicking on the link doesn’t work). It’s a few minutes long, and is most impressive if you watch it at double speed.

So apart from the joys of knowing you have the best job in the world because it takes you to places like this, we are also delighted to have successfully finished the first part of the cruise. After 53 CTD stations and 12 days we have our first results. The colourful cartoon at the end of this post shows some of our data. The image will be new to most people, so Sheldon and I have made an attempt to explain what you are seeing when you look at it.

The first thing to know is that you are seeing a vertical slice through the deep ocean, along the track shown in the map. The ocean is wide and deep, but we have greatly stretched the depth axis to show the currents we are interested in. The vertical axis is actually pressure (in decibars) but is roughly equivalent to depth in metres. There are two panels; the left on shows temperature of the water, and the right one shows how salty it is (salinity). The sections is shown as though you are looking through a giant wall of water towards the north; Canada is on the left and Greenland is on the right. I’ve shown the direction that the water moving with the cartoon arrows, and labelled the different types of water (oceanographers like to give them names that are clues as to where the water comes from).

Top left and top right in the shallow waters of the Canadian and Greenland continental shelves are the very cold, fresh waters fuelled by ice melt: both melting sea ice coming from the high Arctic, and melting land ice running off Canada and Greenland. The Canadian side is colder, thicker and faster because it’s a direct pipe taking water south out of the Arctic, coming through passages like Nares Strait, Lancaster Sound and Hudson Strait. The Greenland side is flowing north and you can see that a common feature at all depths in the Labrador Sea is that the water circulates clockwise in the basin, north on the east and south on the west.

Centred around 200-300 metres on both sides of the Labrador Sea are cores of recirculating warm and salty Atlantic waters, entering on the east side (called Irminger Water) and leaving, having been cooled and freshened (diluted), on the west side. In the top couple of hundred metres of the central Labrador Sea there sits light surface water that has been warmed by the spring sun and freshened by water mixing in from the Arctic currents around the edge of the sea. The surface water sits over something we call Labrador Sea Water; this thick layer of well-mixed water is special to this region and hugely important to the global climate system. Wintertime cold winds pull heat out of the central Labrador Sea; the newly cooled water is dense and so it sinks to deeper levels, forcing other warmer water around it to rise to the surface. The warmer water is cooled too, sinks, and more water rises to the surface. This great stirring, circular motion is called convection and is extremely efficient at mixing up a vast volume of water. In the past convection has reached 2200m, but it looks as though last winter it reached to about 1500m. Eventually this stirred up water, carrying carbon and oxygen absorbed from the air, travels all the way to the Southern Ocean as part of the global ocean circulation.

Finally, down at the bottom is the deep banana shape made by the dense waters that flow over the shallow sill in the north-east Atlantic between Greenland, Iceland and Scotland. The coldest, densest waters come from Denmark Strait, and you can see how, on their circuit of the Labrador Sea, they are warmer on the west than the east. This is caused by mixing with overlying waters, which in this case are the dense overflows from the sill east of Iceland. These NE Atlantic deep waters have taken a longer and more roundabout route to get to the Labrador Sea.

The next part of the programme is to carry out a survey of the ocean currents around the southern tip of Greenland. We will post results as soon as we get them.

Images: Photos of ice and Greenland (including a very happy Penny Holliday), a image of the temperature and salinity that we have measured in the Labrador Sea, and a map of our cruise track to yesterday.