Over the past week we made great progress in our journey of the sea, surveying an eddy off the west coast of Greenland with repeated ADCP and CTD surveys to investigate in detail the structure and content of these dynamic water features. We also deployed 2 more APEX floats in the centre of the eddy.
Johannes and Marie discussing the next Apex float deployment (credit: Sunke Schmidtko).
Float deployment in the eddy centre (credit: Arne Bendinger)
During the last few days while we finished the Labrador Sea part of our cruise and had our mid cruise celebration, I had the chance to sort out my thoughts and go through notes of conversations with more of the people on board. One thing I realized is that I never mentioned the amazing crew and captain of the Maria S. Merian. Without their patience, experience and watchful eye neither the mooring work, nor our CTD stations would have gone as smoothly as they did.
Sandra Schilling, 2nd Officer on the Maria S. Merian (Photo by Arne Bendinger)
Besides doing a great job manoeuvring the vessel around always changing CTD station plans, the watch officers are always happy to have us come up to the bridge to say enjoy the sunset or answer questions about the many instruments on board. The watch officer during my CTD shift is 2nd officer Sandra Schilling and she has been on board the Merian for just under a year. I think it is amazing to see women in these leading roles and I am glad I got to meet Sandra on this cruise. I asked Sandra if she misses being on land, since 8 month of the year she spends at sea, but Sandra told me she feels happiest at sea and at the end of her time on land she always feels excited to be back on board for the next voyage. Apparently the coolest thing about her job is to navigate in unchartered waters. Pun intended!
As the current week is coming to an end near the Cape Farewell, Greenland I am also ready to describe more of the great group of people I share this cruise with. I like interdisciplinary nature of our cruise. One of the scientists from Canada, fresh from finishing her honors thesis is Ciara Willis. Ciara described to me a lifelong passion for marine biology that started at age 4 inspired by conservation issues in Nova Scotia. Ciara recently finished a degree in Marine Biology and Statistics in which she took part in projects in both Canada and the US and is now on this cruise sampling nutrients and vitamins from the CTD casts to investigate microbial activity in the sea as part of a research project at her University.
Picture of Ciara Willis doing sampling in the Chemistry Lab
Ocean microbes are poorly understood and hard to cultivate in laboratories. Because microbes have such a fast lifecycle and are at the origin of the food chain for all other large aquatic species it is key to understand changes in their habitat to adapt better to climate change. One of the cool features of microbes such as phytoplankton is that they are a source of oxygen in the water through photosynthesis similar to plants. I think it is amazing to think that microbes in the ocean can behave like plants on the surface of the earth. Ciara’s hobbies at sea include bird watching and reading.
We are now closing in on the next and last part of our cruise which is to run CTD stations along Cape Farewell Greenland and then continue with the Eastern part of the OSNAP array, recovering moorings. The US research ship R/V Armstrong is also doing mooring recoveries in the vicinity and word has it we might even see each other in the coming days as a Rendevouz at Sea. Last December I already had the pleasure to visit this cool oceanographic research vessel and it will be exciting to see the ship in scientific action on the open seas!
Well, this cruise has been singular – definitely the best weather for deployments and recoveries that I have experienced while at sea. I’ve been noticing the things folks do in their spare time. Every cruise is different; every cruise has a different feel to it. The different people and personalities and work experiences coalesce into a singular experience.
On this cruise, I have learned that I am not awful at crosswords! Every day, Collin Dodson prints out a stack of the most recent New York Times crosswords, and people work on them through the day.
Every single person in the lab working on the exact same New York Times crossword at the same time.
Dave Wellwood has a disco ball in his salt lab, and music.
Keenan Foley has been trying to keep a stowaway bird alive by providing it a little bowl of water. We think it might be a juvenile Ringed Plover?
A stowaway bird (maybe a juvenile ringed plover?) has come out to visit for each mooring deployment. We think it has been on board since we left port. Keenan’s fresh water supply for the bird is pictured to the right.
The science party made cups to shrink, a tradition. Regular sized cups, when put under great pressure – as happened when being pulled deep underwater, will shrink to cups a quarter or so of their original size. We decorate cup with sharpies and tie them to the CTD rosette cage for a ride to the bottom of the sea.
Decorated cups in a laundry bag, tie-wrapped to a rosette frame, ready to be brought to the bottom of the ocean.
And James Kuo has been working his rope skills. It’s James’ birthday today, and Eric made a special cake, James (an experienced winch operator) got to run the Lebus winch and drop the last anchor on the last deployment.
The OSNAP portion of this cruise is almost wrapped up. We have had four successful mooring deployments thanks to a great crew, and we have just one more sound source mooring to recover. It is time to savor the last few days at sea, the simple skyline. Time to get things documented and submitted, work out agent and shipping logistics, to dream of fresh green vegetables, and of heading home.
Men’s World Cup on the ship’s satellite television? Must be OSNAP time.
It is still gray and cool outside, approx. 4C and 40F. But the rain is gone. I saw the sun reflecting off the ocean surface in a break in the clouds once this morning, the ocean surface is dark silver. Not the sun itself, just a derivative of the sun. I’ll take it. I have never been in the Irminger Sea this close to the southern tip of Greenland before; the ocean here seems more unpredictable than the Iceland Sea, where I have spent my last three OSNAP cruises. Just an impression – it seems like you need to watch your back out here. Water has been flat so far, though. So far.
We deployed our first OSNAP mooring yesterday: M4, the farthest offshore mooring which just captures the outer edge of the DWBC off the east coast of Greenland. This is the second mooring I have had the satisfaction of deploying, and it is a great pleasure seeing a mooring put in the water in a calm, controlled, effective manner. One technique used by this mooring team is the use of a YaleGrip to transfer line tension or load off a partially payed out mooring line. A person might need to do this to move a wire from one winch to another, or to take tension off a wire to attach and inline instrument where the wire termination is not favorable to secondary shackles – let’s say at the end of an electrical-mechanical (EM) cable. I have never seen them used by any other mooring deployment group; it is possible I had not paid careful attention on previous cruises.
A YaleGrip in the rigging van. The one pictured is the smallest we have out here, and is for the thinnest wire mooring cables. The color coding at the ends indicated the strength of the grip.
Yale grips work like ‘finger traps’, the children’s toy made of woven strips of paper overlapped into a finger-sized tube. Put a finger in each side, and try to pull them out … stuck!
A finger trap toy.
The grips are each a set of four Kevlar flat ropes that are wrapped around a taught wire. The grip begins with a loop (that can be later attached to a cleat or tie-off) secured in place with electrician’s tape. The loop end is located at the inboard end of the mooring wire, and the grip reaches toward the overboard end of the wire. Once the loop end is secured, the tension can then be slowly released from the original wire safely.
A YaleGrip being used to transfer tension off the termination of an EM cable so that the inline instrument can be attached.
This may sound dry in text, but to see it done in action is not. Once the loop of the YaleGrip is taped in place, two people send 1-2 meter lengths flying through the air in great arcs as the grip is put in place, wrapped around the mooring wire. It is an interesting contrast to see the highest of technical moorings still at the mercy of the old craft. As Jim Dunn puts it, “if you had a tug of war, the YaleGrip would win.” I just like the on-the-fly old school nature of the load transfer; it has a certain beauty to it.
Putting on the grip.
Johannes Karstensen and Penny Holliday, on the MSMerian, are on the east side of Greenland now, and the plan (at least as of 15:00 on 15 June 2018) is for the Merian crew to recover OSNAP moorings M1, 2, and 3 tomorrow. And we will follow in their wake on the 17th to begin deploying mooring in the same locations.
Well, here we are again – in the middle of the gray raw North Pacific in June; must be OSNAP time!
Amy Bower and I are the only OSNAP people on a ship full of Ocean Observatories Initiative (OOI) folks. But almost everyone on this ship is from WHOI. I will really miss sailing with Bill (Johns) and Stuart (Cunningham) and well, all the rest of the UMiami and SAMS crew, and sometimes the NIOZ crew, as I have done almost each year since 2014. Your shipmates become like family, and it was nice to have the same science crew together as we bounced from ship to ship each year. And I will miss seeing Rockall. This year, though, since the third and final seeding of RAFOS float deployments were completed in 2016, Amy and I are onto something else.
The RV Armstrong is here primarily for the turn-around of the OOI Global Irminger Sea Array off the eastern tip of Greenland (http://oceanobservatories.org/array/global-irminger-sea/). Amy arranged with the National Science Foundation (NSF) for four additional days of shiptime and mooring crew time to deploy four moorings for OSNAP east of Greenland, and also to recover two of the sound source moorings used for tracking the RAFOS floats. We took over this mooring array, instrumented with CTDs and current meters, from the UK as a swap: they took over some moorings in the Iceland Basin closer to their home country. Although this is a turn-around year for these moorings, we are only doing the re-deployment. Johannes Karstensen and Penny Holliday, onboard the RV MSMerian, will recover the moorings that were deployed by Penny onboard the RRS Discovery in 2016. Johannes and Penny will be recovering at about the same time that we are deploying, and we will have to carefully coordinate our timing so that we do not literally get our equipment tangled up together. Stay tuned on that one.
This cross-slope array will measure the properties and transport of the Deep Western Boundary Current which flows along the ocean bottom from north to south. The DWBC is composed of two primary water sources, the Denmark Strait Overflow Water (DSOW) and the Iceland-Scotland Overflow Water (ISOW). The DSOW is ‘newer’; its source is the dense (relatively cold and fresh) water that overflows the sill at the Denmark Strait, at the head of the Irminger Sea. Above it resides the relatively saltier and warmer ISOW, which originally came from the head of the Iceland Sea, in a similar deep overflow, but much farther upstream. Both are principal components of the subpolar overturning circulation.
One thing I like about being at sea is learning new things; things that have nothing to do with sitting in a chair at a desk on a computer. This morning were the first release tests for the surface mooring (SUMO) at the OOI Irminger Sea Array. Talking with Jim Dunn, a salty mooring technician from WHOI, I learned that it is common practice for the OOI team to test releases by lowering them to 1000 meters depth on the CTD frame, and to let them sit for 20 minutes to get cold before doing the test. The release needs to be acclimated and under pressure to make for a good test. Seems like every group has a slightly different depth and duration for wet tests of the releases. Some groups do not do a wet test at all. I’ll plan to stick to the OOI protocol for our own mooring releases.
As well, I got a good show-and-tell from Jim Dunn and Meaghan Donohue, another salty mooring technician from WHOI, about how wire is wound on a reel with respect to the winch. On this ship, we have a Lebus winch, a double barreled winch where the barrels can be moved independently, at independent speeds, and also oriented differently from each other, or skewed, to control the spread of the loops on the reel – so they do not get tangled. The tension is controlled by the number of loops wrapped around the two barrels. Nominally there are six loops wrapped around the winch barrels as the mooring line and instrument are fed over the fantail into the ocean. After one reel of wire is spooled out, the wire is tied off, and the next reel of wire is moved into place. Instruments are put on the mooring either between the two wires, or clamped onto the wire itself.
A more traditional winch, a “normal” winch, is a TSE winch – with a single barrel. The single barrel cannot have reels of wire fed to it, the wire tangles easily. This means that all reels must be carefully fed onto the single barrel winch before deployment. All segments, starting with the mooring bottom, are wrapped onto the barrel in order from bottom to top. Then, at deployment time, the line is payed out from top to bottom. This means that to deploy with a Lebus is generally twice as fast as deploying with a TSE.
The two winches have one upstream difference: the wirerope or rope may be wound on the spools in opposite directions. This winding preference is correctable at sea, but it takes a long, long time to rewind spools of wire on a 3000 meter mooring, with the wire split onto many spools. And at sea, it is best to be prepared. Months before leaving for sea, I notified WHOI’s Rigging Shop that these moorings would be deployed on this ship with a Lebus winch.
Our OSNAP mooring deployments are days off. This morning (Wednesday 06 June 2018) we went out to make sure the OSNAP mooring wire rope was wound on the spools correctly, and it was. Thank you, WHOI Rigging Shop. For the Lebus winch, the top of the wire is on the outside of the spool, and the opposite holds true for the TWE winch. If there are no instruments clamped to a wire segment, this wrap direction is inconsequential. But if the wire segment is ‘marked’, which means an instrument like a microcat will be attached with clamps to the wire, rather than being deployed in-line, the wirerope is taped at the correct depth where the instrument will be attached on the mooring. For this reason, marked reels need to be wound properly with respect to the winch used.
Jim also told me that moorings are deployed anchor first in ice-covered water. Which I did not know and had never thought about. You can’t steam into anchor-over position dragging a mooring cable through the ice, like you do with a mooring deployment in open water. So in ice-covered water, the desired anchor position is where the mooring deployment starts. Which means the exact opposite holds true for the winch type and wire wrapping relationship if you have an ice-deployed mooring.
What amazes me is that the same attention to detail needs to be paid to nearly every system set or tasks performed on a research cruise. I think it will be great sailing with this new group of folks.
The Lebus winch in action, its two barrels slightly skewed. Meaghan and Jim are at the center of the action, along with ‘deck boss’ John Kemp.
An unmarked reel – terminations are only labeled with shot length and the spool does not include ‘MARKED’ on the labelling.
A marked spool. The cable termination is labeled ‘top’ and the spool is labelled ‘marked’.
Most of the MSM-74 scientists in the CTD watch room. I am in the middle with the blue shirt, to the right are from nearest to farthest: Sunke Schmidtko, Marie Hundsdoerfer, Ciara Willis and Johannes Karstensen. On the left are: Arne Bendinger, Rene Witt, Ilmar Leimann, Dasha Atamanchuk and Claire Normandeau. Missing from the photo are: Thea Siuts and Alexandre Barboni (Photo Credit: Joachim Ribbe).
Some of you have maybe wondered what life on a research ship is like. Maybe because you are about to embark on a cruise of your own, or maybe you are just curious. For me this is my first oceanographic cruise and even though I have only been on board for a week, I feel the ship routine settling in. Time to write a blog entry about a life at Sea! Most of the scientific work on board MSM-74 is centered on mooring and CTD work and we are all assigned shifts in which we carry out shared scientific duties. My shift for example is from 8 Am to noon and from 8 PM to midnight. During this time, we watch the CTD as it is collecting ocean data in the control room and then take bottle samples of salt and oxygen once the CTD is back on deck. During mooring work we are mostly on deck helping the crew and the three GEOMAR technicians Christian Begler, Rene Witt and Wiebke Martens with getting instruments ready. Often other shifts will help out on mooring work as there is a lot to do and the work can be physically demanding.
Working hard on cleaning up the recovered moorings.(Photo credits: Nicolai Bronikowski)
Technician team from GEOMAR. From left to right: Rene Witt, Wiebke Martens and Christian Begler. (Photo credits: Nicolai Bronikowski)
Every day at 1 PM we have science meetings were progress and plans are discussed by the chief scientist of our cruise Johannes Karstensen from GEOMAR. This is the time ask questions and sometimes it is also a good place to share the results of your work. For example, today Penny Holliday who I interviewed in Blog #2, described her OSNAP work and some of the surprising results that came out of OSNAP with respect to the role of the Labrador Sea in the overturning circulation.
Science Meeting photo from Penny’s talk. (Photo credit: Joachim Ribbe)
Our kitchen team feeds us well with three hot meals a day. Breakfast is from 7:30 to 8:30, Lunch is 11:30 to 12:30 and dinner is from 5:30 to 6:30 PM. And don’t forget the cake at 3 PM! Typically meals are eaten by the first shift to relieve the other one so they can eat as well. Everyday the fantastic chefs of MSM-74 prepares vegetarian as well as meat options for everyone on board. If one is afraid of missing out on a meal the person can request their meal to be kept in the fridge to be eaten later. Sylvia, the stewardess also runs the ships store were twice a week one can purchase a few necessities such as fruit gummies, chocolate or toiletries. The typical after work beer is allowed on board of course so the shop also offers duty free beverages such as beer and liquor.
Eating “Mustard Eggs” “Eggs with mustard sauce and beetroot” for dinner. A traditional German dish! (Photo Credit: Joachim Ribbe).
After a hard day working on deck there are various ways to relax such as going to the ships own Sauna with a real Finnish made sauna room and beach chairs to relax afterwards. In ships storage area there are table tennis, darts as well as a foosball table and they often become the center of socializing after work shifts are over. In the ship’s own bar one can purchase drinks and relax in leather chairs to the sound of music or an interesting conversation. Game nights are also held there and it’s a good meeting place to talk more to the crew.
Typically, there are two scientists that share a room, except for the technicians and principal investigators that get their own cabin on board the ship. The way the shifts tend to work out one goes to bed as the other gets up for their shift. Which is a good system for those that need a bit of alone time or are light sleepers. And one can wake up each other Curtains help keeping light out and for the most part you don’t notice people entering or leaving. If one feels like they need to be out and relax, when the weather is good there is a nice little bench on the port side of the main deck and for those who like to sunbath in the chill air, there are beach chairs on the observation deck
I hope this summary of typical day on board and the different routines help paint a clear picture of life at sea on the Maria S. Merian. We are now close to Greenland on our month long cruise and I am excited for the next couple of days enjoying Greenland’s coastline.
The temperature time series from 4000 m depth in the central Labrador Sea spans two years and is characterized by small and big waves and swirls. It is full of mysteries. As a postdoc from GEOMAR it‘s my second research expedition from St. John‘s to Reykjavik and my task on board is to assess the quality of the data to decide if the instruments can be re-deployed. This means that I am one of the first to look at the data after we recover the instruments from the water – in this case from 4000 m depth. Considering that we can hardly enter this region ourselves, we send measuring instruments there every two years to have them record what we cannot see.
Already a first glance at the data reveals that it‘s not as calm down there as one may think. Numerous oscillations in pressure, temperature and salinity reflect a colorful chaos of many different signals and only through careful analyses we may have the chance to decipher the causes underlying this rich variability. Where does the water originate from? When and where has it been at the surface? Which known or yet undetermined processes have changed it? And which time scales of variability are dominant? This deep, there is no clearly distinguishable seasonal cycle because the distance to the surface is too large. Instead, other mechanisms have left their imprint on the water near the sea floor, most of which cannot be identified by this initial glance. In fact, they may remain elusive even after rigorous analyses.
At any rate, this first look at the data tells me that the instrument has gone through an exciting two years – and that an engaging analysis is waiting for us. Bearing in mind that measurements can drift and have offsets, I always remember that no instrument is perfect and that it only shows us one small fraction of what is happening 4000 m below sea level. Much remains a mystery.
There are many fantastic people from all corners of the world on board of our cruise and in the next few entries I like to introduce some of these people I have the pleasure dealing with every day. One of our scientists, Penny Holliday is an ocean going oceanographer from NOC (National Oceanography Centre), who joined our cruise from Southampton, UK. Penny has worked in Ocean science for over two decades and leads the UK OSNAP program.
Penny told me what really got her interested in Oceanography was the possibility to work on so many projects and how connected everything about the ocean is. Penny herself calls her starting point in oceanography a coincidence. Penny was analysing a hydrographic time series when she noticed that her data set could not be explained without digging deeper into the wider Atlantic circulation. This was her starting point in studying the currents in the North Atlantic, which is the focus of the OSNAP program.
But why does this transport matter? It may not be obvious to think about the cold North Atlantic as an important driver of our pleasant weather in Europe. Penny told me that without the currents in the North Atlantic transporting water South-North which is called the Meridional Overturning Circulation, the weather in Europe would be much colder than it is now. Indeed, understanding the way this circulation changes and what drives it are in Penny’s view the key to adapting better to climate change.
I also asked Penny what she has most enjoyed about Oceanography and she admits it’s the travel and the opportunity to do lots of different things. To Penny one of the best things about oceanography are its interdisciplinary focus, with opportunity to work with lots of people. Penny is frequently on ships and her number one advice is to take the time to meet as many people as possible, make friends and be open to learn about topics that may not be directly related to your research focus.
Penny working on the mooring spool together with GEOMAR student Ilmar Leinmann (Photo credit: Penny Holliday)
On our cruise the last few days were filled with extracting and deploying moorings (K7-K10) and taking CTDs along the 53 North Array. The array stretches from the Newfoundland-Labrador shelf between depths of few hundreds to over 3000 meters deep. Most of the instruments we recover have been sampling for over two years and our task is to extract the data and ready them for the next mooring deployment with the OSNAP program. For us as young scientists we get to learn a lot of practical and technical skills changing batteries and calibrating the sensors and we feel the responsibility of doing a good job. After all the continued success of the program depends on new and accurate data.
Map of the 53 North Array and the total cruise plan for MSM 74.
And we are off! MSM 74 – the oceanographic cruise from St. John’s to Reykjavik is making its way to the Labrador Sea. In these 5 weeks a group of 21 scientists and 24 crew on board the German research vessel “Maria S Merian”, will brace the tough North Atlantic in the name of science. The mission: we will recover and re-deploy German, British and US moorings with measurement devices as well as take 80 CTD casts from the surface to the ocean floor to assist the scientists from the OSNAP program with their effort to estimate the Subpolar Overturning circulation and associated transport of heat and freshwater. In this blog we will detail some of the work being done, why it matters to oceanography and what life on board feels like. We hope you will enjoy reading this blog.
Day 1 – Day 3: Our journey begins in St. John’s – the capital of the easternmost province of Canada: Newfoundland and Labrador. St. John’s is a vibrant little city on the Atlantic coast inside a natural harbour of ragged rocks towering around the fjord. The night before putting out to sea snow fell and for a moment coated much of the city in a fine layer of fine white dust. It must have been an unusual sight to see snow in the end of May for most of our team arriving from places where summer already started. Our team consists of 21 scientists, 6 of which are bio-geochemists from Dalhousie University (Canada) and 15 physical oceanographers from GEOMAR (Germany), Memorial University (Canada), NOC (UK) and EPPS (France).
St. John’s Harbour view from Signal Hill
St. John’s Harbour view from Signal Hill
Last night in St. John’s (May 24/25) and snow
After re-fuelling or bunkering as they say in nautical language, the ship’s ready for the voyage. The pilot boards the ship and helps the captain navigate safely into the open ocean. We all say goodbye to mainland until the end of cruise and are greeted by 2-4 meter swells. We began the journey with safety drills and figuring our safety equipment like entering the free-falling lifeboat and lifejackets.
After this was done it was time for our CTD test station (Station 27), just outside St. John’s. CTD stands for: Conductivity, Temperature and Depth sensor and is used to measure very precisely the temperature of the water. From conductivity, temperature and pressure, the salinity and density can be worked out using standardized equations for sea water. These variables are the most important physical variables captured on all ocean research cruises. However, our CTD cast has many more instruments attached such as an ADCP to measure current speeds, an oxygen sensor to measure dissolved oxygen, a flourometer to measure plant life activity, an altimeter to detect the distance to the seabed, and a UVP (underwater vision profiler) that takes high resolution pictures of living beings under water like plants, marine life and other particles. The CTD is attached to the so called rosette, which includes water bottles that can be closed at different depths and collect samples of sea water. These are then analyzed by the bio-geochemists for gasses such as oxygen or carbon dioxide as well as nutrients.
Everyone was present to learn about the different steps in taking a CTD cast and the necessary water sample preparations that needed to be done. Unfortunately, at this point, some of our scientific crew started to battle the effects of sea sickness and the ship’s doctor was doing his best encouraging us and gave us patches to counteract the sickness feelings. Now we are on our way to our first real mooring and CTD station site and we should arrive there this evening. Looking forward to what the day will bring.
The eastern subpolar North Atlantic has a special role in the Atlantic Overturning Circulation (AMOC) and global climate change. The waters in this regions are subtropical-origin warm and salty water masses, which are carried by the North Atlantic Current. They either move further northward into the Nordic Seas or cyclonically circulate to the Irminger Sea and Labrador Sea and then transform into dense waters. Substantial heat is released along their pathways, which is pivotal to maintaining a relatively warm climate in Northern Europe.
As a component of the Overturning in the Subpolar North Atlantic Program (OSNAP), WHOI-OUC jointly deployed gliders (underwater autonomous vehicles) in the Iceland Basin. The Iceland Basin lies east of the Reykjanes Ridge and west of the Rockall Plateau. The battery in each glider can afford continuous scientific sampling up to 6 months. Therefore, a new mission needs be triggered every half year. This is very challenging because it is not easy to find suitable ships, especially in winter, to recover and deploy vehicles. We had to rent small boats in Iceland and launch gliders near the coast. The glider section is about 260 nautical miles (more than 425 km) south of Iceland. With an averaged horizontal flying speed of 0.2 m/s, the glider takes three to four weeks to navigate to the working site. If the glider needs to swim back to the coast, the vehicle had to stop scientific samplings one month before the battery run out. In other words, about one third (two months over 6 months) of energy will be spent on the non-scientific task!
Despite the various logistics we have to deal with, 6 glider missions have been successfully completed between June 2015 and December 2017. More than 3000 hydrographic profiles have been collected. Moving at approximately 0.2 m/s, gliders ‘fly’ through the ocean from surface to 1000 m. In each dive-climb cycle, they navigate along a sawtooth trajectory and measure temperature, conductivity (salinity), pressure and oxygen. The horizontal sample-spacing averages 3 km, but near the surface and 1000-m turnaround points distance ranges from hundreds of meters to 6 km. The surveyed section is along 58°N with endpoints at 24.5°W and 21°W, respectively. The section is about 200 km in length and a one-way transect is usually completed in 7–10 days.
Hydrographic properties in the Iceland Basin for mesoscale eddy and frontal circulation patterns near 58°N. The left panels show the ocean state on 3 -13 August, 2015, for absolute dynamic topography (a), glider potential temperature (c), and glider salinity (e). The corresponding ocean state on 14-20 December 2016 is displayed in the right panels (b, absolute dynamic topography; d, potential temperature; f, salinity). Glider transect is marked by black lines in a) and b). The isobaths in panel a) and b) are represented by gray lines. The gray contour lines from panel c) to f) display the relative potential density.
The In-situ observations indicate two circulation regimes in the Iceland Basin: a mesoscale eddy like pattern and northward flowing NAC pattern. When a mesoscale eddy is generated, the rotational currents associated with the eddy lead to both northward and southward flow in the Iceland basin. This is quite different from the broad northward flow associated with the NAC when there is no eddy. The transition between the two regimes coupled with the strong temperature front in the Iceland basin can modify the meridional temperature flux on the order of 0.3PW. The dramatic variability induced by alternating eddy and frontal patterns is also found in high-resolution (1/12°) HYCOM simulations. In addition, a separation of large scale and mesoscale processes in the model results suggests that eddies in the Iceland Basin make significant contributions to the variability of the total basinwide poleward heat flux on time scales from subseasonal to interannual.
Detailed examinations of satellite altimetry data suggest that the alternative occurrence of eddy and front are quite common in the Iceland Basin. Therefore, the observed two circulation regimes detected from glider data are generally representative of long-term conditions. The velocity change associated with the eddy and front scenarios contribute to high Eddy Kinetic Energy (EKE). The surface EKE from altimetry data suggest that enhanced EKE is located in the eastern part of the subpolar region, especially in the Iceland Basin and Rockall Trough, coincident with the branches of the NAC. Similar EKE map is also reproduced by the eddy-resolving (1/12°) HYCOM simulations. In addition, the model results reveal that EKE along the OSNAP East line has nice correspondence with the meridional heat transport variability, with the highest values located in the Iceland Basin. As a result, the eddy and front structures captured by the gliders are the dominant processes to generate the temperature transport variability in the Iceland Basin.
a) Mean surface Eddy Kinetic Energy (EKE) from 1993 to 2015 from the satellite data. Unit: m^2/s^2. Magenta dash line represents the OSNAP East. Black diamonds denote the end points for the glider transect. The isobaths are illustrated by white contour lines. b) Standard deviation of the meridional heat transport at each longitude in numerical simulations (red). The mean surface geostrophic EKE from altimeter observations (1992-2015) and numerical model (1992-2014) are displayed in blue and black, respectively. The vertical black dashed lines mark the endpoints of the glider transect, where the meridional heat transport has largest variability.
The results from the glider observations provide a fresh perspective on the dynamics responsible for the poleward heat transport in the subpolar North Atlantic Ocean, revealing that the alternating eddy and front patterns contributes significantly to the total poleward heat transport variability on time scales from subseasonal to interannual. This is different from our understanding about the mechanisms for oceanic heat transport variability, where large-scale circulation changes are believed to be the main driver. Our results emphasize the importance of resolving mesoscale processes in observations and numerical simulations to realistically capture their roles in modulating heat transport variability in the northern North Atlantic. High-resolution observational arrays capable of capturing both large scale and mesoscale variability, such as the OSNAP observing system (which includes moorings, gliders, Argo floats and satellite altimetry), are needed to measure the basinwide ocean MHT in the subpolar North Atlantic.
Results were recently published in Nature Communications:
Zhao, J., A. Bower, J. Yang, and X. Lin, 2018. Meridional heat transport variability induced by mesoscale processes in the subpolar North Atlantic. Nature Communications, 9, 1124, doi: 10.1038/s41467-018-03134-x
Science has many aspects. The collection of data on the process of region you are studying; the actual digging through the data to find out what is going on (which is what most people seem to associate with science); writing down the results so they are documented and others can learn what you learned; discussing the results with colleagues in your fields and hearing about new methods and results; and the training of new scientists. Sometime all of these happen within a very short time frame.
After finishing a proposal and a paper draft at the end of January, February started with a short research cruise. This may not have been an OSNAP cruise, but all hydrographic cruises share very similar aspects. The run-up to the cruise is a lot about getting the logistics arranged and preparing a cruise plan. Does everyone have
The RV Pelagia, our home for the duration of this cruise.
the right paperwork to go on board? How are we going to divide the tasks on board? How many measurements stations will be able to do and where? And most importantly… will all the instruments work and the data be good? Once on board things start to fall into place. Those who are back in their familiar environment show the ropes to the newcomers. Instruments are prepared and plans discussed with the ship’s crew. During the cruise, while data collection progresses, we process the initial results and get an idea of whether our science goals will be fulfilled. Once land is in sight on the other end of the cruise everyone is tired and ready to go home.
Unless, due to some haphazard planning, you need to proceed directly to a scientific conference. While cruise departure and arrival day are never fixed until you actually departed or arrived, dates of meetings with several thousand participants tend to be quite fixed. The Ocean Sciences Meeting is a biannual meeting with all fields of oceanography. About 5000 people met in Portland, OR, this week to discuss their work. This happens in “sessions”, submeetings organized by topic, of which there were nearly 500. The new OSNAP results were presented in
Closing remarks at the OSM18.
the AMOC (Atlantic Meridional Overturning Circulation) session. Several of us had oral talks. Susan Lozier presented the (near) final numbers of the overturning over the whole OSNAP line. Penny Holliday shows us the circulation estimates from the OSNAP hydrographic sections in 2014 and 2016. Bill Johns detailed the Iceland Scotland Overflow Water flow along the east flank of the Reykjanes Ridge. I presented our investigation of variability west of the Reykjanes Ridge. Feili Li compared Labrador Sea Water formation with Labrador Sea overturning. More OSNAP talks were held in other sessions (see OSM blog post). Since there are too many of us to all get talks (even if they only last 15 min) some are requested to present posters. Poster sessions are held during the last two hours of the day. Presenters stand next to their posters and the rest of use walk around and either browse poster titles to find something that interests us or seek out poster titles we identified beforehand in the program. Often the most interesting discussions are held at posters we unintendedly come across and these are great chances to meet new people. Between the talks and posters we catch up with old friends or meeting with co-authors on papers or potential new collaborators.
Now that I’ve returned from the Ocean Sciences Meeting I’m starting a new chapter. My first PhD student, Roos Bol, has started her position at NIOZ this week. She recently finished her MSc thesis at the NOC in Southampton and I’m very excited to be working with her. She’ll be investigating our OSNAP data from the Irminger Current array and will be coming along on this summer’s OSNAP cruise. Over the next four year I’ll expect to be teaching her all about data collection, data processing, writing down results and giving presentations at conferences.