From Chief Scientist, Craig Lee – University of Washington, Applied Physics Lab
It’s Thursday midnight, and we’re making our last measurements of seawater chemistry before concluding this year’s field effort and returning to Greenland. We’ve been working to understand the oceanography of this critical region for over a decade. Why?
The Arctic Ocean connects to the lower latitude oceans (Pacific and Atlantic) though only a small handful of gateways. Bering Strait connects the Arctic to the Pacific Ocean, while Fram Strait, east of Greenland, and the Canadian Arctic Archipelago, west of Greenland, and the Barents Sea opening, connect it to the Atlantic. These gateways are important because they allow freshwater and heat to move between the Arctic and the rest of the world’s oceans. Such exchanges can have large impacts on the currents that carry water around the entire globe.
In our case, we are concerned with the waters between Baffin Island and Greenland, and in particular with the southward flow of relatively fresh waters from the Arctic Ocean into the Labrador Sea, and the northward flow of relatively warm Atlantic Ocean water along the Greenland coast.
Why fresh water? During wintertime, the cold, dry air and strong winds cool the upper layer of the Labrador Sea. As the upper layer cools it gets heavier (more dense). When it becomes heavier than the waters below, the situation is unstable, and the heavy upper layer sinks, similar to what happens when water is poured on top of oil. This is called “convection”, a process that is a critical part of the atmosphere-ocean engine that moves heat and freshwater around the global oceans. Salt content also contributes to the density of seawater. Waters exiting the Arctic (Baffin Island Current) are fresher, and thus less dense (lighter), than those in the Labrador Sea. Fresh Arctic waters that enter the Labrador Sea can make the surface layer lighter. Because lighter surface layers require more cooling to trigger convection, fresh Arctic waters that enter the central Labrador Sea can reduce convection and slow the ocean currents that it drives.
Why heat? The Greenland ice sheet melts from the top, due to warming by the sun, but may also melt from below, due to warming from the ocean. Waters from the Atlantic Ocean provide a source of heat for melting the ice sheet. These waters flow north in a surface current offshore of western Greenland (West Greenland Current), and in a current below the surface, located just beyond the shallow waters of the west Greenland shelf (West Greenland Slope Current). We are interested in the heat being carried northward in these currents due to their potential for accelerating melting of the Greenland ice sheet. Rates of ice sheet melting (in both Greenland and the Antarctic) have large impacts on forecasts of sea level rise, making this an important area of research.
Why Davis Strait? The Canadian Arctic Archipelago is a complex system of many interconnected narrow channels and small basins that lead from the Arctic to Baffin Bay. That complexity makes it difficult to measure. Fortunately for us, nearly all of these channels funnel into Baffin Bay. Davis Strait (the red line on the chart that marks where we’ve been working) bounds the southern end of Baffin Bay, and thus provides a convenient “choke point.” By measuring at this one location (rather than in the many channels to the north), we can capture all of the water going in and out of the Canadian Arctic Archipelago. This includes south-going freshwater from the Arctic, and north-going heat from the Atlantic. The Arctic outflow also has implications for ocean acidification and ecosystems, but that’s a story for another post.
Holly Hogan: Seabird Observer for Canadian Widlife Service, Environment Canada
I grew up in St. John’s NewfoundIand, where I also did my MSc. Degree at Memorial University of Newfoundland (MUN).
Newfoundland is an island stuck well out into the flow of the Labrador Current. For this reason, the Island is famous for both it’s cold wet foggy terrible weather and it’s incredible diversity of marine life. Located forty-five minutes from St. John’s is the second largest colony of Leach’s Storm-Petrels in the world, and the largest Atlantic Puffin Colony in North America (Witless Bay Islands Ecological Reserve). Add another hour and a half to the drive and you are on the doorstep of the largest Leach’s Storm-Petrel Colony in the world (Baccalieu Island Ecological Reserve) or the second largest Northern Gannet Colony in North America (Cape St. Mary’s Ecological Reserve). As someone with an affinity for the natural world the attraction is obvious. I worked for the Canadian Wildlife Service, Environment Canada for close to a decade, and then managed both the Witless Bay and Baccalieu Ecological Reserves for the provincial government, Department of Environment and Conservation. In recent years I have been conducting offshore seabird surveys for the Canadian Wildlife Service, under the Environment Canada Seabirds At Sea (ECSAS) program.
These surveys provide important data on pelagic seabird distribution throughout the year, including patterns of dispersal from breeding areas, migration routes and wintering areas. Over time, these data will show not only patterns of dispersal, but also trends in species abundance, diversity and distribution over time. Of particular interest on this cruise is the post-breeding dispersal of Dovekies, or Little Auks (Alle alle) from their breeding colonies to wintering areas. Several million Dovekies (approximately 80% of the world’s population) breed in northwestern Greenland. Many of these migrate to coastal waters of northeastern North America via the Davis Strait. Dovekie chicks generally leave the colony with one parent (usually male). However, the amount of time spent with the family group is not well understood. During this cruise, I will be paying particular attention to Dovekie parent/chick associations whenever viewing conditions permit. Adults and chicks have different plumages at this stage, which allows the distinction to be made: the adults have a solid white cheek patch that rises well above the eye. The cheek patch of the chick is more buffy; appears less striking and does not rise as far above the eye. In the right light, the dark brown hue on the chick’s back can be seen. (see photo) These data will add to the growing body of data on family group dispersal during migration, and will provide important insight to this question.
As would be expected, Dovekies and Northern Fulmars have been the most abundant species seen to date. Bird post
Graduate student Leah Johnson, from the University of Washington is our guest blogger and writes about Chief Scientist Craig Lee’s moorings in the Davis Strait.
The long term monitoring of Davis Strait ensues from the dedication of several participating labs and scientists. The Integrative Observing Platforms (IOP) lab from the Applied Physics Lab, University of Washington is one of these groups. IOP has been involved with this campaign from its inception, and is largely responsible for the deployment and maintenance of a moored array of instruments that span across the strait (i.e. ‘moorings’).
The entire array is carefully designed, with each instrument placed strategically in order to capture the spatial and temporal variability of fluxes connecting the Arctic and subpolar North Atlantic. Each mooring is equipped with it’s own suite of instruments and floats, attached together by a synthetic line and anchored to the bottom of the ocean. The line and instruments are held upright by the floats and are therefore situated vertically in the water column, well below the surface of the sea (diagram – see description of instruments below).
Deployment and recovery of these moorings are just as carefully engineered as the design itself. The longer moorings are maneuvered through an A-frame on the ship’s stern. Each instrument is raised off deck by the A-frame and carefully lowered into the water so as not to collide with the often rocking and swaying ship. Instruments are handled one at a time; starting with the top of the mooring and working successively down the line. During deployments, the ship moves at a steady and slow pace, allowing the instruments and floats to extend horizontally along the sea surface. The final step is to attach an anchor to the end of the line. When the anchor is released from the A-frame, it plunges to the depths of the ocean, bringing the mooring line with it. The instruments remain suspended in the water column below the surface of the ocean for the next two years, recording data all the while. When it is time for recovery, the science team sends a signal to the acoustic release at the bottom of the mooring and commands it to let go of the anchor. The entire line of instruments and floats rise to the surface and are hauled onboard the ship, along with the two years of stored information about the ocean interior across the Strait.
The moored array encompasses a broad suit of instruments that tell the story of the annual fluxes through Davis Strait. Below is a summary of instruments incorporated in this array:
Ocean Physics: Each mooring line is equipped with a ‘CTD’ that measures the water’s conductivity (salinity), temperature, and depth (pressure). In addition to measuring these tracers, each line is equipped with current meters (RCM-8 and ADCPs) that determine both the magnitude and direction of the water flow. Continuous measurements of current velocities, temperature and salinity supply the information needed to construct an annual budget for heat and salt transport through the Strait.
Marine Mammals and Fish: Measurements along the array extends beyond physics and branches out in search for marine life. Several lines are equipped with a marine mammal receiver that records sound traveling though the ocean. This data is processed to differentiate sounds of marine mammals and help identify the presence of certain species throughout the year. In addition to the sound receiver, several moorings are equipped with a fish tag detector. This detector will identify and count fish that have been tagged by collaborators at the British Institute of Oceanography.
RAFOS-Seaglider communication: Seagliders are autonomous underwater vehicles (or AUVs) that maneuver independently through the water and collect measurements of temperature, salinity and depth. Seagliders orient themselves at the sea surface via GPS, which can be hazardous in the presence of sea ice. The IOP lab has surpassed this limitation by programming seagliders to communicate with RAFOS sound sources underwater that provide a spatial reference. RAFOS are included in the moored array, allowing seagliders to survey the array line during times of ice cover and develop a more complete spatial image of the temperature and salinity fluctuations through the strait.
Post by Lisa Robbins from onboard the R/V Atlantis:
One of the instruments that we are running during the cruise is a portable spectrometer that measures discrete seawater samples for pH using 3 different wavelengths – 730, 434, and 578. This pH spectrometer system is very convenient because of its size and ease of set up.
The system has three main components: a light source (to left), a fiber optic cable leading to and from cuvette holder, and the spectrometer shown in separate picture.
After a quartz cuvette is filled with seawater, the cuvette is checked for bubbles and lint and finger prints that will cause inaccurate measurements.
Indicator dye is added and then the cuvette goes in the holder where light from the halogen lamp passes through it to the spectrometer. We add 2 separate doses of mCP to a cuvette filled with seawater and measure the 3 wavelengths two times. Based on the wavelength characteristics, a pH can be calculated. We also use a seawater standard (Dickson Certified Reference Material (CRM)) daily to make sure our spec is giving correct numbers.
While you can see obvious changes in color of the seawater of the cuvettes which reflect pH differences – the spec can “see” and record subtle, very minute differences. These small differences in pH, are actually very important in understanding how the oceans vary over space and time.
The pH data, in conjunction with data on carbon parameters and oxygen and hydrogen isotopes (also see post “Measuring the Ocean – One Drop at a Time”), help us characterize the surface and subsurface waters for saturation state, carbon fluxes, and influences of different freshwater sources (like sea ice melt or glacial melt) on the chemistry. Ultimately, these data will help us predict how the ocean and coastal environments will change over time.
Nearly five hundred pH measurements and several blistered fingers later, this is what the lab looks like below.
September 22, 2015 – Post from Lisa Robbins on the R/V Atlantis
Yesterday was an exciting day for the crew and scientists aboard the R/V Atlantis. Just before 2pm our captain and his crew received a “mayday” and EPIRB (Emergency Position Indicating Radio Beacon) signal from a fishing ship, Atlantic Charger, sinking about 100miles away from us in the Labrador Sea. Nine of its fishermen deployed 5 lifeboats and waited while a number of ships came to its rescue, including the R/V Atlantis. About 10 hours after the distress call in seas reaching 20′ or more and gale force winds (about 40 knots) – at about 11 PM (local), the Atlantis arrived on scene. Two other ships had just arrived on scene also, but had not yet picked up the fishermen. The captains of the ships assessed that all of the crew were OK -The fishermen were all wearing survival suits and could endure the very chilly 3°C water and the rafts gave them some protection from the howling winds, All of the ships then coordinated the safe retrieval of the fishermen in the high seas and winds. The men were transferred onto one of the ships and the Atlantis retrieved 3 life rafts, seen in the photo below, with the Atlantis crew members that were on duty. After the successful retrieval of men and rafts, we turned around and headed back for the scientific stations that were left!
Link to the CBC article on the sinking of the Atlantic Charger:
Science on board the ship came to a short hiatus on Saturday, September 19th, as the ship stopped in Sisimuit, Greenland to drop off a few scientists. The R/V Atlantis came into port and transported the scientist to land via the ship dinghy. Shortly thereafter, the ship was on the way to the next sampling station.
Andrew Cogswell of the Bedford Institute of Oceanography submitted this entry from the R/V Atlantis.
The rosette sampling order is completed the same way each time based on the volatility of the parameter being investigated. We all play “ring around the rosette” until samples are collected. This is the torture I mentioned in Part 1. The water is below zero at some depths and really makes you question your choice of career as it cascades over your increasingly useless and painful digits. Coupled with the wind and freezing temperatures on the open deck, it can be a less than pleasant experience. Once the water has reduced your hands to frozen stumps, water sampling is complete. The water is then paraded back to the lab (just feet from the CTD for those of you on the Hudson) for sample preparation and/or storage. The torture now enters it’s second stage as feeling returns to your fingers. Joking aside, time at the rosette can be a pleasant experience. Scientists emerge bleary eyed from the lab to take samples and usually return to the lab full of energy after getting some much needed arctic air and great conversation as we make our way around the rosette.
The CTD is then cleaned and prepped for the next cast and the process repeats itself. This is not meant to be an in depth review. I’ve simplified a great deal and left out some information for the sake of brevity (OK, that did not work – sorry). It’s a messy business. Water sampling at the end of the cast get the camera lens wet, but now you know how we get the water and monitor the environment.
Andrew Cogswell of the Bedford Institute of Oceanography has submitted this guest scientist entry from the R/V Atlantis.
Time: 2032 UTC
Longitude: 59 05.1 W
Latitude: 66 19.5 N
Conditions: wicked good (5-10 kts wind, fog)
Upcoming Conditions: ughhhhhh (Monday – 40 kts wind)
What is a CTD, you say? Right now, it seems like a self-induced water torture device designed to make the victim experience piercing pain in each finger as you purposefully collect bone numbing water sample after bone numbing water sample, but I digress. The acronym stands for Conductivity, Temperature and Depth; each parameter represented by a different sensor which collects these data and either stores them internally or transmits them through a cable back to the ship where they are viewed live and stored by operators. OK, Coles Notes version (you can stop here if you want).
The name, “CTD”, vastly understates the complexity of this bundle of oceanographic wizardry. It was originally branded the STD (Salinity, Temperature, Depth – Wow, poor acronym choice!) in 1960 but was later sold as the CTD in 1970 (Phew, that was close! Find out more by reading Instrumentation and Metrology in Oceanography by Marc Le Menn). Since that time, the CTD has gained momentum, with new sensors occasionally being developed to add to the ever growing arsenal of this “Swiss Army Tool” of water sampling. As such, a world wide community of CTD users and data providers are established and require high levels of instrument precision and accuracy based on a generally agreed upon set of international standards. Data generated by CTD’s are sent by organizations the world over to central data repositories like the World Ocean Database (formerly, the National Oceanographic Data Center).
A modern CTD, like the one aboard the Atlantis, is truly amazing! When combined, the bundle of probes which measure water column characteristics, is about the size of a large microwave oven. The list of sensors on the CTD aboard the Atlantis is extensive and includes a primary and secondary set of temperature and conductivity (salinity) probes, oxygen, fluorometer, pH, Photosynthetically Active Radiation (PAR), pressure,(depth) and an altimeter. Whoa, that’s a lot going on at the same time! Each instrument requires it’s own form of baby sitting that could involve: soaking in fresh water between casts, bathing in a standard solution, covering a sensor head, etc… To further complicate the issue (or compliment probe measurements I suppose), this hyper-complicated mass of temperamental electronics is housed in a large cylindrical frame, upon which mounts 24 – 20L Niskin bottles. These vertically positioned bottles employ an ingenious series of high tension bands that run through the center of the bottle to caps on either end. Small but strong plastic wires at the top of the bottles radiate to ridged hooks on a central “carousel”, holding the bottles open.
A large electro-magnetic cable is “terminated” to the “CTD Rosette”. Many kilometers of cable (~6 km in our case), snakes its way through a “block” or wheel on the crane which protrudes from the starboard side of the ship. The cable is wound tightly on a winch drum, which pays out the desired amount of cable required for the depth of deployment. The data from the CTD makes it’s way up the cable during the cast and is visualized using software at the “Command and Control Center” in the Computer Room on the Atlantis. The bottles are fired at pre-determined depths, and each bottle contains enough water (hopefully) to meet the sampling demands of our scientists in the lab.
Alrighty then, here is our typical order of events. You might want to grab a drink or get up and stretch a little before reading. Long before the cast, a spreadsheet of required sampling is produced along with the depths samples are required from. Depending on the area being sampled, different questions are being asked and require a unique subset of our analytical suite. Each bottle on the rosette is then labelled with a unique sequential numerical identifier (a little sticker with numbers). All samples drawn from a bottle inherit this identifier for analysis. As we transit towards our stations, we are watching a screen which provides us with an approximate arrival time. We typically use this time to prepare our sample bottles and label them with stickers. Approximately 20 minutes from station, we make sure the rosette bottles are labelled with stickers, cock the bottles, remove sensor coverings and tubing and tie on tag lines to rings on the rosette frame. Once on station, the ship’s SSSG (Shipboard Scientific Support Group) technicians correspond with the bridge to acquire approval for launching the gear over the starboard side of the ship. The technician coordinates with the winch operator (housed in the next level up from the working deck) and the deck crew to deploy the CTD over the rail of the ship and into the water (science staff BTW – we don’t sit at computers or stand in labs with coffee cups all day discussing the latest pocket protectors and episodes of Big Bang Theory. OK, that happens sometimes, but who doesn’t love a good pocket protector, right!)
An operator in the Computer Room at the CTD control center (me) turns the CTD on via the “Deck Unit”. Some time is required for pumps to engage that will move water through the CTD sensor package, and then the system is brought to the surface. The CTD acquisition software is turned on to log the data and the descent is initiated by a command to the winch operator to descend to 100 m at 30 m/min. At 100 m, control of the winch is assumed by the SSSG technician in the Computer Room and descent to the final depth is initiated at 60 m/min until near the bottom where the speed of descent is reduced to minimize the likelihood of impact (and making lots of people very agitated). The SSSG technician and the CTD computer operator can acquire the water depth from a sounder or on board multibeam echosounder system. At 5 m off bottom, the CTD is stopped and the sensors are given time (~1 min) to come to equilibrium prior to firing the first bottle. The SSSG technician then brings the CTD up to the next required depth and the process is repeated at predefined intervals until the CTD is at the surface. At the surface, the science crew and SSSG tech prepare for receiving the CTD on the starboard side of the ship. The CTD deck unit is shut off and the deck crew use long poles with hooks on the end to latch on to the CTD and use small tugger winches in coordination with the crane to bring the CTD back up over the rail and into position on the deck. Once on deck, the CTD is ratcheted down and the science staff assume their positions to acquire samples from the rosette. OMG, I’m tired just thinking about it!
End of Part 1 – Rosette Blog – Andrew Cogswell – Bedford Institute of Oceanography
The Davis Strait is located between Northern Canada and Greenland. It is the largest strait in the world with an extreme tidal range of 30-50 feet. Cold water flows from the Arctic Ocean through the Davis Strait to the North Atlantic Ocean in the Labrador Current while warmer water from the North Atlantic Drift moves from the south into the strait. As a connector between the Arctic Ocean and the Atlantic Ocean, the Davis Strait is a unique environment to study water chemistry. During the summer sea ice melt, the seawater is “fresher” than in the winter when freezing of the ice caps is occurring and the water is more saline. Just how do all of these factors affect the water chemistry in the Davis Strait and what are the implications for ocean acidification? This research cruise is looking at water sample chemistry across the strait and at depth by measuring a variety of parameters such as pCO2, pH, alkalinity, oxygen isotopes, dissolved inorganic carbon, and dissolved organic carbon, among others, to look for answers.
USGS Ocean Acidification researchers on the R/V Atlantis are using an underway flowthrough system aboard the R/V Atlantis to measure the chemical composition of the surface ocean. The underway flowthrough system collects seawater from a port in the ship’s hull, which then flows through a faucet in the lab into instruments such as the water isotope analyzer. These instruments measure chemical properties at a sampling frequency of as much as one data point per second. Since the flow rate through the instrument is about one drop per second, the ship is measuring the ocean about one drop at a time!