SO GasEx Blog
By David Ho, LDEO
Well, it finally happened. We were supposed to get in at 2 am, then it was changed to 4 am, then to 8 am, then to 11 am, and we finally docked at 12.01 pm. It was a fitting end to the cruise in 2 ways: The first is just the unpredictability of everything, and the second is that Herb won the pool predicting when we would get in. Herb and Richard from the galley fed us really well the entire cruise, and being a vegetarian, it was certainly the best cruise I’ve ever been on in terms of the food selection.
The agent in Montevideo was great, and had all the containers waiting for us. With everyone helping unload the ship and load the containers, everything going back to the US via ocean freight was unloaded in less than 4 hours. The air freight will go out on Monday.
Now it’s time for everyone from the scientific party to…well…party. We will meet up soon for drinks and food before disbanding and returning to our respective homes.
After anchoring all night off Montevideo, the moment the ship started moving was probably the happiest moment in the entire cruise for Burke.
A view of the ship’s berth in Montevideo.
Shipping containers getting loaded with scientific gear.
By David Ho, LDEO
Chris was prescient when he wrote his blog. We were suppose to get into Montevideo earlier today, but it turns out the port had no berths for us until tomorrow. So, it’s 11 pm on Friday night, and we’re sitting in the mouth of the Río de la Plata, a few miles off the coast of Montevideo. We can see the lights of the vibrant city, much like prisoners on Alcatraz could see the great city of San Francisco, but everything the city has to offer is entirely out of our reach. To make things worse, we’re out of honey and Vegemite. It’s officially a crisis.
The scientist and crew onboard all have extreme cases of channel fever. People pass the time by playing board games, watching movies, catching up on work, and sitting around discussion things they miss on land (e.g., favorite foods, activities, etc). We all hope that tomorrow will come soon, and we’ll finally be dockside and unloading our gear. Stay tuned.
Pete with the empty jar of Vegemite moments before its burial at sea.
Alejandro and Bertrand engage in an international game of chess.
Scrabble hawk Bob takes on another unsuspecting victim in Byron, while Geoff and Sarah catch up on some work in the background.
By David Ho, LDEO
About 3 years ago, I took on the challenge of planning and championing a gas exchange experiment in the Southern Ocean. I had no illusion that it was going to be easy, but I had plenty of help from the group that I assembled, which consisted of leadership from the previous GasEx experiments, and others who were as passionate about understanding air-sea gas exchange as I was. Our first job was to sell the idea to the community at large, and to the various funding agencies. After that, the real planning began.
From the beginning, SO GasEx was going to be a collaborative experiment, requiring everyone involved to work together towards a common goal. Since many of us involved in the planning of this experiment had previously worked on GasEx-98 and/or GasEx-2001, we knew the challenges involved in staging an experiment that requires the ship to operate in very different modes; combining that with trying to operate in the harsh conditions of the Southern Ocean added to the challenge.
On the cruise, every detail, from lab assignments on the ship, to distribution of water from the CTD, to scheduling of different sampling events, had to be planned carefully. As I mentioned in a previous blog, there are various projects on the ship that required it to operate in different modes. Without the cooperation of all participants involved, this would have been a difficult task.
Many people on the cruise made my job easier, both in my role as co-Chief Scientist and as a PI for the 3He/SF6 component of the experiment. My co-Chief Scientist Chris Sabine was a pleasure to work with. He and I shared responsibilities for various tasks and decisions making (and we had to make some difficult decisions). While we were on the same page on most things, sometimes we would disagree but our divergent opinions lead us to compromises and to better solutions than either of us had thought of. I’m most grateful for the fact that Chris took care of navigating the NOAA-specific bureaucracy, which made it a lot easier for me to concentrate on the scientific aspects of the cruise.
Kevin Sullivan did a masterful job of creating the 3He/SF6 tracer patches, and measured all the SF6 samples from the CTD casts. Matt Reid and Paul Schmieder took turns to chase the tracer patches around for weeks, and never lost it (the patch, but I’m not sure about their sanity). Pete Strutton, Dave Hebert, Roberta Hamme, Burke Hales and Bob Castle helped with the study site selection. Geoff Lebon, Steve Archer, Mike Rebozo, Sarah Purkey helped with various aspects of the tracer injection and sampling. Paul Covert and Byron Blomquist helped us with computer issues. Mete Uz, Program Manager of the Global Carbon Cycle Program in NOAA’s Climate Program Office, rallied the troops on land when it wasn’t clear if the ship could stay at our study site in high winds, and made sure that we were able to get back on track. The Captain and the crew of the NOAA Ship Ronald H Brown, in their various roles, ensured that we were safe, well fed, and to a large extent, able to execute our various scientific projects.
I want to acknowledge Kathy Tedesco, former Program Manager of the Global Carbon Cycle Program in NOAA’s Climate Program Office, with whom I worked closely during the planning stages of the experiment. She was professional yet approachable, and without her help, planning for SO GasEx would have been immensely more difficult.
Even though we did not encounter sustained wind speeds in the 15-25 m/s range at our study site, we had periods of sustained winds up to ~15 m/s, which will be a valuable addition to existing measurements of gas transfer velocities from previous experiments and other parts of the global ocean. Also, we encountered a range of wind speeds (see picture below), which should allow us to effectively evaluate existing parameterizations between wind speed and gas exchange.
The experiment had more hours of eddy covariance CO2 and DMS measurements than any other previous experiments, and the most number of 3He/SF6 samples ever taken in one gas exchange experiment. The combination of CO2, DMS, O3 flux measurements with 3He/SF6 measurements of gas transfer velocities is unprecedented; along with ancillary measurements of waves, turbulence, and bubbles from a buoy that was able to remain with the tracer patch, they should allow us to elucidate mechanisms controlling air-sea gas exchange, and determine if these mechanisms are unique to the Southern Ocean. The detailed carbon system (DIC, pCO2, TAlk), DMS, productivity, and phytoplankton measurements could also help us understand what controls CO2 and DMS dynamics in our Lagrangian patch. All in all, I think SO GasEx was a success, and the data will bear this out in time.
Today, we will pull into Montevideo, Uruguay, and the SO GasEx cruise will be officially over; however, the fun is just beginning. Over the next months, the next chapter will unfold, with all the PIs working up their respective data, coming together to synthesize their results, and disseminating their findings to the community at large.
The entire SO GasEx scientific party on the fantail, taken on the last day before arriving in Montevideo. The weather was completely unrepresentative of what we experienced during our trip, and a welcomed relief to everyone.
Wind speed histograms from SO GasEx, showing winds averaged over 24 hours and spanning 3 CTD stations, which is the time period necessary for one 3He/SF6-derived gas transfer velocity calculation. We encountered a nice range of wind speeds, from 4 to 14 m/s.
We enjoyed a nice sunset on our last evening out at sea…
…and were visited by a school of hundreds of dolphins right after sunset; a nice way to end the cruise.
Future gas exchange scientists? Kathy Tedesco’s niece and nephew proudly sporting their SO GasEx T shirts.
By Steve Archer, Plymouth Marine Laboratory
Back to the weather – it’s the limey again: flying fish off the bow, egrets off the stern, warmth, gentle rolling, blue seas: relief. The ship and folk on it have taken a bit of a pounding over the last couple of days but there’s a lot more of a relaxed atmosphere onboard today. It’s a fine way to finish up. For one, it’s a great day for packing up and clearing up after the gales (see Mike below), especially if you can do it outside. My equipment has to get flown back to the UK then Canary Islands for the next experiment in a few weeks time but first I’ve got to rebuild a couple of boxes that took a ‘green one’ over the side.
However, to a few of us, the high winds and seas that we’ve struggled through on the transect to Montevideo have been a bonus in scientific terms; we obtained what we hope are sea-to-air flux rates and transfer velocities, from the highest winds and biggest waves of the experiment (see photo). If the measurements have been successful this will certainly extend the range of wind speeds over which the fluxes between ocean and atmosphere of DMS have been recorded; shedding more light on what controls the rates of exchange at that critical, high end of the wind-speed-spectrum. Every cloud has some silver lining!
So cheerio to the generally grey, cold and not-so-windy-this-time Southern Ocean; and cheerio to my uncle Chriso who passed away the other day; his enthusiasm for fishing, wildlife, boat-building and the sea had a big influence on me as a child. There will be a lot of fish sighing with relief now he’s gone, amongst many things, he was a master-craftsman-angler; he would have done a decent job of rebuilding those two crates too!
Mike ‘dries out’
South Atlantic spray.
Cheerio to the SO; what a difference a day makes.
By Chris Sabine, NOAA/PMEL
As mentioned in the last few blogs, we finished our last CTD cast on Friday and started the 1300 mile trek to Montevideo, Uruguay where we will unload the ship and head our separate ways. For those of us used to traveling at the speed of a car or plane, the transit home can literally feel like the “slow boat to China”. When we first left station the ship was making a blazing 12.5 nautical miles per hour (or knots for you sailors). We had high hope of getting into port before our 9 am Thursday schedule, but that all changed on Sunday night.
We had spent the last two weeks before leaving the study site desperately hoping for high winds and rough seas; something, anything to finish off the Southern Ocean Gas Exchange experiment with flair. But it was not to be. We had decent 15-20 knot winds but not the big storm we had all dreamed about as we were writing our proposals. Despite that, we were reasonably satisfied and looking forward to a relatively quick trip home.
Sunday night, however, we drove into that perfect storm and just the kind of conditions we had been hoping for back at the study site. First the wind kicked up to 40 knots then 50 knots. Initially the seas were calm and the wind was just blowing the tops off of the small ocean swells we had been plowing through with ease. Over time, however, the sea started building and the 1000 miles of open ocean between us and Montevideo seemed to grow wider and more angry. With the ship’s vent problems (see the back on track blog), we were forced to slow our progress so we did not get too many bubbles into the ship’s cooling water systems. By late Sunday night the 12 knots had turned into 1 knot and our hopes of getting in early were whisked away on the wind.
Our experience with these wind events over the last month or so had been that they blow through quickly, but apparently this low pressure system liked what it saw and decided to hang around. Monday we ranged from essentially no speed over ground to as much as 4 knots for a couple of hours. Winds were 30-40 knots and the seas were 15-20 feet with the occasional 30 footer just to test that everything was tied down properly. Our hopes of getting in early had changed to hopes of getting in on time but even those looked doubtful as night fell with very little progress towards shore.
Tuesday brought a new promise as we were making 3.5 knots when I woke up. It didn’t really hit me how sad that was until I found myself on the treadmill running twice as fast as the ship. On Tuesday the winds were a little better, 20-30 knots but it was still impressive to sit in the staging bay looking out over the fantail and watch the waves break over the side and stern of this ship. At least the atmospheric flux guys are getting some measurements out of this. Most of us have completed all the packing we can do for now and are desperately trying to think of ways to entertain ourselves. It is difficult to focus on anything when the whole world is tossing and turning. At least we all have our sea legs so seasickness is not too much of a problem.
Now it is Wednesday. The winds have dropped a little more and the seas are starting to calm as well. We still have a little less than 500 miles to go, but we are hopeful that we are through the worst of it and conditions will only improve from here. I suppose only time will tell.
Crew and scientists on the fantail tying down items battered by the rough seas
The CTD against a backdrop of whitecap covered ocean that we rarely saw at the study site
By Alejandro Cifuentes, University of Connecticut
Let me introduce you to my good friend the correlation function (whom you may already know well) and its relevance in the air-sea flux calculations (momentum, energy and mass). The correlation function is a powerful statistical tool, specifically in the analysis of time series measurements. The combination of the time averaged measurement of a normally distributed random series coupled with the correlation function can ultimately define the behavior of the series. As we try to understand and interpret nature’s behavior we are typically given the response of a suite of physical variables that are arranged in time (i.e., wind velocity, temperature, relative humidity, pressure, CO2 concentrations, etc.). Ultimately the correlation function becomes a consistent statistical approach for digesting the data and supplying a physical interpretation.
So consider the fluctuating time series of wind velocities, applying the correlation function will tell us about the momentum exchange. The energy flux (vertical transfer) transported as sensible heat can be described by the correlation function applied to the vertical wind velocity fluctuation and temperature fluctuation. Ultimately, the mass flux (vertical transport) is determined as the correlation between the fluctuation of a compound (i.e. CO2) and the vertical wind velocity fluctuation. This method evolved into what is now known as Direct Covariance (a.k.a. the Eddy Correlation) Method, recently introduced to me (just six months ago) by my advisor Dr. James Edson as I stepped into his domains of the Air-Sea interaction. The whole process has become increasingly familiar with time, especially the power of the correlation function which has yet even more to offer. Based on it, a spectral analysis of the series via Fourier transform can be developed and more information can be squeezed out of our precious time series. This describes very roughly the use and the power of the correlation function in the flux calculations and the concept behind the Eddy Correlation Method. For details on the procedure and hardware required on this process I recommend checking Ludo’s recipe posted on the blog: “Shake and Bake” … baby!
The correlation function is not to be confused with the relation function for the fluxes; the relation concept might escape the realm of statistics, but is no less fascinating. Remember, four cooks in the kitchen…the relation function here is defined as any interaction (you can read correlation too!) between us, the cooks (a.k.a. the CO2 flux team). Before February 22nd, I didn’t know Chris Zappa (or Dr. Zap, an evil doctor with unholy snoring powers, but with great advice regarding work), Ludovic nor Byron. Through time, the domain of our relation function has grown in both appreciation and complexity. Ludo and I have worked in tandem during much the SOGasEx campaign. As you might expect, a good relation developed. Our electronics were no exception; they too felt the power of the relation function. Our Data Acquisition Systems (DAS) began to mimic one another. Without fail, if Ludo’s DAS crashed, mine would follow (a stochastic process? I think not!). The Licors 7500 adopted the same tendency. In the end, a good relation function was able to do the trick, for the sake of the experiment but mainly for the sake of the fluxes.
So you can imagine we went through on the Brown for nearly two months time: discussions, arguments, chats, advice, guidance, laughs, dancing, a lot of singing and some more laughter. One certainty: all the variables helped to achieve our overall success.
PS: Kate, thank you once more for your help editing.
Below is a look to our highly Entropic Data Acquisition Systems.
GASEX-DAS I: Not to be deceived, high entropy levels got nothing to do with disorder or chaos!
DAS II: Ludo’s system, maybe reaching its own “Heat Death” …
Air-Sea Interaction: It’s happening, can you see it? … Look at those fluxes!
By Carlos Del Castillo, The Johns Hopkins University-APL
The loud popping sound was immediately followed by pressurized 4°C seawater being sprayed all over the room. We are working inside the wet lab on board the NOAA Ship Ronald H. Brown (see Richard’s blog entry) and one of the clean seawater lines that feeds our instruments just burst. A high-pressure water line does not just burst and calmly spills water. The line swings left and right, up and down, squirting water on everything and everyone. But no worries, we are in the wet lab. It is supposed to be wet. Before the indoor shower, we had settled into an easy, boring routine for our long transit to the proposed research site, so the burst line was almost a welcomed distraction. Almost welcomed because a busted line means some data will be lost, and the inevitable invasion of air bubbles into our system. We do not like bubbles in the wet lab. Air bubbles dramatically change the optical properties of water and create a lot of noise in our data. Bubbles must be dealt with. Bubbles are the enemy. We battle bubbles along three fronts. The water that flows through our optical instruments enters the boat through an intake that is several meters below the sea surface. There are not many bubbles at this depth unless the weather is bad. Weather is almost always bad in the Southern Ocean. The second line of defense is a “debubbler.” This plastic contraption uses a vortex to trap bubbles and send them back to the ocean – where they belong- while tunneling bubble-free water to our instruments. Bubble-free water is good. In our quest for bubble free water we keep all the lines that feed the instruments submerged in a water bath as our third line of defense. By doing this, we keep the water inside the lines very cold to avoid degassing– or the formation of un-welcomed bubbles that will eventually migrate to our instruments. In this case, the water bath is a large sink where we also keep the instruments to avoid temperature fluctuations. The water in the bath is the same 4°C seawater that flows through the instruments.
In this expedition we encountered our first un-welcomed bubbles in bottled water. As in most countries, bottle water in Chile can be found in two varieties, sparkling water and regular water, or “agua con gas y agua sin gas.” Sparkling water seems to be the most popular and the default offering unless otherwise specified. So, if one does not add the “sin gas” modifiers, one may get bubbles. Agua con gas is not all that bad, we are just not used to it. The wet lab gang prefers to drink our bubbles with beer.
Our instruments in the wet lab measure several parameters. We have two acs’s (absorption, attenuation, spectral) that measure light absorption and attenuation from ~400 through ~700 nm at 4 nm resolution. These are the successors to the veritable WET Labs ac9 (same measurements but at 9 wavelengths). Light attenuation is measured along a fixed path length and represents the loss of incident light due to light absorption by chromophores (i.e. colored dissolved organic matter –CDOM- and photopigments), and losses due to light scattered away from a narrow detection angle. The absorption measurements include incident light losses due only to absorption by chromophores. The measurements are achieved by using two cells, or in this case plastic flow through cylinders. The attenuation tube (c) has an opaque inner wall so that scattered light is absorbed by the tube and counted as light loss. The absorption tube (a) has a highly reflective inner wall so that light scattered forward and away from the direction of the incident light field is not absorbed by the inner walls and reaches the detector. The cell in this case works as a waveguide. Clearly, backscattered light is lost, but most of the light scattering is forward scattering. In addition we have a Turner Designs C-6 fluorometer that measures the fluorescence of CDOM and phytoplankton, and a ctd that measures salinity and water temperature.
The color of a substance is an expression of its chemical characteristics. In the case of seawater, its optical properties – or its color – can give us information about the concentrations of chlorophyll and organic matter in seawater. These measurements are very important to further our understanding of the carbon cycle. Our instruments only measure these parameters along the thin line that is the track of the research vessel. However, several NASA research satellites are equipped with ocean color sensors that provide daily coverage over the globe. The data provided by these satellites are essential to our understanding of the global carbon budget and climate change. Data from these sensors, however, has to be interpreted using complex mathematical algorithms. These algorithms are created and validated using field data like the data provided by our instruments in the wet lab. Curiously enough, satellite ocean color sensors can be affected by bubbles. White caps (or “espuma”) formed in the ocean when winds exceed ~ 14 knots, are nothing more than bubbles at the air-sea interface. White caps change the optical properties of surface waters making it more difficult for the satellites to detect the true color of the ocean. Also, bubbles injected into the water column by large braking waves interfere with satellite color measurements. Again, bubble-free water is good.
So, here we are in our wet lab, happily bubble free and drinking liquids without gas – at least until the next water line bursts.
The tangle of hoses that is our underway system
Scott Freeman (standing on the right) and Carlos Del Castillo (with the funny hat) calibrating one of the acs’s using pure water.
Carlos Del Castillo cleaning the interior of one of the optical tubes of an acs.
By David Ho, LDEO
A couple nights ago, we had our last CTD cast (see below) and are now on our way to Montevideo. We’re scheduled to arrive on the morning of April 10th. While I doubt any of us miss sampling from the CTD, least of all Paul and Matt who had to find the center of the tracer patch at 9 am and 9 pm, it did provide a nice routine to the day. Now, I just see people wondering around the ship aimlessly, overwhelmed by their newfound freedom.
As Pete mentioned in his blog, once the CTD is on deck, it is sampled in order of time sensitivity. Gases go first, in the order of their volatility, and then other things like nutrients and particles. There are varieties and different levels of complexity in people’s sampling methods:
- My method for 3He is by far the loudest (involving banging the aluminum channels with a dead blow hammer, and then tightening stainless steel clamps with an impact wrench). It’s no doubt one of the reasons why many people are happy to be done with the CTD.
- Roberta’s other nobel gases takes the most amount of time (read about it here).
- SF6 is pretty standard, but it’s imperative that Kevin doesn’t get any bubbles or a headspace in the sample.
- Sara and Roberta sample oxygen in a funny looking bottle, and measure the water temperature during sampling. They add reagents before capping the bottles, and then shake the bottles rigorously.
- Bob, Geoff, and Paul are responsible for the CO2 parameters (pCO2, DIC, TAlk), and all those samples need to be poisoned to ensure that biological activity doesn’t alter the sample in the bottle.
- Steve is by far the most stealth sampler. He stands in the background with his bottles ready to sample DMS, and has the bottle numbers written on his hand (or rather, glove; while the rest of us use sample sheets). When it’s his turn, he just shows the bottle to the sample cop, and then samples from the appropriate bottle. Contrast this with the rest of us, who yell out our sample numbers to the cop.
- Unlike most of us, Carlos doesn’t use a noodle (either Tygon or silicon tubing) for his samples, because they could contaminate his DOC samples.
- Charlie always shows up right before he’s due to sample (and all of us yell “Charlie!” like they called “Norm” when he came into Cheers), and holds about 5 (small) bottles for nutrients in his hands and samples the bottles rapidly, also sans noodle.
- Scott seems to have the easiest sampling gig. He only samples one Niskin bottle, and gets the whole Niskin bottle to himself. He connects his noodle to the bottle and drain the entire content into a small drum. He finishes by opening the bottom of the Niskin bottle and draining the rest of the water and suspended solids into a contraption that looks like a beer funnel.
- Pete, Dave, Veronica, Bob, and Bruce then basically takes all the water that is left for productivity and filtering for chlorophyll and particles.
- Sara bats clean up, and takes 2 samples for salinity per CTD in bottles that resemble old medicine bottles.
All of this takes about an hour, after which some people start analyzing their samples, while others wait to ship the samples back to the lab for analysis.
The group poses in front of the last CTD cast before sampling
Sampling for 3He
Sampling for oxygen
Sampling for pCO2
By Christopher Zappa, LDEO
A previous blog entry discussed the carbon measurements from the MAPCO2 buoy using SAMI-CO2 systems, while another post explained how the buoy tracks the patch with the help of the holey sock drogues. The MAPCO2 buoy allows us to measure physical processes very near the ocean surface that we typically can’t measure from the ship because the ship disturbs the flow of the ocean. My project employed a variety of instruments that use sound to measure the ocean currents based on the Doppler velocity backscattered from particles in the ocean. Dave Hebert talked about how he measures the ocean currents using the ship’s ADCP to track the tracer patch. One instrument we use on the buoy is a high-resolution ADCP to measure the currents much closer to the ocean surface. Instead of profiling 1000 m as the ship’s ADCP, this “Dopbeam,” as we call it, measures the profile of velocity over 1 meter with 1-cm bins. While the wind puts energy into the waves that eventually break, the wind also controls the near-surface ocean currents directly and through wave breaking. These fine-scale near-surface currents eventually become chaotic, or turbulent, and develop very small “eddies,” or energetic circular motions. Wave breaking will also generate these fine-scale turbulent eddies. We measure these fine-scale near-surface eddies that mix up the top few meters of the ocean and that work to regulate the gas transfer.
A few days ago, the MAPCO2 buoy was taken out of the water…for the third and final time. Each time, getting the buoy on deck is only half the job. Scientists scurry quickly to download the data that have been accumulating on the instrument. This is an essential task in order to make sure that all is well while the buoy was in the water. Luckily, we had only one problem during all three deployments combined. On the final retrieval, the underwater camera housing was flooded and the camera was damaged (see picture below). Damage caused by the ocean is always a danger with any instrument that goes over the side of a ship and remains underwater for days and weeks on end.
Now that the buoy is out of the water and all the data have been collected, I have only a few systems running (WaMoS II and the wave breaking video). Slowly, there is a sense that the cruise is over… and it’s a little sad. There are signs throughout our day that the experiment on site is coming to a close. Today, we had our last Fire and Abandon Ship Drills. In fact, as I write this we are performing our last CTD of the experiment. After that, we set sail for Montevideo, Uruguay. Even the king penguins were sad to see us go. Soon enough, we will be back on land, getting rid of our “sea legs.” There will be no more crawling into the small bunks, no more rolling back and forth as we sleep. No more day-to-day monotony of data gathering. Nope, we can finally have a nice, frosty, ice-cold, refreshing BEER. And watch the Red Sox beat the Yankees at Fenway. OK, maybe I’m not so sad.
Dopbeam mounted in its titanium cage being prepared to be deployed from the MAPCO2 buoy. The Dopbeam is roughly 2 feet long and 3 inches in diameter.
Retrieval of the MAPCO2 buoy with the Dopbeam mounted in its cage chained below.
Underwater camera housing mounted on MAPCO2 buoy before deployment.
Underwater camera housing after third deployment. The housing is flooded with ocean water. Notice the orange rust at the top.
Camera damaged by the ocean water.
Even the penguins, which flock around the CTD every day, were sad to see us go.
By Ludovic Bariteau, CIRES/NOAA PSD
Among the numerous measurements made on the ship are the flux measurements. I have learned and simplified this flux recipe from Chris Fairall, my spiritual Guru.
Yield Unlimited servings
Time About 45 days
Ingredients required for determination of air-sea fluxes:
- Wind speed and direction
- Air temperature and humidity
- Atmospheric pressure
- Downward shortwave and longwave radiations
- Sea surface temperature
- CO2, DMS and Ozone
Utensils and Personnel used for the GasEx recipe
- A ship, the RHB.
- 4 cooks. Persons used on this project are: Ale, Dr Zap, Byron and I.
- On the foremast: 3 sonic anemometers, 3 motion packs, 5 Licors 7500 (fast CO2/hygrometer), 3 mean RH/T (Relative Humidity/Temperatures) sensors and an optical rain gauge.
- 4 Eppley radiometers setup on a wood pole
- 3 Licors 6262
- 1 fast ozone instrument and 1 fast DMS instrument with the sampling inlets located on the jackstaff
- A bunch of data loggers, computers, cables, tie wraps…
The previous sensors used for fluxes have been adapted for observations over the ocean. They are designed for marine applications and thus are protected from the corrosive effect of sea salt and spray. These instruments are also used because of their accuracy and frequency response. Our sampling is typically done at 10 or 20 Hz in order to get the turbulent fluctuations of the atmospheric variables (wind, temperature, humidity, gas …).
We most certainly make sure that all sensors are freshly calibrated.
- Get the sonic anemometers and motion packs. These instruments are the center pieces of the flux system, so taking good care of them is very important.
- Put these sensors together forward on the ship. The jackstaff is a perfect location for that as it is ahead of the engine exhausts, and it’s as far away as possible from any obstacles. Nevertheless the ship’s central superstructure will always create some flow distortion. The wind is deflected upward, and the wind speed is modified. Some modest flow distortion corrections are done later in the recipe.
- Add the other sensors to the mast: Licors, RH/T, sampling inlets…
- Secure everything with tie wraps, clamps, bolts…
- Install the rest of the equipment on the ship (ozone, DMS, radiometers, Licors 6262); forward on the ship is an excellent spot.
- Put the RHB in the Southern Ocean for ~45 days and let everything shake gently… or vigorously.
- Meanwhile, log all sources of data to a central data acquisition system, commonly called “DAS”.
- Put the cooks at work (they were already working on previous steps). They will get the data out and bake them. The baking process is very straightforward. Take the three components of the wind vector and mix them with the motion data. Rotate them to fixed earth coordinates and you get the corrected wind velocities (it’s a bit more complicated than that!).
- Add your favorite variables to the corrected wind components: more sonic for momentum flux, some moisture for latent heat flux, some CO2, DMS or O3, for gas fluxes… it’s your choice!
Finally, take everything out of the RHB and bring the data home for meticulous analysis.
- Bulk meteorological variables and eddy-correlation fluxes based on preliminary analysis during the cruise taste good fresh and hot. But quality controlled fluxes produced later during post-processing are even better. Scientists love them as it brings them tons of information!
What you need to make good fluxes! From back to front: Sonics and motion packs standing up high with the sampling inlets of various sensors, Licors, RH/T sensor. Other sensors are down below on the mast.
Flux kitchen and the 4 cooks. All recipes are prepared with tradition. Left to right: Ale, Ludovic, Byron and Chris.
A good baking process removes the motion peak in the power spectra of the wind components. Measured (black broken line) and corrected (blue solid line) vertical velocity power spectra. The green straight line represent the -2/3 inertial subrange slope.
Freshly baked fluxes! Covariance spectra for the longitudinal component of the momentum flux (blue) and for the sensible heat flux (red).
By Byron Blomquist, University of Hawaii
Oceans and forests are the lungs of our planet. Oxygen that makes life possible for animals (like us) was originally produced by the first microscopic plants in ancient oceans. We rely on green plants to sustain us. And as they exhale oxygen they inhale carbon dioxide, converting it to wood, leaves and the carbonate shells of marine plankton. Some of this carbon is returned to the atmosphere as CO2 through respiration when bacteria, fungi and animals feed on plants and organic matter. A small amount settles into long term storage as coal, oil and chalk deposits. This in brief is the system we call the carbon cycle, and the ocean surface is part of the planetary lung, like the lungs in our bodies, that carbon transits during its cycle.
It has been our goal over the past few weeks to examine a patch of our planet’s lung and observe the details of gas exchange between the ocean and atmosphere, to better understand how our planet “breathes”. Ultimately, we would like to accurately predict when, where, and how much CO2 (or dimethylsulfide, DMS) passes through the ocean surface, since this information is critical to understanding how the climate system functions and to predicting how it may change in the future. But gas exchange is controlled or influenced by numerous physical processes like wind stress, ocean currents, temperature and, in the case of CO2 and DMS, by biological activity in the surface ocean, which itself is modulated by nutrients, seasonal cycles, sunlight, ocean currents, population dynamics, etc. Unravelling the mystery is more than any one of us can hope to achieve alone or more than any one group of scientists can achieve in a single study, but it keeps us focused to have the big picture in mind as we labor in the trenches of our sub-disciplines.
Those of us involved in observing atmospheric flux – the rate at which gases are going into and out of the ocean – have managed to keep our feet dry and our hands warm so far. Our daily routine, between eating and sleeping, consists of monitoring our sometimes finicky instruments and coping with an avalanche of data streaming at 10-20 samples a second per channel, 24 hours a day. We sift through the accumulating gigabytes, identifying and removing the bad data (typically occurring when wind blows from behind, sending the ship’s exhaust and vapors from the galley’s deep frier to our instruments on the bow). Then, from small turbulent variations in gas concentration and wind velocity, aided by considerable mathematical manipulation, we can observe the rate of gas exchange.
The graph above, called a covariance spectrum, summarizes an hour of DMS and wind data. It shows us the flux of DMS is upward – that is, it comes out of the ocean – because the points on the curve are positive. And the sweep of the jagged curve reveals the flux is carried on turbulent eddies at frequencies from 0.002 to 2 Hz (or eddies from roughly 5 meters to more than a kilometer in size) and the dominant frequency is about 0.1 Hz (100 meters). The area under the curve is the flux – in this case about 370 micrograms of DMS per square meter per day. We have seen the ocean “breathe”, and in collaboration with our friends and colleagues on SO GasEx we may be able to discover some details of how this “breathing” actually works.
By Paul Schmieder, LDEO
I am a graduate student at Lamont-Doherty Earth Observatory (LDEO) working in the Environmental Tracer Group, and at sea I am assisting the LDEO and NOAA/AOML team with the collection and analysis of SF6. SF6 is my tracer of choice, both out in the open ocean and in coastal waterways.
Nearly two weeks ago, in the early morning hours of March 21st, we successfully injected a second patch of tracer containing both 3He and SF6 gases infused in seawater. Deliberately, this tracer patch was smaller in area than the first patch in order to obtain higher SF6 (and 3He) concentrations in the water. Higher concentrations would allow us to conduct a longer survey. Our plan to increase the SF6 concentrations was successful! Surveys through the patch conducted on the day following injection yielded concentrations as high as 1024 fmol/L (fmol = femtomol = 10^-15 mol). The peak concentrations have now fallen to ~20 fmol/L, a difference of 2 orders of magnitude since the start of the survey.
Since the time of injection, the patch has displayed a pulsed migration to the east, with periods of fast advection and moments where the patch remained stationary. Overall the center of the patch advected 80 km to the east. Approximately 8 days ago, the MAPCO2 buoy, which was deployed at the same time as the tracer, began to migrate along a different path than the portion of the patch we were following (picture below). We retrieved the buoy two days ago, and to my surprise there was tracer present 50 km to our south. Currently, the patch has decided to migrate in a new direction to the southwest. Using ADCP current measurements as a guide, we should be able to keep up.
Matt Reid (LDEO) and myself have been holding down the fort, mapping out the tracer 24 hours a day for 13 consecutive days now, and it looks like we might have 2 days of survey remaining. The routine of the daily SF6 surveys is punctuated, though, with the excitement of both ‘Pump and Dump’ and the pending CTD casts. It is our duty to direct the ship to the CTD station, and it is always a bit of a struggle to predict where we might find the highest tracer concentrations, and there is the added pressure to arrive at station on-time. We don’t always get the highest concentration, nor do we always hit our waypoints on schedule, but in the end I think we have fulfilled our duties and successfully obtained the samples we need.
This is a composite map of the SF6 concentrations for the second tracer patch. The concentrations are plotted on a logarithmic scale with units of fmol/L. The black dots show the position of the MAPCO2 buoy in time, migrating from west to east.
When David asks “Where’s the tracer, man?” this is my response…
By David Ho (LDEO) and Pete Strutton (Oregon State University)
Despite the years of planning that have gone into SO GasEx, we should never discount the role of serendipity in pushing back the frontiers of science. Penicillin, Teflon®, Post-it® Notes, Formula 409®, Viagra®, and indeed the Americas themselves all owe their discovery to an element of luck. So it is that one of the major discoveries of SO GasEx actually hasn’t been about air-sea gas exchange at all, but has been the first reported sighting of the Southern Ocean amphibious squirrel (Sciurus australisaqua) in almost a century. It is a rarely seen, and therefore assumed to be extinct, creature described in the travel diaries of Charles Darwin, Ferdinand Magellan, James Cook, and Francis Drake. In fact, Ernest Shackelton and his crew are believed to have survived on seals caught using these amphibious rodents as bait.
For those who have not had the privilege of seeing one first hand, the Southern Ocean amphibious squirrel is substantially larger than an eastern gray squirrel that one often finds in New York City. In the aforementioned diaries, there are descriptions of these rodents that suggest that they could grow to the size of capybaras. The Southern Ocean amphibious squirrel is mostly white with some brown and black speckles, and characterized by its smooth hairless body, except for the white bushy tail.
We consulted Walter Rodin from Department of Zoology at Université Paris, who specializes in giant rodents. He believes that the Southern Ocean amphibious squirrel is descended from a species of rodent which underwent an evolutionary explosion during the Miocene and Pliocene (2 to 23 million years ago), creating many species of rodent in what is now Argentina, Brazil, and Uruguay.
Our news about the Southern Ocean amphibious squirrel, embargoed still because we are awaiting decision from Science Magazine, is in line with the recent announcement of the discovery of new species of giant sea creatures in the Southern Ocean. The emergence of these creatures, including the Southern Ocean amphibious squirrel, could be a result of climate change, although no effort has been made to study the connection.
This is not a Southern Ocean amphibious squirrel
Neither is this
By Will Drennan, University of Miami
ASIS, the University of Miami’s “Air-Sea Interaction Spar” buoy, was recovered by the Ronald H Brown over a week ago, after a week at sea. The comment most people make when seeing ASIS for the first time is “Wow, that’s big”. At 6 x 2 x 2 m (36 x 6 x 6 ft), and weighing close to a ton, it is indeed one on the larger pieces of kit on the deck. As Mike Rebozo can tell you, it can also be difficult to deploy and recover. While he’s likely lost count of how many times ASIS has gone over the side of various ships over the past decade, the real question is how many of Mike’s grey hairs are a result of ASIS ?
The role of ASIS in SO GasEx is to make measurements at, and close to, the ocean surface. Above the surface, we measure basic meteorological parameters, as well as the air-sea fluxes of CO2, water vapour, heat and momentum. In collaboration with Ian Brooks and Sarah Norris of the University of Leeds, we are also measuring aerosol fluxes and concentrations. At the surface, we measure surface waves and wave slopes at various scales. This is particularly important for gas transfer work, as small scale waves are thought to be significant control on gas transfer rates. Below the water, we measure temperature, salinity and energy dissipation rates (a measure of surface mixing, which acts as a control on gas transfer). There is also one of Mike DeGrandpre’s SAMIs (see Mike’s blog) measuring carbon dioxide, dissolved oxygen, and light (PAR). Finally we also measure how ASIS moves in the water. Equipped with three ARGOS beacons giving position, we wanted to make sure to find it again.
While many of these atmospheric measurements are also made on board the Brown, a ship disturbs the near surface too much to measure many air-sea processes, such as small scale waves. ASIS was designed precisely to fill the need for a platform for such high resolution near-surface measurements. On its previous cruise on the Brown, during Gasex-2001, ASIS was christened “Big Bird”, after its less than graceful flight over the deck during deployments. The bird is still big, but hopefully the flights are becoming more graceful.
ASIS being deployed
ASIS in the water
By Veronica Lance, LDEO
If you have been following the science of the Southern Ocean GasEx project, you know that our major goal is to measure and better understand what controls the rates of exhange of carbon dioxide (and other gases) between the atmosphere and the surface ocean. Where do phytoplankton fit into this picture?
Phytoplankon, the microscopic single-celled “plants” of the sea function similarly to terrestrial plants – that is they take up inorganic carbon, then, using the energy of sunlight and an important enzyme (“RuBisCO”) form chemical bonds among carbon atoms leading to the production of simple organic carbon molecules such as carbohydrates. This “fixed” carbon plant material forms the base of the food chain – small metazoans and zooplankton feed on phytoplankton, which in turn feed fishes and marine mammals. In the Southern Ocean, this “food chain” has been found to be quite short and direct as compared with many other ocean environments…. As few as 3 links to the “top”: Diatoms … krill … whales!
Our understanding is, that over geological time scales, the ocean has been acting like a big sponge soaking up some of the high concentrations of atmospheric carbon dioxide during warm periods and perhaps ventilating carbon dioxide out of the oceans back into the atmosphere during cold, glacial periods. In modern times (the “Anthropocene Age”) the ocean has been soaking up some proportion of the huge amounts of carbon released into the atmosphere by the burning of fossil fuels and by other respiration processes accelerated by industrialized methods (for example, large scale agricultural practices). In an imaginary bathtub-in-a-closed-room model ocean, the gases in the atmosphere (room air) will equilibrate with those in the water (bathtub) – that is, the water will absorb the gases until it can absorb no more and the conditions will be steady or stable. If we make now make our bathtub very, very deep and add some phytoplankton, the conditions are no longer stable. The phytoplankton will use up some of that dissolved inorganic carbon. Eventually some of that carbon material (now in organic forms such as dead phytoplankton cells or fecal pellets from animals farther up the food chain or bacterial clusters of decaying matter) will sink very deep and become isolated from the surface waters where it was formed. As the organic carbon disappears from the surface ocean, more carbon dioxide from the atmosphere has a chance to be soaked into the surface ocean. The fate of the sunken carbon is that it could be respired again on a relatively short time scale (geologically speaking, years to hundreds of years) and be circulated back into the surface ocean (for example by upwelling) OR it could be buried into the sediments for relatively long time scales (thousands to hundreds of thousands of years). This process has been given the descriptive phrase “biological pump” (see picture below). ￼
In 1952, Steeman-Nielsen described the method he developed for estimating organic carbon productivity in the sea using radioactive carbon (14C) as a tracer. In light of the many high-tech methods being used on this cruise, this one feels old-fashioned now – but the beauty and satisfaction of this method is that it pretty much always works! There are some finer details about what this method actually does or does not measure which I am not getting into here, but in a general sense, we can get a good estimate of the rate of net carbon uptake by phytoplankton throughout the depths of the ocean where sunlight penetrates (the “euphotic zone”) on a daily basis in a given water mass (“primary productivity”). These rates will go into the bigger carbon flux equations that the SO GasEx project is all about.
I’m sure my colleagues think I am nuts, but I enjoy doing these incubations. While we are at sea, I see almost every sunrise and many sunsets in all kinds of weather. Some of the scientists aboard collect water samples and bring them back to the lab for analysis. My 14C samples get analyzed “live” and so it is satisfying to be able to walk off the ship at the end of the cruise already knowing something about my observations and being able to start thinking about how they fit into the bigger pictures of the SO GASEX project and the regulation of primary productivity in the Southern Ocean (see Fig. 2 for example of data).
For the SO GasEx project, I do several different kinds of measurements, but I am doing the primary productivity work as a collaboration between my Lamont group (with Bob Vallaincourt and John Marra) and Pete Strutton (aka “bottle cop”) of Oregon State University. Basically, I collect water from the CTD rosette from several representative depths in the ocean into clear, polycarbonate, well-washed bottles. Next, I inoculate the water sample with a small amount of the radiotracer 14C and put the “spiked” jars into the on-deck incubator. The incubator (see pic below) is simply a plexiglass box which contains several tubes which are shaded to imitate light levels at the respective depths of the ocean from where we collected the samples. Seawater is pumped through the box to keep the samples at ambient temperatures. The spiked sample jars go into their respective light tube and there they will stay from dawn to dusk or from dawn to the following dawn (depending on the precise observation desired – I am doing both types on SO GasEx). The community of organisms trapped in the bottle are both “fixing” and respiring carbon – and some of the tracer 14C along with it. At the end of the incubation, the jars are gathered from the incubator and the seawater samples are filtered. The filters collect all the organisms in the jar – some of which have now incorporated some of the radiotracer. The filter goes through a few more procedures and then is placed into a liquid scintillation counter which is a way of determining the disintegration rates and ultimately the amount of the 14C tracer in the sample organisms. With a few more calculations, we end up knowing something about the rate of carbon uptake in the water column. A plot of an early station in SO GasEx is shown below. At the same time, Pete sets up similar dawn-to-dawn incubations using the stable isotope 15N as a tracer to determine the rate of nitrate fixation (perhaps the subject of another blog someday). The ratio of carbon uptake to nitrogen uptake gives us some clues as to how fast the fixed carbon might be sinking into that very deep bathtub ocean. Every morning at 0430, Pete knocks on the door of my rad van where I have been prepping my samples. Together in the pre-dawn greyness, we go out to the incubator to harvest our previous days’ samples and put out the next set (see pics below).
￼p.s. All this talk about radioactivity might provoke some health and safety concerns. We are concerned, but more for scientific reasons than health or human safety. This is why: First, the amount of radioactivity we work with is very small with respect to human health concerns. Second, humans are not plants, so any 14C tracer to which we might be accidentally exposed is not taken up into our bodies. Third, it is easily washed off of surfaces with a bit of soap and water – which is later properly disposed. Our biggest concern is not to leave any traces of 14C on surfaces of the ship. Why worry about the ship? Because other scientists who use the Ronald H. Brown measure ambient concentrations of carbon isotopes including 14C. Natural 14C concentrations are very low so that even miniscule contaminations, hardly noticed by our scintillation counting methods, could skew the measurements of the natural concentrations. So, out of respect for future science, we go through several steps to insure no radioactive carbon escapes out of our control. Our work is done inside a special container van (“rad van”) placed outside on the deck of the ship (see pic below). We wear special lab coats and booties which remain inside the rad van – it’s kind of like going through an air-lock. The samples which go out to the incubators have a short trip of only a few meters from the van to the incubator and are well-sealed.
The “biological pump” cartoon drawn by Zackary Johnson.
Light tubes in incubator with flowing seawater.
Harvesting an incubation just before sunset.
Pete and I setting out our daily 24-h 14C and 15N sets at dawn.
Rad van being set into place on the deck of the NOAA ship Ronald H. Brown.
At work inside rad van. The red lights are to keep the phytoplankton “asleep” before they go into the incubator for the day.
Thanks to Bruce Hargreaves, Bob Vallaincourt and Paul Schmeider for photos.
By Bertrand Lubac, Naval Research Laboratory
[Après donc Tocqueville et BHL, me voici à mon tour parti à la rencontre des Etats-Unis. Pour ma part, les USA se limitent pour le moment au bâtiment océanographique le Ronald H. Brown, à son équipage et à la trentaine de scientifiques participant à la campagne de mesures SO GasEx. Plus précisément, le noyau dur autour duquel je gravite est l’équipe d’optique marine, appelée aussi dans le cercle des initiés l’équipe « Espuma ». Cette équipe vous a déjà était présentée par Richard Miller, et un de ces membres éminents, Christopher Buonassissi, vous a tout dernièrement fait partager son grand enthousiasme à être de la partie. Aujourd’hui c’est à mon tour de m’allonger sur le divan du blog pour vous raconter dans les grandes lignes les événements qui m’ont conduit jusqu’ici].
The point of departure has been the “Laboratoire d’Océanologie et des Géosciences” in Wimereux, a small seaside resort in the North of the France, where I met Professor Hubert Loisel. This led me to a PhD on the remote sensing of ocean color from 2004 to 2007. The principle of ocean color is to extract information on the biogeochemical and optical parameters of the ocean surface water from a radiometric signal measured by a sensor onboard a satellite. To accomplish this, two general steps are necessary to develop algorithms that relate satellite measurements to in-water information: atmospheric corrections and bio-optical inverse models. My research is mainly focused on the second step (bio-optical inverse models) and has led to a particular study that examines the influence of the marine particles on the variability of remote sensing reflectance, which defines ocean color.
This research topic has now led me to Dr Zhongping Lee. In November 2007, just after my PhD defence, Dr Lee invited me to tour his laboratory, as part of the Naval Research Laboratory (NRL) located at the Stennis Space Center. My first feeling was a mix between astonishment and wonder being faced with such human and material richness combined at NRL. This visit provided us with the opportunity to define a common research project that will be conducted during a postdoctoral fellowship at the University of Southern Mississippi (USM), also located at the Stennis Space Center.
Following this initial journey, there has been a long battle to obtain all the documents necessary to come and work in the USA. Today these administrative steps are almost finished and my postdoc at USM should start at the beginning of May. In the meantime, Zhongping Lee has given me the great chance to take part in the GasEx expedition in order to familiarize me with my new toys such the multispectral volume scattering meter (MVSM) to measure the volume scattering function of the marine particles (see picture below), and get to know the USA research and culture, and to overcome my seasickness.
As some researchers have previously confided in you, there is no marked break between work and rest on the boat. So, when the weather is not too bad and doesn’t force us to remain prostrate in our lab, days go by quickly due to a very busy daily schedule. During the GasEX III cruise, my job is to collect remote sensing reflectance spectra using a handheld spectral radiometer (see picture below), the volume scattering function of surface seawater using the MVSM, and the aerosol optical density using a sunphotometer. With these measurements we hope to improve remote sensing algorithms for primary production and optical properties of the Southern Ocean. In addition to the science, I must in my case add English courses as part of my job. One course in particular with Dr. Richard Miller is teaching me the basics to survive in Mississippi: “how’s it going “ – “Peachy”… But all this work doesn’t enable us to forget what the ship’s rules don’t allow us to have – a cool beer and a tenderness time with our girlfriends that remain at home.
After this cruise, the adventure will go on in Slidell, Louisiana and in Mississippi and I hope the adventure will always be as exciting…
[Et là-bas, on murmure « Tiens bon la rampe ! »].
The Multispectral Volume Scattering Meter (MVSM) was developed at the Marine Hydrophysical Institute in Sevastopol, Ukraine (M. E. Lee and M. R. Lewis, 2003). The MVSM performs light scattering measurements at angles going from 0.5° to 179°, with a resolution of 0.3° at eight wavelengths (443, 490, 510, 532, 555, 565, 590, and 620 nm)
Remote sensing reflectance measurements made using a handheld spectralradiometer on the ship’s bow
Thanks to Scott Freeman for this English version of the French book “Voyage au bout de la nuit”
By David Ho, LDEO
Being out at sea requires that we adapt to different situations and adjust our plans accordingly. Some of these adjustments are expected, while others are genuine surprises.
For instance, when we inject the tracer patch, we select an area that is relatively stable so we don’t end up chasing the tracer patch around the Southern Ocean. However, because there’s no guarantee that winds and currents won’t change, we really don’t know where the patch is going to go. As a result, we don’t have fixed survey lines and have to adjust them minute by minute. That’s expected.
During this cruise, we’ve had some surprises. For instance, what happened to the SuperSoar was a surprise (see Burke’s blog), but given the fact that they are pushing the cutting edge of water sampling technology, it’s not difficult to accept that it could happen.
What happened to us today topped that.
It was about 9:00 am, and time for our morning CTD. Paul and I were discussing something in the Hydro Lab and getting ready for sampling when we heard a loud thud. I said to him facetiously, “I hope that wasn’t the CTD going into the screws [the propellers].” I went to the Staging Bay to check things out, and ran into Carlos on the way who said to me with a panicked voice, “we just lost the CTD.”
I once heard an episode of WNYC’s Radio Lab about Stress, where they talked about what happens to us when we’re under stress. One of the common experiences that people under extreme stress has is that time slows down and thoughts become clear and lucid.
In the few steps that it took to get to the Staging Bay, all the different scenarios under which we could have “lost the CTD” crossed my mind. I was expecting to see the end of a frayed cable dangling in front of me; what I saw was more surprising.
The CTD was hanging off the side of the ship, and the block that used to hang from the CTD boom was laying on the deck. See pictures below for what I fail to convey with words. Apparently, the rosette was accidentally pulled into the block, breaking the block and sending the CTD crashing approximately 20 feet into the side of the ship. Disaster!
The good news out of all this is that nobody was hurt and the rosette/CTD package was eventually recovered. However, the rosette frame was severely damaged and eight sample bottles were crushed.
For the 9:00 am station, we adapted and went to our storm contingency plan, when we expected not to be able to deploy the CTD: Submersible pump. Even though the pump only had enough hose and cable to sample down to about 40 m, it was better than nothing. It was a nice sunny day and a communal atmosphere on deck as we took turns sampling water pumped up to the surface.
We’re working hard to put another rosette/CTD package together, but it will not be ready in time for the upcoming 9:00 pm station. This will be another pumped sampling station. We hope to have the CTD ready for the morning station tomorrow.
Damaged rosette/CTD hanging off the side of the ship
The broken block on deck
Recovering the damaged rosette/CTD
Close-up of the damage
Preparing the submersible pump
Sampling from the submersible pump
A new rosette/CTD being assembled in the Staging Bay
UPDATE: Sara, Geoff, Jonathan, Clay, and Bob worked hard all day and assembled a new rosette/CTD in time for the 9 am morning cast the next day. We’re back in business. Nice going!
The newly assembled rosette/CTD package, ready for the next cast
By Dale Hubbard, Oregon State University
There are approximately 60 people, including the crew and the science party, aboard the Ronald H. Brown. The good folks in the galley serve three meals each day, there are snacks available after hours, and there’s a seemingly unlimited supply of things to drink. This is a very good thing (it certainly beats going hungry and being dehydrated), yet it poses a quandary: once we’ve metabolized all of that food & drink, what to do with all of our waste?
There are basically two types of sewage generated aboard the vessel: grey water, which originates from sinks, showers, laundry, and the dishwasher; and black water, which originates from the toilets. (The engines also generate wastewater of a more industrial nature, e.g. oily waste, but this is contained separately and later pumped ashore when the ship is in port, as oily waste is illegal to discharge at sea.) Aboard the Ronald H. Brown gray water and black water are commingled and contained within a holding tank of approximately 5000 gallons capacity. Sewage aboard the Ronald H. Brown is not treated—it is mechanically ground up en route to the tank, then the contents are pumped overboard. Once the sewage tank has accumulated 4400 gallons, it’s time to break off from our study site and make a run for it.
Since our project involves continuously observing a relatively small patch of water in order to collect time-series measurements, we must move at least 3 nautical miles off-site before the ship evacuates the contents of its sewage tank. Sewage contains an assortment of compounds that serve as phytoplankton nutrients, so dumping the holding tank inside of our study area would drastically alter the biological and chemical processes within. Therefore, at least twice each day we must leave the patch to undertake what many aboard refer to as a “Pump and Dump.”
Unfortunately, several times during the course of a Pump & Dump, the ship’s underway seawater line entrained some of the sewage. This caused caused a great deal of excitement in the lab, as steaming through this particular hydrographic feature generates some of the most dramatic measurements observed during the cruise. This secondary “patch” is exemplified by elevated pCO2 and nitrate (both byproducts of the degradation of metabolic waste) and elevated temperature (see pictures below).
On at least one occasion we’ve been able to resolve a sewage signal in the data from our underway transmissometer, an instrument which essentially measures water clarity (or lack thereof) by passing a beam of light through a sample stream of water. Eeeewwww…
In order to pick these Pump and Dump events out when we’re processing the data long after the cruise is over, it’s important that we remember to log them carefully.
Effect of “Pump & Dump” on pCO2 and temperature. Pump and dump signal, from approximately 12:00-12:30, manifested in approximately 20 ppm increase in pCO2 (white trace) and approximately 0.5o C increase in surface seawater temperature (red). “H2O” parameter is water vapor measured inside of shipboard pCO2 equilibrator and also reflects higher surface seawater temperature. The surface salinity values are highly variable (and rather irrelevant) because it had been raining.
Effect of “Pump & Dump” on NO3 concentration. “Amplitude” values represent voltage generated by photodiode detector (note scale is reversed). The ~0.1 V decrease between approximately 12:00 -12:30 represents an approximately 3mM increase in NO3. The variation in amplitude at approximately 13:30 is a standard sequence—a blank, 20 mM, and 9.5 mM KNO3 solutions.
By Bob Vaillancourt, LDEO
The most common measurement to make for a biological oceanographer is for chlorophyll a (abbreviated “Chl a”). This is the pigment that is common to all phytoplankton, so is a convenient proxy for the size of the plant crop in the ocean at a given time. We have two ways of measuring Chl a: by direct measurement of its concentration on discrete water samples captured in a bottle, or indirectly, by measuring the amount of fluorescent light the plants emit.
Fluorescence is a phenomenon by which a material (in this case, Chl a) absorbs light energy, then re-emits a portion of this energy as light at a lower energy. In the case of phytoplankton, their Chl a (and other pigments) absorb energy in the more energetic blue-green portion of the spectrum, and re-emit (or “fluoresce”) in the less energetic red portion. This light is too weak to observe with the human eye, so we use special instrument called fluorometers to measure it.
Typically, we lower a submersible fluorometer over the side of the ship to measure the “vertical profile” of Chl a fluorescence. If we don’t have time to stop the ship, then we can make “underway” measurements by piping surface seawater into the ship’s lab and running it through benchtop fluorometers. We then look at this profile (or time-series) as a “proxy” or suitable substitute, for phytoplankton concentration. As chlorophyll concentration increases, generally so does the level of fluorescence- but not always. So it is important to realize the situations when chlorophyll fluorescence is not a good proxy for concentration. We most often see this in surface waters where light levels are highest.
Figure 1 shows a time series of surface sunlight (upper graph, blue line) measured on the deck of the ship, and Chl a (lower graph, green and black symbols) measured at a depth of 3 meters, near the surface. As sunlight increased throughout the day, we observe a suppression, or “quenching” of Chl a fluorescence by about a factor of nearly two between early morning and mid-afternoon (approx 15:00 GMT). We see this happening on rather short time scales too, as dips in sunlight, perhaps caused by the passing of clouds overhead, cause momentary relaxation of quenching in the fluorescence traces at approximately 1200 and 1700 hrs (red arrows). The Chl a concentration, meanwhile, showed a nearly constant level throughout the day. Quenching of Chl a fluorescence causes a huge departure from the normal co-variation between concentration and fluorescence. But does this happen at all depths?
The next figure shows similar data, but taken on two vertical profiles: one during mid-day (Station 7, left graph), and the other near mid-night (Station 4, right graph). You see that during the daytime, quenching of fluorescence occurs down to about 20 meters depth, and decreases fluorescence by a factor of about ten, when compared to Chl a concentration measurements made on captured samples. During night-time, however (right graph), the Chl a concentration data (green symbols) and Chl a fluorescence track each other nicely.
Another way of viewing these data is by property-property plots (see figure 3). Here we see that when plotted this way, the night-time data show a nice linear relationship (although over a limited range), but the day-time data, corrupted by fluorescence quenching show no such correlation. So, if one were to use the Chl a concentration data to calibrate their chlorophyll fluorometers, it makes sense to use nighttime data only.
Solar Irradiance (upper) and corresponding Chl a (lower) level changes through the day on March 16. Green symbols are concentration values (units of micrograms per liter) and black dots are fluorescence values (units of voltage). As sunlight increases through day, the fluorescence from chlorophyll is quenched, without a corresponding decrease in concentration.
Two vertical profiles of Chla fluorescence (black symbols) and corresponding concentration values (green symbols) for mid-day station 7 (left graph) and mid-night station 4 (right graph). During daytime, Chl a fluorescence in the upper 20 meters is quenched and does not track Chl a concentration. The quenching phenomenon disapears during the night-time.
Property-property plots of Chl a concentration (x-axis) versus Chl a fluorescence (y-axis) for mid-day (black symbols) and mid-night (red symbols) from Figure 2. Night-time fluorescence, devoid of quenching, shows linear relationship to Chl a concentration.