Southern Ocean GasEx Blog

Dispatches from the Southern Ocean Gas Exchange Experiment

Archive for April, 2008

Shake and Bake!

Posted by sogasex on April 4, 2008

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
  • Rainfall
  • 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.

Method

  1. 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.
  2. 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.
  3. Add the other sensors to the mast: Licors, RH/T, sampling inlets…
  4. Secure everything with tie wraps, clamps, bolts…
  5. Install the rest of the equipment on the ship (ozone, DMS, radiometers, Licors 6262); forward on the ship is an excellent spot.
  6. Put the RHB in the Southern Ocean for ~45 days and let everything shake gently… or vigorously.
  7. Meanwhile, log all sources of data to a central data acquisition system, commonly called “DAS”.
  8. 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!).
  9. 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.

  10. 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!

Bon appétit!

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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.

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Flux kitchen and the 4 cooks. All recipes are prepared with tradition. Left to right: Ale, Ludovic, Byron and Chris.

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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.

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Freshly baked fluxes! Covariance spectra for the longitudinal component of the momentum flux (blue) and for the sensible heat flux (red).

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Deep Breathing

Posted by sogasex on April 3, 2008

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.

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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.

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Where’s the tracer, man?

Posted by sogasex on April 2, 2008

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.

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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.

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When David asks “Where’s the tracer, man?” this is my response…

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Amphibious Rodents

Posted by sogasex on April 1, 2008

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.

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This is not a Southern Ocean amphibious squirrel

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Neither is this

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