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The Plume Puzzle

09/05/2010, 8:18 PM by Lollie Garay

The Plume Puzzle 

 

The science team has been back home for months now enjoying home, family, and friends. At this writing, some of the samples and equipment that were shipped on the Knorr have made their way back to the various universities and researchers.

 

Already, emails with updates and questions have been circulating between team members as the work of deciphering what we did begins to unfold. For now, the task is to measure, document, and analyze all the water, sediment, and biological samples that were collected. But as one researcher said, it’ll be years before all the information is completely synthesized and understood!

 

On the last day at sea, Chief Scientist Tish Yager gathered the science team, the Captain, and members of the logistical support team for a final science meeting. As I listened to each researcher share their “surprises” and comments in turn, I reflected on how similar to my classroom students many of them sounded! How? 

 

By the number of unanswered questions they were leaving with! It’s a standard I use in my science classes to evaluate my teaching: if we’re successful in our work, then we end up with more questions than answers, which in turn leads to more investigating and discovery! And that’s exactly what I was hearing from the science team.

 

 

Tish posted some information on the amount of casts, deployments, and other interesting numbers in the July 14 blog. I’ve summarized more here on the other “surprises” and comments shared by the science team.

To begin with, Tish explained that the low-salinity water of the Amazon plume extended farther than previously thought. Fresh water and ”coastal” assemblages of phytoplankton were found farther away from the mouth than expected. She also said that pCO2 levels (partial pressure of CO2) in the plume were way below the saturation level with the atmosphere, and lower than expected from mixing ocean with river waters alone.

Despite the low pCO2, we still observed very high rates of community respiration in the surface waters. This suggests that photosynthesis is really cranking - enough to draw down the CO2 through net photosynthesis or autotrophy. 

Deb Steinberg found characteristic changes in the zooplankton community as we moved through the plume. Certain animals were present only in certain parts of the plume. Could it be that the zooplankton community is changing in response to the phytoplankton variation, or to some change in the river-ocean continuum?

Deb also shared her surprise at finding tricho sinking into the sediment traps. Tricho in the surface water is not unusual, but the fact that it is sinking IS. She also found zooplankton that was eating it. Before the ANACONDA study, it was believed that most tricho production stayed and was recycled at the surface. These findings shed new light on the fate of tricho!

Will Berelson was very excited about his seafloor and sediment trap data, describing visible quantities and color in the traps as “incredible, delicious results!” He found significant carbon flux to the deep sea under the plume. His surprise was that the greatest flux is from the lower salinity stations where coastal diatoms are blooming. DDAs further out in the plume are also fluxing to the seafloor, but to a lesser extent.  All the export fluxes measured in the plume were higher than those observed at oceanic salinity (>35), outside the plume. The bottom line is that the plume appears to be drawing down a lot of carbon from the atmosphere and sending it to the deep ocean floor, instead of holding it in the subplume layer where it could mix back into the atmosphere at some later time.

In an earlier post, Will described opal as the glass SlO2 that diatoms make their shells from and explained that opal that falls to the seafloor is reflected in the sediment pore water. His sediment data shows opal with and without carbon. The opal without carbon indicates that the carbon is being respired faster than the tests dissolve. "Tests" are the "shells" of the phytoplankton.   Diatom "tests" are silicate.  If the carbon is remineralized faster than the shells dissolve, then you see a silicate signal in the sediments without seeing a comparable carbon signal.

 

Joe Montoya described his data findings as “intriguing”, adding that it will months to organize it all. Most of his data has to be run on a mass spectrometer back in his lab.

 

Joaquim Goes was looking at a suite of pigments in the underway line. He found some very interesting indications about how the phytoplankton community shifted as we sailed through the plume north to south, east to west. There were also certain pigments more associated with the low pCO2 than others. His data set along with the underway salinity, pCO2 and O2 data will give us a REALLY neat story about how the plume influences the phytoplankton community, which in turn influences the carbon drawdown in the plume!

 

 

Victoria Coles beamed with pride as she announced the success of  “117 beautiful (CTD) casts”. Her “surprises” included all kinds of fascinating features; layering we don’t understand; fossil plume layers under fresh plume associated with DDAs; and vertical migration of the phytoplankton within or just below the plume, which might explain where some of the nutrient recycling is coming from. Victoria also described the river of fresh water past Barbados “streaming out like a hose”!

                                   

I had talked earlier about the ongoing underway sampling which started on June 3 and continued until June 23. About 200 hourly samples were collected during the transit periods by a team of volunteers from the science team. Thanks to Patricia Medeiros and Christine Ewers for explaining the process as I documented their work! .

During the course of the voyage, 39 blogs were posted and thousands of pictures  and hours of video taken!  Over 100 messages/questions were posted by viewers following our journey. The underwater camera was deployed 9 times.

As I write these numbers, I can think of many other things we could document for posterity...but that would be another blog :)

I end this as I began - with the idea of the Amazon plume as a puzzle we are trying to put together. There are many pieces we have, but not enough for completion. And those we have, don’t fit quite right, YET. This is only the beginning of the work that the ANACONDA and ROCA teams have in solving this puzzle. 

This site will change as we discover more surprises. I hope you’ll continue the journey with us!

Lollie

 

 

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  • Do the bacteria in the water make us sick?

    Only a few of them.  Bacteria are in every habitat on Earth, growing in soil, hot springs, radioactive waste, water, as well as in organic matter and the live bodies of plants and animals. Bacteria recycle nutrients, with many steps in nutrient cycles depending on these organisms, such as nitrogen fixation.