Finishing up – Update #9

We’ve made it to the last update for the cruise.  Hard to believe we’ve finished up already!  It will be nice to head back, see family members, and sleep in a real bed.

Updates from the final two cruise days are below.  I’ve also included some information on what happens to the project now that the cruise is over.  Thanks for following along with us on this adventure!

Day 15
This was our final day to do science.  In order to make it back to port in time, we needed to leave to head back between noon and 3pm.

So we started off the day as usual, with a CTD cast, followed by a trace metal CTD cast.  The waves calmed down a bit from yesterday, but it was still rather rough while we were sampling.

Last deployment of the trace metal CTD

A common tradition on research vessels that do CTD work is to decorate styrofoam cups and send them down with the CTD.  Depending on how deep the CTD goes, the cups are crushed by the pressure into miniature versions.  If you do it right, mostly by stacking the cups together, they retain their original shape.  Once the CTD comes back up, everyone has a personalized souvenir from the cruise.

Decorated cups before going down with the CTD

Getting the shrunken cups out from the laundry bag that went down with the CTD

Since we had time for another CTD cast, we attached our decorated styrofoam cups and sent it down to 2km.  We tried to finish our typical sampling scheme by doing a PAR cast, but it ended up being too rough for that.  The instrument kept getting pulled into the shadow of the boat, which, since we were measuring light through the water, would really throw off the results.  It was also too rough to deploy the towfish.

Our souvenirs with an original size cup in the back

We finished up our final science day by retrieving the last drifter.  Once drifters are in the water long enough, say a few days, they start to become a magnet for fish.  Barnacles begin to grow on them, and where there’s a small organism, there’s a bigger one coming trying to eat it.  The end result of which is that we tried to fish for a bit around the drifter before pulling it in.  Saw lots of Mahi, and someone even had a small shark on a line for a bit, but we didn’t manage to catch anything.  So we pulled in the drifter and headed for home.

Pulling in the last drifter

Day 16
Today was our final day out at sea.  It was a completely gorgeous day, sunny and calm.  We alternated between packing up the labs and sitting out on deck enjoying the weather.  A lot of the equipment had to be rinsed in fresh water and then dried before being stored, since saltwater is a strong corrosive.  With the nice weather, we were able to get a lot of that done as well, which should help us load up faster once in port.  We arrived back in Delaware at around midnight, signaling the official end to the cruise.

What happens next?
The cruise is now over, but the project we are all a part of will continue.  It won’t be near as exciting as several weeks spent at sea, but this is where we make the work we’ve done collecting data matter.  Since daily updates would become rather boring and meaningless at this point, I’d like to give you an idea of the next steps in the science process.  Here’s what will happen:

Analysis.  The first step is to continue the analysis we began on board.  We have initial results from several experiments, but there are more to be run that we haven’t even started yet.  They tend to be the ones that are more complicated and require either more time or different instruments.

We also have initial data from the CTD casts, the PAR casts, and the atmospheric chemistry measurements.  All of these data have bad data points in the files, including points where the ship’s smoke stack interfered air measurements, or when the CTD recored weird temperatures and salinities before it entered the water.

Everything needs to be plotted in graphs and analyzed to see if it makes sense.  If it looks good, then we start comparing various data sets to find relationships between them.  Some of it may be causes and effects we expected to see, or we might find something new.  Finally, we have to run statistics on it all to make sure what we find is significant, and not just lost in the error bars on the measurements.

Modeling.  A major way we plan to use the data we gather, after it is processed and analyzed, is in models.  The plan is to construct ocean and atmospheric models based on the conditions on our cruise.  The models begin with basic equations representing physical, chemical, and biological processes.  For example, there may be a gravity term, so that in the model, denser water and air will tend to sink below lighter water and air.  Or a reproductive term, where if phytoplankton take up nutrients, the number of them will increase.

Then, we add in the information we get from the data.  Based on what we found on the cruise, and the base equations of the model, we can figure out what is happening in the places or times we didn’t measure.  We may also get a better idea of how the different pieces work together, and understand the processes that drive our results from measurements.

Writing papers.  The final step in any project is to write scientific papers about the findings.  None of what we do will ever be accepted until it is published in a peer-reviewed journal.  This means that when we submit a paper to a journal, it goes out to other scientists to review before it is published.  They look at the data, at your methods, and at the conclusions you drew from the work.  If there are any mistakes, or it doesn’t look right, or you are missing something, they let you know.  The paper won’t be published until it is fixed, or until you can successfully defend why you did what you did.

From this project, there will be a series of papers published.  We don’t know what they will be just yet, but there will probably be several different types.  For instance, there may be an overarching paper describing how all the different parts of the project work together to describe the influence of rain on the ocean.  Each lab group may also have a paper or two on their specific part of the project.  Another paper may describe the model and how it works.  It is hard to tell ahead of time exactly what will be publishable and how to organize it into different papers.

Overall, the work to finish this project may take several years in total.  In part, this is because different projects overlap.  In order to keep the science going, a plan for a new project has to be submitted to a funding agency before the old project is over.  Often, scientists will be writing the papers from the last project while collecting data for the next.  Given that and the other responsibilities of scientists, who are often professors as well, it is no wonder the project will extend for so long past the end of the cruise.

Farewell from the DANCE crew!

This has been the final post on this research cruise.  I hope you enjoyed following along with us as we traveled the high seas!

More posts in this series:

Update #6 
Update #7
Update #8

Rough Seas – Update #8

These few days were interesting as the weather patterns brought some rain that we wanted, but also some rough weather.  The ship’s motion went from a gentle rolling to feeling more like an amusement park ride!

Day 13
Around mid-morning, we made it back to our eddy #2 and the three drifters we had previously deployed.  At first glance, it looked like two of the drifters had gotten tangled together, despite being deployed 1km apart.  We went ahead and did a normal and trace metal CTD cast.
Preparing the trace metal CTD for deployment
The weather outlook for the next day or so is not that great.  We are expecting rain, which is good for the project, but the winds are supposed to pick up as well.  Already we can tell the seas are beginning to get a bit rough.  Since day 15 will be our last science day, and might still be rough, we decided to pick up two of the drifters now.
We went for the two that were tangled together, but they ended up not being tangled, just floating side by side.  After battling some large waves, during which almost everyone on the back deck got soaked, we managed to pull in both drifters.
Pulling the drifter over the side railing

Rinsing off the drifters with freshwater after retrieving them.
Then, we traveled back to the last drifter and did a PAR cast as well as another CTD cast.  It was too rough to deploy the towfish, so we stopped sampling for the day and waited for the rain to arrive.
One drifter had a passenger that we returned to the sea

Day 14
The rain did arrive today, but the seas were very rough.  Too rough, in fact, to deploy any sort of scientific equipment.  The danger is, in rough seas, that the boat rolls quite a bit side to side.  It has to be stationary to deploy the CTD, and that leaves us at the mercy of the swell.  If the swell is too much, the cable holding the CTD will lose tension as we roll to one side, then snap back tight as we roll to the other.  Too much of a snap and the cable breaks!
It rained pretty good in the morning, but we were unable to collect any because the salt spray was reaching the height of the bucket, which is several decks up.  The seas calmed down a bit later on – not enough to deploy any equipment, but we were able to collect rain from a second shower in the afternoon.
The rest of the day was spent planning out our final science day tomorrow and discussing packing up and loading up to go back home.
Atmospheric chemistry
If you think about the process we are studying, where rain deposits nutrients to the surface ocean, causing the phytoplankton to respond, atmospheric chemistry comes in at the very beginning.  We want to know how the nutrients got in the rain to begin with.
The majority of the atmosphere is made up of nonreactive chemical compounds, mainly oxygen and nitrogen.  We are interested in the ~1% that is reactive, specifically, how pollutants get into the rainwater.  The main indicator of man-made pollution is nitric oxide, or NO.  During the process of combustion, say when you drive your car, or when our ship is steaming through the ocean, the heat from the process breaks apart N2 molecules and produces nitric oxide.  There are a few natural sources of nitric oxide, including lightning and certain soil microbes, but they are episodic or not significant enough to be important in a marine environment.
Setting up instruments on the fly bridge before we departed – Photo courtesy of Doug Martins
Once nitric oxide is produced, it can react with ozone (O3) in the atmosphere to form nitrogen dioxide (NO2).  If there is sunlight available, the nitrogen dioxide can split back up into nitric oxide and oxygen, which goes back to ozone.  Essentially, it is a balanced reaction.  Both processes happen at once, keeping the relative levels the same in the atmosphere.  However, since one process requires energy input by sunlight, the balance levels are different overnight than they are during the day.  So at night, there is a tendency to build up nitrogen dioxide.
Now let’s talk about how these molecules get into rainwater.  Nitrogen dioxide is more soluble in water than nitric oxide, which means it can more easily dissolve and be included in the water.  Nitrogen dioxide can also react with water to form nitric acid, which is super soluble.  Once nitric acid gets into the rain water, it splits apart to form nitrate, a form that phytoplankton can use.  The rest of the process is straightforward – the nitrate-filled rain falls and supplies nutrients to the surface ocean.
Performing some maintenance on the atmospheric chemistry insturments
In order to measure this process occurring in the atmosphere, we measure nitrogen dioxide and nitric oxide (NO2 and NO).  The air in general over the ocean is very clean.  Thus, anything we measure is from air masses than used to be over land and have picked up pollution from sources there.  There has been a slight problem with the ship’s smoke plume interfering with the instruments.  About 50% of the time, we end up measuring air that is contaminated by the plume.  The relative ratios of the two molecules we are measuring are so different in the plume versus in clean ocean air, that it isn’t an issue to identify those points and remove them from our analysis.
Our atmospheric chemist hard at work analyzing data.
As a side project, we are also measuring nitrogen dioxide and ozone in the total atmospheric column above us.  In part this is to detect plumes of pollution that are above the bottom atmospheric layer, which our other instrument would not detect.  The other part is to validate satellite measurements. We can measure the same molecules in the atmosphere via satellite, but we need observations on the surface to make sure those calculations are done correctly.  This is only the third time this instrument has been used over water (instead of land), and the first time it is out on the open ocean (instead of coastal zones).
Eventually, the measurements we make will be analyzed to help us learn more about the process of depositing nutrients from rain.  They will help increase the accuracy of satellite measurements of the atmosphere, and will also be used to help validate an atmospheric model.
Thanks for reading!  As you know, we are getting to the end of our cruise.  The next post will be the last of the daily updates, and I’ll also talk about what lies ahead for us after this phase of the project finishes.

More posts in this series:

Update #6 
Update #7
Update #9

Searching for rain – Update #7

Greetings from a happy science crew!  We are nearing the end of our voyage and everything seems to be working out well.  There was a time before the cruise began, that we all thought the worst might happen.  That we would end up at sea for weeks running after rain and never finding any.  Everyone would be frustrated and grumpy and it would just be awful.

Instead, we’ve got rain by the bucket!  Literally!

Day 11
This day was a bit of a bipolar experience.  Since the night before, we were heading further south in search of rain.  For much of the day, people were just sitting around.  We caught up on some lab work, thought out some contingency plans, and kept an eye on the radar.  It was quiet and a bit tense as the rain system we were chasing kept moving south and we couldn’t quite catch up with it.

Our chief scientist keeping an eye on the radar as it begins to rain

Then, around 5pm, we started getting a few sprinkles.  The sky wasn’t too dark and we weren’t sure we had really found the rain we were looking for.  Gradually, the rainfall began to increase and it rained steadily for good, long time.  A wave of relief and energy swept through the ship.  Our rain gauge recorded about 1.2cm of rainfall, and, due to the low wind conditions, we managed to completely fill our rain bucket!  And there was much rejoicing.
Gazing out at the stormy seas
A few hours later, after the rain had stopped, we jumped into action.  We hadn’t done any before sampling of this location, having prioritized the quest for rain.  We made up for it by doing two CTD casts: one right outside the area that had been rained on, and one right smack in the middle of it.  After we did the second cast, we deployed one drifter to keep track of that water mass so we could sample it again later.  Then we dropped the towfish in the water and circled the drifter for a few hours collecting water late into the evening.
Sampling the CTD cast in wet weather
Day 12
After a late night of sampling, it was back up and at it again early this morning.  We did another series of CTD casts, one normal and one trace metal, followed by a PAR cast before pulling the drifter back on board and heading north.  After the rain stopped the day before, the winds picked up a good bit, creating some decent waves.  Getting the drifter out of the water proved to be a bit of a challenge, and everyone involved ended up wet.

Catching the drifter in some decent sized waves
Thankfully we had the rest of day to recover from the intense sampling and lack of sleep.  We are steaming back to our eddy #2 to pick up sampling there again tomorrow.  Everyone is using the time wisely to catch up on lab work and prepare for our last spurt of sampling the next few days before heading home.
Aerosol sampling
I’ve mentioned that we’ve been sampling aerosols most nights we’ve been out.  In order to sample, we must be headed into the wind so that there is no contamination from the ship’s smoke stacks.  Since we can’t do much other sampling while we are moving, we’ve been doing aerosols at night while most people are asleep.
The aerosol sampling is run by a graduate student who is using the data as part of a Masters project, and is assisted by a visiting undergraduate trainee.  These lucky two stay up all night keeping an eye on the sampling and sleep during the day while the rest of us are running around making noise.  It’s a tough job being on the opposite schedule of everyone else, but they’ve done great so far.
Preparing the aerosol sampler to run
The aerosols we are interested in are basically different types of land-based pollutants.  Our scientific equipment isn’t measuring the types of aerosols – its collecting iron particles that are present in the air.  That means this project falls under the trace-metal clean category.

Setting up the aerosol sampler
The aerosol sampler consists of a series of filters.  Air is pulled through the filters, and each filter collects particles of different sizes, from large to small.  It takes several hours of continual running to collect enough to measure.  Once enough air has been filtered, each filter is taken out and cut into smaller pieces.  Then, the samples are “leeched” with deionized water (clean water), so that the particles on the filter are released into the water and dissolved.  Now the iron from the air is in a form to be analyzed in a trace metal clean lab.
The aerosol crew working in the lab
We already know that iron is a micronutrient for phytoplankton.  Even if it isn’t limiting, we are still interested in where the iron comes from that gets in the surface ocean.  We think a lot of it is deposited from the atmosphere, but there aren’t many measurements.  The goal of the aerosol sampling is to get a better idea of how much iron is deposited.  There are several questions we can answer with this analysis.
By comparing the amount of iron in the air to the amount in the rain, we can see if iron is more likely to be deposited in wet or dry conditions.  There is another aerosol sampler running on the Eastern Shore area of Virginia, collecting the same types of samples.  If we compare the two, we can determine how much iron leaves the air between the coast and the open ocean.  We can also determine potential types of pollution and source locations by using pollutant maps to track where the aerosols originated.
Most of this work will be done after the cruise is over, as part of a Masters project.  But for now, the data we collect on aerosols here will help us specifically understand this system, and understand the importance of rain in depositing iron to the surface ocean.
As always, thanks for reading.  Stay tuned for the (most likely) exciting end to our cruise – see how it all works out!

More posts in this series: