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:

Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #4
Update #5

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:

Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #4
Update #5

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:

Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #4
Update #5

Update #6 
Update #8 
Update #9

Headed south - Update #6

We've got less than a week to go at sea, so we're going all out for this last leg.  Keep reading to hear about our new sampling location, our quest for rain, and a bit about tracking weather out at sea.

Day 9

Now that we've finished up in our first region of study, the eddy to the east of Delaware, we've moved to a new location.  While we were sampling earlier, we noticed that an eddy further to the south was getting a fair amount of rain.  The weather report for after Bertha shows that this region has a good chance to get more rain, either over the weekend, or into next week.

Sea Surface Height map showing our starting point, our first eddy, and our new location to the south.

Early in the afternoon we arrived at our new station.  The first task was to do a CTD profile to see what the water column was like in this eddy.  We noticed a deeper surface mixed layer, possibly an after effect of the recent stormy weather.  Once we completed the first CTD cast, we decided where to deploy the three drifters.

At sea again - Update #5

Since our last update, we have made it back out to sea!  There were no ill effects from Bertha, no incredibly large waves or rough seas - all smoothing sailing.  We've finished up our sampling in this eddy we've been hanging around.  Now, we are headed south to another eddy to start the whole process over again.

Keep reading for our daily updates, and then some details about the biological oceanography experiments we are doing.

Day 7

We left port at around 4am, and spent most of the day steaming back to our one lonely drifter.  We had a very small chance of some rain towards the evening, but it broke up before it reached us.  Once we made it to the drifter, we did a late CTD cast, around 10pm, and then turned on the aerosol sampler for the night.

Day 8

Repeating our sampling scheme from previous days, we turned off the aerosol sampler in the early morning to head back to our drifter in time for a sunrise CTD cast.  Thanks to our stop at port, we now have a working winch for the trace metal CTD and were able to get that going as well.

Successfully recovering the trace metal CTD after the first cast with the new winch

As this is our last day sampling this particular spot, we decided to make the most of it.  We did two PAR casts, the normal one around noon, and an extra around 10am.  The angle of the sun may change the attenuation coefficient, so we wanted to test this theory.  We also did two more normal CTD casts, both to get temperature and salinity data, not to collect any samples.

Preparing the CTD for deployment

Then we deployed the towfish in the afternoon and towed it in a circle around the drifter.  We finished up the day by recovering the last drifter and heading south.  We have a new spot picked out that looks like it may get some rain in the near future.  I'll have more details on that once we arrive.

At one point, right before lunch, we were quite near the drifter and noticed it was attracting some fish.  There was a mad fishing scramble, and we ended up catching close to half a dozen mahi.  Dinner was quite delicious, as our chef cooked up fresh teriyaki mahi with fried rice.

Catching Mahi

Biological oceanography

Almost every time we do a CTD cast, we sample the water at various depths.  Once the CTD comes back up, the water is portioned into pre-labeled bottles to be further analyzed or used for experiments.  There are several types of biological analysis we can do:

Collecting initial water samples from the CTD

Measuring Nutrients.  We take a sample of water and measure the amount of nutrients in it.  It gets more specific than just nitrogen and phosphorus, as we want to know what form these nutrients are in.  Certain forms are more easily used by phyotoplankton than others.  The results are given as concentrations and can show how much of each nutrient is currently in the water sample.

Measuring Chlorophyll.  We take at least a liter of water and filter it through a relatively small filter.  Small phytoplankton are left on the filter, and the sea water goes through.  The filter is dissolved in acetone, releasing the chlorophyll that was caught on it.  Since chlorophyll is a specific color (think of green leaves and plants), we can use light to determine how much there is.  The amount of chlorophyll tells us how many phytoplankton there are in that water sample - this is called abundance.

Filtering samples for chlorophyll

It takes both these types of measurements to give an accurate picture of what is going on in the water.  For example, low nutrients could mean a bad area for phytoplankton to grow.  But, if the chlorophyll measurements are high, we know we took our samples right after the phytoplankton used up all the nutrients.  Likewise, if chlorophyll measurements are high and so are nutrients, then we caught the phytoplankton in the middle of the growing stage.  They haven't yet used up all the nutrients to grow and reproduce.

Processing samples in front of a different filtering apparatus

Taking nutrients and chlorophyll straight from the CTD samples gives us a snapshot of what is happening at each depth the CTD sampled.  However, if we also run experiments on the samples, we can learn a lot more.

One type of experiment is an incubation experiment.  In this case, we place water samples in plastic bottles and incubate them, or allow them to sit.  Then, chlorophyll and nutrients are measured at different time points to see how things change.  In some cases, the bottles are clear, and are kept in an environment that is similar to where the sample was taken from.  We have special clear chambers, called incubators, set up on the deck of the ship.  Each one has a different number of layers of a black mesh over it, to set different light levels.  Water is continuously pumped through these chambers to keep them at close to the same temperature they were sampled at.  In other cases, we want to see how things progress if there is no light input, so we use dark bottles instead of clear ones.  These bottles are also placed in the on board incubators, to keep everything else the same.

The never ending labeling that goes with all these samples

Another type of experiment is called a bioassay.  Sampled water is divided into bottles and then different types of nutrient treatments are added.  For example, we have an iron-only treatment, a nitrate and iron treatment, and a rainwater treatment, among others.  These bottles are then incubated and chlorophyll and nutrient measurements are taken over time.  By comparing how many phytoplankton grow in the bottles with different nutrients added, we can determine which nutrient was the limiting factor.  Since one of our treatments is rainwater, we can also see how the growth in the rainwater bottles compares to the other treatments.  This will give us an indication of how phytoplankton might respond to a rain event in the ocean.

Our incubators on the back deck

By examining the results from all these experiments together, we can get a good idea of what is happening and why.  A lot of the experiments are being run while we are on board, but some samples are being refrigerated or frozen for further analysis in a normal laboratory on land.  We have a few preliminary results from our first few samples.  They still need some extra work, but there is enough information to show that things are going well and we are getting significant results so far.  This is confirmation that the experiments are being carried out correctly and that we chose the right ones to perform.

Thanks for reading!  That's all I've got for today.  Stay tuned for the next update - on our new location, new plans, and hopefully some rain.

More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #4
Update #6 
Update #7 
Update #8 
Update #9

Waiting out Bertha - Update #4

Everything went pretty smoothly while we were waiting for Bertha to pass.  We got in one more science day before heading for port to wait out the storm.

If you want to see our cruise track and current location, you can check out this website that tracks most ships, including ours.

Below are our normal daily updates.  Since not too much happened, I've included a section at the end to start explaining the science that is happening on board in more detail.  This time, I'll be talking about trace metal chemistry.

Day 5

For the most part, this day looked a lot like day 4.  We had the aerosol sampler out overnight, and were headed south, into the wind.  Around 2am, we turned it off and returned to the center of the eddy we've been in for the past few days.  After another sunrise CTD cast, we deployed the towfish and began towing it in a circle around our drifters.

At one point, it began raining really hard while the towfish was out.  So there was a mad scramble to get the rain collector out to catch more rain.  It ended up being only a brief shower, but we got a bit of rain out of it.  Then, we finished up with the towfish and proceeded to do the daily noon PAR cast.  After that, we completed another shallow CTD cast to get the conditions after the brief rain event.

Rather wet scientists after dashing out in the rain to turn on the rain collector

Up until this point, we hadn't been getting quite as many surface samples as we wanted from the towfish.  So when we did the shallow CTD cast, we decided to sample from the ship's underway system at the same time.  The underway system is always on and samples at the bottom of the ship.  However, there is a good chance that the samples wouldn't be representative of the surface water, since there are probably extra organisms growing in or near the sampling system.  We compared the samples to the CTD surface cast, and it turned out the values did not match, so we probably won't use the underway system for sampling nutrients or chlorophyll.

Our final task of the day was to retrieve two of the three drifters.  We decided to leave one out to continue collecting data, but didn't want to risk more than one with Bertha approaching.  We will return for the last one after Bertha has passed.

Pulling the drifter and attached drogue out of the water

Day 6

Not much went on today.  We used this time to catch up on lab work and relax.  We arrived back in port at around 2pm, and spent time calling friends and family and catching up with the internet while the crew fueled up the ship and did some maintenance work.

Passing the lighthouse on our way back into port

Trace metal oceanography

In the cruise updates, I've mentioned deploying our trace metal CTD, at least until the winch for it broke.  Now, I'd like to give you a general idea of what I mean when I say "trace metal".

I've already talked a bit about nutrients and phytoplankton.  Measuring nutrients is one of the main activities for this cruise.  Major nutrients in the ocean are essentially various forms of nitrogen, phosphorus, and carbon.  If enough nutrients of each type are available, phytoplankton will grow and reproduce.  If one type is missing or used up, growth will slow and stop.  We call the missing type the "limiting nutrient".  In oceanographic history, scientists discovered a quandry.  They found large amounts of all nutrients, but for some reason, the phyotplankton weren't growing and using them up.  The regions where this phenomenon occurred became known as High Nutrient Low Chlorophyll (HNLC) regions.  Something besides the nutrients was acting as the limiting factor.

It was eventually discovered that along with the major nutrients, phytoplankton also need incredibly small amounts of other nutrients, called micronutrients.  One of these was iron.  There is not a lot of iron floating around in the ocean, but it normally doesn't act as a limiting factor except in certain HNLC regions.

So, once it was discovered that iron was another important, albeit small, nutrient, scientists set out to measure it as well.  This was where they ran into problems.  Iron is available is such low concentrations that any measurements were contaminated.  The ship itself contaminated the water, any metal on the CTD or the chain or the winch also contaminated the water.  Basic laboratory equipment and normal lab coats and gloves contaminated samples.  It was virtually impossible to get an accurate iron measurement with standard oceanographic equipment.

Working in the trace metal clean laboratory on board - Photo courtesy of Bettina Sohst.

This was where "trace metal clean" protocols came in.  Scientists figured out how to make their working environment clean enough that accurate iron measurements could be made.  They set up clean laboratories with special ventilating systems to keep any traces of iron out.  Plastic bottles used to collect samples are rigorously cleaned, using acid baths that leave no trace behind.  Special CTD set-ups were designed to ensure no contamination of the ocean during sampling.

Trace metal CTD about to be deployed

In our case, we have a trace metal clean CTD and the towfish is also trace metal clean.  There is a clean laboratory set up in a "van" on the ship - it is a portable lab the size of a shipping container that can be attached to the back deck.  When we do a trace metal cast, the trace metal CTD goes in on the opposite side of the ship as the normal CTD, so there is no contamination.  The trace metal CTD doesn't collect any samples in the upper 10m of the water, to avoid any contamination from the ship.  In order to sample the surface water for iron, we use the towfish.  It is put in the water while the ship is moving, and is held out to one side, so that it collects water untouched by the ship.  Every time we use it, it gets flushed with seawater before any samples are collected.  When not in use, all nozzles and openings are covered with disposable plastic to keep contamination to a minimum.

Preparing to deploy the towfish

As you can imagine, measuring for iron requires just as many precautions.  None of the measurements are being performed on board for that reason.  We are collecting the samples and properly storing them to be tested in a stationary lab once we get back.

Now, when I mention our trace metal CTD, you will know that I really mean a "trace metal clean" CTD where samples can be taken to measure the micronutrient iron.

Coming up, we're back out at sea, taking more measurements and we’ll be deciding soon where to go next.

More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #3
Update #5
Update #6 
Update #7 
Update #8 
Update #9

Rainfall - Update #3

The big news for this update is that we got some rain!  Getting rain this early in the cruise is a huge relief for us.  We would like to have another chance later to sample an area before, during, and after a rain event, but at least we have one series of data now!

Below are the daily updates for days 3 and 4 of our cruise.  And some plans for avoiding Bertha.

Our first sight of rain, looking out over the back of the ship

Day 3

We spent most of the overnight hours steaming away to the south, which is into the wind.  While mostly everyone is sleeping, the aerosol sampler on top of the bridge is turned on.  To avoid contamination from the ship's smoke stacks, it can only be on while we are headed into the wind.  Around 3am, the students keeping tabs on the aerosol sampling turned it off so we could head back towards our drifters.

Turning on the aerosol sampler

All three drifters had been staying inside the eddy and were following roughly the same path.  When we went to look up their current location to head back towards them, we realized we weren't getting any signal from them!  After a mad scramble to figure out why there was no data from them, we ended up doing a quick estimate of where they should be, and started heading there instead.

It turned out, that instead of losing three expensive drifters, it was a mild case of operator error.  The software program that receives the signal had accidentally been shut down the night before, so we weren't getting any of the data.  Luckily, the drifters still collected data the entire time, we just couldn't see it.

Once we made it back to the vicinity of the drifters, we did a CTD cast and a trace metal CTD cast as well.  That's when it began to rain.  We put out rain catchers, but had trouble collecting anything as the wind was blowing the rain sideways, instead of down into our bucket.

 

Our weather forecast expert hard at work on the bridge

We held off on sampling until the rain stopped, then did another CTD cast to see how the mixed layer changed.  We had planned another trace metal CTD cast as well.  But when we went to turn on the winch, there was loud POP and some sparks and smoke.  Turns out it is broken, and we don't have the equipment on board to fix it.

Holding onto the trace metal CTD as the winch issues were investigated.

The evening plan was to put the aerosol sampler and rain bucket back out overnight and head into the wind again.  Which leads us to...

Day 4

It rained again!  We turned off the aerosol sampler and closed the bucket to head back to the area where our drifters are around 2am.  Then, between 3 and 6am, we got another good bit of rain.  BUT...  we didn't catch much because it was all after we took down the bucket!  We will still be able to see the effects of the rain on the surface ocean, we just won't be able to do controlled laboratory tests with it.

Getting the rain catcher set up to run overnight.

We did our early morning CTD cast, as usual.  Then, we deployed the towfish, which collects surface water samples.  Our cruise track for this portion should look pretty interesting, as we circled several times to the left around the drifter location.

Consulting over the CTD profile data to determine where to sample

Just before noon, we retrieved the towfish from the water and did a PAR cast and another shallow CTD cast.  We got lucky and right after finishing these casts, it started raining again!  Being rather desperate for samples, we dropped everything and started chasing the rain, hoping to collect some more.  We got a bit, but not too much.  The rain seemed to dissipate as the system traveled north, and the main section was always just out of reach.

Eventually we gave up and returned to our original position near the drifters.  We did a short CTD cast to see if there were any changes from the brief rain event, and then went into our nightly aerosol collecting routine.

Plans for Bertha

Bertha is now a tropical storm and is forecast to become a hurricane on Wednesday.  The latest forecast update we received showed a significant change in position.  Instead of barely clipping our current position, there is now a 20-40% chance we will encounter tropical storm force winds (above 30 knots).  Since we will need to refuel in the next couple of days anyways, we decided to head towards port Monday evening.  We should put in late afternoon Tuesday, and be back out sampling by Thursday morning, if all goes well.  Our stop will kill multiple birds with one stone, as we avoid the storm, replace the broken winch, fix a broken refrigerator, refuel, and swap out some crew members.

Forecast track for Bertha.  Our approximate location is the red dot.

Everyone is happy to have a bit of a break.  We haven't had much of a daily repeated sampling program as the weather can change quickly.  A lot of decisions need to be made on the fly, and the correct people roused from their bunks in the middle of the night.  This will give us a good chance to recover and be back at it later in the week.

As always, the rest of the updates are under the "Research Cruise" label.  Updates will continue, even while we are in port, so stay tuned! 

More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #2
Update #4
Update #5
Update #6 
Update #7 
Update #8 
Update #9