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

Adjustments to ship life - Update #2

We have now been at sea for two full days.  It feels like forever, but there's still so much to do before we are done!

Now that we've been out here for a bit, it seems like we have adjusted to ship life.  Seasickness hit a few people rather hard the first day, but everyone is in much better shape now.  We've had time to test our scientific sampling procedures and make the necessary adjustments so everything goes smoothly.

It's also a bit of an adjustment to sleep on a ship.  The rocking motion can help put you to sleep, but then when it changes, it feels like someone is shaking you back awake!  Any issues with comfort we may have are more than made up for with the food.  Filling, home-style meals with excellent desserts and lots of snacking options helps keep everyone happy.  And that's on top of the chest freezer dedicated to nothing but ice cream.

So, without further mention of food, here's some highlights from our first two days at sea.

Day 1

Our first day at sea was dedicated to testing our sampling procedures.  We decided to do a test once we reached open ocean, where the depth was greater than 1 km.  On our way there, as we were crossing the continental shelf break, we spotted some pilot whales.  Whale watching is the best activity to cure seasickness.  Actually, seeing the horizon line is what really helps, and the fresh air certainly doesn't hurt.

Whale watchers hard at work

It was such a good idea that the group expanded in size

Once we reached our test station, we began ironing out the kinks in our procedures.  Pretty much every test we did had something that needed fixed.  When we deployed the CTD, we had to bring it right back up again so the marine technicians could attach a sensor we forgot.  The drifters turned out to be numbered wrong - the data from drifter 4 registered as drifter 5, and vice versa.  And the salinity values seemed a bit off.  The PAR sensor had a very tangled cord and the on board measurement correction didn't record.  The pump for the towfish didn't work at first and it took a lot of messing around before it did.  Basically, most of the day was spent running around getting everything in proper working order.

First CTD cast about to enter the water.

Getting the towfish set up for deployment

That's why we had set aside the first day as a test run.  Because things will go wrong and there will be problems.  Better to fix it at the beginning, before it matters, than try and get it working as you go.

Deploying the towfish off the port side

After a day spent getting ready, we packed everything back up and headed to the middle of that eddy due east to start sampling the next day.

Day 2

The second day at sea was closer to what we expect a normal sampling day to be.  Weather updates indicated that there would be scattered rain in our current study area starting later this night and possible going on for two days.  This was excellent news, as we could sample the "dry" conditions now, when it hadn't rained for the past 7 days.  Then, we could sample during the rain the next day, and finish up sampling after the rain passed.

Retrieving samples from the first CTD cast

We started out sampling with a sunrise CTD cast.  The surface mixed layer was only 10m deep, and we made sure to sample the deep chlorophyll maximum, which was around 80m.  This first CTD cast gave us information on the water column.  We use the information from lowering the CTD to determine when to collect water samples on the way back up.  Then, we deployed the trace metal clean CTD off the other side of the ship, which also used this information to determine where to collect samples.

Getting the trace metal CTD ready for deployment

Once the CTDs were back on board, we deployed the drifters.  We used three of them, to make sure the data was reasonable.  And, if one drifted off in a crazy pattern, we would still have the other two to compare.  They were deployed in a triangular formation, where each side was about 1km long.

We returned to our original sampling position to do the PAR cast around noon.  There were some strong currents in the area today!  The 80m PAR cable went off the ship at an angle, and we could only measure down to 55m.  We decided to do one more CTD cast, only this time down to 2km to get the full water column profile.

Getting samples from the deep CTD cast

After that, we deployed the towfish and started steaming around the area, collecting data.  We spotted some jumping fish off the side of the ship as we went.  So we tried to collect some fish as well, but no luck yet.

The day finished with a weather update, including an update on what is now Tropical Storm Bertha.  We'll be keeping an eye on that one and staying out of the way.  Based on current tracks, it looks like we will decide on Monday if we need to head back into port or if we can weather it out.

To read the rest of the posts in this series, click on the Research Cruise label at the bottom of the post. 

More posts in this series:
Upcoming Cruise
Cruise Delays
Upcoming Cruise, Part II
Update #1
Update #3
Update #4
Update #5
Update #6 
Update #7 
Update #8 
Update #9