Thursday, March 24, 2016

A first look at the data we collected

It's been a week since our cruise came to end. Despite all the fun we had onboard, after 38 days at sea, most people were aching to be back on dry land. Within minutes of clearing port customs, the science party and crew started scattering in all directions - some to beach, some to the airport, most to the pub.

The Revelle back in port.
After many hugs and handshakes, we all said our goodbyes and went our separate ways. Most of us are now back in our respective hometowns (I am writing from Seattle), but a few restless souls returned to the ship for the second leg of our cruise. They will pick up where we left off and continue northwards into the Bay of Bengal. Their final stop be in Phuket, Thailand. I can't imagine what it is like to do these types of cruises in succession. It's been almost two weeks since I collected my last sample, but I feel like my body is still recovering from the grueling experience. I am sure this line of work gets easier with experience, but I still have to admire the people who do these research cruises for a living.

As the saying goes, all good things must come to end. Now that the cruise is over, there is really not much left to add to this blog. To wrap things up, I plan to post all the content that I couldn't share from ship. These are mostly videos of us doing deck work. But before I do that, I would like to showcase some of the data we collected on our cruise. The whole point of our cruise was to collect data, so I would be negligent to not mention them in this blog.

A schematic of our cruise track and station locations.
Figure 1: A schematic of our cruise track and station locations. Red arrows show our transit routes, where we did not stop to collect data. We ended up doing 83 of the 89 stations we originally hoped to do. Pretty darn amazing considering all the setbacks we faced.

Just to recap, on our cruise, we completed 83 stations out of the 89 we originally set out to do. This is a remarkable accomplishment considering the enormous obstacles we had to overcome - not the least of which is losing our primary rosette. All the data we analyzed onboard the ship will become publicly available once they pass through quality control. These data will eventually be hosted on CCHDO, an online database that hosts CTD and bottle data for all the CLIVAR/GO-SHIP hydrographic cruises.

We also successfully deployed six SOCCOM floats on the cruise. All of our floats have self-activated and have completed several profiles of the upper ocean. These data are already publicly available via the SOCCOM website.

To help contextualize the float data, I will first present some of the hydrographic data we collected on our cruise. These are data we obtained from our rosette deployments.  Below, I show depth-latitude1 plots of temperature2, salinity, oxygen and nitrate for stations 1-82 on our transect. The faint gray dots show where we collected water samples at each station. The red dashes highlight the stations where we deployed Argo floats.
Figure 2: Plots showing depth-latitude sections of ship-based measurements of temperature, salinity, oxygen and nitrate from the 2016 I8S cruise. Station numbers are shown at the top of each plot; float deployment locations are highlighted in red. These plots show data for the full depth of the ocean. The only exception is at station 37, where the cast prematurely ended at 2000m due to mechanical issues with the winch. These data are preliminary and have yet to undergo complete post-processing.

Figure 3: Same as the previous figure but with a zoomed in look at the upper 500 meters(m).
The plots above show how temperature, salinity, oxygen and nitrate vary from north to south in the Southern and southern Indian ocean. Starting with the most obvious, we see that upper ocean temperatures decrease from north to south. This is most clearly shown in the plots of the upper 500m (Figure 3). The salinity data show a similar pattern. Combined, these relationships tell us that the Southern Ocean is generally colder and wetter than the southern Indian Ocean. These are well known facts. Let's dig a bit deeper.

This transition between the cold, wet Southern Ocean and the warm and salty southern Indian occurs over a relatively short distance. For example, between 50o S and 43o S, ocean temperatures in the upper 500m differ by about 10 oC. In the open ocean, this constitutes a huge jump in a temperature. We call these jumps fronts. Like their atmospheric counterparts, ocean fronts are associated with enhanced mixing, turbulence and eddy activity. If you take a closer look at the transition region between roughly 50o S and 43o S, you will notice alternating bands in the different water properties. These are the signatures of strong eddies, which are large vortices (think ocean tornadoes). These eddies are good at transporting water masses over large distances and they generate a lot of mixing in their vicinities. Ocean eddies express themselves as bumps or depressions in the sea surface. We can observe these surface expressions via satellite altimetry, an example of which is shown below.

Figure 4: Plot of sea surface height anomalies on February 24, 2016. This is a snapshot of the eddy-field through which we transited. The numbered labels represent our station locations.  Plot credit: Viviane Mendez.

Oxygen and nitrate concentrations show a trend that is opposite to that of temperature and salinity. That is, oxygen and nitrate concentrations in the Southern Ocean are higher than those than in southern Indian Ocean. The high nitrate concentrations in the Southern Ocean has to do with the large scale upwelling of deep water around Antarctica. This something I described in more detail ins a previous post. Oxygen concentration is higher in the Southern Ocean largely because cold water can absorb more oxygen gas than warm water.

Figure 5: A blown-up perspective of the oxygen data shown in Figure 2. I have added annotations to highlight the upwelling of deep water in the Southern Ocean, and the formation and spreading of Antarctic Bottom Water (AABW). This plot shows how we can use oxygen data to infer circulation pathways in the deep ocean.
Even though oxygen and nitrate do not directly influence ocean dynamics, they tell us a lot about how the ocean moves. We can use these variables as tracers to visualize the ocean's internal circulation. Let's take oxygen for example. Above, I show a zoomed-in plot of the oxygen data from Figure 2. I have also added annotations to highlight the major overturning circulation pattern of the Southern Ocean.

The spatial patterns of oxygen concentration reveal important features of the overturning circulation of the Southern Ocean. For example, we can trace the path of low oxygen water from the intermediate depths southern Indian Ocean as it moves southward and rises to the near surface layers of the Southern Ocean. Additionally, this oxygen data reveal the formation and spreading of Antarctic Bottom Water (AABW). AABW is created during sea-ice formation in certain locations around Antarctica. As sea ice forms, it leaves behind a residue of highly saline water called brine. This brine is cold, salty and much denser than all the seawater around it. As a result, it sinks to the bottom ocean, carrying with it high concentrations of oxygen from the surface. This is why the deepest waters of the global ocean have higher oxygen levels than the waters at intermediate depths.

There is a lot more to be said about this dataset (people have spent their entire careers analyzing these data), however I will now switch focus to our float data. We deployed our floats at stations 11, 25, 36, 41, 48 and 56. These locations represent different dynamical and biological regimes of the Southern Ocean. The nice thing about deploying floats at a CTD/rosette station is that it allows to compare the initial float data with shipboard measurements from the rosette. Shipboard data are of the highest quality available, so they provide the best benchmarks for our floats.

Figure 6: Comparison of the first profile from float 9602 (aka Eep) with shipboard data from the station where the float was deployed. The solid lines represent the float data. The other lines represent the CTD/bottle data from station 36. The shipboard nitrate and oxygen measurements were obtained from discrete bottle samples, collected at 36 different depths in the ocean. These are represented by circles. 
The first comparison is for float 9602, otherwise known as Eep. Eep was deployed at station 36, which (at the time) was in the center of a very active eddy field (see Figure 4). Several hours after Eep made its splash, it reported its first profile of the upper 2000m of the ocean. The plot above compares Eep's inaugural profile with the shipboard data we collected at station 36. Overall, the two data sources compare remarkably well. The floats were able to capture the general profile patterns of the temperature, salinity, oxygen and nitrate at this particular location. There are notable disagreements, but the magnitude of those discrepancies are only a few percent of the measured values. I should add that both the float and ship-based data are still raw and will undergo further processing.

Figure 7: Like Fig. 6 but for float 9637 aka Z-Pod. These comparisons, while not perfect, are very encouraging and show that our floats are working well.

The second comparison is for float 9637, aka Z-Pod. We deployed Z-Pod at station 41, which was also situated in the middle of a very active eddy field. Like Eep, Z-Pod did a pretty good job of capturing the basic profile patterns of temperature, salinity, oxygen and nitrate at this location. As before, the comparisons are not perfect, but this could be due to natural processes. For example, being in active eddy field, the float could have easily drifted into an eddy, carrying water from a different region. However, some of these discrepancies are bound to be due to instrument error and bias. But at this stage, all we can do is speculate. More analysis needs to be done

I have done similar comparisons for the other floats and the stories are the same. The floats are working well and they are reporting reasonable data, which is very encouraging.

Again, there is a lot more to be said about this data but I will end my discussion here. I am really excited of all this new data and I look forward to monitoring these floats over the next few years. Even though the cruise is over, my work is just beginning.


1 On the y-axes, I actually plotted pressure in units of deci-bars (db) instead of depth in meters (m). This is a common practice in physical oceanography, for reasons I won't get into. It just so happens that ocean pressure (in deci-bars) and depth (in meters) are numerically similar. For example, in the Southern Ocean, 1000 db is roughly equal to 990 m. Therefore, for the purposes of this discussion, you can think of depth (m) and pressure (db) as being interchangeable.

2 Another technical side note: Here, I actually plotted potential temperature which is slightly different from normal temperature. This again has to do with pressure. Potential temperature accounts for the fact that water warms under compression. This effect creates the false impression the ocean is being warmed from below. By using potential temperature, we remove the effect of warming due to compression.

Tuesday, March 15, 2016

A day in the life of a CTD watch - part 3/3

We are almost back to shore!

In about 12 hours, we will return to Fremantle for the final stop of the I08S cruise.

It’s hard to believe that the cruise is almost over. Just 10 days ago, in the midst of our caffeine fueled, non-stop sampling expedition, my time on this ship felt like it would never come to an end. But looking back, two days removed from our last station, those 25 days of sampling are already starting to feel like a distant memory. It’s funny how the mind works.

This cruise has been an overwhelmingly positive experience for me. Never have I learned and accomplished so much in such a short period of time. In hindsight, I am amazed at how quickly we, the CTD watch, went from being complete neophytes at sea to being reasonably competent sea-going oceanographers. Now we can sling together bowline knots and tag-line several tons of oceanographic equipment like it’s nobody’s business. 

OK, that's enough nostalgia for now. The purpose of this blog post is to finish my description of what we do as CTD watch standers. I’ve already talked about how prep, deploy and recover the rosette. Here, I will show you how collect water samples.

Water floweth from the rosette.
When I said our lives revolve around the rosette, I meant that literally. Our rosette has 36 Niskin bottles, numbered 1-36, arranged in a circle. The bottles are sampled sequentially. For a particular station, we may collect as many as 12 different samples on every Niskin bottle. On a full station, we collect samples for CFCs, oxygen, dissolved inorganic carbon (DIC), pH, alkalinity, oxygen and nitrogen isotopes, dissolved organic carbon (DOC), radio-carbons, nutrients, chlorophyll and salinity (check out this cruise blog post for more info about why collect these samples). Since some analyses are sensitive to atmospheric exposure, samples have to collected in a specific order. CFCs and oxygen always go first.  They are followed by DIC, pH, alkalinity and the list goes on. 

Whatcha looking at? Andrew Barna collecting samples to measure oxygen concentration.
At first, the whole process might seem chaotic. There is a lot of shouting, bumping and swaying as people try to fill their sample bottles while the ship is moving at full speed. On the busiest days, the atmosphere inside the sampling room has the same buzz as a Farmer’s market on a Saturday morning.   

Alison being sample cop. Be careful or she might write you a ticket.
However, there is order to this apparent pandemonium. Everyone knows what to do and is aware of the order in which things must happen. As a fail-safe, there is always a “sample-cop” who keeps track of what everyone samples and issues permission to sample a specific bottle. On our shift, Alison usually plays the role of sample cop, but occasionally (usually when relatively few samples are being collected) she would delegate this responsibility to one of the students on the CTD watch.

Natalie filling in as sample cop. When it's not too crazy, Alison lets one of us be sample cop.
Sampling the rosette can take anywhere from 45 minutes to two and half hours, depending on how many people show up and the number of samples they collect. This also depends on how close we are to meal time.

Maverick, Dave and David huddling around the rosette to collect their samples.

John Ballard collecting samples for nutrient analysis. Nutrients people like to work alone.

Joseph Gum treating his samples for oxygen analysis.
By my description, you might think this is mind-numbingly repetitive work. It is, BUT there is rarely a dull moment in the sampling room. The rosette is somewhat of a social hub. Besides, the mess hall, this is the one place on the ship where all the science party congregate regularly. While stand around the rosette, we share stories and tell jokes to let time slip by faster. In our boredom, we even created names and elaborate backstories for some of the Niskin bottles. It’s all in good in fun and it makes what could easily be a miserable chore something that we actually look forward to doing.

Drip, drip, little April shower! Natalie and Sarah having good time while filtering their radiocarbon samples . 

Andrew and David sharing a laugh.

Dave "poisoning" his alkalinity sample.

Charlene, the CFCs queen, doing her last lap around the rosette on this cruise

Me (yellow bib) about to collect my last nitrate sample.
Once all the samples are collected, we dump the excess water and start prepping for the next station, which at that point is often less than an hour away.

Dave emptying the Niskins at the end of sampling session as Natalie starts prepping the rosette for the upcoming launch.
I hope this series of posts gave you a feel for the work we do on a research vessel. After conversing with some of the more senior scientists, I have to appreciate how hectic and taxing this cruise has been. Since our stations are relatively shallow and closely spaced together, the sampling never really stops. As soon as we are done with one station, we are pulling up to the next. I am reassured by my colleagues that not all cruises are like this. Even still, this cruise has whet my appetite for more time at sea.

That's all for now. As this cruise comes to an end, I will also try to wrap up this blog. It has been a great pleasure sharing my experience with all of you.

Till next time,

Sunday, March 13, 2016

A day in the life of a CTD watch - part 2/3

At the end of the first part of this post, I started to describe how we recover the rosette from the water after a cast is complete. Just to recap, a CTD watch stander helps to get the rosette into and out of the water as safely and as efficiently as possible. We do a bit of everything. You will find us in the lab and out on the deck, doing whatever it takes to ensure that each station goes by smoothly.

Hannah getting ready to recover the rosette. Her pole has a hook at the end, which will slip off as soon as she latches onto the rosette. Photo credit: Cara Nissen.
I have already talked about how we prep and launch the rosette. Now I will describe how we get it back onto the ship. I should mention here that every crew has their own way of doing things. Even on our cruise, the day and night shift crew did things a bit differently. It all depends on who is running the show and the circumstances that they are up against. The method I describe here is the method the night shift crew used for most of the cruise.

As with the rosette launch, our job is provide stability as the winch raises the rosette into the air. The winch does all the upward lifting while we provide lateral support. Strong winds and large swells can cause the rosette to swing uncontrollably once its in the air, which is a very dangerous situation that everyone wants to avoid. It is our job to prevent that from happening.

First person perspective of a rosette recovery. Here, Dave and I make first contact with the rosette after it breaches the surface. Once we are latched in, we try to keep our ropes taut as the winch lifts the package into the air.
For recoveries, we typically use three lines of stability. We establish the first two by hooking onto the rosette as soon it breaks the surface. We do this by using long poles with hooks attached to one end; the hooks are tied off to the ship by a long rope. After we hook into the rosette, we slip our poles and wrap our ropes around a metal cleat to gain leverage. Once we are in position, we try to keep our ropes to tight as the winch hoists the rosette out of the water.

Hannah and Seth providing support during a recovery. Josh (the res-tech) directs operations. Photo credit: Cara Nissen.
As the winch lifts the rosette into the air, we (the tag-liners) try to keep the rosette stable. Above, Dave is about to latch the third hook onto rosette; Natalie and I have already established the first two lines of stability.
After the rosette clears the deck, we establish a third line of stability with another hook and rope. The first two lines can only control for swings parallel to the ship. The third line helps to damp the swings that are perpendicular to the ship. This is probably superfluous in most parts of the ocean, but in the Southern Ocean, where the currents are strong and the winds are violent, this final line of support is absolutely necessary.

Yet another recovery. Here, Natalie is the third line of support. John (white helmet) is the on duty res-tech who directs operations from the ground. This is one of the many night recoveries we did on this cruise.
With all three lines of support providing lateral stability, the winch operator slowly lowers the rosette onto its landing pad. This usually takes a couple tries and requires a fair bit of coordination between the res-tech and the winch operator. After the rosette is safely on the ground, we strap it in and haul it into the hangar for sampling.

Day shift crew leading the rosette into the hangar where the samplers await. This is not as hard as it looks. The rosette sits on a moving track that is powered by a motor. We sometimes need to give it an extra push to get over small bumps. Photo credit: Cara Nissen.
In the next installment of this series, I will describe how we collect water samples from the rosette. That's all for now!

Dave and Maverick collecting samples from the last cast. 


Saturday, March 12, 2016


Natalie with the last salts sample of the cruise. I surmise that her expression is a mixture of relief, happiness and sadness (that this is all over). I think we all felt the same way.
You read that right. After 83 stations and 25 days of almost non-stop sampling, the science portion of the I08S cruise has finally come to an end! Ok, that's not entirely true. We may have done our last station, but there is still a lot of work left to do. Some groups have to do underway samples on the transit back to Fremantle. Additionally, there is the whole business of trying to make sense of all the data we collected. One could argue that the science is just beginning. But for now, we will just savor the moment.

The night-shift CTD watch enjoying a well-deserved rest.

Sunrise after our last night of sampling. We are now heading east back to Fremantle.
We have a four day transit back to Fremantle. Over that time, we will try to rewind our body clocks to a normal sleep schedule while trying to get our belongings in order for the final disembarkation. I will also try to wrap up this blog. I have few more posts in the works that I hope to publish within the next week.

Stay tuned for more. We are almost at the end  - at the end of this chapter at least.


Thursday, March 10, 2016

A day in the life of a CTD watch - part 1/3

One of the last wandering albatrosses we saw on our cruise, captured here at about 40S in the southern Indian Ocean. This species has a strong preference for the cold, deep waters around Antarctica.
The last series of posts have been about Argo floats. Deploying these floats for SOCCOM was one of my responsibilities onboard the Revelle. However, I have spent the vast majority of my time on this cruise working as a CTD watch stander. I am one of five CTD watch standers on this cruise. We are divided into day and night shifts. Seth and Hannah work on the day shift, from noon to midnight; Natalie, Dave and I work on the night shift, from midnight to noon.

The starry eyed night shift watch. We love to have meetings at the top of the rosette - not really. Photo courtesy of Joseph Gum.
As watch standers, our lives revolve around the rosette. We assist with all stages of the rosette's deployment, recovery and sampling. Additionally, we work closely with the chief scientist and help her in whatever way we can. You can think of us Santa's little helpers. On the busiest days a normal day, we work continuously throughout our shift.

The rosette. Unfortunately, we lost this one, and all of our best instruments, to the ocean; it is currently sitting on top of the Kerguelen Plateau. It was a huge loss at the time, but the crew managed to assemble a second rosette from spare parts in less than 24 hours. It was a remarkable accomplishment.
This is the rosette that took us through most of our cruise. Even though it was a backup, it has served us quite well.
My days begin at around 11pm, an hour before my shift starts. I usually get a cup of tea and a light meal before heading to the lab. At 11:50pm, we switch off with the day shift and pick up wherever they left off. More often than not, we take over in the middle of a sampling session so we have to be ready to go the moment our shift starts.

Natalie inspecting the rosette before deployment.
One of the main tasks of the CTD watch is prepping the rosette for deployment. We begin this process 30 minutes before arriving at a station. This involves cocking each Niskin bottle open, closing all the spigots, sealing all the vents and inspecting the rosette for any potential malfunctions. When that's done, we walk around the rosette to double check then triple check that everything is in order.

Dave doing prep work.
After the rosette is prepped for deployment, we change into our deck gear to help with the launch. This is one of the more fun parts of our job. For the launch, our job is to maintain taut tag-lines as the winch operator raises the rosette over the deck. We take instructions from the on-duty research tech (res-tech for short), who also directs the winch operator.

Rosette deployment on probably the nicest day we had on this cruise. Dave, Natalie and I are working the tag lines. Our job is to stabilize the rosette as the winch lowers it into the water. John (center), the on-duty res-tech, directs the deck operations. Photo courtesy of Cara Nissen.
Rosette launch is one of our favorite parts of the job because it is an excuse for us to be outside and it makes us feel like real seamen :). I have many videos of us in action but I'll have to wait till I get to shore to upload them.

Once the rosette is in the water, we change into our normal clothes and head to the computer lab. In the computer lab, we sit at the CTD console, which is a checkerboard of monitors that displays live readouts from the rosette's instruments. For this part of the job, we monitor the rosette as it moves through the water and log all important events. Additionally, we are in constant communication with the winch operator via a speaker phone and guide him as he lowers the instrument to the seafloor.

The CTD console. This where we sit to monitor the rosette when it is in the water.
For a single cast, we lower the rosette to just above the seafloor then collect water samples as we bring it back to the surface. The trickiest part of this process is the bottom approach. As the name suggests, this is when the rosette approaches the bottom of the ocean. Ideally, we want to stop 10 meters above the seafloor, but this is easier said than done. Even though we have instruments that give us estimates of the ocean depth, none of them have the range and accuracy to be reliable on their own.

With almost $1M USD worth of instruments (literally) on the line, we can't afford to make any mistakes. If we overshoot and hit the bottom, we can damage the instruments onboard the rosette. With so much at stake, we are always supervised when doing bottom approach.

Alison draws near to supervise bottom approach.
We use two main instruments to guide the rosette to the bottom. The first is the shipboard multi-beam sonar. The multi-beam is mounted on the bottom of the ship and faces the seafloor. It works by sending a pulse sound waves at a specific frequency into the ocean then listening for the same pulse after it reflects off the ocean bottom. With knowledge of the speed of sound through seawater, the echo's arrival time, the multi-beam can produce an estimate of ocean depth.

The ship's multi-beam is very useful, but it measures seafloor depth over a relatively large area. If the seafloor terrain is very rugged, the multi-beam's depth estimate may be tens of meters different from depth directly beneath the ship or rosette. To obtain a more localized depth estimate, we use an altimeter that is mounted on the bottom of the rosette.

The altimeter onboard the rosette works in a similar fashion to the shipboard multi-beam. However, it is much smaller than the shipboard multi-beam and not nearly as powerful. The altimeter we have been using for most of the cruise can only detect the ocean bottom from 50 meters away. But once it does, it produces the most accurate estimate of distance to the seafloor.

Hannah working at the CTD console. Courtney provides expert guidance as Charlene looks on.
Under the normal circumstances, the multi-beam's depth estimate is good enough to get the rosette close enough to the bottom for the altimeter to kick in. From there, we rely entirely on the altimeter to safely get us to 10m off the seafloor.

To complicate things even further, both the altimeter and ship board multi-beam are known to "misbehave" and produce incorrect information at any given time. On rare occasions, we have to resort to old bathymetry maps to help us figure out the true ocean depth. This was a bit overwhelming at first, but after a few days on the job we learned how to weigh all pieces of information appropriately and make the right decisions.

Once we safely lower the rosette to 10m off the ocean bottom, we fire the first Niskin bottle to collect a water sample. After logging some notes, we then instruct the winch operator to raise the rosette to a new depth, where we would fire another bottle to collect another water sample. We usually do this for 36 different depths, the last one being at the surface.

Lowering the instrument to the ocean bottom and bringing it back to the surface usually takes about 3 hours. It can be a tedious process, but everyday presents a new challenge (usually in the form of equipment malfunction), which keeps things interesting.

As the rosette approaches the surface, we grab our life vests and helmets to help with the rosette recovery. This where we literally get to snatch the rosette out of the water. It's my favorite part of the job. However,  I'll continue this discussion in my next blog post, where I will also describe how we collect samples once the rosette is back on the ship.

Day shift crew recovering the rosette at the end of a cast.
Until next time,

How Argo floats work: words plus an animated explanation

Now that all of our floats are in the water, what happens next? Throughout this blog, I have described bits and pieces of how Argo floats work but I think we're a bit overdue for a complete explanation.

Kaia drifting away.
Just to recap, Argo floats are free drifting, battery operated, observational platforms that sample the upper 2000m of the ocean. On these platforms, we mount instruments or sensors that measure different properties of the ocean. All Argo platforms have a sensor called a CTD, which stands for conductivity, temperature and depth. From conductivity we can infer salinity, so a CTD is able to measure temperature and salinity at different depths of the ocean.

Schematic explaining how Argo floats cycle through the ocean. Source:
Argo floats are programed to sample the ocean on a 10 day cycle. The floats spend most of their time "parked" at a depth of 1000m. In this state, they floats are in hibernation mode and simply drift with the prevailing currents. However, every 10 days or so the floats wake from their slumber to begin sampling.

To initiate sampling, the float first descends to its maximum depth of 2000m. From there, the CTD switches on and begins recording temperature and salinity. The float ascends to the surface while measuring temperature and salinity along the way. When the float reaches the surface, it transmits its most recent data to land via satellite. The engineers at the UW lab receives this data instantly. When the data transfer is complete, the floats descends back to its parking depth to repeat the entire process. The entire cycle is depicted in the schematic above. Each float is designed to last 5-7 years, so they produce about 200 ocean profiles in their lifetimes.

This is the standard operation of a normal Argo float. One thing to note is that these floats have no propellors. They rise and sink through the ocean by changing their density. Each float is equipped with a bladder (a thick balloon) that is connected to a pump inside the float. The bladder is located in a chamber at the bottom of the float, which has a small opening to allow water flood in. By inflating its bladder, the float effectively expands its volume, becomes less dense and moves up through the ocean. When it deflates its bladder, the float decreases its volume, becomes less dense and sinks.

That's basically how a float works. If that wasn't clear enough, I think a certain video will do the trick. Michelle Weirathmueller is a talented graduate student in our department who makes amazing animated videos about oceanography. Not too long ago, she did an animated short explaining how Argo floats work. Please checkout her blog post!

My explanation and Michelle's video only discuss regular Argo floats. The floats we deploy for SOCCOM are a bit different. The first difference is that most SOCCOM floats have ice avoidance capability. Normal Argo floats need to transfer their data every 10 days, but due to the presence of sea ice, this is not always possible in the Southern Ocean. The float cannot transmit its data through ice and if it tries to penetrate its way to the surface, it will likely damage itself.

If the water temperature is very close to the freezing point (approximately -2 degrees celsius), it is usually a good indicator of sea ice. In this scenario, the float retains its data and returns to its parking depth before reaching the surface; they usually turn back at a depth of about 15 meters. Currently, these ice-enabled floats are able to store a year's worth of profiling data before running out of storage space. Whereas normal Argo floats report their data every day, we sometimes don't hear back from SOCCOM floats for several months.

Rick showcasing the difference between the internal electronics of a SOCCOM "bio-Argo" float (left) and a regular Argo float that only measures temperature and salinity (right).
Another special feature of SOCCOM floats is that they have additional sensors to measure biological activity in the ocean. These extra sensors measure oxygen concentration, nitrate concentration, pH, chlorophyll and backscatter.

One of the ultimate goals of SOCCOM is to further our understanding of the ocean's biological pump. The ocean's biological pump is an immensely important concept, but I won't get into its details here. In short, the biological pump refers to the cycling of carbon between the atmosphere and the deep ocean. Since carbon dioxide is involved, this process has a huge impact on the global climate.

It just so happens that a huge portion of this ocean-atmosphere carbon exchange occurs through the Southern Ocean. This is linked to the large scale upwelling of nutrients and deep water formation I mentioned a couple blog posts ago. Direct observations of the ocean's biological pump is very sparse, but these ice-enabled, bio-Argo floats will allow us to observe these processes in near-real time, throughout the year. This is a huge step forward.

That's all for now! At some point, I will share some of the data we have received from the floats we just deployed.


Sunday, March 6, 2016

Hello, southern Indian Ocean.

Southern Indian Ocean sunrise. We got to sample with this view in background.
It's getting warm again! That's what I said when the outside temperature rose above 50 F (10 C). It's funny how a trip to the Antarctic can completely changes your perspective on things. We crossed into  the balmy subtropics a few days ago, which means we can finally stash away our heavy thermal layers and foul weather gear.

Natalie and Dave are super excited to be out of sub-freezing weather.
After an eventful and turbulent two weeks in the Southern Ocean, operations onboard our ship are going much more smoothly. Early on, we suffered setbacks to due to major equipment loss and failure. However, due to the resourcefulness and commitment of everyone onboard, we overcame our hardships. We have now completed 63 stations with 7 days of sampling to go. This puts on track to finish most, if not all, of the 89 stations we originally set out to complete. Everyone is crossing their fingers for a seamless finish to our cruise.

The final unboxing.
My friend Kaia. She was the last float to be deployed on our cruise. Photo courtesy of Cara Nissen.
In other news, we deployed Kaia yesterday!! Kaia was the sixth and final float deployment of this cruise. Everything went smoothly from start to finish. Our float even got a final farewell from a curious albatross. Special thanks to Cara Nissen for being out on the deck to capture the moment! All these deployment photos came from her camera.

Dave helping me with the deployment. 

And down she goes. This is so much easier when the ship is not heaving several meters in the air. 
I'm a bit bummed that the deployments have come to an end because I was just starting to get the hang of it. I was hoping for more opportunities to deploy with the other students onboard, but the Southern Ocean is a tough place to learn. There will always be next time.

Splash down. Kaia was safely released into the water.

[Cue jaws soundtrack]. Don't worry, the float and was fine. The albatross kinda just sat there and watched this weird looking fish sink from the surface. This is actually a photo of Z-Pod.

In other good news, we have been receiving some great data from the floats we just deployed. I'll blog about them in another post.