Whales, dolphins, and seabirds, oh my!

RVOceanStarr-1

Hi all! I’m on a ship called the R/V Ocean Starr, and we’re out on the 2014 California Current Cetacean and Ecosystem Assessment Survey, or CalCurCEAS for short. We are collecting data that will allow NOAA scientists to estimate the abundance of whales and dolphins off the west coast of the U.S. They’ll also be able to use these data to better understand what affects the distribution of marine mammals – where do they like to hang out, and why? We’re gathering this data using two primary methods: visual and acoustic, and are also conducting photo-ID and biopsy sampling of species of special interest.

In addition to the marine mammal portion of the survey, we’re looking at the pelagic ocean ecosystem in the region.  This means taking measurements of various properties of the water, doing net tows, and using acoustic backscatter to look at biomass in the upper part of the water column. There are also two observers onboard to survey seabirds.

I’m out here with an awesome science team and a great crew. There are two other acousticians besides me: Emily T. Griffiths and Amy Van Cise. Emily has been onboard for the first two legs. She makes sure we stay on track and don’t get into (too much) trouble. Amy is a PhD student at Scripps Institution of Oceanography studying pilot whales, and she’s here for the third leg of the cruise, just like me. The three of us all love ice cream and get along famously.

I have one or two shiny new blog posts that I’m hoping to share soon (with comics! woo!), and I might even have a couple of surprise guest posts! Stay tuned…

Harmful algal bloom forecasting: Chasing toxin producers

It started with “drunk” pelicans. While studying aquatic sciences at the University of Santa Barbara, Liz Tobin noticed that there was something wrong with the fish-gulping birds.  They exhibited unusual behavior, getting hit by cars, and sometimes simply falling out of the sky. The pelicans suffered from seizures induced by domoic acid poisoning, a particularly dangerous affliction when it hit mid-flight.  Biologists traced the source of the poisoning to rapid springtime growth (bloom) of Pseudo-nitzschia, a tiny, single-celled organism, distantly related to the giant kelps thriving in nearby coastal waters.  Small fish and shellfish consume these algae, and although they are not harmed, they store the toxins produced by algal cells and pass them on to their predators, including seabirds and marine mammals.

Scientists refer to these incidents as harmful algal blooms, or HABs.  They are not restricted to the waters of southern California, though.  And Pseudo-nitzschia cells are not the only culprits.  There are a number of other algal species that can cause trouble for local marine ecosystems. HABs occur in coastal waters around the globe, with larger and more frequent blooms being linked to a warming sea surface [1] and also to increased nutrient runoff from land [2], which is a common by-product of animal or plant agriculture.  Local economies suffer due to tourism losses and local residents can’t harvest shellfish from their beaches.

After wrapping up a bachelor’s degree at UCSB, Liz moved on to graduate school at the University of Washington so that she could study harmful algal species in Puget Sound.  One of the species she’s interested in is Alexandrium catanella, another single-celled marine alga that produces a suite of deadly neurotoxins causing paralytic shellfish poisoning, or PSP.  Alexandrium blooms can become so intense that they give the water a reddish-brown tinge, often called a “red tide” (although they don’t always cause water discoloration).

Oysters

If you eat a shellfish that has accumulated Alexandrium toxins, a series of unpleasant events unfolds. First, your fingers and toes will tingle and your lips will feel numb.  Next, you may become nauseous and unsteady on your feet.  If the toxins hit you at full force, your diaphragm will become paralyzed, which means that you are unable to pull oxygen into your lungs.  Without prolonged artificial respiration, a severe case of PSP can lead to death in a matter of hours.

In recent years, poisoning cases in Washington State have been rare, but they do happen. Washington Department of Health aims to prevent outbreaks by regularly testing shellfish along Puget Sound beaches.  Commercially harvested shellfish are tested exhaustively before hitting the markets. Unfortunately, it’s tough to predict the severity, location, and timing of an Alexandrium bloom ahead of time. That’s where Liz’s work fits in: she’d like to improve our ability to forecast where those blooms will happen ahead of time so that public health officials, fisheries managers, and the shellfish industry have more time to react.

LifeCycle

Alexandrium cells have a comfort zone, she explains.  They grow and divide furiously when the days are long and the surface waters are warm.  Once the spring bloom ramps up, zooplankton, fish, and shellfish feed on the algae, eventually decimating Alexandrium populations by early to mid summer.  Less Alexandrium cells means less food for their predators, and their predators begin to die off or find food elsewhere.  By late August, with newly lowered predation pressures and plenty of sunlight, a second bloom typically occurs.  As the season draws to a close, Alexandrium  algal cells feel the effects of shorter days and less sunlight.  They struggle to grow and divide and at some point cut their losses and transit down to the sediment to wait out winter.  -Settled into the muddy seafloor, they shift to survival mode, also known as the “cyst” stage.  The exact conditions that send them into their cyst stage are poorly understood, as are  the details of how they wake up and make their way to the surface come springtime.

Liz is particularly interested in how the Alexandrium cells swim, even though they are mostly at the whim of the currents.  Tides rush in and out twice each day, racing through narrows and washing languidly over mud flats.  Rivers pour into Puget Sound with irregular pulses of freshwater from rain and springtime snow melt. Alexandrium algal cells propel themselves through the water using a small whip-like appendage called a flagellum, but because of their tiny size – only about a third of the width of a single human hair – they can’t overcome even the weakest currents. However, if Liz knows their vertical swimming capabilities, she can better understand how quickly Alexandrium cells migrate from the seafloor to the surface (where blooms occur) and back again.

A lot of researchers, Liz included, study Alexandrium in the lab.  They blend solutions of water and various chemicals to imitate seawater, and observe how the cells behave and react to a variety of environmental triggers.  One of the labs she works in is a tiny bunker-like space on the second floor of the Ocean Teaching Building.  Two long black tables running along either side of the room are covered by a hodge-podge of beakers, elaborate video recording setups, and circuit boards sprouting nests of red and white wires.  At the back of the room, a giant insulated door opens to a fully programmable walk-in refrigerator, where algal cells can be subjected to controlled shifts in temperature and light.

Even at their best, however, lab experiments can’t possibly recreate the many complexities that exist in the natural world.  Liz knew that if she could monitor the emergence of the Alexandrium cells from the sediments she could combine those observations with detailed fluid flow models to better predict where the cells would eventually concentrate.  The only problem was that there were no “off-the-shelf” instruments that were capable of doing what she wanted.  So she set out to build her own.

soldering

When she starts describing the instrument she’s working on, I interrupt.  Pushing my notebook and pen across the table, I ask her to sketch her design for me.  She draws a tube a few inches in diameter, sitting upright on the seabed.  On one side of the tube a camera in waterproof housing points into a tiny window to capture any Alexandrium cells swimming past.  The end of a plankton trap sits on top, ready to catch any upward-swimming cells so they can be later compared with the video. She pauses her drawing to look up at me.  “It’s just like what we would do in the lab,” she says, “but instead of a camera looking at a tank, I have a camera looking into a chamber on the seafloor”.

As of mid-July 2013, Liz’s prototype of her seafloor camera was nearly ready to be deployed for testing.  If it works, she’ll try to capture Alexandrium cells emerging from the seafloor just prior to the late-summer bloom.  Her vision for the future, she tells me, is a network of these instruments deployed across Puget Sound, monitoring cyst emergence in real time.  Instead of only knowing about blooms once they are in full swing, they could be predicted days or weeks in advance, avoiding unnecessary closures and potentially saving lives.

[1] Climate change and harmful algal blooms, NCCOS http://www.cop.noaa.gov/stressors/extremeevents/hab/current/CC_habs.aspx

[2] Anderson, Donald M., Patricia M. Glibert, and Joann M. Burkholder. “Harmful algal blooms and eutrophication: nutrient sources, composition, and consequences.” Estuaries 25, no. 4 (2002): 704-726.
http://www.whoi.edu/fileserver.do?id=47044&pt=2&p=28251

 

Whales in a Noisy Ocean

Noisy-Neighbors_600px

In the ocean, sound rules.  Unlike on land, where animals (just like us humans!) get a lot of information from light, animals in the ocean have evolved to take advantage of sound, which is much more effective than light under water.  Light gets absorbed quickly, but some sounds, like the low-frequency calls of blue whales, can travel hundreds of kilometers under water, under the right conditions.

Whales have developed really fascinating ways of using moans and clicks and songs to help them get the things they need in life – friends, mates, food… what more could a whale want?  Some whales find food by making sounds and then listening for echoes that bounce off of their prey.  Using those echoes, they can figure out where their food is (mmm, delicious fish!).  Whales can also use sound to communicate with each other.  A mother and calf might need to keep track of each other as they swim.  Or a male might show off his sweet singing voice to attract a female.

comms3panel

Unfortunately, noise in the ocean is on the rise, and it’s making life tougher for whales. Some of the sources of human-caused noise include ship traffic, seismic exploration for oil & gas and sonar testing. It’s worth noting, though, that there is noise in the ocean that is not caused by humans. Earthquakes, volcanoes, breaking waves, rain and even lightning are some of the things that add to the background noise. The thing is, whales have spent thousands of years evolving to deal with these natural noise sources – but in the last few decades they have suddenly had to get used to the growing din caused by human activities. And, as Chris Clark from the Bioacoustics Research Program at Cornell University explains, “it’s not just one ship. It’s ten thousand ships”. It’s the same as if only one person litters on the side of the road, it might not be such a big deal. The problem arises when everyone does it, all at the same time.

Noisesources

Scientists are still not sure exactly how noise affects whales – different whales might be more or less sensitive to particular sounds, and might respond in different ways. For example, right whales in the Bay of Fundy showed lower levels of stress hormones when ship traffic stopped briefly following the 9-11 terrorist attacks [1]. Killer whales off the coast of Washington state and British Columbia have increased the volume of their calls so that they can be heard above vessel traffic [2]. And in the most severe cases, some beaked whale strandings have been linked to mid-frequency naval sonar operations [3].

Excessive noise in the ocean causes a sort of masking effect – meaning that the noise is loud enough that the whales can’t hear what they normally would need to hear in their environment, whether it’s echoes from fish, or a signal from another whale. Not being able to find a mate or find food or find each other is a serious problem, especially for species that are already endangered.

But there is still hope. Now that we’re starting to realize how harmful noise can be, we’re finally in a position to actually do something about it. Small steps can make a big difference. Even slowing ships down can substantially reduce the overall noise. In recent years, the US Navy has funded a lot of basic research that has taught us a huge amount about how marine mammals hear and use and produce sounds. We’ve still got a long way to go, but now that we’re aware that there is a problem, we can work on ways to fix it.

This post was done with help from Chris Clark and Kevin White from the Bioacoustics Research Program at Cornell University.  The PDF version can be downloaded here.

References

[1] http://news.sciencemag.org/sciencenow/2012/02/shhh-ocean-noises-stress-out-wha.html
[2] Holt, Marla M., et al. “Speaking up: Killer whales (Orcinus orca) increase their call amplitude in response to vessel noise.” The Journal of the Acoustical Society of America 125.1 (2008): EL27-EL32.
[3] D’Amico, Angela, et al. Beaked whale strandings and naval exercises. Space and Naval Warfare Systems Center, San Diego CA, 2009.

Seismic tomography: the easy way

When I was an undergrad, I had to take a year of geophysics, and on the first day, the professor explained that geophysics meant finding things underground without digging.  The rest of my lab group here at the UW are all marine geophysicists, and they routinely have to find things underground without digging, but with the added complication of having to get through a couple of kilometers of water, too.

You may remember my interview with Rob Weekly a few weeks back. This week’s interview is with my office-mate, Dax Soule. Dax studies marine geology and geophysics in the School of Oceanography at the University of Washington. Like Rob, he focuses on active source seismology. In fact, he’s looking at some of the same data as Rob, just different parts. And since we already went over a lot of the basic background in Rob’s post, I’m going to jump right into some fun tomography stuff. In a nutshell, tomography means building up a 3D picture of what’s underground by measuring how long it takes for seismic waves to travel through. In tomography, you’re not sampling the material directly, but you’re measuring how the seismic velocity varies. Seismic velocity is a measure of how quickly a seismic wave can travel through a certain type of rock, so if you know the velocity structure you can make inferences about the geological structure.

Imaging the earth’s crust

When you’re doing seismic tomography, it’s a bit like peeling back the layers of an onion: you have to figure out the shallow stuff before the deep. Rob’s work focused on obtaining a three-dimensional seismic velocity structure from the seafloor down to about 2.5-3 km depth. Dax is taking Rob’s results and extending downward to include the entire depth of the crust. He’s looking between the seafloor and the Mohorovicic discontinuity, or the “Moho”, which is the boundary between the earth’s crust and the mantle.

In seafloor maps of the region, you can see that there’s a bathymetric high – a plateau where the water depth is shallower than the surrounding seafloor. A seismic reflection study a few years back [1] showed that this plateau likely corresponds to a thickening of the oceanic crust at this location. Dax’s tomography work will help to clarify exactly what’s going on, and will give a more detailed picture of how the crustal thickness varies in the area.

Dax explained that measuring crustal thickness variations near a mid-ocean spreading center can tell you about how that crust was produced – was a episodic or constant? And where was the source of new crust – was it on the axis of the ridge, or off-axis?

How the experiment works

Here’s a little cartoon showing the basic geometry of the seismic experiment.SeismicRays_600px

A seismic source is generated near the sea surface, and the energy travels through the water column and into the sea floor. Once in the earth’s crust, the energy is converted into to types of waves: primary waves (p-waves) and secondary waves (s-waves). There are many different types of paths that these waves can take as they travel through the earth, and each type of path is known as a “phase”. In the above figure, the two phases that are shown are Pg and PmP. Rob used the Pg phase arrivals to image the upper portion of the crust. Dax looks at the PmP phases, which are the ones that bounce off the Moho.

Dax goes through the data and manually picks out the PmP phase arrival times. This part of the job is not the most exciting, but someone’s got to do it! Fortunately, all that work does pay off, and once Dax has his picks, he can start digging into the tomography part of his work.

Five easy steps
Here’s a handy-dandy summary of the steps that Dax goes through to build up a tomographic inversion.

five-easy-steps_600px

So that’s what my office-mate does… good to know!  Dax is still working through the data and the very complex inversion code, so stay tuned for a future post on what he finds deep in the crust, and what the crustal thickness can tell us about seafloor production at the Endeavour Ridge.

Reference
[1] Carbotte, Suzanne M., Mladen R. Nedimović, Juan Pablo Canales, Graham M. Kent, Alistair J. Harding, and Milena Marjanović. “Variable crustal structure along the Juan de Fuca Ridge: Influence of on‐axis hot spots and absolute plate motions.” Geochemistry, Geophysics, Geosystems 9, no. 8 (2008).

When the wall comes tumbling down: Elwha River sediment transport

Elwha River Valley from Hurricane Ridge (Photo by Steve Voght, http://www.flickr.com/photos/voght/2720398016/in/set-72157606472551601)
Elwha River Valley from Hurricane Ridge (Photo by Steve Voght, http://www.flickr.com/photos/voght/2720398016/in/set-72157606472551601)

If you live in western Washington, you are probably aware that the biggest dam removal ever done in the US is happening right in our back yard.  Nearly one hundred years ago, developers on the Olympic Peninsula wanted to harness the hydroelectric power of the Elwha River.  They built two dams: the Elwha Dam, eight kilometers upstream from the ocean, and the Glines Canyon Dam an additional thirteen kilometers further up.  Unfortunately, the builders ignored permitting requirements, and did not make any accommodation for fish passage. The dams failed a safety review in the 1970s and in 1992 Congress passed the Elwha River Fisheries and Restoration Act.  This eventually led to the decision to remove the dams entirely rather than to attempt the difficult and expensive task of bringing them up to code.

ElwhaDamFish

Together, the two dams blocked a full 90% of the watershed’s fish habitat, and were holding back enough sediment to fill more than 10,000 Olympic-size swimming pools.  Planning their removal was not a trivial task.  It’s sort of a goldilocks scenario:  take them out too quickly and there’s a danger of flooding.  But take them out slowly, and it can be bad for fish because of prolonged turbid conditions.  After much careful deliberation, a 2-year period of dam removal was deemed just right.

Elwha_map_600px

Emily Eidam is a 2nd year graduate student at the University of Washington, in the Marine Geology and Geophysics option within the School of Oceanography.  She is looking specifically at what is going to happen to the mud that leaves the reservoirs during and shortly after dam removal.  How will that sediment be transported and deposited in coastal waters?  At this point, the lower dam has been completely removed, and all that’s left of the upper dam is a short chunk due to be removed with explosives this summer.  But what a last portion it is:  piled behind what remains of the Glines Canyon Dam is the mother lode of sediment.  Once it goes, Emily and her colleagues expect a large flux of muddy sediment to flow seaward.

Emily, a geologist and civil engineer, says that this is what she’s waiting for: the big pulse of muddy sediment.  When river water flows into the ocean, it is usually less dense than the salty seawater, forming a plume over the surface.  But sometimes, as a result of a big storm or a landslide, the river water takes on an unusually high volume of sediment and briefly becomes denser than seawater, plunging down instead of floating at the surface.  Geologists know that this happens, but don’t fully understand how it works because it’s incredibly difficult to capture these super dense, or hyperpycnal flows.  They don’t happen often, and when they do they only last for a few hours to a few days.

elwha-plume
Sediment plume flowing out from the Elwha River into the Strait of Juan de Fuca (http://gallery.usgs.gov/photos/10_22_2012_kof6IVt22C_10_22_2012_0). This is a surface plume, and although this aerial photograph looks dramatic, it’s difficult to tell where all that sediment will be deposited without taking in situ measurements.

In a way, the Elwha River dam removal provides the perfect opportunity to study hyperpycnal flows, because it’s creating ideal and predictable conditions for such flows to happen.  To ensure that they capture an event, Emily and her lab group have rigged up special tripods that sit on the seafloor and measure, well, just about everything a marine geologist could possibly want.  Video cameras record suspended sediment particles.  A variety of oceanographic sensors measure everything from temperature and salinity to current speed throughout the water column.  The “murkiness” of the water is estimated using instruments that send out a burst of light, and measure how much is scattered back by suspended particulate matter.  Sediment collected in traps provides data on size distributions of settling material.

hyperpycnal

In addition to the data collected on the tripods, Emily and her lab group conduct ship-based surveys several times per year, taking additional oceanographic measurements, and also collecting sediment samples from the seabed.

Because of the difficulty in predicting when and where they’re going to happen, real-time measurements of hyperpycnal flows are sparse (at best) – so capturing one will be amazing!  But in the meantime, they are collecting an enormous dataset that can be used to understand where sediment leaving the river gets deposited, and how it gets there.  Most of us don’t spend much time thinking about how sediment from a river becomes part of the seabed, but understanding how it works can help scientists interpret geological records that contain clues about ancient coastlines and rivers, changes in sea level, and even past climate.

Want to keep up with Emily and her lab group’s adventures?  Check out their website and blog.  The Elwha project was also recently featured on UW News.

Learn more about Elwha River history and dam removal:
http://www.elwhabiodiversity.org/elwha/
http://www.video-monitoring.com/construction/olympic/js.htm
http://www.coastalwatershedinstitute.org/projects.htm
http://www.pbs.org/americanfieldguide/teachers/salmon/history.pdf

claimtoken-515c64eba5e9b

Diatom survival: It’s in their genes

Please welcome Sara Bender to the Science+comics interview series!  This week we’re taking a peek into the world of diatoms, and how they take up nutrients. Check it out!


Diatoms are tiny, single celled organisms that live near the surface of the ocean.  They are a type of phytoplankton, which are small, drifting organisms that form the base of the marine food web.  Many of them are so tiny that they can’t even be seen with the naked eye – even smaller than the width of a human hair.  Although they are not plants, they use photosynthesis to drive their metabolic processes, taking in carbon dioxide and releasing oxygen.  Also, like plants, they need nutrients such as nitrogen and phosphorous to survive.  Because of coastal upwelling and runoff from land, shallow, coastal regions tend to have the highest nutrient concentrations, and also the highest diatom concentrations.

Sara Bender studies phytoplankton ecology with the Armbrust Lab, and is a PhD student in her final year of Biological Oceanography at the University of Washington.  One of the things that Sara has looked at is how diatoms take up nitrogen. How do they do it, and how have they adapted to the conditions that exist at different locations? Sara has looked at three species in particular, all from very different environments. In a way, these species are sort of like the “lab rats” of the diatom research world, and many researchers have used them for experiments in the past and present. Let’s meet Sara’s special “pet diatoms”, shall we?

Diatom-characters

Now, here’s where Sara’s research gets really interesting: she uses cutting edge techniques developed for the medical field, and applies them to her pet diatoms. Her advisor, Ginger, along with a team of researchers, actually sequenced the very first diatom genome (Thaps) in 2004! Since then, both Fracy and Psemu have also had their genomes sequenced, and the number of diatom genomes is on the rise!

So how does Sara use these genetic sequences to learn about diatoms? Well, let’s back up a bit and talk about what is in a genome. DNA is made up of a specific sequence of nucleotides. You can think of these nucleotides as a very short alphabet – one with only four letters: A, T, C, and G. These letters are grouped together into genes that form the genome, which contains information that the cell can use to carry out different operations. Sara is interested in a particular type of operation: she wants to know how diatoms pull nitrogen out of the water. She asks questions like: how have different diatoms adapted to different conditions? And how might diatoms respond if conditions change in the future, as a result of climate change, for example?

diatom-genes

Sara looks for similarities and differences between genes from her three test species. And as it turns out, just because different organisms have some of the same genes, it doesn’t mean that they express them in the same way – or at all. After looking at which genes are present, Sara is able to form hypotheses. For example, let’s say that one diatom has ten of a specific type of nitrogen transporters, and the other two diatoms only have one of those, you might guess that the diatom with the ten transporters had to adapt to some particular condition in its environment.

Diatoms-chat

To test her hypotheses she looks at the next step in the process: the gene transcription step. This is where the information contained in genes gets transcribed into RNA. If this happens, the RNA can be translated into a protein, which can then be used to carry out some cell function. Sara looks at whether particular genes get transcribed in order to better understand how the cell functions under certain conditions. She can simulate different environments in the lab and then look at how the diatoms react based on the level of gene transcription.

Since diatoms play such a significant role in the marine food web, it’s really important to understand how they might be affected by changes in the ocean – whatever happens to them can have cascading effects on other organisms higher up in the food web.

Sara will be graduating this summer, and after that she’s going to the Woods Hole Oceanographic Institution (WHOI) to do a post-doc in Dr. Mak Saito’s lab. While she’s there, Sara will take her knowledge of diatom transcriptomics and translate it into studying phytoplankton proteomics- making the transition from genes to proteins. But fear not, she plans on continuing to unravel the mysteries of phytoplankton nutrient uptake in her future endeavors.

The biggest waves are the ones you can’t see!

Your weekly dose of ocean science + comics!

Name:  Andy Pickering
Job: 5th year PhD student, Physical Oceanography, University of Washington. Works with the Wave Chasers Lab at APL
Research: Ocean physics, internal waves

What lives underwater, is hundreds of meters tall, and can swipe a submarine out of its way like it’s a fly? An internal wave, that’s what! They don’t all get to be so big, but once a wave is released from the shackles of the air-sea interface, who knows what crazy things it might get up to?

Oh wait – Andy Pickering knows! He and his lab group study internal waves. Internal waves are kind of like surface waves – they need that density gradient to even exist. So in order to figure out how they propagate under water, Andy needs to know how the density varies underwater. There is often a surface mixed layer where the density is constant for tens or hundreds of meters, and after that it tends to increase with depth.

Although density is a continuous function of depth, the density gradient can be modeled as a series of very thin slices of constant density. And once you do that, internal waves are no longer confined to the interface; they can propagate vertically as well. Internal waves can travel very far, and just like waves crashing on the beach, internal waves can break as they approach the seafloor.

surfing-internal-waves-no-cite

One of the very important implications of internal waves breaking is that they can cause turbulence, which has a surprisingly significant effect on ocean circulation models. Because this kind of turbulence happens on such a small scale relative to a global ocean circulation model, it’s really tough to incorporate it properly. Especially since it is not fully understood yet.

Andy and his lab group are participating in a large project called IWISE (Internal Waves in Straits Experiment). The goal of the project is to better understand the behavior of internal waves in a strait environment by taking tons of measurements in one particular strait: The Luzon Strait.

If you were ever looking for an awesome spot to find out how tides interact with shallow ridges to produce gnarly internal waves, look no further, my friend. As the tides slosh back and forth over the two ridges that run between Taiwan and the Philippine island of Luzon, enormous internal waves are generated that roll west into the South China Sea and east into the Pacific Ocean. These waves are so massive that the perturbations that they cause at the sea surface can be seen from space!

luzon-strait

In addition to all the craziness from tides barreling over the shallow ridge, there’s also the Kuroshio current to deal with. The Kuroshio is sort of like the Gulf Stream, except in the Pacific Ocean instead. It pushes warm, tropical water Northward along the western edge of the Pacific Ocean basin. Like other ocean currents, it moves around a bit over time, and sometimes it dips further into the Luzon Strait than others.

Data for the IWISE experiment were collected in 2010 and 2011, and both moorings and ship-based instruments were used. The two most important instruments for Andy’s research are the CTD (conductivity-temperature-depth sensor) and the ADCP (acoustic Doppler current profiler). The CTD measures the density of the seawater at different depths, and the ADCP measures current speed and direction at different depths. With these key bits of data, Andy can look at how the ridges affect the generation of internal waves, and even at how this Kuroshio current adds to the mix.

internal-wave-data-collection

Andy has been looking at the data and in particular at the energy flux generated by the tides colliding with the shallow ridges. He’s seeing that the ridges are actually creating interference effects because they’re so close together. Some of that energy is dissipated away locally, but Andy is also interested in looking at how much might be escaping, and whether it could make a significant contribution to deep ocean mixing.

The amount of deep ocean mixing is critically important for constraining global ocean circulation models and also global climate models so we can better understand things like climate change and global warming. So in a way, when Andy is not wasting time doing interviews with me, he’s busy saving the planet! Awesome.

If you want to know more about Andy’s lab group, the Wave Chasers, check out this pilot put together by Wide Eye Productions:  http://vimeo.com/wideeye/wavechasers.  It’s really cool, and well-worth a couple of minutes of your time.

Eavesdropping on dolphins

Please welcome my next science+comics interview victim, Alexis!

Name: Alexis Rudd
Job: PhD student in Zoology at the University of Hawaii
Research: Alexis uses passive acoustic monitoring to study whales and dolphins off Hawaii

News Flash!! Whales and dolphins, a.k.a. cetaceans, hang out near the Hawaiian Islands! Okay, not a news flash at all, everyone knows that. But you may be surprised to learn that we don’t actually know much about them – what they’re doing, where they’re going, and why – especially once you get out to the deeper rougher waters further from shore. So why is it important to know about their hangout spots and behaviors? It’s because that kind of information can help us design and implement effective management and conservation strategies. Yes, cetaceans hang out near Hawaii, and we want to keep it that way!

Here’s the thing. Whales and dolphins (and loads of other animals) like to spend time where food is available. In the ocean, the big driver behind food abundance is primary productivity – phytoplankton, or plants that live in the sunlit upper layers of the ocean. And just like on land, different places in the ocean are more productive than others: some places are lush and green with plants and all the life they support, and other places are sort of like deserts – yes, animals live there, but it’s on a whole different scale. Here’s an image of productivity (actually, it’s an indicator of productivity – chlorophyll concentration, which satellites pick up by its color).

oceandesert_600px

This picture shows green where there is a lot of productivity, and blue where there’s not much. So the deepest blues show where the ocean “deserts” are. The green places tend to be where nutrients are available – things like nitrogen and phosphate (yup, same stuff that’s in fertilizers for your garden), which might run off the land, or be brought up to the surface in upwelling zones.

But – not to worry! – it’s not exactly a dead zone around Hawaii. It just means that cetaceans might need to look for an oasis sometimes. One theory is that cold, nutrient-rich water gets pulled to the surface by cyclonic (counter-clockwise) eddies, triggering a cascade of activity up the food web – a very enticing fish/squid/zooplankton buffet indeed.

To address these kinds of theories, Alexis needs to figure out whether cetaceans are indeed seeking out certain environmental and oceanographic conditions. Often, studying cetaceans means getting on a boat and looking for them visually. This works reasonably well in calm waters, but it gets pretty tough to pick out a dolphin or a whale when the water is choppy. The prevailing winds are westerlies, and they come sweeping across the Pacific from California. Calm zones form on the leeward side of the islands, but the wind speeds up as it squeezes through the gaps, creating regions of high wind and rough seas.

windpatterns_600px

Instead of looking for cetaceans visually, Alexis listens for the sounds they make. And here’s where the super creative part of her research comes in: she tags along on a tugboat that brings supplies to the different islands. Being the persistent scientist that she is, Alexis went out every two weeks for a year and a half, installing her underwater recording package (hydrophone) on the barge behind the tugboat. This setup was ideal in a lot of ways: first of all, people need their supplies all year round, so this vessel does regular trips. Second, having the hydrophone on a barge – separated from the loud tug engines – makes it easier to pick out cetacean sounds. Here’s what the basic setup looks like:

tugboat_600px

As the tugboat moves from island to island, it provides a great acoustic “view” of a very large area – the calm leeward side of the islands and also the windier regions between the islands. So Alexis is able to get a great “big-picture” idea of what’s going on.

She’s now collected hundreds of hours (!!) of recordings, and is going through the process of checking and documenting all of the identifiable cetacean calls. She links each call up to the location where the barge was at that time so that she can gather up all the data at the end and figure out whether there are correlations between the animals’ presence and environmental or oceanographic conditions.

Alexis has an excellent and very informative blog, and I encourage you to head on over and check it out: http://bioacoustics.blogspot.com/

She also did a guest blog post over at Scientific American Blogs, where she talks about the experience of partnering with commercial shipping to do her research: Towing my weight: partnering with commercial shipping for whale and dolphin research.

By the way, this is how an ocean themed interview should be conducted:

pirate_interview

… with pirate hats all around.

Marine seismology with Robert Weekly

Introducing our very own Robert Weekly – that’s right, he’s the first science+comics interviewee from within our “quakes and whales” lab group!

Name: Robert Weekly
Job: Graduate student – Marine Geology & Geophysics, University of Washington School of Oceanography
Research: Marine geophysics, mid-ocean ridge processes

Fifty-some years ago, if you’d assumed that the seafloor was a vast and immovable backdrop to the rolling sea above, you wouldn’t have been alone. It wasn’t until the mid-1960s that scientists started seeing evidence that tectonic plates were shifting entire continents and ocean basins. Part of the reason that it wasn’t more obvious before was the incredibly slow rate of new crust formation: we’re talking a few centimeters per year, about the same speed that your fingernails grow.

globalMOR

Oceanic crust is constantly being created and destroyed at plate boundaries. Many of us who live near subduction zones are familiar with the effects of oceanic lithosphere plunging under continental or oceanic crust – and the resulting large volcanoes and devastating earthquakes that put many people at risk. The creation of new seafloor, on the other hand, happens along a vast mid-ocean ridge system, snaking its way around the globe, like stitches on a really messed up baseball (see figure above). At these mid-ocean ridges, hot material from deep within the earth’s mantle leaks towards the surface and pools into magma chambers just below the seafloor. This magma inevitably forces its way up through cracks in the seafloor, ever so slowly forcing entire slabs of lithosphere apart. This intruded magma eventually cools and hardens, becoming the newest addition to the ocean crust.

MORdiagram

In a lot of ways, the seafloor is similar to a desert: barren, stark landscapes without much in the way of life-sustaining features. Mid-ocean ridges, on the other hand, are basically an oasis – an explosion of life driven by a heat source from below. But, although we are learning more all the time, no one really understands how the underlying magma “plumbing” helps drive the system.

That’s where Robert’s research comes in. In a nutshell, Robert is trying to figure out what’s going on underneath mid ocean ridges and how that contributes to the formation of new oceanic crust. He does that by looking at how seismic waves travel through the seafloor – you can think of it like a giant CT scan for the earth – except, WAY harder because you can only look at it from one side, and it’s HUMONGOUS. Imagine a CT scanner that needed to be a hundred kilometers long. Woah.

There are two ways that he can take a peek under the seafloor (you know, without going down and digging a massive hole): using active or passive seismic experiments. And he’s done a bit of both up at the Endeavour segment of the Juan de Fuca Ridge, which is a hydrothermally active chunk of mid ocean ridge that’s just a couple hundred kilometers off the coast of Vancouver Island.

Passive-source seismology
Rob spent a long time looking at one of the largest seismic datasets out there: three years worth of continuously recorded data on eight different seismometers on the seafloor. By listening for earthquakes, it was possible to put together a picture of what was happening, in fairly high resolution, near the center of the Endeavour segment. There is a magma chamber directly under the Endeavour, feeding the hydrothermal system and supplying magma to the ridge. What you’d expect is that the magma would spread outward from that central chamber. But instead, Robert saw an unexpected intrusion of magma coming down from another ridge segment to the north!

Passive_seis_600px

Active-source seismology
This research gave some fascinating results, but ultimately brought up even more questions. And to answer those, Robert needed to look at a larger area. For that, he used an active-source seismic dataset collected in September 2009 over the same region. Active-source seismology means that instead of listening for a source, you generate your own source. In this case, it meant a sound source on a ship.

Here’s a diagram to describe how it works:

Active_seis_600px

First, an airgun is set off near the sea surface, which sends a sound wave through the water column and then down into the seafloor. The waves travel through the seafloor, taking different paths depending on the structure of the underlying crustal material. Robert can then use the signals recorded on each of the instruments to create an image of the subsurface.

All of this work brings us a little bit closer to understanding the complex geologic processes controlling the formation of oceanic crust and the accompanying biological and chemical processes that produce incredible mid-ocean ridge environments.

References

Look for Rob’s paper coming out in a special edition of G-Cubed in the next few months!