Ocean-gazing

As I have mentioned, one of my favorite parts of the cruise experience is getting outside on the deck and just staring out at the ocean.  When the ocean is flat and calm, it is a peaceful and introspective experience, and I enjoy just watching the ocean breathe (as I call it), listening to some relaxing tunes (Bonobo is still the best), and reflecting on life.  Looking out at the endless expanse of the ocean in all directions is a unique experience that just can’t be replicated elsewhere.  It’s lonely and foreboding and awe-inspiring all at the same time.  Normally, stargazing and sunsets/sunrises are another highlight, but as I’ve said those are a rare occurrence on this particular cruise.  Watching the ocean is also an enjoyable experience from a beach, but it is decidedly different out in the middle of the ocean, and usually when I’m at a beach I’d much rather be in the water than just looking at it.  One major difference that I’ve noticed is the smell.  When you’re sitting on a beach, you smell a combination of saltiness, fishiness, and sometimes a slightly unpleasant decaying seaweed/kelp smell (which I’ve noticed is stronger in CA than HI) that I had always associated with the ocean.  In the middle of the ocean, there is no saltiness, no seaweed, no fishiness, just pure fresh air with no discernable scent (besides the occasional diesel exhaust).  Whenever I’m out on deck, I’m always hoping to see sea life, but those hopes are unfortunately rarely satisfied.  The most that I’ve seen on this cruise is whale spouts way off in the distance, but I’m always on the lookout for sharks, schools of fish, and what to me would be the best possible thing, a giant squid.  On past cruises, I’ve seen a school of tuna, a few mahi mahi, lots of tiny squid that come up at night to feed, and lots of flying fish.  I still have yet to see any sharks (other than while scuba diving), or any whales up close, although apparently there was a blue whale within 100 m of the boat last week that I missed.

Before this cruise, I did not really appreciate the entertainment value of rough seas.  On the rare rough days during my previous cruises, I would usually just stay inside.  But, I’ve learned to appreciate rough seas for entirely different reasons.  It literally makes everything an adventure.  Walking through the halls on the boat, sitting at a desk, or standing out on the deck, the world around you is constantly moving.  You have to adjust your weight on your feet, or if you’re sitting your abs have to constantly adjust, and you never move in a straight line.  Going up and down stairs, your feet alternate from feeling like lead to feeling nearly weightless.  Yesterday was the most fun I’ve had in rough seas.  It was a rare, perfectly clear day, but we still had 6-10+ ft swells.  It isn’t relaxing but it is quite exhilarating.  Musically, hard rock and metal are a much better accompaniment than relaxing instrumental music like Bonobo.  I stood out on the deck for over an hour just surfing the swells, watching the bow bounce up and down, and laughing when the boat slammed into a particularly large swell, sending up a 40 ft blast of spray, and often producing a temporary rainbow.  The tedium of the daily routine on the boat necessitates finding little things to enjoy to avoid going crazy, especially when you’re on the boat for 30+ days.  On the down side, rough seas do make it more difficult to sleep and create a lot more noise in the data, but otherwise I’ve learned to enjoy them.  It sounds like my limits of enjoyment will be tested over the coming days however, we are supposed to have possible 5-9 m seas on the 30^th, which could tip the balance from fun to scary and dangerous.  We’ve had as high as maybe 6 m (~20 ft) so far, so this looks like it’ll be the worst storm yet.  So far, none of the storms have been quite as bad as predicted, and hopefully that trend continues.

My Daily Routine

My shift is from 4 pm-12 am, which is actually pretty much perfect as far as my normal sleeping schedule.  I get up around 10-10:30 am, take a shower and relax for a bit before lunch at 11:30.  After lunch, I either relax in my room watching TV shows or reading, and I normally try to go outside and get some fresh air if the weather isn’t too terrible.  This is usually the highlight of my day; despite the cold of the north Atlantic, I do enjoy staring out at the endless ocean, listening to some tunes, and getting lost in thoughts and reflections.  This was a much more frequent activity on my previous cruises, I would normally be outside during the day and also at night to look at the stars, but it’s just a lot less inviting (and normally completely overcast) here, so I don’t get outside for more than an hour a day and I have yet to see any stars.  I’d like to think that it’ll change, but we seem to be right in the path of every storm that is generated between NE Canada and Greenland, so sunshine and clear skies (and thus stars/sunrises/sunsets) will likely remain a rare event.  Storms do offer their own form of entertainment however, last night I enjoyed looking out the window of the mess hall and watching the swells build and the waves crash against the side of the ship.  The extra rolling of the ship does make it even more difficult to sleep than normal and increases the noise level in the data, but otherwise I don’t really mind rough seas.  It definitely makes walking down hallways and up/down stairs much more adventurous.  Sometimes when the ship is really moving, it can actually feel like you’re going up stairs when you are going down.  Hallways feel more like winding hills, and you kind of bounce off either wall as you walk along, which I find much more entertaining than a boring straight flat hallway.  As far as exercise, I have been less active than on previous cruises.  I would normally work out in the gym for 1-2+ hours every other day, but the gym on this boat is just not inviting and it’s hard to get motivated.  They have added an elliptical trainer since my first time on this boat, which is definitely better than the treadmill, but I will never understand the logic of putting only free weights on a boat.  The Kilo Moana’s gym was by far the best, they had a treadmill (which I didn’t use), an exercise bike (which I used a lot), and a weight machine that you could do tons of different exercises on which was usable regardless of the sea conditions.  Free weights definitely get pretty sketchy when the ship starts moving, and with the bench and the weight rack, they take up just as much space as a machine would, so I can’t understand why there is not a weight machine of some kind.  For exercise, I mostly do pushups and crunches in my room, although I’ll have to force myself to go to the gym some more.  Pushups are also interesting when the seas are rough, when the ship is rolling one way, you feel like superman and can do them with almost no effort, then it rolls the opposite way and it’s tough to even do one.

As I’ve mentioned, my job on the ship is to help my advisor with processing the data we collect.  The only part I’ve done entirely on my own is the backscatter processing, and I already described that in my last post, so I won’t talk about the specifics here.  It only takes maybe an hour out of my 8 hour shift, but I have to stay in the computer lab the entire time so there is a lot of bored down time while I’m on my shift.  This is spent wasting time on the internet, chatting with the other people in the lab, and working a little bit on writing my first PhD paper (which I need to do a lot more of).  I have now moved on to using my advisor’s script to process the bathymetry, and as soon as he gets the scripts together for the gravity and magnetics, I’ll work on those as well.  It’s not really necessary for me to do any of this since he is the one writing the scripts (except for the backscatter) and there is more than enough time for him to process the data during his shift.  I have processed bathymetry data before as well, so I’m already pretty familiar with everything that his script is doing.  However, the valuable part for me will be getting some actual experience processing both gravity and magnetic data, neither of which I have done much of before, and both of which will be a part of my PhD work.  Apparently the magnetic processing script is pretty much good to go, but I think my advisor is still finishing up the gravity script.  I’ll give some more details on that when I start working with it.

My Job Onboard

As you might imagine, most days on the ship follow a pretty similar routine.  This particular cruise, because there is really only one major scientific operation going on (mapping) is even more routine than the others that I have been on.  The only deck work for this cruise is occasionally going out to drop an XBT.  XBT’s look a little bit like a missile or torpedo with a lead tip and a thin copper wire attached to them.  You just drop it over the side and let the wire uncoil until it reaches its max depth (different XBT’s are rated for different depths), then cut the wire and finish. They are used to get a temperature profile in the water column, which is the main variable that affects the speed of sound (salinity and pressure also have an effect, but these don’t vary spatially as much as temperature).  It is important to know how the speed of sound in the water varies since it determines the travel time of the sound waves emitted by the sonar system and thus significantly affects the distance calculations used to determine water depths (bathymetry).  Sound speed in water is ~1500 m/s (5x faster than in air), and doesn’t vary a whole lot, but even small variations change the depth calculations. 

There are two main jobs during the mapping operations: watch-standing and data processing.  The students from U. of Iceland and the MATE program handle the watch-standing duties. These duties mostly consist of watching the data displays on a large panel of computer monitors (there are 37 total, but not all are being used), making sure that the instruments are running, and making both an electronic log and a digital log every 30 minutes of our position, course, etc.  They also log if there are any problems with any of the systems, when we launch an XBT, and when the ship makes a turn to start the next survey line.  The watch-standing job could probably be done by one person, but they have 2-3 of them on 4 hour watches (then 8 hours off), so most of the time they are just relaxing, chatting it up, listening to music, or on their laptops.  I was on watch-standing duties during my first cruise, but since we were doing a seismic survey we had to log which airguns fired every 3 minutes and did a lot of deck work both deploying and recovering the OBS’s, so it was a lot more “action-packed,” although I still had plenty of down time.

My job is to help my advisor with the data processing, which includes bathymetry, backscatter, gravity, and magnetic data.  So far, I have only actually been working on the backscatter data, although I will work on the other data types soon (I'm starting on bathymetry tonight).  Data processing involves copying the raw data files over from the ship server, then running a script, which is just a text file that calls various programs that are specialized to read the raw files, pull out the desired data (all of the data types are embedded in a single file), clean up obvious noise and artifacts, create a grid of the data, filter the grid to clean it up further and fill gaps, and then plot it in a visual format so we can actually see what it looks like.  The time-consuming part is in the beginning, getting the script written and working properly, and testing various options for filters and methods of cleaning up the data.  Once the script is written, it is pretty much an automated process of just running it each day on the latest data, with perhaps some minor changes if there was a storm and the data is particularly noisy or something like that.  For the backscatter data, I started with a script that was written by another professor at UH who was on the ship a few months ago, and modified it for our current cruise.  For me, that is always the easiest way to construct a script and learn how it works.  Since I have very little training in programming or coding, it is difficult for me to just write a script from scratch, so it always helps for me to start with a working script that someone else wrote. Then, I can look in detail at what they do in each step, read the man pages (a manual that describes what each of the individual programs in the script do and the various options that you can use), and modify it to suit the data that I am looking at.  For those who aren’t experienced with writing scripts, I’ll reproduce a couple selected lines here and explain them so you get the idea:

mblist -F-1 -Idatalist-pmb59-1 -R-38/-20/55/65 -D4 >! mb.xya.bi

mblist is a program included in a package of programs called mb-system (used solely for processing multibeam sonar data, hence the “mb” in the name). It is used to pull various data types (backscatter, bathymetry, navigation, etc) from the raw files and place it into a binary file “mb.xya.bi.” The –F option tells it what format the raw file is in (every sonar system has a slightly different output format), -I tells it the name of the file that contains a list of the raw files, -R gives the geographic range (minimum longitude/max longitude/min latitude/max latitude) where the program will look (it will ignore anything outside that range which can be useful for getting rid of data that is really badly located; we had some data points that were near the equator), -D tells it what type of data to pull out (4 indicates the amplitude of the sonar return, aka backscatter), the “>” just tells it the name of the file to put the data in, and the ! means to overwrite the file if it already exists.

set R = "-R-35.52/-29.45/57.72/59"

This is a standard way of setting a variable on a unix-based computer.  It’s just a short way to define something so you don’t have to write it out every time.  In this case, I’m defining the “R” variable as the numbers in quotes, so I don’t have to rewrite it every time I use the –R option in a program.  As I said above, the –R option gives the geographic range.  You can define any variable as anything, and then you refer to that variable later with a $ sign in front of it (e.g. $R, $X, $name, etc.).

xyz2grd mb2.xya.bi -bi3 $R -Gmba.grd -I.0002

xyz2grd is a program that is part of a package of programs called gmt (generic mapping tools), probably the most common set of programs that I use in data processing and mapping.  It reads the binary file from mblist and turns it into a grid, which is just a file that has an x (longitude) ,y (latitude), and z (sonar amplitude) value at each point in a grid. –bi3 tells it that the input (i) file is a 3 column binary (b) file, the $R is the –R variable from above, -G tells it the name of the grid file I’m creating, -I gives the grid cell spacing in degrees (.0002 degrees is ~20 m, although with longitude this decreases toward the poles).

grdfilter mba.grd -Fb.0022 -Gfilt.grd

grdfilter is a gmt filtering program that you use to remove spikes and smooth out data, or fill gaps in the data. mba.grd is the name of the grid file I created with xyz2grd, -F tells it the type of filter, “b”, and the filter width (.0022).  In this case I use a boxcar filter, which is a simple running average that goes through each point on the grid and computes the average value over .0022 degrees (~220 m, or 11 20 m grid cells, 5 on either side of the point that it is evaluating), and uses that as the value at that point. That way if you have a large spike in the data at one or two points or generally rough noisy data, it will be averaged out with the surrounding data points.  A wider filter will average more points and smooth the data more; the key is finding a balance between de-spiking and not averaging out real data that you want to keep. –G again just gives the name of the filtered grid.

grdimage mba_all.grd -JM7i $R -P -Css_eq.cpt -Ba60mg20m -Xc -Y.85i >! $name.ps

grdimage is the gmt program that actually creates a plot of the data. mba_all.grd is the name of the grid that I want to plot, -J gives the map projection type (M = Mercator), and the width of the data plot (7i = 7 inches), $R is the –R variable, -P indicates I want it in portrait orientation rather than landscape, -C is the color file to be used in plotting (it tells it what values of backscatter intensity (the z values in the grid) that correspond to what gray values), -B tells it the spacing of lat/lon labels on the map frame (a60m = annotate (print the lat or lon value) every 60 minutes, g20m = put grid lines every 20 minutes), -Xc tells it to center the plot on the page in the x direction, -Y.85i tells it to offset the base of the image .85 inches from the bottom of the page, > tells it the name of the image file (I define the “name” variable like I defined the $R variable), and the ! again means to overwrite if there is an existing file of that name. .ps means it is a postscript file, which is an uncompressed image file format.

ps2pdf $name.ps >! $name.pdf

ps2pdf is another standard unix program (i.e. not specific to gmt or mb-system) that simply converts a postscript file(.ps) into a smaller pdf file with little to no loss in resolution so it's much faster to view.

There are tons of more programs within mb-system and gmt that all do different things and all have their own options, but this gives some examples of the basic structure of the code in a script file.  In order to learn what each program and option does, you just read the man page for that program and play with the options until you get the desired results.  For those that found this a bit overwhelming, unfortunately it gets a lot more complicated when you start having to add loops to perform the same operations on multiple files and string all of these programs together in the right order to get the final grids and plots.  For me, the best way to learn all of this is always to start with a working script that someone else (usually my advisor) wrote, dissect and analyze it, and then modify it to suit my purposes.  Although my favorite part of the process is still the geologic interpretation and analysis of the final maps as opposed to the programming part, I have to admit it is extremely satisfying when you finally get the code running that you've been working on for hours or days (or weeks), and up pops a beautiful map of the seafloor.

The Scientific Mission and Background

Introduction

This research cruise focuses on the southern end of the Reykjanes Ridge, located ~1000 km south of Iceland in the north Atlantic.  The Reykjanes Ridge is part of the Mid-Atlantic Ridge spreading center, part of the global mid-ocean ridge system that extends for over 70,000 km around the entire earth.  The previous cruises were also along spreading centers, but in those cases they were backarc spreading centers that were all situated on the upper plate of the Tonga or Mariana subduction zones (see old posts for a brief introduction to subduction zones and backarc spreading centers). 

Mid-ocean ridge basics

Mid-ocean ridges are in most ways much simpler than backarc spreading centers, because you remove the complications introduced by the plate subducting into the mantle, which has major effects on the characteristics of the spreading center.  At mid-ocean ridges, the lithosphere (which includes the crust and the upper-most part of the mantle) is pulling apart, causing it to thin and stretch, and crack.  In the upper few km of the crust where the rock is cool and brittle, this extension is accommodated by faulting.  In the deeper parts of the crust and lithosphere, extension is accommodated by ductile stretching (like silly putty or toothpaste).  This thinning of the lithosphere causes the underlying mantle to rise (a process called upwelling) and fill the space.  As it rises, the pressure is reduced on the mantle, causing it to partially melt, intrude into the plate boundary and create new crust.  On the earth’s surface, most people think of melting as a simple process of adding heat until the material reaches its melting temperature, but in reality the process of melting depends on three factors: temperature, pressure, and composition.  If you brought a piece of mantle up to the surface, it would already be at a temperature well above its melting point, but the extreme pressure in the interior of the earth prevents the hot mantle from melting.  Most people think of the mantle as a liquid because it does flow over long timescales, but in fact, due to the high pressures it is actually a solid.  So, at a mid-ocean ridge, as the mantle rises and pressure decreases, the components of the mantle with the lowest melting temperature melt first in a process called partial melting (i.e. the entire mantle does not melt).  These components (which are the chemical components of basalt) separate from the remaining mantle, rise upward intrude into the crust, and accumulate in a magma chamber a few km under the ridge axis.  Usually, less than 10% of the mantle volume actually melts, and the remainder becomes “depleted” in the elements that melt easily.  Once enough melt has accumulated in the magma chamber and driving pressure is adequate, these materials break through the upper crust in dikes, and once they reach the seafloor spread out as lava flows.  So while geologists often talk of spreading rates as being a few cm per year, in reality this spreading mostly happens in discrete short events, with long intervening periods of little to no activity.  Spreading rates are just an average over long time periods of these discrete, shorter events.  The duration of these events and the time between them is determined by the spreading rate, with higher spreading rates favoring shorter events with much shorter time gaps between them.  Spreading rate is also the primary controlling factor on the morphology of the spreading center, with broad, smooth, shallow volcanic peaks associated with fast spreading rates, and deep faulted valleys associated with slow spreading rates. Backarc spreading centers in subduction zones are more complicated because you have this same process (called “depressurization melting”) interacting with the water and other materials introduced into the mantle by the subducting plate.

The Reykjanes Ridge and the Iceland hot spot

While the majority of the variations along the global mid-ocean ridge system can be explained by variations in spreading rate, the Reykjanes Ridge has an extra complicating factor.  Iceland, like Hawaii and numerous other island chains around the world, is underlain by a hot spot, also known as a mantle plume.  Hot spots are plumes of anomalously hot upwelling mantle that are thought to rise all the way from the core-mantle boundary (although the source of hot spots is still very much debated).  In Iceland, you have two sources of melt interacting, depressurization melting from the spreading center, and additional melting due to the extra heat from the hot spot.  This is why Iceland is a huge island sitting well above sea level, while the rest of the Mid-Atlantic Ridge is 1000+ m under water.  The Reykjanes Ridge extends through the western portion of Iceland and because of the influence of the hot spot, it becomes shallower and more volcanically active toward the north as it approaches the hot spot. 

           
If you look at the majority of the Mid-Atlantic Ridge (just look at google maps), it has a characteristic “stair-step” appearance.  This stepped appearance is caused by spreading center segments (oriented roughly N-S), with intervening fracture zones (oriented roughly E-W) that connect the ends of the segments.  You can see that the overall trend of the ridge is not N-S; in the north Atlantic the overall ridge is oriented in a NE-SW direction, but the spreading direction is ~E-W.  Spreading centers tend to form perpendicular to the spreading direction, so instead of having a linear spreading center oriented in a NE-SW direction (oblique to the E-W spreading), the overall oblique orientation is accommodated by the stair-step pattern.  Just think of it as using stairs to go up/down a hill rather than a straight ramp.

            
If you look at the Reykjanes Ridge south of Iceland, it does not have this stair-step appearance.  Instead it appears to be a linear oblique spreading center with no fracture zones.  If you zoom in far enough, you can actually see that the individual spreading segments are still oriented ~N-S, but instead of long (~100’s of km) segments separated by fracture zones, there are short (a few 10’s of km) segments that overlap with no fracture zones between them.  We are looking at the southern end of this ridge, where it transitions from an oblique spreading center back to the normal stair-step pattern toward the south.  The question we are trying to answer is what has caused the previous stair-step pattern to be erased and replaced with this completely different seafloor fabric.  The currently accepted (though not well-supported) theory is that it is entirely a hot spot effect.  This theory claims that hot mantle from the hot spot has migrated south along the ridge, softening the lithosphere and erasing the fracture zones as it migrates southward.  The competing theory (which is favored by my advisor and the other professor at UH that he wrote the proposal with) is that it is largely due to the Reykjanes Ridge propagating southward at a slightly different angle than the previous spreading center, erasing the stair-step pattern and replacing it with this new seafloor fabric.  The reason that a propagating spreading center forms is mostly thought to be due to a change in overall plate motion, in this case the new spreading direction has been rotated slightly clockwise.  Instead of rotating the original spreading center in a clockwise direction, the earth responds to this change in plate motion by forming a new spreading center at an oblique angle (rotated slightly clockwise) compared to the previous one, which then propagates and replaces the old spreading center.  If you look at a map, you can see that the Reykjanes Ridge is indeed rotated slightly clockwise relative to the rest of the Mid-Atlantic Ridge toward the south.  Mapping the southern end of the Reykjanes Ridge across the zone where the seafloor fabric changes should help us to clearly distinguish between these two models.

The planned survey area showing the ship tracks in black lines, with waypoints as white circles, overlain on a very coarse (~2 km resolution) bathymetry map. Two prominent fracture zones, the Pendragon, which has been mostly erased by the Reykjanes Ridge propagation, and the Bight fracture zone, which is just beginning to be erased, are labeled.  The red lines outline the exclusive economic zones of Iceland and Greenland. Iceland would like that red line extended to the bottom of our survey area.

The discussion of exactly what we’re looking for requires a lot of background to understand, some of which I’m not entirely familiar with, but I’ll attempt to explain some of the main things that will help us distinguish between the two models.  One of the major features created by a propagating spreading center is called a pseudofault.  As the rift propagates, it creates a zone of new crust that has a v-shape, because the older part of the rift continues spreading and opening as the tip continues propagating, somewhat like a zipper.  Along the boundaries of this v-shaped zone is a sharp edge that looks somewhat like a fault (hence the name pseudofault), separating the old seafloor from that which is created along the propagating spreading center.  On our way south from Iceland to the survey area, we attempted to map this boundary, and we’ll go along the same area on the way up, so hopefully we will be able to see this boundary in detail and determine whether it is indeed a pseudofault.  Another even more definitive structure that we will look for is a zone of transferred lithosphere.  Imagine a simple N-S spreading center, spreading in an E-W direction, dividing the North American and Eurasian plates.  Then imagine a new spreading center forming 100 km E of the old one, starting in the N and propagating in a slightly SW direction.  Now, that 100 km slice of lithosphere that was once on the Eurasian (E) side of the original spreading center is on the North American (W) side of the new spreading center, meaning that a piece of Eurasian lithosphere has been “transferred” over to the North American plate. This piece of transferred lithosphere rotates as the spreading center propagates, so if we see a zone of seafloor with faults and volcanic ridges that are at an oblique orientation to the surrounding seafloor, this will be pretty much slam dunk evidence that the propagating rift model is correct.  With the scale of mapping that we have right now, it simply isn’t possible to see this, so we need more detailed maps to see if there indeed is a zone of transferred and rotated lithosphere.

Instrumentation and Data Collection

Compared to my previous cruises, this is one is pretty basic as far as instrumentation.  We are not doing any seismic work, there are no AUV’s or towed cameras, and we likely will not be taking any rock samples unless the multibeam sonar fails for some reason.  The main instrument is the multibeam sonar system, which all research ships are equipped with, and is mounted to the hull.  I’ve explained this before in past posts, but I’ll give a brief summary here as well.  Sonar systems both emit and receive sound pulses that bounce off of the seafloor.  It is called a multibeam system because the sound waves are produced from multiple transducers that emit sound in a fan-shaped pattern giving us a wide swath of data on the seafloor rather than a single track.  There are two types of data that can be recovered from the sonar system: bathymetry and backscatter.  Bathymetry is simply a measure of the time it takes for the sound to travel to the seafloor and back to the receiver array.  Knowing the speed of sound in water and how it changes with depth, the travel times can be converted into a distance measurement, and you can get an image of the topography of the seafloor.  Along with the travel time, the receivers also measure the intensity of the reflected sound waves, which is the backscatter.  If the sound reflects off of a hard surface (a lava flow or a sunken ship for example) the intensity of the return is very high, but if the sound reflects off of a soft or rough surface (sediment for example), much of the energy is scattered and the intensity is weaker.  Backscatter images essentially look like a black and white image of the seafloor and allow us to see structures such as faults and lava flows, and distinguish them from sedimented regions.

A much higher resolution (~100 m) bathymetry map of the northern portion of the Reykjanes Ridge to give you an idea of how much better resolution you can get when mapping with a ship compared to just satellites.  Now you can see (hopefully) that although the overall orientation of the ridge is NE-SW, in detail the actual segments of the spreading center (along the central red portion) are oriented in a more N-S direction, perpendicular to the spreading direction.  This is from two combined surveys, one with dense tracks right along the axis, and the other with further-spaced tracks that go much further off the axis.  The rows of yellow dots are aligned along "flow-lines" that are parallel to the spreading direction.

Along with the multibeam sonar data, which is the primary mapping tool, we will be collecting both gravity and magnetic data as well.  Gravity data is collected with a gravimeter, which is mounted in the main computer lab as close as possible to the center of the ship (to reduce the accelerations due to ship motion).  There are different designs for various gravimeters and I won’t get into the technical details, but basically they measure slight variations in gravity due to local variations in mass.  For instance, if we are passing over a large volcanic seamount, the local increase in mass causes a slight increase in gravity.  Gravity data is useful for looking at variations in crustal thickness and can help illuminate structures in the lithosphere that may be obscured by sediment and therefore are not visible in the sonar data.

Satellite gravity map showing the entire Reykjanes Ridge. It looks superficially similar to the bathymetry, but you can see more structure in the off-axis areas because the gravity can "see through" the low density sediments that obscure the underlying structure in the bathymetry data.  The fracture zones are clearly visible toward the southern end as the blue "stripes" going roughly horizontally, and you can clearly see that they progressively disappear as you go north.

Magnetic data is measured with a magnetometer that basically looks like a missile, towed a few 100 m behind the ship to reduce the magnetic effects of the metal hull.  Magnetic minerals (particularly magnetite) in the seafloor rocks produce a magnetic field, which varies in intensity mostly due to the quantity of these minerals in the rock.  But the more important piece of data is the orientation of the magnetic field.  While the lava is still molten, the magnetic minerals align with the orientation of the earth’s magnetic field, and when the lava cools this orientation is permanently frozen into the rock.  The earth’s magnetic field has switched polarity thousands of times over its history, and the rocks formed at various points in earth history still record the orientation of the field at the time they formed.  This allows geologists to correlate these reversals recorded in rocks all over the earth. Along spreading centers, these reversals create stripes of positively or negatively magnetized rocks as they form at the spreading center and migrate further off-axis.  By dating lava flows near these boundaries and measuring how wide the stripe of crust is between them, we can determine both current and past spreading rates.  For instance, the last reversal has been dated at 780,000 years ago, so if we know that this reversal is 7.8 km away from the axis (to make the math easy), we can estimate the spreading rate at 10 cm per year.

An example of magnetic data from the northern part of the Reykjanes Ridge.  There are two forms of the same data shown here.  The black wiggly lines are the actual data collected along the straight black lines that are the ship tracks, which also represent the "0" line if these were plotted as a graph. Where the wiggles are above the line, the seafloor is positively magnetized and where the wiggles fall below the line, it is negative.  The colored background is a grid produced from interpolating between the survey lines, with warm colors representing positive and cool colors representing negative magnetization.  You can see the first reversal as the first transition from the positive (red) magnetization right along the axis, to the dark blue just off the axis, and at least 7-8 more reversals are recorded as you go further away from the axis.

Onboard the Langseth (round 2)

Life on the boat

We are on day 4 of our 33 day mapping survey, and everything has gone mostly smoothly so far.  I'm still in the process of adjusting to life on the boat, although I am no longer on any seasickness meds, and hopefully won't need any more unless we hit rough seas.  A few of the University of Iceland students had some difficulties with seasickness, but everyone seems to be adjusting by now.  The sleeping adjustment is not going so well, however.  I got maybe 4-5 hours of sleep total over the first 3 nights.  Last night I took 1 1/4 ambien pills, which got me ~4-5 hours of actual sleep but also made it difficult to get out of bed, and I've felt pretty groggy and exhausted most of the day. Basically, I'm pretty much screwed no matter what I do.  One would think that once I am exhausted enough, my body would just give up the fight and let me sleep like a normal human being, but insomnia does not care about logic or reason and it is always victorious.  If I could just find a reliable way to get 4-5 hours of sleep every night, the whole cruise experience would be so much better.  I'm not looking forward to struggling with this for the next 29 days, it is by far the worst part of being on a cruise for me, and it has a negative impact on everything else.  Despite the hardships, I have a much easier-going, positive attitude than I did on my first cruise, and it gets easier each time I do it.  I've enjoyed talking to the younger U. of Iceland students and telling them stories from my past cruise experiences, it's odd feeling like one of the experienced senior scientists, but also really cool.  Plus, I get senior scientist accommodations, my room is at least 4 times the size of my room the first time I was on the Langseth (although the bed is the same tiny size). I'm just trying to see it all as a challenge and an adventure (as Calvin's dad in Calvin & Hobbes would say, I'm "building character"), and sticking with the cliche of taking it one day at a time.

The Food

The food has been better than I remember from my first time on this ship, but still pales in comparison to the Kilo Moana (I guess I shouldn't be surprised, the food on that boat is ridiculously good).  The quality of the ingredients, the variety of types of food, and the ability of the cooks just are not comparable.  For instance, tonight we had grilled ahi, which should have been amazing, but instead it was extremely overcooked and I could definitely tell that it was not very fresh (although I do admit that coming from Hawaii, I am spoiled as far as fresh seafood, so I have to give the cooks a little bit of a break). Only 4 days in, the quality and quantity of fresh fruits and veggies is already looking pretty grim, so that does not bode well for the next 29 days. I also have to factor in that the cooks can only work with what they can procure at the port, so some of the quality and quantity issues can be chalked up to what was available in Reykjavik. Overall, the food has been pretty decent and I certainly can't complain about not having to buy food, cook, or do dishes for a month.  

The People

As far as cruises go, we have a pretty small number of both scientists and crew onboard.  There are 36 total people, 16 scientists and 20 crew.  This ship is normally used for seismic experiments, which require more people: techs for the ocean-bottom seismometers that receive and record the seismic energy, crew to operate the airguns, and marine mammal observers to make sure no whales or dolphins are nearby that could be negatively affected by the loud noise generated by the airguns.  For this cruise, we are just doing sonar mapping as well as collecting gravity and magnetics data, so no specialized scientists or crew are required (more details on that in my next post).  My first cruise in 2009 (see old blog entries) was a seismic experiment, so there were many more people onboard, and the other two cruises had multiple science teams for dredging, towed camera mapping, and AUV mapping. I recognize a few of the crew members, particularly the tech that I shared a watch with on my first cruise and who is the main person working with the science party.  He's a pretty awesome guy and definitely helps improve the experience for everyone in the main computer lab.  The science party consists of me, my advisor, and a post-doc student from UH, two Icelandic scientists, six grad students (most have just started or are just about to start their grad program) from the University of Iceland, and two students who are part of the MATE program, which basically provides internship experience at sea for those who may wish to pursue a seagoing career. Only one of them has seagoing experience, and his experience was limited to mapping in the great lakes, so they are all pretty much newbies.  Like every other cruise I've been on, some of the crew are friendly and some seem to want nothing to do with the scientists, this seems to be a consistent theme on every boat.

The North Atlantic

My previous three cruises were all in the tropical Pacific, which, as I have found, has a very different personality than the North Atlantic.  The warm, humid air, blue skies, and beautiful deep blue water have been replaced by cold air, icy winds, gray skies, and menacing dark gray water.  In the past I was able to break up the monotony of staring at computer screens by enjoying beautiful sunrises/sunsets, stargazing, or just simply staring off into the vast never-ending blue of the ocean, watching the ocean breathe and feeling the exhilarating fresh ocean breeze.  None of those experiences have been possible here, I've probably spent a total of 30-40 minutes on deck since I've been onboard.  I haven't seen a single sunrise, sunset, or star, and the weather has been consistently gray, wet, and gloomy.  I haven't given up all hope that we might get a few days of clear skies, but I'm certainly not counting on it. I guess the bright side is that we haven't hit any serious storms and the seas have been reasonably calm and cooperative, but I'll be surprised if it stays this calm for the entirety of the cruise.  If I ever get to the point of writing my own proposals for research cruises, I'll be sure to stick to warmer waters in the Pacific.  Thankfully that is where most of the world's subduction zones are anyway, so it shouldn't be too difficult to avoid places like this for my own future research.  As I finished writing this, I looked at one of the monitors in the computer lab and saw a sliver of sunlight, there is hope yet!      

Iceland!

     It has been over a year and a half since my last cruise experience, but I'm back onboard the R/V Marcus G. Langseth for another one.  Before I get into the details of the cruise itself and the scientific mission, I wanted to summarize my experiences over the last few days in Iceland.  My previous cruises have all been in the tropical western or southwestern Pacific (the Lau basin (Tonga, Fiji, Samoa) and the southern Mariana Trough (Guam)), so Iceland is definitely a change of pace.  For details on my previous cruises see the older entries in this blog.  Since I am already onboard the ship at this point and we are just now departing Reykjavik, I'm just going to try to summarize my impressions and experiences in Iceland from the last 5 days.  I'll try to be somewhat organized about it so it doesn't sound too much like me rambling, but as you know if you've read my previous blog posts, my writing style is somewhat of a free flow of thoughts, so a little rambling is inevitable :)  Here it goes, I hope you enjoy...

The Landscape

     The first thing that struck me on the bus ride from the airport in Keflavik (~45 min drive southwest of Reykjavik) was the lack of trees and the relatively flat landscape (I learned later that the southern part of Iceland is really the only flat part, the rest of it is much more mountainous, as you'd expect from a volcanic island).  The landscape consisted of lava flows (most of the exposed lava is ~10,000 years old at most) largely covered with silvery gray to yellow-green moss, with some patches of grass and a few shrubs here and there.  As we got nearer to Reykjavik, I started seeing trees, but apparently the majority of them have been planted.  My initial impression was reinforced when I learned that only 1% of Iceland is covered in trees.  Apparently it used to be 25%, but a combination of human deforestation, and lava flows/ash took care of most of them.  One of the Icelanders I met on the boat said they have a saying, "If you get lost in the forest in Iceland, just stand up."

     In order to see a bit more of what Iceland has to offer, I took two organized tours that covered most of the SW portion of Iceland. Although the tours were a bit pricy, I'm definitely glad that I did them, because I saw some amazing and beautiful things that were unlike anything I've seen before.  

The Golden Circle

     The first tour was the famous Golden Circle tour, which apparently is the most popular tour around here. Despite the popularity and large number of tourists, it was still pretty fantastic. I posted the full set of pictures on my facebook page, I'll try to post a few of the highlights on the blog as well, but with the slow internet connection on the ship I can't make any guarantees.  

     Our first stop was probably the least interesting unless you are really into agriculture, it was at Frioheimar greenhouse that uses geothermally heated water to maintain the temperature and water the plants.  They also pump in volcanic CO2 to help with photosynthesis. I got some coffee and a nice fresh-baked piece of bread, checked out the tomato plants, and listened to a spiel from one of the owners (it's a family-owned greenhouse) about the place and how it operates.  It is 100% organic, instead of pesticides they brought in flies to eat the few pests that exist here (probably wouldn't be adequate in warmer climates), and they bring in bumblebees to pollinate the plants. 

     Next, we saw the majestic and awe-inspiring Gulfoss (Golden) waterfall.  Although it certainly wasn't the tallest waterfall I've seen (~32 m total drop divided into two steps) or the largest (Niagara falls has a much higher volume of water), it still might be my favorite waterfall of all that I've seen (Rainbow falls near Mammoth, CA, Yosemite falls, and Akaka falls on the Big Island are close competitors). Describing it with words won't do it justice, so I'll try to post a picture.

Gulfoss Waterfall

    The next stop was the Geysir geothermal area, another popular tourist stop.  There is a restaurant where we had lunch and a gift shop, the usual tourist stuff.  There are a number of hot springs scattered around and the Strokkur geyser that shoots water 10-15 m into the air every ~4-5 minutes.  This was all very cool, but as far as geysers go, not quite as impressive as Old Faithful in Yellowstone or even the geyser in Calistoga, CA.  It was funny watching the tourists who got way too close running away screaming every time it went off.  ~90% of the people seemed to spend their time just sitting by the geyser waiting for it to go off and taking pictures, but I decided to do a little exploring, and I am very glad that I did.  I walked up the ridge above the geyser to get a better view of the area, and on the other side of the ridge was a beautiful little valley that to me captures the term "idyllic" better than any other place I've seen.  I still can't exactly explain why I liked this place so much, but I was giggling like a schoolgirl when I got to the top of the ridge and saw it laid out before me.  At the base of the valley were some small farms, scattered houses, horses (Icelandic horses were brought in by the Vikings and are one of the few pure breeds remaining), and a beautiful little meandering stream cutting through it. Objectively, there are probably other similar valleys around the world that are prettier, but there was something magical about this place and I (and my camera) loved every second of it.  I laughed out loud at the tourists that were crowded around the geyser the whole time and had no idea what was just over the ridge.

Strokkur Geyser

The Idyllic Valley in Geysir

     On the way to the last stop, we saw the largest lake in Iceland, Thingvallavatn, and a little more of the countryside, which consists of farms and small ridges, lakes, streams, etc.  The final stop was not necessarily the most aesthetically impressive, but definitely the most interesting from a geologic standpoint.  We took a short walk along the active rift zone that ultimately connects to the Reykjanes Ridge spreading center that is the focus of our current research (more on that later).  The walk took us through a small valley with vertical basalt cliffs on either side and up to a viewpoint where you could see a nice panorama of the lake.  There were lots of signs of active tectonics, cracks and fissures ripping through the ground and lava flows (some with very nice pa'hoe'hoe surfaces), although it did not appear to be geothermally active.  Apparently, you can snorkel or SCUBA dive along the rift at Silfra, which sounds pretty amazing.  Visibility is supposedly 150+ meters! (in comparison, great visibility in Hawaii is ~20-30 m, and usually you're happy with 10-15), and the water is so clean (glacial water filtered naturally through the rock) that you can just drink it while you snorkel. Of course, the water is a tad colder than Hawaii, you actually need a drysuit even just for snorkeling. If I come back to Iceland, I'll definitely have to try that.

The Rift Zone

Fissures in the rift zone and Thingvallatn Lake in the background

South Shore Adventure

     The next day I went on another tour called the South Shore Adventure, which went along the south coast as far as the small town of Vik, ~180 km east of Reykjavik. The drive to the first stop was characterized by flat farmland to the south and mountains to the north, with small waterfalls coming down the steep slopes in some areas.  I particularly took note of one farmhouse that was situated right below a small canyon with a beautiful ~20 m high waterfall, and I have to admit I was a little jealous that they pretty much have their own personal waterfall to enjoy whenever they want.

     Our first stop was at Myrdasjokull glacier, which was pretty freaking awesome.  It was my first up close encounter with a glacier (I had technically seen one way off in the distance on the Golden Circle tour) and I took an excessive number of pictures.  You can do a tour where you actually get to walk over the glacier, but we weren't allowed to actually walk on it.  I walked along the edge of the glacier so I could see it up close, much further than the rest of the tourists went, but apparently our tour guide did not appreciate my adventurousness.  Once she saw me up there, she came up and yelled at me to come back down, and in the process managed to get her foot soaked in a mud puddle, which I felt kinda bad about.  Parts of the glacier were covered in black volcanic ash and in some cases you could see ash interlayered with the ice.  There was a lot of glacial till beyond the toe of the glacier, which consists of rocks and sediment that have been carried along the base of the glacier and rounded (somewhat similar to rounded stream pebbles), as well as some small moraines (ridge-like piles of sediment pushed to the edges of the glaciers as it migrates downslope.

Myrdasjokull

     The second stop was at a black sand beach, which would more accurately be called a black pebble beach.  Having seen multiple black sand beaches on Big Island, that aspect wasn't particularly special, but there was a nice exposure of columnar basalt right next to the beach as well. Columnar jointing forms in a thick basaltic lava flow when the lava cools and fractures at 120 degree angles, creating hexagonal columns of rock.  These weren't the best example I've seen, they were quite perfect hexagons, but it is always a spectacular thing to see how something natural can be so perfectly geometric.  The best example I've seen is Devil's Post Pile near Mammoth, CA, which has nearly perfect hexagonal columns.  If you walk along the top, which has been smoothed by a long-gone glacier, it is like walking on a floor with hexagonal tiles.

Columnar Basalt

     The next stop was our lunch stop in the town of Vik, which is a very small town (probably a few 100 people) along the south coast. Here I had the tastiest meal I had during my entire stay, marinated grilled lamb with stir-fried veggies.  Otherwise, there isn't a whole lot to say about Vik.

     After that, we went to the Skogar museum, which displays some artifacts and preserved structures showing how Icelanders lived over the last few 100 years.  It was pretty small, but worth checking out. There was everything from the first Icelandic-translated Bible to clothes, fishing equipment, horse-riding equipment, housewares, and some preserved homes in the outdoor part of the museum. One thing that impressed me was how even the most common everyday items (e.g. spoons made from whale bones) had intricate carvings, an art that seems to be mostly lost today unfortunately.  The houses were small, constructed very close together, and covered with earth and grass for insulation.  The interior decor reminded me of houses in the American old west.

     After the museum, we saw Skogafoss waterfall, which has an impressive 60 m drop and also an impressive quantity of water.  It was very beautiful and you could view it from the base, the very top, and another viewpoint about 2/3 of the way to the top.  I think Gulfoss waterfall has the edge for being more unique and awe-inspiring, but Skogafoss was definitely worth checking out.

Skogafoss Waterfall

     The final stop was at Seljalandsfoss waterfall, which wasn't particularly tall (~25 m) and didn't have a huge amount of water flowing, but was still quite spectacular.  The best feature is that you can walk all the way around the waterfall 360 degrees, so it made for some more unique pictures.  There were also two small "bonus" waterfalls a short walk away that most people didn't bother walking to, but I made sure to check out.  Thankfully I didn't get yelled at this time for being too adventurous, but I'm definitely glad I checked them out.

Seljalandsfoss Waterfall

     Overall, I really enjoyed the tours and saw some amazing things that took my breath away and invigorated my soul. I will never get tired of the exhilarating feeling of soaking in the spectacular beauty of nature.  It's one of the things that makes life worth living and one of the main reasons I chose to become a geologist.  The fact that the things I saw were all during touristy bus tours definitely piqued my desire to discover the more remote places in Iceland.  I saw a very tiny portion of the country, less than half of the south shore, so the wonders of the other shores and the interior of the country are certainly a tantalizing thought. It is truly unlike anywhere else I've been and I'd love to come back here, rent a car, and explore the rest of this beautiful country.  However, there are also a multitude of other places around the world that I'd like to explore so who knows if I actually will come back.

Reykjavik

     I spent four nights and 5 days in Reykjavik, the capital city of Iceland.  It is a big city by Icelandic standards (~120,000 population, plus another ~100,000 in the surrounding area, the vast majority of the total population of ~330,000 in Iceland), but quite small by American standards.  I enjoyed wandering around downtown Reykjavik, exploring the city, sampling the food and beverages, and meeting some new people.  It is a very clean city by American standards, with narrow European-style streets, unique, charming, and colorful buildings and a fun nightlife, especially given the city's small size.  I spent most of my time in the downtown area, there are pretty much two main streets with the majority of the shops, bars, and restaurants.  I never felt even remotely unsafe, never saw anything sketchy going on, and didn't see any homeless people.  After talking to one of the Icelanders on the ship, it sounds like most of the homeless stay in shelters near the harbor, or according to my tour guide, many have moved away to other countries in search of a job and a home. It makes sense that you don't find many people living on the streets given the weather, they probably wouldn't last very long. I tried a bunch of different restaurants, some of the food was good, but overall the cuisine did not impress me a whole lot. Although I did see a subway and a domino's delivery car, it was refreshing to not see a mcdonald's for once.  Every other country I've been to has mcdonald's, it was nice to find a place that doesn't.  The highlights of the food were an italian meat soup in a bread bowl that I had the first day and some asian-style noodles that I had at a little noodle shop. The most infamous Icelandic foods are fermented shark or whale, they just sound too awful to even be worth trying.  It sounds like nowadays they are mostly eaten as a tradition, very few (especially in the younger generation) actually enjoy them.  There is another infamous local liquor called brennivin, which is traditionally consumed with the fermented shark, presumably to cleanse your palate from the horrible taste.  I didn't try brennivin while in Iceland, but an Icelandic student from UH brought some to a party once, so I have tried it, and once was enough.  Apparently (from talking to a bartender in Reykjavik), it is made with cumin seed, but as far as I'm concerned it was the worst tasting alcoholic beverage I've ever had.  Each night that I went out, I made sure to go to at least three entirely new bars, just to get a good sampling of the local spots.  My favorite one was also the most Icelandic, called Hressingarskalinn.  On Saturday night, they had a local cover band that was awesome, one of the best cover bands I've seen anywhere.  They had a female singer who sung everything from AC/DC to Daft Punk, Journey, and Pink Floyd.  It was a mostly local crowd with a few tourists, the live music was in the front room, and they also had a dance floor in the back room that came alive later in the evening. Another of my favorites was The English Pub, they had live music as well, although it was usually just one or two guys with guitars rather than a full band. The Lebowski Bar was also a lot of fun, they had live music as well, and the bar was based on the movie the Big Lebowski.  There were photos from the movie on the wall and ~20 versions of white russians were served.  My main complaints with Reykjavik are the weather (even when the sun was out, it was cold), and the prices.  Including the tours, the food/drinks, and the two nights in the hotel that I had to pay for, I probably dropped $1000 in 5 days.  Thankfully I won't be spending any money for the next month!  This was also my first experience traveling in a foreign country entirely by myself, on my other cruises, I was always hanging out with at least one other grad student.  Traveling by myself was a good experience for me to have and I like that I can do whatever I want without worrying about what someone else wants to do, but I think I still prefer to travel with at least one other person.  I'm proud of myself for stepping out of my comfort zone, I did manage to meet some new people and I definitely enjoyed myself, but it still was a little lonely at times.  Most of the people I met were fellow travelers from France, Australia, Canada, Scotland, and DC, but I didn't meet too many Icelanders.  I never got any negative vibes or dirty looks from anyone, but I didn't find the locals to be extremely friendly. Perhaps it was my fault and I should have been more outgoing, but I didn't necessarily feel comfortable side-busting a group of friends that were just chillin and drinking together.  Another random thing was having the sun set around midnight, which was quite odd. Well, I think that's all I've got on Iceland. I'll start the cruise blog in a day or two...

Halgrimskirkja church, the main landmark in Reykjavik

Laugavegur street in Reykjavik, "the strip" where most bars/restaurants/shops are