Headed for Home Port

Rick Murray, Chief Scientist

I’m typing this while we are just southwest of Martha’s Vineyard, and will be heading into Woods Hole in the early morning tomorrow (Wednesday, December 3).  On board all scientific measurements are completed, reports are written, the laboratories and coring equipment are essentially packed, and many of us are looking forward to reaching shore tomorrow morning.  People are relaxed, tired, happy and satisfied at work well done, and partially sad that the cruise is winding up.

For this final blog post, I felt it appropriate to share a “Dedication” with which our science party prefaced our Cruise Report, and the “Executive Summary” of the Cruise Report as well.

Thanks for visiting along with us during our research cruise.  Stay tuned for more great science to come from it!

Dedication

This cruise is the last full research expedition of the venerable and eminent R/V Knorr.  As the last full complement of scientists to sail with her, it has been our privilege to share this ride.  In admiration and respect for the men and women who have journeyed with her as crew, technicians, scientists, and visitors over the past 40 years, we dedicate this Cruise Report to the spirit of exploration, scientific inquiry, and the pursuit of excellence that the R/V Knorr has exemplified for so many days, nights, and miles traversing the vast unknowns of the sea.

Executive Summary

During Cruise KN-223 we successfully gathered 10 Multicores, 18 Gravity Cores, and 12 Long Cores from 16 different stations throughout the western North Atlantic Ocean.  We occupied sites ranging in latitude from the Researcher Ridge (~ 15o N) to the Sohm Abyssal Plain and northern Bermuda Rise (~ 35o N).

We successfully achieved our primary and most important goal, namely, of collecting sedimentary porewaters and making geochemical measurements of sufficient fidelity to prove the porewater’s utility in unraveling the paleo-ocean chemistry of bottom water during the Last Glacial Maximum.  Our stations, several of which were identified during the cruise itself, were strategically located to investigate meridional gradients in bottom water chemistry and physical properties.  Our deepest water sites also fulfilled a prime objective of sampling pelagic sediment that seems to be completely oxygenated from the seafloor to the basaltic basement, which will allow the reconstruction of nutrient utilization during the Last Glacial Maximum.  This range of oxygenation will also provide further materials for pathfinding research into subseafloor microbial energetics.

Our geochemical focus resulted in gathering sediment porewaters using strategies tailored for the different targeted chemical species.  These strategies resulted in 386 samples being squeezed for porewaters that were distributed into 2,625 different aliquots for shipboard and shorebased analyses, and 427 different in situ Rhizon samples resulting in an additional 1,752 porewater aliquots for shipboard and shorebased analyses.  Our shipboard analytical protocols included a novel approach to measuring the density of porewaters using a method that has never been attempted before for porewaters anywhere, let alone at sea in near real time.  Other measurements were performed to standards of precision and accuracy that are unprecedented, reflecting the collected experience and continual evolution of our analytical teams.

In our quest to locate adequate shallow water coring locations along the Researcher Ridge, we also performed detailed mapping that yielded surprising data germane to developing an improved understanding of this feature that is located along the North Atlantic-South Atlantic plate boundary.  While we failed in our goal to find appropriate shallow water sites to core, the geological and geophysical knowledge gained during this surveying has the potential to contribute significantly to discussions regarding the response of plate boundaries to changes in spreading directions and the synchronous or asynchronous generation of magma in regions of ocean crustal extension along boundaries that are perpendicular to ridge axes.

To serve our colleagues at the NOSAMS Facility at WHOI and therefore the oceanographic community at large, we also on two occasions gathered significant volumes of deep water for use as radioisotope standards.  Our last coring station was added late in the cruise to gather sediment at a key location for study of deep-water changes by the sedimentary paleoceanographic community.  Finally, we coordinated our coring calendar and cruise track to rescue a malfunctioning Slocum glider on behalf of Rutgers University and the US Navy.

We Asked: What are you thankful for on the R/V Knorr?

Claire McKinley – Dissolved Gas Analyst

In honor of Thanksgiving we asked the science party and crew what they have been thankful for during their time on the ship. On a holiday that is usually spent with close friends and family, there has been a lot of talk about our usual Thanksgiving traditions and how loved ones on shore are spending their day. The Thanksgiving meal began here at 11:30 a.m. in order to insure the optimum number of people could enjoy the meal together. We are all grateful for our stewards who worked very hard to pull off a wonderful turkey that was ready at 11:30 a.m.!

Mary Dzaugis, Sedimentologist: There’s just a lot of things! I am thankful for a good group of people and Kit Kat Bars and Peanut M&Ms.

Tom Lanagan, Mary Dzaugis, and Paul Walczak finish up their Thanksgiving meal.

Chris Moser, OSU Coring Technician: Good Shipmates.

Justine Sauvage, Dissolved Gas Analyst: Beautiful sediment colors, beautiful dissolved oxygen profiles, and beautiful sunrises!

Kira Homola, Geochemist: I am thankful that we have excellent stewards.

Sierra Davis, Geophysicist: I am thankful for all that I have learned and the brand new experiences. And of course for Harry and Lee who often make cake.

Rick Murray, Chief Scientist: Good Shipmates.

David Smith, Microbiologist: The outstanding efforts by the stewards to make sure it feels like Thanksgiving on the ship.

Amy Simoneau, Scientific Services Support Group (SSSG) Technician: Wearing shorts on Thanksgiving.

Claire McKinley, Dissolved Gas Analyst: I am thankful for all of the absolutely lovely human beings on the ship. Everyone is dedicated to the science that we are doing but above that they are dedicated to teaching and learning. I have learned so much in the last six weeks.

We asked: What did you eat for breakfast?

Claire McKinley – Dissolved Gas Analyst

Operations are running 24 hours a day seven days a week on the Knorr. Most of the science party works on a noon to midnight or a midnight to noon shift.  We generally have a crossover meeting to talk about the day’s events and communicate information and plans for the next 12 hours. These meetings are always a little challenging because one half of the team is ready for bed and the other half of the team is just getting going. The crew and coring teams work on totally different schedules as well. In order to illustrate the differences in individual schedules we asked: What did you eat for breakfast. For clarity we defined breakfast as the meal you ate first when you woke up on November 17th.  We also asked each person to provide some context for the timing of their meal. The interviews are presented in chronological order.

Rob Pockalny, Geophysicist: Coffee first, two eggs over easy, hashbrowns, toast, coffee. I’m officially on from noon to midnight but usually I work from 6:00am to midnight. I have to process and analyze data to plan for the next several days.

Mary Dzaugis, Sedimentologist: An orange at 10:00 am, and then lunch at 11:45. I am on the noon to midnight shift.

Casey Hearn, Sedimentologist: A pear. I am on the noon to midnight shift. I usually don’t eat a big meal until dinner.

David Smith, Microbiologist: A pastrami sandwich, asparagus and Navy Bean Soup. I am on the noon to midnightshift.

Tom Lanagan, Woods Hole Coring Team: One piece of seafood lasagana and one piece of meat lasagana. The Long Core operations are not at a consistent scheduled time. I slept in to prepare for arriving at the next site.

Steve Hovan, Sedimentologist: A bowl of granola cereal and tomato juice. I am on the midnight to noon shift.

Dennis Graham, Laboratory Manager/Geochemistry: Does toothpaste count? I’ll have coffee a little later and probably a cup of yogurt. I am on the midnight to noon shift.

Zak Kerrigan, Microbiologist: (Note for the reader: Zak did not want to answer the question until he was done with his coffee.) Coffee, and then I don’t eat breakfast until about 1:00 a.m. And then it is whatever was for dinner. The steward makes up plates and puts them in the ‘fridge for us.

Rick Murray (Chief Scientist): (Note for the reader: Zak is pretty sure Rick has a hollow leg.).  For breakfast I had two eggs over medium, a large amount of hash browns (if I don’t have potatoes each day I whither away), 4 pieces of bacon, and several pieces of French toast. After that, I went back for more French toast.  I don’t keep any consistent shift when on station as I’m involved in the coring operations for the whole time, but when on transit I try to keep a 6 a.m. to 9 p.m. “shift”.

Seven and a half hours into his midnight watch, Steve Hovan eyes up the donuts as Chief Steward Harry Burnett monitors his consumption.

Where Are We? Or, a Brief Guide to Celestial Navigation

Justine Sauvage – Dissolved Gas Analyst

The daily routine of life at sea can be happily offset by our exposure to a diverse set of skills, in the form of scientists, coring experts, and a full crew including mates, engineers, and stewards. One of my favorite things to do while at sea is getting a taste of all the specialties on board that I’m not very familiar with. During some down time or after my shift I like to go for a ‘round’ and see what the ship has to offer. The bridge is a fun place to go explore. First of all it contains some pretty neat navigational and positioning tools (GPS, radar, gyroscope, the ship’s control system, etc.), a global communication and weather report system for the area we are sailing in (think of it as the ship’s news channel, complete with upcoming storms, potential pirate attacks, distress messages, and mermaid sightings), monitors showing our heading, course, and position on nautical maps, a whole bunch of communication and signaling flags (one of them is the Whiskey flag, which means ‘ship in need of medical assistance’ – don’t think too hard about any potential link).

View of the bridge withChief Mate Derek Bergeron and Able-Bodied Seaman Mike Singleton on watch).

A full set of celestial navigation apparatus is also mandatory on the bridge (i.e. the ship’s chronometer, a sextant, and books containing all the information required to perform latitude-longitude position calculations, such as the Nautical Almanac). Lacking any sense of orientation on land, I figured I could possibly compensate for that at sea by learning some celestial navigation skills. The Chief Mate Derek is up for the task, so let’s jump on the opportunity. My training started yesterday and is far from complete. After having gone once through the entire gymnastics of figuring out my position on the earth solely based on celestial navigation tools, I gained even more respect and fascination for the sailors who faced the seas during the pre-GPS centuries, as well as today.

The entire process goes as follows:

Drawing sun lines
The general principle to figure out our position on the surface of the earth consists of drawing some position lines (also known as ‘sun lines’, circular lines of position based on an observer’s distance from a celestial body’s geographic position) at different times of day. For example, we could draw one line at sunrise, local apparent noon (which will give us our latitude) and one in the afternoon. Taking into account the ship’s heading and speed, we can advance our individual lines of position to a common time (i.e. stack them on top of each other) to get our position (the spot where all the sun lines intersect each other).

Time
Firstly, we need a very precise idea of ‘time’, more precisely Greenwich Mean Time. The entire celestial navigation process is extremely sensitive to the smallest uncertainties in time (as well as many other factors). A few minutes timing error could translate to a deviation of many miles from our actual position. The Greenwich atomic clock in the U.K. continuously transmits ‘time information’ (beep-noises) through the radio waves, which we can receive on the bridge if we tune the radio to the right frequency.

Angle between horizon and sun:
The two most important variables in the celestial navigation process are the angle between the horizon and a celestial body (in this case the sun) and the time at which this angle is measured. Measuring the angle is done with a sextant, which I consider the most intriguing object found on the bridge. Using a series of built-in mirrors, we get the sun and horizon in the same frame and then adjust the sextant’s parameters and orientation until the sun appears exactly tangent to the horizon. Once we have everything lined up exactly, we immediately note the time and angle (this sounds relatively straightforward but is far more tricky in practice).

Calculation gymnastics:
Using the angle of the sun and the time at which the angle was taken, we can use the Nautical Almanac to derive the local hour angle of the sun, its declination and the sun’s assumed altitude. These three variables are then used as inputs for another manual (with the fancy name of “Sight Reduction Tables for Marine Navigation”) from which we can finally determine the azimuth line and the altitude intercept, the information required to draw a sun line on our map.
This process will be repeated multiple times a day when the sun is at different angles above the horizon.

Nautical Almanac on the left, Sight Reduction Tables for Marine Navigation on the right.

Putting it all together:
Once we have acquired our three sun lines; we slide the first two along until they intersect the third at a common time. This intersection gives us our hard-earned, estimated position on the earth’s surface.

Blue diagnoal line is the ship’s desired course on November 13th. Pink line is our first sun line, taken at 09:32, green line is the second sun line, taken at 14:15, and the blue line is the final sun line, taken at 15:46. Stacking all the sunlines to intersect at a common time gives us our position.

A little assessment…
Comparing our celestially derived postion to the GPS reading we found that we were off only by about 5 miles…not too bad for a first try!!

Now I can say “Yes, I’ve been to Barbados.” (Except I sort of didn’t really….)

Rick Murray – Chief Scientist

Sometimes in the course of human events, science–like life–throws a curveball at you when you’ve been expecting a different pitch altogether. And that’s how we ended up tied to a pier in Barbados, but didn’t really visit there…after all, 4 hours isn’t that long a time.

Until now we’ve been busy surveying and coring the Researcher Ridge area, which consists of quite shallow water depths (by our standards, such as 1-3 km deep) surrounded by deeper water (4-5 km of water). First, we took some cores (including Long Cores) in deep water to the south and west of the Ridge. Our plans were to do some deep-water work at first, and then we were very much hoping to find some small pockets of fine-grained material suitable for coring in the shallower regions. At least that was the plan…

Starting at our deep-water sites, we had some coring difficulties that were significant and unexpected, but not unreasonable given the complexity of our apparatus and the challenge of doing deep-sea oceanography. Most notably, some of the Long Core system’s electronics had issues, but fortunately not before we got some extremely enticing results from a Long Core taken at one of our two deep-water sites. We soon realized we would need to somehow get some specialized parts sent to the nearest location for us to do more Long Cores. But, first, we wanted to go hunting for some shallow water sites suitable for coring when we got the Long Core operational again.

And that’s where we got “the different pitch altogether.” Although we were able to make some terrific maps of the undersea terrain that will help scientists understand how the Researcher Ridge originally formed, these maps, along with our deep-sea pinger that showed the sedimentary layers, indicated that there were essentially no suitable sites for taking Long Cores. Oh, how we tried! Through much mapping—thank goodness for our lead on-board geophysicist (Rob Pockalny) and sedimentologist (Steve Hovan)–we tested several potentially interesting sites with our gravity corer, but to no avail. It’s only a small stretch to say, in fact, that we looked at every suitable site along the submerged mountain chain. Each time, we came across the dreaded “foraminiferal sands”. These sediments are the result of ocean currents that wisp away the finest grains of mud, leaving behind coarse microshells that are remarkably similar to the sand on a beach—except made of microfossils. These “foram sands” are impenetrable even for our Gravity Core, which drives into the seafloor driven by 800 lbs of mass. Our Gravity Cores either came up empty, or nearly so (10-20 cm of recovery, at most). Some of us call such sands “Suitcase Sands”–because when you get them, it is time to pack your suitcase and move on…

So, while we are confident we will overcome the difficulties with our man-made apparatus, the winner on the Researcher Ridge was Mother Nature. She wasn’t going to give us a good coring spot in the shallow areas anyway. Where there is enough sediment to deploy the Long Core is clearly beyond our control. That’s just how things turn out sometimes.

And why Barbados? Many of our objectives on this mission rely on Long Core results in deep water, both around here and as we move north. In fact, our initial Long Core results are important enough that we want to return to one of our stations here and take another Long Core before we head north. And to do any Long Cores, anywhere, we need to fix those electronics. And Barbados is the nearest location to receive air freight. To get there and back consumes 3-4 days of our contingency ship time. But, what we lost in time to pick up our supplies we essentially gained back since we no longer had to core the shallow sites on the Ridge. And taking those cores would have taken a lot of time. While our overall calendar is unaffected, we still needed to get the parts to Barbados.

And here’s the end of our Barbados saga…through a series of contacts made by WHOI personnel here at sea and on shore, we were able to have a young Danish fellow (who dropped any other plans he may have had) fly from Europe to hand-deliver the required specialized electronic parts to a pier in Barbados. After receiving suitable permission from the Barbados authorities, we swooped in, tied up to the pier, waited for the taxi to arrive from the airport with our new BFF (Best Friend Forever) from Denmark, grabbed the electronics (along with some fresh vegetables from a local supplier), and got on our way—only 4 hours later. We didn’t even leave the ship.

You’re probably not surprised to learn that the pier in Barbados looks a heck of a lot like every other pier I’ve been to around the world.

Coring guru Jim Broda (WHOI) with Ulrik Hanghoj, our exhausted Danish courier, as Jim explains the importance of the materials in the hand-delivery (green tube in his hand). Photo by Rick Murray.

“Better” Living through Chemistry

Kira Homola – Geochemist

One of the incredible advantages of our science team, and somewhat rare for oceanographic cruises, is the fact that we run chemical analyses while underway. The analyses of pore water that are performed shipboard, when we are not busy squeezing, freezing, and Rhizoning mud, are:

Dissolved Inorganic Carbon (DIC): Performed as soon as the water is extracted, the DIC analysis involves bubbling acid through the sample to force any carbon dissolved in the water into a gas, then extracting this gas and measuring it for total carbon content, a quantity that helps us understand the carbonate system (how carbon species are cycling between atmosphere, ocean, and organic matter).

Alkalinity: Also performed ASAP, this analysis involves titrating (slowly adding acid while measuring the pH of the sample with an electrode until a transition occurs) the sample to determine the total alkalinity, also required for quantifying the carbonate system.

Ion Chromatography (IC): Here, a small amount of sample is run through a column packed with resin beads that are designed to attract certain ions in the seawater. A solution called the eluent is run along with the samples to carry them through the column. We have two Ion Chromatographs on board. The first contains a column full of beads that attract chloride, sulfate, and bromide. Because the ions have different properties, they travel through the column at different rates. A conductivity sensor measures how effectively the solution flowing from the column conducts current. As each chemical species conducts differently, a comparison of these conductivity values allows us to determine the concentration of each species in the sample. Similarly, the second instrument contains a column tuned to nitrate, nitrite, and bromide. Here, the sensor measures the attenuation of the UV light spectrum passing through the sample. Nitrate and nitrite pass through the column at different rates, thus they pass the sensor at different times, allowing us to compare their attenuation peaks to determine the concentration of each ion.
Kira Homola setting up an IC run.

Chloride Titration: Another titration performed measures the concentration of chloride in a sample using a conductivity electrode. This method gives us a more accurate chloride dataset than the IC

Dennis Graham and Ted Present monitor the chloride titrations.

Density: Last, but certainly not least, we inject water into a new instrument that vibrates a small U-shaped tube full of the sample pore water. Depending on how fast the tube oscillates, the machine can calculate the density of the pore water. Ultimately, this density will be converted to chlorinity. Thus chloride is measured in three ways to determine it as precisely as possible for application to the cruise’s main science objective: reconstructing ocean circulation during the Last Glacial Maximum based on the chloride content of the water at different depths in the ocean.
The geochemistry lab, with all its wonderful instruments.
Now that I’ve thoroughly worn you out, it’s time to go run more samples!

Where Does the Mud Go?

Kira Homola – Geochemist

So, how does each section get subsectioned? Below is an image of two cutting templates, the top being the most common sampling scheme, and the bottom being the most complex. Now let’s take a closer look at each one of the whole round samples, lab by lab.
Templates of how we parse each core section.

Microbiology
MB1: This 10 cm whole round is subsampled into 60 mL syringes and frozen for future microbial analysis at the University of Rhode Island.
MB2: A 10 cm whole round is shared by Nan Xiao and Max Amenabar, where 60 mL samples are frozen for future DNA analysis in Japan, and 40 mL samples are added to microbial cultivations on ship for metabolism analysis back at Montana State University.
NX1: This 15 cm whole round will be subsampled and incubated by Nan back in Japan, where she will analyze the water produced by microbes to quantify their oxygen consumption.
NX2: This 15 cm whole round will also be incubated by Nan, where subsamples will be mixed with different nutrients and then analyzed by NanoSIMS, an instrument that can visualize and quantify whether microbes incorporate the nutrients into their cells.
Microbiology whole rounds, after mud has been extracted with many different sizes of syringes.

Sedimentology and Oxygen
MST: The only parts of the 1.5 meter sections not cut into a bunch of tiny pieces, these samples are run through a Multi-Sensor-Track (MST), an instrument that measures sediment density, resistivity, p-wave velocity, and magnetic susceptibility. These sections then sit for 24 hours to equilibrate (reach a constant temperature throughout) before being measured for oxygen using a fiber optic optode that is inserted through holes drilled into the core liner at 5 cm intervals.
Casey and Ann running samples in the MST van.

At long last, the cores are split by the sedimentology group and inspected to determine their lithologies (the composition of the sediments), as well as any core disturbances, interesting trace fossils, or inclusions. Smear slides are also made and examined under a petrographic microscope to confirm the lithology and to identify and quantify microfossil and mineral content. Finally, the cores are measured for conductivity, wrapped in cellophane, and placed in refrigerated storage, destined for permanent archive at the University of Rhode Island’s Graduate School of Oceanography core repository (supported by the NSF).
The sedimentology team hard at work (Ann Dunlea, Mike Barber, and Jules Dill).

Geochemistry
NBL: This 5 cm whole round is the only type of sample frozen in its entirety, with all the mud kept in the core liner and placed in a -20˚C freezer. Once back at URI, these samples will be placed in a vacuum chamber and crushed, to force the gasses out of the pore water. These gasses will then be extracted and analyzed for the concentrations of the noble gasses, as the amount of each gas in the sample depends on its temperature at the time the water was buried.
IWRZ: These 5 cm whole rounds are sampled for pore water (or interstitial water – hence the IW) using devices called Rhizones, a porous cylindrical filter will a small glass capillary inside that feeds a flexible tube. The filters are inserted into the mud, and syringes are attached to the end of their tubes. When the syringes are propped open, placing suction on the Rhizon, water slowly travels up the tube and into the syringe. Once about 12 mL of water has been collected in the syringe (this takes between 30 minutes and 12 hours, depending on the type of mud), it is aliquoted (divided up between a bunch of different vials), with one IW sample analyzed on board and the rest stored or frozen for future analysis back home. The remaining mud is then divided up, with some frozen and some kept cold for future analysis. The only IW samples from the Rhizon analyzed on board are the Nitrate and Nitrite, both nutrients used by seafloor organisms.

Rhizon whole rounds being sampled.

IWSQ: These 5 cm whole rounds are extracted intact from their PVC liners, and the mud is scraped off the outside of the sample to reveal “clean” mud. Because we want to look at the water within the sediment as a function of depth, it is very important that we sample only from the center of the core, as water can travel between the core liner and the mud and contaminate the outsides of the whole rounds. By cleaning each piece, we remove this “gap water” and retain only mud that has not been in contact with water that could contaminate its true signal. Once cleaned, each chunk of mud is placed inside a Manhiem Squeezer, a large press that pushes a piston down inside a cylinder where the mud is contained, forcing the pore water out of the sediment and through two filters to a syringe. We aim to collect 50 mL of pore water from each sample, but the actual volumes extracted depend on the type of mud and can vary from 12 to 60 mL. Each squeeze can take between 30 minutes to 2 hours, depending on how readily the water will come out of the sediment. Once we get every last drop we can, the syringe is capped and later aliquoted (subdivided) for further pore water analysis. Then the squeeze cake (the compressed mud) is sliced up into little pie pieces and frozen for later analysis.
A squeeze cake in the process of being subsampled, with scrapings from a number of different Rhizon cakes around the edges.

Cores Galore!

Kira Homola – Geochemist
Mike Barber – Sedimentologist

We’ve had some insightful posts about the nitty-gritty science performed on the R/V Knorr this cruise, but what is the big picture? How do we obtain our samples and how are they parsed out? What gets done to them once they leave the core barrel and disappear into the bowels of the ship?
Emily gave an excellent overview of our different cores, and mentioned the complicated process of creating a template for dividing them amongst the various lab groups to maximize our science gleanings. Let’s look a little deeper at how we core:

The Multicore: The Seafloor (“Sediment – Water Interface”)

The multicore tool is a nifty device that deploys multiple core barrels at once. The WHOI multicore tool, our current instrument, drops eight polyethylene core barrels, each 70 cm in length and 4” in diameter, into the surface of the seafloor. This device has a two-part mechanism, with a solid frame suspended from the cable, and a core rosette hanging from a set of weights that is free to very gently descend once the frame touches the seafloor, thus allowing the core barrels to drop into the mud. Once the weights reach the bottom of their descent, they trigger the core caps, with the top cap dropping down to seal in the bottom water, and the bottom cap swinging down on a spring-loaded leaver arm to slice through the sediment and seal it in. The whole apparatus is then hoisted to the surface, and the eight core barrels are extracted from the frame to be sampled. Each core barrel typically contains between 20 cm and 60 cm of seafloor sediment as well as a pristine sample of the bottom water.
Rick Murray and the coring techs prep the multicore tool for deployment.

The bottom water is siphoned off and collected by the geochemists, and the eight core barrels are divided up: one to be measured for oxygen, one to be sliced up by the microbiologists, and two for the geochemists (one to be sliced up and squeezed and one to be Rhizon sampled). The remainder are archived by the sedimentology group.

The Gravity Core: Seafloor Indicator

The first instrument deployed at all of our sites, the gravity core is a relatively simple device consisting of a 17 foot long PVC core barrel, 4 inches in diameter, with 700 pounds of weight at the top. The device is lowered on a cable over the side of the ship to about 100 meters above the seafloor, then lowered quickly into the sediment. There is a sharp metal cutter attached to the base of the PVC pipe that slices into the seafloor upon descent and a clever core catcher that keeps the sediment from sliding back out as the core is pulled up out of the bottom.
The gravity core being deployed.

The gravity core is our test and location instrument, as the sediment recovered (or lack thereof) gives us an excellent indicator of whether the site has favorable attributes for further coring by the Long Core. The gravity core is cut and sampled almost exactly like the Long Core (described below), and may be split and examined early in the process to more completely evaluate the site for further coring efforts. At fully sampled sites (where sediment is recovered from all three coring instruments), the gravity core acts as the midrange link between the shallow but less disruptive multicore tool and the deeper penetrating Long Core system, allowing us to correlate and construct a continuous sediment record.
A sign of a great recovery – the entire outside of the core barrel coated in pelagic clay!

The Long Core System – The Bigger Picture

The Long Core is what it’s all about: a one-of-a-kind instrument designed by the WHOI team that is designed to penetrate a spectacular 45 meters into the seafloor. The R/V Knorr is the only ship in the U.S. fleet that can deploy this device. A complex system of winches, davits, collars, rotating arms, electronics, and technicians required to deploy and recover the instrument occupy the entire aft deck of the ship.

The Long Core system’s barrel consists of a series of three meter steel tubes that are connected together with locking collars to form the entire 45 meter length. Inserted inside the barrel is a five inch PVC core liner that will contain the sediment recovered. This core barrel assembly extends the length of the starboard aft deck, with a slot cut out of the hangar area to accommodate its deployment and recovery. Attached to the top (shipboard aft) end of the core barrel is the core head, a 22,500 pound cylinder held by a rotating clamp on the end of an arm. At intervals around the core barrel are three collars attached by cables to the deployment davits (cranes that extend over the side to raise and lower the core). The davits and arm pick the Long Core up, extend it about 3 meters over the side of the ship, and let out cables at precise rates. The davit farthest from the back of the ship, holding the bottom end of the core, pays out cable the fastest, and the davit closest to the core head pays out the slowest, causing the core to rotate into a vertical position. The collars are then slid down and off the bottom of the barrel, leaving it hanging safely from the arm at the aft starboard corner of the ship. The arm then swings the core around to the center stern of the ship, under the A-Frame (a large structure designed to extend out past the back of the ship for deploying heavy equipment). The last piece of the Long Core assembly is then put in place – the dog dish, as the coring team likes to call it, containing all of the electronics and the acoustic release that drops the core, as well as the link to the braided synthetic rope (designed specifically for heavy lifting) that will lower and raise the whole device to and from the seafloor, up to 20,000 feet below.

Once the Long Core nears the bottom, the coring technicians adjust the coring tool’s height above the seafloor, using the acoustic source on the dog dish. At ~50 meters above the bottom, the acoustic release is tripped, and the core barrel and weight stand detach from the dog dish and descend into the seafloor. A piston inside the core barrel remains in place at the top as the core descends, creating enough relative negative pressure inside the liner to keep the mud intact (with regard to expanding or compressing during coring). The Long Core also include a cutter and core-catcher, generally similar to a gravity core. If all goes well, the core returns to the surface containing up to 45 meters of sediment. To raise the coring tool back onto the deck, the deployment process is performed in reverse, neatly returning the core barrel to its horizontal position so the core liner and sediment can be removed.
The Long Core suspended from its davits as it is being lowered into the water.

Then the real fun begins, as the PVC liner is extruded from the core barrel, cut with a pipe cutter into 1.5 meter sections, capped, and passed to the sedimentology group. These hard-working individuals then spend the next 6-8 hours cutting the 1.5 meter sections into an impressively large number of carefully documented smaller pieces, to the joy of the rest of the science party.

How a Section is Sectioned

To accommodate all of the science groups on board, the core curators have worked closely with all of us to plan and draw up a cutting template, to provide the maximum number of samples while still maintaining a complete picture of the overall core. Each small sample section (called a whole round) is cut from the main 1.5 meter section with a pipe cutter, capped on one side, covered with cellophane on the other, and sent off to the correct lab.
Justine Sauvage delivering whole rounds from the sedimentology team to the geochemistry lab.

Life Beneath The Seafloor

Zak Kerrigan, Microbiologist

Although a secondary objective to the geochemical investigations of this expedition, the search for life in one of Earth’s most extreme environments is a priority to the microbiologists involved, as well as those awaiting the samples on shore.

For almost 100 years scientists have been studying the microscopic life that subsists in the accumulated sediment on the bottom of the ocean. Colonizing and living for millions of years, this unseen world of organisms rival that of all of the big game on the African continent by mass and contain as much carbon as all of the trees in the Amazon jungle. While the numbers are impressive by themselves, it is nothing compared to the myriad ways these organisms are able to survive. They are able to ‘eat’ and ‘breathe’ chemicals that would be deadly to you and me and seem to be quite happy to do so. Understanding the ways in which life is able to survive in this environment expands our understanding of the limits of life on Earth as well as implications for where we may find life on other worlds.

For each pore water sample that is taken for the chemistry team, an adjacent bit of sediment is set aside for microbial analysis. The job of the microbiologists on this cruise is to collect portions of the sea floor using procedures that limit the possibility of introducing organisms that reside here on the surface. Going home and spending a couple months in the lab only to find out that you have managed to collect only your everyday, common kitchen germs would be unpleasant, to say the least.

Unfortunately, the tools required for this undertaking have yet to be available at Costco and affordably priced. For some reason, the demand just hasn’t made it economically viable to create such a product line. Therefore, we have to spend quite a few days in arts and crafts modifying available instruments to suit our needs. This involves delicately cutting off (with hacksaws and steak knives) the tips of a variety of medical syringes so they can be plunged into our slice of mud and extracted in the expectation that the innermost portions of the core never see the light of day or the air we breathe. However, before the syringes can be used in our sections of core we sterilize them in a device called an autoclave. This machine “cooks” the contents using very high temperature steam that turns any life-based chemicals into unrecognizable bits and pieces that don’t show up in DNA analysis. This ensures that any life we find later on should be only from the samples we collected.

Besides Dr. David Smith and myself from URI, we have two visiting microbiologists interested in some very unique aspects of deep sub-seafloor microbial life. Dr. Nan Xiao, from Kochi Institute in Japan, is collecting samples in an attempt to grow some of these organisms in a laboratory environment. She is also conducting experiments to qualify the types of microbes that exist in deep sediment so we may have a better understanding of the microbial diversity. Max Amenabar, a graduate student from Montana State University, is planning to cultivate some of these organisms as well, but his research is focused on the determining the various nutrients (food) that microbes from the bottom of the ocean can live on. Combining these with the many samples we are taking back to URI to store for future research, once a core comes on board we certainly have our hands full.

With two sites complete and five or six more to go, we have only begun to get our feet wet. Luckily, the food has been fantastic, there is never a concern of running out of music to keep us going, and watching the sunrise over the tropical Atlantic just doesn’t seem to get old.

Nan Xiao (Kochi Institute in Japan) and Zak Kerrigan (University of Rhode Island-Graduate School of Oceanography) take microbiology samples. Ann Dunlea (Boston University) photobombs in the background.

 

Syringes inserted into sediment for microbiology samples.

Selecting a Coring Site, or, How a Coring Site is Selected

Rob Pockalny
Geophysicist

The selection of a good coring site begins well before the ship leaves the dock and requires significant background knowledge, on-the-fly data interpretation, and honestly….a little luck.

In advance of the cruise, all available data from the study area are accessed through national data archives at NOAA and the NSF-funded GeoMapApp program. These data include the most up-to-date maps of the seafloor, seismic data that penetrates the upper layers of ocean sediment and crust, and previous sediment cores from the region. The seafloor maps combine low-resolution topography data derived from satellites, and high-resolution bathymetry data from previous cruises. This is pretty much the same data you see when you use GoogleEarth. The seismic data provide an “acoustic x-ray” of the sediment layers to give us a measure of sediment thickness. The sediment cores give us a quick description of the upper 2-3 meters of sediment that we are likely to encounter with our deeper coring system that can reach depths of up to 40 meters. In some cases, these seismic data and sediment core descriptions were collected nearly 40-50 years ago, when most of the senior science team were still in elementary school.

During the cruise, we use three different types of sonar data to help us locate potential coring sites. Seafloor bathymetry and backscatter data are obtained from a multibeam sonar system that is very similar to fishfinders used by recreational fisherman. In our case, the multibeam system is located on the hull of the ship and provides a swath of data that is about 3 times the water depth. These 5 to 15 km wide swaths of bathymetry data quickly allow us to image the depth and shape of the seafloor. Also, the strength of backscatter data (i.e., the loudness of the echo) tell us if there is sediment or bare rock on the seafloor. We also use a sonar system called the “Chirp” that penetrates the sediments and echoes off the different buried layers to give us an estimate of sediment thickness and internal structure of the sediments. You can hear the chirping of this sonar about every 10 seconds throughout the ship, and this can make sleeping very difficult if you are in the berths below the waterline.

During a survey, we use all three sonar systems simultaneously to identify potential targets. During most of the cruise we are surveying in “recon mode” at about 10-12 knots (about normal bicycling speed) to locate potential coring sites that are sediment covered and meet our water depth requirements. Once a potential site is identified, we go into “site survey mode” where we slow down to 7 knots to get a better look at the sediment layers imaged by the Chirp data. Once we find a site that meets our water depth and sediment thickness needs, we have the ship do a quick crossing line at right angles at our preferred site. This crossing line is to ensure the sediment layer pattern we saw on the first pass is consistent throughout the target area.

Shipboard multibeam sonar data, draped over low-resolution color topography.

The final decision to core at any location is a team effort where the various shipboard scientists confer to make sure the site meets our requirements and ensures that the coring effort has a high probability of success. The probability part is where the luck comes in. Sometimes the luck is with you and the cores are full of sediment, which makes for happy scientists and coring technicians. Other times, and typically when you think you finally have the ocean depths figured out, King Neptune humbles you and rejects your attempts to core the briny deep.

Since the site surveys often require the geophysics team to stay up for 24 hours or more, we often go to sleep without knowing whether the coring site is successful or not until we wake up. One of the best feelings is waking up and getting a smile, a high five, or a fist bump when the core is successful. If it isn’t successful… well it’s just bad luck.