Thompson Cruise
June 16 - July 14

• Cruise Report (PDF)
• CTD contour plots and along-track data from the underway system (courtesy Peggy Sullivan/NOAA)

July 12: Sampling along the 70-meter line

The final objective of our cruise is to sample a north-south transect from an area in the northern Bering south of Saint Lawrence Island to a spot in the southern Bering north of the Alaska Peninsula.

This transect runs down the middle of the Bering Shelf. The water in this area is about 70m deep, which gives the line its name.

The data we collect along this line are perhaps the most important hydrographic data of the cruise. The information we glean from the data is also unique.

Right: Scientists climb the multicore as the cruise nears its end. (Dana Africa) See larger image

What's so great about the 70m isobath?

In most parts of the ocean, a transect down the middle of the continental shelf would be very confusing. Tides bring offshore water onto the shelf during part of the day. As the tide turns, that water is replaced by water from near shore. This would make it difficult to interpret hydrographic data from a narrow shelf.

But here, along the Bering shelf, the shelf is so wide -- 500km -- that tidal currents cannot replace the shelf water, so the properties we measure here are actually representative of the shelf water.

By sampling along a north-south transect, the hydrography group can quantify differences between the northern and southern Bering shelf. They can also determine the geographic location of the transition zone between the northern and southern shelf. And, by making these measurements over many years, they can observe whether changing climate causes a latitudinal shift these zones. Left: The CTD gets little rest between stations along the 70-meter line.

What do differences between north shelf and south shelf mean?

Differences in hydrography between the northern and southern Bering shelf are subtle, but biologically important. In the north, the temperature of the bottom water rarely rises above -1.7 deg C. And, the relatively gradual increase in temperature between the bottom and surface waters allows phytoplankton to accumulate in deep water.

This accumulation of algal biomass in subsurface water is observed as high chlorophyll fluorescence by instruments on the CTD, and is called a sub-surface chlorophyll maximum (SCM).

It also indicates presence of a concentrated food source that lasts for most of the summer. The cold bottom-water means that any food that reaches the seafloor enters a virtual refrigerator, so that bottom-dwelling organisms also have a long-term food supply.

In contrast, the benthic refrigerator is not as cold in the south and there is no pronounced SCM. This means food resources further south are transient. The geographic location of the transition zone between these two regimes changes with water temperature and changing climate. Thus, the changes in hydrography along the 70-meter line allow us to assess how changing climate affects the entire ecosystem.

Water sampling marathon

The hydrography team is busy: 58 stations and more than 400 samples to process in just a few days. They work round the clock, collecting samples, determining water properties and measuring nutrients. By the end of the line they are exhausted.

Right: Eric Wisegarver will analyze more than 500 nutrient samples in over a three-day period using this amazing contraption of pumps, tubes, reagents, and detectors.

Cruise recap

The rest of the science team is tired too. Some have been in Alaska for nearly 12 weeks. But we have been fortunate. Despite some rough weather and the usual equipment breakdowns, as we come to the end of the 70-meter line on the final expedition of a four-year field program it is clear that we have accomplished our objectives:

• We have described the water properties in the Bering Sea along with its biological communities.
• We have determined the rates at which food is produced and we are piecing together the puzzle of where it goes in this ecosystem.
• Over the past four years we have studied the base of the food chain during the ice-covered early spring, during the spring phytoplankton bloom, and later in the summer as the food is divided up among different components of the food web.
• We've observed first-hand the importance of melting sea ice in stimulating productivity.
• We've collected data on how this ecosystem functions that can serve as a baseline for future investigations as the Bering Sea slowly warms in step with other high latitude ecosystems.

Individual investigators have also had the chance to test a number of hypotheses about how sub-arctic marine ecosystems operate. We've learned what krill like to eat, how nutrients are recycled, about who eats whom, and about the processes that make this such a productive fishing ground.

I am looking forward to going home in a few days, but I have now grown familiar with the sites, animals, and rhythm of the Bering Sea. As this cruise draws to an end, I realize that I'll miss it.

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July 8: Benthic Nirvana

As we entered the final week of the cruise we found ourselves unexpectedly ahead of schedule. I had padded the cruise schedule with an extra 12 hours in case we ran into bad weather or other delays. But we had canceled some earlier sampling activities due to bad weather, and our deck operations had become more efficient. We found ourselves at the northernmost point in our cruise with an extra 24 hours to spare.

What to do with our extra day? I asked for suggestions and received five mutually-exclusive requests. Some ideas were just not feasible to carry out with just one day. And, a huge storm had developed in the southern Bering Sea with 50-knot winds (right). If we headed south, we would run into really bad weather. So, we headed north to sample the Saint Lawrence Island polynya. See a larger image of the storm

Our choice: the polynya

The St. Lawrence polynya is a region south of the island that remains largely ice free even during the coldest winter months. Right: the St. Lawrence polynya in early spring. (Craig Kasemodel/PolarTREC)

The island blocks sea ice moving from north to south, leaving a region of open water in its wake. The open water allows this region to become productive in early spring, and the food produced in the water is efficiently delivered to the seafloor. This results in a rich community of benthic (bottom-dwelling) invertebrates and fine-grained gooey mud. Sampling this region would be our reward for working so efficiently during the rest of the cruise.

The best day

It was my favorite day of the cruise -– even better than the 4th of July pyrotechnics. The weather had been foggy and drizzly for weeks. The night before we reached the polynya, the wind picked up and seas became rough. I worried that we would be unable to sample this extraordinary spot. In the morning, the wind died down, the clouds parted, and the sun rose beautifully behind the silhouette of St. Lawrence Island.

We collected hydrographic data, measured primary productivity in the water and the rate of particle sinking, using the suite of tracers that we've been measuring throughout the cruise. Sean Brennan collected grab samples and pulled up fantastic creatures from the seafloor. Left: Chief Scientist David Shull holds up a large and spectacular amphipod from Benthic Nirvana (photo: Megan Shatz)

When it was time for us to multicore (right), several scientists arrived to watch. They knew how important it was for me to sample this site. The sea was peaceful. It felt like we were at the very end of the world. As Sean sieved the sediment from his grab samples he began singing a song by Kurt Cobain. We had reached Benthic Nirvana. (photo: John Wilson)

The last leg of the journey

After sampling Benthic Nirvana, we returned to the scheduled sampling routine. We made our way to the 70-meter line. This is a sampling line that runs from St. Lawrence Island in the north to the southern Bering Sea right down the middle of the Bering Shelf. It is the most important line to our hydrography team, which has been making measurements along this line for several years.

Saint Lawrence Island has disappeared behind us. We will pass St. Matthew Island tomorrow. The next land that we see will be the Alaska Peninsula and Dutch Harbor. The storm is still blowing in the southern Bering Sea, but it is moving away and I've scheduled our southern cruise track so that we'll hopefully avoid the worst of it.

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July 4: Sediments, the Bering Sea recycling center

Scientists aboard the Thompson are charting Bering Sea hydrography and nutrients, measuring phytoplankton productivity and the rate at which the plankton are eaten by zooplankton, and determining the fate of the rest of the uneaten plankton biomass.

Some of this food settles to the seafloor where it feeds a diverse array of benthic (bottom-dwelling) creatures. As this food is eaten by organisms in the water and the sediments, some of the nutrients contained within are recycled back into the water to fuel more phytoplankton productivity.

Right: A collection of benthic critters from the northern Bering shelf.

The level of summertime productivity on the Bering shelf depends to some degree on how efficiently these nutrients are recycled. But, where does the food that eventually arrives at the seafloor come from? And, what processes determine how efficiently nutrients are recycled? These are two of the questions that researchers on this cruise are addressing.

Natural tracers in the benthos: They are what they eat

Sean Brennan (right) has been collecting as many benthic organisms has he can on this cruise.

To collect large quantities of sediment, Sean uses a grab sampler. Shaped like a clam shell, the grab bites off a big chunk of mud each time it is deployed. Sean samples the sediment itself with a syringe and sieves the rest of the sediment to separate the animals from the mud and sand.

Sean is working for UAF professor Katrin Iken, who uses stable isotopes of carbon and nitrogen to study the Bering Sea food web. In addition to collecting benthic animals, Sean collects samples from the CTD bottles (for phytoplankton) and from the MOCNESS (for zooplankton). Organisms in all of these samples will be analyzed for their isotopic ratios of carbon and nitrogen.

It turns out that the ratio of carbon isotopes in an organism's body matches the isotopic ratio in what it eats. (You are what you eat.) But, the isotopic ratios of nitrogen get larger as an organism eats higher on the food chain. (You are what you eat plus a little extra 15N.)

By comparing the ratios of stable carbon and nitrogen isotopes in the phytoplankton, zooplankton, and benthos, researchers can work out who is eating whom.

The role of the seafloor in nutrient cycling

The other group studying sediments uses a very different device to sample the bottom. In order to collect many undisturbed samples of the bottom for use in experiments, my research team uses a multicore (left). (photo: Jason Pavlich)

The multicore carries up to eight sampling tubes within a steel frame that looks like a little like a lunar lander. When the multicore hits the bottom, the tubes are slowly pressed into the mud; stoppers on top and bottom then close over the tubes to trap the sediment.

We use the sediment collected by the multicore in different ways. Tubes of mud are transferred to a cold room kept at near-ocean-bottom temperatures and incubated for several days. Changes in the concentration of dissolved oxygen, nitrogen gas, and nutrients in the overlying water are used to calculate rates of sediment respiration and nutrient cycling. The vertical distribution of dissolved chemicals in the sediment are measured to help understand what processes control the nutrient recycling rates.

The multicoring group uses different methods to measure concentrations of solutes that vary over different spatial scales. Right: Several ways to collect pore water to measure solute distributions in the sediment. From left to right: microelectrode, hydraulic squeezer, centrifugation. See larger image

They use a microelectrode to measure oxygen, which varies significantly over a distance of just a tenth of a millimeter. They use a hydraulic jack to squeeze pore water (water contained between grains of sediment) out of cores in millimeter increments to measure changes in nitrate and nitrite, which are important nutrients. They slice the cores in centimeter-wide sections and place the mud into a centrifuge to extract the pore water down the length of the core. (The centrifuge is supported by gimbals that allows it to spin while the ship is rolling.)

The sediment incubations and measurements of solute distributions will allow the multicore team to decipher the role of the Bering shelf sediments in recycling the nutrients that fuel productivity in surface waters.

Independence Day celebration

We have been inching our way toward the northern Bering shelf. We completed an east-west transect from Nunivak Island past St. Matthew Island to the edge of the continental shelf (see our ship's track). There, we deployed the sediment traps again and sampled a deep station (2700 m). The multicore team successfully cored this site and observed algal detritus (the remains of algae that have sunk to the seafloor) on the sediment surface. This indicates that some of the food produced in surface waters and on the Bering shelf reaches the deep sea, perhaps via submarine canyons.

We then turned northeast and steamed inshore, starting a transect that cuts across the entire Bering shelf perpendicular to its isobaths (lines of equal depth).

Today we celebrated the 4th of July in mariner fashion. Steak, sausages, and salmon were cooked outside on the barbecue. I called a temporary halt to science activities so that we could all enjoy dinner together. The highlight of the festivities was a pyrotechnic display (right) off the fantail (aft deck). The captain taught us how to fire marine flares (hand-held and rocket) in case of emergency. Then, we practiced shooting flares off the stern of the ship. (The captain had notified all surrounding vessels that we would be testing flares so no other ships showed up to rescue us.) It was great fun and a terrific way to celebrate Independence Day. (Pyrotechnic photo: Jonathan Whitefield)

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June 30: Students at sea

Oceanographic cruises accomplish more than research. They also serve as training grounds for the next generation of marine scientists. There are seven students aboard the Thompson -- some at sea for the first time; others already seasoned sea-going scientists. Over the last few weeks I have enjoyed getting to know these student scientists. I'd like to introduce them to you.

Elizabeth Siddon

Elizabeth (Ebett) Siddon grew up in coastal New Hampshire but finds southeastern Alaska remarkably beautiful. Ebett is in a PhD program at the UAF School of Fisheries in Juneau, AK.

Though she came to Alaska for kelp, she stayed for fish larvae. Ebett's thesis examines the distribution of pollock and other fish larvae and their energetics (how much energy is packed into each tiny fish). She has found fewer fish larvae on this cruise than she found last year and is still pondering why. Perhaps the answer to that question will form a chapter in her dissertation.

Wesley Strasburger

Wesley Strasburger has been closely connected with the ocean for as long as he can remember. Growing up in Wrangell, a small town on Alaska's Inside Passage, Wes worked in the fishing industry for several years before entering the graduate program in Fisheries at UAF in Juneau.

Wesley is studying the ecology of larval fish asking questions like: Do they compete with each other? Who eats them? What biological interactions determine their abundance and spatial distribution?

Lorelei Smith

Lorelei Smith is an undergraduate in the UAF School of Fisheries and is on this research cruise by accident. (Actually, someone else's accident.)

Lorelei hails from the Yukon Territory in Canada where she worked in civil engineering. Lorelei's interest in fisheries developed when she became a member of several fisheries advisory boards in Canada and was involved in the development of management strategies for North Pacific salmon.

Lorelei is helping Ebett and Wes conduct their research on fish larvae. She was invited to participate in this cruise after another scientist was seriously injured in a freak roller-derby accident. The replaced scientist is recovering at home while Lorelei happily collects fish larvae for her.

Sean Brennan

Sean Brennan grew up in Utah. But after one summer as a US Forest Service intern working in the Tongass National Forest he decided that Alaska would be his new home. Yet another student at UAF, Sean studies rare earth elements in Alaskan streams and in the salmon that are born there. His goal is to develop a method for determining the geographic origin of salmon based on measurements of these elements in salmon ear bones.

On this cruise, he is working for Dr. Katrin Iken of UAF, collecting samples that will be analyzed for natural isotopes of carbon and nitrogen in order to better understand the Bering Sea food web.

Matthew Baumann

Matthew Baumann is a Chicago native. This chemistry major's interest in aquatic systems was kindled during a summer internship at the University of Wisconsin—Milwaukee's Great Lakes Water Institute. It was there he was introduced to naturally-occurring radionuclides that can be used to track the rates of geochemical processes.

There he was also introduced to a girl named Julie. When Julie moved to Rhode Island, Matt entered the PhD program at the University of Rhode Island's Graduate School of Oceanography, where he is studying the handy radionuclide that we met in an earlier blog post -– Thorium-234.

Matt's dissertation focuses on the use of Th-234 to track the fate of organic matter in the Bering Sea. And, although he has sadly lost track of Julie, he is still doing a fine job of keeping track of the Bering Sea's organic matter.

Jessica Cross

Jessica Cross is another chemistry major-turned oceanographer. But, when this native Floridian entered college she thought she was destined to be a literary critic. She loves books. To her horror she discovered that her professors apparently did not. Instead they deconstructed books into a set of simple formulas that facilitated their interpretation and critical evaluation. This ran against the very core of Jessica's relationship with literature. So, she switched majors to chemistry and began working as a laboratory assistant studying proteins.

Ironically, the thing about chemistry that she enjoyed the most was deconstructing complex proteins into simple formulas that facilitated their interpretation and shed light on their function. To Jessica, deconstructionism works in science, not in literature.

But how did a Floridian chemistry major end up as an oceanography major in Alaska? During an internship at the University of Miami she met a post-doctoral research associate who would later become her PhD advisor at UAF. Now, Jessica studies dissolved carbon dioxide in seawater and how increased concentration of carbon dioxide in the atmosphere leads to ocean acidification. She also maintains the flow-through seawater instruments on the ship including a nitrate sensor, a CO2 sensor, and a flow cytometer that counts tiny phytoplankton.

Jessica Faux

Like many of the students I have met on this cruise, an experience during an internship helped to direct Jessica Faux into marine science. In her case, it was an internship at a pharmacy. As a pharmacy major, Jessica loved learning about how drugs affect the human body.

However, she learned during her internship that counting pills for twelve hours a day was not nearly as interesting. So, she switched to biology (with a chemistry minor) and after receiving a teaching certificate began teaching middle-school science.

Listening to the great questions from her middle school students helped Jessica to realize that she had questions about science too. To answer those questions, she enrolled in a PhD program at the University of Maryland Chesapeake Biological Laboratory. She now studies proteins in the ocean, asking the question why some proteins make their way into the food web whereas others are not consumed and are preserved in the ocean.

My students

I'll close this entry on students at sea with a quick story about former students at sea -– my former students. I teach Introduction to Oceanography at Western Washington University to about 80 students each year. With a class this large it is difficult to keep track of every student. So, one can never be certain whether your course has made an impact on their lives. But, when I boarded the Thompson, I discovered my course might be making an impact after all.

I have three former Introduction to Oceanography students on this cruise, all working in different capacities. The most recent student from the class, Rachel Allison, just graduated from Western and is working for me as a summer research assistant. I took former student Greg Brusseau with me on a research cruise in 2008. Now he is on the ship working as a marine technician with the University of Washington. Finally, former student Kyle Pieti is also on the ship as a member of the Thompson deck crew.

Right: WWU Introduction to Oceanography students Greg (2007), Rachel (2008), Kyle (2006)

Progress report

We sampled Zhemchug canyon, but the seas were too rough to permit my team to successfully core the site. We did manage to deploy and recover the sediment traps (left), sample the hydrography and plankton, and even crush a few decorated Styrofoam cups (right) by sending them to the bottom of the canyon (3400 meters deep) in a mesh bag attached to the CTD.

We then sailed northeast and turned due east when approached St. Matthew Island (latitude 60 degrees). This is my favorite part of the Bering Sea. North of 60 degrees latitude the ecosystem changes. We'll encounter different species of plankton. The sediment becomes muddier and harbors more clams and starfish than the sandier sediments further south. We might even collect some soft corals in grab samples. To me, this is where the cruise gets really interesting.

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June 26: Profusion of plankton

Zooplankton (animals that drift in the water) are one of the main consumers of the organic matter produced by phytoplankton. In turn eaten by fish and other zooplankton, they form an important part of the Bering Sea food chain. Some zooplankton live their entire lives floating with the currents; others begin as zooplankton and become fish, or crabs, or other large critters with more control over their motion in the ocean.

Hungry microzooplankton

Several groups of scientists on the Thompson are studying zooplankton abundance, growth, distribution, and reproduction. Diane Stoecker of the University of Maryland is studying the smallest of the zooplankton, termed microzooplankton. These are mostly single-celled organisms (protozoans) that she can collect using the bottles on the CTD rosette.

Right: Diane Stoecker at the microscope and a predatory ciliate named Laboea. (ciliate photo: Diane Stoecker)

Diane performs experiments to determine how fast these tiny creatures feed on phytoplankton. Her results indicate that these greedy little consumers can eat phytoplankton as fast as the phytoplankton can grow. They tend to be somewhat picky, preferring smaller phytoplankton, and their eating habits can thus change both the overall biomass and the species composition of phytoplankton.

The biggest little plankton

Microzooplankton might be voracious eaters of small phytoplankton, but much of the phytoplankton in the Bering Sea is big. Diatoms are the whoppers of the Bering Sea phytoplankton, some measuring a tenth of a millimeter across, and they can form chains that can stretch for several millimeters. (In the world of plankton, this is pretty big.) It takes a bigger grazer to tackle these algae and in the Bering Sea -- this means krill.

Left: Tracy and Megan about to deploy their bongo net to catch krill. (krill photo: Tracy Shaw)

Tracy Shaw from Oregon State University and Megan Schatz of the University of Washington use a bongo net to collect their krill samples. A bongo is essentially two nets in one; when towed trough the water it can catch a lot of krill. Tracy and Megan use krill in feeding experiments to find out what they eat and how their feeding habits affect the rest of the plankton. It turns out that krill don't just eat diatoms: Tracy and Megan's krill are also eating Diane Stoecker's microzooplankton.

Catching medium sized plankton

Intermediate in size between the microzooplankton and krill are many many different species of zooplankton including copepods, juvenile krill and other tiny animals. Alexei Pinchuk of the University of Alaska Fairbanks uses a net called a Calvet to collect these organisms. The Calvet looks like a big pair of pants when towed through the water. In addition to studying copepods and other species of zooplankton that inhabit the waters of the Bering Sea, Alexei has been studying the rate of reproduction in krill in order to assess how changes in climate might affect their populations.

Above: Alexei carries his calvets after sampling and one of the organisms he catches -– a copepod. (copepod photo by Tracy Shaw)

MOCNESS: the can-do plankton net

The biggest, baddest, and most complicated plankton net on this cruise is the MOCNESS. The MOCNESS actually is nine nets in one. It is computer controlled and it even has its own on-board CTD so that it can sample water properties while collecting plankton samples. The MOCNESS is towed behind the ship and the nets are opened and closed at different depths in order to determine the vertical distribution of zooplankton.

The MOCNESS belongs to Alexei Pinchuk, but Elizabeth Siddon and Wesley Strasburger of the University of Alaska Fairbanks are using it to collect fish larvae. Like many marine animals, fish begin life as zooplankton but once they become large enough they leave the plankton to become free-swimmers. Siddon studies the composition of larval fish communities and how much food energy is packed into each tiny fish. Strasburger is studying ecological interactions among different species of fish larvae and other zooplankton.

Right: Elizabeth and Wesley completing a MOCNESS tow and one of their target organisms: a pollock larva. (larva photo by Tracy Shaw)

Travel update

We have collected a lot of plankton in the last few days. We passed the Pribilof Islands two days ago and sampled water near the Pribilof Canyon (a submarine canyon that cuts into the Bering shelf and extends into the deep sea). Fish larvae and other forms of plankton were quite abundant in this productive region. We sampled a deep station (2700 meters deep) near the mouth of the canyon and deployed the sediment traps for a second time. Now we are moving northwest along the "shelf break," a region where the bottom slope and water depth increases as the Bering shelf transitions into the deep sea.

The weather forecast indicates more stormy weather approaching as we head toward a station at Zhemchug canyon, the largest submarine canyon in the world. We'll sample it if the weather holds …

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June 23: Tracking carbon and nutrients with nature's tracers

A survey of water properties shows a snapshot of the ocean: how many nutrients? How much dissolved oxygen? How many plankton or fish? But, the answers we need on this expedition involve rates. The rate of food supply, for example, determines the growth rates of plankton or fish. The rate of nutrient uptake by phytoplankton relative to its rate of resupply sets the nutrient concentrations that we observe.

So how do we estimate the rates of these processes with a snapshot? One way is to set up timed experiments that allow us to observe the rate of change in the properties of interest. Another way is to measure one of the many naturally occurring time-keepers in the ocean. Or, one can do both -- add an easily-measured tracer to an experiment to find out how fast a process is occurring.

Scientists on our cruise are taking advantage of several of nature's tracers to determine rates of organic matter (food) production, its rate of transport to the seafloor, and rates of nutrient cycling. These include Thorium-234, Carbon-14, and Nitrogen-15.

The Thorium storyum

Pat Kelly and Matt Baumann of the University of Rhode Island are measuring a naturally-occurring radioactive element to track the transport of particles and organic matter in the Bering Sea. This element has an impressive-sounding name: Thorium-234. Thorium is named after Thor, the Norse god of thunder. The numbers 234 refer to the total number of protons and neutrons in its nucleus (90 protons + 144 neutrons = 234).

What makes Thorium so special? In part, it is its pedigree. Thorium is the "daughter" (the radioactive decay product) of Uranium-238, the most abundant form of uranium on the planet. Uranium-238 is dissolved in seawater and has a really long half life (4.5 billion years, approximately the age of the Earth). Its daughter Thorium, however, has a very different lifestyle. Thorium is insoluble in seawater so it sticks to particles like glue. Like uranium, Th-234 is radioactive, but its half life is a mere 24 days.

These properties make Th-234 a very special tracer. Because it's radioactive, its concentration acts like a stopwatch. Old particles have very little Th-234 but recently formed particles have much more. Because it sticks to particles, which sink, we can use its concentration can be used to calculate how fast particles are sinking out of the water. Th-234's concentration in Bering Sea sediments can be used to calculate how fast particles arrive there.

RIght: Pat Kelly inserts filtered samples containing Thorium-234 into a lead-lined detector. The lead protects the samples from the radioactivity of the ship and the outside world, not other way around.

Pat and Matt also measure the concentration of thorium and organic matter in sediment traps (floating tubes that catch falling particles). This allows them to track where the organic matter goes, how much leaves the surface water, how much accumulates in sediments to feed the organisms there, and the path it takes to get there.

Carbon-14 and the base of the food chain

The Bering Sea food chain begins with phytoplankton. And the rate of phytoplankton production (creation of organic matter via photosynthesis) determines the rate that the rest of the food chain can eat. Jonathan Whitfield of the Bermuda Institute of Ocean Sciences uses a better known radioactive tracer -- Carbon-14 -- to determine this rate.

Rather than looking for natural C-14, Jonathan injects water samples with C-14 and then measures how much of it enters phytoplankton. This is a direct measure of productivity: creation of organic carbon from inorganic carbon molecules. Jonathan then incubates his seawater samples on deck at different light levels. He adjusts the light level by placing the bottles in mesh bags that allow a known amount of light to enter the bottles.

Above, right: Jonathan Whitefield drops a sample bottle into an on-deck incubator. The seawater in the bottle has been inoculated with Carbon-14 which will allow him to measure the rate of phytoplankton productivity.

Nitrogen-15 and plankton

Kali McKee, of Columbia University's Lamont-Doherty Earth Observatory, uses yet another tracer to track the amount of nitrogen plankton consume when growing. Nitrogen is an important nutrient and its availability can limit the growth rate of summer phytoplankton in the Bering Sea.

Right: Kali injects seawater samples with Nitrogen-15, a stable (non-radioactive) isotope of nitrogen, and incubates the samples much like Jonathan. At the end of her experiments she measures the N-15 inside the plankton via a mass spectrometer.

Through the use of these natural and introduced tracers, scientists can determine where the most food is being produced by phytoplankton, how fast it is created, and where it goes once it is produced.

A little gale doesn't stop science

Much has happened over the last few days of the cruise. After heading northeast along the Alaskan Peninsula, we turned north and then southwest heading from Bristol Bay into deeper water. We ran into a gale with 35 knot winds that slowed our progress for about three days and we cancelled several operations including the MOCNESS (plankton) tows and multicore (sediment) deployments.

Despite our best efforts to protect our gear, a few instruments were damaged in the stormy weather. But, with some creativity and the enthusiastic help of the crew of the R/V Thompson we repaired all of our equipment and as the wind abated we got right back to work. We are now heading northeast again, crossing the Bering shelf in calmer seas, and we're back to work measuring nature's tracers.

Right: Sediment traps are recovered as seas begin to subside following a gale. One trap was broken during deployment.

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June 20: Mapping Bering Sea water properties

Hydrography (mapping of water properties) is an important component of our expedition and one of the principal uses of the CTD and rosette that we worked so hard to fix at the start of the cruise. Co-chief scientist Nancy Kachel leads the hydrography group, working the night shift between midnight and noon and keeping the expedition on track.

Learning a lot from seawater

The hydrography group quantifies the properties of seawater that determine its density (temperature and salinity) and basic biology (nutrients, dissolved oxygen, light, and chlorophyll, which is a measure of phytoplankton biomass).

Right: Fred Menzia of NOAA concentrates on a titration to determine the oxygen content of a seawater sample.

Hydrographic surveys performed several times a year allow observation of changes in phytoplankton biomass and the supply and uptake of nutrients by the plankton.

According to Kachel, the hydrography of the southern Bering Sea has been well documented, but the northern portion has not been well studied -- at least not until this project began.

All together, now

The instrument weighs nearly 3,000 pounds fully loaded with water. Deploying it requires a pallet jack and a whole lot of pushing. It is deployed from an overhead boom (left) designed specifically for this purpose and lowered into the water with a winch.

Right: Dave Kachel helps to push the heavy CTD out of the staging bay in preparation for deployment.

As the CTD passes through the water, members of the hydrography group monitor all the electronic measurements in real time via computers on board the ship. They can "fire" (close) the bottles at any depth with a mouse click.

The "ice cream truck" arrives!

Once the CTD is back on board, the researchers crowd around like kids around an ice cream truck, each wanting water from particular bottles for their research projects. In addition to collecting samples for nutrients, the hydrography group collects samples for oxygen and chlorophyll so that they can calibrate the electronic sensors on the CTD.

Right: University of Alaska Fairbanks graduate student Jessica Cross collects a sample for dissolved oxygen.

Baby fish and the "cold pool"

During the first week of our cruise, we sailed eastward from Dutch Harbor toward Bristol Bay along the northern coast of the Aleutian Island chain. In addition to hydrography, much of our time was spent collecting fish larvae (especially cod and pollock), which are transported by currents along the Aleutian Island chain from their spawning grounds to the southwest.

We can see important hydrographic features when we view a temperature section (right). The horizontal axis represents horizontal distance along the Aleutian Island chain (inshore is to the right). The vertical axis represents water depth. (One decibar (DB) of pressure = one meter of water depth.) The colored contours represent temperature.

See larger image of the temperature section.

The temperature section shows warmer water offshore and near the sea surface and a depth zone at 20 - 30 meters where the temperature changes dramatically. It also shows a broad pool of really cold water (colored blue) in the middle of the section. This is the southern portion of the "cold pool", a huge region of water colder than 2 degrees C that covers much of the central portion of the Bering Shelf.

Cold water ... and cannibalism

The size of the cold pool varies from year to year with important consequences. Cod and pollock avoid water colder than 2 degrees C. When the cold pool is very large, these cannibalistic fish are squeezed into a smaller volume of water and will actually eat each other. This cold water on the Bering Shelf slowly winds its way into the Arctic Ocean. The temperature and extent of the cold pool thus influences the temperature of water entering the Arctic Ocean and its response to climate change.

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June 18: Overview

We have embarked on a 28-day research cruise in the Bering Sea aboard the University of Washington's research vessel Thomas G Thompson to study how the melting of sea ice affects the productivity of the Bering Sea ecosystem. In past cruises, we have observed the dramatic effect of melting ice on productivity (the production of food by phytoplankton) when we observed ice-edge blooms of algae that occurred in spring as the sea ice retreated. We tracked the food produced during these blooms using various sampling methods and naturally-occurring stable and radioactive isotopes.

This is the final cruise of the Bering Sea Project, which began in 2007. Our objective for this cruise is to assess how the organic matter (food) produced in spring has worked its way through the ecosystem and how the other aspects of the ecosystem (such as its nutrients and biological communities) have responded. To do this, we'll conduct a broad oceanographic survey of the Bering Sea. We'll perform experiments at particular stations to study its physical and chemical properties, living creatures, productivity, and its sediments.

Ninety percent of science is showing up

Science doesn't always go as planned. The day before we were scheduled to sail from Dutch Harbor, Alaska, 12 scientists were stranded in three different airports, a few for nearly three days. The vagaries of airplane mechanical problems and Dutch Harbor weather had undermined months of planning.

As airplanes were fixed and weather improved, the stranded scientists trickled into Dutch Harbor. After delays in Seattle and Anchorage, the plane carrying the last science-team arrival (Rachel Allison, left) touched down in Dutch Harbor just before departure time.

Pre-cruise preparations

Our primary instrument is the CTD. CTD stands for conductivity-temperature-depth – basic properties of seawater that determine its density. But, our CTD does much more than measure conductivity, temperature, and depth. It also measures light intensity, dissolved oxygen concentration, and seawater fluorescence (which is correlated with chlorophyll concentration, which is correlated with the biomass of phytoplankton), particle concentration. And, it has twelve 30-liter water sampling bottles arranged in a rosette. The bottles have caps with O-rings on both ends and coated stainless steel springs inside to close them when collecting water from a particular depth. This water is necessary for all the various seawater measurements the different scientists will make and for the experiments they will conduct.

Unfortunately, the new 30-liter bottles leaked. Badly. The inner springs did not have enough tension to properly hold the end caps in place when full of seawater. And, the springs gouged the O-rings when the bottles were cocked, making the problem worse. The leaks could compromise the most important data we planned to collect and they had to be stopped.

It took a day and a half of experimentation, a tube of silicone aquarium sealant, and 24 heavy-duty cable ties, but we stopped the leaks and got the bottles working. At the same time, the snap server, a computer server that handles most of the data we would collect during the cruise failed and was replaced and reprogrammed in the nick of time.

These kinds of problems are typical of oceanographic research. There are no hardware stores at sea so scientists and the ship's crew need lots of spare parts and creative approaches to problem solving. We also practice what to do in case problems arise at sea. As we prepared to leave Dutch Harbor, we practiced the first of what will be weekly training sessions -- the abandon-ship drill.

Right: Scientists donned immersion suits that would keep them warm and afloat in the unlikely event that we needed to abandon the Thompson. We also met to discuss the how we would accomplish the scientific mission with help from the ship's crew.

Underway at last

Finally, after many months of preparation, several days stranded in airports, frantic days of trouble-shooting and problem solving, we reached our first station. We sampled the water, using the CTD, zooplankton (such as krill and fish larvae) using bongo nets and a MOCNESS (Multiple Opening/Closing Net and Environmental Sampling System), and the sediments using a multicorer.

Right: Graduate student Jessica Cross and marine science trainee Russel Rejda recover the CTD and 30-L bottle rosette. So far, so good…

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• Bering Sea Home
• Meetings + Events
• Cruise Planning
• Calendar
• Field Notes
• Field Notes Summary
• 2010
• Forage Fish and Salmon Survey
• Carbon Cycling
• Pollock Surveys
• Thompson (June-July)
• Thompson (May-June)
• Visit to Unalaska
• Polar Sea (Mar-Apr)
• Visit to Togiak
• 2009
• Seabird Telemetry
• At-Sea Patch Dynamics
• Savoonga LTK
• Ichthyoplankton
• Healy (Apr-May)
• Healy (Mar)
• 2008
• Bogoslof + Pribilofs
• Healy (July)
• Healy (Mar-May)
• Healy (Mar)
• Hydrography
• Ichthyoplankton
• Seabird Telemetry
• Pollock
• Sea Ice
• Sounds of the Sea
• Spectacled Eiders
• Walrus
• Winter Oceanography

Acronyms Revealed!
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The BEST-BSIERP Bering Sea Project is a six-year study of the Bering Sea ecosystem,
from the benthos and the atmosphere to human communities, and everything in between.
NORTH PACIFIC RESEARCH BOARD  :: NATIONAL SCIENCE FOUNDATION

Contact the BEST-BSIERP Program Manager with project-related questions.
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