Healy Cruise #3
July 3-31, 2008

The third Healy cruise of 2008 followed two earlier cruises that focused on conditions directly associated with the retreating ice edge.

Scientists examined summer conditions on the eastern Bering Sea shelf. Although this region is ice-free in summer, ice earlier in the year influences the subsequent development of physical and biological conditions.

Activities included mooring deployment, physical oceanography studies, a hydrographic survey, zooplankton and ichthyoplankton net hauls, sediment sampling, biological rate measurements, water sampling, and seabird and marine mammal surveys.

Cruise Links

• Cruise Plan
• Preliminary conductivity-temperature-depth (CTD) data are now available for the waters of the region.

A Vertically-Integrated Logbook

Posts by Tom Van Pelt, NPRB staff and marine observer

All photos by Tom Van Pelt except where noted.

July 31: Mud People

We're nearing the end of the planned science stations, and there's a distinct aroma of the barn ... meaning that the science crew is ready to wrap the cruise up and get home. Most of the folks on the Healy have been on for four weeks of hard work and they're ready for a break. But the beat goes on until we reach Dutch Harbor. Left: Sediment scientists and the multicorer.

Down in the science labs, I caught up with David Shull (right), assistant professor at Western Washington University, to talk with him about the seafloor work on board -- I wanted to learn more about what the "mud people" are doing.

Life on the bottom

Bottom sediments support a broad variety of benthic (living in or on the seafloor) organisms, including brittle stars, bivalves, worms, and crustaceans. These animals depend on organic matter falling down through the water column and delivering key nutrients like nitrogen and phosphorous. In the Bering Sea, which freezes in the winter and then becomes ice-free in the spring, there is very strong seasonal variation in what lives and dies in the water. Therefore, there is strong variation in what reaches the seafloor. There is also spatial variation, depending on currents, storms, and freshwater inputs.

Not just mud for mud’s sake

Together with Al Devol, David is addressing a set of hypotheses that focus on the role of the sediments in the Bering Sea. But they're not just interested in mud for mud's sake, but how mud is affected by the dynamics in the water column above, and how mud itself affects the life in the water column.

The first step is to sample the mud. For their work, the team needs intact samples of both the mud and the surface water overlaying the mud. Enter the "multi-corer."

Multi-corer to earth, over.

Looking like a skeletal lunar lander, the multi-corer (right) stands nearly ten feet high on eight spindly legs. The frame supports a plunger with six strong plastic tubes pointing downward with open mouths.

The plunger is heavily weighted, and locked in place with heavy pins while it sits on deck. When its hoisted off the deck, the pins are released and the plunger is poised to drop the moment tension is taken off the hoisting wire.

The positioning of the ship is critical -- when the multi-corer touches bottom, the ship needs to hold steady to avoid jerking the instrument across the seafloor.

The multi-corer is owned by Oregon State University, and like a prized racehorse, it travels only with its keeper. Chris Moser has managed the multi-corer for years; he oversees the operation with the confidence of long experience.

Down in the dark depths, the multi-corer's eight feet hit bottom; released of the wire's force holding it up, the lead-weighted central plunger drops down, forcing the tubes a foot or more into the sediment. Then Chris gives the command to reel in the wire. The wire tightens; the mud's suction holds the tubes fast. Strain builds, showing as spiking wire tension on Chris's screen. Suddenly the tension overcomes the suction and the multi-corer is jerked out of the bottom with sediment core samples held fast; caps automatically snap closed over the open-mouthed tubes, supporting the mud on its long journey to the surface.

When the multi-corer breaks the surface and is brought on deck, clean core samples of bottom sediments plus clean samples of the water overlaying the mud equals a happy bunch of mud people. Now the lab work begins.

Muddy lab work

Some mud goes into the cold room, Heather Whitney's zone. Heather is a grad student in Al Devol's lab at UW. She manages the incubation of mud and overlying water, kept at a temperature similar to the cold seafloor. Measuring changes in the overlying water chemistry –- e.g., the "respiration," or oxygen consumption, of the mud -- allows the team to infer how much organic matter the mud receives at that location.

Mud with little organic matter will consume less oxygen; mud with abundant organic matter will consume lots of oxygen. The team also measures changes in nitrogen gas and in other nutrients in the overlying water.

Then it's time to slice the cores into layers, and put each layer separately into a centrifuge to spin out the water held in the tiny spaces between sediment grains. Those water samples will be analyzed to develop two-dimensional profiles of the nutrients in the mud.

After the cold room incubations, the cores are frozen. Back at home, they'll be put under a CAT scanner at David's local hospital to reveal the patterns of animal burrows in the sediments. Finally, the animals will be strained out of the mud, identified, and counted.

Another line of analysis is the influence of "bioirrigation” -- how much nutrient exchange in bottom sediments is driven by tiny animals burrowing around in the sediment. The tool for this investigation is an awesomely complicated apparatus that measures radon, using it as a measurable marker that can be scaled to bioirrigation rates. Right: Shull's assistant Greg Brusseau monitors the radon apparatus.

Much ado about mud -- why?

What’s the point of studying mud? Mud is feeding habitat for commercially-caught species like king crab, and also for threatened species such as spectacled eiders, and for species valuable for subsistence, like walrus. Knowing more about spatial and temporal variation in bottom sediment nutrients will contribute to understanding those important species.

Mud and BEST-BSIERP

Dave and Al's projects will provide critical information for modeling the ecosystem dynamics of the Bering Sea, and for evaluating how the ecosystem might respond to changing ice cover in the Bering Sea. Left: a sediment sample.

Bottom sediments are part of a circular feedback mechanism. Supply of organic matter to the benthos influences the animal community living in the sediments; then the activity of the sediment animals changes how nutrients are used. For example, depending on animal activity, nitrogen -- a critical nutrient for marine life -- can remain in sediments or can be returned to the water column, a phenomenon called "denitrification." So mud animal activity changes the amount of nutrients that cycle back up to the surface, influencing productivity of plankton ... and we're back at the start of the circle.

July 30: Micro Life

Turns out the planktonic world doesn't break down as neatly as we learned in school.

There are zooplankton (tiny marine animals that move with ocean currents) and phytoplankton (tiny marine plants), but there is also a complex world of even tinier one-celled animals that may be both "heterotrophic" (eat other animals) and also "autotrophic" (create their own energy through photosynthesis). And these micro-sized animals play an important and mysterious role in the Bering Sea ecosystem. Above: Diane Stoecker with plankton friends. (plankton image courtesy John Casey/BIOS)

Small world

Phytoplankton are one-celled photosynthetic organisms; they include large diatoms as well as many types of smaller cells. When nutrients and light are abundant in the Bering Sea, large diatoms dominate the phytoplankton community. Diatoms are popular food for copepods and krill, the familiar large zooplankton that themselves are food for fish.

Above: phytoplankton (segmented, left) and microzooplankton (round, right). (Diane Stoecker)

In summer, nutrients (mostly nitrate) get used up, and small phytoplankton dominate in surface waters on the Bering Sea shelf. On this cruise, Diane, working together with her assistant Kristin Blattner, has found that a high percentage of phytoplankton are small-- and by small, they mean very very small. Less than 20 microns in size (much smaller than the width of a human hair), most of these small phytoplankton are simply too tiny to be efficiently eaten by krill. So what eats those small phytoplankton?

Micro-zooplankton

Diane is finding that a high percentage of the phytoplankton production in the Bering Sea's summertime surface waters is eaten by micro-zooplankton -- microscopic, mostly one-celled organisms.

To quantify this micro-grazing, she and Kristin do a lot of filtering and incubating. Above: Kristin filters seawater.

They rely on the "dilution" method, which basically boils down to preparing two bottles of seawater. One is "WSW", whole sea water that's only been roughly filtered to remove large zooplankton. The other is mostly "FSW", filtered sea water, that contains much smaller concentrations of phytoplankton and microzooplankton.

Those bottles are incubated in tanks on the Healy's deck under conditions that replicate normal light and temperature. After the incubation, the WSW and FSW bottles are analyzed using a fluorometer that measures the amount of chlorophyll, and therefore phytoplankton, present in the bottles.

Encountering food

It’s important to point out that micro-zooplankton aren't much for hunting- they generally find their food by simply bumping into it. Scientists call this bumping the "encounter rate". So in the dilute FSW solution, the encounter rate is very low, since there isn't much food to bump into -- thus the micro-zoops do much less grazing per unit of phytoplankon in the FSW bottles.

With that in mind, by comparing how well the phytoplankton do in the minimal-grazing environment of the FSW bottle versus the normal-grazing WSW bottle, Diane can work out the effect of micro-zooplankton on phytoplankton.

Diane does this at dozens of stations across the Healy's Bering Sea study area, so she can develop a picture of spatial variation in micro-zooplankton dynamics. Right: Diane on deck with the incubators.

One micro-burger, please

So the traditional story of zooplankton grazing on phytoplankton just got more complicated -- we need to consider the important intermediate role of micro-zooplankton. Diane has found that many zooplankton will preferentially eat micro-zooplankton over small phytoplankton. As she puts it, microzooplankton are "like little hamburgers" compared to the spiky and crunchy diatoms and other phytoplankton.

After the micro-zoops have become fat and happy grazing away on small phytoplankton, they become food for krill. So the micro-zoops form a kind of nutritional bridge between small phytoplankton and krill, which are critical food for fish like the commercially important walleye pollock. It's part of the complex, interwoven, and seasonal ecosystem dynamics of the Bering Sea that the BEST-BSIERP project aims to understand.

July 29: Grazing the Deep

Large zooplankton—commonly called “krill” -- eat a lot of phytoplankton, the open ocean's version of green grass -- floating in the water column, near enough to the surface to create energy from the sun's rays. But how much phytoplankton do krill eat? Does their diet differ by season or by species? Do they prefer certain kinds of phytoplankton?

Answers lie in on-board experiments run by Megan Bernhardt and Gigi Engel from Evelyn Lessard's lab at the University of Washington, and Tracy Shaw from NOAA Hatfield Marine Lab.

Let's Bongo

The first step is to capture live krill. For live catches, the tool of choice is the "bongo net", a double-headed beast of a net. Its trashcan-sized openings and long net with relatively large mesh gently and efficiently catch krill. When deployed, the net is winched off the deck and out over the water, then the wire is reeled out and the bongo slips down into the depths. As it’s reeled up again, it fishes through the whole water column.

Right: Deploying Bongos on the second Healy cruise. (Carin Ashjian)

Once on deck, the nets are rinsed down into the "cod-ends"; one of the scientists unlatches the cod-end’s plastic cans containing concentrated krill and seawater, and dumps it into a cooler. The team gathers around the cooler and selects healthy individuals for their experiments.

Zoop soup -- literally

Out come the incongruous Chinese soup spoons, perfectly shaped for selecting individual krill, according to Tracy. Left: Gigi Engel and Tracy Shaw spoon out krill.

The team's next step is to prepare temporary homes for the wee animals. The team collects water using specially-designed "Niskin bottles" which can open and close at specific depths.

The krill team takes some 50 liters of seawater that has high concentrations of krill food, assuming that the krill they caught in the bongo were in or were headed for that rich layer.

The team prepares seven bottles of seawater and adds a known number of krill to four of the bottles. Three bottles are left alone as a control. All seven bottles are then "incubated" for 24 hours in a spinning tank (above) that duplicates the light, motion, and temperature of the krill's subsea habitat. Above: Gigi and Megan Bernhardt rinse the incubator.

Grazing rates

Using a combination of chemical analyses and traditional microscope work, the water in each bottle is analyzed before and after the experiment to determine how densities of phytoplankton changed during the incubation. They also analyze the water in the control bottles, since phytoplankton densities change even without krill grazing. Left: Krill sample. (Jillian Worssam, PolarTREC)

Subtracting the natural rate of change from the change in the krill bottles, the team arrives at a number representing krill grazing rates. Microscope work also reveals which species of phytoplankton are preferentially grazed by the krill. Repeating this work in spring and summer cruises in successive years then provides information on seasonal and annual changes.

Who cares?

Krill grazing is a key process that drives effects up and down the trophic chain. For example, if krill are not well-matched to their prey, more of the phytoplankton produced in the near-surface waters of the Bering Sea will fall to the seafloor, where benthic animals will thrive on the abundant food drifting down. However, when krill graze effectively, the sun's energy will be passed along to krill and then on to the animals that prey on them, like commercially important fish stocks of pollock and salmon. So fishermen and other stakeholders in the Bering Sea are -- or perhaps should be -- interested in krill grazing.

Also, one of the overarching goals of the BEST-BSIERP study is to build a model that integrates real-world information on many of the key ecosystem processes in the Bering Sea, and data on krill grazing rates will be a key input into the integrated model.

Eyeballing their ages

Other questions that excite the krill crowd are: How old are the krill? When and how often do they reproduce? Information on krill reproduction is another key feature of the overall Bering Sea ecosystem process -- especially considering the cyclical nature of the Bering Sea, which is strongly controlled by the extent of winter ice cover. Like all animals, zooplankton want to time their reproduction to periods of abundant food supplies. Data on krill age and reproduction help BEST-BSIERP scientists understand the dynamics of krill's role in the ecosystem.

Right: Another krill. (Jillian Worssam, PolarTREC)

So how do you age a krill? It’s all in the eyes. Karen Taylor, Rachel Pleuthner, and Charlie Morgan from Rodger Harvey's lab at the University of Maryland spend their nights clipping off krill eyeballs. "Lipifusion" is a feature of krill eyes that it is scaled to the krill's age and is measurable.

Lipifusion is not “countable” like tree rings; instead, you need a scale of reference. So this group is collaborating with another BEST-BSIERP researcher, Alexei Pinchuk, who will capture live female krill that are "gravid" (about to release eggs). Alexei will then raise known-age krill at the Alaska SeaLife Center in Seward. Then, by putting the known-age eyeballs through the same analysis that the unknown-age eyeballs went through, the team will have an age scale.

It’s a bit grim, especially if you're a krill, but the information gained from the eyeball-clipping will help model the population dynamics of the Bering Sea zooplankton, and add accuracy to the overall BEST-BSIERP ecosystem modeling effort.

July 24: A Mighty Haul of Zooplankton

Alexei Pinchuk (right) has been busy aboard the Healy, leading an effort to quantify the distribution and abundance of the zooplankton communities in the cruise's eastern Bering Sea study region.

Zooplankton are a key ecological currency of the Bering Sea. A wide range of animals, from whales to birds, relies on a steady diet of zooplankton to fuel their growth and reproduction. BEST-BSIERP zooplankton studies are in place to answer questions such as: Where are they? How many are there? What are the environmental variables that structure their abundance and distribution?

The MOCNESS monster

Alexei's study tool of choice is the mighty MOCNESS plankton net -- the "Multiple Opening and Closing" NEt SyStem -- a vaguely sinister-looking rectangle of stainless steel equipped with nine nets that can be remotely opened and closed. Left: MOCNESS deployment on another cruise. (courtesy WHOI)

When the MOCNESS is underwater, a small battery-driven motor connected to the ship by a wire trips a trigger that allows one net at a time to passively fall open while simultaneously forcing the previous net closed. Sensors on the net frame also deliver information on the net's depth, the angle of the net's opening, and on key properties of the water such as temperature and salinity.

Twenty minutes in the life of a MOCNESS

On an oceanographic research cruise, much of the action happens at night, when zooplankton aren't hiding from daylight predators. The MOCNESS is lifted above the deck by a wire coming through a massive pulley attached to a ten-meter high frame that pivots fore-and-aft. Once the MOCNESS is clear of the deck, Chuck "Run-Amok" Bartlett, one of the ship's Marine Science Technicians, uses a joystick to dangle the MOCNESS over the water off the stern.

As the ship holds a steady speed of 2 knots, he slowly pays out wire until the MOCNESS is immersed. Alexei, Chuck, and the others are well-practiced -- this is the 51st MOCNESS deployment of the cruise. Sitting at his laptop, Alexei monitors the net and confirms that its sensors are working properly; a calm command delivered to Chuck sitting nearby starts the wire moving again and we watch on Alexei's laptop as the net drops smoothly towards the bottom.

The depth here is 105 m; when the net's depth meter shows it at 90 m, Alexei signals Chuck to halt the wire. We see the net's progress on screen: a mouse click and the second net opens, closing the first net; a command to Chuck and the wire begins to reel in, pulling the net upwards at a steady rate. The second net is equipped with a precise mesh size and a collecting can at its end, allowing water to pass through but trapping zooplankton in the can.

At 75 m, another mouse click drops open the third net, and so on, at steady intervals until the net is raised out of the water and lowered onto the deck. Here, Alexei and helpers Charlie and Jillian rinse the nets and decant the sampling cans into jars for transport back to the lab on land, where numbers and biomass of different zooplankton species will be determined. A flowmeter mounted on the net lets Alexei estimate the density of zooplankton in the different ocean layers that each net fished. Right: Zooplankter Cliona sp. (Russ Hopcroft)

Why multiple openings and closings?

Horizontal layers and vertical boundaries define life in the ocean. What looks from the surface like a featureless vastness is in fact broken up into layers and blocks, driven by current flows and differentials in temperature and salinity. Sunlight and availability of nutrients further stratify the ocean waters into zones that are more or less favorable for different kinds of life. As a botanist wouldn't mix plant samples from forests, meadows, and deserts into one jumbled-up sample bag, a zooplanktologist wants to sample animals from discrete layers in the ocean -- thus the MOCNESS openings and closings.

How does it all fit together?

Alexei's work -- deploying the MOCNESS at dozens and dozens of stations across the eastern Bering Sea continental shelf area -- will build a three-dimensional map of zooplankton distribution and abundance in the region, forming the foundation for understanding what shapes this map.

Alexei's records of temperature, salinity, and fluorescence (an index of phytoplankton density in the water) provide a starting point for understanding the controlling factors, but this is where the “integrated ecosystem research” of BEST-BSIERP comes into force: other scientists on board measure chlorophyll, currents, nutrients, and other factors known to influence zooplankton populations, so Alexei will be able to profit from their work in broadening his understanding of the controlling factors.

Still other scientists working on zooplankton-eating fish, birds, and marine mammals will be able to draw on Alexei's data to help interpret their own studies. Alexei had done similar sampling on the springtime cruise when sea ice dominated the ecosystem, so by making comparisons with results from this summer cruise, he'll be able to better understand how ice shapes zooplankton populations and consequently what influence climate change and disappearing sea ice might have.

Note: To date, Pinchuk's work has not revealed any plankton resembling the image above.

July 22: Where, When and How Many?

Mark Rauzon (right) and I make bird and mammal observations any time the Healy is underway and there is enough visibility. We stand on the port (left) side of the bridge.

We stand more than 65 feet above the surface of the ocean, with a commanding view across the waves -- that is, when the fog occasionally clears, which hasn’t been often.

An imaginary strip of ocean

To measure bird and marine mammal abundance, we establish an imaginary strip of water that runs ahead and to the side of the ship, and we identify and count every animal that occurs in that strip. We use a computer linked to the ship’s GPS; software records our position to document our survey line, and we input numerical and behavioral data on the animals we see in the strip. We also use concentration, sharp vision, and long experience with the marine birds and mammals in the region.

Codes make data recording more efficient. “Three nofu” is three NOrthern FUlmars; “bin two” is the location we spotted the birds within the strip; and “on scan” means that the bird were flying when we spotted them. Left: Northern Fulmar in flight.

After the field season, our data will enable the project’s principal investigator, Kathy Kuletz, to compute density by species, which can then be analyzed against other biological or physical variables. The data can be mapped in a GIS for visual interpretation or for spatial analyses.

Identifying and counting birds and mammals can look pretty confusing when we’re surrounded by swirling birds, or it can look dead boring when we’re plowing through seas with no birds in sight. It’s rarely boring because we never know what’s going to appear next -- a rare or endangered species like the Short-tailed Albatross? Or an unusual aggregation of plankton-eating Fork-tailed Storm-Petrels? Or something unexpected, like a Mottled Petrel (courtesy Birdfinders UK) appearing out of the fog like a visitor from a different and far-away world?

Why does this matter?

Aside from nearness to breeding colonies, the key force that drives seabird and marine mammal distribution and abundance is prey availability. Its all about food. And this is where the BEST-BSIERP project comes in -- birds and mammals eat fish and plankton, plankton eat phytoplankton, phytoplankton are fed by nutrients and carried by currents, and all of these things are influenced by currents and by sea ice.

Our understanding of seabirds and marine mammals will deepen when BEST-BSIERP combines information about bird and mammal abundance and distribution at sea with information on prey distribution and oceanographic variables.

A better understanding of seabird and marine mammal interaction with the Bering Sea ecosystem will be helpful as fisheries managers use new ecosystem-based management approaches aiming to minimize fishery impacts on other parts of the ecosystem, and also can be used in predictive models of changes in the Bering Sea resulting from a changing climate. Left: Evening near St. Matthew Island.

Flying underwater

Near midnight we were just south of St. Matthew Island (above) when the fog cleared and the wind dropped. Common and Thick-billed Murres (right) treated us to a magical sight as they dove into the clear water, flying just under the surface, compact powerful shapes stroking away from the oncoming steel hull, gleaming pale-green and streaming silver bubbles as they rose back to the surface. (Francis Wiese)

 

July 21: Four Hundred and Twenty Feet of Icebreaking Steel

What is BEST-BSIERP? And why is Tom on an icebreaker in the central Bering Sea in July?

BEST-BSIERP is a big acronym for a very big project, aiming to develop a fuller understanding of the ecosystem dynamics of the Bering Sea in the context of changing climate.

I joined the cruise 17 July, boarding Healy at St. Paul Island, one of the Pribilof Islands in the central Bering Sea. The Healy (right) is the largest ship in the Coast Guard: Four hundred and twenty feet of icebreaking steel, as the sticker on a crewman’s battered hardhat proclaims.

It takes a village to support science

So why is an icebreaker busy with oceanographic and ecological research out here in the Bering Sea, in the ice-free summer? In fact, the Healy is unique in the Coast Guard; her mission is explicitly to support science, and NSF and NPRB have been able to engage the ship as a key vessel to support BEST-BSIERP.

On this 29-day cruise, some 45 scientists are working aboard the ship, supported by the ship’s crew of 80 enlisted men and 16 officers -- it’s like a small floating village, if a village could be entirely focused on marine research. Left: BEST-BSIERP scientists Tom Weingartner and Diane Stoecker en route to board the Healy. (Jillian Worssam, PolarTREC)

Earning my keep

My colleague Mark Rauzon and I are working as seabird and marine mammal observers aboard the ship as she makes her way through the Bering Sea. We stand on the bridge, scanning the ocean and sky to measure marine bird and mammal abundance. But when we’re not moving -- when we stop at “stations” to deploy a broad array of instruments to sample the habitat, capture marine plants and animals, or gather oceanographic data -- I’m learning about the projects aboard and how they link together.

A vertically-integrated blog

Over the next few days I’d like to introduce you to those projects, and I’ll attempt to explain how they fit into the larger picture of BEST-BSIERP and the Bering Sea ecosystem. That’s where the “vertically integrated” part comes in -- I’ll progress in a top-to-bottom fashion, starting at the surface tomorrow with a look at the marine bird and mammal research and moving through the water column to end up at the muddy depths of the seafloor.

 

Science Brought to You By ...

Right: The science group on HLY0803 takes time out for a picture.

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