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ODU Oceanographer Uses Sturdy Camera to Track the Carbon Cycle into the Ocean's Depths

  • Bochdansky in a shipboard laboratory.
  • Camera housing built by ODU machinist Kevin Colvin

The deep ocean composes most of the Earth's biosphere in terms of volume, yet what we have discovered about living things and chemical processes at depths of a mile or more is not only meager, but also sometimes contradictory.

These gaps in scientific knowledge are drags on global climate change research, according to Old Dominion University oceanographer Alexander Bochdansky, and the longer it takes to get answers the bigger the problem becomes.

Bochdansky is the lead author, together with colleagues in the Netherlands and Austria, of a new study, "Role of Macroscopic Particles in Deep-Sea Oxygen Consumption," that literally sheds light on what goes on in the deep, dark ocean. The article was published this week by the Proceedings of the National Academy of Sciences.

"The ocean below 1,000 meters, an environment that does not ever see any sunlight, is the largest environment on our planet," Bochdansky said. "But despite its size, relatively few scientists worldwide study this habitat because it is the most difficult place to reach with submersibles and unmanned probes. In fact, we know the surface of the moon in much more detail than the deep sea, and most places of the deep sea are just as unexplored as Mars."

This is frustrating for scientists because the deep ocean is a repository of information about the chemical nature of our biosphere going back for many decades, and in some cases, for centuries.

Scientists believe if they could better understand the biology and chemistry of the deep ocean they would finally be able to deal with what Bochdansky calls "the elephant in the room when it comes to global climate change."

To tackle this problem, Bochdansky and his colleagues participated in the 2007-08 research expedition called Archimedes III on the Dutch research vessel Pelagia. They conducted tests on a 2,500-mile cruise from Fortaleza, Brazil, along the equator to the Sierra Leone basin and then northwest toward the Cape Verde Islands.

They lowered an instrument bundle commonly referred to as a conductivity, temperature, depth (CTD) rosette to depths of up to 6,000 meters at 17 research stations along the cruise path. The instrument could take water samples at various depths, as well as record temperatures and other information.

But a customized addition to the bundle was needed to carry out Bochdansky's plan. This is a super-waterproof video camera with flashlights on either side. The video and light housings were constructed by Kevin Colvin, who runs the master machine shop at ODU's Frank Batten College of Engineering and Technology.

"It had to be very thick-walled to withstand a pressure of up to 8,700 pounds per square inch, and was machined from one solid billet of stainless steel," Bochdansky explained. No glass could provide the strength and topical clarity needed for the camera window, so the researchers solicited the donation of a sapphire crystal window from Meller Optics Inc. in Rhode Island.

The researchers were looking with the camera for particles - sometimes called marine snow - that are visible to the unaided eye and heavy enough to sink. These particles that include bits of decaying organic matter often are colonized by tiny microbes. These same microbes, which do not sink when freely suspended, dominate oxygen consumption in the ocean's surface waters. This means that freely suspended microbes drive chemical processes at the surface, including the degrading of organic carbon.

With the help of the camera, the researchers found that macroscopic particles do indeed exist, even as deep as 3.5 miles down, and that they seem to dominate oxygen consumption in the areas where they are found, indicating that they are colonized by microbes.

But why does it make a difference whether or not these microbes are concentrated on large particles?

"Many mechanisms change when organisms are in close proximity to each other or to nutritious substrates," Bochdansky explained. "Just imagine, instead of having to drive around town to go to the grocery store to buy food, all you have to do is to stretch out your hand and have all the food within arm's length without even leaving your bed.

"These microbes can process much more organic carbon than when it is freely dissolved at much lower concentrations where they have to hunt for it. The presence of particles can thus mean that processes in the deep sea occur faster than they would if the same number of organisms were evenly distributed in the water column."

Recently, researchers across the globe realized that current models and measurements of the deep sea are inconclusive, meaning that more activity seems to be present in the deep sea than should occur based on known inputs of carbon from the surface ocean.

Bochdansky said there are many possibilities for these discrepancies, including measurement problems. "However, it is also possible that processes in the deep sea are faster because most of the organisms are located on particles. Our data suggest that there are more large particles - visible on our video recordings - present in the deep ocean than we expected, and that there are huge empty spaces that contain very little life between these particles. This was confirmed in our analysis of oxygen. When large particles were present, oxygen was correspondingly low, which led us to the conclusion that oxygen is respired primarily by microbes located on large particles.

"The fact that several paradoxical observations in the deep sea could be explained by the presence of large particles made our findings very interesting to oceanographers studying processes, which was one important reasons why this manuscript was published in the Proceedings of the National Academy of Sciences."

Because the deep ocean is so far removed from the activities on the surface, chemically it still represents a state that existed decades, and in some places even centuries, ago.

Currently there has been an increased interest in the deep ocean by the international scientific community for several reasons:

• The deep sea lags the events in the surface sea by many years and decades, so we can still measure a state when the world was not influenced by human carbon dioxide emissions. Bochdansky said we need to measure the deep sea now in order to set a baseline, and before the changes we cause translate to the deep ocean.

• The deep ocean changes much more slowly than other environments, and activities are dampened and small changes can be measured much more accurately than in the highly fluctuating surface waters. Therefore, any small changes in the deep ocean reflect significant changes in the surface ocean and the world's climate.

• Finally, the deep ocean represents a potentially huge storage reservoir for anthropogenic carbon, the carbon we emit through cars, industry and agriculture. The ocean currently absorbs approximately 50 percent of man-made carbon dioxide globally. This can only continue as long as the deep ocean has not come to an equilibrium with the surface ocean. A deeper understanding of how the world responds to global climate change thus also depends on processes in the deep sea.

"One small part of this overall scientific endeavor is to understand how organisms in the ocean live, and how they are distributed," Bochdansky said. "We built a simple video system to do just that in the deep sea."

Bochdansky is an assistant professor of ocean, earth and atmospheric sciences at ODU. His colleagues in the research are Hendrik van Aken of the Royal Netherlands Institute for Sea Research and Gerhard Herndl of the University of Vienna.

The work was conducted under a grant from the National Science Foundation and the Dutch Science Foundation for a comprehensive study of microbes that live in the deep oceans and how these tiny creatures may play a role in the oceans' reaction to climate change.

Eukaryotic microbes of the deep sea, most of which are flagellates that feed on bacteria, are important to the study of the carbon cycle. But they have resisted study because they live so far below the surface, and because their activities and very existence may be severely impacted if they are hauled up three or four miles onto a research vessel.

The grant also has allowed Bochdansky and his colleagues to do research with a custom-built pressure culture system that allows them to incubate deep-sea samples and then monitor the microbes at the same pressure and temperature that they encounter in nature.

"Our main hypothesis is that the abundance and taxonomic composition of protists (eukaryotic microbes) serve as sensitive indicators of the strength and type-particulate or dissolved-of input of organic carbon into the deep ocean system," the ODU faculty member said in an interview in 2008.

The oceans sequester large amounts of carbon that otherwise might be the atmospheric carbon dioxide that is a major constituent of greenhouse gases. For example, phytoplankton and other organisms on the ocean surface absorb carbon dioxide as they grow. Death and decay of this organic growth results in carbon sinking into the deep ocean. Decay is facilitated by bacteria, and the bacteria may be consumed by protists. So Bochdansky believes that the distribution and ecology of the microbes serve as indicators of how much carbon is present in these vast, dark zones.

This article was posted on: April 21, 2010

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