Mugshot: Co-chief Scientist Thorsten Dittmar, photo by grad student JiYoungPaeng
Why DOM?
DOM is important in many aspects. DOM contains several chemical elements essential for the growth of algae in the ocean, e.g., nitrogen, phosphorous or iron. Bacteria can release these nutrients from DOM and in this way promote the growth of algae which in turn serve as food for fishes and other animals living in the ocean. Thus DOM is important for marine food webs and, ultimately, for fisheries.
DOM also contains large amounts of carbon. Carbon dioxide (CO2), an important greenhouse gas, has strongly increased in the atmosphere mainly due to the burning of fossil fuels. The man-made (anthropogenic) increase in CO2 has already warmed our atmosphere, and the expected global warming over the next century will be a major challenge for mankind.
What we don’t know
If, for any reason, only 1% of the carbon in DOM were released each year to the atmosphere, this would double the warming rate on earth. Unfortunately, we don't know whether this can happen, or whether we can protect ourselves from the greenhouse gas by turning more CO2 into DOM.
We do not yet know for sure where the large amounts of DOM in the ocean come from and why some compounds are accumulating in the deep ocean. It is not clear why bacteria don't feed on the DOM in the deep-sea and turn it into CO2. We need to answer these important questions in order to better understand the cycling of carbon on earth and better predict global climate.
FSU’s new environmental geochemistry program
I am also involved in the new Biogeochemical Dynamics Program at FSU. The Biogeochemical Dynamics Program is an interdisciplinary research-oriented, graduate-only program within the FSU College of Arts and Sciences which focuses on environmental biogeochemistry.
Mangroves’ newly-recognized level of even greater importance
Mangroves, the backbone of tropical ocean coastlines, are far more important to the global ocean's biosphere than previously thought.
While their foul-smelling muddy forests may not have the scientific allure of tropical reefs or rain forests, my colleagues at several German research institutions and I have noted that these woody coastline-dwelling plants provide more than 10 percent of essential dissolved organic carbon supplied to the global ocean from land.
See Dittmar, T., N. Hertkorn, G. Kattner, and R.J. Lara, 2006. Mangroves, a major source of dissolved organic carbon to the oceans. Global Biogeochemical Cycles, 20, GB1012.
This research was featured in several articles on the web, for example: Mangroves Importance and Decline Studied.
In Dr. Dittmar's class, Professor Speer gives students a scheduled briefing
Black carbon
Black carbon in the marine system is an emerging field. The publication record is very thin at the moment. There's only one paper (from one single station) on dissolved black carbon in the open ocean (Dittmar T and Koch BP (2006) Thermogenic organic matter dissolved in the abyssal ocean. Marine Chemistry 102, 208-217.)
Whenever we burn organic matter, whether wood, leaves or fossil fuels, not only carbon dioxide is produced but also a whole suite of "thermogenic" organic matter, or black carbon. Combustion-derived matter comprises a wide suite of compounds, ranging from charcoal (yes, the same stuff we use for BBQ), soot (that lines our chimneys) or graphite (the grey stuff in pencils).
Though very different in chemical structure, these molecules have one thing in common: they are very stable in the environment. Some of them do not decay within hundreds of years, others are stable even over millions of years (the soot in your chimney will stay there virtually forever).
Because of these stable properties, black carbon is transported by rivers into the ocean and accumulates in marine sediments. Therefore, black carbon could be a significant sink in the carbon cycle.
Co-Chief Scientist Thorsten Dittmar takes a relaxing work break on the deck of the Research Vessel Roger Revelle, photo by grad student JiYoungPaeng
Global warming or global cooling?
That means whenever we burn something we produce a lot of carbon dioxide (greenhouse warming short term), but we also sequester a small amount of carbon as black carbon (possibly very long term). This sequestration may have a long-term (hundreds of thousands of years) cooling effect on earth's climate.
This is largely theory, because we don't know much about the turnover and stability of black carbon in the marine environment. My hypothesis is that some of the black carbon is actually soluble (especially after bacteria and fungi in soils and sediments have worked on it) and ends up in the dissolved organic matter pool of the ocean. Marine dissolved organic matter could thus be one of the largest black carbon pools on earth if this hypothesis were true.
Collect, concentrate, and analyze back on campus
If true, we have to learn more on how black carbon behaves in the ocean, how fast it decays there and whether or not it accumulates. That's our scientific goal on this cruise: to collect first scientific information on dissolved black carbon for a larger oceanic region.
We need a lot of water for this (4 liters per sample and 250 samples, that makes about 1000 liters or 260 gallons over the whole cruise). We concentrate the samples on board (from 1000 liters to 1.5 liters), and then analyze them back home at FSU with a new technique (that we established last summer at FSU) on black carbon.
The shipboard course I teach
I am also teaching a course aboard the ship, Marine Field Methods, 4 credit hours. The class met weekly prior to departure, during the cruise, and will continue to meet this semester after our return.
Experience onboard a research vessel is essential for a career in oceanography and related fields. This course provides a multidisciplinary hands-on experience of the field methods most commonly used in oceanography. It gives graduate students the opportunity to gain a greater appreciation of the complexity of marine dynamics through the active participation in ocean science field research.
Moreover, the information we gathered on this cruise and the results of the analyses we perform in our FSU labs will augment the existing body of knowledge on the ocean’s physical and chemical functions. This affords our students a prime opportunity to contribute to the bridging of existing knowledge gaps in the field. The cruise is a win-win situation. Thanks, students, FSU, NSF, NOAA, Captain and crew of the R/V Revelle. It’s been a real pleasure.
Outreach coordinator’s comment
Please note that Dr. Dittmar’s publications between 2002 and 2004 include three of the “most requested” marine chemistry articles. One of them #1; another #3. He has exceptional capabilities in explaining scientific processes in a manner non-scientists can easily understand.