"How much carbon is consumed by microbes?"

 READ HENRIK'S DAILY BLOG FROM THE EXPEDITION HERE...

My role on the cruise

My main tasks within this project are to investigate how much of the organic matter that reaches the sea-floor is actually degraded there and released back to the overlying water column as carbon dioxide and nutrients and how much is buried deeper into the sediments.

To investigate this I will measure the rates of oxygen consumption in the sea-floor and the flux of carbon dioxide and nutrients across the sediment-water interface. These rate measurements will be performed in situ by so called Benthic Landers which are autonomous instruments that are released from the ship and sinks down to the sea-floor by their own gravity.

After landing on the sea-floor the landers will perform a number of pre-programmed actions including inserting a chamber in the bottom, which will measure the oxygen uptake and release of carbon dioxide and nutrients from the sea-floor by the use of various sensors as well as by taking water samples. Another lander will specifically measure the bacterial activity using very fine-tipped electrodes that will probe into the bottom at high resolution. Furthermore, by measuring how fast sediment is accumulating on the sea-floor and the carbon content of the same sediments we can calculate how much carbon is buried in the sea-floor.

LANDING ON THE SEA FLOOR - article on Henrik's lander research. (PDF)

My institution

I am a Lecturer in Sediment Biogeochemistry at SAMS and a member of the Biogeochemistry and Earth science department. My main tasks are to do science and teach on biogeochemical processes in coastal, shelf and deep-sea sediments.

Personal thoughts on the cruise

What are you most looking forward to about the cruise?
"To see the Arctic at close range and to go into the sea-ice. I have been working several times above the polar circle (in south Greenland and in the White Sea) but I have never been working this far north before. It would be particularly exciting to see some polar bears and other marine mammals that are relatively common in this area."
 
What will you miss most when you are away?
"My family! I have a wife and two kids that I won't see for two months more or less. They have gone on vacation to Sweden (which is our home country) to visit relatives at the end of June and I won't see them until Ireturn from the cruise towards the end of August. As a marine scientist I have spent quite a lot of time away on scientific cruises so I'm used to the situation, but still I miss the family of course."

What are you dreading most about this cruise?
"Bad weather preventing us from doing all the exciting science that we set out to do. Although summer is the best time (weatherwise) to work in the Arctic, the weather can be unpredictable and changing fast."

What was your most exciting experience ever on a cruise?
"I recently was on a Japanese cruise where we used a ROV (Remotely Operated Vehicle) to place our instrumentation on the sea-floor at 1500m depth off the Japanese coast. The ROV is like an unmanned submarine tethered to the ship and it is equipped with robotic arms and high definition video so that you can sit on the ship and see on a big screen with your own eyes what is going on in the deep ocean in real time. We visited some really interesting places and saw some very strange and exciting creatures."

What was your worst experience on a cruise?
"To be stuck on a ship in the aftermath of a hurricane in the NE Atlantic. We couldn't work for one week and I had to secure myself to the bed to be able to sleep and not falling out."

What great luxury would you like to have on the cruise (but know you cannot)?
"Video-skyping with my family so that I could see and talk to them at the same time. Most probably we won't even be able to e-mail to each other for most parts of the cruise as we will be out of satellite coverage when we head into the ice north of Svalbard."
 

More detail about my science

The major questions I shall be asking on this expedition:

• How much of the biogenic debris that falls down to the seafloor from the overlying water column is actually consumed by the bacteria and animals living there (i.e. how much of this debris will be recycled as carbon and nutrients back into the overlying water column)? How much is buried deeper down in the sediments?
• Which are the main biogeochemical processes responsible for the degradation of the biogenic debris that reaches the seafloor (i.e. what type of bacteria are actually degrading the biogenic debris and how important are animals for this process)?
• How will the above questions be affected by changes in water column productivity as imposed by a diminishing ice cover?

I have ten years experience within the field of benthic biogeochemistry and early digenesis of organic matter. During my PhD, at Gothenburg University (Sweden), I worked on benthic carbon cycling in deep-sea and continental shelf sediments (Stahl et al 2004a+b), with emphasis on different factors influencing the recycling and burial efficiencies of organic carbon (Stahl et al 2004c). During my postdoc at the Marine Biological Laboratory in Helsingør (Copenhagen University, Denmark), I became particularly interested in animal-sediment relationships and how they affect benthic oxygen dynamics (Behrens et al 2007). In a recent study I showed that the presence of a common burrowing brittle star in natural densities could more than double the total sediment oxygen uptake rate compared to sediments without the brittlestars, by indirectly stimulating heterotrophic bacterial respiration as well as re-oxidation of reduced compounds at depth in the sediment (Stahl et al, in prep).

Over the years I have also gained extensive practical experience with both laboratory and in situ benthic flux measurements (Stahl et al 2004a-c, Tengberg et al 2004). My expertise also encompasses microsensor technology including the development and usage of novel planar optodes, which enable 2D imaging of oxygen and pH distributions across the sediment water interface with high spatial and temporal resolution (Stahl and Glud 2005; Stahl et al 2006).

Selected relevant references:

• Stahl H., Tengberg A., Brunnegard J. and Hall P.O.J. (2004a). Recycling and burial of organic carbon in sediments of the Porcupine Abyssal Plain, NE Atlantic. Deep-Sea Research I 51:777-791
• Stahl H, Hall P.O.J., Tengberg A, Josefson A.B., Streftaris N, Zenetos A and Karageorgis A.P. (2004b). Respiration and sequestering of organic carbon in shelf sediments of the oligotrophic northern Aegean Sea. Marine Ecology Progress Series 269:33-48.
• Stahl H, Tengberg A, Brunnegård J, Björnbom E, Forbes T.L., Josefson A.B., Kaberi H.G., Karlé I.M., Olsgard F, Roos P. and Hall P.O.J. (2004c). Factors influencing organic carbon recycling and burial in Skagerrak sediments. Journal of Marine Research 62: 867-907
• Behrens J., Stahl H., Seffensen J.F. and Glud R.N. (2007) Oxygen dynamics around buried lesser sandeel, Ammodytes tobianus (Linnaeus, 1785): Mode of ventilation and metabolic requirements. Journal of Experimental Biology, 210: 1006-1014.
• Stahl H, Hall P.O.J. and Glud R.N. (2008) Importance of two different species of ophiuroids (Amphiura filiformis and Ophiura albida) for benthic mineralization processes in coastal sediments of the SE Kattegat (in prep)
• Tengberg A., Stahl H., Gust G. and Hall P. (2004) Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics. Progress in Oceanography 60:1-28
• Stahl H and R.N Glud (2005) Two dimensional optical O2 measurements in marine bioturbated sediments. Geochimica et Cosmochimica Acta 69(10): A114-A114
• Stahl H., Glud A., Schröder C.R., Klimant I., Tengberg A. and Glud R.N. (2006). A lifetime-based measuring scheme for pH planar optode imaging in marine sediments. Limnolology and Oceanography: Methods 4:336-345

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