3:30 PM - 3:45 PM
[BPT02-19] Long term monitoring of oxygen distributions at sea floor, Sagami bay, Japan.
Keywords:sediment-water interface, oxygen, optode, meiobenthos
Oxygen (O2) distributions at the sediment water interface (SWI) are fluctuated by physical, chemical and biological interactions. Especially, bioturbation and bioirrigation at SWI enhance O2 supply into the sediment, and such benthic activities play significant role on maintaining oxic environment at sediment surface. However, studies of these interactions in deep sea SWI have been limited due to technical limitations for the instrument developments and the operations. In order to investigate the SWI, we constructed a planar O2 optode system to visualize O2 distributions across SWI. This system was optimized for low O2 concentrations, which value was equivalent to the typical O2 minimum zone, ~50μM. Using with a platform (so-called lander) to mount the planar O2 optode, the system was set on the sea floor. On 21/Jan/2008, the deployment for the measurement was stated at Sagami bay, 1170m in water depth by extension of the power cable from Hatsushima deep-sea observatory. Until 31/Jan/2008, the two dimensional O2 profiles were obtained at 1 hour interval. Throughout the deployment, 245 O2 profile images and the corresponding grayscale images were obtained. Throughout the analysis of the images, we found the following aspects and phenomena: (1) O2 penetration depth ranged 5~8mm. (2) O2 irrigations sporadically enhanced the O2 penetration depth to ~10mm. (3) O2 concentrations in the sediment were fluctuated by time. (4) Microtopography and hydrodynamics affected to the O2 concentrations on the sediment surface. (5) Meiobenthic activities suggesting anoxic metabolism were found below O2 penetration depth. In the presentation, we present these characteristics with the O2 images obtained from the in situ measurement.