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In situ microscale variation in distribution and consumption of 2 : A case study from a deep ocean margin sediment (Sagami Bay, Japan)
Author(s) -
Glud Ronnie N.,
Stahl Henrik,
Berg Peter,
Wenzhöfer Frank,
Oguri Kazumasa,
Kitazato Hiroshi
Publication year - 2009
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2009.54.1.0001
Subject(s) - benthic zone , bay , sediment , oceanography , pelagic zone , geology , sediment–water interface , in situ , environmental science , geomorphology , chemistry , organic chemistry
A transecting microprofiler documented a pronounced small‐scale variation in the benthic O 2 concentration at 1450‐m water depth (Sagami Bay, Japan). Data obtained during a single deployment revealed that within a sediment area of 190 cm 2 the O 2 penetration depth varied from 2.6 mm to 17.8 mm (average; 6.6 ± 2.5 mm) and the diffusive O 2 uptake, calculated from the vertical concentration gradient within the diffusive boundary layer, ranged from 0.6 mmol m −2 d −1 to 3.9 mmol m −2 d −1 (average; 1.8 ± 0.7 mmol m −2 d −1 , n = 129). However, correction for microtopography and horizontal diffusion increased the average diffusive O 2 uptake by a factor of 1.26 ± 0.06. Detailed 2D calculations on the volume‐specific O 2 consumption exhibited high variability. The oxic zone was characterized by a mosaic of sediment parcels with markedly different activity levels. Millimeter‐ to centimeter‐sized ‚‚hot spots’’ with O 2 consumption rates up to 10 pmol cm −3 s −1 were separated by parcels of low or insignificant O 2 consumption. The variation in aerobic activity must reflect an inhomogeneous distribution of electron donors and suggests that the turnover of material within the oxic zone to a large extent was confined to hot spots. The in situ benthic O 2 uptakes, measured during four cruises, reflected a seasonal signal overlying the observed small‐scale variability. The annual benthic mineralization balanced ~50% of the estimated pelagic production. However, the central bay is characterized by a significant downslope sediment transport, and mass balance estimates indicate 90% retention of the total organic material reaching the bottom of the central bay.