scholarly journals Sink or link? The bacterial role in benthic carbon cycling in the Arabian sea oxygen minimum zone

2013 ◽  
Vol 10 (6) ◽  
pp. 10399-10428 ◽  
Author(s):  
L. Pozzato ◽  
D. Van Oevelen ◽  
L. Moodley ◽  
K. Soetaert ◽  
J. J. Middelburg
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Particulate Organic Matter ◽  
Arabian Sea ◽  
Experimental Period ◽  
Oxygen Minimum Zone ◽  
Trophic Levels ◽  
Isotope Tracer ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic aquatic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea Oxygen Minimum Zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient in these sediments. Moreover, metazoans directly consume labile particulate organic matter resources and thus compete with bacteria for phytodetritus.

scholarly journals Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

2013 ◽  
Vol 10 (11) ◽  
pp. 6879-6891 ◽  
Author(s):  
L. Pozzato ◽  
D. Van Oevelen ◽  
L. Moodley ◽  
K. Soetaert ◽  
J. J. Middelburg
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Particulate Organic Matter ◽  
Experimental Period ◽  
Oxygen Minimum Zone ◽  
Trophic Levels ◽  
Isotope Tracer ◽  
Oxygen Conditions ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus.

scholarly journals Sediment release of dissolved organic matter to the oxygen minimum zone off Peru

2020 ◽  
Author(s):  
Alexandra N. Loginova ◽  
Andrew W. Dale ◽  
Frédéric A. C. LeMoigne ◽  
Sören Thomsen ◽  
Stefan Sommer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Pore Water ◽  
Oxygen Minimum Zone ◽  
Water Interface ◽  
Sediment Release ◽  
Bottom Waters ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterized by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilized by microbial communities. The degradation of POM is associated with dissolved organic matter (DOM) production and reworking. The release of recalcitrant DOM to the overlying waters may represent an important organic matter escape mechanism from remineralization within sediments but received little attention in OMZ regions so far. Here, we combine measurements of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) with DOM optical properties in the form of chromophoric (CDOM) and fluorescent (FDOM) DOM from pore waters and near-bottom waters of the ETSP off Peru. We evaluate diffusion–driven fluxes and net in situ fluxes of DOC and DON in order to investigate processes affecting DOM cycling at the sediment–water interface along a transect 12° S. To our knowledge, these are the first data for sediment release of DON and pore water CDOM and FDOM for the ETSP off Peru. Pore-water DOC and DON accumulated with increasing sediment depth, suggesting an imbalance between DOM production and remineralization within sediments. High DON accumulation resulted in very low pore water DOC / DON ratios (> 1) which could be caused by either an imbalance in DOC and DON remineralization, or to the presence of an additional nitrogen source. Diffusion driven fluxes of DOC and DON exhibited high spatial variability. They varied from 0.2–0.1 mmol m−2 d−1 to 2.52–1.3 mmol m−2 d−1 and from −0.042–0.02 mmol m−2 d−1 to 3.32–1.7 mmol m−2 d−1, respectively. Generally low net in situ DOC and DON fluxes as well as steepening of spectral slope (S) of CDOM and accumulation of humic-like FDOM at the near-bottom waters over time indicated active microbial DOM utilization at the sediment–water interface, potentially stimulated by nitrate (NO3−) and nitrite (NO2−). The microbial DOC utilization rates, estimated in our study, may be sufficient to support denitrification rates of 0.2–1.4 mmol m−2 d−1, suggesting that sediment release of DOM contributes substantially to nitrogen loss processes in the ETSP off Peru.

scholarly journals Sediment release of dissolved organic matter to the oxygen minimum zone off Peru

2020 ◽  
Vol 17 (18) ◽  
pp. 4663-4679
Author(s):  
Alexandra N. Loginova ◽  
Andrew W. Dale ◽  
Frédéric A. C. Le Moigne ◽  
Sören Thomsen ◽  
Stefan Sommer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Pore Water ◽  
Nitrogen Loss ◽  
Oxygen Minimum Zone ◽  
Water Interface ◽  
Sediment Release ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterised by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilised by microbial communities, and the degradation of POM is associated with the production and reworking of dissolved organic matter (DOM). The release of DOM to the overlying waters may, therefore, represent an important organic matter escape mechanism from remineralisation within sediments but has received little attention in OMZ regions so far. Here, we combine measurements of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) with DOM optical properties in the form of chromophoric (CDOM) and fluorescent (FDOM) DOM from pore waters and near-bottom waters of the ETSP off Peru. We evaluate diffusion-driven fluxes and net in situ fluxes of DOC and DON to investigate processes affecting DOM cycling at the sediment–water interface along a transect at 12∘ S. To our knowledge, these are the first data for sediment release of DON and pore water CDOM and FDOM for the ETSP off Peru. Pore water DOC accumulated with increasing sediment depth, suggesting an imbalance between DOM production and remineralisation within sediments. High DON accumulation resulted in very low pore water DOC ∕ DON ratios (≤1) which could be caused by an “uncoupling” in DOC and DON remineralisation. Diffusion-driven fluxes of DOC and DON exhibited high spatial variability and ranged from 0.2±0.1 to 2.5±1.3 mmolm-2d-1 and from -0.04±0.02 to 3.3±1.7 mmolm-2d-1, respectively. Generally low net in situ DOC and DON fluxes, as well as a steepening of spectral inclination (S) of CDOM and an increase in humic-like DOM at the sediment–water interface over time, indicated active microbial DOM utilisation. The latter may potentially be stimulated by the presence of nitrate (NO3-) and nitrite (NO2-) in the water column. The microbial DOC utilisation rates, estimated in our study, are potentially sufficient to support denitrification rates of 0.2–1.4 mmolm-2d-1, suggesting that the sediment release of DOM may on occasion contribute to nitrogen loss processes in the ETSP off Peru.

scholarly journals Spectroscopic detection of a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean

2012 ◽  
Vol 9 (7) ◽  
pp. 2585-2596 ◽  
Author(s):  
R. Röttgers ◽  
B. P. Koch
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Degradation Product ◽  
Oxygen Minimum Zone ◽  
Particulate Fraction ◽  
Deep Chlorophyll Maximum ◽  
Subsurface Waters ◽  
Minimum Zone ◽  
Absorption Shoulder ◽  
Oxygen Minimum

Abstract. Measurements of light absorption by chromophoric dissolved organic matter (CDOM) from subsurface waters of the tropical Atlantic and Pacific Oceans showed a distinct absorption shoulder at 410–415 nm. This indicates an underlying absorption of a pigment whose occurrence is partly correlated with the apparent oxygen utilization (AOU) but also found in the deep chlorophyll maximum. A similar absorption maximum at ~415 nm was also found in the particulate fraction of samples taken below the surface mixing layer and is usually attributed to absorption by respiratory pigments of heterotrophic unicellular organisms. In our study, fluorescence measurements of pre-concentrated dissolved organic matter (DOM) samples from 200–6000 m confirmed a previous study suggesting that the absorption at ~415 nm was related to fluorescence at 650 nm in the oxygen minimum zone. The absorption characteristics of this fluorophore was examined by fluorescence emission/excitation analysis and showed a clear excitation maximum at 415 nm that could be linked to the absorption shoulder in the CDOM spectra. The spectral characteristics of the substance found in the dissolved and particulate fraction did not match with those of chlorophyll a degradation products (as found in a sample from the sea surface) but can be explained by the occurrence of porphyrin pigments from either heterotrophs or autotrophs. Combining the observations of the fluorescence and the 415-nm absorption shoulder suggests that there are high concentrations of a pigment degradation product in subsurface DOM of all major oceans. Most pronouncedly we found this signal in the deep chlorophyll maximum and the oxygen minimum zone of tropical regions. The origin, chemical nature, turnover rate, and fate of this molecule is so far unknown.

scholarly journals Composition and Vertical Flux of Particulate Organic Matter to the Oxygen Minimum Zone of the Central Baltic Sea: Impact of a sporadic North Sea inflow

2018 ◽  
Author(s):  
Carolina Cisternas-Novoa ◽  
Frédéric A. C. Le Moigne ◽  
Anja Engel
Keyword(s):  
Organic Matter ◽  
Baltic Sea ◽  
North Sea ◽  
Particulate Organic Matter ◽  
Oxygen Minimum Zone ◽  
Chl A ◽  
Sinking Particles ◽  
Minimum Zone ◽  
Transparent Exopolymeric Particles ◽  
Oxygen Minimum

Abstract. Sinking particles are the main form to transport photosynthetically fixed carbon from the euphotic zone to the ocean interior. Oxygen (O2) depletion may improve the efficiency of the biological carbon pump. However, how the lack of O2 mechanistically enhances particulate organic matter (POM) fluxes is not well understood. In the Baltic Sea, the Gotland Basin (GB) and the Landsort Deep (LD) exhibit permanent bottom-water hypoxia, this is on occasions alleviated by Major Baltic Inflow (MBI), such as the one that occurred in 2014/2015 which oxygenated the bottom waters of the GB (but not of the LD). Here, we investigate the distribution and fluxes of POM in the GB and the LD in June 2015 and how they were affected by the 2015 MBI. Fluxes and composition of sinking particles were different in the GB and the LD. In the GB, POC flux was 18 % lower at 40 m than at 180 m. Particulate nitrogen (PN) and Coomassie stainable particles (CSP) fluxes decreased with depth, and particulate organic phosphorous (POP), biogenic silicate (BSi), Chl a, and transparent exopolymeric particles (TEP) clearly peaked within the core of the oxygen minimum zone (OMZ), which coincided with a high flux of manganese oxide (MnOx)-like particles. Contrastingly, in the LD, POC, PN, and CSP fluxes decreased 28, 42 and 56 % respectively from 40 to 180 m. POP, BSi, and TEP fluxes, however, did not decrease with depth and only a slightly higher flux was measured at 110 m. MnOx-like particle flux was two orders of magnitude higher in the GB relative to the LD. MnOx-like particles formed after the inflow of oxygenated water into the deep GB may form aggregates with POM. Our results suggest, that when the deep waters of GB were oxygenated (2014/2015 North Sea inflow), not only transparent exopolymeric particles, as indicated previously, but also POC, POP, BSi, and Chl a may bind to MnOx-like particles. POM associated with MnOx-like particles may accumulate in the redoxcline, where they formed larger particles that eventually sank to the seafloor. We propose that this mechanism would alter the vertical distribution and the flux of POM, and it may contribute to the higher transfer efficiency of POC in the GB. This is consistent with the fact that the OM reaching the seafloor was fresher and less degraded in the GB than in the LD.

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