Future trends in oxygen minimum zone volume are sensitive to model representation of iron

2020 ◽  
Author(s):  
Wanxuan Yao ◽  
Karin Kvale ◽  
Angela Landolfi ◽  
Wolfgang Koeve ◽  
Eric Achterberg ◽  
...  
Keyword(s):  
Oxygen Minimum Zone ◽  
Low Latitude ◽  
Surface Ocean ◽  
Minimum Zone ◽  
The Difference ◽  
Business As Usual ◽  
The Impact ◽  
Production Response ◽  
Oxygen Minimum

<p>Increasing the complexity of the representation of iron in an earth system model can lead to significant differences in surface ocean nutrient pathways in a pre-industrial climate. These differences persist even after automated calibration forces the models to achieve similar fit to the same observational data. We explore the impact of these nutrient pathway differences in the context of climate change by forcing the models (one without iron, one with a seasonally-cyclic iron mask, and one with a fully dynamic iron module) with the RCP8.5 business-as-usual atmospheric CO<sub>2</sub> concentration scenario from years 1800 until 2100. We find that while the global oxygen inventory drops across all models over this period, different trends in the oxygen minimum zone (OMZ) volume arise. Models with iron represented simulate decreases between 60 and 80 percent in OMZ volume, while the model without iron simulates an OMZ volume increase of 10 percent. The difference is attributed to the role of iron limitation in regulating the low latitude primary production response to warming and stratification. We further quantify the corresponding denitrification trends and impact on ocean nitrate inventory. This study illustrates that model structural uncertainty further challenges predictions under a changing climate, and highlights the strong role of iron in regulating nutrient cycling and ocean deoxygenation.</p>

scholarly journals Zooplankton diel vertical migration and downward C flux into the oxygen minimum zone in the highly productive upwelling region off northern Chile

2020 ◽  
Vol 17 (2) ◽  
pp. 455-473 ◽  
Author(s):  
Pritha Tutasi ◽  
Ruben Escribano
Keyword(s):  
Vertical Migration ◽  
Diel Vertical Migration ◽  
Net Primary Production ◽  
Oxygen Minimum Zone ◽  
Zooplankton Biomass ◽  
Taxonomic Structure ◽  
Northern Chile ◽  
Minimum Zone ◽  
The Impact ◽  
Oxygen Minimum

Abstract. Diel vertical migration (DVM) can enhance the vertical flux of carbon (C), and so contributes to the functioning of the biological pump in the ocean. The magnitude and efficiency of this active transport of C may depend on the size and taxonomic structure of the migrant zooplankton. However, the impact that a variable community structure can have on zooplankton-mediated downward C flux has not been properly addressed. This taxonomic effect may become critically important in highly productive eastern boundary upwelling systems (EBUSs), where high levels of zooplankton biomass are found in the coastal zone and are composed by a diverse community with variable DVM behavior. In these systems, presence of a subsurface oxygen minimum zone (OMZ) can impose an additional constraint to vertical migration and so influence the downward C export. Here, we address these issues based on a vertically stratified zooplankton sampling at three stations off northern Chile (20–30∘ S) during November–December 2015. Automated analysis of zooplankton composition and taxa-structured biomass allowed us to estimate daily migrant biomass by taxa and their amplitude of migration. We found that a higher biomass aggregates above the oxycline, associated with more oxygenated surface waters and this was more evident upon a more intense OMZ. Some taxonomic groups, however, were found closely associated with the OMZ. Most taxa were able to perform DVM in the upwelling zone withstanding severe hypoxia. Also, strong migrants, such as eucalanid copepods and euphausiids, can exhibit a large migration amplitude (∼500 m), remaining either temporarily or permanently within the core of the OMZ and thus contributing to the release of C below the thermocline. Our estimates of DVM-mediated C flux suggested that a mean migrant biomass of ca. 958 mg C m−2 d−1 may contribute with about 71.3 mg C m−2 d−1 to the OMZ system through respiration, mortality and C excretion at depth, accounting for ca. 4 % of the net primary production, and so implies the existence of an efficient mechanism to incorporate freshly produced C into the OMZ. This downward C flux mediated by zooplankton is however spatially variable and mostly dependent on the taxonomic structure due to variable migration amplitude and DVM behavior.

scholarly journals Cryptic role of tetrathionate in the sulfur cycle: A study from Arabian Sea oxygen minimum zone sediments

2019 ◽  
Author(s):  
Subhrangshu Mandal ◽  
Sabyasachi Bhattacharya ◽  
Chayan Roy ◽  
Moidu Jameela Rameez ◽  
Jagannath Sarkar ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Potential Role ◽  
Sediment Cores ◽  
Oxygen Minimum Zone ◽  
Sulfur Cycle ◽  
Metagenome Analysis ◽  
Minimum Zone ◽  
Oxygen Minimum

ABSTRACTTo explore the potential role of tetrathionate in the sulfur cycle of marine sediments, the population ecology of tetrathionate-forming, oxidizing, and respiring microorganisms was revealed at 15-30 cm resolution along two, ∼3-m-long, cores collected from 530- and 580-mbsl water-depths of Arabian Sea, off India’s west coast, within the oxygen minimum zone (OMZ). Metagenome analysis along the two sediment-cores revealed widespread occurrence of the structural genes that govern these metabolisms; high diversity and relative-abundance was also detected for the bacteria known to render these processes. Slurry-incubation of the sediment-samples, pure-culture isolation, and metatranscriptome analysis, corroborated thein situfunctionality of all the three metabolic-types. Geochemical analyses revealed thiosulfate (0-11.1 μM), pyrite (0.05-1.09 wt %), iron (9232-17234 ppm) and manganese (71-172 ppm) along the two sediment-cores. Pyrites (via abiotic reaction with MnO2) and thiosulfate (via oxidation by chemolithotrophic bacteria prevalentin situ) are apparently the main sources of tetrathionate in this ecosystem. Tetrathionate, in turn, can be either converted to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria); 0-2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. Notably tetrathionate was not detectedin situ- high microbiological and geochemical reactivity of this polythionate is apparently instrumental in the cryptic nature of its potential role as a central sulfur cycle intermediate. Biogeochemical roles of this polythionate, albeit revealed here in the context of OMZ sediments, may well extend to the sulfur cycles of other geomicrobiologically-distinct marine sediment horizons.

scholarly journals Cryptic role of tetrathionate in the sulfur cycle: A study from Arabian Sea oxygen minimum zone sediments

2019 ◽  
Author(s):  
Subhrangshu Mandal ◽  
Sabyasachi Bhattacharya ◽  
Chayan Roy ◽  
Moidu Jameela Rameez ◽  
Jagannath Sarkar ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Potential Role ◽  
Sediment Cores ◽  
Oxygen Minimum Zone ◽  
Sulfur Cycle ◽  
Metagenome Analysis ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. To explore the potential role of tetrathionate in the sulfur cycle of marine sediments, the population ecology of tetrathionate-forming, oxidizing, and respiring microorganisms was revealed at 15–30 cm resolution along two, ~ 3-m-long, cores collected from 530- and 580-mbsl water-depths of Arabian Sea, off India’s west coast, within the oxygen minimum zone (OMZ). Metagenome analysis along the two sediment-cores revealed widespread occurrence of the structural genes that govern these metabolisms; high diversity and relative-abundance was also detected for the bacteria known to render these processes. Slurry-incubation of the sediment-samples, pure-culture isolation, and metatranscriptome analysis, corroborated the in situ functionality of all the three metabolic-types. Geochemical analyses revealed thiosulfate (0–11.1 µM), pyrite (0.05–1.09 wt %), iron (9232–17234 ppm) and manganese (71–172 ppm) along the two sediment-cores. Pyrites (via abiotic reaction with MnO2) and thiosulfate (via oxidation by chemolithotrophic bacteria prevalent in situ) are apparently the main sources of tetrathionate in this ecosystem. Tetrathionate, in turn, can be either converted to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria); 0–2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. Notably tetrathionate was not detected in situ – high microbiological and geochemical reactivity of this polythionate is apparently instrumental in the cryptic nature of its potential role as a central sulfur cycle intermediate. Biogeochemical roles of this polythionate, albeit revealed here in the context of OMZ sediments, may well extend to the sulfur cycles of other geomicrobiologically-distinct marine sediment horizons.

scholarly journals The role of benthic foraminifera in the benthic nitrogen cycle of the Peruvian oxygen minimum zone

2012 ◽  
Vol 9 (12) ◽  
pp. 17775-17817 ◽  
Author(s):  
N. Glock ◽  
J. Schönfeld ◽  
A. Eisenhauer ◽  
C. Hensen ◽  
J. Mallon ◽  
...  
Keyword(s):  
Benthic Foraminifera ◽  
Oxygen Minimum Zone ◽  
Substantial Contribution ◽  
Individual Species ◽  
Intermediate Water ◽  
Near Surface ◽  
Nitrate Loss ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The discovery that foraminifera are able to use nitrate instead of oxygen as energy source for their metabolism has challenged our understanding of nitrogen cycling in the ocean. It was evident before that only prokaryotes and fungi are able to denitrify. Rate estimates of foraminiferal denitrification were very sparse on a regional scale. Here, we present estimates of benthic foraminiferal denitrification rates from six stations at intermediate water depths in and below the Peruvian oxygen minimum zone (OMZ). Foraminiferal denitrification rates were calculated from abundance and assemblage composition of the total living fauna in both, surface and subsurface sediments, as well as from individual species specific denitrification rates. A comparison with total benthic denitrification rates as inferred by biogeochemical models revealed that benthic foraminifera account for the total denitrification on the shelf between 80 and 250 m water depth. They are still important denitrifiers in the centre of the OMZ around 320 m (29–56% of the benthic denitrification) but play only a minor role at the lower OMZ boundary and below the OMZ between 465 and 700 m (3–7% of total benthic denitrification). Furthermore, foraminiferal denitrification was compared to the total benthic nitrate loss measured during benthic chamber experiments. Foraminiferal denitrification contributes 1 to 50% to the total nitrate loss across a depth transect from 80 to 700 m, respectively. Flux rate estimates ranged from 0.01 to 1.3 mmol m−2 d−1. Furthermore we show that the amount of nitrate stored in living benthic foraminifera (3 to 705 µmol L−1) can be higher by three orders of magnitude as compared to the ambient pore waters in near surface sediments sustaining an important nitrate reservoir in Peruvian OMZ sediments. The substantial contribution of foraminiferal nitrate respiration to total benthic nitrate loss at the Peruvian margin, which is one of the main nitrate sink regions in the world oceans, underpins the importance of previously underestimated role of benthic foraminifera in global biochemical cycles.

scholarly journals Zooplankton diel vertical migration and downward C into the Oxygen Minimum Zone in the highly productive upwelling region off Northern Chile

2019 ◽  
Author(s):  
Pritha Tutasi ◽  
Ruben Escribano
Keyword(s):  
Community Structure ◽  
Vertical Migration ◽  
Diel Vertical Migration ◽  
Oxygen Minimum Zone ◽  
Taxonomic Structure ◽  
Northern Chile ◽  
Daily Rate ◽  
Minimum Zone ◽  
The Impact ◽  
Oxygen Minimum

Abstract. The daily vertical movement of zooplankton, known as diel vertical migration (DVM), can enhance the vertical flux of carbon (C) and so contributing to the functioning of the biological pump. The magnitude and efficiency of this active transport of C may depend on the size and taxonomic structure of the migrant zooplankton. However, the impact that a variable community structure can have on zooplankton-mediated downward C has not been properly addressed. This taxonomic effect may become critically important in highly productive eastern boundary upwelling systems (EBUS), where zooplankton biomass becomes aggregated in the coastal zone, but comprised by a highly variable community structure (size-composition). In these systems, presence of a subsurface oxygen minimum zone (OMZ) can impose an additional constraint to vertical migration and so influencing the downward C export. Here, we address these issues based on a high-resolution zooplankton sampling at three stations off northern Chile (20°S−30°S) during November 2015. Automated analysis of zooplankton composition and taxa-structured biomass allowed us to estimate daily migrant biomass by taxa, amplitude of migration and daily rate of migration, defined as the daily exchange of biomass between the upper mixed layer and below the thermocline. We found that high biomass aggregates above the oxycline, associated with more oxygenated surface waters and this condition was more evident upon a more intense OMZ. Some taxa however, were found closely associated with the OMZ. We found that most taxa were able to perform DVM in the upwelling zone withstanding severe hypoxia. Even, several strong migrants, such as copepods Eucalanidae and Euphausiids, can exhibit a large migration amplitude (~500 m), remaining either temporarily or permanently during the day or night condition within the core of the OMZ and so contributing to the release of C below the thermocline. Our estimates of DVM-mediated C flux showed that migrant biomass (5099 ± 2701 mg C m−2d−1) may contribute with about 678 ± 465 mg C m−2d−1 to the OMZ system through respiration, mortality, and production of fecal pellets, implying the existence of a very efficient mechanism to incorporate freshly produced C into the OMZ. This downward C by zooplankton is however strongly depending on taxonomic structure due to variable migration amplitude and behavior affecting the daily rate of diel vertical migration.

Phylogenetic analyses and nitrate-reducing activity of fungal cultures isolated from the permanent, oceanic oxygen minimum zone of the Arabian Sea

2015 ◽  
Vol 61 (3) ◽  
pp. 217-226 ◽  
Author(s):  
Cathrine Sumathi Manohar ◽  
Larissa Danielle Menezes ◽  
Kesava Priyan Ramasamy ◽  
Ram M. Meena
Keyword(s):  
Deep Sea ◽  
Arabian Sea ◽  
Phylogenetic Analyses ◽  
Terrestrial Ecosystems ◽  
Active Role ◽  
Oxygen Minimum Zone ◽  
Reduction Activity ◽  
Minimum Zone ◽  
Oxygen Minimum

Reports on the active role of fungi as denitrifiers in terrestrial ecosystems have stimulated an interest in the study of the role of fungi in oxygen-deficient marine systems. In this study, the culturable diversity of fungi was investigated from 4 stations within the permanent, oceanic, oxygen minimum zone of the Arabian Sea. The isolated cultures grouped within the 2 major fungal phyla Ascomycota and Basidiomycota; diversity estimates in the stations sampled indicated that the diversity of the oxygen-depleted environments is less than that of mangrove regions and deep-sea habitats. Phylogenetic analyses of 18S rRNA sequences revealed a few divergent isolates that clustered with environmental sequences previously obtained by others. This is significant, as these isolates represent phylotypes that so far were known only from metagenomic studies and are of phylogenetic importance. Nitrate reduction activity, the first step in the denitrification process, was recorded for isolates under simulated anoxic, deep-sea conditions showing ecological significance of fungi in the oxygen-depleted habitats. This report increases our understanding of fungal diversity in unique, poorly studied habitats and underlines the importance of fungi in the oxygen-depleted environments.

scholarly journals The role of benthic foraminifera in the benthic nitrogen cycle of the Peruvian oxygen minimum zone

2013 ◽  
Vol 10 (7) ◽  
pp. 4767-4783 ◽  
Author(s):  
N. Glock ◽  
J. Schönfeld ◽  
A. Eisenhauer ◽  
C. Hensen ◽  
J. Mallon ◽  
...  
Keyword(s):  
Benthic Foraminifera ◽  
Oxygen Minimum Zone ◽  
Substantial Contribution ◽  
Individual Species ◽  
Intermediate Water ◽  
Near Surface ◽  
Nitrate Loss ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The discovery that foraminifera are able to use nitrate instead of oxygen as an electron acceptor for respiration has challenged our understanding of nitrogen cycling in the ocean. It was thought before that only prokaryotes and some fungi are able to denitrify. Rate estimates of foraminiferal denitrification have been very sparse and limited to specific regions in the oceans, not comparing stations along a transect of a certain region. Here, we present estimates of benthic foraminiferal denitrification rates from six stations at intermediate water depths in and below the Peruvian oxygen minimum zone (OMZ). Foraminiferal denitrification rates were calculated from abundance and assemblage composition of the total living fauna in both surface and subsurface sediments, as well as from individual species specific denitrification rates. A comparison with total benthic denitrification rates as inferred by biogeochemical models revealed that benthic foraminifera probably account for the total denitrification in shelf sediments between 80 and 250 m water depth. The estimations also imply that foraminifera are still important denitrifiers in the centre of the OMZ around 320 m (29–50% of the benthic denitrification), but play only a minor role at the lower OMZ boundary and below the OMZ between 465 and 700 m (2–6% of total benthic denitrification). Furthermore, foraminiferal denitrification has been compared to the total benthic nitrate loss measured during benthic chamber experiments. The estimated foraminiferal denitrification rates contribute 2 to 46% to the total nitrate loss across a depth transect from 80 to 700 m, respectively. Flux rate estimates range from 0.01 to 1.3 mmol m−2 d−1. Furthermore we show that the amount of nitrate stored in living benthic foraminifera (3 to 3955 μmol L−1) can be higher by three orders of magnitude as compared to the ambient pore waters in near-surface sediments sustaining an important nitrate reservoir in Peruvian OMZ sediments. The substantial contribution of foraminiferal nitrate respiration to total benthic nitrate loss at the Peruvian margin, which is one of the main nitrate sink regions in the world ocean, underpins the importance of the previously underestimated role of benthic foraminifera in global biogeochemical cycles.

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