APPENDIX
Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical
South Pacific Oceans
Carolin R. Löscher1,4, Hermann W. Bange1, Ruth A. Schmitz2, Cameron M. Callbeck3, Anja Engel1, Helena Hauss1, Torsten Kanzow1, Rainer Kiko1, Gaute Lavik3, Alexandra
Loginova1, Frank Melzner1, Judith Meyer1, Sven C. Neulinger2, Markus Pahlow1, Ulf Riebesell1, Harald Schunck2, Sören Thomsen1, and Hannes Wagner1
Abstract
Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next de-cades to centuries in response to climate change and altered ocean circulation. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs), which are connected to the most productive upwelling systems in the ocean. There are numerous feedbacks among oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and bio-logical interactions in order to adequately assess past and potential future changes. In the following, we summarize one decade of research performed in the framework of the Collaborative Research Center 754 (SFB754) focusing on climate–biogeochemistry interactions in tropical OMZs. We investigated the influence of low environmental oxygen conditions on biogeochemical cycles, organic matter formation and remineralization, greenhouse gas production and the ecology in OMZ regions of the eastern tropical South Pacific compared to the weaker OMZ of the eastern tropical North Atlantic. Based on our findings, a coupling of primary production and organic matter export via the nitrogen cycle is proposed, which may, however, be impacted by several additional factors, e.g., micronutrients, particles acting as microniches, vertical and horizontal transport of organic material and the role of zooplankton and viruses therein.
Manuscript published in Biogeosciences
1GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany. 2Institute of General Microbiology, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 1–9, 24118 Kiel, Germany. 3Max Planck Institute for Ma-rine Microbiology, Celsiusstraße 1, 28359 Bremen, Germany
4Corresponding author: cloescher@geomar.de
145
Selective organic matter mineralization leads to overestimation of oceanic nitrogen loss
Philipp F. Hach1, Gaute Lavik1, Judith Meyer2, Cameron M. Callbeck1, Tim Kalvelage1,3, Helena Osterholz2, Ulf Riebesell2, Thorsten Dittmar4, Marcel M. M. Kuypers1,5
Abstract
Phytoplankton growth in the Ocean is nitrogen limited because the fixation of N2 cannot make up for the removal of fixed inorganic nitrogen (nitrate, nitrite and ammonium) by anaerobic microbial processes.
Biogeochemical and ocean circulation models are used to quantify oceanic gain and loss of fixed nitrogen (N). These models generally assume that biological uptake and release of inorganic N and phosphorus (P) occurs with a nearly constant N:P ratio of 16:1 (Redfield 1958) and that negative deviation of this so-called Redfield ratio is due to the loss of fixed inorganic N as N2 gas (Gruber & Sarmiento 1997). Here we show that preferential organic P remineralization strongly biases N-loss estimates for one of the main regions of oceanic N-loss, the Peruvian Oxygen Minimum Zone (OMZ). The analysis of the elemental and molecular composition of organic matter from the Peruvian OMZ revealed a strong preference in organic P mineralization relative to N upon organic matter breakdown. The resulting preferential release of inorganic P accounts for nearly half of the inorganic N:P ratio based N-deficit for Peruvian OMZ waters, which was so far solely attributed to N-loss processes. This substantially lower N-deficit agrees well with low N-loss rates determined from 15N-incubations. Our combined results indicate that N-loss estimates based on inorganic nutrient stoichiometry might be overestimated by as much as 50%
for marine OMZ waters.
Manuscript in preparation
1Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany. 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany. 3Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Switzerland. 4University of Oldenburg, Postfach 2503, 26111 Oldenburg, Germany.
5Corresponding author; mkuypers@mpi-bremen.de
APPENDIX
Corrosive metabolism of the oil-field sulfide-oxidizing nitrate-reducing epsilonproteobacterium Sulfurimonas sp. strain CVO
Sven Lahme1,4, Cameron M. Callbeck2, Ian Head1, Casey Hubert3
Abstract
Nitrate injection for souring and corrosion control is widely applied in the oil industry. However, in vitro and in situ trials have shown that nitrate injection has the potential to accelerate iron corrosion under certain conditions. In this regard, sulfide-oxidizing nitrate-reducing bacteria (soNRB) are frequently as-sociated with oil exploitations and have been linked to MIC during souring control via nitrate injection.
To gain a better mechanistic understanding of nitrate- and soNRB-mediated corrosion, we conducted a detailed metabolic analysis of the oil field soNRB Sulfurimonas sp. strain CVO during MIC at varying nitrate to sulfide (N/S) ratios. Strain CVO accelerated corrosion to 0.20–0.27 mm/y at high N/S ratios (>1.4) and corrosion decreased by nearly 50% during nitrate limitation (N/S ≤1.3). Detailed S and N compound speciation revealed formation of a variety of potentially corrosive metabolic intermediates (e.g. biogenic S0, S2O32–, SO32–, NO2–) and sterile incubations with individual S and N compounds revealed biogenic S0 and NO2– as the main corrosion agents. In addition, the presence of FeS on iron coupons had a stimulating effect on both S0 and NO2– corrosion and reaction rates. Additional RNA sequencing was conducted to identify genes involved in the formation of these corrosive intermediates. Gene expression analysis suggests involvement of a putative polysulfide reductase (psrABC) in oxidation of H2S to S0. On the other hand, genes coding for sulfide quinone reductases (sqr) as well as a truncated thiosulfate-oxidizing multi-enzyme complex (soxCDYZ) showed high expression during S0 oxidation phase. In addition, various genes coding for hypothetical cytochrome c proteins showed increased expression in the presence of metallic iron and might be involved in iron storage or additional redox processes. The combination of corrosion and gene expression analysis allowed identification of metabolic key-processes involved in corrosive events and refines our understanding of oil-field MIC processes to improve existing souring and corrosion mitigation strategies.
Manuscript in preparation
1School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU UK. 2Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany. 3Department of Geosciences, University of Calgary, Calgary, Canada, T2N 1N4, Canada.
4Corresponding author; sven.lahme@newcastle.ac.uk
147
A new player in the Marine N cycle? Genome and physiology of a new diazotroph isolate from the Peruvian oxygen minimum zone
Clara Martínez-Pérez1, Wiebke Mohr1, Anne Schwedt1, Cameron M. Callbeck1, Harald Schunck2, Gaute Lavik1, Jimena Barrero-Canosa1, Laura Zeugner1, Bernhard Fuchs1, Marcel
M. M. Kuypers1 Abstract
Phytoplankton growth in the Ocean is nitrogen limited because the fixation of N2 cannot make up for the removal of fixed inorganic nitrogen (nitrate, nitrite and ammonium) by anaerobic microbial processes.
Biogeochemical and ocean circulation models are used to quantify oceanic gain and loss of fixed nitrogen (N). These models generally assume that biological uptake and release of inorganic N and phosphorus (P) occurs with a nearly constant N:P ratio of 16:1 (Redfield 1958) and that negative deviation of this so-called Redfield ratio is due to the loss of fixed inorganic N as N2 gas (Gruber & Sarmiento 1997). Here we show that preferential organic P remineralization strongly biases N-loss estimates for one of the main regions of oceanic N-loss, the Peruvian Oxygen Minimum Zone (OMZ). The analysis of the elemental and molecular composition of organic matter from the Peruvian OMZ revealed a strong preference in organic P mineralization relative to N upon organic matter breakdown. The resulting preferential release of inorganic P accounts for nearly half of the inorganic N:P ratio based N-deficit for Peruvian OMZ waters, which was so far solely attributed to N-loss processes. This substantially lower N-deficit agrees well with low N-loss rates determined from 15N-incubations. Our combined results indicate that N-loss estimates based on inorganic nutrient stoichiometry might be overestimated by as much as 50%
for marine OMZ waters.
Manuscript in review
1Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Ger-many. 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.