Supplementary material to "Bacteriohopanetetrol-x: constraining its application as a lipid biomarker for marine anammox using the water column oxygen gradient of the Benguela upwelling system"

Abstract. Interpreting lipid biomarkers in the sediment archive requires a good understanding of their application and limitations in modern systems. Recently it was discovered that marine bacteria performing anaerobic ammonium oxidation (anammox), belonging to the genus Ca. Scalindua, uniquely synthesize a stereoisomer of bacteriohopanetetrol (“BHT-x”). The ratio of BHT-x over total bacteriohopanetetrol (BHT, ubiquitously synthesized by diverse bacteria) has been suggested as a proxy for water column anoxia. As BHT has been found in sediments over 50 Myr old, BHT-x has the potential to complement and extend the sedimentary biomarker record of marine anammox, conventionally constructed using ladderane lipids. Yet, little is known about the distribution of BHT-x in relation to the distribution of ladderanes and to the genetic evidence of Ca. Scalindua in modern marine systems. Here, we investigate the distribution of BHT-x and the application of the BHT-x ratio in relation to distributions of ladderane intact polar lipids (IPLs), ladderane fatty acids (FAs) and Ca. Scalindua 16S rRNA genes in suspended particulate matter (SPM) from the water column of the Benguela upwelling system (BUS), sampled across a large oxygen gradient. In BUS SPM, high BHT-x abundances were restricted to the oxygen-deficient zone on the continental shelf (at [O2] < 45 µmol L−1, in all but one case). High BHT-x abundances co-occurred with high abundances of the Ca. Scalindua 16S rRNA gene (relative to the total number of bacterial 16S rRNA genes) and ladderane IPLs. At shelf stations with [O2] > 50 µmol L−1, the BHT-x ratio was < 0.04 (in all but one case). In apparent contradiction, ladderane FAs and low abundances of BHT and BHT-x (resulting in BHT-x ratios > 0.04) were also detected in oxygenated offshore waters ([O2] up to 180 µmol L−1), whereas ladderane IPLs were undetected. The index of ladderane lipids with five cyclobutane rings (NL5) correlates with in situ temperature. NL5-derived temperatures suggested that ladderane FAs in the offshore waters were not synthesized in situ but were transported down-slope from warmer shelf waters. Thus, in sedimentary archives of systems with known lateral organic matter transport, such as the BUS, relative BHT and BHT-x abundances should be carefully considered. In such systems, a higher BHT-x ratio may act as a safer threshold for deoxygenation and/or Ca. Scalindua presence: our results and previous studies indicate that a BHT-x ratio of ≥ 0.2 is a robust threshold for oxygen-depleted waters ([O2] < 50 µmol kg−1). In our data, ratios of ≥ 0.2 coincided with Ca. Scalindua 16S rRNA genes in all samples (n=62), except one. Lastly, when investigating in situ anammox, we highlight the importance of using ladderane IPLs over BHT-x and/or ladderane FAs; these latter compounds are more recalcitrant and may derive from transported fossil anammox bacteria remnants.

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Bacteriohopanetetrol-x: constraining its application as a lipid biomarker for marine anammox using the water column oxygen gradient of the Benguela upwelling system

10.5194/bg-2021-257 ◽

2021 ◽

Author(s):

Zoë Rebecca van Kemenade ◽

Laura Villanueva ◽

Ellen C. Hopmans ◽

Peter Kraal ◽

Harry J. Witte ◽

...

Keyword(s):

16S Rrna ◽

Water Column ◽

16S Rrna Genes ◽

Rrna Genes ◽

Ammonium Oxidation ◽

Oxygen Gradient ◽

Upwelling System ◽

Benguela Upwelling ◽

Ladderane Lipids

Abstract. Interpreting lipid biomarkers in the sediment archive requires a good understanding of their application and limitations in modern systems. Recently it was discovered that marine bacteria performing anaerobic ammonium oxidation (anammox), belonging to the genus Ca. Scalindua, uniquely synthesize a stereoisomer of bacteriohopanetetrol (‘BHT-x’). The ratio of BHT-x over total bacteriohopanetetrol (BHT; ubiquitously synthesized by diverse bacteria) has been suggested as a proxy for water column anoxia. As BHT has been found in sediments over 50 Myr old, BHT-x has the potential to complement and extend the sedimentary biomarker record of marine anammox, conventionally constructed using ladderane lipids. Yet, little is known about the distribution of BHT-x in relation to the distribution of ladderanes and to the genetic evidence of Ca. Scalindua in modern marine systems. Here, we investigate the distribution of BHT-x and the application of the BHT-x ratio in relation to distributions of intact polar (IPL) ladderane lipids, ladderane fatty acids (FAs) and Ca. Scalindua 16S rRNA genes in suspended particulate matter (SPM) from the water column, sampled across a large oxygen gradient in the Benguela upwelling system (BUS). In BUS SPM, high BHT-x abundances were constrained to the oxygen deficient zone on the continental shelf (at [O2] < 45 µmol L−1, in all but one case). High BHT-x abundances co-occurred with high abundances of the Ca. Scalindua 16S rRNA gene (relative to the total number of bacterial 16S rRNA genes) and ladderane IPLs. At shelf stations with [O2] > 50 µmol L−1, the BHT-x ratio was < 0.04 (in all but one case). In apparent contradiction, ladderane FAs and low abundances of BHT and BHT-x (resulting in BHT-x ratio’s > 0.04) were also detected in oxygenated offshore waters ([O2] up to 180 µmol L−1), whereas ladderane IPLs were undetected. NL5-derived temperatures suggested that ladderane FAs in the offshore waters were not synthesized in situ but derived from warmer shelf waters. Thus, in sedimentary archives of systems with known lateral organic matter transport, such as the BUS, relative BHT and BHT-x abundances should be carefully considered. In such systems, a higher BHT-x ratio may act as a safer threshold for deoxygenation and/or Ca. Scalindua presence: in the BUS, at [O2] > 50 µmol L−1, the BHT-x ratio was < 0.18 at both off -and onshore sites (in all but one case) and a ratio > 0.18 corresponded in all cases (except one) with the presence of Ca. Scalindua 16S rRNA genes. Lastly, when investigating in situ anammox, we highlight the importance of using ladderane IPLs over BHT-x and/or ladderane FAs; these latter compounds are more recalcitrant and may derive from transported fossil anammox bacteria remnants.

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BHT-x: Constraining its Application as a Lipid Biomarker for Marine Anammox Using a Modern Water-Column Oxygen Gradient

10.3997/2214-4609.202134027 ◽

2021 ◽

Author(s):

Z. Van Kemenade ◽

L. Villanueva ◽

E. Hopmans ◽

P. Kraal ◽

H. Witte ◽

...

Keyword(s):

Water Column ◽

Oxygen Gradient ◽

Lipid Biomarker

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Coupled benthic cycling of iron, phosphorus and sulfur in the Benguela upwelling system

10.5194/egusphere-egu2020-19291 ◽

2020 ◽

Author(s):

Kristin Anna Ungerhofer ◽

Gert-Jan Reichart ◽

Peter Kraal

Keyword(s):

Water Column ◽

Bottom Water ◽

Solid Phase ◽

Oxygen Depletion ◽

Biogeochemical Cycles ◽

Sediment Surface ◽

Upwelling System ◽

Benguela Upwelling ◽

Bottom Waters ◽

The Impact

The Benguela upwelling system (BUS) offshore Namibia is among the most productive ocean regions worldwide and is a globally important reservoir of biodiversity and biomass. The forcing of cold, nutrient-rich deep waters up the coastal shelf leads to high rates of primary productivity in surface waters, intense carbon remineralization and consequently to (bottom water) oxygen depletion on the shelf that varies temporally and spatially with the intensity of the upwelling. Recurring events of deoxygenation have a severe impact on marine ecosystems, for instance increased mortality and altered biogeochemical cycles of key elements such as carbon (C), iron (Fe), phosphorus (P) and sulfur (S). Therefore, it is crucial that we establish a clear mechanistic framework of the impact of oxygen depletion on (global) biogeochemical cycles, not only to allow for the reconstruction of climate-ocean feedbacks in upwelling regions in the past, but to enable predictions of future behavior. During an expedition with RV Pelagia in February of 2019, we collected water column and sediment samples from the shelf and slope off Namibia (100 to 1517 m water depth, bottom water O2 between 0.5 and 175 &#181;mol L-1) and measured nutrient fluxes in on-board sediment incubations to understand the early diagenetic behavior of those key elements and trace metals underlying the (periodically) oxygen-depleted waters of the BUS. We analyzed dissolved concentrations as well as solid-phase speciation of key elements such as iron (Fe), manganese (Mn), phosphorus (P) and sulfur (S) to understand the chemical and physical processes controlling their distribution along the depth/redox-transect. Our results show intense P cycling on the shelf, as evidenced by very high pore-water P concentrations, an enhanced efflux of PO4 to suboxic bottom waters and indications of phosphorite formation at depth in the sediment. N/P ratios well below Redfield indicate N depletion and (relative) P accumulation in the water column, a shift in nutrient stoichiometry that can impact the composition of microbial communities in such waters. Meanwhile, the slope sediments are overlain by oxic bottom waters, retain P more efficiently and exhibit N/P ratios close to Redfield stoichiometry. The capacity of the sediment to buffer toxic sulfide and prevent its release to the water column was dependent on the abundance of sulfide oxidizers at the sediment surface. Furthermore, the variable accumulation of sulfide affected Fe speciation and sedimentary P retention. Overall, we show an intimate coupling between sedimentary cycles of essential elements in the Benguela upwelling system, a stark contrast between shelf and slope environments that is further enhanced by local variation of oxygen depletion and a very strong role of microbes in driving the cycles.

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Disentangling oxygen depletion in the Benguela Upwelling System: A biophysical approach.

10.5194/egusphere-egu2020-21909 ◽

2020 ◽

Author(s):

Natalia Herran ◽

Martin Schmidt

Keyword(s):

Water Column ◽

Ecological Model ◽

Regional Scale ◽

Sediment Resuspension ◽

Oxygen Depletion ◽

Chain Reactions ◽

Upwelling System ◽

System A ◽

Benguela Upwelling ◽

Biophysical Approach

Understanding the multilevel complexity of marine ecosystems is one of the greatest challenges on ecosystem modeling so far, due to the dualism of governing hydrodynamical processes acting on a regional scale and complex biogeochemical chain reactions that happen locally on the marine environment. A coupled hydrodynamic-ecological model based on nitrogen stoichiometry has been developed to better understand the short-term nutrient and oxygen coastal dynamics in the Benguela Upwelling System (BUS). The model shows that the effect of internal waves in the Benguela region re-shapes the benthic ecosystem due to the increased of turbulence on the ocean floor with a consequently increase of fine sediment on the water column. We show that an increase on organic-rich sediment resuspension on the water column enhance oxygen consumption and ultimately contribute to the apparent deoxygenation of the Namibian coastal shelf.

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