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Rippeth T, Shen S, Lincoln B, Scannell B, Meng X, Hopkins J, Sharples J. The deepwater oxygen deficit in stratified shallow seas is mediated by diapycnal mixing. Nat Commun 2024; 15:3136. [PMID: 38605081 PMCID: PMC11009404 DOI: 10.1038/s41467-024-47548-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 04/01/2024] [Indexed: 04/13/2024] Open
Abstract
Seasonally stratified shelf seas are amongst the most biologically productive on the planet. A consequence is that the deeper waters can become oxygen deficient in late summer. Predictions suggest global warming will accelerate this deficiency. Here we integrate turbulence timeseries with vertical profiles of water column properties from a seasonal stratified shelf sea to estimate oxygen and biogeochemical fluxes. The profiles reveal a significant subsurface chlorophyll maximum and associated mid-water oxygen maximum. We show that the oxygen maximum supports both upward and downwards O2 fluxes. The upward flux is into the surface mixed layer, whilst the downward flux into the deep water will partially off-set the seasonal O2 deficit. The results indicate the fluxes are sensitive to both the water column structure and mixing rates implying the development of the seasonal O2 deficit is mediated by diapcynal mixing. Analysis of current shear indicate that the downward flux is supported by tidal mixing, whilst the upwards flux is dominated by wind driven near-inertial shear. Summer storminess therefore plays an important role in the development of the seasonal deep water O2 deficit.
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Affiliation(s)
- Tom Rippeth
- School of Ocean Sciences, Bangor University, Anglesey, LL59 5AB, Wales, UK.
| | - Sijing Shen
- School of Ocean Sciences, Bangor University, Anglesey, LL59 5AB, Wales, UK
| | - Ben Lincoln
- School of Ocean Sciences, Bangor University, Anglesey, LL59 5AB, Wales, UK
| | - Brian Scannell
- School of Ocean Sciences, Bangor University, Anglesey, LL59 5AB, Wales, UK
| | - Xin Meng
- School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP, UK
| | - Joanne Hopkins
- Marine Physics and Ocean Climate, National Oceanography Centre, Liverpool, L3 5DA, UK
| | - Jonathan Sharples
- School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP, UK
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2
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Schade H, Arneth N, Powilleit M, Forster S. Sand gapers' breath: Respiration of Mya arenaria (L. 1758) and its contribution to total oxygen utilization in sediments. MARINE ENVIRONMENTAL RESEARCH 2019; 143:101-110. [PMID: 30477876 DOI: 10.1016/j.marenvres.2018.11.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 11/15/2018] [Accepted: 11/15/2018] [Indexed: 06/09/2023]
Abstract
To estimate the contribution of a Mya arenaria population to total oxygen utilization (TOU) at different temperatures, the respiration rate of M. arenaria was measured for a full size range at 5 and 15 °C. In this study we measured respiration rates in a closed system while the clams were burrowed in sandy sediment, resembling their natural habitat. Rates were measured over a sufficient time span (24 h) to average varying activity phases during the measurements. We calculated a size-dependent respiration rate for M. arenaria and its variation with temperature. Temperature strongly affects the total population respiration and the contribution of different size classes to respiration of the total M. arenaria population. M. arenaria was estimated to contribute up to 70% to the total oxygen utilization of benthic communities analyzed in this study very much depending on the size distribution of the bivalve population present. Given a specific size distribution, smaller individuals had a stronger influence on the total oxygen utilization at colder temperature, while the influence of larger individuals grew with warmer temperature. Even though sizes contribute differently, a significant relation between abundance and respiration could be drawn in most cases analyzed. However, this relation should not be used as a general rule, but when estimating a population's metabolism the size distribution within that population has to be regarded.
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Affiliation(s)
- Hanna Schade
- Rostock University, Institute for Biological Sciences, Marine Biology, Albert-Einstein-Str. 3, D-18059, Rostock, Germany.
| | - Nikolas Arneth
- Rostock University, Institute for Biological Sciences, Marine Biology, Albert-Einstein-Str. 3, D-18059, Rostock, Germany
| | - Martin Powilleit
- Rostock University, Institute for Biological Sciences, Marine Biology, Albert-Einstein-Str. 3, D-18059, Rostock, Germany
| | - Stefan Forster
- Rostock University, Institute for Biological Sciences, Marine Biology, Albert-Einstein-Str. 3, D-18059, Rostock, Germany
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3
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Hicks N, Liu X, Gregory R, Kenny J, Lucaci A, Lenzi L, Paterson DM, Duncan KR. Temperature Driven Changes in Benthic Bacterial Diversity Influences Biogeochemical Cycling in Coastal Sediments. Front Microbiol 2018; 9:1730. [PMID: 30190707 PMCID: PMC6115492 DOI: 10.3389/fmicb.2018.01730] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 07/11/2018] [Indexed: 11/13/2022] Open
Abstract
Marine sediments are important sites for global biogeochemical cycling, mediated by macrofauna and microalgae. However, it is the microorganisms that drive these key processes. There is strong evidence that coastal benthic habitats will be affected by changing environmental variables (rising temperature, elevated CO2), and research has generally focused on the impact on macrofaunal biodiversity and ecosystem services. Despite their importance, there is less understanding of how microbial community assemblages will respond to environmental changes. In this study, a manipulative mesocosm experiment was employed, using next-generation sequencing to assess changes in microbial communities under future environmental change scenarios. Illumina sequencing generated over 11 million 16S rRNA gene sequences (using a primer set biased toward bacteria) and revealed Bacteroidetes and Proteobacteria dominated the total bacterial community of sediment samples. In this study, the sequencing coverage and depth revealed clear changes in species abundance within some phyla. Bacterial community composition was correlated with simulated environmental conditions, and species level community composition was significantly influenced by the mean temperature of the environmental regime (p = 0.002), but not by variation in CO2 or diurnal temperature variation. Species level changes with increasing mean temperature corresponded with changes in NH4 concentration, suggesting there is no functional redundancy in microbial communities for nitrogen cycling. Marine coastal biogeochemical cycling under future environmental conditions is likely to be driven by changes in nutrient availability as a direct result of microbial activity.
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Affiliation(s)
- Natalie Hicks
- The Scottish Association for Marine Science, Scottish Marine Institute, Oban, United Kingdom
| | - Xuan Liu
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Richard Gregory
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - John Kenny
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Anita Lucaci
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Luca Lenzi
- Centre for Genomic Research, Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - David M. Paterson
- Sediment Ecology Research Group, School of Biology, Scottish Oceans Institute, University of St Andrews, Fife, United Kingdom
| | - Katherine R. Duncan
- The Scottish Association for Marine Science, Scottish Marine Institute, Oban, United Kingdom
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
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4
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Aldridge JN, Lessin G, Amoudry LO, Hicks N, Hull T, Klar JK, Kitidis V, McNeill CL, Ingels J, Parker ER, Silburn B, Silva T, Sivyer DB, Smith HEK, Widdicombe S, Woodward EMS, van der Molen J, Garcia L, Kröger S. Comparing benthic biogeochemistry at a sandy and a muddy site in the Celtic Sea using a model and observations. BIOGEOCHEMISTRY 2017; 135:155-182. [PMID: 32009696 PMCID: PMC6961523 DOI: 10.1007/s10533-017-0367-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 07/22/2017] [Indexed: 06/10/2023]
Abstract
Results from a 1D setup of the European Regional Seas Ecosystem Model (ERSEM) biogeochemical model were compared with new observations collected under the UK Shelf Seas Biogeochemistry (SSB) programme to assess model performance and clarify elements of shelf-sea benthic biogeochemistry and carbon cycling. Observations from two contrasting sites (muddy and sandy) in the Celtic Sea in otherwise comparable hydrographic conditions were considered, with the focus on the benthic system. A standard model parameterisation with site-specific light and nutrient adjustments was used, along with modifications to the within-seabed diffusivity to accommodate the modelling of permeable (sandy) sediments. Differences between modelled and observed quantities of organic carbon in the bed were interpreted to suggest that a large part (>90%) of the observed benthic organic carbon is biologically relatively inactive. Evidence on the rate at which this inactive fraction is produced will constitute important information to quantify offshore carbon sequestration. Total oxygen uptake and oxic layer depths were within the range of the measured values. Modelled depth average pore water concentrations of ammonium, phosphate and silicate were typically 5-20% of observed values at the muddy site due to an underestimate of concentrations associated with the deeper sediment layers. Model agreement for these nutrients was better at the sandy site, which had lower pore water concentrations, especially deeper in the sediment. Comparison of pore water nitrate with observations had added uncertainty, as the results from process studies at the sites indicated the dominance of the anammox pathway for nitrogen removal; a pathway that is not included in the model. Macrofaunal biomasses were overestimated, although a model run with increased macrofaunal background mortality rates decreased macrofaunal biomass and improved agreement with observations. The decrease in macrofaunal biomass was compensated by an increase in meiofaunal biomass such that total oxygen demand remained within the observed range. The permeable sediment modification reproduced some of the observed behaviour of oxygen penetration depth at the sandy site. It is suggested that future development in ERSEM benthic modelling should focus on: (1) mixing and degradation rates of benthic organic matter, (2) validation of benthic faunal biomass against large scale spatial datasets, (3) incorporation of anammox in the benthic nitrogen cycle, and (4) further developments to represent permeable sediment processes.
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Affiliation(s)
- J. N. Aldridge
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - G. Lessin
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - L. O. Amoudry
- National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street, Liverpool, L3 5DA UK
| | - N. Hicks
- Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll, PA37 1QA UK
| | - T. Hull
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - J. K. Klar
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH UK
- LEGOS, University of Toulouse, IRD, CNES, CNRS, UPS, 14 avenue Edouard Belin, 31400 Toulouse, France
| | - V. Kitidis
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - C. L. McNeill
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - J. Ingels
- Coastal and Marine Laboratory, Florida State University, 3618 Coastal Highway 98, St Teresa, 32358 FL USA
| | - E. R. Parker
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - B. Silburn
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - T. Silva
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - D. B. Sivyer
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - H. E. K. Smith
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH UK
| | - S. Widdicombe
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - E. M. S. Woodward
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - J. van der Molen
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - L. Garcia
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
| | - S. Kröger
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, NR33 0HT UK
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5
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Currie AR, Tait K, Parry H, de Francisco-Mora B, Hicks N, Osborn AM, Widdicombe S, Stahl H. Marine Microbial Gene Abundance and Community Composition in Response to Ocean Acidification and Elevated Temperature in Two Contrasting Coastal Marine Sediments. Front Microbiol 2017; 8:1599. [PMID: 28878754 PMCID: PMC5572232 DOI: 10.3389/fmicb.2017.01599] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 08/07/2017] [Indexed: 02/01/2023] Open
Abstract
Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO2) and elevated temperature (ambient +4°C) on the abundance of taxonomic and functional microbial genes. Specific quantitative PCR primers were used to target archaeal, bacterial, and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase (amoA) and bacterial nitrite reductase (nirS) were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes (amoA and nirS) were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.
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Affiliation(s)
- Ashleigh R. Currie
- Biogeochemistry and Earth Science, Scottish Association for Marine Science, Scottish Marine InstituteOban, United Kingdom
| | - Karen Tait
- Plymouth Marine LaboratoryPlymouth, United Kingdom
| | - Helen Parry
- Plymouth Marine LaboratoryPlymouth, United Kingdom
| | - Beatriz de Francisco-Mora
- Biogeochemistry and Earth Science, Scottish Association for Marine Science, Scottish Marine InstituteOban, United Kingdom
| | - Natalie Hicks
- Biogeochemistry and Earth Science, Scottish Association for Marine Science, Scottish Marine InstituteOban, United Kingdom
| | - A. Mark Osborn
- School of Biological Sciences, University of HullHull, United Kingdom
- School of Science, Royal Melbourne Institute of Technology University, BundooraVIC, Australia
| | | | - Henrik Stahl
- Biogeochemistry and Earth Science, Scottish Association for Marine Science, Scottish Marine InstituteOban, United Kingdom
- Natural Science and Public Health, Zayed UniversityDubai, United Arab Emirates
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6
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Thompson CEL, Silburn B, Williams ME, Hull T, Sivyer D, Amoudry LO, Widdicombe S, Ingels J, Carnovale G, McNeill CL, Hale R, Marchais CL, Hicks N, Smith HEK, Klar JK, Hiddink JG, Kowalik J, Kitidis V, Reynolds S, Woodward EMS, Tait K, Homoky WB, Kröger S, Bolam S, Godbold JA, Aldridge J, Mayor DJ, Benoist NMA, Bett BJ, Morris KJ, Parker ER, Ruhl HA, Statham PJ, Solan M. An approach for the identification of exemplar sites for scaling up targeted field observations of benthic biogeochemistry in heterogeneous environments. BIOGEOCHEMISTRY 2017; 135:1-34. [PMID: 32009689 PMCID: PMC6961521 DOI: 10.1007/s10533-017-0366-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 06/08/2017] [Indexed: 05/16/2023]
Abstract
Continental shelf sediments are globally important for biogeochemical activity. Quantification of shelf-scale stocks and fluxes of carbon and nutrients requires the extrapolation of observations made at limited points in space and time. The procedure for selecting exemplar sites to form the basis of this up-scaling is discussed in relation to a UK-funded research programme investigating biogeochemistry in shelf seas. A three-step selection process is proposed in which (1) a target area representative of UK shelf sediment heterogeneity is selected, (2) the target area is assessed for spatial heterogeneity in sediment and habitat type, bed and water column structure and hydrodynamic forcing, and (3) study sites are selected within this target area encompassing the range of spatial heterogeneity required to address key scientific questions regarding shelf scale biogeochemistry, and minimise confounding variables. This led to the selection of four sites within the Celtic Sea that are significantly different in terms of their sediment, bed structure, and macrofaunal, meiofaunal and microbial community structures and diversity, but have minimal variations in water depth, tidal and wave magnitudes and directions, temperature and salinity. They form the basis of a research cruise programme of observation, sampling and experimentation encompassing the spring bloom cycle. Typical variation in key biogeochemical, sediment, biological and hydrodynamic parameters over a pre to post bloom period are presented, with a discussion of anthropogenic influences in the region. This methodology ensures the best likelihood of site-specific work being useful for up-scaling activities, increasing our understanding of benthic biogeochemistry at the UK-shelf scale.
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Affiliation(s)
- C. E. L. Thompson
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
| | - B. Silburn
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - M. E. Williams
- National Oceanography Centre, 6 Brownlow St, Liverpool, L3 5DA UK
| | - T. Hull
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - D. Sivyer
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - L. O. Amoudry
- National Oceanography Centre, 6 Brownlow St, Liverpool, L3 5DA UK
| | - S. Widdicombe
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - J. Ingels
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - G. Carnovale
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - C. L. McNeill
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - R. Hale
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
| | - C. Laguionie Marchais
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - N. Hicks
- Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll, PA37 1QA UK
| | - H. E. K. Smith
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - J. K. Klar
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
- LEGOS, University of Toulouse, IRDm CNES, CNRS, UPS, 14 av. Edouard Belin, 31400 Toulouse, France
| | - J. G. Hiddink
- School of Ocean Sciences, Bangor University, Menai Bridge, LL59 5AB UK
| | - J. Kowalik
- Navama – Technology for Nature, Landshuter Allee 8, 80637 Munich, Germany
| | - V. Kitidis
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - S. Reynolds
- School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3QL UK
| | - E. M. S. Woodward
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - K. Tait
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH UK
| | - W. B. Homoky
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN UK
| | - S. Kröger
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - S. Bolam
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - J. A. Godbold
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
- Biological Sciences, University of Southampton, Life Sciences Building, Highfield, Southampton SO17 1BJ UK
| | - J. Aldridge
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - D. J. Mayor
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - N. M. A. Benoist
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
| | - B. J. Bett
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - K. J. Morris
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - E. R. Parker
- Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT UK
| | - H. A. Ruhl
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH UK
| | - P. J. Statham
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
| | - M. Solan
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH UK
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7
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Silburn B, Kröger S, Parker ER, Sivyer DB, Hicks N, Powell CF, Johnson M, Greenwood N. Benthic pH gradients across a range of shelf sea sediment types linked to sediment characteristics and seasonal variability. BIOGEOCHEMISTRY 2017; 135:69-88. [PMID: 32009692 PMCID: PMC6961502 DOI: 10.1007/s10533-017-0323-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 03/16/2017] [Indexed: 05/27/2023]
Abstract
This study used microelectrodes to record pH profiles in fresh shelf sea sediment cores collected across a range of different sediment types within the Celtic Sea. Spatial and temporal variability was captured during repeated measurements in 2014 and 2015. Concurrently recorded oxygen microelectrode profiles and other sedimentary parameters provide a detailed context for interpretation of the pH data. Clear differences in profiles were observed between sediment type, location and season. Notably, very steep pH gradients exist within the surface sediments (10-20 mm), where decreases greater than 0.5 pH units were observed. Steep gradients were particularly apparent in fine cohesive sediments, less so in permeable sandier matrices. We hypothesise that the gradients are likely caused by aerobic organic matter respiration close to the sediment-water interface or oxidation of reduced species at the base of the oxic zone (NH4 +, Mn2+, Fe2+, S-). Statistical analysis suggests the variability in the depth of the pH minima is controlled spatially by the oxygen penetration depth, and seasonally by the input and remineralisation of deposited organic phytodetritus. Below the pH minima the observed pH remained consistently low to maximum electrode penetration (ca. 60 mm), indicating an absence of sub-oxic processes generating H+ or balanced removal processes within this layer. Thus, a climatology of sediment surface porewater pH is provided against which to examine biogeochemical processes. This enhances our understanding of benthic pH processes, particularly in the context of human impacts, seabed integrity, and future climate changes, providing vital information for modelling benthic response under future climate scenarios.
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Affiliation(s)
- B. Silburn
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
| | - S. Kröger
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
| | - E. R. Parker
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
| | - D. B. Sivyer
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
| | - N. Hicks
- Scottish Marine Institute, Oban, Argyll PA37 1QA UK
| | - C. F. Powell
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
| | - M. Johnson
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
- University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ UK
| | - N. Greenwood
- Centre for Environment Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT UK
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