Benthic pH gradients across a range of shelf sea sediment types linked to sediment characteristics and seasonal variability

Briony Silburn, Silke Kroger, Ruth Parker, David Sivyer, Natalie Hicks, Claire Powell, Martin Johnson, Naomi Greenwood

Research output: Contribution to journalArticle

9 Citations (Scopus)
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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.
Original languageEnglish
Pages (from-to)69-88
Number of pages19
JournalBiogeochemistry
Volume135
Issue number1-2
DOIs
Publication statusPublished - 31 Mar 2017

Keywords

  • Sediment pH
  • Oxygen
  • Carbon cycle
  • Microelectrode profiles
  • Celtic Sea
  • Shelf sea biogeochemistry

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