The relation between temperature and silica benthic exchange rates and implications for near-seabed formation of diagenetic opal

Varkouhi, Shahab; Wells, Jonathan

doi:10.1016/j.ringps.2020.100002

Cited by 24 publications

(19 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The deposition flux of BSi at the sediment-water interface (SWI) (J BSi,in ) was then calculated based on equation 6, which states that J BSi,In equates to the sum of the flux of BSi out of the sediment (assumed to equate to the integrated rate of BSi dissolution, R db ) and the BSi burial flux (J BSi,bur ) (Burdige, 2006;Freitas et al, 2021). J BSi,bur was estimated at the base of the model domain (50.4 cm), following the mass accumulation equation 7 (Varkouhi and Wells (2020) and references therein), which is controlled solely by advection. The sedimentation rate at depth (ω z ) was corrected for compaction following equation 8 (Berner, 1980).…”

Section: Processing the Simulated Datamentioning

confidence: 99%

Benthic Silicon Cycling in the Arctic Barents Sea: a Reaction-Transport Model Study

Ward

Hendry

Arndt

et al. 2022

Preprint

View full text Add to dashboard Cite

Abstract. Over recent decades the highest rates of water column warming and sea ice loss across the Arctic Ocean have been observed in the Barents Sea. These physical changes have resulted in rapid ecosystem adjustments, manifesting as a northward migration of temperate phytoplankton species at the expense of silica-based diatoms. These changes will potentially alter the composition of phytodetritus deposited at the seafloor, which acts as a biogeochemical reactor, pivotal in the recycling of key nutrients, such as silicon (Si). To appreciate the sensitivity of the Barents Sea benthic system to the observed changes in surface primary production, there is a need to better understand this benthic-pelagic coupling. Stable Si isotopic compositions of sediment pore waters and the solid phase from three stations in the Barents Sea reveal a coupling of the iron (Fe) and Si cycles, the contemporaneous dissolution of lithogenic silicate minerals (LSi) alongside biogenic silica (BSi) and the potential for the reprecipitation of dissolved silicic acid (DSi) as authigenic clay minerals (AuSi). However, as reaction rates cannot be quantified from observational data alone, a mechanistic understanding of which factors control these processes is missing. Here, we employ reaction-transport modelling together with observational data to disentangle the reaction pathways controlling the cycling of Si within the seafloor. Processes such as the dissolution of BSi are active on multiple timescales, ranging from weeks to hundreds of years, which we are able to examine through steady state and transient model runs. Steady state simulations show that 60 to 98 % of the sediment pore water DSi pool may be sourced from the dissolution of LSi, while the isotopic composition is also strongly influenced by the desorption of Si from metal oxides, most likely Fe (oxyhydr)oxides (FeSi), as they reductively dissolve. Further, our model simulations indicate that between 2.9 and 37 % of the DSi released into sediment pore waters is taken up with a fractionation factor of approximately −2 ‰, most likely representing reprecipitation as AuSi. These observations are significant, as the dissolution of LSi represents a source of new Si to the ocean DSi pool and precipitation of AuSi an additional sink, which could address imbalances in the current regional ocean Si budget. Lastly, transient modelling suggests that at least one-third of the total annual benthic DSi flux could be sourced from the dissolution of more reactive, diatom-derived BSi deposited after the surface water bloom at the marginal ice zone. This benthic-pelagic coupling will be subject to change with the continued northward migration of Atlantic phytoplankton species, northward retreat of the marginal ice zone and the observed decline in DSi inventory of the subpolar North Atlantic Ocean over the last three decades.

show abstract

Section: Processing the Simulated Datamentioning

confidence: 99%

Benthic Silicon Cycling in the Arctic Barents Sea: a Reaction-Transport Model Study

Ward

Hendry

Arndt

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…opal-CT porcellanites and cherts at very low surface temperatures commonly between 0 and 4 °C in near-seabed sediments (e.g., Bohrmann et al, 1990;Botz and Bohrmann, 1991) is in contrast with the established models of later diagenetic precipitation of opal-CT in deep-sea deposits, which require the dominance of higher transformation temperatures (from 18 to 56 °C; Pisciotto, 1981a). Moreover, the inverse correlation between age and formation temperature of opal-CT, implying silica transformation at higher temperatures in young deposits challenges very low surface temperatures being a major control on opal-CT precipitation near the seabed (Varkouhi and Wells, 2020). The analysis of near-seabed opal transformation at very low temperatures was, however, not undertaken in this study as silica transformation reaction diagnosed in the surface sediment does not represent an opal-A to opal-CT transition zone, and the diatom ooze persists well below this horizon, e.g., to a penetration depth of 166.2 mbsf at the ODP Site 751 from the Antarctic, according to Botz and Bohrmann (1991) and Varkouhi and Wells (2020).…”

Section: Revised Versus Initial Stability Fieldmentioning

confidence: 84%

“…This matter is of particular significance as the equatorial eastern rims of the North and South Pacific Ocean were some of the major depocentres of biogenic opal during the Middle Miocene to Early Pliocene (Ingle, 1980(Ingle, , 1981Behl, 1999). In 39 of the selected borehole sites, pelagic biogenic opal is deposited with fine detrital sediments formed through chemical alteration of windblown volcanic ash (or volcanic glass) on the seabed, in addition to products of continental weathering processes from the source regions (i.e., siliceous oozes that are accompanied by clay, silt, and sometimes volcanic ash and tuff; according to Varkouhi and Wells, 2020). Though detrital-based, small proportions of marine calcareous nannofossils (sometimes benthic and planktonic foraminifers) are admixed with the diatomaceous sediments from these sites, with the peak proportion being for the Leg 167 of ODP, Sites 1016 and 1022 (15% of total sediment volume; Shipboard Scientific Party, 1997aParty, , 1997b.…”

Section: Depositional Settingmentioning

confidence: 99%

“…Moreover, the inverse correlation between age and formation temperature of opal-CT, implying silica transformation at higher temperatures in young deposits challenges very low surface temperatures being a major control on opal-CT precipitation near the seabed (Varkouhi and Wells, 2020). The analysis of near-seabed opal transformation at very low temperatures was, however, not undertaken in this study as silica transformation reaction diagnosed in the surface sediment does not represent an opal-A to opal-CT transition zone, and the diatom ooze persists well below this horizon, e.g., to a penetration depth of 166.2 mbsf at the ODP Site 751 from the Antarctic, according to Botz and Bohrmann (1991) and Varkouhi and Wells (2020).…”

Section: Revised Versus Initial Stability Fieldmentioning

confidence: 99%

See 1 more Smart Citation

Temperature–time relationships and their implications for thermal history and modelling of silica diagenesis in deep-sea sediments

2021

Self Cite

View full text Add to dashboard Cite

“…A lesser role for subsequent formation of diagenetic opal on physical‐property response than pioneer dissolution of biogenic opal is commonly due to the restraining influences of authigenic phases other than opal‐CT (e.g. authigenic clays) that precipitate mostly concomitant with silica diagenesis and restrict substantial formation of opal‐CT through affecting the solubility and chemical kinetics of pore‐water silica (Emerson & Hedges, 2008; Loucaides et al, 2010; Varkouhi, Tosca, et al, 2020, Varkouhi et al, 2021; Varkouhi & Wells, 2020). The prominent increase in sediment bulk density over a vertical extent of a few metres results from porosity reduction, and compressional velocity increases owe to cementation of pore space by opal‐CT (Varkouhi, Cartwright, et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Arrested versus active silica diagenesis reaction boundaries—A review of seismic diagnostic criteria

et al. 2021

Self Cite

View full text Add to dashboard Cite

This paper evaluates previously proposed diagnostic criteria that can be used to determine whether or not there is active migration of the opal‐A to opal‐CT transition zone (TZA/CT). The criteria are based on the interpretation of 2D and 3D seismic surveys and are therefore geometrical. They involve an assessment of the relationship of the TZA/CT with polygonal fault systems, differential compaction structures and tectonic folds. The most robust evidence for an inactive ‘reaction front’ between opal‐A and opal‐CT bearing sediments is the discordance of the TZA/CT relative to present‐day isotherms. Any of these may be persuasive as diagnostic criteria for the upward arrest of the diagenetic transformation at a regional scale, but actual truncation of the TZA/CT at the modern seabed is definitive for arrested diagenesis. This study argues that diagenetic assessment based solely on a single criterion independently is not reliable as an indicator for the current state of a silica transition. As a conclusion, the analysed seismic/structural criteria should be synthesised to provide a more credible interpretation for silica diagenesis. The use of modern 2D and 3D seismic data for the reconstruction of the diagenetic history of opaline silica bearing sediments offers a new approach to the study of silica diagenesis at a regional scale.

show abstract

The relation between temperature and silica benthic exchange rates and implications for near-seabed formation of diagenetic opal

Cited by 24 publications

References 41 publications

Benthic Silicon Cycling in the Arctic Barents Sea: a Reaction-Transport Model Study

Benthic Silicon Cycling in the Arctic Barents Sea: a Reaction-Transport Model Study

Temperature–time relationships and their implications for thermal history and modelling of silica diagenesis in deep-sea sediments

Arrested versus active silica diagenesis reaction boundaries—A review of seismic diagnostic criteria

Contact Info

Product

Resources

About