221 research outputs found
Early diagenesis of phosphorus in continental margin sediments
No full textMost of the organic material in the oceans that reaches the sea floor is deposited on continental margins and not in the deep sea. This organic matter is the principal carrier of phosphorus (P) to sediments. A part of the organic material is buried definitely. The other part decomposes, resulting in a release of dissolved HP0 42-to the pore water. This HP0 42-either returns to the overlying water and becomes available for uptake by phytoplankton, or is retained in the sediment in an organic or inorganic form.Quantification of the P release from and P retention in sediments on relatively short time scales of days to years is necessary for a correct understanding of the nutrient dynamics in regional seas such as, for example, the North Sea. An accurate assessment of the modem global ocean burial flux of reactive P (i.e potentially bioavailable P) and the burial flux in the geological past is important for understanding the global oceanic P cycle. This, in turn, can provide insight in possible controls on organic C burial and atmospheric concentrations of C0 2 and 0 2 , because P may limit oceanic primary production and thus determine the amount of organic material in the oceans on geological time scales.The research presented in this thesis concentrates on the short-term processes controlling sediment P release and retention in temperate, non-upwelling, continental margin environments. The research commenced with a laboratory study on the effect of organic matter deposition and macrofauna on sediment-water exchange and retention of P in Fe oxide-poor, sandy sediments (Chapter 2). A suspension of dead algal cells (Phaeocystis sp.) was applied to sediment in experimental systems (boxcosms), either once or every week during 19 weeks. The results demonstrate that deposition of organic matter on this type of sediment enhances pore water concentrations and sediment-water exchange of HP0 42-. The enhanced HP0 42-release was due to microbially mediated mineralization of the organic material and due to direct release of HP0 42-from the algal cells (lysis). A major portion of the algal material remained at the sediment-water interface and this organic layer probably regulated the sediment-water exchange of HP0 42-directly. The activity of the macrofauna was mainly limited to reworking of the sediment. The effect of the macrofauna on the sediment-water exchange Of HP0 42-was negligible. In the boxcosms to which organic material was added only once, the concentration of NaOH-extractable sediment P increased following the addition, especially in the presence of macrofauna.Sorption of P to Fe oxides is the most important short-term process responsible for the retention of P in sediments. Using a combination of differential X-ray diffraction (DXRD) and extraction procedures, the character of the Fe oxides that bind P in 4 North Sea sediments was studied (Chapter 3). The results indicate that poorly crystalline ferrihydrite and akageneite were present in the fine sediment fraction (< 10 μm) of surface samples from all locations. Combination of these results with bulk sediment extractions of Fe and P and sorption characteristics for P provides evidence for the dominant role of poorly crystalline Fe oxides for the binding of P in these North Sea sediments. These poorly crystalline Fe oxides are suggested to act as both a temporary and permanent sink for P.The redox conditions in continental margin sediments can vary both seasonally and spatially. To obtain more insight in the redox conditions in North Sea sediments, the Mn and Fe cycle at 15 locations in 4 different sedimentary environments was studied in 2 contrasting seasons (Chapter 4). The quality and quantity of the organic matter deposited in each environment was found to determine whether sediments become sufficiently depleted of 0 2 and NO 3-to allow for (1) Fe and Mn reduction and (2) escape of dissolved Fe 2+and Mn 2+to the overlying water. A steady- state diagenetic model describing solid phase and pore water metal profiles was developed and applied to Mn and Fe data for 11 and 3 stations, respectively. The model results demonstrate that (1) reversible sorption in combination with sediment mixing can enhance diffusive transport of dissolved metals; (2) precipitation of Fe 2+and Mn 2+in the form of reduced authigenic minerals can explain the reversal of the pore water Fe 2+and Mn 2+gradients at depth at many stations, and (3) in most North Sea sediments, Fe and Mn oxides do not play an important role as redox intermediates in organic C oxidation (accounting for < 4 %); only in the depositional environment of the Skagerrak, metal oxide reduction may contribute substantially to organic C oxidation (-20%).Reversible sorptive reactions can both constrain and enhance the flux of HP0 42-from the sediment to the overlying water. The role of sorption in sediment-water exchange of HP0 42-in North Sea sediments was investigated for 15 locations in 2 seasons (Chapter 5). P sorption data, pore water HP0 42-profiles, solid phase results and measured and calculated rates of sediment- water exchange of HP0 42-were combined. Sorption was found to play an important role in controlling sediment-water exchange of HP0 42-during at least part of the year in 3 of the 4 North Sea environments. At most stations, adsorption limits the flux of HP0 42-to the overlying water. At one station in the Skagerrak, however, desorption is responsible for the maintenance of a flux of HP0 42-to the overlying water. A onedimensional reaction-diffusion model describing the sedimentary P cycle was developed and applied to the results for 2 stations, The model results show that both enhanced retention and enhanced release due to sorption can be adequately described when simultaneous equilibrium and first-order reversible sorptive reactions are assumed.P bound in authigenic minerals may not be solubilized again, whereas Fe-bound and organic P can still be released upon deep burial. Therefore, more insight in the extent of authigenic P mineral formation in continental margin sediments is important. A combination of pore water and solid phase analysis was used to determine whether authigenic carbonate fluorapatite (CFA) is currently forming at two locations on a North Atlantic continental platform (Chapter 6). Results of selective extractions suggest that an authigenic P phase is forming at the expense of Fe-bound P at both stations. A steady-state diagenetic model for the P cycle was developed and applied to the data of I station. The model results indicate that CFA formation can account for the observed increase of authigenic P with depth at this station. Furthermore, the results show that an intense cycling of P between Fe-bound P and pore water HP0 42-at the redox interface can create conditions beneficial for CFA formation. This internal P cycle is driven by downward, bioturbational transport of mainly in-situ formed Fe-bound P into the reduced sediment zone. Losses from the internal P cycle due to CFA formation and HP0 42+diffusion are compensated for by sorption of HP0 42-released from organic matter to Fe oxides. Fe bound P thus acts as an intermediate between organic P and CFA. Burial of CFA can account for between 25 and 70% of the total burial flux of reactive P and thus may act as an important sink for P in this low sedimentation, continental margin environment
Enhanced phosphorus regeneration during formation of eastern Mediterranean sapropels (abstract of paper presented at AGU Fall Meeting, San Francisco, CA, 10-14 Dec 2001)
No full textControls on phosphorus regeneration and burial during formation of eastern Mediterranean sapropels
No full textThe carbon (C) and phosphorus (P) geochemistry of sapropels from four sites in the eastern Mediterranean Sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on P regeneration and burial in sediments. Sediment Corg/Porg (with ORG=organic) ratios above Redfield indicate enhanced regeneration of P relative to C from organic matter during formation of the most recent sapropel S1 and a Pliocene sapropel (ODP-site 969E; i-282c). Release of P from Fe-oxides was relatively unimportant. Increased burial of Ca-P (authigenic carbonate fluorapatite and/or biogenic hydroxyapatite) occurred but was of minor importance compared to the enhanced P release from organic matter. For sapropel S1, Corg/Porg and Corg/Preac, (with REAC=reactive, defined as the sum of organic, Fe-bound, authigenic and biogenic Ca-P) ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth. Whether the water column in the deep basin was dysoxic/semi-euxinic (S1) or euxinic (Pliocene) does not appear to affect the estimated burial efficiencies of Porg and Preac. Enhanced Corg burial under the euxinic water column explains the much higher Corg/Porg and Corg/Preac ratios in the Pliocene sapropel (on average ~2860 and ~760, respectively) compared to sapropel S1 (on average ~530 and ~160, respectively
Enhanced regeneration of phosphorus during formation of the most recent eastern Mediterranean sapropel (S1)
No full textPhosphorus regeneration and burial fluxes during and after formation of the most recent sapropel S1 were determined for two deep-basin, low-sedimentation sites in the eastern Mediterranean Sea. Organic C/P ratios and burial fluxes indicate enhanced regeneration of P relative to C during deposition of sapropel S1. This is largely due to the enhanced release of P from organic matter during sulfate reduction. Release of P from Fe-bound P also increased, but this was only a relatively minor source of dissolved P. Pore-water HPO42? concentrations remained too low for carbonate fluorapatite formation. An increased burial of biogenic Ca-P (i.e., fish debris) was observed for one site. Estimated benthic fluxes of P during sapropel formation were elevated relative to the present day (~900 to 2800 vs. ~70 to 120 mol m?2 yr?1). The present-day sedimentary P cycle in the deep-basin sediments is characterized by two major zones of reaction: (1) the zone near the sediment-water interface where substantial release of HPO42? from organic matter takes place, and (2) the oxidation front at the top of the S1 where upward-diffusing HPO42? from below the sapropel is sorbed to Fe-oxides. The efficiency of aerobic organisms in retaining P is reflected in the low organic C/P ratios in the oxidized part of the sapropel. Burial efficiencies for reactive P were significantly lower during S1 times compared with the present day (~7 to 15% vs. 64 to 77%). Budget calculations for the eastern Mediterranean Sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of P both contributed to a significant increase in deep-water HPO42? concentrations during sapropel S1 times. Provided that sufficient vertical mixing occurred, enhanced regeneration of P at the seafloor may have played a key role in maintaining increased productivity during sapropel S1 formation
pH-Dependent iron oxide precipitation in a subterranean estuary
No full textAuthor Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Geochemical Exploration 88 (2006): 399-403, doi:10.1016/j.gexplo.2005.08.084.Iron-oxide coated sediment particles in subterranean estuaries can act as a geochemical barrier (“iron curtain”) for various chemical species in groundwater (e.g. phosphate), thus limiting their discharge to coastal waters. Little is known about the factors controlling this Fe-oxide precipitation. Here, we implement a simple reaction network in a 1D reactive transport model (RTM), to investigate the effect of O2 and pH gradients along a flow-line in the subterranean estuary of Waquoit Bay (Cape Cod, Massachusetts) on oxidative precipitation of Fe(II) and subsequent PO4 sorption. Results show that the observed O2 gradient is not the main factor controlling precipitation and that it is the pH gradient at the mixing zone of freshwater (pH 5.5) and seawater (pH 7.9) near the beach face that causes a ~7-fold increase in the rate of oxidative precipitation of Fe(II) at ~15 m. Thus, the pH gradient determines the location and magnitude of the observed iron oxide accumulation and the subsequent removal of PO4 in this subterranean estuary.Financial support was provided by the Netherlands Organisation for Scientific Research (NWO) and WHOI Guest Student Program (grants to C. Spiteri), the Royal Netherlands Academy of Arts and Sciences (KNAW) (fellowship to C.P. Slomp) and US National Science Foundation NSF-OCE0095384 and NSF-OCE0425061 (grants to M.A. Charette)
Biogeochemical redox proxies in sediments from Schandelah during the Toarcian (Early Jurassic)
No full textAuthor contributions:
The sampling was led by Bas van de Schootbrugge and measurements performed by Nina Papadomanolaki, with supervision of Niels A. G. M. van Helmond and Caroline P. Slomp. Measurements were gathered, processed and analysed by Itzel Ruvalcaba Baroni
Phyto- and zooplankton paleofluxes during the deposition of sapropel S1 (eastern Mediterranean): biogenic carbonate preservation and paleoecological implications
No full textThe relative and absolute abundances and accumulation rates of foraminifera and calcareous nannofossils were quantified in a
box core containing sapropel S1 from the Florence Rise area (SE of Cyprus; 2302 m water depth). The main objective of this study
was to reconstruct in detail variations in paleoecological conditions of water masses during the deposition of this sapropel. In
particular, we qualitatively evaluated the importance of carbonate dissolution on planktonic assemblages to better interpret the
abundance profiles obtained from the two investigated taxa.
Selective carbonate corrosion in the core is shown by (1) the decrease in shell mass weight of selected species of planktonic
foraminifera, (2) the decrease in accumulation rate of dissolution-susceptible holococcoliths and coccolith species, and (3) the
absence of pteropods. However, the presence of other relatively dissolution-susceptible coccolith species throughout all of the S1
interval suggests moderate dissolution.
Florisphaera profunda shows a marked increase in paleofluxes within the sapropel coupled with a decrease in the accumulation
rate of the upper–middle photic zone coccoliths, suggesting an ecological depth-separation of the water column, probably
characterised by higher nutrient availability at depth and nutrient-depleted surface waters between ~10 and 6.5 kyr BP. In the
same interval Turborotalita quinqueloba and Globigerina bulloides, two foraminiferal species frequently occurring during periods
of high fertility, increase in relative abundance. The maximum increase in relative abundance of Globigerinoides ruber (var. alba
and rosea) marks the climatic optimum phase and the maximum stratification in surface water that occurred at the beginning of
sapropel S1 deposition when the bottom waters were anoxic. An important change in foraminiferal assemblages occurs at ~8 kyr
BP and corresponds with a negative shift in CaCO3, Ba and Corg contents. This short interval marks the establishment of relatively
less anoxic conditions in the bottom water, introducing the last phase of sapropel formation.
After ~6.5 kyr BP, a progressive re-establishment of normal oceanographic conditions occurred before the real end of the
sapropel S1. This transition is well recorded by the reoccurrence and major accumulation rate of the mixing indicator foraminiferal
species Globorotalia inflata and by the gradual decrease in abundance of F. profunda
NMP_UU_CO2P
No full textNew biogeochemical box model, written in R and described in :
Papadomanolaki, N.M., Sluijs, A. & Slomp, C.P. (2021). Eutrophication and deoxygenation forcing of marginal marine organic carbon burial during the PETM. Paleoceanography and Paleoclimatology.
11-box model, incorporating marine fluxes of particulate organic carbon, dissolved and particulate phosphorus and dissolved oxygen.
The model geography corresponds to the Late Paleocene, with an open ocean configuration similar to LOSCAR (Zeebe et al., 2009; Zeebe, 2012), and further includes the continental shelf, the Arctic Ocean and the European Epicontinental Seaway.
This setup includes can be used to run all simulations presented in the original publication, including four different CO2 scenarios and sensitivity studies on e.g. the impact of stratification
Oxidation and origin of organic matter in surficial eastern Mediterranean hemipelagic sediments
No full textAerobic mineralisation of Corg in surface sediments of the deep (>2000 m water depth) eastern Mediterranean Sea has been quantified by analysis of detailed box core Corg concentration versus depth profiles and the modelling environment for early diagenetic problems MEDIA. The reactive fraction comprises 60–80% of the total Corg reaching the sediments and is largely oxidised within the surficial 10 cm. A non-reactive Corg fraction (GNR) dominates at depths >10 cm, and makes up 20–40% of the total Corg flux to the sediments. First-order rate constants for decomposition of the reactive fraction calculated from the Corg profiles range from 5.4 × 10-3 to 8.0 × 10-3 y-1 to 8.0 × 10-3 y-1. Total mineralization rates in the surface sediment are between 1.7 and 2.6 µmol C cm-2 y-1 and thus are typical for oligotrophic, deep-sea environments. The low fluxes and rapid remineralisation of Corg are accompanied by 210Pbexcess surface mixed layers which are only 2 cm deep, among the thinnest reported for oxygenated marine sediments. Model results indicate a mismatch between the Corg profiles and O2 microprofiles which were measured onboard ship. This can be attributed to a combination of decompression artefacts affecting onboard measurement of the O2 profiles or the leakage of oxygen into the core during handling on deck. Furthermore, the used Db values, based on 210Pb, may not be fully appropriate; calculations with higher Db values improve the O2 fits. The surficial sediment δ13Corg values of -22 become less negative with increasing depth and decreasing Corg concentrations. The major 13C change occurs in the top 3 to 4 cm and coincides with the interval where most of the organic carbon oxidation takes place. This indicates that the reactive fraction of organic matter, commonly assumed to be marine, has a more negative δ13Corg than the refractory fraction, usually held to be terrestrial. Palaeoproductivity estimates calculated from the sediment data by means of literature algorithms yield low surface productivities (12–88 gC m-2 y-1), which are in good agreement with field measurements of primary productivity in other studies. Such values are, however, significantly lower than those indicated by recent productivity maps of the area derived from satellite imagery (>100 gC m-2 y-1)
Flow and nutrient dynamics in a subterranean estuary (Waquoit Bay, MA, USA) : field data and reactive transport modeling
No full textAuthor Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 72 (2008): 3398-3412, doi:10.1016/j.gca.2008.04.027.A two-dimensional (2D) reactive transport model is used to investigate the controls on
nutrient (NO3-, NH4+, PO4) dynamics in a coastal aquifer. The model couples density
dependent flow to a reaction network which includes oxic degradation of organic
matter, denitrification, iron oxide reduction, nitrification, Fe2+ oxidation and sorption of PO4 onto iron oxides. Porewater measurements from a well transect at Waquoit
Bay, MA, USA indicate the presence of a reducing plume with high Fe2+, NH4+, DOC
(dissolved organic carbon) and PO4 concentrations overlying a more oxidizing NO3--rich plume. These two plumes travel nearly conservatively until they start to overlap in the intertidal coastal sediments prior to discharge into the bay. In this zone, the aeration of the surface beach sediments drives nitrification and allows the
precipitation of iron oxide, which leads to the removal of PO4 through sorption. Model
simulations suggest that removal of NO3-
through denitrification is inhibited by the
limited overlap between the two freshwater plumes, as well as by the refractory nature
of terrestrial DOC. Submarine groundwater discharge is a significant source of NO3-
to the bay.This research was funded by the Netherlands Organisation for Scientific Research
(NWO) and WHOI Guest Student Program (C. Spiteri), the Royal Netherlands
Academy of Arts and Sciences (KNAW) and the Netherlands Organization for
Scientific Research (NWO VIDI-grant) (C.P. Slomp), the US National Science
Foundation NSF-OCE0095384 and NSF-OCE0425061 (M.A. Charette) and the
Georgia Sea Grant of the National Sea Grant College Program of the U.S. Department
of Commerce’s National Oceanic and Atmospheric Administration under NOAA
Grant #NA04OAR4170033 (C. Meile)
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