Papers by Michael E. Böttcher
Geoscientific Model Development, Jan 17, 2019
Sediments play an important role in organic matter mineralisation and nutrient recycling, especia... more Sediments play an important role in organic matter mineralisation and nutrient recycling, especially in shallow marine systems. Marine ecosystem models, however, often only include a coarse representation of processes beneath the sea floor. While these parameterisations may give a reasonable description of the present ecosystem state, they lack predictive capacity for possible future changes, which can only be obtained from mechanistic modelling. This paper describes an integrated benthic-pelagic ecosystem model developed for the German Exclusive Economic Zone (EEZ) in the western Baltic Sea. The model is a hybrid of two existing models: the pelagic part of the marine ecosystem model ERGOM and an early diagenetic model by . The latter one was extended to include the carbon cycle, a determination of precipitation and dissolution reactions which accounts for salinity differences, an explicit description of the adsorption of clay minerals, and an alternative pyrite formation pathway. We present a one-dimensional application of the model to seven sites with different sediment types. The model was calibrated with observed pore water profiles and validated with results of sediment composition, bioturbation rates and bentho-pelagic fluxes gathered by in situ incubations of sediments (benthic chambers). The model results generally give a reasonable fit to the observations, even if some deviations are observed, e.g. an overestimation of sulfide concentrations in the sandy sediments. We therefore consider it a good first step towards a threedimensional representation of sedimentary processes in coupled pelagic-benthic ecosystem models of the Baltic Sea.
Frontiers in Marine Science, Nov 8, 2018
Goldschmidt2021 abstracts, 2021
Sediments play an important role in organic matter mineralisation and nutrient recycling, especia... more Sediments play an important role in organic matter mineralisation and nutrient recycling, especially in shallow marine systems. Marine ecosystem models, however, often only include a coarse representation of processes beneath the sea floor. While these parametrisations may give a reasonable description of the present ecosystem state, they lack predictive capacity for possible future changes, which can only be obtained from mechanistic modelling. This paper describes an integrated benthic-pelagic ecosystem model developed for the German Exclusive Economic Zone 5 (EEZ) in the Western Baltic Sea. The model is a hybrid of two existing models: the pelagic part of the marine ecosystem model ERGOM and an early diagenetic model by Reed et al., 2011. The latter one was extended to include the carbon cycle, a determination of precipitation and dissolution reactions which accounts for salinity differences, an explicit description of adsorption of clay minerals and an alternative pyrite formation pathway. We present a one-dimensional application of the model to seven sites with different sediment types. The model was calibrated with observed pore water profiles and validated 10 with results of sediment composition and bioturbation rates collected within the framework of the SECOS project.
Scientific Reports, Jan 24, 2019
Microbial life below the seafloor has changed over geological time, but these changes are often n... more Microbial life below the seafloor has changed over geological time, but these changes are often not obvious, as they are not recorded in the sediment. Sulphur (S) isotope values in pyrite extracted from a Plio-to Holocene sequence of the Peru Margin (Ocean Drilling Program, ODP, Site 1229) show a down-core pattern that correlates with the pattern of carbon (C) isotopes in diagenetic dolomite. Early formation of the pyrite is indicated by the mineralogical composition of iron, showing a high degree of pyritization throughout the sedimentary sequence. Hence, the S-record could not have been substantially overprinted by later pyrite formation. The Sand C-isotope profiles show, thus, evidence for two episodes of enhanced microbial methane production with a very shallow sulphate-methane transition zone. The events of high activity are correlated with zones of elevated organic C content in the stratigraphic sequence. Our results demonstrate how isotopic signatures preserved in diagenetic mineral phases provide information on changes of past biogeochemical activity in a dynamic subseafloor biosphere. The exploration of the sub-seafloor biosphere over the last two decades has provided detailed information on microbial distribution, metabolic activity, and subsurface redox zonation (Parkes et al. 1 ; D'Hondt et al. 2,3 ; Jørgensen et al. 4 ; Kallmeyer and Wagner 5). While the ongoing processes are now relatively well understood, it remains poorly assessed how the microbial activity responded to past oceanographic, palaeo-climatic, and depositional conditions. Large changes in sub-surface microbial activity occur over timescales of 100,000 years or more and these are triggered by oceanographic variations, such as glacial-interglacial cycles (Aiello and Bekins 6 ; Contreras et al. 7 ; Meister 8). Resulting changes in subsurface geochemical conditions cannot simply be traced by the present downcore distribution of microbial activity or by the modern porewater chemistry. Instead, tracing variations of deep biosphere conditions over geological time relies on proxies that are preserved in the solid-phase diagenetic record for millions of years (e.g. Kelts and McKenzie 9 ; Meister et al. 10 ; Schrag et al. 11). Elemental and isotopic signatures may be preserved if they are enclosed inside of diagenetic mineral phases, ideally, if they are partitioned in the crystal lattice. Diagenetic minerals may themselves be the product of specific microbial processes, and information on these processes becomes permanently trapped at the time of precipitation. A range of different mineral archives, such as dolomite, siderite, rhodochrosite or quartz, has been suggested as indicators of specific metabolic pathways (as compiled in Meister 8). Furthermore, several isotope systems are indicative of microbial activity (e.g. Kaplan and Rittenberg 12 ; Claypool and Kaplan 13 ; Jørgensen 14). Specifically, light stable isotopes bear the advantage that they show large isotope variations mostly considered to result from kinetic fractionation effects of enzymatically-controlled reactions. Particularly large isotope fractionation is observed for S isotopes between oxidized and reduced S (e.g., Hoefs 15). Recently, Parnell et al. 16 observed that S isotopes are excellent markers for past microbial activity in sand injections that occur within long records of continental margin deposits. This insight is intriguing as S isotope records are available in many organic carbon-rich sedimentary sequences, providing potential archives of past sub-seafloor microbial activity.
The weathering rate of carbonate minerals is several orders of magnitude higher than for silicate... more The weathering rate of carbonate minerals is several orders of magnitude higher than for silicate minerals. Therefore, small amounts of carbonate minerals have the potential to control the dissolved weathering loads in silicate-dominated catchments. Both weathering processes produce alkalinity under the consumption of CO2. Given that only alkalinity generation from silicate weathering is thought to be a long-term sink for CO2, a misattributed weathering source could lead to incorrect conclusions about long-and short-term CO2 fixation. In this study, we aimed to identify the weathering sources responsible for alkalinity generation and CO2 fixation across watershed scales in a degrading permafrost landscape in northern Norway, 68.7-70.5 °N, and on a temporal scale, in a subarctic headwater catchment on the mountainside of Iskorasfjellet, characterized by sporadic permafrost and underlain mainly by silicates as the alkalinity-bearing lithology. By analysing total alkalinity (AT) and dissolved inorganic carbon (DIC) concentrations, as well as the stable isotope signature of the latter (δ 13 C-DIC) in conjunction with dissolved cation and anion loads, we found that AT was almost entirely derived from weathering of the sparse carbonate minerals. We propose that in the headwater catchment, the riparian zone is a hotspot area of AT generation and release due to its enhanced hydrological connectivity, and that the weathering load contribution from the uphill catchment is limited by insufficient contact time of weathering agent and weatherable material. By using stable water isotopes, it was possible to explain temporal variations in AT concentrations following a precipitation event due to surface runoff. In addition to carbonic acid, sulphuric acid, probably originating from pyrite oxidation, is shown to be a potential corrosive reactant. An increased proportion of sulphuric acid as a potential weathering agent may have resulted in a decrease in AT. Therefore, carbonate weathering in the studied area should be considered not only as a short-term CO2 sink, but also as a potential CO2 source. Finally, we found that AT increased with decreasing permafrost probability, and attributed this relation to an increased
Journal of Marine Science and Engineering, Jun 23, 2015
Mangroves serve as either sinks or sources for inorganic and organic nutrients and can mitigate a... more Mangroves serve as either sinks or sources for inorganic and organic nutrients and can mitigate anthropogenic nutrient pollution, control the production in adjacent systems, and prevent eutrophication. To better understand the nutrient dynamics in a subtropical mangrove, we employed a three-way approach in the Nanliu River Estuary, southern China: Pore water profiles and sediment incubations revealed benthic early diagenesis as well as sediment-water exchange of dissolved nutrients and oxygen, while tidal sampling of estuarine and mangrove water identified source and sink functions of the entire mangrove forest. Fluxes of oxygen during incubations were always directed into the sediment, indicating heterotrophy of the system. There was a net uptake of dissolved inorganic nitrogen, mainly caused by nitrate influx, while ammonium and nitrite showed variable flux direction. Despite high pore water concentrations, phosphate and silica showed net uptake. Fluxes of dissolved
Scientific Reports, Oct 4, 2018
Evidence for relationships between seismotectonic activity and dissolved weathering fluxes remain... more Evidence for relationships between seismotectonic activity and dissolved weathering fluxes remains limited. Motivated by the occurrence of new springs emerging after the 2016 Kumamoto earthquake and supported by historical groundwater data, this study focuses on the long-term effect of nearsurface structural deformation on the contribution of deep, highly saline fluids to the solute fluxes from the Aso caldera, Kyushu, Japan. Available hydrologic and structural data suggest that concentrated, over-pressured groundwaters migrate to the surface when new hydraulic pathways open during seismic deformation. These new springs have a hydrochemical fingerprint (including δD H2O , δ 18 O H2O , δ 7 Li, δ 11 B, δ 18 O SO4 , and δ 34 S SO4) indistinguishable from long-established confined groundwater that likely reflects a mixture of infiltrated meteoric water with high-sulfate hydrothermal fluids. A comparison of historical hydrochemistry data and patterns of past seismicity suggests that discharge of deep fluids is associated with similar deformation structures to those observed during the Kumamoto earthquake, and that seismic activity plays an important role over historic timescales in delivering the majority of the solutes to the caldera outlet, sustaining fluxes that are amongst the world's highest. This upwelling mechanism might be relevant for other systems too, and could contribute to the over-proportional share of active volcanic areas in global weathering fluxes. Active volcanic areas contribute a disproportionately large component to the global flux of dissolved elements delivered from the land to the oceans, both in comparison to other lithologies 1,2 and to inactive volcanic systems 3. Several processes may cause enhanced solute fluxes from active volcanic areas, including the reaction of ecosystem-recycled CO 2 with relatively young fresh mineral material 4-6 , volcanic acid mediated rock alteration in geothermal fields 7-12 , and deep, solute-rich crustal fluids released to the surface through crustal pathways 13-16. These processes have distinct implications for weathering budgets and particularly for the long-term global carbon cycle. However, the distribution, source, and discharge mechanism of deep fluids, and their impact on watershed hydrochemistry and long-term lateral weathering fluxes, are not well understood in the global context because of limited study opportunities. Earthquakes can trigger an increase in dissolved geochemical fluxes 13-20 partly by opening new pathways for deep fluid discharge to the surface 13-16. Even though active volcanism is sometimes accompanied by seismotectonic processes that may systematically facilitate the release of solute-rich deep fluids 21,22 , the role of seismotectonic processes in sustaining the high apparent weathering fluxes from volcanic systems is not known.
Supplementary Figure S1. Miller-Tans plots of DIC * 13 C-DIC (mM * ‰) vs DIC (mM)
Goldschmidt2021 abstracts, 2021
Mineralogical Magazine, 1997
The FTIR spectra of synthetic BaMg(CO3)2 (norsethite) are measured at ambient temperature and atm... more The FTIR spectra of synthetic BaMg(CO3)2 (norsethite) are measured at ambient temperature and atmospheric pressure, and the influence of formation conditions on the FTIR spectra is investigated. The results are compared with those for natural norsethite from Långban (Sweden) and Rosh Pinah (Namibia). The Raman spectrum of synthetic norsethite is reported, too. A number of first-order internal modes of the carbonate ion group (ν1, ν2, ν3, ν4) are found to be infrared and Raman active. Additonally, the (ν1+ν3) and (ν1+ν4) combination modes and the (2*ν2) overtone are observed in the FTIR and Raman spectrum, respectively. The carbon isotopic-shift coefficient for ν2 due to the substitution of 12C by 13C (ν2(13CO32-)/ν2(12CO32-) = 0.971 ± 0.002), observed by FTIR spectroscopy, agrees with the theoretical value of 0.969.
Limnology and Oceanography: Methods, 2015
Biogenic, seasonal, and stochastic fluctuations at various scales characterize coastal marine hab... more Biogenic, seasonal, and stochastic fluctuations at various scales characterize coastal marine habitats and modulate environmental stress. The relevance of most past studies into climate change impacts is weakened by the usually intentional exclusion of fluctuations from the experimental design. We describe a new outdoor mesocosm system for benthic research ("benthocosms") which permit the control and manipulation of several environmental variables while admitting all natural in situ fluctuations. This is achieved by continuously measuring the relevant variables (e.g., temperature, pH, O 2 , CO 2) in situ, defining these in real time as reference values in the control software and simulating target climates by delta treatments. The latter constitute the manipulative addition of predefined changes (e.g., "warming", "acidification") to the reference values. We illustrate the performance of the system by presenting the environmental data of four seasonal experiments which together represent an entire year. The "Kiel Outdoor Benthocosms" allow realizing nearnatural climate change experiments on complex benthic communities under controlled scenarios.
Chemical Geology, 2015
Brachiopods are long-lived, long-ranging, extant organisms, of which some groups precipitate a re... more Brachiopods are long-lived, long-ranging, extant organisms, of which some groups precipitate a relatively diagenetically stable low magnesium calcite shell. Previous work has suggested that the incorporation of Mg into brachiopod calcite may be controlled by temperature (Brand et al., 2013). Here we build upon this work by using laser ablation sampling to define the intra-shell variations in two modern brachiopod species, Terebratulina retusa (Linnaeus, 1758) and Liothyrella neozelanica (Thomson, 1918). We studied three T. retusa shells collected live from the Firth of Lorne, Scotland, which witnessed annual temperature variations on the order of 7°C, in addition to four L. neozelanica shells, which were dredged from a water depth transect (168-1488 m) off the north coast of New Zealand. The comparison of intra-shell Mg/Ca profiles with shell δ 18 Oc o n firms a temperature control on brachiopod Mg/Ca and supports the use of brachiopod Mg/Ca as a palaeoseasonality indicator. Our preliminary temperature calibrations are Mg/Ca = 1.76 ± 0.27 e (0.16 ± 0.03)T , R 2 =0. 7 5 ,f o rT. retusa and Mg/Ca = 0.49 ± 1.27 e (0.2 ± 0.11)T , R 2 =0. 3 2 ,f o r L. neozelanica (errors are 95% confidence intervals).
Seventy-nine interstitial water samples from six sites (Ocean Drilling Program Sites 1119-1124) f... more Seventy-nine interstitial water samples from six sites (Ocean Drilling Program Sites 1119-1124) from the southwestern Pacific Ocean have been analyzed for stable isotopes of dissolved sulfate (δ 34 S), along with major and minor ions. Sulfate from the interstitial fluids (δ 34 S values between +20.7‰ and +57.5‰ vs. the Vienna-Canyon Diablo troilite standard) was enriched in 34 S with respect to modern seawater (δ 34 S ≈ +20.6‰), indicating that differing amounts of microbial sulfate reduction took place at all investigated sites. Microbial sulfate reduction was found at all sites, the intensity depending on the availability of organic matter, which is controlled by paleosedimentation conditions (e.g., sedimentation rate and presence of turbidites). In addition, total reduced inorganic sulfur (essentially pyrite) as a product of microbial sulfate reduction was quantified in selected sediments from Site 1119.
Early diagenesis in sediments of the subtropical Beibu Gulf, South China Sea: Constraints from trace elements, and stable S and C isotopes
EGU General Assembly Conference Abstracts, Apr 1, 2012
After the flood: Sulfur authigenesis and isotope discrimination in a rewetting coastal fen
Pelagic anomalies and isotope signatures of molybdenum in temperate tidal systems
EGUGA, Apr 1, 2012
Dissolved Mo was assumed to behave conservatively in oxic seawater for a long time. Seasonal obse... more Dissolved Mo was assumed to behave conservatively in oxic seawater for a long time. Seasonal observations in the water column of tidal basins of the German Wadden Sea, however, have shown pronounced negative anomalies with decreases down to 50% of ...
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Papers by Michael E. Böttcher