| 1. |
- Broman, Elias, et al.
(författare)
-
Low Abundance of Methanotrophs in Sediments of Shallow Boreal Coastal Zones With High Water Methane Concentrations
- 2020
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Coastal zones are transitional areas between land and sea where large amounts of organic and inorganic carbon compounds are recycled by microbes. Especially shallow zones near land have been shown to be the main source for oceanic methane (CH4) emissions. Water depth has been predicted as the best explanatory variable, which is related to CH4 ebullition, but exactly how sediment methanotrophs mediates these emissions along water depth is unknown. Here, we investigated the relative abundance and RNA transcripts attributed to methane oxidation proteins of aerobic methanotrophs in the sediment of shallow coastal zones with high CH4 concentrations within a depth gradient from 10–45 m. Field sampling consisted of collecting sediment (top 0–2 cm layer) from eight stations along this depth gradient in the coastal Baltic Sea. The relative abundance and RNA transcripts attributed to the CH4 oxidizing protein (pMMO; particulate methane monooxygenase) of the dominant methanotroph Methylococcales was significantly higher in deeper costal offshore areas (36–45 m water depth) compared to adjacent shallow zones (10–28 m). This was in accordance with the shallow zones having higher CH4 concentrations in the surface water, as well as more CH4 seeps from the sediment. Furthermore, our findings indicate that the low prevalence of Methylococcales and RNA transcripts attributed to pMMO was restrained to the euphotic zone (indicated by Photosynthetically active radiation (PAR) data, photosynthesis proteins, and 18S rRNA data of benthic diatoms). This was also indicated by a positive relationship between water depth and the relative abundance of Methylococcales and pMMO. How these processes are affected by light availability requires further studies. CH4 ebullition potentially bypasses aerobic methanotrophs in shallow coastal areas, reducing CH4 availability and limiting their growth. Such mechanism could help explain their reduced relative abundance and related RNA transcripts for pMMO. These findings can partly explain the difference in CH4 concentrations between shallow and deep coastal areas, and the relationship between CH4 concentrations and water depth.
|
|
| 2. |
- Brüchert, Volker, et al.
(författare)
-
Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment
- 2018
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 15:2, s. 471-490
-
Tidskriftsartikel (refereegranskat)abstract
- The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O2 microelectrode profiling, intact sediment core incubations, 35 S-sulfate tracer experiments, porewater dissolved inorganic carbon (DIC), δ13 CDIC, and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope, and allowed us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 20 to 50 cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 82% of the depthintegrated carbon mineralization. Oxygen uptake rates and 35 S-sulfate reduction rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC/NH4 + ratios in porewaters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end member calculations, the terrestrial organic carbon contribution varied between 32% and 36%, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using isotope end member apportionment over the outer shelf of the Laptev and East Siberian Sea suggests that about 16 Tg C per year are respired in the outer shelf sea floor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C per year are degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5 Tg per year.
|
|
| 3. |
- Ehrnsten, Eva, et al.
(författare)
-
Understanding Environmental Changes in Temperate Coastal Seas : Linking Models of Benthic Fauna to Carbon and Nutrient Fluxes
- 2020
-
Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 7
-
Forskningsöversikt (refereegranskat)abstract
- Coastal seas are highly productive systems, providing an array of ecosystem services to humankind, such as processing of nutrient effluents from land and climate regulation. However, coastal ecosystems are threatened by human-induced pressures such as climate change and eutrophication. In the coastal zone, the fluxes and transformations of nutrients and carbon sustaining coastal ecosystem functions and services are strongly regulated by benthic biological and chemical processes. Thus, to understand and quantify how coastal ecosystems respond to environmental change, mechanistic modeling of benthic biogeochemical processes is required. Here, we discuss the present model capabilities to quantitatively describe how benthic fauna drives nutrient and carbon processing in the coastal zone. There are a multitude of modeling approaches of different complexity, but a thorough mechanistic description of benthic-pelagic processes is still hampered by a fundamental lack of scientific understanding of the diverse interactions between the physical, chemical and biological processes that drive biogeochemical fluxes in the coastal zone. Especially shallow systems with long water residence times are sensitive to the activities of benthic organisms. Hence, including and improving the description of benthic biomass and metabolism in sediment diagenetic as well as ecosystem models for such systems is essential to increase our understanding of their response to environmental changes and the role of coastal sediments in nutrient and carbon cycling. Major challenges and research priorities are (1) to couple the dynamics of zoobenthic biomass and metabolism to sediment reactive-transport in models, (2) to test and validate model formulations against real-world data to better incorporate the context-dependency of processes in heterogeneous coastal areas in models and (3) to capture the role of stochastic events.
|
|
| 4. |
- Fotherby, Angus, et al.
(författare)
-
Modelling the Effects of Non-Steady State Transport Dynamics on the Sulfur and Oxygen Isotope Composition of Sulfate in Sedimentary Pore Fluids
- 2021
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- We present the results of an isotope-enabled reactive transport model of a sediment column undergoing active microbial sulfate reduction to explore the response of the sulfur and oxygen isotopic composition of sulfate under perturbations to steady state. In particular, we test how perturbations to steady state influence the cross plot of δ34S and δ18O for sulfate. The slope of the apparent linear phase (SALP) in the cross plot of δ34S and δ18O for sulfate has been used to infer the mechanism, or metabolic rate, of microbial metabolism, making it important that we understand how transient changes might influence this slope. Tested perturbations include changes in boundary conditions and changes in the rate of microbial sulfate reduction in the sediment. Our results suggest that perturbations to steady state influence the pore fluid concentration of sulfate and the δ34S and δ18O of sulfate but have a minimal effect on SALP. Furthermore, we demonstrate that a constant advective flux in the sediment column has no measurable effect on SALP. We conclude that changes in the SALP after a perturbation are not analytically resolvable after the first 5% of the total equilibration time. This suggests that in sedimentary environments the SALP can be interpreted in terms of microbial metabolism and not in terms of environmental parameters.
|
|
| 5. |
- Grasse, Patricia, et al.
(författare)
-
GEOTRACES inter-calibration of the stable silicon isotope composition of dissolved silicic acid in seawater
- 2017
-
Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 32:3, s. 562-578
-
Tidskriftsartikel (refereegranskat)abstract
- The first inter-calibration study of the stable silicon isotope composition of dissolved silicic acid in seawater, delta Si-30(OH)(4), is presented as a contribution to the international GEOTRACES program. Eleven laboratories from seven countries analyzed two seawater samples from the North Pacific subtropical gyre (Station ALOHA) collected at 300 m and at 1000 m water depth. Sampling depths were chosen to obtain samples with a relatively low (9 mmol L-1, 300 m) and a relatively high (113 mmol L-1, 1000 m) silicic acid concentration as sample preparation differs for low- and highconcentration samples. Data for the 1000 m water sample were not normally distributed so the median is used to represent the central tendency for the two samples. Median delta Si-30(OH)(4) values of +1.66& for the low-concentration sample and +1.25& for the high-concentration sample were obtained. Agreement among laboratories is overall considered very good; however, small but statistically significant differences among the mean isotope values obtained by different laboratories were detected, likely reflecting inter-laboratory differences in chemical preparation including pre-concentration and purification methods together with different volumes of seawater analyzed, and the use of different mass spectrometers including the Neptune MC-ICP-MS (Thermo Fisher (TM), Germany), the Nu Plasma MC-ICP-MS (Nu Instruments (TM), Wrexham, UK), and the Finnigan (TM) (now Thermo Fisher (TM), Germany) MAT 252 IRMS. Future studies analyzing delta Si-30(OH)(4) in seawater should also analyze and report values for these same two reference waters in order to facilitate comparison of data generated among and within laboratories over time.
|
|
| 6. |
- Gustafsson, Erik, et al.
(författare)
-
Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea
- 2019
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 16:2, s. 437-456
-
Tidskriftsartikel (refereegranskat)abstract
- Enhanced release of alkalinity from the seafloor, principally driven by anaerobic degradation of organic matter under low-oxygen conditions and associated secondary redox reactions, can increase the carbon dioxide (CO2) buffering capacity of seawater and therefore oceanic CO2 uptake. The Baltic Sea has undergone severe changes in oxygenation state and total alkalinity (TA) over the past decades. The link between these concurrent changes has not yet been investigated in detail. A recent system-wide TA budget constructed for the past 50 years using BALTSEM, a coupled physical-biogeochemical model for the whole Baltic Sea area, revealed an unknown TA source. Here we use BALTSEM in combination with observational data and one-dimensional reactive transport modelling of sedimentary processes in the Fårö Deep, a deep Baltic Sea basin, to test whether sulfate reduction coupled to iron (Fe) sulfide burial can explain the missing TA source in the Baltic Proper. We calculated that this burial can account for 26% of the missing source in this basin, with the remaining TA possibly originating from unknown river inputs or submarine groundwater discharge. We also show that temporal variability in the input of Fe to the sediments since the 1970s drives changes in sulfur burial in the Fårö Deep, suggesting that Fe availability is the ultimate limiting factor for TA generation under anoxic conditions. The implementation of projected climate change and two nutrient load scenarios for the 21st century in BALTSEM shows that reducing nutrient loads will improve deep water oxygen conditions, but at the expense of lower surface water TA concentrations, CO2 buffering capacities and faster acidification. When these changes additionally lead to a decrease in Fe inputs to the sediment of the deep basins, anaerobic TA generation will be reduced even further, thus exacerbating acidification. This work highlights that Fe dynamics play a key role in the release of TA from sediments where Fe sulfide formation is limited by Fe availability, as exemplified for the Baltic Sea. Moreover, it demonstrates that burial of Fe sulfides should be included in TA budgets of low oxygen basins.
|
|
| 7. |
- Huang, Tzu-Hao, et al.
(författare)
-
Separating Si phases from diagenetically-modified sediments through sequential leaching.
- 2023
-
Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836.
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon (Si) phases such as biogenic silica, lithogenic silicate and authigenic silica/silicate in marine sediments provide valuable information about past Si cycling. Wet-chemical sequential leaching methods are often applied to extract different Si phases from marine sediments to study Si diagenetic processes in shallow subsurface. The potential of this method to separate Si phases from deeply-buried and diagenetically-modified sediments has not been systematically examined. We applied a sequential leaching protocol to drill core sediments retrieved from the Ulleung Basin, East/Japan Sea. We performed geochemical (elemental abundance and stable Si isotopes, δ30Si) and microscopic (X-ray diffraction and scanning electron microscope) analyses to monitor leaching efficiency in separating different Si phases. We show that, prior to alkaline leaching, applying weak acid is able to remove metal oxide and/or clay-like phases. The following Na2CO3 leaching, based on a commonly-adopted protocol, is able to dissolve some but not all diatoms. The results of elemental contents and δ30Si values of leachates suggest that, in diagenetically-modified sediments, either a longer digesting time or a harsher alkaline leaching is needed to dissolve all diatoms. This is attributed to increased resistance of diatoms to Na2CO3 leaching as a result of reduced surface area and/or improved SiO2 tetrahedron ordering during diagenetic processes over time and burial depths. Lithogenic silicate minerals can be dissolved by NaOH and potentially separated from diatoms if the latter is completely removed in the preceding leaching steps. Even if a trace amount of diatom is left undissolved in the NaOH leaching, it is still possible to separate the two through a mass balance calculation given the knowledge of composition for the two end-members. We conclude that a successful separation of Si phases in diagenetically modified sediments relies on the knowledge of elemental abundance and even δ30Si values of the leachates, as well as information such as species of Si-skeleton organisms, contents and maturation degree of biogenic silica.
|
|
| 8. |
- Humborg, Christoph, et al.
(författare)
-
High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave
- 2019
-
Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The summer heat wave in 2018 led to the highest recorded water temperatures since 1926 - up to 21 degrees C - in bottom coastal waters of the Baltic Sea, with implications for the respiration patterns in these shallow coastal systems. We applied cavity ring-down spectrometer measurements to continuously monitor carbon dioxide (CO2) and methane (CH4) surface-water concentrations, covering the coastal archipelagos of Sweden and Finland and the open and deeper parts of the Northern Baltic Proper. This allowed us to (i) follow an upwelling event near the Swedish coast leading to elevated CO2 and moderate CH 4 outgassing, and (ii) to estimate CH4 sources and fluxes along the coast by investigating water column inventories and air-sea fluxes during a storm and an associated downwelling event. At the end of the heat wave, before the storm event, we found elevated CO2 (1583 mu atm) and CH4 (70 nmol/L) concentrations. During the storm, a massive CO2 sea-air flux of up to 274 mmol m(-2) d(-1) was observed. While water-column CO2 concentrations were depleted during several hours of the storm, CH4 concentrations remained elevated. Overall, we found a positive relationship between CO2 and CH4 wind-driven sea-air fluxes, however, the highest CH4 fluxes were observed at low winds whereas highest CO2 fluxes were during peak winds, suggesting different sources and processes controlling their fluxes besides wind. We applied a box-model approach to estimate the CH4 supply needed to sustain these elevated CH4 concentrations and the results suggest a large source flux of CH4 to the water column of 2.5 mmol m(-2) d(-1). These results are qualitatively supported by acoustic observations of vigorous and widespread outgassing from the sediments, with flares that could be traced throughout the water column penetrating the pycnocline and reaching the sea surface. The results suggest that the heat wave triggered CO2 and CH4 fluxes in the coastal zones that are comparable with maximum emission rates found in other hot spots, such as boreal and arctic lakes and wetlands. Further, the results suggest that heat waves are as important for CO2 and CH4 sea-air fluxes as the ice break up in spring.
|
|
| 9. |
- Hutchings, Alec M., et al.
(författare)
-
Creek Dynamics Determine Pond Subsurface Geochemical Heterogeneity in East Anglian (UK) Salt Marshes
- 2019
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Salt marshes are complex systems comprising ephemerally flooded, vegetated platforms hydraulically fed by tidal creeks. Where drainage is poor, formation of saline-water ponds can occur. Within East Anglian (UK) salt marshes, two types of sediment chemistries can be found beneath these ponds; iron-rich sediment, which is characterized by high ferrous iron concentration in subsurface porewaters (up to 2 mM in the upper 30 cm); and sulfide-rich sediment, which is characterized by high porewater sulfide concentrations (up to 8 mM). We present 5 years of push-core sampling to explore the geochemistry of the porewater in these two types of sediment. We suggest that when organic carbon is present in quantities sufficient to exhaust the oxygen and iron content within pond sediments, conditions favor the presence of sulfide-rich sediments. In contrast, in pond sediments where oxygen is present, primarily through bioirrigation, reduced iron can be reoxidised and thus recycled for further reduction, favoring the perpetuation of iron-rich sedimentary conditions. We find these pond sediments can alter significantly over an annual timescale. We carried out a drone survey, with ground-truthed measurements, to explore the spatial distribution of geochemistry in these ponds. Our results suggest that a pond's proximity to a creek partially determines the pond subsurface geochemistry, with iron-rich ponds tending to be closer to large creeks than sulfide-rich ponds. We suggest differences in surface delivery of organic carbon, due to differences in the energy of the ebb flow, or the surface/subsurface delivery of iron may control the distribution. This could be amplified if tidal inundations flush ponds closer to creeks more frequently, removing carbon and flushing with oxygen. These results suggest that anthropogenic creation of drainage ditches could shift the distribution of iron- and sulfide-rich ponds and thus have an impact on nutrient, trace metal and carbon cycling in salt marsh ecosystems.
|
|
| 10. |
- James, Daniel H., et al.
(författare)
-
Assessing Sedimentary Boundary Layer Calcium Carbonate Precipitation and Dissolution Using the Calcium Isotopic Composition of Pore Fluids
- 2021
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- We present pore fluid geochemistry, including major ion and trace metal concentrations and the isotopic composition of pore fluid calcium and sulfate, from the uppermost meter of sediments from the Gulf of Aqaba (Northeast Red Sea) and the Iberian Margin (North Atlantic Ocean). In both the locations, we observe strong correlations among calcium, magnesium, strontium, and sulfate concentrations as well as the sulfur isotopic composition of sulfate and alkalinity, suggestive of active changes in the redox state and pH that should lead to carbonate mineral precipitation and dissolution. The calcium isotope composition of pore fluid calcium (delta Ca-44) is, however, relatively invariant in our measured profiles, suggesting that carbonate mineral precipitation is not occurring within the boundary layer at these sites. We explore several reasons why the pore fluid delta Ca-44 might not be changing in the studied profiles, despite changes in other major ions and their isotopic composition, including mixing between the surface and deep precipitation of carbonate minerals below the boundary layer, the possibility that active iron and manganese cycling inhibits carbonate mineral precipitation, and that mineral precipitation may be slow enough to preclude calcium isotope fractionation during carbonate mineral precipitation. Our results suggest that active carbonate dissolution and precipitation, particularly in the diffusive boundary layer, may elicit a more complex response in the pore fluid delta Ca-44 than previously thought.
|
|
| 11. |
- Jilbert, Tom, et al.
(författare)
-
Anthropogenic Inputs of Terrestrial Organic Matter Influence Carbon Loading and Methanogenesis in Coastal Baltic Sea Sediments
- 2021
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Coastal regions globally have experienced widespread anthropogenic eutrophication in recent decades. Loading of autochthonous carbon to coastal sediments enhances the demand for electron acceptors for microbial remineralization, often leading to rearrangement of the sediment diagenetic zonation and potentially enhancing fluxes of methane and hydrogen sulfide from the seafloor. However, the role of anthropogenic inputs of terrestrial organic matter (OMterr.) in modulating diagenesis in coastal sediments is often overlooked, despite being of potential importance in regions of land-use and industrial change. Here we present a dated 4-m sediment and porewater geochemistry record from a eutrophic coastal location in the northern Baltic Sea, to investigate sources of recent carbon loading and their impact on modern diagenetic processes. Based on an end-member mixing model of sediment N/C ratios, we observe that a significant fraction of the late-20th century carbon loading at this location was contributed by OMterr.. Furthermore, analysis of lignin in this material shows depleted ratios of syringyl/vanillyl (S/V) and cinnamyl/vanillyl (C/V) phenols, indicative of enhanced inputs of woody gymnosperm tissue likely from forest industries. The rapid loading of organic matter from combined terrestrial and autochthonous sources during the late 20th century has stimulated methanogenesis in the sediment column, and shoaled the sulfate-methane transition zone (SMTZ) to a depth of 5–20 cm. Optical parameters of colored dissolved organic matter confirm that OMterr. is actively degrading in the methanogenic layer, implying a role for this material in diagenetic processes. Porewater CH4, SO42− δ13C-DIC, and ∑S2− data suggest that the modern SMTZ is a broad zone in which organoclastic sulfate reduction, methanogenesis and anaerobic oxidation of methane (AOM) co-occur. However, fluxes of CH4 and SO42− show that rates of these processes are similar to other marine locations with a comparably shallow SMTZ. We suggest that the shallow depth of the modern SMTZ is the principal reason for high observed diffusive and ebullitive methane fluxes from sediments in this area. Our results highlight that anthropogenic activities lead to multiple pathways of carbon loading to coastal sediments, and that forest industry impacts on sedimentation in the northern Baltic Sea may be more widespread than previously acknowledged.
|
|
| 12. |
- Kahma, T. I., et al.
(författare)
-
Macroalgae fuels coastal soft-sediment macrofauna : A triple-isotope approach across spatial scales
- 2020
-
Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 162
-
Tidskriftsartikel (refereegranskat)abstract
- Shallow coastal zones may provide cross-habitat nutrient subsidies for benthic communities offshore, as macrophyte matter can drift to deeper sediments. To study the relative importance of carbon and nutrient flows derived from different primary food sources in a coastal ecosystem, the diets of clam Macoma balthica, polychaete Marenzelleria spp. and mussel Mytilus trossulus were examined across environmental gradients in the northern Baltic Sea using a triple-isotope approach (i.e. 13C, 15N and 34S) and Bayesian mixing models (MixSIAR). Our results suggest that in shallow habitats, production from Fucus vesiculosus is the primary energy source for M. balthica. The proportion of macroalgae-derived matter in the diet of M. balthica and Marenzelleria spp. decreased following a depth gradient. Our models for M. trossulus indicate that the pelagic POM dominates its diet. Our results indicate a trophic connectivity between shallow macrophyte-dominated and deeper habitats, which receive significant amounts of nutrient subsidies from shallower areas.
|
|
| 13. |
- Ren, Hong, et al.
(författare)
-
Measurement report: Vertical distribution of biogenic and anthropogenic secondary organic aerosols in the urban boundary layer over Beijing during late summer
- 2021
-
Ingår i: ATMOSPHERIC CHEMISTRY AND PHYSICS. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:17, s. 12949-12963
-
Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol (SOA) plays a significant role in atmospheric chemistry. However, little is known about the vertical profiles of SOA in the urban boundary layer (UBL). This knowledge gap constrains the SOA simulation in chemical transport models. Here, the aerosol samples were synchronously collected at 8, 120, and 260m based on a 325m meteorological tower in Beijing from 15 August to 10 September 2015. Strict emission controls were implemented during this period for the 2015 China Victory Day parade. Here, we observed that the total concentration of biogenic SOA tracers increased with height. The fraction of SOA from isoprene oxidation increased with height, whereas the fractions of SOA from monoterpenes and sesquiterpenes decreased, and 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), a tracer of anthropogenic SOA from toluene oxidation, also increased with height. The complicated vertical profiles of SOA tracers highlighted the need to characterize SOA within the UBL. The mass concentration of estimated secondary organic carbon (SOC) ranged from 341 to 673 ngC m(-3). The increase in the estimated SOC fractions from isoprene and toluene with height was found to be more related to regional transport, whereas the decrease in the estimated SOC from monoterpenes and sesquiterpene with height was more subject to local emissions. Emission controls during the parade reduced SOC by 4 %-35 %, with toluene SOC decreasing more than the other SOC. This study demonstrates that vertical distributions of SOA within the UBL are complex, and the vertical profiles of SOA concentrations and sources should be considered in field and modeling studies in the future.
|
|
| 14. |
- Roth, Florian, et al.
(författare)
-
High spatiotemporal variability of methane concentrations challenges estimates of emissions across vegetated coastal ecosystems.
- 2022
-
Ingår i: Global change biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 28:14, s. 4308-4322
-
Tidskriftsartikel (refereegranskat)abstract
- Coastal methane (CH4 ) emissions dominate the global ocean CH4 budget and can offset the "blue carbon" storage capacity of vegetated coastal ecosystems. However, current estimates lack systematic, high-resolution, and long-term data from these intrinsically heterogeneous environments, making coastal budgets sensitive to statistical assumptions and uncertainties. Using continuous CH4 concentrations, δ13 C-CH4 values, and CH4 sea-air fluxes across four seasons in three globally pervasive coastal habitats, we show that the CH4 distribution is spatially patchy over meter-scales and highly variable in time. Areas with mixed vegetation, macroalgae, and their surrounding sediments exhibited a spatiotemporal variability of surface water CH4 concentrations ranging two orders of magnitude (i.e., 6-460nM CH4 ) with habitat-specific seasonal and diurnal patterns. We observed (1) δ13 C-CH4 signatures that revealed habitat-specific CH4 production and consumption pathways, (2) daily peak concentration events that could change >100% within hours across all habitats, and (3) a high thermal sensitivity of the CH4 distribution signified by apparent activation energies of ~1eV that drove seasonal changes. Bootstrapping simulations show that scaling the CH4 distribution from few samples involves large errors, and that ~50 concentration samples per day are needed to resolve the scale and drivers of the natural variability and improve the certainty of flux calculations by up to 70%. Finally, we identify northern temperate coastal habitats with mixed vegetation and macroalgae as understudied but seasonally relevant atmospheric CH4 sources (i.e., releasing≥100μmol CH4 m-2 day-1 in summer). Due to the large spatial and temporal heterogeneity of coastal environments, high-resolution measurements will improve the reliability of CH4 estimates and confine the habitat-specific contribution to regional and global CH4 budgets.
|
|
| 15. |
- Roth, Florian, et al.
(författare)
-
Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems
- 2023
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- Coastal ecosystems can efficiently remove carbon dioxide (CO2) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH4) emissions from these ecosystems may counterbalance atmospheric CO2 uptake. Still, knowledge of mechanisms sustaining suchCH4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here we show that these habitats emit CH4 in the range of 0.1 – 2.9 mg CH4 m−2 d−1 to the atmosphere, revealing in situ CH4 emissions from macroalgae that weresustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO2-equivalent CH4 emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO2 uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO2 release of unvegetated sediments by 57%. Accounting for CH4 alongside CO2 sea-air fluxes and identifying the mechanisms controlling these emissions is crucial to constrain the potential of coastal ecosystems as net atmospheric carbon sinks and develop informed climate mitigation strategies.
|
|
| 16. |
- Song, Zhaoliang, et al.
(författare)
-
High potential of stable carbon sequestration in phytoliths of China's grasslands
- 2022
-
Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:8, s. 2736-2750
-
Tidskriftsartikel (refereegranskat)abstract
- Phytolith carbon (C) sequestration plays a key role in mitigating global climate change at a centennial to millennial time scale. However, previous estimates of phytolith-occluded carbon (PhytOC) storage and potential in China's grasslands have large uncertainties mainly due to multiple data sources. This contributes to the uncertainty in predicting long-term C sequestration in terrestrial ecosystems using Earth System Models. In this study, we carried out an intensive field investigation (79 sites, 237 soil profiles [0-100 cm], and 61 vegetation assessments) to quantify PhytOC storage in China's grasslands and to better explore the biogeographical patterns and influencing factors. Generally, PhytOC production flux and soil PhytOC density in both the Tibetan Plateau and the Inner Mongolian Plateau had a decreasing trend from the Northeast to the Southwest. The aboveground PhytOC production rate in China's grassland was 0.48 x 10(6) t CO2 a(-1), and the soil PhytOC storage was 383 x 10(6) t CO2. About 45% of soil PhytOC was stored in the deep soil layers (50-100 cm), highlighting the importance of deep soil layers for C stock assessments. Importantly, the Tibetan Plateau had the greatest contribution (more than 70%) to the PhytOC storage in China's grasslands. The results of multiple regression analysis indicated that altitude and soil texture significantly influenced the spatial distribution of soil PhytOC, explaining 78.1% of the total variation. Soil phytolith turnover time in China's grasslands was mainly controlled by climatic conditions, with the turnover time on the Tibetan Plateau being significantly longer than that on the Inner Mongolian Plateau. Our results offer more accurate estimates of the potential for phytolith C sequestration from ecological restoration projects in degraded grassland ecosystems. These estimates are essential to parameterizing and validating global C models.
|
|
| 17. |
- Sun, Xiaole, 1983-, et al.
(författare)
-
Climate Dependent Diatom Production is Preserved in Biogenic Si Isotope Signatures
- 2011
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:11, s. 3491-3499
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to reconstruct diatom production in the subarctic northern tip of the Baltic Sea, Bothnian Bay, based on down-core analysis of Si isotopes in biogenic silica (BSi). Dating of the sediment showed that the samples covered the period 1820 to 2000. The sediment core record can be divided into two periods, an unperturbed period from 1820 to 1950 and a second period affected by human activities (from 1950 to 2000). This has been observed elsewhere in the Baltic Sea. The shift in the sediment core record after 1950 is likely caused by large scale damming of rivers. Diatom production was inferred from the Si isotope composition which ranged between δ30Si −0.18‰ and +0.58‰ in BSi, and assuming fractionation patterns due to the Raleigh distillation, the production was shown to be correlated with air and water temperature, which in turn were correlated with the mixed layer (ML) depth. The sedimentary record showed that the deeper ML depth observed in colder years resulted in less production of diatoms. Pelagic investigations in the 1990's have clearly shown that diatom production in the Baltic Sea is controlled by the ML depth. Especially after cold winters and deep water mixing, diatom production was limited and dissolved silicate (DSi) concentrations were not depleted in the water column after the spring bloom. Our method corroborates these findings and offers a new method to estimate diatom production over much longer periods of time in diatom dominated aquatic systems, i.e. a large part of the world's ocean and coastal seas.
|
|
| 18. |
- Sun, Xiaole, 1983-, et al.
(författare)
-
Effect of diatom growth and dissolution on silicon isotope fractionationin an estuarine system
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Si isotopes provide a powerful tool to reveal past and present patterns in diatom production. Most studies have focused on Si fractionation factors during diatom growth in open ocean systems and have found lower Si isotope values in diatom shells (biogenic silica). Recent findings indicate that even the fractionation of Si isotopes during the physicochemical dissolution of diatom shells in the opposite direction produces higher δ30Si values in the remaining biogenic silica (BSi), allowing for the interpretation of diatom production patterns over geological time scales. However, estuarine and coastal primary production represents approximately 30-50% of global marine production, and there are hardly any studies on Si isotope fractionation during either diatom growth or dissolution. In this study, Si isotope fractionation during diatom growth and the dissolution of the frustule were measured. Two species of diatoms from the Baltic Sea, one of the largest estuarine systems in the world, were selected for this study. The results show that both species of diatoms during growth yields an identical Si isotope fractionation factor of 0.99925 for 29Si and 0.9984 for 30Si. In contrast to findings from open ocean species, no Si isotope fractionation during dissolution was observed even after 90% of the diatoms dissolved. Whether there is isotope fractionation during dissolution or not will have profound implications for studies using Si isotopes to interpret the Si cycle in marine and estuarine systems. We propose that the small size of the diatoms living in estuarine systems with low salinity may explain the non-existence of Si isotope fractionation during dissolution. Therefore, we suggest that Si isotopes are an instrumental variable holding information about original environmental conditions of estuarine and even coastal systems. Finally, we tested the Si isotope fractionation patterns gained from the lab experiments on a sediment core, corroborating the observed dissolved silicates (DSi) uptake rates in the above water column during diatom growth.
|
|
| 19. |
|
|
| 20. |
- Sun, Xiaole, 1983-
(författare)
-
Isotope-based reconstruction of the biogeochemical Si cycle : Implications for climate change and human perturbation
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global silicon (Si) cycle is of fundamental importance for the global carbon cycle. Diatom growth in the oceans is a major sequestration pathway for carbon on a global scale (often referred to as the biological pump). Patterns of diatoms preserved in marine sediment records can reveal both natural and anthropogenic driven environmental change, which can be used to understand silicon dynamics and climate change. Si isotopes have been shown to have great potential in order to understand the Si cycle by revealing both past and present patterns of dissolved Si (DSi) utilization, primarily when diatoms form their siliceous frustules (noted as biogenic silica, BSi). However, studies using Si isotopes are still scarce and only a few studies exist where stable Si isotopes are used to investigate the biogeochemical Si cycle in aquatic systems. Therefore, this thesis focuses on developing analytical methods for studying BSi and DSi and also provides tools to understand the observed Si isotope distribution, which may help to understand impacts of climate change and human perturbations on marine ecosystems. The Baltic Sea, one of the biggest estuarine systems in the world, was chosen as the study site. BSi samples from a sediment core in Bothnian Bay, the most northern tip of the Baltic Sea, and diatom samples from the Oder River, draining into the southern Baltic Sea were measured and reported in Paper II and III, after establishing a method for Si isotope measurements (Paper I). Si isotope fractionation during diatom production and dissolution was also investigated in a laboratory-controlled experiment (Paper IV) to validate the observations from the field. The major result is that Si isotope signatures in BSi can be used as an historical archive for diatom growth and also related to changes in climate variables. There is isotopic evidence that the Si cycle has been significantly altered in the Baltic Sea catchment by human activities.
|
|
| 21. |
- Sun, Xiaole, 1983-, et al.
(författare)
-
Large-Scale Summertime Variability of Carbonate Chemistry Across the East Siberian Sea: Primary Production Versus Ikaite Dissolution
- 2024
-
Ingår i: Journal of Geophysical Research: Oceans. - 2169-9275 .- 2169-9291. ; 129:1
-
Tidskriftsartikel (refereegranskat)abstract
- Sea-ice dynamics can affect carbon cycling in polar oceans, with sea-ice ikaite acting as a potentially important carbon pump. However, there is no large-scale direct field evidence to support this. Here we used a unique data set that combined continuous measurements of atmospheric and water CO2 concentrations with water chemistry data collected over 1,200km along the East Siberian Sea, the widest Arctic shelf sea. Our results reveal large spatial heterogeneity of sea-ice ikaite contents, which directly interact with carbonate chemistry in the water column. Our findings demonstrate that the CO2 drawdown by sea-ice ikaite dissolution could be as important as that by primary production. We suggest that the role of ikaite in regulating the seasonal carbon cycle on a regional scale could be more important than we previously thought. Effects of the warmer climate on sea ice loss might also play a role in the ikaite inventory.
|
|
| 22. |
- Sun, Xiaole, et al.
(författare)
-
Silicon isotope enrichment in diatoms during nutrient-limited blooms in a eutrophied river system
- 2013
-
Ingår i: Journal of Geochemical Exploration. - : Elsevier BV. - 0375-6742 .- 1879-1689. ; 132, s. 173-180
-
Tidskriftsartikel (refereegranskat)abstract
- We examined the Si isotope fractionation by following a massive nutrient limited diatom bloom in a eutrophied natural system. The Oder River, which is a eutrophied river draining the western half of Poland and entering the southern Baltic Sea, exhibits diatom blooms that cause extreme Si isotope fractionation. The rapid nutrient depletion and fast BSi increase observed during the spring bloom suggest a closed system Rayleigh behavior for DSi and BSi in the river at certain time scales. A Si isotope fractionation factor ((30)epsilon(Dsi-Bsi)) of -1.6 +/- 0.31%. (2 sigma) is found based on observations between April and June, 2004. A very high delta Si-30 value of up to +3.05 parts per thousand. is measured in BSi derived from diatoms. This is about 2 times higher than previously recorded delta Si-30 in freshwater diatoms. The Rayleigh model used to predict the delta Si-30 values of DSi suggests that the initial value before the start of the diatom bloom is close to +2 parts per thousand, which is relatively higher than the previously reported values in other river water. This indicates that there is a biological control of the Si isotope compositions entering the river, probably caused by Si isotope fractionation during uptake of Si in phytoliths. Clearly, eutrophied rivers with enhanced diatom blooms deliver Si-30-enriched DSi and BSi to the coastal ocean, which can be used to trace the biogeochemistry of DSi/BSi in estuaries.
|
|
| 23. |
- Sun, Xiaole, 1983-, et al.
(författare)
-
Silicon isotope enrichment in diatoms during nutrient-limited bloomsin a eutrophied river system
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We examined the Si isotope fractionation in diatoms by following a massive nutrient limited diatom bloom from a eutrophied natural system. We hypothesized that the Si isotope fractionation should be larger in comparison to observations in less nutrient rich environments. The Oder River, which is a eutrophied river draining the western half of Poland and entering the southern Baltic Sea, shows that a diatom bloom may cause extreme Si isotope fractionation. The rapid nutrient depletion and fast biogenic silica (BSi) increase observed during the spring bloom suggests a Rayleigh behavior for a closed system for dissolved Si (DSi) and BSi in the river at certain time scales. An enrichment factor (ε) of up to -1.6‰ is found based on observations between April and June, 2004. A very high δ30Si value of up to +3.05‰ is measured in diatoms. This is about 2 times higher than previously recorded δ30Si in freshwater diatoms. The Rayleigh model used to predict the δ30Si values of DSi suggests that the initial value before the start of the diatom bloom is close to +2‰. This indicates that there is a biological control of the Si isotope compositions entering the river, probably caused by Si isotope fractionation during uptake of Si in phytoliths. Clearly, eutrophied rivers with enhanced diatom blooms deliver 30Si-enriched DSi and BSi to the coastal ocean, which can be used to trace the biogeochemistry of DSi/BSi in estuaries.
|
|
| 24. |
- Sun, Xiaole, 1983-, et al.
(författare)
-
Stable silicon isotope analysis on nanomole quantities using MC-ICP-MS with a hexapole gas-collision cell
- 2010
-
Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 25:2, s. 156-162
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate in this study that a single focusing multiple collector inductively coupled plasma massspectrometer (MC-ICP-MS) equipped with a hexapole gas-collision cell (GV-instrument Isoprobe) canprecisely determine the d29Si (2S.D., 0.2&) using a total Si consumption of less than 14 nmole (390 ngSi). Testing and evaluation of background, rinse time, and major matrix effects have been performed ina systematic way to establish a procedure to measure d29Si in small quantities. Chemical purificationprior to analysis is required to remove potential interferences. For data collected during a four-yearperiod, the average d29Si value of IRMM-018 relative to NBS-28 was found to be 0.95& (n ¼ 23,2S.D. 0.16&) with a 95% confidence interval (0.95 0.028&). The mean d29Si value of the Big-Batchstandard was found to be 5.50& (n ¼ 6, 2S.D. 0.26&). Although determination of the d30Simeasurements is not possible, with our current instrument we demonstrate that this system providesa fast and long-term reliable method for the analysis of d29Si in purified samples with low Siconcentration (18 mM Si).
|
|
| 25. |
- Sun, Xiaole, et al.
(författare)
-
Stable silicon isotopic compositions of the Lena River and its tributaries : Implications for silicon delivery to the Arctic Ocean
- 2018
-
Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 241, s. 120-133
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon isotope values (delta Si-30(DSi)) of dissolved silicon (DSi) have been analyzed in the Lena River and its tributaries, one of the largest Arctic watersheds in the world. The geographical and temporal variations of delta Si-30(DSi) range from +0.39 to +1.86% with DSi concentrations from 34 to 121 mu M. No obvious patterns of DSi concentrations and delta Si-30(DSi) values were observed along over 200 km of the two major tributaries, the Viliui and Aldan Rivers. In summer, the variations of DSi concentrations and delta Si-30(DSi) values in the water are either caused by biological uptake by higher plants and phytoplankton or by mixing of water masses carrying different DSi concentrations and delta Si-30(DSi) values. DSi in tributaries from the Verkhoyansk Mountain Range seems to be associated with secondary clay formation that increased the delta Si-30(DSi) values, while terrestrial biological production is likely more prevalent in controlling delta Si-30(DSi) values in Central Siberian Plateau and Lena Amganski Inter-River Area. In winter, when soils were frozen, the delta Si-30(DSi) values in the river appeared to be controlled by weathering and clay formation in deep intrapermafrost groundwater. During the spring flood, dissolved silicate materials and phytoliths were flushed from the upper thawed soils into rivers, which reset delta Si-30(DSi) values to the values observed prior to the biological bloom in summer. The results indicate that the Si isotope values reflect the changing processes controlling Si outputs to the Lena River and to the Arctic Ocean between seasons. The annual average delta Si-30(DSi) value of the Lena Si flux is calculated to be +0.86 +/- 0.3 parts per thousand using measured delta Si-30(DSi) values from each season. Combined with the estimate of + 1.6 +/- 0.25 parts per thousand for the Yenisey River, an updated delta Si-30(DSi) value of the major river Si inputs to the Arctic Ocean is estimated to be + 1.3 +/- 0.3 parts per thousand. This value is expected to shift towards higher values in the future because of the impacts from a variety of biological and geochemical processes and sources under global warming.
|
|
