| 1. |
- Cabral dos Santos, Alex, 1990, et al.
(författare)
-
Carbon and alkalinity outwelling across the groundwater-creek-shelf continuum off Amazonian mangroves
- 2021
-
Ingår i: Limnology And Oceanography Letters. - : Wiley. - 2378-2242. ; 6:6, s. 369-378
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral fluxes (i.e., outwelling) of dissolved organic (DOC) and inorganic (DIC) carbon and total alkalinity were estimated using radium isotopes at the groundwater, mangrove creek, and continental shelf scales in the Amazon region. Observations of salinity and radium isotopes in the creek indicated tidally driven groundwater exchange as the main source of carbon. Radium-derived transport rates indicate that mangrove carbon is exported out of the continental shelf on timescales of 22 ± 7d. Bicarbonate was the main form (82% ± 11%) of total dissolved carbon in all samples, followed by DOC (13% ± 12%) and CO2 (5% ± 4%). DIC (18.7 ± 15.7 mmol m−2d−1) exceeded DOC (3.0 ± 4.1 mmol m−2d−1) outwelling at all spatial scales. The interpretation of outwelling across the mangrove-ocean continuum is related to the spatial and temporal scales investigated. At all scales, outwelling represented a major coastal carbon pathway driving bicarbonate storage in the ocean.
|
|
| 2. |
- Catalán, Núria, 1985-, et al.
(författare)
-
Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes
- 2024
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- Climate change induced shifts in treeline position, both towards higher altitudes and latitudes induce changes in soil organic matter. Eventually, soil organic matter is transported to alpine and subarctic lakes with yet unknown consequences for dissolved organic matter (DOM) diversity and processing. Here, we experimentally investigate the consequences of treeline shifts by amending subarctic and temperate alpine lake water with soil-derived DOM from above and below the treeline. We use ultra-high resolution mass spectrometry (FT-ICR MS) to track molecular DOM diversity (i.e., chemodiversity), estimate DOM decay and measure bacterial growth efficiency. In both lakes, soil-derived DOM from below the treeline increases lake DOM chemodiversity mainly through the enrichment with polyphenolic and highly unsaturated compounds. These compositional changes are associated with reductions in bulk and compound-level DOM reactivity and reduced bacterial growth efficiency. Our results suggest that treeline advancement has the potential to enrich a large number of lake ecosystems with less biodegradable DOM, affecting bacterial community function and potentially altering the biogeochemical cycling of carbon in lakes at high latitudes and altitudes. Shifts in the treeline may induce changes in organic matter composition of lakes at high altitude and latitude. Here, the authors experimentally unravel effects of soil-derived DOM for lake carbon biogeochemistry and bacterial carbon use efficiency.
|
|
| 3. |
- Chmiel, Hannah Elisa, 1983-, et al.
(författare)
-
Uncoupled organic matter burial and quality in boreal lake sediments over the Holocene
- 2015
-
Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 120:9, s. 1751-1763
-
Tidskriftsartikel (refereegranskat)abstract
- Boreal lake sediments are important sites of organic carbon (OC) storage, which have accumulated substantial amounts of OC over the Holocene epoch; the temporal evolution and the strength of this Holocene carbon (C) sink is, however, not well constrained. In this study we investigated the temporal record of carbon mass accumulation rates (CMARs), and assessed qualitative changes of terrestrially derived OC in the sediment profiles of seven Swedish boreal lakes, in order to evaluate the variability of boreal lake sediments as a C sink over time. CMARs were resolved on a short-term (centennial) and long-term (i.e. over millennia of the Holocene) time scale, using radioactive lead (210 Pb) and carbon (14C) isotope dating. Sources and degradation state of terrestrially derived OC were identified and characterized by molecular analyses of lignin phenols. We found that CMARs varied substantially on both short-term and long-term scales, and that the variability was mostly attributed to sedimentation rates and uncoupled from the OC content in the sediment profiles. The lignin phenol analyses revealed that woody material from gymnosperms was a dominant and constant OC source to the sediments over the Holocene. Furthermore, lignin-based degradation indices, such as acid-to-aldehyde ratios, indicated that post-depositional degradation in the sediments was very limited on longer time scales, implying that terrestrial OC is stabilized in the sediments on a permanent basis.
|
|
| 4. |
|
|
| 5. |
- Hawkes, Jeffrey A., et al.
(författare)
-
An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry : Are we getting the same answer?
- 2020
-
Ingår i: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 18:6, s. 235-258
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution mass spectrometry (HRMS) has become a vital tool for dissolved organic matter (DOM) characterization. The upward trend in HRMS analysis of DOM presents challenges in data comparison and interpretation among laboratories operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with reference samples so that data can be robustly compared among research groups. To this end, four identically prepared DOM samples were each measured by 16 laboratories, using 17 commercially purchased instruments, using positive-ion and negative-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified similar to 1000 common ions in both negative- and positive-ion modes over a wide range of m/z values and chemical space, as determined by van Krevelen diagrams. Calculated metrics of abundance-weighted average indices (H/C, O/C, aromaticity and m/z) of the commonly detected ions showed that hydrogen saturation and aromaticity were consistent for each reference sample across the instruments, while average mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
|
|
| 6. |
- Hawkes, Jeffrey A., et al.
(författare)
-
Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation
- 2015
-
Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 8:11, s. 856-
-
Tidskriftsartikel (refereegranskat)abstract
- Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood(1,2). Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401 degrees C. In laboratory experiments, where we heated samples to 380 degrees C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years(3).
|
|
| 7. |
- Hawkes, Jeffrey A., et al.
(författare)
-
Evaluation of the Orbitrap Mass Spectrometer for the Molecular Fingerprinting Analysis of Natural Dissolved Organic Matter
- 2016
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 88:15, s. 7698-7704
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the application of the LTQ-Orbitrap mass spectrometer (LTQ-Velos Pro, Thermo Fisher) for resolving complex mixtures of natural aquatic dissolved organic matter (DOM) and compared this technique to the more established state-of-the-art technique, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS, Bruker Daltonics), in terms of the distribution of molecular masses detected and the reproducibility of the results collected. The Orbitrap was capable of excellent reproducibility: Bray-Curtis dissimilarity between duplicate measurements was 2.85 +/- 0.42% (mean +/- standard deviation). The Orbitrap was also capable of the detection of most major ionizable organic molecules in typical aquatic mixtures, with the exception of most sulfur and phosphorus containing masses. This result signifies that the Orbitrap is an appropriate technique for the investigation of very subtle biogeochemical processing of bulk DOM. The lower costs (purchase and maintenance) and wider availability of Orbitrap mass spectrometers in university departments means that the tools necessary for research into DOM processing at the molecular level should be accessible to a much wider group of scientists than before. The main disadvantage of the technique is that substantially fewer molecular formulas can be resolved from a complex mixture (roughly one third as many), meaning some loss of information. In balance, most biogeochemical studies that aim at molecularly fingerprinting the source of natural DOM could be satisfactorily carried out with Orbitrap mass spectrometry. For more targeted metabolomic studies where individual compounds are traced through natural systems, FTICR-MS remains advantageous.
|
|
| 8. |
- Hawkes, Jeffrey A., et al.
(författare)
-
Molecular alteration of marine dissolved organic matter under experimental hydrothermal conditions
- 2016
-
Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 175, s. 68-85
-
Tidskriftsartikel (refereegranskat)abstract
- Marine dissolved organic matter (DOM) is a large (660 Pg) pool of reduced carbon that is subject to thermal alteration in hydrothermal systems and sedimentary basins. In natural high-temperature hydrothermal systems, DOM is almost completely removed, but the mechanism and temperature dependence of this removal have not been studied to date. We investigated molecular-level changes to DOM that was solid-phase extracted (SPE-DOM) from the deep ocean of the North Pacific Ocean. This complex molecular mixture was experimentally exposed to temperatures between 100 and 380 degrees C over the course of two weeks in artificial seawater, and was then characterised on a molecular level via ultrahigh-resolution Fourier-transform ion cyclotron mass spectrometry (FT-ICR-MS). Almost 93% of SPE-DOM was removed by the treatment at 380 degrees C, and this removal was accompanied by a consistent pattern of SPE-DOM alteration across the temperatures studied. Higher molecular weight and more oxygen rich compounds were preferentially removed, suggesting that decarboxylation and dehydration of carboxylic acid and alcohol groups are the most rapid degradation mechanisms. Nitrogen containing compounds followed the same overall trends as those containing just C, H and O up to 300 degrees C. Above this temperature, the most highly altered samples contained very little of the original character of marine DOM, instead being mainly composed of very low intensity N- and S-containing molecules with a high H/C ratio (>1.5). Our results suggest that abiotic hydrothermal alteration of SPE-DOM may already occur at temperatures above 68 degrees C. Our experiments were conducted without a sedimentary or mineral phase, and demonstrate that profound molecular alteration and almost complete removal of marine SPE-DOM requires nothing more than heating in a seawater matrix.
|
|
| 9. |
- Karlsson, Emma, 1980-
(författare)
-
Compositional clues to sources and sinks of terrestrial organic matter transported to the Eurasian Arctic shelf
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The amount of organic carbon (OC) present in Siberian Arctic permafrost soils is estimated at twice the amount of carbon currently in the atmosphere. The shelf seas of the Arctic Ocean receive large amounts of this terrestrial OC from Eurasian Arctic rivers and from coastal erosion. Degradation of this land-derived material in the sea would result in the production of dissolved carbon dioxide and may then add to the atmospheric carbon dioxide reservoir. Observations from the Siberian Arctic suggest that transfer of carbon from land to the marine environment is accelerating. However, it is not clear how much of the transported OC is degraded and oxidized, nor how much is removed from the active carbon cycle by burial in marine sediment.Using bulk geochemical parameters, total OC, d13C and D14C isotope composition, and specific molecular markers of plant wax lipids and lignin phenols, the abundance and composition of OC was determined in both dissolved and particulate carrier phases: the colloidal OC (COC; part of the dissolved OC), particulate OC (POC), and sedimentary OC (SOC). Statistical modelling was used to quantify the relative contribution of OC sources to these phases. Terrestrial OC is derived from the seasonally thawing top layer of permafrost soil (topsoil OC) and frozen OC derived from beneath the active layer eroded at the coast, commonly identified as yedoma ice complex deposit OC (yedoma ICD-OC). These carbon pools are transported differently in the aquatic conduits. Topsoil OC was found in young DOC and POC, in the river water, and the shelf water column, suggesting long-distance transport of this fraction. The yedoma ICD-OC was found as old particulate OC that settles out rapidly to the underlying sediment and is laterally transported across the shelf, likely dispersed by bottom nepheloid layer transport or via ice rafting.These two modes of OC transport resulted in different degradation states of topsoil OC and yedoma ICD-OC. Terrestrial CuO oxidation derived biomarkers indicated a highly degraded component in the COC. In contrast, the terrestrial component of the SOC was much less degraded. In line with earlier suggestions the mineral component in yedoma ICD functions as weight and surface protection of the associated OC, which led to burial in the sediment, and limited OC degradation. The degradability of the terrestrial OC in shelf sediment was also addressed in direct incubation studies. Molecular markers indicate marine OC (from primary production) was more readily degraded than terrestrial OC. Degradation was also faster in sediment from the East Siberian Sea, where the marine contribution was higher compared to the Laptev Sea. Although terrestrial carbon in the sediment was degraded slower, the terrestrial component also contributed to carbon dioxide formation in the incubations of marine sediment.These results contribute to our understanding of the marine fate of land-derived OC from the Siberian Arctic. The mobilization of topsoil OC is expected to grow in magnitude with climate warming and associated active layer deepening. This translocated topsoil OC component was found to be highly degraded, which suggests degradation during transport and a possible contribution to atmospheric carbon dioxide. Similarly, the yedoma ICD-OC (and or old mineral soil carbon) may become a stronger source with accelerated warming, but slow degradation may limit its impact on active carbon cycling in the Siberian Shelf Seas.
|
|
| 10. |
- Kellerman, Anne M., et al.
(författare)
-
Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology
- 2014
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3804-
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the small continental coverage of lakes, they are hotspots of carbon cycling, largely due to the processing of terrestrially derived dissolved organic matter (DOM). As DOM is an amalgam of heterogeneous compounds comprising gradients of microbial and physicochemical reactivity, the factors influencing DOM processing at the molecular level and the resulting patterns in DOM composition are not well understood. Here we show, using ultrahigh-resolution mass spectrometry to unambiguously identify 4,032 molecular formulae in 120 lakes across Sweden, that the molecular composition of DOM is shaped by precipitation, water residence time and temperature. Terrestrially derived DOM is selectively lost as residence time increases, with warmer temperatures enhancing the production of nitrogen-containing compounds. Using biodiversity concepts, we show that the molecular diversity of DOM, or chemodiversity, increases with DOM and nutrient concentrations. The observed molecular-level patterns indicate that terrestrially derived DOM will become more prevalent in lakes as climate gets wetter.
|
|
