| 1. |
- Andren, M., et al.
(author)
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Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland
- 2016
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In: Journal of Geophysical Research-Solid Earth. - : American Geophysical Union (AGU). - 2169-9313. ; 121:4, s. 2315-2337
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Journal article (peer-reviewed)abstract
- Chemical analysis of groundwater samples collected from a borehole at Hafralaekur, northern Iceland, from October 2008 to June 2015 revealed (1) a long-term decrease in concentration of Si and Na and (2) an abrupt increase in concentration of Na before each of two consecutive M 5 earthquakes which occurred in 2012 and 2013, both 76km from Hafralaekur. Based on a geochemical (major elements and stable isotopes), petrological, and mineralogical study of drill cuttings taken from an adjacent borehole, we are able to show that (1) the long-term decrease in concentration of Si and Na was caused by constant volume replacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fractures and (2) the abrupt increase of Na concentration before the first earthquake records a switchover to nonstoichiometric dissolution of analcime with preferential release of Na into groundwater. We attribute decay of the Na peaks, which followed and coincided with each earthquake to uptake of Na along fractured or porous boundaries between labradorite and analcime crystals. Possible causes of these Na peaks are an increase of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixing between groundwater components. Both could have been triggered by preseismic dilation, which was also inferred in a previous study by Skelton et al. (2014). The mechanism behind preseismic dilation so far from the focus of an earthquake remains unknown.
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| 2. |
- Skelton, A., et al.
(author)
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Changes in groundwater chemistry before two consecutive earthquakes in Iceland
- 2014
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In: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:10, s. 752-756
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Journal article (peer-reviewed)abstract
- Groundwater chemistry has been observed to change before earthquakes and is proposed as a precursor signal. Such changes include variations in radon count rates(1,2), concentrations of dissolved elements(3-5) and stable isotope ratios(4,5). Changes in seismicwave velocities(6), water levels in boreholes(7), micro-seismicity(8) and shear wave splitting(9) are also thought to precede earthquakes. Precursor activity has been attributed to expansion of rock volume(7,10,11). However, most studies of precursory phenomena lack sufficient data to rule out other explanations unrelated to earthquakes(12). For example, reproducibility of a precursor signal has seldom been shown and few precursors have been evaluated statistically. Here we analyse the stable isotope ratios and dissolved element concentrations of groundwater taken from a borehole in northern Iceland between 2008 and 2013. We find that the chemistry of the groundwater changed four to six months before two greater than magnitude 5 earthquakes that occurred in October 2012 and April 2013. Statistical analyses indicate that the changes in groundwater chemistry were associated with the earthquakes. We suggest that the changes were caused by crustal dilation associated with stress build-up before each earthquake, which caused different groundwater components to mix. Although the changes we detect are specific for the site in Iceland, we infer that similar processes may be active elsewhere, and that groundwater chemistry is a promising target for future studies on the predictability of earthquakes.
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| 3. |
- Skelton, A., et al.
(author)
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Hydrochemical Changes Before and After Earthquakes Based on Long-Term Measurements of Multiple Parameters at Two Sites in Northern IcelandA Review
- 2019
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In: Journal of Geophysical Research-Solid Earth. - : American Geophysical Union (AGU). - 2169-9313 .- 2169-9356. ; 124:3, s. 2702-2720
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Journal article (peer-reviewed)abstract
- Hydrochemical changes before and after earthquakes have been reported for over 50years. However, few reports provide sufficient data for an association to be verified statistically. Also, no mechanism has been proposed to explain why hydrochemical changes are observed far from earthquake foci where associated strains are small (<10(-8)). Here we address these challenges based on time series of multiple hydrochemical parameters from two sites in northern Iceland. We report hydrochemical changes before and after M >5 earthquakes in 2002, 2012, and 2013. The longevity of the time series (10 and 16years) permits statistical verification of coupling between hydrochemical changes and earthquakes. We used a Student t test to find significant hydrochemical changes and a binomial test to confirm association with earthquakes. Probable association was confirmed for preseismic changes based on five parameters (Na, Si, K, O-18, and H-2) and postseismic changes based on eight parameters (Ca, Na, Si, Cl, F, SO4, O-18, and H-2). Using concentration ratios and stable isotope values, we showed that (1) gradual preseismic changes were caused by source mixing, which resulted in a shift from equilibrium and triggered water-rock interaction; (2) postseismic changes were caused by rapid source mixing; and (3) longer-term hydrochemical changes were caused by source mixing and mineral growth. Because hydrochemical changes occur at small earthquake-related strains, we attribute source mixing and water-rock interaction to microscale fracturing. Because fracture density and size scale inversely, we infer that mixing of nearby sources and water-rock interaction are feasible responses to small earthquake-related strains. Plain Language Summary Changes in groundwater chemistry before and after earthquakes have been reported for over 50years. However, few studies have been able to prove that the earthquakes caused these changes. Also, no study has explained why these changes are often reported far from where the earthquake occurred. Here we address these challenges based on measurements of groundwater chemistry made at two sites in northern Iceland over time periods of 10 and 16years. We used statistical methods to prove that the earthquakes caused changes of ground water chemistry both before and after the earthquakes. We showed that changes of groundwater chemistry before earthquakes were caused by slow mixing between different groundwaters, which triggered reactions with the wall rock that changed groundwater chemistry, and that changes of groundwater chemistry after earthquakes were causes by rapid mixing between different groundwaters. That these changes were detected far from where the earthquakes occurred suggests that cracking of the wall rock at a very small scale was all that was needed for mixing of different groundwaters and reactions with the wall rock to occur.
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| 4. |
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| 5. |
- Lyon, S. W., et al.
(author)
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Controls on snowmelt water mean transit times in northern boreal catchments
- 2010
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In: Hydrological Processes. - 0885-6087 .- 1099-1085. ; 24:12, s. 1672-1684
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Journal article (peer-reviewed)abstract
- Catchment-scale transit times for water are increasingly being recognized as an important control on geochemical processes. In this study, snowmelt water mean transit times (MTTs) were estimated for the 15 Krycklan research catchments in northern boreal Sweden. The snowmelt water MTTs were assumed to be representative of the catchment-scale hydrologic response during the spring thaw period and, as such, may be considered to be a component of the catchment's overall MTT. These snowmelt water MTTs were empirically related to catchment characteristics and landscape structure represented by using different indices of soil cover, topography and catchment similarity. Mire wetlands were shown to be significantly correlated to snowmelt MTTs for the studied catchments. In these wetlands, shallow ice layers form that have been shown to serve as impervious boundaries to vertical infiltration during snowmelt periods and, thus, alter the flow pathways of water in the landscape. Using a simple thought experiment, we could estimate the potential effect of thawing of ice layers on snowmelt hydrologic response using the empirical relationship between landscape structure (represented using a catchment-scale Pe number) and hydrologic response. The result of this thought experiment was that there could be a potential increase of 20-45% in catchment snowmelt water MTTs for the Krycklan experimental catchments. It is therefore possible that climatic changes present competing influences on the hydrologic response of northern boreal catchments that need to be considered. For example, MTTs may tend to decrease during some times of the year due to an acceleration in the hydrologic cycle, while they tend to increase MTTs during other times of the year due to shifts in hydrologic flow pathways. The balance between the competing influences on a catchment's MTT has consequences on climatic feedbacks as it could influence hydrological and biogeochemical cycles at the catchment scale for northern latitude boreal catchments. Copyright (C) 2010 John Wiley & Sons, Ltd.
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| 6. |
- Nicolaescu, T-M, et al.
(author)
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Prognostic relevance of pre-treatment c-reactive protein to albumin ratio in patients with diffuse large b cell lymphoma
- 2022
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In: Annals of Oncology. - : Elsevier. - 0923-7534 .- 1569-8041. ; 33:7, s. S832-S832
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Journal article (other academic/artistic)abstract
- Background: Previous studies have shown that a high level of pre-treatment C-reactive protein to albumin ratio (CAR) is associated with poor outcomes in patients with diffuse large B cell lymphoma (DLBCL). However, these were single-centre studies with a relatively small number of patients. The aim of our study was to further investigate the prognostic value of CAR in a larger cohort and whether the addition of CAR to the International Prognostic Index (IPI) would result in a better discriminatory ability.Methods: All adult patients treated 2000–2013 with R-CHOP/CHOP-like treatment for DLBCL in four counties of Sweden were included (n=414). The study population was divided into high respectively low CAR group using the Budczies et al.’s cut-off finder. The groups were compared in terms of differences in clinical characteristics, response to treatment and survival. The prognostic ability of IPI vs IPI plus CAR was compared by receiver-operating-characteristic curve (ROC), net reclassification improvement (NRI) and the integrated discrimination improvement index (IDI).Results: The high CAR group was associated with higher IPI score, lower performance status, high LDH, bulky disease and more advanced Ann Arbour stage. The high CAR group had a higher proportion of patients with progressive disease (24.2% vs 6.4%, p<0.001) and a lower proportion of patients with complete remission (61.5% vs 85.7%, p<0.01). The high CAR group had poorer 5-year OS (49% vs 70%; p<0.001) and EFS (45% vs 68%; p<0.001). After adjustment for BMI, bulky disease and IPI, high CAR values independently predicted poor OS (HR: 1.58, 95% CI 1.18–2.11; p=0.002) and EFS (HR: 1.57, 95% CI 1.18–2.10; p=0.002). When assessed by NRI, the addition of CAR to IPI seems to better identify patients with better prognosis compared with IPI alone. However, the area under the ROC curve and IDI did not show any significant improvement in model performance.Conclusions: CAR seems to be a useful prognostic biomarker in patients with DLBCL. Although the addition of CAR to IPI could identify some additional patients with better prognosis, the discriminatory ability of IPI was not improved. IPI remains the standard model for risk stratification in patients with DLBCL.
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| 7. |
- Rosen, P. O., et al.
(author)
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Ice export from the Laptev and East Siberian Sea derived from O-18 values
- 2015
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In: Journal of Geophysical Research-Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 120:9, s. 5997-6007
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Journal article (peer-reviewed)abstract
- Ice export from the vast Arctic Siberian shelf is calculated using O-18 values and salinity data for water samples collected during the International Siberian Shelf Study between August and September 2008 (ISSS-08). The samples represent a wide range of salinities and O-18 values due to river water inputs and sea ice removal. We estimate the fraction of water that has been removed as ice by interpreting observed O-18 values and salinities as a result of mixing between river water and sea water end-members as well as to fractional ice removal. This method does not assume an ice end-member of fixed composition, which is especially important when applied on samples with large differences in salinity. The results show that there is net transport of ice from both the Laptev and the Eastern Siberian Seas, and in total 3000 km(3) of sea ice is exported from the shelf. The annual total export of ice from the entire region, calculated from the residence time of water on the shelf, is estimated to be 860 km(3) yr(-1). Thus, changes in ice production on the shelf may have great impact on sea ice export from the Arctic Ocean.
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