| 1. |
- Hirst, Catherine, 1989-, et al.
(författare)
-
Iron isotopes reveal seasonal variations in the mechanisms for iron-bearing particle and colloid formation in the Lena River catchment, NE Siberia
- 2023
-
Ingår i: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 363, s. 77-93
-
Tidskriftsartikel (refereegranskat)abstract
- Large Arctic rivers are an important source of iron (Fe) to the Arctic Ocean, though seasonal variations in the terrestrial source and supply of Fe to the ocean are unknown. To constrain the seasonal variability, we present Fe concentrations and isotopic compositions (δ56Fe) for particulate (>0.22 µm) and colloidal (<0.22 µm–1 kDa) Fe from the Lena River, NE Russia. Samples were collected every month during winter baseflow (September 2012–March 2013) and every 2–3 days before, during and after river ice break-up (May 2015).Iron in particles have isotope ratios lower than crustal values during winter (e.g., δ56FePart = −0.37 ± 0.16‰), and crustal-like values during river ice break-up and spring flood (e.g., δ56FePart = 0.07 ± 0.08‰), indicating a change in the source of particulate Fe between winter and spring flood. Low isotope values are indicative of mineral dissolution, transport of reduced Fe in sub-oxic, ice-covered sub-permafrost groundwaters and near-quantitative precipitation of Fe as particles. Crustal-like isotopic compositions result from the increased supply of detrital particles from riverbank and soil erosion during river ice break-up and flooding. Iron colloids (<0.22 μm) have δ56Fe values that are comparable to or lower than crustal values during winter (e.g., δ56FeCol = −0.08 ± 0.05‰) but similar to or higher than crustal values during spring flood (e.g., δ56FeCol = +0.24 ± 0.11‰). Low δ56Fe ratios for colloidal Fe during winter are consistent with precipitation from isotopically light Fe(II)aq transported in sub-permafrost groundwaters. Higher colloidal δ56Fe ratios during the spring flood indicate that these colloids are supplied from surface soils, where Fe is fractionated via oxidation or organic carbon complexation, similar to during summer. Approximately half of the annual colloidal Fe flux occurs during spring flood while most of the remaining colloidal Fe is supplied during summer months. The total amount of colloidal Fe transported during winter was relatively low. The seasonal variation in colloidal Fe isotope values may be a useful tool to trace the source of colloidal Fe to the Arctic Ocean and monitor future changes in the sources and supply of Fe from the permafrost landscape to the Lena River basin.
|
|
| 2. |
- Kutscher, Liselott, 1976-
(författare)
-
Export and sources of organic carbon in the Lena River basin, Northeastern Siberia
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost areas are considered to be one of the largest terrestrial storages of carbon. In a warming climate these areas are expected to experience changes in carbon transport to rivers and the oceans due to permafrost thawing, which could enhance erosion, change water flow pathways and increase greenhouse gas emissions. Large amounts of the carbon transported from the terrestrial environment to rivers are in the form of natural organic matter (NOM). The Lena River basin in northeastern Siberia, which is mainly underlain by continuous permafrost, is the largest contributor of NOM to the Arctic Ocean. In this study we present a spatial data set of NOM, including concentrations and stable carbon isotope values (δ13C) of dissolved (DOC) and particulate organic carbon (POC) as well as carbon and nitrogen ratios (C/N) from 77 sample stations in the Lena River and its tributaries. The samples were collected during two field seasons in July 2012 and June 2013.The results from this study showed large spatial variations in concentrations, annual export and fluxes of organic carbon. These variations were primarily due to variations in discharge and topography. The δ13C and C/N indicated that terrestrial sources such as plants and soil organic matter (SOM), were the main sources of the dissolved organic matter (DOM), while particulate organic matter (POM) was mainly derived from aquatic produced material or SOM. There were clear differences in δ13C and C/N of DOM between sampling years, indicating more surficial flow pathways in samples collected earlier in the summer compared to samples collected later in the summer. The δ13C of POM was correlated with water temperatures and topography, showing that tributaries with origin in mountainous areas in general had soil derived POM and lower water temperatures, while tributaries from lowland areas had higher water temperatures and more influence of aquatic sources. We suggest that this pattern is probably due to differences in water flow pathways. Shifts in export of NOM from drainage areas underlain by permafrost will likely be dependent of spatial changes in hydroclimate and the depth of the active layer in a warming climate.
|
|
