| 1. |
- Charkin, Alexander N., et al.
(författare)
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Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas : a case study in the Buor-Khaya Gulf, Laptev Sea
- 2017
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 11:5, s. 2305-2327
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that increasing terrestrial water discharge to the Arctic Ocean may partly occur as submarine groundwater discharge (SGD), yet there are no direct observations of this phenomenon in the Arctic shelf seas. This study tests the hypothesis that SGD does exist in the Siberian Arctic Shelf seas, but its dynamics may be largely controlled by complicated geocryological conditions such as permafrost. The field-observational approach in the southeastern Laptev Sea used a combination of hydrological (temperature, salinity), geological (bottom sediment drilling, geoelectric surveys), and geochemical (Ra-224, Ra-223, Ra-228, and Ra-226) techniques. Active SGD was documented in the vicinity of the Lena River delta with two different operational modes. In the first system, groundwater discharges through tectonogenic permafrost talik zones was registered in both winter and summer. The second SGD mechanism was cryogenic squeezing out of brine and water-soluble salts detected on the periphery of ice hummocks in the winter. The proposed mechanisms of groundwater transport and discharge in the Arctic land-shelf system is elaborated. Through salinity vs. Ra-224 and Ra-224/Ra-223 diagrams, the three main SGD-influenced water masses were identified and their end-member composition was constrained. Based on simple mass-balance box models, discharge rates at sites in the submarine permafrost talik zone were 1.7 x 10(6) m(3) d(-1) or 19.9 m(3) s(-1), which is much higher than the April discharge of the Yana River. Further studies should apply these techniques on a broader scale with the objective of elucidating the relative importance of the SGD transport vector relative to surface freshwater discharge for both water balance and aquatic components such as dissolved organic carbon, carbon dioxide, methane, and nutrients.
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| 2. |
- Gdaniec, Sandra, et al.
(författare)
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231Pa and 230Th in the Arctic Ocean : Implications for boundary scavenging and 231Pa-230Th fractionation in the Eurasian Basin
- 2020
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 532
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Tidskriftsartikel (refereegranskat)abstract
- 231Pa, 230Th and 232Th were analyzed in filtered seawater (n=70) and suspended particles (n=39) collectedalong a shelf-basin transect from the Barents shelf to the Makarov Basin in the Arctic Ocean during GEOTRACESsection GN04 in 2015. The distribution of dissolved 231Pa and 230Th in the Arctic Ocean deviates from the linearincrease expected from reversible scavenging. Higher 232Th concentrations were observed at the shelf, slope andin surface waters in the deep basin, pointing at lithogenic sources. Fractionation factors (FTh/Pa) observed at theNansen margin were higher compared to FTh/Pa in the central Nansen Basin, possibly due to the residual occurrenceof hydrothermal particles in the deep central Nansen Basin. Application of a boundary scavengingmodel quantitatively accounts for the dissolved and particulate 230Th distributions in the Nansen Basin.Modelled dissolved 231Pa distributions were largely overestimated, which was attributed to the absence of incorporation of water exchange with the Atlantic Ocean in the model. 231Pa/230Th ratios of the suspended particlesof the Nansen Basin were below the 231Pa/230Th production ratio, but top-core sediments of the Nansenmargin and slope have high 231Pa/230Th-ratios, suggesting that scavenging along the Nansen margin partly actsas a sink for the missing Arctic 231Pa.
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| 3. |
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| 4. |
- Phillips, Helen R. P., et al.
(författare)
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Global distribution of earthworm diversity
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 366:6464, s. 480-
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Tidskriftsartikel (refereegranskat)abstract
- Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, and biomass. We found that local species richness and abundance typically peaked at higher latitudes, displaying patterns opposite to those observed in aboveground organisms. However, high species dissimilarity across tropical locations may cause diversity across the entirety of the tropics to be higher than elsewhere. Climate variables were found to be more important in shaping earthworm communities than soil properties or habitat cover. These findings suggest that climate change may have serious implications for earthworm communities and for the functions they provide.
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| 5. |
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| 6. |
- Valk, Ole, et al.
(författare)
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Decrease in Th-230 in the Amundsen Basin since 2007 : far-field effect of increased scavenging on the shelf?
- 2020
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Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 16:1, s. 221-234
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Tidskriftsartikel (refereegranskat)abstract
- This study provides dissolved and particulate Th-230 and Th-232 results as well as particulate( )(234)Th data collected during expeditions to the central Arctic Ocean (GEO-TRACES, an international project to identify processes and quantify fluxes that control the distributions of trace elements; sections GN04 and GIPY11). Constructing a time series of dissolved Th-230 from 1991 to 2015 enables the identification of processes that control the temporal development of Th-230 distributions in the Amundsen Basin. After 2007, Th-230 concentrations decreased significantly over the entire water column, particularly between 300 and 1500 m. This decrease is accompanied by a circulation change, evidenced by a concomitant increase in salinity. A potentially increased inflow of water of Atlantic origin with low dissolved Th-230 concentrations leads to the observed depletion in dissolved Th-230 in the central Arctic. Because atmospherically derived tracers (chlorofluorocarbon (CFC), sulfur hexafluoride (SF6)) do not reveal an increase in ventilation rate, it is suggested that these interior waters have undergone enhanced scavenging of Th during transit from Fram Strait and the Barents Sea to the central Amundsen Basin. The Th-230 depletion propagates downward in the water column by settling particles and reversible scavenging.
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