| 1. |
- Gustafsson, Erik, et al.
(författare)
-
Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO2 flux induced by mineralization of terrestrial organic carbon
- 2017
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189.
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOCter and POCter) supplied to the shelf. Rivers supply on average 8.5 Tg C yr−1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr−1 DOCter and POCter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ13CDOC) in shelf waters, we estimate that only some 20 % of the riverine DOCter is labile. According to our model results, an additional supply of approximately 14 Tg C yr−1 eroded labile POCter is however required to describe the observed stable isotope values of DIC (δ13CDIC). Degradation of riverine DOCter and POCter results in a 1.8 Tg C yr−1 reduction in the uptake of atmospheric CO2, while degradation of eroded POCter results in an additional 10 Tg C yr−1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO2 (1.7 Tg C yr−1). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr−1), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr−1).
|
|
| 2. |
|
|
| 3. |
- Humborg, Christoph, et al.
(författare)
-
Riverine transport of biogenic elements to the Baltic Sea – past and possible future perspectives
- 2007
-
Ingår i: Hydrology and Earth System Sciences. - 1027-5606 .- 1607-7938. ; 11:5, s. 1593-1607
-
Tidskriftsartikel (refereegranskat)abstract
- The paper reviews critical processes for the land-sea fluxes of biogenic elements (C, N, P, Si) in the Baltic Sea catchment and discusses possible future scenarios as a consequence of improved sewage treatment, agricultural practices and increased hydropower demand (for N, P and Si) and of global warming, i.e., changes in hydrological patterns (for C). These most significant drivers will not only change the total amount of nutrient inputs and fluxes of organic and inorganic forms of carbon to the Baltic Sea, their ratio (C:N:P:Si) will alter as well with consequences for phytoplankton species composition in the Baltic Sea. In summary, we propose that N fluxes may increase due to higher livestock densities in those countries recently acceded to the EU, whereas P and Si fluxes may decrease due to an improved sewage treatment in these new EU member states and with further damming and still eutrophic states of many lakes in the entire Baltic Sea catchment. This might eventually decrease cyanobacteria blooms in the Baltic but increase the potential for other nuisance blooms. Dinoflagellates could eventually substitute diatoms that even today grow below their optimal growth conditions due to low Si concentrations in some regions of the Baltic Sea. C fluxes will probably increase from the boreal part of the Baltic Sea catchment due to the expected higher temperatures and heavier rainfall. However, it is not clear whether dissolved organic carbon and alkalinity, which have opposite feedbacks to global warming, will increase in similar amounts, because the spring flow peak will be smoothed out in time due to higher temperatures that cause less snow cover and deeper soil infiltration.
|
|
| 4. |
- Humborg, Christoph, et al.
(författare)
-
Sea-air exchange patterns along the central and outer East Siberian Arctic Shelf as inferred from continuous CO2, stable isotope, and bulk chemistry measurements
- 2017
-
Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 31:7, s. 1173-1191
-
Tidskriftsartikel (refereegranskat)abstract
- This large-scale quasi-synoptic study gives a comprehensive picture of sea-air CO 2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record of both surface water and air CO 2 concentrations, in total 76,892 measurements. Overall, the central and outer parts of the ESAS constituted a sink for CO 2 , and we estimate a median uptake of 9.4 g C m -2 yr -1 or 6.6 Tg C yr -1 . Our results suggest that while the ESS and shelf break waters adjacent to the LS and ESS are net autotrophic systems, the LS is a net heterotrophic system. CO 2 sea-air fluxes for the LS were 4.7 g C m -2 yr -1 , and for the ESS we estimate an uptake of 7.2 g C m -2 yr -1 . Isotopic composition of dissolved inorganic carbon (δ 13 C DIC and δ 13 C CO2 ) in the water column indicates that the LS is depleted in δ 13 C DIC compared to the Arctic Ocean (ArcO) and ESS with an offset of 0.5‰ which can be explained by mixing of δ 13 C DIC -depleted riverine waters and 4.0 Tg yr -1 respiration of OC ter ; only a minor part (0.72 Tg yr -1 ) of this respired OC ter is exchanged with the atmosphere. Property-mixing diagrams of total organic carbon and isotope ratio (δ 13 C SPE-DOC ) versus dissolved organic carbon (DOC) concentration diagram indicate conservative and nonconservative mixing in the LS and ESS, respectively. We suggest land-derived particulate organic carbon from coastal erosion as an additional significant source for the depleted δ 13 C DIC .
|
|
