Showing papers by "Robert Clement published in 2015"

Quantifying landscape‐level methane fluxes in subarctic Finland using a multiscale approach

Abstract: Quantifying landscape-scale methane (CH4) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH4 emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, versus larger areas with net CH4 uptake, in controlling landscape-level fluxes. We measured CH4 fluxes from multiple microtopographical subunits (sedge-dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape; lichen heath and mountain birch forest. An inter-comparison was carried out between fluxes measured using static chambers, up-scaled using a high resolution landcover map derived from aerial photography, and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH4 fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water-table depth was not a key factor in controlling CH4 release. In contrast, chamber measurements identified net CH4 uptake in birch forest soils. An inter-comparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH4 emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km2 area. For the full growing season (May to October), approximately 1.1 to 1.4 g CH4 m−2 was released across the 100 km2 area. This was based on up-scaled lawn emissions of 1.2 to 1.5 g CH4 m−2, versus an up-scaled uptake of 0.07 to 0.15 g CH4 m−2 by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH4 emissions in northern Finland, and in aapa mire regions in general.

Late winter biogeochemical conditions under sea ice in the Canadian High Arctic

Abstract: With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO 2 ) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO 2 measurements during spring, summer or autumn, but there are few data for the winter or winter–spring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11′ N, 104° 47.44′ W) in the Canadian High Arctic. Results show relatively low surface water (1–10 m) nitrate (<1.3 µM) and total inorganic carbon concentrations (mean±SD=2015±5.83 µmol kg −1 ), total alkalinity (mean±SD=2134±11.09 µmol kg −1 ) and under-ice pCO 2sw (mean±SD=286±17 µatm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season. Keywords: Sea ice; carbon cycling; biogeochemical cycles; nutrients; Arctic Ocean; ocean acidification. (Published: 9 December 2015) Citation: Polar Research 2015, 34 , 24170, http://dx.doi.org/10.3402/polar.v34.24170

Late winter biogeochemical conditions under sea ice in the

Abstract: With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winterspring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (788 43.11? N, 1048 47.44? W) in the Canadian High Arctic. Results show relatively low surface water (1� 10 m) nitrate ( B1.3 mM) and total inorganic carbon concentrations (mean9SD � 201595.83 mmol kg � 1 ), total alkalinity (mean9SD� 2134911.09 mmol kg � 1 ) and under-ice pCO2sw (mean9SD� 286917 matm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season.