Variability of Organic Carbon Burial By SW Greenland Lakes: The Role of Location and Regional Climate

Abstract:

Lakes are a key feature of arctic landscapes and can be an important component of regional organic carbon budgets. Although numerous, arctic lakes are comparatively under-studied and organic carbon burial rates are not well prescribed. Moreover, it has been proposed that regional warming will increase aquatic production in the Arctic. Here we test this hypothesis using 210Pb-dated sediment cores from SW Greenland, an area that did not warm appreciably during the 20th century. Organic carbon accumulation rates (OC AR) were estimated for 16 lakes that cover a climate gradient from the dry, continental interior to the wetter coastal margin. The study span a range of water chemistries (conductivity values range 25–3400 uS/cm), lake areas (<4–77 ha), and maximum depths (range ~10–50 m); the average OC AR rate (derived from all lakes) corrected for sediment focussing (using the mean 210Pb flux method) was low (<3 g C m^2/yr). Twelve lakes showed an increase in mean OC AR for the time period covered by 210Pb, possibly attributable to global environmental change processes (for example, reactive N deposition) rather than climate warming. There are ca. 20,000 lakes in the study area ranging from ~1 ha to >130 km^2, although over 83% of lakes are <10 ha. The mean post-1950 OC AR (3.5 g C m^2/yr) was extrapolated to all lakes <100 ha and a lower rate of ca. 2 g C m^2/yr to large lakes (>1000 ha) and suggests a regional annual lake OC burial rate of ca. 11 x 10^9 g C/yr after 1950. These burial rates are also compared with estimates of CO2 fluxes from the lakes. The implications of these data and their associated limitations (problems of determining C burial in remote lakes, regional upscaling, in-lake spatial variability, post-depositional mineralization) for regional carbon sequestration by lakes are discussed.