Carbon and nitrogen biogeochemistry of a high-altitude Himalayan lake sediment: Inferences for the late Holocene climate

A study was conducted to decipher changes in paleoenvironmental conditions of the Kashmir Valley (India) using stable isotopic compositions and elemental concentrations of total organic carbon (TOC) and total nitrogen (TN) in a sediment core from the Wular Lake. The Chronology of the core established through radiocarbon dating estimated the age of the core bottom to be 3752 Cal years BP, covering the late Holocene. Using carbon isotopic compositions of TOC (δ¹³C), nitrogen isotopic compositions of TN (δ¹⁵N), and TOC - TN contents, the study identified changes in biology and associated biogeochemical processes in the Wular Lake during the late Holocene. Changes in C and N biogeochemistry of the lake through the last 3752 Cal years BP suggested overall drier condition during 3752–1500 Cal years BP that transitioned into a wetter condition at around 1500 Cal years BP until at least 295 Cal years BP. Evidence for relatively intense drier events were observed within the dry and wet phases at around 2500 and 500 Cal years BP. Changes in δ¹³C and TOC contents in the sediment core revealed that the inorganic C dynamics and productivity (along with organic C contents) in the lake were largely regulated by variations in respired CO₂ and HCO₃⁻ availability along with terrestrial matter supply through the Jhelum River. Similarly, variations in δ¹⁵N and TN contents showed changes in N dynamics of the lake with varying nitrification and decomposition throughout the studied period. Observed dry and wet phases in the region might be due to the weakening and strengthening of the precipitation, which was linked to negative and positive phases of the North Atlantic Oscillation, respectively.