Weather, Climate, and Methane: Linking Short and Long Term Changes in Available Energy to Observed Methane Emission from Shallow Subarctic Lakes

Abstract:

Many studies have noted that there is a positive relationship between temperatures in freshwater systems and methane production by Archaea, but not all freshwater systems are alike. In the Arctic and Subarctic, small, very shallow lakes are a common feature. We hypothesize that such lakes’ sediment temperatures (where methane production occurs) are particularly sensitive and responsive to solar shortwave flux (SW), because direct solar heating of the sediments can partly bypass the need for physical mixing of warm water downwards across stratifications in the water column (such mixing is necessary for heating the bottom sediments in deeper lakes).

Ebullitive (bubble) fluxes of methane are far more varying, and may represent the additional methane production not being diffusively lost. Although trigger events such as air pressure changes are known to transiently produce bubbling, we show a link to SW input on both shorter and longer timescales than previously demonstrated. However, it is difficult to separate SW-driven increases due to autochthonous production leading to increased methane production from SW-driven temperature increases in sediment speeding methane production in the current dataset.

We show that in a shallow (ca. 1 m deep) lake (Villasjön, in Stordalen Mire, Sweden), during summer (June-August) methane bubbling is closely tied to available SW input on timescales of a few days. For the study area in northern Sweden, the available SW appears linked to the phase of the North Atlantic Oscillation (NAO). Relationships between the winter NAO and snow cover, which impacts lake ice-out date, and available summer SW are also considered. Linking methane production in shallow lakes to the NAO may allow back-projections of methane production in the Stordalen region to the 1860s. We compare these back-projections to recently published back-projections based on lake ice-out dates for Stordalen dating back to 1916.