Figure 6. Seasonal differences in methane cycling between sea ice, surface water and atmosphere.

In winter deep convection transports brine, charged with methane, into the WML. Methane efflux may occur by convection in leads, while efflux through impermeable sea ice is restricted. In spring, basal melting starts and transports methane (dissolved or re-dissolved gas bubbles) into the MWL. In summer, stabilized by thermal stratification and less turbulence, methane remains entrained in both layers. In autumn, sea surface temperatures drop, enabling methane efflux by surface water convection. Water masses below the WML are not affected by this methane cycling.