Linking the northern hemisphere sea-ice reduction trend and the quasi-decadal Arctic sea-ice oscillation

The nature of the reduction trend and quasi-decadal oscillations in northern hemisphere sea-ice extent is investigated. The trend and oscillations that seem to be two separate phenomena have been found in data. This study proposes a hypothesis that the Arctic sea ice reduction trend in the last three decades triggered the quasi-decadal Arctic sea ice oscillation (ASIO) due to a positive ice/ocean-albedo feedback, based on a conceptual model and data analysis. The theoretical, conceptual model predicts that the quasi-decadal oscillations are triggered by the thinning sea-ice, leading to the ASIO, which is driven by the strong positive feedback between the atmosphere and ice-ocean systems. Such oscillations are predicted to be out of phase between the Arctic Basin and the Nordic Seas with a phase difference of 3Pi/4, and with the Nordic Seas leading the Arctic. The wavelet analysis of the data reveals that the quasi-decadal ASIO occurred actively since the 1970s following the trend (i.e., as sea ice became thinner and thinner), although the atmosphere experienced quasi-decadal oscillations during most of the last century. The analysis also confirms the prediction of such out-of-phase between these two regions, which varied from 0.62 Pi in 1960 to 0.25 Pi in 1995. Furthermore, a coupled ice-ocean general circulation model (GCM) was used to simulate two scenarios, one without the greenhouse gas warming and the other having realistic atmospheric forcing along with the warming. The quasi-decadal ASIO is excited in the latter case compared to the no-warming case. The wavelet analyses of the simulated ice volume were also conducted to derive decadal ASIO and similar phase relationship between the Arctic Ocean and the Nordic Seas. An independent data source was used to confirm such decadal oscillation in the upper layer thickness, which is consistent with the model simulation.