Arctic Sea Ice Melt Onset in the Laptev Sea and East Siberian Sea in Association with the Arctic Oscillation and Barents Oscillation

Arctic summer sea ice has been declining in recent decades. In this study, we investigate the beginning of the Arctic melting season, i.e., sea ice melt onset (MO), in the Laptev Sea (LS) and East Siberian Sea (ESS) along the Northern Sea route. Three leading modes are identified by EOF decomposition, which we call the LE-mode, L-mode, and E-mode. In positive phases these modes exhibit earlier MO in the two seas, a seesaw-like structure in the southwest–northeast direction with earlier MO in the LS, or in the southeast–northwest direction with earlier MO in the ESS. The LE-mode, L-mode, and E-mode are closely related to the Arctic Oscillation (AO) in April, the Barents Oscillation (BO) in April, and the AO in May, respectively. When the AO in April is positive, a low pressure anomaly northwest of the LS and ESS brings warm, moist air masses from the lower latitudes toward the LS and ESS and causes earlier MO, corresponding to the positive LE-mode. When the BO in April is negative, a cyclonic anomaly around the Barents Sea tends to warm and moisten the LS and cause earlier MO there, corresponding to the positive L-mode. When AO in May is positive, a low pressure anomaly northeast of the LS and ESS brings more warm, moist air toward the ESS and causes earlier MO there, corresponding to the positive E-mode. In the 1980s, the negative LE-mode was prominent whereas in the early 1990s the positive LE-mode was dominant. Since the mid-1990s, the L-mode and E-mode have appeared more frequently.