8.4 Sea Ice Kinematic Characteristics in the Outflow Region of the Arctic Ocean

Wednesday, 1 May 2013: 9:15 AM
South Room (Renaissance Seattle Hotel)
Ruibo Lei, Polar Research Institute of China, Shanghai, China; and P. Heil, J. Wang, Z. Zhang, Q. Li Sr., and N. Li

In August 2010, the Chinese National Arctic Research Expedition (CHINARE-2010) deployed four satellite-tracked buoys on the ice north of 84°N, to determine ice motion and deformation during drifting from the central Arctic Ocean into the Fram Strait. Over an operational lifetime of 3-11 months, and the CHINARE buoys travelled between 986 and 4300 km.

The dynamic setting of the Transpolar Drift Stream (TDS) and the Fram Strait shaped the ice motion and deformation. On a synoptic scale, the ice drift was largely forced by surface winds, with atmospheric forcing accounting for 33-71% of ice-drift variability. The daily mean ice velocities derived from the buoy measurements ranged from 0.01 to 0.64 m/s. The mean ice velocity was about twice that avaraging over the entire Artic Ocean. The magnitude of ice velocities remained relatively steady above 82°N. When the ice drifted toward and through the Fram Strait, the ice velocities increased markedly, especially for the meridional velocities. The correlation between the velocities of pair buoys depended on the correlation of the surface wind speed. The ratio of ice velocity to wind speed depended on the magnitude of the wind speed. This ratio was relatively large (2.5%) when the wind speed was below 3 m/s, but was approximately invariable (1.8%) when the wind speed was above 3 m/s. Due to internal ice stress, the semi-diurnal inertial signal was vigorous in the power density spectrum of the absolute ice velocities. However, this signal was weakened when the ice drifted into the MIZ due to the reduction of internal ice interactions. As sea ice drifted through the Fram Strait, the acceleration and convergence of the ice was responsible for further substantial ice-field deformation.

From a comparison between our updated ice kinematic data and the historic data from 1990, we find that the ice-drift time from the central Arctic Ocean into Fram Strait was at a low level after 2007. The relatively short ice travel time in the current state for the Arctic outflow region may further result in a change in Arctic sea ice to younger and thinner. The atmospheric Dipole Anomaly (DA) derived wind anomalies more effectively influence the ice-drift time via accelerating meridional ice velocity and reducing the curvature of ice-drift trajectory. About 37% of the variations in ice-drift time can be explained by a monthly mean DA index at the 99.9% significance level. The monthly meander coefficients of the ice-drift trajectories ranged from 1.09 to 22.25. When the direction distribution of wind heading was broad or mostly pointed to the opposite direction of the TDS in the negative phase of DA, the meander coefficient of the ice drift trajectory increased. Thus, a positive (negative) DA can promote (restrict) sea ice export from the central Arctic Ocean to the Fram Strait, which is effective on both seasonal and decadal scales. In part, the enhanced positive DA anomaly in recent years can explain the rapid decline of Arctic sea ice. Strong positive (negative) phase of the Arctic Oscillation (AO) drives relatively large zonal cyclonic (anticyclonic) surface wind anomaly or regime. The zonal anomalous sea ice flow under the AO regime increases the sea ice travel time. However, the ice travel time was more dependent on meridional ice velocity (P<0.01). Thus, the statistical relationship between the AO index and ice travel time was smaller (0.42) than the DA index (0.61), and the significance level was also lower for the AO regime (P<0.05) than for the DA regime (P<0.001).

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