Spatial and temporal variability of oceanic heat flux to the Arctic ice pack



[1] In order to simulate the large-scale structure and temporal variability of oceanic heat flux (Fw) to the Arctic perennial ice pack, observations of heat in the mixed layer and ice dynamics are compared with parameterizations and climatologies. Long-term drifting platform observations of seawater temperature and salinity (primarily from automated buoys) are used to describe the annual cycle of temperature above freezing (ΔTf) in the mixed layer beneath the ice pack, which are modulated by ice-ocean friction velocities (u*) determined from the platform drifts to produce estimates of Fw between 1975 and 1998. On average, ΔTf is not negligible in winter, especially in the Transpolar Drift, which implies a positive Fw to the ice pack by means other than solar heating. A parameterization based solely on the solar zenith angle (with a 1 month lag) is found to largely describe the observed ΔTf (with root mean square error of 0.03°C), despite the lack of an albedo or open water term. A reconstruction of Fw from 1979 to 2002 is produced by modulating parameterized ΔTf with u* on the basis of daily ice drift estimates from a composite satellite and in situ data set. The reconstructed estimates are corrected for regional variations and are compared to independent estimates of Fw from ice mass balance measurements, indicating annual Fw averages between 3 and 4 W m−2 depending on the selection of under-ice roughness length in the ice-ocean stress calculations. Although the interannual variations in ΔTf are fixed by the parameterization in the derived reconstruction, the dynamics indicate an overall positive trend (0.2 W m−2 decade−1) in Arctic Fw, with the largest variations found in the southern Beaufort Gyre.