Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Spatial and Temporal Variability of Oceanic Heat Flux in the Arctic
Richard A. Krishfield1
1Geology & Geophysics, Woods Hole Oceanographic Institution, Clark 128, MS 23, Woods Hole, MA, 02543-1541, USA, Phone 508-289-2849, Fax 508-457-2175, rkrishfield@whoi.edu
Models indicate that the equilibrium mean thickness of the Arctic ice pack may be sensitive to small changes in annual average oceanic heat flux (Fw), but the sparseness and variability of direct observations has made it difficult to produce credible regional estimates at annual and longer timescales. In order to obtain a better understanding of the large-scale structure and temporal variability of Fw in the Arctic, observations of heat in the mixed layer and ice dynamics are compared with parameterizations and climatologies.
First, long term drifting platform observations of temperature and salinity (primarily from SALARGOS and IOEB buoys) are used to describe the annual cycle of temperature above freezing (Taf) in the mixed layer beneath Arctic pack ice between 1975 and 1998, and estimate Fw by modulating the observed Tafs with ice-ocean friction velocities (u*) determined from the platform drifts. In the Transpolar Drift, Taf is not negligible in winter, which implies a positive Fw to the ice pack by means other than solar heating. In the Beaufort Gyre, variability of Taf (and Fw) between different years is apparent and sometimes not negligible in winter.
Next, a parameterization based solely on the solar zenith angle (with a 1 month lag) is found to largely describe the observed Tafs (with root-mean-square error less than 0.05 °C), despite the lack of an albedo or open water term. Correlations between the observed annual Tafs and the parameterization are high (median R2 = 0.75), compared to Tafs determined from a hydrographic dataset based on the US-Russian EWG Atlas (median R2 = 0.16). Deviations of observed Tafs from the parameterization cannot consistently be explained by local open water fraction anomalies (determined from satellite ice concentration data), but are likely due to heat advected horizontally, or entrained from below the halocline (such as from synoptic storms).
Finally, a monthly Fw "climatology" from 1979 to 2002 is produced by modulating parameterized Tafs with u* based on daily ice drift estimates from a composite AVHRR, SSMI, and IABP dataset. Correlations are moderate between the derived climatology and Fw estimates from the drifting observations (median R2 = 0.52). Although the interannual variations in Taf are fixed by the parameterization in the derived climatology, the dynamics cause an overall positive trend in Arctic Fw after 1989, except in the southern Beaufort Sea.
Abstract Categories: Changes in the Sea
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