Pacific Halocline paper GRL 2004

Published in Geophysical Research Letters, September 2005
Citation: Woodgate, Rebecca A.; Aagaard, Knut; Swift, James H.; Falkner, Kelly K.; Smethie, William M., Jr., 2005, Pacific ventilation of the Arctic Ocean's lower halocline by upwelling and diapycnal mixing over the continental margin, Geophys. Res. Lett., Vol. 32, No. 18, L18609, 10.1029/2005GL023999
Copyright 2005 American Geophysical Union. Further reproduction or electronic distribution is not permitted.

Pacific winter waters, a major source of nutrients and buoyancy to the Arctic Ocean, are thought to ventilate the Arctic's lower halocline either by injection (isopycnal or penetrative) of cold saline shelf waters, or by cooling and freshening Atlantic waters upwelled onto the shelf. Although ventilation at salinity (S) > 34 psu has previously been attributed to hypersaline polynya waters, temperature, salinity, nutrient and tracer data suggest instead that much of the western Arctic's lower halocline is in fact influenced by a diapycnal mixing of Pacific winter waters (with S ~ 33.1 psu) and denser eastern Arctic halocline (Atlantic) waters, the mixing taking place possibly over the northern Chukchi shelf/slope. Estimates from observational data confirm that sufficient quantities of Atlantic water may be upwelled to mix with the inflowing Pacific waters, with volumes implying the halocline over the Chukchi Borderland region may be renewed on timescales of order a year.

Figures
For details, see paper

Figure 1. The Chukchi Borderland-Mendeleev Ridge (CBLMR) region, with CBL2002 stations (red); Barrow Canyon and Chukchi shelf mooring sites (blue); Chukchi Sea CTD locations (magenta hatched) from Bourke and Paquette (1976) ~ 71°N, and Münchow et al. (2000) and SBI (pers.comm.) ~ 74°N; and CTD lines of Setal05 (magenta line at ~150°W) and McLaughlin et al. (2004) (light pink lines). Grey shaded contours indicate bottom depth, with interval 500 m (with waters shallower than 500 m contoured at 50 m intervals in green).

Figure 2. T-S scatter-plot of CBL2002 data, dot color indicating silicate value as per color scale. Solid lines show typical Atlantic (black) and Pacific (red) halocline profiles, as in Figure 3.

Figure 3. T-S scatter-plot of CBL2002 data (grey), showing typical Atlantic (black) and Pacific (red) halocline profiles, and hypersaline polynya waters (green). Arrows mark changes due to the diapycnal mixing process (blue) and the intrusion of polynya waters (green).

Figure 4. Distribution of silicate (left), temperature (middle) and pressure (right) on the 34 psu isohaline from CBL2002 data. Background contours are bottom depth (interval 500m, with light colors shallower).

Figure 5. Distribution of CFC-11 on the 34 psu isohaline from CBL2002 data. Background contours as in Figure 4.

Figure 6. DO-S scatter-plot of CBL2002 data, dot color indicating silicate value as per color scale. Solid lines show typical Atlantic (black) and Pacific (red) halocline profiles.

Figure 7. Location map with depth contours as in Figure 4 (top) and typical profiles for DO-S (middle) and T-S (bottom) within the diapycnally ventilated region (left panels) and outside that region (right). Within each column, color indicates location as per map. Grey dots represent stations with similar profiles (background in bottom figures).

We gratefully acknowledge financial support for this work from the National Science Foundation (NSF), and the Office of Naval Research (ONR) High Latitude Dynamics program, under grant numbers NSF-OPP-0117480, NSF-OPP-0117040 and ONR N00014-02-1-0305.

Pacific Ventilation of the Arctic Ocean's Lower Halocline by Upwelling and Diapycnal Mixing over the Continental Margin

Rebecca A Woodgate, Knut Aagaard, Jim Swift, Kelly Falkner and Bill Smethie