Surface geostrophic currents across the Antarctic circumpolar current in Drake Passage from 1992 to 2004
The Southern Ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region. Recently, a secular trend has been reported in wind stress around the Southern Ocean and it is thought the...
| Published in: | Progress in Oceanography |
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| Main Authors: | , |
| Format: | Book |
| Language: | English |
| Published: |
2007
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| Subjects: | |
| Online Access: | http://hdl.handle.net/1834/17158 https://doi.org/10.1016/j.pocean.2006.07.010 |
| Summary: | The Southern Ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region. Recently, a secular trend has been reported in wind stress around the Southern Ocean and it is thought theoretically that the strength of the ACC is closely related to wind stress, so one consequence should be a corresponding increase in ACC transport and hence changes in the rate of the global overturning. There are no long-term data sets of ACC transport and so we must examine other data that may also respond to changing wind stress. Here we calculate surface currents in Drake Passage every seven days over 11.25 years from 1992 to 2004. We combine surface velocity anomalies calculated from satellite altimeter sea surface heights with measured surface currents. Since 1992, the UK has regularly occupied WOCE hydrographic section SR1b across the ACC in Drake Passage. From seven hydrographic sections surface currents are estimated by referencing relative geostrophic velocities from CTD sections with current measurements made by shipboard and lowered acoustic Doppler current profilers. Combining the seven estimates of surface currents with the altimeter data reduces bias in the estimates of average currents over time through Drake Passage and we show that surface current anomalies estimated by satellite and in situ observations are in good agreement. The strongest surface currents are found in the Subantarctic and Polar Fronts with average speeds of 50 cm/s and 35 cm/s, respectively and are inversely correlated, so that maximum westward flow in one corresponds to minimum westward flow in the other. The average cross-sectional weighted surface velocity from 1992 to 2004 is 16.7 ± 0.2 cm/s. A spectral analysis of the average surface current has only weakly increasing energy at higher frequencies and there is no dominant mode of variability. The standard deviation of the seven day currents is 0.68 cm/s and a running 12 month ... |
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