Shelf circulation in the Gulf of California: A description of the variability

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Abstract
The first long‐term measurements (1983–1984) of winds, temperature, bottom pressure, and currents made in the Gulf of California are used to describe the dynamically important spatial and temporal scales and to compare and contrast the shelf circulation on opposite sides of the Guaymas Basin. In addition, a qualitative assessment of possible forcing mechanisms of gulf shelf circulation and an account of an energetic coastal‐trapped wave event are presented. Winds over the gulf are weak and variable with maximum wind speeds of 10–15 m/s and sustained wind events of less than a week. Low‐frequency (e‐folding scale = 160 m). A similar relationship is only weakly apparent (correlation = 0.39) on the Santa Rosalia shelf. Cross‐gulf geostrophy is observed with 35% of the along‐gulf current, averaged across the gulf, related to dp/dx measured between Guaymas and Santa Rosalia. On the Guaymas and Santa Rosalia shelves, dp/dx (measured across each shelf) explains approximately 20% of the variability in alongshelf currents. In the alongshelf momentum balance, dp/dy accounts for approximately 40% of the low‐frequency variability in dv/dt at the Guaymas shelf break, consistent with the dynamics of freely propagating coastal‐trapped waves. The same balance is only weakly apparent (<10% of variance explained) at Santa Rosalia. At higher frequencies, temperature fluctuations at Guaymas are coherent and in phase to 200‐m depth, coherent (0.74) with the alongshelf near‐surface current at the shelf break (M8), and exhibit a spring‐neap modulation consistent with internal tides.