Water exchange between the Gulf of California and the Pacific Ocean: results from a one-year global HYCOM simulation

The mean and seasonal water exchange between the gulf of California and the Pacific Ocean (PO) are analyzed with a one-year global HYCOM simulation. At the mouth of the gulf there are six alternating layers of inflow and outflow of mean transport with inflow in the uppermost layer (0-68 m) and the largest outflow in the second layer (68-198 m). The three uppermost layers have the largest mean transports, and they can be identified more than two thirds along the length of the gulf with approximately the same thickness. The difference in the transport between the interior of the gulf and the transport at the mouth in the upper layer, shows that there must be an upward mean transport (upwelling) into the upper layer along almost the entire length of the gulf. The two deepest layers have smaller mean transports, but the deepest layer has an outflow that is about half of the inflow of the surface layer implying a very large vertical transport into that layer. We obtained the seasonal exchange by fitting annual and semiannual harmonics to the monthly mean transports in each layer. The maxima and minima of the seasonal exchange are larger than the mean and they occur in summer and autumn showing that most of the exchange with the PO occurs during those two seasons. The maximum inflow (~ 0.8 Sv, 1 Sv = 1 × 106 m3/s) in the upper layer occurs at the beginning of July and the maximum outflow at the beginning of November (~ 0.4 Sv). The transport in the second layer is out of the gulf all year round. The fourth layer (380-822 m) has the smallest mean transport of all layers but, together with the first layer, has the largest seasonal transport. The net outflowing transport is about 0.2972 Sv, which gives a turnover time of approximately 14 years for the gulf.