Transport variability in the Lanzarote passage (eastern boundary current of the North Atlantic subtropical Gyre)

Observations from a four-year current meter mooring at 28°44′N, 13°28′W in the Lanzarote passage are used to describe the transport variability of the Eastern Boundary Current of the North Atlantic Subtropical Gyre. Three different water masses are found in the passage: North Atlantic Central Water in the upper levels (roughly $\text{0}\text{–}\text{600}\text{m}$), Antarctic Intermediate Water (roughly $\text{600}\text{–}\text{1100}\text{m}$) and Mediterranean Water in the layer above the bottom at $\text{1300}\text{m}$. The mean southward transport of NACW is $\text{−0.8±1.1}\text{Sv}$ $\text{(1}\text{Sv}\text{=10}{}^9\text{kg}\text{s}{}^{\mathrm{-1}}\text{)}$ which is the transport of the easternmost branch of the Canary Current. Fluctuations of NACW transport are large, ranging from $\text{−3.4}\text{Sv}$ southward to $\text{1.7}\text{Sv}$ northward. Every autumn a consistent northward transport is observed, which may be related with the eastern boundary upwelling dynamics. The mean transports of AAIW and MW are $\text{0.1±0.4}\text{Sv}$ northward and $\text{−0.05±0.09}\text{Sv}$ southward, respectively. Fluctuations of transport of AAIW and MW are large, from 1.0 to $\text{−1.0}\text{Sv}$ and from −0.32 to $\text{0.23}\text{Sv}$, respectively. Thus, the mass transports for each water mass show a high standard deviation of comparable magnitude to the mean. This highlights the importance of the temporal variability of the currents in this passage. A remarkable feature of our observations is that the mean transports of NACW and AAIW during an El Niño event are significantly different.