SOCIB_EPR_ALMO_201512: Entry Information

The ALMO cruise was designed to investigate the connection, in terms of circulation and water masses variability, between the Ibiza Channel (IC), a ‘choke’ point in the basin scale circulation, and the Almería-Oran frontal system in the Alborán Sea. The IC is a narrow (80 km) channel between mainland Spain and Ibiza Island that exerts a controlling influence on an important North/South exchange of different water masses and are known to affect local ecosystems (Alameney et al. 2010). The Northern Current (NC) flows southward through the channel, seasonally strengthening, and carrying more saline waters of longer residence in the Mediterranean south. Less saline waters of more recent Atlantic origin intermittently flow northward. In addition, mesoscale eddies arrive to the channel and can impede or bock this exchange. Variability in this exchange is high, with changes in transport of watermass north and south, of the same order as the seasonal signal occurring over periods of days to weeks (Heslop et al. 2012). The Almería-Oran front, located south of the IC in the Alborán Sea, is generally viewed as the interface between Mediterranean and Atlantic Waters, it forms a steep gradient in salinity as fresher Atlantic Water (AW), from inflow through the Gibraltar Strait and forming the west flowing Atlantic Jet meets the more saline surface waters of the Mediterranean (Modified Atlantic Water, MAW). The connection, between these two important governing points of the Mediterranean basin scale circulation system, is however little studied. The ALMO cruise sampled 5 transects along the path of the NC, from south of the IC to the Almeria-Oran front, in order to investigate this interconnection. Is the Almeria-Oran front dominant driver in the Alborán Sea? Does a stronger density gradient form if cold fresh winter mode water (WIW) is carried to the frontal region? Does a strong Almeria-Oran front lead to a short circuit for the fresher Atlantic inflows through the IC? The understanding of this interconnection is important for our understanding of high frequency (weeks to months) variability in the Mediterranean circulation and so for improving model forecasting.

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