different origins and different residence times (Minas et al. 1991). During their
progress from the Western Mediterranean towards the Alboran Sea, the biogeochemical properties of the intermediate and deep Mediterranean water masses are
progressively modified by mixing with adjacent water masses, as well as by the
accumulation of organic matter from the euphotic zone (by vertical flux or lateral
advection) and bacterial activity (Minas et al. 1991).
The WIW is formed in winter in the NW Mediterranean (Salat and Font 1987;
Millot 1999) and flows along the continental slope of the Iberian Peninsula (VargasYáñez et al. 2012), reaching the Balearic Sea by spring (Pinot and Ganachaud 1999;
Pinot et al. 2002) and the Alboran Sea by summer or beginning of autumn (Font
1987). Its recent origin, in comparison with other intermediate water masses, is
reflected in its biogeochemical features. In the NW Mediterranean, its oxygen
content is relatively high (Minas et al. 1991; Balbín et al. 2014) but it decreases
progressively during its transit towards the Alboran Sea. In the Alboran Sea, there
are very few data on the biogeochemical features of this water mass. Ramírez (2007)
found a relative maximum of dissolved oxygen and a relative minimum of nutrient
concentrations at 200 m depth, linked to a temperature minimum (θ) ranging from
13.09
C to 13.20
C at stations located at the border of the continental slope, where
according to Parrilla and Kinder (1987) the WIW flows towards the Strait of
Gibraltar. The presence of a temperature (θ) minimum was detected in summer
and autumn at salinities ranging from ~37.90 to 38.30 (Ramírez 2007), while it was
much less defined or even absent in winter and spring. At the θ minimum the
dissolved oxygen concentration was on average 202.88 μM, while the mean nitrate,
phosphate, and silicate concentrations were 6.55 μM, 0.25 μM, 3.75 μM, respectively. All these findings suggest the presence of WIW, but θ minimum values were
higher than the typical θ minimum associated to the WIW in the Alboran Sea
(Parrilla and Kinder 1987), indicating a warmer WIW. This could be due to the
high variability observed in the formation of this water mass and to the variability of
its circulation in the Western Mediterranean (Pinot et al. 2002; Vargas-Yáñez et al.
2012), which affect the mixing with other water masses.
The most important intermediate water mass in the Alboran Sea is the LIW
(Parrilla et al. 1986; Parrilla and Kinder 1987; Minas et al. 1991). After reaching
the NW Mediterranean, this water mass flows towards the Alboran Sea along the
continental slope below the WIW (Font 1987; Millot 1999). It has been suggested
that due to this seasonality the greater volume of LIW arrives to the Alboran Sea by
summer-early autumn (Font 1987). The thermohaline and geochemical signatures of
LIW remain clearly distinctive when they enter into the Alboran Sea. Nevertheless,
during its journey towards the Alboran Sea, the LIW mixes with WIW and Mediterranean deep waters (Parrilla and Kinder 1987) modifying its levels of dissolved
oxygen. These levels are also modified by microbial respiration in the core of LIW
(Minas et al. 1991). Thus when the LIW arrives to the Alboran Sea it presents lower
dissolved oxygen levels and higher nutrients concentrations than in the NW Mediterranean (Minas et al. 1991). Averaged dissolved oxygen values in the LIW for the
whole Alboran Sea have been estimated to be 4.21 mlÁl
À1 (Manca et al. 2004),
although the lowest values are found in the Western Alboran basin (Minas et al.
210
T. Ramírez et al.
progress from the Western Mediterranean towards the Alboran Sea, the biogeochemical properties of the intermediate and deep Mediterranean water masses are
progressively modified by mixing with adjacent water masses, as well as by the
accumulation of organic matter from the euphotic zone (by vertical flux or lateral
advection) and bacterial activity (Minas et al. 1991).
The WIW is formed in winter in the NW Mediterranean (Salat and Font 1987;
Millot 1999) and flows along the continental slope of the Iberian Peninsula (VargasYáñez et al. 2012), reaching the Balearic Sea by spring (Pinot and Ganachaud 1999;
Pinot et al. 2002) and the Alboran Sea by summer or beginning of autumn (Font
1987). Its recent origin, in comparison with other intermediate water masses, is
reflected in its biogeochemical features. In the NW Mediterranean, its oxygen
content is relatively high (Minas et al. 1991; Balbín et al. 2014) but it decreases
progressively during its transit towards the Alboran Sea. In the Alboran Sea, there
are very few data on the biogeochemical features of this water mass. Ramírez (2007)
found a relative maximum of dissolved oxygen and a relative minimum of nutrient
concentrations at 200 m depth, linked to a temperature minimum (θ) ranging from
13.09
C to 13.20
C at stations located at the border of the continental slope, where
according to Parrilla and Kinder (1987) the WIW flows towards the Strait of
Gibraltar. The presence of a temperature (θ) minimum was detected in summer
and autumn at salinities ranging from ~37.90 to 38.30 (Ramírez 2007), while it was
much less defined or even absent in winter and spring. At the θ minimum the
dissolved oxygen concentration was on average 202.88 μM, while the mean nitrate,
phosphate, and silicate concentrations were 6.55 μM, 0.25 μM, 3.75 μM, respectively. All these findings suggest the presence of WIW, but θ minimum values were
higher than the typical θ minimum associated to the WIW in the Alboran Sea
(Parrilla and Kinder 1987), indicating a warmer WIW. This could be due to the
high variability observed in the formation of this water mass and to the variability of
its circulation in the Western Mediterranean (Pinot et al. 2002; Vargas-Yáñez et al.
2012), which affect the mixing with other water masses.
The most important intermediate water mass in the Alboran Sea is the LIW
(Parrilla et al. 1986; Parrilla and Kinder 1987; Minas et al. 1991). After reaching
the NW Mediterranean, this water mass flows towards the Alboran Sea along the
continental slope below the WIW (Font 1987; Millot 1999). It has been suggested
that due to this seasonality the greater volume of LIW arrives to the Alboran Sea by
summer-early autumn (Font 1987). The thermohaline and geochemical signatures of
LIW remain clearly distinctive when they enter into the Alboran Sea. Nevertheless,
during its journey towards the Alboran Sea, the LIW mixes with WIW and Mediterranean deep waters (Parrilla and Kinder 1987) modifying its levels of dissolved
oxygen. These levels are also modified by microbial respiration in the core of LIW
(Minas et al. 1991). Thus when the LIW arrives to the Alboran Sea it presents lower
dissolved oxygen levels and higher nutrients concentrations than in the NW Mediterranean (Minas et al. 1991). Averaged dissolved oxygen values in the LIW for the
whole Alboran Sea have been estimated to be 4.21 mlÁl
À1 (Manca et al. 2004),
although the lowest values are found in the Western Alboran basin (Minas et al.
210
T. Ramírez et al.