General charactheristics of the Cantabrian sea

• Temperature

Surface water temperature in summer can reach 22ºC, while in winter it drops to 11ºC, so it is really influenced by seasonality.The Cantabrian Sea constitutes a transition zone between the cold northern waters and the warmer tropical seas, what describes an ecotone for cold water fauna and flora species.

However, the temperatures reached in the cantabrian are extraordinarily high taking into account its location. But why?

These unusually warm temperatures are due to the Gulf Stream influence, which comes from the North Atlantic gyre and transports massive amounts of water. In this gyre, is where the model of the Global Conveyor Belt (Figure 1) initiates and describes the so-called thermohaline circulation. In the upper latitudes, warm water arrives and loses heat, giving place to a denser water body that sinks. As the denser water sinks, water keeps moving to replace it, which creates a circulation. The deep water circulates to the south until the Antarctic, where it cools down again and sinks. From this point, the belt splits into 2 branches, one going to the Pacific Ocean and the other to the Indian. As the water gets closer to the equator, it warms up and upwells. In this way, the Cantabrian sea gets influenced by the warm and shallow current that returns to the starting point in the Atlantic northern part.

Figure 1: Global Conveyor Belt.

• Salinity

Salinity refers to the salt contents in sea water. A very high number of mineral salts compose the sea water, therefore NaCl is the dominant one. This compound gives the characteristic flavor to the water even though other salts such as KCl, borates or carbonates are present.

The mean salinity in the Cantabrian sea surface is 35,5 g/L, it decreases in high precipitation periods and nearby river beds.

In estuaries the salinity is lower as the river runs, but in deep estuaries due to density salinity increases with depth. The strong vertical salinity gradient known as halocline can be seen at 700m depth in the Cantabrian sea.

• Density

Density is driven by temperature and salinity differences, the Cantabrian sea density is around 1025 kg/m3, due to the high salt content is slightly higher than the density of pure water (1000 kg/m3).

Apart from these salts, the water acquires its maximum density at 4ºC, above and below that value is lighter, that is why the deep water is always more or less at that temperature, and in case of freezing rises to the surface in the ice form.

Circulation

The North Atlantic Ocean has a general circulation formed by two big gyres: the anticyclonic subtropical gyre and the cyclonic subpolar gyre. The picture shows the main features of the circulation in the Bay of Biscay (Figure 2), highlighting the shelf and upper layers of the ocean.

Figure 2: Schematic view of the ocean circulation of the Bay of Biscay. Koutsikopoulos y Le Cann (1996) siguiendo OSPAR (2000).

The orientation of the coast, the topography, and the winds, condition the circulation patterns on the platform (up to 600 m). Winter climatic conditions, influenced by winds from the south-west, give rise to a surface water circulation pattern, characterized by a poleward slope current. This current intermittently reaches the north Spanish coast more or less around Christmas time, called the "Christmas Current" by Pingree and Le Cann (1992).

It flows northward following the Galician and Portuguese coast, and helped by south-westerly winds, transports warm and salty water along the continental shelf. When this current enters the Bay of Biscay, it flows through the east part of the Cantabrian shelf and the continental slope. When the topography changes abruptly (at Cape Ortegal for example), water escapes the slope. That water that escapes is injected into the oceanic region to form anticyclonic gyres that contain a core of warm water that leaves the slope.The slope current weakens at the end of winter, disappearing completely at the beginning of spring.

Galerna

Figure 3: The Galerna phenomena. 

The "galernas" (Figure 3) are known as an abrupt and unexpected change of wind towards the NW, which takes place suddenly breaking a situation of good weather. Eventually, it occurs in the spring months and especially in summer.

This change of wind is accompanied by a noticeable drop in temperature, increased cloud cover and, sometimes, precipitation. The abruptness and its drastic change in the weather conditions it's what makes this phenomena spectacular.

The World Meteorological Organization defines the gale (most proximal english word) as a wind with a speed between 24-40 knots, or force 8 ( 61 to 74 Km/h) on the Beaufort scale. Unfortunately, most of the current definitions do not consider the sudden changes in temperature, pressure, humidity and wind spin. which are characteristic of it. On average, there are 2-3 galernas per year, although the probability is higher.

It may have originated in the terms of the Breton language gwall (bad) horn (corner) or gwall-kern (plural of horn). In France it is called galerne and is often referred to as entrée maritime subite.

Since always, the galernas have been associated with the death or great misfortune for the coastal sailors of the Bay of Biscay. They have caused major catastrophic events over the centuries, the first known record was given in the 19th century which includes the Galerna de Sábado de Gloria.

Hay una palabra seria, con regusto de sal y de lágrimas, un galicismo hondo y temible, sonoro y lúgubre, que va siempre enlazado al holocausto de las gentes pescadoras del Cantábrico: la galerna (R. González Echegaray, 1981).

There is a serious word, with an aftertaste of salt and tears, a deep and fearsome galicism, sonorous and gloomy, which is always linked to the holocaust of the fishing people of the Cantabrian: the galerna.

The most famous accidents associated with the galernas have been the Galerna del Sábado de Pascua in 20 of april of 1878 with 300 drowned fishermen, the 26 of april of 1890 with 54 drowned fishermen, the 12th july 1908 with 40 drowned fishermen, Bermeo's galerna in 1912 with 141 drowned fishermen and the one in 7th of june 1987; with 8 deaths due to wind provoked accidents, most of them in dry land.  

The nation's concern about this phenomenon led the Government to take action on safety at sea (Fisheries Management Act, 1884).

To find out more about the Galerna, listen to our interview with Jose Ignacio Alvarez Usagabia, director of the Basque Country Meteorological Center since 1979 to 2005:

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