European Station for Time series in the ocean (ESTOC) station

Location of European Station for Time series in the ocean (ESTOC) station
Location of European Station for Time series in the ocean (ESTOC) station

Cool facts or discoveries

Cool story 1

The intermediate waters (700-1500 m) present a large variability of mixing due to the presence of Antarctic Intermediate Water and Mediterranean Water in the area. Occasionally, Meddies (Mediterranean Water eddies) are observable in the region although rarely arrive so far south as the ESTOC site.

Vertical temperature and salinity sections across a meddy measured in July 1993 in the Canary Islands basin at around 36°N, 28°W. This meddy revealed a double maximum for both temperature and salinity. The values reached 13.2°C and 36.4 g/l at 850 m deep and 12.3°C and 36. 5 psu at a depth of 1,250 m . Maximum anomalies compared with surrounding waters reached 4.1°C and 1.1 g/l at a depth of 1,250 m. Total diameter is 120 km.
Credit: Tychensky et Carton, 1998

The Meddies travel to the Canary Islands and are probably destroyed by crashing against the islands. These big structures of Mediterranean Water have a diameter of around 100 km and two cores in the vertical, at approximately 700 and 1000-1400 m, showing high salinity and temperature compared to the surrounding waters. However, the shallower core is frequently broken at these latitudes. Only three Meddies were detected by the mooring’s current/temperature meters during the period 1994- 2000 and only one has been observed in the monthly sampling carried out at the time-series station. This Meddy event occurred in July 1996.

Caption: Intrusions of warmer, more saline Mediterranean water at depth by a Meddy in 1996 at ESTOC.

Cool story 2

Chlorophylls are complex molecules found in all photosynthetic plants, including phytoplankton (microscopic plants living in suspension in the oceans).  Chlorophyll, contained within the plant's cells, allows the plant to utilize sunlight to produce energy for their metabolism.  There are several types of chlorophyll including chlorophyll-a which is the principal photosynthetic pigment common to all phytoplankton. Chlorophyll-a can thus be used as a measure of phytoplankton biomass.

Increases of chlorophyll-a coincide with deeper mixed layers in winter of each year at ESTOC. The maximum values are located near 100 meters depth most of the time and near the surface during winter blooms (a bloom is a phytoplankton population explosion-blooms. This phenomenon occurs when sunlight and nutrients are readily available to the plants, which allow them to grow and reproduce)

The Deep Chlorophyll maximum (DCM) is a typical characteristic of the Chlorophyll-a vertical distribution in the subtropical gyres and is observed. This is a concentration of phytoplankton below the surface waters. Below 75 meters depth in the subtropics, phytoplankton finds a good balance between their need in sunlight (rapidly absorbed by seawater) and nutrients (whose concentrations is higher at depth). The thickness of the Deep Chlorophyll maximum layer is barely more than 50m at ESTOC during the stratification season (summer and fall) of the water column. There is significant inter-annual chlorophyll variability in summer at ESTOC, with values occasionally exceeding and penetrating deeper (around 100 m) than those during the winter bloom.
The initiation of a winter maximum was observed during late fall of 1998 with a chlorophyll increase in the surface in late October 1998, and followed by later maxima from January to March 1999. This winter maximum was the highest observed to date at ESTOC.
This variability was observed from satellite using SeaWiFS data and some studies noted the 1999 phytoplankton bloom as the highest peak in chlorophyll observed in the gyre. The deep winter mixing of 1999, which likely gave rise to this unusual winter phytoplankton maximum, might have been linked with the concurrent, strong 1997/1998 ENSO event (El Niño-Southern Oscillation).
Also, in winter of 1999, an extensive winter bloom was observed along the NW African margin around Cape Blanc.

Caption: Chlorophyll-a vertical profiles evolution with time, showing the high winter Chlorophyll-a peaks penetrating deeper than the rest of the year.

Cool story 3

Tropical hurricane is the generic term for a low pressure system over tropical or sub-tropical waters, with intense convective activity and winds circulating in an anti-clockwise direction in the northern hemisphere (clockwise in the southern hemisphere).

A tropical storm is a tropical cyclone with mean wind speeds of at least 70 km/h. The Tropical storms hardly ever cross the ESTOC observatory. Nevertheless, the Tropical storm called Delta crossed ESTOC on November 28th of 2005, coinciding with the cruise Poseidon 330 (Mersea project that aimed to turn around the mooring.

The observatory was deployed on 27th and Dolan buoy fixed to the mooring. Thus, the atmospheric perturbations caused by Delta were recorded at the observatory, despite some malfunctions of the Dolan buoy temperature sensor. The low sampling frequency did not allow for a higher resolution record of the phenomenon, however another oceanographic buoy which belongs to the ACOMAR network (Real-Time Monitoring for Alert, Control and Maritime Observations in Canary Islands) also recorded the event by taking meteorological measurements every five minutes.

ESTOC is the oceanic reference for the marine coastal system.

Data recorded by ESTOC during the Tropical Storm DELTA in November 2005

Scientists or technicians in charge of the observatory

Dr. Maria Jose Rueda
Dr. Andres Cianca

Name of their institution

Instituto Canario de Ciencias Marinas (ICCM), Canary Islands, Spain

Distance from shore

70 nautical miles (~7 hours ~steaming depending on the ship speed)

Max depth

3670 m