www.sea-technology.com October 2015 / st 19
Mastodon Mooring System
To Measure Seabed Temperature
Data Logger With Ballast, Release Device at European Continental Shelf
By Pascal Lazure • David Le Berre • Laurent Gautier
S
ea temperature is an essential environmental parameter
because it infuences both the dynamics of the ocean and
the structure of the whole benthic ecosystem. For decades,
sea surface temperature (SST) has been measured by satel-
lites whose spatial resolution is constantly being improved.
The spatial and temporal variability of SST is now relatively
well-known for most of the ocean.
In coastal areas, including the European Continental
Shelf (depths ranging from 0 to 150 m), the vertical profle
of temperature depends mainly on turbulence conditions. In
some areas, such as the eastern English Channel, the strong
tidal current constantly mixes the water column, and the
SST can be extrapolated directly to the seabed.
However, in most coastal areas, thermal stratifcation
occurs seasonally from spring to autumn and assessment
of seabed temperatures requires in-situ devices. The de-
ployment of a temperature sensor for several months on
the seabed entails a mooring system, because most of the
depths are diffcult or impossible to reach by scuba diving.
Although temperature data loggers are now affordable, the
deployment of a mooring system for several months is gen-
erally a risky and expensive operation. These barriers are
probably the reason that seabed temperature time series are
so scarce for coastal areas.
The goal of the Mastodon mooring system is to record
the spatial and temporal changes in the seabed temperature
during the stratifed period that lasts for at least six months at
middle latitudes. The required precision of the temperature
measurement was set at 0.1° C, a commonly adopted value
for coastal observatory systems. The low cost of the instru-
ment enabled deploying several instruments in the same
area to ensure suffcient in-situ spatial resolution.
3D diagram of the mooring system: (1) electronics; (2) foat compartment;
(3) traffc cone; (4) ballasts; (5) rope spool; and (6) wire grate.