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Plinian volcanic eruption are of peculiar interest for teph-
rochronology as far as huge amount of tephra are ejected
into the stratosphere (mushroom shape), and consequently
widespread giving rise to ash-fall sometimes around the
world.
Tephropalynology This is essentially the joint application
of tephrochronology and palynology, which involves the
correlation and dating of pollen-based palaeoenvironmen-
tal reconstructions using tephra layers as the linkage. It
also encompasses pollen- based studies of the impacts of
tephra fall in various environments.
Tephrostratigraphy ‘Tephrostratigraphy’ is the study of
sequences of tephra layers and related deposits and their
relative ages. It involves definition, description and the
identification and characterization (‘fingerprinting’) of
tephras or tephra sequences using their physical, mineral-
ogical, or geochemical properties.
Thalli (Thallus) Entire body of a multicellular non- moving
organism in which there is no organization of the tissues
into organs.
Thermal stratification In the water column of a lake, a con-
dition that may develop during the summer in which the
warmer, less dense layer (epilimnion) overlies a colder
denser layer (hypolimnion) over a short vertical distance
and prevents mixing between them.
Thermocline (sometimes metalimnion in lakes) is a thin but
distinct layer in a large body of fluid (e.g., water, such as
an ocean or lake, or air, such as an atmosphere) in which
temperature changes more rapidly with depth than it does
in the layers above or below.
Thermokarst Lake formed by meltwater from the thawing
permafrost.
Thin-section laboratory preparation of rocks, miner-
als, sediments or organic compounds for use with a
microscope.
Topographic drainage basin a surface area occupied by a
drainage system bounded by drainage divide and draining
into a water body.
Tracer Anything that allows us to follow or ‘trace’ a pro-
cess. A conservative tracer is one that can only be altered
by mixing in the ocean interior.
Transduction Transfer of genetic material or characteris-
tics from one microorganism to another by a viral agent
(as a bacteriophage)
Transformation The genetic alteration of a cell resulting
from the direct uptake and incorporation of exogenous
genetic material (exogenous DNA) from its surroundings
and taken up through the cell membrane(s).
Transporter proteins are specific proteins involved in
facilitated diffusion, where it binds to larger molecule
needed within the cell and guide it into the cell, moving
particles against the concentration gradient.
Trophic network (food web) Representation of all food
chains existing in a single ecosystem.
Trophic status the degree of biological production within a
aquatic ecosystem.
Trophodynamics (trophic dynamics) The dynamics of
nutrition or metabolism
Tunnel technical means to limit maar-lake surge and over-
spill (Albano, Nemi, Averno, Laacher See lakes). They
were excavated across the-lake rims as early as 394 BC
by Romans in Lake Albano and most were still in use in
the XXth century. Canals dug out had the same function
(Monticchio, Eifel maars).
Turbidite a sediment deposited from a turbidity current and
characterized by the development of graded bedding and
moderate sorting of particles.
Turbulent kinetic energy For a water parcel of a water
body, the turbulent kinetic energy (TKE) represents the
part of the kinetic energy that is due to turbulence in the
water column. This part of kinetic energy is not related
to any mean advective current (average of speeds is
zero)
UFE Units of Fishing Effort. The surface of the nets used
is multiplied by how long they are set in the water, which
determines a certain number of UFE, a fishing effort cor-
responding to 1 m^2 of net set for 1 h.
Ultracentrifugation technique using a high-velocity cen-
trifuge in order to separate colloidal or submicroscopic
particles
Varves annual layer of sediment.
Vertical diffusivity (or Kz) Kz is the vertical coefficient of
diffusion in the water body, considering both molecular
and turbulent diffusion. Modelling of turbulence in the
form of a diffusion law is an approximation, this model
being one of the most simple. Other models of turbulence
for water bodies exist.
Viral loop (or shunt) The viral-mediated movement of
nutrients from organisms to pools of dissolved and non-
living particulate organic matter in aquatic systems.
Viral lysis (or lytic cyle) lysis of host cell associated to the
production of new viral particules by diverting the host
cellular machinery
Virome The genomes of all the viruses that inhabit a par-
ticular organism or environment
Vivianite hydrated iron phosphate mineral
(Fe(II) 3 (PO 4 ) 2 .8(H 2 O)) in the monoclinic crystal system.
Volcanology the branch of geology that deals with volca-
nism, its causes and phenomena.
WFD Water Framework Directive. European directive to
improve the quality of surface and subterranean water.
Water fountain kinds of natural geysers in degassing lakes.
They can last long (Lake Monticchio, 5 m high) or be
related to a single violent event (Lake Nyos, 50–80 mGlossary