Early diagenesis and benthic fluxes in the Adriatic and Ionian seas
Spagnoli F; Mariangela Ravaioli; Patrizia Giordano; Michele Giani; Gabriella Bartholini;
Various research projects investigated early
diagenesis and benthic fluxes in Adriatic and
Ionian seas in the past (IGM-CNR Bologna
projects, MAST, EUROMARGE, PRISMA1,
PITAGEM and VECTOR). In these projects early
diagenesis were investigated by pore water
analyses, while benthic fluxes were determined by
direct measurements (benthic chamber
deployments and on deck incubations) or pore
water modelization. From the integration of these
previous data different diagenetic environments
and benthic fluxes have been identified: they
resulted from different particulate and dissolved
continental inputs, different distances from
sediment sources (mainly the Po River), different
bottom sediment (carbonatic or silicoclastic) and
organic matter (fresh marine or old continental
organic matter) composition, different depths
(increasing reworking and pressure with depth),
different oxygenation of water column.
In the Northern Adriatic it is possible to
distinguish: 1) the central area on the North of the
Po River, characterized by carbonate sediments,
low upward phosphate fluxes, due to authigenic
apatite precipitation, low ammonia fluxes and
downward DIC fluxes due to low reactive organic
matter inputs and carbonate precipitation; 2) areas
in front of northern rivers, characterized by
terrigenous and low reactive organic matter inputs
that produce low phosphate, ammonia and DIC
fluxes by oxic and suboxic or even anoxic (in lower
oxygenated waters) organic matter mineralization;
3) areas in front of the Po River mouths,
characterized by high ammonia, phosphate and
DIC fluxes due to the high sedimentation rate and
reactive organic matter inputs that degrade in
anoxic and even sulphidic environments. In this
area, when bottom waters reach anoxic conditions,
also Fe, Mn and phosphate fluxes increase due to
the dissolution of Fe and Mn oxi-hydroxide
surface layer; 4) the Po River prodelta distal area,
South of the Po River until Ancona offshore,
where partially degraded organic matter and
silicate inputs originate weak diagenesis processes
and nutrient benthic fluxes.
In the Central Adriatic it possible to discriminate:
1) the coastal Western muddy area, characterised
by sediments and partially degraded organic matter
coming from Po and Appennine rivers that
generate higher DIC and ammonia fluxes, mainly
by sub-oxic mineralization; 2) the Mid-Adriatic
Depression area, characterized by oxic
mineralization due to the low reactivity of already
degraded organic matter and low accumulation
rates; this produces low upward fluxes of all
nutrients, with the exception of nitrate flowing
into the sediment; 3) a central area, extending also
in the northern Adriatic, characterized by low
sedimentation rate, no sedimentation or even
erosion, with low and irregular benthic fluxes of
organic matter degradation products.
As regard the Southern Adriatic and Ionian seas
only some regional differences can be highlighted.
The Gulf of Manfredonia is characterized by high
benthic fluxes of nutrients indicating consistent
inputs of reactive autochthonous organic matter
attributable to local high primary productivity. The
Southern Adriatic basin, characterized by oxic and
suboxic-non sulphidic organic matter degradation
with higher strength occuring in the Otranto
Channel.
Calculated benthic fluxes in these areas show weak
oxygen fluxes into the sediments and weak DIC
fluxes outside the sediments while ammonium and
nitrate fluxes are complicated by
nitrification/denitrification processes occurring in
the oxic zone.
In the Ionian Sea sediments remineralisation
processes takes place mainly by oxic reactions
consequent to refractory organic matter inputs, for
the low productivity of the basin, the greater water
column thickness and the higher distance from
riverine inputs. In the Ionian Sea higher nutrient
benthic fluxes are encountered in basin area with
respect to slope ones due to higher accumulation
rates of partially reactive organic matter.
2010 - Abstract in atti di convegno
V.E.C.T.O.R., workshop finale. Roma, 18-19 ottobre 2010, pp. 43–43, Roma, 18-19/10/2010
Keywords: Adriatic Sea