CONCLUSIONS1. Contourite deposits are increasingly recognised in shallow-water set-tings, including continental shelves where bottom currents the sea floor may derive from a variety of processes including thermohaline, wind-driven, tide- or wave-induced circulation.2. The South Adriatic Shelf shows a maze of macro-scale erosional and depositional features (hundreds of meters to few kilometers wide) inclu-ding, respectively, large flow-parallel and flute-shaped scours and large-scale asymmetric dunes. These features appear shaped by a portion of the seaso-nal DSW flow whose dynamical proper-ties (buoyancy and kinetic energy) pre-vent the inception of the cascading pro-cess.3. Our finding, complementing previous views of the impact of the NAdDW on the SAM, introduces a new case of shal-low-water contourite system formed on the shelf over several hundreds of km. Numerical model results (map) show the preferential patterns of DSW migra-tion on the slope and along the Western Adriatic Shelf following the extreme cooling of winter 2012.4.The variability of erosional and depositional features documented on the shelf reflects the “DSW pathway” impinging. Maximum energy contribution is given by relatively less dense waters and in response to strong momentum injections from the atmosphere into the formation basin.

Time-average potential density anomaly distribution in the Adriatic Sea in March 2012. Thick black line represents the 29.2 kg m-3 isopycnal.

Bonaldo, D., Benetazzo, A., Bergamasco, A., Campiani, E., Foglini, F., Sclavo, M., Trincardi, F., Cariniel, S., submitted. Interactions among Adriatic continental margin morphology, deep circulation and bedform patterns. Marine Geology.

Canals, M., Danovaro, R., Heussner, S., Lykousis, V., Puig, P., Trincardi, F., Calafat, A., de Madron, X., D., Palanques A., Sánchez-Vidal, A., 2009. Cascades in Mediterranean submarine grand canyons. Oceanography, 22 (1), 26-43.

Foglini, F., Campiani, E., Trincardi, F., submitted.The reshaping of the South West Adriatic Margin by cascading of dense shelf waters. Marine Geology.

Vandorpe, T. P., Van Rooij, D., Stow, D. A., & Henriet, J. P., 2011. Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain. Geo-Marine Letters, 31(5-6), 391-403.

Verdicchio, G., Trincardi, F., 2008a. Mediterranean shelf-edge muddy contourites: examples from the Gela and South Adriatic basins. Geo-Marine Letters, 28(3), 137-151.

Viana, A. R., Faugères, J. C., Stow, D. A. V., 1998. Bottom-current-controlled sand deposits - a review of modern shallow-to deep-water environments. Sedimentary Geology, 115(1), 53-80.

studyarea

0 25 50 75 10012.5km

-1300

0 mWater depth

Bari

Brindisi

Lecce

Otranto

Taranto

ITALY - PUGLIA REGION

Adriatic Sea

Ionian Sea

1

2

3

45

Straitof

Otranto

BariCanyon

20°E18°E16°E14°0'0"E12°E

46°N

44°N

42°N

40°N

0 110 22055km

BA

ITALY

Water depth0 m

-3600 m

Site of Noth AdriaticDense Water(NAdDW) formation

Flow directionof LIW

Inferred flowdirection ofNAdDW

Adriatic Sea

Tyrrhenian Sea IonianSea

-200

-1200

-500

m

A BSud Adriatic Slope

NAdDW

LIW

-0

Bottom circulation in the SAM slope is domi-nated by Levantine Intermediate Water (LIW) and Northern Adriatic Dense Water.

SAM

CROATIA

ALBANIA

Straitof

Otranto

SHALLOW-WATER CONTOURITE SYSTEM FORMED BY THE FLOW OF DENSE SHELF WATERS

Trincardi F.1, Bonaldo D.1, Campiani F.2, Foglini F.2, Maselli V.2, Pellegrini C.21ISMAR CNR, Venice, Italy - 2 ISMAR CNR, Bologna, Italy

corresponding author: claudio.pellegrini@bo.ismar.cnr.it

INSTITUTE of MARINE SCIENCE

NATIONAL RESEARCH COUNCIL

www.ismar.it

POSTER NUMBER: C09 - P05

The Adriatic Sea is one of the key areas of Dense Shelf Water (DSW) formation in the Mediterranean Sea. The North Adriatic Dense Water (NAdDW) forms in the northernmost part of the Adriatic Sea through winter cooling and flows southward driven by its excess density with respect to the ambient water, impacting the slope and the deep basin of the South Adriatic Margin (SAM) through a process of “ca-scading”.Our finding complements previous views of the NAdDW

impact, recognising that part of this water mass, due to its high kinetic energy imparted by the atmosphere during the formation phase, remains trapped on the shelf flowing as a contour-pa-rallel bottom current.Similar shallow-water contourite systems can be expected aside other areas of DSW cascading.

Multi Beam Bathymetry of the South Adriatic Margin (20 m grid, vertical exaggeration of 5X), based on data collecteted by ISMAR over the last 10 years with a variety of Multi Beam Echosounders. Note the extreme morphological complexity of the shelf and slope both impacted by the seasonal flow of Dense Shelf Waters.

5

1000 m

N

A

10 m

1000 m

N

S

CHIRP sonar profile A

u

3D view of the large dune field (df) located down current of a shelf morphological relief (mr) undergoing erosion. The dune crests show extremely variable wavelengths, and are rectilinear to sinuous displaying variable orientations from NW-SE, in the southern portion of the field, to NE-SW in the northern region. The CHIRP sonar profile A, across the entire dune field documents the asymmetric profile of the dunes with a steeper down-current (southward) face. The dunes are up to 10 m thick and develop above a regional erosional unconformity (u), generated during the last glacial low stand and locally exposed in the dune troughs.

N

df

mr

10.000 m

N

4

N

5000 mThe flow of contour-parallel DSW is responsible of the formation of largefields of sandy bedforms and minor scours, on the shelf (CHIRP sonar profile A), and of the erosion of the flanks of the canyons, in the upper slope. This second process, in particu-lar, led progressively to the discon-nection of the canyon heads (inclined black arrows) from the outer shelf and the “reshaping” of the margin.

On the outer shelf and upper slope the NAdDW generates a field of large scours elongated parallel to the regional bathymetric contour (horizontal black arrows, below).

10 m

1000 m CHIRP sonar profile A

NNW SSE

A

10.000 m

10.000 m

AB

N

1000 m10 m

NW

SE

CHIRP sonar profile A

lowstand shelf-edge delta

CHIRP sonar profile B25 m

1000 m

NW SE

bottom-current depositwith sigmoidal reflectors outer-shelf

bottom-current scour outer-shelfbottom-current scour

The outer shelf is also cha-racterised by large-scale muddy bedforms with thick-ness variations, large scours and lens-shaped reflector geo-metry (profile B). Contour-cur-rent deposits thicken at the shelf edge, pinching out lan-dward and seaward.

The outer shelf is very irregular for the presence of erosive remnants draped by recent se-diment (profile A). Close to the shelf edge a delta deposit origi-nated during the last glacial eustatic low stand (on the right side of profile A).

3

NN

5000 m

AB

W E

10 m

500 m CHIRP sonar profile B

1000m

25m

W

E

5 m

500 m

CHIRP sonar profile A

wave-cut terraces

erosional scours generatedby DSW currents

bottom-current erosional features and small-scale remnants

small-scale bedforms

unconformities linked to 100-kyr Milanković cyclicity

2

CHIRP sonar profiles showing the sea floor morphology and under-lying stratigraphy in areas impacted by DSW. Profile B shows a disconti-nuous mud drape on the erosional remnants.

Shelf sector characterized by marked sea floor roughness. Small scale bedform fields (profile A) and large contour-parallel scours, hi-ghlighting differences in seafloor erodibility (profile B), are carved by DSW currents.

CHIRP sonar profile C NE1000 m

25 m

S3

CHIRP sonar profile A

S

N

HST bottom current bedforms erosive remnantsdraped exposed

1000 m

25 m

CHIRP sonar profile B

SW

NE

1000 m

25 m

upslope migrating bedforms of Sequence 3

S3

giant scoursSW

N

1 The broad shelf southward of the Bari Canyon is cha-racterised by a varietyof depositional/erosional fea-tures:

small-scale bedforms (profile A);linear erosive remnants (profile B);giant scours (profile C).

All these features are elon-gated NW-SE, consistent with the activity of bottom hugging contour-parallel currents from the NW.

CHIRP sonar profiles B and C document large-scale erosional morphologies up to 50 m deep and 2 km long ascribed to the impact of DSW trapped on the shelf; be-neath the scoured area, a stack of 100-kyr depositional sequences is detected with prevailing progradational geometry. In addition, the reflector geometry within se-quence 3 (S3, from 230-250 to 330-350 k year BP) documents an earlier phase of bottom current activity that led to the formation of asymmetric landward-migra-ting bedforms.

A

B

C

5000 m

BariCanyon