www.elsevier.com/locate/margeo

Marine Geology 227

High-resolution stratigraphy of the Mediterranean outflow contourite

system in the Gulf of Cadiz during the late Pleistocene:

The impact of Heinrich events

E. Llave a,*, J. Schonfeld b, F.J. Hernandez-Molina c, T. Mulder d, L. Somoza a,

V. Dıaz del Rıo e, I. Sanchez-Almazo f

a Instituto Geologico y Minero de Espana, Servicio de Gelogıa Marina, C/Calera 1, 28760 Tres Cantos, Madrid, Spainb IFM-GEOMAR Leibniz-Institute of Marine Sciences, Wischhofstr. 1-3, D-24148 Kiel, Germany

c Facultad de Ciencias del Mar, Univ. de Vigo, 36200 Vigo, Spaind Departement de Geologie et Oceanographie, UMR CNRS 5805 EPOC, Univ. Bordeaux 1, Avenue des facultes, 33405 Talence Cedex, France

e Instituto Espanol de Oceanografıa, C/Puerto Pesquero s/n, 29640 Fuengirola, Spainf Departamento de Estratigrafıa y Paleontologıa, Facultad de Ciencias, Univ. de Granada, C/Fuentenueva s/n, 18002 Granada, Spain

Received 6 August 2004; received in revised form 11 November 2005; accepted 17 November 2005

Abstract

A detailed, high-resolution stratigraphic analysis of the Mediterranean Outflow contourite system at the continental slope of the

Gulf of Cadiz has been carried out through the correlation between a dense network of seismic reflection profiles (sparker, airgun,

3.75 kHz and parametric echosounder — TOPAS), Calypso giant piston and standard gravity cores. From such correlation we

determine a stacking pattern constituted by four main seismic units (a–d) that are internally structured into ten subunits. Each

subunit shows a single sequence formed by transparent seismic facies at the base to smooth, parallel reflectors of moderate to high

amplitude facies at the top, being well correlated in the cores with a coarsening-upward sequence. The latest Pleistocene–Holocene

deposits form glacial/interglacial depositional sequences related to cycles with a frequency range below the Milankovitch band that

corresponds to millennial timescale climatic changes such as Dansgaard–Oeschger (1.5 ka) and Bond Cycles (10–15 ka). Oxygen

isotope records of planktonic foraminifera and the occurrence of ice-rafted debris (IRD) in the most recent contourite subunits show

clear evidence of the influence of the North Atlantic climatic conditions, especially the climatic Heinrich events (H) in the slope

sedimentation of the Gulf of Cadiz and then in the circulation of the Mediterranean Outflow Water (MOW). The coarser contourite

deposits are mostly associated with the Last Glacial Maximum, Younger Dryas and Heinrich events on the central area of the

middle slope. During globally cooler conditions, the MOW was denser so that it was more active in deeper areas than today. On the

other hand, during warm periods the MOW became less dense favoring an increased intensity of the MOWon the distal area of the

upper slope. Therefore, spatial and vertical fluctuations of the MOW contourite system are strongly affected by global climate and

oceanographic changes, being clearly influenced by iceberg discharges and probably also, by the resumption of thermohaline

circulation in the North Atlantic Ocean during ice melting periods.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Gulf of Cadiz; contourite deposits; Late Pleistocene; paleoclimate changes; Heinrich events; Mediterranean Outflow Water;

paleoceanography

0025-3227/$ - s

doi:10.1016/j.m

* Correspondi

E-mail addr

(2006) 241–262

ee front matter D 2005 Elsevier B.V. All rights reserved.

argeo.2005.11.015

ng author. Tel.: +34 91 7287276; fax: +34 91 7287202.

ess: e.llave@igme.es (E. Llave).

E. Llave et al. / Marine Geology 227 (2006) 241–262242

1. Introduction

One of the main interests in the study of the

morphologic, sedimentary and stratigraphic character-

istics of contourite deposits on continental margins is

the possibility to infer the nature of climate-driven

paleocirculation patterns and their evolution through

time (e.g. Viana et al., 1998; Faugeres et al., 1999;

Rebesco and Stow, 2001; Llave et al., 2001; Hall et

Fig. 1. (A) General circulation pattern (summary using data from the followin

Grazzini et al. (1989), Faugeres et al. (1993), Garrison (1996), Iorga and Loz

(2000). (B) Western Iberian margin circulation patterns where Heinrich eve

from the following authors: Lebreiro et al., 1996; Abrantes et al., 1998; Baas

al., 2000; Sanchez-Goni et al., 2002; Lowemark and Schafer, 2003). It is

Contourite depositional System (CDS).

al., 2001; Mulder et al., 2002, 2003). This study aims

to describe the high-resolution seismic stratigraphy of

a bMediterranean-forcedQ Contourite Depositional Sys-

tem (CDS) of the Gulf of Cadiz as related to millen-

nial scale climate and oceanographic changes. In

addition, we propose a model for changes of the

MOW pattern into the Gulf of Cadiz under the influ-

ence of the North Atlantic Ocean ice-rafting events

during the Late Pleistocene. We combine evidence

g authors: McCave and Tucholke (1986), Bearmon (1989), Vergnaud-

ier (1999), Schonfeld and Zahn (2000), Cacho et al. (2000), Bard et al.

nts identification studies have been carried out (summary using data

et al., 1998; Thomson et al., 1999; Schonfeld and Zahn, 2000; Bard et

labeled those dated cores used in this study within Gulf of Cadiz

E. Llave et al. / Marine Geology 227 (2006) 241–262 243

from well-dated sediment cores with information on

the internal architecture, lateral extent and overall

thickness of sediment drifts as revealed from ultra-

high-resolution seismic reflection data.

The CDS of the Gulf of Cadiz (Fig. 1) has imprinted

significant variations as a function of global climatic

and eustatic conditions since it began to develop in the

Early Pliocene (about 5 Ma), when the Strait of Gibral-

tar took its present morphology and the Mediterranean

Outflow Water (MOW) circulation pattern established

(Kenyon and Belderson, 1973; Nelson et al., 1993;

Maldonado and Nelson, 1999). The high rates of accu-

mulation and expanded sedimentary records of the CDS

permit high-resolution examination of past environ-

mental change (Llave et al., 2001; Stow et al., 2002;

Voelker et al., submitted for publication). Controversy

still surrounds the identification of periods of maximum

MOW activity and the development of coarser contour-

ites in the Gulf of Cadiz in relation to global climate

and sea level (Stow et al., 2002). Whereas some authors

invoke a stronger MOW activity during glacial condi-

tions (Melieres, 1974; Vergnaud-Grazzini et al., 1989;

Schonfeld, 1997; Baringer and Price, 1999; Cacho et

al., 2000; Schonfeld and Zahn, 2000; Llave et al., 2000,

2001, 2004a,b; Stow et al., 2002; Habgood et al.,

2003), others consider an intensification of the current

and concomitant development of coarser contourites

during ice-melting periods (Gonthier et al., 1984; Fau-

geres et al., 1984, 1985a,b, 1986; Caralp, 1988, 1992;

Cremer et al., 1993; Rohling and Bryden, 1994; Nelson

et al., 1993, 1999; Thomson et al., 1999; Sierro et al.,

1999; Hall and Mc Cave, 2000).

High-resolution paleoclimate records from the last

glacial epoch suggest that iceberg discharge periods in

the North Atlantic, namely Heinrich (H) events (Hein-

rich, 1988), led to abrupt changes in surface water

hydrology as a reduced glacial deep water production

and a sluggish deep water circulation (e.g. Keigwin and

Jones, 1994; Oppo and Lehman, 1995; Vidal et al.,

1997, 1999; Zahn et al., 1997; Broecker and Hemming,

2001; Clark et al., 2002; Schonfeld et al., 2003). It has

also been suggested that during the Last Glacial Max-

imum (LGM) and Heinrich events, the NADW flow, as

part of the Meridional Overturning Circulation (MOC),

was weaker and the boundary between MOW and the

underlying water masses was deeper (Schonfeld and

Zahn, 2000).

One possibility to study the influence of these Hein-

rich events in the CDS of the Gulf of Cadiz is to

recognize the widespread occurrence of sediment layers

with abundant coarse-grained lithic components of Ice-

Rafted Detritus (IRD) or Heinrich layers documented

during fast ice sheet disintegration phases in the north-

ern hemisphere (Ruddiman, 1977; Heinrich, 1988;

Bond et al., 1992, 1993; Grousset et al., 1993). These

Heinrich layers have not only been recognized in the

North Atlantic but also in piston and gravity cores

obtained as far south as the Portuguese margin, as

indicative of the arrival of icebergs (Schonfeld, 1993;

Mienert, 1994; Lebreiro et al., 1996, 1997; Zahn et al.,

1997; Baas et al., 1997, 1998; Abrantes, 1988; Thom-

son et al., 1999; Bard et al., 2000; Schonfeld and Zahn,

2000; Broecker and Hemming, 2001; Sanchez-Goni et

al., 2002; Lowemark and Schafer, 2003; Abreu et al.,

2003), also in the Gulf of Cadiz (Bouldoire et al., 1996;

Cacho et al., 2001; Reguera, 2001; Colmenero, 2001;

Lowemark, 2001; Mulder et al., 2002; Sierro et al.,

2005; Voelker et al., submitted for publication), and

even in the Moroccan continental margin (Kudrass

and Thiede, 1970; Kudrass, 1973) (Fig. 1).

Although these Heinrich layers have been recog-

nized in the Gulf of Cadiz’ sedimentary record, a lot

of studies are still needed to establish the influence of

these climatic changes in the MOW’s paleocirculation

and then their influence in the CDS during the Late

Pleistocene.

2. Oceanographic setting

Present day circulation in the Gulf of Cadiz is dom-

inated by the exchange of water masses through the Strait

of Gibraltar, which consists of a highly saline and warm

near-bottom Mediterranean Outflow Water (MOW) into

the Atlantic Ocean and an influx of a less saline Atlantic

Inflow Water (AI) at the surface into the Mediterranean

Sea (Madelain, 1970; Melieres, 1974; Zenk, 1975;

Thorpe, 1976; Ambar and Howe, 1979; Ochoa and

Bray, 1991; Baringer and Price, 1999) (Fig. 1).

The AI comprises the North Atlantic Superficial

Water (NASW) that flows from the surface to a water

depth around 100 m, and the North Atlantic Central

Water (NACW), that flows between 100 and 700 m

depth, with 12–16 8C and 34.7–36.25 salinity units.

The MOW forms a salt-rich tongue that moves to the

north along the Iberian slope; to the west from Cape St.

Vincent; and to the SW as far as the Canary Islands and

then westwards (Iorga and Lozier, 1999). MOW after

passing the Strait of Gibraltar registers a decrease in

temperature, salinity and velocity caused by its rapid

mixing with it the NACW, and it divides into two main

cores (Fig. 1B):

– Mediterranean Upper Core (MU), following the base

of the upper slope, between 400 and 600 m depth

E. Llave et al. / Marine Geology 227 (2006) 241–262244

(Ambar, 1983) until Cape San Vicente, with a mean

velocity of about 46 cm/s, 13.72 8C and 37. 07

salinity units.

– Mediterranean Lower Core (ML), which constitutes

the more saline, lower core and the MOW’s principal

nucleus, at a depth of 600–1200 m, with 13.6 8C and

37.42 salinity units (Zenk and Armi, 1990; Baringer,

1993; Bower et al., 1997). This is the main water

flux flowing in the study area which is affected by

the slope morphology, and divides into three minor

branches between the Cadiz and Huelva meridians

(68 20V–78) (Kenyon and Belderson, 1973; Melieres,

1974; Nelson et al., 1993, 1999; Garcıa, 2002; Her-

nandez-Molina et al., 2003): (a) Intermediate Branch

(IB); (b) Principal Branch (PB), which is believed to

transport, at present, the MOW’s major flow (Made-

lain, 1970); (c) Southern Branch (SB).

Below the MOW, North Atlantic Deep Water

(NADW) is present and shows only slow movements

(Zenk, 1975). It is a cold (3–8 8C) and less saline

(34.95–35.2 salinity units) water mass that flows at

depths N1.500 m from the Greenland–Norwegian Sea

region towards the south. In the Gulf of Cadiz, the

NADW is joined by part of the saltier but warmer

MOW. This mixture flows southwards down the eastern

part of the Atlantic Ocean (Knauss, 1978).

2.1. Influence of iceberg discharges on the intermediate

water circulation in the Gulf of Cadiz

The Late Quaternary contourite record from the mid-

slope of the Gulf of Cadiz highlights this region as

being very sensitive to the rapid climatic and oceano-

graphic variability in the North Atlantic. The significant

impact of Heinrich events on the depositional environ-

ments beyond the erratic influx of IRD is a result of

atmospheric, hydrologic, and oceanographic connec-

tions. A cold and less-saline surface water layer could

have been originated by the southward flow of NASW

following the Iberian margin (Bard et al., 2000; Colme-

nero-Hidalgo et al., 2002; Abreu et al., 2003). It has

been demonstrated that Heinrich events correspond to

cold and dry climate periods in the Iberian Peninsula

(Sanchez-Goni et al., 2000, 2002). Increasing terrige-

nous input from Iberia is caused by aridity during

Heinrich events (Boessenkool et al., 2001; Roucoux

et al., 2001; Combourieu-Nebout et al., 2002) and

lower sea level (Hernandez-Molina et al., 1994, 2000;

Somoza et al., 1997). The MOW circulation during cold

events was intensified, but the MOW spread at deeper

levels in the water column than today (Cacho et al.,

2000; Schonfeld and Zahn, 2000; Rogerson, 2002).

These results provide a background to reconstruct the

influence climate and oceanography on the contourite

sedimentation pattern during the last glacial period.

3. Methodology

This work is based primarily on the analysis and

interpretation of ultrahigh-resolution seismic data (Fig.

2) and its correlation with piston and gravity cores (Fig.

1B). This has been possible because the remarkably

good correlation between the penetration of the seismic

systems and the length of the coring system and the

closeness between the sediment core locations and

seismic sections.

Ultra high-resolution seismic data (Fig. 2) collected

with the TOPAS PS 018 Simrad (TOpographic PAram-

eter Sonar) system and 3.75 kHz during the oceano-

graphic research cruises TASYO 2000 and IMAGES V

on board R/V Hesperides and R/V Marion Dufresne,

respectively. Ship positioning was achieved with a

differential Global Positioning System (DGPS) and

Global Positioning System (GPS).

Calypso giant piston cores MD9923-36 and

MD9923-41 cores were retrieved during the IMAGES

V cruise with R/V Marion Dufresne in 1999. Standard

gravity cores ANAS01-21 and ANAS01-22 were col-

lected during the ANASTASYA scientific cruise with

R/V Cornide de Saavedra in 2001 (Fig. 1B). Ship

positioning was achieved with a Global Positioning

System (GPS).

The different steps to achieve the proposed objec-

tives are: (a) the identification and general age back-

ground of the main discontinuities and seismic units

from previous studies, as correlating our ultra-high

seismic profiles with the most recent deposits described

in Sparker medium-high resolution seismic profile car-

ried out by Llave et al. (2001) and Llave (2003); (b) a

derivate chronostratigraphy of Late Quaternary deposi-

tional sequences from the seismic stratigraphy correlat-

ed to dated giant piston and gravity cores, using a sound

velocity in sediments of 1 600 m/s; (c) a sequential

analysis of the Late Pleistocene–Holocene contouritic

deposits; and (d) paleoceanographic evidences from

cyclic contourite deposition.

3.1. Ultrahigh-resolution seismic data

The TOPAS PS 018 Simrad (TOpographic PAram-

eter Sonar) system is a hull-mounted seabed and sub-

bottom echosounder based on a parametric acoustic

array, which operates using non-linear acoustic proper-

Fig. 2. Location of ultra-high and medium resolution seismic profiles. The data were positioned using GPS and DGPS systems.

E. Llave et al. / Marine Geology 227 (2006) 241–262 245

ties of the water (Dybedal and Boe, 1994). The system

transmitted approximately every 1 s (~10 m at cruise

speeds of 10 kt) with a beam angle of approximately 58,and a modulated frequency sweep (chirp) between 1.5

and 4 kHz. The data were deconvoluted and corrected

for spherical spreading with a linear time-varying gain

prior to presentation. The vertical resolution of the

TOPAS records is very high (less than 0.5 m) and the

penetration in this area ranges from a few to several

tens of meters.

The 3.75 kHz sub-bottom profiler uses a narrow,

high-energy beam, which yields deep penetration and

good horizontal resolution, using a central frequency

chirp source. Vertical resolution is approximately 0.3 m;

40 m penetration was routinely achieved on most MD

coring sites. The quality of this system in terms of

penetration and resolution clearly surpasses that of

analog 3.5 kHz systems.

3.2. Core sampling and dating

Cores MD9923-36 and MD9923-41 were routinely

logged on board R/V Marion Dufresne with a Geotek

Multisensor Core Logger for p-wave velocity, gamma-

ray attenuation density (GRAPE) and magnetic suscep-

tibility. Logging of the individual core sections was

performed continuously to avoid artificially lowered

magnetic susceptibilities towards the beginning and

end of each section (Nurnberg et al., 2003). The cores

were opened at GEOMAR Kiel after the cruise, de-

scribed, and sampled in 5 cm intervals for stable iso-

topes, sedimentological, and micropaleontological

studies. The samples were weighed, washed through a

63 Am mesh, the residues were dried, weighed, and

further subdivided into 63–250 Am and N250 Am frac-

tions. Lithic particles of quartz, feldspar, calcite, dolo-

mite, basalt, and hematite coated grains that are inferred

to represent ice-rafted debris (IRD), were counted in the

size fraction N250 Am.

Stable oxygen and carbon isotope measurements

were carried out on 8 to 15 well-preserved specimens

of Globigerina bulloides from the size fraction

N250 Am. The tests were ultrasonically rinsed in meth-

anol prior to isotope analysis. The measurements were

carried out in the isotope laboratories at the University

of Bremen (MD9923-41) and at GEOMAR (MD9923-

36) where Carbo Kiel automated carbonate preparation

devices linked on-line to Finnigan MAT 251 and

252 mass spectrometers are operated. The mass spectro-

meters of these laboratories are intercalibrated with an

able 1

ain depositional sequences and discontinuities differentiated in

edium resolution seismic profiles (sparker and airgun), and in

igh resolution seismic profiles (3.75 kHz and TOPAS)

eismic units

parker and airgun TOPAS and 3.75 kHz

uaternary Holocene H H2 d d2 d223/5 ka

d21YD (10-11 ka)

Late

Pleistocene

d1H2 (24 ka)

H1 c

H3 (32 ka)

b b4H4 (39 ka)

b3H5 (40.7 ka)

b2H6 (57 ka)

b1MIS 4 (65 ka)

a a35b (85 ka)

a25d (105 ka)

a1MIS 6 (135 ka)

dapted from Llave et al. (2001).

E. Llave et al. / Marine Geology 227 (2006) 241–262246

internal carbonate standard (Solnhofen Limestone) to

insure data compatibility. Long-term reproducibility

was 0.08x for d18O as calculated from replicate anal-

yses of the internal standard. All isotope values are

reported on the VPDB (Vienna PDB) scale.

Radiocarbon dating was performed on 12 samples

from core MD9923-41. We used 5 monospecific sam-

ples of Globigerina bulloides (488 to 784 tests), 2

samples of Globigerinoides ruber (white) (800 tests),

4 samples of the pteropod Clio sp. (1 to 10 specimens),

and 1 specimen of Cavolina sp., each from the

N250 Am size fraction. Radiocarbon ages were deter-

mined via accelerator mass spectrometry (AMS) using

the 3MV Tandetron system at the Leibniz-Labor of Kiel

University. The precision of the 14C ages ranges from

F25 to F570 yr (stdv). Carbon-14 ages younger than

20 ka were transferred to calendar years by using the

web-based Calib 4.3 program (http://radiocarbon.pa.qu-

b.ac.uk/calib/calib.html) and an ocean reservoir correc-

tion of �400 yr. For older datings, we used the calendaryear — correction provided by Laj et al. (1996) and

Voelker et al. (2000).

Two samples for radio carbon dating are from cores

ANAS01-21 and ANAS01-22. The cores were opened

on board and sampled every centimeter; nevertheless,

several consecutive samples from each core were com-

bined in order to get enough planktonic tests for geo-

chemistry analyses. The depth intervals sampled

correspond with an important lithological change oc-

curred in both cores and were 240–242 cm in

ANAS01-22 and 153–156 cm in ANAS01-21. The sedi-

ments were sieved in wet conditions with distillate water

and the residues N63 Am were dried at 40 8C and

weighted. These residues were subdivided and the plank-

tonic foraminifer tests were picked in the fraction

N250 Am. Two monospecific samples of Neogloqua-

drina pachyderma (ANAS01-22) and Globigerinoides

ruber (white) (ANAS01-21) were used for the dating.

After picking around 600 tests of each one of the species,

they were cleaned ultrasonically with distillate water

3 times a few seconds and dried at 40 8C. Radiocarbonages were determined via accelerator mass spectrometry

(AMS) using the 3MV Tandetron system at the Leibniz-

Labor of Kiel University. In this case, the precision of the14C ages ranges from F40 to F1 600 yr (stdv).

4. Results

4.1. Seismic stratigraphy analysis

Following the previous nomenclature established by

Llave et al. (2001), the Late Pleistocene–Holocene

regional seismic unit is named as H (see Table 1),

bounded at the base by a highly reflective and erosive

or non-depositional surface that has been named MIS 6

(Fig. 3 and Table 1). This seismic unit shows two

principal seismic facies with a different configuration

(Fig. 3A):

– In the Faro–Albufeira mounded drift, we observed a

prograding seismic configuration is recognized in

which generally sigmoid to oblique-progradational

landward reflection pattern migrates upslope. This

creates downlapping progradational bodies, which

are in concordance to toplap terminations (Fig. 3B).

– In the Faro–Cadiz sheeted drift, we observed an

aggrading facies is observed. This facies is charac-

terised by with weak parallel-laminated, laterally

continuous reflectors, which are uniformly distribut-

ed across the drift system with an onlap reflection

configuration (Fig. 3C).

A cyclic trend, as observed in the sediment facies of

the cores and in the seismic facies in the TOPAS and

3.75 kHz seismic profiles, allowed us to determine, in

the Late Pleistocene–Holocene sedimentary record, 4

minor seismic units denominated as a, b, c and d (from

T

M

m

h

S

S

Q

A

Fig. 3. (A) Sparker seismic profile indicating the main seismic units within the Quaternary contourite sedimentary record from Llave et al. (2001). (B) 3.75 kHz seismic profile across the mounded

Faro–Albufeira drift indicating the main Late Pleistocene seismic units. (C) TOPAS seismic profile across the Faro–Cadiz sheeted drift indicating the main seismic units within the main Late

Pleistocene seismic units. In B and C, MD9923-36 and MD9923-41 core locations are showed but see Fig. 5 for further details.

E.Llave

etal./Marin

eGeology227(2006)241–262

247

Fig. 4. Spatial distribution and main depocenters of the Late Pleistocene–Holocene seismic unit. White dotted lines indicate the depocenters

orientation. Black lines show the channel locations, and black dotted lines the canyon locations. The thickness unit is milliseconds (twtt).

E. Llave et al. / Marine Geology 227 (2006) 241–262248

oldest to youngest) (Table 1 and Fig. 3B and C). Units

a, b, and d were further subdivided, each into minor

subunits (a1, a2, a3, b1, b2, b3, b4, c, d1 and d2). The

subunits are bounded by continuous reflectors of

strong-medium amplitude underlined by a change in

seismic facies. Within depositional sequences from a to

d there is a marked cyclic trend of seismic facies (Fig.

3) comprising a semi-transparent, low amplitude and

not well stratified pattern unit in the lower part that

passes up into an smooth, highly stratified parallel

reflectors of moderate-high amplitude in the upper

part. This facies evolve at the top in an erosive contin-

uous surface of high amplitude (Fig. 3).

The Late Pleistocene–Holocene seismic unit isopach

map shows a constant thickness displaying a flatter

geometry over all the middle continental slope (Fig.

4). A decrease in thickness is observed close to con-

touritic channels, in sectors affected by diapiric struc-

tures and Guadalquivir Bank uplift (Fig. 4). Several

depocenters are revealed by the spatial distribution

achieve in the isopach map (Fig. 4): (i) in the Faro–

Albufeira mounded drift the seismic unit reaches a

maximum thickness of 100 ms (twtt) with a ENE–

WSW direction; (ii) in the southwestern part of the

Faro–Cadiz sheeted drift sector, the maximum thick-

ness is of 80 ms (twtt) showing a NE–SE direction; (iii)

Fig. 5. (A) MD9923-36 Calypso piston core and (B) MD9923-41 Caly

susceptibility and grain size curves (after Mulder et al., 2002). For locatio

the seismic profiles see Fig. 3.

in the central part of Bartolomeu Dias sheeted drift,

there is a third depocenter about 50 ms (twtt) of thick-

ness with a NNE–SSW that changes to NW–SE direc-

tion; (iv) in the central area of the middle slope,

however, depocenters of 80 ms (twtt) show a preferen-

tial NE–SW orientation between diapiric ridges but a

NW–SE orientation between the MOW channels.

4.2. Cores description and correlation with ultrahigh-

resolution seismic data

The cores MD9923-36 and MD9923-41 collected

from the Faro–Albufeira mounded drift and from the

Faro–Cadiz sheeted drift, respectively (see Figs. 1 and 3

for location) recovered successions of thoroughly bio-

turbated, fine and coarse-grained contourite sequences

with typical thicknesses of 0.2–1.2 m (Thouveny et al.,

1999; visit http://www.pangaea.de/ for core descrip-

tions). They are mainly composed of clayey silt or

clay with thin, intercalated layers of sand or silty sand

(Fig. 5). The sand layers are more frequent in core

MD9923-36 from the Faro–Albufeira mounded drift

(Fig. 5A) than in core MD9923-41 from the south

Faro–Cadiz sheeted drift (Fig. 5B). The higher abun-

dance of contouritic sand layers reflects occasionally

enhanced winnowing which is also indicated by the

pso piston core, and the correlation between their d18O, magnetic

n of these piston cores in the CDS see Fig. 1B, and for location in

E. Llave et al. / Marine Geology 227 (2006) 241–262 249

E. Llave et al. / Marine Geology 227 (2006) 241–262250

lower sedimentation rates in the northern core

MD9923-36. The predominance of mud deposition

and higher sedimentation rates in core MD9923-41

points, on the other hand, to a generally lower near-

bottom current strength at this location. The sand con-

tent is much lower at the top of MD9923-41 than in the

uppermost samples of core MD9923-36 which also

indicates less winnowing and a lower current velocity

during the Late Holocene (Heilemann, 2000) on the

southern Faro–Cadiz sheeted drift as compared to the

Faro–Albufeira mounded drift area (Fig. 5).

Two IRD peaks occurred in core MD9923-41 that

corresponds to Heinrich events H1 and H4 (Fig. 5B). In

core MD99923-36, however, several peaks with mas-

sive abundances of lithic particles are recognized (Fig.

5A). The majority of lithic grains from these levels were

subrounded quartz. The grains were commonly glauco-

nite-impregnated and are therefore considered as rede-

posited shelf sand and not as IRD. Only those levels

were designated to Heinrich events where at least 5% of

the grains were identified as dolomite derived from the

Laurentide Ice Sheet (Baas et al., 1997; Schonfeld and

Zahn, 2000; Schonfeld et al., 2003).

The ANAS01-21 and ANAS01-22 gravity cores

were collected in the Faro–Cadiz sheeted and the de-

formed sheeted drifts, respectively. Both areas are char-

acterised by high sedimentation rates (Fig. 6). The

dominance of mud with scattered shell fragments

throughout is the main lithological feature of these

cores (Fig. 6). Thin sand layers are present at the

bottom and top of the cores only (Fig. 6). Two sandy

and muddy sand layers (d21 and d22) of about 15–75 cm

in thickness were identified within the most recent unit

d of the ANAS cores by a correlation with the upper-

most part of the MD cores (Fig. 6).

The correlation of seismic profiles with the cores

reveals the lithology of the different seismic units (Figs.

3, 5 and 6):

– Unit a: its upper part has been correlated with the

bottom of core MD9923-36. The seismic transparent

facies is hence related to sediments mainly com-

posed of mud, whereas seismic reflective facies are

related to coarser, silty sediments in the core.

– Unit b: the subunits b1, to b4 are characterised by

transparent facies at the base and more reflective

facies towards the top. They are related to predom-

inantly muddy deposits overlain by silty sediments

as observed in the cores.

– Unit c: is the most reflective unit in the Late Pleis-

tocene deposits. It is characterised by several high

amplitude reflectors intercalated with more transpar-

ent and thinner ones. These are related to silty/sandy

horizons with intercalated mud layers.

– Unit d: is in general very transparent and related to

extended muddy horizons in the top part of the

cores. Within this unit, there are more reflective

bodies on the top of d1 and d2 subunits. They are

related to silty/sandy beds, whereas the transparent

bodies are related to mud deposits.

4.3. Chronostratigraphy

The chronostratigraphic framework of IMAGES

cores MD9923-36 and ’41 revealed a Late Pleistocene

to recent age for the seismic units a, b, c and d (Fig. 5).

The chronostratigraphy of core MD992341 is based

on radiocarbon datings and the recognition of Heinrich

events. A close correlation of the oxygen isotope curve

with the parallel-core M39008-3 (Cacho et al., 2001)

inferred additional age control points for the upper part

of core MD9923-41 (Fig. 7).

The chronostratigraphic framework was further im-

proved in the lower part of this core by correlation of

the planktonic oxygen isotope record with the GISP2

ice core d18O record (Meese et al., 1997). Midpoints of

sudden cold–warm transitions of the planktonic oxygen

isotopes reflecting the beginning of Dansgaard/Oesch-

ger interstadials were tied to equivalent structures of the

GISP2 record (Dansgaard et al., 1993; Shackleton et al.,

2000) (Fig. 7).

The chronostratigraphy of core MD9923-36 is based

on the recognition of Heinrich events and a comparison

with stacked standard records (Imbrie et al., 1984;

Martinson et al., 1987). The age-model was refined

by graphic correlation of the planktonic oxygen isotope

curve with core MD9923-41 down to Heinrich event

H4, and with core MD952042 below this level (Cayre

et al., 1999; Shackleton et al., 2000) (Fig. 7). The

graphic correlation was performed with Analyse Series

Version 1.1 (Paillard et al., 1996).

The planktonic d18O records of cores MD9923-36

and MD9923-41 exhibit typical glacial to interglacial

variations (Fig. 5). According to the age models, our

records reach back in time to between approxi-

mately 24 ka (ANAS01-21) and 91.85 ka (MD9923-

36) (Tables 2 and 3). The planktonic d18O records

from cores or intervals with high sedimentation rates

show a millennial-scale variability during the last

glacial–interglacial transition and in the earlier part

of the records (Cacho et al., 2001), which can be

used for graphical correlation (Colmenero-Hidalgo et

al., 2004). The short-term variability seemingly mir-

rors Dansgaard/Oeschger cycles as observed in Green-

Fig. 6. ANAS01-21 and ANAS01-22 gravity cores and the TOPAS seismic profiles which crosses the deformed sheeted drift and Faro-Cadiz

sheeted drift respectively. For location of these ANAS01 gravity cores in the CDS of the Gulf of Cadiz see Fig. 1B.

E. Llave et al. / Marine Geology 227 (2006) 241–262 251

land ice cores (Dansgaard et al., 1993; Meese et al.,

1997). AMS 14C-datings ascertained the correlation of

the d18O curves from different cores. In particular the

comparison of oxygen isotope curves and AMS-dat-

ings from gravity core M93008-3 and giant piston

core MD9923-41 (Fig. 5B), which are 1.15 km

Fig. 7. Correlation of that data with the parallel-core M39008-3 (Cacho et al., 2001) in the upper part of the MD9923-41 core and with the GISP2

ice core d18O record in the lower part of the core. Thin gray lines are the correlations (given in the Tables 2 and 3). Thick gray line is H1. Crosses

are midpoints of cold/warm transitions which were used for correlating MD9923-41 with GISP2. Dots are 14C-datings and H as defined by IRD

scans.

E. Llave et al. / Marine Geology 227 (2006) 241–262252

apart, revealed variations in sediment thickness of

only a few tens of centimeters (Table 2). As such,

no significant stretching of the uppermost core meters

by the Calypso device is considered (Thouveny et al.,

2000; Skinner and McCave, 2003).

The age model of the cores is corroborated by the

recognition of Heinrich climatic events as depicted by

horizons with coarse terrigenous debris (Fig. 5). In

core MD9923-36, H1, H2, H4, and probably also H6

were identified. Core MD9923-41 shows only H1 and

H4 (Mulder et al., 2002). The concentration of ice-

rafted debris is with 2 to 12 grains N250 Am per gram

dry sediment about one order of magnitude lower than

off northern and southern Portugal (Baas et al., 1997;

Schonfeld and Zahn, 2000; Schonfeld et al., 2003).

The occurrence of IRD in core MD9923-36 (Fig. 5A)

is superimposed by probably shelf-derived sands as

described above. In both cores, Heinrich events and

cold climatic periods show higher sand contents, no-

tably the Younger Dryas, H4, and Marine Oxygen

Isotope Stage (MIS) 4. The sand content, i.e. grain

size and magnetic susceptibility curves show along the

MIS 3 interval in core MD9923-41 an inverse but

coherent cyclicity of D/O climatic oscillations as in-

ferred by the d18O curve (Fig. 5B).

Sand-rich, contouritic beds are marked by a high

reflectivity in the seismic records. This correlation

allows a chronological assessment of the contouritic

sedimentation. The oldest seismic unit a is developed

between the MIS 6 (135 ka) and the Heinrich event

H6 (59.4 ka). It has to be emphasized that the

boundary between both units is drawn with the top

of the sand-rich, highly reflective and stratified MIS 4

interval, where H6 is situated (Fig. 5). The seismic

unit b is positioned between H6 (59.4 ka) and H3

(30.5 ka). H3 is not depicted by IRD in this area, but

it coincides with a couple of time-equivalent sandy

contourites deposited during late D/O Interstadial 5.

The following seismic unit c is bracketed by H3

(30.5 ka) and H2 (23.8 ka), again with a sandy

contourite on top. The youngest seismic unit d is

developed between the H2 (23.8 ka) and present.

The subunits differentiated within each seismic unit

are limited by other contouritic beds developed dur-

Table 2

Age-model for core MD992341

Depth (cm) 14C Lab.

number

14C-age

(ka B.P.)

1sigma-

error (yr)

Correlation

with core

Depth therein

(cm)

14C-age§

(ka B.P.)

Calibrated

age (cal. ka)

Remarks

0 0.000 Core top

5 KIA14636 1.585 25 1.143

25 M39008-3 8 2.660 2.863

65 KIA14637 5.845 35 6.257

95 M39008-3 68 6.954 7.874

151 M39008-3 112 7.901 8.844

205 M39008-3 172 8.320 9.283

255 KIA14638 9.120 50 9.732

285 M39008-3 332 9.450 10.717

315 M39008-3 347 9.686 11.017

370 KIA14639 11.130 50 12.689

395 M39008-3 418 11.348 13.344

445 SU81-18 250 12.460 14.705

475 M39008-3 463 13.540 16.201 H1

485 KIA14640 14.210 80 16.465

565 KIA14641 15.010 110 Discarded1

580 KIA14642 15.720 100 18.206

675.9 GISP2 193,883 20.832 c/w transition

732.5 GISP2 198,598 23.405 Trans. to IS2

755 KIA14643 20.940 130 24.257

805 KIA14644 21.530 190 24.846

937.5 GISP2 205,577 27.832 Trans. to IS3

980.2 GISP2 207,552 29.011 Trans. to IS4

1005 KIA14645 26.290 240 29.776

1111.9 GISP2 212,681 32.296 Trans. to IS5

1176.6 GISP2 214,647 33.618 Trans. to IS6

1275.8 GISP2 217,689 35.273 Trans. to IS7

1285 KIA14646 32.040 560 Discarded2

1412.8 GISP2 223121 38.388 Trans. to IS8

1435 KIA14647 33.250 570 38.850 Diff. corr.3

1470 MD952039 1020 34.150 39.379 H4

1602.8 GISP2 227,549 41.151 Trans. to IS10

1678.8 GISP2 230,290 42.529 Trans. to IS11

1777.3 GISP2 235,822 45.371 Trans. to IS12

The chronostratigraphic framework was further improved by correlation of the oxygen isotope curve with the parallel-core M39008-3 (Cacho et al.,

2001) in the upper part of the core and with the GISP2 ice core d18 O record in the lower part of the core.1Radiocarbon age is too young possibly due to recrystallization of pteropod shell.2Radiocarbon age is too young, possibly due to contamination with tap water precipitates.3This dating is in the range of low geomagnetic intensities und high age offsets around IS8.

The data provided by Voelker et al. (2000) suggest a correction of 5600 yr.§Reservoir correction of 400 yr substracted.

E. Llave et al. / Marine Geology 227 (2006) 241–262 253

ing Heinrich events, the Younger Dryas and other

cold climatic periods.

A correlation of the lithological succession and

new AMS 14C-datings corroborate the Holocene and

Late Pleistocene age of the most recent contouritic

sand layers recovered with the ANAS gravity cores

(Fig. 6). ANAS01-21 was retrieved from the Faro–

Cadiz sheeted drift, and revealed that the last minor

depositional sequence d2 developed since the Younger

Dryas to present. Core ANAS01-22 was recovered

from an eroded edge of the Faro–Cadiz sheeted

drift, and the fine-grained deposits sampled corre-

spond to the lower part of the b2 depositional se-

quence (developed between H6 and H5 since MD

core datings). This shows that the muddy deposits

close to the bottom of the b2 unit have an age of

around 47 ka (Fig. 6).

5. Discussion

The determination of the stacking pattern and evo-

lution of the contourite depositional system in the Gulf

of Cadiz through dating and facies analysis contribute

answering questions of MOW variability in time and

Table 3

Age-model for core MD992336

Depth

(cm)

Correlation

with core

MD992341

(cm)

Correlation

with core

MD952042

(m)

Calibrated

age

(cal. ka)

Remarks

20 10 0.000

35 30 3.221

45 85 7.164

55 90 7.519

70 95 7.874

135 151 8.844

151 205 9.283

185 280 10.034

200 285 10.199

225 305 10.458

235 315 10.588

255 345 11.447

265 370 11.913

285 440 14.669

290 475 16.201 H1

330 555 17.746

385 590 18.455

400 610 18.881

410 620 19.094

420 635 19.413

440 650 19.732

470 670 20.157

495 690 20.583

525 730 21.227

545 751 21.644

560 778 22.214

590 795 22.888

601 805 23.026

625 825 23.303

655 845 23.766 Ca. H2

685 920 27.736

700 960 28.614

710 985 29.209

720 1010 29.655

730 1035 30.102

755 1095 32.123

765 1135 32.913

775 1155 33.455

795 1220 34.560

810 1270 35.287

825 1305 35.929

830 1325 36.700

840 1375 38.320

850 1435 38.663 Ca. H4

875 1485 39.469

970 1424 40.749

1025 1512 43.616

1055 1544 44.829

1080 1588 46.215

1160 1668 50.979

1220 1750 56.357

1315 1848 60.936

1355 1876 62.220

1403 1953 65.554 Event 4.2

1505 1982 70.549

Table 3 (continued)

Depth

(cm)

Correlation

with core

MD992341

(cm)

Correlation

with core

MD952042

(m)

Calibrated

age

(cal. ka)

Remarks

1600 2053 74.981

1660 2072 76.710

1685 2085 77.893

1715 2100 79.259

1780 2115 80.624

1801 2123 81.353

1830 2157 84.499

1840 2170 85.721

1875 2200 88.542

1900 2213 89.764

1945 2233 91.645

The chronostratigraphy is based on the correlation of the planktonic

oxygen isotope curve with core MD9923-41 down to Heinrich event

H4, and with core MD952042 below this level (Cayre et al., 1999;

Shackleton et al., 2000).

E. Llave et al. / Marine Geology 227 (2006) 241–262254

space related to climatic changes. These results

revealed high frequency cyclicity in the contourite

sedimentary record, with a frequency range below

the Milankovitch band that corresponds to cooling

Bond Cycles (10–15 ka), which ended in an Heinrich

climatic event (Bond et al., 1993). The coincidence

between climate and contourite cyclicity discloses a

straightforward interpretation of Late Pleistocene–Ho-

locene MOW dynamics in the context of northern

hemisphere climate variability.

5.1. Architectural stacking patterns on late quaternary

contourite deposits

A broad Late Quaternary contourite system of about

100–75 ms (twtt) thickness is develop in a mid-slope

setting at 500 to 1100 m water depth. It is characterised

by a sigmoid–oblique prograding, stacking pattern in

the northern margin (Faro–Albufeira mounded drift),

where is located the main depocenter, and by a broad

aggrading stacking pattern in its basinward prolonga-

tion (Faro–Cadiz and Bartolomeu Dias sheeted drift).

This contourite depositional system (CDS) is a conse-

quence of MOW interaction with an irregular sea bot-

tom, Coriolis forcing and the decreasing speed of

different undercurrent branches along the slope

(Melieres, 1974; Malod, 1982; Maldonado and Nelson,

1999; Nelson et al., 1999; Llave et al., 2001; Hernan-

dez-Molina et al., 2003).

The internal seismic signature of the CDS is char-

acterised by a sedimentary succession that comprises

continuous high amplitude reflections with parts that

display an acoustically parallel internal seismic signa-

Fig. 8. Late Pleistocene climatic curve as depicted by the Greenland ice core record (Dansgaard et al., 1993; Grootes et al., 1993; Meese et al., 1997)

in relation to sedimentation rate changes in core MD9923-36 and MD9923-41. Note that changes from cool to warm conditions are accompanied

with a decrease in sedimentation rate in the deeper core MD9923-36 but a slight increase in sedimentation rate, if at all, in the shallower core ’41.

Grey bars indicate the Heinrich climatic events.

E. Llave et al. / Marine Geology 227 (2006) 241–262 255

ture of low to medium amplitude reflections. The re-

petitive nature of the succession has made possible to

distinguish minor seismic units a, b, c and d, and to

further subdivide them into ten subunits. Cyclic

changes in the sedimentation rates during the Late

Pleistocene are also observed, where in general terms

high values are registered during cold climatic condi-

tions (Rogerson, 2002), as it is traced by the MD9923-

41 core (Fig. 8). On the other hand, higher sedimenta-

tion rates during ice-melting periods or cool–warm

transitions are described in those deposits located in

the northern area of the CDS of the Gulf of Cadiz, as it

is depicted by the MD9923-36 core data (Fig. 8).

The non-uniform distribution of age-control points

in the cores and possibility of hiatuses in the sediment

successions displayed by seismic sections do not justify

a serious application of frequency analyses at the pres-

ent stage. However, the time distance between seismic

unit and subunit boundaries and the repetitive changes

are related to the climatic variations during the Late

Fig. 9. Paleocirculation sketch during: (A) glacial conditions, when the MOW is denser, deeper and then the principal and southern branches (PB and SB) are the main fluxes; and (B) interglacial

conditions, period when the MOW is not so dense and flows in less deep waters, being the intermediate branch and the Mediterranean upper core (IB and MU) the principal nucleus.

E.Llave

etal./Marin

eGeology227(2006)241–262

256

E. Llave et al. / Marine Geology 227 (2006) 241–262 257

Pleistocene, suggesting an influence of 5th order pre-

cession cycles (19–23 ka). Precessional cycles have

already been constrained to drive the terrigenous supply

at the northern Iberian margin (Thomson et al., 2000)

and on the continental shelf and upper slope of the Gulf

of Cadiz (Hernandez-Molina et al., 2002). Then the

cyclic trend in the sedimentary facies is in common

mode with the cyclic climatic changes.

Anyway, the tight coupling of sandy contourites

with Heinrich climatic events and D/O stadials super-

imposes a millennial-scale variability. A common pat-

tern in this different variability is the transition from

warm or interglacial climatic conditions to a cold inter-

val, which is volumetrically much more important due

to mud deposition than the formation of thin sandy

contourites during cold climatic phases or cold–warm

transitions.

In this sense, it is proposed that the contourite

stacking pattern on the middle slope of the Gulf of

Cadiz is influenced by the repetition of cold and

warm climatic intervals (Fig. 8). This Late Pleistocene

climate variability exerted (Dansgaard et al., 1993;

Grootes et al., 1993; Meese et al., 1997) have direct

influenced on Gulf of Cadiz’s water masses circulation

pattern and then on the depositional systems.

5.2. Changes in the MOW contourite depositional sys-

tem as response to global climate changes: the impact

of Heinrich events

An enhanced Mediterranean circulation during the

Heinrich events and Glacial Maximum conditions in

comparison to warmer intervals has been proposed by

Cacho et al. (2000). A smaller and denser MOW that

would mix more vigorously with North Atlantic waters

is supposed to have prevailed during cool stages (Bar-

inger and Price, 1999). This view is controversial since

the MOW volume was certainly lower due to a reduced

cross-section of Gibraltar Strait during the glacial sea

level lowstands (Bryden and Stommel, 1984; Zahn,

1997; Matthiesen and Haines, 1998). This setting may

well have diminishing the water exchange between the

Mediterranean Sea and the Atlantic Ocean (Bethoux,

1984; Bryden and Stommel, 1984; Duplessy et al.,

1988). But, on the other hand, owing to this reduced

exchange, the lowered temperatures (Paterne et al.,

1986; Rohling et al., 1998), and a generally dryer

Mediterranean, the glacial MOW had a significantly

higher salinity and density (Zahn et al., 1987; Thunell

and Williams, 1989; Zahn, 1997; Schonfeld, 1997;

Cacho et al., 2000). Then, an intensive and deeper

MOW is originated (Thomson et al., 1999; Schonfeld

and Zahn, 2000; Rogerson, 2002). A deep and vigorous

MOW would result in a stronger interaction with the

seafloor at greater depths, being the Southern and Prin-

cipal Branches (SB and PB) the main MOW fluxes

(Fig. 9A), facilitate the transport and deposition of

coarser material, and finally would develop higher

sand contents in contourites, as can be observed in

the sedimentary record of the MD9923-41 southern

core. This scenario agrees well with our observations

as sandy contourites are developed in different places

under these different climatic conditions. Therefore, a

variable spatial influence of the MOW during each

climatic stage can be considered (Fig. 9A): the lower

Mediterranean branch enhanced during cool periods,

favoring the development of sandy contourites in the

central area of the middle slope (Fig. 9A).

During warm climatic periods and at high sea-level,

riverine sediments and terrigenous sands were trapped

on the shelf and predominantly fine suspension

reached the distal areas of the margin. The density

of the MOW was lower than during cool climatic

conditions (Zahn et al., 1987; Schonfeld, 1997;

Cacho et al., 2000), and then the interaction of the

MOW with the seafloor was more intensive at shal-

lower depths, result of the Intermediate Branch and

Mediterranean Upper Core (IB and MU) main fluxes

(Fig. 9B). At these warm conditions, sandy contourites

developed in shallower areas where in general the

upper Mediterranean branches were enhanced. This

conclusion again is in agreement with our observation

of higher, Late Holocene sand content in the top of the

northern core MD9923-36. It also offers an explana-

tion why many authors reported a period of winnow-

ing and contourite sand deposition associated with

interglacials instead of during glacials: they considered

sediment cores from depths near the top of today’s

upper MOW core, in the northern area of the Gulf of

Cadiz (Faro Drift), (Faugeres et al., 1984, 1985c,

1986; Gonthier et al., 1984; Stow et al., 1986),

where there is an intensification of the MOW during

warm climatic conditions.

6. Summary and conclusions

The strategy for reconstructing the Late Quaternary

Mediterranean Outflow Water (MOW) contourite sys-

tem variability and evolution has been based on seismic

and sedimentologic facies, sedimentary characteristics,

microfossils, benthic stable oxygen and carbon isotopes

and magnetic susceptibility studies. The combined ap-

proach, by the correlation of ultrahigh-resolution seis-

mic reflection profiles with giant piston and gravity

E. Llave et al. / Marine Geology 227 (2006) 241–262258

cores, facilitates an analysis of sedimentary facies with

a robust chronostratigraphic framework. The 20 m

Calypso piston cores recovered have pushed back the

record of change to around 45 ka, revealing very high

mean accumulation rates of 40 cm/ka. The composition

of these contourite facies is typically of mixed biogenic

and siliciclastic inputs. The core analyses has made

possible to reconstruct the general sedimentary condi-

tions and determine the main controlling factors for the

formation of these contourite deposits, demonstrating

the viability of a reliable, high-resolution chronostrati-

graphy in the CDS deposits, and hence the identifica-

tion of paleoceanographic changes.

Oxygen isotope records during the Late Pleistocene

to Holocene of planktonic foraminifera and the occur-

rence of ice-rafted debris in the most recent contourite

subunits show clear evidence of the influence of the

climate variability and Heinrich events in slope sedi-

mentation of the Gulf of Cadiz and then in the circula-

tion of the MOW. The presence of IRD in sandy

contourite beds in the Gulf of Cadiz middle slope is

further constrained. Up to four IRD layers related to

Heinrich events H1 through H6 have been detected in

20 m long giant piston cores. This study indicates a

close connection between the North Atlantic and the

hydrologic conditions in the Gulf of Cadiz.

During the Late Pleistocene to Holocene, major

contouritic sedimentation took place during cool cli-

matic conditions, where more sediment reached the

slope. Using contourite grain size as a proxy for

MOW strength, the data show MOW intensification

during cold phases having also played a stronger role

during these cold intervals in deeper waters because an

increase in density. This led to a higher sand content

in contourite deposits showing a reflective seismic

facies. Our observations indicate indeed an enhance-

ment of the lower MOW branch during climatic cool-

ing and a stronger upper MOW branch circulation

during warm intervals. In this context, the spatial

occurrence of sandy contourites was controlled by

variations in bathymetric position and current strength

of the MOW.

This new information complemented the compre-

hension of the paleoceanographic patterns on the

basis of the high-resolution seismic work. Thus we

conclude that the combined study of sedimentary

archives and seismic records is a key to understand

the cyclic nature of sedimentary, the past MOW

circulation pattern, and climatic changes, providing

implications for a better predictability of the environ-

mental consequences of present and future climatic

changes.

Acknowledgments

This work was supported by the following pro-

jects CICYT: PB94-1090-C03-03 (FADO), MAR-98-

02-0209 (TASYO) and Ren2002-04117-C03-01/02/03

(GADES). In addition, our results are related to the

Special Actions: REN2002-11669-E (MVSEIS Project)

and REN2002-11668 (MOUNDFOURCE Project), as

well as the IGCP-432 Project dContourites, Bottom

Currents and Palaeocirculations.T J. Schonfeld acknow-

ledges funding by the Deutsche Forschungsgemein-

schaft (Grant No. ZA157/15, ’16, Ti/240/9, We992/30,

and Du129/33). Authors thank the crew and Scientific

teams of GINNA/IMAGES V cruises on the R/V Marion

(IPEV).

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