Marine Micropaleontology, 13 (1988) 265-289 265 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Late Glacial to Recent Deep-sea Benthic Foraminifera from the Northeastern Atlantic (Cadiz Gulf) and

Western Mediterranean (Alboran Sea): Paleooceanographic Results

MICHELLE-HELI~NE CARALP

UA 197, C.N.R.S., Institut de G~ologie du Bassin d'Aquitaine, Universit~ de Bordeaux 1-351, cours de la Libdration, 33405 Talence Cedex (France)

(Received May 20, 1987; revised and accepted December 30, 1987)

Abstract

Caralp, M.-H., 1988. Late glacial to recent deep-sea benthic foraminifera from the northeastern Atlantic (Cadiz Gulf) and western Mediterranean (Alboran Sea): paleooceanographic ,results. Mar. Micropaleontol., 13: 265-289.

Deep-sea benthic foraminifera of the region of water exchange between the Mediterranean and the Atlantic Ocean, at the Gibraltar Strait, show significant water-mass relationships for the past 18,000 years.

Cores used in this benthic foraminifera analysis were selected, according to the context of the distribution of various deep bottom water masses, on each side of the Gibraltar Strait:

(1) on the Atlantic side of the Strait, two cores (KS 8228, KS 8229) are located in the present day NADW, and one (KC 8221 ) in the upper part of the present Mediterranean outflow water,

(2) on the Mediterranean side of Gibraltar, two cores (KC 8241, SU 8107) are located in the deep water mass, and one (KS 8230) in the intermediate water mass.

In the two deep basins (1500-2800 m~depth in the Gulf of Cadiz, 1200-1300 m depth in the Alboran Sea), the paleooceanographic changes appear to be in an opposite way for the past 18,000 years. The Alboran basin shows a paleooceanographic evolution from a well-oxygenated, nutrient-rich environment at about 18,000 yr B.P. to a nu- trient-poor, oxygen-depleted environment from 13,000 to the present time; moreover, for the time-span synchronous with the well-known development of sapropels in the eastern Mediterranean basins between 10,000 and 7000 yr B.P., the faunal assemblage shows most unusual characteristics implying drastic environmental conditions. Conversely, in the Gulf of Cadiz, the environment pass as from a biotope occupied by an oxygen-depleted, nutrient-poor water mass at about 18,000 years B.P. to a biotope occupied by NADW since the Younger Dryas; this agrees with previous data obtained in the northeastern Atlantic Ocean (Caralp, 1987).

In the epibathyal zones (550-800 m depth), on both sides of the Gibraltar Strait, paleohydrographic changes do not seem so important. According to the present and very late Holocene assemblages, which are similar on both sides of the Strait with a strong east-west flow, two other stratigraphic episodes have shown the same conditions of water exchanges: the end of the isotopic stage 2 and the Younger Dryas. Conversely, during the last glacial maximum, the Belling-Allered and the lower Holocene, westward water fluxes were probably lower. At no time, the hypothesis of a reversal or a stop in the east-west exchanges between Mediterranean and Atlantic Ocean may be justified.

0377-8398/88/$03.50 © 1988 Elsevier Science Publishers B.V.

266

Introduction (1984a-c) for the Mediterranean Sea. Other workers have tried to use species of

The area of water exchange between the benthic foraminifera as environmental and Mediterranean and the Atlantic ocean, at the oceanographic tracers. For example, the distri- Gibraltar Strait, is significant to the northeast- bution of some bathyal and abyssal calcareous ern Atlantic Ocean, because of the influence of benthic foraminifera have been correlated with Mediterranean outflow water on the hydro- overall distributions of deep-water masses graphic characteristics of the entire North At- (Lohmann, 1978; Schnitker, 1974, 1979, 1980); lantic (Reid, 1979). Comparative studies of the Corliss, 1979), with one or several physico- bathyal sedimentation on both sides of the Gi- chemical properties such as temperature, sal- braltar Strait during the late Quaternary may inity and dissolved oxygen (Streeter, 1973; contribute to the understanding the conditions Streeter and Shackleton, 1979; Mullineaux and and steps of the last deglaciation in this marine Lohmann, 1981; Caralp et al., 1982; Miller and area. During the oceanographic cruise FAE- Lohmann, 1982), with hydrostatic pressure re- GAS IV on board of the N.O. NOROIT in No- lated to bottom water temperatures (Belanger vember, 1982, many cores were taken in the Gulf and Streeter, 1980 ), and with productivity (Be- of Cadiz on the Atlantic side of the Gibraltar langer, 1982; Streeeter et al., 1982). Strait, and in the Alboran Sea on the Mediter- Many of these studies show high correlations ranean side (Faug~res et al., 1984). Various between assemblage or species occurrences and current isotopic, sedimentologic, geochemical physico-chemical properties of the bottom- and micropaleontological analyses done on water, thereby leading through extrapolation to these cores are published (Vergnaud-Grazzini the corresponding water mass. However, as et al., 1986; Faug~res et al., 1986; Stow et al., pointed outbyCorlisset al. (1986),thevalidity 1986; Grousset et al., 1988). On the basis of of such methods in the whole ocean is not really these results, it is possible to speculate on the proven; he gives as an example Uvigerina pere- environmental and paleooceanographic history grina, a species whose correlations have been of this key-area since the last glacial maximum, established with low-oxygen bottom water

The present report is focused on the record (Streeter and Shackleton, 1979; Corliss, 1979) of the deep-sea benthic foraminifera that can or with high amounts of organic carbon and be used: (1) for their distribution or (2) as fine-grained sedment (Miller and Lohmann, "markers" of particular bottom waters. 1982 ); he shows that, in the deep Indian ocean

The distribution of recent benthic foramini- water (Corliss, 1983), this species varies inde- fera within the North Atlantic Ocean and the pendently of dissolved oxygen. Mediterranean Sea have been studied by many Moreover, Corliss (1985) reveals that in a authors, including those who investigated into faunal assemblage of benthic foraminifera, the the bathymetric distribution of faunal assem- various species found together do not live ex- blages. Examples are Phleger et al. (1953), actly in the same ecological conditions: some Caralp et al. (1970), Pujos-Lamy (1973) and live on the seafloor, others at 2 or several cen- Caralp (1984) for the Atlantic Ocean, and Todd timeters within the bottom sediments. Thus, in (1958), Parker (1959), Bandy and Chierici a same assemblage, the distribution of some (1966), Blanc-Vernet (1969), Cita and Zocchi species may be controlled directly by the bot- (1978), Hermann (1981) and Bizon and Bizon tom water properties and of other species by the

267

physico-chemical conditions within the sedi- acteristic (Strait of Sicily) on the sedimenta- ments. These examples show clearly the diffi- tion which is devoid of sapropel deposits in this culty involved when using benthic foraminifera area (Ross and Kennett, 1984; Muerdter, 1984 ), as paleohydrological "tracers": understanding and their ecologicalcontrols is yet limited. (c) the nature of some sedimentary basins,

Being aware of the advantages and disadvan- e.g. the eastern Mediterranean (Massiota et al., tages of these methods the evolution of benthic 1976), the area of Cyprus during the last degla- foraminifera in the northeastern Atlantic ciation (Buckley et al., 1982) and the Mediter- Ocean, since the last glaciation, has been doc- ranean ridge (Parisi, 1983). umented and oceanographic hypotheses imply-

ing sluggish circulation and an oxygen depletion Oceanographic setting and circulation of the deep water during isotopic stages 3 and 2, have been proposed (Caralp, 1987). In the Mediterranean Sea, the eastern part has been Depth sequences of water masses at the pres- particularly well investigated in the context of: ent time are different on both sides of the Strait

(a) a wide sapropelic environment occuring of Gibraltar (Gaspard and Richez, 1985). during the early Holocene in the easternmost Oceanographic exchanges in this area are all- part of the Mediterranean Sea (Cita and Po- important in understanding the sedimentary denzani, 1980; Mullineaux and Lohmann, 1981; characteristics of the studied zone. The pres- Parisi, 1983; Katz and Thunell, 1984), ent-day state may be summarized as follows

(b) The influence of a physiographic char- (Fig. 1):

l ~ ° J ~o ~o ~o ~o ~o ) PORTUGAL

M 0 W

. 3 7 ~ SPAIN MALAGA

0 _ ), ATLANTIC Sur face Wate~.r. : ~- ~ - - . . . . . . . . .

600 ~ p ro j , , ted~ 8 2 2 1 . ~ ~ ~ ~ ' ~ ...,.projected ~ 2 3 0 . ^ = ~ \ \ . . . . . . . . . . . . . . _ _

30OOA N A D W B

Fig. 1. Location of cores studied and schematic diagram of present-day circulation within the Gibraltar area (Gulf of Cadiz- Alboran Sea). M O W = Mediterranean Outflow Water, N A D W = North Atlantic Deep Water, M I W = Mediterranean Intermediate Water; W D W = Western Deep Water. Four cores are located on traverse AB and two cores are projected.

268

(a) Atlantic sector: Gulf of Cadiz combe and Tchernia, 1960) and an oxygena- (1) The surface water extends down to 600 tion about 4.2 ml/1 (Wrist, 1961 ).

m and flows eastward, (2) The Mediterranean Outflow Water (c) Strait of Gibraltar sector

(MOW), a high-salinity countercurrent from The sill depth of Gibraltar is about 310 m. the Gibraltar Strait, between depths of 600 and ( 1 ) The surficial water flows with a potential 1200 m (Worthington, 1976; Reid, 1979), is temperature higher than 14 o C and a salinity of marked by a mean temperature of about 13°C, about 36.18%o (Bethoux, 1980). In the east of a salinity higher than 36.5%0 (Meli~res, 1974), the Strait it changes to denser Mediterranean and an oxygenation of about 4.5 ml/1. These waters. values have been extrapolated from the results (2) A mediterranean outflow, denser than given by Madelain (1976) and Reid (1979) for 37.90%0 (Bethoux, 1980) with a temperature of the Chain Station 71 (36°16'N; 9°33'W). about 13°C (Bryden and Stommel, 1982) and

(3) Underneath, the North Atlantic Deep an oxygenation of about 4.4 + 0.1 ml/l (Made- Water (NADW) flows southward from the lain, 1976), flows westward. It originates prin- North Atlantic Straits, its origin being in a deep cipally from the western deep water mass, with water source of the Norwegian-Greenland Sea a little contribution from the intermediate water (Swift et al., 1980). At the Chain Station this mass. water is characterized by a temperature range These two water masses are strongly between 3 and 8 ° C, salinity range between 34.95 stratified. and 35.2%0, and high oxygenation (5.3-5.5 ml/ 1 ). S a m p l i n g a n d a n a l y t i c a l m e t h o d s

(b) Mediterranean sector: Alboran Sea Cores used in this benthic foraminiferal (1) The surface water extends down to 150- analysis have been selected in view of the dis-

200 m, and flows eastward from the Atantic tribution of the various deep bottom water Ocean with a mean temperature of about 15 ° C, masses (Fig. 1 ). Furthermore, sedimentologi- and a salinity between 36.2 and 36.6%c (La- cal investigations (Faug~res et al., 1984) have combe and Tchernia, 1960; Bethoux and Prieur, underlined the hemipelagic character of the 1984 ), sedimentary sequences and the absence of tur-

(2) An intermediate water mass (MIW), bidites and hiatuses. formed during the winter in the easternmost On the Atlantic side of Gibraltar, two cores Mediterranean i.e. the Levantine Basin (Wrist, (KS 8228 and KS 8229 ) are located within the 1961 ), between 200 and 1000 m, flows westward present-day NADW, and one core (KC 8221 ) along the Spanish continental slope in the A1- in the upper part of the present Mediterranean boran Sea and in the Strait of Gibraltar (Mil- outflow water. On the Mediterranean side of lot, 1987) with a mean temperature of about Gibraltar, two cores (KC 8241 and SU 8107) 14°C (Lacombe and Tchernia, 1960) and a are located in the deep water mass, andonecore westward decreasing salinity which is higher (KS 8230) in the intermediate water mass. than 38.4%0 (Bethoux, 1980); oxygenation is From each core, 10 g of bulk sediment were about 4.2 ml/l (Minas et al., 1984), sampled at 10-cm intervals. Calcareous benthic

(3) A western deep water mass (WDW), foraminifera were sorted out, identified and formed during the winter, south of the Gulf of counted from the granulometric fraction larger Genoa (Italy), in the Ligurean Sea, exists be- than 250 ttm. Lohmann (1978) and Lutze and low 1000 m, with a temperature of about 12.7 ° C Coulbourn (1984) discussed the advantages of a salinity of about 38.4%0 at 2000 m depth (La- studying benthic foraminiferal larger than 250

269

TABLE I

Location, water depth and length of cores analyzed.

Cruise Core no. Latitude Longitude Water depth Core length (m) (m)

Faegas IV KS 8228 35 ° 49' 89 N 8 ° 43' 07 W 2798 7.70 Faegas IV KS 8229 35°59'00 N 8°00'00 W 1445 6.74 Faegas IV KC 8221 36°53'29 N 7°39'00 W 580 6.25 Faegas IV KS 8230 36 ° 27' 16 N 3 ° 53' 18 W 795 7.45 Faegas IV KC 8241 35°59'65 N 4°24'08 W 1282 3.30 CEPAG SU8107 35°56'6 N 3°48'0 W 1375 9.10

/Lm, namely (1) better observation of faunal as- TABLE II semblage variations because of the smaller

14C dates obtained on the coarse fraction of cores KC 8221, number of species, and (2) the elimination of KS 8230 and KC 8241 (from Devaux, 1985; Vergnaud- several small forms which are more easily dis- Grazzini et al., 1986) placed than larger forms. However, the size se- lection has a great drawback because it omits Cores Core Ages

certain smaller taxa that may also be of consid- depth (yr B.P.) erable hydrological significance (Schnitker, (cm) 1979; Schroeder et al., 1987).

Appendix I gives the listing of all the species KC 8221 190-200 15,630_ 1000 of calcareous benthic foraminifera found in the 223-225 16,460 ± 1200 cores. References to previous taxonomic stud- KS 8230 23- 30 2010± 220

153-160 9880 ± 1000 ies and illustrations of Atlantic species are con- 195-200 12,840 ± 1000 tained in: Phleger et al., 1953; Parker, 1958; KC 8241 77- 80 4850± 290 Todd, 1958; Cita and Zocchi, 1978; Lohmann, 117-160 7160± 550 1978; Parisi, 1981; Bizon et al., 1984; Caralp, 157-160 8900± 880

221-224 11,460 ± 540 1984; Ross and Kennett, 1984.

For each sample, the total number of speci- mens and species of calcareous benthic fora- minifera were counted. A diversity index

zini et al., 1986) by oxygen isotope analysis of (number of specimens/number of species) was calculated after Cita and Zocchi (1978). This planktonic foraminifera (Globigerina bul- study is based mainly on the species that are loides) from the following five cores: KS 8228, abundant in the cores. For the six cores studied, KC 8221, KS 8230, KC 8241, SU 8107. 14C dat- all the faunal data are given in Appendix II ings have been performed on the sediment frac- (Gulf of Cadiz), III (Strait of Gibraltar) and tion larger than 50/~m (Vergnaud-Grazzini et IV (Alboran Sea). al., 1986) in cores KC 8221, KS 8230 and KC

8241; they are given in Table II. Stratigraphic data The biostratigraphic distribution of plank-

tonic foraminifera was also examined in the six The stratigraphic framework was established cores selected (Duprat, 1983; Devaux, 1985).

(Duprat, 1983; Devaux, 1985; Vergnaud-Graz- Thus, following Pujol (1980), it was possible to

270

¢[ ° a +o KS 8 2 2 8 K C 8 2 2 1 K S 8 2 3 0 K C 8 2 4 1 S U 8 1 0 7 o a

~ ~ ~ +,. o.~, .: 3, 2 +,~ 3. 2. +; o,~, ~ ++,, o, -I'+. :, ~ ++,, o,w,,-_0 P- 12010+220

¢< 14850 + 230

, : , +.:+o ®+oo . . . . . . . - 3oooo ~ + o o o o . . . . . . . . . _ . . . . . . . . . 9 e e . .

~11000 . . . . . t8"900+- 8 8 ~ , ~ _ -- -- - - ~11000 +,. +ooo

+ 2800 ~o 3, _ _ C, 3- , 3- P++28000

b u l l b u l l 2m~ b u l l . U v i g 4- 4. \ , ,

rn bu l i, GULF OF CADIZ W E S T < \ \ > A S T A L B O R A N S E A

Fig. 2. Oxygen isotopic records, t4C datings and isotopic stages of the cores mentioned in this study.

match isotopic stratigraphy with biostratigra- Resul ts phy in the same cores. Furthermore, using these results, we were able to extrapolate isotopic General characteristics of the benthic stages to the cores for which only the biostra- foraminifera tigraphic information was available (KS 8229 ).

All these isotopic records, 14C datings and Three parameters of the benthic foramini- correlations are given in Fig. 2. For all cores feral assemblage were given particular atten- studied, except for core SU 8107 which is given tion in this study: number of calcareous in Duprat (1983), detailed isotopic results are individuals, number of species, and a diversity published in Pujol and Vergnaud-Grazzini (in index (number of specimens/number of spe- prep.), cies, Cita and Zocchi, 1978). These numbers

From these isotopic and biostratigraphic data, were used to assess the benthic productivity and according to the late Quaternary sequences which is a faunal characteristic depending on established by Duplessy et al. (1981), Shack- circulation, food supply and oxygenation letonet al. (1983),Bergeret al. (1985 ), six time (Buckley et al., 1982). Figure 3a-c represent spans will be taken into account in our benthic these data. foraminiferal results as follows: In the Gulf of Cadiz (cores KS 8228 and KS

(1) from about 18,000 to 15,000 yr B.P. 8229) it appears that from 18,000 B.P. to the (2) from about 15,000 to 13,000 yr B.P., this present time, microfaunas were always poor in

time-span is related to Terminat ion I A in Du- individuals and in species. Quantitative varia- plessy et al. (1981). tions are limited for all three parameters, ex-

(3) from about 13,000 to 11,000 yr B.P. = cept during the Younger Dryas episode where Bolling-Allemd. the number of specimens appears to have

(4) from about 11,000 to 10,000 yr B.P. -- slightly increased. The environmental condi- Younger Dryas. tions seem unfavorable to allow the develop-

(5) from about 10,000 to 7000 yr B.P. = early ment of numerous individuals and species. Holocene, this t ime-span includes Terminat ion In the Alboran Sea (cores KC 8241 and KS IB (Duplessy et al., 1981 ), 8107), a major change occurs at the end of iso-

(6) from 7500 yr B.P. to the present time = topic stage 2 (13,000 yr B.P.). During istopic late Holocene. Correlations of these time spans stage 2, the microfaunal assemblage was diver- are noted in the figures when necessary, sifted in species and rich in individuals. Above

271

1,oo I ~ o ~ o I , ~)o . . , I Io.o 2~o I ~ o . ,9o

l a t e H o l o c e n e

' ~~~- ] ~!~!'"';o~:.., ,,i ~_.~ t ~ t~/:~'~-°;-~~::-'~°~___ - D , , . . ," ........ l-~,°°°'" o _ , 1 ~

a) NUMBER OF SPECIMENS

io 1,o 2,o 1,o 2,o 3o , .1 12 2,0 1p 20 3.o lo ~ 32

~ - ! - ~ , . . . . . . . . . . .

2

blNUMBER OF SPECIES

Io I Io 2o f Io 2o 3o 40 ..j Io 2o I Io .~ 3o I Io 2o 3o

C) DIVERSITY INDEX

G U L F of CADIZ ~.~-- WE ST EA S T --~l~- ALBORAN SEA

Fig. 3. Distr ibution of the three fo]]owing parameters in the cores studied: (a) number of calcareous individuals, (b) number of species, (c) diversity index.

272

$

K S . 8 2 2 8 K S . 8 2 2 9 "g

C . w u e l l e r s t o r f i H . e l e g a n s C.ku I= .n bergi C.wu.I C. kull.nber9, "~ ,~ o I ,o 2o ,o =o ,o ,o , ' i lO ;o ,o 2o 3o

• " • i , i | , | ",'*,

10 B~LLING i i ~ ALLER00

1 3 0 0 0 I 130

® 2 O 0

c mi

Fig. 4. Distribution of Cibicides wuellerstor[i, Hoeglundina elegans and Cibicidoides kullenbergi in cores KS 8228 and KS 8229 (Gulf of Cadiz ); results given in specimens/10 g of bulk sediment.

~l K C 8 2 2 1 K S 8 2 3 0 _ w

~<> ° l i u. medi201 . . . . . . . . i 40, % i A scalariSto 20 % i ~.ar iminen~s10 % ~ U. med t l 20 . . . . . . * 40! % [ A scala is P a r i . _10%| . . . . . . 51 10%is, .~° °'¢~<

~ Younger ~_ ~. Oryal u~ 1.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7000

170 ~ _ _ _ early H o l o c 10000 Gelling ~ Younger -D r ya$ . . . . . . . . . . . . . . . . . . . 11000 AI lerod 190 el -A[le oOO ooo p

cn ~ cm

W E S T 4F - _ _ ~ . ~ E A S T

Fig. 5. Distribution of epibathyal species in the two cores: KS 8230-KC 8221 from the sides of' the Gibraltar Strait (results given as percentage ).

13,000 yr B.P., the microfaunal assemblage be- the microfauna is rather homogeneous down came poor, with the lowest number both for in- core, showing only a slight decrease in individ- dividuals and species; this suggests a uals and species after 13,000 yr B.P. West of deterioration of benthic ecological conditions Gibraltar, these values are more irregular (core that have persisted until today. KC 8221 ) and show peaks at the end of isotopic

On either side of the Gibraltar Strait, the mi- stage 2, during the Younger Dryas and during crofauna is always rich and diversified along the the latest Holocene. two cores studied (core KS 8230 at the east, core KC 8221 at the west ), but numerical variations Spatio-temporal distribution o[ species are low in comparison with those in the deep Alboran Sea. East of the Strait (core KS 8230), Several species have notable abundances of

2 7 3

~., a.

KS 8 2 2 9 KC 8 2 2 1 K S 8 2 3 0 KC 8 2 4 1 SU 81 0 7

>.: 20 4o 6o 20 40 61o.(141 20 50 loo 15o %00 2o0 >. o

10000 30 -- -- -

110 . . . . . I

13000 13 130 . . . . . . . . . . . . . . 10000

¢ 0 ~ - - ~ . . . . . . . 13000

c m m c m

c m

GULF OF C A D I Z W E S T ~ ~ E A S T A L B O R A S E A

Fig. 6. Distribution of Cibicides pseudoungerianus in all cores, except in the westernmost deep core; results given in speci- mens/10 g of bulk sediment.

K S . 8 2 2 8 ~ o~ ~" S U . 8 1 0 7 ~ ~'' GLOBOBULIMINA and Diversity .~ : GLOBOBULIMINA and "~ CHILOSTOMELLA I n d e x CHILOSTO MELLA Diversity I n d e x -

so ,o ~ 5 ~ : 20 40 ~ 5 1.s 2s .~ ,.

too £ ~ o o 11o . . . . . . . . . . . . . .

140 1000 130 Younger Dryas

160 11000 B61i.- Allered

• 190 '13000

cm GU,F c,o,z (,) 295 000

cr/

A L B O R A N S E A

Fig. 7. Distribution of Globobulimina and Chilostomella association in the two deep basins (Gulf of Cadiz, Alboran Sea) associated with the diversity index; results given as percentage.

indiv iduals a n d interpretable eco log ica l rela- one or several p h y s i c o c h e m i c a l e n v i r o n m e n t a l t ions , such as a n a r r o w b a t h y m e t r i c distribu- parameters .

t i on at the p r e s e n t t ime, or a corre la t ion wi th T h e first group o f spec ies c o n s i s t s o f f orms

274

= Ks .Kc221 Ks23o ! Kc241 suso i ~1 ,o%1 1,o% lO 20% 2o ,o% 2o ,0% - :

o if! i; ~o~;~ '~ ~-- 1so i . . . . . . . . . 1~ ~ . ~ _ . ~ . 1~o . . . . . . . . . . . . ~11°°°°

170 -- -- - 180 ' 13000 190

2151 I , 220 P"

> " ~

,

~ / 280 / /

cm cml // cm cn~ / , cm

Gulf ot CADIZ WEST 4 E A S T A L S 0 R A N S E A

Fig. 8. Distribution ofGyroidina alti/ormis in the cores studied; (results given as percentages; the dotted area underlines the highest percentages).

J=

K C 8 2 2 1 K S 8 2 3 0 KC 8 2 4 1 S U 81 0 7

• ,,~} I 210 , 410% / / 110 20 30% , 210 , 40% 10 20% I

I f Holocene

110 ~ . . L . : :: :- : ~ . . . . . . . 110 . . . . . . . . . . . . . . e ; ; i y " 7000 Holocene :i:i;!;~!:~..~____ ~_ . . . . . . . . . . . . . . . . . . . . . 1~o ~ ~ - _10000

. . . . . . . . . ~ 15C . . . . . . . . . . . . . . . . . r ~ 160 ":':':':':':':':':':':"'" Dun er u~ 17C

. . . . r B¢lI.AllerCd 19C >

21 ~ 220 . . . . . .

cm,

/~ / cm cm

W E S T 4{ ~ E A S T A L B O R A N S E A

Fig. 9. D i s t r i b u t i o n of Hyalinea balthica in the cores studied (results given as percentages; the dotted area underlines the highest percentages ).

presently living in a "young", well-oxygenated are present, with significant variations, in the water-mass like modern NADW (Lohmann, two Gulf of Cadiz cores, from the end ofisotopic 1978; Schnitker, 1980). These species are Cib- stage 2 until the present time. The distribution icides wuellerstorfi, Hoeglundina elegans, Cibi- of the three best-represented species is given in cidoides kullenbergi and C. robertsonianus; they Fig. 4.

275

TABLE III

Microfaunal results and paelohydrological interpretations from the two deep-sea basins: Gulf of Cadiz, Alboran Sea

G U L F O F CADIZ (1 5 0 0 - 2 8 0 0 m) A L B O R A N SEA (1200 - 1400 m)

St ra t igraphy Signif icant features of bent ic Inferred , , Signif icant features of ben th ic Inferred years BP foraminiferal assemblages pa leohydro logy fo~min i f e r a l assemblages pa leohydro logy

0 - r ich microfauna in t h e t o p level, 5,3 to 5,5 ml/I - low diversi ty 4,2 ml / l

Late - modera te be low, wi th H. elegans, N A D W in the deep G u l f - some Uvigerina and . under -oxygena ted water Holocene C. kullenbergi, C. wuellerstorfi, (mixed wi th a part o f M O W GIobobulimina . low flux of nu t r imen t s

C. robertsonianus at 1500 m depth) - f lux of Gyroidina altiformis . Uvigerina only at 1500 m depth at the base of the episode

7 0 0 0

Ear ly - lower diversity slight decrease of the - very low diversi ty . low oxygena t ion Holocene - less abundance o f the same N A D W circula t ion Globobulimina present . lack of food supply

species - very poo r microfauna . weak water circulat ion 10000

- increase o f diversi ty "¢ - abundance o f H . elegans, C. kuUen- increase of N A D W flux ~ - l ow diversi ty

Younger bergi, C. wuellerstorfi, C. robertso- Dryas nianus only at 2 8 0 0 m

- some Uvigerina and P. ariminensis (mixed waters near 1500 m) <m - dominance o f Globobulimina and near related condi t ions only at 1500 m dep th ~ abundance ofHyalinea balthica

1 1 0 0 0 ~ '~ • low diversi ty m - decrease of diversi ty

B611ing - decrease and disappearance o f . in i t ia t ion of an hydrologica l ~ - decrease o f t axa excep t Globobu- . decrease of nu t r ien t s Aller6d Globobulimina, slight increase of change limina, M. Barleeanum, Miliolidae . decrease of oxygenat ion

H. elegans, C. wuellerstorfi, C. . waters similar t o N A D W at . sluggish ci rculat ion kullenbergi 2 7 0 0 m d e p t h

13000

- same fauna, b u t slight decrease - very sl ight decrease of o f Globobulimina only at same condi t ions the microfauna same cond i t ions 15oo m dep~ ¢ ¢ ¢

15000 ~ i

• -~ - low diversi ty low o f nu t r i en t s - h igh diversi ty . abundance of nu t r iment : • ! - h igh abundance of C. pseudounge- o - abundance of Gtobobulimina and . under -oxygena ted wa te r • 6 rianus, M. barleeanum, Globobuli- . renewal o f deep waters

Ozilostornella . absence o f N A D W or no ~ ¢ mina, Miliolidae . fair ly good oxygena t ion

18000 - o ther species scarce renewal o f deep wate rs - presence of U. peregrina

The second group of species consists of forms opposite distribution: moreover, U. mediterra- which now live in the epitbathyal zone (Parker, nea and A. scalaris rise in abundance during the 1985 ) and seem to be linked to the intermediate Bolling-Allerod, decrease or disappear in the water mass in the Alboran Sea and to the Med- Younger Dryas and increase strongly at the be- iterranean outflow in the Atlantic. These spe- ginning of the Holocene. P. ariminensis absent cies are Uvigerina mediterranea, Planulina during the Bolling-Allerod and the early Hol- ariminensis and Amphicoryna scalaris and they ocene, is present during the Younger Dryas and are abundant only in the two cores (KS 8230, the late Holocene. KC 8221 ) from the sides of the Gibraltar Strait The third group of species consists of "ubiq- (Fig. 5 ). At the present time, i.e. at the top of uitous" forms which may be found in high num- these two cores, the distribution of these three bers in both the epi- and mesobathyal areas. The species is similar. Along the two cores, it ap- abundance of these species suggests high food pears that the three species have a parallel dis- supply (Arnold, 1983 ). Cibicides pseudounger- tribution (low percentages during isotopic stage Janus is the dominant species of this group fol- 2, higher percentages from the end of isotopic lowed by Melonis barleeanum. C. stage 2 until the present time) in the eastern pseudoungerianus (Fig. 6) is present in all co- core (KS 8230). In the western core (KC 8221 ), res, except in the westernmost deep core (KS these three species have a more irregular and 8228). West of Gibraltar (KC 8221), this spe-

276

TABLE IV

Microfaunal results and paleohydrological interpretations from both sides of the Gibraltar Strait (epibathyal cores }

T i WEST OF GIBRALTAR STRArr (580 m) EAST OF GIBRALTAR STRAIT (785 m) !

Stratigraphy Significant features of benthic Significant features of benthic years BP forarninfferal assemblages INFERRED PALEOHYDROLOGY foraminiferal assemblages

0 - very, high diversity, i - Average diversity, - abundance of U'. mediterranea, C. pseudo- strong east - west exchanges T - presence of Uvigerina, H. balthwa,

Late ungerianus, A. scalaris - high influx of [ - nutriments n ot very A. scalaris, P. arvninensis Ioloc~ne - presence ofM. barleeanum, P. ariminensls, nutriments I abundant - decrease of C. pseudoungerianus, M

Buhmina and Gyroidina oxygenation slightly diminished barleeanum - some H. elegans at the top 4.4 ml/l ~ 0,1 ml/I - abundance ofG. ahiformls during

the early part of the episode )0

- low diversity weak east - west exchanges ~. Average diversity Early - increase of U ,iger ~ a, A scalaris - low influx of - nutriments not very ~ fewer individuals but continuation

[olocene - absence ofP. arimineusis nutriments abundant of the same species as before - decrease ofBulimina spp.

~00 - high diversity ,.¢ - abundance of species strong east - west exchanges < Average diversity

(ounger - Flux ofHyalinea balthica abundance of nutriments ~_ flux oftIyalinea balthica Dryas - presence ofM. barleeanum, C. pseudo- probably good oxygenation - presence of C. pseudoungerianus,

ungerianus, Bulimina, P. ariminensis M. barleeanurn, Bulimina. U. medi- - absence ofA. scalaris f~ terranea, P. ariminensis - some Hoeglundina elegans

11~ ~00 - low diversity ~ - low diversity

3¢lling- - presence ofA. scalaris weak east - west exctmnges ~ller0d - absence ofP. ariminensis, H. balthica - low flux of - decrease of uutriments appearance o fA. scalarts

- decrease of C. pseudoungerianus and nutriments O2 ? 0 2 slightly ~ - presence ofBulurnina, U. mediter- the other species Pyrite diminished ranea, P. ariminensis, H. balthica ,

! decrease of C. pseudoungerianus, M. barleeanum ¢x

, 0 0 - - - high diversity and species density ~ - high diversity - abundance ofHyalinea bahhica strong east - west exchanges ~ - increase and abundance ofH. balthiea

~'~ - presence ofP. ariminensis, Uvigerina, abundance of nutriments - presence of C. pseudoungerianus. Bulimina, M. barleeanum probably good oxygenation or slight ] M. barleeanum, U. mediterranea, P.

.~ - absence ofA. scalaris diminution 1 ariminensis, decrease of U. peregrina ,00 ~

- low diversity index weak east - west exchanges i Average diversity I --~ - moderate abundance C. pseudoungerianus, - low flux of - abundance of nutnment I high abundance of U. peregrina

M. barleeanum, H. balthica nutriments O2 ? oxygenation slightly ¢ - presence of H. bahhica, M. barleea- Pyrite diminished hum, C. pseudoungerianus, P. arimi-

~ ~i nensts

cies exists, but is never very abundant; only the and Lohmann, 1981 ). West of Gibraltar, these top of the cores shows high numbers. East of species were present, in the two deeper cores Gibraltar, C. pseudoungerianus is abundant during isotopic stage 2, until the early Boiling- during isotopic stage 2 until 13,000 years B.P. Allerod in core KS 8228, where they represent Above this boundary, this species rapidly dis- a high percentage of a benthic assemblage char- appears in the two deeper cores (KC 8141, SU acterized by a low diversity index (Fig. 7). East 8107), but remains the same in the uppermost of Gibraltar, in the Alboran Sea, these forms core (KS 8230) until the upper part of the Hol- are encountered throughout the two cores (KC ocene, where it is absent. 8241, SU 8107), but constitute higher percent-

A fourth group of species, Globobulimina, (G. ages of the benthic assemblage between 13,000 affinis and closely related forms) and Chilosto- yr B.P. and the lower part of the late Holocene, meUa, existed in low-oxygen conditions that i.e. in the period where the diversity index be- prevailed in the eastern Mediterranean just be- comes very low (Fig. 7 ). fore the deposition of sapropels (Mullineaux The species Gyroidina altiformis lives from

277

the circalittoral to the bathyal zone (Bandy and characteristics in the two deep basins. The A1- Chierici, 1966). Mullineaux and Lohmann boran Sea had a rich and diverse foraminiferal ( 1981 ) demonstrated its capability to recolon- assemblage, indicating a high benthic produc- ize a biotope at the end of an anoxic episode, tivity (Fig. 6) and a significant nutr iment in- East of Gibraltar, G. alti[ormis appeared in the put in quite well-oxygenated waters. A seasonal early Holocene as a minor consti tuant of the renewal of bottom water must have occurred in fauna; it became very abundant (50% of the the Mediterranean at this time. The Cadiz fauna) during a short t ime-span in the lower basin, on the other hand, supported only small part of the late Holocene (Fig. 8). West of Gi- populations of Globobulimina (Fig. 7) because braltar, this species is sporadic and never of low-oxygen bottom water and lack of food abundant, supply (Ruddiman and McIntyre, 1981 ). This

The last species Hyalinea balthica is a circa- suggests the existence of a bottom water mass littoral and epibathyal species regarded as a whose characteristics were strongly different useful indicator of cold shelf water-masses from those of the present time (Caralp, 1987). (Blanc-Vernet, 1982; Ross, 1984; Cossement et In the vicinity of the Gibraltar Strait (inter- al., 1985). This form occurs in the Alboran Sea mediate water-mass and Mediterranean out- and on both sides of the Gibraltar Strait, and flow) the abundance of the benthic epibathyal shows high percentages in two cold strati- microfauna was higher in the east than in the graphic periods (Fig. 9): the first one at the end west; this might be related to a decreasing food of isotopic stage 2 in cores located on each side supply from east to west and then to a low ex- of Gibraltar, and the second one during the change of water-mass. Younger Dryas in the same area and in the Al- boran Sea. From about 15,000 to 13,000 yr B.P.: Fig. lOb

The faunas and the environmental interpre- tations are summarized in Tables III and IV. Microfaunas and paleohydrographic condi-

tions stayed the same in the two deep basins, Discuss ion but not in the Gibraltar Strait area. Foramini-

feral assemblages show a high similarity on both Using present and previous results, it is pos- sides, with diversified and rich faunas. Various

sible to interpret the faunal variations and to species previously with higher individual num- propose hypotheses that explain the paleo- ber in the east area, reach a great abundance in oceanographic evolution of the region. Further- the west (Hyalinea balthica, Fig. 9, for exam- more, sedimentological and geochemical results ple). These features occurring at the end of iso- obtained on the same area and which have led topic stage 2 are in good agreement with: (1) to paleohydrological interpretations, will be re- the sedimentological results of Stow et al. ferred to in the following hypotheses. Six suc- (1986) which localize in the western core cessive episodes have been established starting (8221), a first and distinct peak of coarser- with the last glacial maximum (Tables III and grained contourites in a fine-grained muddy de- IV, Fig. 10). posit, and (2) the clay data given by Grousset

et al. (1988) who observe high ratios of smec- From about 18,000 to 15,000 yr B.P.: Fig. lOa tite and kaolinite at the same level. All these

features suggest an accentuation of hydrologi- For this cold interval, the most important cal exchanges between Mediterranean and At-

feature is the contrast between hydrographic lantic, subsequent to the deglaciation.

278

8228 8229 8221 8230 8241 8107 ~, A ~ ~ A A A -I A T L A ~ WATER

5oo /

.

1 ] ,,= i Intermeolaze W a t e r 3 0 ~ % N A D W W a t e r

m PRESENT DATA C) -11000-13000 years BP 3000.P'~L~

BOLLING A LLEROD o ~ ~

500 1 0 0

1000

3000.1-'-~ f ) 0 - 7 0 0 0 y e a r s BP 3 ~ b)-13000 - 15000 years BP LATE HOLOCENE

o ,~,,

5O0

e l - 7 0 0 0 - 100OOyears BP 3 o o ~ a) -15000"18000 years B P EARLY HOLOCENE

0 L ' OXYGENATiON BENTHIC PRODUCTIVITY E X C H A N G E S V l . , :

E W 1 ~--~$1ightiy ~ low " L w e a k ] ~ | |depleted W-E s u r ~

[ .... ]b ig. ~ very d)-lOOOO - 11ooo years BP l o w c, c o r e m YOUNGER DRYAS

Fig. 10. H y p o t h e t i c a l evo lu t ion of t he deep wate r s t r uc tu r e in t he A t l a n t i c - M e d i t e r r a n e a n zone of exchange f rom abou t

18,000 yr B.P. to t he p r e s e n t t ime .

From 13,000 to 11,000 yr B.P.: Bolling-Allerod: the Cadiz basin, the initiation of a change in the Fig. I0c faunal assemblages occurs: microfaunas corre-

lated with oxygen-under-saturated water On the neighbouring mainland, the climate masses progressively disappear (Fig. 7),

during this episode, was warmer and more hu- whereas those able to live in well-oxygenated mid than those of the previous glacial episodes waters, such as NADW {Fig. 4), begin to ap- (Duplessy et al., 1981; Pons and Reille, 1986). pear, (namely Hoeglundina elegans, Cibicides Changes observed in the deep marine micro- kullenbergi) or to increase (C. wuellerstorfi), but fauna are as follows, the benthic productivity remains low.

In the deep Alboran Sea, a rapid fall of the At this same time, in the epibathyal zone of benthic productivity and nutr iments is indi- the Gibraltar Strait, the benthic microfauna is cated by the decrease of the foraminiferal den- characterized by a decrease in the numbers of sity for the entire assemblages (Fig. 7) and for species and individuals (Fig. 3): this decrease the "ubiquitous" species (Fig. 6). Given the in- is more important in the west than in the east, crease of Globobulimina percentages (Fig. 7), the water overlying the core KC 8221 becoming and the fall of benthic productivity, it appears less productive. Compared with the previous that the water mass became progressively less episode, paleohydrological conditions seem to oxygenated. These changes may indicate a re- be slightly different with perhaps a diminution duction in deep water formation. Conversely in of the Mediterranean outflow.

279

From about 11,000 to 10,000 yr B.P.: Younger From about 10,000 to 7000 yr B.P.: early Holo- Dryas, Fig. lOd cene: Fig. lOe

This cold and dry episode (Rind et al., 1986 ) This episode marks the last phase of the de- with very contrasting seasons (Duplessy et al., glaciation. In the Gulf of Cadiz, no increase of 1981; Pons and Reille, 1986) and summer max- benthic abundance at the bottom is perceptible. imum insolation (Berger, 1979, 1983) had se- Microfaunas were even less abundant than in rious effects on paleohydrography, the Younger Dryas; but species living in the

In the Gulf of Cadiz, a water mass character- present day NADW progressively reached ized by microfaunas living in the modern higher bathymetric levels to a depth of 1500 m NADW (Fig. 4 ) occupies the deep level, at about (Fig. 4 ). 2800 m in core ks 8228. These waters appar- In the Alboran Sea, this episode of about 3000 ently did not reach higher bathymetric levels years takes on individual characteristics which ( 1500 m in core KS 8229), where the faunal as- differ strongly from those of previous ones. All semblage is different, mainly with Uvigerina the analyses of benthic microfauna indicate that (Appendix II). ecologic conditions become unfavorable to

In the Alboran Sea, hydrological conditions benthic life. The decrease of species diversity remained practically unchanged from the and density and the absence of "ubiquitous" Bolling-Allerod. The only important faunal species (C. pseudoungerianus: Fig. 6), suggest a feature is the development of Hyalinea balthica lack of food supply and consequently a very low (Fig. 9), found at all depths of the Alboran Sea benthic productivity. Moreover, the dominant from 700 to 1400 m, and to the west side of the species (Fig. 7) are those able to live in low- Gibraltar Strait (KC 8221). Ross (1984)ex- oxygenated and somewhat isolated water plained that this species has migrated into the masses (Mullineaux and Lohmann, 1981 ). This Mediterranean at the Plio-Pleistocene bound- means that in the western Mediterranean, i.e., ary which coincides with climatic cooling, and in the deep part of the Alboran Sea, early Hol- became more dominant during glacial rather ocene hydrological conditions were drastic for than interglacial periods. The synchronism of benthic foraminifera, the available nutriments H. balthica peaks in all cores (Fig. 9), except being more and more scarce or not available in for the two deepest of the Gulf of Cadiz, agrees a sluggish circulation of a low-oxygenated with the cooling of the Younger Dryas episode, water-mass. Thus, these conditions are corn-

Furthermore, in the Gibraltar Strait epibath- parable but not so drastic to those of stagnation yal zone, the diversity index (Fig. 3)was higher events in the eastern Mediterranean where a and the benthic assemblages much more ho- well-known sapropel deposit exists. Ages given mogeneous than during the Bolling-Allerod, for this deposit (S 1) are between 9000 and 7500 suggesting similar paleohydrological condi- yr B.P. (Van Straaten, 1972), about 8000 yr tions on both sides of the strait. These faunal B.P. (Cita and Podenzani, 1980; Mullineaux characteristics agree with the existence of a and Lohmann, 1981;Parisi, 1983),younger than second peak of coarser-grained contourite max- 8800 yr B.P. (Buckley et al., 1982 ) and between ima at the upper part of the Younger Dryas, in- 9000 and 7000 years B.P. (Jenkins and Wil- terpreted by Faug~res et al. (1986) as an liam, 1984) and then in good accordance with increased westward circulation of the bottom the early Holocene in the Western Mediterra- water through the Gibraltar Strait. It is the only nean area. Thus, Vergnaud-Grazzini et al. interval for which the significance of sediment ( 1986 ) from the postglacial ~ 13C values estab- movements is shown by the presence of some lished that benthic foraminifera records of the displaced faunas in the benthic assemblages, whole Mediterranean (including the Alboran

280

Sea and the Gibraltar Strait) display a maxi- Gibraltar Strait, they detected a constant con- mum of decrease at about 9000-8000 yr B.P. in tamination by a Mediterranean input, but con- a general decreasing trend beginning at about versely they never found proof of any bottom 16,000 yr B.P. Other than the benthic forami- transport from the Atlantic towards the A1- nifera, the characteristics of the deposits in the boran Sea since 18,000 yr B.P. two parts of the Mediterranean are different; the extreme conditions of the eastern Mediter- Since 7000 yr B.P.: late Holocene, Fig. 10[ ranean were never reached in the west. What is observed in the Alboran Sea is a reflection of In this last episode, ecologic and hydro- the well-known stagnation in the eastern graphic conditions similar to those of the pres- Mediterranean. ent time are more or less rapidly reached in each

In the epibathyal zone, on both sides of the physiographic area. Gibraltar Strait, the benthic microfauna is The North Atlantic Deep Water occupies the slightly impoverished, compared with previous deep bathymetric zone of the Gulf of Cadiz from Younger Dryas, with a low species number, spe- the bottom to at least 1500 m. In addition to the cially in the west. These changes are less sig- better faunal preservation near the top of the nificant than those in the deep Alboran Sea. cores, the higher diversity index indicates a bet- These facts allow to speculate that, during the ter bottom productivity. However, these waters early Holocene, the water mass exchanges be- remain until present probably poor in available tween the east and west were probably weaker nutriments; Cibicides wuellerstorfi is scarce, and than in the Younger Dryas but no proof of a this species is low when the surface productiv- strong paleohydrological change is given by the ity, the source of available nutrients, falls below benthic foraminiferal results. The evidence of a critical value (Belanger, 1982). a stopping or a reversal of the hydrographic In the Alboran Sea, environmental condi- changes was previously much debated {Dies- tions become probably better than in the early ter-Haass, 1973, 1974; Huang et al., 1974; Ross Holocene, but they remain poor with regard to and Kennett, 1984). If a reversal might have benthic microfaunal development: the diver- existed at the Gibraltar Strait between 18,000 sity index and the foraminiferal density are al- yr B.P. and the present time, it would be during ways low. One particular assemblage at the base this episode characterized in the deep Alboran of the Holocene needs attention. After the hy- Sea, by the sluggish circulation and at about drological isolation during the lower Holocene, 600-800 m by a faunal impoverishment in the the faunal change begins with a very strong de- western part of the Gibraltar Strait. Berthoux velopment of Gyroidina alti[ormis (Fig. 8) in {1984) explained on the basis of physical data otherwise very poor faunal assemblages. Mul- that, owing to the narrowness of the Gibraltar lineaux and Lohmann { 1981 ), Ross and Ken- Strait, the heat budget ofthe Mediterranean sea nett {1984) and Katz and Thunell (1984) depends on a strong evaporation: he estab- consider that the Gyroidina environment is lished that, from the last glacial maximum (at transitional between conditions of sapropelic about 18,000 yr B.P.) until the present, the and normal sedimentation. After this short- Mediterranean Sea remains a concentration lived bloom of Gyroidina, some species previ- basin which supplies the Atlantic with dense ously extant remain or reappear, always in a waters. Furthermore, Grousset et al. (1988) lower number, in still under-oxygenated envi- studying the trace elements (La/Ta, Th/Ta) ronments with a low benthic productivity, are in the same cores, clearly separated the Atlan- consistent with the low degree of nutrients re- tic from the Mediterranean input. In the west- cycling within the Mediterranean, underlined ern core located in the MOW west of the by Boyle et al. {1985}.

281

In the epibathyal zone on both sides of the northeastern Atlantic ocean (Caralp, 1987);the Gibraltar Strait, the ecological conditions in late environment passed from a biotope occupied by Holocene are stable in the east and are improv- an under-oxygenated, nutrient-poor water mass ing in the west. In this latter part, the diversity with a probably sluggish circulation at about index and the specimen abundance of species 18,000 years ago, to a biotope occupied by such as Cibicides pseudoungerianus, Amphico- NADW at the present time. The hydrographic ryna scalaris, Uvigerina mediterranea, Buli- conditions began to change about 13,000 years mina sp. increase. This faunal homogenisation ago, but became mature only since the Younger on both sides of the Gibraltar Strait at about Dryas. 600 m can be explained by an increase of inter- (b) The deep area of Alboran Sea shows, on mediate water mass exchanges from east to the contary, a paleohydrographicevolutionfrom west, and a stronger Mediterranean outflow in a well-oxygenated, nutriment-rich environ- the late than in the early Holocene. This fact ment at about 18,000 years B.P. to a nutriment- may be compared with similar events observed poor environment which is the consequence of for the whole benthic assemblage between a reduction or non-renewal of oxygen. A change 15,000 and 13,000 yr B.P. and during the ofthese hydrographic conditions at about l3,000 Younger Dryas in the same cores. This last yr B.P., becomes very important between 10,000 homogenisation is, therefore, slightly different, and 7000 yr B.P. because no strong development of a particular (5) The Alboran Sea foraminiferal assem- species is seen (no Hyalinea balthica for exam- blage for the time-span between 10,000 and 7000 ple). This difference could be explained by cli- yr B.P. shows most unusual characteristics. matic conditions that are still cold, in the two This seems to be the consequence of a strong first events, whereas they are temperate in the and unfavorable water-stratification. It ap- upper Holocene. pears tha t th is 3000 year-long event in the A1-

boran Sea is synchronous with the well-known Conc lus ions development of sapropels in the eastern Medi-

terranean basins. Evolution away from these (1) Benthic foraminifera data help under- peculiar conditions during the Holocene has

stand the hydrographic evolution of the Atlan- been very slow. tic-Mediterranean area on both sides of the (6) On both sides of the Gibraltar Strait, in Gibraltar Strait. These faunas show succes- the epibathyal zone, the Mediterranean inter- sions from 18,000 yr B.P. to the present time, mediate water outflows westward. Compared which differ with bathymetric levels and geo- with present foraminiferal assemblages, benthic graphic locations of the cores, faunal evidence indicates the continuation of

(2) The different faunal sequences are inter- this east-west outflow through the Gibraltar preted in terms of possible water mass relation- Strait for at least the past 18,000 years, without ships. Hypotheses about the evolution of these stopping or reversal in good agreement with water masses in the deep and epibathyal zones Bethoux (1984), Faug~res et al. (1986), Grous- are presented, set et al. (1988).

(3) In the two deep basins (Cadiz on the At- (7)Increased epibathyal east-west flow, lantic side of Gibraltar, Alboran on the Medi- however, occurred three times: at the end of the terranean side), hydrographic conditions isotopic stage 2, during the Younger Dryas, and changed apparently in opposite directions dur- at very late Holocene. On the other hand, it ing the past 18,000 years: seems that the fluxes were lower during the last

(a) The evolution of the Gulf of Cadiz is part glacial maximum, the Bolling-Allerod, and the of the paleohydrographic evolution of the lower Holocene.

282

Acknowledgments Bulimina gibba Fornasini; Parker (1958), p. 261, pl. 2, figs. 21-22. BiloeulineUa labiata (Schlumberger); Bizon G. and J.J.

I am indebted to B.K. Sen Gupta (Louisiana (1984), p. VII, fig. 10. State University, Baton Rouge ), to D. Schnit- Bulimina marginata d'Orbigny; Ross and Kennett (1984),

ker (Darling Center, Universty of Maine, Wal- p. 322, pl. II, fig. 7. Bulimina mexieana (Cushman); Phleger et al. (1953), pl.

pole) and to K.G. Miller (Lamont-Doherty 6, fig. 1. Geological Observatory, Palisades) for helpful Cancris auriculus (Fichtell and Moll); Loeblich and Tap- discussions and constructive reviews of this pan (1964), p. 588, figs. 462-3a, b, c.

Cassidulina gr. laevigata d'Orbigny; Rosset-Molinier p a p e r . (1972), pl. 11, fig. 18.

Isotopic data were obtained in the Labora- Cassidulina crassa d'Orbigny; Parker (1958), p. 271, pl. 4, toire de G~ologie dynamique, Paris VI, Univer- fig. 12. sity by C. Vergnaud-Grazzini and in the Centre ChilostomeUa oolina Schwager; Barker {1960), p. 112, pl.

des Faibles Radioactivit~s, Centre National de 55, figs. 14-17. Chilostomella ovoidea Reuss; Barker (1960), p. 112, pl. 55,

la Recherche Scientifique (C.N.R.S.), Gif/ figs. 15-16,20. Yvette by J.C. Duplessy. Planktonic biostrati- Cibicides lobatulus (Walker and Jacob); Phleger et al. graphic data were obtained by the Laboratoire {1953), pl. 11, fig. 9 and 14. Associ~ au CNRS no. 197, Bordeaux I, Univer- Cibicides pseudoungerianus (Cushman); Barker (1960), sity by C. Pujol and M. D e v a u x . I t h a n k all of p. 194, pl. 94, fig. 9; Pujos (1976), pl. XI, fig. 2. This very

discussed specific name is given here to specimens which them for their help. had been bound to C. aft. C. floridanus (Cushman) by var-

The coring cruise of the French R/V Noroit ious mediterranean authors and to C. mediocris Finlay in was supported by Ifremer. the Atlantic Ocean.

Cibicides wuellerstorfi (Schwager); Corliss and Honjo (1981),p. 374, p. 18, figs. 1-3.

Appendix I m Systematic index Cibicidoides kuUenbergi (Parker); Lohmann (1978), pl. 2, figs. 5-7. Cibicidoides robertsonianus (Brady); Phleger et al. ( 1953 ),

A total of 78 species of calcareous benthic pl. 11, figs. 15 17. Foraminifera have been identified, using mainly Cornuspira involvens (Reuss }; Barker ( 1960 ), p. 22, pl. 11,

Loeblich and Tappan (1964). In following list, figs. 1-3. Cruciloculina sp.

for each of these is given an explanatory biblio- Dentalina sp. graphical reference. These references, wher- Discospirinatenuiussima (Carpenter); Barker (1960),p. ever possible, relate to the Northeastern 30, pl. 15, figs. 6-7. Atlantic or Mediterranean literature. Ehrenbergina undulata Parker; Phleger et al. (1953), pl.

10, figs. 14-15a, b, 16. EpistomineUa exigua (Brady); Barker (1960), p. 212, pl.

Articulina tubulosa (Seguenza); Todd (1958), p. 187, pl. 103, figs. 13-14. 1, fig. 1. Fursenkoina sp. Amphicorynascalaris (Batsch); Venec-Peyre (1984),p. 76, Globobulimina affinis (d'Orbigny); Parker (1958), p. 262, pl. V, figs. 1-3. pl. 2, fig. 25, Caralp (1984), pl. II, figs. 11-12. Anomalina sp. Globobulimina pseudospinescens (Emiliani ); Ross and Ammonia sp. always displaced in studied cores. Kennett (1984), p. 321, pl. I, fig. 12. Bolivina dilatata Reuss; Ross and Kennett ( 1984 ), p. 321, Gyroidina alti[ormis Stewart R.E. and K.C.; Parker (1958), pl. 1, fig. 1. p. 265, pl. 3, figs. 10-12. Bolivina quadrilatera (Schwager); Caralp (1984), pl. II, Gyroidina neosoldanii (Brotzen); Herb (1971), pl. 4, fig. fig. 10. 13; pl. 15, fig. 5; Caralp (1984), pl. VI, figs. 1-2. Bolivnia subaenariensis Cushman; Barker (1960), p. 110, Gyroidina orbicularis (d'Orbigny); Corliss and Honjo pl. 53; figs. 10-11. (1981), pp. 359-360, pl. 4. Bulimina aculeata d'Orbigny; Pflum and Frerichs ( 1976 ), Hanzawaia rhodiensis (Terquem); Parker ( 1958 ), p. 267, pl. 1, fig. 8. pl. 3, figs. 21-23. Bulimina costata d'Orbigny; Venec-Peyre ( 1984 ), p. 77, pl. Hoeglundina elegans (d'Orbigny); Corliss ( 1979 ), p. 12, pl. VI, fig. 4. 5, figs. 11-13.

283

Hyalinea balthica (Schroeter); Ross (1984), p. 137; pl. 1. Pyrgo lucernula (Schwager); Mullineaux and Lohmann Lagena sp. (1981), pp. 30-31, pl. I, figs. 14-15. Laticarininapauperata (ParkerandJones);Lutze (1977), Pyrgo murrhina (Schwager); Corliss and Honjo, {1981), p. 428, pl. 2, fig. 6. p. 376. Lenticulinaperegrina (Schwager); Barker (1960), p. 144, PyrgoeUa sphaera (d'Orbigny); Mullineaux and Lohmann pl. 68, figs. 11-16. {1981), p. 31, pl. 1, figs. 16-17. Leaticulina div. sp. Quinqueloculina aff. Q. lamarkiana d'Orbigny; Mullineaux Melonis barleeanum (Williamson); Corliss (1979), p. 10, and Lohmann (1981), p. 31, pl. 1, figs. 1-2. pl. 5, figs. 7-8. Quinqueloculina aff. Q. venusta Karrer; Lohmann ( 1978 ), Melonispompilio'ides (Fichteland Moll); Lohmann (1978), p. 32, pl. 4, figs. 8-9. pl. 1, figs. 12-13. Rectuvigerina sp. MiliolineUa irregularis (d'Orbigny); Mullineaux and Loh- Robertina translucens Cushman and Parker; Parker ( 1958 ), mann (1981), p. 30, pl. 1, figs. 3-4. p. 263, pl. 2, fig. 34. Nonion commune d'Orbigny; Venec-Peyre (1984), p. 80, Sigmoilina tenuis (Czjzek); Parker (1958), p. 257, pl. 1, pl. IX, fig. 2, displaced species in studied cores, fig. 24. Nummoloculina contraria (d'Orbigny); Barker (1960), p. Sigmoilopsis schlumbergeri (Silvestri); Lutze (1979), pl. 22, pl. 11, figs. 10-11. 3, fig. 1. Ophthalmidium acutimargo (Brady); Loeblich and Tap- Siphonina bradyana Cushman; Cushman (1931), p. 158, pan (1964), p. 449, fig. 340-2a-b. pl. 14, fig. 4a-c. Oridorsalis umbonatus (Reuss); Lohmann (1978), p.26, Siphonina reticulata (Czjzek); Cushman (1931), p. 158, pl. 4, figs. 1-3. pl. 14, fig. la-c. Osangularia culter (Parker and Jones); Lohmann (1978), Sphaeroidina buUoides d'Orbigny; Barker (1960); p. 174, pl. 3, figs. 7-10. pl. 84, fig. 1-2. Paromalinacrassa (Cushman); Pujos-Lamy (1973),p.224, Spiroloculinacanaliculatad'Orbigny;Pujos (1976),p.225, pl. II, fig. 5. pl. X, fig. 14. Paromalinapolymorpha(Costa);Brady(1884),p. 676,pl. Trifarina angulosa (Williamson); Ross and Kennett XCVII, figs. 3-6. {1984), pl. II, fig. 9. Planorbulina mediterranensis d'Orbigny; Parker {1958), Trifarina bradyi Cushman; Barker (1960), p. 140, pl. 67, p. 276, pl. 4, fig. 44. figs. 1-3. Planulina ariminensis (d'Orbigny); Cita and Zocchi Triloculina tricarinata (d'Orbigny); Barker (1960), p. 6, (1978), p. 461, pl. 3, figs. 7-8. pl. 3, fig. 17. Pseudonodosaria sp. Triloculina trigonula (Lamarck); Barker (1960), p. 6, pi. PuUenia bulloides (d'Orbigny); Lohmann (1978), p. 26, pl. 3, figs. 15-16. 1, figs. 10-11. Uvigerina mediterranea Hofker; Venec-Peyre (1984), p. 78, PuUenia quinqueloba (Reuss); Phleger et al. (1953), p. 47, pl. VII, fig. 3. pl. 10, fig. 20. Uvigerina peregrina Cushman; Lutze (1979), pl. 1, fig. 3a, Pyrgo anomala (Schlumberger); Ross and Kennett (1984), b; Bizon G. and J.J. (1984), p. 137, pl. X, fig. 7. p. 322, pl. II, fig. 11. Valvulineria bradyana d'Orbiny; Cita and Zocchi (1987), Pyrgo guerreri (Silvestri); Bourdillon (1982), pl. VII, figs. p. 459, pl. 1, figs. 7 and 10. 6-8. Vulvulina sp.

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