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Organic matter accumulation during the Holocene in the Guadalquivir marshlands (SW Spain)

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Organic matter accumulation during the Holocene in the

Guadalquivir marshlands (SW Spain)

JOSEE. ORTIZ

1

*, TRINIDAD TORRES

1

, JOSE E. LOPEZ-PAMO

2

, VICENTE SOLER

3

,

JUAN F. LLAMAS

1

, DANIEL BARETTINO

2

and MARIA J. GARCIA

1

^Laboratory of Biomolecular Stratigraphy, E.T.S.I. Minas Madrid, Universidad Politecnica de Madrid, Madrid, Spain

2lnstituto Geoldgico y Minero de Espana, Madrid, Spain

3lnstituto de Agrobiologia y Productos Naturales (CSIC), La Laguna, Tenerife, Spain

The distribution of biomarker compounds and magnetic susceptibility observed in the sediment from a 20 m core drilled in the marshlands of the estuarine region of the Guadalquivir River (southwest coast of Spain) has allowed us to reconstruct the palaeoenvironmental evolution of this area during the Holocene. Several organic compounds (n-alkanes, ra-ketones, n-alkanols, n-alkanoic acids and organic sulphur), as well as different biomarker ratios, have been used to show changing environmental conditions through time. These geochemical proxies suggest good preservation of the organic matter, although some diagenesis has occurred to particular organic compounds, especially the n-alkanoic acids. Our data indicate a major allochthonous supply of terrestrial plants, with less influence from aquatic plants or algae through the core. There are markedly different palaeoenvir­ onmental conditions between the uppermost 5 m (last 6 k a c a l . B.P.) and the rest of the core. From 5 m (ca 6 k a c a l . B.P.) to 19 m (ca 8 k a c a l . B.P.) depth the palaeoenvironmental conditions were almost constant. Based on organic sulphur content and n-alkane content logs, anoxic conditions prevailed from 8 to 6 k a c a l . B.P., while oxic conditions with enhanced convection of water (prevalence of fluvial input), and consequently a greater organic matter supply, predominated in the upper 5 m of the core. Similarly, little variation in the magnetic susceptibility profile below 5 m indicates stable environmental conditions, while in the upper 5 m conditions shifted to one with elevated water input and clastic sediment supply. This is linked to palaeofloral alterations in the Guadiamar/Guadalquivir drainage basins and/or anthropogenic effects. We propose that from ca 8 to 6 ka cal. B.P. a stable landscape physiognomy in the surroundings of the estuarine area of the Guadalquivir River, with a predominance of pines and grassland. However, over the last 6 k a c a l . B.P. a variation in the terrestrial plant biomarker compounds suggests an alternation of relatively dry and humid phases and/or the impact of human populations on altering the vegetation community have occurred.

1. I N T R O D U C T I O N

After t h e L a s t G l a c i a l M a x i m u m , t h e H o l o c e n e m a r i n e t r a n s g r e s s i o n r e s u l t e d in t h e e m e r g e d l o w l a n d s of t h e d o w n - v a l l e y part of t h e G u a d a l q u i v i r R i v e r b e c o m i n g flooded a n d t h e r i v e r i n e e n v i r o n m e n t c h a n g i n g i n t o a m a r s h l a n d ( m a r i s m a s a c c o r d i n g to t h e l o c a l d e s c r i p t i o n ; G o y et al. 1996; R o d r i g u e z Vidal et al. 1997; D a b r i o et al. 2 0 0 0 ) . T h i s l e d t o t h e p a l a e o - r i v e r l i n k e d gravel d e p o s i t i o n c h a n g i n g i n t o d a r k c o l o u r e d m u d or v e r y fine-grained s a n d c o n t a i n i n g a b u n d a n t o s t r a c o d s a n d p o l l e n as w e l l as s o m e s c a t t e r e d b r a c k i s h w a t e r m o l l u s c shells ( Z a z o et al. 1999; Yll et al. 2 0 0 3 ; R u i z et al. 2 0 0 5 ) . P r e v i o u s studies of t h e area h a v e f o c u s s e d n o t only on t h e coastal

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m o r p h o l o g y a n d its e v o l u t i o n ( Z a z o et al. 1994; G o y et al. 1996; R o d r i g u e z Vidal et al. 1997; B o r j a e f a / . 1999), b u t also on sedimentology (Dabrio et al. 2000; Lario et al. 2002; Lobo et al. 2005; Ruiz et al. 2005) and environmental evolution ( Z a z o et al. 1999; Yll et al. 2 0 0 3 ) .

In 1999, a b o r e h o l e w a s drilled in the vicinity of V i l l a m a n r i q u e ( H u e l v a P r o v i n c e , A n d a l u s i a , S p a i n ) at the m o u t h of the G u a d i a m a r R i v e r n e a r its confluence with t h e G u a d a l q u i v i r R i v e r (Figure 1). E s t u a r i n e areas are g o o d e n v i r o n m e n t s for s t u d y i n g t h e origin of s e d i m e n t a r y o r g a n i c m a t e r i a l d u e to t h e r a p i d a c c u m u l a t i o n of fine-grained s e d i m e n t , sealing t h e m f r o m b a c t e r i a l r e m i n e r a l i z a t i o n ( H e d g e s and Keil 1999), this c o r e w a s s a m p l e d for p a l a e o e n v i r o n m e n t a l r e c o n s t r u c t i o n p u r p o s e s .

T h e m a i n p u r p o s e of this study w a s to d e t e r m i n e the origin of t h e o r g a n i c matter, t h e p a l a e o e n v i r o n m e n t a l c o n d i t i o n s p r e v a i l i n g d u r i n g the H o l o c e n e , a n d the status of the area before and after any a n t h r o p o g e n i c effects, e s p e c i a l l y from m i n i n g . A m u l t i d i s c i p l i n a r y study, i n c l u d i n g s e d i m e n t o l o g i c a l d e s c r i p t i o n , m a g n e t i c susceptibility and c h a r a c t e r i z a t i o n of t h e o r g a n i c m a t t e r content, p a r t i c u l a r l y t h e lipid fraction at a m o l e c u l a r level ( b i o m a r k e r s ) , of d i v e r s e s a m p l e s t a k e n a l o n g t h e c o r e w a s carried out. Specifically, m e t a l l u r g i c a l s e t t l e m e n t s that w e r e d e p e n d e n t on m i n i n g districts (Iberian P y r i t e B e l t ) a r o u n d alluvial valleys of s o u t h - w e s t e r n I b e r i a n P e n i n s u l a ( G u a d a l q u i v i r and G u a d i a n a ) h a s b e e n d o c u m e n t e d for t h e last 5 0 0 0 y e a r s B.P. ( L e b l a n c et al. 2 0 0 0 ; N o c e t e et al. 2 0 0 5 ) .

2 . G E O G R A P H I C A L A N D G E O L O G I C A L S E T T I N G

T h e b o r e h o l e ( 2 0 m - l o n g , 9 2 c m - w i d t h ) w a s drilled in t h e vicinity of V i l l a m a n r i q u e d e la C o n d e s a (37° 1 1 ' 7 " N , 6° 1 2 2 9 " W ) , c l o s e to t h e confluence of the G u a d i a m a r and t h e G u a d a l q u i v i r rivers n e a r t h e m o u t h of this latter in t h e Gulf of C a d i z ( A t l a n t i c O c e a n ; F i g u r e 1). T h i s area is d o m i n a t e d by extensive m a r s h l a n d s , c o v e r i n g 1800 k m2, m o s t of t h e m p r o t e c t e d and l o c a t e d w i t h i n the D o n a n a N a t i o n a l P a r k and in its north b o u n d a r y i m p o r t a n t m a s s i v e s u l p h i d e d e p o s i t s b e l o n g i n g t o the I b e r i a n P y r i t e belt a r e found.

T h e c o a s t of the G u l f of C a d i z ( S W S p a i n ) c a n b e d e s c r i b e d as a s e m i d i u r n a l m e s o t i d a l o n e ( B o r r e g o et al. 1993). T h e s e c h a r a c t e r i s t i c s , t o g e t h e r with the c o a s t m o r p h o l o g y a n d the e n e r g y ( m e d i u m ) and direction of t h e w a v e s ( s o u t h - e a s t e r l y ) , favour t h e d e v e l o p m e n t of b r o a d littoral l o w l a n d s , usually s h e l t e r e d by spits, w h e r e tidal flats a n d fresh w a t e r m a r s h e s e x t e n d s o m e k i l o m e t r e s inland.

T h e G u a d a l q u i v i r R i v e r is o n e of the l o n g e s t in Spain, w i t h a total l e n g t h of 5 8 0 k m . In its l o w e r c o u r s e , n e a r t h e m o u t h , the s u b s t r a t u m c o n s i s t s of soft n o n - c o n s o l i d a t e d P l i o - P l e i s t o c e n e s e d i m e n t s . In fact, d u r i n g the P l i o c e n e and P l e i s t o c e n e m o s t of this area w a s c o v e r e d b y t h e sea and d u r i n g t h e late P l e i s t o c e n e / H o l o c e n e the actual river m o u t h a r e a acted as an e x t e n s i v e m a r s h l a n d with deltaic and alluvial influence, in s o m e c a s e s b e i n g this latter d o m i n a n t , d e p e n d i n g m o s t l y on g l o b a l sea level oscillations ( D a b r i o et al. 2 0 0 0 ) . Silts and a r g i l l a c e o u s s e d i m e n t s are p r e d o m i n a n t , with s o m e i n t e r b e d d i n g of sand a n d gravel. T h e b o r e h o l e w a s situated over d a r k lutites ( m a i n l y silt) d e p o s i t e d in an e x t e n s i v e m a r s h l a n d d u r i n g the H o l o c e n e (Torres 1 9 7 5 ; G o n z a l e z - D e l g a d o et al. 2 0 0 4 ) . T h e G u a d a l q u i v i r m a r s h l a n d is e n c l o s e d b y natural spits bars w h i c h , in t h e G u l f of C a d i z , w e r e c o n s t r u c t e d over four e p i s o d e s ( Z a z o et al. 1994): 6 . 5 - 4 . 7 k a c a l . B.P., 4 . 4 - 2 . 7 k a c a l . B . P , 2 . 4 - 0 . 7 k a c a l . B.P. and the last 5 0 0 cal. year. D u r i n g t h e sea level fall linked to the last glacial period, the G u a d a l q u i v i r river, as well as others that flow into the G u l f of C a d i z , e x c a v a t e d incised valleys. T h e following rapid sea level rise d u r i n g the H o l o c e n e resulted in the d o w n - v a l l e y a r e a s of t h e s e rivers e v o l v i n g into e s t u a r i e s . In fact, a c c o r d i n g to different studies ( G o y et al. 1996; B o r r e g o et al. 1999; D a b r i o et al. 2 0 0 0 ) t h e filling of t h e estuaries of the G u l f of C a d i z b e g a n d u r i n g the H o l o c e n e t r a n s g r e s s i o n . D u r i n g t h e p o s t - g l a c i a l t r a n s g r e s s i o n m a x i m u m , at 6 . 5 - 6 k a c a l . B.P. ( Z a z o et al. 1994) the t r a n s g r e s s e d areas c h a n g e d from b r a c k i s h to m o r e o p e n m a r i n e and t h e estuaries r e a c h e d their m a x i m u m surficial e x t e n s i o n ( D a b r i o et al. 2 0 0 0 ) . A f t e r w a r d s , the e s t u a r i n e filling followed a twofold p a t t e r n c h a r a c t e r i z e d b y a p r o g r e s s i v e c h a n g e from vertical a c c r e t i o n to lateral p r o g r a d a t i o n . At 4 k a cal. B.P. a partial e m e r g e n c e of tidal flats a n d spit b a r r i e r s o c c u r r e d b e c a u s e of i m p o r t a n t fluvial s e d i m e n t input. P r e v a l e n c e of coastal p r o g r a d a t i o n over vertical a c c r e t i o n at 2 . 4 k a c a l . B.P. c a u s e d the e x p a n s i o n of tidal flats a n d t h e r a p i d g r o w t h of s a n d y b a r r i e r s . F u r t h e r c h a n g e s reflect a n t h r o p o g e n i c i m p a c t s a n d t h e filling of t h e e s t u a r i e s c o n t i n u e d t o t h e p r e s e n t d a y ( G o y et al. 1996; D a b r i o et al. 1999, 2 0 0 0 ) .

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7 ° 0 0 ' O 6 ° 3 0 ' O

Holocene

Plio/PIcistoccnc

Dunes/eolian deposits [X^>| Spit bar complex, beach | | Marsh

Fluvial terraces, aluvial

3 7 W N Pleistocene _ . . . . .

K » j Fluvio-mannc, colian deposits I Deltaic/alurial fan deposits

Barrier island-lagoon I- -1 Prc-Pleistoccne sediments

0 5 10 15 20 2 5 k m

3 6 ° 5 0 ' N

Q> Rota

Figure 1. Geography and geology of Gulf of Cadiz region (southwest Spain), with location of the Guadalquivir/Guadiamar estuarine areas (modified from Gonzalez-Delgado et al. 2004). The location of the Villamanrique core (1) is shown on the map of the Iberian Peninsula, along with the core studied by Gonzalez-Vila et al. (2003) in the Guadiana River estuarine area (2). The main sulphide ore deposits are shown in grey.

T h e m e a n a n n u a l t e m p e r a t u r e in t h e a r e a is 1 6 . 9 ° C a n d t h e p r e c i p i t a t i o n is 6 1 4 m m ( R i v a s - M a r t i n e z a n d R i v a s y S a e n z 2 0 0 6 ) . A c c o r d i n g t o Y l l et al. ( 2 0 0 3 ) t h e v e g e t a t i o n is d o m i n a t e d b y M e d i t e r r a n e a n s c r u b in t h e h i g h z o n e s of t h e D o n a n a N a t i o n a l P a r k a n d b y A t l a n t i c - t y p e s c r u b in t h e d e p r e s s i o n s . Pinus picea, Quercus suber, Pistacia

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d e p r e s s i o n s ) Armeria arenaria, Carex wad Artemisia campestris occur. I n t h e salt m a r s h e s Salicornia a n d r u s h e s a r e p r e d o m i n a n t .

2.1. Borehole description

T h e stratigraphy of t h e V i l l a m a n r i q u e b o r e h o l e is p r e s e n t e d in F i g u r e 2. It w a s o b t a i n e d u s i n g a rotary r i g e q u i p p e d w i t h a c o r e barrel that r e c o v e r e d 9 2 c m d i a m e t e r c o r e s u s i n g a w i r e - l i n e d e v i c e . T h e c o r e r e c o v e r y w a s n e a r l y a b o u t 1 0 0 % a n d fine-grained s a n d s and lutites are the p r e d o m i n a n t m a t e r i a l s , e x c e p t at the b o t t o m w h e r e c o n g l o m e r a t e s , p r o b a b l y of P l e i s t o c e n e a g e a p p e a r ( 2 0 - 2 5 k a B.P., cf. D a b r i o et al. 2 0 0 0 ) . In s o m e c a s e s , fossil r e m a i n s are a b u n d a n t , especially o y s t e r s , Cardium s p . and Barnea sp., w h i c h are typical of intertidal areas. F o r a m i n i f e r a tests and o s t r a c o d e valves, m a i n l y Loxoconcha sp., a p p e a r in s o m e h o r i z o n s , and p l a n t r e m a i n s are also o b s e r v e d t h r o u g h o u t the c o r e a n d are e s p e c i a l l y a b u n d a n t b e t w e e n 14.55 a n d 13.55 m , 10.95 a n d 10.15 m and 9.15 a n d 5.55 m , w h i l e pyrite clasts are p r e s e n t b e t w e e n 13.55 and 10.95 m a n d 9.95 a n d 9.35 m.

M i c r o f a u n a a n d p l a n t r e m a i n s are very scarce in t h e u p p e r m o s t 3.35 m , a n d s o m e b r a c k i s h a n d terrestrial g a s t r o p o d a n d p e l e c y p o d f r a g m e n t s a r e t h e only faunal r e m a i n s in this z o n e . C l a y and m i c a grains are v e r y a b u n d a n t and d o m i n a t e over q u a r t z a n d feldspar. S e d i m e n t o l o g y a n d fossils i n d i c a t e that they w e r e d e p o s i t e d in a b r a c k i s h m u d d y m a r s h l a n d (marisma), and t h e p e l e c y p o d shells found a r o u n d 8 m p r o b a b l y reflect t h e F l a n d r i a n flooding event (cf. Z a z o et al. 1999), c o i n c i d i n g with t h e m a x i m u m in t h e post-glacial t r a n s g r e s s i o n . W e refer t o the s a m p l e d h o r i z o n s of t h e b o r e h o l e b y d e p t h , in c e n t i m e t r e , from t o p t o b o t t o m (e.g. s a m p l e d level V M - 5 2 5 is from 5 2 5 c m ) .

3 . M A T E R I A L S A N D M E T H O D S

T h e c o r e w a s split l o n g i t u d i n a l l y in half, p h o t o g r a p h e d a n d stored frozen at —20°C until r e q u i r e d for a n a l y s i s . F o u r s a m p l e s w e r e t a k e n for A M S r a d i o c a r b o n d a t i n g . S o m e o t h e r s w e r e t a k e n for lipid a n a l y s i s a n d m a g n e t i c susceptibility d e t e r m i n a t i o n .

3.1. AMS radiocarbon dating , A M S r a d i o c a r b o n d a t i n g w a s u n d e r t a k e n on b u l k organic m a t t e r of s a m p l e s V M - 1 2 0 , V M - 3 7 8 , V M - 5 7 9 a n d V M - 1 7 0 3 , at B e t a - A n a l y t i c , I n c . , Florida, following p r e - t r e a t m e n t w i t h dilute HC1 to e n s u r e t h e a b s e n c e of c a r b o n a t e . M a t e r i a l m e a s u r e d u s i n g the A M S t e c h n i q u e w a s a n a l y s e d b y r e d u c i n g t h e s a m p l e c a r b o n to g r a p h i t e ( 1 0 0 % ) . T h e g r a p h i t e w a s t h e n e x a m i n e d for 1 4C c o n t e n t with an a c c e l e r a t o r m a s s s p e c t r o m e t e r , and the r a d i o c a r b o n a g e w a s c a l c u l a t e d . T h e a g e w a s c a l i b r a t e d u s i n g the I N T C A L 9 8 r a d i o c a r b o n a g e calibration p r o g r a m (Stuiver et al. 1998).

3.2. Lipid extraction and analysis (biomarker analysis)

A total of 2 6 s a m p l e s w e r e t a k e n a l o n g t h e c o r e . A b o u t 4 0 - 4 5 g of freeze-dried s e d i m e n t (at 5 0 ° C for 2 4 h) p e r s a m p l e w e r e g r o u n d e d a n d b i o m a r k e r s w e r e e x t r a c t e d following t h e L a b o r a t o r y of B i o m o l e c u l a r S t r a t i g r a p h y p r o t o c o l ( L u c i n i et al. 2 0 0 0 ) , w h i c h c o n s i s t s of: 24 h s o x h l e t e x t r a c t i o n w i t h d i c h l o r o m e t h a n e a n d m e t h a n o l 2:1 ( s u p r a s o l v M e r c k ) a n d c o n c e n t r a t i o n of t h e isolated lipid e x t r a c t u s i n g a rotary evaporator. T h r e e lipid e x t r a c t fractions w e r e o b t a i n e d u s i n g liquid c h r o m a t o g r a p h y in a s i l i c a - a l u m i n a glass c o l u m n ( 1 4 . 2 g of silica, 7.7 g of a l u m i n a ; 7 0 - 2 3 0 m m m e s h ) u s i n g solvents of different polarity (80 m l in all c a s e s ) : h e x a n e , d i c h l o r o m e t h a n e / h e x a n e 8 0 % a n d m e t h a n o l t o yield neutral, p o l a r and acid fractions. P r i o r to a n a l y s i s in gas c h r o m a t o g r a p h m a s s s p e c t r o m e t e r ( G C - M S ) , acidic a n d p o l a r fractions w e r e m e t h l y l a t e d w i t h t r i m e t h y l s i l y l d i a z o m e t h a n e and silylated w i t h a m i x t u r e of N , 0 - b i s ( t r i m e t h y l s i l y l ) trifluoroacetamide ( B S T F A ) and p y r i d i n e at 7 0 ° C for 2 h .

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D e p t h O m L i t h o l o g y 5 m 10 m 1 5 m -i 20 m -i D a t i n g s (cal. y r B.P.) VM-120: 1,080 ±100 VM-378: 5,830 + 90

•A

o o O c P , o o o a y VM-570: 6,150 + 130

Lithology and Fossil Legend

Lutite Lost core Sand | ^ X ^ ff) Gastropoda ^ V ege t a l ^ T remains «:—> Ostracods Pelecipoda VM-1703: 7,730 ± 70 ka I I I I I 1 f m c "«3 Fj w Sand 5

Figure 2. Stratigraphy and chronology of Villamanrique borehole core. Calibrated ages (cal. B.P.) obtained from the radiocarbon method are included.

S a m p l e s w e r e injected into an H P 6 8 9 0 gas c h r o m a t o g r a p h e q u i p p e d w i t h a selective m a s s d e t e c t o r ( H P 5 9 7 3 ) a n d an A T M - 5 c o l u m n ( 2 5 0 x 0.25 m m ; 0.20 |xm). H e l i u m w a s t h e carrier g a s . T h e o v e n t e m p e r a t u r e w a s p r o g r a m m e d from 6 0 to 3 0 0 ° C at 6 ° C / m i n (hold t i m e 2 0 m i n ) . T h e injector w a s m a i n t a i n e d at 2 7 5 ° C . C o m p o n e n t s w e r e identified w i t h t h e D a t a A n a l y s i s p r o g r a m a n d the W i l e y L i b r a r y ; rc-alkane d i s t r i b u t i o n s w e r e o b t a i n e d f r o m

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the G C / M S c h r o m a t o g r a m s of m / z 5 7 in fraction A, rc-ketones from m / z 5 8 in fraction B , n - a l k a n o l s from m / z 83 in fraction C, n - a l k a n o i c acids from t h e m / z 7 4 in fraction B a n d o r g a n i c s u l p h u r from t h e m / z 6 4 in fraction A .

3.3. Magnetic susceptibility

T h e m a g n e t i c susceptibility w a s m e a s u r e d at a r e s o l u t i o n of a p p r o x i m a t e l y 10 c m intervals u s i n g a KLY-2 K a p p a b r i d g e from A G I C O , e q u i p p e d with t h e S U F A R software. A total n u m b e r of 67 s a m p l e s w e r e t a k e n a l o n g t h e 2 0 m - l o n g core. T h e e q u i p m e n t is a u t o m a t i c a l l y z e r o e d a n d the errors are e s t i m a t e d u s i n g t h e Sufar software b a s e d on m u l t i v a r i a t e statistical a n a l y s i s . T h e m a g n e t i c susceptibility a n d its a n i s o t r o p y c a n b e m e a s u r e d from 3 A/m to 4 5 0 A/m in 21 m e a s u r e m e n t s .

4 . R E S U L T S 4.1. Chronology

T h e a g e s are p r e s e n t e d in Table 1 a n d F i g u r e 2. T h e results s h o w that the b o r e h o l e c o v e r s m o s t of the H o l o c e n e . F i g u r e 3 s h o w s d a t i n g versus depth a s s u m i n g a c o n s t a n t s e d i m e n t a t i o n b e t w e e n p o i n t s . T h i s e n a b l e s t h e a g e of u n d a t e d i n t e r m e d i a t e h o r i z o n s to b e c a l c u l a t e d . T h e s e results i n d i c a t e the e x i s t e n c e of t w o distinct p h a s e s ; the first e x t e n d s from the b o t t o m of the c o r e to m e t r e 5 (ca 8 to ca 6 k a cal. B . R ) , with a m e a n s e d i m e n t a t i o n rate of 7 m m / year, w h i l e t h e s e c o n d , at the u p p e r m o s t 5 m (after 6 k a cal. B . R ) , yields a m e a n s e d i m e n t a t i o n rate of 0.54 m m / y e a r , c o i n c i d i n g with results of L a r i o et al. ( 2 0 0 2 ) for different H o l o c e n e estuaries from S W Iberia, i n c l u d i n g t h o s e from t h e G u a d a l e t e , G u a d a l q u i v i r and T i n t o - O d i e l rivers.

4.2. n-Alkanes

T h e logs of the different i n d e x e s related to t h e n - a l k a n e c o n t e n t u s e d in this paper, that is t h e c a r b o n p r e f e r e n c e i n d e x ( C P I ) , n - a l k a n e p r e d o m i n a n t c h a i n , l o n g - c h a i n / s h o r t - c h a i n ratio, t e r r i g e n o u s / a q u a t i c ratio, P a q i n d e x and relative p e r c e n t a g e s of t h e C2j, C 2 9 a n d n - a l k a n e s are s h o w n in F i g u r e s 4a, 5 a a n d 6 a - d .

T h e C P I ( B r a y a n d E v a n s 1961) r e p r e s e n t s the p r e d o m i n a n c e of o d d over e v e n n - a l k a n e s of a c e r t a i n c h a i n l e n g t h r a n g e and is c a l c u l a t e d as the

y 2 [ ( £ Q

+

c< + 2

+ • • • +

Q + s ) / ( E

Q-i + c< + i + • • • +

C, + C ;+2 + - - • + C ,+g ) / ( E C,+i + C ,+ 3 + . . . + Q + g ) ] ratio, w i t h i = 2 5 . It can b e u s e d as a p r o x y for t h e p r e s e r v a t i o n potential of t h e o r g a n i c m a t t e r w h e n t h e r e is a clear p r e d o m i n a n c e of h i g h e r plant w a x e s , that is, d u e to d i a g e n e t i c p r o c e s s e s their C P I g r a d u a l l y d e c r e a s e s d o w n t o 1 ( H e d g e s a n d P r a h l 1993) b e c a u s e of bacterial d e g r a d a t i o n that p r o d u c e s a s a m e c o n t e n t of o d d and e v e n c h a i n a l k a n e s , a l t h o u g h C P I m a y also reflect c h a n g e s in t h e c o n t r i b u t i o n from different p l a n t species ( C r a n w e l l 1 9 7 3 ; R i e l e y et al. 1 9 9 1 ; F a r r i m o n d a n d F l a n a g a n 1996; Z h a n g et al. 2 0 0 4 ) . T h e values of t h e C P I p r o x y in t h e V i l l a m a n r i q u e c o r e ( F i g u r e 4 a ) a r e b e t w e e n 13.6 ( V M - 1 0 0 )

Table 1. C dating for sediments from Villamanrique core

Sample Depth (cm) Laboratory code l 3C /1 2C (°/oo) Conventional I 4C age (ka B.P.) Calibrated age (ka B.P.)

VM-120 120 Beta-180647 - 2 5 . 2 1,180 ± 4 0 1,080 ± 8 0

VM-378 378 Beta-162117 - 2 5 . 2 5,100 ± 4 0 5,830 ± 9 0

VM-579 579 Beta-180649 - 2 4 . 5 5,390 ± 4 0 6,150 ± 130

VM-1703 1703 Beta-162116 - 2 3 . 9 6,900 ± 40 7,730 ± 7 0

All samples were analysed in an accelerator mass spectrometer (AMS) in the Beta Analytic Radiocarbon Dating Laboratory (Miami, USA). The ages were calibrated using the INTCAL 98 radiocarbon age calibration program (Stuiver et al. 1998).

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0

1800

2 0 0 0 ' 1 1 1 1 1 1 1 1

0 1000 2000 3000 4000 5000 6000 7000 8000

A g e (cal y r B . P . )

Figure 3. Age-depth relationship for Villamanrique core. Dates (Table 1) have been obtained via the radiocarbon method. Standard deviations for each calibrated age are represented.

a n d 2.1 ( V M - 5 0 5 ) and v a r y o n l y a little b e t w e e n 18.05 a n d 5.50 m , w i t h a m e a n v a l u e a r o u n d 7, w h e r e a s in t h e u p p e r 5 m a s a w - t o o t h p a t t e r n is o b s e r v e d , w i t h m i n i m a at s a m p l e s V M - 1 8 4 0 , V M - 5 0 5 a n d V M - 4 5 0 .

T h e p r e d o m i n a n t n - a l k a n e c h a i n , as w e l l as t h e n - a l k a n e l o n g - c h a i n / s h o r t - c h a i n ratio ( c a l c u l a t e d as

(Ct + Q + i + Q+ 2 ••• + C„)/(J2 C„+i + C„+2 + . . . + Cp), w i t h i = 14, n = 2 3 , p - 3 7 , b a s e d on D u a n a n d M a

( 2 0 0 1 ) a n d X i e et al. ( 2 0 0 3 ) , a n d t h e t e r r i g e n o u s / a q u a t i c r a t i o - T A RH C i n d e x ( c a l c u l a t e d as t h e C27 + C29 + C3 1/

C 1 5 + C17 + C 1 9 r a t i o , defined i n S i l l i m a n et al. ( 1 9 9 6 ) , B o u r b o n n i e r e and M e y e r s ( 1 9 9 6 ) and T e n z e r et al. ( 1 9 9 9 ) ) c a n s e r v e as i n d i c a t o r s of c h a n g e s in t h e t e r r i g e n o u s / a q u a t i c m i x t u r e of h y d r o c a r b o n s , o w i n g t o t h e different n - a l k a n e profiles of a l g a e , a q u a t i c m a c r o p h y t e s and v a s c u l a r p l a n t s . I n fact, t h e h y d r o c a r b o n d i s t r i b u t i o n of p h y t o p l a n k t o n a n d a l g a e is d o m i n a t e d b y l o w m o l e c u l a r w e i g h t n - a l k a n e s , m a x i m i z i n g at C1 7 ( G e l p i et al. 1970;

B l u m e r et al. 1 9 7 1 ; C r a n w e l l et al. 1987). S u b m e r g e d / f l o a t i n g m a c r o p h y t e s m a x i m i z e at C21, C23 a n d C25

( C r a n w e l l 1 9 8 4 ; O g u r a et al. 1 9 9 0 ; V i s o et al. 1993) as w e l l as m a n y Sphagnum s p e c i e s ( B r y o p h y t a ) ( B a a s et al. 2 0 0 0 ; N o t t et al. 2 0 0 0 ; P a n c o s t et al. 2 0 0 2 ) , w h i l e e m e r g e n t m a c r o p h y t e s h a v e n - a l k a n e c o m p o s i t i o n s s i m i l a r t o terrestrial p l a n t s , t h a t is, m a x i m i z i n g at C27 a n d C29 ( C r a n w e l l 1 9 8 4 ) . Terrestrial p l a n t s c o n t a i n h i g h p r o p o r t i o n s of

h i g h e r m o l e c u l a r w e i g h t n - a l k a n e s (C27, C2g a n d C3 I) in their e p i c u t i c u l a r w a x y coatings ( E g l i n t o n a n d H a m i l t o n

1 9 6 3 , 1 9 6 7 ; E g l i n t o n a n d C a l v i n 1 9 6 7 ; C r a n w e l l et al. 1 9 8 7 ; R i e l e y et al. 1 9 9 1 ; N o t t et al. 2 0 0 0 ; P a n c o s t et al. 2 0 0 2 ; L i u a n d H u a n g , 2 0 0 1 ) . D o w n c o r e v a l u e s for t h e p r e d o m i n a n t n - a l k a n e c h a i n , as w e l l as t h e n - a l k a n e l o n g - c h a i n / s h o r t - c h a i n r a t i o a n d t h e t e r r i g e n o u s / a q u a t i c r a t i o - T A RHc i n d e x are s h o w n in F i g u r e s 5 a a n d 6a,b. A l l t h e s a m p l e s m a x i m i z e m a i n l y at C31 a n d C29 for t h e n - a l k a n e s ( F i g u r e 5 a ) . T h e n - a l k a n e l o n g - c h a i n / s h o r t - c h a i n r a t i o ( F i g u r e 6a) p r o v i d e s v a l u e s g r e a t e r t h a n 6, e x c e p t in t w o c a s e s ( V M - 1 8 4 0 a n d V M - 5 0 5 ) a n d a similar profile is o b s e r v e d in t h e T A RH C i n d e x ( F i g u r e 6 b ) w i t h v a l u e s h i g h e r t h a n 4, w i t h m i n i m a at V M - 1 8 4 0 , V M - 5 0 5 and V M - 5 5 0 .

F i c k e n et al. ( 2 0 0 0 ) p r o p o s e d a p r o x y (Paq i n d e x ) t o d e t e r m i n e t h e s u b m e r g e d / f l o a t i n g a q u a t i c m a c r o p h y t e input relative t o t h e e m e r g e n t a n d terrestrial p l a n t i n p u t to l a k e s e d i m e n t s b a s e d o n n - a l k a n e s of a s a m p l e . T h e profile of t h e P a q i n d e x v a l u e s c a l c u l a t e d as t h e C2 3 + C2 5/ C23 + C25 + C2g + C3 1 r a t i o ( F i c k e n et al. 2 0 0 0 ) a l o n g t h e

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CPI-w-alkanes CPI-w-ketones 0 2 4 6 8 10 12 14 16 0 4 8 12 16 2 0 2 4

0 I — • — • — • — • — • — • — • — I I i • i — i — i — i — i — i —

2 0 0 0 1— ' — ' —1— ' —1—1—1—1 1 1

Figure 4. Downcore plots of (a) n-alkane and (b) n-ketones CPI values. CPI for n-alkanes = l/i[(^2Ci + Q+ 2 + . . . + Q + s ) / ( E Q _ i +

Q + , + . . . + C,+7) + (E Q + Q+ 2 + . . . + Q + s ) / ( E C,-+i + Q +3 + . . . + Q+ 9 ) ] , with i = 25; CPI for n-ketones = '/2[(E Q + Q +2 + . . . +

Ci+s) + ( E Q+ 2 + C; + 2 + . . . + Cm o) / 2 ( E Q + i + C,-+ 3 + . . . + Q+ 9) ] , with i = 21.

V i l l a m a n r i q u e c o r e a p p e a r in F i g u r e 6 c . M o s t v a l u e s a r e l o w e r or a r o u n d 0 . 1 , w h i l e t h e h i g h e s t v a l u e s of t h e

P a q i n d e x a r e o b s e r v e d in s a m p l e s V M - 1 8 4 0 , V M - 1 2 3 0 , V M - 5 0 5 a n d V M - 4 5 0 . ' M o r e specific c o n s i d e r a t i o n s a b o u t t h e origin of t h e o r g a n i c m a t t e r c a n b e m a d e b y t a k i n g i n t o a c c o u n t t h e

d i s t r i b u t i o n of t h e C27 , C 2 9 a n d C 3 1 n - a l k a n e s (cf. S c h w a r k et al. 2 0 0 2 ) . Typically, g r a s s e s a n d h e r b s give h i g h

c o n c e n t r a t i o n s of t h e C3 1 n - a l k a n e , w h i l e d e c i d u o u s tree a s s e m b l a g e s , t y p i c a l of t e m p e r a t e a n d h u m i d a r e a s , a r e

d o m i n a t e d b y t h e C27 - a l k a n e . C o n i f e r s , e s p e c i a l l y p i n e s , a r e rich in t h e C 2 9 h o m o l o g u e , b u t also s h o w a n i m p o r t a n t

c o n t e n t of t h e C31 n - a l k a n e . R o m m e r s k i r c h e n et al. ( 2 0 0 6 ) s t u d i e d t h e n - a l k a n e c o n t e n t in d i v e r s e s p e c i e s of g r a s s e s

a n d trees in s o u t h e r n Africa, r e s u l t i n g in d o m i n a n t n - C3 1 a l k a n e c o n t e n t i n b o t h C3 a n d C4 g r a s s e s , w h i l e

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p r e d o m i n a n t . A n a l y s i s of p r e s e n t - d a y p l a n t s of n e a r b y areas to t h e V i l l a m a n r i q u e c o r e p e r f o r m e d in o u r l a b o r a t o r y r e v e a l s that d e c i d u o u s tress m a x i m i z e at C2 7 n - a l k a n e , w h e r e a s in h e r b s t h e C3i n - a l k a n e is d o m i n a n t (cf. Ortiz et al. 2 0 0 4 ) .

T h u s , t h e e n r i c h m e n t in C27 n - a l k a n e c a n b e attributed t o t h e c o l o n i z a t i o n by m a n y species of d e c i d u o u s trees and, therefore, t h e e x i s t e n c e of m o r e h u m i d a n d t e m p e r a t e c o n d i t i o n s . O n t h e other h a n d , h i g h a m o u n t s of n - C3) in s e d i m e n t s c a n b e a s s o c i a t e d to dry p h a s e s , either cold or w a r m , w i t h t h e d e v e l o p m e n t of an i m p o r t a n t g r a s s - v e g e t a t i o n c o v e r a n d / o r the d e v e l o p m e n t of c o l d - c l i m a t e p i n e s .

In this study, w e will u s e t h e relative p e r c e n t a g e s of t h e C27 , C29 and C3 1 n - a l k a n e s is % C , = C , / 1 0 0 ( C2 7 + C2 9 + C3 J) , with i = 2 7 , 2 9 and 31 ( F i g u r e 5 d ) . T h e p e r c e n t a g e of t h e C2 7 n - a l k a n e r a n g e s b e t w e e n 4 % ( V M - 1 0 0 ) and 2 3 % ( V M - 5 0 5 ) , w h e r e a s t h e p e r c e n t a g e of t h e C2 9 h o m o l o g u e is b e t w e e n 3 3 % ( V M - 4 5 0 ) a n d 8 8 % ( V M - 1 0 0 ) a n d t h e o n e for t h e C3 1 n - a l k a n e varies b e t w e e n 1 2 % ( V M - 1 0 0 ) a n d 5 7 % ( V M - 2 8 5 ) .

4.3. n-Ketones

n - K e t o n e s , in c o - o p e r a t i o n w i t h n - a l k a n e s and o t h e r t y p e s of o r g a n i c c o m p o u n d s , p r o v i d e i n f o r m a t i o n a b o u t o r g a n i c m a t t e r s o u r c e s and their p r e s e r v a t i o n in s e d i m e n t s . L o n g - c h a i n k e t o n e s h a v e several p o s s i b l e o r i g i n s ( A r p i n o et al. 1970; V o l k m a n et al. 1981): (a) e p i c u t i c u l a r w a x e s of p l a n t s or a l g a e , (b) m i c r o b i a l o x i d a t i o n of t h e c o r r e s p o n d i n g n - a l k a n e s a n d (c) m i c r o b a l jS-oxidation a n d d e c a r b o x y l a t i o n of n-fatty acids. W h e n a m i s m a t c h in

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5 5 6 J. E . O R T I Z ETAL.

Zn-C„Ji:n-C„ TAR„, Paq Relative TAR,, percentage (%)

0 5 10 15 20 25 30 35 0 50 100 150 200 250 0 0.2 0 4 0.6 0.8 1.0 0 20 40 60 80 100 0 2 4 6 8 10 12 14 16

O

1200

Figure 6. Downcore plots of (a) n-alkane long-chain/short-chain ratio [Q^C,• + Q+i + C;+2 • • • + C , ) / £ Ca +i + C „+ 2 + . . . + Cp),

with i = 14, n = 23, p = 37], (b) terrigenous/aquatic ratio for n-alkanes: T A RH C = (C27 + C29 + C3 1) / ( C15 + C1 7 + C19 ) n-alkanes, (c)

Paq index ( C2 3 + C25 ) / ( C23 + C25 + C29 + C3i) n-alkanes, (d) relative percentage of C27 , C2g and C3 1 n-alkane isomers (%C, = C(/

100(C27 + C29 + C3 1) n-alkanes, with i = 27, 29 and 31) and (e) terrigenous/aquatic ratio for n-alkanoic acids: T A RF A = ( C24 + C26 + C2g)/

( C1 4 + C1 6 + Cl g) n-alkanoic acids.

t h e C P I b e t w e e n n - a l k a n e s a n d k e t o n e s o c c u r s , this i n d i c a t e s that n o t j u s t m i c r o b i a l o x i d a t i o n o c c u r r e d ( X i e et al. 2 0 0 3 ) ; a l t e r n a t i v e s o u r c e s i n c l u d e origins 1 o r 3 .

T h e C P I of k e t o n e s ( C P Ik = [ ( £ C , • + C ,+ 2 + . . . + C ,+ 8) + ( £ Q+2 + Q+2 + . . . + Q+ I 0) ] / 2 ( £ +

Q + 3 + . . . + Ci+g), w i t h i = 2 1 ) a l o n g t h e V i l l a m a n r i q u e c o r e i s r e p r e s e n t e d in F i g u r e 4 b , w h e r e a s t h e p r e d o m i n a n t n - k e t o n e profile a p p e a r s in F i g u r e 5b. T h e v a l u e s of the C P IK in the V i l l a m a n r i q u e c o r e ( F i g u r e 4 b ) are b e t w e e n

2 4 . 6 ( V M - 1 5 5 0 ) a n d 2.1 ( V M - 1 2 3 0 ) . T h e d i s t r i b u t i o n r a n g e of c a r b o n n u m b e r s of n - k e t o n e s is C2 3- C3 3 and t h e y

e x h i b i t o d d o v e r e v e n c a r b o n n u m b e r p r e d o m i n a n c e in all s a m p l e s , m a x i m i z i n g at C29 o r C3 1 ( F i g u r e 5 b ) .

4.4. n-Alkanols

n - A l k a n o l s p r o v i d e useful i n f o r m a t i o n a b o u t o r g a n i c m a t t e r s o u r c e s and their p r e s e r v a t i o n in s e d i m e n t a r y r e c o r d s a n d are e x p e c t e d to b e at least as b i o a v a i l a b l e as the n - a l k a n e s ( F i c k e n etal. 1998a). T h e y c a n b e u s e d to d i s t i n g u i s h b e t w e e n c o n t r i b u t i o n s from a l g a e , a q u a t i c m a c r o p h y t e s and land plants to the o r g a n i c m a t t e r p r e s e r v e d in the s e d i m e n t s . A q u a t i c a l g a e a n d p h o t o s y n t h e t i c b a c t e r i a c o n t a i n n - a l k a n o l s w i t h an e v e n n u m b e r of c a r b o n a t o m s r a n g i n g f r o m C1 6 to C2 2 ( R o b i n s o n et al. 1 9 8 4 ; V o l k m a n et al. 1999). A d o m i n a n c e of h i g h e r m o l e c u l a r w e i g h t

n - a l k a n o l s , C2 2- C3 0, w i t h an e v e n c a r b o n p r e d o m i n a n c e , h a s b e e n a s c r i b e d t o c o n t r i b u t i o n s from e p i c u t i c u l a r

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distinctive c h a i n l e n g t h p a t t e r n s ( F i c k e n et al. 1998a,b; F i c k e n et al. 2 0 0 0 ) a n d R o m m e r s k i r c h e n et al. ( 2 0 0 6 ) f o u n d a g e n e r a l p r e d o m i n a n c e of the C3 2 n - a l k a n o l in C4 p l a n t s .

C y a n o b a c t e r i a a n d a q u a t i c m a c r o p h y t e s are r e p o r t e d t o b e m a j o r p r o d u c e r s of C22 - C26 n - a l k a n o l s , w i t h a

p r e d o m i n a n c e of n - C2 4 ( F i c k e n et al. 1 9 9 8 a , b ; V o l k m a n et al. 1 9 9 9 ; Filley et al. 2 0 0 1 ) , and Sphagnum s p e c i e s

m a x i m i z e in the C2 4- C28 n - a l k a n o l s ( B a a s et al. 2 0 0 0 ; P a n c o s t et al. 2 0 0 2 ) . S o m e t i m e s t h e n - a l k a n o l profile d o not

c o r r e l a t e well w i t h the c o r r e s p o n d i n g d i s t r i b u t i o n s of p l a n t s c a l c u l a t e d o n the basis of p o l l e n c o u n t s , w h i c h m a y i n d i c a t e a p r e f e r e n t i a l m i c r o b i a l a t t a c k on t h e shorter c h a i n h o m o l o g u e s ( F i c k e n et al. 1998b).

T h e m a i n d i s t r i b u t i o n r a n g e of c a r b o n n u m b e r s of n - a l k a n o l s in V i l l a m a n r i q u e c o r e s a m p l e s is b e t w e e n C2 2

a n d C3 0. N e v e r t h e l e s s , t h e r e are s a m p l e s in w h i c h t h e n - a l k a n o l profile s h o w s a d i s t r i b u t i o n r a n g i n g from t h e C1 4

i s o m e r t o t h e C3 2 h o m o l o g u e , b u t in all c a s e s w i t h v e r y l o w a b u n d a n c e s . T h e y h a v e an e v e n - t o - o d d c a r b o n n u m b e r

p r e d o m i n a n c e , m a x i m i z i n g at C2 6 or C2 8 ( F i g u r e 5 c ) , e x c e p t s a m p l e V M - 1 8 4 0 , w h i c h m a x i m i z e s at CI 8.

4.5. n-Alkanoic acids

L i k e a l i p h a t i c h y d r o c a r b o n s , n - a l k a n o i c a c i d in l a k e s e d i m e n t s c o m e from o r g a n i c m a t t e r d e r i v e d from p l a n t s and m i c r o - o r g a n i s m s . L o n g - c h a i n n - a l k a n o i c acids ( C2 4- C3 0) , with p r e d o m i n a n c e of e v e n c h a i n s , are m a j o r

c o m p o n e n t s of t h e w a x y c o a t i n g s on l a n d p l a n t l e a v e s , flowers a n d p o l l e n ( E g l i n t o n a n d C a l v i n 1 9 6 7 ; R i e l e y et al. 1 9 9 1 ; M e y e r s a n d I s h i w a t a r i 1993) w h i l e a l g a e and b a c t e r i a m a x i m i z e at shorter c h a i n l e n g t h s C i2- C1 8 ( E g l i n t o n

a n d C a l v i n 1967; C r a n w e l l et al. 1987). Sphagnum s p e c i e s m a x i m i z e in t h e n - C2 4 a n d C2 6 h o m o l o g u e s ( B a a s et al.

2 0 0 0 ; P a n c o s t et al. 2 0 0 2 ) . In o r d e r to c a l c u l a t e t h e l a n d v e r s u s a q u a t i c i n p u t s of o r g a n i c m a t t e r into a l a k e , B o u r b o n n i e r e and M e y e r s ( 1 9 9 6 ) and T e n z e r et al. ( 1 9 9 9 ) u s e d t h e t e r r i g e n o u s / a q u a t i c r a t i o ( T A RFA) :

( T A R F A) = ( C2 4 + C2 6 + C2 8) / ( C ,4 + C1 6 + C1 8) .

H i g h e r v a l u e s for this ratio i n d i c a t e i n c r e a s e d terrestrial p l a n t s r e l a t i v e t o a q u a t i c biota, b u t they can also i n d i c a t e d e g r a d a t i o n of a q u a t i c fatty acids r e l a t i v e to l a n d - d e r i v e d c o m p o n e n t s . S o m e t i m e s d i a g e n e t i c p r o c e s s e s c a n m o d i f y T A RF A. S h o r t - c h a i n acids a r e often preferentially d e g r a d e d by m i c r o b e s d u r i n g early d i a g e n e s i s ( C r a n w e l l 1974,

1976; H a d d a d et al. 1 9 9 2 ; H o and M e y e r s 1994). O n t h e o t h e r h a n d , m i c r o b i a l s y n t h e s i s of s e c o n d a r y fatty acids from p r i m a r y o r g a n i c m a t t e r p r o d u c e s s h o r t - c h a i n c o m p o n e n t s ( K a w a m u r a et al. 1987). T h e n - a l k a n o i c acids are p r e s e n t in t h e C1 4- C3 0 r a n g e , w i t h a p r e d o m i n a n c e of e v e n n u m b e r e d c h a i n s a n d s h o w i n g a b i m o d a l distribution w i t h m a x i m a at C1 6- C i8 or C2 6- C2g ( F i g u r e 5 d ) . In s o m e c a s e s t h e C] 6 a n d C1 8 h o m o l o g u e s a r e p r e d o m i n a n t . 4.6. Organic sulphur S u l p h u r u n d e r g o e s c y c l i c t r a n s f o r m a t i o n s , w h i c h c a n b e v i e w e d f r o m different levels of o r g a n i z a t i o n a n d c o m p l e x i t y ( J 0 r g e n s e n 1 9 8 3 ; K i l l o p s a n d K i l l o p s 1984). It is a s s i m i l a t e d b y m o s t b a c t e r i a as w e l l as b y a l g a e a n d o t h e r p l a n t s in t h e form of s u l p h a t e , w h i c h t h e n u n d e r g o e s an a s s i m i l a t o r y r e d u c t i o n via s u l p h i t e to s u l p h i d e , w h i c h is u l t i m a t e l y transferred to a m i n o acids as s u l p h y d r y l g r o u p s (Siegel 1975). T h e r e d u c e d o r g a n i c s u l p h u r is a g a i n r e l e a s e d i n t o t h e e n v i r o n m e n t after t h e d e a t h a n d d e c o m p o s i t i o n of t h e o r g a n i s m s ( J 0 r g e n s e n 1983).

T h e a s s i m i l a t o r y s u l p h u r t r a n s f o r m a t i o n s in living o r g a n i s m s c r e a t e a c y c l e b e t w e e n i n o r g a n i c and o r g a n i c states of sulphur. In addition, s o m e b a c t e r i a c a n also p e r f o r m a d i s s i m i l a t o r y m e t a b o l i s m of s u l p h u r c o m p o u n d s . T h e s e o r g a n i s m s i n c o r p o r a t e o n l y a s m a l l fraction of t h e m e t a b o l i z e d s u l p h u r into t h e cells, a n d m o s t of t h e s u l p h u r is u s e d in e n e r g y m e t a b o l i s m as an e l e c t r o n a c c e p t o r or d o n o r in a m a n n e r that is similar t o t h e w a y o x y g e n is u s e d in a e r o b i c o r g a n i s m s ( J 0 r g e n s e n 1 9 8 3 ; C h a p m a n 2 0 0 1 ) . S o m e s p e c i a l i z e d b a c t e r i a p e r f o r m s u l p h a t e r e s p i r a t i o n a n d r e l e a s e s u l p h i d e . O t h e r s r e o x i d i z e t h e s u l p h i d e , either p h o t o t r o p h i c a l l y w i t h C 02 or c h e m o t r o p h i c a l l y w i t h 02

or N O ^ ( J 0 r g e n s e n 1 9 8 3 ; K i l l o p s and K i l l o p s 1 9 8 4 ) . In c o m b i n a t i o n , all t h e s e different o r g a n i s m s drive t h e s u l p h u r c y c l e of e c o s y s t e m s .

T h e m i c r o b i a l s u l p h u r c y c l e b e g i n s w i t h t h e s u l p h a t e i n p u t into t h e o c e a n s or p a l u s t r i n e - l a c u s t r i n e e n v i r o n m e n t s t h a t is i n c o r p o r a t e d into t h e t r o p h i c c h a i n b y a n a e r o b i c s u l p h a t e - r e d u c i n g b a c t e r i a (Desulphovibrio sp. and

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Table 2. Correlation coefficients (R) between the relative percentages of C27 , C29 and C3i n-alkanes for Villamanrique core

% c2 9 % C3 1 % c2 7 -0.1844 -0.9070 p = 0.378 p = 0.000 % c2 9 -0.5811 p = 0.002 p: significant level. 5.05 m t h e v a l u e s a r e a l m o s t c o n s t a n t , e x c e p t for t h e m a x i m u m in s a m p l e V M - 1 2 3 0 , w h i l e in t h e u p p e r m o s t 5 m t h e variations are very m a r k e d .

T o e x a m i n e t h e r e l a t i o n s h i p b e t w e e n the relative p e r c e n t a g e s of C2 7, C2 9 a n d C3l n - a l k a n e s a m u l t i v a r i a t e a n a l y s i s w a s p e r f o r m e d (Table 2), s h o w i n g a s t r o n g n e g a t i v e c o r r e l a t i o n coefficient b e t w e e n n - C2 7 a n d n - C3 ] p e r c e n t a g e s , reflecting different o r g a n i c m a t t e r inputs in the V i l l a m a n r i q u e area. T h i s i n d i c a t e s that w h e n t h e h e r b a c e o u s v e g e t a t i o n i n c r e a s e d in this area it w a s a c c o m p a n i e d with a similar d e c r e a s e of d e c i d u o u s trees (high % n - C3 1 a n d l o w % n - C2 7) and vice-versa. T h e p e r c e n t a g e of the n - C2 9 a l k a n e s h o w s a n e g a t i v e c o v a r i a n c e with t h e p e r c e n t a g e of t h e n - C3 1 h o m o l o g u e . A l t h o u g h the p r e v a l e n c e of fluvial-derived o r g a n i c m a t t e r detritus is interpreted a l o n g t h e V i l l a m a n r i q u e c o r e , the results can be related t o t h e p a l a e o e n v i r o n m e n t a l evolution b e c a u s e t h e c a t c h m e n t area of t h e G u a d i a m a r R i v e r is small and t h e originally p l a n t r e m a i n s t r a n s p o r t e d by t h e river c o m e from t h e s a m e c l i m a t i c region, that is, with t h e s a m e kind of v e g e t a t i o n .

F i g u r e 6d s h o w s slight variations from t h e b o t t o m of the c o r e to 5.05 m , with values for the C2 7 n - a l k a n e r a n g i n g f r o m 1 2 % t o 1 8 % and values for t h e n - C3 1 h o m o l o g u e b e t w e e n 4 0 % a n d 4 5 % . Values for n - C2 9 are similar to t h o s e for n - C3 1, s u g g e s t i n g a p r e d o m i n a n c e of p i n e and g r a s s - v e g e t a t i o n . T h e s e results c o i n c i d e with t h e p o l l e n a n a l y s i s p e r f o r m e d for t h e M a r i - L o p e z (cf. Z a z o et al. 1999; Yll et al. 2 0 0 3 ) a n d M a r i s m i l l a s (Yll et al. 2 0 0 3 ) b o r e h o l e s , drilled in t h e D o n a n a N a t i o n a l Park, in w h i c h t h e r e are m o n o t o n o u s arboreal p o l l e n / n o n - a r b o r e a l p o l l e n values d u r i n g m o s t of t h e H o l o c e n e (until 2.15 m ) , s u g g e s t i n g a stable l a n d s c a p e p h y s i o g n o m y . F u r t h e r m o r e , h e r b a c e o u s taxa a n d s m a l l s h r u b s a r e m u c h m o r e a b u n d a n t than trees, Pinus a n d Quercus b e i n g t h e o n l y o n e s with a significant i m p o r t a n c e .

S a m p l e s V M - 9 5 0 , V M - 8 0 0 a n d V M - 6 5 0 c a n b e h i g h l i g h t e d b e c a u s e t h e p e r c e n t a g e of n - C3 ] rises, d i m i n i s h i n g b o t h n - C2 7 a n d n - C2 9 values, w h i c h is i n t e r p r e t e d as an i n c r e a s e on h e r b s at t h e e x p e n s e of o t h e r k i n d s of p l a n t s and, in o u r o p i n i o n , reflects dry e p i s o d e s . L i k e the variations in o t h e r p r o x i e s , s a m p l e s V M - 1 8 4 0 , 1230 and 5 0 5 constitute an e x c e p t i o n , b e c a u s e the v a l u e for t h e n - C2 7 is over 2 0 % and the n - C3 ! p e r c e n t a g e d e c r e a s e s similarly. T h i s s u g g e s t s a relative rise in rainfall, resulting in t h e d e v e l o p m e n t of d e c i d u o u s trees.

In c o n t r a s t with t h e p r e c e d i n g interval, in the u p p e r m o s t 5 m t h e r e are i m p o r t a n t oscillations in t h e relative p e r c e n t a g e s of n - a l k a n e s ( F i g u r e 6 d ) . F r o m 5.05 to 4 . 5 0 m {ca. 6.0 to 5.9 k a c a l . B.P.) t h e m o s t i m p o r t a n t c o l o n i z a t i o n of g r a s s v e g e t a t i o n w a s p r o d u c e d ( n - C3, % m a x i m u m ) , t o g e t h e r with a d e c l i n e in d e c i d u o u s tree a s s e m b l a g e s ( 9 % of n - C2 7) , w h i c h i n d i c a t e s dry c o n d i t i o n s a n d c o i n c i d e s with t h e e n d of t h e p o s t - g l a c i a l t r a n s g r e s s i o n m a x i m u m ( Z a z o et al. 1994; B o r r e g o et al. 1999; D a b r i o et al. 2 0 0 0 ) .

B e t w e e n 4 . 5 0 and 3.40 m (ca. 5.9 t o 5.2 k a cal. B.P.) t h e r e is a slight d e c r e a s e in % n - C3, , t o g e t h e r with a r e c o v e r y of the % C2 7 n - a l k a n e , p r o b a b l y l i n k e d to a rise in precipitation. T h i s is followed by a d e c r e a s e in t h e C2 7 n - a l k a n e to 7 . 8 % in 2.85 m (ca. 4.2 k a cal. B.P.), reflecting dry c o n d i t i o n s ; this c o i n c i d e s with the p a l a e o e n v i r o n m e n t a l i n t e r p r e t a t i o n of Yll et al. ( 2 0 0 3 ) b a s e d on p o l l e n analysis of t h e D o n a n a N a t i o n a l P a r k b o r e h o l e s .

A t 1.95 m (ca. 2.5 k a cal. B.P.) an i m p o r t a n t i n c r e a s e in n - C2 7, u p t o 3 3 % , o c c u r s , with 2 7 % n - C3 1, w h i c h suggests a s h a r p c h a n g e in the e n v i r o n m e n t a l c o n d i t i o n s , p r o b a b l y l i n k e d t o an a u g m e n t a t i o n of p r e c i p i t a t i o n s , w h i c h p r o d u c e d a significant d e v e l o p m e n t of d e c i d u o u s trees.

S a m p l e V M - 1 0 0 (ca. 0.7 k a c a l . B.P.) is unusual in that the C2 9 n - a l k a n e contributes 8 3 % , w h e r e a s n - C2 7 is around 4 % a n d n - C3 ] is 1 3 % , w h i c h indicates an i m p o r t a n t d e v e l o p m e n t of conifers paralleled by a decline in d e c i d u o u s trees. In the M a r i L o p e z b o r e h o l e Z a z o et al. (1999) o b s e r v e d in the t o p m o s t 2.15 m an increase in h e r b a c e o u s t a x a

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a n d the progressive substitution of Quercus b y Juniperus a n d Pinus, w h i c h they interpret as the i m p a c t of h u m a n p o p u l a t i o n s . T h e values obtained in s a m p l e V M - 6 5 suggest m o r e h u m i d c o n d i t i o n s . In general, w e o b s e r v e d that s a m p l e s with h i g h e r p e r c e n t a g e s of t h e C2 7 n - a l k a n e p r e s e n t h i g h e r P a q index values t h a n the general trend, both

indicating h i g h e r w a t e r availability in the area.

T h e d i s t r i b u t i o n of n - k e t o n e s o b s e r v e d in s e a g r a s s - d e r i v e d o r g a n i c m a t t e r ( H e r n a n d e z et al. 2 0 0 1 ) w a s not f o u n d in V i l l a m a n r i q u e c o r e s e d i m e n t s . N o r w e r e t h e n - k e t o n e profiles of a l g a e , e m e r g e n t a n d s u b m e r g e n t p l a n t s s h o w n b y W e n c h u a n et al. ( 1 9 9 9 ) d e t e c t e d i n o u r c h r o m a t o g r a m s . L i k e w i s e , the l o n g - c h a i n ( C 3 7 - C 4 0 ) u n s a t u r a t e d m e t h y l a n d e t h y l k e t o n e s , w h i c h are m a i n l y p r o d u c e d b y h a p t o p h y t e m i c r o a l g a e in m a r i n e w a t e r s ( V o l k m a n et al. 1980, 1 9 9 5 ; R e c h k a a n d M a x w e l l 1988) a n d in coastal a n d terrestrial h a b i t a t s ( M a r l o w e et al. 1984; C o n t e et al. 1994) w e r e n o t found.

In a n y c a s e , t h e C P I v a l u e s of n - a l k a n e s a n d n - k e t o n e s s h o w s i m i l a r t r e n d s ( F i g u r e 4 a , b ) . O n l y in t h r e e c a s e s ( 6 . 5 , 8.0 a n d 15.5 m ) t h e r e is a m i s m a t c h , in t h e form of a h i g h i n c r e a s e in t h e k e t o n e C P I v a l u e s , w h i c h w a s , in o u r o p i n i o n , d u e t o m i c r o b i a l o x i d a t i o n a n d d e c a r b o x y l a t i o n of n-fatty a c i d s . Similarly, t h e p r e d o m i n a n t n - k e t o n e c h a i n profile is s i m i l a r to t h e n - a l k a n e o n e ( F i g u r e 5 a , b ) , this i n d i c a t i n g the possibility of m i c r o b i a l o x i d a t i o n of n - a l k a n e s , w h i c h h a d their o r i g i n in terrestrial p l a n t s , y i e l d i n g the c o r r e s p o n d i n g k e t o n e s .

T h e p r e d o m i n a n t n - a l k a n o l c h a i n log ( F i g u r e 5c) i n d i c a t e s a major i n p u t of land p l a n t s ( E g l i n t o n a n d H a m i l t o n , 1967; R i e l e y et al. 1991), w h i c h is r e i n f o r c e d b y t h e s i m i l a r p a t t e r n s f o u n d in t h e n - k e t o n e a n d n - a l k a n e profiles ( p r e d o m i n a n t n - a l k a n e a n d n - k e t o n e c h a i n s , n - a l k a n e l o n g - c h a i n / s h o r t - c h a i n r a t i o , T A RHc > F i g u r e 5 a , b ; 6 a , b ) .

In c o n t r a s t , t h e i n t e r p r e t a t i o n of the p r e d o m i n a n t n - a l k a n o i c acid c h a i n s ( F i g u r e 5 d ) a n d T A RF A ratio

( F i g u r e 6 e , l o w values) d o e s not c o r r o b o r a t e the i n f o r m a t i o n o b t a i n e d from t h e T A RHc i n d e x a n d o t h e r p r o x i e s

a l t h o u g h t h e y all p r o v i d e , at least in theory, t h e s a m e i n f o r m a t i o n a b o u t o r g a n i c m a t t e r o r i g i n . T h u s , t h e r e is a p o o r c o v a r i a n c e b e t w e e n t h e i n f o r m a t i o n p r o v i d e d b y t h e n - a l k a n e s , n - k e t o n e s a n d n - a l k a n o l s a n d that o b t a i n e d from t h e n - a l k a n o i c acid profiles (see F i g u r e 5 a - d ; F i g u r e 6 b , e ) . In fact, t h e n - a l k a n o i c a c i d p r e d o m i n a n t c h a i n - l o g s h o w s m a x i m a in e i t h e r l o w o r h i g h m o l e c u l a r w e i g h t h o m o l o g u e s ( F i g u r e 5 d ) . In all c a s e s , short c h a i n n - a l k a n o i c a c i d s are p r e s e n t t o g e t h e r w i t h l o n g - c h a i n n - a l k a n o i c a c i d s ( C 2 4- C 3 0 ) in t h e s a m e c h r o m a t o g r a m s , t h e latter i n d i c a t i n g land p l a n t i n p u t s . Similarly, w h e n t h e C26 a n d C28 i s o m e r s are p r e d o m i n a n t , short c h a i n n - a l k a n o i c a c i d s are also

p r e s e n t . In o u r o p i n i o n this l a c k of c o r r e s p o n d e n c e c a n b e d u e t o t h e g r e a t e r lability of n - a l k a n o i c a c i d s to d e g r a d a t i o n a n d m o d i f i c a t i o n t h a n o t h e r lipid b i o m a r k e r s , s u c h as n - a l k a n e s ( M e y e r s a n d E a d i e 1993). In fact, t h e y are usually m o r e useful as i n d i c a t o r s of the a m o u n t s of o r g a n i c m a t t e r r e c y c l i n g in lake s e d i m e n t s t h a n as r e c o r d e r s of t h e original s o u r c e s of o r g a n i c matter.

In brief, t h e difference b e t w e e n t h e profiles of n - a l k a n e s a n d n - a l k a n o i c a c i d s ( F i g u r e 5 a , d ) p r o b a b l y reflects a c o m b i n a t i o n of c o n t i n u a l m i c r o b i a l d e g r a d a t i o n a n d r e s y n t h e s i s of fatty a c i d s in t h e s e d i m e n t a n d p a r t i a l r e p l a c e m e n t of o r i g i n a l l y d e p o s i t e d fatty a c i d s b y s e c o n d a r y , m i c r o b i a l fatty a c i d s (Tenzer et al. 1999; X i e et al. 2 0 0 3 ) , a n d usually p r o d u c e s a p r e d o m i n a n c e of s h o r t - c h a i n c o m p o n e n t s ( K a w a m u r a et al. 1987).

T h e organic sulphur log (Figure 7a) indicates the existence of t w o m a i n zones in the core, from ca. m e t r e 5 to the b o t t o m of the core with p r e s e n c e of organic sulphur, and the u p p e r m o s t part, l a c k i n g this c o m p o u n d . A s o n e of the m a i n r e q u i r e m e n t s for the activity of the sulphate-reducing bacteria is the p r e s e n c e of sulphate ions, together with r e d u c i n g conditions (J0rgensen 1 9 8 3 ; B o n d e a u a n d Westrich, 1984), w e interpret the h u g e d r o p o b s e r v e d in the u p p e r m o s t 5 m as the transition from m a r i n e to freshwater conditions in this area c a u s e d b y the p r e d o m i n a n c e of fluvial input, that is, with a lower sulphate supply, bacterial sulphate reduction, should d e c r e a s e in an i m p o r t a n t way.

In fact, B a t e s et al. ( 1 9 8 4 ) i n t e r p r e t e d c h a n g e s in s u l p h u r c o n t e n t w i t h d e p t h in c o r e s f r o m the E v e r g l a d e s ( F l o r i d a ) as c h a n g e s in s u l p h u r l o a d i n g over t i m e , w h i c h in t u r n , d e p e n d m a i n l y o n the d i s s o l v e d s u l p h a t e c o n t e n t input, b u t also o n t h e m i c r o b i a l activity a n d r e d o x p o t e n t i a l (Berner, 1984). T h i s m i g h t also i n d i c a t e the e x i s t e n c e of a relatively i m p o r t a n t w a t e r c o l u m n , p r o d u c i n g stratification w i t h a p r e v a l e n c e of a n o x i c c o n d i t i o n s , f r o m the b o t t o m of t h e c o r e to 3.40 m , w i t h t h e e x c e p t i o n of s a m p l e S V M - 5 0 5 . A c c o r d i n g to C a b r e r a et al. ( 2 0 0 2 ) , a h i g h s u l p h u r c o n t e n t in s e d i m e n t s reflects a very active s u l p h u r c y c l i n g w h i c h is m a i n l y r e l a t e d t o s u l p h a t e - r e d u c i n g b a c t e r i a , b u t also involves a n a e r o b i c p h o t o s y n t h e t i c s u l p h u r b a c t e r i a and, t h e r e f o r e , r e d u c i n g c o n d i t i o n s .

In o u r o p i n i o n , the o r g a n i c s u l p h u r c o n t e n t of the V i l l a m a n r i q u e b o r e h o l e ( F i g u r e 7 a ) is a g o o d r e l i a b l e p r o x y for reflecting fluvial input a n d the o x i c / a n o x i c c o n d i t i o n s .

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Wang X-C, Chen RF, Berry A. 2003. Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain

n-alkanes and stable carbon isotope compositions. Estuarine, Coastal and Shelf Science 58: 917-928.

Wenchuan Q, Dickman M, Sumin W, Ruijin W, Pingzhong Z, Jianfa C. 1999. Evidence for an aquatic plant origin of ketones found in Taihu Lake sediments. Hydrobiologia 397: 149—154.

Xie S, Lai X, Yi Y, Gu Y, Liu Y, Wang X, Liu G, Liang B. 2003. Molecular fossils in a Pleistocene river terrace in southern China related to paleoclimate variation. Organic Geochemistry 34: 789-797.

Yll R, Zazo C, Goy JL, Perez-Obiol R, Pantaleon-Cano J, Civis J, Dabrio C, Gonzalez A, Borja F, Soler V, Lario J, Luque L, Sierro F, Gonzalez-Hernandez FM, Lezine AM, Denefle M, Roure JM. 2003. Quaternary palaeoenvironmental changes in south Spain. In

Quaternary Climatic Changes and Environmental Crises in the Mediterranean Region, Ruiz Zapata MB, Dorado Valino M, Valdeolmillos

Rodriguez A, Gil Garcia MJ, Bardaji Azcarate T, De Bustamante Gutierrez I, Martinez Mendizabal I (eds). Universidad de Alcala de Henares: Alcala de Henares; 201-213.

Yuan F, Linsley BK, Howe SS, Lund SP, McGeehin JP. 2006. Late Holocene lake-level fluctuations in Walker Lake, Nevada, USA.

Palaeogeography, Palaeoclimatology, Palaeoecology 240: 497—507.

Zazo C, Goy JL, Somoza L, Dabrio CJ, Belluomini G, Improta S, Lario J, Bardaji T, Silva PG. 1994. Holocene sequence of sea-level fluctuations in relation to climatic trends in the Atlantic-Mediterranean linkage coast. Journal of Coastal Research 10: 9 3 3 - 9 4 5 . Zazo C, Dabrio CJ, Gonzalez A, Sierro F, Yll EI, Goy J L , Luque L, Pantaleon-Cano J, Soler V, Roure J M , Lario J, Hoyos M, Borja

F. 1999. The record of the latter glacial and interglacial periods in the Guadalquivir marshlands (Mari Lopez drilling, S.W. Spain). Geogaceta

26: 119-122.

Zhang Z, Zhao M, Yang X, Wang S, Jiang X, Oldfield F, Eglinton G. 2004. A hydrocarbon biomarker record for the last 40 kyr of plant input to Lake Heqing, southwestern China. Organic Geochemistry 35: 595-613.

References

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