Temporal variability of flooding events of Guadiana River (Iberian Peninsula) during the middle to late Holocene: Imprints in the shallow-marine sediment record

https://doi.org/10.1016/j.palaeo.2020.109900Get rights and content

Highlights

  • Flooding events recorded in a shallow marine sediment core over the last 5800 years

  • High fine-grained sediment inputs under flood events and humid conditions

  • Low input of terrigenous sediments under dry conditions

  • NAO influenced sediment supply during the last 500 years at centennial scales

  • Increase flooding events during the LIA along the Atlantic Iberian Peninsula margin

Abstract

Sedimentological, geochemical and benthic foraminiferal proxies were used to interpret changes of depositional environments in a mud entrapment inside the Guadiana River paleo-valley, northern Gulf of Cadiz, to understand the temporal variability of fluvial flooding events and to detect patterns of latitudinal climatic variability in western Iberia.

The period between ca. 5800 and ca. 1250 cal yr BP was characterized by slowly accumulating coarse-grained sediments, high content of biogenic sand components, and high abundances of shallow-water benthic foraminiferal species. After ca. 1250 cal yr BP, the sedimentary environment was dominated by fine-grained sediments, with high abundances of opportunistic benthic foraminiferal species and successful colonizers, and high values of geochemical ratios indicative of enhanced terrigenous supply. Sedimentation rates increased drastically over the last ca. 500 years.

The genesis of these environments was mainly driven by the variable frequency of fluvial flooding events driven by the regional climate variability. Low terrigenous sediment input under dry conditions prevailed in the older sedimentary unit. Flood frequency and terrigenous sediment supply increased during the younger unit. The variability of the North Atlantic Oscillation at centennial scales highly influenced the sediment supply during the last ca. 500 years, with high terrigenous supply during negative NAO conditions. Our results corroborate an N-S gradient along the Atlantic Iberia during middle and late Holocene, with more humid conditions in the northwestern and drier conditions towards the southeast. The gradient weakened over the past ca. 500 years, with increased rainfalls and flood events during the Little Ice Age.

Introduction

Holocene climatic fluctuations and associated changes in vegetation, ocean circulation and sedimentary environments exhibit a spatially variable pattern (Mayewski et al., 2004). A long-term cooling trend evidenced during the late Holocene in North Atlantic records (Marsicek et al., 2018) is associated to the southward shift of the Intertropical Convergence Zone that has promoted a progressive change of the North Atlantic Oscillation index (NAO) (Wanner et al., 2008). In this sense, the NAO has evolved from generally positive to variable or even negative values during the late Holocene (e.g. Trouet et al., 2009; Olsen et al., 2012). These changes have influenced long-term trends in atmospheric circulation and weather patterns, which in turn affected climatic variables such as regional patterns in temperature, rainfall and storm events (Toomey et al., 2013).

The influence of rainfall patterns on sediment production is very significant in fluvial drainage basins, with consequences for sediment transport to adjacent continental margins. Particularly, rainfall modifications affect the frequency and volume of river runoffs (Vallefuoco et al., 2012), associated flooding events (Sommerfield et al., 2002), and interfere with atmospheric processes of different intensities and periodicities, such as storms (Lesueur et al., 1996; Zhao et al., 2017). On the continental shelf, storms, major oceanographic reorganizations, or earthquakes may leave individual stratigraphic features in the geologic record (Gomez et al., 2007; Cosentino et al., 2017). The depositional signals of such interactions involve unconformities, gravity-driven mass flow, storm events, or drastic changes in sedimentation rates due to varying sediment supply. The latter process is ultimately recorded in the shelf depositional systems in the form of mud depocenters that can be exploited as high-resolution archives to reconstruct the climatic, oceanographic and geologic past (e.g. Walsh and Nittrouer, 2009; Gao and Collins, 2014; Bassetti et al., 2016; Penaud et al., 2020). These mud depocenters can extend over wide areas on a continental shelf (e.g. mudbelts), or can be locally confined by the preexisting physiography (e.g. mud entrapments; Hanebuth et al., 2015).

Depositional signals in shallow-water muddy depocenters may also be significantly altered by the onset of human occupation of the river basins, including the effect of diverse practices such as deforestation, forest firing, agriculture, mining and river damming (e.g. Chester and James, 1999; Boone and Worman, 2007; Gonzalez et al., 2007; Jabaloy-Sánchez et al., 2010; Chester, 2012; Mendes et al., 2015). These activities established an erosional regime in the drainage basins (Gomez et al., 2007) and led to a further imprint of flood events in the sedimentary shelf record (Sommerfield and Wheatcroft, 2007; Budillon et al., 2012).

The northern margin of the Gulf of Cadiz, located in southwest Iberian Peninsula, is a key area to understand spatial patterns of climatic variability between the Atlantic and Mediterranean. On the continental shelf off the Guadiana River (Fig. 1), late Holocene sedimentary formations can be considered as an outstanding paleoenvironmental archive of detailed temporal resolution (Mendes et al., 2010, Mendes et al., 2012a, Mendes et al., 2013; Rosa et al., 2011). The Guadiana River drains the southwestern Iberian Peninsula and therefore provides significant information about the transitional area between NW Atlantic and SW Mediterranean climates. Consequently, the goals of this study are: (1) to interpret changes in depositional environments in the area, which are directly influenced by the Guadiana River supplies; (2) to understand the influence of flooding events and other factors such as occurrence of storm events and recent anthropogenic actions on river supply patterns; (3) to compare the Guadiana record with those from other modern Iberian Atlantic depocenters to reveal latitudinal changes of the climatic variability during mid to late Holocene times.

Section snippets

Regional setting

The study area is located in the central part of the northern Gulf of Cadiz on the inner continental shelf (southwestern Iberian Peninsula) off the Guadiana River mouth (Fig. 1).

Material and methods

This study was based on a multi-proxy analysis of two sediment cores (GeoB19522-2 and GeoB19522-3), in order to reveal the recent infilling pattern of the main Guadiana River paleo-valley. The sediment cores were collected at site GeoB19522, at 17 m water depth (37°8′29.34” N, 7°16′46.8” W; Fig. 1), using an available high-resolution seismic profile that crossed the Guadiana River paleo-valley, during RV Poseidon cruise POS482 CADISED (Cadiz Shelf Sediment Depocentres), in March 2015 (Lantzsch

Overall architecture of the recent paleo-valley infilling phase

The seismo-acoustic profile collected across site GeoB19522 displays the Guadiana River paleo-valley and its sedimentary infill. The most recent valley erosional surface is related to the Last Glacial Maximum (LGM), whereas the most recent depositional unit is regarded as a mud entrapment (Fig. 1c). Core GeoB19522-3, located over the landward flank of the paleo-valley, penetrated almost the whole mud entrapment unit, approximately 4 m thick, and recorded two sub-parallel internal reflectors (

Depositional environments

During the last ca. 5800 cal yr BP two major depositional environments were identified, based on the combined analysis of various independent proxies. The lower Unit A extends from ca. 5800 to ca. 1300–1200 cal yr BP, whereas the upper Unit B extends from ca. 1300 to 1200 cal yr BP to the core top (Fig. 7).

Conclusions

Two major depositional environments have been distinguished in sediment core GeoB19522-3 recording the conditions since Holocene sea level highstand. This record was retrieved from a mud entrapment, which has formed in the drowned paleo-valley of the Guadiana River located on the adjacent shelf. Most of the middle to late Holocene (ca. 5800–1250 cal yr BP) times were characterized by low accumulation rates of coarse-grained sediment, high species richness, and high abundances of benthic

Funding

This study was made possible by the CADISED (Cadiz Shelf Sediment Depocentres) survey (MARUM research cruise POS482, Germany), and was also supported by projects UID/0350/2020 CIMA of the Portuguese Science Foundation (FCT) and CGL2011-30302-C02-02 and CTM2017-88237-P of the Spanish Ministry of Economy and Competitiveness. Isabel Mendes also thanks to FCT for Research Assistant contract DL57/2016/CP1361/CT0009.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank captain and crew of RV Poseidon for their professionalism during the research expedition CADISED. We acknowledge Margarida Ramirez (CIMA-UAlg) for technical support in grain size analyses, Rubens Cesar Lopes Figueira (LaQIMar) and Paulo Alves Ferreira (LaQIMar) for radionuclides (210Pb and 137Cs) results discussion. We also thank the reviewers Marc Hijma (Deltares) and an anonymous reviewer for their helpful and constructive comments.

References (139)

  • D.K. Chester

    Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal

    Geomorphology

    (2012)
  • C. Cosentino et al.

    Benthic foraminifera as indicators of relative sea-level fluctuations: Paleoenvironmental and paleoclimatic reconstruction of a Holocene marine succession (Calabria, south-eastern Tyrrhenian Sea)

    Quat. Int.

    (2017)
  • J.M. De la Rosa et al.

    Metal binding by humic acids in recent sediments from the SW Iberian coastal area

    Estuar. Coast. Shelf Sci.

    (2011)
  • J. Delgado et al.

    Analysis of the spatial variation of heavy metals in the Guadiana Estuary sediments (SW Iberian Peninsula) based on GIS-mapping techniques

    Estuar. Coast. Shelf Sci.

    (2010)
  • J. Delgado et al.

    Sea-level rise and anthropogenic activities recorded in the late Pleistocene/Holocene sedimentary infill of the Guadiana Estuary (SW Iberia)

    Quat. Sci. Rev.

    (2012)
  • P.-A. Dessandier et al.

    Variations in benthic foraminiferal assemblages in the Tagus mud belt during the last 5700 years: Implications for Tagus River discharge

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (2018)
  • P. Diz et al.

    Distribution of live benthic foraminifera in the Ría de Vigo (NW Spain)

    Mar. Micropaleontol.

    (2008)
  • M. Durand et al.

    Late Holocene record from a Loire River incised paleovalley (French inner continental shelf): insights into regional and global forcing factors

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (2018)
  • F. Frontalini et al.

    Benthic foraminifera for heavy metal pollution monitoring: a case study from the central Adriatic Sea coast of Italy

    Estuar. Coast. Shelf Sci.

    (2008)
  • S. Gao et al.

    Holocene sedimentary systems on continental shelves

    Mar. Geol.

    (2014)
  • J. García-Lafuente et al.

    The Gulf of Cádiz pelagic ecosystem: a review

    Prog. Oceanogr.

    (2007)
  • J. García-Lafuente et al.

    Water mass circulation on the continental shelf of the Gulf of Cádiz

    Deep Sea Res. II

    (2006)
  • E. Garel et al.

    Tidal and river discharge forcing upon water and sediment circulation at a rock-bound estuary (Guadiana estuary, Portugal)

    Estuar. Coast. Shelf Sci.

    (2009)
  • E. Garel et al.

    Decadal morphological response of an ebb-tidal delta and down-drift beach to artificial breaching and inlet stabilization

    Geomorphology

    (2014)
  • E. Garel et al.

    Characterisation of coastal counter-currents on the inner shelf of the Gulf of Cadiz

    J. Mar. Syst.

    (2016)
  • A. Goineau et al.

    Live (stained) benthic foraminifera from the Rhône prodelta (Gulf of Lion, NW Mediterranean): Environmental controls on a river-dominated shelf

    J. Sea Res.

    (2011)
  • R. Gonzalez et al.

    Sedimentological and paleoenvironmental characterisation of transgressive sediments on the Guadiana Shelf (Northern Gulf of Cadiz, SW Iberia)

    Quat. Int.

    (2004)
  • R. Gonzalez et al.

    Sediment and pollutant transport in the Northern Gulf of Cadiz: a multi-proxy approach

    J. Mar. Syst.

    (2007)
  • E. Gràcia et al.

    Holocene earthquake record offshore Portugal (SW Iberia): testing turbidite paleoseismology in a slow-convergence margin

    Quat. Sci. Rev.

    (2010)
  • J.M. Gutiérrez-Mas et al.

    Recent marine lithofacies in Cadiz Bay (SW Spain): sequences, processes and control factors

    Sediment. Geol.

    (2009)
  • T.J.J. Hanebuth et al.

    Hazard potential of widespread but hidden historic offshore heavy metal (Pb, Zn) contamination (Gulf of Cadiz, Spain)

    Sci. Total Environ.

    (2018)
  • A. Jabaloy-Sánchez et al.

    Human-driven coastline changes in the Adra River deltaic system, southeast Spain

    Geomorphology

    (2010)
  • H. Lantzsch et al.

    Holocene evolution of mid-shelf mud-belt depocentres on a high-energy, low-accumulation shelf (NW Iberia)

    Quat. Res.

    (2009)
  • J. Lario et al.

    Holocene palaeotsunami catalogue of SW Iberia

    Quat. Int.

    (2011)
  • P. Lesueur et al.

    Shelf mud fields formation within historical times: examples from offshore the Gironde estuary, France

    Cont. Shelf Res.

    (1996)
  • F.J. Lobo et al.

    The sedimentary record of the post-glacial transgression on the Gulf of Cadiz continental shelf (Southwest Spain)

    Mar. Geol.

    (2001)
  • F.J. Lobo et al.

    Contrasting styles of the Holocene highstand sedimentation and sediment dispersal systems in the northern shelf of the Gulf of Cadiz

    Cont. Shelf Res.

    (2004)
  • M.M. de Mahiques et al.

    A high-resolution Holocene record on the Southern Brazilian shelf: Paleoenvironmental implications

    Quat. Int.

    (2009)
  • V. Martins et al.

    Tracing the late Holocene evolution of the NW Iberian upwelling system

    Mar. Micropaleontol.

    (2006)
  • V. Martins et al.

    Sedimentary processes on the NW Iberian Continental Shelf since the Little Ice Age

    Estuar. Coast. Shelf Sci.

    (2012)
  • P.A. Mayewski et al.

    Holocene climate variability

    Quat. Res.

    (2004)
  • I. Mendes et al.

    Factors influencing recent benthic foraminifera distribution on the Guadiana shelf (Southwestern Iberia)

    Mar. Micropaleontol.

    (2004)
  • I. Mendes et al.

    Inner shelf paleoenvironmental evolution as a function of land-ocean interactions in the vicinity of the Guadiana River, SW Iberia

    Quat. Int.

    (2010)
  • I. Mendes et al.

    Living, dead and fossil benthic foraminifera on a river dominated shelf (northern Gulf of Cadiz) and their use for paleoenvironmental reconstruction

    Cont. Shelf Res.

    (2013)
  • I. Mendes et al.

    Multi-proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the Adra River, southeast Iberian Peninsula

    Estuar. Coast. Shelf Sci.

    (2015)
  • M. Mil-Homens et al.

    Footprint of roman and modern mining activities in a sediment core from the southwestern Iberian Atlantic shelf

    Sci. Total Environ.

    (2016)
  • Y. Milker et al.

    Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea

    Mar. Micropaleontol.

    (2009)
  • J.A. Morales

    Evolution and facies architecture of the mesotidal Guadiana River delta (S.W. Spain-Portugal)

    Mar. Geol.

    (1997)
  • A. Moreno et al.

    The Medieval Climate Anomaly in the Iberian Peninsula reconstructed from marine and lake records

    Quat. Sci. Rev.

    (2012)
  • J. Moreno et al.

    Foraminiferal evidence of major environmental changes driven by the sun-climate coupling in the western Portuguese coast (14th century to present)

    Estuar. Coast. Shelf Sci.

    (2019)
  • Cited by (10)

    View all citing articles on Scopus
    View full text