Reconstruction of the environmental history of a coastal insular system using shallow marine records: the last three millennia of the Cíes Islands (Ría de Vigo,NWIberia)

Abstract

The coastal lagoon‐beach complex at the Cíes Islands located at the opening of the Ría de Vigo (NW Iberia) is an important ecosystem currently threatened by anthropogenic impacts and climate variations. We used multiproxy marine sediment analyses to reconstruct the millennial environmental dynamics of this insular system and, in particular, the recent history of its coastal lagoon. Geophysical surveys were used to obtain bathymetry and identify the major sedimentary units of its closest submarine basin as well as their sediment sources. Core samples were taken in the middle and distal parts of the sedimentary body, where several prograding sedimentary units are thinner, allowing continuous sampling of the facies. Lithological, textural, elemental and chronological analyses were carried out on two cores. The detailed palynological studies on one of the cores included the analyses of the pollen, non‐pollen palynomorphs and dinocysts dating back three millennia. Our results revealed noticeable environmental changes affecting this area during the last 3000 years, due mainly to changing climate and oceanic conditions but also to the impact of historic human occupation of the islands. Several cold events (the 2.8 ka BP event and the Little Ice Age) characterized by enhanced upwelling alternated with warmer stormy periods of prevailing downwelling conditions in the ria. These circumstances altered the balance amongst the lacustrine, marsh, dune and lagoon systems, opening ephemeral inlets and modifying the trophic stage of the shallow waters surrounding the archipelago. Here we provide a background of the human and climatic impacts affecting these highly sensitive habitats, which may serve to improve their future management strategies.

Recent Evolution (1956–2017) of Rodas Beach on the Cíes Islands, Galicia, NW Spain

“…The most important changes in the Rodas system occurred between 1956 and 1981, during which the net retreat exceeded 30 m in the north and south sectors. This led to the appearance of an inlet in the northern part of Rodas that connects the lagoon with the sea during winter storms, while the inlet that formed up until the 1950s in the southern sector disappeared gradually [37]. The differences in this period are primarily due to the human activities in the area, such as sand extraction [43].…”

“…These works do not include the last decade of information. A historical reconstruction of the system was recently conducted using marine records [37]. Other studies have investigated the influence of wildlife on the ecosystems of the archipelago [38][39][40], mainly focusing on the impacts of seagull colonies on the soil and vegetation.…”

Aeolization on the Atlantic coast of Galicia (NW Spain) from the end of the last glacial period to the present day: Chronology, origin and evolution of coastal dunes linked to sea‐level oscillations

“…Generally, the local record is characterized by the absence of suitable absolute ages or the lack of detailed sedimentological and/or micropaleontological studies (Mosquera‐Santé, 2000) that would allow a more precise description of the evolution of this coast. The abundant literature during the last three decades (Durán, 2005; García‐Gil et al, 1999, 2020; García‐Moreiras et al, 2019; Méndez & Vilas, 2005; Muñoz‐Sobrino et al, 2016; Rey‐Salgado, 1993) has not provided significant progress. Stratigraphic sequences from the marine drillings (by vibrocorer or gravity) on the surface of the continental shelf and the seabed of the Galician Rias (Figure 1) have not achieved an understanding of the coastal evolution during glacio‐eustatic variations.…”

“…Stratigraphic sequences from the marine drillings (by vibrocorer or gravity) on the surface of the continental shelf and the seabed of the Galician Rias (Figure 1) have not achieved an understanding of the coastal evolution during glacio‐eustatic variations. This is due to the interpretation of isolated data (Costas et al, 2009; González‐Villanueva et al, 2015) or misunderstanding continental deposits (aeolian and/or fluvial) with marine sediments (Cartelle, 2018; Martínez‐Carreño et al, 2017; Muñoz‐Sobrino et al, 2016). Furthermore, when an aeolian origin has been admitted for coastal sand that today remains totally or partially flooded (Costas et al, 2009; Mohamed et al, 2010), the requirement for extensive emerged areas covered with sand (which can be mobilized by wind) is ignored.…”

Holocene environmental change on the Atlantic coast of NW Iberia as inferred from the Ponzos wetland sequence

“…Only the palynological sequence of Area Longa covers the last glacial (G omez-Orellana et al 2007). A number of pollen sites record different periods of the MIS 3 (Nonn 1966;Mary et al 1977;Granja & De Groot 1996;G omez-Orellana et al 2007G omez-Orellana et al , 2013; and other groups of sites record the second half or the last third of the Holocene (Santos et al 2001;Garc ıa Anton et al 2006;Bao et al 2007;Costas et al 2009;Granja et al 2010Granja et al , 2016G omez-Orellana et al 2014;Muñoz Sobrino et al 2016;S aez et al 2018). Finally, pollen sequences recording the Lateglacial or the beginning of the Holocene are limited to the deposits of Moug as (G omez-Orellana et al 1998) and Urdaibai (Iriarte Chiapusso et al 2006).…”