Salinity and water temperature assessment of the tidal marshes from the W Portuguese coast, as an ecological tool to palaeoenvironmental reconstructions based on Foraminifera and Ostracoda assemblages
A seasonal study of temperature and salinity of estuarine and sediment interstitial water of tidal marshes was undertaken along three estuaries of W Portuguese coast (Minho, Tejo and Mira).The climatic N-S transition from wet Atlantic to Mediterranean features appear clearly imprinted in the distribution of tidal marsh assemblages, like foraminifera and ostracoda, mainly reflecting the water salinity gradient control.The Minho low estuary tidal marsh tends to be flooded by estuarine water ranging from 0.5‰ to 32‰ in each tide cycle, even during dry seasons. However, the marsh hydrological balance sustains a more stable environment where the salinity of interstitial water measurements yielded 8‰ to 16‰. In contrast the Tejo and Mira salt marsh flooding waters record a narrow range between 33‰ and 36‰, in spring, and between 29‰ and 36‰ in autumn. The climatic control of evaporation/ precipitation balance produces an enhanced salinity of marsh interstitial water, that can reach hypersaline conditions, with maximum records of 53‰ in Tejo and 48‰ in Mira lower estuaries.These environmental differences along the W Portuguese coast are recorded by the tidal marsh assemblages, namely foraminifera and ostracoda. In the low salinity Caminha salt marsh, living foraminifera are essentially composed by the agglutinated species Haplophragmoides manilaensis, Miliammina fusca, Pseudothurammina limnetis Psammosphaera sp. and Trochamminita salsa. The modern ostracoda assemblage includes Leptochytere baltica, Leptochytere psammophila, Leptocythere sp. A and Tuberoloxoconcha sp.1. In the Tejo and Mira salt marsh Ammonia beccarii, Ammonia tepida, Haynesina germanica, Jadammina macrescens, Trochammina inflata, are the dominant foraminifera and Loxoconcha malcomsoni, Terrestricythere cf. elisabethae, Tuberoloxoconcha cf. atlantica and Xestoleberis labiata prevail as well as many other more marine ostracoda species, such as Basslerites teres and Leptocythere fabaeformis.This study highlights that the knowledge of driven ecological parameters of modern assemblages (usually preserved in fossil record), is fundamental to support reliable paleoclimatic and palaeoenvironmental reconstructions.
Copyright (c) 2016 Estudos do Quaternário / Quaternary Studies
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