HOLOCENE ENVIRONMENTAL CHANGES ON THE ALGARVE COAST: A DIATOM-BASED STUDY

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Modern diatom assemblages as tools for paleoenvironmental reconstruction: a case study from estuarine intertidal zones in southern Iberia

Publication . Gomes, Ana; Boski, T.; Moura, Delminda; Szkornik, Katie; Witkowski, Andrzej; Connor, Simon; Laut, Lazaro; Sobrinho, Frederico; Oliveira, Sónia

Diatoms are unicellular algae that live in saline, brackish and freshwater environments, either floating in the water column or associated with various substrates (e.g., muddy and sandy sediments). Diatoms are sensitive to changes in environmental variables such as salinity, sediment texture, nutrient availability, light and temperature. This characteristic, along with their short lifespan, allows diatoms to quickly respond to environmental changes. Since the beginning of the 20th century, diatoms have been widely used to study the Holocene evolution of estuaries worldwide, particularly to reconstruct ecological responses to sea-level and climate changes. However, diatoms have been poorly studied in estuarine intertidal zones, due to the complexity of these environments, which have both fluvial and marine influences.

2017Conference object

Open access

O registo de diatomáceas e foraminiferos da Ria Formosa (Sul da Península Ibérica): uma contribuição para a compreensão da evolução Holocénica do sistema lagunar.

Publication . Gomes, Ana; Pereira, Laura; Boski, T.; Connor, Simon; Mendes da Silva de Sousa, Carlos A; Oliveira, Sónia; Santana, Paulo

As part of a multi-proxy study to reconstruct the Holocene evolution of the Ria Formosa Lagoon, diatom and foraminifera assemblages were analyzed in a ca. 24.6-m-deep borehole, which crossed the entire infill sequence of the local paleovalley. Except in a few samples, diatom assemblages were generally poorly preserved, whereas foraminiferal assemblages were mostly well preserved. In the core depths interval from 23.5 and 3.2 m, both proxies indicate a marine environment installed during the progressive flooding of the fluvial valley during the Holocene. Above 3.2-m, both proxies

2013Conference object

Open access

The Holocene history of the Guadiana estuary as told by diatoms and chrysophyte cysts

Publication . Gomes, A.I.; Boski, T.; Moura, Delminda; Szkornik, Katie; Connor, Simon; Witkowski, Andrzej

In order to tell the history of the Guadiana Estuary since the Last Glacial Maximum, a core collected therein, and spanning more than 13200 cal. years B.P., was studied regarding its diatom and chrysophyte cyst fossil records. Additionally, a diatom-based transfer function was used to reconstruct paleo-salinity and paleo-duration of tidal inundation to better understand the estuary’s evolution in relation to sea-level rise and climate changes. This study identifies some important climatic events, such as the Allerød climatic optimum, the Younger Dryas and three dry and cold events at 10600, 9100 and 7600 cal. years B.P., most of which were not identified by other proxies. Moreover, it also revealed that, prior to 13200 cal. years B.P., there was a mudflat environment in the place where the core was collected, consistent with an estuary slightly confined in the narrow valley under marine/tidal influence. Afterwards, this environment evolved into a salt marsh. The strongest marine influence was inferred to the period between 10000 and 7000 cal. years B.P., embracing a phase of rapid sea-level rise, non compensated by sedimentation, that favored the development of a mudflat. From this period onwards, diatom assemblages seem to indicate an evolution to a more enclosed environment, probably similar to the actual configuration of the area.

2015-09Conference object

Open access

A new diatom species from a transitional environment (Arade river estuary, Portugal): Tetramphora witkowskii sp. nov.

Publication . Gomes, Ana; Hamilton, Paul Brian; Solak, Cüneyt Nadir; Boski, Tomasz; Moura, Delminda; Ertorun, Nesil; Yedidağ, Ferhan

Due to the environmental complexity created by physical and chemical gradients, transitional biomes host a large biological diversity. There has been some effort to better understand the diversity of diatoms living in these transitional environments, although many diatom species remain undescribed from these habitats. Gathering this knowledge will significantly improve our ability to halt biodiversity loss due to anthropogenic activities and assess individual water bodies' ecological status. More detailed studies on diatoms from transitional environments will also further enhance the research that uses them as proxies to reconstruct past environmental changes. The current research documents a new diatom species from the genus Tetramphora, found on the saltmarshes of the Arade River Estuary (Southern Portugal), and its autecology. As with the other twelve recognised species of the genus, Tetramphora witkowskii sp. nov. presents an asymmetrical valve outline, a biarcuate raphe system, slit like areolae, axial costae, a central hyaline area, and a dorsal central thickening. Tetramphora witkowskii sp. nov. is characterised by having finely silicified valves with a nearly flat face, 28.0-33.0 mu m in length and 6.0-6.5 mu m in width. The new species has a stria density of 24-27 in 10 mu m with narrow, longitudinally oriented areola openings. It presents proximal raphe endings covered by a projected dorsal-side flap and a developed sternum with thickened costae, weakly formed on the dorsal side of the central area. Tetramphora witkowskii sp. nov. was found as a benthic epipelic diatom with a preference for brackish to salt water with circumneutral pH. Further research is required to better understand this species' colony and frustule shape, the number, morphology, and position of the chloroplasts, genetic signature, geographical distribution, and environmental tolerance.

2025-05-09Journal article

Open access