1. A major hydrobiological change in Dasht-e Arjan Wetland (southwestern Iran) during the late glacial--early Holocene transition revealed by subfossil chironomids
- Author
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Aubert, Cyril, Djamali, Morteza, Jones, Matthew, Lahijani, Hamid, Marriner, Nick, Naderi-Beni, Abdolmajid, Sharifi, Arash, Ponel, Philippe, and Gandouin, Emmanuel
- Subjects
Global temperature changes -- Environmental aspects ,Paleogeography -- Holocene ,Earth sciences - Abstract
The late glacial - early Holocene transition is a key period in the earth's history. However, although this transition is well studied in Europe, it is not well constrained in the Middle East and palaeohydrological records with robust chronologies remain scarce from this region. Here we present an interesting hydrobiological record showing a major environmental change occurring in the Dasht-e Arjan Wetland (southwestern Iran, near to Persepolis) during the late glacial - early Holocene transition (ca. 11 650 years cal BP). We use subfossil chironomids (Insecta: Diptera) as a proxy for hydrological changes and to reconstruct lake-level fluctuations. The Arjan wetland was a deep lake during the Younger Dryas marked by a dominance of Chironomus plumosus/anthracinus-type, taxa adapted to anoxic conditions of deep waters. At the beginning of the Holocene, a drastic decrease (more than 80% to less than 10%) of Chironomus plumosus/anthracinus-type, combined with diversification of littoral taxa such as Polypedilum nubeculosum-type, Dicrotendipes nervosus-type, and Glyptotendipes pallens-type, suggests a lake-level decrease and a more vegetalized aquatic environment. We compare and contrast the chironomid record of Arjan with a similar record from northwestern Iran. The palaeoclimatic significance of the record, at a local and regional scale, is subsequently discussed. The increase in Northern Hemisphere temperatures, inferred by geochemical data from NGRIP, at the beginning of the Holocene best explains the change from the Younger Dryas highstand to early Holocene lowstand conditions in the Dasht-e Arjan wetland. However, a contribution of the meltwater inflow from small local glaciers in the catchment basin is not excluded. Key words: Younger Dryas, climate change, Karst, lake-level change, Zagros. La transition tardiglaciaire - Holocene precoce represente une periode cle de l'histoire de la terre. Si cette transition est bien etudiee en Europe, ce n'est toutefois pas le cas au Moyen-Orient, et les profils paleohydrologiques associes a des chronologies robustes demeurent rares pour cette region. Nous presentons unprofil hydrobiologique interessant qui montre un important changement environnemental s'etant produit dans la zone humide de Dasht-e Arjan (sud-ouest de l'Iran, pres de Persepolis) durant la transition tardiglaciaire-Holocene precoce (vers 11 650 ans cal BP). Nous utilisons des subfossiles de chironomides (insectes : dipteres) comme indicateurs de changements hydrologiques et pour reconstituer les fluctuations du niveau de lacs. Le milieu humide d'Arjan etait un lac profond durant le Dryas recent, caracterise par une preponderance de taxons de type Chironomus plumosus/anthracinus adaptes aux conditions anoxiques des eaux profondes. Une baisse drastique (de plus de 80 % a moins de 10 %) de ces taxons au debut de l'Holocene, combinee a la diversification de taxons littoraux de types Polypedilum nubeculosum, Dicrotendipes nervosus et Glyptotendipes pallens, indiquerait une baisse du niveau du lac et un milieu aquatique plus vegetalise. Nous comparons le profil des chironomides d'Arjan a un profil semblable du nord-ouest de l'Iran. La signification paleoclimatique du profil, aux echelles locales et regionales, est ensuite abordee. L'augmentation des temperatures dans l'hemisphere nord audebut del'Holocene, infereeapartir dedonnees geochimiques duNGRIP, est cequi expliquele mieux le passage deconditions dehaut niveau du Dryas recent aux conditions debas niveau del'Holocene precoce dans la zone humide de Dasht-e Arjan. Un effet de l'apport d'eau de fonte de petits glaciers locaux dans le bassin versant n'est toutefois pas exclu. [Traduit par la Redaction], Introduction The late Pleistocene to early Holocene transition marks the final part of the 'Last Glacial - Interglacial Transition' or 'Last Termination' (Lowe and Walker 1997; Hoek et al. 2008). [...]
- Published
- 2019
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