Two millennia of Caspian Sea level change and Hyrcanian forest dynamics: A multi-proxy record from the Anzali Lagoon, northern Iran

A multi-proxy study of a 5-m-long sediment core from the Anzali Lagoon (southwest Caspian coasts) was conducted to reconstruct Caspian Sea level fluctuations and concurrent vegetation history in the Hyrcanian forests over the past two millennia. The record reveals several major transgressive and regressive phases. Highstands during the Parthian period-early Sasanian (2070–1745 cal yr BP), the early Little Ice Age (LIA; 640–445 cal yr BP), and the late LIA (445–130 cal yr BP) are marked by Caspian Sea indicator organisms such as dinocysts, foraminifera, and bivalves. It suggests breaching of the Anzali spit and incursion of the Caspian water into the lagoon. In contrast, lowstands during the Sasanian-early Medieval (1745–1185 cal yr BP) and late Medieval (1185–640 cal yr BP) periods are characterized by lagoonal isolation and dominant freshwater riverine influence. The pollen record, integrating signals from the local wetland, coastal lowlands, and montane slopes, documents the response of regional vegetation to these hydro-climatic shifts along with human activities. High values of Alnus pollen suggest that a dense alder forest was persistently dominating the lowland assemblages around the Anzali Lagoon. The late Medieval warm/dry period exerted a pronounced influence on vegetation, which was marked by a decline in aquatic/subaquatic plants, the hygrophilous tree Pterocarya , and non-arboreal pollen (NAP). Two episodes of probable anthropogenic deforestation have been identified in the pollen diagram. The first, coinciding with the Sasanian lowstand, is likely contemporaneous with the construction of the Gorgan defensive wall and is evidenced by a sharp decline in arboreal pollen and a peak in Vitis vinifera , suggesting a probable viticulture. The second, an Alnus decline during the late LIA highstand, is linked to agricultural expansion around the lagoon, as indicated by a rise in Cerealia-type pollen.