Peat stratigraphy and changes in peat formation during the Holocene in Latvia

An overview of peatland development and peat formation during the Holocene in Latvia is presented. Altogether, 24 peatlands each with at least three ¹⁴C dates, plant macrofossil data and degree of peat decomposition were assembled in order to compare and discuss spatial and temporal changes. A series of 2000-year time windows for the entire Holocene were produced, showing peatland development processes as reflected by peat composition. The results show that the oldest peatlands started to develop at the beginning of the Early Holocene (11,600-8200 cal. BP), mainly in depressions in the uplands. Peat macrofossil composition is characterised by remains of plants growing under conditions of excess humidity, represented by various Hypnum species and sedges (Carex lasiocarpa, Carex appropinquata and Carex teretiuscula), and less frequently by woody plants. The degree of peat decomposition indicates a wet-dry-wet pattern for the Holocene climate, which accords with other regional climatic studies. Climate change influenced groundwater and lake levels, promoting the establishment of peatlands during the Early Holocene. Warm and dry conditions resulted in low peat accumulation rates throughout the Middle Holocene (8200-4200 cal. BP). The present study shows that a large number of bogs became established in the Late Holocene (4200-0 cal. BP), formed by a wide variety of various raised-bog-type peats (cotton grass-Sphagnum, Sphagnum fuscum and cotton grass peat), which continue to accumulate at the present day. The Early, Middle and Late Holocene as recognised in the present study correspond closely to a recent global scheme suggested by the INTIMATE-SQS working group on the subdivision of the Holocene.