Mid to Late Holocene Storminess and Fire History on the Baltic Coast of Latvia

Normunds Stivrins^1*Cerina Aija¹Mara Kitenberga²Edyta Kalinska³Alekss Maksims¹Angelica Feurdean⁴Siim Veski⁵

• ¹University of Latvia, Riga, Latvia
• ²Latvijas Valsts mezzinatnes instituts Silava, Salaspils, Latvia
• ³Uniwersytet Mikolaja Kopernika w Toruniu, Torun, Poland
• ⁴Goethe-Universitat Frankfurt am Main, Frankfurt, Germany
• ⁵Tallinna Tehnikaulikool, Tallinn, Estonia

Coastal peatlands are sensitive archives of past environmental change, preserving evidence of both atmospheric and surface disturbances. Here, we reconstruct Mid-to Late Holocene storminess and fire dynamics from a 330-cm peat sequence recovered from Bog Bažu in northwestern Latvia, located ~3 km inland from the Baltic Sea coast. A multi-proxy approach combining macroscopic charcoal, sand grain counts, quartz grain surface characteristics, and plant macrofossils was used to assess how storms and fires influenced peatland development over the past ~5400 years. The charcoal record reveals 30 fire episodes with a mean return interval of ~170 years, with highest fire frequencies between 4500– 3900 and 3000–800 cal yr BP. Sand influx analysis identifies 46 episodes of enhanced storminess, characterised by a dominance of cracked quartz grains indicative of high-energy aeolian transport. Sixteen intervals show partial temporal overlap between fire and storm peaks, suggesting that thunderstorms may have occasionally linked the two disturbance regimes, particularly during relatively dry phases when fire susceptibility was enhanced. In contrast, wetter periods are associated with weaker coupling between storminess and fire activity. Plant macrofossil evidence indicates a gradual transition from fen to ombrotrophic bog around 4200 cal yr BP, followed by a shift from pine-dominated vegetation to dwarf-shrub communities, likely increasing landscape-fire susceptibility. Despite chronological uncertainties, this study provides the first integrated reconstruction of storminess and fire history from a Baltic Sea coastal peatland and highlights the role of recurrent natural disturbances in shaping long-term peatland development, ecological stability, and recovery capacity under varying hydroclimatic conditions.