A division in peat stratigraphy which separates well-humidified peat from unhumidified peat. Recurrence surfaces are found in raised bogs and blanket bogs which are nourished only by rainfall. It has therefore been suggested that recurrence surfaces are due to a change to damper climate. Recurrence surfaces of many dates have been found, often several in one bog, although not so many fitting into one age range. During the late prehistoric and early historic phases of the past 6,000 years, the peat bogs of northern Europe appear to have undergone a number of desiccations (warm, dry summers), revealed in the bog cores as dry, often wooded, surfaces. The dry phases were generally followed by wet conditions in which peat accumulation was rapid. These overlying layers of renewed peat growth are also known as recurrence horizons.