EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Biogeosciences, 10, 5703–5728, 2013 Open Access www.biogeosciences.net/10/5703/2013/ Biogeosciences doi:10.5194/bg-10-5703-2013 Biogeosciences Discussions © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Access Climate Climate of the Past of the Past Discussions River flooding as a driver of polygon dynamics: modern vegetation Open Access Open Access data and a millennial peat record from the AnabarEarth River System lowlands Earth System Dynamics Dynamics (Arctic Siberia) Discussions R. Zibulski1, U. Herzschuh1,2, L. A. Pestryakova3, J. Wolter1, S. Muller¨ 4, N. Schilling2, S. Wetterich1, Open Access L. Schirrmeister1, and F. Tian1 Geoscientific Geoscientific Open Access 1Alfred-Wegener-Institut Helmholtz-Zentrum fur¨ Polar- und Meeresforschung, 14473 Potsdam,Instrumentation Germany Instrumentation 2 University of Potsdam, Institute of Earth and Environmental Sciences, 14476 Potsdam-Golm,Methods Germany and Methods and 3Northeast Federal University, Department for Geography and Biology, 677000 Yakutsk, Russia 4Freie Universitat,¨ Institute of Geological Science, 12249 Berlin, Germany Data Systems Data Systems Discussions Open Access Correspondence to: R. Zibulski ([email protected]) Open Access Geoscientific Geoscientific Received: 31 January 2013 – Published in Biogeosciences Discuss.: 1 March 2013 Model Development Revised: 19 July 2013 – Accepted: 23 July 2013 – Published: 28 August 2013 Model Development Discussions Open Access Abstract. The spatial and temporal variability of a low- accumulated during the annual spring snowmelt),Open Access character- centred polygon on the eastern floodplain area of the lower ized by an abundance ofHydrologyMeesia triquetra andand a dominance Hydrology and Anabar River (72.070◦ N, 113.921◦ E; northern Yakutia, of benthic diatoms (e.g.EarthNavicula System vulpina), indicative of a Earth System Siberia) has been investigated using a multi-method ap- relatively high pH and a high tolerance of disturbance. A proach. The present-day vegetation in each square metre comparison of the local polygonSciences vegetation (inferred from Sciences was analysed, revealing a community of Larix, shrubby Be- moss and macrofossil spectra) with the regional vegetation Discussions Open Access tula, and Salix on the polygon rim, a dominance of Carex (inferred from pollen spectra) indicated that theOpen Access moss asso- and Andromeda polifolia in the rim-to-pond transition zone, ciation with Scorpidium scorpioides became established dur- Ocean Science and a predominantly monospecific Scorpidium scorpioides ing relatively favourableOcean climatic Science conditions, while the asso- coverage within the pond. The total organic carbon (TOC) ciation dominated by Meesia triquetra occurred during peri- Discussions content, TOC / TN (total nitrogen) ratio, grain size, vascular ods of harsh climatic conditions. Our study revealed a strong plant macrofossils, moss remains, diatoms, and pollen were riverine influence (in addition to climatic influences) on poly- Open Access analysed for two vertical sections and a sediment core from gon development and the type of peat accumulated.Open Access a transect across the polygon. Radiocarbon dating indicates Solid Earth that the formation of the polygon started at least 1500 yr ago; Solid Earth Discussions the general positions of the pond and rim have not changed since that time. Two types of pond vegetation were identi- 1 Introduction fied, indicating two contrasting development stages of the Open Access Open Access polygon. The first was a well-established moss association, Polygon mires are the most common type of arctic mire. Of- dominated by submerged or floating Scorpidium scorpioides ten these mires occur in an advanced stage of succession, The Cryosphere known as low-centredThe polygons Cryosphere (Minke et al., 2007). Low- and/or Drepanocladus spp. and overgrown by epiphytic di- Discussions atoms such as Tabellaria flocculosa and Eunotia taxa. This centred polygons evolve when frost-heave processes form stage coincides temporally with a period in which the poly- ridges (the polygon rims) above ice wedges, and depressions gon was only drained by lateral subsurface water flow, as between the ridges that are often water-filled (the polygon indicated by mixed grain sizes. A different moss associa- pond). Although these mires only cover about 3 % of the arc- tion occurred during times of repeated river flooding (indi- tic land area, they contain more than 15 % of the world’s soil cated by homogeneous medium-grained sand that probably carbon (Post et al., 1982); hence they play an important role in the arctic carbon cycle (Hobbie et al., 2002). Improving Published by Copernicus Publications on behalf of the European Geosciences Union. 5704 R. Zibulski et al.: River flooding as a driver of polygon dynamics our understanding of polygon dynamics is therefore a key nated by a stable high pressure system over the Siberian land- scientific objective. Due to the harsh living conditions, plants mass, resulting in low temperatures (mean January tempera- with short life cycles are common as well as those capable ture: −36.1 ◦C) and only a thin snow cover. Summers are of asexual reproduction. Woody shrubs and herbs are conse- dominated by Icelandic and Aleutian lows; they are short and quently replaced at higher latitudes by cryptogams, as a result relatively cool, with mean July temperatures of 12 ◦C (Sasky- of their lower requirements for light, temperature, and nutri- lakh Climate Station, 71.967◦ N, 114.083◦ E; Rivas-Martinez ents (Frahm, 2001). Most of the biomass in the arctic tun- and Rivas-Saenz, 2007). dra is therefore fixed in peat from decomposed bryophytes The study area is underlain by 500 to 600 m of permafrost (Longton, 1997). (Yershov et al., 1991). Temperature increases at the begin- Climate and the nature of the soil substrate are the main ning of the Holocene initiated thermokarst processes that factors influencing the formation of polygons, while their di- led to permafrost degradation and widespread subsidence mension, form, and position within landscapes are controlled (Czudek and Demek, 1970). The study area is characterized by complex positive feedbacks between vegetation, ice, wa- by meander terraces, polygon mires and in a wider surround- ter, and peat (Minke et al., 2007). Investigations have pre- ing thermokarst lakes and alas depressions. The uppermost viously been conducted into the ecology of polygonal land- parts of the soils are wet and organic-rich, and are classified scapes and the way in which they function. For example, the as Histic Fluvisols (Jones et al., 2010). hydrology of the active layer has been investigated in relation Polygon fields in the Anabar River lowlands were ob- to the form of the polygon (Riordan et al., 2006; Yoshikawa served from helicopter flights to be restricted to areas along and Hinzman, 2003) and the displacement of soil by frost- the flanks of rivers. The studied polygon is located within a heave processes (Mackay, 2000). The dependence of the en- polygon field on the Anabar River floodplain, about 800 m ergy and water balances in the polygonal tundra on precipi- to the east of the riverbank and within the curve of an aban- tation and weather conditions has already been investigated doned meander. It lies about 15 km north of Saskylakh on the (Boike et al., 2008). Investigations into the shape and sed- North Siberian Lowland, in the north-eastern part of Yakutia iment characteristics of river-influenced polygons in north- (Fig. 1b). The Anabar River is fed by the Bol’shaya Kuon- ern Russia have mainly been carried out in the Lena River amka and the Malaya Kuonamka rivers, which originate on delta (Boike et al., 2013; Fiedler et al., 2004). During the the Anabar Shield. It drains into the western part of the last decade studies have been conducted with a special fo- Laptev Sea ∼ 400 km west of the Lena River delta and has cus on the carbon content (Zubrzycki et al., 2013), and on a discharge that is highly variable, both seasonally and an- the net ecosystem CO2 exchange, for example in low-centred nually. In contrast to rivers in southern Yakutia, the Anabar polygons on Samoylov Island (Runkle et al., 2013). Other in- River freezes to the bottom during winter, followed by a rapid vestigations have used polygon sediments to trace short-term increase in discharge in spring that reaches a maximum of changes in vegetation (De Klerk et al., 2011) and long-term 5000 m2 s−1 (data from Saskylakh station; Huh and Edmond, changes in landscape dynamics (Minke et al., 2009; Zoltai 1999). and Vitt, 1990, 1995). While previous studies have identified The lower part the Anabar River in particular is a mean- the general processes that lead to the formation of polygon dering and partly braided river system (Fig. 1b). The polygon mires, the polygon dynamics and associated driving factors field in which our site is located is drained by several small remain only poorly understood. streams flowing into the Anabar River in summer, but can be In the North Siberian Lowland,