Pirita Oksanen and Sandy Harrison, University of Bristol, School of Geographical Sciences

Evolution of wetlands since the Last Glacial Maximum

AcknowledgementsMost basal peat dates from circumboreal zone are taken from Gorham et al. 2005 and McDonald et al. 2006. Continental and ice-sheet outlines are compiled by Patrick Bartlein, University of Oregon. QUEST is financed by NERC.

Mires at ca 6000 BP, basal peat dates

Mires at ca. 10 000 BP, basal peat dates

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Introduction

We are creating a global wetland database by compiling information on the age, type and distribution of wetlands and accumulation of organic material. The public database will be of great help in review studies and as a reference collection.Within QUEST-Deglaciation project the collected dataset will be used to document the evolution of wetlands since the Last Glacial Maximum. The end products will include a series of

maps showing the change in wetland extent and type through time. The data set will also be used to construct and validate

Earth System model simulations. The global synthesis will help to better understand e.g. the patterns of wetland initiation, the role of wetlands in the terrestrial carbon cycle during the last Ice Age and deglaciation, and to identify gaps in the existing

wetland research.Wetlands can be defined as terrestrial, both natural and

artificial, ecosystems that are at least part of the year water saturated such as bogs, fens, marshes, swamps, flood plains

or rice paddies. Open water aquatic ecosystems (lakes, rivers, sea-shores) are excluded from this database unless they are

closely related to terrestrial wetlands (e.g. bog pools and thermokarst lakes) or have at some stage been terrestrial

wetlands.Modern wetlands accumulating peat or similar organic matter

are likely to be best represented in the database, because they are easily recognised and tell their own history since their

formation. Former peatlands currently buried by mineral matter or water are more difficult to discover. Ex-wetlands without deposits can be recognised only from historical records and

indirectly from regional pollen diagrams.

Sites with datings currently in the database, compared to modern mire distribution.

Current state

Good coverage of studied, currently existing peatland sites is mapped from circumarctic and boreal zones; basal peat dates from these sites are included in the database. A few

former peatland sites are recognised. Identifying sites from the rest of the world and compiling stratigraphical data from all sites is underway.

ResultsPeatlands started to form around 15,000 years ago in the high latitudes of the

northern hemisphere when deglaciation advanced. Only in Beringia major peat accumulation may have occurred during the last Ice Age. In the same time peat

accumulation is registered in the southern hemisphere and southernmost Europe. By ca. 7000 years ago the pattern of peatland distribution in the northern areas is similar to today. In the arctic regions accumulation seems to have decreased after ca. 5000 yrs ago, while in the boreal regions the accumulation may have increased

from around the same time. However, the rates vary widely between and within individual sites and the amount of data is not adequate yet.

The biggest change in the evolution of northern mires is the replacement of formerly common rich fens (dominated by sedges, grasses and brownmosses) by Sphagnum dominated bogs, aapa mires and palsa mires. Methane releases are generally higher from fens than bogs, although ranges are large for all wetland types. In addition to climate, local factors affect mire development and the change into bogs and other

Sphagnum mires is not synchronous, but some regional patterns can be distinguished nevertheless. In continental regions bogs are not common before ca. 6000 yrs ago, and aapa and palsa mires started to form after ca. 5000 yrs ago, palsa mires more expansively only after ca. 3000 yrs ago. In oceanic regions raised bogs

are generally older than in continental regions, but blanket bogs in larger scale started to develop after ca. 4500 yrs ago.

Initiation dates of Sphagnum peat growth in Europe

Mires at ca. 13 000 BP, basal dates

Mires at ca. 21000 BP, basal dates

Contact p.oksanen@bristol.ac.uk. Wetland data synthesis web sitehttp://www.bridge.bris.ac.uk/projects/deglaciation/QUEST_wet.html