Pirita O. Oksanen, University of Bristol, School of Geographical Sciences

Searching for 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.Wetlands at ca 6000 BP, basal peat dates

Wetlands at ca. 10 000 BP, basal peat dates

Introduction

QUEST-Deglaciation project aims to improve palaeoenvironmental databases as means of better understanding the causes of changes in climate, atmospheric composition and biogeochemical cycles since the Last Glacial Maximum, and for evaluating and improving Earth system model simulations.

A global wetland database, compiling information on the age, type and distribution of wetlands and peat accumulation since the Last Glacial Maximum, is under construction. The public database will be of great help in review studies and as a reference collection.

Within QUEST-Deglaciation 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 identify gaps in the existing wetland research and better understand e.g. the patterns of wetland initiation or the role of wetlands in the terrestrial carbon cycle during the last Ice Age and deglaciation. Wetlands play an important role in the terrestrial carbon cycle today, but it is unclear what their part as carbon sinks and e.g. methane sources was during the last Ice Age and deglaciation. Most modern peatlands, now storing some 500 Gt

of carbon, are of the Holocene age, but there were large areas suitable for wetlands during the Last Glacial Maximum.

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.

Results

During the Last Glacial Maximum peat accumulation is registered in the southern hemisphere, southernmost Europe and some areas currently covered by sea. In the high-latitudes of the northern hemisphere peatlands started to form around 15,000 years ago when deglaciation advanced. 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 brown mosses) 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.

Wetlands at ca. 13 000 BP, basal dates

Wetlands at ca. 21000 BP, basal dates

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

Lappalainen et al. 1996

Global wetland distribution based on the sites currently in the database