Multiproxy evidence of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland

‘Little Ice Age’ (LIA) climatic deteriorations have been abundantly documented in various archives such as ice, lake sediments and peat bog deposits. Palaeoecological analyses of peat samples have identified these climatic deteriorations using a range of techniques, for example palynology, plant macrofossils, testate amoebae or carbon isotopic analyses. The use of inorganic geochemistry and the reconstruction of dust fluxes has remained a challenge in tracing the nature of LIA climatic changes. Although the idea of enhanced erosion conditions and storminess is commonly discussed, the conditions for dust deposition in peatlands over Europe during the LIA are rarely favourable, because the natural forest cover over Europe was much more important than nowadays, preventing dust deposition. This intense forest canopy masks the deposition of dust in peatlands. In northern Poland, near the Baltic shore, the Słowin´skie Błota area was deforested around AD 1100, ie, just before the LIA, and therefore constitutes a key area for the reconstruction of LIA climatic change. With the support of a well-constrained chronology, climatic fluctuations are recorded in an ombrotrophic bog using inorganic geochemistry, plant macrofossils and carbon isotopic analyses. The reconstruction of LIA climatic changes is in good agreement with other records from Poland and NE Europe. However, a c. 50-year discrepancy can be observed between various records. This discrepancy is possibly due to progressive time-dependent cooling gradient from north to south Europe.

Last millennium palaeoenvironmental changes from a Baltic bog (Poland) inferred from stable isotopes, pollen, plant macrofossils and testate amoebae

Mariusz Lamentowicz, Edward Mitchell

The Baltic coast of Northern Poland is a region of considerable potential interest for paleoclimatic studies because this region is under the influence of both oceanic and continental climates and that these two influences have likely changed through time. Also unlike many more intensively studied regions of Europe human impact was more limited until the 19th century. We present a multiproxy high-resolution record from Stążki mire, an ombrotrophic mire located in northern Poland 35 km from the Baltic sea coast. We combined four proxies from the peat: testate amoebae, stable isotopes (δ13C) of Sphagnum stems, pollen, and plant macrofossils supported by dendroecological data to assess the palaeoenvironmental changes that took place during the last millennium. The general aim of this study was to test if a range of proxies (testate amoebae, pollen, plant macrofossils and tree rings) could allow inferring a climatic signal from a peat monolith despite the considerable anthropogenic impact on the Pomerania landscape since the Early Medieval period. Combining internal (e.g. macrofossils and testate amoebae) and external (pollen) signals is key to distinguishing human from climatic signals in palaeoenvironmental studies of peatlands. Our more specific aims were to: a) reconstruct the last millennium palaeoenvironment in a Baltic raised bog and its surroundings, b) identify the major wet-dry shifts and correlate those events with climate change and human impact, c) assess the resilience of the Baltic bog ecosystem following human impact. We noted two disturbance periods in the history of the mire. The two major disturbances in the history of the mire were dry periods [(I) 1100-1500 AD and (II) 1650-1900 (2005) AD]. These are reflected in all indicators and can be interpreted as the mixture of climate impact and human activities. However, the pollen record shows little evidence of human indicators during the first dry shift. The second disturbance can be related to local peat exploitation of the mire and then in the 20th century with limited artificial drainage. From 1500 AD all proxies show that the water table abruptly rose in the mire. The beginning of this shift occurred during the Little Ice Age and therefore it is likely a climatic signal. Alternatively, this wet shift could have been interpreted as a re-wetting mire surface after peat burning, but this interpretation is rejected because there is no evidence of major local fire in the macrofossil record. The macrofossil data shows that Sphagnum fuscum dominated the pristine mire vegetation but then declined and finally disappeared. This pattern is comparable with the timing of extinction of Sphagnum austinii in Western Europe. This study illustrated the value of palynological analysis of peat archives (especially for last millennium) to assess the magnitude of anthropogenic land-use changes. For example the comparison of Fagus (beech) and Carpinus (hornbeam) history with the palaeohydrological record allowed us to exclude climate change as the most important factor for the decline and expansion of these tree species. This study is the first direct comparison of testate amoeba and stable isotope data.

2008

Palaeoecological evidence for anthropogenic acidification of a kettle-hole peatland in northern Poland

Mariusz Lamentowicz, Edward Mitchell

We studied the Holocene developmental history of a small kettle-hole peatland in northern Poland using radiocarbon dating and analyses of pollen, plant macrofossils, and testate amoebae with the aim to sort out the influences of climate change, autogenic succession, and human impact. The mire followed the classical succession from lake to a Sphagnum-dominated peatland, but peat accumulation only started about 3000 years before present. A rapid shift to wetter conditions, lower pH, and higher peat accumulation rate took place about 110-150 years before present, when the vegetation shifted to a Sphagnum-dominated poor fen with some bog plants. While the first shift to a peat-accumulating system was most likely driven by climate, the second one was probably caused by forest clearance around the mire. This shift towards a Sphagnum-dominated vegetation mirrors both in pattern and timing the changes observed in similar situations in North America and New-Zealand. While human activities have overall caused the loss of vast expanses of peatlands worldwide in recent centuries, locally they may have also allowed the development of communities that are now ironically considered to have a high conservation value. However, in the case of the site studied and possibly elsewhere the likely anthropogenic shift to bog vegetation was at the expense of a species-rich poor fen, which today has even higher conservation value than ombrotrophic bogs. Thus this study also illustrates the value of palaeoecology for peatland management and biodiversity conservation.

2007

Multiproxy study of anthropogenic and climatic changes in the last two millennia from a small mire in central Poland

Mariusz Lamentowicz

The Żabieniec kettle-hole is the first peatland in central Poland analysed quantitatively with four biotic proxies (plant macrofossils, pollen, testate amoebae and chironomids) in order to reconstruct past environmental change. Palaeoecological data were supported by historical and archaeological records. We focused on autogenic vegetation change and human impact in relation to climatic effects. The aims of our study were: (a) to describe the development history of the mire during the last 2000 years, (b) to date and reconstruct the anthropogenic land-use changes, and (c) to discuss a possible climatic signal in the peat archive. The combination of proxies revealed dramatic shifts that took place in the peatland since the Roman Period. Żabieniec was a very wet telmatic habitat until ca AD 600. Then the water table declined and the site transformed into a Sphagnum-dominated mire. This dry shift took place mainly during the Early Medieval Period. Human impact was gradually increasing and it was particularly emphasized by deforestation since AD 1250 (beginning of the Late Medieval Period). Consequently, surface run-off and aeolian transport from the exposed soils caused the eutrophication of the mire. Furthermore, chironomids and testate amoebae reveal the beginning of a wet shift ca AD 1350. Openness considerably increased in the Late Medieval and the Modern Periods. The highest water table during the last 1000 years was recorded between AD 1500 and 1800. This wet event is connected with deforestation but it could be also associated with the Little Ice Age. Our study shows plant succession in the Żabieniec peatland, which can be explained with the recent landscape transformation. However, such changes are also possibly linked with the major climatic episodes during the last two millennia, such as the Medieval Warm Period and the Little Ice Age.

Springer Netherlands2009

Multiproxy study of anthropogenic and climatic changes in the last two millennia from a small mire in central Poland

Mariusz Lamentowicz

Springer Netherlands2009

Last millennium palaeoenvironmental changes from a Baltic bog (Poland) inferred from stable isotopes, pollen, plant macrofossils and testate amoebae

Mariusz Lamentowicz, Edward Mitchell

2008