Black carbon (BC) is fine particulate matter produced by the incomplete combustion of biomass and... more Black carbon (BC) is fine particulate matter produced by the incomplete combustion of biomass and fossil fuels. It has a strong climate warming effect that is amplified in the Arctic. Long-term trends of BC play an important role in assessing the climatic effects of BC and in model validation. However, few historical BC records exist from high latitudes. We present five lake-sediment soot-BC (SBC) records from the Fennoscandian Arctic and compare them with records of spheroidal carbonaceous fly-ash particles (SCPs), another BC component, for ca. the last 120 years. The records show spatial and temporal variation in SBC fluxes. Two northernmost lakes indicate declining values from 1960 to the present, which is consistent with modeled BC deposition and atmospheric measurements in the area. However, two lakes located closer to the Kola Peninsula (Russia) have recorded increasing SBC fluxes from 1970 to the present, which is likely caused by regional industrial emissions. The increasing...
Finland has some of the world's longest records of lake and river ice cover duration. Break-u... more Finland has some of the world's longest records of lake and river ice cover duration. Break-up dates of the river Tornionjoki have been registered since 1693 and break-up dates of many lakes since the early 19th century. However, most of the lake records originate from southern and central Finland. Ice cover records are considered to be even better indicators of past climate than temperature records. Direct human impact on ice cover dynamics is small, especially in Northern Finland. The projected climate warming will most probably lead to longer and warmer ice-free season and increased nutrient and carbon input from the catchment areas. In response, the total primary production is likely to increase and species composition changes will take place. Here, we use a diatom-based transfer function for the first time to quantitatively infer ice cover durations for the Holocene at four lakes in subarctic Fennoscandia. In general, all four lakes show relatively similar trends with the o...
Northern peatlands represent the biggest wetland complex in the world releasing 20 to 45 Tg CH4 t... more Northern peatlands represent the biggest wetland complex in the world releasing 20 to 45 Tg CH4 to the atmosphere annually. Recent research on the relationship between wetlands and past atmospheric concentrations of methane (ACM) over the Holocene, as revealed by ice-cores, has focused on the aerial extent of peatlands. Based on the frequency distribution of the basal peat radiocarbon dates
Paleoclimate reconstructions based on biological proxies present methodological challenges, espec... more Paleoclimate reconstructions based on biological proxies present methodological challenges, especially during non-analog conditions, such as the early Holocene. Here, two chironomid-based training sets from Finland were amalgamated to create a more accurate transfer function of summer air temperature. The aim was to reconstruct Holocene paleoclimate in northernmost Lapland, in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models. The results showed that the combined calibration model had improved performance statistics. The temperature trends inferred from the downcore chironomid record using the original and combined models were very similar. However, there were major changes in their absolute values with the combined model showing greatly improved accuracy. The chironomid-based temperature reconstruction showed significant correlation with the previous pollen-based reconstructions from northwestern Finnish Lapland. Ho...
Spheroidal carbonaceous particles (SCP) are a well-defined fraction of black carbon (BC), produce... more Spheroidal carbonaceous particles (SCP) are a well-defined fraction of black carbon (BC), produced only by the incomplete combustion of fossil fuels such as coal and oil. Their past concentrations have been studied using environmental archives, but, additionally, historical trends of BC concentration and deposition can be estimated by modelling. These models are based on BC emission inventories, but actual measurements of BC concentration and deposition play an essential role in their evaluation and validation. We use the chemistry transport model OsloCTM2 to model historical time series of BC concentration and deposition from energy and industrial sources and compare these to sedimentary measurements of SCPs obtained from lake sediments in Northern Europe from 1850 to 2010. To determine the origin of SCPs we generated back trajectories of air masses to the study sites. Generally, trends of SCP deposition and modelled results agree reasonably well, showing rapidly increasing values ...
Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern... more Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern Finnish Lapland are studied by comparison of various biological and sedimentological proxies with the 200-year long climate record, specifically reconstructed for the site using a data-set of European-wide meteorological data. The multi-proxy evidence of simultaneously changing diatom, Cladocera, and chrysophyte assemblages along with the increased rates
... Subarctic Fennoscandian Lakes Jan Weckstriim, Atte Korhola, and Tom Blom Laboratory of Physic... more ... Subarctic Fennoscandian Lakes Jan Weckstriim, Atte Korhola, and Tom Blom Laboratory of Physical Geography, Department of Geography, PO Box 9 (Siltavuorenpenger 20 A), FIN-00014 University of Helsinki, Finland. Abstract ...
We report a method for reconstructing temperatures from proxy data based on Bayesian multi-scale ... more We report a method for reconstructing temperatures from proxy data based on Bayesian multi-scale smoothing. The main features of the method is that it makes possible a simultaneous utilization of multiple proxies and sites to achieve a regional `consensus' reconstruction of temperature, it enables various types of uncertainties (e.g., chronology) to be taken into account, and that it also allows significant features to be detected from the emerging time series. Applying the method to multiple proxy data derived from lakes in Finnish Lapland suggests that, contrary to the conventional view, Holocene climate cooling in the North Atlantic region started already c. 8.5 kyr, and that climate since then was punctuated by several quasi-cyclical climate events, the forcing mechanisms of which are not yet fully understood. Our study suggests that inconsistencies in climate reconstructions between different proxy sources may be at least partly spurious; there is probably no single narrat...
Wetlands have been considered as the most important natural source of the atmospheric methane con... more Wetlands have been considered as the most important natural source of the atmospheric methane concentration (AMC) prior to anthropogenic influences. According to ice cores, AMC varied significantly during the Holocene, the causes of which are not completely understood. In particular, the reasons for the increased AMC during the late Holocene (from 5 ka onwards) have been debated widely, including an anthropogenic explanation. Initially, this increase was associated with increased emissions from northern wetlands, but estimated peat initiation rates seem not to support the conclusion. Based on a new data set of 954 basal peat radiocarbon dates that accounts more properly for the horizontal growth dynamics of northern peatlands (by containing only sites with multiple basal dates per site), we show here that the most extensive lateral expansion of high-latitude peatlands occurred only after 5 ka, parallel with the rise of CH 4 in the ice cores. Because this explosive increase in the extent of peatlands resulted in the formation of moist minerotrophic fen ecosystems that emit high amounts of CH 4 for a long time since their formation, and because many Arctic peatlands have remained minerotrophic throughout their development, northern peatlands cannot be neglected when seeking cause(s) for the late-Holocene rise in CH 4. A similar event in future could enhance climate change by causing a rapid shift in atmospheric greenhouse gas concentrations.
The application of molecular approaches to palaeovegetation reconstruction in peat is still relat... more The application of molecular approaches to palaeovegetation reconstruction in peat is still relatively rare, with molecular level studies of carbohydrate organic geochemistry being generally uncommon. In this report, neutral monosaccharides derived via acid hydrolysis were ...
The premise of this article is that climate effects on lakes can be quantified most effectively b... more The premise of this article is that climate effects on lakes can be quantified most effectively by the integration of process-oriented limnological studies with paleolimnological research, particularly when both disciplines operate within a common conceptual framework. To this end, the energy (E)-mass (m) flux framework (Em flux) is developed and applied to selected retrospective studies to demonstrate that climate variability regulates lake structure and function over diverse temporal and spatial scales through four main pathways: rapid direct transfer of E to the lake surface by irradiance, heat, and wind; slow indirect effects of E via changes in terrestrial development and subsequent m subsidies to lakes; direct influx of m as precipitation, particles, and solutes from the atmosphere; and indirect influx of water, suspended particles, and dissolved substances from the catchment. Sedimentary analyses are used to illustrate the unique effects of each pathway on lakes but suggest that interactions among mechanisms are complex and depend on the landscape position of lakes, catchment characteristics, the range of temporal variation of individual pathways, ontogenetic changes in lake basins, and the selective effects of humans on m transfers. In particular, preliminary synthesis suggests that m influx can overwhelm the direct effects of E transfer to lakes, especially when anthropogenic activities alter m subsidies from catchments.
Palaeoclimatic records derived from a variety of independent proxies provide evidence of post-gla... more Palaeoclimatic records derived from a variety of independent proxies provide evidence of post-glacial changes of temperature and soil moisture in northern Fennoscandia. We use pollen percentage, pollen influx, stomatal and chironomid records from Toskaljavri, a high-altitude lake in northern Finland, to assess how treelines and alpine vegetation there have responded to these climate changes. The evidence suggests that the cool, moist climate of the early Holocene supported birch forest in the area 9600 cal. yr BP onwards and that a rise of temperature triggered the immigration of pine at 8300 cal. yr BP. At 6100-4000 cal. yr BP altitudinal treeline in the area was formed by pine, in contrast to the modern situation where mountain birch reaches a higher elevation. Alpine vegetation also demonstrates clear changes. Plant communities typical of dry, oligotrophic heaths of northern Fennoscandia expanded during the dry climatic period at 7000-4000 cal. yr BP and decreased in response to cooler and moister conditions after 4000 cal. yr BP. Alpine plant communities favouring moist sites show an inverse pattern, expanding after a change towards moister climate after 4000 cal. yr BP. In a redundancy analysis (RDA), a statistically significant proportion of the variability in the total chironomid assemblages was captured by changes in the pollen types reflecting alpine vegetation typical of moist sites. Although chironomid community changes appeared to follow the major patterns in the alpine vegetation succession, the present study does not support a direct link between the changing treeline position and chironomid stratigraphy. Rather, the data indicate that the terrestrial and aquatic environments have each responded directly to the same ultimate cause, namely changing Holocene climate.
Over recent decades, palaeolimnological records from remote sites have provided convincing eviden... more Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with A celebration of Prof. Rick Battarbee's contributions to palaeolimnology, edited by Holmes et al. This paper has been written as a contribution to celebrating Rick Battarbee's influence on palaeolimnology. Some of us have benefitted from his leadership (and friendship) in transnational European projects during the last decade (e.g., ALPE, ALPE2, MOLAR, CHILL-10000, EMERGE, EUROLIMPACS), which together with some other initiatives spawned pan-European remote lake research. Others have respected Rick as a teacher, colleague and a friend. To some extent, this review follows the chronological order of topics addressed in these projects, which also respond to the growing social awareness about each issue. Rick also facilitated bridges between North American and European schools, and beyond. We expect his attitude towards collaboration will pervade and persist through the palaeolimnological community for years to come, and global change will certainly provide stimulating and challenging questions with which to do so.
Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still amo... more Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still among the least impacted lakes by humans. Hence they provide an excellent setting for studies on long-term climatic variability without the overriding effects of direct anthropogenic perturbation. On the other hand, these ecosystems are highly vulnerable to even moderate anthropogenic influence like long-distance airborne transport
Proceedings of the National Academy of Sciences of the United States of America, 2005
Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread speci... more Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.
Weather variation and climate fluctuations are the main sources of ecosystem variability in remot... more Weather variation and climate fluctuations are the main sources of ecosystem variability in remote mountain lakes. Here we describe the main patterns of seasonal variability in the ecosystems of nine lakes in Europe, and discuss the implications for recording climatic features in their sediments. Despite the diversity in latitude and size, the lakes showed a number of common features. They
ABSTRACT Clastic-biogenic varved lake sediments from Nautajarvi, Finland, covering the last ca. 1... more ABSTRACT Clastic-biogenic varved lake sediments from Nautajarvi, Finland, covering the last ca. 10000 years have previously been investigated with respect to varve chronology, laminae composition and thickness variations, palaeomagnetic secular variation, the pollen record and the diatom composition of selected sections. In this study, we provide detailed information on the seasonal sedimentation of different varve components and palaeolimnological indicators (diatoms, chrysophycaean cysts) using near-bottom sediment-trap monitoring. The monitoring results confirm previous interpretations of the formation of clastic-biogenic varves in Fennoscandian lakes. The results also indicate that seasonal sediment fluxes correspond with environmental changes. Higher snow storage in winter and the discharge intensity during the following spring snowmelt clearly increase the suspended sediment load, transportation and net accumulation of detrital mineral matter during spring and early summer. A prolonged autumn and subsequent freezing and thawing cycles in winter, conversely, result in an incremental but slow accumulation of assorted mineral matter and organic particles during winter, whereas the subsequent spring flooding and detrital sediment yield are diminished and thinner clastic laminae are formed. The accumulation rates of diatoms and chrysophyte cysts suggest that these algal groups are more dependent on seasonal processes (e.g. spring and autumnal overturn) than on rapid, short-lived environmental episodes such as the spring discharge peak.
The initiation and lateral expansion patterns of five small sub-arctic peatlands in the Fennoscan... more The initiation and lateral expansion patterns of five small sub-arctic peatlands in the Fennoscandian tree-line region were studied by 21 accelerator mass spectrometry (AMS) 14 C-dated basal-peat samples representing three to six dates per site. The radiocarbon dates were converted to calendar years and are based on the median probability. When combined with earlier basal-peat dates from the region, four distinctive periods can be observed in the cumulative record of the dates. The early Holocene, from c. 10 000 to 8000 cal. yr BP, was characterized by the fast initiation and rapid expansion of peatlands, whereas at 8000-4000 cal. yr BP lateral expansion was modest. The most intensive period of peatland expansion occurred at the beginning of the late Holocene at c. 4000 to 3000 cal. yr BP, after which it slowed down towards the present. All these periods are in rough agreement with the main Holocene climatic periods in the area, namely the relatively warm and moist early Holocene, the warm and dry Holocene thermal maximum (HTM) at 8000-4000 cal. yr BP, and the start of the cooler and moister trend (neoglacial cooling) from c. 4000 cal. yr BP to the present, indicating a broad-scale climatic control on the lateral growth of sub-arctic peatlands in Fennoscandia. In order to study the lateral expansion of peatlands and to evaluate their Holocene succession patterns, more studies based on multiple dates from the same peatland are needed.
Black carbon (BC) is fine particulate matter produced by the incomplete combustion of biomass and... more Black carbon (BC) is fine particulate matter produced by the incomplete combustion of biomass and fossil fuels. It has a strong climate warming effect that is amplified in the Arctic. Long-term trends of BC play an important role in assessing the climatic effects of BC and in model validation. However, few historical BC records exist from high latitudes. We present five lake-sediment soot-BC (SBC) records from the Fennoscandian Arctic and compare them with records of spheroidal carbonaceous fly-ash particles (SCPs), another BC component, for ca. the last 120 years. The records show spatial and temporal variation in SBC fluxes. Two northernmost lakes indicate declining values from 1960 to the present, which is consistent with modeled BC deposition and atmospheric measurements in the area. However, two lakes located closer to the Kola Peninsula (Russia) have recorded increasing SBC fluxes from 1970 to the present, which is likely caused by regional industrial emissions. The increasing...
Finland has some of the world's longest records of lake and river ice cover duration. Break-u... more Finland has some of the world's longest records of lake and river ice cover duration. Break-up dates of the river Tornionjoki have been registered since 1693 and break-up dates of many lakes since the early 19th century. However, most of the lake records originate from southern and central Finland. Ice cover records are considered to be even better indicators of past climate than temperature records. Direct human impact on ice cover dynamics is small, especially in Northern Finland. The projected climate warming will most probably lead to longer and warmer ice-free season and increased nutrient and carbon input from the catchment areas. In response, the total primary production is likely to increase and species composition changes will take place. Here, we use a diatom-based transfer function for the first time to quantitatively infer ice cover durations for the Holocene at four lakes in subarctic Fennoscandia. In general, all four lakes show relatively similar trends with the o...
Northern peatlands represent the biggest wetland complex in the world releasing 20 to 45 Tg CH4 t... more Northern peatlands represent the biggest wetland complex in the world releasing 20 to 45 Tg CH4 to the atmosphere annually. Recent research on the relationship between wetlands and past atmospheric concentrations of methane (ACM) over the Holocene, as revealed by ice-cores, has focused on the aerial extent of peatlands. Based on the frequency distribution of the basal peat radiocarbon dates
Paleoclimate reconstructions based on biological proxies present methodological challenges, espec... more Paleoclimate reconstructions based on biological proxies present methodological challenges, especially during non-analog conditions, such as the early Holocene. Here, two chironomid-based training sets from Finland were amalgamated to create a more accurate transfer function of summer air temperature. The aim was to reconstruct Holocene paleoclimate in northernmost Lapland, in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models. The results showed that the combined calibration model had improved performance statistics. The temperature trends inferred from the downcore chironomid record using the original and combined models were very similar. However, there were major changes in their absolute values with the combined model showing greatly improved accuracy. The chironomid-based temperature reconstruction showed significant correlation with the previous pollen-based reconstructions from northwestern Finnish Lapland. Ho...
Spheroidal carbonaceous particles (SCP) are a well-defined fraction of black carbon (BC), produce... more Spheroidal carbonaceous particles (SCP) are a well-defined fraction of black carbon (BC), produced only by the incomplete combustion of fossil fuels such as coal and oil. Their past concentrations have been studied using environmental archives, but, additionally, historical trends of BC concentration and deposition can be estimated by modelling. These models are based on BC emission inventories, but actual measurements of BC concentration and deposition play an essential role in their evaluation and validation. We use the chemistry transport model OsloCTM2 to model historical time series of BC concentration and deposition from energy and industrial sources and compare these to sedimentary measurements of SCPs obtained from lake sediments in Northern Europe from 1850 to 2010. To determine the origin of SCPs we generated back trajectories of air masses to the study sites. Generally, trends of SCP deposition and modelled results agree reasonably well, showing rapidly increasing values ...
Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern... more Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern Finnish Lapland are studied by comparison of various biological and sedimentological proxies with the 200-year long climate record, specifically reconstructed for the site using a data-set of European-wide meteorological data. The multi-proxy evidence of simultaneously changing diatom, Cladocera, and chrysophyte assemblages along with the increased rates
... Subarctic Fennoscandian Lakes Jan Weckstriim, Atte Korhola, and Tom Blom Laboratory of Physic... more ... Subarctic Fennoscandian Lakes Jan Weckstriim, Atte Korhola, and Tom Blom Laboratory of Physical Geography, Department of Geography, PO Box 9 (Siltavuorenpenger 20 A), FIN-00014 University of Helsinki, Finland. Abstract ...
We report a method for reconstructing temperatures from proxy data based on Bayesian multi-scale ... more We report a method for reconstructing temperatures from proxy data based on Bayesian multi-scale smoothing. The main features of the method is that it makes possible a simultaneous utilization of multiple proxies and sites to achieve a regional `consensus' reconstruction of temperature, it enables various types of uncertainties (e.g., chronology) to be taken into account, and that it also allows significant features to be detected from the emerging time series. Applying the method to multiple proxy data derived from lakes in Finnish Lapland suggests that, contrary to the conventional view, Holocene climate cooling in the North Atlantic region started already c. 8.5 kyr, and that climate since then was punctuated by several quasi-cyclical climate events, the forcing mechanisms of which are not yet fully understood. Our study suggests that inconsistencies in climate reconstructions between different proxy sources may be at least partly spurious; there is probably no single narrat...
Wetlands have been considered as the most important natural source of the atmospheric methane con... more Wetlands have been considered as the most important natural source of the atmospheric methane concentration (AMC) prior to anthropogenic influences. According to ice cores, AMC varied significantly during the Holocene, the causes of which are not completely understood. In particular, the reasons for the increased AMC during the late Holocene (from 5 ka onwards) have been debated widely, including an anthropogenic explanation. Initially, this increase was associated with increased emissions from northern wetlands, but estimated peat initiation rates seem not to support the conclusion. Based on a new data set of 954 basal peat radiocarbon dates that accounts more properly for the horizontal growth dynamics of northern peatlands (by containing only sites with multiple basal dates per site), we show here that the most extensive lateral expansion of high-latitude peatlands occurred only after 5 ka, parallel with the rise of CH 4 in the ice cores. Because this explosive increase in the extent of peatlands resulted in the formation of moist minerotrophic fen ecosystems that emit high amounts of CH 4 for a long time since their formation, and because many Arctic peatlands have remained minerotrophic throughout their development, northern peatlands cannot be neglected when seeking cause(s) for the late-Holocene rise in CH 4. A similar event in future could enhance climate change by causing a rapid shift in atmospheric greenhouse gas concentrations.
The application of molecular approaches to palaeovegetation reconstruction in peat is still relat... more The application of molecular approaches to palaeovegetation reconstruction in peat is still relatively rare, with molecular level studies of carbohydrate organic geochemistry being generally uncommon. In this report, neutral monosaccharides derived via acid hydrolysis were ...
The premise of this article is that climate effects on lakes can be quantified most effectively b... more The premise of this article is that climate effects on lakes can be quantified most effectively by the integration of process-oriented limnological studies with paleolimnological research, particularly when both disciplines operate within a common conceptual framework. To this end, the energy (E)-mass (m) flux framework (Em flux) is developed and applied to selected retrospective studies to demonstrate that climate variability regulates lake structure and function over diverse temporal and spatial scales through four main pathways: rapid direct transfer of E to the lake surface by irradiance, heat, and wind; slow indirect effects of E via changes in terrestrial development and subsequent m subsidies to lakes; direct influx of m as precipitation, particles, and solutes from the atmosphere; and indirect influx of water, suspended particles, and dissolved substances from the catchment. Sedimentary analyses are used to illustrate the unique effects of each pathway on lakes but suggest that interactions among mechanisms are complex and depend on the landscape position of lakes, catchment characteristics, the range of temporal variation of individual pathways, ontogenetic changes in lake basins, and the selective effects of humans on m transfers. In particular, preliminary synthesis suggests that m influx can overwhelm the direct effects of E transfer to lakes, especially when anthropogenic activities alter m subsidies from catchments.
Palaeoclimatic records derived from a variety of independent proxies provide evidence of post-gla... more Palaeoclimatic records derived from a variety of independent proxies provide evidence of post-glacial changes of temperature and soil moisture in northern Fennoscandia. We use pollen percentage, pollen influx, stomatal and chironomid records from Toskaljavri, a high-altitude lake in northern Finland, to assess how treelines and alpine vegetation there have responded to these climate changes. The evidence suggests that the cool, moist climate of the early Holocene supported birch forest in the area 9600 cal. yr BP onwards and that a rise of temperature triggered the immigration of pine at 8300 cal. yr BP. At 6100-4000 cal. yr BP altitudinal treeline in the area was formed by pine, in contrast to the modern situation where mountain birch reaches a higher elevation. Alpine vegetation also demonstrates clear changes. Plant communities typical of dry, oligotrophic heaths of northern Fennoscandia expanded during the dry climatic period at 7000-4000 cal. yr BP and decreased in response to cooler and moister conditions after 4000 cal. yr BP. Alpine plant communities favouring moist sites show an inverse pattern, expanding after a change towards moister climate after 4000 cal. yr BP. In a redundancy analysis (RDA), a statistically significant proportion of the variability in the total chironomid assemblages was captured by changes in the pollen types reflecting alpine vegetation typical of moist sites. Although chironomid community changes appeared to follow the major patterns in the alpine vegetation succession, the present study does not support a direct link between the changing treeline position and chironomid stratigraphy. Rather, the data indicate that the terrestrial and aquatic environments have each responded directly to the same ultimate cause, namely changing Holocene climate.
Over recent decades, palaeolimnological records from remote sites have provided convincing eviden... more Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with A celebration of Prof. Rick Battarbee's contributions to palaeolimnology, edited by Holmes et al. This paper has been written as a contribution to celebrating Rick Battarbee's influence on palaeolimnology. Some of us have benefitted from his leadership (and friendship) in transnational European projects during the last decade (e.g., ALPE, ALPE2, MOLAR, CHILL-10000, EMERGE, EUROLIMPACS), which together with some other initiatives spawned pan-European remote lake research. Others have respected Rick as a teacher, colleague and a friend. To some extent, this review follows the chronological order of topics addressed in these projects, which also respond to the growing social awareness about each issue. Rick also facilitated bridges between North American and European schools, and beyond. We expect his attitude towards collaboration will pervade and persist through the palaeolimnological community for years to come, and global change will certainly provide stimulating and challenging questions with which to do so.
Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still amo... more Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still among the least impacted lakes by humans. Hence they provide an excellent setting for studies on long-term climatic variability without the overriding effects of direct anthropogenic perturbation. On the other hand, these ecosystems are highly vulnerable to even moderate anthropogenic influence like long-distance airborne transport
Proceedings of the National Academy of Sciences of the United States of America, 2005
Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread speci... more Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.
Weather variation and climate fluctuations are the main sources of ecosystem variability in remot... more Weather variation and climate fluctuations are the main sources of ecosystem variability in remote mountain lakes. Here we describe the main patterns of seasonal variability in the ecosystems of nine lakes in Europe, and discuss the implications for recording climatic features in their sediments. Despite the diversity in latitude and size, the lakes showed a number of common features. They
ABSTRACT Clastic-biogenic varved lake sediments from Nautajarvi, Finland, covering the last ca. 1... more ABSTRACT Clastic-biogenic varved lake sediments from Nautajarvi, Finland, covering the last ca. 10000 years have previously been investigated with respect to varve chronology, laminae composition and thickness variations, palaeomagnetic secular variation, the pollen record and the diatom composition of selected sections. In this study, we provide detailed information on the seasonal sedimentation of different varve components and palaeolimnological indicators (diatoms, chrysophycaean cysts) using near-bottom sediment-trap monitoring. The monitoring results confirm previous interpretations of the formation of clastic-biogenic varves in Fennoscandian lakes. The results also indicate that seasonal sediment fluxes correspond with environmental changes. Higher snow storage in winter and the discharge intensity during the following spring snowmelt clearly increase the suspended sediment load, transportation and net accumulation of detrital mineral matter during spring and early summer. A prolonged autumn and subsequent freezing and thawing cycles in winter, conversely, result in an incremental but slow accumulation of assorted mineral matter and organic particles during winter, whereas the subsequent spring flooding and detrital sediment yield are diminished and thinner clastic laminae are formed. The accumulation rates of diatoms and chrysophyte cysts suggest that these algal groups are more dependent on seasonal processes (e.g. spring and autumnal overturn) than on rapid, short-lived environmental episodes such as the spring discharge peak.
The initiation and lateral expansion patterns of five small sub-arctic peatlands in the Fennoscan... more The initiation and lateral expansion patterns of five small sub-arctic peatlands in the Fennoscandian tree-line region were studied by 21 accelerator mass spectrometry (AMS) 14 C-dated basal-peat samples representing three to six dates per site. The radiocarbon dates were converted to calendar years and are based on the median probability. When combined with earlier basal-peat dates from the region, four distinctive periods can be observed in the cumulative record of the dates. The early Holocene, from c. 10 000 to 8000 cal. yr BP, was characterized by the fast initiation and rapid expansion of peatlands, whereas at 8000-4000 cal. yr BP lateral expansion was modest. The most intensive period of peatland expansion occurred at the beginning of the late Holocene at c. 4000 to 3000 cal. yr BP, after which it slowed down towards the present. All these periods are in rough agreement with the main Holocene climatic periods in the area, namely the relatively warm and moist early Holocene, the warm and dry Holocene thermal maximum (HTM) at 8000-4000 cal. yr BP, and the start of the cooler and moister trend (neoglacial cooling) from c. 4000 cal. yr BP to the present, indicating a broad-scale climatic control on the lateral growth of sub-arctic peatlands in Fennoscandia. In order to study the lateral expansion of peatlands and to evaluate their Holocene succession patterns, more studies based on multiple dates from the same peatland are needed.
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Papers by Atte Korhola