PAGES Magazine articles

Didier Galop1, T. Houet1, F. Mazier1, G. Leroux2 and D. Rius1

1Laboratory GEODE UMR 5602 CNRS (GEOgraphie De l’Environnement), University of Toulouse, France; didier.galopuniv-tlse2.fr

2ECOLAB UMR 5245 CNRS, University of Toulouse, France

Reconstruction of the relationship between pastoral activities and vegetation history in the central Pyrenees demonstrates the importance of grazing pressure in the maintenance of floristic diversity in highland regions that have been abandoned.

In the context of biodiversity management, as encouraged by the European Union Habitats Directives and by the implementation of national strategies, the preservation of traditional agro-pastoral farming activities (in particular extensive grazing), is a major issue acting to maintain or restore open land that is favorable to biodiversity. Here, we present a case from the Pyrenean Mountains, which is considered the most important mountainous massif in southern Europe due to its biodiversity and high levels of endemism. Since the mid 20th century, agricultural activities in these mountains have significantly declined, often accompanied by a change in grazing practices. From a pastoral point of view, the current situation in the Pyrenees is complex. In the Eastern Pyrenees, grazing areas are being abandoned, which is resulting in an expansion of heathland and forest. Conversely, in the Central and Western Pyrenees, an intensification of grazing is observed. This intensification creates problems that are characteristic of overgrazed areas; soil erosion and the fragmentation of animal habitats by fences. European and national policies are attempting to face this situation, where over-grazing and abandonment coexist, through support of conservation organizations, such as the Pyrenees national park, the regional natural parks, natural reserves, and nature charities, which participate in the local implementation of the networking program “Natura 2000” (Magda et al., 2001). The development of a co-management structure, with involvement of local and governmental environmental managers, is encouraged in order to set up strategies reconciling biodiversity conservation with restoration or maintenance of agro-pastoral activities. Pastoral activities are considered essential for maintaining open land, preventing the expansion of invasive species, and forestalling secondary succession of forests following past anthropogenic activities. For the majority of cases, a return to extensive grazing activities is highly recommended. However, this suggestion is often based on present-day observations with a temporal record spanning no more than 10 years (Canals and Sebastià, 2000).

The potential of incorporating historical ecology and paleoecology in conservation biology is now recognized, including their applicability to biodiversity maintenance, conservation evaluation and changing disturbance regimes. Paleo-studies can provide guidelines for environmental managers (Swetnam et al., 1999; Valsecchi et al., 2010). The effects of long-term, human-induced disturbances (i.e., grazing pressure) on ecosystem dynamics and their biodiversity still need to be further investigated.

A Human-Environment Observatory: Insights on future dynamics

The Upper Vicdessos Valley (Ariège, eastern Pyrenees) is representative of a common scenario in the Pyrenean massif where agro-pastoral activities have reached an extremely low level, now characterized only by extensive grazing. Successional processes involving encroachment of open land and overgrowth by trees are now occurring rapidly at all altitudes. Hill slopes have all been subjected to an overwhelming encroachment of fallow land (Betula, Fraxinus, Corylus) whereas altitude zones used for summer grazing are progressively colonized by heathland (principally Juniperus communis, Calluna vulgaris, Cytisus scoparius). After thousands of years of intense agro-silvo-pastoral activities (going back to the late Neolithic period, Galop and Jalut, 1994), a rapid decline in human activities linked to rural depopulation took place during the first half of the 20th century.

The Vicdessos Valley is therefore a particularly interesting case study. Since 2009, a Human-Environment Observatory (http://w3.ohmpyr.univ-tlse2.fr/presentation_ohm_pyr.php) headed by the laboratory GEODE was set up by the Institute of Ecology and Environment of the French National Center for Scientific Research (INEE-CNRS). It aims to monitor past and present evolutions of human-environment interactions in order to anticipate future dynamics and consequently to provide a scientific basis for understanding the functioning of social-ecological systems. This implies a close collaboration with local and governmental planners in charge of management and conservation of landscapes and ecosystems. The observatory is a multidisciplinary consortium bringing together scientists to work on integrated micro-regional research (Pyrenean Valley scale). It involves observations and measures of present dynamics (e.g., meteorological and climatic observations, experimental approaches, monitoring of plant and animal communities) and studies of past human activities over long-term timescales. The latter uses instrumental and documentary data sources, tree demography (dendrology), old maps, agricultural statistics, aerial photographs, and long-term sedimentary proxy data (e.g., sedimentology, biogeochemistry, pollen and charcoal) from lakes and bogs in the valley.

From over-grazing to abandonment: 200 years of grazing activities

Figure 1: Trajectories of changes observed since the beginning of the 19th century in the Bassiès Valley based on historical and paleodata. a) Evolution of the Auzat commune population; b) Comparison between the evolution of grazing pressure recorded in agricultural statistics of the Auzat commune and the estimated palynological richness (E(Tn)) inferred from pollen records from the Orry de Théo peat bog; c) Ash content (mineral fraction; LOI 550°C) recorded in the Orry de Théo peat bog; d) Charcoal (>150 µm) accumulation rate reconstructed in the Orry de Théo peat profile; e) Pollen accumulation rates (g cm-2 a-1) of selected taxa recorded in the Orry de Théo peat bog. This reconstruction shows, at a local scale, the change from a scenario of over-grazing to a near-total abandonment of summer pastoral farming activities. In the 1950s, an important period of transition is noted during which grazing pressure can no longer curb the development of heathland species and tree recolonization (dashed gray line).

Figure 2: Maps based on aerial photographs (French National Geographic Institute) showing vegetation and land-use changes in the Bassiès Valley between 1962 and 2008. The grazing decline (orange area) is concomitant with increasing forest density, principally dominated by an expansion of Pinus uncinata and birch (aqua and purple areas). This density increase has been particularly rapid during the last 20 years as shown by the repeat photographs taken in the valley’s pastoral zones between 1976 and 2009.

In the Vicdessos Valley, the hanging valley of Bassiès (altitude between 1400 and 2500 m asl) lies one of the study sites of the observatory. The research focuses on the impact of grazing activities on high-altitude ecosystems. Paleoecological data, including pollen and charcoal (>150 µm) accumulation rates and loss-on-ignition (LOI), have been retrieved from the small peat bog of Orry de Théo. This sequence illustrates the history of vegetation cover, soil erosion and fire in relation to grazing activities over the last 200 years (Fig. 1). Rarefaction analysis was undertaken on pollen data to estimate the variations of palynological richness assumed to reflect the floristic diversity, and vegetation and landscape dynamics over time (Berglund et al., 2008). The comparison of the palynological richness with documentary sources (demographic data and book records of number of cattle in the valley) provides valuable insights on the role of human-induced disturbances such as grazing activities on floristic and landscape diversity. Figure 1 shows a positive association between grazing pressure and floristic richness. This correlation remains high until around the 1920s despite a decrease in sheep numbers, whereas the presence of cattle leads to soil degradation. A threshold is reached in the 1950s: the decline of flocks associated with a modification of pastoral practices leads to under-grazing and limits the soil erosion. At the same time, the overgrowing of Juniper and Calluna heathlands and the expansion of trees (Pinus and Betula), no longer controlled by browsing, are favored. Fire signatures recorded between 1950 and 1970 may indicate the use of fire by the shepherds to restore and clear their pastures. From the beginning of the 1980s, a significant reduction in the number of farmers in the valley has progressively led to a near-total disappearance of grazing activity. In these previously grazed areas, an inevitable and probably irreversible (except through expensive restoration actions) return to forest has led to a decline in floristic diversity. Landscape dynamics are illustrated by reconstructions based on aerial photographs taken between 1962 and 2008 as well as repeat photographs showing the progression of pine-dominated forest between 1976 and 2009 (Fig. 2). The correspondence between paleoecological data and documentary sources confirms the complementarity of the approaches.

The local case study of the Bassiès Valley gives information on diversity baselines, thresholds, and the resilience of mountainous ecosystems to anthropogenic disturbances. This study is also rich in lessons on the loss of floristic diversity related to the variability or the decline in grazing activities and to pine-dominated secondary succession in a context of under-grazing. This kind of integration of data is already being used by managers to affirm the necessity or futility of restoration actions, and especially to avoid thresholds and to reverse the trajectories of key processes.

references

Berglund, B.E., Gaillard, M.-J., Björkman, L. and Persson, T., 2008: Long-term changes in floristic diversity in southern Sweden: palynological richness, vegetation dynamics and land-use, Vegetation History and Archaeobotany 17: 573-583

Canals, R.-M. and Sebastià, M.-T., 2000: Analyzing mechanisms regulating diversity in rangelands through comparative studies: a case in the southwestern Pyrenees, Biodiversity and Conservation 9: 965-984

Galop, D. and Jalut, G., 1994: Differential human impact and vegetation history in two adjacent Pyrenean valleys in the Ariège basin, southern France, from 3000 BP to the present, Vegetation History and Archeobotany 4: 225-244

Swetnam, T.W., Allen, C.D. and Betancour, J.L., 1999: Applied historical ecology: using the past to manage the future, Ecological applications 9(4): 1189-1206

Valsecchi, V., Carraro, G., Conedera, M. and Tinner, W., 2010: Late-Holocene vegetation and land-use dynamics in the southern Alps (Switzerland) as a basis for nature protection and forest management, The Holocene 20(4): 483-495

For full references please consult: pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Thomas Foster

University of West Georgia, Carrollton, USA; tfosterwestga.edu

This article discusses how long-term regional data from historic documents, palynology and archeology are combined to inform decisions about biodiversity management in the southeastern United States.

The United States proactively manages federally owned lands with an objective to mitigate/limit the impacts of land-use activities on the long-term stability of the environment. For example, the United States Department of Defense (DoD) manages around 25 million acres of national military land. Impacts of military land use can include soil erosion, loss of endangered species, and degradation of habitats (Goran et al., 2002). Management involves planning and assessment that takes into consideration the types of environment to be managed and how they have changed over time, in order to maintain lands for training and operations. Fort Benning, founded in 1920, is a military base in Georgia and Alabama in the southeastern United States. It covers an area of 1052 km2 and is situated near the fall line of the Coastal Plain where soils consist of clay beds and sandy alluvial deposits (Fenneman, 1938). The pre-European (before ca. AD 1825) forest was primarily a pine-blackjack oak forest (Black et al., 2002). This article summarizes some recent research on long-term environmental changes and how it is being used to manage current ecological problems.

Ecological Problems

At Fort Benning, management challenges include protection of federally endangered Red Cockaded Woodpecker (Picoides borealis) and habitats important to rare species, such as the Gopher Tortoise (Gopherus polyphemus) and relict Trillium (Trillium reliquum) (Addington, 2004), as well as combating erosion (Fehmi et al., 2004). Proscribed forest fires have to be scheduled so as to maximize ideal training environments (e.g., reduced undergrowth) and preserve a forest composition that is conducive to species diversity and protects endangered species. Environmental managers at Fort Benning not only need to understand the long-term dynamics of the landscape but must also have the management tools for planning.

Therefore, as highlighted in a series of recent publications (Dale et al., 2002; Dale et al., 2004; Dale and Polasky, 2007; Foster, 2007; Foster et al., 2004; Foster and Cohen, 2007; Foster et al., 2010; Goran et al., 2002; Olsen et al., 2007), the DoD has funded research at Fort Benning focused on identifying long-term ecological metrics, human population settlement, and human activities that may have altered the environment.

Data Sources

Figure 1: Graph showing the relative abundance of forest cover at Fort Benning, Georgia from 1827-1999 (adapted from Olsen et al., 2007). Data were collected from historic documents and satellite imagery.

Environmental management at Fort Benning has included the use of archeology, historic documents, historic and modern satellite images, and pollen from sediment cores. For example, historical “witness tree” records reveal pre-European settlement forest composition. Witness trees are boundary markers recorded on land survey maps that were created when lands were acquired by the state and federal government in the late 18th to early 19th century in Georgia and Alabama. The corner trees and four "witness trees" were recorded at the corners of each survey lot (approximately 82 ha), and the species of the trees were noted on maps and field notes. These data provide a record of the forest composition at the time that the Native Americans were removed by state and federal agencies in the early 19th century and represent the pre-European forests and the forests under Native American management. These data were synthesized into a GIS and compared to historical satellite images (1974-1999; Fig. 1). Knowledge of human settlement and its intensity was revealed by systematic sampling of the military base with archeological investigation. The entire base was examined for human activity at 5 to 30 m intervals. The remains of human activity were analyzed for behavior type, intensity, population density, and economic activity. Lastly, long-term forest composition change was provided by analyzing pollen sequences from peat cores. Cores were dated with 137Cs/210Pb and 14C (Foster and Cohen, 2007).

Findings

As revealed through archeological investigations, Native Americans had lived in the Fort Benning region for at least 10,000 years though their management of the forest had changed dramatically in the last 1000 years (Foster, 2007; Kane and Keeton, 2000). European settlement and military activities within the last 100-200 years further affected the modern environment. Comparisons of the Native American managed forest to satellite imagery during the 20th century indicates that the land cover at Fort Benning has changed significantly (Olsen et al., 2007). The prevailing trend is a decrease in pine and increase in deciduous forest (Fig. 1). Pine forest cover decreased from nearly 80% to below 40% from 1827 to 1999. The increase in deciduous forest is mostly associated with riparian areas, as the riparian areas became larger (Olsen et al., 2007). Forest cover was cut down soon after this area was settled by United States citizens, which resulted in increased soil erosion and habitat degradation (Foster and Cohen, 2007).

Figure 2: A) Pollen abundance from the Hite Bowl site, Fort Benning, Georgia (adapted from Foster and Cohen 2007). B) Same as A) for the Beaver Dam site. These two plots illustrate the localized effect of human activity on vegetation cover.

Analysis of pollen and charcoal from sediment cores revealed that change in forest composition was localized and affected by human activity. Figure 2 shows the significant changes in pollen composition since Native Americans were removed from the region around 1830. Pinus and Nyssa have increased in some localized areas whereas Sphagnum has decreased. The Native Americans had localized effects on pine and some hardwood species.

Lessons for management

Archeological data, in combination with analysis of pollen, charcoal and fungi from sediment cores (Foster and Cohen, 2007), indicate that the long term effects of human activity are highly localized. Sediment core data indicates that in areas where Native American settlement was dense, pine forest has increased dramatically since European and military settlement (Foster and Cohen, 2007). While in the areas where native people were less densely settled, pine forest has remained approximately the same (Fig. 2; Foster and Cohen, 2007).

Overall, the management plan at Fort Benning has prescribed intensive land use in some areas while preserving others. Based on comparisons of forest composition inside the base to that outside the base, this plan has increased the habitat for endangered species, such as the Red-Cockaded Woodpecker (Picoides borealis), to a level that is higher than the regions outside of the military boundary (Olsen et al., 2007). Long-term data have also revealed the localized effects of management policies and are being used to design better policies that are sensitive to the range of biological diversity at Fort Benning.

The combination of long-term data on human settlement and economic activity combined with long-term ecological data reveal that the modern management of forest ecosystems is complicated and regionally variable. Though these data were recovered using diverse methods and varying units of investigation, they can be combined for regional analysis of long-term environmental change. Management decisions that cross ecological regions will likely include variable human activities and ecological conditions. In the case of Fort Benning, modern management has increased pine density beyond that created by pre-European settlement in one region and decreased pine density in another region beyond that of the pre-European forests. An understanding of this process can only be gained through regional analysis of long-term environmental data combined with anthropological understanding of human activities. These data permit modern forest managers to understand the long-term effects of anthropogenic change and the interaction of those changes with the forest ecosystem. Such a long-term perspective is leading to better informed management practices.

data

Data referenced in this article are available at http://semp.cecer.army.mil

references

Black, B.A., Foster, H.T. II and Abrams, M.D., 2002: Combining environmentally dependent and independent analyses of witness tree data in east-central Alabama, Canadian Journal of Forest Research 32: 2060-2075

Dale, V.H., et al., 2004: Selecting a Suite of Ecological Indicators for Resource Management. In: L.A. Kapustka, H., et al. (Eds), Landscape Ecology and Wildlife Habitat Evaluation: Critical Information for Ecological Risk Assessment, Land-Use Management Activities and Biodiversity Enhancement Practices, ASTM STP, ASTM International, 3-17

Foster, H.T. II, Black, B. and Abrams, M.D., 2004: A Witness Tree Analysis of the Effects of Native American Indians on the Pre-European Settlement Forests in East-Central Alabama, Human Ecology, 32(1): 27-47

Foster, H.T. II and Cohen, A., 2007: Palynological evidence of the effects of the deerskin trade on eighteenth century forests of southeastern North America, American Antiquity 72(1): 35-51

Olsen, L.M., Dale, V.H. and Foster, H.T. II, 2007: Landscape Patterns as Indicators of Ecological Change at Fort Benning, Georgia, Landscape and Urban Planning 79(2): 137-149

For full references please consult: http://pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Colleen E. McLean1, D.T. Long2 and B. Pijanowski3

1Department of Geological and Environmental Sciences, Youngstown State University, USA; cemcleanysu.edu

2Department of Geological Sciences, Michigan State University, USA

3Department of Forestry and Natural Resources, Purdue University, West Lafayette, USA

Sediment geochemistry and diatom biostratigraphy can be used to identify stressor-response relationships in aquatic ecosystems for improved regional management strategies.

Aquatic ecosystems in the Great Lakes region of North America have been significantly altered since Euro-American settlement in the late 1700s. Human activities contributing to environmental degradation initially included population increase, land use change, and dramatic industrialization (Alexander, 2006). An understanding of the state of modern aquatic ecosystems can be gleaned from reconstructing the environmental history of the region. Integrating historical records with high-resolution paleolimnological data is an effective way to capture stressor-response relationships and evaluate human influence. These relationships facilitate an understanding of comprehensive aquatic ecosystem response, and are useful for developing predictive tools for future anthropogenic influences. Having such tools is critical for developing sustainable management strategies, and can be used directly by decision makers at the regional scale.

Impacts in the Laurentian Great Lakes Region

A sediment core from Muskegon Lake, Michigan, USA, was analyzed for multiple proxies to assess the system’s response and recovery to human activity, with particular attention to ecosystem recovery since the introduction of environmental legislation in the United States (e.g., Clean Air and Clean Water Acts). Muskegon Lake is a 16.91 km2 inland water body located in the Laurentian Great Lakes region (86°18’ W, 43°14’N) (Parsons et al., 2004). Its mean depth is 7 m with a maximum depth of 23 m. Muskegon Lake itself is the end point of a drowned river mouth system that connects the Muskegon River Watershed to the coastal zone of Lake Michigan through a navigation channel (Steinman et al., 2008). This proximity to the Great Lakes and general ecological setting make it an important fishery, though invasive species, habitat loss and degradation continue to be factors of concern (Lake Michigan Lakewide Management Plan, 2004).

Figure 1: Trends of land use change since 1900 (Ray and Pijanowski, 2010) for the Muskegon River Watershed (location green on map inset), population data for Muskegon county since 1860 (US Census) and regional scale human impacts since Euro-American settlement. WWTP = Wastewater Treatment Plant.

Muskegon Lake has a history of intense anthropogenic activity since the early 1800s (summarized in Fig. 1). During the lumber peak in the 1880s, the city of Muskegon had more than 47 sawmills. Following the depletion of lumber resources, Muskegon developed an industrial base, with oil and chemical industries being prominent (Alexander, 2006). In the mid-1900s, foundries, metal finishing plants, a paper mill and petrochemical storage facilities were built on the shore of Muskegon Lake (Steinman et al., 2008). Expansion of heavy industry and shipping in 1960s and 1970s contributed to over 100 000 m3/day of wastewater discharged from industrial and municipal sources into the lake until a tertiary Waste Water Treatment Plant (WWTP) was installed in 1973 (Freedman et al., 1979; Steinman et al., 2008). Currently, there are eight abandoned hazardous waste sites (USEPA Superfund sites) in the region and fish consumption advisories have been issued due to significant levels of PCB (Polychlorinated biphenyls) and mercury.

Environmental response to regional impacts

Figure 2: A) Profiles of select anthropogenic elements with concentrations normalized to highest concentration of each element, B) Normalized sediment phosphorus (P) profile (as a measure of water quality) with measured concentrations of water column soluble reactive P and water column total P from 1972 and 2005 (Freedman et al., 1979; Steinman et al., 2008), and C) Relative abundances of select fossil diatoms indicative of water quality changes.

Analyses of geochemical data from the sediment core showed suites of elements that corresponded to the source of the sediment, including terrestrial in wash, primary productivity, redox sensitive and anthropogenic related material (Long et al., 2010; Yohn et al., 2002). Elements influenced by terrestrial processes (e.g., Al, K, Ti and Mg) reflected drowned river mouth conditions of Muskegon Lake, and recorded deforestation-induced erosion in the late 1800s. Productivity related elements (e.g., P and Ca) indicated changes with nutrient inputs to the lake (presumably related land use change). Redox sensitive elements (e.g., Fe and Mn) were important for interpreting the redox state of the system. Elements associated with anthropogenic activity (e.g., Cr, Pb and Sn) had similar profiles, which closely track the history of human activity (see Fig. 2A), though concentration peaks for individual elements varied by specific industrial activity. For example, driven in part by policy mandates (e.g., discontinued use of leaded gasoline) Pb decreased to ~60 ppm in modern sediment from a peak of ~325 ppm, reflecting significant recovery from peak concentrations of anthropogenic elements. However, the Pb values did not return to the pre-disturbance Pb concentration of ~11 ppm. The geochemical reference condition was evaluated using sediment concentration profiles of the anthropogenic proxy group, which best indicates the pre-Euro/American settlement conditions. Results show that modern concentrations of anthropogenic elements have not decreased to the historical geochemical reference condition (e.g., Pb).

Biological change in Muskegon Lake, inferred from fossil diatoms, suggests that the pre-settlement community structure is markedly different from that of modern assemblages. Figure 2 includes specific diatom biostratigraphic changes that correspond to the timeline of various human stressors, including water chemistry changes resulting from agricultural development, industrialization and urbanization of the watershed. For example, taxa indicating high nutrient conditions (e.g., Stephanodiscus spp.) have peak abundances dated between 1930s and 1970s when nutrient inputs were increasing due to agriculture and urbanization. Moreover, productivity regimes in the lake, reconstructed from diatom habitat structure, identified a significant shift from planktonic- to benthic-dominated productivity in the top 25 cm of the core; this shift is dated to after the installation of the WWTP in 1973. Much of the water quality improvements in the past 30 years, reported by Freedman et al. (1979) and Steinman et al. (2008), and also noted in Figure 2, are presumably attributed to the WWTP installation. Decreases in lake-wide averages of total phosphorus and soluble reactive phosphorus at the water surface range from 68 to 27 μg/L and from 20 to 5 μg/L, respectively from 1972 to 2005. In addition, average chlorophyll-a concentrations have declined by 19 μg/L over this period, while Secchi disk depths (a measure for water transparency) have increased from 1.5 to 2.2 m (Freedman et al., 1979; Steinman et al., 2008). This partial recovery corresponds to the shift in dominant habitat of primary productivity, as the relative abundance of planktonic dominated taxa at the bottom of the core (i.e., in pre-settlement times) is between 56 and 77%, peaks at 88% in 24 cm depth (dated to 1970 at the peak of cultural eutrophication), and then quickly decreases to 26-37% in the top 8 cm of the core. The productivity shift in the top 8 cm (benthic taxa become 54-64% dominant) may also be influenced by the invasion of Dreissena polymorpha (zebra mussel).

This study identified causal agents at the regional scale directly linked to human activities such as deforestation, agriculture, industry and urbanization with an integration of geochemical and biological data inferred from fossil diatoms. Overall, the state of the lake system has dramatically improved as the result of environmental management efforts, and this study can be used as an indicator for the response of the larger Lake Michigan that it feeds into (Wolin and Stoermer, 2005). However, recent proxy trends (e.g., sediment P) do not indicate that the system has stabilized, suggesting that modern stressors such as climate variability (Long et al., 2010; Magnuson et al., 1997), invasive species (Lougheed and Stevenson 2004; Steinman et al., 2008) and further land use alterations (Ray and Pijanowski 2010; Pijanowski et al., 2007; Tang et al., 2005) whose influence remain uncertain, are likely to influence system recovery.

Recovery challenges and recommendations

Efforts to manage the watershed have reduced the loading of metals and nutrients, improving the ecological health of Muskegon Lake as evidenced by geochemistry and diatom biostratigraphy. The current geochemical conditions demonstrate significant recovery from high concentrations of anthropogenic elements and the fossil diatom record from this core suggests that efforts to reduce nutrient loading have been successful. Despite improvements, these data indicate that the system is still changing in response to human impacts at the regional watershed scale, suggesting that management strategies also need to target non-point source inputs. As such, it is recommended that modern remediation targets consider the legacy and overprint of multiple stressors, as well as be aware of emerging stressors that could further alter ecological dynamics in the larger Great Lakes Region.

acknowledgements

We thank the Great Lakes Fisheries Trust for funding this research, and the Aqueous and Environmental Geochemistry Laboratory at MSU for providing financial and technical support. Glen Schmitt and the Michigan Department of Environmental Quality are recognized for help in the field. Special thanks to Dr. Nadja Ognjanova-Rumenova for diatom taxonomical processing and identification.

references

Alexander, J., 2006: The Muskegon: The Majesty and Tragedy of Michigan’s Rarest River, Michigan State University Press, 1-214 pp

Freedman, P., Canale, R. and Auer, M., 1979: The impact of wastewater diversion spray irrigation on water quality in Muskegon County lakes, U.S. Environmental Protection Agency, Washington, D.C. EPA 905/9-79-006-A

Long, D.T., Parsons, M.J., Yansa, C.H., Yohn, S.S., McLean, C.E. and Vannier, R.G., 2010: Assessing the response of watersheds to catastrophic (logging) and possible secular (global temperature change) perturbations using sediment-chemical chronologies, Applied Geochemistry 25: 143-158

Pijanowski, B., Ray, D.K., Kendall, A.D., Duckles, J.M. and Hyndman, D.W., 2007: Using backcast landuse change and groundwater travel-time models to generate land-use legacy maps for watershed management, Ecology and Society 12(2): 25

Steinman, A., Ogdahl, M., Rediske, R., Ruetz, C.R. III, Biddanda, B.A. and Nemeth, L., 2008: Current Status and Trends in Muskegon Lake, Michigan, Journal of Great Lakes Research 34: 169-188

For full references please consult: http://pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Lucí Hidalgo Nunes

Department of Geography, State University of Campinas, Brazil; luciige.unicamp.br

The growing severity of floods and landslides in the state of São Paulo, Brazil, is related to rapid environmental changes, such as urbanization, deforestation and settlement in hazardous areas, rather than to natural events, and unless more sustainable land-use practices are adopted the impact of these (un)natural disasters might become more severe.

Michael Reid1 and Peter Gell2

1University of New England, Australia; mreid24une.edu.au

2University of Ballarat, Australia

Paleoecological records from billabongs (floodplain lakes) in southern Australia can be used to develop ecosystem response models that describe how the underlying hydrology and geomorphology of these aquatic ecosystems control their resilience to anthropogenic stressors.

Chris R. Brodie1,2

1Department of Geography, Durham University, UK

2Department of Earth Sciences, Hong Kong University, Hong Kong: brodiehku.hk

Acid treatment of organic materials, necessary to remove inorganic carbon prior to isotopic analysis, adds an unpredictable and non-linear bias to measured C/N, δ13C and δ15N values questioning their reliability and interpretation.

Michael Zemp1, H.J. Zumbühl2, S.U. Nussbaumer1,2, M.H. Masiokas3, L.E. Espizua3 and P. Pitte3

1World Glacier Monitoring Service, Department of Geography, University of Zurich, Switzerland; michael.zempgeo.uzh.ch

2Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Switzerland

3Argentine Institute of Snow Research, Glaciology and Environmental Sciences, (IANIGLA), CCT-CONICET Mendoza, Argentina

Reconstructions of glacier front variations based on well-dated historical evidence from the Alps, Scandinavia, and the southern Andes, extend the observational record as far back as the 16th century. The standardized compilation of paleo-glacier length changes is now an integral part of the internationally coordinated glacier monitoring system.

Glaciers are sensitive indicators of climatic changes and, as such, key targets within the international Global Climate Observing System (GCOS, 2010). Glacier dynamics contribute significantly to global sea level variations, alter the regional hydrology, and determine the vulnerability to local natural hazards. The worldwide monitoring of glacier distribution and fluctuations has been well established for more than a century (World Glacier Monitoring Service, 2008). Direct measurements of seasonal and annual glacier mass balance, which are available for the past six decades, allow us to quantify the response of a glacier to climatic changes. The variations of a glacier front position represents an indirect, delayed, filtered and enhanced response to changes in climate over glacier-specific response times of up to several decades (Jóhannesson et al., 1989; Haeberli and Hoelzle, 1995; Oerlemans, 2007). Regular observations of glacier front variations have been carried out in Europe and elsewhere since the late 19th century. Information on earlier glacier fluctuations can be reconstructed from moraines, early photographs, drawings, paintings, prints, maps, and written documents. Extensive research (mainly in Europe and the Americas) has been carried out to reconstruct glaciers fluctuations through the Little Ice Age (LIA) and Holocene (e.g., Zumbühl, 1980; Zumbühl et al., 1983; Karlén, 1988; Zumbühl and Holzhauser, 1988; Luckman, 1993; Tribolet, 1998; Nicolussi and Patzelt, 2000; Holzhauser et al., 2005; Nussbaumer et al., 2007; Zumbühl et al., 2008; Masiokas et al., 2009; Nesje, 2009; Holzhauser, 2010; Nussbaumer and Zumbühl, 2011). However, the majority of the data remains inaccessible to the scientific community, which limits the verification and direct comparison of the results. In this article, we document our first attempt towards standardizing reconstructed glacier front variations and integrating them with in situ measurement data of the World Glacier Monitoring Service (WGMS).

Standardization and database

The standardization of glacier front variations is designed to allow seamless comparison between reconstructions and in situ observations while still providing the most relevant information on methods and uncertainties of the individual data series. The standardized compilation of in situ observations is straightforward: the change in glacier front position is determined between two points in time and supplemented by information on survey dates, methods and data accuracies. The reconstruction of paleo-glacier front positions and their dating is usually more complex and based on multiple sources of evidence. Spatial uncertainty can arise from ambiguous identification of the glacier terminus, while temporal uncertainty is associated with the dating technique used in each case. A good example is the use of oil paintings, where it is important to distinguish between the time of first draft (e.g., a landscape drawing in the field) and production of the painting itself, which could happen several years later.

Figure 1: Fluctuations of the Mer de Glace, France, during and following the LIA, reconstructed from a variety of sources (Nussbaumer et al., 2007). Length changes (relative to AD 1644 = maximum of LIA) were derived from documentary data as shown in the compilation below the x-axis, where small horizontal lines indicate uncertainties concerning the date of the document. Landmarks are indicated beside the y-axis. In situ measurements for the 1911–2003 period were obtained from the Laboratory of Glaciology and Geophysical Environment in Grenoble. Images a–d: The Mer de Glace (a) in 1804 drawn by Jean-Antoine Linck, (b) in 1842 mapped by James David Forbes, (c) in the 1850s photographed by Henri Plaut, and (d) in 2005 (Nussbaumer et al., 2007).

The concept of integration of reconstructed front variations into the relational glacier database of the WGMS was jointly developed by natural and historical scientists. The glacier reconstruction data are stored in two data tables. The first table contains summary information of the entire reconstruction series including a figure of the cumulative length changes, investigator information, and references. The second table stores the individual glacier front variation data, minimum and maximum glacier elevation, and metadata related to the reconstruction methods and uncertainties. The metadata are stored in a combination of predefined choices of methods and open text fields. This ensures a standardized description of the data, but also provides space for individual remarks. Both data tables are linked by a unique numeric glacier identifier to the main table of the WGMS database with general information of the present-day glacier. This database relationship enables the direct comparison of reconstructed with observed front variations. Figure 1 shows an example for the Mer de Glace glacier with the sum of available meta-information stored within the database.

Results and discussion

Figure 2: Reconstructed and measured cumulative glacier front variations in the Alps, Norway and southern South America since the Little Ice Age (LIA). The zero value on the y-axis corresponds to the most extensive front position of glaciers during the LIA. The period with direct front measurements is indicated by light green background. Gray vertical bars show the total number of available data for the selected glaciers. Note the significantly lower number of data points available from the Southern Andes.

The WGMS database contains detailed inventory information of about 100,000 glaciers worldwide. In addition, in situ observations of frontal variations of 1,800 glaciers, mass balance data of 230 glaciers, and reconstructed frontal variations of the 26 glaciers mentioned below are now readily available in standardized and digital form. The reconstructed front variations extend the direct observations (mostly from the 20th century) by two centuries in Norway and by four centuries in the Alps and South America. Also available are moraines data back to the mid-Holocene. The direct comparison of long-term reconstructions with in situ observations reveals some striking features (Fig. 2).

The investigated glaciers in the western and central Alps show several periods of marked advances during the LIA, that are similar or even larger than LIA extent around AD 1850. Reconstructions reveal dramatic glacier advances that started in the late 16th century, overran cropland and hamlets, and reached maximum lengths at ca. AD 1600 and 1640 (Zumbühl, 1980; Nussbaumer et al., 2007; Steiner et al., 2008). Further maxima in glacier extent were reached around AD 1720, 1780, 1820 and 1850. After this last event, the direct measurement series show an impressive glacier retreat of 1-3 km, with intermittent minor re-advances in the 1890s, 1920s and between AD 1965 and 1985.

The historically based reconstructions for glaciers in southern Norway (Nussbaumer et al., 2011; Nesje, 2009) indicate that the maximum glacial extent of the LIA peaked around AD 1750 at Jostedalsbreen and in the late 1870s at Folgefonna. The reconstructed front variation series of Nigardsbreen (an outlet glacier of Jostedalsbreen) shows that the maximum LIA expansion occurred in AD 1748, and that it was preceded by a period of strong frontal advance that lasted (at least) 3-4 decades. Other sources report devastation of pastures by neighboring glaciers at that time (Nussbaumer et al., 2011). Direct observations at Nigardsbreen and other glaciers in southern Norway reveal a regional pattern of recent intermittent re-advances mainly during the 1990s. It is worthwhile to note that the extent of Nigardsbreen in the 17th century was similar to that of the present day (Nesje et al., 2008), and that the period of glacier re-advances in the 1990s is short (both in time and extension) considering the overall retreat of 1-4 km since the LIA maximum.

In southern South America, datable evidence for past glacier variations is most abundant in the Patagonian Andes. Despite recent efforts in this region and in other Andean sites to the north (Espizua, 2005; Espizua and Pitte, 2009; Jomelli et al., 2009; Masiokas et al., 2009), the number of chronologies of glacier fluctuations prior to the 20th century is still limited. In the southern Andes, most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. Based on the available evidence, Glaciar Frías (northern Patagonian Andes) probably contains the best-documented history of fluctuations since the LIA in southern South America, covering the period between AD 1639-2009.

Conclusions and outlook

Reconstructed LIA and Holocene glacier front variations are crucial for understanding past glacier dynamics and enable an objective assessment of the relative significance of recent glacier fluctuations (i.e., 20th and late 19th century changes) in a long-term context. The standardized compilation and free dissemination of reconstructed and in situ observed glacier fluctuation records offer several benefits for both data providers and users. Their incorporation within the international glacier databases guarantees the long-term availability of the data series and increases the visibility of the scientific results (which in historical glaciology are often the work of a lifetime). Furthermore, the database facilitates comparisons between glaciers and between different methods, and opens the field to numerous scientific studies and applications.

As the next steps of this new initiative, we aim to: (1) integrate a greater number of time series, (2) incorporate records that cover the entire Holocene, and (3) include data from other regions (e.g., the Himalayas, North America). Ideally, the growing new dataset will facilitate collaboration between the glacier monitoring and reconstruction communities and become an additional tool for the comparison of present-day to pre-industrial climate changes. This should eventually result in new scientific findings (e.g., related to the climatic interpretation of past and present glacier fluctuations).

International glacier databases: Requesting and submitting data

Worldwide collection of standardized data on the distribution and changes of glaciers has been internationally coordinated since 1894. Today, the World Glacier Monitoring Service (www.wgms.ch) is in charge of the compilation and dissemination of glacier datasets in close collaboration with the US National Snow and Ice Data Center (www.nsidc.org) and the Global Land Ice Measurement from Space initiative (www.glims.org) within the framework of the Global Terrestrial Network for Glaciers (www.gtn-g.org).

For available data or guidelines on data submission please check these websites and/or contact us directly: wgmsgeo.uzh.ch

acknowledgements

We are grateful to Wilfried Haeberli and Heinz Wanner for their valuable assistance. This work has been supported by the Swiss National Science Foundation (grant 200021-116354). The collection and processing of data from Argentinean glaciers was supported by Agencia Nacional de Promoción Científica y Tecnológica (grants PICT02-7-10033, PICT07-03093 and PICTR02-186), and the Projects CRN03 and CRN2047 from the Inter American Institute for Global Change Research (IAI).

references

Holzhauser, H., Magny, M. and Zumbühl, H.J., 2005: Glacier and lake-level variations in west-central Europe over the last 3500 years, The Holocene 15(6): 789-801

Masiokas, M.H., Rivera, A., Espizua, L.E., Villalba, R., Delgado, S. and Aravena, J.C., 2009: Glacier fluctuations in extratropical South America during the past 1000 years, Palaeogeography, Palaeoclimatology, Palaeoecology 281(3-4): 242-268

Nussbaumer, S.U., Zumbühl, H.J. and Steiner, D., 2007: Fluctuations of the Mer de Glace (Mont Blanc area, France) AD 1500–2050: an interdisciplinary approach using new historical data and neural network simulations, Zeitschrift für Gletscherkunde und Glazialgeologie 40(2005/2006): 1-183

WGMS, 2008: Global Glacier Changes: facts and figures, Zemp, M., Roer, I., Kääb, A., Hoelzle, M., Paul, F. and Haeberli, W. (Eds.), UNEP, World Glacier Monitoring Service, Zurich, Switzerland, 88 pp

Zumbühl, H.J., 1980: Die Schwankungen der Grindelwaldgletscher in den historischen Bild- und Schriftquellen des 12. bis 19. Jahrhunderts. Ein Beitrag zur Gletschergeschichte und Erforschung des Alpenraumes, Denkschriften der Schweizerischen Naturforschenden Gesellschaft (SNG), Band 92. Birkhäuser, Basel/Boston/Stuttgart, 279 pp

For full references please consult: http://pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Thomas J. Crowley

Braeheads Institute, Maryfield, Scotland, UK; tcrowley111googlemail.com

The Brazil Current may have played a key role in shunting heat towards the Antarctic during the meridional overturning shutdown at the end of the last ice age.

The remarkable relationship between late Pleistocene carbon dioxide variations and Antarctic temperatures has been as inscrutable as the faint smile of a stone Buddha. Recently, a string of papers provide promise of unlocking the secrets of that relationship by shedding light on ocean circulation/carbon dynamics involving the key first phase of carbon dioxide rise at the end of the last glacial period. During an interval that has long been termed the “Late Glacial”, and is broadly correlative with Heinrich Event 1 (H1, ~17.8-14.6 cal ka), significant carbon reservoir changes at the time of the first major CO2 rise have been related to Antarctic ocean circulation changes (Marchitto et al., 2007; Anderson et al., 2009; Rose et al., 2010). In turn, these changes link to variations in North Atlantic Deep Water (NADW) overturning rate (Anderson et al., 2009; Toggweiler and Lea, 2009), which cause a see-saw in sea surface temperature (SST) patterns between the North and South Atlantic (Crowley, 1992; Toggweiler and Lea, 2009).

Figure 1: A) Comparison of zonal poleward ocean heat transport (1 PW = 1015 Watts) in the Atlantic sector for the model runs illustrated in Figure 2. Figure from Maier-Reimer et al., 1996. B) Difference of surface current (25 m) between the control and perturbed run, illustrating the effects of an NADW shutdown (in this case due to an open central American isthmus) on global ocean circulation (Figure from Maier-Reimer et al., 1990). Red dot refers to location of sub-Antarctic core illustrated in Figure 2.

In this note, I point out that an overlooked feature of the NADW see-saw provides additional insight into the nature of the “bolt of warmth” that characterized Antarctic temperature change at this time. As noted in Crowley (1992), shutdown of NADW production “banks” about 1 petawatt (PW) of heat in the South Atlantic, which would otherwise be exported north of the equator to compensate for southward outflow of NADW across the equator. An early modeling study indicates that adjustment of the South Atlantic to this shutdown involves an enormous 1 PW increase in heat transport (Maier-Reimer et al., 1990; Fig. 1A), which is shunted southward into higher latitudes via the Brazil Current, i.e., the western boundary surface current of the South Atlantic (Fig. 1B).

It is remarkable that the South Atlantic model heat transport for the perturbation run is greater than for the Gulf Stream in the control run (Fig. 1A). In a sense the deglacial Brazil Current vertical section and transport is dynamically similar to the Gulf Stream at present—the strong flow is required to compensate for both the increased northward transport of Antarctic Bottom Water and the decreased southward transport of both NADW and North Atlantic Intermediate Water. Enhanced Southern Ocean inflow into Atlantic Basins is supported by geochemical assays (Negre et al., 2010).

Figure 2: Comparison of the sub-Antarctic record (core RC11-120; Hays et al., 1976), using higher-resolution sampling from Martinson et al. (1987) and converted to an updated marine chronology (Lisiecki and Raymo, 2005), with the Vostok deuterium isotope record and ice core GT4 chronology (Petit et al., 1999). H1 interval is Heinrich Event 1.

In the illustrated model example, convergence of the stronger Brazil Current with sub-Antarctic waters leads to stronger currents (Fig. 1B) and presumably enhanced convergence in the frontal zone (cf., Marchitto et al., 2007), with changes extending zonally downstream at least as far as the eastern Indian Ocean. These changes are likely responsible for the observed zonal changes in the Antarctic Circumpolar Current (cf., Anderson et al., 2009). The heat injection, along with a sea-ice melt feedback, likely explains the long-known (Hays et al., 1976) rising temperatures in the sub-Antarctic at the time of H1 (e.g., Fig. 2), and the parallel rise recorded in Antarctic ice cores. Additional adjustments can be expected from the warming effects of surface warming on the Antarctic overturning circulation, with potential implications for possible tapping of the deeper ocean glacial carbon reservoir in the Southern Ocean (Toggweiler and Samuels, 1995; Rose et al., 2010). It is conceivable that warmer surface waters could have prevented recharge of very cold and saline deep Antarctic waters, leading to a transient enhanced vertical stratification (tidal mixing would probably break down this barrier after a few hundred years; R.-X. Huang, pers. comm.).

It therefore appears that the Brazil/Malvinas-Falkland Convergence (where the southerly vectors of the Brazil Current merge with the easterly flow of the Subantarctic in Figure 1B) may be the pressure point where the heat accumulated in response to stalled Atlantic overturning circulation is injected into southern high latitudes, thereby driving the planet into deglaciation through positive feedbacks from ocean-circulation releasing carbon stored in the deep ocean around Antarctica. Closer inspection of data from the Malvinas/Falkland region might provide enhanced insight into kinematics of this process. The postulated response should also be testable with the present generation of coupled climate/carbon models and would be much more realistic if started from a glacial base state. The transient model response would be especially intriguing to examine, for it could provide fascinating insight into the time-space evolution of the heat package injected into the sub-Antarctic region and the partitioning of the heat between the ocean and the atmosphere (Seager et al., 2002).

Even though the model results invoked herein represent an uncoupled run from twenty years ago, I suggest that the system response is so constrained by conservation of volume arguments—overturning shutdown in the north blocking heat export from the South Atlantic—that newer model simulations are likely to respond in the same manner. Elements of this argument can even be traced back to (or at least anticipated in) Henry Stommel’s classic explanation for differences in strength of the Gulf Stream and Brazil Current (Stommel, 1965). His interpretation was certainly supported by the 1990 simulation (Maier-Reimer et al., 1990).

data

Data for Fig. 2 from Martinson et al. (1986) and NOAA/NGDC Paleoclimatology website.

references

Crowley, T.J., 1992: North Atlantic Deep Water cools the Southern Hemisphere, Paleoceanography 7: 489-497

Maier-Reimer, E., Mikolajewicz, U. and Crowley, T., 1990: Ocean GCM sensitivity experiment with an open Central American Isthmus, Paleoceanography 5: 349-366

Negre, C., Zahn, R., Thomas, A.L., Masque, P., Henderson, G.M., Martinez-Mendez, G., Hall, A.R. and Mas, J.L., 2010: Reversed flow of Atlantic deep water during the last glacial maximum, Nature 468: 85-88

Rose, K.A., Sikes, E.L., Guilderson, T.P., Shane, P., Hill, T.M., Zahn, R. and Spero, H.J., 2010: Upper-ocean-to-atmosphere radiocarbon offsets imply fast deglacial carbon dioxide release, Nature 466: 1093-1097

Toggweiler, J.R. and Lea, D.W., 2009: Temperature differences between the hemispheres and ice age climate variability, Paleoceanography 25: doi:10.1029/2009PA001758

For full references please consult: http://pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Nicholas Graham1 and Eugene Wahl2

1Hydrologic Research Center, and Scripps Institution of Oceanography, USA; ngrahamhrc-lab.org

2NOAA, National Climatic Data Center, Paleoclimatology Branch/World Data Center for Paleoclimatology, Boulder, USA

The last millennia Paleoclimate Reconstruction (PR) Challenge is a model-based venue for experimenting with climate reconstruction methods. The overall idea has been described before (Ammann, 2008) and a modified version of the Challenge is now "live" and available for participation. It is designed to engage the scientific paleoclimate community in examining its methods in a common framework for the purpose of evaluating their relative strengths and weaknesses. A key design element of the Challenge is to allow true "apples to apples" comparison of reconstruction methods across identical experimental platforms. The ultimate goal is to improve last two millennia PR methods so that paleoclimate science can offer the best possible information to help understand both natural and anthropogenic climate change.

The Challenge is organized around 4 themes. In each theme, a set of long (1,000+ yrs) forced global climate model (GCM) integrations is used to formulate simulated paleoclimate proxy data (pseudo-proxies) and to provide pseudo-instrumental climate data for calibration and examination of reconstruction fidelity. Several different GCM runs provide a range of simulated climate evolutions that present different reconstruction scenarios. In each Theme, the reconstruction method used is at the prerogative of the participants.

Theme 1: Reconstruction of Northern Hemisphere temperature with strongly limited proxy data set (implemented)

Figure 1: Map showing the location of the 14 simulated extratropical tree-ring-chronology sites (black dots) in the Northern Hemisphere that were used in Theme 1 for the reconstruction of Northern Hemisphere temperature with strongly limited proxy data set. Underlying colors represent average annual temperatures (1961-1990). Figure by W. Goss, NOAA-NCDC Paleoclimatology/WDC for Paleoclimatology).

This theme focuses on the capacity of a very limited set of proxy data sites to enable reconstruction of hemispheric (20-90° N) mean annual temperature. The pseudo-proxy data-set consists of 14 extratropical tree-ring-chronology sites in the Northern Hemisphere (Fig. 1). It is designed to mimic the dataset used by Esper et al. (2002).

Theme 2: Reconstruction of Northern Hemisphere temperature and spatial patterns with a richer, but still somewhat limited proxy data set (in process of implementation)

This theme focuses on the capacity of a less limited set of proxy-data sites to enable reconstruction of hemispheric (again defined as 20-90°N) mean annual temperature and spatial temperature patterns. The pseudo-proxy data set consists of 66 tree-ring sites in the Northern Hemisphere at >40°N and is designed to mimic the dataset used by D'Arrigo et al. (2006).

Theme 3: Reconstruction of Northern Hemisphere temperature and global spatial patterns using a relatively rich proxy data set (to be implemented)

This theme focuses on the capacity of a richer and more spatially diverse set of proxy data sites to enable reconstruction of hemispheric (here defined as 0-90°N) mean annual temperature and global spatial temperature patterns. The pseudo-proxy data set contains 104 sites from different archives spread across the globe. It is designed to mimic the dataset used by Mann et al. (1998) and in numerous reconstruction simulation experiments (e.g., Mann et al., 2007; Smerdon et al., 2010).

The above three themes are designed to explore how proxy richness and spatial extent affect reconstruction fidelity of the Northern Hemisphere mean temperature (Themes 1-3), and of spatial temperature patterns in the Northern Hemisphere (Theme 2) and globally (Theme 3).

Theme 4: Reconstruction of spatial drought patterns (currently in development)

This theme is still under development; it will be based on a pseudo-proxy dataset designed to mimic that used in the North American Drought Atlas (NADA; cf., Cook et al., 2004). A timetable for implementation is being developed.

The Paleoclimatology Branch of NOAA's National Climatic Data Center/World Data Center for Paleoclimatology is providing the simulated proxy and instrumental data sets of the PR-Challenge and is also archiving the contributed reconstructions so that they can be cross-compared: www.ncdc.noaa.gov/paleo/pubs/pr-challenge/pr-challenge.html.

The PR-Challenge implementation team consists of Nicholas Graham, Rosanne D'Arrigo, Kevin Anchukaitis, Eugene Wahl, and David Anderson. We gratefully acknowledge Edward Cook for valuable ideas and encouragement, and Caspar Ammann for his inception of the PR Challenge project. Tree-ring pseudo-proxy formulation used the "VS-Lite" tree growth model developed by Suz Tolwinski-Ward and collaborators (Tolwinski-Ward et al., 2010).

The PR-Challenge is sponsored by NOAA's Office of Oceanic and Atmospheric Research/Climate Program Office (Climate Change Data and Detection Program, grant NA08OAR4310732) and the PAGES/CLIVAR Intersection.

references

Amman, C., 2008: The Paleoclimate Reconstruction Challenge, PAGES news 16(1): 4

D'Arrigo, R., Wilson, R. and Jacoby G., 2006: On the long-term context for late 20th century warming, Journal of Geophysical Research 111: doi:10.1029/2005JD006352

Esper, J., Cook, E.R., and Schweingruber, F.H., 2002: Low-frequency signals in long tree-ring chronologies for reconstructing of past temperature variability, Science 295: 2250-2253

Mann, M.E., Bradley, R.S. and Hughes, M.K., 1998: Global-scale temperature patterns and climate forcing over the past six centuries, Nature 392: 779-787

Tolwinski-Ward, S.E., Evans, M.N., Hughes, M.K. and Anchukaitis, K.J., 2010: An efficient forward model of the climate controls on interannual variation in tree-ring width, Climate Dynamics, doi:10.1007/s00382-010-0945-5

For full references please consult: http://pastglobalchanges.org/products/newsletters/ref2011_2.pdf

Sami Hanhijärvi

Department of Environmental Sciences, University of Helsinki, Finland; sami.hanhijarvihelsinki.fi

Meeting of the PAGES Arctic2k Working Group – San Francisco, USA, 11-12 December 2010

The Arctic has witnessed increased warming in comparison to other parts of the globe. Due to this amplification, the Arctic is a key region for climate studies, and is potentially central in elucidating the processes that govern the 19th and 20th century global warming. The PAGES Arctic2k Working Group was initiated to research the climate of the Arctic region within the past 2000 years. The Working Group had its second meeting in San Francisco, which was attended by 10 participants.