Holocene and Last Interglacial Cloudiness in Eastern Baffin Island, Arctic Canada
This study presents Last Interglacial and Holocene vegetation and climate changes at Fog Lake on eastern Baffin Island, Arctic Canada. The vegetation cover is reported as vegetation structural types, or biomes. July air temperature and sunshine during the growing season (June-July-August-September) were reconstructed from pollen assemblages with the modern analogue technique. The vegetation of the Last Interglacial period evolved from a prostrate dwarf-shrub tundra to a low- and high-shrub tundra vegetation. The succession of four arctic biomes was distinguished from the Last Interglacial sediments, whereas only one arctic biome was recorded in the Holocene sediments. From ca. 8300 cal. year BP to present, hemiprostrate dwarf-shrub tundra occupied the soils around Fog Lake. During the Last Interglacial, growing season sunshine was higher than during the Holocene and July air temperature was 4 to 5° C warmer than present. A Principal Component Analysis helped in assessing relationship between floristic gradients and climate. The major vegetation changes through the Last Interglacial and Holocene were driven by July air temperature variations, whereas the minor, or subtle, vegetation changes seem rather correlated to September sunshine. This study demonstrates that growing season sunshine conditions can be reconstructed from arctic pollen assemblages, thus providing information on feedbacks associated with cloud cover and summer temperatures, and therefore growing season length.
Space-time evolution of the climate of northern Canada and Alaska during the Holocene
We use extensive modern and fossil pollen databases to investigate climate variability north of 50°N in North America during the past 12,000 years. Mean annual, July and January temperature and annual precipitation is reconstructed at 100-year intervals to evaluate climate variability at several temporal and spatial scales across Northern Canada and Alaska. Hovmuller diagrams depicting the regional evolution of the climate on different timescales across northern Canada and Alaska show both low and high frequency climate variability occurring throughout the Holocene. Orbital timescale variability is time-transgressive from west to east, while the regional expression of the LIA/MWP is seen across the continent. High-latitude reconstructions show slightly higher variability compared to lower mid-latitude reconstructions. Recent observed regional warming is unprecedented in terms of century to millennial-scale temperature variability found during the Holocene.
Large-scale paleoenvironmental analyses using pollen databases
Pollen data from lake sediment cores are a major source of paleoclimate information, and databases of pollen diagrams are publically available. The databases are extensive enough that continental-scale maps of Holocene climate variability can be made for Europe and North America. Maps show reasonable synoptic climate patterns and time series illustrate the nature of Holocene climate variability. There is also synchronicity between Europe, North American and North Atlantic millennial-scale climate variability. In addition to paleoclimate reconstructions, these databases are used for other paleoenvironmental analyses, including analysis of carbon dynamics in ecosystems through time.
Testing the reliability of pollen-based diversity estimates
Rarefaction analysis is a common tool for estimating pollen richness. Using modern and fossil pollen data from the Canadian Arctic, Greenland, and Scotland, we examine the effects of pollen concentration (grains/cc) and evenness (the distribution of species abundances) on palynological richness. Our results show that pollen richness and concentration have a strong negative correlation at low pollen concentrations. There is a positive correlation between pollen evenness and richness, although the strength of this relationship is difficult to determine. Rarefaction analysis on samples of low concentration or high evenness is likely to lead to pollen richness being less underestimated than on samples of high concentration or low evenness. These findings corroborate theoretical research on these issues.
Review of Palynological Studies in Archaeological Interpretation in East Asia, focusing on Southern Korea
Reconstructing Paleoclimate and Historical Terrestrial Carbon Storage from Pollen Data Using Inverse Modelling Approach
A long-standing issue exists between data concerning the discrepancy of paleocarbon storage reconstructions since the Last Glacial Maximum by means of pollen, carbon isotope, and general circulation model (GCM) analysis. In this study, a new estimate of past biospheric carbon stocks is reported using a new paleocarbon model (PCM), which is defined as a physiological process vegetation model (BIOME4) coupled to a process- based biospheric carbon model (DEMETER). The PCM was constrained to fit pollen data to obtain realistic estimates. It was estimated that the probability distribution of climatic parameters, as simulated by BIOME4, was compatible with pollen data while DEMETER successfully simulated the carbon storage values with the corresponding outputs of BIOME4. The carbon model was validated with observable global vegetation biomass and soil carbon, and the inversion scheme was tested against 1491 surface pollen spectra sample sites procured in Africa and Eurasia. Results showed that this method can successfully simulate most biomes at selected pollen sites, and that the coefficient of determination (R2) calculated between the observed and reconstructed modern climates vary from 0.70 to 0.96. Comparisons between the simulated biome-average terrestrial carbon variables with the available observations also indicated a consensus: R2 variability of 0.92 for vegetation carbon density and 0.81 for soil carbon density. Results demonstrate the reliability and feasibility of this paleoclimate reconstruction method and its efficiency in reconstructing historical terrestrial carbon storage.
High-Resolution Pollen Records From the Southern Boreal Forest/Aspen Parkland Ecotone in Saskatchewan, Canada
The Canadian southern boreal forest and northern prairies have been well-studied at a coarse resolution over the entire Holocene, but less so on a high-resolution scale. We present results from three high-resolution pollen studies from the southern boreal forest in Saskatchewan. These results show that high-resolution pollen can detect centennial-scale climate changes in the region, and confirm that high-resolution pollen is a tool to detect major forest fire frequency and the effects of recent climate change on the boreal forest. Hence, high-resolution pollen studies can complement annual-resolution dendrological studies. North Flat Lake (53°36'47"N, 106°29'46"W) is located at the present-day southern boreal forest/aspen parkland ecotone. The radiocarbon-dated core was sampled at ∼23 year resolution and spanned AD 115-1885. Principal Components Analysis and Constrained-Incremental-Sum-of-Squares clustering divided the pollen relative abundance record into three distinct zones. The first pollen zone (AD 115- 794) was characterized by higher amounts of Pinus cf. banksiana, Asteroideae and Poaceae. The second pollen zone (AD 795-1375) was characterized by a decrease in Pinus cf. banksiana and increases in Picea and arboreal Betula. The third pollen zone (AD 1376-1885) was characterized by a further increase in Betula. We associate the second and third pollen zones with the Medieval Climate Anomaly (MCA) and the succeeding Little Ice Age (LIA). Pollen-climate transfer function analysis (based upon many researchers' compiled data) showed that the first millennium AD was more arid than the second millennium AD, which agrees with previously-published diatom-inferred paleo-salinity reconstructions for the Canadian prairies. This pollen analysis also suggested that the LIA was more arid than the MCA, although not as arid as the first millennium. Lakes L03 (54°35'19"N, 104°57'37"W) and L02 (54°39'11"N, 104°53'59"W) are located close to the transition between the boreal plains and the boreal shield. Radiocarbon-dated Lake L03 spanned AD 1430-2003 and was sampled at ∼4 year resolution. L03 showed strong peaks in Alnus, Salix and Sphagnum relative abundances beginning at AD 1436, AD 1652 and AD 1808, which lasted for ∼47 years. These are attributed to vegetation response to fire, the primary disturbance in the boreal forest. 210Pb-dated Lake L02 covered AD 1811-2003 and was sampled at ∼2 year resolution. Fires occurred at ∼1885 and ∼1908, denoted by severe declines in overall pollen absolute abundance and initial sharp peaks in Sphagnum and Dryopteris relative abundances, succeeded by peaks in Alnus and Salix, and lastly by Betula. These fires are confirmed by the historical record and forest inventory surveys. L02 showed a significant increase in Pinus cf. banksiana pollen relative abundance with concomitant decline in Betula and Alnus absolute and relative abundances. The 112-year instrumental climate record from nearby Prince Albert, Saskatchewan, showed a significant increase (0.02 °C/yr) in mean annual temperature and constant annual precipitation. Researchers have shown that fire frequency has lengthened over the past century. Hence, these pollen changes are attributed to these two factors.
A Palynological Approach for the Reconstruction of Holocene Environments of the Sacramento-San Joaquin Delta, California
We present results of a palynological study, carried out within the framework of Project REPEAT, that delineates the role of vegetation and plants communities in the formation of peat deposits in the Sacramento- San Joaquin Delta of California. The study shows how the general climatic setting affected the process of peat formation and demonstrates the influence of the local environmental and hydrological conditions. The study compared three cores, situated in locations with different environmental setting and elevation: Webb Track Levee, Brown's Island and Frank's Wetland. Three- hundred and twenty pollen samples were analyzed using standard palynological procedures. The modern pollen grains of California species of grasses and sedges were analyzed in order to identify key species of the diverse Holocene community of the Delta. The pollen data indicate that since about 6500 years BP, when peat first started to form, general climatic conditions in the area have not changed dramatically. However, recognizable shifts in forest vegetation occurred at least twice: once between about 5000 and 4500 years BP and again between 3000 and 2500 years BP. In both cases, higher percentages of conifer pollen are found at all three locations. Local variations in wet/dry conditions at the different locations can be tracked using the proportion of pollen from sedge and grasses species. The ratios of arboreal/non-arboreal pollen for Brown's Island and Frank's Wetland are similar but there are significant differences in pollen percentages of species within both groups, which can also be related to differences in local conditions. Pollen concentrations are consistent with peat accumulation rates. The minimum accumulation rate occurred between 2500 and 1000 years BP, which coincides with the least developed arboreal plant communities. A salinity index calculated from pollen criteria shows a minimum for the same period. The pollen data correlate well with environmental magnetic results and with sedimentary records. According to the study, minor fluctuations in general climatic conditions led to major changes in hydrological dynamics in the Delta, which is reflected in the compostion of the plant community and is imprinted in the pollen assemblages.