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Samuli Helama Hannu Herva Joonas Uusitalo Andy Moir Kari Mielikäinen Pekka Nöjd Markku Oinonen Raimo Sutinen 《Boreas: An International Journal of Quaternary Research》2023,52(3):427-439
High altitude and latitude findings of subfossil peatland pine trees were unearthed from the region of NW Finnish Lapland and dated by 14C and tree-ring methods. The depositional history of the trees illustrated two distinct peatland pine phases dated to Middle Holocene intervals 4900–4400 and 4100–3400 cal. a BC. It seems evident that both thermal and hydroclimatic fluctuations have played roles of varying importance in the establishment of this pine population and its demise. The presence of these pines, from a site ~60 km north of the coniferous timberline and conditions ~1 °C and 100 degree-days colder than those at the present-day timberline, concurs with previous studies demonstrating the association between the high-latitude summer-temperature cooling and circumpolar timberline retreat since the Middle Holocene due to Milankovitch forcing. On the other hand, the peatland pine recruitment was made possible by drier than present surface conditions during the previously reconstructed Middle Holocene drought anomaly (Hyvärinen-Alhonen event). Our data suggest this event was not continuous but reached its two-phase climax during the peatland pine phases, with an interruption of several centuries with moister surface conditions between 4400 and 4100 cal. a BC. The findings highlight the sensitivity of well-dated peatland tree assemblages in terms of recording past climatic evolution and events and the need for new collections from north and south Fennoscandia and the Baltic region, for more detailed analyses over extended time intervals and regions. 相似文献
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Bernd R. Schöne Nicholas A. Page David L. Rodland Jens Fiebig Sven Baier Samuli O. Helama Wolfgang Oschmann 《International Journal of Earth Sciences》2007,96(3):525-540
We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ 18O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available. 相似文献
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An assemblage of geoduck clam shells from the marine environment of coastal British Columbia was studied. Shells were cut
and the widths of internal shell growth increments, annuli, were measured from the hinge plate. The largest shells showed
more than one hundred annual increments. Shell growth exhibited juvenile maxima at ontogenetic ages 3–6 years. The growth
maximum was followed by a distinct decline that continued until the death of each individual. Further, this ontogenetic growth
trend was mathematically removed from the data in order to examine growth variations other than ageing. The longest growth
records from the oldest shells were compared to monthly indices of the Pacific Decadal Oscillation (PDO). It was found that
the PDO exerts the strongest influence on the shell growth during the very start of the growing season, in February and March.
We also detected increased magnitude of growth variations towards the end of the 20th century. Similar trends were apparent
in the PDO record. Moreover, the shell specimen displaying the strongest trend of increasing variance had the strongest PDO-linked
regional growth signal. Our results support the view that PDO exerts a governing influence on the biological and ecological
system along Northeast Pacific coastal areas. Incorporation of geoduck shell growth increment analyses into multi-disciplinary
studies dealing with palaeoceanography and archaeology is suggested as a promising future approach. 相似文献
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Helama Samuli Stoffel Markus Hall Richard J. Jones Phil D. Arppe Laura Matskovsky Vladimir V. Timonen Mauri N&#;jd Pekka Mielik&#;inen Kari Oinonen Markku 《Climate Dynamics》2021,56(11):3817-3833
Holocene climate variability is punctuated by episodic climatic events such as the Little Ice Age (LIA) predating the industrial-era warming. Their dating and forcing mechanisms have however remained controversial. Even more crucially, it is uncertain whether earlier events represent climatic regimes similar to the LIA. Here we produce and analyse a new 7500-year long palaeoclimate record tailored to detect LIA-like climatic regimes from northern European tree-ring data. In addition to the actual LIA, we identify LIA-like ca. 100–800 year periods with cold temperatures combined with clear sky conditions from 540 CE, 1670 BCE, 3240 BCE and 5450 BCE onwards, these LIA-like regimes covering 20% of the study period. Consistent with climate modelling, the LIA-like regimes originate from a coupled atmosphere–ocean–sea ice North Atlantic-Arctic system and were amplified by volcanic activity (multiple eruptions closely spaced in time), tree-ring evidence pointing to similarly enhanced LIA-like regimes starting after the eruptions recorded in 1627 BCE, 536/540 CE and 1809/1815 CE. Conversely, the ongoing decline in Arctic sea-ice extent is mirrored in our data which shows reversal of the LIA-like conditions since the late nineteenth century, our record also correlating highly with the instrumentally recorded Northern Hemisphere and global temperatures over the same period. Our results bridge the gaps between low- and high-resolution, precisely dated proxies and demonstrate the efficacy of slow and fast components of the climate system to generate LIA-like climate regimes.
相似文献16.
Ogurtsov M. G. Jungner H. Lindholm M. Helama S. Dergachev V. A. 《Geomagnetism and Aeronomy》2009,49(7):1056-1062
Paleoclimatological reconstructions of temperature of the Earth’s Northern Hemisphere for the last thousand years have been
studied using the up-to-date methods of statistical analysis. It has bee indicated that the quasisecular (a period of 60–130
years) cyclicity, which is observed in the climate of the Earth’s Northern Hemisphere, has a bimodal structure, i.e., being
composed of the 60–85 and 85–130 year periodicities. The possible relation of the quasisecular climatic rhythm to the corresponding
Gleissberg solar cycle has been studied using the solar activity reconstructions performed with the help of the solar paleoastrophysics
methods. 相似文献
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Construction of statistically reliable sclerochronology using subfossil shells of river pearl mussel
Sclerochronology is based on series of skeletal growth records that have been correctly aligned in time. These chronologies
have so far been derived from living bivalves and corals. Here we demonstrate the possibility of constructing the sclerochronology
from a suite of river pearl mussel (Margaritifera margaritifera (L.)) shells with unknown but at least partly overlapping geological age. Subsequent to measuring of the annual shell growth
increments, the sample series were iteratively compared to each other and to the mean series of other samples. This comparison
forms the basis of the applied procedure, termed cross-dating, in which more inter-correlative sample series can be progressively
added into the mean chronology in step-wise fashion. After cross-dating, the correlation of the 16 sample series (0.52) indicated
that the subfossil sclerochronology bore common growth signal that was comparable to previously recorded chronologies from
modern samples. The cross-dated sclerochronology represented growth variations over a time window of 91 years. Variability
in chronology was found to be statistically reliable, with sample replication in at least six series (this equalled to chronology
sub-interval of 78 years). In the wider paleontological context, these results show the possibility of constructing statistically
reliable sclerochronologies from fossil specimens at any given locality bearing an abundance of skeletal remains. Such chronologies
will be important in their ability to provide paleolimnological records with comparable quality to recent proxy and observational
series. Sclerochronologies can be numerically examined for paleolimnological variations using standard time-series analysis
tools: a dominant frequency-band at inter-annual and multi-annual time-scales was found in our sample by spectral analysis. 相似文献
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The several competing reconstructions of Northern Hemisphere temperature variability exists with partly conflicting evidence. Here we considered a specific problem of choosing “the best” reconstruction, in a frame of assumptions, that they are produced by smooth dynamical system as well as instrumental time series. Using some sophisticated measures of similarity, we could not match to all existing hemispheric paleoclimate reconstructions with hypothesis about any deterministic system which can produced its as typical projection of their trajectories. The results cast doubt on the conventional techniques frequently used to reconstruct past climate variability. 相似文献