Stream flow intensity of the Saavanjoki River, eastern Finland, during the past 1500 years reflected by mayfly and caddisfly mandibles in adjacent lake sediments

Luoto, Tomi P.; Helama, Samuli; Nevalainen, Liisa

doi:10.1016/j.jhydrol.2012.10.029

Cited by 15 publications

(8 citation statements)

References 34 publications

(56 reference statements)

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“…Apart from the instrumentally observed variations, the NAO has been shown to exhibit centennial fluctuations with pervasively positive and negative phases during the MWP and LIA (Trouet et al, 2009;Mann et al, 2009). In fact, the NAO sensitivity of the climate has been described near the study region using several multi-proxy data sets for the MWP and LIA, showing seasonal variations in winter (warmer and moister) and summer (cooler and less rainy) climate, in accordance with the expected NAO influence (Helama et al, 2009b;Luoto and Helama, 2010;Helama and Holopainen, 2012;Luoto et al, 2013;Nevalainen et al, 2013). Moreover, the temperature variations through the MWP and LIA could be linked to the periods of more and less intensive phases in the formation of North Atlantic deep water (Helama et al, 2009c).…”

Section: Low-frequency Temperature Variationssupporting

confidence: 58%

Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland

Matskovsky

Helama²

2014

Clim. Past

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Abstract. Here we analyse the maximum latewood density (MXD) chronologies of two published tree-ring data sets: one from Torneträsk region in northernmost Sweden (TORN; Melvin et al., 2013) and one from northern Fennoscandia (FENN; Esper et al., 2012). We paid particular attention to the MXD low-frequency variations to reconstruct summer (June–August, JJA) long-term temperature history. We used published methods of tree-ring standardization: regional curve standardization (RCS) combined with signal-free implementation. Comparisons with RCS chronologies produced using single and multiple (non-climatic) ageing curves (to be removed from the initial MXD series) were also carried out. We develop a novel method of standardization, the correction implementation of signal-free standardization, tailored for detection of pure low-frequency signal in tree-ring chronologies. In this method, the error in RCS chronology with signal-free implementation is analytically assessed and extracted to produce an advanced chronology. The importance of correction becomes obvious at lower frequencies as smoothed chronologies become progressively more correlative with correction implementation. Subsampling the FENN data to mimic the lower chronology sample size of TORN data shows that the chronologies bifurcate during the 7th, 9th, 17th and 20th centuries. We used the two MXD data sets to reconstruct summer temperature variations over the period 8 BC through AD 2010. Our new reconstruction shows multi-decadal to multi-centennial variability with changes in the amplitude of the summer temperature of 2.2 °C on average during the Common Era. Although the MXD data provide palaeoclimate research with a highly reliable summer temperature proxy, the bifurcating dendroclimatic signals identified in the two data sets imply that future research should aim at a more advanced understanding of MXD data on distinct issues: (1) influence of past population density variations on MXD production, (2) potential biases when calibrating differently produced MXD data to produce one proxy record, (3) influence of the biological age of MXD data when introducing young trees into the chronology over the most recent past and (4) possible role of waterlogging in MXD production when analysing tree-ring data of riparian trees.

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Section: Low-frequency Temperature Variationssupporting

confidence: 58%

Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland

Matskovsky

Helama²

2014

Clim. Past

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“…Integration of this dendroclimatic proxy data into multi-proxy comparisons with sedimentary midge (Luoto and Helama, 2010), mayfly and caddisfly , and cladoceran fossil assemblages have resulted in palaeoclimatological and palaeolimnological reconstructions indicative of varying climate conditions during the MCA and LIA. During the MCA the summers were likely warm and dry, as contrasted by the snowy winters, in comparison to summers of the LIA that were generally wetter, whereas the winters may have actually been less snowy and undergone shortening of the ice-free season during the LIA (Luoto and Helama, 2010;Luoto et al, 2013;Nevalainen et al, 2013;Luoto and Nevalainen, 2015). The results presented thus far have, therefore, supported the concept of the MCA and LIA.…”

Section: Introductionsupporting

confidence: 71%

“…These palaeohydrological indications appear consistent with the long-term climatic evolution of continental Europe and Fennoscandia with evidence for wide-spread megadroughts between AD 1000 and 1200 . Reconstructed by multiple proxies for southern Finland, these fluctuations represent summertime droughts during the Medieval Climate Anomaly (MCA) and increased moisture during the following centuries characteristic of the Little Ice Age (LIA) conditions (Luoto and Helama, 2010;Luoto et al, 2013;Nevalainen et al, 2013;Luoto and Nevalainen, 2015). This depiction would demonstrate why the lake and peatland sites can be so deviant in accumulation rates of the same plant part and under the same climatic fluctuations, the marked alterations originating from the prevailing processes of necrology and biostratinomy (Gastaldo, 1988).…”

Section: Discussionmentioning

confidence: 99%

Rereading a tree-ring database to illustrate depositional histories of subfossil trees

Helama

Luoto

Nevalainen

et al. 2017

Palaeontologia Electronica

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“…NAO) is anticipated to result in contrasting trends in respective records, according to their target season sensitivity. These results are in line with a predominantly positive NAO phase during the MCA, associated with generally wet winters but dry summers (Trouet et al, 2009), while a negative NAO phase during the LIA has been linked with dry winters and wet summers (Luoto and Helama, 2010;Luoto et al, 2013;Luoto and Nevalainen, 2017). While the view of a prolonged positive phase during the 20 MCA has been challenged by recent proxy observations (Ortega et al, 2015), additional support of generally positive NAO phase overlapping the MCA have also been presented (Wassenburg et al, 2013;Baker et al, 2015).…”

Section: Fennoscandiasupporting

confidence: 60%

Arctic hydroclimate variability during the last 2000 years – current understanding and research challenges

Linderholm¹,

Nicolle²,

Francus³

et al. 2017

Preprint

Self Cite

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Abstract. Along with Arctic amplification, changes in Arctic hydroclimate have become increasingly apparent. Reanalysis data show increasing trends in Arctic temperature and precipitation over the 20 th century, but changes are not homogenous 30 across seasons or space. The observed hydroclimate changes are expected to continue, and possibly accelerate, in the coming century, not only affecting pan-Arctic natural ecosystems and human activities, but also lower latitudes through changes in atmospheric and oceanic circulation. However, a lack of spatiotemporal observational data makes reliable quantification of Arctic hydroclimate change difficult, especially in a long-term context. To understand hydroclimate variability and the mechanisms driving observed changes, beyond the instrumental record, climate proxies are needed. Here we bring together 35 the current understanding of Arctic hydroclimate during the past 2000 years, as inferred from natural archives and proxies and palaeoclimate model simulations. Inadequate proxy data coverage is apparent, with distinct data gaps in most of Eurasia and parts of North America, which makes robust assessments for the whole Arctic currently impossible. Hydroclimate proxies and climate models indicate that the Medieval Climate Anomaly (MCA) was anomalously wet, while conditions Clim. Past Discuss., doi:10.5194/cp-2017Discuss., doi:10.5194/cp- -34, 2017 Manuscript under review for journal Clim. Past Discussion started: 17 March 2017 c Author(s) 2017. CC-BY 3.0 License. 2 were in general drier during the Little Ice Age (LIA), relative to the last 2000 years. However, it is clear that there are large regional differences, which are especially evident during the LIA. Due to the spatiotemporal differences in Arctic hydroclimate, we recommend detailed regional studies, e.g. including field reconstructions, to disentangle spatial patterns and potential forcing factors. At present, it is only possible to carry out regional syntheses for a few areas of the Arctic, e.g. Fennoscandia, Greenland and western North America. To fully assess pan-Arctic hydroclimate variability for the last two 5 millennia additional proxy records are required.

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Stream flow intensity of the Saavanjoki River, eastern Finland, during the past 1500 years reflected by mayfly and caddisfly mandibles in adjacent lake sediments

Cited by 15 publications

References 34 publications

Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland

Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland

Rereading a tree-ring database to illustrate depositional histories of subfossil trees

Arctic hydroclimate variability during the last 2000 years – current understanding and research challenges

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