Organic lacustrine sediment varves as indicators of past precipitation changes: a 3,000-year climate record from Central Finland

Saarni, Saija; Saarinen, Timo; Lensu, Anssi

doi:10.1007/s10933-015-9832-8

Cited by 19 publications

(18 citation statements)

References 48 publications

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“…Indeed, in agreement with the population growth records for Finland (Kuosmanen et al, 2016, and references therein), marked human-induced land-use changes in the catchments of varved lakes in southwestern and south-central Finland became discernible at ∼ 1400 AD (Tiljander et al, 2003;Ojala and Alenius, 2005). This interval coincides with the onset of the LIA, during which both precipitation (Väliranta et al, 2007;Helama et al, 2009;Luoto, 2009;Saarni et al, 2015) and soil erosion rate (Tiljander et al, 2003;Ojala and Alenius, 2005;Saarni et al, 2016) increased in south-central Finland. However, this period is characterized by a shift to suppressed primary productivity at our study site, implying no influence of enhanced external nutrient inputs.…”

Section: Temporal Fluctuations In the Organic Matter Inputsupporting

confidence: 82%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.

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Section: Temporal Fluctuations In the Organic Matter Inputsupporting

confidence: 82%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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“…CC BY 4.0 License. of the LIA, during which both precipitation (Väliranta et al, 2007;Helama et al, 2009;Luoto, 2009;Saarni et al, 2015) and soil erosion rate (Tiljander et al, 2003;Ojala and Alenius, 2005;Saarni et al, 2016) increased in south-central Finland.…”

Section: ) 25mentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century

Jokinen¹,

Virtasalo²,

Jilbert³

et al. 2018

Preprint

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment.Here 5 we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented, and besides gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. The 10 progressive deoxygenation since the beginning of 1900s was originally triggered by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the anthropogenic eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s through fueling primary productivity, while we find no evidence of anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal 15 water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality. 25Biogeosciences Discuss., https://doi

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“…Proxies measured with annual resolution on these mixed varved are 1) total varve thickness, 2) growing season lamina (GSL) thickness, 3) winter lamina (WL) thickness (Saarni et al, 2015), and 4) relative X-Ray densitometry (Ojala and Francus, 2002). Correlations with climate parameters vary from sites to sites and sometimes throught times in a single site (Saarni et al, 2015).…”

Section: Mixed (Clastic-biogenic) Varvesmentioning

confidence: 99%

“…Correlations with climate parameters vary from sites to sites and sometimes throught times in a single site (Saarni et al, 2015). Only a handfull number of lacustrine sequences, all of them from Scandinavia, have been sucessfully 20 correlated to precipitation or moisture.…”

Section: Mixed (Clastic-biogenic) Varvesmentioning

confidence: 99%

“…Only a handfull number of lacustrine sequences, all of them from Scandinavia, have been sucessfully 20 correlated to precipitation or moisture. At Lake Nautajärvi annual and winter precipitation was reconstructed using relative X-Ray densitometry (Ojala and Alenius, 2005), while at Lake Kallio-Kourujärvi, the growing season lamina was linked to annual precipitation (Saarni et al, 2015). Rydberg and Martinez-Cortizas (2014) showed that high accumulation of snow resulted in high mineral matter content, and Wohlfarth et al (1998) found a significant correlation between early spring/summer precipitation with total varve thickness in north-central Sweden.…”

Section: Mixed (Clastic-biogenic) Varvesmentioning

confidence: 99%

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

Linderholm¹,

Nicolle²,

Francus³

et al. 2017

Preprint

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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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Organic lacustrine sediment varves as indicators of past precipitation changes: a 3,000-year climate record from Central Finland

Cited by 19 publications

References 48 publications

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century

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

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Organic lacustrine sediment varves as indicators of past precipitation changes: a 3,000-year climate record from Central Finland

Cited by 19 publications

References 48 publications

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20&lt;sup&gt;th&lt;/sup&gt; century

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

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A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century