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Aquatic ecosystem responses to Holocene climate change and biome development in boreal central Asia

Aquatic ecosystem responses to Holocene climate change and biome development in boreal central Asia
Aquatic ecosystem responses to Holocene climate change and biome development in boreal central Asia
Borealecosystems are highly vulnerable to climatechange, and severe ecological impacts in the near future are virtually certain to occur. We undertook a multiproxy study on an alpine lake (ESM-1) at the modern tree-line in boreal, southern Siberia. Steppe and tundra biomes were extensive in eastern Sayan landscapes during the early Holocene. Boreal forest quickly expanded by 9.1 ka BP, and dominated the landscape until c 0.7 ka BP, when the greatest period of compositional turnover occurred. At this time, alpine meadow landscape expanded and Picea obovata colonised new habitats along river valleys and lake shorelines, because of prevailing cool, moist conditions. During the early Holocene, chironomid assemblages were dominated by cold stenotherms. Diatoms for much of the Holocene were dominated by alkaliphilous, fragilarioid taxa, up until 0.2 ka BP, when epiphytic species expanded, indicative of increased habitat availability. C/N mass ratios ranged between 9.5 and 13.5 (11.1–15.8 C/N atomic ratios), indicative of algal communities dominating organic matter contributions to bottom sediments with small, persistent contributions from vascular plants. However, ?13C values increased steadily from ?34.9‰ during the early Holocene (9.3 ka BP) to ?24.8‰ by 0.6 ka BP. This large shift in magnitude may be due to a number of factors, including increasing within-lake productivity, increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically ‘mature’, and declining soil respiration linked to small, but distinct retreat in forest biomes. The influence of climatic variables on landscape vegetation was assessed using redundancy analysis (RDA), a linear, direct ordination technique. Changes in July insolation at 60 °N significantly explained over one-fifth of the variation in species composition, while changes in estimates of northern hemisphere temperature and ice-rafted debris events in the North Atlantic were also significant, but considerably less important. The potential importance of climate and biomedevelopment (tundra, steppe, cold deciduous forest and taiga) on different trophic levels (i.e. chironomid and diatom communities) in lake ESM-1 was also assessed using RDA. Climate predictors had a more significant influence on Holocene chironomid assemblages, especially July insolation at 60 °N, estimates of regional precipitation and estimates of northern hemisphere temperature, while only the development of the taiga biome had a significant impact on these primary consumers. Diatom communities also had a small, but significant influence on Holocene chironomid populations, perhaps linked to variation in faunal feeding strategies. In contrast, climatic and biome predictors explained similar amounts of variation in the Holocene diatom assemblage (approximately 20% each), while chironomids themselves as predictors explained just under 7% of diatom variation. Lake acidity was inferred using a diatom inference model. Results suggest that after deglaciation, the lake did not undergo a process of gradual acidification, most likely due to the presence of continuous permafrost and low levels of precipitation, preventing base cations and dissolved organic carbon entering the lake (except for the period between 1.7 and 0.7 ka BP). We conclude that lakes in continental, boreal regions undergo different models of lake ontogeny than oceanic boreal regions. Unlike other regions discussed, climate is a more important driver of ecosystemchange than catchment changes. We also demonstrate that the start of the period coincident with the onset of the Little Ice Age resulted in important thresholds crossed in catchment vegetation and aquatic communities
0277-3791
119-131
Mackay, Anson w.
8b55734f-3c1c-4b7e-9677-000271d13137
Bezrukova, Elena V.
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Leng, Melanie
494cb2de-b710-419c-8ef2-9dadc78cfde9
Meaney, Miriam
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Nunes, Ana
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Piotrowska, Natalia
84dabb87-76d8-4db8-82fe-a51d94bf4b19
Self, Angela
48bb713c-54ad-4bf9-a31f-d7a5232e63f2
Shchetnikov, Alexander
db2afbbb-9634-4a1b-8f74-2a5f1826e907
Shilland, Ewan
8ee497d8-dae4-447a-9545-d10f5f992e3d
Tarasov, Pavel
50062a54-e378-4c21-b414-df85d3d8295d
Wang, Luo
02a1f59a-488a-423a-8f2f-8f22ea99aab3
White, Dustin
5c77fb12-78b8-4a94-b25a-8697ccf5480b
Mackay, Anson w.
8b55734f-3c1c-4b7e-9677-000271d13137
Bezrukova, Elena V.
6b800b14-283f-4430-85ed-a6e28d77acf3
Leng, Melanie
494cb2de-b710-419c-8ef2-9dadc78cfde9
Meaney, Miriam
b4babcea-2603-4ee5-9a77-fbc7c6ba28eb
Nunes, Ana
a5435a52-a263-41d0-b732-874bbf4c8e4d
Piotrowska, Natalia
84dabb87-76d8-4db8-82fe-a51d94bf4b19
Self, Angela
48bb713c-54ad-4bf9-a31f-d7a5232e63f2
Shchetnikov, Alexander
db2afbbb-9634-4a1b-8f74-2a5f1826e907
Shilland, Ewan
8ee497d8-dae4-447a-9545-d10f5f992e3d
Tarasov, Pavel
50062a54-e378-4c21-b414-df85d3d8295d
Wang, Luo
02a1f59a-488a-423a-8f2f-8f22ea99aab3
White, Dustin
5c77fb12-78b8-4a94-b25a-8697ccf5480b

Mackay, Anson w., Bezrukova, Elena V., Leng, Melanie, Meaney, Miriam, Nunes, Ana, Piotrowska, Natalia, Self, Angela, Shchetnikov, Alexander, Shilland, Ewan, Tarasov, Pavel, Wang, Luo and White, Dustin (2012) Aquatic ecosystem responses to Holocene climate change and biome development in boreal central Asia. Quaternary Science Reviews, 41, 119-131. (doi:10.1016/j.quascirev.2012.03.004).

Record type: Article

Abstract

Borealecosystems are highly vulnerable to climatechange, and severe ecological impacts in the near future are virtually certain to occur. We undertook a multiproxy study on an alpine lake (ESM-1) at the modern tree-line in boreal, southern Siberia. Steppe and tundra biomes were extensive in eastern Sayan landscapes during the early Holocene. Boreal forest quickly expanded by 9.1 ka BP, and dominated the landscape until c 0.7 ka BP, when the greatest period of compositional turnover occurred. At this time, alpine meadow landscape expanded and Picea obovata colonised new habitats along river valleys and lake shorelines, because of prevailing cool, moist conditions. During the early Holocene, chironomid assemblages were dominated by cold stenotherms. Diatoms for much of the Holocene were dominated by alkaliphilous, fragilarioid taxa, up until 0.2 ka BP, when epiphytic species expanded, indicative of increased habitat availability. C/N mass ratios ranged between 9.5 and 13.5 (11.1–15.8 C/N atomic ratios), indicative of algal communities dominating organic matter contributions to bottom sediments with small, persistent contributions from vascular plants. However, ?13C values increased steadily from ?34.9‰ during the early Holocene (9.3 ka BP) to ?24.8‰ by 0.6 ka BP. This large shift in magnitude may be due to a number of factors, including increasing within-lake productivity, increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically ‘mature’, and declining soil respiration linked to small, but distinct retreat in forest biomes. The influence of climatic variables on landscape vegetation was assessed using redundancy analysis (RDA), a linear, direct ordination technique. Changes in July insolation at 60 °N significantly explained over one-fifth of the variation in species composition, while changes in estimates of northern hemisphere temperature and ice-rafted debris events in the North Atlantic were also significant, but considerably less important. The potential importance of climate and biomedevelopment (tundra, steppe, cold deciduous forest and taiga) on different trophic levels (i.e. chironomid and diatom communities) in lake ESM-1 was also assessed using RDA. Climate predictors had a more significant influence on Holocene chironomid assemblages, especially July insolation at 60 °N, estimates of regional precipitation and estimates of northern hemisphere temperature, while only the development of the taiga biome had a significant impact on these primary consumers. Diatom communities also had a small, but significant influence on Holocene chironomid populations, perhaps linked to variation in faunal feeding strategies. In contrast, climatic and biome predictors explained similar amounts of variation in the Holocene diatom assemblage (approximately 20% each), while chironomids themselves as predictors explained just under 7% of diatom variation. Lake acidity was inferred using a diatom inference model. Results suggest that after deglaciation, the lake did not undergo a process of gradual acidification, most likely due to the presence of continuous permafrost and low levels of precipitation, preventing base cations and dissolved organic carbon entering the lake (except for the period between 1.7 and 0.7 ka BP). We conclude that lakes in continental, boreal regions undergo different models of lake ontogeny than oceanic boreal regions. Unlike other regions discussed, climate is a more important driver of ecosystemchange than catchment changes. We also demonstrate that the start of the period coincident with the onset of the Little Ice Age resulted in important thresholds crossed in catchment vegetation and aquatic communities

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Published date: 18 May 2012
Organisations: Archaeology

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Local EPrints ID: 345470
URI: http://eprints.soton.ac.uk/id/eprint/345470
ISSN: 0277-3791
PURE UUID: 7a789e47-1287-428e-81f8-b4f26b04998c

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Date deposited: 22 Nov 2012 12:02
Last modified: 16 Jul 2019 21:49

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Contributors

Author: Anson w. Mackay
Author: Elena V. Bezrukova
Author: Melanie Leng
Author: Miriam Meaney
Author: Ana Nunes
Author: Natalia Piotrowska
Author: Angela Self
Author: Alexander Shchetnikov
Author: Ewan Shilland
Author: Pavel Tarasov
Author: Luo Wang
Author: Dustin White

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