Holocene aquatic ecosystem change in the boreal vegetation zone of northern Finland (original) (raw)
Lake Ecosystem Responses to Holocene Climate Change at the Subarctic Tree-Line in Northern Sweden
Ecosystems, 2010
A Holocene sediment sequence from Lake Seukokjaure, a subarctic lake at tree-line in northern Sweden, was analyzed to assess major changes in the structure and functioning of the aquatic ecosystem in response to climate change and tree-line dynamics. The compiled multi-proxy data, including sedimentary pigments, diatoms, chironomids, pollen, biogenic silica (BSi), carbon (C), nitrogen (N) elemental and stableisotope records, and total lake-water organic carbon (TOC) concentration inferred from near-infrared spectroscopy (NIRS), suggest that the Holocene development of Lake Seukokjaure was closely coupled to changes in terrestrial vegetation with associated soil development of the catchment, input of allochthonous organic carbon, and changes in the light regime of the lake. A relatively productive state just after deglaciation around 9700 to 7800 cal years BP was followed by a slight long-term decrease in primary production. The onset of the local tree-line retreat around 3200 cal years BP was accompanied by more diverse and altered chironomid and diatom assemblages and indications of destabilized soils in the catchment by an increase in variability and absolute values of d 13 C. An abrupt drop in the C/N ratio around 1750 cal years BP was coupled to changes in the internal lake structure, in combination with changes in light and nutrient conditions, resulting in a shift in the phototrophic community from diatom dominance to increased influence of chlorophytes, likely dominated by an aquatic moss community. Thus, this study emphasizes the importance of indirect effects of climate change on tree-line lake ecosystems and complex interactions of in-lake processes during the Holocene.
Sediment isotope tracers from Lake Saarikko, Finland, and implications for Holocene hydroclimatology
Quaternary Science Reviews, 2010
Multi-component isotopic analyses on a sediment core from Lake Saarikko, Finland, give insight into Holocene climate changes in northern Europe. Oxygen isotopic records from aquatic cellulose and authigenic carbonate reflect consistent, similar trends in hydrological balance, and are employed jointly to infer relative changes in lake water temperature. Other geochemical and isotopic tracers shed light on fluctuations in lake level and nutrient cycling, facilitating the interpretation of the oxygen isotopic archives. In the early Holocene (w10 000e9000 cal yr BP), the lake level was low and dry conditions prevailed despite low temperatures. Higher lake levels and depleted oxygen isotopic values w9000e7500 cal yr BP were probably caused by several factors: higher effective humidity, an isotopically depleted precipitation source, a cold event around 8300 cal yr BP, and increased spring snowmelt. In contrast, higher summer temperatures, lower effective humidity, lower lake levels and enriched oxygen isotopic values were experienced during the mid-Holocene ∼7500e3300 cal yr BP. The occurrence of the warmest inferred lake water and the most enriched cellulose oxygen-isotope values ∼6000e5000 cal yr BP is consistent with a summer temperature maximum inferred from other proxy sources from the region. The late Holocene was characterized by higher effective humidity and higher lake levels. Increase in spring snowmelt and colder temperatures, most likely related to the Little Ice Age, induced a drastic change in the lake hydrology and probably caused the formation of its present outlet ∼800 cal yr BP. Changes in the lake hydrological balance and climate variables inferred from oxygen isotopic records can be related to atmospheric circulation, most clearly to changes in the dominance and strength of westerly air-flow as well as summertime anticyclonic circulation.
Hydrobiologia, 2015
Lake Säkylän Pyhäjärvi has been an important fishing site and drinking water source for the local population for centuries. The lake has undergone significant changes: (1) the water level was lowered in the 1600s and in the 1850s; (2) planktivorous coregonid fish were successfully introduced in the early 1900s; (3) nutrient input from intensified agriculture has increased since the 1950s and (4) the effects of the current variable climate on the lake and its catchment have become more evident since the 1990s. We determined the phases of oligotrophication, eutrophication and recovery and elucidated the ecosystem changes by combining palaeolimnological records with detailed neolimnological data. The sedimentary diatom and cladoceran assemblages first showed a relatively eutrophic period followed by oligotrophic periods, linked with the artificial changes in water level and consequent shifts in macrophyte abundance. The oligotrophic period in the early 1900s is thought to represent the target trophic state for the lake. After the 1950s, introduction of vendace resulted in higher planktivory reflected by an increased relative abundance of small-bodied pelagic cladocerans. Signs of eutrophication occurred due to increased nutrient load. During the last 10 years, signs of recovery have been recorded. A complex history such as that of Lake Pyhäjärvi illustrates the difficulties in selecting management targets, and the risk of setting false targets, for lakes based solely on monitoring data-both neolimnological and palaeolimnological approach are needed.
A multi-proxy palaeoecological study of Alanen Laanijärvi, a boreal-forest lake in Swedish Lapland
Boreas, 2005
Chironomids, pollen and spores were used to reconstruct Holocene aquatic and terrestrial environments at Alanen Laanijärvi, northern Sweden. Chironomid analysis revealed a pattern of limnological evolution from oligotrophic conditions in a relatively deep lake during 8.6 to 5.5 cal. ka BP, followed by a period of lake shallowing from 5.5 to 2.7 cal. ka BP. Increases in acidity and littoral habitat complexity may have occurred from 2.7 cal. ka BP to the present, though some compositional changes may have resulted from human disturbance. Chironomid-inferred mean July air temperatures range between 9.8 C in the Early Holocene to 11.3 C in the Late Holocene. Limitations on chironomid-based quantitative temperature interpretations may exist because of low taxon richness. Diatoms were recovered from the upper sediments only, from about AD 1800. Pollen and spore analysis revealed an early colonizing vegetation of juniper, sedges and birch soon after local deglaciation, followed by birch forests until about 8.3 cal. ka BP. Alder stands occurred locally to 5.5 cal. ka BP, when pine and spruce forests developed and remain to the present day. These results suggest that little major terrestrial vegetation change may occur in some northern environments with predicted future global warming, where it is predicted to be most severe. Aquatic environments may, however, be greatly affected by a shift in precipitation regime, causing changes in allochthonous organic input, lake depth and possibly the amount of human activity or disturbance in the watershed.
Quaternary International, 2005
Three independent varve (annually laminated) chronologies, verified by paleomagnetic dating, were used in the present biostratigraphical study to investigate the history of the Baltic basin in central Finland. Diatom analyses of the studied sediment sequences show the transition from the Ancylus Lake taxa to small-lake diatoms at the isolation boundary. These three varved profiles provide the following data and information on early Holocene events in central Finland: (i) a shoreline displacement curve between the deglaciation at ca. 9000 BC and ca. 7000 BC, (ii) relative emergence of the land area between 116 and 96 m above the present day sea level, which proceeded at a rate of ca. 2.6 cm year À1 , (iii) the calendar year age for the Lake Ancylus at ca. 8250-8200 BC, and (iv) the calendar year age for the Betula/Pinus pollen zone boundary (ca. 8100 BC) and Alnus arrival (ca. 7100 BC). r
Journal of Paleolimnology
Algal communities act as sensitive indicators of past and present climate effects on northern lakes, but their responses can vary considerably between ecosystems. Functional trait-based approaches may help us better understand the nature of the diverse biotic responses and their underlying ecosystem changes. We explored patterns in diatom (Bacillariophyceae) growth forms and species composition during the Neoglacial in two shallow lakes typical of subarctic regions, including a dark-colored woodland lake and a clear tundra lake. Sediment carbon and nitrogen elemental and isotope biogeochemistry and spectral indices were used to track broadscale changes in lake productivity, the inflow of organic carbon from land, and benthic substratum over the past three millennia. The biogeochemical indices tracked declines in land-lake connectivity as well as lake-water and sediment organic enrichment above and below the subarctic treeline driven by Neoglacial cooling. This broadscale environment...
2003
Abstract¨S ediment cores from two neighbouring lakes (Viitna Linajarv and Viitna Pikkjarv) in northern Estonia were studied to determine lake-level fluctuations during the Holocene and their impact on biogeochemical cycling. Organic matter and pollen records dated by radiocarbon and radiolead indicated a water level rise in both lakes during the early Holocene (c. 10 000-8000 BP). A regression followed around 7500 BP and several transgressions occurred during the latter half of the Holocene, c. 6500 and 3000 BP. Human impact during the last centuries has caused short-term lake-level fluctuations and accelerated sediment accumulation in the lakes. The differences in water depth led to variations in sediment formation. During 10 000-8000 BP (Preboreal and Boreal chronozones) mineral-rich sediments with coloured interlayers deposited in L. Linajarv. These sediments indicate intensive erosion from the catchment and oxygen-rich lake, which favoured precipitation of iron oxides and carbonates. Fluctuations in water depth, leaching of nutrients from catchment soils and climatic changes increased the trophÿ of L. Linajarv around 6000 BP. The subsequent accumulation of gyttja, the absence of CaCO and the decrease in 3 both the C / N ratio and phosphorus content in the sediments also indicate anoxic conditions in the hypolimnion.T he similarity in the development of L. Linajarv and L. Pikkjarv and their proximity made it possible to discern the impact of water depths changes on biogeochemical cycling in lakes.
Vegetation History and Archaeobotany, 2006
Holocene environmental and climatic changes are reconstructed using analyses of biological proxies in lake sediments from Vuolep Njakajaure, a lake located near the altitudinal treeline in northern Sweden (68 • 20 N, 18 • 47 E). We analysed biological proxy indicators from both aquatic and terrestrial ecosystems, including diatoms, pollen and chironomid head capsules, in order to reconstruct regional Holocene climate and the development of the lake and its catchment. During the early Holocene and after 2500 cal b.p., Fragilaria taxa dominated the diatom assemblages, whereas planktonic Cyclotella taxa prevailed during the major part of the Holocene (7800-2300 cal b.p.), Communicated by Pim van der Knaap C. Bigler ( ) · M. L. Heinrichs · R. I. Hall
The Holocene, 2002
Quantitative reconstruction s are made of Holocene changes in climatic and environmenta l conditions from analyses of pollen, chironomids and diatoms in identical stratigraphic levels of a sediment core from Vuoskkujávri (68°20¢43 N, 19°06¢00 E, 348 m a.s.l.) near Abisko in northern Sweden (Lapland). Transfer functions, based on regional calibration sets, are applied to reconstruct Holocene patterns in mean July air temperature (using all three indicators), mean January air temperature (pollen), annual precipitation (pollen) and lakewater pH (diatoms). During periods with 'good' t to the modern calibration sets all mean July air-temperature inferences based on the three proxy indicators reveal a general trend of decreasing temperature: pollen-inferred mean July air temperature shows a decrease of c. 1.1°C since 7500 cal. yrs BP; the chironomids show a decrease of c. 1.2°C since the early Holocene; whereas the diatoms show a decrease of c. 1.5°C since 6000 cal. yrs BP. Pollen-inferred mean January air temperature indicates that winters may have been warmer by c. 3.0°C during the early Holocene, followed by a gradual cooling until 8500 cal. yrs BP (c. 1.0°C warmer than today) and a subsequent warming until 7000 cal. yrs BP (c. 2.0°C warmer than today). Since 7000 cal. yrs BP, a gradual cooling towards the present-day values is inferred. According to the pollen, annual precipitation may have been considerabl y higher during the early Holocene than today (c. +150 mm) and increased until 7000 cal. yrs BP (c. +320 mm). Since 7000 cal. yrs BP, annual precipitation decreased continuously towards present-day values. Diatom-inferred pH trends show that natural acidication of c. 0.5 pH units followed deglaciation; present-day values were reached c. 5000 cal. yrs BP. The early Holocene is identi ed as a problematic time period for the application of modern calibration sets, as diatoms show 'poor' t to the calibration set from 10 600 to 6000 cal. yrs BP, pollen from 10 600 to 7500 cal. yrs BP, and chironomids from 10 250 to 10 000 cal. yrs BP. Compared with estimates from the COHMAP GCM model, mean July air-temperature inferences based on biological proxies at Vuoskkujávri suggest a more moderate decrease in temperature over the past 9000 years.
Journal of Paleolimnology, 2018
We assessed the utility of using the sediment total organic carbon/total nitrogen (C/N) ratio as an indicator of paleoclimate changes in the eastern Baltic area during the late glacial and early Holocene. The C/N ratio in sediments from Lake Lielais Svētiņ u, eastern Latvia, was compared with other sediment variables that are used as proxies of past climate and environment. Analysis revealed that although the organic matter (OM) content in late glacial sediments was extremely low, the C/N ratio captured information about OM origin, and fluctuations in the ratio tracked climate oscillations. The C/N ratio was significantly positively correlated with pollen-inferred mean summer temperature. Therefore, C/N ratio was lower under colder conditions, indicating a predominantly phytoplankton origin of OM, and was higher during warmer conditions, when there was more vegetation around the lake. A strong positive correlation between C/N ratio and the paleopigment beta carotene suggested that elevated phytoplankton production resulted from higher nutrient availability that was controlled largely by the input of terrestrial OM to the lake during warmer climate episodes. Thus, C/N ratio was a good indicator of paleoclimate changes, at least for the late glacial period, when generally cold conditions prevailed. This study also demonstrates the power of multi-proxy paleolimnological analyses for investigating past environmental changes in lakes and their watersheds.