| Title | Palaeolimnology of Lake Hess (Patagonia, Argentina): multi-proxy analyses in short sediment cores |
| Abstract | By contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess (41° 22´ 20 S, 71° 44´ 0 W) located in the Nahuel Huapi National Park, in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi-pristine lake which receives melt waters from the Tronador ice cap. Chronology was based on 137Cs and 210Pb measurements of the upper sediments and the inferred sedimentation rate of 23.2 mg cm-2 y-1 (0.15 cm y-1) was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility profiles. Results from the multiproxy analyses in the longest core (83 cm) identify three main phases of change. From the bottom up to 42 cm (ca. A.D.1800), the sediment is composed of light-grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone (A.D. 1770-1850), pigment concentrations were very low. From 42 cm to ca. 25 cm (A.D. 1800-1940), the sedimentary record is composed of alternating black and dark organic-matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm (ca. A.D. 1940) showing a strong increase in organic matter content, algal nutrients, and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. |
| Source | Hydrobiologia (The Hague. Print) 631, pp. 289–302 |
| Keywords | palaeolimnologypigmentschironomidsPatagoniaSouth America |
| Journal | Hydrobiologia (The Hague. Print) |
| Editor | Kluwer Academic Publishers, Boston, Paesi Bassi |
| Year | 2009 |
| Type | Articolo in rivista |
| DOI | 10.1038/embor.2010.56 |
| Authors | Guilizzoni P., Massaferro J. (1), Lami A., Piovano E. (2), Ribeiro Guevara S. (3), Formica S. (2), Daga R. (3), Rizzo A. (3), Gerli S. |
| Text | 53082 2009 10.1038/embor.2010.56 ISI Web of Science WOS 000267040900018 palaeolimnology pigments chironomids Patagonia South America Palaeolimnology of Lake Hess Patagonia, Argentina multi proxy analyses in short sediment cores Guilizzoni P., Massaferro J. 1 , Lami A., Piovano E. 2 , Ribeiro Guevara S. 3 , Formica S. 2 , Daga R. 3 , Rizzo A. 3 , Gerli S. 1 Laboratorio de Biodiversidad Darwin, Instituto de Investigaciones en Biodiversidad y Medioambiente/ Consejo Nacional de Investigaciones Cient1´ficas y Te´cnicas, Quintral 1250, 8400 Bariloche, Argentina 2 The Centro de Investigaciones en Ciencias de la Tierra, Universidad de Co´rdoba, Av Velez Sarsfield 1611, 5016 Co´rdoba, Argentina 3 Laboratorio de Ana´lisis por Activacio´n Neutro´nica, Comisio´n Nacional de Energ1´a Ato´mica, Av Bustillo km 9.5, 8400 Bariloche, Argentina By contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess 41° 22´ 20 S, 71° 44´ 0 W located in the Nahuel Huapi National Park, in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi pristine lake which receives melt waters from the Tronador ice cap. Chronology was based on 137Cs and 210Pb measurements of the upper sediments and the inferred sedimentation rate of 23.2 mg cm 2 y 1 0.15 cm y 1 was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility profiles. Results from the multiproxy analyses in the longest core 83 cm identify three main phases of change. From the bottom up to 42 cm ca. A.D.1800 , the sediment is composed of light grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone A.D. 1770 1850 , pigment concentrations were very low. From 42 cm to ca. 25 cm A.D. 1800 1940 , the sedimentary record is composed of alternating black and dark organic matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm ca. A.D. 1940 showing a strong increase in organic matter content, algal nutrients, and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. 631 Palaeolimnology of Lake Hess Patagonia, Argentina multi proxy analyses in short sediment cores Guilizzoni_et_al_Hess.pdf Articolo in rivista Kluwer Academic Publishers 0018 8158 Hydrobiologia The Hague. Print Hydrobiologia The Hague. Print Hydrobiologia The Hague. Print Hydrobiologia. The Hague. Print Hydrobiologia Dordrecht The Hague. Print Hydrobiologia Boston The Hague. Print Hydrobiologia London The Hague. Print GERLI STEFANO piero.guilizzoni GUILIZZONI PIERO andrea.lami LAMI ANDREA TA.P02.005.002 Uso della paleolimnologia come strumento per lo studio del paleoclima e dell evoluzione climatica |
