Late Holocene ecological response to environmental changes in Lago Fagnano, Tierra del Fuego

RECASENS, C.; ARIZTEGUI, D.; MAIDANA, N. I.; WALDMANN, N.; MOY, C.; DUNBAR, R.; AUSTIN JR., J.A.; ANSELMETTI, F.

Ginebra

Congreso; 5th Geosciences Meeting; 2007

Swiss Academy of Sciences

<!-- /* Font Definitions */ @font-face {font-family:Times; panose-1:2 2 6 3 5 4 5 2 3 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:536902279 -2147483648 8 0 511 0;} @font-face {font-family:ArialMT; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-alt:Arial; mso-font-charset:77; mso-generic-font-family:swiss; mso-font-format:other; mso-font-pitch:auto; mso-font-signature:50331648 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:DE-CH; mso-fareast-language:DE;} p.MsoHeader, li.MsoHeader, div.MsoHeader {margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; tab-stops:center 235.15pt right 470.3pt; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:DE-CH; mso-fareast-language:DE;} p.Abstractaddress, li.Abstractaddress, div.Abstractaddress {mso-style-name:Abstract_address; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:DE;} p.Abstractauthors, li.Abstractauthors, div.Abstractauthors {mso-style-name:Abstract_authors; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:DE;} p.Abstractbodytext, li.Abstractbodytext, div.Abstractbodytext {mso-style-name:Abstract_body_text; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:DE;} p.Abstracttitle, li.Abstracttitle, div.Abstracttitle {mso-style-name:Abstract_title; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:16.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:Times; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:DE; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:595.05pt 842.0pt; margin:2.0cm 3.0cm 2.0cm 3.0cm; mso-header-margin:35.45pt; mso-footer-margin:47.9pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> A high-resolution diatom stratigraphy of a sediment core from Lago Fagnano has been used to document the paleoecological changes of this lake during the late Holocene. Located at 54°S in Tierra del Fuego, Argentina, Lago Fagnano occupies a tectonic depression along the Magallanes-Fagnano fault system. Climate in this area is highly influenced by the westerly winds, the Southern Ocean circumpolar flow and the South Pacific gyre, which makes of Tierra del Fuego a key site for paleoclimatic and paleoecological reconstructions in the Southern Hemisphere. Water and surface sediment grab samples were collected in the lake in order to constrain the modern limnology. Preliminary results of the physical and chemical parameters of the water column reveal a well-mixed lake with no evidence of water stratification. Taxa identification and counting of diatoms from sediment samples of the modern lake bottom show a highly diverse diatom community, though species from the Discostella genus are visibly dominant. These results, along with the water data, are essential to characterise the present limnological conditions of the basin and for further interpretation of the sedimentary record. The 160 cm gravity core used for the high-resolution diatom analysis exhibits alternating light and dark laminae, which have been assimilated to varves, allowing to estimate an age of 200 years for the base of the core. Ongoing radiocarbon dating in terrestrial macrofossils may confirm this hypothesis. Sediment density and magnetic susceptibility profiles show relatively uniform values occasionally interrupted by peaks, which are interpreted as turbidites. Rock-eval pyrolysis reveals a relatively uniform distribution of organic and inorganic carbon along the core. Sediment samples collected at estimated decadal to sub-decadal frequency were used for diatom identification and counting. Combining the different diatom assemblages found in the sedimentary record with the modern limnology will provide very valuable paleoecological information. A good interpretation of this dataset is important to develop diatom-based transfer functions, a final goal of this study that will be further applied at various temporal scales.