Summer phytoplankton composition and nitrogen limitation of the deep, naturally-acidic (pH∼2.2) Lake Caviahue, Patagonia, Argentina     

Sara G. Beamud  Mónica M. Diaz  Fernando L. Pedrozo 《Limnologica》2007,37(1):37-48

During the warm seasons of 1998-2004, the naturally-acidic (pH∼2.2) Lake Caviahue was sampled for conductivity, temperature, oxygen, light, nutrients, and phytoplankton (density, biomass and chlorophyll a) with a view to studying the summer phytoplankton population changes with relation to environmental factors, as well as the significance of nitrogen limitation on the phytoplankton yield. Lake Caviahue is characterized by its low transparency, CO₂, and N concentration; significant P values; a distinctive vertical distribution of phytoplankton biomass with high values along the water column; and sometimes maximum meta-hypolimnion values. Biodiversity is very low as a result of extreme environmental conditions, Chlorophyceae being the prevailing algae group. Two types of bioassays were carried out to assess nitrogen limitation. For the first bioassay, a solution of ammonium-nitrogen chloride and/or wastewater (rich in ammonium and phosphorus) was used, while one of the lake's sediments was the source of nutrients for the second bioassay. Contrary to the case of acidic mining lakes, N-ammonium proved to be a significant supportive capacity limiting factor as to phytoplankton yield. The present paper provides for the first time information on phytoplankton nitrogen limitation in a naturally-acidic lake.  相似文献   

Climatically induced lake level changes during the last two millennia as reflected in sediments of Laguna Potrok Aike,southern Patagonia (Santa Cruz,Argentina)   总被引：1，自引：0，他引：1  

Torsten?HaberzettlEmail author  Michael?Fey  Andreas?Lücke  Nora?Maidana  Christoph?Mayr  Christian?Ohlendorf  Frank?Sch?bitz  Gerhard?H.?Schleser  Michael?Wille  Bernd?Zolitschka 《Journal of Paleolimnology》2005,33(3):283-302

The volcanogenic lake Laguna Potrok Aike, Santa Cruz, Argentina, reveals an unprecedented continuous high resolution climatic record for the steppe regions of southern Patagonia. With the applied multi-proxy approach rapid climatic changes before the turn of the first millennium were detected followed by medieval droughts which are intersected by moist and/or cold periods of varying durations and intensities. The total inorganic carbon content was identified as a sensitive lake level indicator. This proxy suggests that during the late Middle Ages (ca. AD 1230–1410) the lake level was rather low representing a signal of the Medieval Climate Anomaly in southeastern Patagonia. At the beginning of the Little Ice Age the lake level rose considerably staying on a high level during the whole period. Subsequently, the lake level lowered again in the course of the 20th century.  相似文献   

Revised stratigraphic framework of the Cretaceous in the Bajo Grande area (Argentinean Patagonia) inferred from new U–Pb ages and palynology     

《Cretaceous Research》2016

The revision of the stratigraphy of the Cerro Bayo in the Bajo Grande area (Argentinean Patagonia) and the new ²⁰⁶Pb/²³⁸U age of 116.85 ± 0.26 Ma constrain the dating of the Baqueró flora, one of the most abundant Aptian floras of southern Gondwana. This flora, preserved in the Baqueró Group, represents an extinct biome that flourished ca. 118 Ma ago and was affected by increasing regional volcanism during the subsequent four millions years. The outcrops of the Cerro Bayo are characterized by fluvio-lacustrine deposits divided into three facies associations that include nine lithofacies. The first palynological record for the locality confirms the correlation of the lower part of the outcrops with the Anfiteatro de Ticó Formation (the oldest unit of the Baqueró Group). The new radiometric age and stratigraphy support recognition of the Bajo Tigre Formation (the middle unit of the Baqueró Group) in the area and date the earliest stage in angiosperm diversification in southern South America. Stratigraphic relationships among the Baqueró, Chubut and Divisadero groups are briefly discussed.  相似文献   

Bajada del Diablo impact crater-strewn field: The largest crater field in the Southern Hemisphere     

R.D. Acevedo  J.F. Ponce  M. Rocca  J. Rabassa  H. Corbella   《Geomorphology》2009,110(3-4):58-67

Recent remote sensing analyses and field studies have shown that Bajada del Diablo, in Argentina, is a new crater-strewn field. Bajada del Diablo is located in a remote area of Chubut Province, Patagonia. This amazing strewn field contains more than 100 almost circular, crater-type structures with diameters ranging from 100 to 500 m in width and 30 to 50 m in depth. It is composed of three separated impact crater fields, which formed simultaneously. The impact was upon a Miocene basaltic plateau and Pliocene–Early Pleistocene pediments. The original crater field (60 km²) was later eroded by Late Pleistocene fluvial processes; thus, three major, separate areas were defined. Due to the erosional processes that have affected the area, it is difficult to determine yet if the crater field has a classic elliptical distribution. Crater structures are similar in target rocks, although showing different response and morphology in relation to rock type. They are simple rings, bowl-shaped with raised rimrock. Basaltic boulders have been deposited as a ring-shaped pile and the ejecta are found toward the NE flanks. The craters present a hummocky bottom, with dry ponds and lakes in the center, but they do not show raised central peaks. The rocks within the craters have strong and stable magnetic signature. No meteorite fragments or other diagnostic landmarks have been found yet. The craters have been partially filled in by debris flows from the rim and windblown sands in recent times. The origin of these crater fields may be related to multiple fragmentation of one asteroid that broke up before impact, perhaps traveling across the space as a rubble pile. Alternatively, multiple collisions of comet fragments could explain the formation of these crater fields. Based on field geological and geomorphological data, the age of this event is estimated to be bracketed between Early Pleistocene and Late Pleistocene (i.e., 0.78–0.13 Ma ago).  相似文献   

Sedimentological and petrographic evolution of a fluvio-lacustrine environment during the onset of volcanism: Volcanically-induced forcing of sedimentation and environmental responses     

Andrea Di Capua  Roberto A. Scasso 《Sedimentology》2020,67(4):1879-1913

This work focuses on the transition from the Las Leoneras to Lonco Trapial Formations, in the lower part of the Early Jurassic succession of the incipient rift phase of the Cañadon Asfalto Basin (western part of Chubut Province – Patagonia, Argentina). Twenty lithofacies have been identified and grouped into seven facies associations on the basis of field characteristics (sedimentological and lithological) and optical microscope analysis, from two localities representing proximal and distal locations in the basin. The spatial relationship between all the lithofacies provided a four-dimensional reconstruction of the palaeoenvironmental evolution, showing how the original, clastic sedimentation in alluvial/fluvial and lake environments was modified by short-lived volcanic events during three volcanic cycles, and how the environment reacted after the input of huge amounts of volcaniclastics. Progradation of small deltas and subaqueous lobes, retrogradation caused by rising lake levels, and frequent erosion of valleys were typical processes in this environment. When explosive volcanism began, the original tectono-climatic control on sedimentation was replaced by the volcanic control, and the volcanically-forced sedimentation broke the equilibrium among production, delivery and accumulation of sediments. The nature of the volcanic eruptions and the different propensity of volcanic lithofacies to produce particles of different size and types (lithics, crystals and glass) are also analyzed. The role of volcanism in the production and transport of great volumes of sediments across sedimentary systems needs to be carefully re-examined, and the analysis on the variability in the composition of volcaniclastic deposits must take into account that volcaniclastic particle types may not simply reflect a linear deepening in the dissection of magmatic arcs through time but are often controlled by the style of the eruptions and the lithological variation of the volcanic products.  相似文献   

Interhemispheric synchrony of Late-glacial climatic instability as recorded in proglacial Lake Mascardi,Argentina     

Daniel Ariztegui  María Martha Bianchi  Julieta Masaferro  Eric Lafargue  Frank Niessen 《第四纪科学杂志》1997,12(4):333-338

Several high-resolution continental records have been reported recently in sites in South America, but the extent to which climatic variations were synchronous between the northern and southern hemispheres during the Late-glacial–Holocene transition, and the causes of the climatic changes, remain open questions. Previous investigations indicated that, east of the Andes, the middle and high latitudes of South America warmed uniformly and rapidly from 13 000 ¹⁴C yr BP, with no indication of subsequent climate fluctuations, equivalent, for example, to the Younger Dryas cooling. Here we present a multiproxy continuous record, radiocarbon dated by accelerated mass spectroscopy, from proglacial Lake Mascardi in Argentina. The results show that unstable climatic conditions, comparable to those described from records obtained in the Northern Hemisphere, dominated the Late-glacial–Holocene transition in Argentina at this latitude. Furthermore, a significant advance of the Tronador ice-cap, which feeds Lake Mascardi, occurred during the Younger Dryas Chronozone. This instability suggests a step-wise climatic history reflecting a global, rather than regional, forcing mechanism. The Lake Mascardi record, therefore, provides strong support for the hypothesis that ocean–atmosphere interaction, rather than global ocean circulation alone, governed interhemispheric climate teleconnections during the last deglaciation. © 1997 John Wiley & Sons, Ltd.  相似文献   

‘Palaeolago Fueguino’, a Late Pleistocene lacustrine basin located in the central sector of Tierra del Fuego: a seismostratigraphic study     

Jorge G. Lozano  Donaldo M. Bran  Federica Donda  Emanuele Lodolo  Federico D. Esteban  Alejandro Tassone 《第四纪科学杂志》2021,36(2):273-287

At ~20 ka bp , lakes Yehuin, Chepelmut and Fagnano constituted a single, large water body in the central part of Isla Grande de Tierra del Fuego (southernmost Patagonia). The evolutionary history of this lake, known as ‘Palaeolago Fueguino’, was probably controlled by the advances, stillstands and retreats of the ‘Fagnano Palaeoglacier’, an outlet glacier that flowed eastward from the Darwin Cordillera ice sheet. A detailed analysis of high-resolution seismic reflection profiles acquired within the three lakes has allowed the identification and correlation of seven unconformities within the lacustrine sedimentary infill, three seismostratigraphic sequences in Lago Fagnano and four in Lago Yehuin. A seismic stratigraphic correlation between these sequences suggests that these basins formerly constituted a single, large lacustrine body. A lake-level curve of the evolutionary stages of each lake, derived from the seismostratigraphic analysis of the sedimentary infill is proposed here, representing a 17.5 ka-long record. It was further integrated with the glacial record of the advances and retreats of the Fagnano Palaeoglacier. This study has implications for interpreting the sedimentary history of lake basins in glaciated mountain ranges.  相似文献   

Warming trends in Patagonian subantartic forest     

《International Journal of Applied Earth Observation and Geoinformation》2019

The forests in the Aysén region (ca. 43–49 °S, Chile) have a high degree of wilderness and cover more than 4.8 million hectares, making it one of the largest areas of subantarctic forest in the Southern Hemisphere. The impact of global warming on this region is poorly documented. The main objective of this work was to analyze the normalized difference vegetation index (NDVI), land surface temperature (LST) and precipitation over Aysen forests in the context of ongoing global warming. We used average monthly images of LST and NDVI derived from the MODIS sensor covering the period 2001–2016 and precipitation from gridded datasets. The Aysén region was divided into three nested spatial scales: i) regional, ii) regional considering only forests, iii) local scale considering an evergreen subantarctic forest area covering around 5 × 5 km and a local deciduous forest area (dominated by Nothofagus pumilio). Trend analysis showed a warming rate of +0.78 K/decade (p ≤ 0.05) over the subantarctic forest zone, greening of +0.01/decade for NDVI (p ≤ 0.05) over the western zone, and a drying trend (p ≤ 0.05) over the eastern zone. The minimum temperature anomalies showed an increase of about 4.5 K during the period under analysis. LST, NDVI and precipitation were also analyzed here. The recent trends in temperature, greening and precipitation over the forests of Aysén detected in this research contribute to a better understanding of global warming impacts on subantarctic forests in the southern tip of South America. Nevertheless, to get a better estimation of the impact of global warming at multiple scales is needed to have better quality and quantity of data in situ.  相似文献   

Summer phytoplankton composition and nitrogen limitation of the deep, naturally-acidic (pH2.2) Lake Caviahue, Patagonia, Argentina     

Sara G. Beamud  Mnica M. Diaz  Fernando L. Pedrozo 《Limnologica》2007,37(1):37

During the warm seasons of 1998–2004, the naturally-acidic (pH2.2) Lake Caviahue was sampled for conductivity, temperature, oxygen, light, nutrients, and phytoplankton (density, biomass and chlorophyll a) with a view to studying the summer phytoplankton population changes with relation to environmental factors, as well as the significance of nitrogen limitation on the phytoplankton yield. Lake Caviahue is characterized by its low transparency, CO₂, and N concentration; significant P values; a distinctive vertical distribution of phytoplankton biomass with high values along the water column; and sometimes maximum meta-hypolimnion values. Biodiversity is very low as a result of extreme environmental conditions, Chlorophyceae being the prevailing algae group. Two types of bioassays were carried out to assess nitrogen limitation. For the first bioassay, a solution of ammonium–nitrogen chloride and/or wastewater (rich in ammonium and phosphorus) was used, while one of the lake's sediments was the source of nutrients for the second bioassay. Contrary to the case of acidic mining lakes, N-ammonium proved to be a significant supportive capacity limiting factor as to phytoplankton yield. The present paper provides for the first time information on phytoplankton nitrogen limitation in a naturally-acidic lake.  相似文献   

Relationship between volcanism and marine sedimentation in northern Austral (Aisén) Basin, central Patagonia: Stratigraphic, U–Pb SHRIMP and paleontologic evidence     

M. Surez  R. De La Cruz  B. Aguirre-Urreta  M. Fanning 《Journal of South American Earth Sciences》2009,27(4):309-325

The northernmost part of the oil-producing Austral Basin, known as Aisén Basin or Río Mayo Embayment (in central Patagonian Cordillera; 43–46°S), is a special area within the basin where the interplay between volcanism and the initial stages of its development can be established. Stratigraphic, paleontologic and five new U–Pb SHRIMP age determinations presented here indicate that the Aisén Basin was synchronous with the later phases of volcanism of the Ibáñez Formation for at least 11 m.yr. during the Tithonian to early Hauterivian. In this basin marine sedimentary rocks of the basal units of the Coihaique Group accumulated overlying and interfingering with the Ibáñez Formation, which represents the youngest episode of volcanism of a mainly Jurassic acid large igneous province (Chon Aike Province). Five new U–Pb SHRIMP magmatic ages ranging between 140.3 ± 1.0 and 136.1 ± 1.6 Ma (early Valanginian to early Hauterivian) were obtained from the Ibáñez Formation whilst ammonites from the overlying and interfingering Toqui Formation, the basal unit of the Coihaique Group, indicate Tithonian, early Berriasian and late Berriasian ages. The latter was a synvolcanic shallow marine facies accumulated in an intra-arc setting, subsequently developed into a retro-arc basin.  相似文献