Precipitation linked to Atlantic moisture transport: clues to interpret Patagonian palaeoclimate (original) (raw)
Related papers
Journal of Climate, 2012
Some aspects of the seasonal precipitation over eastern Patagonia, the southernmost area of South America east of the Andes Cordillera, are examined in this paper. Results indicate that the central-north areas, the southern continental region, and the southernmost islands are three independent regions of seasonal precipitation, and that each of them is associated with specific patterns of atmospheric circulation. Precipitation over the central-north region is significantly related to the precipitation over a wide area of southern South America east of the Andes during the four seasons. Enhanced (reduced) precipitation over this area is associated with weakened (intensified) westerly flow in the region. Precipitation over the southern continental area has a close connection with the dipolar pattern of precipitation over subtropical South America during spring, summer, and autumn. The anomalies of atmospheric circulation at low and upper levels associated with the subtropical dipole are also able to modulate the intensity of the westerlies over the south of eastern Patagonia, affecting the regional precipitation. Precipitation over the islands of the southernmost part of eastern Patagonia is connected with subtropical precipitation in summer and winter. The activity of frontal systems associated with migratory perturbations moving to the east along the Southern Hemisphere storm tracks modulates the variability of seasonal precipitation over this region. * The Unidad Mixta Internacional (3351): Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos is sponsored by the Centre National de la Recherche Scientifique, the Consejo Nacional de Investigaciones Científicas y Té cnicas, and the Universidad de Buenos Aires.
Late glacial and Holocene climate variability, southernmost Patagonia
Quaternary Science Reviews, 2020
Late glacial-Holocene palaeoecological record, constrained by a robust chronology, from a peat bog near Punta Burslem (54°54'S, 67°57'W) on Isla Navarino, southernmost Patagonia documents the shifts in intensity and focus of the Southern Westerly Winds (SWWs) at these high latitudes. Such long-term records are required to reconstruct and better understand the likely regional impacts of a poleward shift and intensification of the SWWs predicted under global warming scenarios. Deglaciation at Punta Burslem occurs sometime before c. 17,000 cal a BP, and the post glacial landscape is dominated by cold tolerant pioneer species. Nothofagus woodland is established by c. 12,250 cal a BP, this moisture sensitive vegetation type retreats in the early to mid-Holocene from c. 9700 to 7050 cal a BP reflecting an intense and sustained drier phase associated with a prolonged poleward contraction of the SWWs. After c. 6000 cal a BP there is a regional trend to cooler and wetter climate. However, we identify at least five periods of rapid climate change (RCC) leading to drier conditions at this southern extreme of Patagonia: c. 5350-4750 cal a BP, c.4300-3300 cal a BP, c. 2600-1850 cal a BP, c. 1350-1100 cal a BP and c. 550-350 cal a BP. From a synthesis of our Isla Navarino records and a latitudinal spread (34°-64°S) of multiproxy records it is proposed that these periods of RCC and relatively drier conditions indicate latitudinal shifts in the location and intensity of the SWWs in response to climatic warming leading to reduced precipitation at the southern margins of Patagonia.
Holocene variability of the Southern Hemisphere westerlies in Argentinean Patagonia (52 S)
High-resolution analyses of allochthonous pollen input into crater lake sediments of Laguna Potrok Aike in the semi-arid Patagonian steppe reflect the variability of zonal wind intensities during the Holocene at 521 southern latitude. These indicators for Southern Hemisphere westerlies (SHW) strength vary on centennial timescales in concert with carbon/nitrogen (C/N) ratios and titanium (Ti) contents, interpreted as differential organic matter sources and minerogenic input to the sediment, respectively. The correlations underline a linkage between hydrological variability and west wind variability in Extra-Andean Patagonia. A shift to generally more intense SHW suggests intensification towards modern wind conditions at that latitude since 9.2 ka cal BP. r
Climate Dynamics, 2007
This study investigates the atmospheric circulation in transient climate simulations with a coupled atmosphere-ocean general circulation model (GCM) for the mid-Holocene (MH) period 7-4.5 ka BP driven with combinations of orbital, solar and greenhouse gas forcings. The focus is on southern South America. Statistical downscaling models are derived from observational data and applied to the simulations to estimate precipitation in south-eastern Patagonia during the MH. These estimates are compared with lake level estimates for Laguna Potrok Aike (LPA) from sediments. Relative to pre-industrial conditions (i.e. 1550-1850), which show extraordinarily high lake levels, the proxy-based reconstructed lake levels during the MH are lower. The downscaled simulated circulation differences indicate higher LPA precipitation during the MH from March to August, higher annual means, and reduced precipitation from September to February. Thus the reconstructed lower LPA lake levels can not be explained solely by the simulated precipitation changes. Possible reasons for this discrepancy are discussed. Based on proxy data from southern South America
Patagonian and southern South Atlantic view of Holocene climate
Quaternary Science Reviews, 2016
We present a comprehensive 10 Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10 Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10 Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n ¼ 13), 4450 ± 220 (n ¼ 7), 1450 or 1410 ± 110 (n ¼ 18), 360 ± 30 (n ¼ 5), and 240 ± 20 (n ¼ 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between~1400 and~1000 and~2300 and~2000 years ago. The most extensive glaciers occurred over the interval from~6100 to~4500 years ago, and their margins over the last~600 years were well within and lower than those in the middle Holocene. The 10 Be ages agree with 14 C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between~6100 and~4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced successive century-scale advances superimposed on a long-term net decrease in size. Our findings indicate that glaciers and sea ice in the Patagonian-South Atlantic sector of the Southern Hemisphere did not achieve their largest Holocene extents over the last millennium. We conclude that a pattern of more extensive Holocene ice prior to the last millennium is characteristic of the Southern Hemisphere middle latitudes, which differs from the glacier history traditionally thought for the Northern Hemisphere.
Recent advances in the chronology and the paleoclimatic understanding of Antarctic ice-core records point towards a larger heterogeneity of latitudinal climate fluctuations than previously thought. Thus, realistic paleoclimate reconstructions rely in the development of a tight array of well-constrained records with a dense latitudinal coverage. Climatic records from southernmost South America are critical corner-stones to link these Antarctic paleoclimatic archives with their South American counterparts. At 55°S on the Island of Tierra del Fuego, Lago Fagnano is located in one of the most substantially and extensively glaciated regions of southernmost South America during the Late Pleistocene. This elongated lake is the largest (~110 km long) and non-ice covered lake at high southern latitudes. A multi-proxy study of selected cores allows the characterization of a Holocene sedimentary record. Detailed petrophysical, sedimentological and geochemical studies of a complete lacustrine laminated sequence reveal variations in major and trace elements, as well as organic-content, suggesting high variability in environmental conditions. The comparison of these results with other regional records allows the identification of major known Late Holocene climatic intervals and to propose a time for the onset of the Southern Westerlies in Tierra del Fuego. These results improve our understanding of the forcing mechanisms behind climate change in southernmost Patagonia.
Quaternary Science Reviews, 2012
Much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid-latitudes, in particular the southwestern Patagonian region (50 e55 S). Its location adjacent to the Drake Passage and near the southern margin of the southern westerly winds (SWW) allows examining the postulated links between the Southern OceaneSWW coupled system and atmospheric CO 2 variations through the last glacial termination. Results from two sites located in the Última Esperanza area (52 S) allow us to infer SWW-driven changes in hydrologic balance during this critical time interval. These findings indicate peatland development under temperate/wet conditions between 14,600 and 14,900 cal yr BP, followed by cooling and a lake transgressive phase that led to a shallow lake during the early part of the Antarctic Cold Reversal (ACR, 13,600e14,600 cal yr BP), followed in turn by a deeper lake and modest warming during Younger Dryas time (YD, w11,800e13,000 cal yr BP), superseded by terrestrialization and forest expansion at the beginning of the Holocene. We propose that the SWW (i) strengthened and shifted northward during ACR time causing a precipitation rise in northwestern and southwestern Patagonia coeval with mid-and high-latitude cooling and a halt in the deglacial atmospheric CO 2 rise; (ii) shifted southward during YD time causing a precipitation decline/increase in NW/SW Patagonia, respectively, high-latitude warming, and invigorated CO 2 release from the Southern Ocean; (iii) became weaker between w10,000 and 11,500 cal yr BP causing a precipitation decline throughout Patagonia, concurrent with peak mid-and high-latitude temperatures and atmospheric CO 2 concentrations.
Late twentieth-century instrumental records reveal a persistent southward shift of the Southern Westerly Winds during austral summer and autumn associated with a positive trend of the Southern Annular Mode (SAM) and contemporaneous with glacial recession, steady increases in atmospheric temperatures and CO2 concentrations at a global scale. However, despite the clear importance of the SAM in the modern/future climate, very little is known regarding its behaviour during pre-Industrial times. Here we present a stratigraphic record from Lago Cipreses (51S), southwestern Patagonia, that reveals recurrent B200-year long dry/warm phases over the last three millennia, which we interpret as positive SAM-like states. These correspond in timing with the Industrial revolution, the Mediaeval Climate Anomaly, the Roman and Late Bronze Age Warm Periods and alternate with cold/wet multicentennial phases in European palaeoclimate records.We conclude that SAM-like changes at centennial timescales in southwestern Patagonia represent in-phase interhemispheric coupling of palaeoclimate over the last 3,000 years through atmospheric teleconnections