A paleolimnological reconstruction of Holocene climate change in southern Patagonia

first_imgTo fully understand the Holocene climatic variability in the sub-polar latitudes of the Southern Hemisphere and its driving mechanisms, like the Southern Hemisphere westerly winds, we undertook a multi-proxy analysis of a lake sediment core from Lago Pato (51°18.020’S, 72°40.716’W; Chile). The bottom sediments of the core are of glaciogenic origin and gave bulk ages of 30 000 – 22 000 cal. yr. B.P. These are overlain by brown, organic rich sediments which are 9500 cal. yr. B.P. old. The hiatus between both stratigraphic units is possibly related to sediment erosion as a result of the outflow of a large lake after regional deglaciation of the Patagonian Ice Sheet.The pollen record and a diverse benthic diatom community in the Holocene sediments point to dry conditions between ca. 9500 and 6035 cal. yr. B.P. This is coincident with the Early Holocene climate optimum recorded in for example the North Atlantic and Antarctica. From 6035 cal. yr. B.P. until the most recent period a higher biological production compared with the Early Holocene can be inferred from all proxies, probably resulting from wetter and/or warmer conditions. Apart from the diatoms, changes in the proxies are small since the Mid Holocene. The establishment of a planktonic diatom flora between 6035 and 3780 cal. yr. B.P. with the presence of the small diatom Discostella stelligera s.l. as well as the larger species Aulacoseira ambigua, A. granulata s.l. and Cyclostephanos cf. patagonicus possibly points to a period with sufficient mixing during autumn, winter or spring as well as enhanced thermal stratification during summer. Between ca. 3780 and 2080 the diatom community is dominated by Discostella stelligera which suggest a reduced water column mixing and a more stable lake stratification. From ca. 2080 cal. yr. B.P. till present an abrupt shift to and dominance of small chain-forming benthic fragilariod diatoms took place. This period is coincident with the Neoglacial cooling and could be the result of a change in lake-level, longer ice-cover, a turbid/low-nutrient environment, or a more alkaline environment. In the most recent sediments also an increase of Cyclotella cf. meneghiniana could be noticed.last_img read more

White facing spell on sidelines

first_img The former Leinster front-rower had been expected to understudy Mike Ross across the autumn series, with Marty Moore already out for three months after shoulder surgery. Now head coach Schmidt and Ireland will be pinning hopes on Leinster’s experienced front-rower Ross recovering from groin trouble as expected to shore up Ireland’s scrum. Leinster’s 34-year-old scrum cornerstone Ross is expected to return to full training next week. With White the latest star to lengthen Ireland’s injury glut, his return gains even greater importance. The big-scrummaging Springboks would have looked to take on Ireland’s set-piece even if the Aviva Stadium hosts were at full strength up front next weekend. White’s absence, allied to Moore’s shoulder surgery, leaves Ireland short of experience at tighthead for the South Africa clash. Schmidt had admitted he promoted White into the squad for his potential debut on the strength of his lengthy top-level club career, expecting the 33-year-old to handle Test intensity better than several promising but young and raw prospects. Now the former Leinster coach must draw on Connacht’s versatile front-rower Rodney Ah You and Munster’s Stephen Archer as potential understudies to Ross. Former schoolteacher Schmidt should at least be able to call on Jack McGrath at loosehead prop as he aims to step up his return from injury, offsetting somewhat Cian Healy’s long-term absence. Ireland will still be shorn of at least 15 stars for the visit of Heyneke Meyer’s Springboks, however, before entertaining Georgia and then Australia across the three-Test Guinness series. Press Association The New Zealand-born tighthead faces surgery next week and could now be sidelined for as long as four months. The 33-year-old was lined up for his international debut against South Arica next weekend. His absence further drains Ireland’s already stretched front-row resources. center_img Connacht prop Nathan White will miss Ireland’s autumn Test series after rupturing a tendon in his upper arm in training with Joe Schmidt’s squad. last_img read more