Late Quaternary fluctuations of the Leeuwin Current and palaeoclimates on the adjacent land masses: Clay mineral evidence

Clay minerals eroded from soils by rivers and wind action become entrained in shallow‐ as well as deep‐water masses of the surrounding seas. Their pattern on the sea floor gives clues to their propagation by ocean currents. Clay mineral assemblages in sediment cores can be used as a useful proxy to decipher past changes in the intensity of ocean currents or in the nature of the palaeoclimatic processes on the adjacent landmasses. Three cores taken from beneath the path of the present‐day Leeuwin Current in the Timor Passage, from off the Australian North West Shelf and off the North West Cape of Western Australia are investigated. They provide a Late Quaternary record of environmental changes. Kaolinite and chlorite are transported into the Timor Passage today by the Indonesian Throughflow, while illite is provided locally from Timor. The Leeuwin Current leaves the Timor Passage with a characteristic clay mineral signature acquired in the Indonesian Archipelago (kaolinite, chlorite and illite). Uptake of clay minerals along its way through the Timor Sea, e.g. illite from the Kimberley area, changes this signature. South of North West Cape chlorite, injected by the rivers of the Pilbara region into the path of the Leeuwin Current, is prominent in surface sediments in less than 1000 m water depth and outlines the flow of the current today. During the last glacial period, the volume of the Indonesian Throughflow decreased and less kaolinite and chlorite reached the Timor Passage. Offshore from North West Cape, a reduction in chlorite during the last glacial may indicate a decrease or absence of the Leeuwin Current and/or a reduction in the input of chlorite due to drier conditions on land. A maximum of illite in recent sediments and the Holocene offshore from North West Cape results from the input of material from rivers periodically draining the adjacent hinterland. Again, a reduction in illite points to a drier climate in the area during the last glacial.     

Glaciers and climate in Pacific Far NE Russia during the Last Glacial Maximum

A combined geomorphological–physical model approach is used to generate three‐dimensional reconstructions of glaciers in Pacific Far NE Russia during the global Last glacial Maximum (gLGM). The horizontal dimensions of these ice masses are delineated by moraines, their surface elevations are estimated using an iterative flowline model and temporal constraints upon their margins are derived from published age estimates. The equilibrium line altitudes (ELAs) of these ice masses are estimated, and gLGM climate is reconstructed using a simple degree–day melt model. The results indicate that, during the gLGM, ice masses occupying the Pekulney, Kankaren and Sredinny mountains of Pacific Far NE Russia were of valley glacier and ice field type. These glaciers were between 7 and 80 km in length, and were considerably less extensive than during pre‐LGM phases of advance. gLGM ice masses in these regions had ELAs of between 575 ± 22 m and 1035 ± 41 m (above sea level) – corresponding to an ELA depression of 350–740 m, relative to present. Data indicate that, in the Pekulney Mountains, this ELA depression occurred because of a 6.4°C reduction in mean July temperature, and 200 mm a^?1 reduction in precipitation, relative to present. Thus reconstructions support a restricted view of gLGM glaciation in Pacific Far NE Russia and indicate that the region's aridity precluded the development of large continental ice sheets. Copyright © 2011 John Wiley & Sons, Ltd.     

Climate variability during the Last Glacial Maximum in eastern Australia: evidence of two stadials?

A high‐resolution, multiproxy record encompassing the last glacial–interglacial transition is presented for Native Companion Lagoon, a coastal site in subtropical eastern Australia. Rates of aeolian sedimentation in the lake were established by trace element analyses of lacustrine sediments and used as a proxy for aridity. In conjunction with sediment moisture content, charcoal and pollen these provide a multi‐decadal record of palaeoenvironmental variability for the period 33–18 k cal. yr BP. Results indicate that the Last Glacial Maximum in eastern Australia spanned almost 10 k cal. yr, and was characterised by two distinct cold dry events at approximately 30.8 k cal. yr BP and 21.7 k cal. yr BP. Provenance of selected sediment samples by trace element geochemical fingerprinting shows that continental sourced aeolian sediments originated primarily from South Australia during these cold events and from sites in central Australia during the intervening time. Used in combination with a pollen record, the provenance of long‐travelled dust to mainland sites shows that the two cold events were characterised by frequent meridional dry southwesterly winds rather than zonal westerly airflow as previously believed. The intervening period was cool and humid, which we infer as being associated with more frequent southeasterly winds of maritime origin. These results lend support to previous research that indicates the Southern Hemisphere experienced a period of widespread climatic amelioration at the height of the last glacial known as the Antarctic Isotopic Maximum. Copyright © 2008 John Wiley & Sons, Ltd.     

Alkenones and coccoliths in ice‐rafted debris during the Last Glacial Maximum in the North Atlantic: implications for the use of UK37′ as a sea surface temperature proxy

The U^K₃₇′ index has proven to be a robust proxy to estimate past sea surface temperatures (SSTs) over a range of time scales, but like any other proxy, it has uncertainties. For instance, in reconstructions of the Last Glacial Maximum (LGM) in the northern North Atlantic, U^K₃₇′ indicates higher temperatures than those derived from foraminiferal proxies. Here we evaluate whether such warm glacial estimates are caused by the advection of reworked alkenones in ice‐rafted debris (IRD) to deep‐sea sediments. We have quantified both coccolith assemblages and alkenones in sediments from glaciogenic debris flows in the continental margins of the northern North Atlantic, and from a deep‐sea core from the Reykjanes Ridge. Certain debris flow deposits in the North Atlantic were generated by the presence of massive ice‐sheets in the past, and their associated ice streams. Such deposits are composed of the same materials that were present in the IRD at the time they were generated. We conclude that ice rafting from some locations was a transport pathway to the deep sea floor of reworked alkenones and pre‐Quaternary coccolith species during glacial stages, but that not all of the IRD contained alkenones, even when reworked coccoliths were present. We speculate that the ratio of reworked coccoliths to alkenone concentration might be useful to infer whether significant reworked alkenone inputs from IRD did occur at a particular site in the glacial North Atlantic. We also observe that alkenones in some of the debris flows contain a colder signal than estimated for LGM sediments in the northern North Atlantic. This is also clear in the deep‐sea core studied where the warmest intervals do not correspond to the intervals with large inputs of reworked coccoliths or IRD. We conclude that any possible bias to U^K₃₇′ estimates associated with reworked alkenones is not necessarily towards higher values, and that the high SST anomalies for the LGM are unlikely to be the result of a bias caused by IRD inputs. Copyright © 2011 John Wiley & Sons, Ltd.     

Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron

The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 °N, 61.0157 °W, 884 m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from ～15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200 m elevation above the lake, suggesting a cooling‐driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia

This study presents results from geomorphological mapping and cosmogenic radionuclide dating (¹⁰Be) of moraine sequences at Otgon Tenger (3905 m), the highest peak in the Khangai Mountains (central Mongolia). Our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during Marine Oxygen Isotope Stage (MIS) 3. Large ice advances also occurred during MIS-2 (at ~ 23 and 17–16 ka), but these advances did not exceed the limits reached during MIS-3. The results indicate that climatic conditions during MIS-3, characterized by a cool-wet climate with a greater-than-today input from winter precipitation, generated the most favorable setting for glaciation in the study region. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2, and again during the last glacial–interglacial transition when precipitation levels increased. Viewed in context of other Pleistocene glacial records from High Asia, the pattern of glaciation in central Mongolia shares some features with records from southern Central Asia and NE-Tibet (i.e. ice maxima during interstadial wet phases), while other features of the Mongolian record (i.e. major ice expansion during the MIS-2 insolation minimum) are more in tune with glacier responses known from Siberia and western Central Asia.     

Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie

Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene.     

Late Pleistocene(MIS 2) climate change on the Northern Tibetan Plateau inferred from pollen and geochemical records from Lake Gomo Co

正Introduction A 405-cm sediment section GM02 from Gomo Co salt lake in the northern Tibetan Plateau was used to reconstruct climate changes during marine isotope stage(MIS)2,including the Last Glacial Maximum(LGM)and last     

中全新世和末次盛冰期北大西洋涛动变化及其与亚洲降水的联系:基于MPI-ESM模拟试验

本文利用古气候模式比较计划第三阶段(PMIP3)中MPI-ESM模式模拟输出,采用主分量分析、回归分析、多窗谱分析等方法,探讨了中全新世(MH)和末次盛冰期(LGM)北大西洋涛动(NAO)变化及其与亚洲降水的关系.结果表明:MH冬季NAO较现代有轻微增大,南部高压中心东移;而LGM冬季NAO明显减弱,南北气压活动中心转为西南-东北走向.MH冬季强NAO信号可通过海洋记忆效应持续至夏季,并以准静止Rossby波形式传至东亚地区,导致乌拉尔山和鄂霍次克海阻高增强、贝加尔湖低压加深,这种倒“Ω”流场增强有利于冷空气南下,并通过热成风原理使得副热带西风急流增强,急流南侧产生上升异常,有利于该区降水产生;而LGM时NAO减弱引起夏季倒“Ω”流场减弱,冷空气南下弱于现代,使得副热带西风急流减弱,其南侧产生下沉异常,最终抑制降水.因此,MH和LGM两阶段的NAO引起大气环流的变化可能对亚洲夏季降水产生影响.     

芒果粉对真空油炸面包虾裹浆特性及其品质的影响

【目的】研究添加芒果粉对真空油炸面包虾裹浆特性及其品质的影响。【方法】以小麦粉和大豆分离蛋白的裹浆作为对照,研究芒果粉替代部分小麦粉和大豆分离蛋白的裹浆流变学特性;以裹涂率、油脂含量、水分含量、色泽及质构特性为考察指标,研究芒果粉替代部分小麦粉和大豆分离蛋白的裹浆对真空油炸面包虾品质的影响;以最佳芒果粉添加量的真空油炸面包虾为研究对象,测定外裹层黄酮物质含量,并采用羟自由基和DPPH自由基体系对产品外裹层黄酮物质的抗氧化性进行分析。【结果】所有配方的裹浆均表现为触变性,呈现剪切稀化特性,具有假塑性流体特征,并符合幂率流体,芒果粉可显著提升裹浆的黏度;芒果粉可显著增大面包虾裹涂率,改善产品质构和色泽特性,降低产品油脂含量并提升其水分含量(P <0.05)。当芒果粉添加量从10%增加到30%时,面包虾产品油脂质量分数从24.84%降低到20.58%,产品的脆性和色泽中的亮度值(L*)、黄度值(b*)均得到了显著提升(P <0.05)。当小麦粉质量分数66%、大豆分离蛋白质量分数4%、芒果粉质量分数30%时,真空油炸面包虾产品的各项品质最佳;真空油炸面包虾产品外裹层黄酮物质质量分数为(46.75±2.87)mg/100g,其对羟自由基和DPPH自由基的清除效果方面都均强于维生素C。【结论】芒果粉可提升裹浆黏度,改善真空油炸面包虾产品品质,其外裹层较强的抗氧化性对于真空油炸裹涂制品延长货架期具有一定积极作用。