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Heinrich Event (heinrich + event)
Selected AbstractsCosmogenic 10BE Age Constraints for The Wester Ross Readvance Moraine: Insights Into British Ice-Sheet BehaviourGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2006Jeremy D. Everest This study presents the first absoluteage constraints from a palaeo-ice-sheet margin in western Scotland. Cosmogenic 10Be from four Lewisian gneiss boulders on the Gairloch Moraine in NW Scotland have yielded reliable exposure ages. Three of these dates, taken from a single moraine ridge, cluster around c. 15.5,18 ka BP, with a weighted mean of 16.3 ± 1.6 ka BP. These findings indicate that the last British Ice Sheet had retreated to the present-day coastline in NW Scotland by this time. It is suggested that the Wester Ross Readvance represents an ice-sheet oscillation during, or in the immediate aftermath of, Heinrich Event 1 (c. 17,18 ka BP). [source] Two-step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1GLOBAL CHANGE BIOLOGY, Issue 6 2010LYDIE M. DUPONT Abstract High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6,14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change. [source] Glacier response in the European Alps to Heinrich Event 1 cooling: the Gschnitz stadial,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2006Susan Ivy-Ochs Abstract The Gschnitz stadial was a period of regionally extensive glacier advance in the European Alps that lies temporally between the breakdown of the Last Glacial Maximum piedmont lobes and the beginning of the Bølling warm interval. Moraines of the Gschnitz stadial are found in medium to small catchments, are steep-walled and blocky, and reflect a snowline lowering of 650,700,m in comparison to the Little Ice Age reference snowline. 10Be surface exposure dating of boulders from the moraine at the type locality at Trins (Gschnitz valley, Tyrol, Austria) shows that it stabilised no later than 15,400,±,1400,yr ago. The overall morphological situation and the long reaction time of the glacier suggest that the climatic downturn lasted about 500,±,300,yr, indicating that the Gschnitz cold period began approximately 15,900,±,1400,yr ago, if not somewhat earlier. This is consistent with published radiocarbon dates that imply that the stadial occurred sometime between 15,400 14C,yr BP (18,020,19,100,cal.,yr) and 13,250 14C,yr BP (15,360,16,015,cal.,yr). A palaeoclimatic interpretation of the Gschnitz glacier based on a simple glacier flow model and statistical glacier-climate models shows that precipitation was about one-third of modern-day precipitation and summer temperatures were about 10,K lower than today. In comparison, during the Younger Dryas, precipitation in this area was only about 10% less and Ts (summer temperature) was only 3.5,4,K lower than modern values. Based on the age of the moraine and the cold and dry climate at that time, we suggest that the Gschnitz stadial was the response of Alpine glaciers to cooling of the North Atlantic Ocean associated with Heinrich Event 1. Copyright © 2005 John Wiley & Sons, Ltd. [source] The microstratigraphic record of abrupt climate changes in cave sediments of the Western MediterraneanGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2001Marie-Agnès Courty The purpose of this paper is to illustrate how calcareous sediments from Pleistocene and Holocene rockshelters and open caves of the Western Mediterranean can provide a stratigraphic record of abrupt climate change. The method proposed here is based on microstratigraphic examination of sedimentary sequences using microscopic techniques. The most important processes for characterizing the sensitivity of each cave to climate variables are: (1) the modes and rate of carbonate sediment production, (2) the nature and intensity of the pedogenic processes responsible for the synchronous alteration of carbonate materials (either those derived from the cave walls or those deposited on the ground surface), and (3) the supply of allogenic sediments, particularly by eolian activity. The cave sediment sequences presented record the marked coolings known as Dansgaard-Oeschger stadials and Heinrich events that occurred during the Pleistocene and the Holocene, as demonstrated by the high resolution records from ice and deep sea cores. At Abric Romanì in northeastern Spain, a series of sharp climatic deteriorations of increasing severity is shown to have occurred synchronously with the transition from the Middle to the Upper Paleolithic, with a period of seasonal frost and strong winds at ca. 37,000 yr B.P., tentatively correlated with Heinrich event 4. At Pigeon Cave, Taforalt (northern Morocco), the transition from the Aterian to Ibero-Maurusian/Epipalaeolithic cultures is dated to around 24,000,20,000 yr B.P. and is punctuated by a series of short cold pulses with evidence for seasonal freezing, soil erosion, and minimal evapotranspiration. In El Miron cave in north-central Spain, the exceptional nature of the Younger Dryas cooling produced a marked destabilization of the cave walls and roof. At El Miron, the stratigraphic evidence for sediment removal due to the rapid percolation of snow melt under a degraded soil cover allows us to reconstruct the nature of the negative excursion at ca. 8200 yr B.P. This example also illustrates how climate-controlled pedogenic processes can create a stratigraphic signature which has often been confused with a sedimentary hiatus. We conclude that cave sediments provide a valuable record of Pleistocene and Holocene climate changes. In appropriate contexts, these sequences allow us to examine the ecological stress generated by these unique global events at a local and regional level and improve our understanding of the complex anthropological processes that occurred at the same time. © 2001 John Wiley & Sons, Inc. [source] Two-step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1GLOBAL CHANGE BIOLOGY, Issue 6 2010LYDIE M. DUPONT Abstract High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6,14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change. [source] Late Quaternary upwelling off tropical NW Africa: new micropalaeontological evidence from ODP Hole 658C,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006Simon K. Haslett Abstract Planktonic foraminifera and radiolaria have been analysed in a Late Quaternary (40,0,ka) sediment sequence from Ocean Drilling Program (ODP) Hole 658C located under a coastal upwelling system near Cap Blanc, offshore northwest Africa, in order to document the palaeoceanographic history of the area. Temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the Late Quaternary. Phase 1 spans 40,14.5,ka and is characterised by moderate upwelling, but Heinrich event 2 is distinguished as a brief episode of strengthened upwelling. Phase 2 begins with a change in a number of variables at ca. 14.5,ka and extends to ca. 5.5,ka. This phase is characterised by a general strengthening of upwelling, but may be subdivided into three minor phases including (a) the recognition of the Younger Dryas, marked by a temporary reduction in upwelling strength, followed by (b) an intensification of upwelling, and (c) upwelling and high productivity between 8 and 5.5,ka. This phase of upwelling corresponds with maximum Holocene cooling, possibly triggered by the collapse of the Laurentide ice sheet. Phase 3 extends from 5.5 to 0,ka and is characterised by weak upwelling and significant calcite dissolution. These phases are related to climatic events, particularly the African Humid Period (AHP), which is coincident with Phase 2. The AHP is characterised by increased precipitation, linked to an intensification of the African monsoon that enhances North East Trade Wind-driven coastal upwelling and is associated with the expansion of continental vegetation across North Africa. Copyright © 2006 John Wiley & Sons, Ltd. [source] The microstratigraphic record of abrupt climate changes in cave sediments of the Western MediterraneanGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2001Marie-Agnès Courty The purpose of this paper is to illustrate how calcareous sediments from Pleistocene and Holocene rockshelters and open caves of the Western Mediterranean can provide a stratigraphic record of abrupt climate change. The method proposed here is based on microstratigraphic examination of sedimentary sequences using microscopic techniques. The most important processes for characterizing the sensitivity of each cave to climate variables are: (1) the modes and rate of carbonate sediment production, (2) the nature and intensity of the pedogenic processes responsible for the synchronous alteration of carbonate materials (either those derived from the cave walls or those deposited on the ground surface), and (3) the supply of allogenic sediments, particularly by eolian activity. The cave sediment sequences presented record the marked coolings known as Dansgaard-Oeschger stadials and Heinrich events that occurred during the Pleistocene and the Holocene, as demonstrated by the high resolution records from ice and deep sea cores. At Abric Romanì in northeastern Spain, a series of sharp climatic deteriorations of increasing severity is shown to have occurred synchronously with the transition from the Middle to the Upper Paleolithic, with a period of seasonal frost and strong winds at ca. 37,000 yr B.P., tentatively correlated with Heinrich event 4. At Pigeon Cave, Taforalt (northern Morocco), the transition from the Aterian to Ibero-Maurusian/Epipalaeolithic cultures is dated to around 24,000,20,000 yr B.P. and is punctuated by a series of short cold pulses with evidence for seasonal freezing, soil erosion, and minimal evapotranspiration. In El Miron cave in north-central Spain, the exceptional nature of the Younger Dryas cooling produced a marked destabilization of the cave walls and roof. At El Miron, the stratigraphic evidence for sediment removal due to the rapid percolation of snow melt under a degraded soil cover allows us to reconstruct the nature of the negative excursion at ca. 8200 yr B.P. This example also illustrates how climate-controlled pedogenic processes can create a stratigraphic signature which has often been confused with a sedimentary hiatus. We conclude that cave sediments provide a valuable record of Pleistocene and Holocene climate changes. In appropriate contexts, these sequences allow us to examine the ecological stress generated by these unique global events at a local and regional level and improve our understanding of the complex anthropological processes that occurred at the same time. © 2001 John Wiley & Sons, Inc. [source] Identification of arid phases during the last 50,cal. ka BP from the Fuentillejo maar-lacustrine record (Campo de Calatrava Volcanic Field, Spain),JOURNAL OF QUATERNARY SCIENCE, Issue 7 2010Juana Vegas Abstract Geochemical (element analysis, molecular analysis of organic compounds), physical, palynological, mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in Fuentillejo maar-lake in the Central Spanish Volcanic Field of Campo de Calatrava, in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies. The upper 20,m of core FUENT-1 show variations in clastic input, water chemistry, vegetation and organic fraction sources in the lake throughout the Late Pleistocene and Holocene. The temporal framework provided by 14C accelerator mass spectrometry dating allows assigning the sequence to the last 50,cal. ka BP. Arid phases identified in the FUENT-1 sequence are correlated to Heinrich events (HE) and to stadials of the Dansgaard/Oeschger (D/O) cycles. Siliciclastic facies with high magnetic susceptibility values, high Juniperus pollen content, a low Paq index (aquatic macrophysics proxy index), a decrease in the relative percentage of the n -C27 and an increase in the n -C31 alkanes are indicative of arid and colder climatic events related to HE 2, HE 1 and the Younger Dryas (YD). Similar short cold and arid phases during the Holocene were identified at 9.2,8.6, 7.5,7 and 5.5,5,cal. ka BP. In dolomite,mud facies, the pollen data show an increase in the herbs component, mainly , Chenopodiaceae, Artemisia and Ephedra , steppe taxa; a low Paq index, a decrease in the relative percentage of the n -C27 alkane and an increase in the n -C31 alkane are also observed. This facies was probably the result of lower lake levels and more saline,alkaline conditions, which can be interpreted as linked to arid,warm periods. These warm and arid phases were more frequent during Marine Isotope Stage (MIS) 3 and the interstadials of MIS 2. HE 4, HE 2, HE 1 and the YD in core FUENT-1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the D/O cycles but do not imply increasing humidity in the area. Fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the North Atlantic region at millennial scale during the last 50,cal. ka BP. Copyright © 2009 John Wiley & Sons, Ltd. [source] Cross-cutting moraines reveal evidence for North Atlantic influence on glaciers in the tropical Andes,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2010Jacqueline A. Smith Abstract Surface exposure dating of boulders on an exceptionally well-preserved sequence of moraines in the Peruvian Andes reveals the most detailed record of glaciation heretofore recognised in the region. The high degree of moraine preservation resulted from dramatic changes in the flow path of piedmont palaeoglaciers at the southern end of the Cordillera Blanca (10° 00, S, 77° 16, W), which, in turn, generated a series of cross-cutting moraines. Sixty 10Be surface exposure ages indicate at least four episodes of palaeoglacier stabilisation (>65, ca. 65, ca. 32 and ca. 18,15,ka) and several minor advances or stillstands on the western side of the Nevado Jeulla Rajo massif. The absence of ages close to the global Last Glacial Maximum (ca. 21,ka) suggests that if an advance culminated at that time any resulting moraines were subsequently overridden. The timing of expanded ice cover in the central Peruvian Andes correlates broadly with the timing of massive iceberg discharge (Heinrich) events in the North Atlantic Ocean, suggesting a possible causal connection between southward migration of the Intertropical Convergence Zone during Heinrich events and a resultant increase in precipitation in the tropical Andes. Copyright © 2010 John Wiley & Sons, Ltd. [source] Hudson Strait ice streams: a review of stratigraphy, chronology and links with North Atlantic Heinrich eventsBOREAS, Issue 1 2003John T. Andrews We review the literature on the occupation of Hudson Strait (800 km long by 90 km wide) by late Quaternary ice streams, and the importance of Hudson Strait as the major source for sediments associated with the North Atlantic Heinrich (H-) events. Glacial erosion of the Paleozoic outcrop on the floor of Hudson Strait and Ungava Bay resulted in the export of detrital carbonate-rich sediments to ice-proximal locations on the slope and floor of the NW Labrador Sea, mainly in meltwater and turbidite plumes, and to ice distal sites thousands of kilometres away largely as iceberg-rafted detritus (IRD). Erosion of bedrock from the Precambrian Superior and Churchill provenances of the Canadian Shield is also indicated by the isotopic analyses of sediments. The major late Quaternary H-events (H-4, H-2 and H-1) are represented in southeast Baffin Island slope sediments as detrital carbonate-rich intervals up to 40 cm in thickness and appear to represent flow along the axis of the Strait. However, the late marine isotope stage #3 event, H-3 (,27 ka), and a younger event (H-0, ,11 ka), are not as dominant in the sedimentary record and probably represent a different glaciological regime with flow across Hudson Strait from eastern Ungava-Labrador. The freezing-on of sediments by supercooling in the rise from the 900 m deep Eastern Basin to the 400 m sill is proposed as the source of the abundant carbonate-rich glaciomarine sediments some 250 km from the outcrop in Eastern Basin. Sediment transport by meltwater and turbidity currents was the major process during H-events in ice-proximal settings. IRD was not a key diagnostic process at sites fronting Hudson Strait. A key feature in the instability of this ice stream might be the great depth (600 m) at the shelf break, and the deep basin, which lies seaward of the outer Hudson Strait sill. [source] | |||||||||||||