- Email: [email protected]
Cirque glacier reconstruction at the eastern margin of the Alps
Abstracts / Quaternary International 279-280 (2012) 346–461
Quaternary, we present a new, more complete overview of the available pollen data from the sub-continent. It includes the latest as well as previously published pollen information, which is often hidden in obscure literature sources and difficult to evaluate due to low taxonomical resolution, different methods of interpretation, poor temporal cover, limited dating control and widely divergent site conditions. Data are presented in a simplified uniform manner as Late Pleistocene and Holocene indications of climate variability for the region derived from principal components analysis of available calibrated sequences. The results cover widely different biomes that include the summer-rain region in the north and east, the winter rain area in the south and the dry zone in the west. Although far from complete, the curves directly reflect major changes of terrestrial environments as result of temperature and moisture changes. Mostly sub-humid but fluctuating conditions are indicated during the “Last Glacial Maximum”, which was followed by a dry Early Holocene phase in several parts of the subcontinent. Marked but non-parallel moisture changes occurred over different transects during the Holocene suggesting that climatic forcing was not uniform over the wide region. Some events, however, seemed to have had a more widespread effect on the sub-continent, e.g., a relatively dry summer rain event ca. 2 ka, which can possibly be related to the ENSO phenomenon. UNDERSTANDING FIRE REGIMES IN COMPLEX SEDIMENT SEQUENCES; AN EXAMPLE FROM THE CALIFORNIA CHANNEL ISLANDS
441
extension of the BIIS to the shelf break is indicated by marine geological records and a thick ice sheet is suggested by recent re-evaluation of upland trimline data. The deep-sea ice-rafted detritus record for the BIIS and cosmogenic rock-exposure age dating indicates maximum extent of the ice coincident with Heinrich event 2 at c. 24 ka, followed by rapid deglaciation during Greenland Interstadial 2. Readavance phases centred on c.21-18 ka (Tampen-Dimlington event), c. 16 ka (Heinrich event 1) and finally during the Younger Dryas event. A number of independent numerical open ocean global palaeotidal model simulations identify that the glacial North Atlantic was close to resonance resulting in extremely high tidal amplitudes in some locations, notably the Hudson Strait. Shelf sea palaeotidal models parameterised with shelf break open ocean boundaries forced by these global tidal models predict megatides (mean spring tidal range in excess of 10 m) in some key ice-marginal locations along the BIIS margin. It is proposed here that the rapid rates of BIIS deglaciation suggested by both the observational database and GIA simulations were the product of rapid atmospheric and oceanic warming linked to meridional migration of the North Atlantic Polar Front compounded by megatidal calving margins which forced high iceberg fluxes and consequent ice sheet drawdown. The deglaciation and inundation of Hudson Strait in the early Holocene reduced the resonance of the North Atlantic generating the damped interglacial ocean tide characteristic of the present day. The deglaciation of Hudson Strait, the source area for many of the classic Heinrich IRD layers, was itself also forced by these megatides.
Andrew C. Scott. Department of Earth Sciences, Royal Holloway Unive, United Kingdom
TRANSIENT SIMULATIONS OF THE CORDILLERAN ICE SHEET
E-mail address: [email protected]
Julien Seguinot. Department of Physical Geography and Quaternary Ge, Sweden
The majority of Quaternary charcoal records covering multi-millennial timescales come from lake or peat bog sequences, mostly with relatively straight forward depositional histories, allowing the use of charcoal statistics such as CHAR. Those records are well suited for global syntheses of charcoal data. Much less attention has been focused on understanding fire regimes over long millennial timescales from more complex sedimentary environments such as over-bank and fluvial deposits, probably because it is difficult to apply the traditional Quaternary techniques outlined above. Here we show how rich information about palaeo-fire regimes can be gained from macroscopic charcoal utilising techniques such as scanning electron microscopy that can aid botanical identification and reflectance microscopy that provides fire temperature data. In addition, detailed sedimentological observations may provide evidence of geomorphic events related to fire, such as post-fire erosion. Here we report on the charcoal records from late Pleistocene sites (c.17-12.5 ka BP) from both in Santa Cruz Island and Santa Rosa Island, belonging to the California Channel Islands. The late Pleistocene sediments exposed on the Islands show significant variation including fluvial channel sands, over-bank silts, muds and coarse fan sediments (including conglomerates). Charcoal occurs throughout the sequence both as scattered fragments, lenses and as thin discontinuous layers. Simple vertical sampling may lead to erroneous conclusions and quantification of the charcoal is dependent on the nature of the sediments and sedimentary environment. Evidence of a change in fire regime related to a switch from forest-dominated system to one dominated by herbaceous plants and grasslands can be determined . A significant record of fire existed before the earliest documented human arrival on the islands.
MEGATIDES IN THE GLACIAL NORTH ATLANTIC AND THEIR ROLE IN RAPID DEGLACIATION James Scourse. Bangor University, United Kingdom E-mail address: [email protected]
Numerical glacial isostatic adjustment (GIA) simulations for the last British-Irish Ice Sheet (BIIS) closely constrained by relative sea-level index point data indicate a thick and extensive ice sheet at the Last Glacial Maximum which experienced rapid deglaciation. Independently,
E-mail address: [email protected]
The Cordilleran Ice Sheet, which covered large areas of rugged terrain and elevated plateaus in western Canada during peak glacial periods, is one of the least understood transient ice sheets. Despite the existence of more than a century of geomorphological and stratigraphical observations, the complexity of the evidence is such that reliable reconstructions of glacier advance and retreat at an ice-sheet scale are essentially lacking. To achieve an ice sheet scale reconstruction, we apply a new generation ice sheet model (Pollard & DeConto, 2009) that is capable to simulate the growth and retreat of the Cordilleran Ice Sheet over a full glacial cycle in high resolution. The sensitivity of the model results to a variety of boundary conditions is investigated. We briefly comment on the comparison of simulations results with available spatial reconstructions and geomorphologic evidence that will eventually guide the final parametrization of the model. CIRQUE GLACIER RECONSTRUCTION AT THE EASTERN MARGIN OF THE ALPS Sabrina Seidl. University of Vienna/Departement for Geodynamics a, Austria E-mail address: [email protected]
The intention of this work is the reconstruction of paleo-glaciers in the easternmost part of the Alps (Schneeberg mountain) with a main focus on chronology and sedimentology. The area is dominantly made up of limestones and hence characterized by steep slopes and cirques. Two different moraine-systems can be deciphered based on geological mapping. The moraines of the older system show a comparable smooth surface without any big boulders and consist of weathered till. The younger moraine-system is characterized by an up to 60 m high laterofrontal dump moraine with a prominent breach-lobe moraine in a lateral position. The morphology with big boulders and small depressions on the surface as well as the generally unweathered appearance of the sediments indicate a formation of this system during the LGM. Predominantly, the younger moraine consists of sandy to gravelly, matrix- to grain-supported diamictons, which often show a weak carbonate cementation near the surface. Clasts with angular to subangular shape are clearly dominant compared to subrounded ones.
442
Abstracts / Quaternary International 279-280 (2012) 346–461
The shape of the clasts and the abundant boulders on top of the ridges indicate a high portion of passive (Boulton, 1978) i.e. supraglacial and englacial transport of debris before deposition. Thus the model of a debris-covered glacier is favored to explain the whole landform. Such an assumption is backed by a low accumulation/ablation area ratio (AAR) based on the reconstruction of the ELA using the maximum elevation of lateral moraines (Lichtenecker, 1938). Furthermore, as there is no indication of a former glacier snout, glacio-fluvial processes should have played a limited role in sediment transport into the forefield. Such setting pinpoints to very cold-arid conditions, which are as well found in paleo-climate reconstructions of the eastern foreland (Frenzel et al. 1992). PLEISTOCENE INTERGLACIAL RECORD FROM BUIVYDZIAI OUTCROP, EASTERN LITHUANIA
proxies will be compared to results of published reconstructions of modern dust trajectories to test the validity of these methods to reconstruct modern dust flux patterns to the SNP. We will further map the spatial pattern of La/Yb and Th/Sc ratios to test their validity as proxies to deconvolve dust and volcanic input to the sediments. The spatial patterns of the productivity proxies will be compared to published estimates of annual biological productivity based on a global pCO2 database and satellite ocean color observations to test the efficiency of the productivity proxies in the SNP. The results from this study will be used for future research focusing on dust flux and productivity changes during the last deglaciation and Holocene. INFLUENCE OF SOLAR VARIABILITY, CO2 AND ORBITAL FORCING DURING THE PREINDUSTRIAL PART OF THE LAST MILLENNIUM IN THE IPSLCM4 MODEL
Vaida Seiriene. Nature research centre, Institute of Geology and G, Lithuania
Jérôme Servonnat. LSCE, France
E-mail address: [email protected]
E-mail address: [email protected]
Multi-proxy investigations were carried out on the Buivyd ziai sediment section to clear up the age and the palaeoenvironmet of sedimentation. Exposure presents 70-80 m sediment thickness, characteristic for the area of maximum extent of Last Glaciation. These sediments so far have a meaning as parastratotype of the Snaigupele (Drenthian-Warthian) Interglacial however the presence of independent Snaigupele Interglacial within the MIS 7 is not supported by many investigators in Baltic countries. Pollen composition of the Snaigupele Interglacial is closest to Merkine (Eemian) interglacial. On the contrary, the abundance of Corylus and broad-leaved trees is approximately twice smaller. Tilia behaves unusually forming an earlier and reduced maximum. Alnus appeared and spread simultaneously with broad-leaved trees (exept Carpinus), much earlier than the Corylus. The Quercus has two optima. All these characteristic features were observed in recently composed pollen diagram except few differences. Plant macrofossils obtained have some similarities with Eemian as well as with Holsteinian ones. The main characteristic features are: prevailance of coniferous trees during all period studied; slight increase in broad-leaved trees and the presence of extinct species. Diatom flora is characteristic to slightly oligotrophic - eutrophic gradually overgrowing palaeobasin. Species of Cyclotella kutzingiana var.schumannii has distinctive features in frustules morphology comparing with recent ones. Species Cyclotella radiosa var. lichvinensis, which became extinct at the end of the Middle Pleistocene are present as well. Two samples from the sand deposits occurred in the bottom of interglacial gyttja layer were taken for Optically Stimulated Luminescence (OSL) dating. Dating results show 300.5 20.9 and 317.3 21.8 ka age.
Climate studies of the last millennium give the possibility to deal with a relatively well-documented climate essentially driven by natural forcings. We have performed two simulations with the IPSLCM4 climate model to evaluate the impact of Total Solar Irradiance (TSI), CO2 and orbital forcing on secular temperature variability during the preindustrial part of the last millennium. The Northern Hemisphere (NH) temperature of the simulation reproduces the amplitude of the NH temperature reconstructions over the last millennium. Using a linear statistical decomposition we evaluated that TSI and CO2 have similar contributions to secular temperature variability between 1425 and 1850 AD. They generate a temperature minimum comparable to the Little Ice Age shown by the temperature reconstructions. Solar forcing explains w80% of the NH temperature variability during the first part of the millennium (1000-1425 AD) including the Medieval Climate Anomaly (MCA). It is responsible for a warm period which occurs two centuries later than in the reconstructions. This mismatch implies that the secular variability during the MCA is not fully explained by the response of the model to the TSI reconstruction. With a signal-noise ratio (SNR) estimate we found that the temperature signal of the forced simulation is significantly different from internal variability over area wider than w5.106 km2, i.e. approximately the extent of Europe. Orbital forcing plays a significant role in latitudes higher than 65 N in summer and supports the conclusions of a recent study on an Arctic temperature reconstruction over past two millennia. The forced variability represents at least half of the temperature signal on only w30% of the surface of the globe. The study of the SNR and local impacts of the forcings suggests that individual temperature reconstructions taken from random location around the Globe are potentially weakly affected by external forcings.
MODERN DUST FLUX AND BIOLOGICAL PRODUCTIVITY IN THE SUBARCTIC NORTH PACIFIC Sascha Serno. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
EVIDENCE OF THE PRESENCE OF THE ROOT VOLE (MICROTUS OECONOMUS) IN CENTRAL SPAIN DURING THE LATE PLEISTOCENE Paloma Sevilla. Dpto. Paleontología. Fac. Geología. UCM-CSIC, Spain E-mail address: [email protected]
The Subarctic North Pacific (SNP) is one of the three principal High Nutrient Low Chlorophyll (HNLC) regions of the modern ocean. Iron limitation is traditionally suggested as the main controlling factor of the HNLC status of the SNP, with iron primarily delivered by atmospheric dust transport from the East Asian desert areas. Our understanding of how dust and export production are linked in the SNP is limited due to the lack of reliable dust flux records and discrepancies among specific paleoproductivity proxies. The lack of reliable modern dust flux reconstructions from SNP marine sediments is due to uncertainties about the dating of the sediments and the impact of sediment input other than dust, such as hemipelagic and volcanic material as well as ice-rafted debris. We will map and compare spatial patterns of two proxies of eolian dust fluxes (230Thnormalized 232Th and 4He fluxes) and different productivity proxies (excess barium, biogenic opal, carbonate and d15N) from 37 multicore coretop sediments across the SNP, obtained during the INOPEX cruise in 2009, to test the traditional hypothesis of eolian iron input primarily controlling the biological productivity in the SNP. The spatial patterns of the dust flux
Cold climate phases during the Pleistocene are well known to have favoured a southward displacement of the geographic range of northern species of mammals. Among the available examples is the case of the Root vole (Microtus oeconomus) mainly linked to subarctic and tundra habitats. Its present distribution in Europe does not extend southern than 46oN latitude, but has been recorded in several Pleistocene localities in France and northern Spain coinciding with cold periods of the Late Pleistocene. New records in three localities at the northern and southern slopes of the Sistema Central provide new evidence that the species extended even farther towards the south in the Iberian Peninsula during these periods. The oldest locality of the three, Cueva de la Buena Pinta (Pinilla del Valle, Madrid), dated 63 ka BP, suggests this migration took place before the Late Glacial Maximum, agreeing with recent evidence of a previous important cooling event. Later records indicate that M. oeconomus was able to survive under milder conditions, as evidenced by its record in the temperate level 1 of La Peña de
Quaternary, we present a new, more complete overview of the available pollen data from the sub-continent. It includes the latest as well as previously published pollen information, which is often hidden in obscure literature sources and difficult to evaluate due to low taxonomical resolution, different methods of interpretation, poor temporal cover, limited dating control and widely divergent site conditions. Data are presented in a simplified uniform manner as Late Pleistocene and Holocene indications of climate variability for the region derived from principal components analysis of available calibrated sequences. The results cover widely different biomes that include the summer-rain region in the north and east, the winter rain area in the south and the dry zone in the west. Although far from complete, the curves directly reflect major changes of terrestrial environments as result of temperature and moisture changes. Mostly sub-humid but fluctuating conditions are indicated during the “Last Glacial Maximum”, which was followed by a dry Early Holocene phase in several parts of the subcontinent. Marked but non-parallel moisture changes occurred over different transects during the Holocene suggesting that climatic forcing was not uniform over the wide region. Some events, however, seemed to have had a more widespread effect on the sub-continent, e.g., a relatively dry summer rain event ca. 2 ka, which can possibly be related to the ENSO phenomenon. UNDERSTANDING FIRE REGIMES IN COMPLEX SEDIMENT SEQUENCES; AN EXAMPLE FROM THE CALIFORNIA CHANNEL ISLANDS
441
extension of the BIIS to the shelf break is indicated by marine geological records and a thick ice sheet is suggested by recent re-evaluation of upland trimline data. The deep-sea ice-rafted detritus record for the BIIS and cosmogenic rock-exposure age dating indicates maximum extent of the ice coincident with Heinrich event 2 at c. 24 ka, followed by rapid deglaciation during Greenland Interstadial 2. Readavance phases centred on c.21-18 ka (Tampen-Dimlington event), c. 16 ka (Heinrich event 1) and finally during the Younger Dryas event. A number of independent numerical open ocean global palaeotidal model simulations identify that the glacial North Atlantic was close to resonance resulting in extremely high tidal amplitudes in some locations, notably the Hudson Strait. Shelf sea palaeotidal models parameterised with shelf break open ocean boundaries forced by these global tidal models predict megatides (mean spring tidal range in excess of 10 m) in some key ice-marginal locations along the BIIS margin. It is proposed here that the rapid rates of BIIS deglaciation suggested by both the observational database and GIA simulations were the product of rapid atmospheric and oceanic warming linked to meridional migration of the North Atlantic Polar Front compounded by megatidal calving margins which forced high iceberg fluxes and consequent ice sheet drawdown. The deglaciation and inundation of Hudson Strait in the early Holocene reduced the resonance of the North Atlantic generating the damped interglacial ocean tide characteristic of the present day. The deglaciation of Hudson Strait, the source area for many of the classic Heinrich IRD layers, was itself also forced by these megatides.
Andrew C. Scott. Department of Earth Sciences, Royal Holloway Unive, United Kingdom
TRANSIENT SIMULATIONS OF THE CORDILLERAN ICE SHEET
E-mail address: [email protected]
Julien Seguinot. Department of Physical Geography and Quaternary Ge, Sweden
The majority of Quaternary charcoal records covering multi-millennial timescales come from lake or peat bog sequences, mostly with relatively straight forward depositional histories, allowing the use of charcoal statistics such as CHAR. Those records are well suited for global syntheses of charcoal data. Much less attention has been focused on understanding fire regimes over long millennial timescales from more complex sedimentary environments such as over-bank and fluvial deposits, probably because it is difficult to apply the traditional Quaternary techniques outlined above. Here we show how rich information about palaeo-fire regimes can be gained from macroscopic charcoal utilising techniques such as scanning electron microscopy that can aid botanical identification and reflectance microscopy that provides fire temperature data. In addition, detailed sedimentological observations may provide evidence of geomorphic events related to fire, such as post-fire erosion. Here we report on the charcoal records from late Pleistocene sites (c.17-12.5 ka BP) from both in Santa Cruz Island and Santa Rosa Island, belonging to the California Channel Islands. The late Pleistocene sediments exposed on the Islands show significant variation including fluvial channel sands, over-bank silts, muds and coarse fan sediments (including conglomerates). Charcoal occurs throughout the sequence both as scattered fragments, lenses and as thin discontinuous layers. Simple vertical sampling may lead to erroneous conclusions and quantification of the charcoal is dependent on the nature of the sediments and sedimentary environment. Evidence of a change in fire regime related to a switch from forest-dominated system to one dominated by herbaceous plants and grasslands can be determined . A significant record of fire existed before the earliest documented human arrival on the islands.
MEGATIDES IN THE GLACIAL NORTH ATLANTIC AND THEIR ROLE IN RAPID DEGLACIATION James Scourse. Bangor University, United Kingdom E-mail address: [email protected]
Numerical glacial isostatic adjustment (GIA) simulations for the last British-Irish Ice Sheet (BIIS) closely constrained by relative sea-level index point data indicate a thick and extensive ice sheet at the Last Glacial Maximum which experienced rapid deglaciation. Independently,
E-mail address: [email protected]
The Cordilleran Ice Sheet, which covered large areas of rugged terrain and elevated plateaus in western Canada during peak glacial periods, is one of the least understood transient ice sheets. Despite the existence of more than a century of geomorphological and stratigraphical observations, the complexity of the evidence is such that reliable reconstructions of glacier advance and retreat at an ice-sheet scale are essentially lacking. To achieve an ice sheet scale reconstruction, we apply a new generation ice sheet model (Pollard & DeConto, 2009) that is capable to simulate the growth and retreat of the Cordilleran Ice Sheet over a full glacial cycle in high resolution. The sensitivity of the model results to a variety of boundary conditions is investigated. We briefly comment on the comparison of simulations results with available spatial reconstructions and geomorphologic evidence that will eventually guide the final parametrization of the model. CIRQUE GLACIER RECONSTRUCTION AT THE EASTERN MARGIN OF THE ALPS Sabrina Seidl. University of Vienna/Departement for Geodynamics a, Austria E-mail address: [email protected]
The intention of this work is the reconstruction of paleo-glaciers in the easternmost part of the Alps (Schneeberg mountain) with a main focus on chronology and sedimentology. The area is dominantly made up of limestones and hence characterized by steep slopes and cirques. Two different moraine-systems can be deciphered based on geological mapping. The moraines of the older system show a comparable smooth surface without any big boulders and consist of weathered till. The younger moraine-system is characterized by an up to 60 m high laterofrontal dump moraine with a prominent breach-lobe moraine in a lateral position. The morphology with big boulders and small depressions on the surface as well as the generally unweathered appearance of the sediments indicate a formation of this system during the LGM. Predominantly, the younger moraine consists of sandy to gravelly, matrix- to grain-supported diamictons, which often show a weak carbonate cementation near the surface. Clasts with angular to subangular shape are clearly dominant compared to subrounded ones.
442
Abstracts / Quaternary International 279-280 (2012) 346–461
The shape of the clasts and the abundant boulders on top of the ridges indicate a high portion of passive (Boulton, 1978) i.e. supraglacial and englacial transport of debris before deposition. Thus the model of a debris-covered glacier is favored to explain the whole landform. Such an assumption is backed by a low accumulation/ablation area ratio (AAR) based on the reconstruction of the ELA using the maximum elevation of lateral moraines (Lichtenecker, 1938). Furthermore, as there is no indication of a former glacier snout, glacio-fluvial processes should have played a limited role in sediment transport into the forefield. Such setting pinpoints to very cold-arid conditions, which are as well found in paleo-climate reconstructions of the eastern foreland (Frenzel et al. 1992). PLEISTOCENE INTERGLACIAL RECORD FROM BUIVYDZIAI OUTCROP, EASTERN LITHUANIA
proxies will be compared to results of published reconstructions of modern dust trajectories to test the validity of these methods to reconstruct modern dust flux patterns to the SNP. We will further map the spatial pattern of La/Yb and Th/Sc ratios to test their validity as proxies to deconvolve dust and volcanic input to the sediments. The spatial patterns of the productivity proxies will be compared to published estimates of annual biological productivity based on a global pCO2 database and satellite ocean color observations to test the efficiency of the productivity proxies in the SNP. The results from this study will be used for future research focusing on dust flux and productivity changes during the last deglaciation and Holocene. INFLUENCE OF SOLAR VARIABILITY, CO2 AND ORBITAL FORCING DURING THE PREINDUSTRIAL PART OF THE LAST MILLENNIUM IN THE IPSLCM4 MODEL
Vaida Seiriene. Nature research centre, Institute of Geology and G, Lithuania
Jérôme Servonnat. LSCE, France
E-mail address: [email protected]
E-mail address: [email protected]
Multi-proxy investigations were carried out on the Buivyd ziai sediment section to clear up the age and the palaeoenvironmet of sedimentation. Exposure presents 70-80 m sediment thickness, characteristic for the area of maximum extent of Last Glaciation. These sediments so far have a meaning as parastratotype of the Snaigupele (Drenthian-Warthian) Interglacial however the presence of independent Snaigupele Interglacial within the MIS 7 is not supported by many investigators in Baltic countries. Pollen composition of the Snaigupele Interglacial is closest to Merkine (Eemian) interglacial. On the contrary, the abundance of Corylus and broad-leaved trees is approximately twice smaller. Tilia behaves unusually forming an earlier and reduced maximum. Alnus appeared and spread simultaneously with broad-leaved trees (exept Carpinus), much earlier than the Corylus. The Quercus has two optima. All these characteristic features were observed in recently composed pollen diagram except few differences. Plant macrofossils obtained have some similarities with Eemian as well as with Holsteinian ones. The main characteristic features are: prevailance of coniferous trees during all period studied; slight increase in broad-leaved trees and the presence of extinct species. Diatom flora is characteristic to slightly oligotrophic - eutrophic gradually overgrowing palaeobasin. Species of Cyclotella kutzingiana var.schumannii has distinctive features in frustules morphology comparing with recent ones. Species Cyclotella radiosa var. lichvinensis, which became extinct at the end of the Middle Pleistocene are present as well. Two samples from the sand deposits occurred in the bottom of interglacial gyttja layer were taken for Optically Stimulated Luminescence (OSL) dating. Dating results show 300.5 20.9 and 317.3 21.8 ka age.
Climate studies of the last millennium give the possibility to deal with a relatively well-documented climate essentially driven by natural forcings. We have performed two simulations with the IPSLCM4 climate model to evaluate the impact of Total Solar Irradiance (TSI), CO2 and orbital forcing on secular temperature variability during the preindustrial part of the last millennium. The Northern Hemisphere (NH) temperature of the simulation reproduces the amplitude of the NH temperature reconstructions over the last millennium. Using a linear statistical decomposition we evaluated that TSI and CO2 have similar contributions to secular temperature variability between 1425 and 1850 AD. They generate a temperature minimum comparable to the Little Ice Age shown by the temperature reconstructions. Solar forcing explains w80% of the NH temperature variability during the first part of the millennium (1000-1425 AD) including the Medieval Climate Anomaly (MCA). It is responsible for a warm period which occurs two centuries later than in the reconstructions. This mismatch implies that the secular variability during the MCA is not fully explained by the response of the model to the TSI reconstruction. With a signal-noise ratio (SNR) estimate we found that the temperature signal of the forced simulation is significantly different from internal variability over area wider than w5.106 km2, i.e. approximately the extent of Europe. Orbital forcing plays a significant role in latitudes higher than 65 N in summer and supports the conclusions of a recent study on an Arctic temperature reconstruction over past two millennia. The forced variability represents at least half of the temperature signal on only w30% of the surface of the globe. The study of the SNR and local impacts of the forcings suggests that individual temperature reconstructions taken from random location around the Globe are potentially weakly affected by external forcings.
MODERN DUST FLUX AND BIOLOGICAL PRODUCTIVITY IN THE SUBARCTIC NORTH PACIFIC Sascha Serno. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
EVIDENCE OF THE PRESENCE OF THE ROOT VOLE (MICROTUS OECONOMUS) IN CENTRAL SPAIN DURING THE LATE PLEISTOCENE Paloma Sevilla. Dpto. Paleontología. Fac. Geología. UCM-CSIC, Spain E-mail address: [email protected]
The Subarctic North Pacific (SNP) is one of the three principal High Nutrient Low Chlorophyll (HNLC) regions of the modern ocean. Iron limitation is traditionally suggested as the main controlling factor of the HNLC status of the SNP, with iron primarily delivered by atmospheric dust transport from the East Asian desert areas. Our understanding of how dust and export production are linked in the SNP is limited due to the lack of reliable dust flux records and discrepancies among specific paleoproductivity proxies. The lack of reliable modern dust flux reconstructions from SNP marine sediments is due to uncertainties about the dating of the sediments and the impact of sediment input other than dust, such as hemipelagic and volcanic material as well as ice-rafted debris. We will map and compare spatial patterns of two proxies of eolian dust fluxes (230Thnormalized 232Th and 4He fluxes) and different productivity proxies (excess barium, biogenic opal, carbonate and d15N) from 37 multicore coretop sediments across the SNP, obtained during the INOPEX cruise in 2009, to test the traditional hypothesis of eolian iron input primarily controlling the biological productivity in the SNP. The spatial patterns of the dust flux
Cold climate phases during the Pleistocene are well known to have favoured a southward displacement of the geographic range of northern species of mammals. Among the available examples is the case of the Root vole (Microtus oeconomus) mainly linked to subarctic and tundra habitats. Its present distribution in Europe does not extend southern than 46oN latitude, but has been recorded in several Pleistocene localities in France and northern Spain coinciding with cold periods of the Late Pleistocene. New records in three localities at the northern and southern slopes of the Sistema Central provide new evidence that the species extended even farther towards the south in the Iberian Peninsula during these periods. The oldest locality of the three, Cueva de la Buena Pinta (Pinilla del Valle, Madrid), dated 63 ka BP, suggests this migration took place before the Late Glacial Maximum, agreeing with recent evidence of a previous important cooling event. Later records indicate that M. oeconomus was able to survive under milder conditions, as evidenced by its record in the temperate level 1 of La Peña de