http://www.clim-past-discuss.net/ Climate of the Past Discussions Latest Articlesenhttp://www.clim-past-discuss.net/6/1629/2010/<b>Application of Fourier Transform Infrared Spectroscopy (FTIR) for assessing biogenic silica sample purity in geochemical analyses and palaeoenvironmental research</b><br /><br />Climate of the Past Discussions, 6, 1629-1653, 2010<br /><br />Author(s): G. E. A. Swann and S. V. Patwardhan<br /><br />The development of a rapid and non-destructive method to assess levels of purity in samples of biogenic silica prior to geochemical/isotope analysis remains a key objective in improving both the quality and use of such data in environmental and palaeoclimatic research. Here a Fourier Transform Infrared Spectroscopy (FTIR) mass-balance method is demonstrated for calculating levels of contamination in cleaned sediment core diatom samples from Lake Baikal Russia. Following the selection of end-members representative of diatoms and contaminants in the analysed samples, a mass-balance model is generated to simulate the expected FTIR spectra for a given level of contamination. By fitting the sample FTIR spectra to the modelled FTIR spectra and calculating the Euclidean distance, the optimum “best-fit” model and level of contamination is obtained. When compared to X-ray Fluorescence (XRF), FTIR method results portray the main changes in sample contamination through the core sequence, permitting its use in instances where other, destructive, techniques are not appropriate. The ability to analyses samples of &lt;1 mg enables, for the first time, routine analyses of small sized samples. Discrepancies between FTIR and XRF measurements can be attributed to FTIR end-members not fully representing all contaminants and problems in using XRF to detect organic matter external to the diatom frustule. By analysing samples with both FTIR and XRF, these limitations can be eliminated to accurately identify contaminated samples and improve the accuracy of climate reconstructions. Future, routine, use of these techniques in palaeoenvironmental research will significantly reduce the number of erroneous measurements and so improve the accuracy of biogenic silica/diatom based reconstructions.Thu, 02 Sep 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1589/2010/<b>Oceanic tracer and proxy time scales revisited</b><br /><br />Climate of the Past Discussions, 6, 1589-1628, 2010<br /><br />Author(s): C. Siberlin and C. Wunsch<br /><br />Quantifying time-responses of the ocean to passive and active tracers is critical for the interpretation of paleodata from sediment cores because surface-injected tracers do not instantaneously spread throughout the ocean. To obtain insights into the time response, a computationally efficient state transition matrix method is demonstrated and used to compute successive states of passive tracer concentrations in the global ocean. Times to equilibrium exceed a thousand years for any one region of the global ocean outside of the injection and convective regions and concentration gradients give time-lags from hundreds to thousands of years between the Atlantic and Pacific abyss, depending on the injection region and the nature of the boundary conditions employed. Equilibrium times can be much longer than radiocarbon ages as the latter are strongly biased towards the youngest fraction of fluid captured in a sample. Pulse-like inputs can produce very different transient approaches to equilibrium in different parts of the ocean generating event identification problems.Wed, 01 Sep 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1551/2010/<b>Greenland Ice Sheet model parameters constrained using simulations of the Eemian Interglacial</b><br /><br />Climate of the Past Discussions, 6, 1551-1588, 2010<br /><br />Author(s): A. Robinson, R. Calov, and A. Ganopolski<br /><br />Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate – ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. Sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i) the diagnosed present-day surface mass balance partition between surface melting and calving, (ii) the modeled present-day elevation at GRIP; and (iii) the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 270 simulations with 90 different model realizations were filtered down to 47 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations result in a range of Eemian ice loss of 0.4–4.1 m sea level (m.s.l.) equivalent, with a more likely value of about 4.1 m.s.l. if the GRIP &delta;¹⁸O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.Mon, 30 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1525/2010/<b>Climate signatures of grape harvest dates</b><br /><br />Climate of the Past Discussions, 6, 1525-1550, 2010<br /><br />Author(s): M. Krieger, G. Lohmann, and T. Laepple<br /><br />Grape harvest dates have been recorded in many European locations for several centuries, and potentially contain important information about past climate. In this study, we systematically analyse the relationship of grape harvest dates recorded in the Burgundy region (France) with different climate data sets in order to understand the connection between climatic conditions and the time of harvest. The results point to a primary dependence of the grape harvest on the temperature from April to August. The strength of this connection depends on the winter to summer temperature relationship and increases over the last 100 years. The grape harvest date is also related to the winter temperature. This connection is non-stationary on interannual, but stable on decadal-to-multidecadal time scales. Therefore, the grape harvest date can be used for independent reconstructions of local April-to-August temperature on interannual time scales as well as remote winter temperature on decadal-to-multidecadal time scales.Tue, 17 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1503/2010/<b>Warm Nordic Seas delayed glacial inception in Scandinavia</b><br /><br />Climate of the Past Discussions, 6, 1503-1523, 2010<br /><br />Author(s): A. Born, M. Kageyama, and K. H. Nisancioglu<br /><br />We simulate the last glacial inception, 115 000 years ago, with a three dimensional thermomechanical ice sheet model of the Northern Hemisphere, forced by a comprehensive coupled climate model. High oceanic heat transport into the Nordic Seas prevents large scale ice growth over Scandinavia. Glacial inception in the region starts on the highest mountains in the south when sea surface temperatures in the Nordic Seas are reduced by at least 3 °C. Ice growth in Northern Scandinavia requires a cooling by at least 4 °C. This is in good agreement with marine proxy data from the Nordic Seas and North Atlantic as well as available terrestrial data. This study thus provides a physical understanding and revised timing of the first glacier advance over Scandinavia.Fri, 13 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1473/2010/<b>Rapid changes in ice core gas records – Part 2: Understanding the rapid rise in atmospheric CO₂ at the onset of the Bølling/Allerød</b><br /><br />Climate of the Past Discussions, 6, 1473-1501, 2010<br /><br />Author(s): P. Köhler, G. Knorr, D. Buiron, A. Lourantou, and J. Chappellaz<br /><br />During the last glacial/interglacial transition the Earth's climate underwent rapid changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A is accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is matter of current debate. In situ measured CO₂ in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10&plusmn;1 ppmv in 230 yr at the same time. Allowing for the age distribution of CO₂ in firn we here show, that atmospheric CO₂ rose by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 larger than the CO₂ signal recorded in situ in EDC. Based on the estimated airborne fraction of 0.17 of CO₂ we infer that 125 Pg of carbon need to be released to the atmosphere to produce such a peak. Most of the carbon might have been activated as consequence of continental shelf flooding during MWP-1A. This impact of rapid sea level rise on atmospheric CO₂ distinguishes the B/A from other Dansgaard/Oeschger events of the last 60 kyr, potentially defining the point of no return during the last deglaciation.Wed, 11 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1453/2010/<b>Rapid changes in ice core gas records – Part 1: On the accuracy of methane synchronisation of ice cores</b><br /><br />Climate of the Past Discussions, 6, 1453-1471, 2010<br /><br />Author(s): P. Köhler<br /><br />Methane synchronisation is a concept to align ice core records during rapid climate changes of the Dansgaard/Oeschger (D/O) events onto a common age scale. However, atmospheric gases are recorded in ice cores with a log-normal-shaped age distribution probability density function, whose exact shape depends mainly on the accumulation rate on the drilling site. This age distribution effectively shifts the mid-transition points of rapid changes in CH₄ measured in situ in ice by about 58% of the width of the age distribution with respect to the atmospheric signal. A minimum dating uncertainty, or artefact, in the CH₄ synchronisation is therefore embedded in the concept itself, which was not accounted for in previous error estimates. This synchronisation artefact between Greenland and Antarctic ice cores is for GRIP and Byrd less than 40 years, well within the dating uncertainty of CH₄, and therefore does not calls the overall concept of the bipolar seesaw into question. However, if the EPICA Dome C ice core is aligned via CH₄ to NGRIP this synchronisation artefact is in the most recent unified ice core age scale (Lemieux-Dudon et al., 2010) for LGM climate conditions of the order of three centuries and might need consideration in future gas chronologies.Wed, 11 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1421/2010/<b>Earth as diode: monsoon source of the orbital ~100 ka climate cycle</b><br /><br />Climate of the Past Discussions, 6, 1421-1452, 2010<br /><br />Author(s): R. Y. Anderson<br /><br />A potential source for Earth's enigmatic ~100 ka climate cycle, which is found in many ancient geological records at low latitudes and also in the pacing of glaciation during the late Pleistocene, is traced to a climatic rectifying process inherent in the monsoon. Seasonal information needed to identify the rectifying mechanism is preserved within varves of a continuous, 200 ka recording of annual maximum surface temperature (<i>T</i>_max) from the equator of Western Pangea. Specific seasonal reactions recorded in varves show how the monsoon reacted to seasonal differences in insolation at equinox to produce a 11.7 ka semi-precession cycle in <i>T</i>_max. At solstice, anti-phasing of insolation in the Northern and Southern Hemispheres, intensified and focused by a highly asymmetric Pangea relative to the equator, produced a strong equatorial maritime monsoon that performed a nonlinear rectifying function similar to that of a simple rectifying diode. Expressed in the resulting varve series are substantial cycles in <i>T</i>_max of 100 ka, 23.4 ka, and 11.7 ka. Importantly, any external or internal forcing of the tropical (monsoon) climate system at higher-than-orbital frequencies (e.g. solar, ENSO) should also be amplified at Milankovitch frequencies by the monsoon.Tue, 10 Aug 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1391/2010/<b>A new interpretation of the two-step <i>&delta;</i>¹⁸O signal at the Eocene-Oligocene boundary</b><br /><br />Climate of the Past Discussions, 6, 1391-1419, 2010<br /><br />Author(s): M. Tigchelaar, A. S. von der Heydt, and H. A. Dijkstra<br /><br />The most marked step in the global climate transition from "Greenhouse" to "Icehouse" Earth occurred at the Eocene-Oligocene (E&ndash;O) boundary, 33.7 Ma. Evidence for climatic changes comes from many sources, including the marine benthic <i>&delta;</i>¹⁸O record, showing an increase by 1.2–1.5&permil; at this time. This positive excursion is characterised by two steps, separated by a plateau. The increase in <i>&delta;</i>¹⁸O values has been attributed to rapid glaciation of the Antarctic continent, previously ice-free. Simultaneous changes in the <i>&delta;</i>¹³C record are indicative of a greenhouse gas control on climate. Previous studies show that a decline in <i>p</i>CO₂ beyond a certain threshold value may have initiated the growth of a Southern Hemispheric ice sheet. These studies were not able to conclusively explain the remarkable two-step profile in <i>&delta;</i>¹⁸O. Furthermore, they did not address the potential role of changes in ocean circulation in the E&ndash;O transition. Here a new interpretation of the <i>&delta;</i>¹⁸O signal is presented, based on model simulations using a simple coupled 8-box-ocean, 4-box-atmosphere model with an added land ice component. The model was forced with a slowly decreasing atmospheric carbon dioxide concentration. It is argued that the first step in the <i>&delta;</i>¹⁸O represents a shift in meridional overturning circulation from a Southern Ocean to a bipolar source of deep-water formation, which is associated with a cooling of the deep sea. This shift can be initiated by a small density perturbation in the model, although there is also a parameter regime for which the shift occurs spontaneously. The second step in the <i>&delta;</i>¹⁸O profile occurs due to a rapid glaciation of the Antarctic continent. This new interpretation is a robust outcome of our model and is in good agreement with proxy data.Wed, 21 Jul 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1351/2010/<b>Refugia of marine fish in the Northeast Atlantic during the Last Glacial Maximum: concordant assessment from archaeozoology and palaeotemperature reconstructions</b><br /><br />Climate of the Past Discussions, 6, 1351-1389, 2010<br /><br />Author(s): A. J. Kettle, A. Morales-Muñiz, E. Roselló-Izquierdo, D. Heinrich, and L. A. Vøllestad<br /><br />Archaeozoological finds of the remains of marine and amphihaline fish from the Last Glacial Maximum (LGM) ca. 21 ka ago show evidence of very different species ranges compared to the present. We show how an ecological niche model (ENM) based on palaeoclimatic reconstructions of sea surface temperature and bathymetry can be used to effectively predict the spatial range of marine fish during the LGM. The results indicate that the ranges of marine fish species that are now in Northwestern Europe were almost completely displaced southward from the modern distribution. Significantly, there is strong evidence that there was an invasion of fish of current economic importance into the Western Mediterranean through the Straits of Gibraltar, where they were exploited by Palaeolithic human populations. There has been much recent interest in the marine glacial refugia to understand how the ranges of the economically important fish species will be displaced with the future climate warming. Recent ENM studies have suggested that species ranges may not have been displaced far southward during the coldest conditions of the LGM. However, archaeozoological evidence and LGM ocean temperature reconstructions indicate that there were large range changes, and certain marine species were able invade the Western Mediterranean. These findings are important for ongoing studies of molecular ecology that aim to assess marine glacial refugia from the genetic structure of living populations, and they pose questions about the genetic identity of vanished marine populations during the LGM. The research presents a challenge for future archaeozoological work to verify palaeoclimatic reconstructions and delimit the glacial refugia.Fri, 16 Jul 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1337/2010/<b>Uncertainty of the CO₂ threshold for melting a hard Snowball Earth</b><br /><br />Climate of the Past Discussions, 6, 1337-1350, 2010<br /><br />Author(s): Y. Hu and J. Yang<br /><br />One of the critical issues of the Snowball Earth hypothesis is how high level of CO₂ is required for triggering the deglaciation. Using Community Atmospheric Model version 3 (CAM3), we study the problem for the CO₂ threshold. Our simulations show large differences from previous results (Pierrehumbert, 2004, 2005). At 0.2 bars of CO₂, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO₂ in Le Hir et al. (2007). It is found that the diversity of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO₂. At 0.2 bar of CO₂, CAM3 yields 117 Wm ⁻² of clear-sky greenhouse effect and 32 Wm⁻² of longwave cloud forcing, versus only about 77 Wm⁻² and 10.5 Wm⁻² in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than in Pierrehumbert (2005).Mon, 12 Jul 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1311/2010/<b>A ~400 ka supra-Milankovitch cycle in the Na, Mg, Pb, Ni, and Co records of a ferromanganese crust from the Vityaz fracture zone, central Indian ridge</b><br /><br />Climate of the Past Discussions, 6, 1311-1335, 2010<br /><br />Author(s): R. Banerjee, S. M. Gupta, H. Miura, and D. V. Borole<br /><br />A ~400 ka (kilo years) supra-Milankovitch cycle, recorded in the sodium, magnesium, lead, nickel and cobalt contents of a 32 mm thick ferromanganese crust from Vityaz fracture zone, central Indian ridge is reported here. To arrive at the geological ages, we used both ²³⁰Th_execcs and Co-chronometric datings. The correlation coefficient between the ²³⁰Th_execcs based dates and Co-chronometric dates for the top 0–8 mm is very high (<i>r</i>=0.9734, at 99.9% significance). The cobalt chronometric age for the bottom most oxide layer of this crust is computed as 3.5 Ma. Red-fit and multi-taper spectral analyses of time series data revealed the existence of the significant ~400 ka cycle, representing the changes in the hydrogeochemical conditions in the ocean due to the Earth's orbital eccentricity related summer insolation at the equator. This is the first report of such cycle from a hydrogenous ferromanganese crust from equatorial Indian ocean.Fri, 09 Jul 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1267/2010/<b>Variations of the Atlantic meridional overturning circulation in control and transient simulations of the last millennium</b><br /><br />Climate of the Past Discussions, 6, 1267-1309, 2010<br /><br />Author(s): D. Hofer, C. C. Raible, and T. F. Stocker<br /><br />The variability of the Atlantic meridional overturing circulation (AMOC) strength is investigated in control experiments and in transient simulations of up to the last millennium using the low-resolution Community Climate System Model version 3. In the transient simulations the AMOC exhibits enhanced low-frequency variability that is mainly caused by transitions between two semi-stable circulation states which amount to a 10 percent change of the maximum overturning. One transition is also found in a control experiment, but the time-varying external forcing significantly increases the probability of the occurrence of such events though not having a direct, linear impact on the AMOC. The transition from a high to a low AMOC state starts with a reduction of the convection in the Labrador and Irminger Seas and goes along with a changed barotropic circulation of both gyres in the North Atlantic and a gradual strengthening of the convection in the Greenland-Iceland-Norwegian (GIN) Seas. In contrast, the transition from a weak to a strong overturning is induced by decreased mixing in the GIN Seas. As a consequence of the transition, regional sea surface temperature (SST) anomalies are found in the midlatitude North Atlantic and in the convection regions with an amplitude of up to 3 K. The atmospheric response to the SST forcing associated with the transition indicates a significant impact on the Scandinavian surface air temperature (SAT) in the order of 1 K. Thus, the changes of the ocean circulation make a major contribution to the Scandinavian SAT variability in the last millennium.Wed, 07 Jul 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1229/2010/<b>Sea-surface salinity variations in the Northern Caribbean Sea across the mid-Pleistocene transition</b><br /><br />Climate of the Past Discussions, 6, 1229-1265, 2010<br /><br />Author(s): S. Sepulcre, L. Vidal, K. Tachikawa, F. Rostek, and E. Bard<br /><br />This study aimed at documenting climate changes in tropical area in response to the Mid-Pleistocene Transition (MPT) by reconstructing past hydrologic variations in the Northern Caribbean Sea and its influence on the stability of the Atlantic Meridional Overturning Circulation (AMOC) during the last 940 kyr. Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δ<i>δ</i>¹⁸O, the difference between the modern and the past <i>δ</i>¹⁸O of seawater (obtained by combining alkenone thermometer data with the <i>δ</i>¹⁸O of the planktonic <i>foraminifera</i> <i>Globigerinoides ruber</i> (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in the studied area are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δ<i>δ</i>¹⁸O record exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 kyr, indicating increased SSS. At a longer timescale, the Δ<i>δ</i>¹⁸O exhibits a shift toward lower values for interglacial periods during the last 450 kyr, when compared to interglacial stages older than 650 kyr. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper interhemispheric temperature gradient and associated with reduced northward cross equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 kyr. Following the MPT, lower salinities during the last five interglacial stages indicate a northernmost ITCZ location, forced by changes in the interhemispheric temperature gradient that is associated with the poleward position of Southern Oceanic Fronts that amplified the transport of heat and moisture to the North Atlantic. These processes may have contributed to amplification of the climate cycles that followed the MPT.Tue, 29 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1209/2010/<b>Objective identification of climate states from Greenland ice cores for the last glacial period</b><br /><br />Climate of the Past Discussions, 6, 1209-1227, 2010<br /><br />Author(s): D. J. Peavoy and C. Franzke<br /><br />We present statistical methods to systematically determine climate regimes for the last glacial period using three temperature proxy records from Greenland: measurements of δ¹⁸O from the Greenland Ice Sheet Project 2 (GISP2), the Greenland Ice Core Project (GRIP) and the North Greenland Ice Core Project (NGRIP). By using Bayesian model comparison methods we find that, in two out of three data sets, a model with 3 states is very strongly supported. We interpret these states as corresponding to: a gradual cooling regime due to iceberg influx in the North Atlantic, sudden temperature decrease due to increased freshwater influx following ice sheet collapse and to the Dansgaard-Oeschger events associated with sudden rebound temperature increase after the thermohaline circulation recovers its full flux. We find that these models are far superior to those that differentiate between states based on absolute temperature differences only, which questions the appropriateness of defining stadial and interstadial climate states. We investigate the recurrence properties of these climate regimes and find that the only significant periodicity is within the Greenland Ice Sheet Project 2 data at 1450 years in agreement with previous studies.Tue, 15 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1163/2010/<b>Clouds and the Faint Young Sun Paradox</b><br /><br />Climate of the Past Discussions, 6, 1163-1207, 2010<br /><br />Author(s): C. Goldblatt and K. J. Zahnle<br /><br />We investigate the role which clouds could play in resolving the Faint Young Sun Paradox (FYSP). Lower solar luminosity in the past means that less energy was absorbed on Earth (a forcing of -50 W m⁻² during the late Archean), but geological evidence points to the Earth being at least as warm as it is today, with only very occasional glaciations. We perform radiative calculations on a single global mean atmospheric column. We select a nominal set of three layered, randomly overlapping clouds, which are both consistent with observed cloud climatologies and reproduce the observed global mean energy budget of Earth. By varying the fraction, thickness, height and particle size of these clouds we conduct a wide exploration of how changed clouds could affect climate, thus constraining how clouds could contribute to resolving the FYSP. Low clouds reflect sunlight but have little greenhouse effect. Removing them entirely gives a forcing of +25 W m⁻² whilst more modest reduction in their efficacy gives a forcing of +10 to +15 W m⁻². For high clouds, the greenhouse effect dominates. It is possible to generate +50 W m⁻² forcing from enhancing these, but this requires making them 3.5 times thicker and 14 K colder than the standard high cloud in our nominal set and expanding their coverage to 100% of the sky. Such changes are not credible. More plausible changes would generate no more that +15 W m⁻² forcing. Thus neither fewer low clouds nor more high clouds can provide enough forcing to resolve the FYSP. Decreased surface albedo can contribute no more than +5 W m⁻² forcing. Some models which have been applied to the FYSP do not include clouds at all. These overestimate the forcing due to increased CO₂ by 20 to 25% when <i>p</i>CO₂ is 0.01 to 0.1 bar.Thu, 10 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1139/2010/<b>Questions of importance to the conservation of global biological diversity: answers from the past</b><br /><br />Climate of the Past Discussions, 6, 1139-1162, 2010<br /><br />Author(s): K. J. Willis and S. A. Bhagwat<br /><br />Paleoecological records are replete with examples of biotic responses to past climate change and human impact but how can we use these records in the conservation of current and future biodiversity? A recently published list of One Hundred Questions of Importance to the Conservation of Global Biological Diversity (Sutherland et al., 2009) highlights a number of key research questions that need a temporal perspective. Many of these questions are related to the determination of ecological processes in order to assess ecosystem function and services, climate change-integrated conservation strategies, and ecosystem management and restoration. However, it is noticeable that not a single contributor to this list was from the paleo-research community and that extremely few paleo-records are ever used in the development of terrestrial conservation management plans. This lack of dialogue between conservationists and the paleo-community is partially driven by a perception that the data provided by paleoecological records are purely descriptive and not of relevance to the day-to-day management and conservation of biological diversity. This paper illustrates, through a series of case-studies, how long-term ecological records (>50 years) can provide a test of predictions and assumptions of ecological processes that are directly relevant to management strategies necessary in order to retain biological diversity in a changing climate. This includes information on diversity baselines, thresholds, resilience, and restoration of ecological processes.Thu, 10 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1111/2010/<b>A shift in the spatial pattern of Iberian droughts during the 17th century</b><br /><br />Climate of the Past Discussions, 6, 1111-1137, 2010<br /><br />Author(s): F. Domínguez-Castro, R. García-Herrera, P. Ribera, and M. Barriendos<br /><br />In this paper, series of drought occurrence and drought extension in the Iberian Peninsula are constructed for the 1600–1750 period from seven rogation series. These rogation ceremony records come from Bilbao, Catalonia, Zamora, Zaragoza, Toledo, Murcia and Seville. They are distributed across the Peninsula and include the areas with the most characteristic Iberian climate types, influenced by the Atlantic and the Mediterranean conditions, described from modern data. A seasonal division of the series shows that spring is a critical season for rogation series in most of Iberia, being Bilbao the only site were the highest number of rogations is detected for a different season. The annual analysis of the series shows a dramatic difference between the period 1600–1652, when droughts are characterized by its local character; and the period 1653–1749, when they affect to broader regions or even to the whole Peninsula. The analysis of spring series confirms the existence of the two periods detected in the annual analysis. Finally, secondary documentary sources are used to further characterise the two most extended droughts in the period, 1664 and 1680, and to verify the extension of the areas affected by droughts recorded through rogation series.Mon, 07 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1077/2010/<b>Climate response to freshwater perturbations in Northern or Southern Hemispheres at the last glacial inception, the last glacial maximum and the present-day</b><br /><br />Climate of the Past Discussions, 6, 1077-1110, 2010<br /><br />Author(s): G. Philippon-Berthier, G. Ramstein, S. Charbit, and C. Ritz<br /><br />Freshwater inputs in North Atlantic due to huge surge of icebergs coming from ice sheets might be responsible for drastic regional and global abrupt climatic transitions. To quantify the sensitivity of climate system to these freshwater inputs, we use a model of intermediate complexity coupled to ice-sheet models for both Northern and Southern Hemispheres. We mimic the Dansgaard-Oeschger and Heinrich Events by forcing the model with appropriate freshwater perturbations. The originality of this study is to investigate with such a global model, the response of the coupled system to freshwater discharges for three different climate contexts, the Last Glacial Maximum (LGM), the Last Glacial Inception (LGI) and the present-day (PD) climates. <br><br> We first show that in all climate contexts, the North Atlantic circulation is more sensitive to freshwater flux when ice sheets are present. Secondly, the "seesaw" mechanism occurs mostly for the North Atlantic freshwater perturbation whereas it remains very weak for the Southern Ocean freshwater release. Moreover, this seesaw is generally enhanced when ice sheets are interactive. The most striking result is that the freshwater perturbation amplifies the inception of the North American ice sheet at LGI the sea-level drop associated is significantly increased and in a much better agreement with data.Tue, 01 Jun 2010 00:00:00 +0200http://www.clim-past-discuss.net/6/1045/2010/<b>Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon</b><br /><br />Climate of the Past Discussions, 6, 1045-1076, 2010<br /><br />Author(s): L. Beaufort, S. van der Kaars, F. C. Bassinot, and V. Moron<br /><br />Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150,000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in Northern Australia and Southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase (August insolation). This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggest that low latitude climatic variation precedes global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronically on the different monsoon systems.Tue, 01 Jun 2010 00:00:00 +0200