ALBERT

Description: Impact of the oceanic geothermal heat flux on a glacial ocean state Climate of the Past Discussions, 11, 3597-3624, 2015 Author(s): M. Ballarotta, F. Roquet, S. Falahat, Q. Zhang, and G. Madec The oceanic geothermal heating (OGH) has a significant impact on the present-day ocean state, but its role during glacial periods, when the ocean circulation and stratification were different from those of today, remains poorly known. In the present study, we analyzed the response of the glacial ocean to OGH, by comparing ocean simulations of the Last Glacial Maximum (LGM, ∼ 21 ka ago) including or not geothermal heating. We found that applying the OGH warmed the Antarctic Bottom Waters (AABW) by ∼ 0.4 °C and increased the abyssal circulation by 15 to 30 % north of 30° S in the deep Pacific and Atlantic basins. The geothermally heated deep waters were then advected toward the Southern Ocean where they upwelled to the surface due to the Ekman transport. The extra heat transport towards Antarctica acted to reduce the amount of sea ice contributing to the freshening of the whole AABW overturning cell. The global amount of salt being conserved, this bottom freshening induced a salinification of the North Atlantic and North Pacific surface and intermediate waters, contributing to the deepening of the North Atlantic Deep Water. This indirect mechanism is responsible for the largest observed warming, found in the North Atlantic deep western boundary current between 2000 and 3000 m (up to 2 °C). The characteristic time scale of the ocean response to the OGH corresponds to an advective time scale (associated with the overturning of the AABW cell) rather than a diffusive time scale. The OGH might facilitate the transition from a glacial to an inter-glacial state but its effect on the deep stratification seems insufficient to drive alone an abrupt climate change.

Description: A Late Pleistocene sea level stack Climate of the Past Discussions, 11, 3699-3728, 2015 Author(s): R. M. Spratt and L. E. Lisiecki Late Pleistocene sea level has been reconstructed from ocean sediment core data using a wide variety of proxies and models. However, the accuracy of individual reconstructions is limited by measurement error, local variations in salinity and temperature, and assumptions particular to each technique. Here we present a sea level stack (average) which increases the signal-to-noise ratio of individual reconstructions. Specifically, we perform principal component analysis (PCA) on seven records from 0–430 ka and five records from 0–798 ka. The first principal component, which we use as the stack, describes ~80 % of the variance in the data and is similar using either five or seven records. After scaling the stack based on Holocene and Last Glacial Maximum (LGM) sea level estimates, the stack agrees to within 5 m with isostatically adjusted coral sea level estimates for Marine Isotope Stages 5e and 11 (125 and 400 ka, respectively). When we compare the sea level stack with the δ 18 O of benthic foraminifera, we find that sea level change accounts for about ~40 % of the total orbital-band variance in benthic δ 18 O, compared to a 65 % contribution during the LGM-to-Holocene transition. Additionally, the second and third principal components of our analyses reflect differences between proxy records associated with spatial variations in the δ 18 O of seawater.

Description: Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA Climate of the Past Discussions, 11, 3665-3698, 2015 Author(s): J. Pawłowska, M. Zajączkowski, M. Łącka, F. Lejzerowicz, P. Esling, and J. Pawlowski This paper presents the reconstruction of climate-driven environmental changes of the last millennium from Hornsund Fjord (Svalbard) based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by the analysis of foraminiferal ancient DNA (aDNA), focusing on non-fossilised monothalamous species. The main climatic fluctuations over the last millennium were the Medieval Warm Period (MWP, 1000–1600 AD), the Little Ice Age (LIA, 1600–1900 AD), and the Modern Warming (MW, 1900 AD–present). Our study indicated that environmental conditions in Hornsund during the MWP and the early LIA (before ~ 1800 AD) were relatively stable, resulting from the distant position of glaciers. The beginning of the LIA (~ 1600 AD) was poorly evidenced by the micropalaeontological record, but well marked in the aDNA data, by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (~ 1600– ~ 1800 AD) was marked by the increase in abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus . In the late LIA (after ~ 1800 AD), conditions in the fjord became glacier-proximal, characterised by increased meltwater outflows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus . During the MW, major glaciers fronts retreated rapidly to the inner bays, limiting the iceberg discharge to the fjord centre and causing the shift in the foraminiferal community reflected in both fossil and aDNA records. Palaeoceanographic changes in the Hornsund Fjord over the last millennium were driven mainly by the inflow of shelf-originated water masses and glaciers' activity. However, the environmental changes were poorly evidenced in the micropalaeontological record, but well documented in our aDNA data. We considerably increased the number of potential proxy species by including monothalamous foraminifera in the palaeoecological studies.

Description: A 250 year periodicity in Southern Hemisphere westerly winds over the last 2600 years Climate of the Past Discussions, 11, 2159-2180, 2015 Author(s): C. Turney, R. Jones, C. Fogwill, J. Hatton, A. N. Williams, A. Hogg, Z. Thomas, J. Palmer, and S. Mooney Southern Hemisphere westerly airflow has a significant influence on the ocean–atmosphere system of the mid- to high-latitudes with potentially global climate implications. Unfortunately historic observations only extend back to the late nineteenth century, limiting our understanding of multi-decadal to centennial change. Here we present a highly resolved (30 yr) record of past westerly air strength from a Falkland Islands peat sequence spanning the last 2600 years. Situated under the core latitude of Southern Hemisphere westerly airflow, we identify highly variable changes in exotic pollen derived from South America which can be used to inform on past westerly air strength and location. The results indicate enhanced airflow over the Falklands between 2000 and 1000 cal. yr BP, and associated with increased burning, most probably as a result of higher temperatures and/or reduced precipitation, comparable to records in South America. Spectral analysis of the charcoal record identifies a 250 year periodicity within the data, suggesting solar variability has a modulating influence on Southern Hemisphere westerly airflow with potentially important implications for understanding global climate change through the late Holocene.

Description: Eastern Andean environmental and climate synthesis for the last 2000 years BP from terrestrial pollen and charcoal records of Patagonia Climate of the Past Discussions, 11, 2121-2157, 2015 Author(s): G. D. Sottile, M. E. Echeverria, M. V. Mancini, M. M. Bianchi, M. A. Marcos, and F. P. Bamonte The Southern Hemisphere Westerly Winds (SWW) constitute an important zonal circulation system that dominates the dynamics of Southern Hemisphere mid-latitude climate. Little is known about climatic changes in the Southern South America in comparison to the Northern Hemisphere due to the low density of proxy records, and adequate chronology and sampling resolution to address environmental changes of the last 2000 years. Since 2009, new pollen and charcoal records from bog and lakes in northern and southern Patagonia at the east side of the Andes have been published with an adequate calibration of pollen assemblages related to modern vegetation and ecological behaviour. In this work we improve the chronological control of some eastern Andean previously published sequences and integrate pollen and charcoal dataset available east of the Andes to interpret possible environmental and SWW variability at centennial time scales. Through the analysis of modern and past hydric balance dynamics we compare these scenarios with other western Andean SWW sensitive proxy records for the last 2000 years. Due to the distinct precipitation regimes that exist between Northern (40–45° S) and Southern Patagonia (48–52° S) pollen sites locations, shifts on latitudinal and strength of the SWW results in large changes on hydric availability on forest and steppe communities. Therefore, we can interpret fossil pollen dataset as changes on paleohydric balance at every single site by the construction of paleohydric indices and comparison to charcoal records during the last 2000 cal yrs BP. Our composite pollen-based Northern and Southern Patagonia indices can be interpreted as changes in latitudinal variation and intensity of the SWW respectively. Dataset integration suggest poleward SWW between 2000 and 750 cal yrs BP and northward-weaker SWW during the Little Ice Age (750–200 cal yrs BP). These SWW variations are synchronous to Patagonian fire activity major shifts. We found an in phase fire regime (in terms of timing of biomass burning) between northern Patagonia Monte shrubland and Southern Patagonia steppe environments. Conversely, there is an antiphase fire regime between Northern and Southern Patagonia forest and forest-steppe ecotone environments. SWW variability may be associated to ENSO variability especially during the last millennia. For the last 200 cal yrs BP we can concluded that the SWW belt were more intense and poleward than the previous interval. Our composite pollen-based SWW indices show the potential of pollen dataset integration to improve the understanding of paleohydric variability especially for the last 2000 millennial in Patagonia.

Description: Hydroclimatic variability in the Levant during the early last glacial (∼ 117–75 ka) derived from micro-facies analyses of deep Dead Sea sediments Climate of the Past Discussions, 11, 3625-3663, 2015 Author(s): I. Neugebauer, M. J. Schwab, N. D. Waldmann, R. Tjallingii, U. Frank, E. Hadzhiivanova, R. Naumann, N. Taha, A. Agnon, Y. Enzel, and A. Brauer The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by μXRF scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca 117–75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several meters thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ∼110–108 ± 5 and ∼93–87 ± 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during MIS 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in-situ beach deposit. Two intervals of higher lake stands at ∼108–93 ± 6 and ∼87–75 ± 7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and GI 24 + 23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period.

Description: Probabilistic precipitation and temperature downscaling of the Twentieth Century Reanalysis over France Climate of the Past Discussions, 11, 4425-4482, 2015 Author(s): L. Caillouet, J.-P. Vidal, E. Sauquet, and B. Graff This work proposes a daily high-resolution probabilistic reconstruction of precipitation and temperature fields in France over the 1871–2012 period built on the NOAA Twentieth Century global extended atmospheric reanalysis (20CR). The objective is to fill in the spatial and temporal data gaps in surface observations in order to improve our knowledge on the local-scale climate variability from the late 19th century onwards. The SANDHY (Stepwise ANalogue Downscaling method for HYdrology) statistical downscaling method, initially developed for quantitative precipitation forecast, is used here to bridge the scale gap between large-scale 20CR predictors and local-scale predictands from the SAFRAN high-resolution near-surface reanalysis, available from 1958 onwards only. SANDHY provides a daily ensemble of 125 analogues dates over the 1871–2012 period for 608 climatically homogeneous zones paving France. Large precipitation biases in intermediary seasons are shown to occur in regions with high seasonal asymmetry like the Mediterranean. Moreover, winter and summer temperatures are respectively over- and under-estimated over the whole of France. Two analogue subselection methods are therefore developed with the aim of keeping unchanged the structure of the SANDHY method while reducing those seasonal biases. The calendar selection keeps the closest analogue dates in the year for each target date. The stepwise selection applies two new analogy steps based on similarity of the Sea Surface Temperature (SST) and the large-scale Two-metre Temperature (T2m). Comparisons to the SAFRAN reanalysis over 1959–2007 and to homogenized series over the whole 20th century show that biases in the interannual cycle of precipitation and temperature are reduced with both methods. The stepwise subselection moreover leads to a large improvement of interannual correlation and reduction of errors in seasonal temperature time series. When the calendar subselection is an easily applicable method suitable in a quantitative precipitation forecast context, the stepwise subselection method allows for potential season shifts and SST trends and is therefore better suited for climate reconstructions and climate change studies. The probabilistic downscaling of 20CR over the period 1871–2012 with the SANDHY probabilistic downscaling method combined with the stepwise subselection thus constitutes a perfect framework for assessing the recent observed meteorological events but also future events projected by climate change impact studies and putting them in a~historical perspective.

Description: Climatic and insolation control on the high-resolution total air content in the NGRIP ice core Climate of the Past Discussions, 11, 5509-5548, 2015 Author(s): O. Eicher, M. Baumgartner, A. Schilt, J. Schmitt, J. Schwander, T. F. Stocker, and H. Fischer Because the total air content (TAC) of polar ice is directly affected by the atmospheric pressure, its record in polar ice cores was considered as a proxy for past ice sheet elevation changes. However the Antarctic ice core TAC record is known to also contain an insolation signature, although the underlying physical mechanisms are still a matter of debate. Here we present a high-resolution TAC record over the whole North Greenland Ice Core Project ice core, covering the last 120 000 years, which independently supports an insolation signature in Greenland. Wavelet analysis reveals a clear precession and obliquity signal similar to previous findings on Antarctic TAC, with different insolation history. In our high-resolution record we also find a decrease of 3–5 % (3–4.2 mL kg −1 ) in TAC as a response to Dansgaard-Oeschger-Events (DO-events). TAC starts to decrease in parallel to increasing Greenland surface temperature and slightly before CH 4 reacts to the warming, but also shows a two-step decline that lasts for several centuries into the warm phase/interstadial. The TAC response is larger than expected considering only local temperature and atmospheric pressure as a driver, pointing to transient firnification response caused by the accumulation-induced increase in the load on the firn at bubble close-off, while temperature changes deeper in the firn are still small.

Description: Stratification of surface waters during the last glacial millennial climatic events: a key factor in subsurface and deep water mass dynamics Climate of the Past Discussions, 11, 2077-2119, 2015 Author(s): M. Wary, F. Eynaud, S. Marjolaine, S. Zaragosi, L. Rossignol, B. Malaizé, E. Palis, J. Zumaque, C. Caulle, A. Penaud, E. Michel, and K. Charlier The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich Events and Dansgaard–Oeschger cycles. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high resolution analyses were conducted on the 12–42 ka BP section of core MD99-2281 retrieved Southwest off Faeroes. Our multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials while surface conditions progressively deteriorate throughout these cold episodes; at the opposite, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes with progressively milder surface conditions and gradual intensification of the deep circulation while the vigor of the subsurface Atlantic inflow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HS): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation at mid-event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.

Description: Glacier response to North Atlantic climate variability during the Holocene Climate of the Past Discussions, 11, 2009-2036, 2015 Author(s): N. L. Balascio, W. J. D'Andrea, and R. S. Bradley Small glaciers and ice caps respond rapidly to climate variations and records of their past extent provide information on the natural envelope of past climate variability. Millennial-scale trends in Holocene glacier size are well documented and correspond with changes in Northern Hemisphere summer insolation. However, there is only sparse and fragmentary evidence for higher frequency variations in glacier size because in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial scale climate forcing and feedback mechanisms. Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland, derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented Northern Hemisphere climatic excursions, including the "8.2 ka" cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th Century warming. In addition, the sediments indicate centennial-scale oscillations in glacier size during the late Holocene. Beginning at 4.1 ka, a series of abrupt glacier advances occurred, each lasting ~100 years and followed by a period of retreat, that were superimposed on a gradual trend toward larger glacier size. Thus, while declining summer insolation caused long-term cooling and glacier expansions during the late Holocene, climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data provide a longer-term perspective on the rate of 20th century glacier retreat and indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.

Description: The 1816 ‘year without a summer’ in an atmospheric reanalysis Philip Brohan, Gilbert P. Compo, Stefan Brönnimann, Robert J. Allan, Renate Auchmann, Yuri Brugnara, Prashant D. Sardeshmukh, and Jeffrey S. Whitaker Clim. Past Discuss., doi:10.5194/cp-2016-78,2016 Manuscript under review for CP (discussion: open, 0 comments) We have used modern weather forecasting tools to reconstruct the dreadful European weather of 200 years ago – 1816 was the ‘year without a summer’; harvests failed, and people starved. We can show that 1816’s extreme climate was caused by the eruption of the Tambora volcano the previous year. This means we have some chance of predicting such extreme summers if they occur in future, though this is still a challenge to today’s forecast models.

Description: Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land Thomas Münch, Sepp Kipfstuhl, Johannes Freitag, Hanno Meyer, and Thomas Laepple Clim. Past, 12, 1565-1581, doi:10.5194/cp-12-1565-2016, 2016 Ice-core oxygen isotope ratios are a key climate archive to infer past temperatures, an interpretation however complicated by non-climatic noise. Based on 50 m firn trenches, we present for the first time a two-dimensional view (vertical × horizontal) of how oxygen isotopes are stored in Antarctic firn. A statistical noise model allows inferences for the validity of ice coring efforts to reconstruct past temperatures, highlighting the need of replicate cores for Holocene climate reconstructions.

Description: Freshening of the Labrador Sea as a trigger for Little Ice Age development Montserrat Alonso-Garcia, Helga F. Kleiven, Jerry F. McManus, Paola Moffa-Sanchez, Wallace Broecker, and Benjamin P. Flower Clim. Past Discuss., doi:10.5194/cp-2016-80,2016 Manuscript under review for CP (discussion: open, 0 comments) This study focuses on understanding climatic and oceanographic variations that took place during the last 1000 years. We studied sediment samples from the Labrador Sea looking for evidence of events of freshwater and iceberg discharges to this region. The importance of this study is to evaluate when these events happened and its possible consequences. The freshening of the Labrador Sea region may have played a major role on the cooling underwent during the 15th to 19th centuries.

Description: The role of basal hydrology in the surging of the Laurentide Ice Sheet William H. G. Roberts, Antony J. Payne, and Paul J. Valdes Clim. Past, 12, 1601-1617, doi:10.5194/cp-12-1601-2016, 2016 There are observations from ocean sediment cores that during the last ice age the Laurentide Ice Sheet, which sat over North America, periodically surged. In this study we show the role that water at the base of an ice sheet plays in these surges. We show that with a more realistic representation of water drainage at the base of the ice sheet than usually used, these surges can still occur and that they are triggered by an internal ice sheet instability; no external trigger is needed.

Description: North American regional climate reconstruction from Ground Surface Temperature Histories Fernando Jaume-Santero, Carolyne Pickler, Hugo Beltrami, and Jean-Claude Mareschal Clim. Past Discuss., doi:10.5194/cp-2016-85,2016 Manuscript under review for CP (discussion: open, 0 comments) Within the framework of the PAGES NAm2k project, we estimated regional trends in the ground surface temperature change for the past 500 years in North America. The mean North American ground surface temperature history suggests a warming of 1.8 °C between preindustrial times and 2000. A regional analysis of mean temperature changes over the last 5 centuries shows that all regions experienced warming, but this warming displays large spatial variability, and is more marked in high latitude regions.

Description: Comparison of simulated and reconstructed variations in East African hydroclimate over the last millennium François Klein, Hugues Goosse, Nicholas E. Graham, and Dirk Verschuren Clim. Past, 12, 1499-1518, doi:10.5194/cp-12-1499-2016, 2016 This paper analyses global climate model simulations of long-term East African hydroclimate changes relative to proxy-based reconstructions over the last millennium. No common signal is found between model results and reconstructions as well as among the model time series, which suggests that simulated hydroclimate is mostly driven by internal variability rather than by common external forcing.

Description: Sea ice-related halogen enrichment at Law Dome, coastal East Antarctica Paul Vallelonga, Niccolo Maffezzoli, Andrew D. Moy, Mark A. J. Curran, Tessa R. Vance, Ross Edwards, Gwyn Hughes, Emily Barker, Gunnar Spreen, Alfonso Saiz-Lopez, J. Pablo Corella, Carlos A. Cuevas, and Andrea Spolaor Clim. Past Discuss., doi:10.5194/cp-2016-74,2016 Manuscript under review for CP (discussion: open, 0 comments) We present a study of bromine, iodine and sodium in an ice core from Law Dome, in coastal East Antarctica. We find that bromine and iodine variability at Law Dome is correlated to changes in the area of sea ice along the Law Dome coast as observed by satellite since the early 1970s. These findings are in agreement with a previous study based on MSA and confirm a long-trem trend of sea ice decrease for this sector of Antarctica over the 20th century.

Description: North Atlantic Oscillation controls on oxygen and hydrogen isotope gradients in winter precipitation across Europe; implications for palaeoclimate studies Michael Deininger, Martin Werner, and Frank McDermott Clim. Past Discuss., doi:10.5194/cp-2016-77,2016 Manuscript under review for CP (discussion: open, 0 comments) This study investigates the NAO-related mechanisms that control winter-precipitation stable oxygen and hydrogen isotope gradients across Europe. The results show that past longitudinal stable oxygen and hydrogen isotope gradients in European rainfall stored in palaeoclimate archives (e.g. speleothems) can be used to infer the past winter NAO modes from its variations.

Description: Holocene hydrological changes in the Rhône River (NW Mediterranean) as recorded in the marine mud belt Maria-Angela Bassetti, Serge Berné, Marie-Alexandrine Sicre, Bernard Dennielou, Yoann Alonso, Roselyne Buscail, Bassem Jalali, Bertil Hebert, and Christophe Menniti Clim. Past, 12, 1539-1553, doi:10.5194/cp-12-1539-2016, 2016 This work represents the first attempt to decipher the linkages between rapid climate changes and continental Holocene paleohydrology in the NW Mediterranean shallow marine setting. Between 11 and 4 ka cal BP, terrigenous input increased and reached a maximum at 7 ka cal BP, probably as a result of a humid phase. From ca. 4 ka cal BP to the present, enhanced variability in the land-derived material is possibly due to large-scale atmospheric circulation and rainfall patterns in western Europe.

Description: Influence of proxy data uncertainty on data assimilation for the past climate Anastasios Matsikaris, Martin Widmann, and Johann Jungclaus Clim. Past, 12, 1555-1563, doi:10.5194/cp-12-1555-2016, 2016 We have assimilated proxy-based (PAGES 2K) and instrumental (HadCRUT3v) observations into a General Circulation Model (MPI-ESM-CR). Assimilating instrumental data improves the performance of Data Assimilation. No skill on small spatial scales is however found for either of the two schemes. Errors in the assimilated data are therefore not the main reason for this lack of skill; continental mean temperatures cannot provide skill on small spatial scales in palaeoclimate reconstructions.

Description: Could the Pliocene constrain the equilibrium climate sensitivity? J. C. Hargreaves and J. D. Annan Clim. Past, 12, 1591-1599, doi:10.5194/cp-12-1591-2016, 2016 The mid-Pliocene Warm Period, 3 million years ago, was the most recent interval with high greenhouse gases. By modelling the period with the same models used for future projections, we can link the past and future climates. Here we use data from the mid-Pliocene to produce a tentative result for equilibrium climate sensitivity. We show that there are considerable uncertainties that strongly influence the result, but we are optimistic that these may be reduced in the next few years.

Description: Multi-timescale data assimilation for atmosphere–ocean state estimates Nathan Steiger and Gregory Hakim Clim. Past, 12, 1375-1388, doi:10.5194/cp-12-1375-2016, 2016 We present a data assimilation algorithm that incorporates proxy data at arbitrary timescales. Within a synthetic-test framework, we find that atmosphere–ocean states are most skillfully reconstructed by incorporating proxies across multiple timescales compared to using them at short or long timescales alone. Additionally, reconstructions that incorporate long-timescale proxies improve the low-frequency components of the reconstructions relative to using only high-resolution proxies.

Description: Holocene biome changes in Asia – an analysis of different transient Earth system model simulations Anne Dallmeyer, Martin Claussen, Jian Ni, Xianyong Cao, Yongbo Wang, Nils Fischer, Madlen Pfeiffer, Liya Jin, Vyacheslav Khon, Sebastian Wagner, Kerstin Haberkorn, and Ulrike Herzschuh Clim. Past Discuss., doi:10.5194/cp-2016-67,2016 Manuscript under review for CP (discussion: open, 0 comments) The vegetation distribution in Eastern Asia is supposed to be very sensitive to climate change. Since proxy records are scarce, hitherto a mechanistic understanding of the past spatio-temporal climate-vegetation relationship is lacking. To assess the Holocene vegetation change, we forced the diagnostic biome model BIOME4 with climate anomalies of different transient climate simulations.

Description: Jens Esmark's Christiania (Oslo) meteorological observations 1816–1838: The first long term continuous temperature record from the Norwegian capital homogenized and analysed Geir Hestmark and Øyvind Nordli Clim. Past Discuss., doi:10.5194/cp-2016-60,2016 Manuscript under review for CP (discussion: open, 0 comments) The detailed and continuous meteorological observations of professor Jens Esmark from the capital of Norway in the period 1816 to 1838 are evaluated, homogenized and reanalyzed with modern methods to characterize the weather in Oslo in this period.

Description: Glacial δ 13 C decreases in the western South Atlantic forced by millennial changes in Southern Ocean ventilation Marília C. Campos, Cristiano M. Chiessi, Ines Voigt, Alberto R. Piola, Henning Kuhnert, and Stefan Mulitza Clim. Past Discuss., doi:10.5194/cp-2016-59,2016 Manuscript under review for CP (discussion: open, 0 comments) Abrupt climate change events of the last deglaciation were accompanied by increases in atmospheric CO 2 presumably originated by outgassing from the Southern Ocean. We present new planktonic foraminiferal stable carbon isotopic data from the western South Atlantic that suggest that the CO 2 added to the atmosphere during abrupt climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing from the Southern Ocean.

Description: Sedimentary archives of climate and sea-level changes during the Holocene in the Rhone prodelta (NW Mediterranean Sea) Anne-Sophie Fanget, Maria-Angela Bassetti, Christophe Fontanier, Alina Tudryn, and Serge Berné Clim. Past Discuss., doi:10.5194/cp-2016-57,2016 Manuscript under review for CP (discussion: open, 0 comments) A 7.38 m-long sediment core was collected from the eastern part of the Rhone prodelta (NW Mediterranean) at 67 m water depth. A multi-proxy study (sedimentary facies, benthic foraminifera and ostracods, clay mineralogy, and major elements from XRF) provides a multi-decadal to century-scale record of climate and sea-level changes during the Holocene. The early Holocene is marked by alternative silt and clay layers interpreted as distal tempestites deposited in a context of rising sea level. This interval contains shallow infra-littoral benthic meiofauna (e.g. Pontocythere elongata, Elphidium spp., Quinqueloculina lata) and formed between ca. 20 and 50 m water depth. The middle Holocene (ca. 8.3 to 4.5 ka cal. BP), is characterized, at the core site, by a period of sediment starvation (accumulation rate of ca. 0.01 cm yr −1 ) resulting from the maximum landward shift of the shoreline and the Rhone outlet(s). From a sequence stratigraphic point of view, this condensed interval, about 35 cm-thick, is a Maximum Flooding Surface that can be identified on seismic profiles as the transition between delta retrogradation and delta progradation. It is marked by very distinct changes in all proxy records. Following the stabilization of the global sea level, the late Holocene is marked by the establishment of prodeltaic conditions at the core site, as shown by the lithofacies and by the presence of benthic meiofauna typical of the modern Rhone prodelta (e.g. Valvulineria bradyana, Cassidulina carinata, Bulimina marginata). Several periods of increased fluvial discharge are also emphasized by the presence of species commonly found in brackish and shallow water environments (e.g. Leptocythere). Some of these periods correspond to the multi-decadal to centennial late Holocene humid periods recognized in Europe (i.e. the 2.8 ka event and the Little Ice Age). Two other periods of increased runoffs at ca. 1.3 and 1.1 ka cal. BP are recognized, and are likely to reflect periods of regional climate deterioration that are observed in the Rhone watershed.

Description: The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison Odile Peyron, Nathalie Combourieu-Nebout, David Brayshaw, Simon Goring, Valérie Andrieu-Ponel, Stéphanie Desprat, Will Fletcher, Belinda Gambin, Chryssanthi Ioakim, Sébastien Joannin, Ulrich Kotthoff, Katerina Kouli, Vincent Montade, Jörg Pross, Laura Sadori, and Michel Magny Clim. Past Discuss., doi:10.5194/cp-2016-65,2016 Manuscript under review for CP (discussion: open, 0 comments) Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evidence for (i) opposing northern and southern precipitation regimes during the Holocene across the Mediterranean basin, and (ii) an east-to-west precipitation gradient or dipole during the early Holocene, from a wet eastern Mediterranean to dry western Mediterranean. Using quantitative climate information from marine and terrestrial pollen archives, we focus on two key time intervals, the early to mid-Holocene (8000 to 6000 cal yrs BP) and the late Holocene (4000 to 2000 yrs BP), in order to test the above mentioned hypotheses on a Mediterranean-wide scale. Palynologically derived climate information is compared with the output of regional-scale climate-model simulations for the same time intervals. Quantitative pollen-based precipitation estimates were generated along a longitudinal gradient from the Alboran (West) to the Aegean Sea (East); they are derived from terrestrial pollen records from Greece, Italy and Malta as well as from pollen records obtained from marine cores. Because seasonality represents a key parameter in Mediterranean climates, special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate a previously described north-south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south-central and eastern Mediterranean region, while drier conditions prevailed from 45° N northwards. These patterns reversed during the late Holocene, with a wetter northern Mediterranean region and drier conditions in the east and south. More sites from the northern part of the Mediterranean basin are needed to further substantiate these observations. With regard to the existence of a west-east precipitation dipole during the Holocene, our pollen-based climate data show that the strength of this dipole is strongly linked to the seasonal parameter reconstructed: Early Holocene summers show a clear east-to-west gradient, with summer precipitation having been highest in the central and eastern Mediterranean and lowest over the western Mediterranean. In contrast, winter precipitation signals are less spatially coherent. A general drying trend occurred from the early to the late Holocene; particularly in the central and eastern Mediterranean. However, summer precipitation in the east remained above modern values, even during the late Holocene interval. Pollen-inferred precipitation estimates were compared to regional-scale climate modelling simulations based on the HadAM3 GCM coupled to the dynamic HadSM3 and the high-resolution regional HadRM3 models. Climate model outputs and pollen-inferred precipitation estimates show remarkably good overall correspondence, although many simulated patterns are of marginal statistical significance. Nevertheless, models weakly support an east to west division in summer precipitation and there are suggestions that the eastern Mediterranean experienced wetter summer and winter conditions during the early Holocene and wetter summer conditions during the late Holocene. The extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question; our model, consistent with other global models, does not suggest an extension of the African monsoon into the Mediterranean. Given the difficulty in modelling future climate change in Southern Europe, more simulations based on high resolution global models and very high resolution regional downscaling, perhaps even including transient simulations, are required to fully understand the patterns of change in winter and summer circulation patterns over the Mediterranean region

Description: Climatic effects and impacts of the 1815 eruption of Mount Tambora in the Czech Lands Rudolf Brázdil, Ladislava Řezníčková, Hubert Valášek, Lukáš Dolák, and Oldřich Kotyza Clim. Past, 12, 1361-1374, doi:10.5194/cp-12-1361-2016, 2016 The paper deals with climatic and human impacts of the strong Tambora (Indonesia) volcanic eruption in April 1815 over the Czech Lands territory based on analysis of documentary data and instrumental records. While climatic effects were related particularly to summers 1815 and 1816 (1816 is known as "a Year Without Summer"), quite important were societal impacts represented after bad harvest by steep increase in prices and shortages of food.

Description: Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere Yurui Zhang, Hans Renssen, and Heikki Seppä Clim. Past, 12, 1119-1135, doi:10.5194/cp-12-1119-2016, 2016 We explore how forcings contributed to climate change during the early Holocene that marked the final transition to the warm and stable stage. Our results indicate that 1) temperature at the Holocene onset was lower than in the preindustrial over the northern extratropics with the exception in Alaska, and the magnitude of this cooling varies regionally as a response to varying climate forcings and diverse mechanisms, and 2) the rate of the early Holocene warming was also spatially heterogeneous.

Description: Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine O. J. Maselli, N. J. Chellman, M. Grieman, L. Layman, J. R. McConnell, D. Pasteris, R. H. Rhodes, E. Saltzman, and M. Sigl Clim. Past Discuss., doi:10.5194/cp-2016-49,2016 Manuscript under review for CP (discussion: open, 0 comments) We analyzed two Greenland ice cores for methanesulfonate (MSA) and bromine (Br) and concluded that both species are suitable proxies for local sea ice conditions. Interpretation of the records reveals that there have been sharp declines in sea ice in these areas in the past 250 years. However, at both sites the Br record deviates from MSA during the industrial period, raising questions about the value of Br as a sea ice proxy during recent periods of high, industrial atmospheric acid pollution.

Description: Sulphur-rich volcanic eruptions triggered extreme hydrological events in Europe since AD 1850 Cristina Di Salvo and Gianluca Sottili Clim. Past Discuss., doi:10.5194/cp-2016-53,2016 Manuscript under review for CP (discussion: open, 0 comments) In Europe, intensities of hydrological extreme events were influenced by volcanic SO 2 concentrations in the Northern Hemisphere. SO 2 -rich eruptions, similar to the Bárðarbunga 2014–15 eruption (Iceland), by affecting Ocean-atmosphere heat exchange, affected the intensity of the NAO with effects on rainfall and flood intensities. SO 2 effects, superimposed to climate change, could enhance frequencies and intensities of extreme events, thus increasing the natural risks in densely populated area.

Description: Arctic sea ice simulation in the PlioMIP ensemble Fergus W. Howell, Alan M. Haywood, Bette L. Otto-Bliesner, Fran Bragg, Wing-Le Chan, Mark A. Chandler, Camille Contoux, Youichi Kamae, Ayako Abe-Ouchi, Nan A. Rosenbloom, Christian Stepanek, and Zhongshi Zhang Clim. Past, 12, 749-767, doi:10.5194/cp-12-749-2016, 2016 Simulations of pre-industrial and mid-Pliocene Arctic sea ice by eight GCMs are analysed. Ensemble variability in sea ice extent is greater in the mid-Pliocene summer, when half of the models simulate sea-ice-free conditions. Weaker correlations are seen between sea ice extent and temperatures in the pre-industrial era compared to the mid-Pliocene. The need for more comprehensive sea ice proxy data is highlighted, in order to better compare model performances.

Description: A universal error source in past climate estimates derived from tree rings Juhani Rinne, Mikko Alestalo, and Jörg Franke Clim. Past Discuss., doi:10.5194/cp-2016-27,2016 Manuscript under review for CP (discussion: open, 0 comments) The climate reconstructions derived from tree rings tend to show erroneous long-term oscillations. The aim of our paper is to describe the phenomenon and to uncover its reasons. In order to derive formulae describing the long-term error, the dependence of the tree rings on the age is not used in the reconstruction. The erroneous oscillations turn out to be due to data paucities over the years. Accordingly, such long-term errors can be present in any tree ring analysis with such paucities.

Description: Palynological evidence for late Miocene stepwise aridification on the northeastern Tibetan Plateau Jia Liu, Ji Jun Li, Chun Hui Song, Hao Yu, Ting Jiang Peng, Zheng Chuang Hui, and Xi Yan Ye Clim. Past, 12, 1473-1484, doi:10.5194/cp-12-1473-2016, 2016 The late Cenozoic basins in the northeastern Tibetan Plateau document both the tectonic uplift process and its associated environmental changes. Here, we investigated a late Miocene sporopollen record from the Tianshui Basin in the northeastern Tibetan Plateau. The results show that a persistent aridification trend parallels the global cooling of the late Miocene, and the stepwise vegetation succession is consistent with the major uplift events of the Tibetan Plateau.

Description: A 368-year maximum temperature reconstruction based on tree-ring data in the northwestern Sichuan Plateau (NWSP), China Liangjun Zhu, Yuandong Zhang, Zongshan Li, Binde Guo, and Xiaochun Wang Clim. Past, 12, 1485-1498, doi:10.5194/cp-12-1485-2016, 2016 We present a 368-year late summer maximum temperature reconstruction based on spruce tree rings. It touches on the critical topic of climate reconstruction in the eastern edge of Tibetan Plateau and represents an extension and enhancement of climate records for this area. The Little Ice Age was well represented and 20th century warming was not obvious in this reconstruction. This temperature variation may be affected by global land–sea atmospheric circulation as well as solar and volcanic forcing.

Description: Atmospheric methane control mechanisms during the early Holocene Ji-Woong Yang, Jinho Ahn, Edward J. Brook, and Yeongjun Ryu Clim. Past Discuss., doi:10.5194/cp-2016-75,2016 Manuscript under review for CP (discussion: open, 0 comments) The early Holocene climate is chracterized as an interglacial boundary condition without substantial human influence. Here we present a high-resolution CH 4 time series during the early Holocene for investigating a natural control process. The results show that changes in the ITCZ position and Asian summer monsoon intensity were able to induce ~ 20 to 40 ppb CH 4 variability in millennial time scale by changing low latitude emission, while the contribution of boreal sources increased gradually.

Description: The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction Harry Dowsett, Aisling Dolan, David Rowley, Robert Moucha, Alessandro M. Forte, Jerry X. Mitrovica, Matthew Pound, Ulrich Salzmann, Marci Robinson, Mark Chandler, Kevin Foley, and Alan Haywood Clim. Past, 12, 1519-1538, doi:10.5194/cp-12-1519-2016, 2016 Past intervals in Earth history provide unique windows into conditions much different than those observed today. We investigated the paleoenvironments of a past warm interval (~ 3 million years ago). Our reconstruction includes data sets for surface temperature, vegetation, soils, lakes, ice sheets, topography, and bathymetry. These data are being used along with global climate models to expand our understanding of the climate system and to help us prepare for future changes.

Description: Deforestation decreases resistance of simulated Easter Island climate to drought Alexander Lemburg, Martin Claussen, and Felix Ament Clim. Past Discuss., doi:10.5194/cp-2016-68,2016 Manuscript under review for CP (discussion: open, 0 comments) The deforestation of Easter Island several hundred years ago might have influenced its local near-surface climate. With a series of numerical model experiments we investigate the impact of deforestation on precipitation and near-surface climate. We find that a deforested Easter Island appears to be significantly less resistant to drought than a forested island and thus, deforestation has probably exacerbated the effects of past climate drought spells on Easter Island's socio-ecological systems.

Description: Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling Yuhui Liu and Chaoyong Hu Clim. Past, 12, 1583-1590, doi:10.5194/cp-12-1583-2016, 2016 The 8.2 ka BP event, a global climate anomaly that occurred 8200 years ago, could provide climate teleconnection information for the simulation of abrupt climate changes, but there are few quantitative reconstructions of this event. This paper provides a 10-year resolution rainfall record from the East Asian monsoon area during the event, showing the reduced rainfall in southwest China during the 8.2 ka BP period was coupled with Greenland cooling with a possible response rate of 110 ± 30 mm/℃.

Description: An improved North-South synchronization of ice core records around the 41 K beryllium 10 peak G. M. Raisbeck, A. Cauquoin, J. Jouzel, A. Landais, J.-R. Petit, V. Y. Lipenkov, J. Beer, H.-A. Synal, H. Oerter, S. J. Johnsen, J. P. Steffensen, A. Svensson, and F. Yiou Clim. Past Discuss., doi:10.5194/cp-2016-79,2016 Manuscript under review for CP (discussion: open, 0 comments) Using records of a long lived radioactive nuclide ( 10 Be) that is formed globally in the atmosphere and deposited within a few years to the earth's surface, we have synchronized 3 Antarctic ice cores to one from Greenland. This permits the climate and other environmental parameters registered in these ice cores to be put on a common time scale with a precision of a few decades, thus allowing different models and mechanisms associated with these parameters to be tested with the same precision.

Description: The historic reality of the cyclonic variability in French Antilles, 1635–2007 Climate of the Past Discussions, 11, 1519-1550, 2015 Author(s): E. Garnier, J. Desarthe, and D. Moncoulon Facing climate change and increasing costs of natural disasters, the exposure evolution analysis requires having a long-term knowledge of the impacts of extreme events. By associating historical and modeling approaches, we aim to build a long term chronology of natural disaster severity and damages. To highlight this new methodology, the overseas departments of French Antilles have been chosen. These territories are strongly exposed to natural disasters, particularly hurricanes. The search with historical archives made it possible to reconstruct, for the first time, the chronology and severity of hurricanes since the 17th century. During the 20th century, a significative increase in the number of cyclones has occurred after the 1950s. The analysis of a longer historical period (since the 1630s) allows us to temperate this idea by showing intensive cyclonic period in the past centuries.

Description: Stability of the vegetation–atmosphere system in the early Eocene climate Climate of the Past Discussions, 11, 1551-1578, 2015 Author(s): U. Port and M. Claussen We explore the stability of the atmosphere–vegetation system in the warm, almost ice-free early Eocene climate and in the interglacial, pre-industrial climate by analysing the dependence of the system on the initial vegetation cover. The Earth system model of the Max Planck Institute for Meteorology is initialised with either dense forests or bare deserts on all continents. Starting with desert continents, an extended desert remains in Central Asia in early Eocene climate. Starting with dense forest coverage, this desert is much smaller because the initially dense vegetation cover enhances water recycling in Central Asia relative to the simulation with initial deserts. With a smaller Asian desert, the Asian monsoon is stronger than in the case with a larger desert. The stronger Asian monsoon shifts the global tropical circulation leading to coastal subtropical deserts in North and South America which are significantly larger than with a large Asian desert. This result indicates a global teleconnection of the vegetation cover in several regions. In present-day climate, a bi-stability of the atmosphere–vegetation system is found for Northern Africa only. A global teleconnection of bi-stabilities in several regions is absent highlighting that the stability of the vegetation–atmosphere system depends on climatic and tectonic boundary conditions.

Description: The Eocene–Oligocene transition at ODP Site 1263, Atlantic Ocean: decreases in nannoplankton size and abundance and correlation with benthic foraminiferal assemblages Climate of the Past Discussions, 11, 1615-1664, 2015 Author(s): M. Bordiga, J. Henderiks, F. Tori, S. Monechi, R. Fenero, and E. Thomas The biotic response of calcareous nannoplankton to environmental and climatic changes during the Eocene–Oligocene transition (~34.8–32.7 Ma) was investigated at high resolution at Ocean Drilling Program (ODP) Site 1263 (Walvis Ridge, South East Atlantic Ocean), and compared with a lower resolution benthic foraminiferal record. During this time interval, the global climate which had been warm during the Eocene, under high levels of atmospheric CO 2 ( p CO 2 ), transitioned into the cooler climate of the Oligocene, with overall lower p CO 2 . At Site 1263, the absolute nannofossil abundance (coccoliths per gram of sediment; N g −1 ) and the mean coccolith size decreased distinctly across the E–O boundary (EOB; 33.89 Ma), mainly due to a sharp decline in abundance of large-sized Reticulofenestra and Dictyococcites , within ~53 kyr. Since carbonate dissolution did not vary much across the EOB, the decrease in abundance and size of nannofossils may highlight an overall decrease in their export production, which could have led to an increased ratio of organic to inorganic carbon (calcite) burial, as well as variations in the food availability for benthic foraminifers. The benthic foraminiferal assemblage data show the global decline in abundance of rectilinear species with complex apertures in the latest Eocene (~34.5 Ma), potentially reflecting changes in the food source, thus phytoplankton, followed by transient increased abundance of species indicative of seasonal delivery of food to the sea floor ( Epistominella spp.; ~34.04–33.54 Ma), with a short peak in overall food delivery at the EOB (buliminid taxa; ~33.9 Ma). After Oi-1 (starting at ~33.4 Ma), a high abundance of Nuttallides umbonifera indicates the presence of more corrosive bottom waters, possibly combined with less food arriving at the sea floor. The most important signals in the planktonic and benthic communities, i.e. the marked decrease of large reticulofenestrids, extinctions of planktonic foraminifer species and more pronounced seasonal influx of organic matter, preceded the major expansion of the Antarctic ice sheet (Oi-1) by ~440 kyr. During Oi-1, our data show no major change in nannofossil abundance or assemblage composition occurred at Site 1263, although benthic foraminifera indicate more corrosive bottom waters following this event. Marine plankton thus showed high sensitivity to fast-changing conditions, possibly enhanced but pulsed nutrient supply, during the early onset of latest Eocene-earliest Oligocene climate change, or to a threshold in these changes (e.g. p CO 2 decline, high-latitude cooling and ocean circulation).

Description: Stability of ENSO and its tropical Pacific teleconnections over the Last Millennium Climate of the Past Discussions, 11, 1579-1613, 2015 Author(s): S. C. Lewis and A. N. LeGrande Determining past changes in the amplitude, frequency and teleconnections of the El Niño–Southern Oscillation (ENSO) is important for understanding its potential sensitivity to future anthropogenic climate change. Palaeo-reconstructions from proxy records provide long-term information of ENSO interactions with the background climatic state through time. However, it remains unclear how ENSO characteristics have changed through time, and precisely which signals proxies record. Proxy interpretations are underpinned by the assumption of stationarity in relationships between local and remote climates, and often utilise archives from single locations located in the Pacific Ocean to reconstruct ENSO histories. Here, we investigate the stationarity of ENSO teleconnections using the Last Millennium experiment of CMIP5 (Coupled Model Intercomparison Project phase 5) (Taylor et al., 2012). We show that modelled ENSO characteristics vary on decadal- to centennial-scales, resulting from internal variability and external forcings, such as tropical volcanic eruptions. Furthermore, the relationship between ENSO conditions and local climates across the Pacific basin varies throughout the Last Millennium. Results show the stability of teleconnections is regionally dependent and proxies may reveal complex changes in teleconnected patterns, rather than large-scale changes in base ENSO characteristics. As such, proxy insights into ENSO likely require evidence to be synthesised over large spatial areas in order to deconvolve changes occurring in the NINO3.4 region from those pertaining to proxy-relevant local climatic variables. To obtain robust histories of the ENSO and its remote impacts, we recommend interpretations of proxy records should be considered in conjunction with palaeo-reconstructions from within the Central Pacific.

Description: Rapid millennial-scale vegetation changes in the tropical Andes Climate of the Past Discussions, 11, 1701-1739, 2015 Author(s): D. H. Urrego, H. Hooghiemstra, O. Rama-Corredor, B. Martrat, J. O. Grimalt, L. Thompson, and Data Contributors We compare eight pollen records reflecting climatic and environmental change from the tropical Andes. Our analysis focuses on the last 50 ka, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations, and precipitation change. Our analysis focuses on the signature of millennial-scale variability in the tropical Andes, in particular, Heinrich stadials and Greenland interstadials. We identify rapid responses of the tropical vegetation to this climate variability, and relate differences between sites to moisture sources and site sensitivity.

Description: Astronomical calibration of the geological timescale: closing the middle Eocene gap Climate of the Past Discussions, 11, 1665-1699, 2015 Author(s): T. Westerhold, U. Röhl, T. Frederichs, S. M. Bohaty, and J. C. Zachos To explore cause and consequences in past climate reconstructions highly accuracy age models are inevitable. The highly accurate astronomical calibration of the geological time scale beyond 40 million years critically depends on the accuracy of orbital models and radio-isotopic dating techniques. Discrepancies in the age dating of sedimentary successions and the lack of suitable records spanning the middle Eocene have prevented development of a continuous astronomically calibrated geological timescale for the entire Cenozoic Era. We now solve this problem by constructing an independent astrochronological stratigraphy based on Earth's stable 405 kyr eccentricity cycle between 41 and 48 million years ago (Ma) with new data from deep-sea sedimentary sequences in the South Atlantic Ocean. This new link completes the Paleogene astronomical time scale and confirms the intercalibration of radio-isotopic and astronomical dating methods back through the Paleocene-Eocene Thermal Maximum (PETM, 55.930 Ma) and the Cretaceous/Paleogene boundary (66.022 Ma). Coupling of the Paleogene 405 kyr cyclostratigraphic frameworks across the middle Eocene further paves the way for extending the Astronomical Time Scale (ATS) into the Mesozoic.

Description: Frequency, magnitude and character of hyperthermal events at the onset of the Early Eocene Climatic Optimum Climate of the Past Discussions, 11, 1795-1820, 2015 Author(s): V. Lauretano, K. Littler, M. Polling, J. C. Zachos, and L. J. Lourens Recent studies have shown that the Early Eocene Climatic Optimum (EECO) was preceded by a series of short-lived global warming events, known as hyperthermals. Here we present high-resolution benthic stable carbon and oxygen isotope records from ODP Sites 1262 and 1263 (Walvis Ridge, SE Atlantic) between ∼54 and ∼52 million years ago, tightly constraining the character, timing, and magnitude of six prominent hyperthermal events. These events, that include Eocene Thermal Maximum (ETM) 2 and 3, are studied in relation to orbital forcing and long-term trends. Our findings reveal an almost linear relationship between δ 13 C and δ 18 O for all these hyperthermals, indicating that the eccentricity-paced co-variance between extreme perturbations in the exogenic carbon pool and deep-sea temperatures persisted during the onset of the EECO, in accord with previous observations for the Paleocene Eocene Thermal Maximum (PETM) and ETM2. The covariance of δ 13 C and δ 18 O during H2 and I2, which are the second pulses of the "paired" hyperthermal events ETM2-H2 and I1-I2, deviates with respect to the other events. This could relate to a relatively higher contribution of an isotopically heavier source of carbon, such as peat or permafrost, and/or to climate feedbacks/local changes in circulation. Finally, the δ 18 O records of the two sites show a systematic offset with on average 0.2‰ heavier values for the shallower Site 1263, which we link to a slightly heavier (e.g. more saline) isotope composition of the intermediate water mass reaching the northeastern flank of the Walvis Ridge compared to that of the deeper northwestern water mass at Site 1262.

Description: A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 1816 Climate of the Past Discussions, 11, 1741-1794, 2015 Author(s): Y. Brugnara, R. Auchmann, S. Brönnimann, R. J. Allan, I. Auer, M. Barriendos, H. Bergström, J. Bhend, R. Brázdil, G. P. Compo, R. C. Cornes, F. Dominguez-Castro, A. F. V. van Engelen, J. Filipiak, J. Holopainen, S. Jourdain, M. Kunz, J. Luterbacher, M. Maugeri, L. Mercalli, A. Moberg, C. J. Mock, G. Pichard, L. Řezníčková, G. van der Schrier, V. Slonosky, Z. Ustrnul, M. A. Valente, A. Wypych, and X. Yin The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It caused a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than fifty sub-daily series from land observatories in Europe and North America, and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level, moreover an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected dataset, the variance of the pressure observations is compared with modern climatologies and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.

Description: Radiative forcing by forest and subsequent feedbacks in the early Eocene climate Climate of the Past Discussions, 11, 997-1029, 2015 Author(s): U. Port, M. Claussen, and V. Brovkin Using the Max Planck Institute for Meteorology Earth System Model, we investigate the forcing of forests and the feedback triggered by forests in the pre-industrial climate and in the early Eocene climate (about 54 to 52 million years ago). Other than the interglacial, pre-industrial climate, the early Eocene climate was characterised by high temperatures which led to almost ice-free poles. We compare simulations in which all continents are covered either by dense forest or by bare soil. To isolate the effect of soil albedo, we choose either bright soils or dark soils, respectively. Considering bright soil, forests warm in both, the early Eocene climate and the current climate, but the warming differs due to differences in climate feedbacks. The lapse-rate and water-vapour feedback is stronger in early Eocene climate than in current climate, but strong and negative cloud feedbacks and cloud masking in the early Eocene climate outweigh the stronger positive lapse-rate and water-vapour feedback. In the sum, global mean warming is weaker in the early Eocene climate. Sea-ice related feedbacks are weak in the almost ice-free climate of the early Eocene leading to a weak polar amplification. Considering dark soil, our results change. Forests cools stronger in the early Eocene climate than in the current climate because the lapse-rate and water-vapour feedback is stronger in the early Eocene climate while cloud feedbacks and cloud masking are equally strong in both climates. The different temperature change by forest in both climates highlights the state-dependency of vegetation's impact on climate.

Description: Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana basin) and high latitude climate signals over the last 140 000 years Climate of the Past Discussions, 11, 1143-1175, 2015 Author(s): O. Rama-Corredor, B. Martrat, J. O. Grimalt, G. E. López-Otalvaro, J. A. Flores, and F. Sierro Sea surface temperatures (SST) in the Guiana basin over the last 140 ka were obtained by measuring the C37 alkenone unsaturation index U 37 ' k in sediment core MD03-2616 (7° N, 53° W). The resulting dataset is unique for this period in the western tropical Atlantic region. SSTs range from 25.1 to 28.9 °C, i.e. glacial-to-interglacial amplitude of 3.8 °C, which is common in tropical areas. During the last two interglacials (MIS1 and MIS5e) and warm long interstadials (MIS5d-a), the sediments studied trace rapid transmission of the climate variability from arctic-to-tropical latitudes and vice-versa. During these periods, MD03-2616 SSTs showed a remarkable parallelism with temperature changes observed in Greenland and SST records of North Atlantic cores. The last deglaciation in Guiana is particularly revealing. MIS2 stands out as the coldest period of the interval analysed, with SSTs reaching as low as 25.1 °C. It contains reminders of northern latitude events such as the Bølling-Allerød warming and the Younger Dryas cooling which ensued. These oscillations were previously documented in the δ 18 O of the Sajama tropical ice core and are present in Guiana with rates of ca. 6 °C ka −1 and changes of over 2 °C. During the glacial interval, significant abrupt variability is observed; e.g. oscillations of 0.5–1.2 °C during MIS3, i.e. about 30% of the maximum glacial–interglacial SST change. Nevertheless, in the MD03-2616 record it is hard to identify unambiguously either the Dansgaard–Oeschger type of oscillations described in northern latitudes or the SST drops associated with the Heinrich events characterising North Atlantic records. Although these specific events form the background of the climate variability observed, what truly shapes SSTs in Guiana is a long-term tropical response to precessional changes, which is modulated in the opposite way to polar variability. This lack of synchrony is consistent with other tropical records in locations to the north or south of Guiana and evidences an arctic-to-tropical decoupling when a substantial reduction in the Atlantic meridional overturning circulation (AMOC) takes place.

Description: Optimal Ranking Regime analysis of TreeFlow dendrohydrological reconstructions Climate of the Past Discussions, 11, 755-803, 2015 Author(s): S. A. Mauget The Optimal Ranking Regime (ORR) method was used to identify 6–100 year time windows containing significant ranking sequences in 55 western US streamflow reconstructions, and reconstructions of the level of the Great Salt Lake and San Francisco Bay salinity during 1500–2007. The method's ability to identify optimally significant and non-overlapping runs of low and high rankings allows it to re-express a reconstruction time series as a simplified sequence of regime segments marking intra- to multi-decadal (IMD) periods of low or high streamflow, lake level, or salinity. Those ORR sequences, referred to here as Z lines, can be plotted to identify consistent regime patterns in the analysis of numerous reconstructions. The Z lines for the 57 reconstructions evaluated here show a common pattern of IMD cycles of drought and pluvial periods during the late 16th and 17th centuries, a relatively dormant period during the 18th century, and the reappearance of alternating dry and wet IMD periods during the 19th and early 20th centuries. Although this pattern suggests the possibility of similarly active and inactive oceanic modes in the North Pacific and North Atlantic, such centennial-scale patterns are not evident in the ORR analyses of reconstructed Pacific Decadal Oscillation (PDO), El Niño–Southern Oscillation, and North Atlantic seas-surface temperature variation. But given the inconsistency in the analyses of four PDO reconstructions the possible role of centennial-scale oceanic mechanisms is uncertain. In future research the ORR method might be applied to climate reconstructions around the Pacific Basin to try to resolve this uncertainty. Given its ability to compare regime patterns in climate reconstructions derived using different methods and proxies, the method may also be used in future research to evaluate long-term regional temperature reconstructions.

Description: On the occurrence of annual layers in Dome Fuji ice core early Holocene ice Climate of the Past Discussions, 11, 805-830, 2015 Author(s): A. Svensson, S. Fujita, M. Bigler, M. Braun, R. Dallmayr, V. Gkinis, K. Goto-Azuma, M. Hirabayashi, K. Kawamura, S. Kipfstuhl, H. A. Kjær, T. Popp, M. Simonsen, J. P. Steffensen, P. Vallelonga, and B. M. Vinther Whereas ice cores from high accumulation sites in coastal Antarctica clearly demonstrate annual layering, it is debated whether a seasonal signal is also preserved in ice cores from lower accumulation sites further inland and particularly on the East Antarctic Plateau. In this study, we examine five metres of early Holocene ice from the Dome Fuji (DF) ice core in high temporal resolution by continuous flow analysis. The ice was continuously analyzed for concentrations of dust, sodium, ammonium, liquid conductivity, and water isotopic composition. Furthermore, a dielectric profiling was performed on the solid ice. In most of the analyzed ice, the multi-parameter impurity dataset appears to resolve the seasonal variability although the identification of annual layers is not always unambiguous. A layer counting based on the same principles as those previously applied to the Greenland NGRIP and the Antarctic EPICA Dronning Maud Land (EDML) ice cores leads to a mean annual layer thickness for the DF ice of 3.0 ± 0.3 cm that compares well to existing estimates. The measured DF section is linked to the EDML ice core through a characteristic pattern of three significant acidity peaks that are present in both cores. The corresponding section of the EDML ice core has recently been dated by annual layer counting and the number of years identified independently in the two cores agree within error estimates. We therefore conclude that, to first order, the annual signal is preserved in this section of the DF core. This case study demonstrates the feasibility of determining annually deposited strata on the central Eastern Antarctic Plateau. It also opens the possibility of resolving annual layers in the Eemian section of the DF ice core where the accumulation is estimated to have been greater than in the Holocene.

Description: Quality assessment of chronologies in Latin American pollen records: a contribution to centennial to millennial scale studies of environmental change Climate of the Past Discussions, 11, 1219-1262, 2015 Author(s): S. G. A. Flantua, H. Hooghiemstra, and M. Blaauw The newly updated inventory of the Latin American Pollen Database (LAPD) offers an important overview of data available for multi-proxy and multi-site purposes. However, heterogeneous paleoecological databases are not suitable to be integrated without an uncertainty assessment of existing chronologies. Therefore, we collected all chronological control points and age model metadata from the LAPD literature to create a complementary chronological database of 5116 dates from 1097 pollen records. We start with an overview on chronological dating and reporting in Central and South America. Specific problems and recommendations for chronology reporting are discussed. Subsequently, we implement a temporal quality assessment of pollen records from northwest South-America to support research on climate forcers and responses at a centennial-millennial time-scale. New chronologies are generated for 233 pollen records based on updated calibration curves. Different time windows are discussed on sample resolution and temporal uncertainty. Approximately one in four pollen diagrams depicts 〈 500 years resolution data at the Younger Dryas/Holocene transition. Overall, our analyses suggest that the temporal resolution of multi-site syntheses of late Pleistocene fossil pollen records in the northwest South-America is ca. 240 years, a resolution which allows analysis of ecological responses to centennial-millennial-scale climate change during the last deglaciation.

Description: Arctic sea ice in the PlioMIP ensemble: is model performance for modern climates a reliable guide to performance for the past or the future? Climate of the Past Discussions, 11, 1263-1312, 2015 Author(s): F. W. Howell, A. M. Haywood, B. L. Otto-Bliesner, F. Bragg, W.-L. Chan, M. A. Chandler, C. Contoux, Y. Kamae, A. Abe-Ouchi, N. A. Rosenbloom, C. Stepanek, and Z. Zhang Eight general circulation models have simulated the mid-Pliocene Warm Period (mPWP, 3.264 to 3.025 Ma) as part of the Pliocene Modelling Intercomparison Project (PlioMIP). Here, we analyse and compare their simulation of Arctic sea ice for both the pre-industrial and the mid-Pliocene. Mid-Pliocene sea ice thickness and extent is reduced and displays greater variability within the ensemble compared to the pre-industrial. This variability is highest in the summer months, when the model spread in the mid-Pliocene is more than three times larger than the rest of the year. Correlations between mid-Pliocene Arctic temperatures and sea ice extents are almost twice as strong as the equivalent correlations for the pre-industrial simulations. It is suggested that the weaker relationship between pre-industrial Arctic sea ice and temperatures is likely due to the tuning of climate models to achieve an optimal pre-industrial sea ice cover, which may also affect future predictions of Arctic sea ice. Model tuning for the pre-industrial does not appear to be best suited for simulating the different climate state of the mid-Pliocene. This highlights the importance of evaluating climate models through simulation of past climates, and the urgent need for more proxy evidence of sea ice during the Pliocene.

Description: Mammal faunal response to the Paleogene hyperthermals ETM2 and H2 Climate of the Past Discussions, 11, 1371-1405, 2015 Author(s): A. E. Chew Scientists are increasingly turning to deep-time fossil records to decipher the long-term consequences of climate change in the race to preserve modern biotas from anthropogenically driven global warming. "Hyperthermals" are past intervals of geologically rapid global warming that provide the opportunity to study the effects of climate change on existing faunas over thousands of years. A series hyperthermals is known from the early Eocene (∼56–54 million years ago), including the Paleocene-Eocene Thermal Maximum (PETM) and two subsequent hyperthermals, Eocene Thermal Maximum 2 (ETM2) and H2. The later hyperthermals occurred following the onset of warming at the Early Eocene Climatic Optimum (EECO), the hottest sustained period of the Cenozoic. The PETM has been comprehensively studied in marine and terrestrial settings, but the terrestrial biotic effects of ETM2 and H2 are unknown. Their geochemical signatures have been located in the northern part of the Bighorn Basin, WY, USA, and their levels can be extrapolated to an extraordinarily dense, well-studied terrestrial mammal fossil record in the south-central part of the basin. High-resolution, multi-parameter paleoecological analysis reveals significant peaks in species diversity and turnover and changes in abundance and relative body size at the levels of ETM2 and H2 in the south-central Bighorn Basin record. In contrast with the PETM, faunal change at the later hyperthermals is less extreme, does not include immigration and involves a proliferation of body sizes, although abundance shifts tend to favor smaller congeners. Faunal response at ETM2 and H2 is distinctive in its high proportion of species losses potentially related to heightened species vulnerability in response to the changes already underway at the beginning of the EECO. Faunal response at ETM2 and H2 is also distinctive in high proportions of beta richness, suggestive of increased geographic dispersal related to transient increases in habitat (floral) complexity and/or precipitation or seasonality of precipitation. These results suggest that rapid ecological changes, increased heterogeneity in species incidence, and heightened species vulnerability and loss may be expected across most of North America in the near future in response to anthropogenically-driven climate change.

Description: Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events Climate of the Past Discussions, 11, 1407-1435, 2015 Author(s): O. Margalef, I. Cacho, S. Pla-Rabes, N. Cañellas-Boltà, J. J. Pueyo, A. Sáez, L. D. Pena, B. L. Valero-Garcés, V. Rull, and S. Giralt Marine Isotope Stage 3 (MIS 3, 59.4–27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard–Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard–Oeschger stadials.

Description: Mode transitions in Northern Hemisphere Glaciation: Co-evolution of millennial and orbital variability in Quaternary climate David A. Hodell and James E.T. Channell Clim. Past Discuss., doi:10.5194/cp-2016-30,2016 Manuscript under review for CP (discussion: open, 0 comments) For the past 2.7 million years the Earth’s climate has switched more than 50 times between a cold glacial and warm interglacial state. We found the trend towards larger ice sheets over the past 2.7 million years was accompanied by changes in the style, frequency and intensity of shorter-term (millennial) variability. We suggest the interaction between millennial climate change and longer-term variations in the Earth's orbit may be important for explaining the patterns of Quaternary climate.

Description: Extreme flood events reconstruction during the last century in the El Bibane lagoon (Southeast of Tunisia): A Multi-proxy Approach A. Affouri, L. Dezileau, and N. Kallel Clim. Past Discuss., doi:10.5194/cp-2016-40,2016 Manuscript under review for CP (discussion: open, 0 comments) The past flood activity was investigated using a sedimentological and geochemical analysis of surfaces sediments from the Southeast of Tunisia catchment in order to trace the origin of sediments deposit in the El Bibane lagoon. Aeolian, fluvial and marine source. This multi-proxy analysis on the BL12-10 core shows that finer material, high content of clay and silt, and high content of the elemental ratio Fe/Ca and Ti/Ca characterize the sedimentological signature of paleoflood levels.

Description: Terrigenous material supply to the Peruvian central continental shelf (Pisco, 14° S) during the last 1000 years: paleoclimatic implications Francisco Javier Briceño-Zuluaga, Abdelfettah Sifeddine, Sandrine Caquineau, Jorge Cardich, Renato Salvatteci, Dimitri Gutierrez, Luc Ortlieb, Federico Velazco, Hugues Boucher, and Carine Machado Clim. Past, 12, 787-798, doi:10.5194/cp-12-787-2016, 2016 Comparison between records reveals a coherent match between the meridional displacement of the ITCZ-SPSH system and the regional fluvial and aeolian terrigenous input variability. The aeolian input intensity and the anoxic conditions recorded by marine sediments showed a close link that suggests a common mechanism associated with SPSH displacement. Changes in sediment discharge to the continental shelf are linked to the southward displacement of the ITCZ-SPSH and Walker circulation.

Description: Solar modulation of flood frequency in central Europe during spring and summer on interannual to multi-centennial timescales Markus Czymzik, Raimund Muscheler, and Achim Brauer Clim. Past, 12, 799-805, doi:10.5194/cp-12-799-2016, 2016 Integrating discharge data of the River Ammer back to 1926 and a 5500-year flood layer record from an annually laminated sediment core of the downstream Ammersee allowed investigating changes in the frequency of major floods in Central Europe on interannual to multi-centennial timescales. Significant correlations between flood frequency variations in both archives and changes in the activity of the Sun suggest a solar influence on the frequency of these hydrometeorological extremes.

Description: Wind regimes during the Last Glacial Maximum and early Holocene: evidence from Little Llangothlin Lagoon, New England Tableland, eastern Australia James Shulmeister, Justine Kemp, Kathryn E. Fitzsimmons, and Allen Gontz Clim. Past Discuss., doi:10.5194/cp-2016-41,2016 Manuscript under review for CP (discussion: open, 0 comments) This paper highlights that small dunes (a lunette) formed on the eastern side of a lake in the Australian sub-tropics at the height of the last ice age (about 21 000 years ago) and in the early part of the current interglacial (9–6000 years ago). This means that it was fairly wet at these times and also that there were strong westerly winds to form the dunes. Today strong westerly winds occur in winter and we infer that the same was also true at those times, suggesting no change in circulation.

Description: The climate reconstruction in Shandong Peninsula, northern China, during the last millennium based on stalagmite laminae together with a comparison to δ 18 O Qing Wang, Houyun Zhou, Ke Cheng, Hong Chi, Chuan-Chou Shen, Changshan Wang, and Qianqian Ma Clim. Past, 12, 871-881, doi:10.5194/cp-12-871-2016, 2016 The upper part of stalagmite ky1 (from top to 42.769 mm depth), consisting of 678 laminae, was collected from a cave in northern China, located in the East Asia monsoon area. The time of deposition ranges from AD 1217±20 to 1894±20. The analysis shows that both the variations in the thickness of the laminae themselves and the fluctuating degree of variation in the thickness of the laminae of stalagmite ky1 have obviously staged characteristics and synchronized with climate.

Description: Optimal site selection for a high-resolution ice core record in East Antarctica Tessa R. Vance, Jason L. Roberts, Andrew D. Moy, Mark A. J. Curran, Carly R. Tozer, Ailie J. E. Gallant, Nerilie J. Abram, Tas D. van Ommen, Duncan A. Young, Cyril Grima, Don D. Blankenship, and Martin J. Siegert Clim. Past, 12, 595-610, doi:10.5194/cp-12-595-2016, 2016 This study details a systematic approach to finding a new high-resolution East Antarctic ice core site. The study initially outlines seven criteria that a new site must fulfil, encompassing specific accumulation, ice dynamics and atmospheric circulation aspects. We then use numerous techniques including Antarctic surface mass balance syntheses, ground-truthing of satellite data by airborne radar surveys and reanalysis products to pinpoint promising regions.

Description: Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores Lucie Bazin, Amaelle Landais, Emilie Capron, Valérie Masson-Delmotte, Catherine Ritz, Ghislain Picard, Jean Jouzel, Marie Dumont, Markus Leuenberger, and Frédéric Prié Clim. Past, 12, 729-748, doi:10.5194/cp-12-729-2016, 2016 We present new measurements of δ O 2 ⁄N 2 and δ 18 O atm performed on well-conserved ice from EDC covering MIS5 and between 380 and 800 ka. The combination of the observation of a 100 ka periodicity in the new δ O 2 ⁄N 2 record with a MIS5 multi-site multi-proxy study has revealed a potential influence of local climatic parameters on δ O 2 ⁄N 2 . Moreover, we propose that the varying delay between d18Oatm and precession for the last 800 ka is affected by the occurrence of ice sheet discharge events.

Description: The role of basal hydrology in the surging of the Laurentide Ice Sheet William H. G. Roberts, Antony J. Payne, and Paul J. Valdes Clim. Past Discuss., doi:10.5194/cp-2016-17,2016 Manuscript under review for CP (discussion: open, 0 comments) There are observations from ocean sediment cores that during the last ice age the Laurentide Ice Sheet, which sat over North America, periodically surged. In this study we show the role that water at the base of an ice sheet plays in these surges. We show that with a more realistic representation of water drainage at the base of the ice sheet than usually used, these surges can still occur and that they are triggered by an internal ice sheet instability: no external trigger is needed.

Description: Paleoclimate in continental northwestern Europe during the Eemian and Early-Weichselian (125–97 ka): insights from a Belgian speleothem Stef Vansteenberge, Sophie Verheyden, Hai Cheng, Lawrence R. Edwards, Eddy Keppens, and Philippe Claeys Clim. Past Discuss., doi:10.5194/cp-2016-15,2016 Manuscript under review for CP (discussion: open, 0 comments) The use of stalagmites for Last Interglacial continental climate reconstructions in Europe has been successful in the past, however to expand the geographical coverage additional data from Belgium is presented. It has been shown that stalagmite growth, morphology and stable isotope content reflect regional and local climate conditions, with Eemian optimum climate occurring between 125.3 and 117.3 ka. The start the Weichselian is expressed by a stop of growth caused by a drying climate.

Description: The WAIS Divide deep ice core WD2014 chronology – Part 2: Annual-layer counting (0–31 ka BP) Michael Sigl, Tyler J. Fudge, Mai Winstrup, Jihong Cole-Dai, David Ferris, Joseph R. McConnell, Ken C. Taylor, Kees C. Welten, Thomas E. Woodruff, Florian Adolphi, Marion Bisiaux, Edward J. Brook, Christo Buizert, Marc W. Caffee, Nelia W. Dunbar, Ross Edwards, Lei Geng, Nels Iverson, Bess Koffman, Lawrence Layman, Olivia J. Maselli, Kenneth McGwire, Raimund Muscheler, Kunihiko Nishiizumi, Daniel R. Pasteris, Rachael H. Rhodes, and Todd A. Sowers Clim. Past, 12, 769-786, doi:10.5194/cp-12-769-2016, 2016 Here we present a chronology (WD2014) for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide ice core, which is based on layer counting of distinctive annual cycles preserved in the elemental, chemical and electrical conductivity records. We validated the chronology by comparing it to independent high-accuracy, absolutely dated chronologies. Given its demonstrated high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere.

Description: Model simulations of early westward flow across the Tasman Gateway during the early Eocene Willem P. Sijp, Anna S. von der Heydt, and Peter K. Bijl Clim. Past, 12, 807-817, doi:10.5194/cp-12-807-2016, 2016 The timing and role in ocean circulation and climate of the opening of Southern Ocean gateways is as yet elusive. Here, we present the first model results specific to the early-to-middle Eocene where, in agreement with the field evidence, a southerly shallow opening of the Tasman Gateway does indeed cause a westward flow across the Tasman Gateway, in agreement with recent micropalaeontological studies.

Description: Sea surface temperature variability in the central-western Mediterranean Sea during the last 2700 years: a multi-proxy and multi-record approach Mercè Cisneros, Isabel Cacho, Jaime Frigola, Miquel Canals, Pere Masqué, Belen Martrat, Marta Casado, Joan O. Grimalt, Leopoldo D. Pena, Giulia Margaritelli, and Fabrizio Lirer Clim. Past, 12, 849-869, doi:10.5194/cp-12-849-2016, 2016 We present a high-resolution multi-proxy study about the evolution of sea surface conditions along the last 2700 yr in the north-western Mediterranean Sea based on five sediment records from two different sites north of Minorca. The novelty of the results and the followed approach, constructing stack records from the studied proxies to preserve the most robust patterns, provides a special value to the study. This complex period appears to have significant regional changes in the climatic signal.

Description: Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes April N. Abbott, Brian A. Haley, Aradhna K. Tripati, and Martin Frank Clim. Past, 12, 837-847, doi:10.5194/cp-12-837-2016, 2016 The Paleocene-Eocene Thermal Maximum (PETM) was a brief period when the Earth was in an extreme greenhouse state. We use neodymium isotopes to suggest that during this time deep-ocean circulation was distinct in each basin (North and South Atlanic, Southern, Pacific) with little exchange between. Moreover, the Pacific data show the most variability, suggesting this was a critical region possibly involved in both PETM triggering and remediation.

Description: Late Pleistocene to Holocene climate and limnological changes at Lake Karakul (Pamir Mountains, Tajikistan) Liv Heinecke, Steffen Mischke, Karsten Adler, Anja Barth, Boris K. Biskaborn, Birgit Plessen, Ingmar Nitze, Gerhard Kuhn, Ilhomjon Rajabov, and Ulrike Herzschuh Clim. Past Discuss., doi:10.5194/cp-2016-34,2016 Manuscript under review for CP (discussion: open, 0 comments) The climate history of the Pamir Mountains (Tajikistan) during the last ~29 kyr was investigated using sediments from Lake Karakul as environmental archive. The inferred lake level was highest from the Late Glacial to the early Holocene and lake changes were mainly coupled to climate change. We conclude that the joint influence of Westerlies and Indian Monsoon during the early Holocene caused comparatively moist conditions, while dominating Westerlies yielded dry conditions since 6.7 cal kyr BP.

Description: 〈b〉Effect of high dust amount on surface temperature during the Last Glacial Maximum: a modelling study using MIROC-ESM〈/b〉〈br〉 Rumi Ohgaito, Ayako Abe-Ouchi, Ryouta O'ishi, Toshihiko Takemura, Akinori Ito, Tomohiro Hajima, Shingo Watanabe, and Michio Kawamiya〈br〉 Clim. Past, 14, 1565-1581, https://doi.org/10.5194/cp-14-1565-2018, 2018〈br〉 The behaviour of dust in terms of climate can be investigated using past climate. The Last Glacial Maximum (LGM; 21000 years before present) is known to be dustier. We investigated the impact of plausible dust distribution on the climate of the LGM using an Earth system model and found that the higher dust load results in less cooling over the polar regions. The main finding is that radiative perturbation by the high dust loading does not necessarily cool the surface surrounding Antarctica.

Description: 〈b〉Influence of radiative forcing factors on ground–air temperature coupling during the last millennium: implications for borehole climatology〈/b〉〈br〉 Camilo Melo-Aguilar, J. Fidel González-Rouco, Elena García-Bustamante, Jorge Navarro-Montesinos, and Norman Steinert〈br〉 Clim. Past, 14, 1583-1606, https://doi.org/10.5194/cp-14-1583-2018, 2018〈br〉 Air–ground temperature coupling is the central assumption of borehole temperature reconstructions. Here, this premise is assessed from a pseudo-reality perspective by considering last millennium ensembles of simulations from the Community Earth System Model. The results show that long-term variations in the energy fluxes at the surface during industrial times, due to the influence of external forcings, impact the long-term air–ground temperature coupling.

Description: 〈b〉Strength and limits of transient mid to late Holocene simulations with dynamical vegetation〈/b〉〈br〉 Pascale Braconnot, Dan Zhu, Olivier Marti, and Jérôme Servonnat〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-140,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 This study discusses a simulation of the last 6000 years realized with a climate model in which vegetation and carbon cycle are fully interactive. The long term southward shift in northern hemisphere tree line and Afro-Asian monsoon rain are reproduced. The results show substantial change in tree composition with time over Eurasia and the role of traces gazes in the recent past. They highlight the limitations due to model set up and multiple pre-industrial vegetation states.

Description: 〈b〉The 4.2 ka BP Event in the Mediterranean Region: an overview〈/b〉〈br〉 Monica Bini, Giovanni Zanchetta, Aurel Persoiu, Rosine Cartier, Albert Català, Isabel Cacho, Jonathan R. Dean, Federico Di Rita, Russell N. Drysdale, Martin Finnè, Ilaria Isola, Bassem Jalali, Fabrizio Lirer, Donatella Magri, Alessia Masi, Leszek Marks, Anna Maria Mercuri, Odile Peyron, Laura Sadori, Marie-Alexandrine Sicre, Fabian Welc, Christoph Zielhofer, and Elodie Brisset〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-147,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 2 comments)〈br〉 The Mediterranean region has returned some of the clearest evidence of a climatically dry period occurring at ca. 4200 years ago. We reviewed selected proxies to infer regional climate patterns between 4.3 and 3.8 cal ka BP. Temperature data suggest a cooling anomaly, even if this is not uniform, whereas winter was drier along with dry summers. However, some exceptions to this prevail, where wetter condition seems to have persisted, suggesting regional heterogeneity.

Description: 〈b〉Varying regional δ〈sup〉18〈/sup〉O–temperature relationship in high resolution stable water isotopes from East Greenland〈/b〉〈br〉 Christian Holme, Vasileios Gkinis, Mika Lanzky, Valerie Morris, Martin Olesen, Abigail Thayer, Bruce H. Vaughn, and Bo M. Vinther〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-169,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 1 comment)〈br〉 This study investigates the linear relationship between the water isotopes of three East Greenland ice cores and regional temperatures. By comparing the water isotopes with nearby instrumental temperature records and reanalysis data, this study demonstrates that it can be problematic to reconstruct temperatures through regression of water isotope data from coastal ice cores. We further show that the varying linear relationship could be connected with changes in sea ice near the drill site.

Description: 〈b〉Identifying teleconnections and multidecadal variability of East Asian surface temperature during the last millennium in CMIP5 simulations〈/b〉〈br〉 Satyaban B. Ratna, Timothy J. Osborn, Manoj Joshi, Bao Yang, and Jianglin Wang〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-164,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 1 comment)〈br〉 We examine the relationships in models and reconstructions between multidecadal variability of East Asian temperature and two extratropical modes of variability. The relationship between East Asian temperature and Pacific multidecadal variability is largely driven by internal variability, whereas with Atlantic multidecadal variability it is more strongly influenced by the presence or absence of external forcing. We discuss the implications for diagnosing teleconnections from reconstructions.

Description: 〈b〉Late Miocene to Recent High Resolution Eastern Equatorial Pacific Carbonate Records: Stratigraphy linked by dissolution and paleoproductivity〈/b〉〈br〉 Mitchell Lyle, Anna Joy Drury, Jun Tian, Roy Wilkens, and Thomas Westerhold〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-157,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 Ocean sediment records document changes in Earth's carbon cycle and ocean productivity. We present 8 Myr CaCO〈sub〉3〈/sub〉 and bulk sediment records matched from 7 eastern Pacific scientific drill sites to identify intervals of excess CaCO〈sub〉3〈/sub〉 dissolution (high carbon storage in the oceans) and excess burial of plankton hard parts indicating high productivity. We define the regional extent of production intervals and explore the impact of the closure of the Atlantic-Pacific Panama connection on CaCO〈sub〉3〈/sub〉 burial.

Description: 〈b〉Equilibrium simulations of Marine Isotope Stage 3 climate〈/b〉〈br〉 Chuncheng Guo, Kerim H. Nisancioglu, Mats Bentsen, Ingo Bethke, and Zhongshi Zhang〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-165,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 1 comment)〈br〉 We present an equilibrium simulation of the climate of Marine Isotope Stage 3, with an IPCC-class model with a relatively high model resolution and a long integration. The simulated climate resembles a warm interstadial state, as indicated by reconstructions of Greenland temperature, sea ice extent, and AMOC. Sensitivity experiments to changes in atmospheric CO〈sub〉2〈/sub〉 levels and ice sheet size show that the model is in a relatively stable climate state without multiple equilibria.

Description: 〈b〉Evaluating the timing and structure of the 4.2 ka event in the Indian summer monsoon domain from an annually resolved speleothem record from Northeast India〈/b〉〈br〉 Gayatri Kathayat, Hai Cheng, Ashish Sinha, Max Berkelhammer, Haiwei Zhang, Pengzhen Duan, Hanying Li, Xianglei Li, Youfeng Ning, and R. Lawrence Edwards〈br〉 Clim. Past, 14, 1869-1879, https://doi.org/10.5194/cp-14-1869-2018, 2018〈br〉 The 4.2 ka event is generally characterized as an approximately 300-year period of major global climate anomaly. However, the climatic manifestation of this event remains unclear in the Indian monsoon domain. Our high-resolution and precisely dated speleothem record from Meghalaya, India, characterizes the event as consisting of a series of multi-decadal droughts between 3.9 and 4.0 ka rather than a singular pulse of multi-centennial drought as previously thought.

Description: 〈b〉Sedproxy: a forward model for sediment-archived climate proxies〈/b〉〈br〉 Andrew M. Dolman and Thomas Laepple〈br〉 Clim. Past, 14, 1851-1868, https://doi.org/10.5194/cp-14-1851-2018, 2018〈br〉 Climate proxies from marine sediments provide an important record of past temperatures, but contain noise from many sources. These include mixing by burrowing organisms, seasonal and habitat biases, measurement error, and small sample size effects. We have created a forward model that simulates the creation of proxy records and provides it as a user-friendly R package. It allows multiple sources of uncertainty to be considered together when interpreting proxy climate records.

Description: 〈b〉Holocene hydrography evolution in the Alboran Sea: a multi-record and multiproxy comparison〈/b〉〈br〉 Albert Català, Isabel Cacho, Jaime Frigola, Leopoldo D. Pena, and Fabrizio Lirer〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-163,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 1 comment)〈br〉 We present a new high-resolution sea surface temperature (SST) reconstruction for the Holocene (last 11 700 years) in the westernmost Mediterranean See. We identify that the Holocene describes three sub-periods. Early-Holocene with warmest SST, the Middle-Holocene with a cooling trend ending at 4200 years which is identified as a double peak cooling event that marks the transition between the Middle and Late Holocene with very different behaviour in both long and short term SST variability.

Description: 〈b〉Spiky Fluctuations and Scaling in High-Resolution EPICA Ice Core Dust Fluxes〈/b〉〈br〉 Shaun Lovejoy and Fabrice Lambert〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-171,2019〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 We analyze the statistical properties of the eight past glacial-interglacial cycles as well as subsections of a generic glacial cycle using the high-resolution dust flux dataset from the Antarctic EPICA Dome C ice core. We show that the high southern latitude climate during glacial maxima, interglacial, and glacial inception is generally more stable but more drought-prone than during mid-glacial conditions.

Description: 〈b〉What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?〈/b〉〈br〉 Thomas Münch and Thomas Laepple〈br〉 Clim. Past, 14, 2053-2070, https://doi.org/10.5194/cp-14-2053-2018, 2018〈br〉 Proxy data on climate variations contain noise from many sources and, for reliable estimates, we need to determine those temporal scales at which the climate signal in the proxy record dominates the noise. We developed a method to derive timescale-dependent estimates of temperature proxy signal-to-noise ratios, which we apply and discuss in the context of Antarctic ice-core records but which in general are applicable to a large set of palaeoclimate records.

Description: 〈b〉The climate of Granada (southern Spain) during the first third of the 18th century (1706–1730) according to documentary sources〈/b〉〈br〉 Fernando S. Rodrigo〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-170,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 Climate of Granada (southern Spain) during the first third of the 18th century is reconstructed. Results suggest that climatic conditions were similar to those of the first decades of the 20th century, when the global warming signal was of less importance than today. In addition, the manuscript presents the instrumental data taken in Granada the year 1729, probably the first instrumental meteorological data recorded in Spain. Some extreme events, as the cold wave of the winter 1729, are studied.

Description: 〈b〉Long-term deglacial permafrost carbon dynamics in MPI-ESM〈/b〉〈br〉 Thomas Schneider von Deimling, Thomas Kleinen, Gustaf Hugelius, Christian Knoblauch, Christian Beer, and Victor Brovkin〈br〉 Clim. Past, 14, 2011-2036, https://doi.org/10.5194/cp-14-2011-2018, 2018〈br〉 Past cold ice age temperatures and the subsequent warming towards the Holocene had large consequences for soil organic carbon (SOC) stored in perennially frozen grounds. Using an Earth system model we show how the spread in areas affected by permafrost have changed under deglacial warming, along with changes in SOC accumulation. Our model simulations suggest phases of circum-Arctic permafrost SOC gain and losses, with a net increase in SOC between the last glacial maximum and the pre-industrial.

Description: 〈b〉Deglacial to postglacial history of Nares Strait, Northwest Greenland: a marine perspective from Kane Basin〈/b〉〈br〉 Eleanor Georgiadis, Jacques Giraudeau, Philippe Martinez, Patrick Lajeunesse, Guillaume St-Onge, Sabine Schmidt, and Guillaume Massé〈br〉 Clim. Past, 14, 1991-2010, https://doi.org/10.5194/cp-14-1991-2018, 2018〈br〉 We present our results from a radiocarbon-dated core collected in central Nares Strait, NW Greenland. Sedimentological and geochemical data reveal that marine sedimentation began ca. 9.0 cal ka BP with the complete opening of the strait occurring at 8.3 cal ka BP. The collapse of the glacial buttress in central Nares Strait led to accelerated glacial fluxes of the bordering ice sheets between 8.3 and 7.5 cal ka BP, while the Humboldt Glacier retreated in eastern Kane Basin ca. 8.1 cal ka BP.

Description: 〈b〉A large increase in the carbon inventory of the land biosphere since the Last Glacial Maximum: constraints from multi-proxy data〈/b〉〈br〉 Aurich Jeltsch-Thömmes, Gianna Battaglia, Olivier Cartapanis, Samuel L. Jaccard, and Fortunat Joos〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-167,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 A long standing question in climate science is concerned with which processes contributed to the increase in atmospheric CO〈sub〉2〈/sub〉 after the last ice age. From the range of possible processes we try to constrain the change in carbon storage in the land biosphere. By combining ice-core and marine sediment data in a modeling framework we show that the carbon storage in the land biosphere increased largely after the last ice age. This will help to further understand processes at work in the Earth system.

Description: 〈b〉A reconstruction of warm water inflow to Upernavik Isstrøm since AD 1925 and its relation to glacier retreat〈/b〉〈br〉 Flor Vermassen, Nanna Andreasen, David J. Wangner, Nicolas Thibault, Marit-Solveig Seidenkrantz, Rebecca Jackson, Sabine M. Schmidt, Kurt H. Kjær, and Camilla S. Andresen〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-174,2019〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 This study shows that warming of ocean waters is related to the retreat of Upernavik Isstrøm, a glacier in Northwest Greenland. We show that in the 1930s and after 2000 the waters in the fjord warmed and the glacier retreated. We found this by investigating microfossils from sediments in Upernavik Fjord; different species occur in response to warmer waters.

Description: 〈b〉Climate evolution across the Mid-Brunhes Transition〈/b〉〈br〉 Aaron M. Barth, Peter U. Clark, Nicholas S. Bill, Feng He, and Nicklas G. Pisias〈br〉 Clim. Past, 14, 2071-2087, https://doi.org/10.5194/cp-14-2071-2018, 2018〈br〉 Multiple components of the global climate system record a transition ~ 430 ka from lower- to higher-amplitude glacial cycles. Statistical analyses of globally distributed climate proxies show that a sequence of events including persistent Asian summer monsoons, weak glaciation, and reorganization of water masses preceded the transition to higher interglacial values for temperature, atmospheric greenhouse gases, and sea level.

Description: 〈b〉Understanding the Australian Monsoon change during the Last Glacial Maximum with a multi-model ensemble〈/b〉〈br〉 Mi Yan, Bin Wang, Jian Liu, Axing Zhu, Liang Ning, and Jian Cao〈br〉 Clim. Past, 14, 2037-2052, https://doi.org/10.5194/cp-14-2037-2018, 2018〈br〉 〈p〉The response of the Australian monsoon to external forcings and related mechanisms during the Last Glacial Maximum (LGM) are investigated by multi-model experiments in CMIP5–PMIP3. Although the annual mean precipitation over the Australian monsoon region decreases, the annual range, or the monsoonality, is enhanced. The precipitation increases in early austral summer and decreases in austral winter, resulting in the amplified annual range, but the main contribution comes from the decreased precipitation in austral winter. The decreased winter precipitation is primarily caused by weakened upward motion, although reduced water vapor also has a moderate contribution. The weakened upward motion is induced by the enhanced land–sea thermal contrast, which intensifies the divergence over northern Australia. The increased Australian monsoon rainfall in early summer, however, is an integrated result of the positive effect of local dynamic processes (enhanced moisture convergence) and the negative effect of thermodynamics (reduced moisture content). The enhanced moisture convergence is caused by two factors: the strengthened northwest–southeast thermal contrast between the cooler Indochina–western Indonesia and the warmer northeastern Australia, and the east–west sea surface temperature gradients between the warmer western Pacific and cooler eastern Indian Ocean, both due to the alteration of land–sea configuration arising from the sea level drop. The enhanced Australian monsoonality in the LGM is not associated with global-scale circulation change such as the shift of the Intertropical Convergence Zone; rather, it is mainly due to the change of regional circulations around Australia arising from the changes in land–sea contrast and the east–west SST gradients over the Indian and western Pacific oceans. This finding should be taken into account when investigating its future change under global warming. Our findings may also explain why proxy records indicate different changes in Australian monsoon precipitation during the LGM.〈/p〉

Description: 〈b〉Impact of different estimations of the background-error covariance matrix on climate reconstructions based on data assimilation〈/b〉〈br〉 Veronika Valler, Jörg Franke, and Stefan Brönnimann〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-168,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 In recent years, the data assimilation approach was adapted to the field of paleoclimatology to reconstruct past climate fields by combining model simulations and observations. To improve the performance of our paleo data assimilation system, we tested various techniques that are well established in weather forecasting, and evaluated their impact on assimilating instrumental data and proxy records (tree rings).

Description: 〈b〉Decadal-scale progression of Dansgaard-Oeschger warming events〈/b〉〈br〉 Tobias Erhardt, Emilie Capron, Sune Olander Rasmussen, Simon Schüpbach, Matthias Bigler, Florian Adolphi, and Hubertus Fischer〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-176,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 0 comments)〈br〉 The cause of the rapid warming events documented in proxy records across the Northern Hemisphere during the last glacial has been a long-standing puzzle in paleo-climate research. Here we use high resolution ice core data from to cores in Greenland to investigate the progression during the onset of these events on muti-annual time scales to test their plausible triggers. We show that atmospheric circulation changes preceded the warming in Greenland and the collapse of the sea ice by a decade.

Description: 〈b〉The relevance of mid-Holocene Arctic warming to the future〈/b〉〈br〉 Masakazu Yoshimori and Marina Suzuki〈br〉 Clim. Past Discuss., https//doi.org/10.5194/cp-2018-175,2018〈br〉 〈b〉Manuscript under review for CP〈/b〉 (discussion: open, 1 comment)〈br〉 A relation between the mid-Holocene (MH) and future Arctic warming mechanism is investigated with focus on the similarities of physical processes. The several key processes are identified which are linked to both multi-model mean response and multi-model variation of the response. This study indicates that the models are required to simulate the MH Arctic climate well to provide more confidence to the future Arctic climate projections.

Description: 〈b〉Ocean carbon inventory under warmer climate conditions – the case of the Last Interglacial〈/b〉〈br〉 Augustin Kessler, Eirik Vinje Galaasen, Ulysses Silas Ninnemann, and Jerry Tjiputra〈br〉 Clim. Past, 14, 1961-1976, https://doi.org/10.5194/cp-14-1961-2018, 2018〈br〉 We analyze the changes in oceanic carbon dynamics, using a state-of-the-art Earth system model, by comparing two quasi-equilibrium states: the early, warm Eemian (125 ka) versus the cooler, late Eemian (115 ka). Our results suggest a considerably weaker ocean dissolved inorganic carbon storage at 125 ka, an alteration of the deep-water geometry and ventilation in the South Atlantic, and heterogeneous changes in phosphate availability and carbon export between the Pacific and Atlantic basins.

Description: Spatial and temporal oxygen isotope variability in northern Greenland – implications for a new climate record over the past millennium Climate of the Past Discussions, 11, 2341-2388, 2015 Author(s): S. Weißbach, A. Wegner, T. Opel, H. Oerter, B. M. Vinther, and S. Kipfstuhl We present for the first time all 12 δ 18 O records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland between 74 to 80° N, 36 to 49° W and 2000 to 3200 m a.s.l. The cores cover an area of 680 km × 317 km, ~200 000 km 2 or 10 % of the area of Greenland. Depending on core length (100–175 m) and accumulation rate (90–200 kg m −2 a −1 ) the records reflect an isotope-temperature history over the last 500–1100 years. The δ 18 O signal in northern Greenland is influenced by temperature, accumulation and the topography of the North Greenland ice sheet between 72 and 80° N. About 12 % of the variability can be attributed to the position of the single drill sites in relation to the ice sheet topography. Lowest δ 18 O mean values occur north of summit and east of the main divide. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources. A stack of all 12 NGT records and the NGRIP record is presented with improved signal-to-noise ratio. This stack represents the mean δ 18 O signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δ 18 O stack indicates isotopically enriched periods compared to their average during medieval times, about 1420 ± 20 AD and from 1870 AD onwards. The period between 1420 AD and 1850 AD was isotopically depleted compared to the average for the entire millennium and represents the Little Ice Age. The 20th century has isotopic values higher than the 1000 years mean and is comparable to the medieval period but lower than about 1420 AD.

Description: Insights into the early Eocene hydrological cycle from an ensemble of atmosphere–ocean GCM simulations Climate of the Past Discussions, 11, 3277-3339, 2015 Author(s): M. J. Carmichael, D. J. Lunt, M. Huber, M. Heinemann, J. Kiehl, A. LeGrande, C. A. Loptson, C. D. Roberts, N. Sagoo, C. Shields, P. J. Valdes, A. Winguth, C. Winguth, and R. D. Pancost Recent studies, utilising a range of proxies, indicate that a significant perturbation to global hydrology occurred at the Paleocene–Eocene Thermal Maximum (PETM; ~56 Ma). An enhanced hydrological cycle for the warm early Eocene is also suggested to have played a key role in maintaining high-latitude warmth during this interval. However, comparisons of proxy data to General Circulation Model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised, despite significant differences in simulated surface temperatures. In this work, we undertake an intercomparison of GCM-derived precipitation and P - E distributions within the EoMIP ensemble (Lunt et al., 2012), which includes previously-published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure and precipitation relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to preindustrial. This is primarily due to elevated atmospheric paleo-CO 2 , although the effects of differences in paleogeography/ice sheets are also of importance in some models. For a given CO 2 level, globally-averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (d P /d T ) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that a number of GCMs underestimate precipitation rates at high latitudes. Models which warm these regions, either via elevated CO 2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO 2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences apparent between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

Description: Paleoclimate reconstruction in the Levant region from the petrography and the geochemistry of a MIS 5 stalagmite from the Kanaan Cave, Lebanon Climate of the Past Discussions, 11, 3241-3275, 2015 Author(s): C. Nehme, S. Verheyden, S. R. Noble, A. R. Farrant, J. J. Delannoy, and P. Claeys Lying at the transition between the temperate Mediterranean domain and subtropical deserts, the Levant is a key area to study the palaeoclimatic response over glacial-interglacial cycles. This paper presents a precisely dated last interglacial (MIS 5) stalagmite (129–84 ka) from the Kanaan Cave, Lebanon. Variations in growth rate and isotopic records indicate a warm humid phase at the onst of the last interglacial at ~129 ka that lasted until ~125 ka. A gradual shift in speleothem isotopic composition (125–122 ka) is driven mainly by the δ 18 O source effect of the Eastern Mediterranean surface waters during Sapropel S5. The onset of glacial inception began after ~122 ka, interrupted by a short wet pulse during Sapropel S4. Low growth rates and enriched oxygen and carbon values until ~84 ka indicate a transition to drier conditions during Northern Hemisphere glaciation.

Description: The influence of non-stationary ENSO teleconnections on reconstructions of paleoclimate using a pseudoproxy framework Climate of the Past Discussions, 11, 3853-3895, 2015 Author(s): R. Batehup, S. McGregor, and A. J. E. Gallant Reconstructions of the El Niño-Southern Oscillation (ENSO) ideally require high-quality, annually-resolved and long-running paleoclimate proxy records in the eastern tropical Pacific Ocean, located in ENSO's centre-of-action. However, to date, the paleoclimate records that have been extracted in the region are short or temporally and spatially sporadic, limiting the information that can be provided by these reconstructions. Consequently, most ENSO reconstructions exploit the downstream influences of ENSO on remote locations, known as teleconnections, where longer records from paleoclimate proxies exist. However, using teleconnections to reconstruct ENSO relies on the assumption that the relationship between ENSO and the remote location is stationary in time. Increasing evidence from observations and climate models suggests that some teleconnections are, in fact, non-stationary, potentially threatening the validity of those paleoclimate reconstructions that exploit teleconnections. This study examines the implications of non-stationary teleconnections on modern multi-proxy reconstructions of ENSO. The sensitivity of the reconstructions to non-stationary teleconnections were tested using a suite of idealized pseudoproxy experiments that employed output from a fully coupled global climate model. Reconstructions of the variance in the Niño 3.4 index, representing ENSO variability, were generated using four different methods to which surface temperature data from the GFDL CM2.1 was applied as a pseudoproxy. As well as sensitivity of the reconstruction to the method, the experiments tested the sensitivity of the reconstruction to the number of non-stationary pseudoproxies and the location of these proxies. ENSO reconstructions in the pseudoproxy experiments were not sensitive to non-stationary teleconnections when global, uniformly-spaced networks of a minimum of approximately 20 proxies were employed. Neglecting proxies from ENSO's center-of-action still produced skillful reconstructions, but the chance of generating a skillful reconstruction decreased. Reconstruction methods that utilized raw time series were the most sensitive to non-stationary teleconnections, while calculating the running variance of pseudoproxies first, appeared to improve the robustness of the resulting reconstructions. The results suggest that caution should be taken when developing reconstructions using proxies from a single teleconnected region, or those that use less than 20 source proxies.

Description: Palaeoclimatic oscillations in the Pliensbachian (Lower Jurassic) of the Asturian Basin (Northern Spain) Climate of the Past Discussions, 11, 4039-4076, 2015 Author(s): J. J. Gómez, M. J. Comas-Rengifo, and A. Goy One of the main controversial items in palaeoclimatology is to elucidate if climate during the Jurassic was warmer than present day, with no ice caps, or if ice caps were present in some specific intervals. The Pliensbachian Cooling event (Lower Jurassic) has been pointed out as one of the main candidates to have developed ice caps on the poles. To constrain the timing of this cooling event, including the palaeoclimatic evolution before and after cooling, as well as the calculation of the seawater palaeotemperatures are of primary importance to find arguments on this subject. For this purpose, the Rodiles section of the Asturian Basin (Northern Spain), a well exposed succession of the uppermost Sinemurian, Pliensbachian and Lower Toarcian deposits, has been studied. A total of 562 beds were measured and sampled for ammonites, for biostratigraphical purposes and for belemnites, to determine the palaeoclimatic evolution through stable isotope studies. Comparison of the recorded uppermost Sinemurian, Pliensbachian and Lower Toarcian changes in seawater palaeotemperature with other European sections allows characterization of several climatic changes of probable global extent. A warming interval which partly coincides with a negative δ 13 C bel excursion was recorded at the Upper Sinemurian. After a "normal" temperature interval, a new warming interval that contains a short lived positive δ 13 C bel peak, was developed at the Lower-Upper Pliensbachian transition. The Upper Pliensbachian represents an outstanding cooling interval containing a positive δ 13 C bel excursion interrupted by a small negative δ 13 C bel peak. Finally, the Lower Toarcian represented an exceptional warming period pointed as the main responsible for the prominent Lower Toarcian mass extinction.