PAGES Magazine articles
Rainer Gersonde1, A. de Vernal2 and E. W. Wolff3
3rd Sea Ice Proxies (SIP) Working Group workshop - Bremerhaven, Germany, 23-25 June 2014
The distinct contrast between recent trends in Arctic and Antarctic sea ice calls for sea ice records extending beyond instrumental observations. Such estimates must rely on well-established sea ice proxy data obtained from marine, ice core and coastal materials and should ideally be supported by sea ice modeling.
A primary goal of the PAGES Sea Ice Proxies (SIP) Working Group is to critically assess different sea ice proxies. This issue was central to the first SIP workshop in 2012 and resulted in the publication of 18 papers. Further proxy development, comparisons and applications in time-series and time-slice reconstructions were stimulated and discussed at the second SIP workshop in 2013.
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Figure 1: Comparison of marine (PS1768-8) and ice core (EDC) records documenting Antarctic sea ice variability during the last climate cycle. In the middle top panel, the location of the EDC and the marine core are presented relative to the modern average winter sea ice extent (WSI, at 40% concentration) and the Antarctic Polar Front (APF). The records show concurring sea ice minima during the Marine Isotope Stages (MIS) 5 and 1, and similar sea ice retreat during the glacial/interglacial transitions. The marine record displays strong variability during MIS 2-4, while the ice core record shows a more stable signal. Data from Esper and Gersonde 2014 and Wolff et al. 2006. |
The third workshop focused on sea ice data syntheses, sea ice modeling and proxy-data/model comparisons. In addition, recent progress in proxy development was presented, such as a new proxy using crustose coralline algae to extend the instrumental observations of Arctic sea ice at annual resolution (Halfar et al. 2013). Recent identification of the source of the biomarker IP25 makes it a more powerful proxy for Arctic sea ice (Brown et al. 2014). Antarctic sea ice estimates are primarily based on diatom records (e.g. Esper and Gersonde 2014) because the establishment of biomarkers as robust proxies for Antarctic sea ice still requires more study. Strong efforts to better understand aerosols (sea salt, halogens, methanesulfonic acid) and their production mechanisms, transport and deposition have enhanced their applicability as sea ice proxies in ice cores (e.g. Levine et al. 2014). While the limitations, strengths and significance of individual proxies can be tested through proxy intercomparison (Fig. 1), a deeper understanding requires more joint projects between paleoclimatologists, and biologists and physicists studying modern sea ice processes. Additionally, the development of new proxies (e.g. DNA-based identification of foraminifers living in sea ice) should be intensified.
Arctic sea ice development in the Holocene at 2000 year time slices was presented. Time-series studies from different sectors of the northern polar realm since the last glacial document the complex pattern of sea ice variability, and allow us to better evaluate sea ice/climate feedbacks during the last glacial-interglacial transition. Similar data, but at lower resolution, were also presented from the Pacific and Atlantic sectors of the Southern Ocean. This provides a picture of bipolar sea ice variability under natural conditions giving a context for modern changes. Antarctic sea ice data have also been developed for the penultimate glacial-interglacial transition and the last interglacial, which may represent conditions that could develop in a future warmer-climate state.
The participants concluded that robust sea ice estimates with large spatial coverage under a broad range of climate conditions should rely on a combination of different proxies according to their specific applicability. Model-data comparisons perform best when there is an abundance of data for assimilation. Data gaps in spatial and seasonal information may be bridged by sea ice modeling. However, such modeling needs further improvement as there remain uncertainties possibly related to sea ice parameterization and applied boundary conditions. The development of bipolar sea ice syntheses for the last two glacial-interglacial transitions and subsequent interglacials presents a crucial step towards improved integration of sea ice as a polar amplification and feedback factor, which is important for more robust projections of future conditions. SIP3 encourages the increased integration and comparison of data and modeling results to improve future paleoclimate research. Although this was the last PAGES-sponsored SIP meeting, SIP intends to continue with sessions at major meetings (e.g. as scheduled at AGU Fall 2014 and INQUA 2015) and through mailings between the participants. To join the SIP mailing list, visit https://listserv.unibe.ch/mailman/listinfo/seaice.pages
affiliations
1Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
2GEOTOP, Université du Québec à Montréal, Canada
3Department of Earth Sciences, University of Cambridge, UK
contact
Rainer Gersonde: Rainer.Gersonde
awi.de
references
Brown TA et al. (2014) Nat Commun 5, doi: 10.1038/ncomms5197
Esper O, Gersonde R (2014) Palaeogeog Palaeoclimatol Palaeoecol 399: 260-283
Halfar J et al. (2013) PNAS 110: 19737-19741
Woods Hole, United States, 15-16 April 2014
A major outcome of the PAGES2k synthesis was the creation of continental-scale reconstructions of mean regional temperatures that span the last millennium or more (PAGES 2k Consortium 2013). Four of the PAGES 2k regions (Asia, Europe, North and South America) also reconstructed spatial variability in temperatures using approaches that fall within a class of methodologies called climate field reconstruction (CFR; Evans 2001). CFR consists of a set of statistical tools that can be used to estimate past climate variability on a regular grid, typically using networks of annual-resolution paleoclimate proxies. They exist on a continuum from simple reconstructions of a single leading spatiotemporal mode (analogous to a weighted mean reconstruction) to more complex methods including hierarchical models that incorporate knowledge of the proxy systems and climate covariance (Tingley and Huybers 2010; Steiger et al. 2014). These reconstructions are desirable as they allow climate variability to be estimated in both space and time, providing targets for general circulation model comparisons and knowledge about the fingerprint of regional-scale climate variability in response to radiative forcing and internal climate system variability.
The PAGES2k proxy dataset provides specific challenges for CFR. The data are highly heterogeneous in space and time, they are known to contain a range of frequency-dependent, seasonal, multivariate climate signals, and include proxy archives that are lower resolution and time-uncertain. During the Phase I synthesis of the PAGES2k project, we identified three primary methodological challenges to developing field reconstructions across all the regional networks. These included (1) the need to develop unbiased approaches to the selection of proxy data from a large database of potential predictors, (2) the incorporation of non-annual and time-uncertain records in climate reconstructions (e.g. Anchukaitis and Tierney 2012), and (3) the complications presented by the PAGES2k Phase II goal to reconstruct hydroclimate, specifically with respect to seasonality and spatial covariance.
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Figure 1: Correlation between March-August mean temperatures and (A) simulated pseudoproxy and (B) actual tree-ring chronologies from the Yamal Peninsula (Briffa et al. 2008; McKay and Kaufman 2014). The pseudoproxy series was created using simulated temperatures from the last millennium NCAR CCSM4 simulation with additional Gaussian noise to mimic the signal-to-noise ratio of the actual chronology. Correlations for the pseudoproxy series are with the corresponding CCSM4 mean surface temperature field, while the actual Yamal chronology is correlated against the GISTEMP (Hansen et al. 2010) combined land-sea temperature field. The star indicates the location of the chronology. |
The PAGES2k Advances in Climate Field Reconstruction workshop brought together paleoclimatologists from across the 2k Network with experts on reconstruction methods to explore these questions and to work toward developing new techniques that address extant challenges. The workshop included a thorough overview from proxy domain experts on the spatial, temporal, and spectral characteristics of different proxy systems, including sources of uncertainty and bias. Existing CFR methods were reviewed in light of their ability to be adapted specifically to the PAGES2k network. A major feature of the workshop was the initiation of a reconstruction methods intercomparison exercise. Using the Arctic 2k data (McKay and Kaufman 2014), researchers representing different CFR approaches were given the actual proxy data as well as a set of pseudoproxies (Smerdon 2012) designed to mimic the spatial, temporal, seasonal, and chronological characteristics of the real network. The goal was to observe differences in estimates of past climate variability as a function of reconstruction method and to provide a testbed for evaluating their origin. Initial efforts exposed practical challenges posed by the sparseness of the network, the signal-to-noise signature of the proxies, and time-uncertainty. These also provided information about the design of more realistic pseudoproxy experiments (e.g. Fig 1). The goal of creating a global reconstruction using the PAGES2k database was also explored.
The workshop developed several concrete goals and recommendations, including: continued development of database structures that allow for expert and community assessment to facilitate open discussion of proxy strengths, weaknesses, biases, selection, and fidelity, a prerequisite for future regional and global reconstructions; continued and expanded development of proxy system models (Evans et al. 2013) for capturing the multivariate, nonlinear, and seasonal aspects of different proxies; incorporation of explicit hierarchical modeling of chronological uncertainty within CFR techniques; and exploration of CFR approaches that transparently integrate scientific knowledge of the proxies and climate systems within the statistical modeling framework (Tingley et al. 2012). Based on initial efforts toward a methods intercomparison, the group has designed a new series of experiments to isolate the influence of model specification, climate signal, network distribution, and time uncertainty. Methods development and testing with respect to incorporating time uncertainty within hierarchical models is ongoing, and a community effort to develop an improved database and a global-scale reconstruction is proceeding.
affiliationS
1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, USA
2School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, USA
contact
Kevin Anchukaitis: kjawhoi.edu
references
Evans MN et al. (2001) In: Markgraf V (Ed) Interhemispheric Climate Linkages, Cambridge, 53-72
Evans MN et al. (2013) Quat Sci Rev 76: 16-28
McKay NP, Kaufman DS (2014) Sci Data 1, doi: 10.1038/sdata.2014.26
Quansheng Ge1, Z. Hao1, X. Shao1, H. Borgaonkar2, J. Luterbacher3, T. Nakatsuka4, M. Sano4, O. Solomina5 and L. Zhou6
3rd Asia2k workshop, Beijing, China, 26-27 May 2014
This workshop constituted the starting point for Phase II of Asia2k and was attended by 40 participants from 11 countries. They reviewed a variety of proxy records from Asia, coordinated the setup of a database following the selection criteria of the 2k Network, and agreed on a timeline towards the production and publication of regional spatial reconstructions of temperature and precipitation covering the past 2000 years.
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Figure 1: Phase I database of the Asia 2k group as published in the PAGES 2k Consortium paper (2013). A major task for the group is to add many of the available non-tree ring records to the database. |
Presentations addressed reconstruction methodologies, paleoclimate modeling, and paleoclimatic records from Asia based on historical documents and natural proxies. New, yet unpublished studies were presented. These included an extreme events record from historical documents, a tree-ring based temperature and drought reconstructions covering the past 2000 years from the Tien-Shan and Altay Mountains, a 2000-year long varved sediment record from northeastern China, a relative humidity variation record for the southwestern Gobi Desert reconstructed from oxygen isotopes in Qinghai spruce, and a two millennia long tree-ring cellulose oxygen isotope chronology from Japan. In addition, 500 year long tree-ring based precipitation records from the Nepal Himalayas, Northwestern Thailand and Pakistan were discussed. All these new proxy records are important contributions to the Asia2k database, especially since the Phase I database only included a limited number of records, all of which are tree ring series (Fig. 1).
To focus the discussions on the upcoming key tasks and plan the next specific steps of the Asia2k project, the participants broke out into three groups. Two groups focused on inventories of paleoclimatic records at high and low-resolution, respectively. Their aim was to develop strategies for compiling published (or soon to be published) proxy records of (sub-)annual to multi-decadal-resolution and their associated metadata from different paleoclimate archives. A third group focused on statistical reconstruction methods and ways forward to arrive at regional-scale spatially explicit reconstructions of temperature and precipitation variations.
In both data-related breakout groups participants agreed to contribute their data when published in papers, encouraged their colleagues to also contribute their datasets, and planned to extract other data from the existing literature. A coordinated publication, such as a special issue, was encouraged to support swift publication of yet unpublished data. The data submission process via the template downloadable from the 2k website was found suitable. When reviewing the submission criteria, the high-resolution group expressed concern that a required minimum record length of 500 years would exclude too many good records. Accordingly, the 2k Network has in the meantime relaxed the criteria for annually-resolved records to a minimum length of 300 years. The low-resolution group on the other hand expressed concern that one date per 500 years would be a too strict criterion. In response, a more flexible definition for required chronological accuracy has been developed. The high-resolution group identified multi-decadal scale variability and extreme climatic events as the main scientific topics. In the low-resolution group the scientific topics of interest included multi-decadal to multi-centennial climatic changes such as of the meridional temperature gradient and of the treeline position.
The reconstruction group agreed to try different reconstruction methods, including downscaling from global reconstructions, and to compare the output with each other. The aim is to start with temperatures first, but not only for annual averages but also for seasonal temperatures. Experts agreed that a full spatial reconstruction of precipitation changes is unlikely to be achieved. Following the suggestion by the 2k Consortium (PAGES 2k Consortium 2014), the generation of independent reconstructions at high and low resolution will be considered, and Asia sub-divided into climatic regions if a full scale spatial reconstruction is not possible due to the lack of sufficient proxy records. Monsoon variability was identified as the scientific question of prime interest that could be addressed with the reconstructions.
The participants also discussed the new group and leadership structure. A steering committee of nine task leaders (the authors of this article) chaired by Quansheng Ge was established. Committee members include representatives of the four biggest countries, data management, and reconstruction methods.
The next step of the Asia2k group is to update the temperature dataset by the end of the year 2014 and to apply a range of reconstruction methods to them. In parallel, the group will start compiling hydroclimatic proxy records. The fourth Asia 2k workshop will be held in Japan in March 2015 with the goal being to compare and review the first-order reconstructions and finalize the data compilation.
affiliations
1Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, China
2Indian Institute of Tropical Meteorology, Pune, India
3Department of Geography, Justus-Liebig-University Giessen, Germany
4Research Institute of Humanity and Nature, Kyoto, Japan
5Institute of Geography, Russian Academy of Sciences, Moscow, Russia
6Department of Geography, Peking University, Beijing, China
contact
Zhixin Hao: haozxigsnrr.ac.cn
references
Nicholas McKay
Fort Collins, USA, 23-26 June 2014
The North America 2k (NAM2k) Working Group recently met at the USGS Powell Center to begin Phase 2 of the NAM2k project in earnest. Phase 2 aims to build on the success of the first phase by expanding the scope of the project, both by including a more diverse and comprehensive array of paleoclimatic evidence for the past two millennia in North America, and by analyzing additional indicators and reconstructions of parameters beyond surface temperature, most notably, hydroclimate. Twenty working group members with expertise in tree rings, lake and marine sediments, corals, speleothems, boreholes, ice cores, glacial landforms, and climate modeling participated in the meeting.
The group reviewed the initial collection of data, and discussed best practices for extracting and combining paleoclimatic information from different natural archives, each with its own uncertainties and biases, and each with a different climate-signal filter. The group found that the initial PAGES 2k Phase 2 Data Selection Criteria were quite restrictive, and difficult or inappropriate to apply to some archives (e.g. boreholes and corals). Consequently, a more relaxed and nuanced approach was adopted. These criteria were reviewed by all PAGES 2k regional groups and have now been adopted network-wide (see: http://pastglobalchanges.org/ini/wg/2k-network/data).
The first and primary goal of the working group is to produce a clearly-formatted digital database of 2k-relevant proxy records for the continent that will facilitate a better understanding of climate variability in North America over the past 2,000 years. The deadline for assembling the next version of the database is the end of 2014. Subsequently, the group targeted three primary projects to be completed before the end of Phase 2 of the PAGES 2k project in 2016:
1) Subregional temperature reconstructions for North America
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Figure 1: Preliminary delineation of sub-continental regions for multiproxy, pollen, and borehole temperature reconstructions. Regions will likely be adjusted to accommodate natural breaks in proxy data coverage. |
Based on the dominant airmasses, ecology, and the availability of proxy data throughout the continent, the group developed initial spatial targets for subcontinental temperature reconstructions (Fig. 1). Within each subregion, depending on data availability, we plan to produce (a) 2,000-yr-long multiproxy temperature index (time series) reconstructions, (b) 100-yr resolution pollen-based temperature reconstructions, and (c) borehole temperature reconstructions. These will be supplemented by a new tree-ring based temperature field reconstruction, which will utilize restandardized “signal free” tree-ring chronologies (Melvin and Briffa 2014).
2) Water isotope proxy synthesis
The group discussed how to take advantage of O and H isotopic composition observations in many archives. With interpretation based on generalized data models for each proxy system, archive and observation (Evans et al. 2013), the group will compile δ18O and δD records from across North America. By comparing both data models and observations, we hope to facilitate comparison and synthesis across records and archives. Because stable isotopes in meteoric waters represent source differences, the temperature path history of air masses, and mixing and precipitation processes, we hope this compilation will support the study of past changes in hydrology and atmospheric circulation, and comparison with the output of isotope-enabled earth system models (e.g. Schmidt et al. 2014).
3) Multiproxy investigation of extreme droughts and pluvials
Gridded, tree-ring-based paleohydrologic reconstructions for North America are well developed (Cook et al. 2004 and updates), and full, multiproxy integration of disparate archives and paleohydrologic parameters into a single reconstruction is beyond the timeline of phase 2 of the NAM2k project. Consequently, the working group decided to focus on multiproxy comparison during periods of particular interest during the past 2k, for which diverse evidence for hydrologic extremes is available. When possible, the group will compare geomorphic evidence and event records (e.g. shorelines) with multiproxy hydrologic, temperature and isotope data, using simple models of hydroclimatic processes (e.g. Graham et al. 2007) to better constrain the timing, amplitude and cause of the changes during these intervals of particular relevance.
The North America 2k working group is planning a brief gathering in San Francisco during the Fall Meeting of the American Geophysical Union this December. Anyone interested in contributing to the project is encouraged to join us. The time, date and location of the meeting will be distributed through the PAGES website. NAM2k is supported by both the USGS Powell Center and PAGES.
affiliations
School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, USA
contact
Nicholas McKay: Nicholas.McKaynau.edu
references
Cook ER et al. (2004) Science 306: 1015-1018
Evans MN et al. (2013) Quat Sci Rev 76: 16-28
Graham NE et al. (2007) Holocene 17: 1197-1210
Joëlle Gergis1, P. Hope2, N. Abram3 and B. Henley1
3rd Aus2k workshop - 26-27 June 2014, Melbourne, Australia
The aim of the 3rd Aus2k workshop was to review progress made by the Aus2k community to date, and to specifically plan how Australasian science will contribute towards Phase 2 of the PAGES 2k Network. Around 40 paleoclimatologists, meteorologists, hydrologists, and oceanographers attended the workshop, resulting in a very constructive and stimulating cross-disciplinary meeting.
The Aus2k working group took the opportunity to hold the workshop jointly with the Australian Climate Change Science Program (ACCSP), and present the results of their joint paleoclimate data-climate model comparison project Variability of Australian climate over the last 1000 years in coupled model simulations and proxy data. The intention was to engage the wider meteorological community with expertise in climate data-model comparison and diagnostic analyses, and work towards the ultimate goal of understanding the mechanisms driving Australasian climate variability over the last 2000 years.
The specific goals of this workshop were to:
• Expand the Aus2k database to incorporate low-resolution material for the development of a common dataset for Australasian climate reconstructions;
The database will be frozen on 31 December 2014. Contacts for data submissions or questions: Bronwyn Dixon, Jonathan Tyler and Ben Henley
• Develop guidelines for the future collection of climate proxy records based on spatial and temporal gaps in the Australasian paleoclimate record;
Nerilie Abram will lead the testing of the number and location of records required to reconstruct specific features of Australian climate and to deal with potential biases caused by non-stationarities.
• Discuss existing multivariate data synthesis techniques being used by the Aus2k and global 2k communities. Discuss setting a post-meeting goal to run a comparison exercise using different reconstruction methods;
An inter-comparison project with Australian and New Zealand data will be coordinated by Ben Henley, Mandy Freund and Andrew Lorrey.
• Assess the feasibility of developing Australasian climate field reconstructions (temperature, precipitation, and geopotential height) to contribute towards the global PAGES 2k Network;
To be led by Joëlle Gergis, Andrew Lorrey and Steven Phipps.
• Foster linkages between the paleoclimate and climate modeling communities, with the aim of closing the loop between proxy development, data synthesis and climate modeling. Modeling contacts: Steven Phipps and Duncan Ackerley; Modern climate: Pandora Hope.
Day one of the workshop showcased recent research developments in regional data synthesis; opportunities for collecting new paleoclimate records from the region in the future; reconstructions of climate drivers such as El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM); and climate modeling being undertaken in Australia and internationally.
A range of projects including paleoclimate runs with CAWCR’s ACCESS model; testing the assumption of teleconnection stationarity; and pseudo-proxy exercises to test the fidelity of paleoclimate reconstructions were discussed and collaborative contacts made.
Day two focused on i) developing the database of Australasian low-resolution records, including data consolidation and directions for future data collection; ii) multi-archive data synthesis techniques being used by Aus2k and the PAGES 2k Network, and iii) climate field reconstructions and climate modeling.
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Figure 1: Locations of annually resolved and lower resolution paleoclimate archives in the Australasian region. |
It was agreed that the Australasian region’s “low resolution” database for Phase 2 would be frozen on 31 December 2014 to allow for consistency in subsequent climate analyses undertaken by the group. It was agreed that reconstructions based on records with higher time uncertainty should form an independent way to verify low frequency trends and variability identified from the more chronologically precise high-resolution material. Figure 1 shows the current spatial distribution of these two datasets.
The final discussion focused on developing a temperature field reconstruction for Australia within the Phase 2 timeframe of the PAGES 2k project. Climate modeling and data assimilation might assist with this. The workshop wrapped up by developing sub-groups based around the five workshop objectives (as listed above) and a clear forward direction that will help deliver Australasia’s best available science in Phase 2 of PAGES’ 2k Network project.
The next Aus2k workshop will be held in Auckland, New Zealand in the austral spring of 2015.
A longer version of this workshop report is available online at http://pastglobalchanges.org/calendar/2014/127-pages/1198-accsp-aus2k-wshop
affiliations
1School of Earth Sciences, University of Melbourne, Australia
2Australian Bureau of Meteorology, Melbourne, Australia
3Research School of Earth Sciences, Australian National University, Canberra, Australia
contact
Joëlle Gergis: jgergisunimelb.edu.au
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Chris Brierley1 and Kira Rehfeld2
London, UK, 12-14 March 2014
Past global changes provide a useful test for evaluating climate models. With modeling efforts increasingly focused on decadal predictions and climate services, there is a growing need to evaluate simulated climate variability. Past climates offer some opportunity for this, but require a slightly different approach than those currently adopted to look at mean changes. University College London’s Geography department hosted a three-day workshop to explore the issues associated with paleoclimate variability.
In some respects, this workshop emerged in response to the problems discovered during a previous PAGES-supported workshop focused on the El Niño-Southern Oscillation (ENSO; Braconnot et al. 2012). Coming out of this workshop, two requirements were identified as pivotal to model evaluation using PaleoENSO: (i) a more integrated approach across regions and disciplines, and (ii) the development of statistical and analytical tools to enable that intercomparison.
A special issue of PAGES news dedicated to ENSO highlighted recent advances across the ENSO regions and disciplines with the aim of kick-starting this more integrated approach (Braconnot et al. 2013). It was recognized that a dedicated activity is required to effectively tackle the two requirements – which are relevant for all modes of climate variability, rather than just ENSO.
In response, a working group on variability was established under the auspices of the Paleoclimate Modelling Intercomparison Project (PMIP3); this workshop was its first meeting. The focus of this meeting was on variability on inter-annual to multi-decadal timescales, in part because on longer timescales models appear to underestimate variability (Laepple and Huybers 2014). It was established that variability comparisons suffer additional difficulties compared with conventional analyses for the mean state.
Indeed, intermediate processing is often required between the models and data, which is its own field of expertise. Some of this intermediate processing relates to forward proxy modeling, represented at the workshop by efforts to model lake isotopic systems (Jones and Imbers 2010). The rest relates to how proxy properties impact a record’s statistics – for example looking at the impact of sampling individual forams (Thirumalai et al. 2013) or seasonal biases (Laepple and Huybers 2013).
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Figure 1: Annual temperatures measured at Kew Gardens, London (Peterson and Vose 1997) as an example of the three potential factors’ impacting climate variability. Neither adding random noise (e.g. instrumental error), nor smoothing (e.g. bioturbation), nor snapshot-type sampling (e.g. individual organisms that only live for a single random month) substantially alters the roughly 1°C of warming; however, the normalized estimates of variability differ in both magnitude and even sign. |
One conclusion was an appreciation that additional meta-data is often required to use a proxy-climate record for variability data model comparisons. This additional information is needed to understand how the individual measurements relate to each other. This becomes much more important for studies of paleoclimate variability than when looking at mean changes, as illustrated with the example of London annual temperatures (Fig. 1). We urge people to consider the following three questions when publishing a proxy record:
•To what extent are your stated errors random?
•Does each sample represent a time-average or a snapshot?
• Is the effective temporal resolution lower than the sampling resolution (e.g. through bioturbation or residence times prior to sedimentation)?
Practically speaking, for large proxy syntheses it is important that age modeling and calibration are replicable. This requires access to the proxy dataset (including depths, proxy measurements and sample size), the age modeling information (i.e. age estimates and errors with their depths), and the calibration information, as well as knowledge of the sampling strategy and proxy processes.
In summary, to obtain reliable and comparable estimates of past climatic variability, we must correct for the additional processes affecting proxy variability. This is not an easy task: it requires input from several disciplines, but has the potential to be much more relevant for the coming decades than studies of mean climate alone.
affiliations
1University College London, UK
2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany
contact
Chris Brierley: c.brierleyucl.ac.uk
references
Full reference list under: http://pastglobalchanges.org/products/magazine/ref2014_2.pdf
Braconnot P et al. (2013) PAGES news 21: 48-49
Jones MD, Imbers J (2010) Global Planet Change 71: 193-200
Laepple T, Huybers PJ (2014) Geophys Res Lett 41: 2528-2534
Laepple T, Huybers PJ (2013) Earth Planet Sci Lett 375: 418-429
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Michel Crucifix1, E. Zorita2 and J.-Y. Peterschmitt3
Namur, Belgium, 25-30 May 2014
This workshop, which gathered 108 delegates, was the twelfth event of the Paleoclimate Modelling Intercomparison Project (PMIP) in a series initiated in 1995 in Collonges-la-Rouge, France. Each of the successive meetings has marked a development in the PMIP project: towards more comprehensive Earth System models, a broader range of past periods, high-standard dataset documentation, state-of-the-art approaches of model-data synthesis, and, more recently, the introduction of transient experiments (last millennium and deglaciation) and methods of data assimilation. Now in its third phase, PMIP’s mission is to model and reconstruct past climates and understand the implications of this research for future climate. It has become an important contributor to our understanding of Earth's climate dynamics and sensitivity.
The workshop started with a review of database technology and the current upload status of PMIP3 experiments (https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:database:status). The PMIP3 database is now fully integrated within the Climate Modelling Intercomparison Project system (http://esgf-node.ipsl.fr/) and synthesis maps are available. To complement reports from PMIP participating groups, guests from the data and modeling community were invited to deliver talks and contribute to discussions in order to provide an outsider view on PMIP’s achievements and perspectives: Eelco Rohling (Australian National University), Simon Tett (University of Edinburgh), Steve Sherwood (University of New South Wales, Australia) and James Zachos (University of California Santa Cruz).
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Figure 1: Data-Model comparison for a "median orbit" Late Devonian simulation. The HadSM3 slab model simulated climate types and evaporation minus precipitation data are compared to lithic indicators of paleoclimate (PALEOMAP project; Scotese and Barrett 1990). Modified from De Vleeschouwer et al. 2014. |
The Namur meeting made it clear that better cooperation and knowledge exchange between researchers working on proxy records and paleo modeling is essential, be it to estimate variability indices throughout the last millennium, estimate the Last Glacial Maximum temperature, or reconstruct Pliocene, Eocene, or even Devonian climates (Fig. 1). There is no magic recipe that would simultaneously provide unbiased reconstructions of past climates, reveal model deficiencies and identify anomalous observations. Effective approach will rely on an ensemble of methods, including advanced physical and biogeochemical modeling, creative visualization diagnostics, careful analysis of observations, innovative experiment design, and technical statistical inference approaches.
The breadth of presentations delivered during the meeting reflected many aspects of this strategy: some focused on well-identified climate phenomena such as the Walker Pacific circulation during the Last Glacial Maximum occurring in the different models; others featured technical advances within a single model (e.g. modeling of oxygen and carbon isotopes), or introduced sophisticated statistical techniques of meta-modeling to simplify and summarize process-based model outputs. An entire session was also devoted to transient experiments.
The range of scientific challenges to be addressed within PMIP keeps expanding; there are now 13 PMIP working groups. Some are defined along time periods, others along crosscutting themes, such as “variability” or “Past2Future”. This structure will be maintained, keeping in mind that working groups are efficient and flexible structures that may merge or evolve as the community recognizes significant progress or feels the need to re-focus its research priorities.
Acknowledgements
The meeting was supported by PAGES, the WCRP, the Universities of Louvain, of Gent and of Namur, the Province de Namur, the Belgian National Fund for Scientific Research, the European Research Council, the Leverhulme Trust, HP and Intel. The program and abstracts are available at http://www.climate.be/pmip3, and info on PMIP at http://pmip3.lsce.ipsl.fr.
affiliations
1Georges Lemaître Centre for Earth and Climate Research, Université catholique de Louvain, Louvain-la-Neuve, Belgium
2Institute for Coastal Research, Helmholz-Zentrum, Geesthacht, Germany
3Laboratoire des Sciences du Climat et de l'Environnement, Institut Pierre et Simon Laplace, Gif-sur-Yvette, France
contact
Michel Crucifix: michel.crucifixuclouvain.be
references
De Vleeschouwer D et al. (2014) Global Planet Change 120: 65-80
Eric C. Grimm1, M. Blaauw2, C.E. Buck3 and J.W. Williams4
Belfast, UK, 13-16 January 2014
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Figure 1: New Bayesian age model for the Brewster Creek (USA) site produced by the Bacon program (Blaauw and Christen 2011) overlaid with the published classical model (Curry et al 2007). The original model is based on the IntCal04 calibration curve, linear interpolation, and ad hoc rejection of reversed dates; while the Bacon model is based on the IntCal13 curve and can accommodate reversed dates. The gray-scale shading represents the relative probability within the 95% higher posterior density region (or Bayesian confidence interval). The thick red line is the linear interpolation between the median probabilities of the calibrated ages in the original model; the thin red lines connect the 95% confidence limits of the calibrated ages but are not a valid statistical representation of the confidence limits of the interpolated ages. |
Paleo databases are critical cyberinfrastructure for paleoenvironmental research, especially for broad scale synoptic studies that place current environmental and climatic changes in context. Chronological control is critical for paleo studies, and chronologies and age models are essential metadata for paleo databases. Paleo databases typically comprise a large number of individual datasets acquired over a long time period. A major challenge for database managers and users is that criteria for estimating chronologies change through time rendering existing chronologies obsolete. In particular, chronologies based on calibrated radiocarbon ages become obsolete with each revision of the calibration curve, regardless of the sophistication of the age modeling technique. In addition, age modeling software has also evolved over the years. New programs, often using Bayesian techniques (Fig. 1), can now provide estimates of the uncertainties for interpolated sample ages. Most age models currently archived do not provide these uncertainties, which are nevertheless critical for assessing the statistical robustness of synchronous change across multiple sites and datasets.
To address these issues, 35 scientists from 12 countries met at the Queen’s University Belfast 14CHRONO Centre for a three-day workshop, which was followed by a one-day software training session attended by an additional eight participants focusing on the clam (Blaauw 2010) and Bacon (Blaauw and Christen 2011) age modeling programs. Initially, the Neotoma Paleoecology Database (www.neotomadb.org) had funding to support a small workshop of its Age Modeling Working Group. Additional funding from PAGES and the US National Science Foundation made it possible to also invite students and scientists involved with other database projects.
During the first day of the workshop, speakers discussed how various databases handle age modeling and chronology issues, calibration of radiocarbon dates, age modeling software, and database interoperability. During the following two days, breakout groups addressed the following topics: (1) Age models based on radiocarbon dating: problems caused by updates to the calibration curve; (2) Age models based on radiocarbon dating: strategies for regenerating chronologies from stored chronological data and age-model metadata; (3) Age models beyond the radiocarbon time scale; (4) Strategies for reducing the need for ad hoc age models; (5) Rankings of the quality and accuracy of dates and chronologies; and (6) Linking databases, calibration programs, and age modeling programs.
The summarized workshop recommendations* are: (1) Chronologies reported in the literature and stored in databases must be reproducible, and publications and databases should store sufficient data and metadata to ensure reproducibility. (2) The output from age modeling software should provide all the information necessary to reproduce age models in easily storable scripts or “age model definition” files, and a common metadata standard should be developed for these files. (3) Databases should archive originally published chronologies; however, database managers cannot be expected to reconstruct chronologies unless sufficient data and metadata are published or otherwise provided to them. (4) Because updates to the radiocarbon calibration curve and new modeling approaches may render published age models obsolete, database managers are encouraged to generate updated age models or to store those developed by other scientists. (5) Because ad hoc models that use different age modeling algorithms for different sections of a stratigraphic sequence are often difficult to reproduce, developers of age modeling software are encouraged to formally incorporate instantaneous sedimentation events, hiatuses, and sharp changes in sedimentation rate into their modeling frameworks. (6) An international open-access database for radiocarbon dates should be developed, and purchasers of radiocarbon dates should be given the option by the radiocarbon laboratories, and encouraged by funding agencies, to contribute their dates to the database.
*Complete recommendations of the workshop are available at: http://pastglobalchanges.org/calendar/past/2014/127-pages/826-age-models-chronologies-and-databases
affiliations
1Illinois State Museum, Springfield, USA
2School of Geography, Archaeology and Palaeoecology, Queen’s University Belfast, Northern Ireland, UK
3School of Mathematics and Statistics, University of Sheffield, UK
4Department of Geography, University of Wisconsin-Madison, USA
contact
Eric C. Grimm: grimmmuseum.state.il.us
references
Blaauw M (2010) Quat Geochron 5: 512-518
Julieta Massaferro1, L. Pérez2, M.E. de Porras3, L. Pérez Becoña4, M. Tonello5 and S. Juggins6
San Carlos de Bariloche, Argentina, 31 March- 6 April 2014
For the first time in Latin America, an intensive one-week course took place on paleoecological data analysis using the free software, R. This course was led by Steve Juggins (Newcastle University, UK), author of the R package “Rioja” for the analysis of Quaternary science data and co-editor of the book Data Handling and Numerical Techniques (Birks et al. 2012).
Twenty early-career paleoecologists from Mexico, Guatemala, Colombia, Chile, Uruguay and Argentina, were selected from over 50 applicants to attend this unique workshop. The course combined theoretical lectures with practicals using datasets from case studies on topics such as exploratory data analysis, data transformation, multiple regression, distance measures and cluster analysis, environmental reconstruction, and age-depth modeling. After the practicals the participants had the opportunity to process their own data. The participants also had the chance to meet other Latin American researchers working with different indicators, and some are now planning to establish an international network to address paleoenvironmental and climatic issues using a multi-proxy approach.
Below we show three examples of analyses made by course participants, illustrating how R was used to analyze preliminary data.
Ordination of pollen samples
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Figure 1: (A) Non-metric multidimensional scaling (NMDS) of a set of pollen samples from modern rodent middens collected along a climatic and vegetation gradient in the Atacama Desert (21°S). The numbers represent the altitudes the samples were taken at. (B) A two-way ordered bubble plot of freshwater ostracods along an altitudinal gradient in Central America. Altitude increases from left to right in the plot, with lowlands <500 and highlands from 500-2000 m a.s.l. Size of dots represents species richness. (C) Canonical Correspondence Analysis of diatom data (1960-2009) in a sediment core from Río de la Plata (red), climate indexes (PDO and SOI), and anomalies in the discharges of the Paraná and Uruguay river discharges (blue arrows). |
María Eugenia de Porras counted pollen in modern rodent middens along a climatic and vegetation gradient from the Atacama Desert to the Altiplano, to identify the modern climate-vegetation signal and develop a modern calibration set. Furthermore, she collected several modern midden samples at every ca. 100 m in altitude to account for pollen signal bias due to the rodent behavior. The results from an ordination analysis (nMDS, Fig. 1A) show that pollen from modern rodent middens reflects a vegetation gradient from the Pre-Puna, to low and high Puna, to High Andean steppe, and therefore the increasing precipitation gradient related to summer rainfalls associated with the South American Summer Monsoon. Furthermore, those samples collected at the same site are grouped together, suggesting that the pollen signal is not biased by the rodent behavior, and thus confirming the potential of middens as paleoclimatic and paleoecological archives.
Ostracods bubble plot
Liseth Pérez established an ostracod training set in Central America across a precipitation and altitudinal gradient to determine the species ecological preferences. The altitudinal distribution of lakes in the study region is strongly skewed towards lowland lakes (Fig. 1B). The highest species abundances and richness are found in the lowlands. There are clearly species restricted to the lowlands and others to the highlands, while few are distributed along the entire altitudinal gradient. Mid-altitude and additional highland lakes will be sampled in future field trips. This type of figure provides a fast overview of species distributional patterns along climatic and environmental gradients.
CCA with diatoms
Laura Pérez Becoña used a Canonical Correspondence Analysis (CCA, Fig. 1C) on diatom data obtained from a sediment core from the Río de la Plata (RdlP), in the inner Uruguayan continental shelf. The analysis combines diatom data (species abundances) for 1960-2009 AD, with instrumental records of climatic (Pacific Decadal Oscillation, PDO and Southern Oscillation Index, SOI) and anomalies in the Paraná and Uruguay River discharges. Positive anomalies in the Paraná and Uruguay River discharges are associated with warm ENSO and PDO phases, which increase the precipitation over the RdlP drainage basin. As a consequence, periods of high river discharge, related to PDO>0 or SOI<0 (El Niño events), are reflected through a higher abundance of freshwater and marine-brackish diatom species in the sedimentary record. In this sense, axis x of the CCA represents a salinity gradient, with fresher conditions (i.e. high RdlP discharge) at the left of the figure moving towards more maritime conditions on the right.
acknowledgements
We thank PAGES, the Municipality of Bariloche, the University of Comahue and the Nahuel Huapi National Park for supporting this course, and the organizing committee, for all the effort. Without their help it would have been impossible for many young scientist to attend the course.
affiliations
1Programa de estudios aplicados a la conservación de la Biodiversidad (CENAC/APN), Bariloche, Argentina
2Instituto de Geología, Universidad Nacional Autónoma de México, México
3Center for Advanced Research in Arid Zones, La Serena, Chile
4Institute of Ecology and Environmental Sciences, University of the Republic, Montevideo, Uruguay
5Institute for Marine and Coastal Research, National University of Mar del Plata, Argentina
6School of Geography, Politics and Sociology, Newcastle University, UK
contact
Julieta Massaferro: julimassaferrohotmail.com
references
Peter Gell1, O. Burge2 and R. Flower3
Queenscliff, Australia, 6-8 November 2013
To ensure protection and “wise use”, many wetlands are included in the Ramsar Convention’s List of Wetlands of International Importance (www.ramsar.org). Many of these wetlands are under increasing pressure from (i) (hydro-)climate change; and (ii) the direct impacts of people, notably through hydrological modification (decreasing water quantity/quality), land use change, and the proliferation of invasive species.
Listing a wetland requires a site description and account of the “natural ecological character”. The site description, undertaken at the time of listing, constitutes a modern baseline against which a wetland’s present condition can be measured. However, evidence from the past often reveals a wider range of “natural” conditions, and can inform the potential trajectory (or trajectories) of change through which the wetland is currently passing. This PAGES workshop provided a valuable opportunity for contemporary and paleo-ecologists to review the knowledge of wetland change needed to better manage wetlands of international significance.
Emerging from the 2010 PAGES Floodplain Lakes meeting in Arkansas, USA (Gell et al. 2011) this workshop focused on the nature of wetland change and variability at key Ramsar sites across the globe. It was a true coming together of disciplines demonstrated by the range of conveners, including paleolimnologists – Peter Gell (Focus 4 Water theme leader), Jessica Reeves (OZIntimate leader) and John Dearing (former Focus 4 leader) and neolimnologists – Max Finlayson (Ramsar Scientific and Technical Review Panel), Jenny Davis (Society of Wetland Scientists) and Nick Davidson (Deputy Secretary General, Ramsar). Staged in historic Queenscliff, on the edge of the Bellarine Ramsar site near Melbourne, the workshop attracted over 70 delegates from 10 countries.
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Figure 1: (A) Recent eutrophication of the coastal lagoon of Ghar El Melh (Tunisia) is currently manifested by development of green filamentous algal mats and excessive growth of Ulva rigida. (B) Sedimentary profiles for δ15N, percentage nitrogen and percentage organic matter in a dated sediment core from this lagoon indicate marked environmental changes occurred during the 1960s following the introduction of agro-chemical methods and artificial fertilizers (from Oczkowski et al. 2011). |
The presentations highlighted the substantial pressures on modern wetlands driving the loss of some sites and compromising the ecological character of others. While many recent changes have been anthropogenic in cause, paleorecords demonstrate that adverse changes may have their origins deeper in time than generally realized; that natural and induced change can be of a non-linear nature, and that the past “natural” character of a wetland can be surprisingly different from the currently perceived state. With respect to wetland management, it was contended that unanticipated natural features of the past – such as forested wetlands lost at a time in history that exceeds living memory – should be considered suitable options as “restoration” goals for degraded sites. Importantly in places where there has been little investment in wetland monitoring, the paleorecord provides the sole means of understanding the nature of past changes (an example is given in Fig 1).
The meeting had deliberate aims with respect to global wetland management. A high priority Ramsar task for 2013-2015 is to report on "Detecting, reporting and responding to change in ecological character" (mandated by the 2013 Conference of the Contracting Parties [COP 11; Resolution XI.17]), and discussion sessions in the workshop focused on framing a Briefing Note to inform the 2015 COP. Clearer understanding of the nature and drivers of environmental change is expected to provide more efficient pathways by which signatory nations may deal with changing conditions which affect their listed wetlands. As recognized at the workshop, understanding these conditions requires parties take account of past, current and future aspects of both global and local-scale forcing of change. The workshop assisted the Ramsar leadership to take steps to enable countries to take such an integrated and comprehensive approach to wetland management.
The workshop was supported by PAGES, the Australian Rural Industries RDC and several Australian NRM agencies, as well as Federation University Australia.
affiliations
1Collaborative Research Network, Federation University Australia, Ballarat, Australia
2School of Biological Sciences, University of Canterbury, New Zealand
3Environmental Change Research Centre, University College London, UK
contact
Peter Gell: p.gellfederation.edu.au
references
Birks HH et al. (2001) Aquat Ecol 35: 405-430
Flower RJ et al. (2001) Aquat Ecol 35: 369-388
Gell P et al. (2011) PAGES news 19(1): 36
Gell P et al. (2013) Hydrobiologia 708: 133-144