PAGES Magazine articles
Patrick J. Baker
9th International Conference on Dendrochronology - Melbourne, Australia,13-17 January 2014
Tree rings are the most widespread and widely used paleoclimatic proxies in the world. They record, directly or indirectly, variability in ambient growing conditions and the occurrence of past ecological and climatological events. While dendrochronology, the science of tree rings, has been an active area of research for nearly a century, in recent decades the focus of dendrochronology has widened and the complexity of the standard analytical tools and their applications has grown dramatically. As such, every four years the international dendrochronology community convenes to discuss advances in the field, be they methodological, theoretical, ecological, or climatological. The 9th International Conference on Dendrochronology brought together 270 scientists from 37 countries, with strong representation from low- and middle-income countries. Generous support from PAGES, the Tree-Ring Society, and the Melbourne Convention and Visitors Bureau provided financial assistance to more than 50 students and early career scientists from developing countries.
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Figure 1: Fire-killed Podocarpus lawrencei from the Snowy Mountains of New South Wales, Australia. A new multi-century tree-ring chronology from Podocarpus lawrencei presented by Matt Brookhouse (ANU) and colleagues is the first of its kind from the southeastern Australian mainland. |
The conference included 12 oral sessions and two symposia on subjects ranging from large-scale climate reconstructions and models to stable isotopes, dendrogeomorphology and insect outbreaks, as well as new climate-sensitive tree-ring records from the Australian mainland (Fig. 1). The opening plenary session talks by Janice Lough (Australian Institute of Marine Science) and Neville Nichols (Monash University, Australia) provided useful context and insights into the marine paleoproxy record for Australia and the major influences on the Australian climate system, respectively. The two symposia, one on divergence and tree-ring based temperature reconstructions and one on civilizations, climate and tree rings, which were organized for the entire conference community without competing parallel sessions, give a breadth of research presented. The “divergence” symposium focused on concerns that tree-ring chronologies and temperature records have begun to diverge over the past 20-30 years at high-latitude Northern Hemisphere sites; specifically, that tree-ring growth is not increasing at a rate commensurate with the observed temperature increases. David Frank (WSL, Switzerland) highlighted the wide range of methodological issues that could generate spurious patterns of divergence. Ed Cook (Lamont-Doherty Earth Observatory, USA) and Patrick Baker (University of Melbourne, Australia) presented results from the Southern Hemisphere suggesting that the opposite pattern (i.e. trees are growing faster than expected given the observed temperature increases) may have occurred in some preliminary tree-ring chronologies from Tasmania and Argentina. The general consensus was that the divergence issue has forced a careful re-examination of approaches to standardization and calibration of tree-ring chronologies and climate data, but the observed instances do not fundamentally challenge the case for tree-ring climate relationships. The “climate and civilizations” symposium moved away from methodological issues and focused on how tree-ring records can help to shed light on the impact of climate variability and climate extremes, in particular on human societies. Amy Hessl (West Virginia University, USA) presented recently published results describing the role of prolonged benign climatic conditions on the rise and expansion of the Mongol empire (Pederson et al. 2014). Dave Stahle (University of Arkansas, USA) presented a fascinating overview of research on the nexus between climate, disease, and societal collapse in Mesoamerica over the past 1000 years (e.g. Burns et al. 2014). Valerie Trouet (University of Arizona, USA) gave a provocative talk suggesting a possible link between the Maunder Minimum and pirate activity in the Caribbean based on tree-ring data and Spanish maritime historical records. These talks provide a glimpse of the diversity and quality of the nearly 250 other talks and posters that were presented over the five days of the conference.
In addition to the scientific content of the meeting, there were several other highlights. These included Lifetime Achievement awards to Ed Cook and Malcolm Hughes (University of Arizona, USA), a service to dendrochronology award to Bruce Bauer (NOAA, USA), and an award for advances in dendrochronology to Rosanne D’Arrigo (LDEO, USA). Kathy Allen (University of Melbourne, Australia) coordinated a hugely successful pre-conference Field Week in Tasmania (with 35 graduate students and early career researchers participating, as well as six local high school students from Hobart). Throughout, Australia showed off its natural beauty and charm and some rather extreme summer weather (with four out of five of the conference days >42°C. Oooof!).
affiliation
Department of Forest and Ecosystem Science, University of Melbourne, Australia
contact
Patrick J. Baker: patrick.baker
unimelb.edu.au
references
Ali Pourmand
Miami, USA, 12-14 May 2014
Speleothems (cave deposits) have emerged as one of the richest archives mined for paleoenvironmental reconstructions (Fairchild and Baker 2012). However, due to their fragile structure and often complex history, cave deposits must be handled with great care for accurate reconstruction of climate variability during Pleistocene and Holocene epochs. In May 2014, the Neptune, Paleoclimate and Stable Isotope Labs at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami, extended the opportunity to 22 enthusiastic participants from seven countries to attend a three-day workshop on processing speleothems.
Each day began with short lectures on the analytical methodologies relevant to the activities of the day. Stalagmites were embedded in epoxy, then sectioned with circular and band saws and hand-polished. Following this, X-ray fluorescence scanning was discussed for high-resolution and non-destructive elemental analysis. We also discussed different sampling techniques using manual drills and an automated micro-mill that can be used to sample for trace element, stable isotope and U-Th analyses. We also focused on how to measure Sr/Ca and Mg/Ca ratios and trace elements by employing inductively-coupled plasma optical emission spectroscopy (ICP-OES). And lastly, direct-dilution and standard calibration techniques were introduced. The methodologies explored are described below in more detail.
Improving cave hydroclimate reconstruction
The oxygen isotope composition of stalagmites is often interpreted as a proxy for changes in rainfall amount. Cave hydroclimate reconstruction, however, can be significantly improved if the oxygen isotopic composition of the water from which speleothems precipitate is known. One such novel analytical technique for hydrogen and oxygen isotopic analyses (δ2H and δ18O values) of fluid inclusions in speleothems is cavity ring-down spectroscopy (Arienzo et al. 2013). This technique is comparable to traditional methods of dual-inlet isotope ratio mass spectrometry (IRMS) or continuous-flow (CF)-IRMS, and has been used successfully to measure the isotopic composition of fluid inclusions in stalagmites from submerged caves in the Bahamas.
Clumped isotopes in speleothem analysis
A new field of rapid growth is the clumping of isotopes in paleothermometry (Ghosh et al. 2006). Isotopologues (molecules with similar chemical but different isotopic composition) have been successfully measured in various carbonate deposits for paleo-temperature reconstructions. Speleothems, however, have thus far proven elusive. Limited available data have shown that cave temperatures reconstructed using clumped isotopes are in excess of expected or monitored temperatures (Daëron et al. 2011). During the workshop, we saw the extraction and purification line for CO2 and how measurements of clumped isotopes are made on the mass spectrometer. New temperature reconstructions based on modern cave deposit experiments confirm previous findings on the complexity of interpreting clumped isotope reconstructions in speleothems.
Multi-collection ICP-MS: a novel technique
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Figure 1: Comparison between U-Th ages determined at the University of Minnesota and the University of Miami on a speleothem from Cathedral Cave, Utah (Modified from Pourmand et al. 2014). |
We also discussed a novel analytical technique for U-Th geochronometry: multi-collection ICP-MS. We saw the procedure for sample dissolution, 229Th-233U-236U spike addition, U and Th purification, and isotope dilution mass spectrometry. Data reduction is performed through an open source algorithm that uses Monte Carlo simulation for propagation of random and systematic uncertainties (Pourmand et al. 2014). A significant advantage of this approach is consideration of U and Th isotope covariances and propagation of decay constants on corrected ages. The agreement between ages measured in two laboratories demonstrates the fidelity of this technique (Fig. 1). The workshop was concluded with presentations by several participants on modern cave monitoring and paleoreconstructions.
affiliation
Department of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, The University of Miami, USA
contact
Ali Pourmand: apourmandrsmas.miami.edu
references
Fairchild IJ, Baker A (2012) Speleothem Science. John Wiley & Sons, 416 pp
Pourmand A et al. (2014) Geostand Geoanal Res 38: 129-148
Arienzo MM et al. (2013) Rapid commun mass spectrom 27: 2616-2624
Pippa L. Whitehouse1 and Lev Tarasov2
Grenoble, France, 22-24 May 2014
The aim of the “Joint model-data workshop for the Late Pleistocene evolution of the Greenland and Antarctic ice sheets” was to bring together scientists from the disciplines of field- and model-based ice-sheet reconstruction to identify outstanding issues in each field, and determine how the different communities could work together towards resolving them. An overarching theme of the workshop was the quantification of uncertainty, associated with both field data and model output.
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Figure 1: Erratics scattered on the bedrock surface of a nunatak in the Ellsworth Mountains, Antarctica. Cosmogenic exposure ages on such erratics can determine the timing of ice-sheet thinning. Photo: M. Bentley. |
In terrestrial studies of past ice extent (e.g. Fig. 1) it was highlighted that dating continues to be an issue due to a lack of dateable material, the presence of recycled carbon, and the difficulty of interpreting cosmogenic isotope data due to inheritance from multiple glacial cycles. The attribution of landform ages based on weathering characteristics is also difficult because processes can be very different from those observed in temperate regions. Relative sea-level data record the isostatic response to ice-load changes; however, such data are sparse, particularly around Antarctica.
Reviews of offshore information highlighted that many landforms relating to past ice extents are undated and sediment cores are often only acquired from trough regions, where the ice-sheet history may be very different to inter-trough regions. In addition, dating difficulties are compounded by the need to account for marine reservoir effects and interpret the stratigraphy “remotely” using underwater imagery.
In both terrestrial and marine regimes the issue of how to scale up point-based observations, e.g. from individual outcrops to ice-sheet scale, remains a challenge, although paleo-flow indicators are proving useful for reconstructing regional ice dynamics. The interpretation of radar-detected layers within the ice itself is offering novel constraints on past ice-sheet configurations over large spatial and temporal scales. However, there is little information relating to pre-Last Glacial Maximum ice margins and it remains difficult to quantify rates of ice-sheet growth.
From a modeling point of view discussion focused on how to better represent the forcing factors and boundary conditions governing past ice dynamics. Constraints on past precipitation and air temperature can be obtained from ice cores, but the interpretation of such records relies on having a reliable chronology. It was also noted that ice cores are generally drilled in ice sheet interiors, and hence may not provide reliable forcing conditions for the whole ice sheet. As an example, air and marine temperatures at the margins of ice sheets exert a strong control on ice dynamics but lack significant paleo constraints.
Models also require information relating to conditions at the ice-bed and ice-ocean interface. It was highlighted that basal topography is poorly resolved in extensive regions and there are a dearth of direct observations relating to till rheology and subglacial hydrology (both of which likely evolve over time). At the ice-ocean interface, models continue to lack realistic representations of ice calving and sub-ice-shelf melt, with the latter being restricted by our lack of knowledge on past ocean conditions.
The group identified a number of immediate research needs: better constraints on past grounded and floating ice extent (ice shelf configuration being an important component in the stress balance of an ice sheet); improved paleoclimate constraints; improved dating methods; and measurements of till strength. On the modeling side, challenges remain with regard to modeling grounding line dynamics, ice-ocean interactions and basal processes. Spatial resolution remains an issue, although adaptive grids can reduce the computational expense of modeling at high resolution. There is also a need to develop robust methods for comparing model output with data.
Finally, the development of open access databases - containing both field data and model output - was identified as an important collaborative need. A key outcome of the meeting was an agreement to promote protocols for database standardization among major Quaternary journals.
acknowledgements
This workshop was supported by the International Association of Cryospheric Sciences, the International Union of Geodesy and Geophysics, the Laboratoire de Glaciologie et Géophysique de l’Environnement, Past Antarctic Ice Sheet Dynamics, and the Scientific Committee on Antarctic Research, and organized by the Meltwater routing and Ocean-Cryosphere-Atmosphere response (MOCA) network.
affiliations
1Department of Geography, Durham University, UK
2Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St John's, Canada
contact
Pippa L. Whitehouse: pippa.whitehousedurham.ac.uk
Jürg Beer
2nd Solar Forcing Workshop, Davos, Switzerland, 20-23 May 2014
Understanding climate change requires quantification of the major forcing factors (e.g. solar, volcanic, greenhouse gases). At the PAGES' Solar Forcing working group’s first workshop in 2012 we addressed the role of solar forcing by trying to quantify it and then feed the results into climate models. The resulting model runs were then compared with paleoclimatic data. This approach turned out to be unsatisfactory for two reasons.
First, direct satellite based measurements of the total solar power arriving at the top of the atmosphere (total solar irradiance, TSI) and its spectral distribution (spectral solar irradiance SSI) have only been available since 1978. Because the Sun has been in a state of very high activity during this period all our detailed instrumental information about the Sun is not representative for periods of normal or low activity such as the Maunder minimum (1645-1715 AD). Also, as a result of degradation effects and discrepancies between different types of instruments there is still no generally accepted composite of TSI even for the instrumental period.
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Figure 1: Seven reconstructions of total solar irradiance for the past 400 years (for details see Schmidt et al. 2012). |
As physical solar models are not yet capable of reproducing observed solar variability, and in particular long-term TSI and SSI changes, the only information on decadal to millennial scale changes in solar activity available today is based on cosmogenic radionuclides such as 10Be and 14C. Although these reveal the relative level of solar activity, converting this into a quantitative solar forcing in Wm-2 remains unsolved. This is the reason why published TSI reconstructions usually resemble each other in shape but have a large spread of amplitudes (Fig. 1).
The second complication in assessing the role of solar forcing is that quantifying the climate’s response to solar forcing is difficult. For example, it seems that SSI plays an important role in atmospheric chemistry and dynamics. But in order to study its effect, quantitative data for all forcings and reliable long-term paleoclimate records for model validation are needed – both of which are currently unavailable at the required quality. Also, different models respond differently to the same forcing change, raising the fundamental question of whether all relevant feedback processes of the climate system have been implemented correctly.
These difficulties motivated us to “put the cart before the horse” and to investigate ways to assess the role of solar forcing directly from paleodata. One challenge of this detection and attribution approach is to detect those climatic events in the past which can unambiguously be attributed to solar forcing changes. This requires a large number of millennial scale records of well-dated paleodata with high temporal and spatial resolution. Fortunately such work is in progress (e.g. the PAGES 2k initiative) and promising new paleodata were presented during the workshop.
Another challenge of this approach is that the state of the climate system at a specific point in time reflects the integral response of the system to all forcings. For example, periods of low solar activity (e.g. Dalton minimum, 1790-1830) can coincide with volcanic eruptions (e.g. Tambora, 1815). Furthermore, due to feedback mechanisms, forcings can also affect the climate system long after their initial occurrence.
To tackle these issues, the workshop participants recommend:
• Choosing periods of extreme solar activity that show minimal interference with volcanic eruptions for solar signal detection and attribution exercises.
• Using the fact that solar forcing has cyclic components with well-defined periodicities to discriminate between solar and volcanic forcing
• Identifying regions of high sensitivity for solar forcing based on existing paleodata and model runs. New local paleodata should be produced for these regions.
• Intensifying efforts to forward-model paleodata.
• >Not using hemispheric or global mean temperature, because these average out regional changes and shifts in climatic features.
This was the last workshop of the PAGES Solar Forcing Working Group. The outcome of this and of the previous meetings will serve as the basis for the Solar Working Group synthesis product consisting of several publications.
affiliation
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
contact
Jürg Beer: beereawag.ch
references
Editors: Chen G, Daniau A-L, de Porras ME, Elmore A, Mills K, Saraswat R, Phipps S, Reyes A and Kiefer T
Climate of the Past
www.clim-past.net/special_issue65.html
This special issue provides a cross-section of the research presented at the PAGES Young Scientists Meeting and addresses the processes of past climatic and environmental change, as well as the methodologies required to study them. All 14 first authors and the first six of the guest editors are early-career researchers who attended the meeting held on 11–12 February 2013 in Goa, India.
Hydrographic changes in the Agulhas Recirculation Region during the late Quaternary
D.K. Naik, R. Saraswat, N. Khare, A.C. Pandey and R. Nigam
Late Glacial–Holocene climatic transition record at the Argentinian Andean piedmont between 33 and 34° S
A.E. Mehl and M.A. Zárate
Blue intensity and density from northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information
J.A. Björklund, B.E. Gunnarson, K. Seftigen, J. Esper and H.W. Linderholm
Orbital- and millennial-scale environmental changes between 64 and 20 ka BP recorded in Black Sea sediments
L.S. Shumilovskikh, D. Fleitmann, N.R. Nowaczyk, H. Behling, F. Marret, A. Wegwerth and H.W. Arz
Environmental and climatic changes in central Chilean Patagonia since the Late Glacial (Mallín El Embudo, 44° S)
M.E. de Porras, A. Maldonado, F.A. Quintana, A. Martel-Cea, O. Reyes and C. Méndez
Seasonal changes in glacial polynya activity inferred from Weddell Sea varves
D. Sprenk, M.E. Weber, G. Kuhn,
V. Wennrich, T. Hartmann and K. Seelos
Reexamining the barrier effect of the Tibetan Plateau on the South Asian summer monsoon
G.-S. Chen, Z. Liu and J.E. Kutzbach
Treeline dynamics with climate change at the central Nepal Himalaya
N.P. Gaire, M. Koirala, D.R. Bhuju and H.P. Borgaonkar
Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland
V.V. Matskovsky and S. Helama
Expressions of climate perturbations in western Ugandan crater lake sediment records during the last 1000 years
K. Mills, D.B. Ryves, N.J. Anderson, C.L. Bryant and J.J. Tyler
Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments
E. Dietze, F. Maussion, M. Ahlborn, B. Diekmann, K. Hartmann, K. Henkel, T. Kasper, G. Lockot, S. Opitz and T. Haberzettl
Similarity estimators for irregular and age-uncertain time series
K. Rehfeld and J. Kurths
Investigating vegetation–climate feedbacks during the early Eocene
C.A. Loptson, D.J. Lunt and J.E. Francis
Uncertainties in the modelled CO2 threshold for Antarctic glaciation
E. Gasson, D.J. Lunt, R. DeConto,
A. Goldner, M. Heinemann, M. Huber, A. N. LeGrande, D. Pollard, N. Sagoo, M. Siddall, A. Winguth and P.J. Valdes
The future of PAGES. Participants at the 2nd PAGES Young Scientists Meeting 2013 in Goa, India.
Thomas Crowley from the University of Edinburgh, a pioneer in the field of paleoclimatology, passed away on May 8, 2014. A few days before, he shared some retrospective thoughts on questions asked by his colleagues and friends, Hans von Storch and Heinz Wanner. His wife Gabi Hegerl helped to edit the interview.
Question: Tom, you are looking back on a long career in geosciences. Could you sketch your path and what attracted you to this field?
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Figure 1: Tom Crowley (1948-2014) |
I started out as a marine geologist and had the good fortune to be involved in a project in the 1970s involving expanded exploration of the world oceans. The project leader was John Imbrie, a truly inspiring scientist. He developed a statistical methodology for converting assemblages of marine organisms into temperature, based on the observation that different types of plants and animals live in different temperature zones. This was formalized using regression methods and applied by the group CLIMAP (Climate: Long range Investigation, Mapping, and Prediction), whose purpose was to record the entire surface of the ocean during the last ice age so that climate modelers, who were just becoming known to the geologists, could test their models under radically different boundary conditions.
In my particular corner of the ocean, from the North Atlantic, East of the Grand Banks to the West coast of Africa, there was a distinct relationship between types of fauna and flora and the ocean currents. You could trace the Canary current, and the North Atlantic current just by looking at the distribution of the organisms. This got me interested in the question: What mechanisms might be invoked to infer changes in the past ocean circulation? It had already been known for almost 50 years that the Gulf Stream during the Last Glacial Maximum (~20,000 yrs BP) flowed from West to East around 40°N rather than northward into the Northeast Atlantic. The question as to what would cause the ocean to do that was a big interest in my life and always fascinated me as a trigger point.
I was extremely fortunate to meet Jerry North, a modeler interested in applying energy balance models to past climates. When moving to Texas to work with Jerry we went out for Mexican lunches every day and expanded our energy balance work to supercontinents. This was a logical and satisfying application for energy balance models, because the land sea distribution primarily dominates the temperature response. I also brought in my background in Paleozoic geology. It seemed like the best of both worlds going into the past to explore things I knew about, and yet applying new techniques of climate modeling to better understand the great Paleozoic glaciations.
Q: What was the most important twist to your career?
I was very fortunate to receive an invitation from Klaus Hasselmann in Hamburg to visit their group and help to apply their ocean models to past climates. We looked at the Central American Isthmus, which had been open for several tens of millions of years before it closed, around the time when ice started to form in the northern hemisphere. We did some experiments opening and closing the Isthmus in order to explore the effect of its closure about three million years ago on global climate. The closure of the Isthmus turned out to be an important event, and the model showed features that bore a lot of resemblance to the geological data. This launched a series of further studies with Ernst Maier-Reimer, Uwe Mikolajewicz and Christoph Heinze, in which we examined the effects of other “ocean gateway” changes such as the Drake Passage. It was very satisfying to be moving along two scientific fronts, learning about ancient climates and using a model that was also being applied for the first detection and attribution studies of modern climate change.
Q: Your Science paper in 2000 was a key publication for paleoscience. Was this your greatest scientific achievement?
I started working on climate change over the last few centuries, because people were getting very interested in that topic. Over time a head of steam built up in terms of reconstructing climates and the climate forcing for those periods. I realized that many of the inferred climate changes could actually be reproduced very simply with an energy balance model, just by changing volcanism or solar variability. This result virtually fell into my lap and I was able to make an important, or at least a valuable contribution, being able to estimate how big the greenhouse gas signal was compared to solar or volcanically forced climate change and the Little Ice Age (LIA). By constraining the LIA climate change we could show that already in the 20th century global warming was taking place at about the size it was expected to be from the forcing. This paper (Crowley 2000) is one I might be known more for than anything else. Yet it is not what I necessarily consider my most important contribution.
Q: What then do you consider your most important scientific contribution?
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Figure 2: Tom Crowley's "most important scientific contribution". Late Precambrian (ca. 600 M yr BP) (A) ice cover and (B) temperature simulations. The annually average temperatures show that large areas of open water still might have existed while the continents were ice covered. The black lines represent the Precambrian landmasses. From Hyde et al. (2000). |
That was a little bit more arcane, involving the subject of Snowball Earth, which is an unusual period of time, about 600 million years ago when the earth was in a deep freeze, with ice on all land and maybe on all of the oceans too. The world was in a supercontinent configuration. The earth was at one of its most critical points with respect to the evolution of life. In my view the origin of life itself is not as important as the evolution of multi-celled animals, which have a much narrower range of environmental restrictions. We knew that in order to study Snowball Earth properly we needed to couple an energy balance model to an ice sheet model. We got a grant from a very open minded NSF program director to allow us to explore Snowball Earth. We discovered that we could simulate a frozen-over earth fairly easily by just continuing to drop CO2. However, we realized that for one of our solutions we did get ice on land, but open water over parts of the ocean (Fig. 2). This indicated that maybe life was still frozen out on land, but had taken up an oasis in the open water area of the ocean that allowed it to breed successive generations of multi-celled intermediate organisms that provided the basis for the great explosion of life at the end of that period. We didn’t claim this was the correct explanation, but it is a legitimate viewpoint that cannot be dismissed despite 14 years of criticism. I feel this paper (Hyde et al. 2000) is probably the most important thing that we ever did.
Q: What is your judgment concerning the hiatus in the global temperature development of the last 15 years?
This oscillation has all the markings of a natural fluctuation, maybe an El Niño imprint. Extended-duration El Niños happen sometimes. However, I think the hiatus in global temperature has not quite been interpreted correctly. Based on my recent work that is just being published (Crowley et al. 2014), the system is now in a basic state that is more or less neutral, or maybe even in a little bit above average global temperatures for the last 15 years. So there may even be some statistical legitimacy for stating, not expecting, that temperatures could drop some 0.1-0.2°C for a few years. Of course temperature is going to bounce back very strongly but we just can’t say unless we can predict natural variability.
Q: How do you feel about the development of climate models?
Climate models have been on such a consistent track for the last 20, 30 years that it is hard to imagine them changing significantly. Basic theory and energy balance still plays a legitimate role, because it keeps reminding people that despite the complexity of the system there are some responses that are almost linear with respect to forcing, and we have to understand why this is so, because it is not obvious. Take the example of the ideal gas law. Sometimes it seems like climate scientists want to solve the ideal gas law by integrating the interactions between every single atom in a box of gas. But of course the alternative way of doing it is to use the pV=nRT relationship to calculate the pressure difference. I think we need to keep going back to these basic concepts like energy balance and realize that they have a great deal to offer.
Q: You traveled around the world in the Royal Navy, did this experience have any bearing on your later scientific career?
I learned many things there, among them one worth sharing with students in particular. I was teaching lower level college classes on navy ships for the Western Pacific fleet to students that would come on their own time to take courses. I really came to respect these students and learned that it is not how smart you are, but how much you care if you are going to get an education. That stuck with me forever.
references
Crowley TJ, North GR (1991) Palaeoclimatology. Oxford University Press, 339pp
Crowley TJ (2000) Science 289: 270-277
A new look and a new name
Following our review of 20 years of PAGES news in the last issue, we realized, based on our track record, that a facelift was overdue. But this time we’ve gone even further and we’ve also changed the name to Past Global Changes Magazine, or PAGES Magazine for short. We believe that this more accurately reflects PAGES news’ evolution in recent years from a simple newsletter into more of a magazine-style publication. We also hope that our new look magazine, with its more descriptive title, will attract a broader audience.
SSC Meeting in Paris
PAGES’ Scientific Steering Committee (SSC) met in Paris in January 2014. In addition to approving four new Working Groups, the SSC also reviewed Working Group annual reports, met with Future Earth representatives and discussed PAGES’ strategic direction in the coming year. The article on the opposite page gives an overview of the ongoing developments. The meeting was preceded by a day-long symposium featuring research talks by PAGES SSC members and a range of Parisian paleo-scientists.
New SSC members
We are pleased to welcome three new members to the SSC in 2014:
- • Peter Gell is a paleolimnologist at the University of Ballarat in Australia, and is leader of the Focus 4 Water Theme.
- • Kathy Willis is a paleoecologist at the University of Oxford, UK, and has also recently been appointed Director of Science at Kew Royal Botanical Gardens in London. She is the leader of the Focus 4 Biodiversity Theme.
- • Michal Kucera is a paleoceanographer and micropaleontologist at the University of Bremen, Germany, and was co-leader of the MARGO glacial sea surface reconstruction initiative.
Current SSC member, Sheri Fritz, was elected to serve on the Executive Committee (EXCOM) to replace outgoing SSC member, John Dearing. We’d like to take this opportunity to thank John in addition to the other members who recently rotated off the SSC, Eric Wolff, Michael Schulz and Fátima Abrantes, for their invaluable support and contributions throughout their terms.
Support for meetings
At its two most recent meetings in October 2013 and January 2014, the EXCOM granted support for a total of 19 scientific and educational meetings, which are either organized by PAGES working groups or relevant to PAGES’ scientific priorities. The PAGES-supported meetings are highlighted in our online calendar at: www.pages-igbp.org/calendar/pages-sponsored-events.
The next deadline for PAGES meeting support applications is 2 June. Details and application forms can be found on the PAGES website > My PAGES > Meeting Support.
Staff update
Welcome to Brigitte Schneiter, who has recently joined our team in the Finance and Office Manager role.
Upcoming PAGES Magazine issues
The next issue of PAGES Magazine will focus on atmospheric dust and will be edited by members of the ADOM Working Group. Contributions to this issue are now closed.
The following issue will be coordinated by the Past4Future project, of which PAGES is a project partner, and will focus on interglacials. Contributions will be sought in the coming months.
PAGES 2nd YSM special issue
Published articles have begun appearing in the Climate of the Past special issue emerging from the PAGES 2nd Young Scientists Meeting in Goa, India in February 2013. All of the first authors and most of the guest editors are early-career researchers who attended the YSM. You can view the papers, some published, some still in discussion at: www.clim-past-discuss.net/special_issue74.html
PAGES’ product database update
Over the last few months we have been working hard to improve the PAGES online product database. This database provides a record of all the products from the Past Global Changes project. We can now allocate products to Working Groups or events to produce an online archive of a group’s activities.
You can view the database at: www.pages-igbp.org/products/latest or go to the relevant
Working Group page and view their products. Please let us know if you see any gaps or errors, and send us any meeting documents e.g. presentations and posters, which we can post to create a complete online archive of an event or activity.
The Earth System Science landscape is being shaken thoroughly these days; the associated changes bear risks as well as opportunities. Accordingly, the coming one to two years will be a time of transition in PAGES’ internal organization and external relationships. The overview below outlines the developments in the global change program framework, the plans for PAGES, and a call for new working groups.
Evolving program setting
At the macro level, Future Earth, the new platform for global sustainability research, is getting ready to assimilate PAGES’ parent organization, the International Geosphere-Biosphere Program (IGBP), by the end of 2015, in addition to two other Global Environmental Change programs, DIVERSITAS, and the International Human Dimensions Programme. The World Climate Research Program (WCRP) will also become an affiliate.
These structural changes serve expanding scientific ambitions: to provide “the knowledge and support to accelerate our transformations to a sustainable world” by integrating research better across disciplines, involving natural and social scientists, and engaging users of scientific information (a.k.a. stakeholders) in developing scientific questions and output strategies.
Over the last half year, Future Earth has become functional by establishing management structures and its first scientific activities. The recently launched website, futureearth.org, and the blog are worth a visit.
Twenty-seven Global Environmental Change projects, PAGES being one of them, have been invited to join the Future Earth network, and PAGES’ Scientific Steering Committee (SSC) has indeed decided to request official membership over the coming months. At the same time, it was decided to strengthen collaborative ties with WCRP to ensure that the traditionally strong paleoclimate research in PAGES has a productive platform.
In the recently submitted funding proposals to the US and Swiss National Science Foundations, PAGES proposed a revised, streamlined science structure. It responds to the changing landscape of science programs and encourages integrative activities related to the sustainability issues prioritized by Future Earth and WCRP.
Science structure changes
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Figure 1: Transition from the current science structure to the new one. The three new topical themes define PAGES’ scientific scope. The distinct methodological cross-cutting themes on chronology, proxies and modeling will be abandoned; the boundaries between the distinct foci will be dissolved and a new category of integrative cross-topical activities will be established. Ongoing Working Groups will be re-mapped onto the theme space and new ones will be solicited. |
The new PAGES science structure was inspired by community feedback solicited at the PAGES Open Science Meeting in 2013 in Goa and by discussions within the frameworks of IGBP, Future Earth and WCRP. The revised scheme reflects the key components of the Earth system: climate, environment, and humans (Fig 1). These three themes define the range of PAGES’ scientific scope. Dissolving the boundaries between them may better reflect the increasingly integrative nature of PAGES’ science than the current siloed foci structure. The Climate theme represents quantitative climate system dynamics from a paleo-perspective. The Environment theme deals with biogeosphere and ecosystem dynamics that interact with climate and introduce long-term feedbacks into the Earth system. The Humans theme covers long-term environmental changes where humans are a major agent and where environmental changes have a demonstrable effect on the functioning of both ecosystem services and societies.
A new format, cross-topical integrated activities, has been introduced to facilitate scientific exchange, synthesis, and outreach across the existing working groups and the Future Earth and WCRP networks. Targets for such cross-topical integrated activities so far include Thresholds, tipping points and multiple equilibria in the Earth system; Extreme events and risk assessment; The Earth system in a warmer world; and Data management in support of data service efforts such as US NSF's EarthCube.
Over the next year, the current structure will be replaced by the new one (Fig. 1) and the ongoing current PAGES Working Groups will be mapped onto the new framework.
Call for new working groups
With the structural changes afoot, and the fact that a significant number of the current working groups are now entering their final phases, it’s an opportune time to announce an open call for new working groups to populate the new science structure, particularly the Humans and Environment Themes.
Based on a review of PAGES working groups, the PAGES SSC recently tightened the definition and organizational requirements of PAGES working groups: Working groups should run in ca. 3-year phases with each phase culminating in an intermediary or final major product (e.g. synthesis article, special issue, database, methodology, web-tool). After completing the phase, the working group either sunsets, or proposes a follow-up phase with a new work plan and another major product at the end.
The next deadline for new Working Group proposals is June 2 for consideration at an Executive meeting in June. The guidelines and application form are available at: http://pastglobalchanges.org/science/wg/intro. You can also contact Thorsten Kiefer (kieferpages.unibe.ch) to discuss your proposal ideas.
Bernd Zolitschka1 and Jennifer Pike2
Natural archives containing yearly information are impressive, not only esthetically (see cover picture) but also in terms of their scientific potential. They hold the key to bridging the divide between long but low-resolution paleoscience and short but detailed climatic and environmental monitoring. Annually layered archives theoretically can combine the best from both worlds by delivering long records at sub-annual resolution. In practice, however, reality often stands in the way by presenting considerable challenges that need to be overcome before producing paleorecords at monitoring quality. Therefore, researchers are working hard to improve methodologies and understanding in order to maximize the yield from annual-resolution archives, and we report in this magazine issue on some of the latest advances and their limitations.
The Varves Working Group
The potential of annually laminated (varved) sediments for developing detailed chronologies of past environmental change was recognized by geologists more than a century ago. However, methodological limitations in the handling of varved sediments and in developing quantitative paleoenvironmental interpretations established a perception of subjective and unreliable results. Since the end of the 20th century, with the advent of new coring techniques and innovative analytical methods, varved records have now been established as an important resource for environmental and climatic research, and scientists are working towards seasonal resolution.
The PAGES Varves Working Group (VWG) is the nucleus for this magazine issue. The group was initiated in 2010 to maximize the gain from varved lacustrine and marine records in association with other annually resolving archives (tree rings, corals, bivalve shells, ice cores, speleothems). Since its inception, the VWG has addressed a number of topics including: methodological achievements; setting up the best possible varve chronologies including age uncertainties; calibration of inherent climatic and environmental signals; data management and processing. Additionally, learning from, and integrating, other annually resolved archives is crucial for developing an understanding of the past.
The VWG organized three dedicated, cross-disciplinary workshops to discuss cutting edge topics in high-resolution natural archives. These workshops were held in Lääne-Virumaa, Estonia (2010; Francus et al. 2010), Corpus Christi, USA (2011; Besonen et al. 2011) and Manderscheid, Germany (2012; Zolitschka et al. 2012). During this most recent workshop the idea of dedicating a PAGES magazine on year-to-year analysis of annually resolved natural archives was born. The following twelve articles document the state-of-the-art of the challenge of working at the highest temporal resolution and of harnessing a maximum of environmental and climatic information. An underlying research question for this PAGES magazine is: How can we use natural archives to approach the temporal resolution of instrumental records? Some of the articles address this by reporting on previous research (Lamoureux and Francus; St. George; Turney et al.; Liangcheng et al.), or new or advanced techniques (Nakagawa; Grosjean et al.; Rasmussen et al.), or new results (Ojala et al.; Kemp; Schöne and Surge; Fairchild et al.; Schwikowski et al.). Overall, the articles demonstrate that the process-level understanding of records has improved tremendously in recent years. Natural annual recorders can provide accurate reconstructions of past behavior of climate-system components on the robust and absolute timescales that are needed to better understand the mechanisms involved, and to test models of future change.
Sediments (lacustrine, marine)
The study of varved sediments is progressing quickly towards analyses at annual and seasonal resolution. High-precision depth control is a necessity for high-resolution studies. When using “destructive methods” that require sampling the sediment core, new cutting and subsampling techniques have been developed that enable core sectioning and parallel core correlation at annual resolutions. These new methods also correct for depth changes due to expansion and contraction during storage (Nakagawa et al.).
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Figure 1: Micro-XRF elemental grid scan of a varved sediment section from the Piánico paleolake (Italy) documenting a subannual geochemical profile for the element Ca (image courtesy of Peter Dulski). |
To reach sub-annual resolution, non-destructive scanning techniques such as element count-rates analyzed by micro-XRF scanning (Fig. 1) are often more effective. Another such method is hyperspectral imaging, which is used to identify organic components and minerals on the basis of their diagnostic light absorption. Not only is this method promising for lake and marine sediments but it is also applicable to tree rings and speleothems (Grosjean et al.).
Just as important as high-resolution chronology and analysis is the understanding of sediment-formation processes. Deposition of abiotic and biotic components can be monitored with sediment traps and time-series data used to calibrate varves and their paleolimnological proxies against instrumental data (Ojala et al.). Long-term monitoring with sediment traps in the Arctic has permitted the identification of quantitative processes that form varves and the documentation of the climate signals conveyed through runoff generation and downstream sediment transport. Thus, previously unrecognized hydroclimatic control mechanisms on sediment delivery are detectable (Lamoureux and Francus).
Marine varved sediments are not restricted to oxygen-depleted or silled basins, or to productive shelves and slopes. They are also found at deep-sea sites with massive particle fluxes that suppress benthic faunal activity and therefore preserve laminations. Thus, the traditionally centennial-resolution quantitative paleoceanographic reconstructions can be increased to annual or seasonal resolution using scanning electron microscope techniques. Moreover, stable isotopes derived from diatoms preserved within varves offer insights into dynamic processes of ocean-atmosphere variability on seasonal timescales (Kemp).
Organisms (trees, bivalves)
Tree-ring width records have been developed at thousands of locations, particularly in the Northern Hemisphere. Their broad regional coverage and extended replication forms the basis of a global network representing a valuable resource for high-resolution climate reconstruction (St. George). In the Southern Hemisphere relatively few tree-ring records are available but new methods are being developed in Australasia to exploit their potential in this region. Analytical advances can characterize wood at the level of single cells, enabling a detailed study of the role of environmental conditions in tree-ring formation. These wood-property chronologies are developed for samples without any seasonal signal in tree-ring width and thus demonstrate the paleoscientific potential of trees in regions where standard analyses have failed. Another exciting possibility in Australasia is radiocarbon calibration using subfossil kauri trees from northern New Zealand that potentially cover the complete range of 14C dating (Turney et al.).
Bivalves, present in many aquatic environments, can record environmental changes at unprecedented temporal resolution - from years to days. Their individually short growth-increment chronologies can be combined by cross-dating segments with overlapping life spans of other individuals to develop composite chronologies covering millennia, while stable isotope data and elemental ratios provide process-driven environmental information (Schöne and Surge).
Physical records from travertine and ice
Calcareous cave deposits (speleothems) are common features in karst environments. Statistical analyses of their growth-rates reflect the mixing of rainfall with groundwater and are used to reconstruct hydroclimate and, more recently, annual temperature changes (Tan et al.). Seasonal climatic signals are transmitted to speleothems via the quantity, chemistry and isotopic composition of percolating water in caves. Advances in high-resolution measurements of stable isotopes, trace elements and organic fluorescence reveal sub-annual variations in speleothem chemistry that result not only in improved chronologies, but also in seasonal climatic and environmental changes (Fairchild et al.).
Polar ice caps provide a wealth of information on past climates and environments as well as a very accurate chronology through counting the annual layers. Historically, ice-core chronologies have relied on manually detecting and counting annual layers; however, the development of novel algorithms for automated and objective annual layer counting has allowed researchers to refine and extend these chronologies. Parallel analysis of different impurity records is also recommended to establish a robust chronology (Rasmussen et al.). High-mountain ice cores have the potential to provide subannual ice-core records; however, annual layer thinning with increasing depth increases dating uncertainties. While new continuous flow analysis-techniques are increasing the spatial resolution, calibration with instrumental data is often still restricted to multi-year resolution, which limits the potential of annual resolution from mountain glacier ice cores (Schwikowski et al.).
A major aim of the VWG is to connect research groups working on different annual archives, eventually leading towards integrated model-data comparisons at an annual to subannual scale. Products of the VWG include overview articles (Ojala et al. 2012; Francus et al. 2013) and the “Varves Image Library” (work in progress), providing easy access especially for young scientists to digital images of a wide range of varved sediments, the “Varve Data Base” (Ojala et al. 2012) with a large variety of data for well-published varved sequences, and the “Varves Literature Archive”, a constantly updated and searchable text file with varve-related publications.
links
Varves Image Library:
pastglobalchanges.org/science/end-aff/varves-wg/varves-image-library
Varves literature archive:
pastglobalchanges.org/download/docs/working_groups/vwg/Varve%20publications.pdf
Varves database:
pastglobalchanges.org/science/end-aff/varves-wg/data
affiliations
1Institute of Geography, University of Bremen, Germany
2School of Earth and Ocean Sciences, Cardiff University, UK
contact
Bernd Zolitschka: zoliuni-bremen.de
references
Besonen M et al. (2011) PAGESnews 19(2): 88-89
Francus P et al. (2010) PAGESnews 18(2): 90-91
Francus P et al. (2013) J Geol Soc Swe 135: 229-339
Layers within layers: quantifying seasonal versus event processes in Arctic clastic varved sediments
Scott F. Lamoureux1 and Pierre Francus2
Advances in the interpretation of Arctic clastic varved sediments have emerged from long-term process monitoring, and micro-sedimentological and micro-geochemical analyses. These developments permit the identification and interpretation of the quantitative processes that form varves and allow novel paleoclimate records to be generated.
Clastic annually laminated (varved) lake sediments are important paleo-records from Arctic regions. They offer high temporal resolution where other natural archives are localized (ice cores) or unavailable (tree rings), and substantially contribute to regional paleoclimate syntheses (Kaufman et al. 2009). Clastic varves are composed of mineral material introduced to the lake by streams and rivers. The climate signal is conveyed through the generation of runoff and downstream sediment transport into the lake. Since the pioneering work of Hardy et al. (1996), who conducted field process studies in Arctic Canada to determine a quantitative relationship between climate, hydrology, sediment transport and varve deposition, a number of sedimentary studies have refined our understanding of the control mechanisms over sediment delivery to lakes and the type of paleoenvironmental information contained within clastic varves.
Hydroclimate controls over sediment transport
A key limitation to most field process studies has been their short-term nature of often only 2-3 years. Sustained monitoring efforts have emerged during the past decade, particularly the Cape Bounty Arctic Watershed Observatory (CBAWO; http://geog.queensu.ca/cbawo) in the Canadian High Arctic. This project, initiated in 2003, develops long-term climate, hydrological and sediment datasets to investigate the processes that contribute to the formation of clastic varves and their paleoclimate record.
The work of Hardy et al. (1996) established a quantitative process relationship between upper air temperatures, discharge, and suspended sediment transport at Lake C2 on northern Ellesmere Island. Based on this relationship, meteorological data from the nearest long-term weather station were used to estimate total suspended sediment transport for the years 1950-1992. These estimates were then compared to the varve thickness record. Results showed strong similarity between the varve record and the modeled results, suggesting that the varve thickness was primarily controlled by summer air temperatures.
However, longer studies at CBAWO and elsewhere have shown limitations to the temperature-runoff relationship. For example in spring, the snowpack becomes exhausted as the season progresses with the result being that sediment transport is controlled at the seasonal scale by the quantity of available snow (Cockburn and Lamoureux 2008). While the melting snow in the catchment controls the total runoff and sediment transport during the spring freshet, few studies have been able to assess the role of major rainfall on sediment transport and varve formation. Some studies in northwestern North America (Cockburn and Lamoureux 2007) and the Arctic (Francus et al. 2002; Chutko and Lamoureux 2008) have suggested rainfall only plays an intermittent role in the formation of clastic varves, but these studies depend on statistical assessment of the varve and related meteorological records, while direct rainfall and sediment transport data from the region were largely non-existent.
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Figure 1: Four years of river discharge and suspended sediment flux at Cape Bounty Arctic Watershed Observatory (CBAWO). Pie size is scaled to the magnitude of flux. Note the contrast between 2006 when snowmelt dominated runoff and sediment transport, compared to 2009 when two major rainfall events were responsible for 89% of sediment transport (after Lewis et al. 2012). |
Therefore the long record from CBAWO provides valuable first systematic indications of the role of major rainfall events (although the likelihood of observing a rainfall event is low and unpredictable in the relatively dry High Arctic). Monitored rainfall events demonstrated that the sediment transport by a single rainfall event can equal, or exceed, that of the snow melt freshet (Lewis et al. 2012; Fig. 1). For example, a 35.7 mm rainfall event lasting several days in July 2009 transported 89% of the seasonal sediment flux, and would have presumably dominated the annual sedimentary structure. Analyses of smaller rainfall events from other years further suggest that the associated increase in runoff and sediment transport is non-linear (Lewis et al. 2012). For example, prior dry soil conditions can result in minimal discharge response and sediment transport. Hence, the sediment response to rainfall depends on both the amount and intensity of the rainfall, and the levels of soil moisture.
The results that have emerged from a decade of observation at CBAWO demonstrate the challenge of quantifying the role of rainfall in the process of varve formation; however, they also suggest that statistical associations of rainfall influence inferred from detailed sedimentology (Francus et al. 2002; Cockburn and Lamoureux 2007; Cuven et al. 2010; Lapointe et al. 2012) are highly plausible. Further refinement of these approaches is warranted, given the challenge of recognizing rainfall character from proxy evidence.
Emergent analysis methods and new proxies
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Figure 2: Results of an image analysis of particles in five varves from marine sediments in Saanich Inlet, British Columbia. This image was obtained using a flatbed scanner under cross-polarized light while particle size analysis was carried out at 220 µm intervals (102 measurements in total). Interpreted seasons are indicated as winter (W) and summer (S) (Lewis et al. 2010). Blue dashed lines indicate the transition from underlying terrigenous sediment to overlying biogenic sediment and red lines indicate the opposite transition. |
There is a substantial need to systematically identify and determine operational proxies for interpreting long-term variations in fine-scale facies. The sedimentological analysis of varves has traditionally been done using thin sections, and the detailed study of intra-varve (or subannual) structures has been fruitful to identify single snowmelt and rainfall events (Cockburn and Lamoureux 2007; Chutko and Lamoureux 2008). Now, new techniques including micro X-ray fluorescence (µ-XRF) core scanning permit even more detailed characterization of subannual sedimentary structures, recognition of additional facies, and analysis of grain sizes (Cuven et al. 2010). Furthermore, semi-automated scanning electron microscopy acquisition and image analysis have made scanning of particle size structures possible even at (sub)annual resolution (Fig. 2). In a recent study, Lapointe et al. (2012) developed a 1750-year particle size distribution record from a High Arctic varve record, and through statistical analysis revealed significant relationships with summer rainfall. Hence, these new sedimentological approaches are providing the means to further discern the influence of rainfall and other climatic events on the sedimentary varve record in the Arctic and elsewhere.
Future developments
Recent work with Arctic varves has uncovered previously unrecognized hydroclimatic controls over sediment delivery to lakes, particularly the important, occasionally dominant, role of summer rainfall on sediment yield. Recognition of these hydroclimatic influences has been advanced through sustained field monitoring efforts, while new methodologies and an emphasis on fine-scale sediment facies analysis in clastic varves has yielded new proxy indicators and novel paleoclimate records. These substantial advances will help to improve the fidelity of paleoclimatic interpretations of Arctic varves and clastic varves in general. The next frontier will be the explicit combination of detailed facies analysis with proxy indicators (e.g. µ-XRF geochemical data) and other novel sedimentological methods such as image analysis.
acknowledgements
Funding has been provided by NSERC, the Canadian International Polar Year Program, and ArcticNet NCE, and field logistics by the Polar Continental Shelf Program.
affiliations
1Department of Geography, Queen’s University, Kingston, Canada
2Institut National de la Recherche Scientifique, Centre Eau Terre et Environnement, Québec, Canada
contact
Scott F. Lamoureux: scott.lamoureuxqueensu.ca
selected references
Full reference list under: pastglobalchanges.org/products/newsletters/ref2014_1.pdf
Chutko KJ, Lamoureux SF (2008) Can J Earth Sci 45: 1-13
Cockburn JMH, Lamoureux SF (2007) Quat Res 67: 193-203
Cuven S et al. (2010) J Paleolimnol 44: 803-817