PAGES Magazine articles

Antarctic Research Centre, Victoria University of Wellington, New Zealand

Holly is an ice-core and aerosol scientist with interests in biogeochemistry, sea ice, dust and climate-relevant aerosol. She is currently working on novel proxies of marine primary production in Antarctica and the Southern Ocean to understand the interactions between phytoplankton and climate on a range of timescales.

Giulia Sinnl

Copenhagen University, Denmark

A physicist on loan to paleoclimatology, Giulia completed her PhD on the timescales of Greenland ice cores, under the supervision of Prof. Sune Rasmussen. Her research has focused on improving our interpretation of the Earth's past climate by adjusting the chronological alignments between paleo-archives, using tools such as annual-layer counting or measuring cosmogenic radionuclides.

Olivia Williams

Oregon State University, Corvallis, USA

Olivia is a paleoclimatologist and stable isotope geochemist currently completing a PhD with Dr. Christo Buizert at Oregon State University. Her project focuses on noble gas ratios as a proxy for previous melting in Greenland ice cores. By improving our understanding of melt in past warm periods, she hopes this project will be useful for understanding the cryosphere of today.

Ailsa Chung

Instituté of Geosciences and the Evironment, Universite Grenoble Alpes, France

Ailsa is doing her PhD in Grenoble on modeling the age of ice in Antarctica by constraining a numerical model with radar observations. She applies the model to predict the age of the ice that might be found at Little Dome C in Antarctica where there are two current ice-core drill sites from the European Beyond EPICA and the Australian Million Year Ice Core projects. When not modeling ice, she can be found climbing and camping in the mountains around Grenoble.

Niklas Kappelt

Department of Geology, Lund University, Sweden

Niklas is a PhD student who is researching a new dating method for ice cores. With a background in chemistry, he previously studied urban air pollution and worked on the development of devices for the removal of pollutants. He transitioned to paleoclimate studies because of his interest in the unique information accessible through ice cores. Dating is a crucial part for the analysis of this data, and his new method is based on cosmogenic radionuclides, which are created in the atmosphere and end up in the ice sheet where they radioactively decay over time.

Florian Painer

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

Florian studied geosciences in Graz, Austria. He is interested in the geological past and the dynamics of the Earth system. Currently he is doing a PhD in glaciology and his research is focuses on the microstructure of ice and how ancient air molecules get caged by the ice (i.e. water) molecules. His work has already taken him to the Greenland Ice Sheet. “Ice is a fascinating material to study and key to understanding the Earth’s past climate,” he said. In his free time, he enjoys hiking in the mountains and being in nature.

Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Switzerland

Lison is a PhD student working on ice-core sciences. Her research focuses on nitrous oxide (N2O), a potent greenhouse gas and ozone-depleting substance. She analyzes air bubbles in Antarctic ice cores to reconstruct past atmospheric N2O concentrations, and to understand the production of N2O in ice using isotope analyses. This study is the result of an international measurement campaign in Switzerland, France, the Netherlands, and the United States. Additionally, Lison has a strong interest in science communication.

Ice cores have become one of the golden standards in paleoclimate research. Because of the physical nature of their proxy records, their capacity to record past greenhouse (and non-greenhouse) gas concentrations, and their high time-resolution, they have become the focus of multiple PAGES working groups. Two early-career research networks, DEEPICE and ICYS, have contributed and edited this Past Global Changes Magazine issue, which contains 26 science highlights on ice cores and new developments in analytical techniques.

Research and training network on understanding Deep icE corE Proxies to Infer past antarctiC climatE dynamic (DEEPICE)

Figure 1: Entering Little Dome C (Antarctica) precinct on the only road. The camp is visible in the background. Photo credit: Barbante©PNRA/IPEV.

DEEPICE (deepice.cnrs.fr) is an innovative training network for a new generation of 15 early-stage researchers in instrumentation, ice-core analysis, statistic tools and glaciological and climatic modeling. It features 10 research organizations and universities, as well as 11 partner organizations from 11 different countries. The overall objective of DEEPICE is to equip a new generation of scientists with a solid background in ice-core-related climate science with a particular focus on Antarctica, a high level of technical and communication expertise, and a large collaborative network across the academic and non-academic world. The DEEPICE project will develop the necessary tools for the analysis of the Beyond EPICA Oldest Ice, the extraction of which will be completed in 2025.

Ice Core Young Scientists (ICYS)

Ice Core Young Scientists (ICYS) (pastglobalchanges.org/icys) is an informal, international network of early-career scientists dedicated to the study of polar and alpine ice cores and ice-core related sciences. Their purpose is to foster personal connections among young scientists from around the world, in order to build a supportive ice-core science community and to inspire future collaborations. ICYS was conceived at the International Partnerships in Ice Core Sciences (IPICS) First Open Science Conference, held in Giens, France, in October 2012. Developed by a small, passionate group of early-career scientists from Europe, Australia and the United States, ICYS exists to foster personal relationships among young ice-core researchers from around the world.

As a young man in his twenties, Claude Lorius experienced the extremely difficult living conditions in Antarctica at the end of the 1950s. In July 1957, together with two French colleagues, he spent an entire year "voluntarily buried" at the Charcot Station. The year 1957 marks the beginning of an exceptional career, during which Lorius went on 22 expeditions, totaling six years in the field.

He was a pioneer in polar glaciology. Based on the isotopic approach originally developed by Willi Dansgaard, Claude Lorius and Liliane Merlivat adapted and applied the approach in Antarctica, and found a linear relationship between the isotopic composition of precipitation (heavy isotopes of hydrogen and oxygen) and the temperature of formation. These results formed the basis for the developement of an "isotope thermometer" and the reconstruction of past temperature variations from deep ice cores.

In 1965, while contemplating the air bubbles released from melting ice cubes in his glass of whisky, he realized that ice could be the window into archives of the atmosphere.

His primary objective then became drilling at Dome C, in the heart of the Antarctic continent, to extract an ice core for analysis. Thanks to logistical support from the US National Science Foundation (NSF), and the perseverance of engineers and drillers, scientists were able to accurately obtain the first analyses of properties such as dust content, crystal size, ice chemistry and air-bubble composition that were trapped in the ice found at the Dome C site.

During the International Geophysical Year (1957–1958), the Soviet Union established a permanent station in East Antarctica, at the Vostok site. Due to his personal contacts, Claude Lorius managed to initiate a collaboration between the French and Soviet teams. Drilling depth reached 2083 meters on 11 April 1982. The oldest ice in this location was estimated to be 150,000 years old, meaning that coring would cover the whole of the previous warm period, the Last Interglacial, which peaked around 130,000 years ago, and entered the previous ice age. The link between major climatic cycles and variations in the Earth’s orbitally forced insolation, as demonstrated in 1976 from deep-sea core records, was confirmed by the Vostok isotopic recording (Lorius and Merlivat 1977). More importantly, however, throughout the last 150,000 years covered by the core, the CO2 concentration was found to be closely correlated with the temperature deduced from the isotopic analysis of this ice (Lorius et al. 1990).

At the end of the 1980s, Claude Lorius, together with other early visionary paleoclimate researchers at the time, such as Hans Oeschger, was instrumental in the establishment of the PAGES initiative. As members of the International Geosphere-Biosphere Programme (IGBP) Working Group, they met for the first time in July 1988 in Bern, Switzerland, to discuss "Techniques for Extracting Environmental Data from the Past". This meeting lay the foundations for what one year later became the birth of PAGES: the IGBP Core Project on Past Global Changes. After the official launch of Past Global Changes (PAGES) as a registered organization in 1991, Claude Lorius served as one of the first PAGES Scientific Steering Committee members from 1991–1996.

Figure 1: Claude Lorius in Antarctica, 2008 (commons.wikimedia.org/wiki/File:Claude.Lorius.jpg).

The start of the 1990s proved a challenging time for the Soviet drillers who were confronted with the end of communism in the USSR. Despite this, operations at the Vostok site continued and American scientists joined the project. Claude Lorius, with the assistance of a colleague from Grenoble, Jean-Robert Petit, put all his energy into ensuring this collaboration continued. In January 1996, the depth of 3350 meters was reached, with this ice record covering 420,000 years (Petit et al. 1999). The record demonstrated that Antarctic climate and greenhouse gases go hand-in-hand throughout this period, characterized by four glacial–interglacial cycles. This confirmed that variations in insolation are at the origin of the major climatic cycles, and those of the greenhouse gases play an amplifying role. This extension of records also put the role of human activity into perspective; throughout the last 420,000 years, the quantities of carbon dioxide and methane present in the atmosphere have never been as high as they are today.

Very quickly, the drilling project took on a European dimension. It was the beginning of “EPICA” (European Project for Ice coring in Antarctica). Claude Lorius was determined for drilling to reach the bedrock in Antarctica at Dome C, and this was achieved in January 2005 when the bedrock was finally reached at 3260 meters. This success owes a great deal to Claude Lorius’ confidence and determination.

One of his primary aims was to show that data from the past can provide relevant information regarding the future evolution of our climate, and to raise the alarm about global warming linked to the increase in the greenhouse gases resulting from human activities. He devoted most of his time to this from the 2000s through activities on the Anthropocene and his messaging in the film “Antarctica: Ice and Sky” (French original: "La glace et le Ciel”) by the Oscar-winning director Luc Jacquet.

Claude Lorius had a concrete vision of how polar ice can contribute to knowledge of our climate and environment. He was a true leader, a tough scientist, and someone whose undeniable charisma inspired a whole generation of researchers. He was a member of the Academy of Sciences and received the CNRS Gold Medal in 2002. He also received numerous prestigious international accolades, including the Tyler, Balzan, Bower and Blue Planet prizes. In 2021 he was decorated “Grand Officier” in the French order of the Legion of Honor – the highest decoration in France.

Claude Lorius passed away on 22 March 2023.

This article was originally published in French for the journal “La météorologie” by Jean Jouzel, Jérôme Chappellaz, Jean-Robert Petit and Dominique Raynaud. Marie-France Loutre and Chené van Rensburg adapted and translated it for this magazine.

REFERENCES

Lorius C, Merlivat L (1977) In: International Association of Hydrogeologists (Eds) Proceedings of the Grenoble Symposium August–September 1975, 125-137

Lorius C et al. (1990) Nature 347: 139-145

Petit JR (1999) Nature 399: 429-436

Achieving global-scale insights into past climate variations requires the careful assembly and standardization of networks of proxy databases (Kaufman et al. 2020; Konecky et al. 2020; Walter et al. 2023). Moreover, it is expected that scientific data are openly and readily shared online. These expectations were formalized through the FAIR Guiding Principles (Wilkinson et al. 2016), which created a standard framework that open scientific data should be findable, accessible, interoperable, and reusable.

Controlled vocabularies are essential infrastructure to meet the FAIR principles, thereby enabling global-scale data syntheses and subsequent scientific research. Controlled vocabularies are sets of terms constrained by specific rules that allow for concise and unambiguous usage (Wojcik 2006). Several community-led controlled vocabularies are emerging in paleoclimatology and paleoecology, including the PaST Thesaurus (ncei.noaa.gov/products/paleoclimatology/paleoenvironmental-standard-terms-thesaurus) employed by the NOAA World Data Service for Paleoclimatology (Morrill et al. 2021) and the steward-curated taxonomies used by the Neotoma Paleoecology Database (Williams et al. 2018). As the volume and variety of empirical data in paleoclimate research expands, controlled vocabularies developed by experts and consistently shared paleodatabases become ever more essential.

Lipid biomarkers are common in climate and environmental studies, especially in the near-recent times, and represent readily analyzed lipids that have homologous series distributions, ratios, and isotope abundances with high utility for the paleoclimate community. Despite this, these have no comprehensive controlled vocabulary for paleoclimate and environmental use, although the International Union of Pure and Applied Chemistry (IUPAC) dictionary (goldbook.iupac.org) exists for many compounds. Here, we present a draft controlled vocabulary that encompasses several major classes of lipid biomarkers commonly applied for paleoclimate research. To facilitate interoperability among data resources, the NOAA World Data Service, LiPDverse, and Neotoma have all agreed to adopt this vocabulary. This vocabulary is being developed as an open process, and we welcome community input.

Figure 1: (A) Schematic representation of the process used to develop a controlled vocabulary for use in the International Lipid Biomarker Database. This vocabulary is based on previously established language frameworks (semantics) developed by global paleodata resources such as Neotoma, NOAA, and LiPD. Each new biomarker name is assigned a long name (e.g. branched diakyl glycerol tetraether Ia), short name (e.g. brGDGTIa), a higher-order name (brGDGT), and equivalent names from the PaCTs, PaST, and IUPAC controlled vocabularies. Usually, the PaST and PaCTs names are more generic than those proposed here. (B) Once the controlled vocabulary is established, we will add those new terms back into other databases for increased interoperability across paleodata resources. We view this as an iterative and ongoing process, with new additions to the controlled vocabulary list to be provided by participating experts and new publications describing lipid biomarker compounds. We invite community input to these names and processes.

Because the task of cataloging and establishing vocabulary rules for thousands of lipid biomarkers is non-trivial, we have begun with some of the most commonly used lipid biomarkers in paleoclimate research: branched and isoprenoidal glycerol dialkyl glycerol tetraethers, n-alkanoic acids, n-alkanes, alkenones, and long-chain diols. We have developed a list of lipid biomarker names as they are commonly used in the paleoclimate literature, and include the IUPAC term for each compound, to avoid ambiguity. This list is published as v 0.1.0 on Google Sheets (tinyurl.com/ILBD010) and is available for comment. We are seeking community input to check for completeness and accuracy within these classes by 31 January 2024. We would also welcome participation by individuals or teams interested in leading development of a list for other classes of lipid biomarkers.

When the community input period is complete, we will update and publish v 1.0.0 of the International Lipid Biomarker Controlled Vocabulary on Zenodo, with updates and future versions possible afterwards. We will also incorporate v 1.0.0 and subsequent versions into the controlled vocabularies maintained by NOAA, LiPDverse, and Neotoma. If there are other databases interested in using this controlled vocabulary, please contact us. With a controlled vocabulary in place, the next steps will be to harmonize the vocabulary in lipid biomarker datasets currently on public paleoclimate databases, and gather and add datasets not yet on these public databases. Anyone interested in contributing vocabulary or datasets can contact Harleena Franklin at harleena@buffalo.edu. Documentation of the process being developed here may be useful to experts seeking to develop controlled vocabularies for other proxies.

affiliationS

1Department of Geology, University at Buffalo, USA

2Department of Geography, University of Wisconsin-Madison, USA

3Department of Chemistry, University at Buffalo, USA

4Department of Earth, Geographic, and Climate Sciences, University of Massachusetts Amherst, USA

5Department of Geosciences, Penn State University, University Park, USA

6School of Earth and Sustainability, Northern Arizona University, Flagstaff, USA

7Climatic Science and Services Division, NOAA's National Centers for Environmental Information, Washington DC, USA

contact

Harleena Franklin: harleena@buffalo.edu

REFERENCES

Kaufman D et al. (2020) Sci Data 7: 115

Konecky BL et al. (2020) Earth System Science Data 12: 2261-2288

Morrill C et al. (2021) Paleoceanogr Paleoclimatol 36

Walter RM et al. (2023) Earth Syst Sci Data 15: 2081-2116

Wilkinson MD et al. (2016) Sci Data 3: 160018

Williams JW et al. (2018) Quaternary Research 89: 156-177

Wojcik R (2006) In: Brown K (Ed) Encyclopedia of Language & Linguistics (2nd edition), Elsevier Science, 139-142

PlioMioVAR workshop, Utrecht, Netherlands, and online, 8 June 2023

Arguably, the most important existential crisis facing modern society is that of climate change, caused by anthropogenic greenhouse gas emission. One way to understand how Earth’s climate responds to changes in greenhouse gas concentrations, and thus how to predict, plan, and guide society through such a crisis, is to study past climate change. During the Miocene Epoch (~23 to 5.3 million years ago), Earth’s climate experienced significant temperature and ice-volume fluctuations, which were coupled to marked changes in atmospheric carbon dioxide (CO2) concentrations. In fact, the Miocene represents the most recent period in geologic history when Earth’s climate experienced CO2 concentrations equal to those predicted for the coming decades by the Intergovernmental Panel on Climate Change (e.g. Fig. 10.20 in Meehl et al. 2007). This, in conjunction with a similar continental configuration, makes the Miocene a crucial and relevant analog to better understand modern climate change.

A large number of studies have published estimates of Miocene ocean temperatures. These studies determined past temperatures using a variety of compounds, known as geochemical proxies (e.g. organic molecule thermometers like Uk37’ or TEX86, or inorganic elemental or isotopic thermometers such as Mg/Ca, clumped isotopes (Δ47), and stable isotopes). Usually, such studies only focused on one or a few specific location(s) in the ocean(s) (e.g. Modestou et al. 2020; Sosdian et al. 2020). There is currently an urgent need from several communities, mainly the climate modeling, paleoclimate, and policy-making communities, to summarize and synthesize data in order to make it more accessible to advance our understanding of modern climate change. The MioOcean Temperature Synthesis working group (a subgroup of PAGES' PlioMioVar working group [pastglobalchanges.org/pliomiovar]) aims to update and synthesize existing ocean-temperature proxy data, compile them all into a databank for open access, and ultimately generate a global temperature atlas for specific Miocene time slices relevant to modern climate change.

The second workshop to date, MioOcean 2 (pastglobalchanges.org/calendar/137169), aimed to bring our large group of researchers together to provide updates on synthesis progress, discuss ongoing issues, find solutions, and specify how the group’s outputs will take shape. One major hurdle for each proxy is to update the method used to translate raw data into temperature. Part of the meeting was dedicated to determining the most state-of-the-art methods of temperature calculation for each proxy, in order to begin recalculating temperature from raw data. Another major hurdle is to consider how to make data from different locations comparable in the time domain, which is solved by the stratigraphers and geochronologists comprising the group who specialize in generating age models for the Miocene sediments and rocks the proxy data are derived from. This group also presented their vision for moving the synthesis forward, and what that might entail. Finally, MioOcean is working in close partnership with a climate modeling initiative, MioMIP (Miocene Model Intercomparison Project). Climate modelers use paleoclimate data to validate and compare model outputs. However, if data are conflicting or have poorly defined uncertainties, that critical comparison and validation work becomes very difficult. To this end, MioOcean hosted several MioMIP participants to receive their feedback and guidance on how best to compile ocean temperature data to ensure that the new compilations are as useful as possible for the modeling community.

Figure 1: (A) Workflow of the MioOcean Temperature Synthesis. (B) Sindia Sosdian, of the MioOcean Steering Committee, facilitating discussion during the meeting.

The workshop followed another conference (MioMEET; Utrecht, 5–7 June 2023) for reasons of sustainability; since the two communities overlap, most participants were already gathered in the beautiful Dutch city. An international group of 32 scientists met in Utrecht on 8 June (MioOcean 2), and 15 participants who were unable to travel also joined online. The workshop was a success in many ways, but most importantly, it was the first time the group was able to gather in person. Online meetings are convenient (assuming one wins the timezone lottery), and much more environmentally friendly, but getting to know one another in real life adds to the energy and motivation of a scientific working group.

ACKNOWLEDGEMENTS

We are deeply grateful to PAGES and UK IODP for their financial support for this workshop, which enabled attendance of several early-career scientists and scientists from lower-income countries, as well as some workshop expenses.

affiliationS

1Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, UK

2School of Earth and Environmental Sciences, Cardiff University, UK

contact

Sindia Sosdian: sosdians@cardiff.ac.uk

references

Meehl GA et al. (2007) In: Solomon SD et al. (Eds) IPCC, 2007. Climate Change 2007: The Physical Science Basis. Cambridge University Press, 749-844

Modestou SM et al. (2020) Paleoceanogr Paleoclimatol 35: e2020PA003927

Sosdian S et al. (2020) Nat Commun 11: 134

1st sedDNA Meeting, Potsdam, Germany, 6–9 June 2023

The first sedimentary DNA (sedDNA) meeting under the overarching theme “Shedding light on current developments in Paleo-Ecological Genomics” took place from the 6–9 June 2023 at the Alfred-Wegener-Institute (AWI), Helmholtz Centre for Polar and Marine Research in Potsdam, Germany (pastglobalchanges.org/calendar/129294). More than 125 colleagues participated in the first-of-its-kind meeting to bring this scientific community together, to exchange ideas and discuss new avenues.

SedDNA symposium with talks and posters

The first two days consisted of 18 invited keynote talks and more than 80 exhibited posters, of which 62 were presented in the poster lightning sessions. The topics covered Quaternary paleo-metagenomic investigations on lake, permafrost, and marine sediments, as well as archaeological sites, to recover changes of different taxonomic communities (plants, mammals, human, microeukaryotes, etc.) and full ecosystems. Moreover, new method developments on sedDNA and sedaDNA (sedimentary ancient DNA), and new advances in bioinformatic tools and statistics, were presented.

Talks were followed by a meeting of the sedaDNA Scientific Society and a great poster session, including the ice-breaker. Networking events, such as an excursion to the UNESCO World Heritage Site at Park Sanssouci and a conference dinner at the scientific campus at Telegrafenberg in Potsdam, gave everyone the opportunity to connect with other members of the sedDNA community.

Method discussions and hands-on workshops

During the third and fourth days, participants dove into methodological discussions during paleo-genetic laboratory tours around AWI, and laboratories led by other ancient DNA research groups were presented to view layouts and set ups. After exchanging experiences and ideas on sedDNA methods in nine breakout groups led by early-career researchers (ECRs), four workshops on metabarcoding and metagenomic pipelines, and detecting critical transitions using sedaDNA records, the latter as part of the Paleo-Ecological Genomics (PaleoEcoGen) (pastglobalchanges.org/paleoecogen) working group (WG),  started in two parallel sessions. Positive feedback was shared throughout the workshop, and peer support by all members of the community was evident throughout.

Figure 1: (Left) Schematic representation of a critical transition between two states triggered by a small forcing. (Right) Simplified workflow of the proposed approach to identify past critical transitions, and evaluate subsequent biological changes based on ancient environmental DNA timeseries derived from lake-sediment cores. Modified from Monchamp et al. (2021).

PAGES PaleoEcoGen workshop

Approximately 25 people took part in a two-day workshop with the PaleoEcoGen WG focusing on the detection of critical transitions in sedaDNA data (Fig.1). The first day of the workshop consisted of a statistical tutorial in R, where an example dataset and R script were presented by Zofia Taranu. In particular, three statistical approaches were introduced: 1) Latent Dirichlet Allocation (LDA; also known as Topic Models) to explore how to reduce the dimensionality of sedaDNA data by identifying groups of co-varying taxa (i.e. grouping taxa into "community types" or topics); 2) Change-point analysis to identify periods of pronounced turnover in community-types, where given that the approach is a type of fuzzy clustering, two or more community types can co-occur in different proportions within a time period; and 3) Dynamic Linear Models (DLMs) to test whether transitions in community-type occurrences were approached critically. During the second day of the workshop, participants ran the R script on their own, either using the example dataset or their own sedaDNA datasets. This gave the group a chance to identify issues and troubleshoot. It was a great opportunity for everyone to work together to improve modeling approaches and cater it to a variety of sedaDNA data, most notably those that differ in time frame and dynamics through time.

ACKNOWLEDGEMENTS

The group thanks PAGES, ERC Glacial Legacy, INQUA, and the AWI for supporting this fantastic meeting. Further, we thank the entire sedaDNA Society, and particularly Eric Capo, for initiating the gathering of the international sedaDNA scientific community.

affiliationS

1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Polar Terrestrial Environmental Systems, Potsdam, Germany

2Institute of Biochemistry and Biology, University of Potsdam, Germany

3Institute of Environmental Sciences and Geography, University of Potsdam, Germany

4Aquatic Contaminants Research Division, Environment and Climate Change Canada, Montréal, Canada

contact

Kathleen R. Stoof-Leichsenring: kathleen.stoof-leichsenring@awi.de

references

Monchamp M-E et al. (2021) PAGES Mag 29 (2): 102

Marine diatoms are highly sensitive to changes in their environment, such as changes in temperature, salinity, and sea ice, which has made them a widely used proxy for paleoenvironmental reconstructions (Koç Karpuz and Schrader 1990; Miettinen et al. 2015; Oksman et al. 2019). For a long time, fossilized diatoms have been used to produce qualitative reconstructions of past climate. In the late 1980s, the demand for quantitative paleodata by the modeling community promoted the development of modern diatom calibration datasets (Caissie et al. 2012; Koç Karpuz and Schrader 1990; Krawczyk et al. 2017; Miettinen et al. 2015) that enabled quantitative estimates of past sea-surface conditions. The development of calibration datasets has been fast since the early 1990s. Today, several diatom datasets exist from the (sub)Arctic regions, together including more than a thousand surface-sediment samples. Each dataset includes information about modern diatom assemblages in the surface-sediment and modern surface-ocean environmental data from the same location. These calibration datasets also allow the study of species autecology, knowledge of which is essential for the robustness of diatoms as a paleo proxy.

However, slightly different methodologies and taxonomies have been used to build these datasets, as they were gathered by different independent research groups. This can lead to inconsistencies in diatom-based climate records. The MARDI (Marine Arctic Diatoms) working group (WG) (pastglobalchanges.org/mardi) was launched in November 2022 to integrate and harmonize the various datasets into one open-access database. Read more about MARDI objectives and activities in this issue (p. 112).

On 6–8 June 2023, 17 diatom enthusiasts (40% early-career researchers) from 10 countries (Canada, Chile, Denmark, Finland, Greenland, India, Italy, Sweden, Turkey, and USA) gathered in Helsinki, Finland, for the 2nd MARDI workshop with the title “Harmonization of (sub)Arctic diatom taxonomy” (pastglobalchanges.org/calendar/136750). The main aim of this workshop was to agree upon the identification criteria of common Arctic diatom taxa – a first critical step to enable integration of the different datasets. Prior to the workshop, about 30 of the most common and taxonomically challenging high-latitude diatom species were listed (Fig. 1). During the workshop, each species was individually discussed, with focus on key features for identification. While consensus was achieved among participants on the majority of the species, important issues that still need to be solved were raised for some. For example, what has previously been identified as the vegetative cell of Bacterosira bathyomphala in sediment stratigraphies could in fact be the primary valve of the heterovalvate resting spore. Such issues can have a significant relevance to paleoenvironmental reconstructions if vegetative cells and resting stages represent different ecological conditions.

Figure 1: Common Arctic diatom taxa were described and discussed in the taxonomic session of the MARDI workshop. Photo credits: Beth Caissie, Christof Pearce and Mimmi Oksman.

A second important topic of the workshop was to discuss different sample-preparation methods and evaluate if certain methods/practices can influence the diatom assemblage by favoring particular physical features (e.g. highly silicified or small/large valves). The common diatom microscopy slide preparation methods were presented, followed by a discussion of their possible (dis)advantages. MARDI has designed an interlaboratory comparison and counting exercise to test disagreement between different methodologies and the statistical reproducibility of sample preparation. Diatom slides for microscopic identification were prepared by workshop participants following the most common methodologies used by diatomists, and these will be analyzed according to the protocol agreed upon during the workshop. Findings from this exercise will be presented in a future publication.

On the third workshop day, participants performed an identification and slide counting practice to test if there were significant identification differences when counting a diatom microscope slide without taxonomic keys, and with limited time for identification. This exercise provided amusement, but also important insight into how challenging diatom taxonomy is, and hence, the element of subjectiveness involved in identification.

The main outcome of the workshop was the agreement on the taxonomy of the main ecologically relevant taxa, and identification of the knowledge gaps that might affect diatom reconstructions. High-quality images of the taxa discussed at the workshop will be uploaded to an open-access database (diatoms.org), with inclusion of detailed descriptions of species morphology and key identification features. This tool will then be available for everyone working with marine Arctic diatoms. For some species, discussions will continue in the form of mini-workshops that MARDI will organize in the upcoming months. These mini-workshops will consist of half to one-day online meetings open to everyone.

Acknowledgements

The MARDI WG wishes to thank PAGES for financially supporting this workshop, as well as the Ecosystems and Environment Research Programme, University of Helsinki, for hosting us during the workshop.

affiliationS

1Department of Glaciology and Climate, Geological Survey of Denmark and Greenland, Copenhagen, Denmark

2Environmental Change Research Unit, Ecosystems and Environment Research Programme, University of Helsinki, Finland

3Department of Earth Sciences, University of New Brunswick, Fredericton, Canada

4Geology, Minerals, Energy, and Geophysics Science Center, United States Geological Survey, Menlo Park, USA

5University of California, Santa Cruz, USA

6Department of Geoscience, Aarhus University, Denmark

contact

Mimmi Oksman: mio@geus.dk

References

Caissie BA (2012) PhD Thesis, University of Massachusetss Amherst, 213 pp

Koç Karpuz N, Schrader H (1990) Paleoceanography 5(4): 557-580

Krawczyk DW et al. (2017) Paleoceanography 32: 18-40

Miettinen A et al. (2015) Paleoceanography 30: 1657-1674

Oksman M et al. (2019) Mar Micropaleontol 148: 1-28

The Volcanic Impacts on Climate and Society (VICS) (pastglobalchanges.org/vics) working group (WG) has, since 2015, aimed to promote work that improves reconstructions of volcanic forcing, enhances understandings of volcanically induced climate variability, and deepens understandings of societal impacts and human responses to eruptions. As Phase 2 of VICS ends, this workshop (pastglobalchanges.org/calendar/26993) offered a valuable opportunity for the community to meet in-person for the first time since 2019, to share results and discuss future directions.

An interdisciplinary group of researchers covering proxy reconstructions, climate modeling, history, archaeology, volcanology, anthropology, biology, atmospheric science and risk mitigation joined the workshop, with around 70 people attending in Bern and ~20 more joining online. The presentations included 13 invited talks covering the wide range of workshop themes, with over two-thirds of the invited talks given by early-career researchers (ECRs).

The chronological scope of the volcanic eruptions and impacts discussed spanned from the Last Glacial Period to the end of the 21st century. Geographically, all continents were covered, with eruptions spanning four orders of magnitude (Volcanic Explosivity Index 4 to 8). Building on previous efforts for the Common Era, sulfur injections from Holocene volcanic eruptions have been reconstructed using polar ice-core records (Sigl et al. 2022; Fig. 1). This reconstruction allows us to estimate the frequency of Little-Ice-Age-type events in the Holocene, constrain global temperature projections in the 21st century (Chim et al. 2023), and quantify the risks of future volcanic eruptions (Cassidy and Mani 2022).

Figure 1: Volcanic stratospheric sulfur injections (VSSI) of eruptions over the past 2500 years from ice cores, grouped by known and estimated locations. Circle areas are proportional to VSSI. Eruptions highlighted in blue were discussed at the workshop. Modified from Sigl et al. (2022).

Model experiments increasingly emphasize that time of year, latitude, and eruption column height, and not just sulfur emissions, are crucial for understanding aerosol dispersal, and climatic effects (Marshall et al. 2019). Forensic geochemical analyses are shedding light on the strength and date of the mysterious Kuwae eruption in Vanuatu – a recurring case study for the VICS community. The search for the timing, size and impacts of this eruption is complemented by ongoing efforts based on oral traditions and intense volcanological fieldwork.

Several contributions emphasized that accurate and precise dating of eruptions is critical for understanding their climate effects (Reinig et al. 2021). Novel tools and integrative approaches in ice-core sciences, dendrochronology, radiocarbon dating, climate modeling and documentary records (e.g. using medieval lunar eclipses, as in Guillet et al. 2023; or ancient Babylonian dust-veil observations) that better constrain the timing of eruptions, potentially to the season, were discussed. Examples included the large caldera-forming eruptions of Samalas (1257 CE), Thera (ca. 1600 BCE), Aniakchak (1628 BCE), and Atitlan, as well as other impactful events.

As the impact of large volcanic eruptions on Northern Hemisphere summer temperature is relatively well understood, many contributions focused on other aspects, including the effects of eruptions on winter climate, monsoon circulation, Sahel precipitation, storm tracks and Southern Hemisphere temperatures. It was highlighted that not all societal impacts of eruptions are necessarily negative (e.g. increased fish catches following the ecosystem response to sea-surface cooling).

Looking towards the future, we discussed how we can use knowledge of past volcanic activity to better prepare for the climatic effects and economic risks of future eruptions (Mani et al. 2021). Negative volcanic effects may particularly occur in regions where most of the world’s present-day food production takes place, posing a significant risk to food security.

The workshop ended with a discussion regarding the future of the VICS WG. The overriding conclusion was that the open, supportive and diverse community that the VICS WG has developed since 2015 needs to be maintained. As the goals of the WG for Phases 1 and 2 have been largely achieved, new aims will be identified: possible developments discussed include a stronger focus on impacts in Asia and the Southern Hemisphere, exploring how past volcanic impacts could inform future work on solar radiation management, a greater focus on time periods earlier than the Holocene, and future predictions.

Acknowledgements

We thank PAGES, the Oeschger Centre for Climate Change (University of Bern), the Swiss National Science Foundation, and the Aarhus University Research Foundation for financial and logistical support.

affiliationS

1Climate and Environmental Physics and Oeschger Centre for Climate Change Research, University of Bern, Switzerland

2Department of History, Trinity College Dublin, Ireland

3School of Culture and Society, Aarhus University, Denmark

4Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Canada

5Department of Geography, University of Cambridge, UK

contact

Michael Sigl: michael.sigl@unibe.ch

references

Cassidy M, Mani L (2022) Nature 608: 469-471

Chim MM et al. (2023) Geophys Res Lett 50: e2023GL103743

Guillet S et al. (2023) Nature 616: 90-95

Mani L et al. (2021) Nat Commun 12: 4756

Marshall L et al. (2019) J Geophys Res-Atmos 124: 964-985

Reinig F et al. (2021) Nature 595: 66-69

Sigl M et al. (2022) Earth Syst Sci Data 14: 3167-3196

Figure 1: Overview of Marine Functional Connectivity (MFC) processes, their long-term drivers, and how geohistorical data can help unravel their changes over time.

Historical records include documents, paintings, museum collections and archaeological artifacts (i.e. evidence of human activities), and organismal remains (e.g. shell middens). These can be used to track the pathways, rates and consequences of species distributions and movements at decadal to millennial timescales. Additionally, they provide information on how human activities have contributed to functional connections and disconnections. For instance, the transport of non-indigenous species along shipping routes (“hitch-hikers” on wooden hulls), and for aquaria and aquaculture, has been documented from at least the 1200s (Hoffmann, 2023; Holm et al. 2019; Lotze et al. 2014), whereas the more recent construction of physical connections, such as the Suez Canal, has led to unprecedented rates of biological invasion (Por 1971).

Geological records, on the other hand, include fossils, sediments and the biogeochemical data that can be derived from them. These provide information about changes in species distributions and ecology and the consequences on MFC of natural environmental changes at millennial to million-year timescales. Sclerochronologic and genetic methods applied to fossil remains (e.g. mollusc shells, mammal bones and teeth, and fish otoliths) further offer high-resolution reconstructions of the life histories of marine organisms and can be used to identify evolutionary events and past environmental changes.

This workshop organized by the Q-MARE working group (pastglobalchanges.org/q-mare), brought together 20 scientists from 10 countries, covering a wide range of disciplines ranging from ecology and paleontology to archaeology and history (pastglobalchanges.org/calendar/134692). The aim was to draft a research roadmap that explores how to obtain and use geohistorical data in the study of MFC. Reiterating the definition of MFC for the workshop participants, the meeting started with the presentations of historical examples and case studies of MFC, and continued with discussion in groups, and altogether, around three main questions: 1) What geohistorical data could be used to understand MFC?; 2) What resources are available for such work?; and 3) How should these data be analyzed and interpreted?

The diversity of data types and resources echoed the multidisciplinarity of the group (Fig. 1). Fossils and their assemblages, historical archives, archaeological remains, ancient DNA, and biogeochemical data can give information on MFC at multiple different temporal and spatial scales. Both vertical and horizontal seascape connectivity can be inferred, as well as the role of long-term drivers of MFC. The group identified specific archives and resources that are available, openly accessible or not, and noted information on how to access them. For each data type, we described the information captured, and any challenges associated with its use and analysis. We highlighted the role of proper recovery and identification of fossil, historical and archaeological material in the correct interpretation of the results. For each of these different data types, we identified examples that illustrate their contribution to understanding MFC. Finally, we concluded with the goal to publish the roadmap in the upcoming months, so stay tuned!

ACKNOWLEDGEMENTS

The Q-MARE working group would like to thank ICES and the SEA-UNICORN COST Action for co-organizing this workshop.

affiliationS

1Department of Palaeontology, University of Vienna, Austria

2Faculty of Science and Engineering, University of Hull, UK

contact

Konstantina Agiadi: konstantina.agiadi@univie.ac.at

REFERENCES

Darnaude A et al. (2022) Res Ideas Outcomes 8: e80223

Holm P et al. (2019) Quatern Res 108: 92-106

Lotze HK et al. (2014) In: Fogarty MJ, McCarthy JJ (Eds) The Sea, Vol. 16: Marine Ecosystem-Based Management. Harvard University Press, 17-55

Por FD (1971) System Zool 20(2): 138-159