Introducing global peat-specific temperature and pH calibrations based on brGDGT bacterial lipids

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids from Bacteria and Archaea that are ubiquitous in a range of natural archives and especially abundant in peat. Previous work demonstrated that the distribution of bacterial branched GDGTs (brGDGTs) in mineral soils is correlated to environmental factors such as mean annual air temperature (MAAT) and soil pH. However, the influence of these parameters on brGDGT distributions in peat is largely unknown. Here we investigate the distribution of brGDGTs in 470 samples from 96 peatlands around the world with a broad mean annual air temperature (−8 to 27 °C) and pH (3–8) range and present the first peat-specific brGDGT-based temperature and pH calibrations. Our results demonstrate that the degree of cyclisation of brGDGTs in peat is positively correlated with pH, pH = 2.49 x CBTpeat + 8.07 (n = 51, R2 65 = 0.58, RMSE = 0.8) and the degree of methylation of brGDGTs is positively correlated with MAAT, MAATpeat (°C) = 52.18 x MBT5me’ – 23.05 (n = 96, R2 67 = 0.76, RMSE = 4.7 °C). 3 These peat-specific calibrations are distinct from the available mineral soil calibrations. In light of the error in the temperature calibration (~ 4.7 °C), we urge caution in any application to reconstruct late Holocene climate variability, where the climatic signals are relatively small, and the duration of excursions could be brief. Instead, these proxies are well-suited to reconstruct large amplitude, longer-term shifts in climate such as deglacial transitions. Indeed, when applied to a peat deposit spanning the late glacial period (~15.2 kyr), we demonstrate that MAATpeat yields absolute temperatures and relative temperature changes that are consistent with those from other proxies. In addition, the application of MAATpeat to fossil peat (i.e. lignites) has the potential to reconstruct terrestrial climate during the Cenozoic. We conclude that there is clear potential to use brGDGTs in peats and lignites to reconstruct past terrestrial climateThis research was funded through the advanced ERC grant “the greenhouse earth system” (T-GRES, project reference 340923), awarded to RDP. All authors are part of the “T-GRES Peat Database collaborators” collective. RDP also acknowledges the Royal Society Wolfson Research Merit Award. We thank D. Atkinson for help with the sample preparation. We acknowledge support from Labex VOLTAIRE (ANR-10- 22 LABX-100-01). Peat from Patagonia and Tierra del Fuego were collected thanks to a Young Researcher Grant of the Agence National de la Recherche (ANR) to FDV, project ANR-2011-JS56-006-01 “PARAD” and with the help of Ramiro Lopez, Andrea Coronato and Veronica Pancotto (CADIC-CONICET, Ushuaia). Peat from Brazil was collected with the context of CNPq project 482815/2011-6. Samples from France (Frasne and La Guette) were collected thanks to the French Observatory of Peatlands. The Canadian peat was collected in the context of the NSERC-Discovery grant of L. Rochefort. Peats from China were obtained under a National Natural Science Foundation of China grant (No. 41372033), awarded to Y. Zheng

The emergence of regional security organisations. A comparative study on ECOWAS and SADC.

The emergence of regional security organisations during the 1990s in Africa proved to be of great significance for the lives of many Africans, including those living in conflict-torn countries such as Liberia, Sierra Leone, Côte d’Ivoire or the Democratic Republic of Congo, but, at the same time, this phenomenon has been understudied. This dissertation explores why regional security organisations with an agenda of democratic governance emerged in Africa in the 1990s. This question is answered with two in-depth case studies on the Economic Community of West African States (ECOWAS) and the Southern African Development Community (SADC). Driven by an empirical puzzle, this study is both hypothesis-testing and hypothesis generating. The study starts by laying out the different possible factors put forward by several bodies of theory in international relations to explain the emergence of ECOWAS and SADC as security organisations. These hypotheses are then tested throughout the history and the evolution of ECOWAS and SADC in order to highlight the circumstances of their creation and their qualified failure as economic communities. This is followed by a comparative analysis of the security and democracy mandates entrusted to ECOWAS and SADC by its member states based on the study of the legal texts that outline the specific objectives of each regional security organisation and the tools they were given to implement their mandates. The study finally analyses the implementation records of ECOWAS and SADC in order to assess the commitment of their member states to their new democracy and security mandate. The research concludes with the two following hypotheses: 1) A security agenda cannot emerge without the involvement of the regional hegemon. 2) What the regional hegemon can do, including affecting the speed of the transformation, is constrained by the acceptance of its leadership by its neighbours (legitimacy) and by state weakness (capability)

The emergence of regional security organisations. A comparative study on ECOWAS and SADC.

The emergence of regional security organisations during the 1990s in Africa proved to be of great significance for the lives of many Africans, including those living in conflict-torn countries such as Liberia, Sierra Leone, Côte d’Ivoire or the Democratic Republic of Congo, but, at the same time, this phenomenon has been understudied. This dissertation explores why regional security organisations with an agenda of democratic governance emerged in Africa in the 1990s. This question is answered with two in-depth case studies on the Economic Community of West African States (ECOWAS) and the Southern African Development Community (SADC). Driven by an empirical puzzle, this study is both hypothesis-testing and hypothesis generating. The study starts by laying out the different possible factors put forward by several bodies of theory in international relations to explain the emergence of ECOWAS and SADC as security organisations. These hypotheses are then tested throughout the history and the evolution of ECOWAS and SADC in order to highlight the circumstances of their creation and their qualified failure as economic communities. This is followed by a comparative analysis of the security and democracy mandates entrusted to ECOWAS and SADC by its member states based on the study of the legal texts that outline the specific objectives of each regional security organisation and the tools they were given to implement their mandates. The study finally analyses the implementation records of ECOWAS and SADC in order to assess the commitment of their member states to their new democracy and security mandate. The research concludes with the two following hypotheses: 1) A security agenda cannot emerge without the involvement of the regional hegemon. 2) What the regional hegemon can do, including affecting the speed of the transformation, is constrained by the acceptance of its leadership by its neighbours (legitimacy) and by state weakness (capability).N.B. Only the abstract and table of contents of this thesis are currently available in ORA

Forest dynamics and tip-up pools drive pulses of high carbon accumulation rates in a tropical peat dome in Borneo (Southeast Asia)

Peatlands of Southeast Asia store large pools of carbon but the mechanisms of peat accumulation in tropical forests remain to be resolved. Patch dynamics and forest disturbance have seldom been considered as drivers that can amplify or dampen rates of peat accumulation. Here we used a modified piston corer, noninvasive geophysical measurements, and geochemical and paleobotanical techniques to establish the effect of tree fall on carbon accumulation rates in a peat swamp forest dominated by Shorea albida in Brunei (Borneo). Carbon initially accumulated in a mangrove forest at over 300 g C m[superscript −2] yr[superscript −1] but declined to less than 50 g C m[superscript −2] yr[superscript −1] with the establishment of a peat swamp forest. A rapid accumulation pulse of 720–960 g C m[superscript −2] yr[superscript −1] occurred around 1080 years ago as a tip-up pool infilled. Tip-up pools are common in the peatlands of northwest Borneo where windthrow and lightning strikes produce tree falls at a rate of 4 trees ha[superscript −1] every decade. A simulation model indicates that tip-up pools, which are formed across the entire forested peat dome, produce local discontinuities in the peat deposit, when peat is removed to create a pool that is rapidly filled with younger material. The resulting discontinuities in peat age at the base and sides of pool deposits obscure linkages between carbon accumulation rates and climate and require new approaches for paleoenvironmental reconstructions. Our results suggest that carbon accumulation in tropical peat swamps may be based on fundamentally different peat-forming processes than those of northern peatlands.Singapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology)National Science Foundation (U.S.) (Grant 1114155)National Science Foundation (U.S.) (Grant 1114161

Landscape Evolution and Human Settlement in the Iroise Sea (Brittany, France) during the Neolithic and Bronze Age

International audienceThe Molène archipelago appears to be particularly rich in Neolithic and Bronze Age remains and an exceptional concentration of megaliths has been brought to light. Several settlements are confirmed by dry-stone structures or by shell middens. These data give precious indications on the occupation chronology of the area. Moreover they allow us, for the first time in Brittany, to reconstruct everyday life during the late Prehistoric period.A prerequisite to this reconstruction was a better understanding of the evolution of the environment during this period, which locally implies a better knowledge of paleogeographic changes related to Holocene sea-level rise as well as on floral and faunal resources. The results obtained through paleogeographic reconstructions show that the archipelago since 4500 BC was already disconnected from the mainland. The megalithic monuments must therefore have been erected and used by islanders present on the archipelago from the middle of the 5th to the 2nd millennium BC. The distribution of the megalithic tombs reveals landscape occupation strategies which respond to both cultural choices and natural constraints. Throughout the entire period, geographic isolation has continued to increase, although it did not imply strong cultural specificities. Nevertheless, the increasing remoteness of the islands has fostered the search for livelihoods based on the intense exploitation of coastal resources. Despite their focus on the sea, these people did not neglect what inland areas could offer as evidenced by the early agro-pastoral practices in the archipelago

Trends in soil solution dissolved organic carbon (DOC) concentrations across European forests

Dissolved organic carbon (DOC) in surface waters is connected to DOC in soil solution through hydrological pathways. Therefore, it is expected that long-term dynamics of DOC in surface waters reflect DOC trends in soil solution. However, a multitude of site studies have failed so far to establish consistent trends in soil solution DOC, whereas increasing concentrations in European surface waters over the past decades appear to be the norm, possibly as a result of recovery from acidification. The objectives of this study were therefore to understand the long-term trends of soil solution DOC from a large number of European forests (ICP Forests Level II plots) and determine their main physico-chemical and biological controls. We applied trend analysis at two levels: (1) to the entire European dataset and (2) to the individual time series and related trends with plot characteristics, i.e., soil and vegetation properties, soil solution chemistry and atmospheric deposition loads. Analyses of the entire dataset showed an overall increasing trend in DOC concentrations in the organic layers, but, at individual plots and depths, there was no clear overall trend in soil solution DOC. The rate change in soil solution DOC ranged between −16.8 and +23 % yr−1 (median  = +0.4 % yr−1) across Europe. The non-significant trends (40 %) outnumbered the increasing (35 %) and decreasing trends (25 %) across the 97 ICP Forests Level II sites. By means of multivariate statistics, we found increasing trends in DOC concentrations with increasing mean nitrate (NO3−) deposition and increasing trends in DOC concentrations with decreasing mean sulfate (SO42−) deposition, with the magnitude of these relationships depending on plot deposition history. While the attribution of increasing trends in DOC to the reduction of SO42− deposition could be confirmed in low to medium N deposition areas, in agreement with observations in surface waters, this was not the case in high N deposition areas. In conclusion, long-term trends of soil solution DOC reflected the interactions between controls acting at local (soil and vegetation properties) and regional (atmospheric deposition of SO42− and inorganic N) scales

CRITICAL PEAT project : The importance of hydrology for Carbon Reactivity along with atmosphere - peatland interactions. Preliminary results from the Frasne peatland monitoring (Jura Mountains, France).

International audienceIn the framework of climate changes, peatland ecosystems are compartments of the Critical Zone of growing importance for greenhouse gas (GHG) exchanges with the atmosphere. Peatlands contain about 30 % of the total organic soil carbon worldwide. Interactions of GHG between atmosphere and peatland are potentially controlled by organic matter production and degradation controlled by biotic functiuns, which are in turn influenced by diverse abiotic factors including (1) water saturation, (2) peat humification degree, and (3) water quality conditioning electron acceptor availability. Delineating the detailed roles of these mechanisms is therefore challenging for long-term peatland management, requiring a detailed spatio-temporal monitoring of a wide range of hydrological and biogeochemical parameters.The Frasne peatland (Jura mountains, eastern France), belonging to a regional natural reserve is an outstanding site for such studies as it is monitored since 2008 in the framework of the national observatory of peatlands (SNO Tourbières),and belongs to the Zones Ateliers (RZA) and French Critical Zone (OZCAR) networks supplying the Europe Long-Term Ecosystem Research (eLTER) database (DEIMS-SDR). The peatland took place in a periglacial context on groundmoraines covering a large-scale karstified synclinal structure. This complex geological setting is combined with eco-physical (peat thicknesses and maturity), and hydrological (water-table depth) heterogeneities at the peatland scale.Based on daily hydrometeorological data (P, T, potential evapotranspiration, groundwater level) and monthly monitoring (hydrochemistry; peat lability, GHG fluxes) in 25 piezometers, the goal of the CRITICAL PEAT project is to identify the hydrological and biogeochemical drivers controlling GHG exchanges between peatland and atmosphere. In this perspective, this contribution aims at presenting preliminary results on the hydroclimatic sensitivity of the system inferred from correlation analyses, and its relationships with water origin and chemistry