Dans le cadre du développement d’étude à haute résolution des changements passés de la végétation, les données palynologiques ont permis de reconstituer l’évolution de la végétation dans les sédiments holocènes prélevés autour de la lagune de Sidi Ali el Mekki (N-E de la Tunisie). Nos résultats montrent qu’au cours les deux derniers millénaires, les changements de végétation de la Tunisie septentrionale traduisent une relation complexe faisant intervenir à la fois les forçages naturels et l’action anthropique. L’étude des sédiments lagunaires a mis en évidence les maquis à olivier et pistachier qui constituaient la végétation dominante alentour à la lagune de Sidi Ali el Mekki lors du premier millénaire de notre ère, ont nettement régressé au profit des steppes à graminées et armoises au cours des derniers 1000 ans, dénotant un impact anthropique croissant dans la zone d’étude.

While it is accepted that the tropical hydrological cycle has intensified during past interglacial periods due to changes in insolation, greenhouse gases, and ice volume, variations in the intensity and spatial distribution of rainfall in the South Asian monsoon domain, as well as the respective influence of these forcings during past warm periods, remain uncertain. Here, we present a pollen record from the Bay of Bengal (IODP Site U1446, located off the Mahanadi river exit, outside the influence of the Bengal fan) that allows reconstruction of vegetation changes in the core monsoon zone of India during two warm periods, the current and last interglacial periods. We compare the data with numerical model simulations (HadCM3 and LOVECLIM1.3) to assess the influence of different forcing mechanisms on the response of summer monsoon rainfall during past interglacials characterized by different levels of warming (Clément et al., 2024). We also present a pollen record from cores (SO93) taken at 16°N from the Ganges-Brahmaputra-Meghna (G-B-M) river-fed Bengal fan, covering the current interglacial period.Results from IODP Site U1446 show tropical forest expansion between 11.7-5 ka and 127-120 ka, defining two Indian humid periods, with the last interglacial showing the strongest monsoon activity, consistent with salinity reconstructions. During the last five millennia of both interglacial periods, moist tropical forest largely declined in favor of savanna marking a significant decrease in summer monsoon rainfall. Although the pollen assemblages from sites SO93 and U1446 show substantial differences in Holocene vegetation cover between the basins, the maximum expansion of the evergreen component of the tropical forest is recorded contemporaneously in both sequences. This suggests a similar Holocene evolution of the summer monsoon from central to northern India. The model-data comparison highlights boreal summer insolation as the primary driver of vegetation dynamics and monsoon intensity during interglacial periods, with CO2 and ice-sheets having a limited effect. These results also show that vegetation remains unaffected by pre-industrial CO2 variations above 250 ppmv, a threshold value that characterizes most interglacials of the last million years.Clément, C., Martinez, P., Yin, Q., Clemens, S., Thirumalai, K., Prasad, S., Anupama, K., Su, Q., Lyu, A., Grémare, A., Desprat, S., 2024. Greening of India and revival of the South Asian summer monsoon in a warmer world. Commun. Earth Environ. 5, 685.

The protocol is dedicated to the preparation of sediment samples from marine cores to analyse pollen and dinocyts.

While it is accepted that the tropical hydrological cycle has intensified during past interglacial periods due to changes in insolation, greenhouse gases and ice volume, their respective influences are uncertain. Here we present a pollen record from Bengal Bay to reconstruct vegetation changes in India's core monsoon zone during two warm periods, the current and last interglacial, comparing the data with numerical model simulations to assess the influence of different forcing mechanisms. Results show tropical forest expansion between 11.7-5 ka and 127-120 ka, defining two Indian humid periods, with the last interglacial showing the strongest monsoon activity, consistent with salinity reconstructions. Model-data comparison highlights boreal summer insolation as the primary driver of vegetation dynamics and monsoon intensity during interglacial periods, with CO2 and ice-sheets having a limited effect. Vegetation remains unaffected by pre-industrial CO2 variations above 250 ppmv, a threshold value that characterizes most interglacials of the last million years. Tropical forest markedly expanded between 11.7 and 5 ka and especially between 127 and 120 ka, due to greater monsoon activity mainly driven by insolation forcing, according to analysis of a Bay of Bengal pollen record and model results.

Abstract. Marine Isotope Stage (MIS) 11 has long been considered a unique Quaternary interglacial due to its orbital similarities with the Holocene, persistence of high atmospheric CO₂ concentrations and extended duration triggering unusual polar ice-sheet loss. Despite its importance, Indian summer monsoon (ISM) variability within the core monsoon zone (CMZ), as well as its impacts on vulnerable tropical forests, remain unexplored. Here, we document, for the first time, MIS 11 ISM-driven vegetation changes and their underlying forcings by combining pollen analysis from IODP Site U1446, strategically retrieved from the Bay of Bengal to represent the CMZ, with model simulations. Our results reveal the distinct roles of insolation, CO₂, ice volume, and millennial-scale variability in driving coupled ISM-vegetation changes, depending on the changing boundary conditions through MIS 11. Orbital- and millennial-scale tropical forest changes mirror southern European vegetation and atmospheric methane variability, ultimately reflecting shifts in the Intertropical Convergence Zone (ITCZ) that impact the tropical regions, a primary source of CH₄ emissions. Our proxy and model reconstructions show that ISM-vegetation changes during MIS 11c closely followed boreal summer insolation, revealing its dominant role under warm background conditions with high CO₂ and reduced ice volume. Conversely, during MIS 11b-a, ISM-vegetation decreased while insolation remained high, indicating that its influence was overshadowed by expanding ice sheets, lower CO₂, and the interaction of orbital and millennial-scale variations. Millennial-scale climate variability during the younger MIS 11b-a substages is expressed by prominent forest contractions tied to southward ITCZ shifts, Atlantic meridional overturning circulation (AMOC) reductions and high-latitude ice sheet dynamics, which were rapidly followed by abrupt forest expansions associated with northward ITCZ shifts, AMOC strengthening and CH₄ overshoots. Conspicuously, the first and most severe forest setback interrupted MIS 11 full interglacial conditions, suggesting that extreme ISM weakening could also occur under similarly warm future conditions. Our findings provide new insights into ISM behavior during MIS 11, highlighting its high sensitivity to climate changes in the context of projected ISM intensification and its effect on the extent and composition of the tropical forest, which is key component of both global carbon and methane cycles.

The seasonal and latitudinal distribution of insolation is considered the main factor controlling the magnitude and timing of interglacial periods. However, despite small differences in insolation forcing, vegetation and hydrology in southern Europe during past interglacials are variable and the gradual change in insolation cannot explain the observed short-lived forest optimum. Here we focus on vegetation and hydroclimatic changes at orbital- and suborbital-scales in southwestern Europe during two past warm interglacial periods with reduced ice-sheets, namely Marine Isotope Stages (MIS) 9e and 5e. We provide new pollen and sea surface temperatures records for MIS 9e from IODP Site U1385. This pollen record shows a forest expansion in southern Iberia over a 14 ky interval, bracketed by the millennial-scale cooling events of Termination IV and MIS 9d. Between 334.5 and 332.5 ka, forest expansion reached a maximum, suggesting increased winter moisture during early MIS 9e. Model-data comparison for MIS 9e and 5e shows that insolation is the main driver of the orbital-scale vegetation and precipitation changes in Iberia, atmospheric CO2 forcing playing a secondary role. The high-frequency component of the MIS 9e and 5e forest timeseries highlights the early interglacial forest and precipitation maxima as prominent suborbital events lasting similar to 2 ky. We propose that the primarily insolation-driven forest and precipitation optima were fostered by the non-equilibrium conditions generated by the millennial-scale deglacial variability during the early interglacials. Additionally, the early end of these optima may have been favored by a cooling and drying event that is part of the persistent intra-interglacial variability.

Interglacials older than 450,000 years ago (ka) are still poorly documented at regional and global scale limiting our knowledge of the wide range of their potential variability and the understanding of the causes of such diversity. Here we present δ18O benthic foraminifera measurements along with sea surface temperature reconstructions and pollen data from IODP site U1385, collected during Expedition 339 « Mediterranean Outflow » on the southwestern Iberian margin, for the Early-Middle Pleistocene interglacials MIS 19, 17, 15 and 13 (~800 to 400 ka). The recorded vegetation and climate changes on land have been directly compared with changes in the eastern North Atlantic subtropical gyre and the global ice volume. This comparison reveals a different structure in the evolution of the Mediterranean forest during these interglacials. The highest forest development occurred during MIS 19e and 15e but in the middle part of MIS 13 (MIS 13c). In contrast with MIS 19, 15 and 13 marked by three more or less similar Mediterranean forest expansions, MIS 17 was characterised by one strong expansion in its middle part (MIS 17c), the strongest of the last 800,000 years, occurring just before the end of the Middle Pleistocene Transition, i.e. the establishment of the strong 100-kyr glacial cycles at ~700 ka. The duration of the first forested phase was also variable depending on the interglacial with a length of ~12,000 years during MIS 19e and 15e, ~9,000 years for MIS 13c and as long as 16,000 years for MIS 17c. Interestingly, two Mediterranean forest expansions are recorded during two phases of ice growth, MIS 19b and 15b, indicating once more the decoupling between the evolution of global ice volume and the southern European environments. The comparison of the U1385 pollen record, located below 40°N, with sequences above 40°N, for example the Lake Orhid pollen record, shows that the structure and magnitude of the interglacials are different below and above this latitude. At Montalbano Jonico, southern Italy at 40°N, the forest expansion is also very strong (80%) during MIS 17 contrasting with the limited development in Lake Orhid. At this site, MIS 19 is further marked by a strong forest development contrasting with the limited expansion of the Mediterranean forest in SW Iberia.

During the last glacial period, the tropical hydrological cycle exhibited large variability across orbital and millennial timescales. However, the response of the Indian summer monsoon (ISM), its related impact on terrestrial ecosystems, and associated forcing mechanisms remain controversial. Here we present a marine record of pollen‐inferred vegetation changes suggesting that eastern India shifted from woody‐savanna mosaics during Marine Isotopic Stage 3 to grasslands during the Last Glacial Maximum resulting from large‐scale drying. Our data shows that ISM maximum is in phase with obliquity and precession maxima suggesting a dominant role of the Indian Ocean interhemispheric temperature gradient on glacial ISM variability. Persistent and abrupt dryland expansions of varying magnitude suggest rapid‐scale onset of aridity during Heinrich Stadial events and during the Toba eruption. We propose that the amplitude of ISM drought events are initiated by high latitude and volcanic forcings, although modulated by precession.

Marine Isotope Stage (MIS) 13, ~500 ky ago, represents a Quaternary interglacial of primary interest due to the unexpected enhancement of monsoon systems under a cool climate characterised by low atmospheric CO2 and larger ice volume than the present interglacial. Yet, key questions remain about its regional expression (intensity, climate variability, length) and underlying forcing factors. Here we examine the SW Iberian vegetation and terrestrial climate during MIS 13 directly compared with the sea surface temperatures using sediments from IODP Site U1385, and combine those terrestrial-marine profiles with climate-model experiments. We show for the first time that MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model approach reveal that that the dominant effect of MIS 13 insolation forcing on the regional vegetation and precipitation regime in SW Iberia is amplified by the relatively large extent of the ice-sheets in high northern latitudes. In qualitative agreement with the pollen-based evidence, model results show that ice-sheet forcing triggers an increase in the SW Iberian tree fraction along with both intensified winter and summer rainfall. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.

The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60 % from 4826 to 8134. Much of the improvement in data coverage has come from northern Asia, and the database has consequently been renamed the Eurasian Modern Pollen Database to reflect this geographical enlargement. The EMPD can be viewed online using a dedicated map-based viewer at https://empd2.github.io and downloaded in a variety of file formats at https://doi.pangaea.de/10.1594/PANGAEA.909130 (Chevalier et al., 2019).

Understanding past variability and forcing mechanisms of the Asian monsoon system is of key importance for better forecasting its behaviour under future global warming scenarios and how this may affect modern societies and economies. So far, knowledge about long-term monsoon variability in mainland Asia is mainly based on proxy records from Chinese speleothems, primarily recording changes of the East Asian Summer Monsoon (EASM). These records have provided evidence for orbital-scale monsoon variability, driven by Northern Hemisphere summer insolation changes, but also for centennial- to millennial-scale reductions in monsoon precipitation. These so-called Weak Monsoon Intervals (WMIs) occurred synchronously to cold intervals in the North Atlantic realm, e.g. during Heinrich Events, pointing at a close hemisphere-scale climatic teleconnection between the North Atlantic and Asia. However, the exact mechanisms that control short-term monsoon variability are still elusive. Moreover, long-term palaeomonsoon proxy records from the core zone of the Indian Summer Monsoon (ISM) are still relatively scarce compared to those from the EASM realm. To identify possible short-term changes in ISM intensity and reconstruct related hydroclimate and vegetation changes on the Indian subcontinent during the interval ~6–74 ka BP, sediments from IODP Site U1446 in the NW Bay of Bengal have been analysed. This site, being located within the reach of the Mahanadi River, is characterized by high riverine input of terrestrial organic matter and thus ideal for high-resolution analyses of pollen content and the stable hydrogen (δD) and carbon (δ13C) isotope composition of n-alkanes from terrestrial plant leaf waxes. Here we present preliminary results of δD and δ13C analyses on odd-numbered long-chain n-alkanes (n-C27 to n-C33,) extracted from the IODP Site U1446 sediments. These indicate several reductions in ISM precipitation during the last glacial, which occurred parallel to cold events in the North Atlantic realm, e.g. during Heinrich events H1, H2, H4, H5 and H6. In combination with pollen and alkenone-based (UK’37) sea surface temperature data from the same sediments, we aim at (1) providing a comprehensive and high-resolution reconstruction of past ISM variability and associated vegetation changes on the Indian subcontinent and (2) understanding the trigger mechanisms of centennial- to millennial-scale WMIs, particularly in relation to changes in Indian Ocean oceanography.

Marine Isotope Stage (MIS) 13, ∼533–478 ka, has received particular attention due to the unexpected enhancement of monsoon systems under a cool climate characterized by lower atmospheric CO2 and larger ice volume than many other interglacials. Key questions remain about its regional expression (intensity, climate variability, length), and underlying forcing factors, in particular at the mid-latitudes. Here we examine the SW Iberian vegetation, terrestrial climate and sea surface temperature (SST) variability during MIS 13 by combining pollen and biomarker data from IODP Site U1385 with climate-model experiments. We show, for the first time, that despite strong precessional forcing, MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model comparison reveal that MIS 13 orbitally driven SW Iberian climate and vegetation changes are modulated by the relatively strong ice-sheet forcing. We find that the Northern Hemisphere ice-sheets prescribed at the MIS 13 climate optimum reinforce the insolation effect by increasing the tree fraction and both winter and summer precipitation. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.

The MIS 17 interglacial, similar to 715-675 ka, marks the end of the Mid-Pleistocene Transition as intensified, long and asymmetrical 100-kyr ice age cycles became eminently established. Increasing arrival of moisture to the Northern Hemisphere high latitudes, resulting from the northwestward migration of the Subpolar Front and the intensification of the Norwegian Greenland Seas (NGS) convection, has been put forward to explain the emergence of this quasi-periodic 100-kyr cycle. However, testing this hypothesis is problematic with the available North Atlantic precipitation data. Here we present new pollen-based quantitative seasonal climate reconstructions from the southwestern Iberian margin that track changes in the position and intensity of the westerlies. Our data compared to changes in North Atlantic deep and surface water conditions show that MIS 17 interglacial was marked by three major changes in the direction and strength of the westerlies tightly linked to oceanographic changes. In particular, we report here for the first time a drastic two-steps northward shift of the westerlies centered at similar to 693 ka that ended up with the sustained precipitation over southern European. This atmospheric reorganization was associated with northwestward migration of the Subpolar Front, strengthening of the NGS deep water formation and cooling of the western North Atlantic region. This finding points to the substantial arrival of moisture to the Northern Hemisphere high latitudes at the time of the decrease in summer energy and insolation contributing to the establishment of strong 100-kyr cycles. (C) 2019 Elsevier B.V. All rights reserved.