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The drivers of the evolution of the South Asian Monsoon remain widely debated. An intensification of monsoonal rainfall recorded in terrestrial and marine sediment archives from the earliest Miocene (23–20 million years ago (Ma)) is generally attributed to Himalayan uplift. However, Indian Ocean palaeorecords place the onset of a strong monsoon around 13 Ma, linked to strengthening of the southwesterly winds of the Somali Jet that also force Arabian Sea upwelling. Here we reconcile these divergent records using Earth system model simulations to evaluate the interactions between palaeogeography and ocean–atmosphere dynamics. We show that factors forcing the South Asian Monsoon circulation versus rainfall are decoupled and diachronous. Himalayan and Tibetan Plateau topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean–atmosphere circulation. The uplift of the East African and Middle Eastern topography played a pivotal role in the establishment of the modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiated as a direct consequence of the emergence of the Arabian Peninsula and the onset of modern-like atmospheric circulation. Our results emphasize that although elevated rainfall seasonality was probably a persistent feature since the India–Asia collision in the Paleogene, modern-like monsoonal atmospheric circulation only emerged in the late Neogene. A modern-like South Asian Monsoon only appeared when East African and Middle Eastern uplift led to the establishment of the Somali Jet around 13 million years ago, according to Earth system modelling using a range of regional palaeogeographies.

The amount of radiative energy received at the Earth's surface depends on two factors: Earth–Sun distance and sunlight angle. Because of the former, high-eccentricity cycles can induce the appearance of seasons in the tropical ocean. In this paper, we use the Earth system model IPSL-CM5A2 to investigate the response of the low-latitude ocean to variations in Earth's orbit eccentricity. Sea surface temperature (SST) and primary production (PP) were simulated under six precession configurations at high eccentricity and two configurations at low eccentricity, representing extreme configurations observed over the past 1 million years. Results show that high eccentricity leads to increased seasonality in low-latitude mean SST, with an annual thermal amplitude of approximately 2.2 °C (vs. 0.5 °C at low eccentricity). Low-latitude mean PP, which already exhibits inherent seasonality under low-eccentricity conditions, sees its seasonality largely increased under high eccentricity. As a consequence, we show that on long timescales the intensity of SST seasonality exhibits only the eccentricity frequency, whereas that of PP additionally follows precession dynamics. Furthermore, the seasonal variations in both SST and PP at high eccentricities are influenced by the annual placement of the perihelion with its direct impact of radiative energy received in tropical regions. This leads to a gradual and consistent transition of seasons within the calendar. We introduce the concept of “eccentriseasons”, referring to distinct annual thermal differences observed in tropical oceans under high-eccentricity conditions, which shift gradually throughout the calendar year. These findings have implications for understanding low-latitude climate phenomena such as the El Niño–Southern Oscillation (ENSO) and monsoons in the past.

Sundaland, the inundated shelf separating Java, Sumatra and Borneo from the Malay Peninsula, is of exceptional interest to biogeographers for its species richness and its position at the junction between the Australasian and Indomalay biogeographic provinces. Owing to its low elevation and relief, its physiography is contingent on relative sea-level change, which drove Quaternary species burst in response to flooding episodes. New findings show that the region was predominantly terrestrial during the Late Pleistocene requiring a reassessment of the drivers of its recent biodiversity history. Here we show that physiographic changes have modified the regional connectivity network and remodelled the pathways of species dispersal. From combined landscape evolution and connectivity models, we found four phases of drainage reorganisation and river captures. These changes have fragmented the environment into multiple habitats connected by migratory corridors that cover 8% of the exposed shelf and stretch across the biogeographic provinces. Our results support the theory that rapidly evolving physiography could foster Quaternary biodiversification across Southeast Asia.

Based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5)-generation previous Institut Pierre Simon Laplace (IPSL) Earth system model, we designed a new version, IPSL-CM5A2, aiming at running multi-millennial simulations typical of deep-time paleoclimate studies. Three priorities were followed during the setup of the model: (1) improving the overall model computing performance, (2) overcoming a persistent cold bias depicted in the previous model generation and (3) making the model able to handle the specific continental configurations of the geological past. These developments include the integration of hybrid parallelization Message Passing Interface – Open Multi-Processing (MPI-OpenMP) in the atmospheric model of the Laboratoire de Météorologie Dynamique (LMDZ), the use of a new library to perform parallel asynchronous input/output by using computing cores as “I/O servers” and the use of a parallel coupling library between the ocean and the atmospheric components. The model, which runs with an atmospheric resolution of 3.75∘×1.875∘ and 2 to 0.5∘ in the ocean, can now simulate ∼100 years per day, opening new possibilities towards the production of multi-millennial simulations with a full Earth system model. The tuning strategy employed to overcome a persistent cold bias is detailed. The confrontation of a historical simulation to climatological observations shows overall improved ocean meridional overturning circulation, marine productivity and latitudinal position of zonal wind patterns. We also present the numerous steps required to run IPSL-CM5A2 for deep-time paleoclimates through a preliminary case study for the Cretaceous. Namely, specific work on the ocean model grid was required to run the model for specific continental configurations in which continents are relocated according to past paleogeographic reconstructions. By briefly discussing the spin-up of such a simulation, we elaborate on the requirements and challenges awaiting paleoclimate modeling in the next years, namely finding the best trade-off between the level of description of the processes and the computing cost on supercomputers.

In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record in the form of strong variance in the precession band (19–23 kyr), because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale monsoon variability in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (<1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost part of the Bay of Bengal spanning the late Miocene (9 to 5 million years ago). Underpinned by a new orbitally tuned benthic isotope stratigraphy, we use X-ray fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Results show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma in the equatorial sector of the Indian Ocean, with no apparent intensification over the latest Miocene.

Although the role of Earth’s orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment 1 , 2 . Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events 3 . Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth’s orbital eccentricity with rhythms of around 100,000 years and 405,000 years—a distinct spectral signature to that of coeval global climate cycles 4 . Simulations with an Earth System Model 5 coupled with an ocean biogeochemical model 6 show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records. .Morphometric analysis of coccolith assemblages spanning the last 2,800,000 years suggests that the evolution of coccolithophores is linked to seasonality changes, paced by Earth’s orbital eccentricity with implications for the carbon cycle.

The numerical model GEOCLIM, a coupled Earth system model for the long-term biogeochemical cycle and climate, has been revised. This new version (v 7.0) allows a flexible discretization of the oceanic module for any paleogeographic configuration, coupling to any general circulation model (GCM), and the determination of all boundary conditions from the GCM coupled to GEOCLIM, notably the oceanic water exchanges and the routing of land-to-ocean fluxes. These improvements make GEOCLIM7 a unique, powerful tool, devised as an extension of GCMs, to investigate the Earth system evolution at timescales (several million years) and with processes that could not be simulated otherwise. We present a complete description of the model, whose current state gathers features that have been developed and published in several articles since its creation and some that are original contributions of this article, like the seafloor sediment routing scheme and the inclusion of orbital parameters. We also present a detailed description of the method to generate the boundary conditions of GEOCLIM, which is the main innovation of the present study. In a second step, we discuss the results of an experiment where GEOCLIM7 is applied to the Turonian paleogeography, with 10 Myr orbital cycle forcings. This experiment focuses on the effects of orbital parameters on oceanic O2 concentration, particularly in the proto-Atlantic and Arctic oceans, where the experiment revealed the largest O2 variations.

Supraglacial clasts originate from rockfalls onto glacier surfaces, accumulating in situ-produced 10Be during rockwall exposure and glacial transport. For small glaciers, the transport-related 10Be component is negligible, enabling millennial erosion rate estimates based on clast concentration measurements. Since 2009, 11 studies – to our knowledge – have analyzed 10Be concentrations in supraglacial clasts across 31 glaciers in Alaska, the Western Alps, and the Himalayas. These studies reveal high variability in 10Be concentration among glaciers. This variability is due to the heterogeneous 10Be content of large rockfalls. In this paper, recommendations are proposed to improve the reliability of the method. In particular, reliability can be increased by amalgamating numerous small clasts taken from large supraglacial areas and by carrying out several (at least five) geochemical analyses per glacier. Erosion rates range from 0.24 to 11 mm yr−1. Comparison with long-term exhumation and contemporary uplift rates reveals three situations: erosion rates that align with, exceed, or fall below uplift and exhumation rates. Low erosion rates suggest permafrost shielding, while high rates may reflect climate-driven thermal changes. These findings highlight the interplay between glacial processes, erosion, and climate dynamics.

Supraglacial clasts originate from rockfalls onto glacier surfaces, accumulating in situ-produced .sup.10 Be during rockwall exposure and glacial transport. For small glaciers, the transport-related .sup.10 Be component is negligible, enabling millennial erosion rate estimates based on clast concentration measurements. Since 2009, 11 studies - to our knowledge - have analyzed .sup.10 Be concentrations in supraglacial clasts across 31 glaciers in Alaska, the Western Alps, and the Himalayas. These studies reveal high variability in .sup.10 Be concentration among glaciers. This variability is due to the heterogeneous .sup.10 Be content of large rockfalls. In this paper, recommendations are proposed to improve the reliability of the method. In particular, reliability can be increased by amalgamating numerous small clasts taken from large supraglacial areas and by carrying out several (at least five) geochemical analyses per glacier. Erosion rates range from 0.24 to 11 mm yr.sup.-1 . Comparison with long-term exhumation and contemporary uplift rates reveals three situations: erosion rates that align with, exceed, or fall below uplift and exhumation rates. Low erosion rates suggest permafrost shielding, while high rates may reflect climate-driven thermal changes. These findings highlight the interplay between glacial processes, erosion, and climate dynamics.

Supraglacial clasts originate from rockfalls onto glacier surfaces, accumulating in situ-produced 10Be during rockwall exposure and glacial transport. For small glaciers, the transport-related 10Be component is negligible, enabling millennial erosion rate estimates based on clast concentration measurements. Since 2009, 11 studies – to our knowledge – have analyzed 10Be concentrations in supraglacial clasts across 31 glaciers in Alaska, the Western Alps, and the Himalayas. These studies reveal high variability in 10Be concentration among glaciers. This variability is due to the heterogeneous 10Be content of large rockfalls. In this paper, recommendations are proposed to improve the reliability of the method. In particular, reliability can be increased by amalgamating numerous small clasts taken from large supraglacial areas and by carrying out several (at least five) geochemical analyses per glacier. Erosion rates range from 0.24 to 11 mm yr−1. Comparison with long-term exhumation and contemporary uplift rates reveals three situations: erosion rates that align with, exceed, or fall below uplift and exhumation rates. Low erosion rates suggest permafrost shielding, while high rates may reflect climate-driven thermal changes. These findings highlight the interplay between glacial processes, erosion, and climate dynamics.