Indian monsoon variations during three contrasting climatic periods : the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 125 (2015): 50-60, doi:10.1016/j.quascirev.2015.06.009.In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.The work of C.Z. was supported by the ANR MONOPOL

Late Pliocene Cordilleran Ice Sheet development with warm northeast Pacific sea surface temperatures

The initiation and evolution of the Cordilleran Ice Sheet are relatively poorly constrained. International Ocean Discovery Program (IODP) Expedition 341 recovered marine sediments at Site U1417 in the Gulf of Alaska (GOA). Here we present alkenone-derived sea surface temperature (SST) analyses alongside ice-rafted debris (IRD), terrigenous, and marine organic matter inputs to the GOA through the late Pliocene and early Pleistocene. The first IRD contribution from tidewater glaciers in southwest Alaska is recorded at 2.9 Ma, indicating that the Cordilleran Ice Sheet extent increased in the late Pliocene. A higher occurrence of IRD and higher sedimentation rates in the GOA during the early Pleistocene, at 2.5 Ma, occur in synchrony with SSTs warming on the order of 1 degrees C relative to the Pliocene. All records show a high degree of variability in the early Pleistocene, indicating highly efficient ocean-climate-ice interactions through warm SST-ocean evaporation-orographic precipitation-ice growth mechanisms. A climatic shift towards ocean circulation in the subarctic Pacific similar to the pattern observed during negative Pacific Decadal Oscillation (PDO) conditions today occurs with the development of more extensive Cordilleran glaciation and may have played a role through increased moisture supply to the subarctic Pacific. The drop in atmospheric CO2 concentrations since 2.8 Ma is suggested as one of the main forcing mechanisms driving the Cordilleran glaciation

Effects of radio-frequency fields on bacterial cell membranes and nematode temperature-sensitive mutants

Membrane-related bioeffects have been reported in response to both radio-frequency (RF) and extremely low-frequency (ELF) electromagnetic fields (EMFs), particularly in neural cells. We have tested whether RF fields might cause inner membrane leakage in ML35 E. coli cells, which express β-galactosidase (lacZ) constitutively, but lack the lacY permease required for substrate entry. The activity of lacZ (indicating substrate leakage through the inner cell membrane) was increased only slightly by RF exposure (1 GHz, 0.5 W) over 45 min. Since lacZ activity showed no further increase with a longer exposure time of 90 min, this suggests that membrane permeability per se is not significantly affected by RF fields, and that slight heating (≤ 0.1°C) could account for this small difference. Temperature-sensitive (ts) mutants of the nematode, Caenorhabditis elegans, are wild-type at 15°C but develop the mutant phenotype at 25°C; an intermediate temperature of 21°C results in a reproducible mixture of both phenotypes. For two ts mutants affecting transmembrane receptors (TRA-2 and GLP-1), RF exposure for 24 h during the thermocritical phase strongly shifts the phenotype mix at 21°C towards the mutant end of the spectrum. For ts mutants affecting nuclear proteins, such phenotype shifts appear smaller (PHA-1) or non-significant (LIN-39), apparently confirming suggestions that RF power is dissipated mainly in the plasma membrane of cells. However, these phenotype shifts are no longer seen when microwave treatment is applied at 21°C in a modified exposure apparatus that minimises the temperature difference between sham and exposed conditions. Like other biological effects attributed to microwaves in the C. elegans system, phenotype shifts in ts mutants appear to be an artefact caused by very slight heating

Palynomorph and dinoflagellate cyst assemblage counts at OPD Site 145-887 from 5.3 to 0.4 Ma

This dataset contains raw palynomorphs counts at ODP Holes 887A and 887C, including dinocyst assemblage, as well counts of others palynomorphs such as acritarchs, pollen grains and tasmanites. Precise depths and estimated age are also provided for each sample

The regional imprints of Dansgaard-Oeschger events on land and marine environments

One of the most important challenges of the IPCC is documenting the regional impact of the present-day global warming. Yet, identifying the regional expression of global changes is the first and necessary step to understand the mechanisms behind them. The best examples of past global warming events, comparable in velocity and magnitude to those expected in the 21st-century, are those associated with the Dansgaard–Oeschger (D–O) cycles that punctuated the last glacial period, ~115,000-27,000 years ago (115-27 ka). Reasonably well-chronologically constrained deep-sea and terrestrial records of D-O cycles provide an excellent opportunity for documenting the nature (shape, amplitude, timing and duration) of the vegetation, fire and oceanic regional responses to past rapid global warming events. Building on the ACER (https://doi.org/10.1594/PANGAEA.870867) and PaleoJump (https://www.tipes.dk/paleojump-a-tipes-database-for-research-on-rapid-climate-transitions/) databases, I will present a new compilation of D-O records from geochemical, sedimentological and micropaleontological data. I will pay particular attention to one of the best dated event, the D-O 8, centered at ~38,000 years ago (38 ka). It followed the Heinrich Stadial 4 cold phase (~40 -38 years ago), and occurred during a period of minima in precession and intermediate ice volume (Marine Isotope Stage 3). Compared to the other D-O events, D-O 8 was marked by strong Greenland warming, ~10°C, and strong increase in atmospheric CH4 and CO2 concentrations, by at around 150 ppb and 20 ppm, respectively, and was associated with a vigorous resumption of the Atlantic Meridional Overturning Circulation. D-O 8 warming has also the advantage to be relatively recent and, therefore, one of the best recorded all around the world

The regional imprints of Dansgaard-Oeschger events on land and marine environments

International audienceOne of the most important challenges of the IPCC is documenting the regional impact of the present-day global warming. Yet, identifying the regional expression of global changes is the first and necessary step to understand the mechanisms behind them. The best examples of past global warming events, comparable in velocity and magnitude to those expected in the 21st-century, are those associated with the Dansgaard–Oeschger (D–O) cycles that punctuated the last glacial period, ~115,000-27,000 years ago (115-27 ka). Reasonably well-chronologically constrained deep-sea and terrestrial records of D-O cycles provide an excellent opportunity for documenting the nature (shape, amplitude, timing and duration) of the vegetation, fire and oceanic regional responses to past rapid global warming events. Building on the ACER (https://doi.org/10.1594/PANGAEA.870867) and PaleoJump (https://www.tipes.dk/paleojump-a-tipes-database-for-research-on-rapid-climate-transitions/) databases, I will present a new compilation of D-O records from geochemical, sedimentological and micropaleontological data. I will pay particular attention to one of the best dated event, the D-O 8, centered at ~38,000 years ago (38 ka). It followed the Heinrich Stadial 4 cold phase (~40 -38 years ago), and occurred during a period of minima in precession and intermediate ice volume (Marine Isotope Stage 3). Compared to the other D-O events, D-O 8 was marked by strong Greenland warming, ~10°C, and strong increase in atmospheric CH4 and CO2 concentrations, by at around 150 ppb and 20 ppm, respectively, and was associated with a vigorous resumption of the Atlantic Meridional Overturning Circulation. D-O 8 warming has also the advantage to be relatively recent and, therefore, one of the best recorded all around the world

When Eastern India Oscillated Between Desert Versus Savannah‐Dominated Vegetation

International audienceDuring 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

Pollen-derived vegetation reconstruction at IODP Site 353-U1446, Bay of Bengal

This data set presents the composition of vegetation in the Mahanadi Basin during the Last Glacial Period (80-20 ka). Percentages of the tropical trees, the arid-taxa, Artemisia, Poaceae and Cyperaceae recorded at IODP Site U1446 (19°5'N, 85°4'E, 1430 m water depth) are shown, as well the Diversity Simpson's index based on pollen record and the Axis 1 sample scores of the Principal Component Analysis, which is used in this study as humidity index (Figures 2 and 3 of the related study). This data set also contained the confidence intervals shown in Figure S10 and the row pollen data. We also included labels, depth (in m CCSF-A) and estimated age (Ka) of the studied samples