As the largest volcanic eruption in the Quaternary period, the ~74 ka Toba super eruption’s impact on the global heat budget and monsoon systems has been prominently debated. Despite particular focus on its consequences in India as one of the key regions of early modern human dispersal — ranging from catastrophic to minimal — high-resolution proxy evidence from geological archives that empirically support the claims has been scarce. In this study, we trace pre- and post-Toba monsoonal dynamics from a finely laminated sedimentary section from the Arabian Sea that brackets Toba tephra as an event marker of the eruption. The sediment core SO130-289KL was retrieved from the northeastern margin of the Arabian Sea outside of the upwelling zone (Sindh continental margin), at a water depth of 571 m, which today lies within the oxygen minimum zone (OMZ). The site is sensitive to both monsoon seasons, as the South Asian summer monsoon controls sedimentary dynamics, whereas the wind strength of the winter monsoon primarily influences the sea surface temperatures (SSTs). Thus, the sediment core sensitively records the evolution of South Asian summer and winter monsoons. In order to reconstruct the regional climatic response to Toba at near-annual resolution, we produced time-series data of elemental and SST variations using µm-scale measurements (100–200 µm resolution) by x-ray fluorescence (µXRF) scanning and mass spectrometry imaging (MSI) techniques, respectively. The µXRF elemental data trace terrestrial components primarily sourced by runoff from the summer monsoon, which are complemented by the glycerol dialkyl glycerol tetraether-based SST calculations from MSI that are affected by OMZ intensity. On the other hand, the alkenone measurements from MSI more sensitively trace SST variations that are primarily governed by the winter monsoon. Supplemented by conventional biomarker and stable hydrogen and carbon isotope measurements, which trace precipitation and vegetation dynamics over the Indus River catchment, respectively, our multi-proxy data contribute to a better understanding of the impact that the Toba eruption had on the regional climate, environment, and eventually, contemporaneous humans.

Tropical peatlands are not currently represented in large-scale terrestrial ecosystem models. Recent work in the central Congo Basin (CCB) measuring peatland processes and reconstructing peatland evolution and past climate provides a unique opportunity to further develop such models. Here, we modify the peatland scheme in the Joint UK Land Environment Simulator (JULES), the land surface component of the UK Earth System Model, in particular changing the vegetation litter composition and the dependence of peat decay on soil moisture. The modifications are informed by field measurements and by comparing the simulated peat accumulation and loss over 20 000 years with peat core records, including the 'Ghost Interval' period when reduced precipitation starting approximately 5000 years before the present (BP) resulted in significant peat loss. We drive JULES with a reconstruction of precipitation from peat core proxy data and other meteorological data from a global palaeoclimate model. The original JULES peatland scheme was unable to accumulate the observed quantities of peat or simulate the losses of peat suggested by palaeo records. Our updated version of JULES simulates peat increases until 3000 BP, when reduced precipitation results in substantial loss until 1000 BP. Correct representation of vegetation cover over time is also crucial for realistic peatland evolution. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

Angkor was the capital of the Khmer Empire during approximately 9th to 15th CE. It relied on a sophisticated water management system to sustain a vast low-density urban population. For the last two decades, the decline of Angkor has been linked to hydroclimatic instability in combination with infrastructural failure. Recent archaeological evidence suggests that the decline of elite occupation within the civic-ceremonial core may have begun earlier, resulting from additional social, political, or economic drivers. Understanding the timing and potential causes of such changes is crucial for assessing the vulnerability of complex urban systems.Sedimentary molecular biomarkers can provide insights into paleoenvironmental and anthropogenic changes. In particular, untargeted molecular fingerprinting is not constrained by predefined compound lists and analyzes thousands of molecular features simultaneously. This enables the detection of complex and overlapping source inputs and facilitates the identification of broader molecular shifts potentially associated with changing land use, ecosystem functioning, and anthropogenic activity.Here we apply an untargeted molecular fingerprinting framework using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) to characterize sedimentary organic matter in lipid extracts from a sediment core retrieved from a pond inside the temple of Angkor Wat. GC×GC substantially increases chromatographic resolution and enables the detection of thousands of chemical features without a priori hypotheses and is thus suitable for the untargeted analyses. We investigate temporal shifts in molecular composition across the Angkorian and post-Angkorian periods to evaluate changes in organic matter inputs, microbial processing, and water quality, and discuss their implications for changes in urban land use and occupation patterns at the temple complex.

Hydrothermal vents release substantial amounts of ancient carbon into the ocean, primarily as carbon dioxide, yet the extent to which this carbon is integrated into marine food webs remains poorly constrained. Here, we present a combination of bulk radiocarbon and stable carbon isotope measurements of particulate organic carbon from water column filters with compound-specific hydrogen and radiocarbon isotope analyses of fatty acids from surface sediments to trace carbon assimilation across benthic and pelagic realms in a low pH, shallow-water hydrothermal system off Taiwan. Isotope correlations indicate that vent-derived carbon dioxide constitutes a substantial fraction of the local microbial and faunal biomass through chemoautotrophic pathways (up to 30

One of Earth's most extensive tropical peatland complexes is in the central Congo Basin. Past climatic drying caused the widespread loss of a large proportion of the peat carbon stock, indicating its vulnerability to climate change. However, the additional effect caused by the interaction of climate change with land-use change-particularly drainage-on peat carbon stores has not been assessed. Here, we simulate the effects of climate and land-use change on Congo Basin peatlands. Our model is driven by an ensemble of 10 climate models to assess changes in peat carbon stocks at global warming levels 1.5, 2, 3 and 4°C. We find that the fate of the peatland carbon store is highly uncertain when we simulate climate change alone (warming level 3°C gives a median change in peat thickness of 0.04 m; range of approx. -5.0 to +0.3 m). By contrast, simulations that couple land-use change with twenty-first-century climate change are unequivocal: the Congo Basin peatlands will become significant emitters of carbon. When the warming level is 3°C, the change in peat thickness of a drained peatland is projected to be -2.6 m; a range of approximately -5.0 to -2.1 m. Our results emphasize the need to protect Congo Basin peatlands from widespread land-use change. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The isoprenoid lycopane occurs in the membranes of cultured archaea, but in environmental samples it has traditionally been interpreted to derive from phytoplankton. In the deposits of the Muschelkalk Sea, a Triassic marginal sea, lycopane contents increased during a freshening trend at the Anisian-Ladinian boundary. Based on peak abundances of lycopane at pycnoclines, we hypothesize an episodic occurrence of haloclines in the Muschelkalk Sea, with freshwater runoff mostly affecting surface waters. Freshwater dissolved inorganic carbon is typically 13C-depleted. An up-section trend of decreasing delta 13C values of the biomarkers of phytoplankton (phytane) and heterotrophic consumers (2,6,10,14,18-pentamethylicosane; regular PMI) from -33%o to -41%o is therefore in accord with freshening. Even lower delta 13C values of lycopane and the co-occurring archaeal lipid biphytane (average: -48%o and -47%o, respectively) agree with archaea as source organisms of lycopane in the Muschelkalk Sea. We put forward a novel application of a common isoprenoid biomarker, linking the occurrence of 13C-depleted lycopane to marine freshening events.

During the early and mid-Holocene, the Sahara and Sahel experienced a humid phase, the so-called African Humid Period (AHP)1. The AHP started around 14.8 thousand years before present (kyr BP), peaked between 9.0 kyr BP and 6.0 kyr BP and experienced short-lived droughts of as yet poorly constrained age and duration2,3. Here we show that the AHP was punctuated by two droughts of decadal-scale duration, at about 9.3 kyr BP and 8.2 kyr BP, and another more tentatively identified drought at 6.3 kyr BP. Our findings arise from a multiproxy time series from the annually layered (varved) sedimentary archive of Lake Yoa in Chad, which covers the past 10.25 kyr continuously. During the more prominent drought at 8.2 kyr BP, pollen and diatom data, along with leaf-wax isotopes and geochemical source area indicators, imply that a reduction in local precipitation and fluvial supply to Lake Yoa caused a lake-level drop accompanied by an expansion of reed belts along the shore. The proxy data, together with our climate simulations, suggest that the 8.2 kyr BP drought event was a direct and rapid response to a potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) owing to sudden freshwater input into the North Atlantic. The results underline the need for improved decadal predictions4 to better anticipate such drought risks in the future.

Pollen analysis was conducted on core materials that were deposited over the last 2000 cal years BP in Mkhuze wetland, KwaZulu-Natal. The objective was to reconstruct past vegetation and infer past changes in climate or possible human disturbances by enhancing both pollen and non-pollen proxy data in the summer rainfall region. Palynological results show a dominance of Poaceae (grasses >70%) that suggests a predominance of grassy vegetation in and around the swamp with some woodland and forest elements from the surroundings. Between 1700 and 1200 cal years BP, fungal spores, cryptogams, wetland plants, Podocarpus, and other forest pollen elements declined. Bushveld tree pollen of Spirostachys increased, indicating a decrease in moisture availability (humidity) and a change from forest to an open savanna vegetation. A peak of microscopic charcoal and Poaceae with a corresponding decrease in Spirostachys pollen around 800-500 cal years BP suggests an increase in wildfires under dry conditions that may have been caused by anthropogenic forest clearance for farming by the Iron Age people. The increase in microscopic charcoal, charred cuticles, a peak of Amaranthaceae pollen, and a corresponding decrease in trees and grasses in the last 280-200 cal years BP may be due to regional drought. The appearance of exotic Pinus pollen during the most recent period corresponds to the introduction of alien vegetation by European settlers. We compared changes in the pollen record of the Mkhuze freshwater swamp with a coeval section of a previously published longer pollen sequence in the nearby Lake St Lucia estuary to confirm if regional vegetation trends can also be observed in the section. Wider regional environmental trends were also assessed using other non-pollen proxies like isotopic data for comparison. Results align with delta O-18, d(13)C and N-15 studies, although some, especially the latter, may not suggest parallel moisture conditions over the distances involved. This indicates that diverse environmental conditions prevailed in the region in the last c. 2000 years BP.

Reconstructing past South Asian monsoon dynamics, which governs wind and rainfall patterns across the Indian subcontinent, is crucial for understanding low-latitude climate. Constraining monsoon drivers requires separating summer and winter components in palaeoclimate archives, but this remains challenging because proxy signals usually integrate seasonal signals. The northeastern Arabian Sea provides a unique setting in which sedimentary and geochemical proxies are driven by the summer monsoon, while sea surface temperature is primarily controlled by winter monsoon winds. Here we employed mass spectrometry and hyperspectral imaging on a sediment core off Pakistan to reconstruct subdecadal changes in sea surface temperature and marine primary production during the last deglaciation (~16,000-12,000 years ago). Atmospheric humidity and vegetation changes were additionally assessed by plant-wax isotope analyses on a subset of samples. We show that summer monsoon winds were driven by the Northern Hemisphere high-latitude climate on centennial-to-millennial timescales. Winter monsoon was primarily characterized by a millennial-scale decline in wind strength driven by increasing global temperatures, with superimposed centennial-scale variability. We identified an inverse relationship between winter monsoon wind strength and the amount of winter non-monsoonal precipitation. Mechanistic insights of seasonal monsoon dynamics improved interpretation of regional palaeoprecipitation records and may enhance climate model performances in low latitudes.

The central Congo Basin hosts the world's largest tropical peat swamp forest (PSF), covering 167 600 km² and storing approximately 29 Pg of carbon below ground. However, estimates of above ground biomass (AGB) remain limited, partly owing to reliance on global wood density (WD) databases that may not reflect local species characteristics. This study assessed the impact of species-specific WD on AGB estimation in five PSF sites of the northern Republic of Congo. Specific WD was collected in one site, and these data were then used to estimate AGB in four additional sites. We collected wood cores using an increment borer from 244 trees to measure the WD of the 20 most abundant species (93% of trees with diameters ≥10 cm). Using global WD values overestimated AGB by 24.7% (p < 0.05). The low average local WD (0.460 ± 0.12 g cm-3) explained this difference. The WD variation was primarily species-driven (58%) and associated with functional traits; pioneer and evergreen species had lower WD. These findings highlight the importance of locally measured WD for accurate biomass and carbon stock estimation in tropical peatland forests. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The central Congo Basin is home to the world's largest tropical peatland complex and is covered with swamp forest. In the face of climate change and future human activities in the region, it is important to understand the factors that determine the nature and dynamics of the peatland vegetation cover. One way to gain insight into these factors is to reconstruct the history of the central Congo Basin peatlands. Analysing lipid biomarkers extracted from peat cores such as plant wax n-alkanes enables past environmental and climatic conditions to be reconstructed. However, there is currently no information on how the production of plant waxes by different plant species influences the abundance and isotopic composition of n-alkanes in peat and other archives in the Congo Basin. In this study we analysed plant wax n-alkane abundances, delta C-13 and delta D values according to photosynthetic pathways (C-3 vs. C-4), angiosperm subclasses (dicotyledons vs. monocotyledons), and source water delta D values in the dominant plant types (trees, shrubs, and herbs) in the peatland area of the Cuvette Department in the Republic of the Congo. Our dataset enables the definition of a new n-alkane distribution index, named GRIND, that distinguishes between C-3 (mostly dicotyledons) and C-4 (monocotyledons) plants as follows: (n-C-27 + n-C-33 + n-C-35)/(n-C-25 + n-C-27 + n-C-29 + n-C-31 + n-C-33 + n-C-35). This index may therefore be used to analyse Central African peat deposits and derive the relative abundance of C-3 and C-4 plant waxes in the past, independently of delta C-13 measurements. Furthermore, delta C-13 values from the central Congo Basin and other African sites suggest that environments with high relative humidity (> 80%) are characterised by very negative delta C-13 values (i.e., < -37 parts per thousand) of n-C-29 and n-C-31 alkanes. This observation highlights the potential of n-alkane delta C-13 in deriving climatic information under high relative humidity conditions in Central African lowlands, and contribute to palaeo-climatic reconstructions. Finally, the delta D values of n-C-29 and n-C-31 alkanes demonstrate that, despite contrasting apparent fractionation values associated with photosynthetic pathways and plant functional types - which can be accounted for using delta C-13 and pollen data in sedimentary deposits - they reliably reflect the delta D of environmental water. This confirms that plant wax n-alkane delta D values are effective tools for reconstructing palaeo-climatic changes in equatorial regions.

On the Greek island Milos and in shallow water at its coast, many spots with hydrothermal activity have been found and studied in the past. The M192 cruise in August 2023 with the German research vessel METEOR followed the idea that these systems may continue along a tran­sect from shal­low, nearshore, photic to the deeper, off­shore, aphotic zone around the island, accompanied by changes in terms of environmental parameters. Volcanism along the Hellenic volcanic arc started during the Early to Middle Pliocene, while the last eruption occurred in 1950 (Nea Kammeni volcano). The intense seismic activity in the area is associated with important geothermal gas venting, with the major systems being found in relatively shallow waters (1–500m depth) at Methana, Milos, Santorini (Kolumbo submarine volcano), Kos and Nisyros.Systematic bathymetry and water column acoustic survey work with METEOR's multibeam with the autonomous underwater vehicle (AUV) MARUM-SEAL on the M192 cruise revealed several previously uncharted hydrothermal vent fields offshore Milos. They are located in the southeast extending from the bays Kiriaki to Paleochori and Thiorychia, as well as in an area northwest of Milos, offshore the bay of Vani. The distribution of the hydrothermal vents seems to be tectonically controlled and follow the prominent faults that have been mapped on Milos.The areal extents of venting were identified by echosounding using the acoustic anomaly the presence of gas bubbles causes in the water column. But selected hydrothermal vents were furthermore visually observed and sampled using the remotely operated vehicle (ROV) MARUM-SQUID. These individual vents revealed pronounced differences; whereas the shallower vents (around 100 m water depth) were noticed as white patches (of sulfur-oxidizing bacteria) on the sandy seafloor with diffuse venting comparable to the shallow vents close to the coast, the deeper vents (around 200 m water depth) featured remarkable chimney structures sometimes several meters in height that are covered with white biofilms and vent fluids reaching temperatures up to 180 °C. Sampled fluids showed mildly reducing and slightly acidic (pH between 5.0 and 7.9) conditions and were rich in dissolved hydrogen sulfide and dissolved metals. These signals extended up to about 10 m into the water column, as recorded by CTD-rosette water sampler stations.To date, shal­low-wa­ter and deep-sea hy­dro­thermal sys­tems have been treated as in­de­pend­ent, seem­ingly un­re­lated en­tit­ies; the results of the M192 expedition presented here are the first foray into re­mov­ing this ar­bit­rary bound­ary.

Chemoautotrophic Campylobacteria utilize the reductive tricarboxylic acid (rTCA) cycle for carbon uptake, a metabolic pathway that is more energy-efficient and discriminates less against 13C than the Calvin–Benson–Bassham cycle. Similar to other hydrothermal systems worldwide, Campylobacteria dominate the microbial community of the shallow-water hydrothermal system off Kueishantao (Taiwan). Compound-specific carbon stable isotope analyses of lipid-derived fatty acids were performed to understand the importance of rTCA and the transfer of fixed carbon to higher trophic levels in the vent area. Of these, C16:1ω7c, C18:1ω7c, and C18:1ω9c fatty acids were strongly enriched in 13C, indicating the activity of rTCA utilizing Campylobacteria. Isotopic fractionation was close to 0 ‰, likely caused by pH values as low as 2.88. Characteristic fatty acids were present not only in the vent fluids but also in adjacent sediments and water filters 20 m away from the vent orifice, albeit with decreasing abundance and diluted 13C signal. Furthermore, δ13C analysis of fatty acids from the tissue of Xenograpsus testudinatus, a crab endemic to this particular vent system, identified the trophic transfer of chemosynthetically fixed carbon. This highlights the interrelationship between chemoautotrophic microbial activity and life opportunities of higher organisms under environmentally harsh conditions at shallow-water hydrothermal systems.

Hydrothermal fluid flow not only shapes mineral deposition on the ocean floor but also creates ecological niches by altering temperature and energy availability. In these niches, microbial life thrives and has an additional, often unrecognized impact on mineral formation. In a newly discovered vent field in medium depths off Milos, Greece, we show how contrasting hydrothermal regimes host fundamentally different bacterial metabolisms. Diffusive flow fosters acidic, sulfate-rich conditions that promote kaolinization and pyrite formation. Fatty acid δ 13 C values down to −39‰ indicate acetyl-CoA-based sulfate reduction as the main metabolism, likely contributing to pyrite formation. In contrast, vigorous venting delivers hot, acidic, carbon-rich, and sulfate-depleted fluids that sustain the activity of sulfide-oxidizing chemoautotrophs. Fatty acid δ 13 C values of up to −4‰ and elemental sulfur accumulation provide evidence of their activity. Without such hydrothermal influence, little microbial activity and only quartz-rich sediments can be observed. Combined multivariate lipid analyses highlight Eh as the strongest environmental control, with increasing average chain length of fatty acids as an adaptation to (hydro-)thermal stress. These results illustrate how different types of fluid flow influence the activity of chemoautotrophic bacterial communities that are involved in the formation of characteristic sulfur minerals in hydrothermal environments.

Carbon storage in soils is important in regulating atmospheric carbon dioxide (CO 2 ). However, the sensitivity of the soil-carbon turnover time (τ soil ) to temperature and hydrology forcing is not fully understood. Here, we use radiocarbon dating of plant-derived lipids in conjunction with reconstructions of temperature and rainfall from an eastern Mediterranean sediment core receiving terrigenous material from the Nile River watershed to investigate τ soil in subtropical and tropical areas during the last 18,000 years. We find that τ soil was reduced by an order of magnitude over the last deglaciation and that temperature was the major driver of these changes while the impact of hydroclimate was relatively small. We conclude that increased CO 2 efflux from soils into the atmosphere constituted a positive feedback to global warming. However, simulated glacial-to-interglacial changes in a dynamic global vegetation model underestimate our data-based reconstructions of soil-carbon turnover times suggesting that this climate feedback is underestimated.

The central Congo Basin contains the world’s most extensive tropical peatland complex, spanning 16.7 million hectares. Until now, radiocarbon dating of basal peats has been limited to 14 samples with poor spatial coverage, and suggested that peat typically initiated during the Holocene. We present 38 new basal dates, improving spatial coverage across the region. Some of the new basal dates are much older than any previous dates, indicating that peat initiated in the central Congo Basin at multiple locations in the Late Pleistocene. Our oldest basal date is 42 300 (41 200–43 800) calibrated years before present, making this one of the world’s oldest extant tropical peatlands, and twice as old as previously believed. The temporal distribution of basal dates suggests that changing climatic wetness has played a role in peat initiation in the region; numerous basal dates correspond with climatically wet phases, whilst few basal dates correspond with dry phases such as the Last Glacial Maximum (LGM). Today we find the central Congo Basin peatlands on wide interfluves between rivers, and on floodplains (mostly of the dendritic left-bank tributaries of the Congo River). We find the oldest basal dates on the floodplains of these left-bank tributaries, indicating a surprisingly high degree of channel stability over many millennia. This contrasts with, for example, peatlands on Amazonian floodplains, which are typically just a few thousand years old. The persistence of peat in the central Congo Basin since before the LGM, likely the most climatically dry period during the last 42 000 yr in this region, suggests that these areas may have played an important biogeographical role as forest refugia during glacial-interglacial cycles.

Human activities have profoundly modified the fluxes in the global sediment cycle. However, the anthropogenic forcing on soil erosion beyond instrumental records or historical documentation is largely unknown. Here we analyze markers for low‐intensity fires and soil erosion in East Java over the past 5,000 years. We find evidence of a substantial human impact on fire occurrence due to the onset/intensification of swidden cultivation around 3,500 years ago, in the absence of changes in regional hydroclimate or vegetation. Highest soil erosion occurred during the past 500 years, coinciding with a transition toward permanent agriculture. Human‐impacted soil erosion was further amplified by intense monsoonal rainfall and strong rainfall seasonality around 2,000 and 300 years ago. With such rainfall anomalies projected to occur with higher frequency and severity in the tropics under the ongoing greenhouse warming, our results suggest an accelerating erosion rate in the future, posing risks for natural resources.

Tropical peatlands represent a critical but poorly constrained component of the global oxygen cycle. Here, we present a 10,600-year record of terrestrial O₂ production from the Congo Basin peatlands, revealing an oxygen surplus of 83 [68–100] Pg. Deep peatlands (>2 m), despite covering 30% of the area, account for over 50% of this flux. Using a novel redox titration method, we show that O₂ release is highly sensitive to hydroclimate, with 80% declines during arid intervals and rapid recovery during wet phases. Globally, peatlands may offset 24–80% of the continental oxidative weathering sinks. However, peatland O2 output occurs in episodic, climate-driven pulses, linking carbon and oxygen cycles across millennial timescales. With precipitation projected to decline by 20–40% by 2100, our findings underscore the dual role of peatlands as vulnerable C sinks and dynamic O₂ sources, while offering rare archives of Earth’s redox evolution.

Dansgaard-Oeschger oscillations and Heinrich events described in Greenland ice cores are also visible in the climate of the monsoon realm as documented in Arabian Sea sediments. However, little is known about these millennial scale fluctuations beyond the reach of the Greenland ice cores. Here, we present high-resolution geochemical and micropaleontological data from two sediment cores located offshore Pakistan, extending the monsoon record to the past 250,000 years in millennial scale resolution. The stable oxygen isotope (d18O) record of the planktic foraminifera G. ruber shows a strong correspondence to Greenland ice core d18O, whereas the d18O signal of benthic foraminifera (U. peregrina and G. affinis) reflects patterns similar to those observed in Antarctic ice core records. Distinct shifts in benthic d18O during stadials are interpreted to show frequent injections of oxygen-rich intermediate water masses of Southern Ocean origin into the Arabian Sea. Alkenone SSTs show variations between 23 and 28°C. Millennial scale SST changes of 2°C are modulated by long-term SST fluctuations. Interstadials and the cold phases of interglacials are characterized by sediments enriched in organic carbon (TOC) whereas sediments with low TOC contents appear during stadials. Abrupt shifts (50-60 year duration) at climate transitions, such as interstadial inceptions, correlate with changes in productivity-related and anoxia-indicating proxies. Interstadial inorganic data consistently show that enhanced fluxes of terrestrial-derived sediments are paralleled by productivity maxima, and are characterized by an increased fluvial contribution from the Indus River. The hydrogen isotopic composition of terrigenous plant waxes indicates that stadials are dry phases whereas humid conditions seem to have prevailed during interstadials. In contrast, stadials are characterized by an increased contribution of aeolian dust probably from the Arabian Peninsula. Heinrich events are especially dry and dusty, indicating a dramatically weakened Indian summer monsoon and increased continental aridity. These results strengthen the evidence that North Atlantic temperature changes and shifts in the hydrological cycle of the Indian monsoon system are closely coupled, and had a massive impact on regional environmental conditions such as river discharge and ocean margin anoxia. These shifts were modulated by changes in the supply of water masses from the Southern Hemisphere.