Search

The paleoclimate and ecosystem variability in Africa during the Plio/Pleistocene has received considerable attention due to its potential links to hominid evolution. However, the reconstruction of this variability hinges critically upon highly temporally resolved proxy data from continuous, well-dated sediment archives. In light of these requirements we use a new XRF core-scanning record from International Ocean Discovery Program (IODP) Site U1478 off the Limpopo River mouth (Mozambique Channel, SW Indian Ocean) spanning the past c. 4 Ma to identify the climate variability in SE Africa. Our results show that the elemental distribution in the Site U1478 cores is mainly controlled by the rate of terrigenous input and – to a lesser extent – by bottom-current transport and post-depositional processes such as propagation of paleoredox boundaries and diagenesis across some intervals. The log(Ti/Ca) ratio, which is used as a tracer of terrigenous sediment input, shows quasi-cyclical variability across the entire record that closely matches the periods of orbital parameters. However, the cyclical behaviour of the log(Ti/Ca) signal varies through time, with the uppermost 106 m of the sequence (0–1.07 Ma) displaying a mix of precession and obliquity signals, the intervals 106–223 m (1.07–2.80 Ma) and 240–257 m (3.68–4.05 Ma) being dominated by precession, and the interval 223–240 m (2.80–3.68 Ma) being controlled by eccentricity. To refine the available chronology for Site U1478, which is based on shipboard biostratigraphic and paleomagnetic data, we have tuned the log(Ti/Ca) record to the LR04 benthic oxygen isotope record, summer insolation at 25° S, and orbital eccentricity depending on the dominant cyclicities in the XRF dataset across individual time intervals. The resulting chronology enables us to evaluate the XRF data as well as the previously available shipboard sedimentological and geochemical datasets within a regional and global climatic context. This allows the connection of a c. 7-m-thick contourite deposit and a prominent paleoredox boundary to hydroclimate and ocean-circulation changes during the early Pleistocene and across the Mid-Pleistocene Transition, respectively. Moreover, a decoupling of the log(Ti/Ca) and the log(Ti/K) records, with the latter indicating the degree of sediment weathering, from 3.2 to 2.8 Ma points to an increased delivery of highly weathered sediments to Site U1478. We attribute this to temporarily wetter and warmer conditions in the catchment of the Limpopo River and/or a change in the sediment source, perhaps associated with the tectonically driven enlargement of the Zambezi River catchment during the late Pliocene/early Pleistocene.

To contribute to a better understanding of Neogene climate evolution in Central Asia, we here present the first orbitally tuned time scale for a drillcore record from the Qaidam Basin (NE Tibetan Plateau) that consists of lacustrine sediments and spans the late Pliocene to early Pleistocene (~3.3 to 2.1 Ma). Our tuning of Core SG-1b is based on the ln(Rb/Sr) ratio derived from XRF core scanning and grain-size distribution data that trace wet-dry climate alternations predominantly paced by orbital obliquity. Based on our ln(Rb/Sr) record, obliquity-precession interferences persisted during the mid-Pliocene warm period, but disappeared during the early Pleistocene. This could indicate that over the course of the late Pliocene a low-latitude-derived climate modulator gained an increasingly prominent role in shaping the environment of the Qaidam paleolake. At the same time, the consistent presence of the precession signal during the early Pleistocene hampers a refinement of the entire tuning on precession time scales. The inferred changes in sedimentation rate from the late Pliocene to the early Pleistocene indicate a long-term decrease in sediment supply into the Qaidam paleolake. This finding is in line with the previously proposed notion of a long-term aridification trend across the Plio-Pleistocene transition in Central Asia.

Soil degradation is a severe and growing threat to ecosystem services globally. Soil loss is often nonlinear, involving a rapid deterioration from a stable eco‐geomorphic state once a tipping point is reached. Soil loss thresholds have been studied at plot scale, but for landscapes, quantitative constraints on the necessary and sufficient conditions for tipping points are rare. Here, we document a landscape‐wide eco‐geomorphic tipping point at the edge of the Tibetan Plateau and quantify its drivers and erosional consequences. We show that in the upper Kali Gandaki valley, Nepal, soil formation prevailed under wetter conditions during much of the Holocene. Our data suggest that after a period of human pressure and declining vegetation cover, a 20% reduction of relative humidity and precipitation below 200 mm/year halted soil formation after 1.6 ka and promoted widespread gullying and rapid soil loss, with irreversible consequences for ecosystem services. Two billion people live in drylands, where small changes in climate and land use can have large impacts on soil stability and food security. It is important to know the thresholds of eco‐geomorphic stability in such settings. Here, we determine the conditions that tipped a trans‐Himalayan dryland into irreversible degradation. We show that in the upper Kali Gandaki valley, Nepal, sustained soil formation terminated after 1.6 ka. Human pressure in the preceding period had reduced vegetation cover, but a 20% drop in relative humidity and a precipitation decrease to below 200 mm/year promoted widespread, rapid badland formation. These values may serve as indicators elsewhere, but local eco‐geomorphic threshold values are likely to differ between landscapes due to other essential variables. We document an eco‐geomorphic tipping point, plunging a landscape at the southern edge of the Tibetan plateau into an erosional stateThe tipping point occurred 1.6 ka ago, it was facilitated by a period of human land use and triggered by late Holocene aridificationAt sustained modern erosion rates of 1 mm/year, soils are removed on a millennial time scale, precluding fast recovery of the landscape

Global climatic changes during the last glacial and deglacial have been related to variations of the Atlantic Meridional Overturning Circulation (AMOC). Here, we present new and refined 231Pa/230Th down‐core profiles extending back to 30 ka BP from the northwestern Atlantic along the Atlantic Deep Western Boundary Current, which is the main component of the southward deep backflow of the AMOC. Besides the well‐known Bermuda Rise records, available high‐resolution 231Pa/230Th data in the northwestern Atlantic are still sparse. Our new records along with reconstructions of deep water provenance from Nd isotopes constrain the timing and magnitude of past changes in AMOC from an additional northwestern Atlantic region forming a depth transect between 3,000‐ and 4,760‐m water depth. Our extended and improved data set confirms the weakening of the AMOC during deglacial cold spells such as Heinrich Event 1 and the Younger Dryas interrupted by a reinvigoration during the Bølling‐Allerød interstadial as seen in the prominent 231Pa/230Th records from the Bermuda Rise. However, in contrast to the Bermuda Rise records, we find a clearly reduced circulation strength during the Last Glacial Maximum in the deep Atlantic. Four new 231Pa/230Th records form a depth transect in the northwestern Atlantic in millennial‐scale resolution back to 30 kaCombined records resolve millennial‐scale deep water variabilities like YD, B/A, HS1, LGM, and HS2Timing and magnitude of record variations are in line with the well‐known Bermuda Rise record with exception of the LGM

Mediterranean climates are characterized by strong seasonal contrasts between dry summers and wet winters. Changes in winter rainfall are critical for regional socioeconomic development, but are difficult to simulate accurately1and reconstruct on Quaternary timescales. This is partly because regional hydroclimate records that cover multiple glacial–interglacial cycles2,3with different orbital geometries, global ice volume and atmospheric greenhouse gas concentrations are scarce. Moreover, the underlying mechanisms of change and their persistence remain unexplored. Here we show that, over the past 1.36 million years, wet winters in the northcentral Mediterranean tend to occur with high contrasts in local, seasonal insolation and a vigorous African summer monsoon. Our proxy time series from Lake Ohrid on the Balkan Peninsula, together with a 784,000-year transient climate model hindcast, suggest that increased sea surface temperatures amplify local cyclone development and refuel North Atlantic low-pressure systems that enter the Mediterranean during phases of low continental ice volume and high concentrations of atmospheric greenhouse gases. A comparison with modern reanalysis data shows that current drivers of the amount of rainfall in the Mediterranean share some similarities to those that drive the reconstructed increases in precipitation. Our data cover multiple insolation maxima and are therefore an important benchmark for testing climate model performance. Comparisons between past regional drivers of precipitation extremes found time series data from Lake Ohrid and modern climate models of the Mediterranean may help to reduce simulation uncertainties in predictions of the Mediterranean climate.

Since the first pollen analyses from core material in the 1960s, the limnotelmatic sequence of Tenaghi Philippon, located within the subsurface of the Drama Basin of NE Greece, has been recognized as an exceptional archive of terrestrial climate and ecosystem dynamics for the Quaternary in Europe. The polleniferous sequence covers the last ∼ 1.35 Ma continuously, spanning at least 19 consecutive glacial-interglacial cycles. Analyses of Tenaghi Philippon as based on the drillcores from the 1960s were restricted to a millennial-scale resolution. Because the original cores have deteriorated, the archive's potential for analyzing abrupt (i.e., centennial- to decadal-scale) climate and ecosystem change has long remained unexplored. Therefore new drilling campaigns were carried out in 2005 and 2009 to recover the 0–60 m and 50–200 m depth intervals of the archive, respectively. The new cores (recovery: 97.8 and 99.0 %, respectively) allow characterization of the evolution of abrupt climate and ecosystem variability across the full range of climatic boundary conditions realized during the late obliquity-dominated ‘41-ka world’ and the eccentricity-dominated ‘100-ka world’. The resulting climate data will also assist paleoanthropologists in resolving the dispersal dynamics of archaic and modern humans into Eurasia. In light of these new research initiatives, and because much of the previous literature on Tenaghi Philippon is from sources that are partially difficult to access, we here provide a review of the geological evolution of the Tenaghi Philippon archive, its present-day environmental conditions and its exploration history. We further give a synopsis of recent work based on the new cores and discuss the perspectives for future studies.

Paleoclimate records from tropical South America typically show precession‐paced variability in rainfall, caused by insolation‐driven changes in the South American Monsoon System, however this mechanism may not be responsible for hydroclimate change outside of the core monsoon domain, such as in the coastal zone of tropical eastern Brazil. Our findings are based on a ∼850 kyr‐long multiproxy record from a marine sediment core collected from the eastern Brazilian margin that represents the longest continuous record of South American hydroclimate to date. Utilizing the ln (K/Al) chemical weathering proxy from the core, we determine that past hydroclimate change in the coastal zone was primarily modulated by obliquity forcing. We demonstrate that high obliquity is associated with an increase in the boreal summer interhemispheric insolation contrast which decreases the zonality of the southern trade winds and reduces moisture advection to the coastal zone. Based on the long‐term coherence between the ln (K/Al) record and benthic δ13C records from the Atlantic during Marine Isotope Stages 16–13, we infer that an increase in the strength of the overturning circulation, caused by Northern Hemisphere high‐latitude forcing, may have produced surface cooling in the western tropical South Atlantic which led to reduced moisture advection to the coastal zone. We suggest that this mechanism may have also caused the amplification in millennial‐scale variability in the coastal hydroclimate system, which began after the decoupling of the coastal hydroclimate system from obliquity forcing. Coastal precipitation in tropical eastern Brazil is dominated by obliquity forcing over most of the past ∼850 kyrMillennial‐scale hydroclimate variability increased during the most recent ∼200 kyr, as modulation by obliquity gradually weakenedNorthern Hemisphere high‐latitude climate fluctuations are linked to hydroclimate variations in the coastal zone of tropical eastern Brazil Coastal precipitation in tropical eastern Brazil is dominated by obliquity forcing over most of the past ∼850 kyr Millennial‐scale hydroclimate variability increased during the most recent ∼200 kyr, as modulation by obliquity gradually weakened Northern Hemisphere high‐latitude climate fluctuations are linked to hydroclimate variations in the coastal zone of tropical eastern Brazil

Efforts to understand long‐term Indian Ocean dynamics and land‐sea linkages in southeast Africa during periods of significant global and regional climate change have been inhibited by a lack of high‐resolution climate records, particularly during the Plio‐Pleistocene. Here we present new biomarker and pollen records from International Ocean Discovery Program (IODP) Site U1478, located at the Upper Agulhas Confluence near the Limpopo River mouth, to establish environmental conditions at the southeast African margin between 4 and 1.8 Ma and address this spatiotemporal gap. Compound‐specific hydrogen isotopes of terrestrial leaf waxes (δDwax) and TEX86, using marine archaeal lipids, document hydroclimate variability and sea surface temperature (SST), respectively, permitting an onshore‐offshore climate comparison. The U1478 records establish the Limpopo catchment response to the switch in Indonesian Throughflow source waters, the mid‐Pliocene Warm Period, and intensification of Northern Hemisphere glaciations at ∼2.7 Ma. Broad coherence between the δDwaxand SST records supports a linkage between Indian Ocean temperatures and southeast African hydroclimate. We hypothesize that additional mechanisms including Indian Ocean cross‐basin SST gradients (ΔSST) and high latitude glaciation acted as hydroclimate controls during the Plio‐Pleistocene. We use ΔSST to evaluate ocean‐atmosphere patterns similar to the Indian Ocean Dipole (IOD) and establish generally wetter conditions in the region associated with positive IOD‐like phases. Additionally, an obliquity signal evident in the δDwaxrecord indicates that glacial‐interglacial variability likely influenced the tropical rain belt position and also controlled rainfall. Hydroclimate and environmental conditions across the Plio‐Pleistocene in southeast Africa may have important implications for regional hominin evolution. Site U1478 biomarkers record Plio‐Pleistocene climate changes in southeast Africa, providing regional context for early hominin evolutionIndonesian Throughflow variability, the mid‐Pliocene warm period, and onset of Northern Hemisphere glaciation impacted Limpopo climateHydroclimate and offshore temperatures are linked, but zonal temperature gradients and glacial variability likely also modulated rainfall Site U1478 biomarkers record Plio‐Pleistocene climate changes in southeast Africa, providing regional context for early hominin evolution Indonesian Throughflow variability, the mid‐Pliocene warm period, and onset of Northern Hemisphere glaciation impacted Limpopo climate Hydroclimate and offshore temperatures are linked, but zonal temperature gradients and glacial variability likely also modulated rainfall

Soil and lake sediments are important paleoclimate archives often forming a source‐sink setting. To better understand magnetic properties in such settings, we studied red soil on low‐magnetic bedrock and subrecent sediments of Caohai Lake (CL) in Heqing Basin, China. Red soil is the only important source material for the CL sediments, it is highly magnetic with susceptibilities (χ) of ~10−5m3/kg. The red soil is dominated by pedogenic nano‐magnetite (~10–15 nm) arranged in aggregates of ~100 nm, with particle interaction that causes a wide effective grain size distribution in the superparamagnetic (SP) range tailing into stable single‐domain behavior. Transmission electron microscopy and broadband frequency χ(f) suggest partial disintegration of the aggregates and increased alteration of the nanoparticles to hematite during transfer of red soil material to CL. This shifts the domain state behavior to smaller effective magnetic grain sizes, resulting in lower χfd% and χ values, and a characteristic change of χ(f). The SP‐stable single‐domain distribution of the aggregates in red soil could be climate dependent, and the ratio of saturation remanence to χ is a potential bedrock‐specific paleoclimate proxy reflecting it. Magnetic properties of the CL sediments are controlled by an assemblage of nanoparticle aggregates and larger‐sized bedrock‐derived magnetite. The results challenge the validity of the previous paleoclimate interpretation from the 168‐m‐long Core‐HQ (900–30 ka) in Heqing Basin. Disintegration of aggregates could lead to SP behavior with low χfd% without extinction of individual magnetite nanoparticles, and the χfd%‐based assumption of SP magnetite dissolution may be wrong. Highly magnetic red soil on low‐magnetic bedrock is dominated by ~10‐ to 15‐nm‐sized magnetite forming ~100‐nm aggregates with SP‐SSD behaviorDuring transfer of red soil material to lake sediments, the aggregates partly disintegrate resulting in domain states with lower χ and χfd%SIRM/χ in red soil represents the specific arrangement of nano‐magnetite particles in the aggregates and is a potential paleoclimate proxy

The intensification of Northern Hemisphere glaciation (iNHG) and uplift of the Tibetan Plateau have been argued to be among the main drivers of climate change in midlatitude Central Asia during the Pliocene/Pleistocene. While most proxy records that support this hypothesis are from regions outside the Tibetan Plateau (such as from the Chinese Loess Plateau), detailed paleoclimatic information for the plateau itself during that time has yet remained elusive. Here we present a temporally highly resolved (~500 years) sedimentological record from the Qaidam Basin situated on the northeastern Tibetan Plateau that shows pronounced glacial‐interglacial climate variability during the interval from 2.7 to 2.1 Ma. Glacial (interglacial) intervals are generally characterized by coarser (finer) grain size, minima (maxima) in organic matter content, and maxima (minima) in carbonate content. Comparison of our results with Earth's orbital parameters and proxy records from the Chinese Loess Plateau suggests that the observed climate fluctuations were mainly driven by changes in the Siberian High/East Asian winter monsoon system as a response to the iNHG. They are further proposed to be enhanced by the topography of the Tibetan Plateau and its impact on the position and intensity of the westerlies. Pronounced glacial‐interglacial climate fluctuations on the NE Tibetan Plateau during the latest Pliocene and early PleistoceneChanges in East Asian Winter Monsoon and the position of the westerlies influenced sediment transport on the NE Tibetan PlateauIntensification of Northern Hemisphere glaciation amplified climate fluctuations on the NE Tibetan Plateau

Paleohydrological data comprising pollen assemblages and leaf‐wax hydrogen isotopes (δDwax) from paleolake sediments in the Qaidam Basin (China) provide evidence for a link between increased moisture availability on the Tibetan Plateau and global cooling during the Mid‐Pleistocene Transition. Notably, they document the persistence of humid and cold conditions during Marine Isotope Stages 24–22 (936–866 ka) suggesting that boundary conditions favorable for extended glaciation on the Tibetan Plateau first developed at ~900 ka. Our δDwaxresults indicate a strong influence of proximal (monsoonal) moisture sources during that glacial, in agreement with the intensification of the interhemispheric moisture transport resulting from Antarctic ice volume increase at ~900 ka. The consistency of our results with other marine and terrestrial climate data sets suggests that extended glaciation on the Tibetan Plateau may have initiated ~500 ka earlier than previously assumed, implying that midlatitude ice sheets actively contributed to global cooling during the Mid‐Pleistocene Transition. The Mid‐Pleistocene Transition (MPT) marks an intensification of global cooling associated with an expansion of Earth's ice sheets. The Tibetan Plateau—today the most extensively glaciated region outside the high latitudes—may have played a pivotal role in this process. However, because its glaciation history is yet poorly constrained, testing this hypothesis has remained difficult. Here we assess the climatic boundary conditions for glacier development on the Tibetan Plateau during the MPT using pollen and organic biomarker data from paleolake sediments (Qaidam Basin, China). Our results suggest a link between increased moisture availability on the Tibetan Plateau and global cooling during Marine Isotope Stages 24–22. We infer that favorable conditions for extended glaciation on the Tibetan Plateau first developed at ~900 ka, that is, ~500 ka earlier than previously assumed, suggesting that ice sheet formation on the Tibetan Plateau indeed played an active role in global cooling during the MPT. Link between increased moisture availability on the Tibetan Plateau and global cooling during Marine Isotope Stages 24‐22Favorable conditions for extended glaciation on the Tibetan Plateau first developed at ~900 kaIce sheet formation on the Tibetan Plateau played an active role in global cooling during the Mid‐Pleistocene Transition