Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand ...to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum.
The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may ...contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ¹³C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean's persistent, central role in abrupt glacial climate change.
The Wda River valley in northern Poland is a polygenetic valley located in a former subglacial meltwater channel that after ice sheet retreat hosted separate and then interconnected lake basins, ...subsequently replaced by a river. In one part of the river system an abandoned Lateglacial valley is found. This dry valley is a unique feature in the area located within the limit of the Scandinavian Ice Sheet during the Last Glaciation in the Central European Lowland. We investigated lacustrine and fluvial sediments and landforms in the valley and applied palynological analysis combined with radiocarbon dating to reconstruct the valley evolution from the early period of river inception in the Lateglacial through the formation of lakes during the Pleistocene/Holocene transition up to the establishment of a modern river system in the early Holocene. Three coeval processes were identified: (1) formation of lake basins in the subglacial channel connected by a river, (2) erosion of the river bed between the lakes, and (3) sediment deposition at the mouths of the channels in the lake basins first generating delta fans and eventually filling the lakes entirely. The valley formation was associated with diachronous melting of dead ice blocks buried in the subglacial channel controlled by the capacity of the hydrological system to evacuate the meltwater. Most of the lake basins in the study area were formed during the Bølling–Allerød period, but one section of the subglacial channel not affected by thermokarst processes survived protected by dead ice blocks throughout the entire Lateglacial. Accelerated dead-ice decay at the beginning of the Holocene triggered widespread lowering of the base level, which caused lake disappearance and the formation of the modern river system. The processes reconstructed in the central section of the Wda River indicate a highly dynamic and diachronous river valley development during the Lateglacial and early Holocene whereby the valley formation was interwoven with the formation of lake basins within the valley triggered by melting of dead ice blocks in the substratum.
•A polygenetic river valley formation in a glaciated terrain is investigated.•A dry, abandoned Lateglacial river valley is documented.•Formation of lakes and river systems intervened in time and space.•Diachronous melting of dead ice blocks steered river and lake formation.
During the last few decades, neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million-year through millennial time-scales. The widespread use of the Nd ...isotope proxy depends on whether the Nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases. Here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water Nd isotopic signature and thus can be used to reconstruct past deep water Nd isotopes. Applying this method downcore on South Atlantic Deep Cape Basin core TNO57-21 (41.1°S, 7.9°E, 4981m), the Nd isotopic composition of the planktonic foraminiferal Fe–Mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction (Piotrowski et al., 2004, 2005, 2008) as reflecting changes in bottom water sourcing. In the case of northeastern North Atlantic core BOFS 8K (52.5°N 22.1°W, 4045m), the planktonic foraminiferal Fe–Mn oxide coatings have different Nd isotopes from reductive sediment leaches. Clearly acid-reductive leaching must be tested in more detail. We observe that the Nd isotopic composition of the deep northeastern Atlantic core shifted during the deglaciation, from glacial values similar to the South Atlantic Cape Basin towards Holocene values similar to the Bermuda Rise (Roberts et al., 2010). Taken as a whole, the Nd isotope record from foraminiferal authigenic coatings suggests large-scale changes in the proportion of northern and southern deep water sources occurred throughout the Atlantic Ocean, with substantial chemical gradients at times, during the last deglaciation.
► Nd isotopes are used to examine changes in deep Atlantic Ocean water mass sourcing. ► We compare leaching and foraminiferal methods of reconstructing past seawater εNd. ► The deep Cape Basin record is underpinned with new foraminiferal-based εNd. ► Deep ocean circulation between the North and South Atlantic is examined. ► A strong glacial εNd gradient existed between the west and east North Atlantic.
Neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components, including ...fish teeth, ferromanganese oxides extracted by acid‐reductive leaching, cleaned foraminifera, and foraminifera with Fe‐Mn oxide coatings. Here we compare Nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera, as well as from oxidatively‐reductively cleaned foraminiferal shells from sediment cores in the North Atlantic. Sedimentary volcanic ash contributes a significant fraction of the Nd when the ferro‐manganese (Fe‐Mn) oxide coatings are leached from bulk sediments. Reductive leachates of marine sediments from North Atlantic core tops near Iceland, or directly downstream from Iceland‐Scotland Overflow Waters, record ɛNd values that are significantly higher than seawater, indicating that volcanic material is easily leached by acid‐reductive methods. The ɛNd values from sites more distal to Iceland are similar to modern seawater values, showing little contamination from Iceland‐derived volcanogenic material. In all comparisons, core top planktonic foraminifera ɛNd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the Nd isotopic signature of deep North Atlantic water masses.
Key Points
Sedimentary neodymium is contaminated by volcanics
Sedimentary neodymium is contaminated by continental material
Foraminifera are better recorders of sea water neodymium
Neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern Atlantic core reveal a history of the global overturning circulation intensity through the last ...deglaciation. From a minimum during the Last Glacial Maximum (LGM), North Atlantic Deep Water (NADW) began to strengthen between 18 and 17 kyr cal. BP, approximately 2000–3000 years before the Bølling warming. It exhibits a gradually increasing baseline intensity that plateaus in the early Holocene, tracks increasing Northern Hemisphere insolation and parallels atmospheric CO
2 concentration. Millennial-scale fluctuations are superimposed on this baseline NADW increase, corresponding to events in Northern Hemisphere climate records. The millennial excursions show sharp increases associated with the pre-Bølling retreat of continental glaciers and the Bølling warming itself, a decrease with Allerød cooling, and a recovery through the Younger Dryas and early Holocene. The data confirm a close link between deep-ocean circulation and North Atlantic climate changes. There is no clear linkage with meltwater pulses, indicating that rapid meltwater additions did not trigger observable mode changes in NADW production. However, rapid changes in North Atlantic sea ice cover show a strong relationship with the millennial perturbations of NADW flux to the deep Southern Ocean. The data indicate that the baseline intensity of NADW reaching the Cape Basin is paced by Northern Hemisphere insolation and that North Atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere.
The objective of the study was to evaluate the encapsulation of seeds of tropical forest species with cellulose gel (CG) from Vitis vinifera and sodium alginate, with and without biostimulant, in ...order to optimise its size, shape and performance for direct seeding. Four species used in direct seeding were selected, i.e., Bixa orellana L., Mimosa bimucronata (DC.) Kuntze, Trema micrantha (L.) Blume and Psidium guajava L.. The experimental design was completely randomised with eight treatments and four repetitions of 100 seeds each. Encapsulation affected the physical quality of the seeds, however, it facilitated their handling and visualisation in germination tests, especially for T. micrantha, with a 4-fold increase in size with alginate gel and 2-fold with CG. Sodium alginate performed better than CG, synchronising the growth of B. orellana seedlings. The biostimulant showed potential to synchronise germination, vigor and seedling growth when associated with dormancy break for M. bimucronata, and promoted seedling growth for P. guajava. Sodium alginate gel has potential for seed enhancement, while CG encapsulation needs to be improved in relation to its physical characteristics, requiring further studies. The biostimulant can be recommended for enhancing uniformity of seed emergence in direct seeding.
Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age ...initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets.
Onchocerciasis is a priority neglected tropical disease targeted for elimination by 2025. The standard strategy to combat onchocerciasis is annual Community-Directed Treatment with ivermectin (CDTi). ...Yet, high prevalence rates and transmission persist following > 12 rounds in South-West Cameroon. Challenges include programme coverage, adherence to, and acceptability of ivermectin in an area of Loa loa co-endemicity. Loiasis patients harbouring heavy infections are at risk of potentially fatal serious adverse events following CDTi. Alternative strategies are therefore needed to achieve onchocerciasis elimination where CDTi effectiveness is suboptimal.
We designed an implementation study to evaluate integrating World Health Organisation-endorsed alternative strategies for the elimination of onchocerciasis, namely test-and-treat with the macrofilaricide, doxycycline (TTd), and ground larviciding for suppression of blackfly vectors with the organophosphate temephos. A community-based controlled before-after intervention study will be conducted among > 2000 participants in 20 intervention (Meme River Basin) and 10 control (Indian River Basin) communities. The primary outcome measure is O. volvulus prevalence at follow-up 18-months post-treatment. The study involves four inter-disciplinary components: parasitology, entomology, applied social sciences and health economics. Onchocerciasis skin infection will be diagnosed by skin biopsy and Loa loa infection will be diagnosed by parasitological examination of finger-prick blood samples. A simultaneous clinical skin disease assessment will be made. Eligible skin-snip-positive individuals will be offered directly-observed treatment for 5 weeks with 100 mg/day doxycycline. Transmission assessments of onchocerciasis in the communities will be collected post-human landing catch of the local biting blackfly vector prior to ground larviciding with temephos every week (0.3 l/m
) until biting rate falls below 5/person/day. Qualitative research, including in-depth interviews and focus-group discussions will be used to assess acceptability and feasibility of the implemented alternative strategies among intervention recipients and providers. Health economics will assess the cost-effectiveness of the implemented interventions.
Using a multidisciplinary approach, we aim to assess the effectiveness of TTd, alone or in combination with ground larviciding, following a single intervention round and scrutinise the acceptability and feasibility of implementing at scale in similar hotspots of onchocerciasis infection, to accelerate onchocerciasis elimination.
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