Climate variability at the southern boundaries of the Namib (southwestern Africa) and Atacama (northern Chile) coastal deserts during the last 120,000 yr

In this study, we present grain-size distributions of the terrigenous fraction of two deep-sea sediment cores from the SE Atlantic (offshore Namibia) and from the SE Pacific (offshore northern Chile), which we ‘unmix’ into subpopulations and which are interpreted as coarse eolian dust, fine eolian dust, and fluvial mud. The downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern Africa and northern Chile for the last 120,000 yr. The two records show a relatively wet Last Glacial Maximum (LGM) compared to a relatively dry Holocene, but different orbital variability on longer time scales. Generally, the northern Chilean aridity record shows higher-frequency changes, which are closely related to precessional variation in solar insolation, compared to the southwestern African aridity record, which shows a remarkable resemblance to the global ice-volume record. We relate the changes in continental aridity in southwestern Africa and northern Chile to changes in the latitudinal position of the moisture-bearing Southern Westerlies, potentially driven by the sea-ice extent around Antarctica and overprinted by tropical forcing in the equatorial Pacific Ocean.     

Late Quaternary climatic events and sea-level changes recorded by turbidite activity, Dakar Canyon, NW Africa

The relationship of sea-level changes and short-term climatic changes with turbidite deposition is poorly documented, although the mechanisms of gravity-driven sediment transport in submarine canyons during sea-level changes have been reported from many regions. This study focuses on the activity of the Dakar Canyon off southern Senegal in response to major glacial/interglacial sea-level shifts and variability in the NW-African continental climate. The sedimentary record from the canyon allows us to determine the timing of turbidite events and, on the basis of XRF-scanning element data, we have identified the climate signal at a sub-millennial time scale from the surrounding hemipelagic sediments. Over the late Quaternary the highest frequency in turbidite activity in the Dakar Canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea-level rise. However, episodic turbidite events coincide with the timing of Heinrich events in the North Atlantic. During these times continental climate has changed rapidly, with evidence for higher dust supply over NW Africa which has fed turbidity currents. Increased aridity and enhanced wind strength in the southern Saharan-Sahelian zone may have provided a source for this dust.     

Variability in terrigenous sedimentation processes off northwest Africa and its relation to climate changes: Inferences from grain-size distributions of a Holocene marine sediment record

Variations in deposition of terrigenous fine sediments and their grain-size distributions from a high-resolution marine sediment record offshore northwest Africa (30°51.0′N; 10°16.1′W) document climate changes on the African continent during the Holocene. End-member grain-size distributions of the terrigenous silt fraction, which are related to fluvial and aeolian dust transport, indicate millennial-scale variability in the dominant transport processes at the investigation site off northwest Africa as well as recurring periods of dry conditions in northwest Africa during the Holocene. The terrigenous record from the subtropical North Atlantic reflects generally humid conditions before the Younger Dryas, during the early to mid-Holocene, as well as after 1.3 kyr BP. By contrast, continental runoff was reduced and arid conditions were prevalent at the beginning of the Younger Dryas and during the mid- and late Holocene. A comparison with high- and low-latitude Holocene climate records reveals a strong link between northwest African climate and Northern Hemisphere atmospheric circulation throughout the Holocene. Due to its proximal position, close to an ephemeral river system draining the Atlas Mountains as well as the adjacent Saharan desert, this detailed marine sediment record, which has a temporal resolution between 15 and 120 years, is ideally suited to enhance our understanding of ocean-continent-atmosphere interactions in African climates and the hydrological cycle of northern Africa after the last deglaciation.     

全新世期间亚洲和非洲干旱区环境的短尺度变化

过去对北非和中国干旱区140 ka BP来环境演化的初步对比表明,两地的干旱度在万年时间尺度上基本同步。这种关系是否也适用于全新世百年尺度的干旱事件,仍是有待研究的问题。本文对撒哈拉地区569个地表淡水指示物和我国北方干旱区158个古土壤和湖泊沉积的14C年代数据进行了时空频数统计分析,揭示出两地沙漠在全新世期间至少经历了三次同时性的、百年-千年尺度的干旱事件, 叠置于季风气候对地球轨道变化响应的总体趋势上;沙漠在纬向上的进退主要受控于季风前沿的伸缩幅度, 说明两个季风系统的短尺度变化可能受统一因素控制。最为显著的干旱事件发生于约4 ka BP。两地干旱区在过去认为的6 ka BP 前后的全新世气候适宜期并没有表现为稳定的湿润环境。我国过去发现的该时期不少的干旱证据被解释为高温所导致的强烈蒸发作用所致。但全新世中期的干旱期在热带的存在及其与冰心记录中低甲烷事件的吻合难以用蒸发来解释,而应与夏季风环流的减弱有关。     

中国东部陆架全新世沉积体系:过程-产物关系研究进展评述

渤、黄、东海是典型的物源供给丰富的宽广陆架环境,形成的全新世沉积记录十分丰富。本区域潮汐作用、陆架环流作用和沉积物重力流导致的物质输运都很活跃;陆架沉积动力过程与全新世沉积体系的空间分布、物质组成、堆积速率、层序年代等特征相联系。全新世陆架与海岸沉积具有高分辨率、空间分布的不连续和沉积记录的片段性等特征。江苏海岸全新世中期海岸沉积、杭州湾全新世早-中期沉积、浙闽沿岸全新世沉积和其他陆架泥质沉积可从物质来源（海面上升中的沉积改造和河流入海通量）、输运-堆积过程、沉积层序形成的先后次序、陆架沉积记录的未来状况等方面进行分析。数值模拟可用以深化本区的过程-产物关系研究。     

Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N

At the western continental margin of the Barents Sea, 75°N, hemipelagic sediments provide a record of Holocene climate change with a time resolution of 10-70 years. Planktic foraminifera counts reveal a very early Holocene thermal optimum 10.7-7.7 kyr BP, with summer sea surface temperatures (SST) of 8°C and a much enhanced West Spitsbergen Current. There was a short cooling between 8.8 and 8.2 kyr BP. In the middle and late Holocene summer, SST dropped to 2.5°-5.0°C, indicative of reduced Atlantic heat advection, except for two short warmings near 2.2 and 1.6 kyr BP. Distinct quasi-periodic spikes of coarse sediment fraction (with large portions of lithic grains, benthic and planktic foraminifera) record cascades of cold, dense winter water down the continental slope as a result of enhanced seasonal sea ice formation and storminess on the Barents shelf over the entire Holocene. The spikes primarily cluster near recurrence intervals of 400-650 and 1000-1350 years, when traced over the entire Holocene, but follow significant 885-/840- and 505-/605-year periodicities in the early Holocene. These non-stationary periodicities mimic the Greenland-[Formula: See Text]Be variability, which is a tracer of solar forcing. Further significant Holocene periodicities of 230, (145) and 93 years come close to the deVries and Gleissberg solar cycles.     

南海西部表层沉积物碳酸盐分布特征及其溶解作用

碳酸盐是海洋沉积物的重要组成部分,在南海表层沉积物中含量最高可超过 70%,因此深入研究现代碳酸盐的分布特征具有十分重要的意义.对南海西部底质的大量取样分析表明,该区 CaCO3含量在上陆坡最高,其中在北部和中南部含量较高,中部和东南部含量较低,其分布特征主要受陆源物质供给量的控制,与陆架的宽度和陆坡的坡度密切相关.CaCO3最富集区出现在水深 400～600 m的上陆坡区,其中水深 500～600 m内的平均含量最高,达 44.37%,水深超过 1 300 m时含量开始明显下降,表明溶解作用增强.对 CaCO3含量与水深关系进行多项式拟合,结果表明,本区没有出现碳酸盐溶解作用突然增强的溶跃面;但在水深 3 500 m附近,拟合曲线出现转折点, CaCO3含量由随水深迅速下降变为相对稳定,因此该水深应为碳酸盐临界补偿深度.     

坦桑尼亚滨海盆地陆坡峡谷沉积特征及其控制因素*

东非陆缘深水盆地具有巨大油气资源潜力,但对陆坡峡谷沉积特征研究较少,制约有利储集层预测。本研究利用三维地震资料,对东非坦桑尼亚滨海盆地陆坡峡谷开展精细研究。结果表明:(1)研究区陆坡发育多条大型海底峡谷;上陆坡处,坡度较陡,峡谷内以侵蚀作用为主,沉积物主要局限在褶皱推覆带的翼部;褶皱推覆带之外的下陆坡区,坡度变缓,峡谷末端发育席状砂质沉积及砂泥混杂的碎屑流沉积,同时在峡谷北侧发育向北延伸的泥质漂积体;在陆坡边缘,发育海底滑塌,形成块体搬运沉积。(2)峡谷沉积受陆源物质供给、褶皱推覆带、北大西洋底流以及陆坡边界断层等因素控制。受东非裂谷海域分支活动影响,研究区陆架窄、陆坡陡,陆源物质可迅速通过陆架,进入陆坡峡谷:与河流相连的峡谷,物源充足、规模较大,有沉积物发育而没有与河流直接相连的峡谷物源有限、规模较小,峡谷内无明显沉积;褶皱推覆带通过改变海底地形来控制峡谷内沉积分布,褶皱翼部发育沉积,核部则以侵蚀为主;褶皱推覆带外,北大西洋底流与峡谷末端重力流发生交互作用,细粒物质被搬运至峡谷北岸形成漂积体;陆坡边缘断层活跃,峡谷被断层切割,形成断崖,并引发海底滑塌,陆坡处不发育水道及朵体沉积,陆源物质通过峡谷被搬运至更深的深海盆地内。     

Holocene Paleohydrology and Paleoclimate at Treeline, North-Central Russia, Inferred from Oxygen Isotope Records in Lake Sediment Cellulose

Lake-water oxygen-isotope histories for three lakes in northern Russia, derived from the cellulose oxygen-isotope stratigraphies of sediment cores, provide the basis for preliminary reconstruction of Holocene paleohydrology in two regions along the boreal treeline. Deconvolution of shifting precipitation δ¹⁸O from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation, the isotopic composition of paleo-waters preserved in frozen peat deposits, as well as other supporting paleoclimatic information. These data indicate that during the early Holocene, when the boreal treeline advanced to the current arctic coastline, conditions in the lower Yenisey River region were moist compared to the present, whereas greater aridity prevailed to the east near the lower Lena River. This longitudinal moisture gradient is consistent with the suggestion that oceanic forcing (increased sea-surface temperatures in the Nordic Seas and reduced sea-ice cover) was a major contributor to the development of a more maritime climate in western Eurasia, in addition to increased summer insolation. East of the Taimyr Peninsula, large tracts of the continental shelf exposed by glacial sea-level drawdown may have suppressed maritime climatic influence in what are now coastal areas. In contrast, during the late Holocene the two regions have apparently experienced coherent shifts in effective moisture. The similarity of the records may primarily reflect reduced North Atlantic influence in the Nordic Seas and southward retreat of coastline in eastern Siberia, coupled with declining summer insolation.     

Geologic controls on the morphology of La Aguja submarine canyon

The seascape of the continental shelf and slope offshore Santa Marta is sculpted by the submarine Aguja Canyon, a deep seafloor incision that extends from the inner shelf to the continental rise along some 115 km. No major modern rivers flow into this canyon, thus ruling out principal fluvial control on the present geometry of this feature. Recently acquired multibeam sonar bathymetry data have provided insight into the three-dimensional geometry of this outstanding feature that disrupts the seafloor relief. In addition, seismic reflection data provide images of the internal structure of the canyon’s subsurface. In this study, we describe the morphology of the Aguja Canyon along a series of transects, interpret the structure under the canyon, and discuss possible geologic processes that played a role during its formation and modification. Seismic data indicate that incision of the canyon’s inner reach is the result of recent motion along the western termination of the active Oca strike–slip fault. Relief in the middle reach may be predominantly controlled by sedimentary processes (erosion, infilling and lateral thalweg migration). In the past, however, the middle reach may have been tectonically controlled. The outer reach appears to be the combined result of tectonics, sedimentary process and mud-diapiric intrusions. We conclude that the Aguja Canyon is predominantly a tectonic feature that accommodates shallow transpressive stresses as dislocation of the seafloor.     

Holocene records of eolian dust deposition from high-elevation lakes in the Uinta Mountains,Utah, USA

Radiocarbon-dated sediment cores from subalpine lakes were used to investigate post-glacial dust deposition in the Uinta Mountains (Utah, USA). Lake sediments were geochemically characterized with ICP-OES, ICP-MS and XRF core scanning. Collections from passive samplers constrain the properties of modern dust, and samples of regolith constrain properties of the local material within the watershed. Ca and Eu are more abundant in dust, whereas Ti and Zr are more abundant in local regolith. As a result, the Ca/Ti and Eu/Zr ratios are indices for the dust content of lake sediment. In all records, the dust index rises in the early Holocene as watersheds became stabilized with vegetation, reducing the influx of local material. After this point, values remained above average through the middle Holocene, consistent with an increased dust content in the sediment. Dust index values drop in the late Holocene in most lakes, suggesting a decrease in dust abundance. Generally synchronous shifts in dust index values in cores from lakes in different parts of this mountain range are evidence of enhanced dust deposition in this region during the middle Holocene, and are consistent with a variety of records for increased aridity in the south-western USA at this time.     

Application of brachiopods in palaeoceanographic reconstructions; Macandrevia cranium (Müller, 1776) from the Norwegian shelf

The brachiopod Macandrevia cranium (Müller, 1776) occurs in Late Weichselian and Holocene sediments from the Norwegian continental shelf. It is particularly well known from the southern Barents Sea where it is a characteristic member of the Holocene macrofpssil assemblages. The Recent biogeography of the species is established. The general distribution is not random, but is almost completely confined to the continental shelves surrounding the North Atlantic and the Norwegian-Greenland Sea. The distribution pattern is compared with information on autecology and possible limiting environmental factors. It is concluded that there is substantial evidence that the distribution of Recent M. cranium is a function of dispersal by the Gulf Stream and its continuations, e.g. the Norwegian Current and the North Cape Current. Thus the stratigraphic occurrence of M . cranium in sediments on the Norwegian continental shelf may be used as an important marker for the presence of Atlantic water. Late Weichselian records of rare specimens of the species are related to incipient influx of Atlantic water following the deglaciation. Early Holocene records of abundant specimens are related to the final intrusion of the Norwegian Current. These records also suggest that the Holocene introduction of the species is time-transgressive in a south-north direction.     

Human responses to Middle Holocene climate change on California's Channel Islands

High-resolution archaeological and paleoenvironmental records from California's Channel Islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses. Available climate records in western North America (7–3.8 ka) indicate a severe dry interval between 6.3 and 4.8 ka embedded within a generally warm and dry Middle Holocene. Very dry conditions in western North America between 6.3 and 4.8 ka correlate with cold to moderate sea-surface temperatures (SST) along the southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). An episode of inferred high marine productivity between 6.3 and 5.8 ka corresponds with the coldest estimated SSTs of the Middle Holocene, otherwise marked by warm/low productivity marine conditions (7.5–3.8 ka). The impact of this severe aridity on humans was different between the northern and southern Channel Islands, apparently related to degree of island isolation, size and productivity of islands relative to population, fresh water availability, and on-going social relationships between island and continental populations. Northern Channel Islanders seem to have been largely unaffected by this severe arid phase. In contrast, cultural changes on the southern Channel Islands were likely influenced by the climatically induced environmental changes. We suggest that productive marine conditions coupled with a dry terrestrial climate between 6.3 and 5.8 ka stimulated early village development and intensified fishing on the more remote southern islands. Contact with people on the adjacent southern California Coast increased during this time with increased participation in a down-the-line trade network extending into the western Great Basin and central Oregon. Genetic similarities between Middle Holocene burial populations on the southern Channel Islands and modern California Uto-Aztecan populations suggest Middle Holocene movement of people at this time from southern California desert environs westward to the southern islands, a migration perhaps stimulated by increased continental aridity.     

Sedimentary structures and sediment transport across the continental slope of Israel from piston core studies

The continental terrace of Israel consists of Nile-derived sediments. They are classified into three major groups, according to their structures: (1) irregularly to wavy laminated, coarse-grained sediments (quartz and skeletal debris) of the flat outer shelf and upper bend of the slope (10–20% of the bulk) which are influenced by currents. These sediments are bioturbated to various degrees. Smectitic silty clays (80–90%) form two structural groups: (2) laminated, turbiditic sediments which accumulate on the slope, particularly in the canyons of the northern slope. Irregular, wavy, thickly laminated, coarse-grained sediments of the upper slope and canyon heads merge downslope with parallel, thinly laminated, fine-grained sediments. Toward the foot of the slope and on the adjacent deep-sea floor lamination becomes indistinct and the sediment is visually homogeneous. (3) Slump-generated mud lumps of various size which accumulate on the lower slope and along the transport axes of the canyons. These are the most visible evidence for large-scale slumping mass movement. Transportational and depositional processes are far more intensive over the steep northern continental slope of Israel, and especially in its canyons than over the gentle southern slope. Very stiff overconsolidated sediments unconformably overlain by the ubiquitous recent silty-clayey sediment were cored on steep sections of the middle continental slope and along the canyon walls. Their preconsolidation stress values suggest that these sections were formerly overlain by more than 40 m of sediment and now are exposed by slumping. The downsliding slabs usually disintegrated into small fragments although several huge fragments could be identified along the canyon axes.     

Ostracod palaeoecology and environmental change in the Laptev and Kara seas (Siberian Arctic) during the last 18 000 years

Fossil ostracod assemblages were investigated in five AMS ¹⁴ C‐dated cores from various water depths of the Laptev and Kara seas ranging from the upper continental slope (270 m) to the present‐day shelf depth (40 m). Six fossil assemblages were distinguished. These represent the varying environmental conditions at the North Siberian continental margin since about 18 ka. In the cores from the shelf the ostracod assemblages reflect the gradual transition from an estuarine brackish‐water environment to modern marine conditions since 12.3 ka, as induced by the regional early Holocene transgression. The core from the upper continental slope dates back to c. 17.6 ka and contains assemblages that are absent in the shelf cores. The assemblage older than 10 ka stands out as a specific community dominated by relatively deep‐water Arctic and North Atlantic species that also contains euryhaline species. Such an assemblage provides evidence for past inflows of Atlantic‐derived waters from as early as c. 17.2 ka, probably facilitated by upwelling in coastal polynyas, and a considerable riverine freshwater influence with enhanced surface water stratification owing to the proximity of the palaeocoastline until early Holocene times. In all studied cores, relative increases in euryhaline species dominant in the inner‐shelf regions are recorded in the mid–late Holocene sediments (<7 ka), which otherwise already contain modern‐like ostracod assemblages with relatively deep‐water species. This observation suggests euryhaline species to be largely sea‐ice‐ and/or iceberg‐rafted and therefore may provide evidence for a climate cooling trend.     

Mid-holocene climate change in Lake Bosumtwi, Ghana

Lake Bosumtwi is one of the most widely studied palaeoclimate archives in West Africa. Results from numerous AMS ¹⁴C dates of samples from four piston cores from Lake Bosumtwi show that an abrupt sedimentary transition from a mid-Holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr B.P. High-resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature, and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial Africa from Ghana to the Congo basin. Northern and Eastern Africa experienced a similar abrupt shift toward aridity during the late Holocene, but at about 5000 cal yr B.P., a difference in timing that illustrates the regional nature of climate changes during the Holocene and the importance of feedback mechanisms in regulating Holocene climate variability. Furthermore, an abrupt change at about 3000 cal yr B.P. occurs at several sites adjacent to the tropical and subtropical Atlantic, which may hint at major changes in the surface temperatures of the tropical Atlantic and/or Pacific at this time.     

Paleoenvironmental context of archaeological sites,implications for subsistence strategies under Holocene climate change,northern Kenya

The Holocene was time of dramatic climate change in East Africa, shifting from wetter climate in the Early–Mid Holocene (∼10–5ka) to drier climates in the Late Holocene, followed by a slight reversal at <1ka. The Holocene was a time of cultural change from hunter‐gatherer and fishing to pastoralism. Recent excavations along the eastern shores of Lake Turkana, Kenya (4°N) provide new archaeological materials, a high‐resolution stratigraphic and paleoenvironmental data set, OSL dates, and cultural records in the context of documented environmental change (falling lake levels). Archaeological site FwJj25 (4.20 ± 0.28ka), on the northeastern margin of Lake Turkana, provides one of the earliest records of pastoralism in the region. The palimpsest record of FwJj5 (0.90 ± 0.06ka) was in a small valley containing a groundwater seep located 5km from the lake. FwJj5 reflects occupation by people who may have covered great distances in accessing resources, but were likely drawn to an environmental refugia of freshwater springs during times of regional aridity. © 2011 Wiley Periodicals, Inc.     

Constraining Holocene sea‐surface conditions in the south‐western Black Sea using dinoflagellate cysts

This paper presents two dinoflagellate cyst records from the south‐western shelf of the Black Sea. A new site, MAR05‐13, from the Sakarya shelf is described and placed into context with site MAR02‐45, ～250 km distant on the Thracian shelf. The records provide a centennial resolution of surface water conditions in the Holocene. Analysis of the data suggests that the surface salinity of the south‐western shelf increased in a gradual and progressive manner. In the period ～11 000–9000 cal a BP the assemblages suggest surface‐water salinities between 7–13 psu. The initial arrival of euryhaline species, ～8100 cal a BP, is linked to the reconnection of the Black Sea and Marmara Sea. The suggested surface water changes related to the reconnection took approximately 1000 years. Following this initial change in assemblages, a further increase in the number of euryhaline species is noted between 5000 and 4000 cal a BP. This is linked to the establishment of more saline surface‐water conditions, close to present‐day values. The record for MAR05‐13 highlights the complexity of the changes in cyst assemblages during the mid‐Holocene. Copyright © 2012 John Wiley & Sons, Ltd.     

Chronology of upper Quaternary offshore successions from the southeastern Mediterranean Sea,Israel

Pleistocene and Holocene transgressions advancing over the shelf that was exposed during glacial maxima drowned any continental and shallow marine sediments deposited during low sea level stands. To complement records from sequences exposed on land, core material from the shallow continental shelf is needed to reconstruct climatic and sea level fluctuations. Two cores drilled offshore Ashqelon off the southern Mediterranean coast of Israel, in a water depth of 10 and 25 m, were analyzed. Sedimentary facies and faunal analyses indicate that most of the sediments were deposited in nearshore environments, with only short intervals of continental episodes. Luminescence dating of alkali feldspar and quartz, as well as ¹⁴C ages of mollusks, date the cores to marine oxygen isotopic stages 6–1, between ∼140 and 5 ka. Comparison between the dating methods shows that most alkali feldspar ages agree with independent sea level and sedimentological constraints while quartz ages are overestimated.     

Asynchronous Holocene climatic change across China

A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the “Holocene optimum,” a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ¹⁸O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here.