A high-precision record of mid-late Holocene sea-level events from emergent coral pavements in the Houtman Abrolhos Islands, southwest Australia

Early work on sea-levels in southwest Australia claimed to recognise a Holocene sea-level highstand which was not seen in better known sea-level records elsewhere at the time. More recent work has confirmed that a mid-Holocene highstand Occurred about 6 kyr ago. As new data on oscillating sea-levels from the region have recently been published, a high continuity, precisely dated and accurately surveyed record was obtained from emergent coral pavements in the leeward Houtman Abrolhos Islands (Serventy Island), a tectonically stable region from where good-quality Holocene sea-level data have been previously obtained from corals. From the mid-Holocene highstand ca. 7 U/Th kyr ago, sea-level declined linearly during the remainder of the Holocene as the carbonate platform prograded leewards. Hydro-isostatic controls are probably significant in the record. (c) 2005 Elsevier Ltd and INQUA. All rights reserved.

Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes

Accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction (ΔRΔR) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔRΔR for the last ∼5.4 ka agree well with their modern value, but large ΔRΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4–8 ka. The latter time interval also has significant variations with similar features in previously published ΔRΔR values for other sites in the Pacific, including southern Peru–northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔRΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔRΔR values, instead of constant (modern) values, for age calibration of Holocene marine samples not only for the SW Pacific sites but also for other tropical and subtropical sites in the Pacific.

Radiocarbon record of solar variability and Holocene climatic change in coastal southern California

EXTRACT (SEE PDF FOR FULL ABSTRACT): Pollen analysis and 5 radiocarbon dates for a 687-cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea level rise during the mid-Holocene, but after 4500 years BP, sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 years BP correlate global cooling events and (except the 3800-year BP event) with carbon-14 production anomalies. The coincidence of climate change and carbon-14 anomalies support a causal connection with solar variability, but regardless of the causal mechanism(s) the delta-carbon-14 curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

Prograded Holocene beach-ridges with superimposed dunes in north-east Ireland: mechanisms and timescales of fine and coarse beach sediment decoupling and deposition

Two depositional models to account for Holocene gravel-dominated beach ridges covered by dunes, occurring on the northern coast of Ireland, are considered in the light of infrared-stimulated luminescence ages of sand units within beach ridges, and 14C ages from organic horizons in dunes. A new chronostratigraphy obtained from prograded beach ridges with covering dunes at Murlough, north-east Ireland, supports a model of mesoscale alternating sediment decoupling (ASD) on the upper beach, rather than macroscale sequential sediment sourcing to account for prograded beach ridges and covering dunes. The ASD model specifies storm or fair-weather sand beach ridges forming at high-tide positions (on an annual basis at minimum), which acted as deflationary sources for landward foredune development. Only a limited number of such late-Holocene beach ridges survive in the observed prograded series. Beach ridges only survive when capped by storm-generated gravel beaches that are deposited on a mesoscale time spacing of 50–130 years. The morphodynamic shift from a dissipative beach face for dune formation to a reflective beach face for gravel capping appears to be controlled by the beach sand volume falling to a level where reflective conditions can prevail. Sediment volume entering the beach is thought to have fluctuated as a function of a forced regression associated with the falling sea level from the mid-Holocene highstand (ca. 6000 cal. yr BP) identified in north-east Ireland. The prograded beach ridges dated at ca. 3000 to 2000 cal. yr BP indicate that the Holocene highstand’s regressive phase may have lasted longer than previously specified.

How fragmented was the British Holocene wildwood? Perspectives on the “Vera” grazing debate from the fossil beetle record

The reconstruction and structure of the European Holocene “wildwood” has been the focus of considerable academic debate. The ability of palaeoecological data and particularly pollen analysis to accurately reflect the density of wildwood canopy has also been widely discussed. Fossil insects, as a proxy for vegetation and landscape structure, provide a potential approach to address this argument. Here, we present a review and re-analysis of 36 early and mid-Holocene (9500-2000 cal BC) sub-fossil beetle assemblages from Britain, examining percentage values of tree, open ground and dung beetles as well as tree host data to gain an insight into vegetation structure, the role of grazing animals in driving such structure and establish independently the importance of different types of trees and associated shading in the early Holocene “wildwood”. Open indicator beetle species are persistently present over the entire review period, although they fluctuate in importance. During the early Holocene (9500-6000 cal BC), these indicators are initially high, at levels which are not dissimilar to modern data from pasture woodland. However, during the latter stages of this and the next period, 6000-4000 cal BC, open ground and pasture indicators decline and are generally low compared with previously. Alongside this pattern, we see woodland indicators generally increase in importance, although there are significant local fluctuations. Levels of dung beetles are mostly low over these periods, with some exceptions to this pattern, especially towards the end of the Mesolithic and in floodplain areas. Host data associated with the fossil beetles indicate that trees associated with lighter canopy conditions such as oak, pine, hazel and birch are indeed important components of the tree canopy during the earlier Holocene (c. 9500-6000 cal BC), in accordance with much of the current pollen literature. Beetles associated with more shade-tolerant trees (such as lime and elm) become more frequent in the middle Holocene (6000-4000 cal BC) suggesting that at this stage the woodland canopy was less open than previously, although open ground and pasture areas appear to have persisted in some locations. The onset of agriculture (4000-2000 cal BC) coincides with significant fluctuations in woodland composition and taxa. This is presumably as a result of human impact, although here there are significant regional variations. There are also increases in the amounts of open ground represented and especially in the levels of dung beetles present in faunas, suggesting there is a direct relationship between the activities of grazing animals and the development of more open areas. One of the most striking aspects of this review is the variable nature of the landscape suggested by the palaeoecological data, particularly but not exclusively with the onset of agriculture: some earlier sites indicate high variability between levels of tree-associated species on the one hand and the open ground beetle fauna on the other, indicating that in some locations, open areas were of local significance and can be regarded as important features of the Holocene landscape. The role of grazing animals in creating these areas of openness was apparently minimal until the onset of the Neolithic.

Holocene deposits from Neptune’s Cave, Nordland, Norway: Environmental interpretation and relation to the deglacial and emergence history of the Velfjord–Tosenfjord area

Neptune’s Cave in the Velfjord–Tosenfjord area of Nordland, Norway is described, together with its various organic deposits. Samples of attached barnacles, loose marine molluscs, animal bones and organic sediments were dated, with radiocarbon ages of 9840+/-90 and 9570+/-80 yr BP being derived for the barnacles and molluscs, based on the superseded but locally used marine reservoir age of 440 years. A growth temperature of c. 7.51C in undiluted seawater is deduced from the d13C and d18O values of both types of marine shell, which is consistent with their early Holocene age. From the dates, and an assessment of local Holocene uplift and Weichselian deglaciation, a scenario is constructed that could explain the situation and condition of the various deposits. The analysis uses assumed local isobases and sea-level curve to give results: that are consistent with previous data, that equate the demise of the barnacles to the collapse of a tidewater glacier in Tosenfjord, and that constrain the minimum extent of local Holocene uplift. An elk fell into the cave in the mid-Holocene at 510070 yr BP, after which a much later single ‘bog-burst’ event at 178070 yr BP could explain the transport of the various loose deposits further into the cave.

Lacustrine evidence of Holocene environmental change from three Faroese lakes: a multiproxy XRF and stable isotope study

The vegetation history of the Faroe Islands has been investigated in numerous studies all broadly showing that the early-Holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10,000 cal yr BP when grasses, sedges and finally shrubs began to dominant the islands. Here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data. These data show that the Faroe Islands were deglaciated by the end of Younger Dryas (11,700 10,300 cal yr BP), at this time relatively high sedimentation rates with high delta C-13 imply poor soil development. delta C-13, Ti and chi data reveal a much more stable and warm mid-Holocene until 7410 cal yr BP characterised by increasing vegetation cover and build up of organic soils towards the Holocene thermal maximum around 7400 cal yr BP. The final meltdown of the Laurentide ice sheet around 7000 cal yr BP appears to have impacted both ocean and atmospheric circulation towards colder conditions on the Faroe Islands. This is inferred by enhanced weathering and increased deposition of surplus sulphur (sea spray) and erosion in the highland lakes from about 7400 cal yr BP. From 4190 cal yr BP further cooling is believed to have occurred as a consequence for increased soil erosion due to freeze/thaw sequences related to oceanic and atmospheric variability. This cooling trend appears to have advanced further from 3000 cal yr BR A short period around 1800 cal yr BP appears as a short warm and wet phase in between a general cooling characterised by significant soil erosion lasting until 725 cal yr BP. Interestingly, increased soil erosion seems to have begun at 1360 cal yr BP, thus significantly before the arrival of the first settlers on the Faroe Island around 1150 cal yr BP, although additional erosion took place around 1200 cal yr BP possibly as a consequence of human activities. Hence it appears that if humans caused a change in the Faroe landscape in terms of erosion they in fact accelerated a process that had already started. Soil erosion was a dominant landscape factor during the Little Ice Age, but climate related triggers can hardly be distinguished from human activities. (c) 2010 Elsevier Ltd. All rights reserved.

Determining the Sun's influence on Lateglacial and Holocene climates: a focus on climate response to centennial-scale solar forcing at 2800 cal. BP

The influence of solar variability on the climate of the Lateglacial and Holocene periods has been the subject of increasing discussion during the last decade. In the Mid-Holocene, several studies have identified cold/wet events that occur at ca 2800 cal. BP and a link with a reduction in solar activity, inferred from the C-14 record, has been postulated. We present results from a multi-proxy study of peat humification, plant macrofossils and testate amoebae from a raised bog at Glen West, northwest Ireland, that indicate that dry bog surface conditions were experienced in the north of Ireland at the time of the solar anomaly starting at 2800 cal. BP. With the aid of C-14 wiggle-matching and tephrochronology, an abrupt shift to wetter conditions is dated to ca 2700 cal. BP, coinciding with a C-14 maximum but clearly post-dating the 2800 cal. BP event identified elsewhere in Europe. We explore the significance of this apparent lag in the Irish record, considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the North Atlantic region. We conclude that these complexities are likely to give rise to time-transgressive climate responses around the North Atlantic that will only be recognised by more critical chronological approaches.

Holocene landscape intervention and plant food production strategies in island and mainland Southeast Asia

In the areas adjacent to the drowned Pleistocene continent of Sunda – present-day Mainland and Island SE Asia – the Austronesian Hypothesis of a diaspora of rice cultivators from Taiwan ∼4200 years ago has often been linked with the start of farming. Mounting evidence suggests that these developments should not be conflated and that alternative explanations should be considered, including indigenous inception of complex patterns of plant food production and early exchange of plants, animals, technology and genes. We review evidence for widespread forest disturbance in the Early Holocene which may accompany the beginnings of complex food-production. Although often insubstantial, evidence for incipient and developing management of rainforest vegetation and of developing complex relationships with plants is present, and early enough to suggest that during the Early to mid-Holocene this vast region was marked by different approaches to plant food production. The trajectory of the increasingly complex relationships between people and their food organisms was strongly locally contingent and in many cases did not result in the development of agricultural systems that were recognisable as such at the time of early European encounters. Diverse resource management economies in the Sunda and neighbouring regions appear to have accompanied rather than replaced a reliance on hunting and gathering. This, together with evidence for Early Holocene interaction between these neighbours, gives cause for us to question some authors continued adherence to a singular narrative of the Austronesian Hypothesis and the ‘Neolithisation’ of this part of the world. It also leads us to suggest that the forests of this vast region are, to an extent, a cultural artefact.

Floodplain environmental change during the Younger Dryas and Holocene in Northwest Europe: Insights from the lower Kennet Valley, south central England

Many lowland rivers across northwest Europe exhibit broadly similar behavioural responses to glacial-interglacial transitions and landscape development. Difficulties exist in assessing these, largely because the evidence from many rivers remains limited and fragmentary. Here we address this issue in the context of the river Kennet, a tributary of the Thames, since c. 13,000 cal BP. Some similarities with other rivers are present, suggesting that regional climatic shifts are important controls. The Kennet differs from the regional pattern in a number of ways. The rate of response to sudden climatic change, particularly at the start of the Holocene and also mid-Holocene forest clearance, appears very high. This may reflect abrupt shifts between two catchment scale hydrological states arising from contemporary climates, land use change and geology. Stadial hydrology is dominated by nival regimes, with limited winter infiltration and high spring and summer runoff. Under an interglacial climate, infiltration is more significant. The probable absence of permafrost in the catchment means that a lag between the two states due to its gradual decay is unlikely. Palaeoecology, supported by radiocarbon dates, suggests that, at the very start of the Holocene, a dramatic episode of fine sediment deposition across most of the valley floor occurred, lasting 500-1000 years. A phase of peat accumulation followed as mineral sediment supply declined. A further shift led to tufa deposition, initially in small pools, then across the whole floodplain area, with the river flowing through channels cut in tufa and experiencing repeated avulsion. Major floods, leaving large gravel bars that still form positive relief features on the floodplain, followed mid-Holocene floodplain stability. Prehistoric deforestation is likely to be the cause of this flooding, inducing a major environmental shift with significantly increased surface runoff. Since the Bronze Age, predominantly fine sediments were deposited along the valley with apparently stable channels and vertical floodplain accretion associated with soil erosion and less catastrophic flooding. The Kennet demonstrates that, while a general pattern of river behaviour over time, within a region, may be identifiable, individual rivers are likely to diverge from this. Consequently, it is essential to understand catchment controls, particularly the relative significance of surface and subsurface hydrology. (c) 2005 Elsevier B.V. All rights reserved.

Seasonal deposition of Holocene banded sediments in the Severn Estuary Levels (southwest Britain): palynological and sedimentological evidence

Banded sediments outcrop widely in the intertidal zone of the Severn Estuary and have been suggested, on the basis of textural analysis, to have formed in response to seasonal variations in sea temperature and windiness (Holocene, 14 (2004) 536). Here palynological and sedimentological analyses of banded sediments of mid-Holocene date from Gold Cliff, on the Welsh side of the Severn Estuary, are combined to test and further develop the hypothesis of seasonal deposition. Pollen percentage and concentration data are presented from a short sequence of bands to establish whether textural variations in the bands coincide with variations in pollen content reflecting seasonal flowering patterns. It is shown that fine-grained band parts contain higher total pollen concentrations, and a higher proportion of pollen from late spring- to summer-flowering plants, than coarse-grained band parts. Pollen in the coarser deposits appears primarily to reflect deposition from the buffering `reservoir' of suspended pollen in the estuarine water-body and from rivers, when there is little pollen in the air in winter, while the finer sediments contain pollen deposited from the atmosphere during the flowering season, superimposed on these `background' sources. The potential of such deposits for refining chronologies and identifying seasonality of coastal processes is noted, and the results of charcoal particle analysis of the bands presented as an example of how they have the potential to shed light on seasonal and annual patterns of human activity. (C) 2004 Elsevier Ltd. All rights reserved.

Some physical drivers of changes in the winter storm tracks over the North Atlantic and Mediterranean during the Holocene

The winter climate of Europe and the Mediterranean is dominated by the weather systems of the mid-latitude storm tracks. The behaviour of the storm tracks is highly variable, particularly in the eastern North Atlantic, and has a profound impact on the hydroclimate of the Mediterranean region. A deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in Mediterranean climate and the civilizations it has supported over the last 12 000 years (broadly the Holocene period). This paper presents a discussion of how changes in climate forcing (e.g. orbital variations, greenhouse gases, ice sheet cover) may have impacted on the ‘basic ingredients’ controlling the mid-latitude storm tracks over the North Atlantic and the Mediterranean on intermillennial time scales. Idealized simulations using the HadAM3 atmospheric general circulation model (GCM) are used to explore the basic processes, while a series of timeslice simulations from a similar atmospheric GCM coupled to a thermodynamic slab ocean (HadSM3) are examined to identify the impact these drivers have on the storm track during the Holocene. The results suggest that the North Atlantic storm track has moved northward and strengthened with time since the Early to Mid-Holocene. In contrast, the Mediterranean storm track may have weakened over the same period. It is, however, emphasized that much remains still to be understood about the evolution of the North Atlantic and Mediterranean storm tracks during the Holocene period.

Changes in the Mediterranean climate during the Holocene: insights from global and regional climate modelling

Palaeoproxy records alone are seldom sufficient to provide a full assessment of regional palaeoclimates. To better understand the possible changes in the Mediterranean climate during the Holocene, a series of palaeoclimate integrations for periods spanning the last 12 000 years have been performed and their results diagnosed. These simulations use the HadSM3 global climate model, which is then dynamically downscaled to approximately 50 km using a consistent regional climate model (HadRM3). Changes in the model’s seasonal-mean surface air temperatures and precipitation are discussed at both global and regional scales, along with the physical mechanisms underlying the changes. It is shown that the global model reproduces many of the large-scale features of the mid-Holocene climate (consistent with previous studies) and that the results suggest that many areas within the Mediterranean region were wetter during winter with a stronger seasonal cycle of surface air temperatures during the early Holocene. This precipitation signal in the regional model is strongest in the in the northeast Mediterranean (near Turkey), consistent with low-level wind patterns and earlier palaeosyntheses. It is, however, suggested that further work is required to fully understand the changes in the winter circulation patterns over the Mediterranean region.

Holocene and Pleistocene pluvial periods in Yemen, Southern Arabia

Arabia is an important potential pathway for the dispersal of Homo sapiens (“out of Africa”). Yet, because of its arid to hyper-arid climate humans could only migrate across southern Arabia during pluvial periods when environmental conditions were favorable. However, knowledge on the timing of Arabian pluvial periods prior to the Holocene is mainly based on a single and possibly incomplete speleothem record from Hoti Cave in Northern Oman. Additional terrestrial records from the Arabian Peninsula are needed to confirm the Hoti Cave record. Here we present a new speleothem record from Mukalla Cave in southern Yemen. The Mukalla Cave and Hoti Cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods, corresponding to Marine Isotope Stages (MIS) 1 (early to mid-Holocene), 5.1, 5.3, 5.5 (Eemian), 7.1, 7.5 and 9. Of these humid periods, highest precipitation occurred during MIS 5.5 and lowest during early to middle Holocene.

Late Holocene methane rise caused by orbitally controlled increase in tropical sources

Considerable debate surrounds the source of the apparently ‘anomalous’1 increase of atmospheric methane concentrations since the mid-Holocene (5,000 years ago) compared to previous interglacial periods as recorded in polar ice core records2. Proposed mechanisms for the rise in methane concentrations relate either to methane emissions from anthropogenic early rice cultivation1, 3 or an increase in natural wetland emissions from tropical4 or boreal sources5, 6. Here we show that our climate and wetland simulations of the global methane cycle over the last glacial cycle (the past 130,000 years) recreate the ice core record and capture the late Holocene increase in methane concentrations. Our analyses indicate that the late Holocene increase results from natural changes in the Earth's orbital configuration, with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation. Critically, our simulations capture the declining trend in methane concentrations at the end of the last interglacial period (115,000–130,000 years ago) that was used to diagnose the Holocene methane rise as unique. The difference between the two time periods results from differences in the size and rate of regional insolation changes and the lack of glacial inception in the Holocene. Our findings also suggest that no early agricultural sources are required to account for the increase in methane concentrations in the 5,000 years before the industrial era.