Atmospheric C variations derived from tree rings during the early Younger Dryas

Atmospheric radiocarbon variations over the Younger Dryas interval, from 13,000 to 11,600 cal yr BP, are of immense scientific interest because they reveal crucial information about the linkages between climate, ocean circulation and the carbon cycle. However, no direct and reliable atmospheric ¹⁴C records based on tree rings for the entire Younger Dryas have been available. In this paper, we present (1) high-precision ¹⁴C measurements on the extension of absolute tree-ring chronology from 12,400 to 12,560 cal yr BP and (2) high-precision, high-resolution atmospheric ¹⁴C record derived from a 617-yr-long tree-ring chronology of Huon pine from Tasmania, Australia, spanning the early Younger Dryas. The new tree-ring ¹⁴C records bridge the current gap in European tree-ring radiocarbon chronologies during the early Younger Dryas, linking the floating Lateglacial Pine record to the absolute tree-ring timescale. A continuous and reliable atmospheric ¹⁴C record for the past 14,000 cal yr BP including the Younger Dryas is now available. The new records indicate that the abrupt rise in atmospheric Δ¹⁴C associated with the Younger Dryas onset occurs at 12,760 cal yr BP, 240 yrs later than that recorded in Cariaco varves, with a smaller magnitude of 40‰ followed by several centennial Δ¹⁴C variations of 20–25‰. Comparing the tree-ring Δ¹⁴C to marine-derived Δ¹⁴C and modelled Δ¹⁴C based on ice-core ¹⁰Be fluxes, we conclude that changes in ocean circulation were mainly responsible for the Younger Dryas onset, while a combination of changes in ocean circulation and ¹⁴C production rate were responsible for atmospheric Δ¹⁴C variations for the remainder of the Younger Dryas.     

High-time resolution AMS C data sets for Lake Baikal and Lake Hovsgol sediment cores: Changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the Holocene

High-time resolution ¹⁴C dating of Lake Baikal sediment cores indicates negative and positive anomalies of calculated linear sedimentation rate (LSR; 1.1 and 35.6 cm/ka, respectively) during the period of climate transition from the last glacial to Holocene. The timing of the Lake Baikal apparent LSR anomalies is consistent with that of the changes in the atmospheric radiocarbon concentration (Δ¹⁴C) during Younger Dryas rapid cooling event. ¹⁴C dating of lipids in the Lake Baikal surface sediments revealed that the sources of sedimentary lipids were different in each basin. In the Northern Basin of Lake Baikal, the ¹⁴C age of total lipids from the surface sediment (4.0 ¹⁴C ka) was found to be older than that of TOC (1.6 ¹⁴C ka). By contrast, the ¹⁴C age of total lipids in the Southern Basin was younger than that of the TOC by ca. 0.7–3.0 ka.In the Lake Hovsgol sediment cores, ages of the main lithologic boundaries during the last glacial–interglacial transition were estimated based on new ¹⁴C data sets. TOC concentration in the cores started to rapidly increase at 13.8 ± 0.3 ¹⁴C ka at the base of the basinwide finely laminated layer deposited during Bølling/Allerød. The base of the layer diatomaceous mud corresponds to the end of Younger Dryas event (10.6 ± 0.1 ¹⁴C ka).     

Radiocarbon reservoir age of high latitude North Atlantic surface water during the last deglacial

The radiocarbon reservoir age of high latitude North Atlantic Ocean surface water is essential for linking the continental and marine climate records, and is expected to vary according to changes in North Atlantic deep water (NADW) production. Measurements from this region also provide important input and/or tests of oceanic radiocarbon using 3-D global ocean circulation models. Here, we present a surface water radiocarbon reservoir age record of the high latitude western North Atlantic for the deglacial period via the use of fossil cold-water corals growing in waters that are rapidly exchanged with nearby surface waters. The reservoir age of high latitude North Atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record (http://radiocarbon.LDEO.columbia.edu) and our marine radiocarbon data. ²³⁰Th/²³⁴U/²³⁸U dates provide the absolute coral ages. Our high latitude North Atlantic Ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and Vedde ash radiocarbon dates from central and eastern North Atlantic show modern values (380±140 year, n=14) during the Bolling and Allerod warm period and a 200 year increase in reservoir age (590±130 year, n=10) during the entire Younger Dryas (YD) cold episode. The reservoir age then decreased to 270±20 year (n=2) at the Preboreal/YD transition, although the dates are too sparse for us to be confident in this estimate. We are not able to resolve the timing of the transition to increased reservoir ages from the mid-Allerod to the YD due to the relatively small change and correspondingly large uncertainty in the estimates. The atmospheric Δ¹⁴C record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12,900 to 12,650 cal years BP, coincident with the shift to high reservoir ages in the early YD cold event. Intrusion of ¹⁴C depleted Antarctic Intermediate Water (AAIW) to the high latitude North Atlantic and reduction of NADW formation are possible causes for the coincident shift to high reservoir ages in the North Atlantic surface ocean and increased atmospheric Δ¹⁴C during the beginning of the YD event.     

Late Pleistocene and Holocene vegetation and climate records from Lake Kotokel, central Baikal region

Climatically driven Late Pleistocene and Holocene vegetation changes were reconstructed based on pollen records from the sediments of Lake Kotokel and Cheremushka Bog, located on the eastern shore of Lake Baikal. The described paleoenvironmental record has higher resolution than records collected from Lake Baikal and unites individual events identified in prior studies of bottom and onshore cores. Remarkable shifts in landscapes and expansions of index plants are as follows. Forest tundra and/or forest steppe landscape with birch, spruce, Artemisia, and Poaceae prevailed at ca. 50–25 ¹⁴C kyr BP. Tundra and/or steppe vegetation dominated by Artemisia and Poaceae was typical for the Last Glacial Maximum. The expansion of shrub birch and willow occurred at ca. 15.5 ¹⁴C kyr BP. Two peaks of spruce expansion at ca. 47.5–42.4 ¹⁴C kyr BP (Karginian time) and at ca. 14.5–13 ka (Bølling-Allerød warm intervals) suggest that the condition were more humid than today. A slight increase in Artemisia at ca. 11–10.5 ¹⁴C kyr BP (13–12 ka) was indicative of the Younger Dryas event. An expansion of birch forests with fir at ca. 12–6.4 ka suggests higher humidity. The currently dominant Scots and Siberian pine forests with birch expanded since 6.4 ka.     

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 2: comparison to other records

A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on ¹⁴C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on ¹⁴C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties.     

Ice sheet extent and early deglacial history of the southwestern sector of the Greenland Ice Sheet

The offshore and coastal geomorphology of southwest Greenland records evidence for the advance and decay of the Greenland Ice Sheet during the Last Glacial Maximum. Regional ice flow patterns in the vicinity of Sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf, with an ice stream centred over Holsteinsborg dyb. High level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using ²⁶Al and ¹⁰Be cosmogenic exposure ages. These limit the maximum surface elevation of the Last Glacial Maximum ice sheet in this part of southwest Greenland to ca 750–810 m asl, and demonstrate that terrain above this level has been ice free since MIS 6. Last Glacial Maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the Outer Hellefisk moraines. Exposure dates record ice surface thinning from 21.0 to 9.8 ka, with downwasting rates varying from 0.06 to 0.12 m yr⁻¹. This reflects strong surface ablation associated with increased air temperatures running up to the Bølling Interstadial (GIS1e) at ca 14 ka, and later marine calving under high sea levels. The relatively late retreat of the Itilleq ice stream inland of the present coastline is similar to the pattern observed at Jakobshavn Isbræ, located 250 km north in Disko Bugt, which also retreated from the continental shelf after ca 10 ka. We hypothesise that the ice streams of West Greenland persisted on the inner shelf until the early Holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet.     

What do Δ14C changes across the Gerzensee oscillation/GI‐1b event imply for deglacial oscillations?

High‐resolution studies were performed on late‐glacial sediments from a small lake in western Denmark with respect to lithology, geochemistry, stable isotopes, pollen stratigraphy and radiocarbon dating on terrestrial macrofossils. One purpose was to detect the so‐called Gerzensee oscillation, or the GI‐1b event, in the later part of the Allerød warm period, and to describe the environmental impact of this short cooling. The other aim was to test the hypothesis that considerable Δ¹⁴C changes occur over this time, which can be related to ocean ventilation/thermohaline circulation changes. We find that the GI‐1b event had a major impact on both terrestrial and limnic ecosystems: large vegetation changes, increased soil erosion and lowered aquatic production. By correlations to events in the GRIP ice‐core and ¹⁴C patterns in the Cariaco basin we also transformed our ¹⁴C dated record into calendar years to calculate Δ¹⁴C values. The ¹⁴C dates show that the GI‐1b event both preceded, and was part of, the 11 400–11 300 ¹⁴C yr BP radiocarbon plateau, and was followed by the 11 000–10 900 ¹⁴C yr BP plateau; thus the later part of the event coincides with a distinct age decline. This delayed age drop (Δ¹⁴C rise) in relation to the hypothetical triggering mechanism behind the event, decreased ocean ventilation, could be explained by redeposited macrofossils at the onset of GI‐1b. This phenomenon, also seen at the onset of Younger Dryas, may also reflect increased soil erosion and redeposition at the start of cold periods. The independent Cariaco Basin record, however, implies that the very end of the cool GI‐1b event is related to a distinct rise in Δ¹⁴C. Likewise, the ¹⁰Be record from GISP2 shows a distinct rise in the middle of the event, precluding decreased solar forcing as the trigger of the climate event, but making it likely that high cosmic ray flux (low solar activity) may be the cause of the rising atmospheric ¹⁴C content. We thus conclude that the Δ¹⁴C changes over the Gerzensee oscillation (GI‐1b), being one of several coolings during the Last Termination, does not seem to be related to ocean ventilation changes. The reason behind this lack of coincidence between rising Δ¹⁴C and a fairly distinct Northern Hemisphere cooling may be due to the fact that the oceanic changes during some of these coolings are too subtle to give an atmospheric ¹⁴C imprint, or that an anti‐phase relationship between the two hemispheres blurs the Δ¹⁴C signal, or, finally, that a partly unknown mechanism may lie behind such coolings. Copyright © 2000 John Wiley & Sons, Ltd.     

Glacial and climate history of the last 24 000 years in the Polar Ural Mountains,Arctic Russia,inferred from partly varved lake sediments

We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS ¹⁴C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.     

MIS 3 mammoth remains from Sweden—implications for faunal history, palaeoclimate and glaciation chronology

The distribution of low-arctic megafaunal remains in time and space from the area previously covered by the Scandinavian Ice Sheet (SIS) suggests the presence of breeding mammoth populations in the circum-Baltic region during the time interval from 44 to 26 ka ago. The transport history of 30 mammoth teeth and bones from southern and north-central Sweden was estimated and the remains were subjected to osteological analyses and ¹⁴C dating. Oxygen isotope analyses of tooth enamel indicate a palaeoclimate considerably more homogenous than that experienced in Sweden today, showing moderate north–south gradients in the δ¹⁸O value of precipitation and temperature. In general, the results support the model of restricted ice sheet distribution during the second half of the Middle Weichselian. The clear discrepancy in the inferred absence of glaciation in the central Swedish uplands and the Baltic basin as evidenced by the Swedish mammoth data versus the Danish OSL-based glaciation chronology in the period from 40 to 30 ka ago is discussed in the light of radiocarbon calibration and glacial dynamics.     

New results on palaeoenvironmental conditions in equatorial Africa derived from alluvial sediments of Cameroonian rivers

The ReSaKo project undertook extended fieldwork across southern Cameroon to explore the palaeoenvironmental information recorded in the alluvial sediments of equatorial African rivers. 160 hand-corings reaching maximum depths of 550 cm were carried out on alluvial ridges and floodplains of major Cameroonian fluvial systems. These multilayered, sandy to clayey alluvia contain sedimentary form-units and palaeosurfaces, which provide excellent additional proxy data archives for the reconstruction of palaeoenvironmental conditions in western equatorial Africa. Coring transects and sedimentary profiles document grain-size shifts and distinguishable sedimentary units in the stratigraphic record, which evidence (fluvial-)morphological adjustments of the fluvial systems in response to external forcing and (river-) intrinsic variability. 76 ¹⁴C-(AMS)-dated samples from organic sediment and macro-rests (fossil organic remains like wood, leafs, etc.) embedded in these sedimentary units indicate Late Pleistocene to recent ages (uncalibrated ¹⁴C-ages: 48–0.2 ka BP). The tentative interpretation of the alluvial record yields excellent additional information on the complex feedbacks between climate, ocean, fluvial as well as ecological systems and human activity in a little-studied region with high sensitive tropical ecosystems. δ¹³C-values (?35.5 to ?18.0‰) of the dated samples indicate the persistence of C₃-dominated gallery forests across the rivers (‘fluvial rain forest refuges’) despite several climatic fluctuations (aridifications, e.g. Last Glacial Maximum around 20 ka BP, Younger Dryas 13–11 ka BP). This research complements earlier results from additional terrestrial and marine proxy data archives on the Late Quaternary history of monsoonal western equatorial Africa.     

Radiocarbon chronology of the late-glacial Puerto Bandera moraines,Southern Patagonian Icefield,Argentina

We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages (n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 ¹⁴C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 ¹⁴C yrs BP to 13,450 ± 150 ¹⁴C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance.Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 ¹⁴C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 ¹⁴C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 ¹⁴C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 ¹⁴C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini had receded to just outboard of the outer Holocene moraines at Lago Frías and Lago Pearson (Anita) prior to 10,400 ± 40 ¹⁴C yrs BP (12,270 ± 100 cal yrs BP) and 9040 ± 45 ¹⁴C yrs BP (10,210 ± 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 ± 40 ¹⁴C yrs BP (9300 ± 80 cal yrs BP).The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe.     

A paleoclimate record of the last 17,600 years in stalagmites from the B7 cave,Sauerland, Germany

Petrographical and geochemical parameters of stalagmites from the B7 cave in Iserlohn–Letmathe (Northern Rhenish Massif, NW Germany) record Late- and postglacial climate changes (temperature and/or precipitation). Fabrics and microfacies of the stalagmite profiles lead to a differentiation of four hierarchies of rhythms. Clastic layers in the stalagmites are caused by flooding events and are time markers. Twenty-four TIMS Th/U-age-dates provide a time calibration of stalagmite growth phases. One stalagmite reveals an early growth period between 17.6 and 16.7 ka BP. Between 9.6 and 5.5 ka BP (Atlantic episode of the Holocene) the growth rate of the stalagmites was higher than before and after this time, with dominant light-porous microfacial laminae and high δ¹⁸O and δ¹³C values representing partly kinetic fractionation effects. This part of the Holocene is interpreted as a mainly warm episode with frequent interruptions of dripping. Within the past 4 ka the profiles with predominant dark compact facies reveal low isotopic values which may be interpreted as a temperature proxy record. The stalagmite records resemble records from an Irish stalagmite. Correlation with the Δ¹⁴C record from European tree rings suggests that colder periods in the North Atlantic were accompanied by drier winters in central Europe.     

Climatic variability during the last 90 ka of the southern and northern Levantine Basin as evident from marine records and speleothems

The influence of the northern Atlantic and tropical monsoonal systems, as recorded by the River Nile, on the climate variability of the southeastern Mediterranean was studied in two cores taken by the R/V Marion Dufresne: one core taken SE of Cyprus representing the northern Levantine Basin (core 9501, 980 m water depth) and the other located ˜380 km further south, represents the southeastern Levantine Basin in an area influenced by the River Nile plume (core 9509, 884 m water depth). The study was performed at relatively high resolution using several proxies: δ¹⁸O of Globigerinoides ruber, sediment characteristics and index colour parameters in core sections representing the last 86 ka. A low-resolution alkenone sea surface temperature record was also measured. The time frame in both cores was mostly constrained by ‘wiggle’ matching with the nearby well-dated δ¹⁸O and δ¹³C record of the Soreq Cave, which is mainly influenced by the eastern Mediterranean water vapor. The sedimentary record of the southern core is strongly influenced by the River Nile contribution throughout the last 86 ka, as evidenced by the higher sedimentation rates compared with the northern core (20 cm/ka vs. 5 cm/ka), continuously darker sediment colour, and higher TOC values (0.6–0.9 vs. 0.25 wt% not including sapropels). During sapropels S1 and S3, present in both cores, the influence of the River Nile became more widespread, reaching as far as Cyprus. Yet, the influence of the River Nile remained stronger in the south, as evident by the higher TOC values in the southern core throughout the entire 90 ka period and the longer duration of S1 in the southern core. An anomalous low δ¹⁸O interval that is not recorded in western Mediterranean occurred between 58 and 49 ka in the Levantine Basin and is more developed in the northern core. This period correlates with D-O interstadial 14 and maximum northern hemisphere insolation during the lastglacial cycle, suggesting that the warming mainly impacted the northern Levant.The Eastern Mediterranean Sea and land area was considerably warmer than the western Mediterranean throughout the LGM – Holocene transition, and the δ¹⁸O_{G. ruber} drop of 4.5‰ is significantly greater than the 3‰ shift found for the western Mediterranean δ¹⁸O_{G. bulloides}, both differences reflecting an increased continental effect from the western to eastern Mediterranean. Comparison between the marine and the land δ¹⁸O records suggests that the origin of rain over the land is composed of mixed signal from the southern and northern Levantine Basin. The study of Δδ¹⁸O_sea–land variations demonstrates that various factors have influenced the sea–land relationship during the last 90 ka. The ‘amount effect’ has an important influence on rainfall δ¹⁸O during interglacial periods (particularly sapropel periods), whereas during glacial periods, increased land distances and elevation differences arising from decrease in sea level may have brought about decrease in δ¹⁸O of rainfall due to Rayleigh distillation processes. These influences were superimposed on those of sea surface water δ¹⁸O changes brought about by continental ice melting, and the strong effects felt in the southern Levantine Basin of the high River Nile input during periods of enhanced monsoonal activity.     

Chronology of Late Weichselian glaciation in the western part of the East European Plain

A database consisting of radiocarbon (¹⁴C), optically stimulated luminescence (OSL), thermoluminescence (TL) and beryllium (¹⁰Be) dates was used for timing the advance of the Late Weichselian Scandinavian Ice Sheet (SIS), determining the age of the Last Glacial Maximum (LGM) and the rate of deglaciation. The study area encompasses the southeastern sector of the last SIS between the Baltic Sea and the LGM position in the western part of the East European Plain, covering the Karelian Ice‐Stream Complex (ISC) area in the east and the Baltic ISC area in the west. The linear advance and recession rates of the last SIS were estimated to be between 110 and 330 m a^?1 and between 50 and 170 m a^?1, respectively. The onset of the last SIS in the Karelian ISC area reached the western shores of Latvia not before 26 OSL ka, and in the Baltic ISC area, on the southern shores of the Gulf of Finland, not before 21 OSL ka. The last SIS reached close to the LGM position earliest in NW Belarus, not earlier than 22.6 cal. ¹⁴C ka BP, and latest in the NE of Belarus, not earlier than 19.1 cal. ¹⁴C ka BP. The Baltic ISC area between the LGM position and the western shores of Latvia was deglaciated in about 8 ka, and in the Karelian ISC area, between the LGM position and the southern shores of the Gulf of Finland, in about 2.6 ka. The whole area between the LGM position and the Baltic Sea was deglaciated between 14.2 ¹⁰Be ka and 13.3 cal. ¹⁴C ka BP.     

Stratigraphical and palynological appraisal of the Late Quaternary mangrove deposits of the west coast of India

The organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the Late Quaternary sequence of Kerala–Konkan Basin. Three generations of such deposits have been identified. The older one is dated to around 43,000–40,000 ¹⁴C yr B.P., with a few dates beyond the range of radiocarbon. The younger ones date from the Middle Holocene to latest Pleistocene (10,760–4540 ¹⁴C yr B.P.) and the Late Holocene (<4000 ¹⁴C yr B.P.). Pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation. Peat accumulation during the period 40,000–28,000 ¹⁴C yr B.P. can be correlated with the excess rainfall, 40–100% greater than modern values, of the Asian summer monsoon. The low occurrence of mangrove between 22,000 and 18,000 ¹⁴C yr B.P. can be attributed to the prevailing aridity and/or reduced precipitation associated worldwide with Last Glacial Maximum, because exposure surfaces and ferruginous layers are commonly found in intervals representing this period. The high rainfall of 11,000–4000 ¹⁴C yr B.P. is found to be the most significant as the mangrove reached an optimum growth around 11,000 ¹⁴C yr B.P. but with periods of punctuated weaker monsoons. From the present and previous studies, it has been observed that after about 5000 or 4000 ¹⁴C yr B.P., the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems. A case study of Hadi profile provided an insight to the relevance of magnetic susceptibility (χ) to record the ecological shift in Late Holocene.     

Differential response at the seafloor during Palaeocene and Eocene ocean warming events at Walvis Ridge,Atlantic Ocean (ODP Site 1262)

The Latest Danian Event (LDE, c. 62.1 Ma) is an early Palaeogene hyperthermal or transient (<200 ka) ocean warming event. We present the first deep‐sea benthic foraminiferal faunal record to study deep‐sea biotic changes together with new benthic (Nuttallides truempyi) stable isotope data from Walvis Ridge Site 1262 (Atlantic Ocean) to evaluate whether the LDE was controlled by similar processes as the minor early Eocene hyperthermals. The spacing of the double negative δ¹³C and δ¹⁸O excursion and the slope of the δ¹⁸O–δ¹³C regression are comparable, strongly suggesting a similar orbital control and pacing of eccentricity maxima as well as a rather homogeneous carbon pool. However, in contrast to early Eocene hyperthermals, the LDE exhibits a remarkable stability of the benthic foraminiferal fauna. This lack of benthic response could be related to the absence of threshold‐related circulation changes or better pre‐adaptation to elevated deep‐sea temperatures, as the LDE was superimposed on a cooling trend, in contrast to early Eocene warming.     

Sea-level history of the Gulf of Mexico since the Last Glacial Maximum with implications for the melting history of the Laurentide Ice Sheet

Sea-level records from the Gulf of Mexico at the Last Glacial Maximum, 20 ka, are up to 35 m higher than time-equivalent sea-level records from equatorial regions. The most popular hypothesis for explaining this disparity has been uplift due to the forebulge created by loading from Mississippi River sediments. Using over 50 new radiocarbon dates as well as existing published data obtained from shallow-marine deposits within the northern Gulf of Mexico and numerical models simulating the impact of loading due to the Mississippi Fan and glacio-hydro-isostasy, we test several possible explanations for this sea-level disparity. We find that neither a large radiocarbon reservoir, sedimentary loading due to the Mississippi Fan, nor large-scale regional uplift can explain this disparity. We do find that with an appropriate model for the Laurentide Ice Sheet, the observations from the Gulf of Mexico can be explained by the process of glacio-hydro-isostasy. Our analysis suggests that in order to explain this disparity one must consider a Laurentide Ice Sheet reconstruction with less ice from 15 ka to its disappearance 6 ka and more ice from the Last Glacial Maximum to 15 ka than some earlier models have suggested. This supports a Laurentide contribution to meltwater pulse 1-A, which could not have come entirely from its southern sector.     

Analysis of the atmospheric 14C record spanning the past 50,000 years derived from high-precision 230Th/234U/238U, 231Pa/235U and 14C dates on fossil corals

Changes in the geomagnetic field intensity, solar variability, and the internal changes of the carbon cycle are believed to be the three controlling factors of past atmospheric radiocarbon (¹⁴C) concentrations (denoted as Δ¹⁴C). Of these three, it is believed that the field intensity is the dominant factor. We analyze an atmospheric Δ¹⁴C record spanning the past 50,000 years based on previously-published ²³⁰Th/²³⁴U/²³⁸U and ¹⁴C dates of fossil corals from Kiritimati, Barbados, Araki and Santo Islands, and identify the role of the Laschamp geomagnetic field excursion on the long term trend of the Δ¹⁴C record. There is a general consistency between the coral Δ¹⁴C record and the Δ¹⁴C output from carbon cycle models based on the global ¹⁴C production estimates. High-precision, high-accuracy ²³⁰Th/²³⁴U/²³⁸U dates and redundant ²³¹Pa/²³⁵U dates anchor the timing of this Δ¹⁴C record. We propose that a significant fraction of the long-term Δ¹⁴C trend may be due to inaccuracies in the generally accepted ¹⁴C decay constant. The uncertainty in estimating the shape of ¹⁴C beta spectrum below 20 keV leads to one of the greatest errors in decay constant estimates. Once the ¹⁴C half-life is validated via redundant techniques, Δ¹⁴C records will provide a better opportunity to examine the roles of carbon cycle and ¹⁴C production influences.     

Revised radiocarbon ages on woolly rhinoceros (Coelodonta antiquitatis) from western central Scotland: significance for timing the extinction of woolly rhinoceros in Britain and the onset of the LGM in central Scotland

Woolly rhinoceros bones, from a number of sites in Britain, have been AMS radiocarbon dated following ultrafiltration pre-treatment. These determinations give a coherent set of ages between >50 and c. 35 cal ka BP. The youngest (35,864–34,765 cal BP) come from the area around Bishopbriggs in western central Scotland and are derived from glaciofluvial sand and gravel overlain by till, both deposited during the Last Glacial Maximum (LGM) glaciation. A previous radiocarbon date from the site suggested that woolly rhinoceros lived c. 27 ¹⁴C ka BP and the region was ice-free at the time. This date has had significant influence on the timing of extinction of woolly rhinoceros and the onset of glaciation over Britain during the LGM. The new dates revise this earlier determination and confirm that woolly rhinoceros became extinct in Britain after c. 35 cal ka BP, that central Scotland was ice-free at this time, and glaciation extended across this region sometime after 35 cal ka BP.     

The onset of dune formation in the Strzelecki Desert,South Australia

This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of ¹⁴C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development.