Substage 5e Research Articles

Testing the accuracy of single-grain OSL dating on Eemian quartz samples

Single-grain OSL dating of quartz is a popular approach to OSL dating, even when incomplete bleaching is not likely to be significant. However, little testing of the accuracy of single-grain dating has been published; particularly for samples older than 50 ka. In this study, we investigate the accuracy of single-grain quartz OSL dating, when a significant number of individual grains are no longer able to accurately measure the burial dose because of saturation effects. We compare standard multi-grain OSL results with those obtained from single-grain OSL measurements for five OIS substage 5e (Eemian) samples (∼128 ka). We show that for these samples, standard multi-grain quartz dose estimation results in dose estimates in good agreement with the predicted doses (four of the five samples recover age control), but that standard frequentist single-grain dating procedures significantly underestimate the age controls, i.e. the measured to predicted dose range between 0.42 ± 0.03 and 0.84 ± 0.06, where the underestimation increases with increasing relative number of grains in saturation. Attempting to remove the inevitable bias in the dose estimation resulting from a significant number of saturated grains (by using the Dc criterion) reduced the underestimation, i.e. the measured to predicted dose ratio range between 0.63 ± 0.05 and 0.94 ± 0.08, but only the sample with the smallest absorbed dose is consistent with the age control. Using Bayesian analysis (“BayLum”) the ratio of measured to predicted dose range between 0.75 ± 0.07 and 1.14 ± 0.08, but only two of the five samples agree with the independent age control. Our results have implications for the evaluation of single-grain OSL dating of quartz in the 100–200 Gy natural dose range.

MIS 5e sea-level history along the Pacific coast of North America

Abstract. The primary last interglacial, marine isotope substage (MIS) 5e records on the Pacific coast of North America, from Washington (USA) to Baja California Sur (Mexico), are found in the deposits of erosional marine terraces. Warmer coasts along the southern Golfo de California host both erosional marine terraces and constructional coral reef terraces. Because the northern part of the region is tectonically active, MIS 5e terrace elevations vary considerably, from a few meters above sea level to as much as 70 m above sea level. The primary paleo-sea-level indicator is the shoreline angle, the junction of the wave-cut platform with the former sea cliff, which forms very close to mean sea level. Most areas on the Pacific coast of North America have experienced uplift since MIS 5e time, but the rate of uplift varies substantially as a function of tectonic setting. Chronology in most places is based on uranium-series ages of the solitary coral Balanophyllia elegans (erosional terraces) or the colonial corals Porites and Pocillopora (constructional reefs). In areas lacking corals, correlation to MIS 5e often can be accomplished using amino acid ratios of fossil mollusks, compared to similar ratios in mollusks that also host dated corals. Uranium-series (U-series) analyses of corals that have experienced largely closed-system histories range from ∼124 to ∼118 ka, in good agreement with ages from MIS 5e reef terraces elsewhere in the world. There is no geomorphic, stratigraphic, or geochronological evidence for more than one high-sea stand during MIS 5e on the Pacific coast of North America. However, in areas of low uplift rate, the outer parts of MIS 5e terraces apparently were re-occupied by the high-sea stand at ∼100 ka (MIS 5c), evident from mixes of coral ages and mixes of molluscan faunas with differing thermal aspects. This sequence of events took place because glacial isostatic adjustment processes acting on North America resulted in regional high-sea stands at ∼100 and ∼80 ka that were higher than is the case in far-field regions, distant from large continental ice sheets. During MIS 5e time, sea surface temperatures (SSTs) off the Pacific coast of North America were higher than is the case at present, evident from extralimital southern species of mollusks found in dated deposits. Apparently, no wholesale shifts in faunal provinces took place, but in MIS 5e time, some species of bivalves and gastropods lived hundreds of kilometers north of their present northern limits, in good agreement with SST estimates derived from foraminiferal records and alkenone-based reconstructions in deep-sea cores. Because many areas of the Pacific coast of North America have been active tectonically for much or all of the Quaternary, many earlier interglacial periods are recorded as uplifted, higher-elevation terraces. In addition, from southern Oregon to northern Baja California, there are U-series-dated corals from marine terraces that formed at ∼80 ka, during MIS 5a. In contrast to MIS 5e, these terrace deposits host molluscan faunas that contain extralimital northern species, indicating cooler SST at the end of MIS 5. Here I present a review and standardized database of MIS 5e sea-level indicators along the Pacific coast of North America and the corresponding dated samples. The database is available in Muhs et al. (2021b; https://doi.org/10.5281/zenodo.5903285).

A transient, perched aquifer model for banana hole formation: Evidence from San Salvador Island, Bahamas

AbstractBanana holes are karst depressions that have primarily been reported from strandplains within the Bahamian archipelago. Banana holes have been hypothesized to form by downward dissolution in the vadose zone and in the phreatic zone by mixing dissolution and/or spatial variability in organic carbon inputs to the water table. While vadose models have been unable to explain overhanging roofs common in banana holes, phreatic models require anomalously high dissolution rates. In this study, we develop a new model for banana hole formation based on field observations, an airborne LiDAR (light detection and ranging) survey, and published geochemical data on San Salvador Island, Bahamas. We detected 3356 depressions in LiDAR data consistent with banana hole morphologies in Marine isotope substage (MIS) 5e and MIS 9/11 strandplains. No banana holes were detected in Holocene strandplains. All banana holes were found in swales between ridges. Of the banana holes found in MIS 5e strandplains, 109 had floor elevations between 6 and 19 m above sea level. These banana holes could not have formed in the phreatic zone because the MIS 5e freshwater lens reached a maximum elevation of 6 m above modern sea level. We also observed banana holes filled with water during wet seasons. While wells next to banana holes were tidal, pools in the banana holes were not, indicating pools were perched. Our observations, supported by hydrological models, suggest banana holes may form in the vadose zone in transient, perched aquifers on exposure zones. Runoff from ridges infiltrates through vadose fast‐flow routes until encountering low permeability exposure zones, where flow is directed laterally. Dissolution by perching on exposure zones would create thin, laterally‐extensive chambers radiating from injection points. Subsequent roof collapse results in their surface expression. Because dissolution occurs when waters become perched, chambers could form throughout low stands and may therefore not reflect rapid phreatic dissolution.

Pleistocene coralline algal buildups on a mid-ocean rocky shore – Insights into the MIS 5e record of the Azores

Located on the northern coast of Santa Maria Island (Azores Archipelago, central North Atlantic), the Lagoinhas section preserves a carbonate buildup correlated with Marine Isotope Substage (MIS) 5e, the warmest interval of the Last Interglacial. The buildup is formed mainly by crustose coralline algae (CCA) identified as Spongites sp., and some subordinate crusts of Lithophyllum sp. and Neogoniolithon sp., as well as cf. Titanoderma sp. Extant CCA buildups are not recorded in the archipelago. Herein, we describe in detail the morphological and taphonomical features of the Lagoinhas CCA buildup and interpret the environment in which it grew. Additionally, this buildup is compared with another of similar age, exposed in the Prainha-Praia do Calhau section on the island's opposite southern coast. The hydrodynamic regime appears to play a crucial role in the development of Azorean CCA buildups during the MIS 5e.

Upper Pleistocene and Holocene Storm Deposits Eroded from the Granodiorite Coast on Isla San Diego (Baja California Sur, Mexico)

This project examines the role of hurricane-strength events likely to have exceeded 119 km/h in wind speed that entered the Gulf of California from the open Pacific Ocean during Late Pleistocene and Holocene times to impact the granodiorite shoreline on Isla San Diego. Conglomerate dominated by large, ellipsoidal to subspherical boulders at the islands south end were canvassed at six stations. A total of 200 individual cobbles and boulders were systematically measured in three dimensions, providing the database for analyses of variations in clast shape and size. The project’s goal was to apply mathematical equations elaborated after Nott (2003) with subsequent refinements to estimate individual wave heights necessary to lift igneous blocks from the joint-bound and exfoliated coast on Isla San Diego. On average, wave heights on the order of 3 m are calculated as having impacted the Late Pleistocene rocky coastline on Isla San Diego during storms, although the largest boulders more than a meter in diameter are estimated to weigh two metric tons and would have required waves in excess of 10 m for extraction. Described for the first time, a fossil marine biota associated with the boulder beds confirms a littoral-to-very-shallow water setting correlated with Marine Isotope Substage 5e approximately 125,000 years ago. A narrow submarine ridge consisting, in part, of loose cobbles and boulders extends for 1.4 km to the southwest from the island’s tip, suggesting that Holocene storms continued to transport rock debris removed from the shore. The historical record of events registered on the Saffir–Simpson Hurricane Wind Scale in the Gulf of California suggests that major storms with the same intensity struck the island in earlier times.

Flank margin caves can connect to regionally extensive touching vug networks before burial: Implications for cave formation and fluid flow

AbstractFlank margin caves are extreme endmembers of vuggy porosity that form as diagenesis drives the progressive coalescence of smaller solutional pore spaces. Due to their morphological isolation during formation, the prevailing hypothesis has been that fluid flow in and out of flank margin caves occurs via the matrix permeability and that adjacent chambers only become hydraulically connected through nonmatrix porosity during burial, collapse, and fracturing. To our knowledge, however, no studies have evaluated how flank margin caves are connected to regional flow systems in modern carbonate platforms. In this study, we evaluate the connectivity of wells, boreholes, blue holes, and flank margin caves in increasingly older bedrock on San Salvador Island, Bahamas, using tidal attenuation analysis. Phreatic karst features are not reported in Holocene bedrock, and permeability magnitudes from wells suggest Holocene deposits connect to the ocean along matrix‐dominated flow paths. Permeability magnitudes in bedrock surrounding wells, boreholes, and karst features deposited during Marine Isotope Substage (MIS) 5e suggest connection to the ocean through matrix and touching vug porosity. Boreholes, blue holes, and flank margin caves in pre‐MIS5 bedrock connect to the ocean via touching vugs. We suggest that increasing bedrock permeability, cave number, and cave size observed within progressively older bedrock on San Salvador is a function of the cumulative number of freshwater lenses emplaced over successive sea‐level stillstands. We suggest that the morphologies of the two largest caves are consistent with dissolution in multiple lenses occupying lower elevations, collapse resulting in breakout domes, and overprinting of collapse chambers during subsequent highstands. As a result, some caves may not reflect connectivity of the bedrock surrounding the main chambers but may reflect connectivity of more diagenetically mature bedrock at lower elevations where their antecedent chambers formed.

Comparison of Modern and Pleistocene (MIS 5e) Coastal Boulder Deposits from Santa Maria Island (Azores Archipelago, NE Atlantic Ocean)

Modern and palaeo-shores from Pleistocene Marine Isotope Substage 5e (MIS 5e) featuring prominent cobble/boulder deposits from three locations, on the southern and eastern coast of Santa Maria Island in the Azores Archipelago, were compared, in order to test the idea of higher storminess during the Last Interglacial. A total of 175 basalt clasts from seven transects were measured manually in three dimensions perpendicular to one another. Boulders that exceeded the minimum definitional diameter of 25 cm contributed to 45% of the clasts, with the remainder falling into the category of large cobbles. These were sorted for variations in shape, size, and weight pertinent to the application of two mathematical formulas to estimate wave heights necessary for traction. Both equations were based on the “Nott-Approach”, one of them being sensitive to the longest axis, the other to the shortest axis. The preponderance of data derived from the Pleistocene deposits, which included an intertidal invertebrate fauna for accurate dating. The island’s east coast at Ponta do Cedro lacked a modern boulder beach due to steep rocky shores, whereas raised Pleistocene palaeo-shores along the same coast reflect surged from an average wave height of 5.6 m and 6.5 m. Direct comparison between modern and Pleistocene deposits at Ponta do Castelo to the southeast and Prainha on the island’s south shore produced contrasting results, with higher wave heights during MIS 5e at Ponta do Castelo and higher wave heights for the modern boulder beach at Prainha. Thus, our results did not yield a clear conclusion about higher storminess during the Last Interglacial compared to the present day. Historical meteorological records pit the seasonal activity of winter storms arriving from the WNW-NW against the scant record of hurricanes arriving from the ESE-SE. The disparity in the width of the marine shelf around Santa Maria Island with broad shelves to the north and narrow shelves to the south and east suggested that periodic winter storms had a more regular role in coastal erosion, whereas the rare episodic recurrence of hurricanes had a greater impact on southern and southeastern rocky shores, where the studied coastal boulder deposits were located.

Late Pleistocene Red Sea Mollusca: 1. Polyplacophora.

This study describes the chiton fauna (Mollusca, Polyplacophora) from the marine Pleistocene coral reef deposits bordering the Red Sea coast and dating to the last interglacial epoch (Marine Isotopic Substage 5e, MIS5e). Twenty-one species were identified, of which only three were previously known from the Pleistocene of the Red Sea (Lucilina sueziensis, Acanthopleura vaillantii and Acanthochitona penicillata). Eight are recorded as fossil for the first time. Six are described as new (Lucilina confusa n. sp., L. aqabaensis n. sp., L. aegyptiaca n. sp., L. colantonii n. sp., "Onithochiton" vandingeneni" n. sp., and Acanthochitona interglacialis n. sp.) and two are assigned at generic level (Callochiton sp. and Craspedochiton sp.). Four of these new species (Lucilina confusa n. sp., L. aegyptiaca n. sp., L. colantonii n. sp. and "Onithochiton" vandingeneni n. sp.) are still living in the Red Sea, bringing to 28 the number of extant species known from the Red Sea. These Pleistocene Red Sea assemblages represent the most diverse chiton fauna yet reported from any interglacial deposit worldwide.

Morphology of fore-reef slopes and terraces, Takapoto Atoll (Tuamotu Archipelago, French Polynesia, central Pacific): The tectonic, sea-level and coral-growth control

A dataset of 41 bathymetric profiles detected by satelline imagery and echo-sounding to a maximum depth of 38 m along the fore-reef slopes of Takapoto Atoll (Tuamotu Plateau, French Polynesia, central Pacific) were qualitatively and quantitatively analyzed in order to identify the main geomorphological features. In addition, scuba-diving investigations from a selected site resulted in defining coral composition and cover rate. Six distinct fore-reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient. Only the north end, and a restricted area of the mid-south-east side extend seawards over an average distance of 150 m, with a relatively low gradient (23°–38°). Most of the outer-slope areas are narrow (<100 m on average) and steep (average slope equals to 45° to up to 70°). Geomorphic features include spur-and-groove systems, sub-horizontal to gently dipping terraces (23–45 m wide) ending seawards in vertical steps (<10 m high) and drop-offs (>10 m high), outer-reef crest-like reliefs (0.5 m–1.5 m high), pinnacles (2 m–17 m high), coral heads (<2 m high), trenchs and concave scars. The recognized seven terrace levels occur at the respective depths of about −5 m, −10 m, −15 m, −20 m, −24 m, −30.5 m and −38 m. Based on comparison with subsurface chronostratigraphy of drilled reef sequences from some other Pacific atolls, the terraces are interpreted as remnants of reef tracts formed during Pleistocene interglacial, high sea-stands, respectively during MIS substage 5e (about −125 ka), MIS substages 7a (about −195 ka), 7c (about −210 ka), 7e (about −240 ka) and 9e (−330 ka). After depth correction of ground lowering during periods of emergence and subsidence effects, terrace elevations were expected to indicate eustatic sea-level positions at each identified high sea-stand, at approximately 7 m (MIS 5e) and 2.2 m (MIS 7a) above present sea level and 9.5 m (MIS 7c), 11 m (MIS 7e) and 8.6 m (MIS 9e) below present sea level. During the post-glacial sea-level rise, from about 9.5 ky, the studied portions of fore-reef slopes were re-flooded. It was assumed that coralgal deposits in the form of thin veneers, coral heads, outer-reef crest-like reliefs and pinnacles have simply overlapped pre-existing structures. Locally, the fore-reef zones are carved by trenchs, i.e. incipient detachment faults, and scars, i.e. imprints of former landslides. Similarly, some drop-offs may be regarded as fault walls. The prevailing direction of faulting–collapsing surfaces is consistent with the SW–NE orientation of the main axis of the atoll and submarine ridges rising up from the north-western floor of the Tuamotu Plateau. Analysis of the composition and distribution of coral communities to −30 m depth revealed high, downslope-increasing coral coverage (24% to 67% on average) and the sharp replacement of robust-encrusting Pocillopora by sub-massive to plate-like Porites from depths greater than −10 m. Significant inter-regional differences were detected with atolls in west Pacific, probably due to local ecological constraints.

Tropical Atlantic Cooling and Freshening in the Middle of the Last Interglacial From Coral Proxy Records

AbstractThe last interglacial (LIG; Marine Isotope Substage 5e, ~127–117 ka) experienced globally warmer than modern temperatures; however, profound differences in regional climate occurred that are relevant to the assessment of future climate change scenarios. Tropical Atlantic sea surface temperature (SST) and hydrology are intrinsic to the spatiotemporal evolution of past and future climate. We present eight monthly resolved coral Sr/Ca and δ18O records (130–118 ka) to reconstruct mean western tropical Atlantic SST and seawater δ18O changes during the LIG. Cooler and fresher than modern surface waters are indicated for the middle of the LIG at ~126 ka. This was followed by a rapid transition to modern‐like SSTs and salinities that characterized the remaining part of the LIG. Our results, which account for differences found among corals, proxies, and SST calibration uncertainties, agree with western tropical Atlantic sediment records. Together, they suggest that an oceanic regime existed that differed from today.

Palaeoenvironment of MIS5 in the North of Western Siberia, reconstructed on the sub-fossil insect, crustacean and plant macrofossil data

Insect, tadpole shrimp and plant macrofodssil assemblages dated to different intervals of MIS5 are presented for three sites in the northern part of the West Siberian plain: Karymkarskyi sor, Belaya Gora and Kiryas. The beetle faunas suggest a relatively warm climate associated with boreal forest and marsh communities of the middle and southern taiga type; this interpretation is in agreement with the paleobotanical studies. Evidence of warm climate is provided by the occurrence of the carabid beetle Trechus secalis, found in Karymkarskyi sor and Belaya Gora sites. This fossil occurrence is referred substages to MIS5e and MIS5c on the basis of TL and U/Th dates, and coincides with the presence of bark beetle remains at the Kiryas locality. Both plant macrofossils from the Belaya Gora locality and tadpole shrimp remains from Kiryas site do not include species indicative of warmer-than-present climate, despite the presence of residues of woody plants. Our data were compared with paleobotanical data from a number of locatities in the central and northern parts of the West Siberian plain that have been dated to MIS5 on the basis of TL and Th/U dates. Most of these sites yielded paleobotanical data indicative of relative warm climate and forest vegetation. The exception is the Elizarovo point site, where the palynological data indicate periglacial environments. Insect, crustacean and plant macrofossil data are well correlated with the results of studies of fossil insect and paleobotanical data from other regions of Northern Eurasia and may confirm warm and humid climate during some periods of MIS5 (substages 5e and 5c) and distribution of forest landscapes and corresponding insect complexes.

Superstorms: Comments on Bahamian Fenestrae and Boulder Evidence from the Last Interglacial

ABSTRACT Mylroie, J.E., 2018. Superstorms: Comments on Bahamian fenestrae and boulder evidence from the Last Interglacial. Sea level during the last interglacial (Marine Isotope Substage 5e [MIS 5e]) was ∼6 m above present, interpreted to represent a warmer climate, with increased storm intensity and storm frequency. Two hypotheses have been advanced to demonstrate an increase in storm intensity during MIS 5e. The first considers fenestrae in eolian calcarenites at elevations up to 43 m in the Bahama Archipelago to be evidence of superstorm washover. Additional observations include rip-up clasts and loss of bedform and root structures as a result of wave scour. Such an event should produce a tempestite with a wide-ranging footprint, but none exists above 10 m. This paper argues that the fenestrae are rainfall slurries, rip-up clasts are weathering products of calcarenite protosol development, and bed-form and root structure absence or presence reflects transgressive-phase vs. regressive-phase eolian forma...

Last interglacial (MIS 5e) sea-level determined from a tectonically stable, far-field location, Eyre Peninsula, southern Australia

ABSTRACTThe last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128–116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust–mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine–lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal–intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial.

Formal subdivision of the Quaternary System/Period: Past, present, and future

The Quaternary System/Period represents the past 2.58 million years and is officially subdivided into the Pleistocene and Holocene series/epochs, with the base of the Holocene assigned an age of 11,700 calendar years before AD 2000. The two lowest stages of the Pleistocene, the Gelasian (base 2.58 Ma) and the Calabrian (base 1.80 Ma), have been ratified and these effectively constitute the Lower Pleistocene Subseries. All other official subdivisions are pending. For the Middle Pleistocene Subseries, three candidate global boundary stratotype sections and points (GSSPs) are under consideration: the Valle di Manche in Calabria and Montalbano Jonico in Basilicata, both in southern Italy, and the Chiba section in Japan. The Matuyama–Brunhes Chron boundary (∼773 ka) serves as the principal guide for the base of the Middle Pleistocene. The base of the Upper Pleistocene Subseries is generally agreed to coincide approximately with that of the last interglacial (Marine Isotope Substage 5e ∼130 ka): the Fronte section near Taranto in southern Italy represents a possible candidate GSSP, but an Antarctic ice core might also serve this purpose. A tripartite subdivision of the Holocene, with subseries/stage boundaries at 8200 and 4200 years B.P., is also under consideration. Additional fine-scale formal subdivision of the Quaternary is being explored, with the Last Glacial Maximum serving as a test case. The “Anthropocene” is both an informal and undefined interval of time that includes the present day. Its duration, formal/informal status, rank, and method of definition are all under debate, with one suggestion that it be defined as a formal unit beginning with the world's first nuclear bomb explosion, on July 16th 1945. Suggested and proposed GSSPs are compared and critiqued. The history leading to ratification of the Quaternary Period in 2009 is examined drawing upon published and unpublished material.

Near-field sea-level variability in northwest Europe and ice sheet stability during the last interglacial

Global sea level during the Last Interglacial (LIG, Marine Isotope Sub-stage 5e) peaked between c. 5.5 and 9 m above present, implying significant melt from Greenland and Antarctica. Relative sea level (RSL) observations from several far- and intermediate-field sites suggest abrupt fluctuations or jumps in RSL during the LIG highstand that require one or more episodes of ice-sheet collapse and regrowth. Such events should be manifest as unique sea-level fingerprints, recorded in far-, intermediate- and near-field sites depending on the source(s) of ice-mass change involved. To date, though, no coherent evidence of such fluctuations has been reported from near-field RSL studies in northwest Europe. This is an important problem because RSL fluctuations during the LIG are portrayed as warning signs for how polar ice sheets may behave in a future, warmer than present, world. Here we review the evidence for RSL change during the LIG using stratigraphic data from the best resolved highstand records that exist in the near-field of northwest Europe, from a range of settings that include lagoonal, shallow marine, tidal flat, salt marsh and brackish-water fluviatile environments. Consideration of previously published stratigraphic records from two sites in the Eemian coastal-marine embayment that existed in the central Netherlands, yields no clear indications for abrupt RSL change during the attainment of the near-field highstand. Nor do we find any such indications common to other records from countries bordering the North Sea, the Baltic Sea and the White Sea. Two modelling experiments that explore the global signal of hypothetical sea-level oscillations caused by partial collapse and regrowth of either the Greenland or Antarctic LIG ice-sheet, show that the North Sea region is relatively insensitive to mass changes sourced from Greenland but should clearly register events with an Antarctic origin, especially those that occur late in the LIG. The lack of evidence for abrupt sea-level fluctuations at this time in northwest Europe concurs with a lack of clear near-field evidence for ice sheet collapse.

First known fossil bird tracks (Pleistocene) on San Salvador island, Bahamas

Two avian footprints discovered in the Grotto Beach Formation (Pleistocene) of San Salvador Island (Bahamas) are the first known vertebrate trace fossils on this well-studied island. The trace fossils, preserved as beddingplane impressions in an oolitic-bioclastic grainstone, match the size and form of tracks made by modern gulls. The tracks are in beach facies located below a paleosol dated from Marine Isotope Substage 5e (~120,000kya). These tracks add to a record of Pleistocene bird tracks reported from Eleuthera Island and bode well for the recognition of more vertebrate trace fossils on San Salvador and other Bahamian islands.

Middle and Late Pleistocene environmental history of the Marsworth area, south-central England

To elucidate the Middle and Late Pleistocene environmental history of south-central England, we report the stratigraphy, sedimentology, palaeoecology and geochronology of some deposits near the foot of the Chiltern Hills scarp at Marsworth, Buckinghamshire. The Marsworth site is important because its sedimentary sequences contain a rich record of warm stages and cold stages, and it lies close to the Anglian glacial limit. Critical to its history are the origin and age of a brown pebbly silty clay (diamicton) previously interpreted as weathered till.The deposits described infill a river channel incised into chalk bedrock. They comprise clayey, silty and gravelly sediments, many containing locally derived chalk and some with molluscan, ostracod and vertebrate remains. Most of the deposits are readily attributed to periglacial and fluvial processes, and some are dated by optically stimulated luminescence to Marine Isotope Stage (MIS) 6. Although our sedimentological data do not discriminate between a glacial or periglacial interpretation of the diamicton, amino-acid dating of three molluscan taxa from beneath it indicates that it is younger than MIS 9 and older than MIS 5e. This makes a glacial interpretation unlikely, and we interpret the diamicton as a periglacial slope deposit.The Pleistocene history reconstructed for Marsworth identifies four key elements: (1) Anglian glaciation during MIS 12 closely approached Marsworth, introducing far-travelled pebbles such as Rhaxella chert and possibly some fine sand minerals into the area. (2) Interglacial environments inferred from fluvial sediments during MIS 7 varied from fully interglacial conditions during sub-stages 7e and 7c, cool temperate conditions during sub-stage 7b or 7a, temperate conditions similar to those today in central England towards the end of the interglacial, and cool temperate conditions during sub-stage 7a. (3) Periglacial activity during MIS 6 involved thermal contraction cracking, permafrost development, fracturing of chalk bedrock, fluvial activity, slopewash, mass movement and deposition of loess and coversand. (4) Fully interglacial conditions during sub-stage 5e led to renewed fluvial activity, soil formation and acidic weathering.

Evolving history of the East Asian summer monsoon intensity during the MIS5: inconsistent records from Chinese stalagmites and loess deposits

As an important component of the global monsoon system, the intensity of East Asian summer monsoon (EASM) influences lives and economic development of more than 2 billion people. The last interglacial period, also known as Marine Isotope Stage 5 (MIS 5), has been thoroughly investigated due to its similarity to the modern interglacial period (MIS 1). According to records from Chinese stalagmites and loess deposits, evolving history of EASM intensity during MIS5 can be divided into 5 sub-stages, i.e., 5a–5e. However, during the 3 warm sub-stages (5a, 5c, and 5e), evolving history of EASM intensity recorded by Chinese stalagmites and loess deposits is apparently different. Oxygen isotope (δ18O) records of stalagmites demonstrate that the EASM intensity during MIS5e, 5c, and 5a is not obviously different. On the other hand, EASM intensity apparently decreased from MIS5e to 5c and 5a based on Chinese loess deposits records. The discrepancy between Chinese stalagmite and loess deposits reveals that δ18O records of stalagmites may not be a pure indicator of EASM intensity. The relationship between δ18O and EASM intensity is not linear. Based on δ18O data of modern precipitation from 21 weather stations within major monsoon area in China (MMAC, ca. 110°E to 122°E, 18°N to 41°N), we speculate that Chinese stalagmite δ18O values recorded changes of δ18O of summer precipitation as well as adjustment from δ18O of winter precipitation. Inconsistent records from Chinese stalagmites and loess deposits indicate that further investigations are needed to study the mechanism and fractionation of δ18O in stalagmites collected in China.

Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic.

The last interglacial interval was terminated by the inception of a long, progressive glaciation that is attributed to astronomically influenced changes in the seasonal distribution of sunlight over the earth. However, the feedbacks, internal dynamics, and global teleconnections associated with declining northern summer insolation remain incompletely understood. Here we show that a crucial early step in glacial inception involves the weakening of the subpolar gyre (SPG) circulation of the North Atlantic Ocean. Detailed new records of microfossil foraminifera abundance and stable isotope ratios in deep sea sediments from Ocean Drilling Program site 984 south of Iceland reveal repeated, progressive cold water-mass expansions into subpolar latitudes during the last peak interglacial interval, marine isotope substage 5e. These movements are expressed as a sequence of progressively extensive southward advances and subsequent retreats of a hydrographic boundary that may have been analogous to the modern Arctic front, and associated with rapid changes in the strength of the SPG. This persistent millennial-scale oceanographic oscillation accompanied a long-term cooling trend at a time of slowly declining northern summer insolation, providing an early link in the propagation of those insolation changes globally, and resulting in a rapid transition from extensive regional warmth to the dramatic instability of the subsequent ∼ 100 ka.

Coral reefs and sea-level change

Abstract Coral reefs provide significant evidence for former sea-level positions because of their geological preservation and suitability for dating. Interpretation of this evidence presumes an understanding of reef geomorphology, modern reef organism distributions, and environmental factors influencing them. Fossil reef terraces, formed during the last interglacial, marine oxygen isotope (MIS) substage 5e (~ 128–116 ka), are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand. Observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level, implying less extensive icesheets than at present. An elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift. Recent compilations suggest elevations up to 8–9 m, but incorporate few observations from reefs where the last interglacial is found below sea level. Oscillation of sea level during MIS 5e has been interpreted from several sites, with recent studies inferring rapid rise of several metres at the end of the interglacial. These interpretations are at the limits to the precision with which corals can currently be dated and their palaeo-water depths inferred. It is not surprising that constraining last interglacial sea-level changes within uncertainties of less than 1–2 m remains controversial, considering sea-level variations recognised between reef sites in the Holocene, and observed geographical variation in isostatic or flexural adjustments. Fossil coral reefs on uplifting margins also provide clear evidence for MIS substages 5c and 5a, and those on Huon Peninsula indicate fluctuations related to Heinrich events (MIS 3). Interpretations show considerable variability between sites, with still greater uncertainties about sea-level timing and elevation during previous interglacials. Future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties. Submerged reefs have already yielded important information about sea-level rise during the last deglaciation. Coring around Barbados and Tahiti, as well as on the Huon Peninsula, has produced a broadly consistent picture of ice melt, reflecting eustatic change since the last glacial maximum. These studies have shown the sensitivity of reefs to rapid sea-level rise associated with meltwater pulses, with some reefs drowning while others back-stepped. Integrated Ocean Drilling Program (IODP) expeditions to Tahiti, and recently the Great Barrier Reef, extended these records, but details of timing, nature and impact of deglacial meltwater pulses remain elusive. Studies of Holocene reefs have indicated different growth strategies; some kept up with sea level, while others caught up when sea level decelerated. Holocene sea level appears to have experienced a gradual rise up to present across the Caribbean, providing accommodation space for reefs to accrete vertically; whereas in the Indo-Pacific sea level has been near its present level since 7 ka, with many reef flats emergent following a slight fall of sea level caused by ocean siphoning. Microatolls on reef flats provide perhaps the clearest evidence of past sea-level position, but, in their absence, novel biological or other sea-level indicators are required to better constrain palaeo-water depths. There is an urgent need for further research from additional key reef locations, not only to decipher processes driving past sea-level change and its geographical variability, but also to better understand how coral reefs will respond in the context of future sea-level rise.