Last Interglacial

POSTER: Eemian seasonal temperature variations recorded by very high-resolution analyses of a MIS 5e stromatolite from Caours (Somme Basin, Northern France): combining petrography and stable isotopes.

by Julie Dabkowski

Co-authored with Andrews Julian, Antoine Pierre, Limondin-Lozouet Nicole, Marca-Bell Alina.
Presented at the EGU 2012, in section CL1.10 "Interglacial climate change - Learning from paleoclimate archives and models"

In many tufa formations, very well crystallised deposits called stromatolites are preserved. They generally present... more In many tufa formations, very well crystallised deposits called stromatolites are preserved. They generally present successive laminations thought to be linked to seasonal climatic and environmental variations in modern to sub-fossil deposits. They thus represent a huge potential for very high resolution records of Pleistocene climate. One of the very first investigations in this way has been performed on a 2.5 cm-radius stromatolite from the Eemian sequence of Caours (Somme Basin, Northern France), where precise petrographical observations have been combined with stable isotope analyse.
Lamina succession observed in macroscopic scale has been shown in thin section to be linked to two major facies. The first is built by well developed, elongate calcite spar crystals including imprints of cyanobacteral bushes. This facies alternates with laminae composed by fractured crystals or micritic layers. The first facies could be linked to summer development of cyanobacteria under optimal temperature and light conditions and the ‘degraded’ or micritic facies to less favourable winter conditions. Stable oxygen and carbon isotope analyses performed on 69 intra-lamina samples show variation strongly concordant with lamina succession. Facies with developed sparry crystals is associated to minimal isotopic values whereas the  ‘degraded’ facies clearly record the highest. At seasonal resolution, carbon isotopic composition has been previously shown in modern tufa to covary positively with oxygen isotopic composition probably driven by temperature dependent phenomena in the aquifer: thus the positive correlation observed in the Caours stromatolites between the isotopic ratios is not surprising.  Oxygen stable isotope composition in tufa calcite is known at this resolution to be directly linked to water temperature: increasing temperature related to decreasing values. This interpretation of geochemical results is thus strongly consistent with facies attribution to seasonal variations. Indeed, maximal temperatures are recorded in well developed calcite laminas assigned to summer conditions.
These preliminary results indicate that seasonal palaeoclimatic information should be available in fossil Pleistocene stromatolites. High-resolution studies combining petrographical and intra-laminae stable isotope analyses allow data comparison and strengthen their interpretations. At this resolution, the oxygen stable isotope composition is thermo-dependent and could be use to quantify water temperature. Analyses of a larger stromatolite from Caours covering several decades would provide a strong record of summer-winter water temperature variations during the Eemian.

Direct terrestrial-marine correlation demonstrates surprisingly late onset of the last interglacial in central Europe

by Mark J. Sier

Sier, Mark J.
Roebroeks, Wil
Bakels, Corrie C.
Dekkers, Mark J.
Brühl, Enrico
De Loecker, Dimitri
Gaudzinski-Windheuser, Sabine
Hesse, Norbert
Jagich, Adam
Kindler, Lutz
Kuijper, Wim J.
Laurat, Thomas
Mücher, Herman J.
Penkman, Kirsty E. H.
Richter, Daniel
van Hinsbergen, Douwe J. J.
2011

An interdisciplinary study of a small sedimentary basin at Neumark Nord 2 (NN2), Germany, has yielded a... more An interdisciplinary study of a small sedimentary basin at Neumark Nord 2 (NN2), Germany, has yielded a high-resolution record of the palaeomagnetic Blake Event, which we are able to place at the early part of the last interglacial pollen sequence documented from the same section. We use this data to calculate the duration of this stratigraphically important event at 3400±350 yr. More importantly, the Neumark Nord 2 data enables precise terrestrial–marine correlation for the Eemian stage in central Europe. This shows a remarkably large time lag of ca. 5000 yr between the MIS 5e ‘peak’ in the marine record and the start of the last interglacial in this region.

Les microfaciès du tuf calcaire éemien (SIM 5e) de Caours (Somme, France): éléments d'analyse paléoécologique du dernier interglaciaire

by Julie Dabkowski

Co-authored with Pierre Antoine, Nicole Limondin-Lozouet, Christine Chaussé and Pierre Carbonel
Published in Quaternaire, 21 (2), 2010

THE MICROFACIES OF THE EEMIAN CAOURS TUFA (SOMME, FRANCE,MIS 5E): DATA TO A PALAECOLOGICAL ANALYSIS OF THE LAST... more THE MICROFACIES OF THE EEMIAN CAOURS TUFA (SOMME, FRANCE,MIS 5E): DATA TO A PALAECOLOGICAL ANALYSIS OF THE LAST INTERGLACIAL
Calcareous tufa deposits are essential record of the climatic evolution and its environmental responses during Pleistocene Interglacial in Western Europe. A petrographical study of 34 thin sections from Caours tufa deposit was compared to other palaeo-ecological data, such as mollusk and ostracod fauna and to the results of sedimentological analyses. In the lowest part, fine detritical alluvial deposits show the transition to interglacial conditions. Above, the tufa deposit is precipitated by cyanobacteria of the fossil genus Broutinella, Ponsella and Ponsinella. Broutinella and Ponsella built well crystallized stromatolites in and at the top of channels. Broutinella also builts a massive tufa qualified as "cauliflower". This facies precipitates in places always in water and associated to aquatic mollusks and ostracods. In massive tufa, Ponsinella dominates the "mille-feuilles" facies associated to dry phases and mainly terrestrial malacofauna. Consequently, the facies diversity compared to malacological data shows palaeoecological variations during the 5e interglacial.

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Les tufs calcaires constituent des enregistrements clés pour l'étude de l'évolution climatique et des réponses environnementales au cours des inter­glaciaires pléistocènes en Europe de l'Ouest. Dans ce cadre, l'étude pétrographique de 34 lames minces de la séquence de tuf du début du Pléistocène supérieur de Caours a été comparée à d'autres données paléoécologiques telles que les faunes de mollusques et d'ostracodes et aux résultats d'analyses sédimentologiques. A la base, les dépôts fluviatiles fins, détritiques, traduisent dans leur partie supérieure le passage aux conditions interglaciaires. La construction du massif de tuf qui suit, résulte de la précipitation de calcite par des cyanobactéries des genres fossiles Broutinella, Ponsella et Ponsinella. Les deux premiers sont responsables de la construction de stromatolithes, bien cristallisés, associés aux zones de chenal. Broutinella intervient égale­ment dans la construction de tuf en dôme de type « chou-fleur », présent dans les milieux toujours en eau, dominés par des faunes de mollusques aqua­tiques et d'ostracodes. Ponsinella est à l'origine d'un faciès « mille-feuille », associé à de nombreux épisodes d'assèchement et à une malacofaune à dominante terrestre. La diversité des faciès et des encroûtements et leur comparaison avec les biomarqueurs, notamment malacologiques, soulignent des variations environnementales intervenues au cours de l'interglaciaire 5e.

Quaternary stratigraphy of the Prophet River, northeastern British Columbia

by Michelle Trommelen

Trommelen, M., Levson, V., 2008. Quaternary stratigraphy of the Prophet River, northeastern British Columbia. Canadian Journal of Earth Science, V 45, p. 565-575, 10.1139/E07-072

Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary... more Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary history of the northwest Canadian Boreal Plains. The region shows evidence of Late Wisconsinan Laurentide glaciation in the form of widespread till, containing abundant erratic clasts derived from the Canadian Shield. Vertical sections along the Prophet River expose non-glacial and advance glacial sediments below this till. Pre-Late Wisconsinan non-glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites. Macrofossils within horizontally laminated organic-rich black clay and silt indicate deposition on the floodplain of the paleo-Prophet River within an oxbow lake. The climate during deposition is interpreted to be similar to present, supporting a dominantly spruce forest. Wood obtained from eight sites provided non-finite radiocarbon ages, and one sample provided an age of 49 300 ± 2000 BP, which is also considered non-finite. Glaciolacustrine clays and silts, deposited during impoundment of eastward-flowing drainage by the advance of the Laurentide Ice Sheet (LIS) in the Late Wisconsinan, overlie the non-glacial sediments throughout the valley. A blanket of clast-poor, clay-rich till up to 20 m thick, and deposited by the LIS, drapes the glaciolacustrine sediments. Since deglaciation, the Prophet River has incised the valley and formed fluvial terraces at different levels above the modern river.

Carr, A.S., Bateman, M.D., Roberts, D.L., Murray-Wallace, C.V., Jacobs, Z., Holmes, P.J. (2010) The last interglacial sea-level highstand on the southern Cape coastline of South Africa. Quaternary Research 73, 351-362

by Andy Carr

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the... more The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0–8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138 ± 7 ka and 118 ± 7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122 ± 7 ka and 113 ± 6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.

Meltwater Pulses: Encyclopedia of Modern Coral Reefs

by Paul Blanchon

Blanchon, P. (2011) Meltwater Pulses. In: Hopley, D. (Ed), Encyclopedia of Modern Coral Reefs: Structure, form and process. Springer-Verlag Earth Science Series, p. 683-690. DOI 10.1007/978-90-481-2639-2

A meltwater pulse is an acceleration in sea-level rise which results from outbursts of pro- or subglacial meltwater... more A meltwater pulse is an acceleration in sea-level rise which results from outbursts of pro- or subglacial meltwater and/or surging of ice-streams into the ocean during ice- sheet disintegration. Radiometric ages of coral-reef drowning and back-stepping indicate that rates of sea- level rise during these meltwater pulses were at least 35 mm/yr and may have been as much as 60 mm/yr, and that these rises persisted for 300–500 years. (...Continues)

Reef Back-Stepping: Encyclopedia of Modern Coral Reefs

by Paul Blanchon

Blanchon, P. (2011) Back-Stepping. In: Hopley, D. (Ed), Encyclopedia of Modern Coral Reefs: Structure, form and process. Springer-Verlag Earth Science Series, p. 77-84. DOI 10.1007/978-90-481-2639-2

Reef back-stepping has been widely recognized from the geological record where it is almost universally interpreted as... more Reef back-stepping has been widely recognized from the geological record where it is almost universally interpreted as a result of rapid rise in relative sea level. Yet ironically, there has been considerable argument over its existence and significance in late Pleistocene and Holocene reefs. (...Continues)

Last Interglacial and Reef Development: Encyclopedia of Modern Coral Reefs

by Paul Blanchon

Blanchon, P. (2011) Last Interglacial and Reef Development. In: Hopley, D. (Ed), Encyclopedia of Modern Coral Reefs: Structure, form and process. Springer-Verlag Earth Science Series, p. 621-639. DOI 10.1007/978-90-481 2639-2

During the LIG, elevated temperatures, together with the smaller latitudinal temperature gradient, led to more... more During the LIG, elevated temperatures, together with the smaller latitudinal temperature gradient, led to more widespread reef development than present, and reefs not only extended further into coastal lowlands but significantly expanded their latitudinal range. The elevation and age of fossil reef-crests from tectonically stable terrains in several areas of the world indicate that the sea level was 3 m higher than the present by 125 ka and peaked at 6 m sometime thereafter (...Continues).

Multi-stage reef development on Barbados during the Last Interglaciation.

by Paul Blanchon

By mapping the vertical and lateral distribution of reefal facies on the west and south coast of Barbados we have... more By mapping the vertical and lateral distribution of reefal facies on the west and south coast of Barbados we have produced a revised model of reef development for the Last Interglaciation. We find that reef architecture around Barbados has significant complexity including evidence for wave exposure-related variations in reef geometry and at least 3 stages of reef development that were controlled by variations in sea level. During the main stage of development, an Acropora palmata-dominated reef-crest aggraded 22m in response to a minimum sea-level rise of 20m. During stage 2, a sea cave was cut 3-4m above the fossil reef-crest, possibly indicating that reef growth was terminated before sea level reached the highstand. Similar sequences elsewhere in the Caribbean indicate that this early reef demise may not be a local phenomenon: several reefs apparently stopped growing between +2 and +4m and only in sheltered areas did they reach the highstand at +6m, as recorded by intertidal notches. This pattern of reef demise has previously been related to rapid sea-level rise at the end of the interglacial, but stratigraphic data are equivocal. The final stage of reef development on Barbados occurred when sea level began to fall. This fall was rapid, leaving a thin but widespread veneer of reef-crest deposits over the proximal reef-front, and discontinuous intertidal and shallow subtidal deposits capping the distal reef-front. Although further dating is required to diferentiate these three stages, our only reliable U/Th TIMS date indicates that almost 50% of the exposed reef had accreted by 129 ka, giving an estimate of 15 ka for the main aggradational stage. Furthermore, reports of relict reef-crests buried beneath these exposed deposits indicate that our revised model is incomplete and that earlier stages of reef growth occurred during the Last Interglaciation. These earlier stages imply that sea-level was at an interglacial level for as long as 20ka supporting the Devils Hole record of interglacial duration. Unfortunately, these estimates could not be verified directly because most of our U/Th data show major stratigraphic age reversals attributed to diagenesis. This pattern is also evident in all other well-dated reefal units in the Caribbean and leads us to conclude that only diagenetically screened, precise, stratigraphically consistent coral dates can be used to directly estimate the duration of the Last Interglaciation.

Reef demise and back-stepping during the last interglacial, northeast Yucatan.

by Paul Blanchon

The elevation of reefs and coastal deposits during the last Interglaciation (MIS-5e) indicates that sea level reached... more The elevation of reefs and coastal deposits during the last Interglaciation (MIS-5e) indicates that sea level reached a highstand of as much as 6 m above the present, but it is uncertain how rapidly this level was attained and how it impacted reef development. To investigate this problem, I made a detailed sedimentological analysis of a well-dated reef from the northeast coast of the stable Yucatan Peninsula. Two linear reef tracts were delineated which are offset and at different elevations. The lower reef tract crops out along northern shore for 575 m and extends from below present mean sea level to +3 m. The reef crest facies consists of large Acropora palmata colonies dispersed within a coral boulder-gravel and is flanked by an A. cervicornis-dominated reef-front and a large area of lagoonal framework formed by coalesced patches of A. cervicornis and Montastraea spp. Constituents in the upper metre of the lower tract are heavily encrusted by a cap of crustose corallines and, in places, are levelled by a discontinuous marine-erosion surface. The upper reef tract crops out ~150 m inland up to an elevation of +5.8 m and parallels the southern section of shore for ~400 m. It also consist of an A. palmata-dominated crest facies flanked by reef-front, back-reef and lagoonal frameworks. In this case, however, lagoonal frameworks are dominated by a sediment-tolerant assemblage of branching coralline algae. Also different is the lack of encrustation by corallines, and the infiltration of upper tract facies by beach-derived shell-gravels from regressive shoreface deposits above. These results indicate that the lower reef tract and lagoonal patch-reefs formed at a sea level of +3 m. Final capping by crustose corallines and discontinuous marine erosion indicates that the lower tract was terminated by the complete demise of corals on the crest but only patchy demise in the lagoon. Areas of continuous framework accretion between the lagoonal patch reefs and the upper reef-tract, however, require that the demise of this reef was ecologically synchronous with initiation of the upper reef-tract, which had back-stepped 100 m into the lagoon. In this new position, the upper tract developed a reef crest that corresponded to a final sea-level position of +6 m. Reef flat development at +5 m and large in-place colonies of A. palmata at the base of the crest unit indicate, however, that sea level must have risen rapidly from +3 to more than +5 m to accommodate back-stepping. This sea-level jump created a higher energy wave field that mobilized back-reef and lagoonal sediments, and the resulting high sediment flux eroded lagoonal framework and prevented the recovery of the submerged lower reef crest. So this single jump in sea level was responsible not only for reef demise and back-stepping but also for marine erosion and suppression of subsequent reef development—features that elsewhere have been used to support multiple sea-level excursions during the last interglacial.

Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand

by Paul Blanchon

Widespread evidence of a +4–6-m sea-level highstand during the last interglacial period (Marine Isotope Stage 5e) has... more Widespread evidence of a +4–6-m sea-level highstand during the last interglacial period (Marine Isotope Stage 5e) has led to warnings that modern ice sheets will deteriorate owing to global warming and initiate a rise of similar magnitude by AD 2100. The rate of this projected rise is based on ice-sheet melting simulations and downplays discoveries of more rapid ice loss. Knowing the rate at which sea level reached its highstand during the last interglacial period is fundamental in assessing if such rapid ice-loss processes could lead to future catastrophic sea-level rise. The best direct record of sea level during this highstand comes from well-dated fossil reefs in stable areas. However, this record lacks both reef-crest development up to the full highstand elevation, as inferred from widespread intertidal indicators at +6m, and a detailed chronology, owing to the difficulty of replicating U-series ages on sub-millennial timescales. Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatan peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3m and back-stepping to +6m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2–3-m jump in sea level. Using strictly reliable 230Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred 121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period.

Reviewer Comment:
“This is the most comprehensive documentation of the last Interglacial 'double peak' available—one that is based upon the two necessary and sufficient pillars of age dating and paleoecology. This paper should finally lay to rest any notion that the last Interglacial was NOT characterized by a rapid sea-level event superimposed upon a normal Milankovitch cycle.”