Glacial Marine Isotope Stage Research Articles

The earliest securely dated hominin fossil in Italy and evidence of Acheulian occupation during glacial MIS 16 at Notarchirico (Venosa, Basilicata, Italy)

ABSTRACTThe Early Middle Pleistocene site of Notarchirico (Basilicata, Italy) is a 7‐m‐thick fluvially emplaced sedimentary sequence rich in volcanic materials coming from the Monte Vulture stratovolcano. This site consists of 11 archaeological layers, some of which have yielded handaxes. One femur attributed to Homo heidelbergensis was also recovered from an upper level. We present in this study new 40Ar/39Ar and electron spin resonance ages that delimit the time of occupation of Notarchirico to between 670 ± 4 ka (14 ka) and 614 ± 4 ka (12 ka), therefore spanning mainly the glacial Marine Isotope Stage 16. Handaxes found in archaeosurface F are now securely dated to between 670 ± 4 ka (14 ka) and 661 ± 4 ka (14 ka) and prove that hominid populations living in southern Italy used Acheulian technology as early as the beginning of this stage. Futhermore, we placed the age of the human femur between 661 ± 4 ka (14 ka) and 614± 4 ka (12 ka). This fossil is therefore the oldest Middle Pleistocene human fossil discovered in Italy so far. Thanks to this new chronological framework, Notarchirico is now a key site in our understanding of the Early Acheulian culture in Western Europe.

The response of deep-water benthic foraminiferal assemblages to changes in paleoproductivity during the Pleistocene (last 769.2 kyr), western South Atlantic Ocean

Benthic foraminiferal assemblages and δ18O records in a core from Santos Basin (western South Atlantic, 2220m water depth) were analyzed to investigate productivity changes during the Pleistocene. The sediment core recorded the last 770kyr, including Marine Isotope Stages (MIS) 19 to 1. The four dominant benthic foraminiferal assemblages were identified using Q-mode Varimax Factor Analysis, and are represented by Globocassidulina crassa, Bolivina spp., Epistominella exigua and Alabaminella weddellensis. From 769.2kyr (MIS 19) to ~300kyr (MIS 8), the highest values of factor 2 (Bolivina spp. assemblage) indicate increased influx of organic matter to the seafloor and a slight decrease in the oxygen concentration at the sediment–water interface. This condition began to change in the stage 8 (~288.9kyr to ~268.3kyr), and it is characterized by high values of factor 1, when the G. crassa assemblage became dominant, indicating an increase in oxygen concentrations and a decrease in the influx of organic matter. Seasonally-pulsed organic matter resulting in a distinct phytodetritus layer accumulated mostly during the glacial MIS 14, 10, 8, 6, and 5.2–5.1, and in the interglacial stage 11 and the end of 9, as indicated by factor 3 (E. exigua assemblage) and factor 4 (A. weddellensis assemblage). The highest peak of the A. weddellensis assemblage during MIS 11 (~401.4kyr) coincides with the Mid-Brunhes Event. The highest benthic foraminiferal accumulation rates occurred during mostly glacial stages, indicating delivery of more organic matter to the seafloor. The changes in benthic foraminifera assemblages in the glacial stages during the Pleistocene indicate changes in primary productivity in surface waters. Increasing the amount of organic matter delivered to the seafloor amplified the benthic foraminiferal response.

Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

High evaporation rates in the desert climate of the Red Sea ensure that, during glacial sea level lowstands when water exchange with the Indian Ocean was more restricted, water salinity and δ18O became unusually extreme. Modeling of the effect on Red Sea sedimentary δ18O has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea-level model could be extended if continuous core material of older sediment became available. We attempt to address this question here by examining seismic reflection data. The upper Pleistocene hemipelagic sediments in the Red Sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea-level lowstands. Seismic impedance changes associated with boundaries to those aragonite-rich layers appear to explain seismic reflection sequences. A segment of Chirp sediment profiler data from the central Red Sea reveals prominent reflections at ∼1, ∼5, ∼23, ∼26 and ∼36 ms two-way travel time (TWT) from the seabed. Based on depths to the glacial marine isotope stages (MIS) in cores, we relate the upper three reflections to the tops of aragonite-rich layers and hence the sea level rises immediately following MIS 2, 6 and 12. The reflection at 26 ms is related to an unusually rapid fall into MIS 12 predicted by one sea level reconstruction, which may have created an abrupt lower boundary to the MIS 12 aragonite-rich layer. With the aid of seismogram modeling, we tentatively associate the ∼36 ms reflection with the top of an aragonite-rich layer formed during MIS 16. Furthermore, some segments of lower frequency (airgun and sparker) seismic data from the central and southern Red Sea show a lower (earlier) Plio-Pleistocene (PP) interval that is less reflective than the upper (late) PP interval. This implies less variability in sediment impedance and that extreme variability in water salinity did not develop; water exchange with the Indian Ocean likely continued throughout this interval. These results suggest that viable relative sea level reconstructions may be recovered from Red Sea sediment δ18O data to at least MIS 16 and perhaps even as far back as the early Pliocene.

Mediterranean Outflow and surface water variability off southern Portugal during the early Pleistocene: A snapshot at Marine Isotope Stages 29 to 34 (1020–1135 ka)

Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stages (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic δ18O signal follows obliquity with the exception of an additional, smaller δ18O peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3. A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065–1091ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (<12°C) SST that in their climatic impact were comparable with the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show a strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes.

Sea-surface dynamics and palaeoenvironmental changes in the North Atlantic Ocean (IODP Site U1313) during Marine Isotope Stage 19 inferred from coccolithophore assemblages

Abstract Coccolithophore assemblages recovered from Integrated Ocean Drilling Program (IODP) Site U1313 are investigated to reconstruct the palaeoceanographic evolution of a sector of the North Atlantic during Marine Isotope Stage (MIS) 19 (~ 790–760 ka) at orbital, suborbital and millennial time-scales. The end of the glacial MIS 20 is marked by the arrival of cold waters, deriving from ice melting at higher latitudes, as recorded by Coccolithus pelagicus pelagicus. The MIS 19c is characterised by an extension of warmer North Atlantic Transitional Waters (NATW) reflecting the intensification of subtropical gyre influence on Site U1313, identified by an increase in warm species Umbilicosphaera sibogae. The influence on the site of cooler NATW is inferred from higher percentages of Gephyrocapsa margereli, which starts increasing from ~ 779 ka. Finally, the transition from MIS 19a to MIS 18 is characterised by a southward shift of the palaeoceanographic system due to a southward extension of the subpolar front, as indicated by an increase of cold subspecies C. pelagicus pelagicus. The evolution of the palaeoproductivity proxy records (number of coccoliths/g of sediment and Nannofossil Accumulation Rate — NAR) and the abundances of small Gephyrocapsa, G. margereli, U. sibogae and C. pelagicus pelagicus show that fluctuations in sea-surface productivity and alternations between cooling and warming phases occurred on the precessional timescale. Spectral analyses of U. sibogae, number of coccoliths/g of sediment and NAR indicate a significant concentration of variance close to half precession (~ 10 kyr); this reflects a nonlinear response of the mid-latitude North Atlantic surface ocean to low-latitude insolation forcing. Furthermore, millennial to multi-centennial instability in sea-surface dynamics is highlighted by spectral and wavelet analyses of U. sibogae, G. margereli and C. pelagicus pelagicus percentages, number of coccoliths/g of sediment and NAR, which reveal the occurrence of rapid events, related to stadial and interstadial-type conditions.

Origin of the forest steppe and exceptional grassland diversity in Transylvania (central‐eastern Europe)

AbstractAimThe forest steppe of the Transylvanian Plain is a landscape of exceptionally diverse steppe‐like and semi‐natural grasslands. Is this vegetation a remnant of a once continuous temperate forest extensively cleared by humans, or has the area, since the last glacial, always been a forest steppe? Understanding the processes that drive temperate grassland formation is important because effective management of this biome is critical to the conservation of the European cultural landscape.LocationLake Stiucii, north‐western Romania, central‐eastern Europe.MethodsWe analysed multi‐proxy variables (pollen, coprophilous fungi, plant macroremains, macrocharcoal) from a 55,000 year discontinuous sequence (c. 55,000–35,000; 13,000–0 cal. yr bp), integrating models of pollen‐based vegetation cover, biome reconstruction, global atmospheric simulations and archaeological records.ResultsNeedleleaf woodland occurred during glacial Marine Isotope Stage (MIS) 3, but contracted at the end of this period. Forest coverage of c. 55% (early Holocene) and 65% (mid‐Holocene) prevailed through the Holocene, but Bronze Age humans extensively cleared forests after 3700 cal. yr bp. Forest coverage was most widespread between 8600 and 3700 cal. yr bp, whereas grasses, steppe and xerothermic forbs were most extensive between 11,700 and 8600 cal. yr bp and during the last 3700 cal. yr bp. Cerealia pollen indicate the presence of arable agriculture by c. 7000 cal. yr bp.Main conclusionsWe have provided the first unequivocal evidence for needleleaf woodland during glacial MIS 3 in this region. Extensive forests prevailed prior to 3700 cal. yr bp, challenging the hypothesis that the Transylvanian lowlands were never wooded following the last glaciation. However, these forests were never fully closed either, reflecting dry growing season conditions, recurrent fires and anthropogenic impacts, which have favoured grassland persistence throughout the Holocene. The longevity of natural and semi‐natural grasslands in the region may explain their current exceptional biodiversity. This longer‐term perspective implies that future climatic warming and associated fire will maintain these grasslands.

The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability

Since the seminal work by Hays et al. (1976), a plethora of studies has demonstrated a correlation between orbital variations and climatic change. However, information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial-scale climate variability is still fragmentary. The Marine Isotope Stage (MIS) 19, an interglacial centred at around 785 ka, provides an opportunity to pursue this question and test the hypothesis that the long-term processes set up the boundary conditions within which the short-term processes operate. Similarly to the current interglacial, MIS 19 is characterised by a minimum of the 400-kyr eccentricity cycle, subdued amplitude of precessional changes, and small amplitude variations in insolation. Here we examine the record of climatic conditions during MIS 19 using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess the stability and duration of this interglacial, and evaluate the climate system's response in the millennial band to known orbitally induced insolation changes. Benthic and planktonic foraminiferal δ18O values indicate relatively stable conditions during the peak warmth of MIS 19, but sea-surface and deep-water reconstructions start diverging during the transition towards the glacial MIS 18, when large, cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal. The glacial inception occurred at ∼779 ka, in agreement with an increased abundance of tetra-unsaturated alkenones, reflecting the influence of icebergs and associated meltwater pulses and high-latitude waters at the study site. After having combined the new results with previous data from the same site, and using a variety of time series analysis techniques, we evaluate the evolution of millennial climate variability in response to changing orbital boundary conditions during the Early–Middle Pleistocene. Suborbital variability in both surface- and deep-water records is mainly concentrated at a period of ∼11 kyr and, additionally, at ∼5.8 and ∼3.9 kyr in the deep ocean; these periods are equal to harmonics of precession band oscillations. The fact that the response at the 11 kyr period increased over the same interval during which the amplitude of the response to the precessional cycle increased supports the notion that most of the variance in the 11 kyr band in the sedimentary record is nonlinearly transferred from precession band oscillations. Considering that these periodicities are important features in the equatorial and intertropical insolation, these observations are in line with the view that the low-latitude regions play an important role in the response of the climate system to the astronomical forcing. We conclude that the effect of the orbitally induced insolation is of fundamental importance in regulating the timing and amplitude of millennial scale climate variability.

Glacial induced closure of the Panamanian Gateway during Marine Isotope Stages (MIS) 95–100 ([formula omitted

The final phase of the closure of the Panamanian Gateway and the intensification of Northern Hemisphere Glaciation (NHG) both occurred during the Late Pliocene. Glacial–interglacial (G–IG) variations in sea level might, therefore, have had a significant impact on the remaining connections between the East Pacific and the Caribbean. Here, we present combined foraminiferal Mg/Ca and δ18O measurements from Ocean Drilling Program (ODP) Site 1241 from the East Pacific and ODP Site 999 from the Caribbean. The studied time interval covers the first three major G–IG Marine Isotope Stages (MIS 95–100, ∼2.5 Ma) after the intensification of NHG. Analyses were performed on the planktonic foraminifera Neogloboquadrina dutertrei and Globigerinoides sacculifer, representing water mass properties in the thermocline and the mixed-layer, respectively. Changes in sea water temperature, relative salinity, and water column stratification strongly suggest that the Panamanian Gateway temporarily closed during glacial MIS 98 and 100, as a result of changes in ice volume equivalent to a drop in sea level of 60–90 m. Reconstructed sea surface temperatures (SST) from G. sacculifer show a glacial decrease of 2.5 °C at Site 1241, but increases of up to 3 °C at Site 999 during glacial MIS 98 and 100 suggesting that the Panamanian Gateway closed during these glacial periods. The Mg/Ca-temperatures of N. dutertrei remain relatively stable in the East Pacific, but do show a 3 °C warming in the Caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification. We infer that the glacial closure of the gateway allowed the Western Atlantic Warm Pool to extend into the southern Caribbean, increasing SST (G. sacculifer) and deepening the thermocline (N. dutertrei). Additionally, ice volume appears to have become large enough during MIS 100 to survive the relatively short lasting interglacial MIS 99 so that the gateway remained closed. Towards the end of MIS 98, during MIS 97 and into MIS 96 temperatures on both sides are mostly similar suggesting water masses exchanged again. Additionally, Caribbean variations in SST and δ18Owater follow a precession-like cyclicity rather than the obliquity-controlled variations characteristic of the East Pacific and many other tropical areas, suggesting that regional atmospheric processes related to the trade winds and the InterTropical Convergence Zone (ITCZ) had a dominant impact in the Caribbean.

Timing of the descent into the last Ice Age determined by the bipolar seesaw

We present planktonic foraminiferal fauna and isotope records from the SE Atlantic that highlight the nature of millennial-scale variability over the last 100 kyr. We derive an hypothesis-driven age model for our records based on the empirical link between variations in Greenland temperature, ocean circulation and carbonate preservation in the deep SE Atlantic. Our results extend earlier findings of an anti-phase (seesaw) relationship between north and south for the largest abrupt events of Marine Isotope Stage (MIS) 3-2 and the last deglaciation. In particular we find that Heinrich Stadials were paralleled by inferred southward shifts of the thermal Subtropical Front. These were followed by pronounced rebounds of the front with the return to interstadial conditions in the north. Our results also shed light on the mechanism of glaciation. In contrast to the last deglaciation, which was a globally symmetric change superposed by interhemispheric asynchronicity, we find that the descent into full glacial conditions at the onset of MIS 4 (~70 ka) displayed interhemispheric synchrony. We suggest that this globally synchronous descent into glacial MIS 4 was preconditioned by orbital changes but that the timing was ultimately determined by abrupt changes in ocean / atmosphere circulation patterns i.e. the bipolar seesaw.

ABUNDANCE BIOZONES AND COMMUNITY STRUCTURES IN THE UPPER QUATERNARY OF ODP HOLE 994C (BLAKE RIDGE, WESTERN ATLANTIC OCEAN) COMPARED WITH MARINE ISOTOPE STAGES, GLACIAL CYCLES, AND TERMINATIONS

Bathyal and abyssal benthonic foraminiferal assemblages have been thought to undergo community- and species-level regime shifts between glacials and interglacials. Comparisons between communities and oxygen isotope curves are, however, few. Comparisons between multiple aspects of the benthonic foraminiferal community and the oxygen isotope curve are made here for the abyssal Upper Quaternary of ODP Hole 994C (Blake Ridge, western Atlantic Ocean). Presumed allochthonous species were removed from the dataset to give an in situ abyssal assemblage dominated by Brizalina lowmani with subordinate Cibicides wuellerstorfi and other species. The total number N of benthonic foraminifera/20 cm3 sediment sample, the point diversity measured using the information function H, and max(pi) (the proportional abundance of the most abundant species in each sample) all fluctuated between samples. These variables apparently mirrored the oxygen-isotope curve based on planktonic foraminifera, and so show potential for tracking marine isotope stages (MIS). However, neither abundance biozone boundaries nor species-level regime shifts (i.e., points of change in percentage carrying capacity, Kp) coincided or showed consistent associations with terminations (pronounced boundaries between isotopic maxima and minima). Cibicides wuellerstorfi was most abundant towards the base of the section, which might indicate stronger current action. Most abundance biozones (ABs) had a Type 0 community structure, but Type 1 community structure was recorded in ABs from the upper part of Glacial Cycle E (glacial MIS 10) and the lower part of Glacial Cycle D (interglacial MIS 9), for which this community structure may mark an extended period of stress. Peaks in percentage abundance of Uvigerina spp. occurred in glacial MIS 2, 6, and 8, but not in MIS 4, 10, and 12. It is, therefore, recommended that workers be cautious when using glacial-interglacial cycles to explain ecostratigraphic events in abyssal Pleistocene successions, especially in the absence of an oxygen-isotope curve.

A coccolithophore based view on paleoenvironmental changes in the open ocean mid-latitude North Atlantic between 130 and 48 ka BP with special emphasis on MIS 5e

As oceanographic changes in the North Atlantic are known to modulate global climate, they are key to the understanding of past and future climate changes. Especially the mid-latitudes of the open ocean North Atlantic may be of interest, regarding the large area covered. We therefore reconstructed past changes in productivity and hydrography from a new sediment core (MD08-3179Cq) taken in the open ocean mid-latitude North Atlantic in the vicinity of the Azores Current System. Concomitant to the reorganizations of environmental conditions in the North Atlantic between 130 and 48 ka BP, changes in coccolithophore assemblages and changes in the abundance of siliceous plankton (diatoms) indicate a southward shift of the Azores Front (AzF), and hence a southward retreat of the North Atlantic subtropical gyre, as well as an increased productivity, during glacial Marine Isotope Stage (MIS) 4, Termination II and during cold substages of MIS 5. Furthermore we hypothesize that the ecological changes led to distinct evolutionary patterns of coccolithophores, resulting e.g. in a dominance of Gephyrocapsa ornata between 76 and 105 ka BP. Additionally, high-resolution analysis of MIS 5e indicate a short reversal towards cool conditions during MIS 5e, corresponding to a basin-wide cooling event. Full interglacial conditions are reached only late in the Azores region. During MIS 5e an increased advection of Subantarctic Mode Water (SAMW), and/or the possibility to occupy new habitats after glacial conditions, result in a distinct coccolithophore productivity peak. As global temperature during MIS 5e are assumed to be similar to the expected future global climate change, MIS 5e serves as a possible scenario for future changes. Taking MIS 5e as a possible analogue for expected future climate change, our results indicate that an expected decrease in marine primary productivity, due to the expansion of the oligotrophic gyres, may be attenuated by increased coccolithophore productivity.

Evidence of silicic acid leakage to the tropical Atlantic via Antarctic Intermediate Water during Marine Isotope Stage 4

AbstractAntarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are the main conduits for the supply of dissolved silicon (silicic acid) from the deep Southern Ocean (SO) to the low‐latitude surface ocean and therefore have an important control on low‐latitude diatom productivity. Enhanced supply of silicic acid by AAIW (and SAMW) during glacial periods may have enabled tropical diatoms to outcompete carbonate‐producing phytoplankton, decreasing the relative export of inorganic to organic carbon to the deep ocean and lowering atmospheric pCO2. This mechanism is known as the “silicic acid leakage hypothesis” (SALH). Here we present records of neodymium and silicon isotopes from the western tropical Atlantic that provide the first direct evidence of increased silicic acid leakage from the Southern Ocean to the tropical Atlantic within AAIW during glacial Marine Isotope Stage 4 (~60–70 ka). This leakage was approximately coeval with enhanced diatom export in the NW Atlantic and across the eastern equatorial Atlantic and provides support for the SALH as a contributor to CO2 drawdown during full glacial development.

The chronostratigraphy of a quaternary sequence at the distal part of the nile littoral cell, Haifa Bay, Israel

AbstractThe current detailed chronostratigraphic framework of the last 1 Ma of an eastern Mediterranean sequence (Haifa Bay, Israel) aims to examine the relative roles of sea‐level changes, climate and tectonics. Seven continuous marine cores, up to ∼120 m long, were recovered from shallow water depths. The cores were dated by optically stimulated luminescence, 14C, magnetostratigraphy, 230Th/234U, 26Al/10Be, occurrence of index fossils and correlated to the global sea‐level curve and Marine Isotope Stages (MIS). The sedimentary sequence accumulated during the last ca. 1.0 Ma consists of 21 transgression–regression units with hiatuses between them. Five marine/terrestrial cycles, which occur in the lower part of the sequence, are attributed to the Jaramillo subchron and the Brunhes–Matuyama boundary, and correspond to MIS 29–21. The top ∼50 m includes three sedimentary cycles deposited in the last ca. 400 ka. The regressive phases during this interval correspond to Glacial MIS 8, 6 and 2, while the transgressions correspond to Interglacial MIS 11, 7, 5 and 1. Thus, for the first time, this study documents the longest Quaternary succession dated so far in a key area of the Levant, sensitive to global history of sea‐level changes and glacial/interglacial fluctuations. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Flux and provenance of ice-rafted debris in the earliest Pleistocene sub-polar North Atlantic Ocean comparable to the last glacial maximum

Relatively little is known in detail about the locations of the early Pleistocene ice-sheets responsible for ice-rafted debris (IRD) inputs to the sub-polar North Atlantic Ocean during intensification of northern hemisphere glaciation (iNHG). To shed new light on this problem, we present the first combined in-depth analysis of IRD flux and geochemical provenance of individual sand-sized IRD deposited in the sub-polar North Atlantic Ocean during the earliest large amplitude Pleistocene glacial, marine isotope stage (MIS) 100 (∼2.52Ma), arguably the key glacial during iNHG. IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single feldspar grains. We find that the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) of individual ice-rafted (>150μm) feldspars deposited at DSDP Site 611A, ODP Site 981 and IODP Site U1308 during MIS 100 records a shift from predominantly Archaean-aged circum-North Atlantic Ocean continental sources during early glacial ice-rafting events to dominantly Palaeozoic and Proterozoic-aged sources during full glacial conditions. The distribution of feldspars in Pb–Pb space for full glacial MIS 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial IRD belt (at IODP/DSDP Site U1308/609) during ambient (non-Heinrich-event) ice-rafting episodes of MIS 2 (∼23.8ka) than that documented for MIS 5d (∼106ka). Comparison of our early Pleistocene and last glacial cycle datasets suggests that MIS 100 was characterised by abundant iceberg calving from large ice-sheets on multiple continents in the high northern latitudes (not just on Greenland).

Suborbital-scale surface and deep water records in the subtropical North Atlantic: implications on thermohaline overturn

We reconstruct millennial-scale variations in sea surface hydrography and deep water flow in the northwestern subtropical Atlantic (Ocean Drilling Program Leg 172 Sites 1056 and 1063) with a focus on Marine Isotope Stage (MIS) 9. Together with published records from this region, the new data also afford a longer-term perspective on millennial-scale changes in meridional overturning circulation spanning two full interglacial intervals (MIS 9 and 11) as well as two full glacial intervals (MIS 10 and 12). Planktic foraminiferal δ 18O values indicate relatively stable conditions during the peak warmth of MIS 9, but three large cold excursions disrupt the otherwise smooth transition toward glacial MIS 8. There is no unique response in the Site 1063 benthic foraminiferal δ 13C values that would suggest a concomitant decrease in the relative flux of NADW during these events. Similarly, there is no persistent correlation between millennial-scale variations in surface and deep water hydrography over the entire MIS 8–13 interval. While millennial-scale variations at the sea surface are most pronounced during glacial intervals (and the transitions toward glacial intervals), millennial-scale variations in the deep water hydrography tend to be largest during the warm periods. This observation supports that rapid changes in thermohaline circulation are sensitive to driving forces other than those directly related to ice sheet size. Time series analysis shows that spectral power in the benthic foraminiferal δ 13C record contains periodicities related to the second (∼10 kyr) and fourth harmonics (∼5 kyr) of precession in this record (∼20 kyr) pointing to the importance of tropical processes.

Persisting maximum Agulhas leakage during MIS 14 indicated by massive Ethmodiscus oozes in the subtropical South Atlantic

The glacial marine isotope stage 14 (MIS 14) appears in many climate records as an unusually warm glacial. During this period an almost monospecific, up to 1.5 m thick, laminated layer of the giant diatom Ethmodiscus rex has been deposited below the South Atlantic Subtropical Gyre. This oligotrophic region is today less favorable for diatom growth with sediments typically consisting of calcareous nannofossil oozes. We have reconstructed temperatures and the stable oxygen isotopic compositions of sea surface and thermocline water (δ18Ow) from planktonic foraminiferal (Globigerinoides ruber and Globorotalia inflata) Mg/Ca and stable oxygen isotopes to test whether perturbations in surface ocean conditions contributed to the deposition of the diatom layer at ∼530 kyr B.P. Temperatures and δ18Ow values reconstructed from this diatom ooze interval are highly variable, with maxima similar to interglacial values. Since the area of the Ethmodiscus oozes resembles the region where Agulhas rings are present, we interpret these hydrographic changes to reflect the varying influence of warm and saline water of Indian Ocean origin that entered the Subtropical Gyre trapped in Agulhas rings. The formation of the Ethmodiscus oozes is associated with a period of maximum Agulhas leakage and a maximum frequency of Agulhas ring formation caused by a termination‐type position of the Subtropical Front during the unusual warm MIS 14. The input of silica through the Agulhas rings enabled the shift in primary production from calcareous nannoplankton to diatoms, leading to the deposition of the massive diatom oozes.

Enhanced Atlantic Meridional Overturning Circulation supports the Last Glacial Inception

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary ( 231Pa/ 230Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change.

Environmental implications of micromammals accumulated close to the MIS 6 to MIS 5 transition at Pinnacle Point Cave 9 (Mossel Bay, Western Cape Province, South Africa)

PP9C is a coastal cave situated on the south coast, Pinnacle Point, Mossel Bay, and contains both archeological deposits, as well as fossil micromammal accumulations. Micromammals were analyzed from facies accumulated close to the transition from MIS (Marine Isotope Stage) 6 to MIS 5, between 130 ± 9 and 120 ± 7 ka. The taphonomy of the assemblages indicates that the majority of micromammals became associated with the site when they were deposited in Spotted eagle owl or Barn owl pellets. Modern comparative studies suggest that these two predator species select a very similar suit of prey species from the available micromammal population and the fossil micromammal assemblages they produce are comparable when tracing palaeoenvironmental change. The fossil assemblages suggest that the period during which the micromammals accumulated was warm and wet, and that the vegetation within the hunting range of the owls accumulating the micromammal assemblages was relatively dense. There is, however, some evidence that at the time of deposition of the older assemblages, conditions were colder, relatively grassier, and may reflect a rather more open environment. This difference may indicate the change from glacial MIS 6 to inter-glacial MIS 5e climatic conditions. These conclusions are supported both by the habitats and habits of the micromammal faunas, as well as by multivariate analysis. E. edwardii and A. namaquensis appear only in the earliest fossil assemblages at PP9C, and their general scarcity suggests that the rocky and open habitat preferred by these two species was never available on a wide scale at Pinnacle Point. The Pinnacle Point fossil sites indicate that the soricid, C. flavescens, was a common component of the local micromammal fauna and occurred in the area during some of MIS 6, and into MIS 5, suggesting that this species was able to adapt to glacial/interglacial cycles, and may utilize drier habitats than commonly reported in the literature. The fossil evidence indicates that C. cyanea, S. infinitesimus and Saccostomys campestris are relative latecomers to the Mossel Bay region. S. campestris appears only in PP9C in surface sediments, and confirms previous suggestions that the arrival of this species to the southern Cape occurred sometime within the Holocene.

Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy

Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25–45 ka), minimal sea ice during the last deglacial (16–11 ka) and early Holocene thermal maximum (11–5 ka) and increasing sea ice during the mid-to-late Holocene (5–0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon.

Quaternary glaciation of Gurla Mandhata (Naimon’anyi)

The Quaternary glaciation of Gurla Mandhata (Naimona’nyi), an impressive, isolated dome-shaped massif situated in a remote region of southern Tibet, was examined using glacial geomorphic methods and dated using 10Be terrestrial cosmogenic nuclides. The oldest moraines, representing an expanded ice cap that stretched ∼ 5 km into the foreland of the Gurla Mandhata massif, likely formed during marine isotope stage (MIS) 10 or an earlier glacial cycle. Another glacial expansion of coalescing piedmont type occurred during the early part of the last glacial cycle or the penultimate glacial cycle, after which glaciers became restricted to entrenched valley types. Impressive latero-frontal moraines at the mouths of most valleys date to the early part of the last glacial cycle and MIS 3. A succession of six sets of moraines within the valleys and up to the contemporary glaciers show that glaciers advanced during the Lateglacial, Early Holocene, Neoglacial and possibly Little Ice Age. The change of style of glaciation throughout the latter part of the Quaternary, from expanded ice caps to deeply entrenched valley glaciers, might reflect: (1) climatic controls with reduced moisture supply to the region over time; and/or (2) tectonic controls reflecting increase basin subsidence due to detachment faulting and enhanced valley incision.