Termination II Research Articles

Multi‐Proxy Evidence for Atlantic Meridional Overturning Circulation (AMOC) Weakening During Deglaciations of the Past 150,000 Years

AbstractDespite decades of research, the cause of deglaciations is not fully understood, leaving a critical gap in our understanding of Earth's climate system. During the most recent deglaciation (Termination I (T I)), abrupt declines in the stable carbon isotope ratio (δ13C) of benthic foraminifera occurred throughout the mid‐depth (1,500–2,500 m) Atlantic. The spatial pattern in δ13C anomalies was likely due to Atlantic Meridional Overturning Circulation (AMOC) weakening and the accumulation of respired carbon, which also yields negative excursions in carbonate ion concentration (). To investigate whether a similar pattern occurred during prior deglaciations, we developed δ13C and records from 1,800 and 2,300 m water depth in the Southwest Atlantic spanning the last 150 ka. The new records reveal negative δ13C and anomalies during Termination II (TII) and the smaller deglaciations of Marine Isotope Stages (MIS) 4/3, 5b/a, and 5d/c, suggesting AMOC weakening is a common feature of deglaciation. The anomalies are more pronounced in the shallower core following MIS 2, 4, and 6 and in the deeper core following MIS 5b and 5d. The depth‐dependent pattern is most likely due to shoaling of Northern Source Water during glacial maxima and deepening during interglacial intervals. Comparison of records from TI and TII suggests similar levels of carbon accumulation in the mid‐depth Atlantic. The Brazil Margin δ13C and results indicate the AMOC plays a key role in the series of events causing deglaciation, regardless of differences in orbital configuration, ice volume, and mean global temperature.

A climatic evaluation of the southern dispersal route during MIS 5e

Homo sapiens dispersals out of Africa are often linked to intensifications of the African and Indian Summer Monsoons. Current models advocate that dispersals along the “southern-route” into Arabia occurred during Glacial Termination-II (T-II), when lower sea-level and reduced Bab-al-Mandab width increased the likelihood of crossing. The precise phasing between sea-level and monsoon precipitation is thus key to assess the likelihood of a successful crossing or the behavioural and technological capacities that facilitated crossing. Based on a precisely-dated stalagmite record from Yemen, we reveal a distinct phase-lag of several thousand years between sea-level rise and major monsoon intensification. Pluvial conditions in Southern Arabia during MIS 5e lasted from ∼127.7 to ∼121.1 ka BP and occurred when sea-levels were already higher than at present. Based on our observations, we propose three models for the dispersal of H. sapiens which all have pertinent implications for our understanding of human technological and behavioural capacities during MIS 5e.

Millennial climate oscillations controlled the structure and evolution of Termination II

The controls that affect the structure and timing of terminations are still poorly understood. We studied a tufa deposit from the Iberian Peninsula that covers Termination II (T-II) and whose chronology was synchronized to speleothem records. We used the same chronology to synchronize ocean sediments from the North Atlantic to correlate major climate events in a common timescale. We identify two stages within T-II. The first stage started with the increase of boreal summer integrated solar insolation, and during this stage three millennial climate oscillations were recorded. These oscillations resulted from complex ocean–atmosphere interactions in the Nordic seas, caused by the progressive decay of Northern Hemisphere ice-sheets. The second stage commenced after a glacial outburst that caused the collapse of the Thermohaline Circulation, a massive Heinrich event, and the onset of the Bipolar Seesaw Mechanism (BSM) that eventually permitted the completion of T-II. The pace of the millennial oscillations during the first stage of T-II controlled the onset of the second stage, when the termination became a non-reversible and global phenomenon that accelerated the deglaciation. During the last the two terminations, the BSM was triggered by different detailed climate interactions, which suggests the occurrence of different modes of terminations.

Fire history of the unique high-elevation Snowmastodon (Ziegler Reservoir) site during MIS 6–4, with comparisons of TII to TI in the southern Colorado Rockies

Paleoecological records detailing fire and vegetation histories during previous interglacials are extremely rare. We present a unique, high-resolution, 10-m long record of fire from a high elevation conifer-dominated site – the Snowmastodon (Ziegler Reservoir) site – in the southern Rocky Mountains, USA, for the period spanning MIS 6 to MIS 4. The charcoal particle influx (CHAR) over the entire Snowmastodon record documents that fire was a significant process on this high elevation landscape during MIS 5e-MIS 5a, just as it is today, but during a period without human influence. Both vegetation and precession cycles influence fire occurrence, with warm stages (MIS 5e, 5c, 5a) exhibiting higher CHAR than cool stages (MIS 6, 5d, 5b, 4). CHAR abruptly increases at the MIS 6-MIS 5e boundary, contemporaneously with a rapid increase in arboreal pollen. A strong positive correlation during MIS 5e between CHAR and Pinus pollen strongly suggests control of charcoal production and deposition through burning of Pinus forests within the region. Subsequently, elevated CHAR is correlated to abundant Abies concolor in MIS 5c, and Picea in MIS 5a, while minimal CHAR occurs during MIS 5b when local vegetation was sagebrush steppe. Comparison of the Termination II (TII) Snowmastodon record with Termination I (TI) from several nearby published sites shows mostly similar patterns of developing forest preceding increased burning, with a lag of several hundred years. This may signify the development of a new fire regime tied specifically to the new vegetation type, as climate warmed and fine fuels accumulated in a forested community.

Timing and structure of Termination II in north China constrained by a precisely dated stalagmite record

The timing and structure of Termination II (T-II) is still debatable as the number of high-quality records is insufficient. This study presents precisely dated stalagmite δ18O data between 133.4±0.3 to 126.6±0.3 ka BP (covering most of T-II) from north China, near the northern limit of the East Asian summer monsoon (EASM), an area sensitive to climate change. The onset of the last interglacial is constrained at 129.4±0.3 ka BP, consistent with south Chinese speleothem records, further supporting the idea that Northern Hemisphere summer insolation plays an important role in initiating glacial terminations. An extended interval of heavy δ18O is observed immediately prior to this abrupt transition, named as the “Weak Monsoon Interval” (WMI) in south Chinese cave records, which was associated with the Heinrich Stadial 11 (H11) in the North Atlantic. A significant millennial-scale interstadial peaking at 132.7±0.3 ka BP is identified preceding the weakest phase of the WMI. A synchronous counterpart is also found in some south Chinese speleothem and North Atlantic alkenone Mg/Ca SST records. It is inferred that the main H11 freshwater penetration possibly occurred after 131.5 ka BP, leaving some aspects of ocean and atmospheric circulation still in interstadial mode from 134 to 131.5 ka BP. Following the onset of the last interglacial, there was a millennial-scale “pause” in our δ18O record, synchronized with a “slowdown” in the rate of decrease in δ18O in south Chinese cave records. This is possibly a large regional climate oscillation, as it is also identified in some North Atlantic records, but one which is too weak to be a Younger Dryas (YD)-type event.In summary, compared to south Chinese cave records, significant millennial-scale climate oscillations before and after the synchronous onset of the last interglacial is the main feature of our record. Nevertheless, the sequence of these climate events remains very different from Termination I (T-I), which is possibly ascribed to the stronger insolation, higher atmosphere CO2, and the resultant faster and greater meltwater pulse to the North Atlantic during T-II than during T-I.

Depositional and sea-level history from MIS 6 (Termination II) to MIS 3 on the southern continental shelf of South Africa

Pleistocene shoreline deposits comprised of calcified shallow marine (palaeobeach) and aeolian (palaeodune) facies found along mid-latitude coastlines can be useful indicators of past sea levels. Here, we describe a succession of such deposits that are presently exposed both above (subaerial) and below (submerged) mean sea level along the southern Cape coast of South Africa, 18 km east of the town of Mossel Bay. The submerged units provide a window on Late Pleistocene coastal processes, as palaeoshoreline deposits in this study extend to water depths of up to 55 m on the mid-shelf. Five sedimentary facies were identified in the strata and were compared to modern depositional environments of the local littoral zone, which include aeolian dune, upper shoreface, foreshore, intertidal swash and back-barrier settings. Twenty-two geological units were observed and mapped. Some of these units were directly dated with optically stimulated luminescence (OSL) dating. OSL ages were obtained for ten samples from the subaerial and twelve samples from the submerged deposits. Those geological units not directly dated were interpreted based on sedimentology and field/stratigraphic relationships to dated units. The stratigraphy and chronology of the succession indicates a record of initial deposition during Termination II (T-II) meltwater events, preceding and leading to marine isotope stage (MIS) 5e. Indicators for multiple sea-level fluctuations between MIS 5d and MIS 4, and sediment deposition at the end of MIS 4 and start of MIS 3 are also found. Both regressive and transgressive depositional cycles are well-preserved in the succession. We propose that palaeodune and palaeobeach deposits along the South Coast of South Africa have no clear preference for deposition during sea-level transgressions or regressions. Sediment deposition more closely mirrors the rate of sea level change, with deposition and preservation either during times of rapid sea-level movement, or oscillation around still-stand events. Periods of relatively slow average rise or fall of sea level are represented by erosional planation surfaces in this record.

Timing and nature of the penultimate deglaciation in a high alpine stalagmite from Switzerland

The timing and nature of the penultimate deglaciation, also known as Termination II (T-II), is subject of controversial discussions due to the scarcity of precisely-dated palaeoclimate records. Here we present a new precisely-dated and highly-resolved multi-proxy stalagmite record covering T-II from the high alpine Schafsloch Cave in Switzerland, an area where climate is governed by the North Atlantic. The inception of stalagmite growth at 137.4 ± 1.4 kyr before present (BP) indicates the presence of drip water and cave air temperatures of above 0 °C, and is related to a climate-induced change in the thermal state (from cold-to warm-based) of the glacier above the cave. The cessation of stalagmite growth between 133.1 ± 0.7 and 131.9 ± 0.6 kyr BP is most likely related to distinct drop in temperature associated with Heinrich stadial 11. The resumption of stalagmite growth at 131.9 ± 0.6 kyr BP is accompanied by an abrupt increase in temperature and precipitation as indicated by distinct shifts in the oxygen and carbon isotopic composition as well as in trace element concentrations. The mid-point of T-II is around 131.8 ± 0.6 kyr BP in the Schafsloch Cave record is significantly earlier compared to the age of 129.1 ± 0.1 kyr BP in the Sanbao Cave record from China. The different ages between both records can be best explained by the competing effects of insolation and glacial boundary forcing on seasonality and snow cover extent in Eurasia.

Mixed Carbonate–Siliciclastic Sedimentation Along the Great Barrier Reef Upper Slope: A Challenge To the Reciprocal Sedimentation Model

Abstract Results of studies involving numerous cores and ODP holes along the Great Barrier Reef (GBR) margin and adjacent Queensland Trough and Queensland Plateau have challenged the use of a reciprocal sedimentation model to describe the sedimentary response of slope and basin settings to glacioeustatic sea-level fluctuations. Upper-slope sedimentation results from the relationships between sea-level fluctuations, antecedent topography, and regional climate that play an important role in the type and amount of sediment deposited on the upper slope during glacial, deglacial, and interglacial times. During the Last Glacial Maximum (LGM, > 20 ka ago) upper-slope sediments generally lacked siliciclastic material and are characterized by very low accumulation rates, whereas early deglacial-time (Termination I, TI) deposits are dominated by a siliciclastic and neritic carbonate pulse. Siliciclastic sedimentation was significantly reduced in the Holocene, while carbonate sedimentation remains elevated. A new borehole, IODP Expedition 325 Hole M0058A (Hole 58A), recovered 82% of a 40.4 m hole on the upper slope east of Noggin Passage on the central GBR margin near Cairns, Australia. Hole 58A provides a detailed sedimentary record during Termination II (TII), Marine Isotope Stage 6/5e (MIS-6/5e), deglacial transition, and through most of interglacial MIS-5. This hole, along with two others (ODP Leg 133 Holes 820A and 819A from the upper slope east of Grafton Passage), show carbonate–siliciclastic cyclicity as the result of glacioeustatic change with the GBR shelf. Sedimentation at Hole 58A is consistent with that of previous studies along the GBR margin (focusing on the LGM to present), and extends the upper-slope sedimentary record back to TII and interglacial MIS-5. A siliciclastic pulse similar to the one during TI occurred during the penultimate deglaciation, TII; however, the maximum neritic aragonite export to the upper slope occurred not during peak MIS-5e highstand when sea level was a few meters above modern position, but subsequently during a time (MIS-5d to 5a) when lowered sea level fluctuated between 30 and 50 m below present sea level. Siliciclastic sediments were reworked and exported to the upper slope when the lowstand fluvial plain was re-flooded, whereas neritic carbonate export to the slope reached a maximum when sea level fell and much of the mid to outer shelf re-entered the photic zone, subsequent to a drowning interval. Thus, this analysis refines the mixed-sedimentation models of upper-slope sedimentation along the central GBR margin during the penultimate deglacial transgression and subsequent interglacial early and late highstand. This study provides further evidence that mixed carbonate–siliciclastic margins do not always behave in a predictable manner and that mixed margins both modern and ancient would benefit from detailed study of sediment transport in the context of sea-level rise and fall.

Termination-II interstadial/stadial climate change recorded in two stalagmites from the north European Alps

Understanding the sequence of events that take place during glacial-interglacial climate transitions is important for improving our knowledge of abrupt climate change. Here, we present a new stacked, high-resolution, precisely-dated speleothem stable isotope record from the northern Alps, which provides an important record of temperature and moisture-source changes between 134 and 111 ka for Europe and the wider North Atlantic realm. The record encompasses the penultimate deglaciation (Termination II (TII)), which lies beyond the limit of radiocarbon dating, thus providing an important new archive for a crucial period of rapid paleoclimate change. Warmer and wetter ice-free conditions were achieved by 134.1 ± 0.7 ka (modelled ages) as indicated by the presence of liquid water at the site. Temperatures warmed further at 133.7 ± 0.5 ka and led into an interstadial, synchronous with slightly elevated monsoon strength during the week monsoon interval. The interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in Atlantic Meridional Overturning Circulation (AMOC) and a reduction in North Atlantic Deep Water (NADW) formation. The interstadial ended with a more extreme cold reversal lasting 500 years in which NADW formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards. The main warming associated with TII was very rapid, taking place between 130.9 ± 0.9 and 130.7 ± 0.9 ka coeval with initial monsoon strengthening. Temperatures then plateaued before being interrupted by a 600-year cold event at 129.1 ± 0.6 ka, associated once again with penetration of polar waters southwards into the North Atlantic and a slowdown in monsoon strengthening. Sub-orbital climate oscillations were thus a feature of TII in the north Atlantic realm, which broadly resemble the Bølling/Allerød-Younger Dryas-8.2 ka event pattern of change observed in Termination I despite monsoon records indicating strong differences between the last and penultimate deglaciation.

Great Basin hydrology, paleoclimate, and connections with the North Atlantic: A speleothem stable isotope and trace element record from Lehman Caves, NV

We present a record of speleothem stable isotope (δ18O, δ13C) and trace element (Mg/Ca, Sr/Ca) variations from Lehman Caves, Nevada for an interval of time (139–128 ka) that encompasses the penultimate glacial termination, Termination II (T-II). Additional growth phases provide data from about 123 ka, a time that correlates with Marine Isotope Stage (MIS) 5e, and about 84 ka and between 82 and 81 ka (MIS 5a). Chronologies from two new stalagmites are anchored by thirty-six uranium–thorium dates. We also present new trace element data from stalagmite LC-2, which has a previously published uranium–thorium chronology and stable isotope record of T-II (Shakun et al., 2011). Our T-II δ18O record broadly replicates that of the Shakun et al. (2011) and Lachniet et al. (2014) records of this time, recording low values from 139 to 135 ka followed by an approximately 3.5‰ increase over an extended interval between 134 and 129 ka. This rise in δ18O values occurs during Heinrich Stadial 11 and the associated Weak Monsoon Interval observed in Chinese caves; our record broadly follows the marine termination, rising boreal summer insolation, and the rise in atmospheric CO2. We infer that this shift results from temperature increase due to increasing atmospheric CO2 and potentially a change in moisture source or precipitation seasonality from greater influence of the North American Monsoon accompanying summer insolation increase. It is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes. Trace element ratios and δ13C values are largely decoupled from δ18O values, showing minimal variation between 139 and 130 ka, for the duration of the Chinese Weak Monsoon Interval. However, these values increase sharply between 130 and 128 ka, which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions. This abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the East Asian summer monsoon, which marks the end of both the Weak Monsoon Interval and Heinrich Stadial 11. Our records demonstrate a link between North Atlantic climate and Great Basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in Atlantic Meridional Overturning Circulation affecting the strength of the Aleutian Low.

Climate science: timing is everything during deglaciations.

Links between various climate records for the North Atlantic Ocean and the Mediterranean Sea have helped to identify a potential mechanism that enhanced sea-level rise during the last interglacial time interval. See Letter p.197 A central goal of palaeoclimate research is that of deciphering the mechanisms responsible for major state shifts in the Earth system, such as between glacial and interglacial conditions. This has proven difficult enough even for the last glacial termination (T-I), much less termination II (T-II), which ended glacial conditions about 130,000 years ago. Gianluca Marino et al. use new and existing data to demonstrate a link, within uncertainties, between Heinrich Stadial 11 (HS11) — a prominent Northern Hemisphere cold event — and the timing of peak sea level rise during T-II. A strong Southern Hemisphere warming also occurred during HS11, consistent with the idea of a bipolar seesaw that would probably have promoted Antarctic ice sheet melting. In contrast, rapid sea level rise in T-1 clearly postdated Heinrich Stadial 1. Possibly in response to differing CO2 and insolation conditions during T-I and T-II, fundamentally different mechanisms seem to be at work in triggering glacial terminations.

Glacial history and paleoceanography of the southern Yermak Plateau since 132 ka BP

The southern Yermak Plateau (YP) is situated at the entrance to the Arctic Ocean in the narrow Marginal Ice Zone (MIZ) between the Polar and Arctic Fronts, north-west of Svalbard. A gravity core JM10-02GC has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the Svalbard–Barents Sea Ice Sheet (SBIS) during the Last Interglacial–Glacial cycle. The distribution of planktic and benthic foraminifera, planktic and benthic oxygen and carbon isotopes and variations in ice-rafted debris (IRD) has been investigated. The sediment core covers the time interval from the Marine Isotope Stage (MIS) 6/5e transition (Termination II, c. 132 ka BP) to the early Holocene. During Termination II (TII), the SBIS retreated and the sea ice margin was in distal position whereas during MIS 5 to MIS 4 the sea ice margin was close to the core site. Several core intervals interpreted as representing MIS 5e, MIS 5c, MIS 5a, MIS 3 and MIS 1 were barren of calcareous microfossils whereas the intervals representing MIS 4 and MIS 2 were characterised by high productivity (HP) of planktic and benthic foraminifera. These “glacial” HP zones were associated with the open water conditions resulting from the advection of Atlantic Water (AW) and retreat of the sea ice margin. The barren zones during MIS 5, MIS 3 and MIS 1 resulted from the proximity of the sea ice margin whereas during MIS 2 the likely cause was an advance of the SBIS.

Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation

Abstract. A maximum in the strength of Agulhas leakage has been registered at the interface between the Indian and South Atlantic oceans during glacial Termination II (T-II). This presumably transported the salt and heat necessary for maintaining the Atlantic circulation at rates similar to the present day. However, it was never shown whether these waters were effectively incorporated into the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern oceans. To resolve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic Basin than previously studied. Analysis of a 60 yr data set from the global-nested INALT01 model allows us to relate density perturbations at the depth of the thermocline to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of variability of individual Globorotalia truncatulinoides δ18O. We reveal high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic Gyre around T-II. Our record closely follows the published quantifications of Agulhas leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support for the view of a prominent role of the Agulhas leakage in the shift from a glacial to an interglacial mode of the Atlantic circulation.

Vegetation and climate in Southern Hemisphere mid-latitudes since 210 ka: new insights from marine and terrestrial pollen records from New Zealand

Paleo-vegetation records developed from marine sedimentary sequences offer considerable potential for examining changes in terrestrial climate beyond the range of 14C dating because they can be independently dated by δ18O stratigraphy. Here we present the first pollen record of vegetation from a marine core site in the Tasman Sea, TAN0513-14 (42°18′S, 169°53′E), ∼110 km west of New Zealand's South Island. An independent chronology provided by correlating the Globigerina bulloides δ18O record at TAN0513-14 to a global isotope stack shows that the record extends back to 210 ka. Glacial to interglacial changes in palynomorph content are characterised by shrub and podocarp-broadleaf forest taxa respectively and are correlated with similar changes in the ca 150 kyr-long terrestrial pollen record from Okarito Pakihi (bog), 110 km to the south southeast. Both records are placed on the same timescale by matching variations in Dacrydium cupressinum and Fuscospora between sites, with a unique tie point provided by the ca 25.4 ka Kawakawa Tephra. Our Southern Hemisphere mid-latitude vegetation records show forest extent is greatest during periods of low ice volume, high mean annual sea surface temperature (MASST) and anti-phased with local insolation intensity. However, there are several features not attributable to changes in mean annual temperature. First, a fundamental change in forest composition occurred at Termination II (TII), with a loss of southern beech (Nothofagus) from the study area. Second, the amplitude of MASST change through MIS 5 is not reflected in corresponding changes in forest extent, suggesting other feature(s) of regional climate (seasonality, frostiness, ice cover) exert important controls over vegetation patterns at these latitudes.

Milankovitch-paced Termination II in a Nevada speleothem?

[1] The Devils Hole (DH) calcite record from the Great Basin, Nevada, provided the first radiometrically dated time series of late-Pleistocene climate fluctuations,. In doing so, DH suggested that the penultimate deglaciation, Termination II (T-II), occurred at 142 ± 3 ka, which is ∼10 kyr before the associated rise in summer insolation, helping to launch the “causality problem” for Milankovitch. The interpretation of the DH record has been subject to considerable discussion ever since. We present the first attempt to reproduce the DH record of an early T-II in the Great Basin based on a stalagmite from Lehman Caves, Nevada, which is ∼400 km northeast of Devils Hole. Our speleothem records at least the latter part of T-II over its period of growth from ∼133–129 ka, which appears to disagree with the early timing of T-II in DH. DH also exhibits important differences from many other paleoclimate records over the past two deglaciations, though these are reduced somewhat after ice-volume correcting DH δ18O. We suggest that the climatic signal in the DH record remains to be fully explained.

Deep water variability on the southern Agulhas Plateau: Interhemispheric links over the past 170 ka

Sortable silt mean grain sizes together with oxygen and carbon isotopic data produced on the benthic foraminiferal species Fontbotia wuellerstorfi are used to construct high‐resolution records of near‐bottom flow vigour and deep water ventilation at a core site MD02‐2589 located at 2660 m water depth on the southern Agulhas Plateau. The results suggest that during glacial periods (marine oxygen isotope stages 2 and 6, MIS 2 and MIS 6, respectively), there was a persistent contribution of a well‐ventilated water mass within the Atlantic to Indian oceanic gateway with a δ13C signature similar to present‐day Northern Component Water (NCW), e.g., North Atlantic Deep Water (NADW). The records of chemical ventilation and near‐bottom flow vigor reflect changes in the advection of northern source waters and meridional variability in the location of the Antarctic Circumpolar Current and its associated fronts. We suggest that during Termination II (TII), changes in chemical ventilation are largely decoupled from near‐bottom physical flow speeds. A mid‐TII climate optimum is associated with a low‐flow speed plateau concurrent with a period of increased ventilation shown in the benthic δ13C of other Southern Ocean records but not in our benthic δ13C of MD02‐2589. The climate optimum is followed by a period of southern cooling around 128 ka coincident with a stronger influence of NCW to interglacial levels at around 124 ka. All proxy records show a near synchronous and rapid shift during the transition from MIS 5a‐4 (73 ka). This large event is attributed to a rapid decrease in NADW influence and replacement over the Agulhas Plateau by southern source waters.

Sub-orbital sea-level change in early MIS 5e: New evidence from the Gulf of Corinth, Greece

New evidence from uplifted marine isotope stage (MIS) 5e carbonate deposits in the Gulf of Corinth demonstrate two rapid, sub-orbitally forced, sea-level oscillations in the early part of MIS 5e. Microbial bioherms with inter-grown marine coralline algae are interpreted as early highstand deposits. Presence of thin vadose flowstone (speleothem) coating inter-bioherm surfaces mark a short-lived regression of > 10 m, followed by sea-level recovery and re-establishment of the highstand, marked by coralline algae coating inter-bioherm cavity surfaces. These marine algae are then coated by a younger vadose flowstone, thick enough to provide an uncontaminated U/Th date of 134.8 ± 2.0 ka. The dated flowstone is itself encrusted by marine fauna and the entire sequence overlain by highstand marine sediments and marine aragonite cements dated to 114–118 ka, part of the sustained MIS 5e highstand. The age of the younger flowstone demonstrates that the early highstand occurred before 134.8 ± 2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than ∼ 136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (± 4) m below present sea-level, 6–18 (± 4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of > 10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr. The flowstone dated at 134.8 ± 2.0 ka is interpreted to record the early part of the ‘Aladdin's Cave' regressive event from Papua New Guinea, although in Greece only the first 16 m of the event is recorded. The new data presented here support a recently published Red Sea TII sea-level curve: they also highlight minor discrepancies in the absolute dating of these early MIS 5e sea-level events worldwide.

Paleoclimatic variations in foraminifer assemblages from the Alboran Sea (Western Mediterranean) during the last 150 ka in ODP Site 977

Detailed analysis of the planktonic foraminifera assemblages of ODP Site 977, situated in the Alboran Sea (36°1,9′N; 1°57,3′W), led us to recognize 42 planktonic foraminiferal events that occurred during marine isotope stages (MIS) 4 and 5. These events were defined by changes in the abundances of Neogloboquadrina pachyderma (right and left coiling), Turborotalita quinqueloba, Globorotalia scitula, Globorotalia inflata, Globigerina bulloides and Globigerinoides ruber (white and pink varieties). Foraminiferal assemblages changed in response to glacial–interglacial and millennial climate variability throughout the last 150 ka. Based on the estimation of sea surface temperatures (SST) using the modern analog technique and the oxygen isotope data measured in G. bulloides, we inferred the oxygen isotopic composition of sea water ( δw). SST increased in the Alboran Sea during the main Dansgaard–Oeschger Interstadials, such as interstadial 19 to 24. Even though N. pachyderma (left coiling) is very scarce before Heinrich Event (HE) 6, three cold pulses can be identified, between 65 and 85 ka ago. Moreover, increases in abundance of T. quinqueloba and G. scitula are recorded during D–O Stadials 20 and 21. The maximum temperature, which was attained during the Last Interglacial, was about 2 °C higher than recent temperature and that reached over the Holocene. Planktic foraminifera assemblages and paleotemperatures remained cold 3 ka after the beginning of Termination II (T-II), 130 ka ago, probably in connection with the occurrence of Heinrich event 11 in the North Atlantic. The abundance of G. bulloides during the deposition of organic rich layers (ORLs) of MIS 5, accompanied by lower isotope values in surface waters ( δw), could indicate the presence of a fresher surface layer associated with an increase in marine surface productivity.

Surface and deep water changes in the subpolar North Atlantic during Termination II and the Last Interglaciation

To reconstruct the history of water mass exchange between the NE Atlantic and the Nordic seas, sediment cores from ∼2 km water depth were studied across Termination II (TII) and through the last interglaciation (MIS5e). During early TII the sudden appearance of the low‐latitude planktonic foraminifera Beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal δ18O. Since other proxies indicate that surface waters were cold and stratified because of meltwater, conditions which prevented near‐surface thermohaline circulation and vertical convection in the Nordic seas, water mass exchange between the two areas occurred at the subsurface. During later TII, surface conditions changed, and this subsurface circulation style was eventually replaced by vertical convection. In the Nordic seas, B. megastoma vanished from the record together with ice‐rafted debris (IRD) at the end of TII, while subpolar foraminiferal abundance rose. Peak interglacial conditions with intensive vertical convection now fully developed, generating a bottom water temperature gradient of ∼4°C between the two areas. However, surface water temperatures deteriorated in the Nordic seas already notably before IRD recurred, and δ18O increased at the end of MIS5e.

A study on refraction of waves in prismatic channels : Beitinjani Khalil and Ernest F. Brater, 1965. J. Wat. Ways Harb. Div. Am. Soc., civ. Engrs. 91 (WW3): 37–64.

Detailed analysis of the planktonic foraminifera assemblages of ODP Site 977, situated in the Alboran Sea (36°1,9′N; 1°57,3′W), led us to recognize 42 planktonic foraminiferal events that occurred during marine isotope stages (MIS) 4 and 5. These events were defined by changes in the abundances of Neogloboquadrina pachyderma (right and left coiling), Turborotalita quinqueloba, Globorotalia scitula, Globorotalia inflata, Globigerina bulloides and Globigerinoides ruber (white and pink varieties). Foraminiferal assemblages changed in response to glacial–interglacial and millennial climate variability throughout the last 150 ka. Based on the estimation of sea surface temperatures (SST) using the modern analog technique and the oxygen isotope data measured in G. bulloides, we inferred the oxygen isotopic composition of sea water (δw). SST increased in the Alboran Sea during the main Dansgaard–Oeschger Interstadials, such as interstadial 19 to 24. Even though N. pachyderma (left coiling) is very scarce before Heinrich Event (HE) 6, three cold pulses can be identified, between 65 and 85 ka ago. Moreover, increases in abundance of T. quinqueloba and G. scitula are recorded during D–O Stadials 20 and 21.The maximum temperature, which was attained during the Last Interglacial, was about 2 °C higher than recent temperature and that reached over the Holocene. Planktic foraminifera assemblages and paleotemperatures remained cold 3 ka after the beginning of Termination II (T-II), 130 ka ago, probably in connection with the occurrence of Heinrich event 11 in the North Atlantic.The abundance of G. bulloides during the deposition of organic rich layers (ORLs) of MIS 5, accompanied by lower isotope values in surface waters (δw), could indicate the presence of a fresher surface layer associated with an increase in marine surface productivity.