Rapid Climate Events Research Articles

Holocene temperature evolution of the subpolar North Atlantic recorded in the Mg/Ca ratios of surface and thermocline dwelling planktonic foraminifers

Mg/Ca ratio measurements have been produced from IMAGES piston core MD99-2251 using two species of planktonic foraminifera: the surface dwelling Globigerina bulloides and the thermocline dwelling Globorotalia inflata. Holocene Mg/Ca values for G. bulloides are higher and more variable (1.8–3.0 mmol/mol), with lower Mg/Ca ratios of 1.1–1.9 mmol/mol recorded for G. inflata. At no time do the thermocline Mg/Ca ratios exceed those of the surface. Comparison of the Mg/Ca records reveals a complex evolution of the upper water mass characteristics through the Holocene. The early Holocene exhibits far less distinction between surface and thermocline ratios and the Mg/Ca calibration derived temperatures in the upper water column, with the 0.4 mmol/mol offset equivalent to a temperature difference of 1–2 °C. Mg/Ca ratios diverge from early to mid Holocene and despite the increase in G. inflata ratios from ~ 6.5 ka onwards, the much more marked increase in G. bulloides after ~ 4 ka results in a clear separation of the surface and thermocline records for the remainder of the Holocene. Despite the long term increase in thermal contrast between surface and subsurface waters, there is a clear correlation between short-lived events evident in both of the Mg/Ca records, reflecting multi-decadal to centennial scale temperature fluctuations. Coolings at ~ 9 and 8.2 ka are well represented in both records, as too are further warm–cold fluctuations at ~ 5.5, 1.5 and 0.8 ka. This indicates that these rapid climate events had a common forcing that was recorded throughout the upper water column. Comparisons with the GISP2 glacio-chemical indicators of atmospheric circulation suggest that the enhanced intensity of the atmospheric circulation during the early Holocene (11–10 ka) probably explain the reduced surface thermal stratification indicated by the Mg/Ca data.

Mid-Holocene vegetation history of the central Mediterranean

This paper provides a synthesis of available palynological data from central Mediterranean lacustrine records, studying the causes of the important vegetation changes which occurred in the mid Holocene. They are illustrated by seven well-dated records, lakes Accesa, Mezzano, Vico, and Pergusa in Italy, Maliq, Voulkaria and Malo J. in the Balkans. A good tool for disentangling climate change and human impact is the combined interpretation of pollen percentage and concentration/influx data. Pollen concentration/influx drops are an indication of increased erosion in the catchment, mainly ascribable to forest reduction. There is no doubt that major synchronous changes could not have been caused by humans alone. Many southern European records show substantial differences between early- and late-Holocene vegetation, suggesting a general evolution from wetter to drier climatic conditions, in agreement with arid phases recognised by other, independent palaeoclimatic methods. Other pollen records show a different trend. The role of changing seasonality seems important for this region of the Mediterranean. Precipitation seasonality increased during the early to mid Holocene with winter precipitation attaining a maximum, and summer precipitation a minimum. At least three rapid climate events with changes in plant biomass are in evidence: an abrupt and short change around 8200 yr BP, another one centred around 6000 yr BP, and one soon after 3000 yr BP. From the beginning of the Bronze Age ( c. 4400 yr BP in this region) human impact overlapped with a climate change, probably bipartite, towards dryness. Our results show that this aridification trend began around 8000 yr BP, and culminated around 4000 yr BP.

Origin and palaeoenvironmental significance of lamination in stalagmites from Katerloch Cave, Austria

AbstractThe origin and environmental dependencies of lamination in stalagmites from Katerloch, common in speleothems from other cave sites, are examined in detail. Petrographic observations and chemical analyses (including isotopes) of stalagmites and modern calcite were combined with multi‐annual cave monitoring. All investigated stalagmites are composed of low‐Mg calcite and show white, porous laminae and typically thinner, translucent dense laminae. The binary lamination pattern results from changes in the calcite fabric: white, porous laminae are characterized by a high porosity and abundant fluid inclusions and also by enhanced vertical growth and thinning towards the flanks. Translucent, dense laminae exhibit a compact fabric and constant thickness of individual growth layers. U‐Th dating supports an annual origin of the lamination and the seasonally changing intensity of cave ventilation provides a robust explanation for the observed relationships between lamination, stable C isotopic compositions and trace elements (Mg, Sr and Ba). The seasonally variable air exchange, driven by temperature contrasts between the cave interior and outside atmosphere, modulates the rate and amount of CO2 degassing from the drip water and affects the hydrochemistry and consequently the fabric of the precipitating calcite. Although cave air composition and drip rate are both major variables in controlling CO2 degassing from the drip water, the seasonally changing ventilation in Katerloch exerts the primary control and the results suggest a secondary (amplifying/attenuating) influence of the drip rate. Drip rate, however, might be the controlling parameter for lamina development at cave sites experiencing only small seasonal cave air exchange. Importantly, the seasonally variable composition of drip water does not reflect the seasonal cycle of processes in the soil zone, but results from exchange with the cave atmosphere. The alternating porous and dense calcite fabric is the expression of a variable degree of lateral coalescence of smaller crystallites forming large columnar crystals. The white, porous laminae represent partial coalescence and form during the warm season: low calcite δ13C values are linked to low δ13C values of cave air and drip water during that time. This observation corresponds to times of reduced cave ventilation, high pCO2 of cave air, low drip water pH, lower calcite supersaturation and typically high drip rates. In contrast, the translucent, dense laminae represent more or less complete lateral coalescence (inclusion‐free) during the cold season (high calcite, drip water and cave air δ13C values), i.e. times of enhanced cave ventilation, low cave air pCO2, increased drip water pH, relatively high calcite supersaturation and typically low drip rates. In essence, the relative development of the two lamina types reflects changes in the seasonality of external air temperature and precipitation, with a strong control of the winter air temperature on the intensity of cave‐air exchange. Thick translucent, dense laminae are favoured by long, cold and wet winters and such conditions may be related closely to the North Atlantic Oscillation mode (weak westerlies) and enhanced Mediterranean cyclone activity during the cold season. Studies of speleothem lamination can thus help to better understand (and quantify) the role of seasonality changes, for example, during rapid climate events.

Isotopic characterization of rapid climatic events during OIS3 and OIS4 in Villars Cave stalagmites (SW-France) and correlation with Atlantic and Mediterranean pollen records

We present a new mid-latitude speleothem record of millennial-scale climatic variability during OIS3 from the Villars Cave that, combined with former published contemporaneous samples from the same cave, gives a coherent image of the climate variability in SW-France between ∼55 ka and ∼30 ka. The 0.82 m long stalagmite Vil-stm27 was dated with 26 TIMS U–Th analyses and its growth curve displays variations that are linked with the stable isotopes, both controlled by the climatic conditions. It consists in a higher resolved replicate of the previously published Vil-stm9 and Vil-stm14 stalagmites where Dansgaard–Oeschger (DO) events have been observed. The good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions, especially high resolution pollen records (ODP 976 from the Alboran Sea, Monticchio Lake record from southern Italy) and the nearby MD04-2845 Atlantic Ocean record, permits to draw a specific climatic pattern in SW-France during the OIS3 and to see regional differences between these sites. Main features of this period are: 1) warm events corresponding to Greenland Interstadials (GIS) that are characterized by low speleothem δ 13C, high temperate pollen percentages, warm temperatures and high humidity; among these events, GIS#12 is the most pronounced one at Villars characterized by an abrupt onset at ∼46.6 ka and a duration of about 2.5 ka. The other well individualized warm event coincides with GIS#8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher δ 13C; 2) cold events corresponding to Greenland Stadials (GS) that are clearly characterized by high speleothem δ 13C, low temperate pollen abundance, low temperature and enhanced dryness, particularly well expressed during GS coinciding with Heinrich events H5 and H4. The main feature of the Villars record is a general cooling trend between the DO#12 event ∼45.5 ka and the synchronous stop of the three stalagmites at ∼30 ka ±1, with a first well marked climatic threshold at ∼41 ka after which the growth rate and the diameter of all stalagmites slows down significantly. This climatic evolution differs from that shown at southern Mediterranean sites where this trend is not observed. The ∼30 ka age marks the second climatic threshold after which low temperatures and low rainfalls prevent speleothem growth in the Villars area until the Lateglacial warming that occurred at ∼16.5 ± 0.5 ka. This 15 ka long hiatus, as the older Villars growth hiatus that occurred between 67.4 and 61 ka, are linked to low sea levels, reduced ocean circulation and a southward shift of the Polar Front that likely provoked local permafrost formation. These cold periods coincide with both low summer 65°N insolation, low atmospheric CO 2 concentration and large ice sheets development (especially the Fennoscandian).

Early-Holocene temperature variability inferred from chironomid assemblages at Hawes Water, northwest England

This paper presents the first high-resolution chironomid-inferred mean July air temperature (C-IT) reconstruction for the early Holocene from England. The reconstruction is based on a core recovered from a terrestrialised carbonate bench at Hawes Water, a small hard-water lake in northwest England. The record shows that temperatures rose rapidly after the Younger Dryas with temperatures reaching 14.0°C at the beginning of the Holocene. Over millennial timescales, the temperature record points to a slight rise in temperatures towards the top of the sequence at around 8000 years before the year 2000 (b2k). The trend is punctuated by a series of cool oscillations (at 11 200, 11 400, 10 700, 10 400, 9300 and 8300 b2k) and by a short period (11 300 to 10 250 b2k) when temperatures were considerably warmer (up to 14.9°C). The five cool oscillations coincide with temperature reversals found elsewhere in the North Atlantic region and in the Greenland ice core records. These cool events correlate well with both meltwater fluxes from the Laurentide and Scandinavian ice sheets and periods of low solar activity. Two of these oscillations (at 9300 and 8300 b2k) vary significantly from the early-Holocene mean. C-IT shift rapidly during both these events and temperatures fall ~1.6°C below the early-Holocene mean trend for ~ 50—60 years. The results presented here provide an insight into the instability of the early-Holocene climate in the British Isles and demonstrate the sensitivity of chironomids to rapid climatic events during the early Holocene.

Rapid climatic events as recorded in Middle Weichselian thermokarst lake sediments

From a Middle Weichselian sediment sequence in the opencast brown coal mine of Reichwalde (eastern Germany), a ∼40 cm thick thermokarst gyttja deposit has been sampled. The AMS 14C dates, although at the limit of detection, indicate an early Middle Weichselian age of the gyttja. Pollen, botanical, and zoological (e.g. chironomids) macroremains have been analyzed. Botanical and chironomid taxa indicate warm climatic conditions in the bottom part of the sequence. For this lower part the botanical data suggest a minimum mean July temperature of 12–14 °C. Following this, a cooling is indicated, coinciding with an increased clastic deposition in the lake. A return to permafrost conditions is reconstructed for the upper part of the sequence. The combined evidence strongly suggests a degradation of permafrost due to increased warming in response to a D/O event as a forcing factor for the thermokarst lake formation.

Triassic–Jurassic boundary events inferred from integrated stratigraphy of the Csővár section, Hungary

Processes and causes of biotic and environmental change at the Triassic–Jurassic transition remain controversial, partly because of a scarcity of Triassic–Jurassic boundary sections studied in detail. Continuous marine strata spanning the boundary are exposed at Csővár, Hungary, where new integrated stratigraphic data were obtained from multidisciplinary investigations to help reconstruct the end-Triassic and Early Jurassic events. Boundary strata are predominantly slope to basinal carbonates deposited in a periplatform basin. The position of the system boundary is constrained by radiolarian, foraminiferan, conodont and ammonoid biostratigraphy. Pronounced radiolarian turnover is observed between assemblages assigned to the Late Rhaetian Globolaxtorum tozeri zone and the Early Hettangian Canoptum merum zone. Benthic foraminifera suffered lesser extinction. Successive conodont faunas of the latest Rhaetian Misikella posthersteini and Misikella ultima zones record a marked drop in diversity and abundance but sporadic survivors persist into the earliest Hettangian. The extinction is also recorded in a reduction of biogenic components in carbonates. Decline of benthic and planktic biota is followed by a negative δ 13C carb excursion of up to − 6‰ that is composed of short-term fluctuations revealed by dense sampling. Carbon and oxygen isotope ratios are positively correlated in the lower part of the section and appear to reflect primary variations. Drivers of the stable isotope trends are interpreted as warming in excess of + 10 °C and concomitant episodic, short-term perturbations of the global carbon cycle, possibly due to methane release from gas–hydrate dissociation induced by rapid climatic events. The main biotic and isotopic events occurred within a single sedimentary cycle but sea-level does not appear to have exerted a critical influence on these changes. The Triassic–Jurassic boundary crisis appears a short but not instantaneous event.

Understanding the past-climate history from Antarctica

Antarctic ice cores have become a unique and powerful resource for studies of climate change. They contain information on past climate, on forcing factors such as greenhouse gas concentrations, and on numerous other environmental parameters. For recent centuries, sites with high snow accumulation are chosen. They have, for example, provided the only direct evidence that carbon dioxide concentrations have increased by over 30% over the last two centuries. They have provided key datasets for other greenhouse gases, and for other forcings such as solar and volcanic. Over longer timescales, the Vostok ice core has shown how greenhouse gas concentrations and climate have closely tracked one another over the last 400 000 years. Other cores have shown detailed spatial and temporal detail of climate transitions, including the Antarctic response during rapid climate events such as Dansgaard-Oeschger events. The new core from Dome C has extended the range of ice cores back beyond 800 000 years, and even older ice could be obtained in future projects.

Large temperature variations over rapid climatic events in Greenland: a method based on air isotopic measurements

Abstract During the last glacial, characterized by a rapid climatic variability, the Greenland ice isotope–temperature relationship is biased due to changes in the hydrological cycle. An alternative palaeothermometry method, based on air isotopes, δ 15 N and δ 40 Ar, provides quantitative estimates of rapid temperature increases and suggests a different shape of rapid events compared to water isotope profiles. The temperature over five Dansgaard–Oeschger events (DO) on the NorthGRIP ice core is reconstructed: DO 18, 19, 20, 23 and 24 associated with warming events of 11, 16, 11, 10 and 16 °C, i.e. roughly twice larger than the amplitude suggested by the water isotopes. Together with similar efforts, our measurements permit to show a large variability between the different DO. To cite this article: A. Landais et al., C. R. Geoscience 337 (2005).

Modelling the oxygen-18 and rapid glacial climatic events: a data–model comparison

Abstract Using a coupled climate model of intermediate complexity that explicitly simulates the oxygen-18 behaviour, we evaluate a recent scenario of abrupt climatic variability during the last glacial period against a sediment core record of the coast of Portugal (MD95-2042). In particular, we focus on a period centred on the Heinrich Event 4 (about 40 kyrs BP) and the surrounding Dansgaard–Oeschger events to explain some features of the sediment core record and question some choices of the suggested scenario. We demonstrate here (1) that the oxygen-18 signal recorded in the planktic foraminifera during D/O events is likely to be due almost entirely to temperature at the location of this core, and (2) that we cannot reproduce the observed oxygen-18 variations in calcite for Heinrich events if we consider that the melting of icebergs occurred elsewhere than in the IRD belt. To cite this article: D.M. Roche, D. Paillard, C. R. Geoscience 337 (2005).

Rapid climate variability during warm and cold periods in polar regions and Europe

Abstract Typical rapid climate events punctuating the last glacial period in Greenland, Europe and Antarctica are compared to two rapid events occurring under warmer conditions: ( i ) Dansgaard–Oeschger event 25, the first abrupt warming occurring during last glacial inception; ( ii ) 8.2 ka BP event, the only rapid cooling recorded during the Holocene in Greenland ice cores and in Ammersee, Germany. The rate of warming during previous warmer interglacial periods is estimated from polar ice cores to 1.5 °C per millennium, without abrupt changes. Climate change expected for the 21st century should however be at least 10 times faster. To cite this article: V. Masson-Delmotte et al., C. R. Geoscience 337 (2005).

Were abrupt Lateglacial and early-Holocene climatic changes in northwest Europe linked to freshwater outbursts to the North Atlantic and Arctic Oceans?

During the Lateglacial and early Holocene, abrupt, millennial-scale climatic variations are recorded in a wide range of high-resolution proxy records from marine and terrestrial archives in NW Europe. Our review of the evidence for these rapid climate events do not show an apparent link to possible forcing factors such as long-term, orbitally induced variations in solar radiation, short-term variations in solar activity as inferred from 14C, atmospheric carbon dioxide concentration, or volcanic sulphate as recorded in the GISP2 ice-core record. There is, however, a remarkable degree of similarity with the number, duration and timing of episodes of increased flux of fresh water to the north Atlantic and Arctic Oceans from the Laurentide ice sheet and from the Baltic ice lake in SW Sweden. These freshwater outburst events occurred when continental runoff from the Laurentide ice sheet was rerouted from the Mississippi River to the Hudson River, St Lawrence River, Hudson Strait and along the Mackenzie River to the Atlantic and Arctic Oceans, and when the Baltic ice lake in SW Sweden drained to Skagerrak. Periods of increased freshwater flow to the North Atlantic and Arctic Oceans may thus provide a mechanism to explain the abrupt and significant Lateglacial and early Holocene climate events in NW Europe. The idea that freshwater outbursts might drive abrupt climate events is not new, but previous work may have underestimated the extent of support from proxy data and overestimated the influence of the Laurentide ice sheet.

Latest Quaternary rock magnetic record of climatic and oceanic change, Tanner Basin, California borderland

A high-resolution record of sediment magnetic properties and stable oxygen isotopes has been determined from marine isotope stage (MIS) 6 to the Holocene (170 ka to present day) for hemipelagic sediments (Site 1014 of Ocean Drilling Program Leg 167) from a subbasin west of the Tanner Basin, off the coast of southern California. The spacing between samples is 10 cm. The sedimentation rate in the top 20 m of the sequence was determined to be 12 cm/k.y. We have taken the intensity of anhysteretic remanent magnetization (ARM) as a measure of the concentration of magnetic minerals. The quantity of magnetic material increased during transitions from warm to cool periods; this change is inferred to have resulted from increased shelf erosion during lower sea levels. During interglacials and possibly interstadials, a reduction occurred in the quantity of magnetic material in the sediment, and magnetic susceptibility therefore dropped. This decrease seems to have resulted from dilution of the magnetic fraction due to increased biogenic deposition during these warm intervals. The ratio of ARM to ARM after 15 mT alternating-field demagnetization (ARM/ARM[15]) is used as a coercivity indicator. The magnetic properties of the sediments from the subbasin west of the Tanner Basin are largely determined by two climatically controlled fluxes of magnetic material. Large and magnetically softer titanohematite grains were deposited during times of decreasing sea level when the concentration of magnetic particles was elevated. Small magnetite grains (<2 μm) control the magnetic properties in sediments deposited during transgressions and times of high sea levels, when detrital titanohematite content was low. The ARM/ARM[15] ratio leads the δ18O curve by 0.3–0.8 m. This offset between the rock magnetic coercivity parameter and intervals of climatic change represents evidence for authigenic growth of magnetite grains near the Fe-redox boundary. The Fe-redox boundary appears to have been at 0.8 m depth during MIS 3 and at 0.3 m during MIS 5. Authigenic growth of magnetite is associated with rapid climate events as recorded by planktonic foraminiferal assemblage shifts. These relationships may have resulted from changes in oxygen concentrations in intermediate-depth waters associated with the climate shifts. Therefore the ratio of ARM/ARM[15] is suggested to be a new indicator (proxy) of past changes in oxygen levels of intermediate water.

Nonglacial rapid climate events: past and future.

The paleoclimate record makes it clear that rapid climate shifts of the 20th century are only a subset of possible climate system behavior that might occur in the absence of glacial conditions, and that climatic surprises could be a challenge for society even in the absence of significant greenhouse warming.

14C geochronology of rapid climatic events during the glacial-holocene transition

14C geochronology of rapid climatic events during the glacial-holocene transition

Correlation of climatic events between East Asia and Norwegian Sea during last deglaciation

Using a high resolution14C chronology, β13C values and organic carbon content, from loess/paleosol and peat profiles in China, we can demonstrate century scale warm-cold East Asian monsoon paleoclimatic fluctuation events and significant precipitation variability within the last deglaciation. The major climatic events recognized are the Bolling (1 300-12 500 a B.P.), Older Dryas (12 500-11 750 a B. P.), Allerod (11 750-11 200 aB.P.) and Younger Dryas (11 200-10 000 aB.P.). The stratigraphic structure of the last deglaciation sediments is characterized by frequent changes in sedimentation phases reflecting climatic instability. These high frequency, rapid climatic events can correlate with fluctuations recorded by sea surface temperatures in the Norwegian Sea. This indicates a pale-oclimate teleconnection between polar, high latitude areas and East Asian monsoon areas through westerlies and the related atmospheric pressure system.