Periods Of Rapid Climate Change Research Articles

Rock-slope failure following Late Pleistocene deglaciation on tectonically stable mountainous terrain

The ages of 31 postglacial rock-slope failures (RSFs) in Scotland and NW Ireland, derived from 89 cosmogenic isotope exposure ages, are employed to analyse the temporal pattern of failure and its relationship to the timing of deglaciation, rates of glacio-isostatic crustal uplift and periods of rapid climate change. RSF ages span almost the whole period since ice-sheet retreat, from 18.2 ± 1.2 ka to 1.7 ± 0.2 ka, or from 17.1 ± 1.0 ka to 1.5 ± 0.1 ka, depending on the production rate used in 10Be age calculation, but catastrophic failure of rock slopes was ∼4.6 times more frequent prior to ∼11.7 ka than during the Holocene. 95% of dated RSFs at sites deglaciated during retreat of the last ice sheet occurred within ∼5400 years after deglaciation, with peak RSF activity 1600–1700 years after deglaciation. This time lag is inferred to represent (1) stress release initiated by deglacial unloading, leading to (2) time-dependent rock mass strength degradation through progressive failure plane development, and ultimately (3) to either spontaneous kinematic release or failure triggered by some extrinsic mechanism. By contrast, 11 dated RSFs at sites reoccupied by glacier ice during the Younger Dryas Stade (YDS) of ∼12.9–11.7 ka exhibit no clear temporal pattern, suggesting that glacial reoccupance during the YDS was ineffective in preconditioning a renewed cycle of enhanced RSF activity. Comparison of timing of individual RSFs with that of deglaciation and rapid warming events at ∼14.7 ka and ∼11.7 ka suggests that glacial debuttressing, enhanced joint water pressures during deglaciation and thaw of permafrost ice in rock joints could have triggered failure in only a small number of cases. Conversely, the timing of maximum RSF activity following ice-sheet deglaciation corresponds broadly with maximum rates of glacio-isostatic crustal uplift, suggesting that the two are linked by enhanced seismic activity. A seismic failure trigger is consistent with full-slope failure at all sites where failure planes are clearly defined. Our results indicate that numerous RSFs must have occurred in areas that were reoccupied by glacier ice during the YDS, but have not been identified because runout debris was removed by YDS glaciers. More generally, they provide the first reliably-dated body of evidence to support the view that retreat of the last ice sheets in tectonically-stable mountainous terrain initiated a period of enhanced rock slope failure due to deglacial unloading and probably Lateglacial seismic activity, implying that most undated RSFs in such areas are probably of Lateglacial or very early Holocene age. They also demonstrate, however, that a low frequency of RSF activity extended throughout the Holocene.

Quantifying bioturbation of a simulated ash fall event

Abstract Tephrochronology allows the establishment of ‘isochrons’ between marine, lacustrine, terrestrial and ice cores, typically based on the geochemical fingerprint of the tephra. The development of cryptotephrochronology has revealed a vast inventory of isochrons which hold the potential to improve stratigraphic correlation and identify systemic leads and lags in periods of rapid climate change. Unfortunately, bioturbation acts to blur these isochrons, reducing the temporal resolution in marine and lacustrine records. In order to better resolve these event horizons, we require a better understanding of bioturbative processes, and the depth and time over which they operate. To this end, an ash fall event was simulated on the intertidal zone of the Eden Estuary, Fife, Scotland and sediment cores were collected over 10 days. A novel approach to tephra quantification was developed, using the imaging software ImageJ. Our results showed limited bioturbation (mixed depth=18 mm), most likely owing to the fine grain size, low-energy environment and the resulting faunal composition of the sediments. These results imply a strong ecological control on bioturbation, and suggest that inferences may be made about palaeoenvironments from the observed bioturbation profiles. supplementary material: The ImageJ macro used in this study, as well as raw tephra concentration data and details of the method validation are available at http://www.geolsoc.org.uk/SUP18725 .

Postglacial climate and fire‐mediated vegetation change on the western Olympic Peninsula, Washington (USA)

The mode and tempo of forest compositional change during periods of rapid climate change, including the potential for the fire regime to produce nonlinear relationships between climate and vegetation, is a long‐standing theme of forest ecological research. In the old conifer forests of the coastal Pacific Northwest, fire disturbances are sufficiently rare that their relation to climate and their ecological effects are poorly understood. We used a 14 700‐year high‐resolution sediment record from Yahoo Lake on the Olympic Peninsula, Washington, USA, to examine vegetation (landscape vegetation from pollen and local vegetation from macrofossils) and fire (landscape fire from total charcoal and local fire from charcoal peaks) in conjunction with independent records of climate. We hypothesized that the successional stage of the local forest will exhibit alternate stable states over a range of fire activity, that species turnover will increase abruptly above a certain level of fire activity and that both responses would be more gradual at the landscape scale than the local scale. Supporting these hypotheses, at the local scale, we found strong evidence for alternate stable states of late vs. early successional communities and inertia of species turnover to changing fire activity. At the landscape scale, vegetation responded more gradually to changing fire activity. From 14 700 to 7000 years ago, high landscape vegetation turnover occurred along with high landscape fire activity, especially during the warm summers of the early Holocene. In several instances, local species turned over completely following fire events but several centuries after climate change. In contrast, during the last 7000 years, the local forest composition was dominated by late‐successional species with little species turnover, despite periods of moderate fire activity. We suggest that the relatively minor climate fluctuations of the past 7000 years were not sufficient to cause large‐scale species turnover after fire. The Yahoo Lake fire and vegetation record of the early Holocene provides a model for dramatic ecosystem change following an anticipated shift to warmer summer temperatures.

Late Holocene Climate Change and the Origin of the “Figurine Complex” In Grand Canyon, Arizona

Abstract Hundreds of split-twig figurines have been recovered from caves in Grand Canyon and are associated with a hunting ritual that dates from 4200–3100 14C yrs before present (BP). The caves chosen for this ritual all have Pleistocene remains of big game animals visible in packrat middens or surface deposits at the entrances. Presumably, Archaic hunter-gatherers identified these sites as entrances to the Underworld where the fossil remains represented ancestral animals. We examine the known chronology for these sites in Grand Canyon and postulate that the origin of this ritual is correlated with a period of rapid climate change that occurred on both global and regional scales beginning at ∼4000 BP. Increasingly variable conditions and the onset of modern El Nino Southern Oscillation (ENSO) patterns in the eastern Pacific at that time probably negatively affected productivity of big game species in years with decreased winter precipitation. Thus, the caves became foci for a hunting ritual with figurine...

A multiproxy record of postglacial climate variability from a shallowing, 12-m deep sub-alpine bog in the southeastern San Juan Mountains of Colorado, USA

Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18–13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8–11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7–7.9, 7.0–6.9, 5.4–5.2, 3.3–3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds resolution to previous regional records and indicates that the periodicity of climate variability changed from 2000–3000 years to 700–1100 years around 6 cal. kyr BP and to <500 years after 3.5 cal. kyr BP. Overall, our record provides important, relatively high-resolution paleoclimatic information for this remote region of the southern Rockies.

High‐resolution record of export production in the eastern equatorial Pacific across the Eocene‐Oligocene transition and relationships to global climatic records

Understanding changes in export production through time provides insight into the response of the biological pump to global climate change, particularly during periods of rapid climate change. In this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the Eocene‐Oligocene transition (EOT). In addition, we consider if these export production variations are dominantly controlled by orbitally driven climate variability. To accomplish these objectives, we report changes in export production in the Eastern Equatorial Pacific (EEP) from Site U1333 across the EOT reconstructed from a high‐resolution record of marine barite accumulation rates (BAR). BAR fluctuations suggest synchronous declines in export production associated with the two‐step increases in oxygen isotopes that define the transition. The reduction in productivity across the EOT suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition. We also report a previously undocumented peak in EEP export productivity before the EOT onset. This peak is consistent with export production proxies from the Southern Ocean, potentially implying a global driver for this precursor event. We propose that this enhanced export production and the associated carbon sequestration in the late Eocene may have contributed to the pCO2 drawdown at the onset of Antarctic glaciation.

Water, plants, and early human habitats in eastern Africa

Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa--Olduvai Gorge. We convert sedimentary leaf- and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water-lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lake-water δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C(4)-dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm · y(-1) and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.

Early–Middle Holocene vegetation history, climate change and human activities at Lago Riane (Ligurian Apennines, NW Italy)

The radiocarbon-dated palaeoecological study of Lago Riane (Ligurian Apennines, NW Italy) presented here forms part of a wider investigation into the relationships between Holocene vegetation succession, climate change and human activities in the northern Apennines. The record of vegetation history from Lago Riane indicates that, since the end of the last glaciation, climate change and prehistoric human activities, combined with several local factors, have strongly influenced the pattern and timing of natural vegetation succession. The pollen record indicates an important change in vegetation cover at Lago Riane at ~8500–8200 cal. years b.p., coincident with a well-known period of rapid climate change. At ~6100 cal. years b.p., Fagus woodland colonised Lago Riane during a period of climate change and expansion of Late Neolithic human activities in the upland zone of Liguria. A marked decline in Abies woodland, and the expansion of Fagus woodland, at ~4700 cal. years b.p., coincided with further archaeological evidence for pastoralism in the mountains of Liguria during the Copper Age. At ~3900–3600 cal. years b.p. (Early to Middle Bronze Age transition), a temporary expansion of woodland at Lago Riane has been provisionally attributed to a decline in human pressure on the environment during a period of short-term climate change.

The Younger-Dryas Cold reversal:Ice-Earth-Oceab Intercations During a Period of Rapid Climate Change

The Younger-Dryas Cold reversal:Ice-Earth-Oceab Intercations During a Period of Rapid Climate Change

Unanticipated biological changes and global warming

Evidence of global warming is now unequivocal, and studies suggest that it has started to influence natural systems of the planet, including the oceans. However, in the marine environment, it is well-known that species and ecosystems can also be influenced by natural sources of large-scale hydro-climatological variability. The North Atlantic Oscillation (NAO) was negatively correlated with the mean abundance of one of the subarctic key species Calanus finmarchicus in the North Sea. This correlation was thought to have broken down in 1996, however, the timing has never been tested statistically. The present study revisits this unanticipated change and reveals that the correlation did not break down in 1996 as originally proposed but earlier, at the time of an abrupt ecosystem shift in the North Sea in the 1980s. Furthermore, the analyses demonstrate that the correlation between the NAO and C. finmarchicus abundance is modulated by the thermal regime of the North Sea, which in turn covaries positively with global temperature anomalies. This study thereby provides evidence that global climate change is likely to alter some empirical relationships found in the past between species abundance or the ecosystem state and large-scale natural sources of hydro-climatological variability. A theory is proposed to explain how this might happen. These unanticipated changes, also called ‘surprises’ in climatic research, are a direct consequence of the complexity of both climatic and biological systems. In this period of rapid climate change, it is therefore hazardous to integrate meteo-oceanic indices such as the NAO in models used in the management of living resources, as it has been sometimes attempted in the past.

Evidence for phase-locked changes in climate between Scotland and Greenland during GS-1 (Younger Dryas) using micromorphology of glaciolacustrine varves from Glen Roy

There is a current need to develop annual/decadal chronologies from periods of rapid climate change in order to understand the rate and timing of climate events and identify how other proxies either lead or lag this climate forcing. Annually-laminated or varved sediments are key proxies for understanding environmental change at such a scale. This paper presents the results of microscale analysis of glaciolacustrine varve sediments from Scotland and develops a new index called varve group, which ranks the number of pulses of sediment observed in the summer component of the varve. The varve group index is compared with data from the Greenland ice-core record and correspondence can be observed between the oxygen isotope records from Greenland during the latter part of GS-1 and the 515-year Lochaber varve group index. The processes that control the number of sediment pulses into the lake basin are discussed and we examine how these factors might control both the isotopic composition of the ice cores and varve group formation. It is proposed that the position of the sea ice in the North Atlantic may provide such a mechanism.

Isotopic paleoecology of Clovis mammoths from Arizona

The causes of megafaunal extinctions in North America have been widely debated but remain poorly understood. Mammoths (Mammuthus spp.) in the American Southwest were hunted by Clovis people during a period of rapid climate change, just before the regional onset of Younger Dryas cooling and mammoth extirpation. Thus, these mammoths may provide key insights into late Pleistocene extinction processes. Here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the San Pedro Valley of Arizona, using the carbon ((13)C/(12)C) and oxygen ((18)O/(16)O) isotope compositions of tooth enamel. These records suggest that Clovis mammoths experienced a warm, dry climate with sufficient summer rainfall to support seasonal C(4) plant growth. Monsoon intensity may have been reduced relative to the preceding time period, but there is no isotopic evidence for severe drought. However, it is possible that the "Clovis drought", inferred from stratigraphic evidence, occurred suddenly at the end of the animals' lives and thus was not recorded in the enamel isotopic compositions. Unlike mammoths that lived before the Last Glacial Maximum, Clovis mammoths regularly increased C(4) grass consumption during summer, probably seeking seasonally green grasslands farther from the river valley. This predictable seasonal behavior may have made mammoths easier to locate by Clovis hunters. Furthermore, Clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction.

Structuring effects of climate-related environmental factors on Antarctic microbial mat communities

Both ground-based and satellite data show that parts of Antarctica have entered a period of rapid climate change, which already affects the functioning and productivity of limnetic ecosystems. To predict the consequences of future climate anomalies for lacustrine microbial communities, we not only need better baseline information on their biodiversity but also on the climate-related environmental factors structuring these communities. Here we applied denaturing gradient gel electrophoresis (DGGE) of the small subunit ribosomal DNA (SSU rDNA) to assess the genetic composition and distribution of Cyanobacteria and eukaryotes in 37 benthic microbial mat: samples from east Antarctic lakes. The lakes were selected to span a wide range of environmental gradients governed by differences in lake morphology and chemical limnology across 5 ice-free oases. Sequence analysis of selected DGGE bands revealed a high degree of potential endemism among the Cyanobacteria (mainly represented by Oscillatoriales and Nostocales), and the presence of a variety of protists (alveolates, stramenopiles and green algae), fungi, tardigrades and nematodes, which corroborates previous microscopy-based observations. Variation partitioning analyses revealed that the microbial mat community structure is largely regulated by both geographical and local environmental factors of which salinity (and related variables), lake water depth and nutrient concentrations are of major importance. These 3 groups of environmental variables have previously been shown to change drastically in Antarctica in response to climate change. Together, these results have obvious consequences for predicting the trajectory of biodiversity under changing climate conditions and call for the continued assessment of the biodiversity of these unique ecosystems.

Late Holocene palaeoecology of Lago Verde: evidence of human impact and climate change in the northern limit of the neotropics during the late formative and classic periods

Multiproxy analysis (pollen, diatom, charcoal) on a 6 m core from Lago Verde (Sierra de Los Tuxtlas), shows evidences of environmental changes and human impact on the evergreen rainforest on the tropical lowlands of eastern Mexico during the last ca. 2,800 years. Prehistoric human occupation is recorded since the late Formative throughout the middle Classic (250 b.c.–ca. a.d. 800) by the presence of maize pollen, a low abundance of tropical arboreal taxa and a high abundance of herbaceous pollen and charcoal particles. This occurred under a scenario of very low lake levels from which dry conditions are inferred based on the dominance of aerophilous and periphytic diatom taxa. After ca. a.d. 800 the site was abandoned and forest regeneration started, at the same time higher lake levels, an indication of more humid conditions, were established. In the absence of human disturbance, tropical forest regeneration was rapid (ca. 200 years). Fluctuations in pollen composition during times of low human population at the site are related to climate variability, with the highest tropical forest diversity and lake levels recorded during the Little Ice Age. Modern human impact is also recorded and compared with the prehistoric deforestation event. Comparison with palaeoecological records from Yucatan and the highlands of central Mexico offers a Mesoamerican perspective of climatic variability giving evidence that the late Formative and early to middle Classic demographic expansion occurred under a scenario of climates dryer than present, with the Postclassic characterized by moister conditions. The end of the Classic (ca. a.d. 800–1000) is identified as a period of rapid climate change which marks one of the most important cultural transitions in Mesoamerica.

Climatic implications of annual to decadal resolution stable isotope data from calcite varves of the Piànico interglacial lake record, Southern Alps

Stable oxygen isotope analyses at annual, 2-, 5-, 10- and 20-varve sample resolutions were carried out on two selected varve intervals from the interglacial sediment record of the Piànico palaeolake. These sediments are particularly suitable for ultra-high-resolution isotope analyses on lacustrine endogenic calcite because of the exceptionally well-preserved varve structure. A bias through detrital contamination can be excluded because microscopically controlled sampling enabled selecting detritus-free samples. The studied sediment intervals comprise 352 and 88 continuous varve series formed during periods of rapid climate change at the onset and end of a marked millennial-scale cool interval during the Piànico Interglacial. The most intriguing result is a pronounced short-term oscillation in the bi-annually resolved isotope record superimposed on the general decreasing and increasing δ 18O trends at the climatic transitions that is recorded at lower sample resolution. Spectral analyses of the bi-annual time series reveal periodicities indicating solar and NAO controls on the δ 18O record. Multiple δ 18O measurements from endogenic calcite of individual varves showed variations of up to 0.6‰, thus larger than the observed inter-annual variability and most likely explained by seasonal effects.

Phenotypic plasticity of leaf shape along a temperature gradient in Acer rubrum.

Both phenotypic plasticity and genetic determination can be important for understanding how plants respond to environmental change. However, little is known about the plastic response of leaf teeth and leaf dissection to temperature. This gap is critical because these leaf traits are commonly used to reconstruct paleoclimate from fossils, and such studies tacitly assume that traits measured from fossils reflect the environment at the time of their deposition, even during periods of rapid climate change. We measured leaf size and shape in Acer rubrum derived from four seed sources with a broad temperature range and grown for two years in two gardens with contrasting climates (Rhode Island and Florida). Leaves in the Rhode Island garden have more teeth and are more highly dissected than leaves in Florida from the same seed source. Plasticity in these variables accounts for at least 6–19 % of the total variance, while genetic differences among ecotypes probably account for at most 69–87 %. This study highlights the role of phenotypic plasticity in leaf-climate relationships. We suggest that variables related to tooth count and leaf dissection in A. rubrum can respond quickly to climate change, which increases confidence in paleoclimate methods that use these variables.

Fire history and the Global Charcoal Database: A new tool for hypothesis testing and data exploration

Version 1 of the Global Charcoal Database is now available for regional fire history reconstructions, data exploration, hypothesis testing, and evaluation of coupled climate–vegetation–fire model simulations. The charcoal database contains over 400 radiocarbon-dated records that document changes in charcoal abundance during the Late Quaternary. The aim of this public database is to stimulate cross-disciplinary research in fire sciences targeted at an increased understanding of the controls and impacts of natural and anthropogenic fire regimes on centennial-to-orbital timescales. We describe here the data standardization techniques for comparing multiple types of sedimentary charcoal records. Version 1 of the Global Charcoal Database has been used to characterize global and regional patterns in fire activity since the last glacial maximum. Recent studies using the charcoal database have explored the relation between climate and fire during periods of rapid climate change, including evidence of fire activity during the Younger Dryas Chronozone, and during the past two millennia.

Persistent border: an analysis of the geographic boundary of an intertidal species

The biological performance of species close to their biogeographic boundaries is of critical interest in a period of rapid climate change and can inform predictions of future patterns of distribution. The classic view is that performance attributes (reproduction, growth, survival) will gradually decline from the centre towards the edge of a species range. A persistent discontinuity in the distribution of the intertidal barnacle Chthamalus montagui on the central south coast of England has enabled us to test hypotheses about its performance and recruitment as the range edge is approached. Although adult density was reduced by over 5 orders of magnitude along a 200 km dis- tance, there was little evidence of impaired performance at the range edge. There have been fluctu- ations in abundance over the last 50 yr at shores approaching the border, which are associated with changes in temperature and suggest thermal sensitivities. A study of recruitment in C. montagui and in other intertidal barnacles revealed a region of very low recruitment for all species close to the bor- der of C. montagui. We propose that reductions in larval supply caused by complex regional hydrog- raphy and suboptimal habitat quality, not adult performance, is most likely responsible for a steep gradient in recruitment as the border is approached, although possible reductions in larval perfor- mance cannot be totally discounted. The location of 'low recruitment cells' caused by oceanographic processes that obstruct the dispersal of propagules needs to be identified when modelling the rate of change of biological assemblages and the location and spacing of reserves.

Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic

The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch ( approximately 11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity ( approximately 3.5 degrees C and approximately 1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes, although the inflow can compensate on decadal timescales by becoming more saline. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change.

Centennial‐scale Holocene North Atlantic surface temperatures from Mg/Ca ratios in Globigerina bulloides

A high‐resolution record of Mg/Ca ratios from the planktonic foraminifer Globigerina bulloides has been produced for IMAGES core MD99–2251 from the subpolar North Atlantic. The record extends from the Younger Dryas‐Preboreal transition through the Holocene at ∼70 year resolution, with a more detailed section at ∼20 year resolution through the interval encompassing the major cooling episode 8200 years ago. Mg/Ca derived temperatures show significant variations through the Holocene, with surface temperatures ranging from ∼8 to 13°C. The onset of the Holocene is marked by an abrupt warming, with a further increase in early Holocene temperatures occurring prior to 9.5 ka. This is followed by a mid‐Holocene period of cooler and more stable conditions before temperatures show a stepped increase at ∼3.5 ka. The late Holocene period has the highest temperatures of the entire interglacial but also exhibits coolings of 2–3°C approximately every 500 years. Variations of this magnitude typify the high‐frequency component of temperature variability and do not seem to be restricted to the 8.2 ka event or the early Holocene, when stronger freshwater forcing associated with the decay of the ice sheets might be anticipated. However, episodes of enhanced drift ice input to North Atlantic are coincident with many of the Mg/Ca temperature minima over the last 6 ka. The long‐term warming trend and stepped increase in temperature at ∼3.5 ka are consistent with other planktonic foraminiferal records and appear to reflect regional‐scale changes in the atmospheric forcing of the North Atlantic Current during periods of rapid climate change. Alternatively, changes in ecology may contribute to the Holocene Mg/Ca record, either by species changing their depth habitat or by a shift in seasonal production patterns.