Climatic bisection of the last interglacial warm period in the Polar North Atlantic

New multiproxy marine data of the Eemian interglacial (MIS5e) from the Norwegian Sea manifest a cold event with near-glacial surface ocean summer temperatures (3–4 °C). This mid-Eemian cooling divided the otherwise relatively warm interglacial climate and was associated with widespread expansions of winter sea-ice and polar water masses due to changes in atmospheric circulation and ocean stability. While the data also verify a late rather than early last interglacial warm peak, which is in general disharmony with northern hemisphere insolation maximum and the regional climatic progression of the early Holocene, the cold event itself was likely instrumental for delaying the last interglacial climate development in the Polar North when compared with regions farther south. Such a ‘climatic decoupling’ of the Polar region may bear profound implications for the employment of Eemian conditions to help evaluate the present and future state of the Arctic cryosphere during a warming interglacial.     

全新世和末次间冰期北大西洋底栖有孔虫氧同位素对比的探索研究

北大西洋（特别是亚极地海区）是对全球气候变化响应最敏感的区域之一,也是全球气候变化研究关注的焦点之一。地质记录和模拟研究指出末次间冰期（MIS 5e）全球地表平均温度比全新世（Holocene）高约1℃,因而可以作为未来全球变暖趋势的历史对照,但目前北大西洋水体温盐变化在这两个时期的对比研究仍然较少。底栖有孔虫氧同位素作为古气候研究常用的指标,与冰量、温度和洋流变化紧密相关。本文统计并对比了北大西洋47个深海沉积物钻孔MIS 5e和全新世的底栖有孔虫氧同位素数据,发现研究区不同深度、不同纬度的数据在这两个间冰期具有系统的差异。MIS 5e氧同位素平均值和极低值比全新世系统性偏轻0.08 ‰,反映了陆地冰量变化对整个区域的影响,且深水温度整体可能比全新世偏高。氧同位素时空分布表明北大西洋中层水（1~2 km）全新世和MIS 5e的有孔虫氧同位素差值（> 0.2 ‰）比深水（> 2 km）更显著,可能记录更大的温度变化幅度,而1.5 km之上MIS 5e氧同位素值变重（平均重约0.36 ‰）则主要响应了大洋环流的变化。此外,高纬地区（45°N以北）深水底栖有孔虫氧同位素值在MIS 5e系统性偏轻约0.12 ‰,比中低纬（0°~45°N）深水变化更显著,可能反映高纬深水变暖程度更高,与海表温度重建和模拟结果相吻合。因此,联合多钻孔的底栖有孔虫氧同位素是分辨区域古海洋变化的有效手段,在未来气候变暖中北大西洋高纬和中层海域的变化是气候模式需要重点关注的区域之一。

     

Global sea-level fluctuations during the Last Interglaciation (MIS 5e)

The geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of sea level during the peak of the Last Interglaciation (Marine Isotope Stage (MIS) 5e, assumed average duration between 130±2 and 119±2 ka). Because sea level was higher than present, deposits are emergent, exposed, and widespread on many stable coastlines. Correlation with MIS 5e is facilitated by similar morphostratigraphic relationships, a low degree of diagenesis, uranium–thorium (U/Th) ages, and a global set of amino-acid racemization (AAR) data. This study integrates information from a large number of sites from tectonically stable areas including Bermuda, Bahamas, and Western Australia, and some that have experienced minor uplift (∼2.5 m/100 ka), including selected sites from the Mediterranean and Hawaii. Significant fluctuations during the highstand are evident at many MIS 5e sites, revealed from morphological, stratigraphic, and sedimentological evidence. Rounded and flat-topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story. Despite predictions of much different sea-level histories in Bermuda, the Bahamas, and Western Australia due to glacio- and hydro-isostatic effects, the rocks from these sites reveal a nearly identical record during the Last Interglaciation.The Last Interglacial highstand is characterized by several defined sea-level intervals (SLIs) that include: (SLI#1) post-glacial (MIS 6/5e Termination II) rise to above present before 130 ka; (SLI#2) stability at +2 to +3 m for the initial several thousand years (∼130 to ∼125 ka) during which fringing reefs were established and terrace morphology was imprinted along the coastlines; (SLI#3) a brief fall to near or below present around 125 ka; (SLI#4) a secondary rise to and through ∼+3–4 m (∼124 to ∼122 ka); followed by (SLI#5) a brief period of instability (∼120 ka) characterized by a rapid rise to between +6 to +9 m during which multiple notches and benches were developed; and (SLI#6) an apparently rapid descent of sea level into MIS 5d after 119 ka. U/Th ages are used to confirm the Last Interglacial age of the deposits, but unfortunately, in only two cases was it possible to corroborate the highstand subdivisions using radiometric ages.Sea levels above or at present were relatively stable during much of early MIS 5e and the last 6–7 ka of MIS 1, encouraging a comparison between them. The geological evidence suggests that significant oceanographic and climatic changes occurred thereafter, midway through, and continuing through the end of MIS 5e. Fluctuating sea levels and a catastrophic termination of MIS 5e are linked to the instability of grounded and marine-based ice sheets, with the Greenland (GIS) and West Antarctic (WAIS) ice sheets being the most likely contributors. Late MIS 5e ice volume changes were accompanied by oceanographic reorganization and global ecological shifts, and provide one ominous scenario for a greenhouse world.     

Radiocarbon reservoir age of high latitude North Atlantic surface water during the last deglacial

The radiocarbon reservoir age of high latitude North Atlantic Ocean surface water is essential for linking the continental and marine climate records, and is expected to vary according to changes in North Atlantic deep water (NADW) production. Measurements from this region also provide important input and/or tests of oceanic radiocarbon using 3-D global ocean circulation models. Here, we present a surface water radiocarbon reservoir age record of the high latitude western North Atlantic for the deglacial period via the use of fossil cold-water corals growing in waters that are rapidly exchanged with nearby surface waters. The reservoir age of high latitude North Atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record (http://radiocarbon.LDEO.columbia.edu) and our marine radiocarbon data. ²³⁰Th/²³⁴U/²³⁸U dates provide the absolute coral ages. Our high latitude North Atlantic Ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and Vedde ash radiocarbon dates from central and eastern North Atlantic show modern values (380±140 year, n=14) during the Bolling and Allerod warm period and a 200 year increase in reservoir age (590±130 year, n=10) during the entire Younger Dryas (YD) cold episode. The reservoir age then decreased to 270±20 year (n=2) at the Preboreal/YD transition, although the dates are too sparse for us to be confident in this estimate. We are not able to resolve the timing of the transition to increased reservoir ages from the mid-Allerod to the YD due to the relatively small change and correspondingly large uncertainty in the estimates. The atmospheric Δ¹⁴C record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12,900 to 12,650 cal years BP, coincident with the shift to high reservoir ages in the early YD cold event. Intrusion of ¹⁴C depleted Antarctic Intermediate Water (AAIW) to the high latitude North Atlantic and reduction of NADW formation are possible causes for the coincident shift to high reservoir ages in the North Atlantic surface ocean and increased atmospheric Δ¹⁴C during the beginning of the YD event.     

Land/ocean correlations during the last interglacial/glacial transition, Baffin Bay, northwestern North Atlantic: A review

Evidence from terrestrial sections, ice cores, and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest North Atlantic during marine isotope stages 5 and 4. The critical physical link between the landbased glacial chronology and marine events in Baffin Bay is the presence of carbonate rich drift along the Baffin Bay coast of Bylot Island and a detrital carbonate facies (Facies B) in Baffin Bay sediments. Cores from Baffin Bay/Labrador Sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards. One occurrence of Facies B is dated between late stage 5 and stage 4 and we correlate this event with the Eclipse Glaciation of Bylot Island and the Ayr Lake stade of the Foxe Glaciation of Baffin Island (= Kogalu aminozone). In contrast on West Greenland, amino acid racemization evidence suggests that the Greenland Ice Sheet developed throughout stage 4 and reached a maximum in stage 3 (Svartenhuk advance >40 ka). The oxygen isotope record in the Devon Island Ice Cap (northwest Baffin Bay) indicates that Baffin Bay was largely open during marine isotope stage 5. Analyses of shallow water molluscan and foraminiferal assemblages, deep-water foraminifera, pollen from Iand sections and deep-sea cores, and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage glaciation.     

Last interglacial (MIS 5e) sea-level determined from a tectonically stable,far-field location,Eyre Peninsula,southern Australia

The last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128–116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust–mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine–lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal–intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial.     

Synchronous climate anomalies in the western North Pacific and North Atlantic regions during the last 14,000 years

A peat cellulose δ¹⁸O record spanning around 14,000 years from the Hani peat mire in northeastern China reveals several abrupt temperature anomalies in the period from the last deglaciation through the Holocene. The timing of these anomalies coincides well with the notable cooling events recorded respectively using the GISP2 ice core and ice-rafted sediment of the North Atlantic Ocean, such as the Older Dryas, Inter-Allerød, Younger Dryas, and the nine ice-rafted debris events. The results demonstrate that this repeating pattern of abrupt temperature deterioration is not limited to the North Atlantic area at high latitude but also exists in the western North Pacific region at middle latitude. The synchronous temperature anomalies possibly are resulted from the joint effects of meltwater discharge into the North Atlantic Ocean and reduced solar activity. In the period from around 8600 to 8200 cal. yrs BP the Hani peat record shows a broad δ¹⁸O peak that may reflect compound climate signals resulting from the two kinds of forcing factors: the temperature drop related to reduced solar activity at around 8600–8250 cal. yrs BP, and the temperature anomaly attributed to the meltwater effect at around 8220 ± 70 cal. yrs BP. This result may provide palaeo-temperature evidence for existence of the sharp “8.2 k” event in the western North Pacific region. In addition, our results have revealed that in the period from the last deglaciation through the Holocene the synchronous temperature anomalies before and after the “8.2 k” event seem to be related to meltwater outflow and reduced solar activity, respectively. It is important that the all temperature anomalies—whether because of reduced solar activity in the late Holocene or from meltwater discharge in the early Holocene—are accompanied by an abrupt decline in the Indian Ocean summer monsoon and abrupt strengthening of the East Asian summer monsoon. It is likely that reduced solar activity and meltwater outflow appear to modulate Earth system changes in the same direction. The influences could be compounded. Reduced solar activity and meltwater outburst both appear to act as triggers for occurrence of the El Niño phenomenon in the equatorial Pacific Ocean, which may result in broad teleconnections between the temperature anomaly in the Northern Hemisphere and abrupt variation of the Asian monsoon.     

Phase relationship and surface water mass change in the Northeast Atlantic during Marine Isotope Stage 11 (MIS 11)

Planktic foraminiferal census data, faunal sea surface temperatures (SSTs) and oxygen isotopic and lithic records from a site in the northeast Atlantic were analyzed to study the interglacial dynamics of Marine Isotope Stage (MIS) 11, a period thought to closely resemble the Holocene on the basis of orbital forcing. Interglacial conditions during MIS 11 persisted for approximately 26 ka. After the main deglacial meltwater processes ceased, a 10- to 12-ka-long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum. This SST peak occurred between 400 and 397 ka, inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values. The ensuing stepwise SST decrease characterizes the overall climate deterioration preceding the increase in global ice volume by  3 ka. This cooling trend was followed by a more pronounced cold event that began at 388 ka, and that terminated in the recurrence of icebergs at the site around 382 ka. Because the water mass configuration of early MIS 11 evolved quite differently from that of the early Holocene, there is little evidence that MIS 11 can serve as an appropriate analogue for a future Holocene climate, despite the similarity in some orbital parameters.     

Time-transgressive deglacial retreat of polar waters from the North Atlantic

A 9300 yr-old zone of disseminated volcanic ash in North Atlantic sediments between 45° N and 65° N provides a time-synchronous reference layer against which we have compared the stratigraphic level of deglacial warming of ocean surface waters. In the Atlantic north of 45° N the most prominent feature of this warming is the replacement of low-carbonate glacial marine sediment containing only a single species of polar Foraminifera by calcareous oozes containing a diverse temperate fauna and flora. The local terminations of glacial conditions marked by this change are not synchronous at these latitudes, but range from 13,500 yr B.P. or older in the southeast near Great Britain to 6,500 yr B.P. or younger in the northwest near Greenland. Regionally, these local warmings trace the progressive westward and northward retreat of polar water from the North Atlantic. Since the withdrawal of polar water from the North Atlantic coincides with the northward shrinkage of temperate-latitude continental ice sheets, it is the best oceanic analog to continental deglaciation.Faunal, floral, lithologic, and isotopic parameters showing evidence for a sudden deglacial warming may not be time-synchronous; those parameters are subject to a range of environmental controls and may thus respond differently to the causal mechanism for global warming.     

Marine evidence for climatic instability during the last interglacial in shelf records from northwest Europe

Data from the Greenland ice sheet and continental records from Europe have indicated climatic fluctuations during the last interglacial (Eemian: Oxygen Isotope Substage 5e). Similar fluctuations have not, however, been documented previously from marine environments. Here, we show the existence of two cold events during substage 5e in two marine, benthic foraminiferal, shelf records from northwest Europe and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation.     

A Pleistocene (MIS 5e) mollusk assemblage from Ezeiza (Buenos Aires Province,Argentina)

A fossil assemblage collected around 3.5 m amsl from Ezeiza, Buenos Aires province, have AMS ¹⁴C ages of ca. 33,000 to ca. 40,000 yr BP, whereas in the literature is a report of a conventional ¹⁴C age of >43,000 yr BP. An OSL age from the overlying deposit corresponds to ca. 22,000 yr. The samples contain marine fossils: mollusks, balanids and corals (Astrangia). La Coronilla (Uruguay, attributed to MIS 5e) is the locality most related to Ezeiza faunistically, despite is not the nearest one. In consequence, the relationship should be addressed to a more similar age and environment than others. The fauna indicates a higher water temperature than today. In Ezeiza exclusively cold water taxa are absent, and we found seven warm taxa with their southern distribution limit displaced northwards today, plus other six at their southern distribution limit. Around 60% of all the species and more than 70% of the individuals are of warm-temperate waters. In sum, although prima facie the numerical ages would locate the deposit in MIS3, faunistic, temperature, and height evidences show that the Ezeiza mollusk assemblage belong to MIS5e. A stronger than presently Brazil warm current, reaching Southern latitudes, may explain the changes in geographical ranges.     

Pliocene and late Pleistocene (MIS 5e) decapod crustaceans from Santa Maria Island (Azores Archipelago: Central Atlantic): systematics,palaeoecology and palaeobiogeography

The presence of decapod crustaceans in the Pliocene and Pleistocene (MIS 5e) fossil record of Santa Maria Island (Azores Archipelago) is herein reviewed. Our study raises the number of fossil decapods from this island from one species to 10 taxa (three for the Pliocene and seven for the Last Interglacial). Four of these 10 taxa are reported for the first time in the fossil record, worldwide. A new species of a mud shrimp is also described (Upogebia azorensis n. sp.). Our study suggests that the Plio–Pleistocene decapod assemblages of the Azores did not differ significantly from modern ones, being dominated by species that are today widespread across the Webbnesia ecoregion, the Mediterranean Sea, and the eastern Atlantic shores, including the Azores. As far as can be judged from the limited fossil record, apparently no tropical crab species with a Cabo Verdean/Senegalese provenance reached the Azores during windows of opportunity associated with Glacial Termination 2 or with the initial setting of the Last Interglacial period. This contribution increases the total number of marine taxa reported for the Pliocene and Pleistocene outcrops of Santa Maria Island to 218 and 155, respectively, highlighting the scientific relevance of its palaeontological heritage.     

Estuarine, barrier-island to strand-plain sequence and related ravinement surface developed during the last interglacial in the Paleo-Tokyo Bay, Japan

Recognition of sequence boundaries and transgressive surfaces (i.e. ravinement surfaces, RS) is now known to be of great importance in stratigraphy. The sedimentary features of deposits immediately above a transgressive surface are well exposed in the Upper Pleistocene Kioroshi Formation of the Kanto Plain in central Japan. The formation comprises mainly coastal and shallow-marine deposits (estuarine, barrier-island and the strand-plain systems) which accumulated along a wavedominated coast in the Late Pleistocene, i.e., the last interglacial to last glacial period. The Kioroshi Formation is bounded above and below by sequence boundaries that formed in the lowstand periods correlative to the glacial periods of oxygen isotope stages 4 and 6, respectively. A significant transgressive surface that was formed by landward migration of barrier islands during the transgressive interval, the ravinement surface (RS), is found within the deposits of the upper shelf environment.

This ravinement surface is characterized by the exotic nature of the overlying sediment veneer (pebbles, shells and scattered mud clasts) which is poorly sorted. The RS shows a very flattened erosional surface in the shore-parallel sense, and the gradient of the surface in shore-normal sense is calculated as 0.0021, where the syndepositional tectonic movement is revised. The RS commonly cuts through the lower sequence boundary. However, in the places where the river or tidal channel valleys incised, the valley-filling sediment shows a deepening-upward sequence recognized as a transgressive systems tract and the RS can be clearly distinguished from the lower sequence boundary.     

Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age

Internal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large (>1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.     

Coastal deformation between the Versilia and the Garigliano plains (Italy) since the last interglacial stage

The opening of the north‐central Tyrrhenian Sea is the result of the Cretaceous–Paleogene alpine collision, which triggered a series of regional uplift, subsidence and transcurrent tectonic mechanisms along the coastal Tyrrhenian sectors of peninsular Italy. These tectonic processes, in conjunction with the effects of glacio‐ and hydro‐isostasy during the Quaternary, produced substantial crustal responses that, in some cases, reached metres in extent. In the study of coastal neotectonics, geomorphological markers of the last interglacial maximum, corresponding to marine isotope stage 5.5, are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr. Through altimetrical, palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913, combined with an additional set of data reported here, a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern Tuscany and southern Latium is presented. The reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors. This has been done by carefully choosing the eustatic marker, among those available at each study site, in order to minimize the margin of error associated with the measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Millennial/submillennial-scale sea-level fluctuations in western Mediterranean during the second highstand of MIS 5e

This paper investigates a series of small-scale, short-lived fluctuations of sea level registered in a prograding barrier spit that grew during the MIS 5e. This interglacial includes three highstands (Zazo et al., 2003) and we focus on the second highstand, of assumed duration ～10 ± 2 ka, given that U–Th ages do not provide more accurate data. Geometry and 3D architecture of beach facies, and thin-section petrography were used to investigate eight exposed offlapping subunits separated by seven conspicuous erosion surfaces, all interpreted as the result of repeated small-scale fluctuations of sea level.Each subunit records a relatively rapid rise of sea level that generated a gravelly shoreface with algal bioherms and a sandy uppermost shoreface and foreshore where most sand accumulated. A second range of still smaller-scaled oscillations of sea level has been deduced in this phase of sea-level fluctuation from lateral and vertical shifts of the foreshore-plunge-step-uppermost shoreface facies.Eventually, progradation with gently falling sea level took place and foreshore deposits underwent successive vadose cementation and subaerial dissolution, owing to relatively prolonged exposure. Later recovery of sea level re-established the highstand with sea level at approximately the same elevation, and there began deposition of a new subunit. The minimum sea-level variation (fall and subsequent rise) required to generate the observed features is 4 m. The time span available for the whole succession of events, and comparison with the Holocene prograding beach ridge complex in the nearby Roquetas (Almería) were used to calculate the periodicity of events. A millennial-suborbital time scale is suggested for fluctuations separating subunits and a decadal scale for the minor oscillations inside each subunit.     

North Atlantic control on precipitation pattern in the eastern Mediterranean/Black Sea region during the last glacial

Based on proxy records from western Black Sea cores, we provide a comprehensive study of climate change during the last glacial maximum and late-glacial period in the Black Sea region. For the first time we present a record of relative changes in precipitation for NW Anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration. The good correspondence between reconstructed rainfall intensity in NW Anatolia and past western Mediterranean sea surface temperatures (SSTs) implies that during the glacial period the precipitation variability was controlled, like today, by Mediterranean cyclonic disturbances. Periods of reduced precipitation correlate well with low SSTs in the Mediterranean related to Heinrich events H1 and H2. Stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater/sediment source concomitant to the meltwater inflow after 16.4 cal ka BP. This change implies intensification of the northern sediment source and, with other records from the Mediterranean region, consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the European continent. The early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the Mediterranean region, leading simultaneously to more humid conditions in central and northern Europe.     

Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core

Reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments. The degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions, which may be linked to larger scale phenomena, such as bottom water circulation, water column ventilation, and organic carbon flux. Phosphorus phases of the <50-μm-sized fraction of deep-sea sediments from core SU 90-09 (North Atlantic, 43°31′N, 30°24′W, 3375 m below sea level) have been analyzed using a sequential extraction technique (SEDEX method) to reconstruct phosphorus geochemistry during Heinrich events 4 and 5. Comparison with Holocene samples from the same site indicates that postdeposition diagenetic transformation has not affected phosphorus distribution in the deep part of the sediments. Total and reactive phosphorus average 0.40 ± 0.04 mg/g and 0.30 ± 0.05 mg/g, respectively, and are comparable to values found in analog deep-sea environments in the North Atlantic. Detrital phosphorus, the phase linked to igneous- and metamorphic-derived material, sharply increases during Heinrich events and covaries with the ice-rafted debris record, whereas authigenic and Fe-bound phosphorus phases, both influenced by redox conditions, decrease or even disappear. These findings suggest that during the deposition of Heinrich layers (HLs), environmental parameters hampered the precipitation of these phases. Large freshwater discharges in relation to iceberg surges may have provoked a temporary stratification of the water column. Accordingly, dysaerobic conditions in the sediments may have fostered the loss of dissolved phosphorus from the sediments to the water column, in a direct and rapid response to the changed conditions. Decreasing trends in organic matter elemental ratios (total organic carbon/organic phosphorus) and Rock-Eval oxygen index values, along with the presence of partly authigenic dolomite and ankerite within HLs, also support this assumption.     

The response of NW Iberian vegetation to North Atlantic climate oscillations during the last 65 kyr

Pollen and oceanographic data from deep ocean core MD95-2039 provide a centennial to millennial scale record of conditions offshore and of the vegetation of north-west Iberia for the period 10–65 ka. The planktonic oxygen isotope record of this core, reflecting predominantly sea surface temperature (SST), shows a pattern of millennial-scale oscillations that is very similar to climatic changes recorded by the Greenland ice core records over the same interval. In turn, tree populations show a pattern of rapid expansions and contractions that follow the pronounced and abrupt isotopic shifts recorded offshore. Through Marine Isotope Stage (MIS) 3, this millennial-scale pattern of vegetation change, alternating between steppe and open woodland, is superimposed on a longer-term pattern of shrinking ericaceous heathland and decreasing size of successive interstadial tree populations. Trees persisted during the Last Glacial Maximum (LGM), at greater abundance than during many of the coldest episodes of MIS 3. This agrees with the marine data which indicate that LGM sea surface temperatures here were significantly warmer than the minima recorded in MIS 3. Our combined marine-terrestrial record, together with data from nearby sequences, provides a stepping stone between terrestrial sequences and the Greenland ice core and North Atlantic marine records. This will permit a better understanding of the behaviour of vegetation across different regions at several scales of climatic forcing.