Planktonic foraminifera and stable isotope record of ODP Site 162-980

Detailed faunal, isotopic, and lithic marine records provide new insight into the stability and climate progression of the last interglacial period, Marine Isotope Stage (MIS) 5, which peaked approximately 125,000 years ago. In the eastern subpolar North Atlantic, at the latitude of Ireland, interglacial warmth of the ice volume minimum of substage 5e (MIS 5e) lasted ~10,000 years (10 ka) and its demise occurred in two cooling steps. The first cooling step marked the end of the climatic optimum, which was 2-3 ka long. Minor ice rafting accompanied each cooling step; the second, larger, step encompassing cold events C26 and C25 was previously identified in the northwestern Atlantic. Approximately 4 °C of cooling occurred between peak interglacial warmth and C25, and the region experienced an additional temporary cooling of at least 1-2 °C during C24, a cooling event associated with widespread ice rafting in the North Atlantic. Beginning with C24, MIS 5 was characterized by oscillations of at least 1-2 °C superimposed on a generally cool baseline. The results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought. The finding that the eastern subpolar North Atlantic cooled significantly before C24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions. Our results also demonstrate a close association between modest ice rafting, cooling, and deep ocean circulation even during the peak of MIS 5e and in the earliest stages of ice growth.

Stable isotopc record of ODP Site 114-704

We report a near-continuous, stable isotopic record for the Pliocene-Pleistocene (4.8 to 0.8 Ma) from Ocean Drilling Program Site 704 in the sub-Antarctic South Atlantic (47°S, 7°E). During the early to middle Pliocene (4.8 to 3.2 Ma), variation in delta18O was less than ~0.5 per mil, and absolute values were generally less than those of the Holocene. These results indicate some warming and minor deglaciation of Antarctica during intervals of the Pliocene but are inconsistent with scenarios calling for major warming and deglaciation of the Antarctic ice sheet. The climate System operated within relatively narrow limits prior to ~3.2 Ma, and the Antarctic cryosphere probably did not fluctuate on a large scale until the late Pliocene. Benthic oxygen isotopic values exceeded 3 per mil for the first time at 3.16 Ma. The amplitude and mean of the delta18O signal increased at 2.7 Ma, suggesting a shift in climate mode during the latest Gauss. The greatest delta18O values of the Gaus anti Gilbert chrons occurred at ~2.6 Ma, just below a hiatus that removed the interval from ~2.6 to 2.3 Ma in Site 704. These results agree with those from Subantarctic Site 514, which suggest that the latest Gauss (2.68 to 2.47 Ma) was the time of greatest change in Neogene climate in the northern Antarctic and Subanthtic regions. During this period, surface water cooled as the Polar Front Zone (PFZ) migrated north and perennial sea ice Cover expanded into the Subantarctic region. Antarctic ice volume increased and the ventilation rate of Southern Ocean deep water decreased during glacial events after 2.7 Ma. We suggest that these changes in the Southern Ocean were related to a gradual lowering of sea level and a reduction in the flux of North Atlantic Deep Water (NADW) with the Initiation of ice growth in the northern hemisphere. The early Matuyama Chron (~ 2.3 to 1.7 Ma) was marked by relatively warm climates in the Southern Ocean except for strong glacial events associated with isotopic stages 82 (2.027 Ma), 78 (1.941 Ma), and 70 (1.782 Ma). At 1.67 Ma (stage 65/64 transition), surface waters cooled as the PFZ migrated equatorward and oscillated about a far northerly position for a prolonged interval between 1.67 and 1.5 Ma (stages 65 to 57). Beginning at ~1.42 Ma (stage 52), all parameters (delta18O, delta13C, %opal, %CaCO3) in Hole 704 become highly correlated with each other and display a very strong 41-kyr cyclicity. This increase in the importance of the 41-kyr cycle is attributed to an increase in the amplitude of the Earth's obliquity cycle that was likely reinforced by increased glacial suppression of NADW, which may explain the tightly coupled response that developed between the Southern Ocean and the North Atlantic beginning at ~1.42 Ma (stage 52).

Pollen record from Muggesfelder See and Plussee in Germany

A basaltic tephra layer consisting of brownish-olive glass shards. and about 0.2 mm thick. was found in cores from four lakes in northwest Germany. According to pollen analysis it was deposited during the early Boreal period (corresponding to about 8700 BP). The petrographic properties. the geochemical composition and the age agree with those of the Saksunarvatn tephra. which was first found on the Faroe Islands. The position of the tephra layer in the pollen stratigraphy and in the absolute time-scale is discussed. Procedures for locating the tephra in other cores are suggested.

Latest Miocene-Pleistocene benthic foraminiferal record of DSDP Hole 23-219

Knowledge of the biology of deep-sea benthic foraminifera was used to interpret the results of multivariate analyses (factor and cluster) on relative abundance data of benthic foraminifera at Deep Sea Drilling Project Site 219 (southeastern Arabian Sea; 1764 m depth) in combination with carbon and oxygen isotope data. Faunal data document major changes in deep-sea ventilation and productivity over the past 5.5 Ma, including the end of the Miocene-Pliocene Indo-Pacific 'biogenic bloom' period at ~4.0 Ma. Interestingly, there is no simple correlation between high productivity and low oxygenation. Productivity fluctuated but became overall more pulsed, whereas overall oxygenation increased. We interpret the records as a combination of local to regional fluctuations in productivity probably caused by changes in monsoonal development, particularly its seasonality, and changes in oxygenation of intermediate depth waters in the Indian Ocean caused by global changes in climate and ocean circulation.

Os isotope record of ODP Site 159-959

The known temporal relationship between the benthic foraminiferal d18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.

Magnetobiostratigraphy and stable isotope record of Paleocene sediments from ODP Hole 122-761B in the subtropical Indian Ocean

Surface and deep water circulation patterns in the eastern Indian Ocean during the Paleocene Epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of Ocean Drilling Program Hole 761B, drilled on the Wombat Plateau. A combination of magnetostratigraphy, biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous, or nearly continuous sedimentation through the Paleocene are punctuated by a series of hiatuses, some of which exceeding a duration of 1 Myr. Therefore, our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions. We compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from Hole 761B with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern Indian Ocean. Although Site 761 was situated at low latitudes during the Paleocene, its surface waters were predominantly influenced by circulation originating from the Southern Ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients. We suggest that deep waters in the eastern Indian Ocean were not directly fed by the Southern or Tethys Oceans. Rather, the more negative delta13C composition of the bottom waters recorded by benthic foraminifera implies the presence and/or active contribution of aged deep waters from the Pacific during this time, at least prior to ~60.2 Ma and subsequent to ~59.0 Ma. The Indian continent, Ninetyeast Ridge, Kerguelen Plateau and Broken Ridge may have played a significant role as submarine barriers to deep water circulation during the Paleocene.

Age determination and stable isotope record of planktonic foraminifera from sediments of the Baffin Shelf

Stable isotopic values on planktonic foraminifera in a suite of cores from basins across the SE Baffin Shelf are used to extract a record of meltwater events during Termination I deglaciation. Resolution and Hatton basins lie on the SE Baffin Shelf at water depths > 500 m, seaward of major conduits for ice drainage from the eastern sector of the Laurentide Ice Sheet (LIS). Accelerator mass spectrometry 14C dates are used to constrain our chronology of events in ten cores. In Resolution Basin, three cores have 14C AMS dates on foraminifera of > 20 ka at their bases; whereas Hatton Basin cores terminate in sediments < 13 kyr. Sedimentation rates varied between 0.1 to 4.5 m/ka. Stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera Neogloboquadrina pachyderma (Ehrenberg) sinistral, from seven of the ten cores. No evidence was found to indicate that test morphology or size affected delta18O. Between 7 and 13.5 ka the surface water on the shelf was on average 1 per mil lower than the open ocean signal. Significant temporal variations were found in both delta18O and delta13C. Evidence for significant low delta18O events occurred between 13 and 8 ka. The delta13C record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka, with positive values between 10.8 and 13.0 ka, negative values between 9 and 10.8 ka, and positive values from 7 to 9 ka. The delta18O data suggest the presence of meltwater on the shelf some 3,000 years prior to the first late glacial dates on terrestrial deglaciation (at circa 10.4 ka). "Hudson Strait must be the real key to the importance of the calving process during deglaciation, because it is potentially the largest marine outlet for the Laurentide Ice Sheet and because it leads into the very center of the ice sheet.....the rates of calving through Hudson Strait during the period of initial ?18O rise unfortunately are unknown." W. F. Ruddiman (1987, p. 151)

Stable isotope record and trace element ratios of Eocene and Oligocene foraminifers from ODP Site 120-748

Stable carbon and oxygen isotope analyses were conducted on well-preserved planktonic and benthic foraminifers from a continuous middle Eocene to Oligocene sequence at Ocean Drilling Program (ODP) Site 748 on the Kerguelen Plateau. Benthic foraminifer d18O values show a 1.0 per mil increase through the middle and upper Eocene, followed by a rapid 1.2 per mil increase in the lowermost Oligocene (35.5 Ma). Surface-dwelling planktonic foraminifer d18O values increase in the lowermost Oligocene, but only by 0.6 per mil whereas intermediate-depth planktonic foraminifers show an increase of about l.0 per mil. Benthic foraminifer d13C values increase by 0.9 per mil in the lowermost Oligocene at precisely the same time as the large d18O increase, whereas planktonic foraminifer d13C values show little or no change. Site 748 oxygen isotope and paleontological records suggest that southern Indian Ocean surface and intermediate waters underwent significant cooling from the early to late Eocene. The rapid 1.2 per mil oxygen isotope increase recorded by benthic foraminifers just above the Eocene/Oligocene boundary represents the ubiquitous early Oligocene d18O event. The shift here is unique, however, as it coincided with the sudden appearance of ice-rafted debris (IRD), providing the first direct link between Antarctic glacial activity and the earliest Oligocene d18O increase. The d18O increase caused by the ice-volume change in the early Oligocene is constrained by (1) related changes in the planktonic to benthic foraminifer d18O gradient at Site 748 and (2) comparisons of late Eocene and early Oligocene planktonic foraminifer d18Ovalues from various latitudes. Both of these records indicate that 0.3 per mil to 0.4 per mil of the early Oligocene d18O increase was ice-volume related.

North Atlantic IODP Site 303-U1308 Middle Pleistocene Heinrich Events record

Heinrich events are well documented for the last glaciation, but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate d18O results from Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) that are used to develop proxy records of ice-rafted detritus (IRD) for the last ~1.4 Ma. Ca/Sr is used as an indicator of IRD layers that are rich in detrital carbonate (i.e., Heinrich layers), whereas Si/Sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals. A pronounced change occurred in the composition and frequency of IRD at ~640 ka during marine isotope stage (MIS) 16, coinciding with the end of the middle Pleistocene transition. At this time, "Hudson Strait" Heinrich layers suddenly appeared in the sedimentary record of Site U1308, and the dominant period of the Si/Sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward. The onset of Heinrich layers during MIS 16 represents either the initiation of surging of the Laurentide Ice Sheet (LIS) off Hudson Strait or the first time icebergs produced by this process survived the transport to Site U1308. We speculate that ice volume (i.e., thickness) and duration surpassed a critical threshold during MIS 16 and activated the dynamical processes responsible for LIS instability in the region of Hudson Strait. We also observe a strong coupling between IRD proxies and benthic d13C variation at Site U1308 throughout the Pleistocene, supporting a link between iceberg discharge and weakening of thermohaline circulation in the North Atlantic.

A sedimentological, faunal, and isotopic record of the middle-to-late Pliocene transition at DSDP Hole 80-548

Hydraulic piston coring at DSDP Site 548, on the upper continental slope southwest of Ireland, recovered a nearly complete Pliocene section spanning 103 m of sediment. The sediments are greenish gray carbonate-rich hemipelagites containing abundant nannofossils and foraminifers. Grain-size analysis demonstrates that the texture of the section is fairly constant, with most of the variation occurring in 63- to 32-µm and < 2-µm fractions. Previous research has shown that the middle-to-late Pliocene transition in the North Atlantic was marked by the appearance of the planktonic foraminiferal species Globorotalia inflata and by the first occurrence of significant quantities of ice-rafted sediment grains in deep-sea sediments. The latter is taken to represent the first important development of Northern Hemisphere glaciation. The first appearance of G. inflata is carefully documented for Site 548 and is demonstrated to be an evolutionary datum at this site, rather than an ecologically controlled first appearance. Surface ocean conditions represented in the sediment section spanning the appearance of G. inflata were strongly cyclic, resulting in large periodic changes in the abundances of Globorotalia puncticulata and N. acostaensis. The benthic foraminiferal population was studied in detail over the middle-to-upper Pliocene transition to establish the nature and behavior of the intermediate-depth water mass in the northeastern Atlantic at the time of ice-sheet growth in the Northern Hemisphere. This water mass is presently warm and saline, having its source in the Mediterranean Sea. The benthic data show that the intermediate-depth water mass was undergoing a series of progressive changes over the interval including the first appearance of G. inflata. These changes are particularly reflected in the relative abundances of Globocassidulina subglobosa (Brady), Uvigerina, and Ehrenbergina. Also, the mean size of individuals in the G. subglobosa populations shows systematic variation, indicating changing intermediate-depth water properties. Oxygen-isotope analyses show that the intermediate-depth water mass was cold during the middle-to-late Pliocene transition. This interpretation is supported by the relative abundances of benthic foraminiferal species. Hence, the intermediate-depth northeastern Atlantic water mass of the middle to late Pliocene was considerably different from the intermediate-depth water mass of the present.

Homogenized radiosonde record at station Ny-Ålesund, Spitsbergen, 1993-2014

Radiosonde measurements obtained at the Arctic site Ny-Ålesund (78.9° N, 11.9° E), Svalbard, from 1993 to 2014 have been homogenized accounting for instrumentation discontinuities by correcting known errors in the manufacturer provided profiles. From the homogenized data record, the first Ny-Ålesund upper-air climatology of wind, temperature and humidity is presented, forming the background for the analysis of changes during the 22-year period. Particularly during the winter season, a strong increase in atmospheric temperature and humidity is observed, with a significant warming of the free troposphere in January and February up to 3 K per decade. This winter warming is even more pronounced in the boundary layer below 1 km, presumably amplified by mesoscale processes including e.g. orographic effects or the boundary layer capping inversion. Though the largest contribution to the increasing atmospheric water vapour column in winter originates from the lowermost 2 km, no increase in the contribution by specific humidity inversions is detected. Instead, we find an increase in the humidity content of the large scale background humidity profiles. At the same time, the tropospheric flow in winter is found to occur less frequent from northerly directions and to the same amount more frequent from the South. We conclude that changes in the atmospheric circulation lead to an enhanced advection of warm and moist air from lower latitudes to the Svalbard region in the winter season, causing the warming and moistening of the atmospheric column above Ny-Ålesund.

Cenozoic record of continental mineral deposit on Broken and Ninetyeast Ridges, Indian Ocean

The mineral component of pelagic sediments recovered from the Indian Ocean provides both a history of eolian deposition related to climatic changes in southern Africa and a record of terrigenous input related to sediment delivery from the Himalayas. A composite Cenozoic dust flux record from four sites in the central Indian Ocean is used to define the evolution of the Kalahari and Namib desert source regions. The overall record of dust input is one of very low flux for much of the Cenozoic indicating a long history of climate stability and regional hyperaridity. The most significant reduction in dust flux occurred near the Paleocene/Eocene boundary and is interpreted as a shift from semiarid climates during the Paleocene to more arid conditions in the early Eocene. Further aridification is recorded as stepwise reductions in the input of dust material which occur from about 35 to 40 Ma, 27 to 32 Ma, and 13 to 15 Ma and correlate to significant enrichments in benthic foraminifer delta18O values. The mineral flux in sediments from the northern Indian Ocean, site 758, records changes in the terrigenous input apparently related to the erosion of the Himalayas and indicates a rapid late Cenozoic uplift history. Three major pulses of increased terrigeneous sediment flux are inferred from the depositional record. The initial increase began at about 9.5 Ma and continued for roughly 1.0 million years. A second pulse with approximately the same magnitude occurred from about 7.0 to 5.6 Ma. The largest pulse of enhanced terrigenous influx occurred during the Pliocene from about 3.9 to 2.0 Ma when average flux values were severalfold greater than at any other time in the Cenozoic.

Paleoenvironmental changes in the western Mediterranean since the last glacial maximum: High resolution multiproxy record from the Algero-Balearic basin

The present study uses a multiproxy approach in order to further understand the evolution of climate responses in the western Mediterranean as of the Last Glacial Maximum. Sediments from ODP Site 975 in the Algero-Balearic basin have been analysed at high resolution, both geochemically andmineralogicallly. The resulting data have been used as proxies to establish a sedimentary regime, primary marine productivity, the preservation of the proxies and oxygen conditions. Fluctuations in detrital element concentrations were mainly the consequence of wet/arid oscillations. Productivity has been established using Ba excess, according to which marine productivity appears to have been greatest during cold events Heinrich 1 and Younger Dryas. The S1 time interval was not as marked by increases in productivity as was the eastern Mediterranean. In contrast, the S1 interval was first characterized by a decreasing trend and then by a fall in productivity after the 8.2 ky BP dry-cold event. Since then productivity has remained low. Here we report that there was an important redox event in this basin, probably a consequence of the major oceanographic circulation change occurring in the western Mediterranean at 7.7 ky BP. This circulation change led to reventilation as well as to diagenetic remobilization of redox-sensitive elements and organic matter oxidation. Comparisons between our paleoceanographic reconstruction for this basin and those regarding other Mediterranean basins support the hypothesis that across the Mediterranean there were different types of responses to climate forcing mechanism. The Algero-Balearic basin is likely to be a key area for further understanding of the relationships between the North Atlantic and the eastern Mediterranean basins.

Pollen record and dating of a sediment profile from Lake Voulkaria, Greece

A palynological investigation of a Holocene profile from Lake Voulkaria, western Greece, was carried out as a contribution to the environmental history of the coastal area of northwestern Acarnania and the Classical city of Palairos. It shows that deciduous oaks dominated the natural vegetation of the area throughout the Holocene. Until ca. 7000 B.C. Pistacia occurred abundantly, while other evergreen woody taxa were rare. At ca. 6300 B.C. an expansion of Carpinus orientalis/Ostrya can be observed. Around ca. 5300 B.C. spreading of Erica indicates a change to a drier climate and/or first human impact. Since ca. 3500 B.C. an increase of evergreen shrubs now clearly indicates land-use. The foundation of the Classical city of Palairos led to a temporary expansion of Phillyrea maquis. Within this period, molluscs of brackish water indicate the use of the lake as a harbour after the construction of a connection to the sea. The deciduous Quercus woodland recovered when human impact decreased in the area, and lasted until modern times.

Lithology and pollen record of 4 profiles from the Bavaria, southern Germany

Palynological investigations of sediments from northern Bavaria (Rhön, Grabfeld, Lange Berge) reveal the Late Glacial and Postglacial history of the regional vegetation. The older sedirnents were found in the Rhön (Schwarzes Moor) and date back into the Bölling Period. At the end of that period pine spread into the Grabfeld. In both areas Lacher Tuff has been found. A radiocarbon date of 10,300 BP was found for the Late Glacial - Postglacial transition and one of 9300 BP for the Preboreal - Boreal transition. Hazel reached its highest values in the Rhön around 7,400 BP. During the Atlanticum a deciduous mixed oak forest covered the Rhön and Grabfeld regions. Beech dominated since the Subatlanticum. In the Lange Berge region, however, a mixed forest with Fagus, Picea, Pinus and Abies developed. In the Rhön first anthropogenic influence was found during the Latene Period. The boundary between zone IX and X has been dated at 820 A.D., and the start of extensive forest clearances at 1000 A. D. A culmination of landuse was found for the Medieval Period. At the end of that period however the Rhön was deserted. New forest clearances started around 1500 A.D., but were interrupted by the 'Thirty Years War'. Afterwards the Rhön got its present appearance.