Orbitally tuned time scale and astronomical forcing in the middle Eocene to early Oligocene determined on ODP and IODP sediment cores

Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, we construct a robust astronomically calibrated age model for the middle Eocene to early Oligocene interval (31-43 Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the Middle Eocene Climate Optimum and the Eocene/Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new time scale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and -U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently we applied orbital tuning of the records to the La2011 orbital solution. The resulting new time scale revises and refines the existing orbitally tuned age model and the Geomagnetic Polarity Time Scale from 31 to 43 Ma. Our newly defined absolute age for the Eocene/Oligocene boundary validates the astronomical tuned age of 33.89 Ma identified at the Massignano (Italy) global stratotype section and point. Our compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during very long eccentricity cycle minima around 35.5 Ma, 38.3 Ma and 40.1 Ma.

Reference list of 120 datasets from time series station Payerne used for exploratory search

The analysis of time-dependent data is an important problem in many application domains, and interactive visualization of time-series data can help in understanding patterns in large time series data. Many effective approaches already exist for visual analysis of univariate time series supporting tasks such as assessment of data quality, detection of outliers, or identification of periodically or frequently occurring patterns. However, much fewer approaches exist which support multivariate time series. The existence of multiple values per time stamp makes the analysis task per se harder, and existing visualization techniques often do not scale well. We introduce an approach for visual analysis of large multivariate time-dependent data, based on the idea of projecting multivariate measurements to a 2D display, visualizing the time dimension by trajectories. We use visual data aggregation metaphors based on grouping of similar data elements to scale with multivariate time series. Aggregation procedures can either be based on statistical properties of the data or on data clustering routines. Appropriately defined user controls allow to navigate and explore the data and interactively steer the parameters of the data aggregation to enhance data analysis. We present an implementation of our approach and apply it on a comprehensive data set from the field of earth bservation, demonstrating the applicability and usefulness of our approach.

Activity and biomass of small benthic biota in the central Arctic Ocean

Sediment samples collected during the expedition "Arctic Ocean '96" with the Swedish ice-breaker ODEN were investigated to estimate for the first time heterotrophic activity and total microbial biomass (size range from bacteria to small metazoans) from the perennially ice-covered central Arctic Ocean. Benthic activities and biomass were evaluated analysing a series of biogenic sediment compounds (i.e. bacterial exoenzymes, total adenylates, DNA, phospholipids, particulate proteins). In contrast to the very time-consuming sorting, enumeration and weight determination, analyses of biochemical sediment parameters may represent a useful method for obtaining rapid information on the ecological situation in a given benthic system. Bacterial cell numbers and biomass were estimated for comparison with biochemically determined biomass data, to evaluate the contribution of the bacterial biomass to the total microbial biomass. It appeared that bacterial biomass made up only 8-31% (average of all stations = 20%) of the total microbial biomass, suggesting a large fraction of other small infaunal organisms within the sediment samples (most probably fungi, yeasts, protozoans such as flagellates, ciliates or amoebae, as well as a fraction of small metazoans). Activity and biomass values determined within this study were generally extremely low, and often even slightly lower than those given for other deep oceanic regions, thus characterizing the seafloor of the central Arctic Ocean as a "benthic desert". Nevertheless, some clear trends in the data could be found, e.g. generally sharply decreasing values within the sediment column, a vague tendency for declining values with increasing water depth of sampling stations, and also differences between various Arctic deep-sea regions.

Plio-Pleistocene diatom biostratigraphy from ODP Leg 177, Atlantic sector of the Southern Ocean

Seven sites were drilled during Ocean Drilling Program Leg 177 in the Atlantic sector of the Southern Ocean (SO) on a transect over the Antarctic Circumpolar Current from the Subantarctic to the Antarctic Zone. At four sites sediments were recovered with a Pliocene/Pleistocene sediment package of up to 580 m allowing the refinement of previous diatom zonation concepts. Samples were analyzed on stratigraphic distribution and abundance of diatom species. A refined diatom biozonation tied to the geomagnetic polarity record is proposed. For the middle and late Pleistocene two zonations applicable to the northern and southern area of the SO were constructed, considering different latitudinal distributions of biostratigraphic diatom marker species. The southern zonation for the Pleistocene relies on the occurrence of species of the genus Rouxia, R. leventerae and R. constricta n. sp. as well as on a revised last occurrence datum (LOD) of Actinocyclus ingens (0.38 Ma, late marine isotope stage (MIS) 11). The use of these new stratigraphic marker species refines the temporal resolution for biostratigraphic age assignment to up to 0.1 Myr. In particular the LOD of R. leventerae as an indicator for the MIS 6/5 boundary (Termination II) will improve future dating of carbonate-free Antarctic sediments. These new data were obtained from sediments of Sites 1093 and 1094 (Antarctic Zone). The northern zonation for the middle and late Pleistocene time interval is based on the Pleistocene abundance pattern of Hemidiscus karstenii which was already proposed by previous investigations (e.g. Gersonde and Barcena, 1998). One new species (R. constricta) and two new combinations (Fragilariopsis clementia, Fragilariopsis reinholdii) are proposed in this study.

Pollen records and age determinations from 2 profiles at Lake Nikolay, Lena Delta

Radiocarbon-dated pollen, rhizopod, chironomid and total organic carbon (TOC) records from Nikolay Lake (73°20'N, 124°12'E) and a pollen record from a nearby peat sequence are used for a detailed environmental reconstruction of the Holocene in the Lena Delta area. Shrubby Alnus fruticosa and Betula exilis tundra existed during 10,300-4800 cal. yr BP and gradually disappeared after that time. Climate reconstructions based on the pollen and chironomid records suggest that the climate during ca. 10,300-9200 cal. yr BP was up to 2-3 °C warmer than the present day. Pollen-based reconstructions show that the climate was relatively warm during 9200-6000 cal. yr BP and rather unstable between ca. 5800-3700 cal. yr BP. Both the qualitative interpretation of pollen data and the results of quantitative reconstruction indicate that climate and vegetation became similar to modern-day conditions after ca. 3600 cal. yr BP. The chironomid-based temperature reconstruction suggests a relatively warm period between ca. 2300 and 1400 cal. yr BP, which corresponds to the slightly warmer climate conditions reconstructed from the pollen. Modern chironomid and rhizopod assemblages were established after ca. 1400 cal. yr BP.

Oxygen isotopes, IRD and SST reconstruction for the interval MIS31-19 of IODP Site 306-U1314

Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic d18O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 (~940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic d18O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic d18O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.

Eocene calcareous nannofossils in DSDP Holes 95-612 and 95-613

Lower Eocene calcareous nannofossil limestone cored at DSDP Site 612 on the middle slope off New Jersey represents an almost complete biostratigraphic sequence; only the lowest biozone (CP9a; NP10*) was not recovered. The thickness of the strata (198 m), the good preservation of the nannofossils, and the lack of long hiatuses justify the acceptance of this section as a lower Eocene reference for the western North Atlantic margin. The widely recognized and very similar nannofossil zonations of Martini (NP zones) and Bukry-Okada (CP zones) are emended slightly to make their lower Eocene biozones coeval; in addition, five new subzones are erected that subdivide zones CP10 and CPU (NP12 and NP13). Established biozone names are retained as they are altered little in concept, but alphanumeric code systems are changed somewhat by appending an asterisk (*) to identify zones that are emended. Zone CP10* (NP12*) is divided into two parts, the Lophodolithus nascens Subzone (CP10*a; NP12*a) and the Helicosphaera seminulum Subzone (CP10*b; NP12*b). Zone CPU* (NP13*) is divided into three parts, the Helicosphaera lophota Subzone (CP11*a; NP13*a), the Cyclicargolithuspseudogammation Subzone (CP11*b; NP13*b), and the Rhabdosphaera tenuis Subzone (CP11*c; NP13*c). At Site 612, a time-depth curve based on nannofossil datums dated in previous studies reveals a smoothly declining sediment accumulation rate, from 4.9 cm/10**3yr in CP10* (NP12*) to 2.8 cm/103 yr. in CP12* (NP14*). The ages of first-occurrence datums not previously dated are approximated by projection onto this timedepth curve and are as follows: Helicosphaera seminulum, 55.0 Ma; Helicosphaera lophota, 54.5 Ma; Cyclicargolithus pseudogammation, 53.7 Ma; Rhabdosphaera tenuis, 52.6 Ma; and Rhabdosphaera inflata, 50.2 Ma. At nearby Site 613 on the upper rise, strata of similar age, 139 m thick, contain an unconformity representing Subzone CPll*b (NP13*b) and a hiatus of approximately 1.1 m.y. duration. The sediment accumulation rate in the lower part of this section (9.7 cm/10**3yr.) is twice that observed for equivalent strata at Site 612. The hiatus and the heightened sediment accumulation rate at Site 613 probably represent the effects of episodic mass wasting on the early Eocene continental slope and rise.

(Table 2) Oxygen and carbon isotope composition of planktonic foraminiferal species from DSDP Holes 93-603B and 93-604, and one benthic species from Hole 93-604

Holes 603C and 604 of DSDP Leg 93 were drilled on the western Atlantic continental rise at water depths of 4633 m and 2364 m, respectively. In Hole 603C, a nearly continuous, undisturbed, and complete section of Pliocene and lower Pleistocene sediments was recovered by hydraulic piston coring; in Hole 604, a section of uppermost Miocene to Pleistocene sediments was incompletely recovered by rotary coring. In order to reconstruct the Pliocene and Pleistocene history of isotopic variations, 139 oxygen and carbon isotope values were determined for planktonic and monospecific benthic foraminifer samples from these holes. Large parts of the Pleistocene history could not, however, be documented because sample intervals were large and sediments at Site 604 were redeposited. Time correlation is based on magnetostratigraphic (Hole 603C) and micropaleontologic (Hole 603C, Site 604) interpretation. Stable isotope analyses were carried out on the planktonic foraminiferal species Globigerinoides ruber, G. obliquus, and Globorotalia inflata from Hole 603C (48 analyses) and from Site 604 (48 analyses); at Site 604, the benthic foraminifer Uvigerina peregrina (43 analyses) was also studied through the section. Age calibration for Hole 603C is based on the magnetostratigraphy of Canninga et al. (1987; doi:10.2973/dsdp.proc.93.130.1987), which uses the time scale of Lowrie and Alvarez (1981).

Holocene DBD and Ti/LOI timeseries from Lake Hajeren on Svalbard, indicators of past glacier activity

The Arctic is warming faster than anywhere else on Earth. Holocene proxy time-series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. However, available datasets are scarce, unevenly distributed and often of coarse resolution. Glaciers are sensitive recorders of climate shifts and variations in rock-flour production transfer this signal to the lacustrine sediment archives of downstream lakes. Here, we present the first full Holocene record of continuous glacier variability on Svalbard from glacier-fed Lake Hajeren. This reconstruction is based on an undisturbed lake sediment core that covers the entire Holocene and resolves variability on centennial scales owing to 26 dating points. A toolbox of physical, geochemical (XRF) and magnetic proxies in combination with multivariate statistics has allowed us to fingerprint glacier activity in addition to other processes affecting the sediment record. Evidence from variations in sediment density, validated by changes in Ti concentrations, reveal glaciers remained present in the catchment following deglaciation prior to 11,300 cal BP, culminating in a Holocene maximum between 9.6 and 9.5 ka cal BP. Correspondence with freshwater pulses from Hudson Strait suggests that Early Holocene glacier advances were driven by the melting Laurentide Ice Sheet (LIS). We find that glaciers disappeared from the catchment between 7.4 and 6.7 ka cal BP, following a late Hypsithermal. Glacier reformation around 4250 cal BP marks the onset of the Neoglacial, supporting previous findings. Between 3380 and 3230 cal BP, we find evidence for a previously unreported centennial-scale glacier advance. Both events are concurrent with well-documented episodes of North Atlantic cooling. We argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling. These findings highlight the climate-sensitivity of the small glaciers studied, which rapidly responded to climate shifts. The start of prolonged Neoglacial glacier activity commenced during the Little Ice Age (LIA) around 700 cal BP, in agreement with reported advances from other glaciers on Svalbard. In conclusion, this study proposes a three-stage Holocene climate history of Svalbard, successively driven by LIS meltwater pulses, episodic Atlantic cooling and declining summer insolation.