ALBERT

Description: This is a dataset that has been acquired in 1995 as part of the U.S.-ROC Deep Seismic Imaging Study of the Taiwan Arc-Continent Collision (TAICRUST) project. This particular line was measured in the Taiwan Strait in September 1995 to image the shallow sediments and upper crust. Additional information from the Cruise EW9509 is stored at the Marine Geoscience Data System (MGDS).

Description: A diatom-based sea-ice concentration (SIC) transfer function is developed using 72 surface samples from west of Greenland and around Iceland, and through comparison with the associated modern SIC. Canonical correspondence analysis on surface sediment diatoms and monthly average of SIC reveals that April SIC is the most important environmental factor controlling the distribution of diatoms in the area, and permits the development of a diatom-based SIC transfer function. The consistency between reconstructed SIC based on diatoms from West Greenland and the instrumental and documentary data during the last ~75 years demonstrates that the diatom-based SIC reconstruction is reliable for studying the palaeoceanography off West Greenland. Relatively warm conditions with strong influence of the Irminger Current (IC) are indicated for the early part of the record (~5000-3860 cal. yr BP), corresponding in time to the latest part of the Holocene Thermal Maximum. The April SIC oscillated around the mean value between 3860 and 1510 cal. yr BP and was above mean afterwards, particularly during the time interval 1510-1120 cal. yr BP and after 650 cal. yr BP, indicating more extensive sea-ice cover in Disko Bugt. A high degree of consistency between the reconstructed April SIC and changes in the diatom species suggests that the sea-ice condition in Disko Bugt is strongly influenced by variations in the relative strength of two components of the West Greenland Current, i.e. the cold East Greenland Current and the relatively warm IC.

Description: Bedding dips in the CRP-3 drillhole were determined in three ways: (1) analysis of a dipmeter log, (2) identification of bed boundaries on borehole televiewer log images, and (3) identification of bed boundaries on digital images of the outer surfaces of oriented cores. All three methods determine both dip magnitude and downdip azimuth of bedding. Dipmeter results document variations in bedding dip throughout the logged interval (20-902 mbsf), whereas core and televiewer results are available at present only for selected depth intervals. Dipmeter data indicate that structural dip is remarkably constant, at 21° dip to azimuth 65°, throughout the Tertiary shelf section, except for the top 100 m where dips appear to be 5-10° shallower. This pattern, in conjunction with the systematically increasing dips throughout CRP-2A, suggests that the growth faulting active during CRP-2A deposition began during the final period of deposition at CRP-3. Normal faults at 260 and 539 mbsf in CRP-3 exhibit neither drag (localized dip steepening) nor significant changes in structural dip across them. Oriented core and televiewer analyses, covering a total of 200 m in the interval 400-900 mbsf, indicate bedding patterns that confirm the dipmeter results. The doleritic breccia at the base of the Tertiary section has steeper dips than overlying structural dips, possibly indicating a sedimentary dip to ENE in these fan sediments. Dip directions in the underlying Devonian Beacon sandstone are surprisingly similar to those in the overlying Tertiary section. Superimposed on the average Beacon dip of 22° to the ENE are localized tilts of up to 20°, probably caused by Tertiary fracturing and brecciation rather than original sedimentary dip variations.

Description: During the late Quaternary, both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions. Nonlinear climatic steps characterized the transitions leading to these extrema, with intermediate excursions particularly well xpressed in the dynamics of the Northern Hemisphere cryosphere. Here we document the impact of these dynamics on the north-eastern North Atlantic Ocean, focussing on the 35-10 ka interval. Sea-surface salinities have been reconstructed quantitatively based on two independent methods from core MD95-2002, recovered from the northern Bay of Biscay adjacent to the axis of the Manche paleoriver outlet and thus in connection with proximal European ice sheets and glaciers. Quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region. Our study evidences strong pulsed freshwater discharges which may have impacted the North Atlantic Meridional Overturning Circulation.

Description: A pale-dark bedded claystone-marlstone succession of Late Hauterivian age (Simbirskites discofalcatus ammonite Zone; Early Cretaceous), exposed in the clay-pit Frielingen, Germany (Lower Saxony Basin), was investigated with respect to its calcareous dinoflagellate cyst content. This study aimed at a better understanding of the usefulness of calcareous dinoflagellate cysts to reconstruct palaeoenvironments, and an evaluation of the postulated palaeoenvironmental trends associated with Lower Cretaceous pale-dark bedding rhythms. The ratio of abundant taxa, character traits of cysts, and the results of statistical species analyses were used for those analyses. Current models of sea level fluctuations and sea surface temperature were modified on the basis of the composition of calcareous dinoflagellate assemblages. Superimposed on a general sea level rise, a regressive interval with high sea surface water temperatures is reflected by the thick bed 118. This distinctively warm interval is represented by a dark bed that has commonly been interpreted to indicate cooler surface waters. It is therefore necessary to review the palaeoenvironmental interpretation of pale-dark bedding rhythms of claystone successions of the Boreal Realm. Factors other than sea surface temperature seem to be important as well. The species Pirumella edgarii was found to favour time intervals with higher sediment input. The newly described species Pirumella? sp. nov. may perhaps indicate similar environments in warmer water masses. The species Pirumella tanyphloia has been emended, we suggest including it in Pirumella multistrata forma tanyphloia. Moreover, the pithonelloid cysts found in Frielingen are currently the oldest of their kind.

Description: The Antarctic Peninsula (AP) has been identified as one of the most rapidly warming region on Earth. Satellite monitoring currently allows for a detailed understanding of the relationship between sea ice extent and duration and atmospheric and oceanic circulations in this region. However, our knowledge on ocean-ice-atmosphere interactions is still relatively poor for the period extending beyond the last 30 years. Here, we describe environmental conditions in Northwestern and Northeastern Antarctic Peninsula areas over the last century using diatom census counts and diatom specific biomarkers (HBIs) in two marine sediment multicores (MTC-38C and -18A, respectively). Diatom census counts and HBIs show abrupt changes between 1935 and 1950, marked by ocean warming and sea ice retreat in both sides of the AP. Since 1950, inferred environmental conditions do not provide evidence for any trend related to the recent warming but demonstrate a pronounced variability on pluri-annual to decadal time scale. We propose that multi-decadal sea ice variations over the last century are forced by the recent warming, while the annual-to-decadal variability is mainly governed by synoptic and regional wind fields in relation with the position and intensity of the atmospheric low-pressure trough around the AP. However, the positive shift of the SAM since the last two decades cannot explain the regional trend observed in this study, probably due to the effect of local processes on the response of our biological proxies.

Description: The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0-200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep Basin. Employing a multi-proxy approach, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEXL86 for temperature) and micropaleontological data (diatom assemblages), we derived new Holocene records of sea ice conditions and upper water column temperatures. The early Holocene (9000-7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~7000-3800 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~2100 yr) was characterized by warmer temperatures and increased sea ice presence, accompanied by reduced local primary productivity, likely in response to a shorter growing season compared to the early or mid-Holocene. The gradual increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation, despite increasing summer insolation. We postulate that, in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of the El Nino-Southern Oscillation (ENSO). However, between 3800 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time.

Description: This dataset characterizes the evolution of western African precipitation indicated by marine sediment geochemical records in comparison to transient simulations using CCSM3 global climate model throughout the Last Interglacial (130-115 ka). It contains (1) defined tie-points (age models), newly published stable isotopes of benthic foraminifera and Al/Si log-ratios of eight marine sediment cores from the western African margin and (2) annual and seasonal rainfall anomalies (relative to pre-industrial values) for six characteristic latitudinal bands in western Africa simulated by CCSM3 (two transient simulations: one non-accelerated and one accelerated experiment).

Description: Our understanding of the centennial-scale variability of the Brazil Current (BC) during the late Holocene is elusive because of the lack of appropriate records. Here we used the Mg/Ca and oxygen isotopic composition of planktonic foraminifera from two marine sediment cores collected at 27° S and 33° S off southeastern South America to assess the late Holocene variability in the upper water column of the BC. Our results show in phase fluctuations of up to 3 °C in sea surface temperatures (SST), and 0.8 per mil in oxygen isotopic composition of surface sea water, a proxy for relative sea surface salinity (SSS). Time-series analyses of our records indicate a cyclicity with a period of ca. 730 yr. We suggest that the observed cyclicity reflects variability in the strength of the BC associated to changes in the Atlantic meridional overturning circulation (AMOC). Positive (negative) SST and SSS anomalies are related to a strong (weak) BC and a weak (strong) AMOC. Moreover, periods of peak strength in the BC occur synchronously to a weak North Brazil Current, negative SST anomalies in the high latitudes of the North Atlantic, and positive (negative) precipitation anomalies over southeastern South America (equatorial Africa), further corroborating our hypothesis. This study shows a tight coupling between the variability of the BC and the high latitudes of the North Atlantic mediated by the AMOC even under late Holocene boundary conditions.

Description: The site for CRP-3, 12 km east of Cape Roberts (77.006°S; 103.719°E)was selecte to overlap the lower Oligocene strata cored in nearby CRP-2/2A, and to sample the oldest strata in the Victoria Land Basin (VLB) for Paleogene climatic and tectonic history. As it transpired there was underlap of the order of 10s of metres. CRP-3 was cored from 3 to 939 mbsf (metres below the sea floor), with a core recovery of 97%. Coring took place from October 9 to November 19, 1999, on 2.0 to 2.2 m of sea ice and through 295 in of water. The Cenozoic strata cored were mostly g1acially influenced marine sediments of early Oligocene age, though they may be earliest Eocene near the base, where at 823 mbsf Devonian Beacon sandstone was encountered. Following CRP-1 and CRP-2/2A, CRP-3 completes the coring of 1500 m of strata on the western margin of the VLB. Core fractures and other physical properties, such as sonic velocity, density and magnetic susceptibility, were measured throughout the core. Down-hole logs for these and other properties were taken from 20 down to 900-919 mbsf. Also, vertical seismic profile data were gathered from shots offset both along strike and up dip from the hole. Sonic velocities in CRP-3 are close to 2.0 km/s in the upper 80 m, but become significantly faster below 95 mbsf, averaging 3.2+0.6 km/s to the bottom of the hole. An exception to this is an interval of dolerite conglomerate from 790 to c. 820 mbsf with a velocity of c. 4.5 km/s. Dip of the strata also increases down-hole from 10° in the upper 100 m to around 22° at the bottom. Over 3000 fractures were logged through the hole, and borehole televiewer imagery was obtained for most of the hole for orienting core and future stress field analysis. Two high-angle crush zones, interpreted as faults, were encountered at c. 260 and c. 540 mbsf, but no stratigraphic displacement could be recognised. A third fault zone is inferred from a low angle shear zone in the upper part of a coarse dolerite conglomerate from 790 to 805 mbsf. Temperature gradient was found to be 28.5°.km-1. Basement strata cored from 823 mbsf to the bottom of the hole are largely light-reddish brown medium-grained sandstone (quartz-cemented quartzarenite) with abundant well-defined parallel lamination. These features are comparable with the middle Devonian part of the Beacon Supergroup, possibly the Arena Sandstone. This interval also includes a body of intrusive rock from 901 to 920 mbsf. It has brecciated contacts and is highly altered but some tholeiitic affinity can be recognised in the trace element chemistry. Its age is unknown. Post-Beacon sedimentation began on deeply eroded quartzarenite with the deposition of a thin sandstone breccia and conglomerate, probably as terrestrial talus, followed by dolerite conglomerate and minor sandstone of probable fluvial origin to 790 mbsf. Sedimentation continued in a marine setting, initially sandstone and conglomerate, but above c. 330 mbsf the strata include mudstone and diamictite also. The older sandstone and conglomerate beds are seen as the products of rapid episodic sedimentation. They are interpreted by some as the product of glaciofluvial discharge into shallow coastal waters, and others as a result of sediment gravity flows, perhaps glacially sourced, into deeper water. The core above c. 330 mbsf has facies that allow the recognition of cyclic sequences similar to those in CRP-2A. Fourteen unconformity-bounded sequences have been recognised from 330 mbsf to the sea floor, and are interpreted in terms of glacial advance and retreat, and sea level fall and rise. Detailed lithological descriptions on a scale of 1 :20 are presented for the full length of the core, along with core box images, as a 300 page supplement to this issue. The strata cored by CRP-3 are for the most part poorly fossiliferous, perhaps as a consequence of high sedimentation rates. Nevertheless the upper 200 m includes several siliceous microfossil- and calcareous nannoplankton-bearing intervals. Siliceous microfossils, including diatoms, ebrideans, chrysophycean cysts and silicoflagellates are abundant and well-preserved in the upper 67 m - below this level samples are barren or poorly preserved, but contain residual floras that indicate assemblages were once rich. No siliceous microfossils were found below 193 mbsf. Calcareous nannofossil have a similar distribution but are generally well preserved. Foraminifera, marine and terrestrial palynomorphs, and marine macrofossils were found consistentlsy down to c. 330 mbsf and sporadically to 525 mbsf. The taxa suggest marine deposition in water depth of c. 50 to 120 m. Below 525 mbsf no microfossils were found, apart from mudstone with similar marine and terrestrial palynomorphs at 781 mbsf, and rare miospores in the conglomerate below 790 mbsf. The terrestrial miospore record, which include several species of Nothofagus and podocarpaceous conifers, suggest low diversity woody vegetation, implying a cold temperate to periglacial climate for the hinterland throughout the period recorded by CRP-3. Important components of the warmer Eocene flora, known from erratics in southern McMurdo Sound, are missing, through the dominance of smectite in clay from strata below 650 mbsf suggests that the landscape prior to the timne of deposition had experienced a more temperate weathering regime. Biostratigraphy for ihe upper part of CRP-3 is provided by diatoms and calcareous nannofossils. The first appearance of Cavitatus jouseanus at 48 mbsf suggests an age of arround 31 Ma for this horizon. The last appearance of Transverspontis pulcheroides at 114 mbsf in an interval of relatively high abundance indicates a reasonably sound age for this horizon at 32.5 ± 0.5 Ma. The absence of particular resistant diatoms that are older than 33 Ma supports an age that is younger than this for the upper 200 m of CRP-3. Marine palynomorphs, which occur sporadically down to 525 mbsf and in a single occurrence at 781 inbsf, have biostratigraphical potential once the many new species in this and other CRP cores are described, and F0 and LO datums established. The mudstone at 781 mbsf has a new clinocyst species, rare Lejeunecysta cysts and a variety of acritarchs and prasinophytes, a varied marine assemblage that is quite different from and presumably younger than the well known Transantarctic Flora of mid to late Eocene age. On this basis and for the moment we conclude that the oldest strata in CRP-3 are earliest Oligocene (or possibly latest Eocene) in age - c. 34 Ma. Over 1l00 samples were taken for magnetic studies. Four magnetozones were recognisd on the basis of NRM intensity and magnetic susceptibility, reflecting the change in sediment composition between quartz sand-dominated and dolerite-dominated. For this report there was time only to produce a magnetostratigraphy for the upper 350 m. This interval is largely of reversed polarity (5 normal intervals total 50 of the 350 m), in contrast to the dominantly normal polarities of CRP-2/2A, and is inferred to be Chron C12R. This extends from 30.9 to 33 Ma. consistent with the biostratigraphic datums from the upper part of CRP-3. The lower limit of reversed polarity has yet to be established. The short period normal events are of interest as they may represent cryptochrons or even polarity changes not recognised in the Geomagnetic Polarity Time Scale. Erosion of the adjacent Transantarctic Mountains through the Kirkpatrick Basalt (Jurassic tholeiitic flows) and dolerite-intruded Beacon Supergroup (Devonian-Triassic sandstone) into granitic basement beneath is recorded by petrographical studies of clast and sand grain assemblages from CRP-3. The clasts in the lower 30 m of the Cenozoic section are almost entirely dolerite apart from a few blocks from the Beacon Supergroup beneath. Above this, however, both dolerite and granitoids are ubiquitous, the latter indicating that erosion had reached down to granitic basement even as the first sediment was accumulating in the VLB. No clasts or sand grains of the McMurdo Volcanic Group were found, but rare silt-size brown volcanic glass occurs in smear slides through most of CRP-3, and is interpreted as distal air fall from alkaline volcanism in northern Victoria Land. Jurassic basalt occurs as clasts sporadically throughout the sequence: in the sand fraction they decline upwards in abundance. The influence of the Devonian Beacon Supergroup is most striking for the interval from 600 to 200 mbsf, where quartz grains, from 10 to 50% of them rounded, dominate the sand fraction. Laminae of coal granules from the overlying Permian coal measures in all but the upper 150 in of the CRP-3 sequence show that these also were being eroded actively at this time. CRP-3 core completed the stratigraphical sampling of the western margin of the VLB by not only coring the oldest strata (Seismic Unit V5) but also the basin floor beneath. This has several important tectonic implications: - most of the Kirkpatrick Basalt and the Beacon Supergroup with the sills of Ferrar Dolerite have been eroded by the time down-faulting displaced the Beacon to form the basin floor. - matching the Beacon strata at the bottom of CRP-3 with the equivalent strata in the adjacent mountains suggests c. 3000 m of down-to-the-east displacement across the Transantarctic Mountain Front as a consequence of rifting and subsequent tectonic activity. - the age of the oldest Cenozoic strata in CRP-3 (c. 34 Ma), which are also the oldest strata in this section of the VLB, most likely represents the initiation of the rift subsidence of this part of the West Antarctic Rift System. This age for the oldest VLB fill is much younger than previously supposed by several tens of millions of years, but is consistent with newly documented sea floor spreading data immediately north of the northern Victoria Land continental margin. These new data sets will drive a re-evaluation of the relationship between initiation of uplift of the Transantarctic Mountains (currently c.55 Ma) and VLB subsidence.