Growth rates and stable carbon and oxygen isotope record of corals from the Red Sea

Monthly delta18O records of 2 coral colonies (Porites cf. lutea and P. cf. nodifera) from different localities (Aqaba and Eilat) from the northern Gulf of Aqaba, Red Sea, were calibrated with recorded sea surface temperatures (SST) between 1988 and 2000. The results show high correlation coefficients between SST and delta18O. Seasonal variations of coral delta18O in both locations could explain 91% of the recorded SST. Different delta18O/SST relations from both colonies and from the same colonies were obtained, indicating that delta18O from coral skeletons were subject to an extension rate effect. Significant delta18O depletions are associated with high extension rates and higher values with low extension rates. The relation between coral skeletal delta18O and extension rate is not linear and can be described by a simple exponential model. An inverse relationship extends over extension rates from 1 to 5 mm/yr, while for more rapidly growing corals and portions of colonies the relation is constant and the extension rate does not appear to have a significant effect. We recommend that delta18O values be obtained from fast-growing corals or from portions in which the isotopic disequilibrium is fairly constant (extension rate >5 mm/yr). The results show that interspecific differences in corals may produce a significant delta18O profile offset between 2 colonies that is independent of environmental and extension-rate effects. We conclude that the rate of skeletal extension and the species of coral involved have an important influence on coral delta18O and must be considered when using delta18O records for paleoclimatic reconstructions.

Calcium carbonate, sedimentation and mass accumulation rates at DSDP Site 85-572

At Site 572, located at 1°N, 114° W (3903 m water depth), we recovered a continuous hydraulic piston cored section of upper Miocene to upper Pleistocene pelagic sediments. The sediment is composed of biogenic carbonate and silica with nonbiogenic material as a minor component. Detailed analysis of the calcium carbonate content shows that the degree of variability in carbonate deposition apparently changed markedly between the late Miocene and Pliocene at this equatorial Pacific site. During this interval carbonate mass accumulation rates decreased from 2.6 to 0.8 g/cm**2 per 10**3 yr. If we assume that variations in CaCO3 content reflect changes in the degree of dissolution, then the detailed carbonate analysis would suggest that the degree of variability in carbonate deposition decreases by a factor of 5 as the dominant wavelength of variations increases significantly. However, if the variability in carbonate concentration is described in terms of changes in mean mass accumulation, calculations then suggest that relatively small changes in noncarbonate rates may be important in controlling the observed carbonate records. In addition, the analysis suggests that the degree of variability observed in pelagic carbonate data may in part reflect total accumulation rates. Intervals with high sedimentation rates show lower amplitude variations in concentration than intervals with lower sedimentation rates for the same degree of change in the carbonate accumulation rate.

Manganese contents and accumulation rates in reduced bottom sediments of the Sea of Okhotsk

Manganese contents in reduced sediments and accumulation rates were investigated. Their values in sediments of most of cores are background (0.03-0.07 %).Anomalous concentrations (up to 2.5 %) and accumulation rates (up to 60 mg/cm**2/ka) occur near the known region of hydrothermal barite mineralization in the Derugin Basin. High accumulation rates of Mn (>10 mg/cm**2/ka) also occur in Holocene sediments to south-east from the Derugin Basin. It can be assumed that high Mn contents and accumulation rates occur there due to transportation of Mn-rich water from the Derugin Basin in the near-bottom layer under the lower border of the Sea of Okhotsk Intermediate Water. Intensive Mn accumulation is also typical for the South Okhotsk Basin near the Bussol Strait. Mn accumulation rates of glacial sediments of the second oxygen isotope stage are less significant, which is presumed to be caused by paleoceanological reasons.

Linear sedimentation rates and approximate mass accumulation rates at DSDP Site 61-462

A 560-meter-thick sequence of Cenomanian through Pleistocene sediments cored at DSDP Site 462 in the Nauru Basin overlies a 500-meter-thick complex unit of altered basalt flows, diabase sills, and thin intercalated volcaniclastic sediments. The Upper Cretaceous and Cenozoic sediments contain a high proportion of calcareous fossils, although the site has apparently been below the calcite compensation depth (CCD) from the late Mesozoic to the Pleistocene. This fact and the contemporaneous fluctuations of the calcite and opal accumulation rates suggest an irregular influx of displaced pelagic sediments from the shallow margins of the basin to its center, resulting in unusually high overall sedimentation rates for such a deep (5190 m) site. Shallow-water benthic fossils and planktonic foraminifers both occur as reworked materials, but usually are not found in the same intervals of the sediment section. We interpret this as recording separate erosional interludes in the shallow-water and intermediate-water regimes. Lower and upper Cenozoic hiatuses also are believed to have resulted from mid-water events. High accumulation rates of volcanogenic material during Santonian time suggest a corresponding significant volcanic episode. The coincidence of increased carbonate accumulation rates during the Campanian and displacement of shallow-water fossils during the late Campanian-early Maestrichtian with the volcanic event implies that this early event resulted in formation of the island chains around the Nauru Basin, which then served as platforms for initial carbonate deposition.

Sediment accumulation rates of sediment cores from the North-West African continental margin

Six soft sediment cores, up to and over 9 m in length, and additional surface samples were selected for study of their planktonic foraminifera to provide information on the Holocene and Pleistocene stratigraphy of the West African continental margin south of the present boundary of the Sahara. The material was collected by the German research vessel "Meteor" during Cruise 25 in 1971. The residues larger than 160 microns determined, counted and statistically evaluated. Stratigraphical correlations with trans- Antlantic regions are given by occurrence of Truncorotalidoides hexagonus and Globorotalia tumidula flexuosa which mark the last interglacial stage. According to the climatic record the two deep-sea cores extend down to the V-zone, considered here as equivalent to the Mindel-Riss-interglacial time, as there are three distinctly warm and two cold periods indicated in the cores by planktonic foraminiferal faunas. Z-zone = Holocene is present in all cores, Y-zone = Wuermian glacial can be divided into five section, three cold and two warm stages; the X-zone can be divided into three warm stages, separated into two cool periods. The earliest warm stage is indicated to be the warmest one. There are excellent correlations to the Camp century ice core from Greenland, to the Mediterranean, to the Carribean and to the tropical Atlantic as well as to the Barnados stage. The W-zone was correlated to the Riss-glacial. V-zone is a warm period, the upper limit of which being not sufficiently defined, which contains also some cool sections. Increasing sedimentation rates from the deep-sea to the upper slope reveal climatic and regional details in Holocene and Late Pleistocene history of the continental margin. These were based mainly on different parameters of planktonic foraminiferal thanatocoenoses which are the main components of the size fraction >160 microns of the pelagic core. They become incerasingly diluted by other faunal and terrigenous components with decreasing slope depths. Estimates of absolute abundances, ranging from 25000 specimens/gm of sediment in the deep sea to less than 100, indicate various sedimentary processes at the continental margin. An ecological correlation by dominant species is possible. Readily computed temperature indices of different scales are presented which indicate, for instance, three distinctly cold sections within the last glacial and seven warm sections within the last interglacial lime. These are used for estimates of sedimentation rates. During cold periods sedimentation rates are higher than during warmer periods. Stratigraphic correlation and faunal record, combined with absolute abundances and sedimentation rates, indicated that in the deep sea turbidity currents not only cause high sedimentation rates for short periods of time, but also that material is occasionally eroded. Effects of upwelling may be detected in the surfacc sediment samples as well as in late Pleistocene and early Holocene samples of the slope by planktonic foraminiferal data which are not influenced by sedimentary processes.

A 31,000-year high-resolution record from two sediment cores off northwest Africa

Benthic foraminiferal assemblage compositions and sedimentary geochemical parameters were analyzed in two radiocarbon dated sediment cores from the upwelling area off NW Africa at 12°N, to reconstruct productivity changes during the last 31 kyr. High-latitude cold events and variations in low-latitude summer insolation influenced humidity, wind systems, and the position of the tropical rain belt over this time period. This in turn caused changes in intensity and seasonality of primary productivity off the southern Northwest African continental margin. High accumulation rates of benthic foraminifera, carbonate, and organic carbon during times of north Atlantic melt water events Heinrich 2 (25.4 to 24.3 kyr BP) and 1 (16.8 to 15.8 kyr BP) indicate high productivity. Dominance of infaunal benthic foraminiferal species and high numbers of deep infaunal specimens during that time indicate a strong and sustained supply of refractory organic matter reworked from the upper slope and shelf. A more southerly position of the tropical rainbelt and the Northeast trade wind belt during Heinrich 2 and 1 may have enhanced wind intensity and almost permanent upwelling, driving this scenario. A phytodetritus-related benthic fauna indicates seasonally pulsed input of labile organic matter but generally low year-round productivity during the Last Glacial Maximum (23 to 18 kyr BP). The tropical rainbelt is more expanded to the North than during Heinrich Events, and relatively weak NE trade winds resulted in seasonal and weak upwelling, thus lower productivity. High productivity characterized by a seasonally high input of labile organic matter, is indicated for times of orbital forced warming, such as the African Humid Period (9.8 to 7 kyr BP). An intensified African monsoon during boreal summer and the northernmost position of the tropical rainbelt within the last 31 kyr resulted in enhanced river discharge from the northward-extended drainage area (or river basin) initiating intense phytoplankton blooms. In the late Holocene (4 to 0 kyr BP) strong carbonate dissolution may have been caused by even more enhanced organic matter fluxes to the sea floor. Increasing aridity on the continent and stronger NE trade winds induced intensive, seasonal coastal upwelling.

Benthic foraminiferal stable isotope stratigraphy of ODP Site 138-846 in the tropical Pacific Ocean

A stable-isotope stratigraphy at Site 846 (tropical Pacific, 3°06'S, 90°49'W, 3307 m water depth), based on the benthic foraminifers Cibicides wuellerstorfi and Uvigerina peregrina, yields a high-resolution record of deep-sea delta18O and delta13C over the past 1.8 Ma, with an average sampling interval of 3 k.y. Variance in the delta18O and delta13C records is concentrated in the well-known orbital periods of 100, 41, and 23 k.y. In the 100-k.y. band, both isotopic signals grow from relatively low amplitudes prior to 1.2 Ma, to high amplitudes in the late Quaternary since 0.7 Ma. The amplitude of delta18O and especially of delta13C decreases in the 41-k.y. band as it grows in the 100-k.y. band, consistent with a transfer of energy into an orbitally-paced internal oscillation. A weak 30-k.y. rhythm, present in both delta18O and delta13C, may reflect nonlinear interaction between the 41-k.y. and 100-k.y. bands in the evolving climate system. In the 23-k.y. and 19-k.y. bands associated with orbital precession, delta18O and delta13C are not coherent with each other on long time scales, and do not evolve like the 100-k.y. and 41-k.y. bands. This suggests that the source of the growing 100-k.y. oscillation is not a nonlinear response to precession, in contrast to predictions of some climate models. Sedimentation rates at this site also vary with a strong 100-k.y. cycle. Unlike the isotope records, the amplitude of 100-k.y. variations in sedimentation rate is relatively constant over the past 1.8 Ma, ranging from about 15 to 70 m/m.y. Prior to 0.9 Ma, sedimentation rates co-vary with orbital eccentricity, rather than with global climate as reflected by delta18O or delta13C. A source of this 100-k.y. cycle of sedimentation rate in the absence of similar ice volume fluctuations may be precessional heating of equatorial land masses, which in an energy balance climate model drives variations of monsoonal climates with a 100-k.y. rhythm. For the interval younger than 0.9 Ma, high sedimentation rates in the 100-k.y. band are consistently associated with glacial stages. This change of pattern suggests that when the amplitude of glacial cycles become large enough, their global effects overpower a local monsoon-driven variation in sedimentation rate at Site 846.

Beryllium concentrations and deposition rates in ODP holes from the north Atlantic

Increases in the production rate of cosmogenic radionuclides associated with geomagnetic excursions have been used as global tie-points for correlation between records of past climate from marine and terrestrial archives. We have investigated the relative timing of variations in 10Be production rate and the corresponding palaeomagnetic signal during one of the largest Pleistocene excursions, the Iceland Basin (IB) event (ca. 190 kyr), as recorded in two marine sediment cores (ODP Sites 1063 and 983) with high sedimentation rates. Variations in 10Be production rate during the excursion were estimated by use of 230Thxs normalized 10Be deposition rates and authigenic 10Be/9Be. Resulting 10Be production rates are compared with high-resolution records of geomagnetic field behaviour acquired from the same discrete samples. We find no evidence for a significant lock-in depth of the palaeomagnetic signal in these high sedimentation-rate cores. Apparent lock-in depths in other cores may sometimes be the result of lower sample resolution. Our results also indicate that the period of increased 10Be production during the IB excursion lasted longer and, most likely, started earlier than the corresponding palaeomagnetic anomaly, in accordance with previous observations that polarity transitions occur after periods of reduced geomagnetic field intensity prior to the transition. The lack of evidence in this study for a significant palaeomagnetic lock-in depth suggests that there is no systematic offset between the 10Be signal and palaeomagnetic anomalies associated with excursions and reversals, with significance for the global correlation of climate records from different archives.

Geochemical and physical sediment properties of sediment cores from the Portuguese shelf

Marine sediments from the Portuguese shelf are influenced by environmental changes in the surrounding continental and marine environment. These are largely controlled by the North Atlantic Oscillation, but additional impacts may arise from episodic tsunamis. In order to investigate these influences, a high resolution multi-proxy study has been carried out on a 5.4 m long gravity core and five box cores from the Tagus prodelta on the western Portuguese margin, incorporating geochemical (Corg/Ntotal ratios, d13Corg, d15N, d18O, Corg and CaCO3 content) and physical sediment properties (magnetic susceptibility, grain-size). Subsurface data of the five box cores indicate no major effect of early postdepositional alteration. Surface data show a higher fraction of terrigenous organic material close to the river mouth and in the southern prodelta. Gravity core GeoB 8903 covers the last 3.2 kyrs with a temporal resolution of at least 0.1 cm/yr. Very high sedimentation rates between 69 and 140 cm core depth indicate a possible disturbance of the record by the AD1755 tsunami, although no evidence for a disturbance is observed in the data. Sea surface temperature and salinity on the prodelta, the local budget of marine NO3- as well as the provenance of organic matter remained virtually constant during the past 3.2 kyrs. A positive correlation between magnetic susceptibility (MS) and North Atlantic Oscillation (NAO) is evident for the past 250 years, coinciding with a negative correlation between mean grain-size and NAO. This is assigned to a constant riverine supply of fine material with high MS, which is diluted by the riverine input of a coarser, low-MS component during NAO negative, high-precipitation phases. End-member modelling of the lithic grain-size spectrum supports this, revealing a third, coarse lithic component. The high abundance of this coarse end-member prior to 2 kyr BP is interpreted as the result of stronger bottom currents, concentrating the coarse sediment fraction by winnowing. As continental climate was more arid prior to 2 kyr BP (Subboreal), the coarse end-member may also consist of dust from local sources. A decrease in grain-size and CaCO3 content after 2 kyr BP is interpreted as a result of decreasing wind strength. The onset of a fining trend and a further decrease in CaCO3 around AD900 occurs simultaneous to climatic variations, reconstructed from eastern North Atlantic records. A strong increase in MS between AD1400 and AD1500 indicates higher lithic terrigenous input, caused by deforestation in the hinterland.

Deep-sea sediment core PS2644 record from the southern Greenland Sea

The PS2644 deep-sea core sequence, retrieved from the northwestern margin of Iceland and covering the last 86 ka, exhibits high sedimentation rates during the last glacial cycle that allow the clear distinction of Greenland stadial (GS)/ interstadial (GI) cycles in the various proxy records. Abundance records of rhyolitic, basaltic and tachylytic tephra grains reveal several maxima. Tephra grains of all types were geochemically analyzed in 44 levels. A total of 92 tephras with a distinctive character have been defined within the glacial sequence of gravity core PS2644-5, whereas the Holocene record is dominated by reworked Vedde Ash grains and not suitable for tephra stratigraphic work. Of the 92 tephras only 19 geochemical populations have been linked with confidence to previously defined tephras such as from the Vedde Ash, Faeroe Marine Ash Zones (FMAZ) II and III and North Atlantic Ash Zone (NAAZ) II. For the glacial period informal names were given to 78 new tephras, most of which are basaltic tephras. Several of these layers have a unique geochemical character and might become new chronostratigraphic markers in the North Atlantic region. Linking the tephra populations to the volcanic system producing them, respectively, revealed that Icelandic eruptions dominate with 83 tephra geochemical populations and Jan Mayen with 9. Around 48% of the informal tephra layers linked to the Icelandic volcanic province are produced from either the Grimsvötn or the Veidivötn-Bardarbunga volcanic systems. The intervals spanning from Greenland Stadial (GS) 3 to Greenland Interstadial (GI) 4 (24.5-29 ka BP), from GI 8 to GS 10 (36.9-40.5 ka BP) and from GI 14 to GI 15.2 (50-56 ka BP) are the periods with the highest number of eruptions, all of which are associated with known tephra zones.

Planktonic foraminifera of the Mediterranean Sea

A high-resolution biochronology is presented for the Late Quaternary of the central Mediterranean. In the Late Pleistocene-Holocene successions three assemblage zones are distinguished on the basis of frequency patterns of planktic foraminifera. The age of these zones is determined by Accelerator Mass Spectrometry (AMS)14C dating. The zonal boundaries are dated at 12,700 yr B.P. (the end of Termination Ia) and 9600 yr B.P. (the start of Termination Ib), respectively. The AMS dates show that major changes in the planktic and benthic realms occurred synchronously over wide areas, although records of individual species may show important regional differences. In the studied areas, resedimentation processes revealed by anomalous successions of14C dates, play a far more important role than indicated by the sedimentological and micropaleontological data. Possibly these processes contribute to the very high accumulation rates in the glacial Zone III. Although the AMS technique has increased the accuracy of14C-measurements, admixture of older carbonate may still lead to substantial age differences between areas with different sedimentary regimes.

(Table 1) Remanence properties of samples from ODP Core 126-792A-7H

A combination of high sedimentation rates and high concentrations of magnetic grains in cores from Ocean Drilling Program Leg 126 resulted in the recovery of detailed direction and intensity records of the Brunhes/Matuyama geomagnetic polarity reversal. Virtual geomagnetic poles (VGPs) computed from azimuthally oriented samples taken from the cores of Hole 792A in the western Izu-Bonin forearc basin reveal that the geomagnetic pole persisted at moderate to high southern latitudes for several thousand years before a rapid migration to northern latitudes. Alternating-field demagnetization behavior, as well as NRM, NRM/ARM, and NRM/IRM intensities for samples from this same interval, and the NRM/IRM intensities derived from unoriented core samples from Holes 790C and 791B, drilled in the ~100-km distant Sumisu Rift, all suggest that the dipole field oscillated widely in intensity before the reversal. The fast polarity change occurred at the low point of an ~1100-yr field intensity cycle. This "reversal cycle" immediately followed earlier intensity cycles whose peaks rivaled or surpassed the normalized intensities of discrete samples from well above and below the reversal interval; furthermore, the troughs indicate a much diminished dipole field at their nadir.

Retreat of top cliff of Kurungnakh Island, Lena Delta, Siberia, Russia, 2010-2014, with links to shapefiles

Thawing-induced cliff top retreat in permafrost landscapes is mainly due to thermo-erosion. Ground-ice-rich permafrost landscapes are specifically vulnerable to thermo-erosion and may show high degradation rates. Within the HGF Alliance Remote Sensing and the FP7 PAGE21 permafrost programs we investigated how SAR and optical remote sensing can contribute to the monitoring of erosion rates of ice-rich cliffs in Arctic Siberia (Lena Delta, Russia). We produced two different vector products: i) Intra-annual cliff top retreat based on TerraSAR-X (TSX) satellite data (2012-2014): High-temporal resolution time series of TSX satellite data allow the inter-annual and intra-annual monitoring of the upper cliff-line retreat also under bad weather conditions and continuous cloud coverage. This published SAR product contains the retreating upper cliff lines of a 1.5 km long part of eroding ice-rich coast of Kurungnakh Island in the central Lena Delta. The upper cliff line was mapped using a thresholding approach for images acquired in the years 2012, 2013 and 2014 for the months June (2013, 2014), July (2013, 2014), August (2012, 2013, 2014) and September (2013, 2014). The cliff top retreat vector product is called 'upper_cliff_TerraSAR-X'. While the 2014 cliff lines show a clear retreat of 2 to 3 m/month, the cliff top lines for 2012 and 2013 are not chronologically ordered. However, lines from the end of the season of a year are always close to the lines from the beginning of the next summer season, indicating low cliff retreat in winter. ii) 4-year cliff top retreat based on optical satellite data (2010-2014): Long-term cliff top retreat could be assessed with two high-spatial resolution optical satellite images (GeoEye-1, 2010-08-05 and Worldview-1, 2014-08-19). The cliff top retreat vector product is called 'upper_cliff_optical'. Results: The long-term cliff top retreat derived from optical satellite data are 35 m cliff retreat within 4 years. The higher-temporal resolution SAR data equivalently show long-term rates of 18 m within 2 years and nearly now degradation activities in winter but maximum erosion rates in summer months.The Intra-seasonal cliff top retreat lines from 2014 show a rate of 2 to 3 m per month.

Recent distribution and accumulation of organic carbon on the continental margin west off Spitsbergen

The study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off Spitsbergen and direct seabed observations using a Remotely Operated Vehicle (ROV). In addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the Barents Sea with short sediment cores from a selected fjord environment (Storfjord). While sedimentation in the fjords is mainly controlled by river/meltwater discharge and coastal erosion by sea ice/glaciers resulting in high supply of terrigenous organic matter, Atlantic water inflow, and thus enhanced marine organic matter supply, characterizes the environment on the outer shelf and slope. Local deviations from this pattern, particularly on the shelf, are due to erosion and out washing of fine-grained material by bottom currents. Spots dominated by marine productivity close to the island have been found at the outer Isfjord and west off Prins Karls Forland as well as off the Kongsfjord/Krossfjord area and probably reflect local upwelling of nutrient-rich Atlantic water-derived water masses. Accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century. Negative correlation of the Isfjord temperature record with reconstructed productivities in the Storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming. Extremely high accumulation rates of marine organic carbon between 5.4 and 17.2 g/m**2/yr mark the Storfjord area, and probably high-latitude fjord environments in general, as a sink for carbon dioxide.

(Table 1) Magnetozone boundaries at DSDP Site 68-502

Obtaining long, continuous, and undisturbed sections of unconsolidated Neogene deep sea sedimentary sections has been limited by (1) practical length of piston cores to about 30 meters and (2) disturbance of sediment by rotary drilling with Glomar Challenger. The relatively high deposition rates of late Neogene sediments in the North Atlantic and in the Caribbean in particular has limited penetration, with conventional piston coring, to sediments not much older than late Pliocene in the Atlantic and not even through the late Pleistocene in the Caribbean. Rotary drilling has penetrated much older sediments in both areas, but the cores suffered extensive drilling disturbance that seriously degrades the Paleomagnetism of the material. Utilization of the hydraulic piston corer on the Challenger combines the advantage of a generally undisturbed recovery and great penetration to produce long, relatively undisturbed sections of late Neogene and Quaternary sediments suitable for paleomagnetic studies. In this chapter we present paleomagnetic data from Site 502. We tried to determine relative azimuthal orientation of successive cores (see Introduction for details). Because the low latitude of the site meant a small (inclination of about 22°) vertical component of magnetization, reversals of magnetization could easily be detected only in changes in the horizontal component, as 180° shifts in the declination direction of magnetization. Based on information from the core orienting device, a fiducial line was drawn the length of each core prior to cutting it into the standard 1.5 meter sections.