Distribution of Recent benthic foraminifera in Arctic galciomarine sediments

Foraminifera were examined in recent (<100 years) fine-grained glaciomarine muds from surface sediments and cores from Nordensheld Bay, Novaja Zemlja, and Hornsund and Bellsund, Spitsbergen. This study presents the first data on modern foraminifera distribution for fjord environments in Novaja Zemlja, Russia. The data are interpreted with reference to the distribution of foraminiferal near Svalbard and the Barents Sea. In Nordensheld Bay, live and dead Nonionellina labradorica and Islandiella norcrossi are most abundant in the outer fjord. Cassidulina reniforme and Allogromiina spp. dominate in the middle and inner fjord. The dominant species are dissimilar to species occurring in other areas of the Barents Sea region, with the exception of Svalbard fjords. The number of live foraminifera (24 to 122 tests/10 cm1) in outer and middle Nordensheld Bay corresponds with values known from the open Barents Sea. However, the biomass (0.03 mg/10 cm**3) is two orders of magnitude less due to smaller foraminiferal test size, which in glaciomarine sediments reflects the absence of larger species, paucity of large specimens, and high occurrence of juvenile foraminifera. The smaller size indicates an opportunistic response to environmental stress due to glacier proximity. The presence of Quinqueloculina stalkeri is diagnostic of glaciomarine environments in fjords of Novaja Zemlja and Svalbard.

Investigations on sediments from Lake Nam Co (Tibetan Plateau)

This study focuses on the analysis of lake sediments retrieved from the deepest part of Lake Nam Co (Tibetan Plateau). One gravity core of 115 cm length, covering the last ~ 4000 cal BP, was analyzed for geochemical and biological parameters. High organic content at ~ 4000 cal BP and the coinciding presence of pyrite framboids until ~ 2000 cal BP point to hampered decomposition of organic material due to anoxic conditions within the lake sediments. At the same time sedimentological and biological proxies suggest a rather high lake level, but still ~ 5 m below the recent one, with less saline lake water due to enhanced monsoonal activity. During this time a change in the source of organic matter to lowered input of terrestrial components is observed. A rather quick shift to a dry environment with less monsoonal influence and a lake level ~ 15 m lower than today at ~ 2000 cal BP lead to the oxygenation of sediment, the degradation of organic matter and the absence of pyrite. Oscillations of the lake level thereafter were of minor amplitude and not able to establish anoxia at the lake bottom again. A wet spell between ~ 1500 cal BP and ~ 1150 cal BP is visible in proxies referring to catchment hydrology and the ostracod-based water depth transfer function gives only a slightly elevated lake level. The last ~ 300 years are characterized by low TOC and rising TN values reflecting enhanced nutrient supply and hence an advancing influence of human activity in the catchment. Decreasing TOC/TN values point to a complete shift to almost solely aquatic biomass production. These results show that hydrological variations in terms of lake level change based on monsoonal strength can be linked to redox conditions at the lake bottom of Nam Co. Comparison with other archives over larger parts of the Tibetan Plateau and beyond exhibits a rather homogeneous climatic pattern throughout the late Holocene.

Pollen profiles from 8 sediment cores from the Degersee, Southern Germany

The discovery of a neolithic pile field in the shallow water near the eastern shore of the Degersee confirmed earlier palynological and sedimentological studies stating that early man was active in the region since more than 6000 years. The already available off-site data were freshly assessed, completed by additional data from old and new cores and the interpretations revised. A common time scale for the off-site data and the on-site data was obtained by AMS dating of terrestrial macro remains of the neolithic section of off-site core De_I+De_H. The ages can thus be parallelled with AMS ages of construction timber on-site. Pollen analyses from all cores provide a further time scale. The continuously and densely sampled pollen profile of the profundal zone embracing the entire Late glacial and Holocene serves as a reference. From the Boreal onwards the relative ages are transformed by AMS ages and varve counts into calibrated and absolute. A transect cored close to the neolithic pile field across the lake marl-platform demonstrates its geological architecture in the shallow water since the Lateglacial. Studies of the microfabric of thin sections of drilled cores and of box cores from the excavations demonstrate that neolithic settlements now at 2-3,5 m water depth had been erected on lake marl freshly fallen dry, thus indicating earlier lake levels dropped by 1.5-2 m. The neolithic section of the highly resolved off-site profile in the lake=s profundal zone has laminated and calcareous zones alternating with massive ones. Assemblages of diatoms and concentrations of trace elements changing simultaneously characterise the calcareous sections as deposits of low lake levels that lasted between some 40 and more than 300 years. The ages of discovered lake shore dwellings fall into calcareous segments with low lake levels. From the end of the Upper Atlantic period (F VII) appear Secondary Forest Cycles in the beech forest, a man-made sequence of repeated vegetational development with an identical pattern: With a decrease of beech pollen appear pollen of grasses, herbs and cultural indicators. These are suppressed by the light demanding hazel and birch, those again by ash, and finally by the shade demanding beech forming a new pollen peak. Seven main Forest Cycles are identified In the upper Neolithic period each comprising some 250, 450 or 800 years. They are subdivided into subcycles that can be broken down by very dense sampling in even shorter cycles of decadal length. Farming settlers have caused minor patchy clearances of the beech-mixed-forest with the use of fire. The phases of clearance coincide with peaks of charcoal and low stands of the lake levels. The Secondary Forest Cycles and the continuous occurrence of charcoal prove a continued occupation of the region. Together with the repeated restoration of the beech climax forest they point to pulsating occupation probably associated with dynamic demography. The synchronism of the many palynological, sedimentological and archaeological data point to an external forcing as the climate that affects comprehensively all these proxies. The fluctuations of the activity of the sun as manifested in the residual d14C go largely along with the proxies. The initial clearances at the begin of the forest cycles are linked to low lake levels and negative values of d14C that point to dry and warm phases of a more continental climate type. The subcycles exist independent from climatic changes, indicating that early man acted largely independent from external forces.

Tab. 1+2: C14-dates cf the older and younger emergence periods

In the neighbourhood of Oobloyah Bay various phenomena ean be eneountered whieh point to a ularge-seale uplift of shorelines, i.e. to an emergence of 200 m. Delta terraces, deltaic fan terraces and glacio-marine sands are regarded by the author as being the most reliable evidence of this. The marine limit documented by glacio-marine sand is to be found at ~170 m a.s.l. Hints of ancient shorelines located at a higher level exist only in the shape of badly preserved raised beaches. They were classified as less reliable records of past sea-levels, due to the lack of marine fossils and/or drift wood, and furthermore because those forms had been strongly influenced by periglacial processes. Deltaic deposits are of more importance in this context. The glacio-marine deltaic sands of several terrace levels contain terrestrial plant remnants which delivered C14dates. Using these dates und the relative elevations of terraces the emergenee of the area investigated could be recorded. This occured in a series of phases (and steps) which were summarized into two periods: an early period of emergenee which took place from at least 25 300 years B.P. to later than 17 340 years B.P. and a later one from at least 12 870 years B.P. up to the present day. The emergence seems to represent a discontinuous but regular sequence of relative sea level movements without intermittent submergence. Since the deltaic fans of the early emergence period were accumulated by sediments through glacio-fluvial channels of an adjacent glacier body the appropriate location of this glacial stage for one of the glaciers delivering meltwater (Nukapingwa Glacier) could be reconstructed. This stage of the glacier appears to belong to a retreating phase of the Mid-Wisconsin (?). The later period of emergence resulted in six rather glacio-marine delta terrace generations at the mouths of the main rivers with glaciofluvial regimen debouching into the Oobloyah Bay. A connection of this emergence with the glacial history of the field area is discussed. If one may rely on the age determinations of land derived plant fossils and their application for the climatic history of the area investigated, it must be concluded that the Heidelberg Valley, to a large extent, was alreaely deglaciated 25 000 years ago. The existence of a "Cockburn"-Phase in the sense of a major readvanee in Late Wisconsin times appears to be doubtful, or has been developed rather weakly.

Chronology and petrology of sediment cor DAPC2

Evidence from paleoclimatic archives suggests that Earth's climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period. Explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean's thermohaline circulation, but the driving mechanism remains to be identified. Here we use multidecadal marine records of faunal, oxygen isotope, and sediment proxies from the northeast Atlantic proximal to the western margins of the last glacial British Ice Sheet (BIS) to document the coupling between ice sheet dynamics, ocean circulation, and insolation changes. The core data reveal successions of short-lived (80-100 years), high-amplitude ice-rafted debris (IRD) events that were initiated up to 2000 years before the deposition of detrital carbonate during Heinrich events (HE) 1 and 2. Progressive disintegration of the BIS 19-16 kyr before present (B.P.) occurred in response to abrupt ocean-climate warmings that impinged on the northeast Atlantic during the early deglaciation. Peak IRD deposition recurs at 180-220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves. The early deglaciation culminated in a major meltwater pulse at ~16.3 kyr B.P. followed by another discharge associated with HE1 some 300 years after. We conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the BIS and possibly other margins of the Eurasian Ice Sheet. Massive but short-lived meltwater surges influenced the Atlantic meridional overturning circulation thereby contributing to North Atlantic climate variability and bipolar climatic asymmetry.

Seawater carbonate chemistry, length and survival of Inland silverside, Menidia beryllina, during experiments, 2012

Absorption of anthropogenic carbon dioxide by the world's oceans is causing mankind's 'other CO2 problem', ocean acidification. Although this process will challenge marine organisms that synthesize calcareous exoskeletons or shells, it is unclear how it will affect internally calcifying organisms, such as marine fish. Adult fish tolerate short-term exposures to CO2 levels that exceed those predicted for the next 300 years (~2,000 ppm), but potential effects of increased CO2 on growth and survival during the early life stages of fish remain poorly understood. Here we show that the exposure of early life stages of a common estuarine fish (Menidia beryllina) to CO2 concentrations expected in the world's oceans later this century caused severely reduced survival and growth rates. When compared with present-day CO2 levels (~400 ppm), exposure of M. beryllina embryos to ~1,000 ppm until one week post-hatch reduced average survival and length by 74% and 18%, respectively. The egg stage was significantly more vulnerable to high CO2-induced mortality than the post-hatch larval stage. These findings challenge the belief that ocean acidification will not affect fish populations, because even small changes in early life survival can generate large fluctuations in adult-fish abundance.

Impacts of ocean acidification on sediment processes in shallow waters of the arctic ocean

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO2 and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO2 covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study.

Polyaromatic hydrocarbons in sediments from the Barents and White Seas

Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants which can be derived from anthropogenic sources, such as combustion and discharges from extraction and transport, and natural processes, including leakage and erosion of fossil carbon. Natural PAH sources contribute, along with biological activities and terrestrial run-off, to the organic carbon content in sediments.The Barents Sea region is far from many anthropogenic sources of PAH, but production and trans-shipment of hydrocarbons is increasing. We present data for polycyclic aromatic hydrocarbon (PAH) concentrations in bottom sediments from 510 stations in the Barents and White Seas, and along the northern coast of Norway.

Sedimentary record of the western Amundsen Sea Embayment after the last glacial maximum

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is very challenging because of the general absence of calcareous (micro-) fossils and the recycling of fossil organic matter. As a consequence, radiocarbon (14C) ages of the acid-insoluble organic fraction (AIO) of the sediments bear uncertainties that are very difficult to quantify. In this paper we present the results of three different chronostratigraphic methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional 14C dating of the AIO in bulk sediment samples yielded age reversals down-core, but at all sites the AIO 14C ages obtained from diatomaceous ooze within the diatom-rich unit yielded similar uncorrected 14C ages ranging from 13,517±56 to 11,543±47 years before present (yr BP). Correction of these ages by subtracting the core-top ages, which are assumed to reflect present-day deposition (as indicated by 21044 Pb dating of the sediment surface at one core site), yielded ages between ca. 10,500 and 8,400 calibrated years before present (cal yr BP). Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1,300 years indicated deposition of the diatom-rich sediments between 14,100 and 11,900 cal yr BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka BP for the diatom-rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves for palaeomagnetic intensity. As a third dating technique we applied conventional 53 radiocarbon dating of the AIO included in acid-cleaned diatom hard parts that were extracted from the diatomaceous ooze. This method yielded uncorrected 14C ages of only 5,111±38 and 5,106±38 yr BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the extracted diatom hard parts prior to sample graphitisation and combustion for 14C dating. The deposition of the diatom-rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes on other parts of the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related.

Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica

A multicentennial and absolutely-dated shell-based chronology for the marine environment of the North Icelandic Shelf has been constructed using annual growth increments in the shell of the long-lived bivalve clam Arctica islandica. The region from which the shells were collected is close to the North Atlantic Polar Front and is highly sensitive to the varying influences of Atlantic and Arctic water masses. A strong common environmental signal is apparent in the increment widths, and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95% confidence level, they are low (r ~ 0.2), indicating that a more complex combination of environmental forcings is driving growth. Remarkable longevities of individual animals are apparent in the increment-width series used in the chronology, with several animals having lifetimes in excess of 300 years and one, at 507 years, being the longest-lived non-colonial animal so far reported whose age at death can be accurately determined. The sample depth is at least three shells after AD 1175, and the time series has been extended back to AD 649 with a sample depth of one or two by the addition of two further series, thus providing a 1357-year archive of dated shell material. The statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age-related trend in shell growth. Comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales, particularly during the period surrounding the transition from the Medieval Climate Anomaly to the Little Ice Age.

Coral and mollusc resistance to ocean acidification adversely affected by warming, 2011

Increasing atmospheric carbon dioxide (CO2) concentrations are expectedto decrease surface ocean pH by 0.3-0.5 units by 2100, lowering the carbonate ion concentration of surfacewaters. This rapid acidification is predicted to dramatically decrease calcification in many marine organisms. Reduced skeletal growth under increased CO2 levels has already been shown for corals, molluscs and many other marine organisms. The impact of acidification on the ability of individual species to calcify has remained elusive, however, as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth. Here, we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years. Calcifiers remain at risk, however, owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall. Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water, limiting dissolution and allowing organisms to calcify. Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coincide with acidification.

Carbonate sedimentation beneath the Carlifornia Current system

A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33° to 42°N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model. Biogenic sedimentation shows responses that are sometimes time-transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decrease in CaCO3, Corg, and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the North Pacific and western North America and the establishment of a strong seasonality in the central California region. A carbonate preservation event occurred at 10 ka that appears to reflect the uptake of CO2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relatively strong coastal upwelling along the central California margin, relatively weak upwelling along the northern California margin, and the northward migration of the divergence zone of the West Wind Drift.