Ground truthing the Cd/Ca-carbon isotope relationship in foraminifera of the Greenland-Iceland-Norwegian Seas

In order to examine whether the paleoceanographic nutrient proxies, d13C and cadmium/calcium in foraminiferal calcite, are well coupled to nutrients in the region of North Atlantic Deep Water formation, we present da ta from two transects of the Greenland-Iceland-Norwegian Seas. Along Transect A (74.3°N, 18.3°E to 75.0°N, 12.5°W, 15 stations), we measured phosphate and Cd concentrations of modern surface sea water. Along Transect B (64.5°N, 0.7°W to 70.4°N, 18.2°W, 14 stations) we measured Cd/Ca ratios and d13C of the planktonic foraminifera Neogloboquadrina pachyderma sinistral in core top sediments. Our results indicate that Cd and phosphate both vary with surface water mass and are well correlated along Transect A. Our planktonic foraminiferal d13C data indicate similar nutrient variation with water mass along Transect B. Our Cd/Ca data hint at the same type of nutrient variability, but interpretations are hampered by low values close to the detection limit of this technique and therefore relatively large error bars. We also measured Cd and phosphate concentrations in water depth profiles at three sites along Transect A and the d13C of the benthic foraminifera Cibicidoides wuellerstorfi along Transect B. Modern sea water depth profiles along Transect A have nutrient depletions at the surface and then constant values at depths greater than 100 meters. The d13C of planktonic and benthic foraminifera from Transect B plotted versus depth also reflect surface nutrient depletion and deep nutrient enrichment as seen at Transect A, with a small difference between intermediate and deep waters. Overall we see no evidence for decoupling of Cd/Ca ratio and d13C in foraminiferal calcite from water column nutrient concentrations along these transects in a region of North Atlantic Deep Water formation.

(Table 2) Survivorship of transplanted seedlings of Picea glauca inside and outside three tree islands in 1994, 1995, 2009 and after 15 years

The northern boundary of boreal forest and the ranges of tree species are expected to shift northward in response to climate warming, which will result in a decrease in the albedo of areas currently covered by tundra vegetation, an increase in terrestrial carbon sequestration, and an alteration of biodiversity in the current Low Arctic. Central to the prediction of forest expansion is an increase in the reproductive capacity and establishment of individual trees. We assessed cone production, seed viability, and transplanted seedling success of Picea glauca (Moench.) Voss. (white spruce) in the early 1990s and again in the late 2000s at four forest stand sites and eight tree island sites (clonal populations beyond present treeline) in the Mackenzie Delta region of the Northwest Territories, Canada. Over the past 20 years, average temperatures in this region have increased by 0.9 °C. This area has the northernmost forest-tundra ecotone in North America and is one of the few circumpolar regions where the northern limit of conifer trees reaches the Arctic Ocean. We found that cone production and seed viability did not change between the two periods of examination and that both variables decreased northward across the forest-tundra ecotone. Nevertheless, white spruce individuals at the northern limit of the forest-tundra ecotone produced viable seeds. Furthermore, transplanted seedlings were able to survive in the northernmost sites for 15 years, but there were no signs of natural regeneration. These results indicate that if climatic conditions continue to ameliorate, reproductive output will likely increase, but seedling establishment and forest expansion within the forest-tundra of this region is unlikely to occur without the availability of suitable recruitment sites. Processes that affect the availability of recruitment sites are likely to be important elsewhere in the circumpolar ecotone, and should be incorporated into models and predictions of climate change and its effects on the northern forest-tundra ecotone.

Inorganic carbon and geochemistry measurements from landfast sea ice in Resolute Passage, Nunavut, Canada, as part of the Arctic-ICE project, May - June 2010

We conducted a six-week investigation of the sea ice inorganic carbon system during the winter-spring transition in the Canadian Arctic Archipelago. Samples for the determination of sea ice geochemistry were collected in conjunction with physical and biological parameters as part of the 2010 Arctic-ICE (Arctic - Ice-Covered Ecosystem in a Rapidly Changing Environment) program, a sea ice-based process study in Resolute Passage, Nunavut. The goal of Arctic-ICE was to determine the physical-biological processes controlling the timing of primary production in Arctic landfast sea ice and to better understand the influence of these processes on the drawdown and release of climatically active gases. The field study was conducted from 1 May to 21 June, 2010.

Consolidation properties and strength characteristics of ODP Site 204-1244 sediments

Eight whole-core samples from Ocean Drilling Program Site 1244, Hydrate Ridge, Cascadia continental margin, were provided to Massachusetts Institute of Technology (Cambridge, Massachusetts, USA) for geotechnical characterization. The samples were collected from depths ranging from 5 to 136 meters below seafloor (mbsf). Seven of the eight whole-core samples were located within the gas hydrate stability zone, whereas the eighth sample was located in the free gas zone. Atterberg limits testing showed that the average liquid limit of the soil is 81% and the average plastic limit is 38%, giving an average plasticity index of 43%. The liquid limit is sensitive to oven drying, shown by a drop in liquid limit to 64% when tests were performed on an oven-dried sample. Loss on ignition averages 5.45 wt%. Constant rate of strain consolidation (CRSC) tests were performed to obtain the compression characteristics of the soil, as well as to determine the stress history of the site. CRSC tests also provided hydraulic conductivity and coefficient of consolidation characteristics for these sediments. The compression ratio (Cc) ranges from 0.340 to 0.704 (average = 0.568). Cc is fairly constant to a depth of 79 mbsf, after which Cc decreases downhole. The recompression ratio (Cr) ranges from 0.035 to 0.064 (average = 0.052). Cr is constant throughout the depth range. In situ hydraulic conductivity varies between 1.5 x 10**-7 and 3 x 10**-8 cm/s and shows no trend with depth. Ko-consolidated undrained compression/extension (CKoUC/E) tests were also performed to determine the peak undrained shear strength, stress-strain curve, and friction angle. The normalized undrained strength ranges from 0.29 to 0.35. The friction angle ranges from 27 to 37. Because of the limited amount of soil, CRSC and CKoUC/E tests were also conducted on resedimented specimens.

Description of sampling sites in Northern Russia

The youngest ice marginal zone between the White Sea and the Ural mountains is the W-E trending belt of moraines called the Varsh-Indiga-Markhida-Harbei-Halmer-Sopkay, here called the Markhida line. Glacial elements show that it was deposited by the Kara Ice Sheet, and in the west, by the Barents Ice Sheet. The Markhida moraine overlies Eemian marine sediments, and is therefore of Weichselian age. Distal to the moraine are Eemian marine sediments and three Palaeolithic sites with many C-14 dates in the range 16-37 ka not covered by till, proving that it represents the maximum ice sheet extension during the Weichselian. The Late Weichselian ice limit of M. G. Grosswald is about 400 km (near the Urals more than 700 km) too far south. Shorelines of ice dammed Lake Komi, probably dammed by the ice sheet ending at the Markhida line, predate 37 ka. We conclude that the Markhida line is of Middle/Early Weichselian age, implying that no ice sheet reached this part of Northern Russia during the Late Weichselian. This age is supported by a series of C-14 and OSL dates inside the Markhida line all of >45 ka. Two moraine loops protrude south of the Markhida line; the Laya-Adzva and Rogavaya moraines. These moraines are covered by Lake Komi sediments, and many C-14 dates on mammoth bones inside the moraines are 26-37 ka. The morphology indicates that the moraines are of Weichselian age, but a Saalian age cannot be excluded. No post-glacial emerged marine shorelines are found along the Barents Sea coast north of the Markhida line.

(Table 1) Luminescence age determination of sediments from the Arkhangelsk area

The Arkhangelsk area lies in the region that was reached by the northeastern flank of the Scandinavian ice sheet during the last glaciation. Investigations of Late Pleistocene sediments show interglacial terrestrial and marine conditions with sea level up to 52 m above the present level. An unconformity in the stratigraphy suggests a hiatus representing the Early Valdaian (Weichselian) and the beginning of the Middle Valdaian. This unconformity could be related to a low base level and isostatic depression of the area north of Arkhangelsk, either caused by ice masses advancing from the Kara and Barents ice sheets and/or to Scandinavian ice over the Kola Peninsula. During Middle Valdaian, from c. 66 ka BP, until the advance of the Late Valdaian glacier, c. 17-16 ka BP, peat formation, and northward fluvial sedimentation occurred coexisting with permafrost conditions in a later phase. Before the glacier advance, the base level rose and thick vertical accumulations of fluvial sediments were formed. Associated with this glacier advance from the north-northwest, ice damming occurred. Fluvial drainage was opposite to the present drainage pattern and deposition appeared in glaciolacustrine ponds in the area outside the limit of the glaciation. After the deglaciation that started c. 15 ka BP, permafrost conditions and downwasting of buried stagnant glacier ice prevailed until at least 10.7 ka BP.

Biostratigraphy of benthic and planktonic foraminifera in Paleocene samples of DSDP HOle 93-605

Paleocene benthic and planktonic foraminifers occur throughout a long interval of the sedimentary succession cored at Site 605. A biostratigraphic zonation based on planktonic foraminifers is proposed for this Paleocene section. Zones identified are Subbotina pseudobulloides Zone, Morozovella trinidadensis Zone, M. uncinata Zone, M. pusilla pusilla Zone, Planorotalites pseudomenardii Zone, and M. velascoensis Zone. Fluctuations in the sedimentation rate occurred at Site 605. Rates of deposition were high during the M. pusilla pusilla and P. pseudomenardii zones, and a depositional hiatus may occur at the base of the M. velascoensis Zone. Qualitative and quantitative analysis of benthic foraminiferal assemblages suggests that the Paleocene sediments of Site 605 were deposited near the upper limit of Nuttallides truempyi, that is, approximately in the middle bathyal zone (600 m or more).

Tritium concentrations of hydrography in the North Atlantic around 40°N

We report, numerically and in graphical form, meaured tritium concentrations from five hydrographic stations in the North Atlantic. Fairly homogeneous concentrations are observed in a surface layer typically 400 m deep. In the thermocline, concentrations decrease steadily down to the sigma-theta = 27.3 density horizon, and are more variable further down. The tritium in the lower part of the thermocline originates from the Subarctic Intermediate Water and the Mediterranean Water. There is a relative tritium maximum associated with the Mediterranean Water on the easternmost station of the section. In the deep water (sigma-theta > 27.8), concentrations east of the Midatlantic Ridge are close to the limit of detection down to 2500m, and undetectable further down, while west of the ridge tritium is found throughout the water column. The deep water tritium is associated with the deep-water advective cores of Arctic origin. The present tritium data can serve as northern boundary values in attempts to use tritium in studies of the North Atlantic main thermocline dynamics. The present data together with data from the literature point to a general division of the North Atlantic main thermocline into two layers separated by an isopycnal surface near sigma-theta = 27.3.

Calcareous nannofossils of ODP Hole 123-765C and DSDP Hole 27-261

Sediments from the Argo Abyssal Plain (AAP), northwest of Australia, are the oldest known from the Indian Ocean and were recovered from ODP Site 765 and DSDP Site 261. New biostratigraphic and sedimentologic data from these sites, as well as reinterpretations of earlier findings, indicate that basal sediments at both localities are of Late Jurassic age and delineate a history of starved sedimentation punctuated by periodic influx of calcareous pelagic turbidites. Biostratigraphy and correlation of Upper Jurassic-Lower Cretaceous sediments is based largely on calcareous nannofossils. Both sites yielded variably preserved nannofossil successions ranging from Tithonian to Hauterivian at Site 765 and Kimmeridgian to Hauterivian at Site 261. The nannofloras are comparable to those present in the European and Atlantic Boreal and Tethyan areas, but display important differences that reflect biogeographic differentiation. The Argo region is thought to have occupied a position at the southern limit of the Tethyan nannofloral realm, thus yielding both Tethyan and Austral biogeographic features. Sedimentary successions at the two sites are grossly similar, and differences largely reflect Site 765's greater proximity to the continental margin. Jurassic sediments were deposited at rates of about 2 m/m.y. near the carbonate compensation depth (CCD) and contain winnowed concentrations of inoceramid prisms and nannofossils, redeposited layers rich in calcispheres and calcisphere debris, manganese nodules, and volcanic detritus. Lower Cretaceous and all younger sediments accumulated below the CCD at rates that were highest (about 20 m/m.y.) during mid-Cretaceous and Neogene time. Background sediment in this interval is noncalcareous claystone; turbidites dominate the sequence and are thicker and coarser grained at Site 765. AAP turbidites consist mostly of calcareous and siliceous biogenic components and volcanogenic smectite clay; they were derived from relatively deep parts of the continental margin that lay below the photic zone, but above the CCD. The Jurassic-Lower Cretaceous section is about the same thickness across the AAP; turbidites in this interval appear to have had multiple sources along the Australian margin. The Upper Cretaceous-Cenozoic section, however, is three times thicker at Site 765 than at Site 261; turbidites in this interval were derived predominantly from the south. Patterns of sedimentation across the AAP have been influenced by shifts in sea level, the CCD, and configuration of the continental margin. Major pulses of calcareous turbidite deposition occurred during Valanginian, Aptian, and Neogene time-all periods of eustatic lowstands and depressed CCD levels. Sediment redeposited on the AAP has come largely from the Australian outer shelf, continental slope, or rise, rather than the continent itself. Most terrigenous detritus was trapped in epicontinental basins that have flanked northwestern Australia since the early Mesozoic.

The hydrographic conditions at depth below 1000 m water depth in the region of the Romanche Fracture Zones

During the "Atlantic Expedition" in1965 (IQSY) a comprehensive bathymetric survey and a few hydrographic stations were made by R.V. "Meteor" in the equatorial region of the Mid-Atlantic Ridge. The survey results are shown in a bythymetric chart covering the western parts of the Romanche- and Chain Fracture Zones. West of the original Romanche Trench another deep trench with a medium depth of 6000 m was discovered. The maximum sounding obtained was 7028 m. Both trenches apparently belong to the same fracture zone, but are distinctly separated from each other. The estern boundary of the trench against the Brasil Basin is formed by a sill rising to a depth of about 4400 m. The serial hydrographic observations give some indications of the flow of the cold Westatlantic deep water in the fracture zone area and its influence on the hydrographic conditions in the East-Atlantic Basin. The upper limit of the nearly homogenious Westatlantic bottom water with an Antarctic components lies about 4400 m. The water mass entering the system of trenches of the Romanche Fracture Zone over the western sill originates from the lower part of the discontinuity layer lying above the bottom water. Potential temperatures of 0.6°C were the lowest observed by "Meteor" in the western trench. There seems to be a remarkable tongue of relatively high salinity and a minimum of oxygen in the deep water of this trench. At present we can only speculate upon the origin of this highly saline deep water tongue underneath the eastward moving relatively thin layer of less saline Westatlantic deep water. In the range of the sill separating both trenches a lee wave is indicated by the distribution of salinity and oxygen, which implies a vertical transport of water masses. Caused by this transport it is assumed that relatively cold water may be lifted temporarily to a depth, where it can pass the northbounding ridge, thus getting directly into the Sierra Leone Basin. In the original Romanche Trench the cold Westatlantic deep water seems to fill the whole trough, but its extension remains limited to the trench itself. The water masses found east of the sill separating the trench from the East-Atlantic Basin originate from the lower part of the discontinuity layer. With potential temperatures of about 1.3°C they are much warmer than those observed in the Romanche Trench bottom water.

Radiochemical analyses and contents of organic carbon and CaCO3 in equatorial Pacific Ocean sediments

Uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial Pacific transect. 230Thexcess activities show discontinuities at the Holocene-glacial boundary as dated by 14C. The glacial sedimentation rates determined by 230Th and 14C are 2.5-3.0 cm/kyr. The Holocene rates from 230Th are much lower than those dated by 14C (1.9-2.3 cm/kyr) because of carbonate dissolution. 230Th sedimentation fluxes exceed water column supply by factors of 1.2-1.8 in the Holocene and 1.8-3.0 in the glacial sections. A number of models have been applied to calculate carbonate dissolution rates. The results show that carbonate dissolution rates in the Holocene (in g/cm**2 kyr) equal 1.5 * 10**-3 exp (1.4D) where D is water depth in kilometers. A point-by- point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0.1-0.2 g/cm**2 kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0.6-1.0 g/cm**2 kyr in the glacial sections of the cores to 0.2-0.6 g/cm**2 kyr in the Holocene. The errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11-14 kyr leads to an error upper limit of about 30% in the estimation of CaCO3 dissolution rates. The response time of CaCO3 and 230Thex concentrations in the mixed layer of sediments due to an impulse of change in CaCO3 dissolution rate has also been discussed, showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change, depending upon the thickness of the mixed layer.

Direct visualization of solute locations in laboratory ice samples, links to videos

Many important chemical reactions occur in polar snow, where solutes may be present in several reservoirs, including at the air-ice interface and in liquid-like regions within the ice matrix. Some recent laboratory studies suggest chemical reaction rates may differ in these two reservoirs. While investigations have examined where solutes are found in natural snow and ice, similar research has not identified solute locations in laboratory samples, nor the possible factors controlling solute segregation. To address this, we examined solute locations in ice samples prepared from either aqueous cesium chloride (CsCl) or Rose Bengal solutions that were frozen using several different methods. Samples frozen in a laboratory freezer had the largest liquid-like inclusions and air bubbles, while samples frozen in a custom freeze chamber had somewhat smaller air bubbles and inclusions; in contrast, samples frozen in liquid nitrogen showed much smaller concentrated inclusions and air bubbles, only slightly larger than the resolution limit of our images (~2 µm). Freezing solutions in plastic versus glass vials had significant impacts on the sample structure, perhaps because the poor heat conductivity of plastic vials changes how heat is removed from the sample as it cools. Similarly, the choice of solute had a significant impact on sample structure, with Rose Bengal solutions yielding smaller inclusions and air bubbles compared to CsCl solutions frozen using the same method. Additional experiments using higher-resolution imaging of an ice sample show that CsCl moves in a thermal gradient, supporting the idea that the solutes in ice are present in liquid-like regions. Our work shows that the structure of laboratory ice samples, including the location of solutes, is sensitive to freezing method, sample container, and solute characteristics, requiring careful experimental design and interpretation of results.

Chemical composition of mineral phases of serpentinized and steatized peridotite from the Mid Atlantic Ridge (15°20'N Fracture Zone, ODP Leg209)

Serpentinization of abyssal peridotites is known to produce extremely reducing conditions as a result of dihydrogen (H2,aq) release upon oxidation of ferrous iron in primary phases to ferric iron in secondary minerals by H2O.We have compiled and evaluated thermodynamic data for Fe-Ni-Co-O-S phases and computed phase relations in fO2,g-fS2,g and aH2,aq-aH2S,aq diagrams for temperatures between 150 and 400°C at 50MPa.We use the relations and compositions of Fe-Ni-Co-O-S phases to trace changes in oxygen and sulfur fugacities during progressive serpentinization and steatitization of peridotites from the Mid-Atlantic Ridge in the 15°20'N Fracture Zone area (Ocean Drilling Program Leg 209). Petrographic observations suggest a systematic change from awaruite- magnetite-pentlandite and heazlewoodite-magnetite-pentlandite assemblages forming in the early stages of serpentinization to millerite-pyrite-polydymite-dominated assemblages in steatized rocks. Awaruite is observed in all brucite-bearing partly serpentinized rocks. Apparently, buffering of silica activities to low values by the presence of brucite facilitates the formation of large amounts of hydrogen, which leads to the formation of awaruite. Associated with the prominent desulfurization of pentlandite, sulfide is removed from the rock during the initial stage of serpentinization. In contrast, steatitization indicates increased silica activities and that highsulfur-fugacity sulfides, such as polydymite and pyrite-vaesite solid solution, form as the reducing capacity of the peridotite is exhausted and H2 activities drop. Under these conditions, sulfides will not desulfurize but precipitate and the sulfur content of the rock increases. The co-evolution of fO2,g-fS2,g in the system follows an isopotential of H2S,aq, indicating that H2S in vent fluids is buffered. In contrast, H2 in vent fluids is not buffered by Fe-Ni-Co-O-S phases, which merely monitor the evolution of H2 activities in the fluids in the course of progressive rock alteration.The co-occurrence of pentlandite- awaruite-magnetite indicates H2,aq activities in the interacting fluids near the stability limit of water. The presence of a hydrogen gas phase would add to the catalyzing capacity of awaruite and would facilitate the abiotic formation of organic compounds.

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.

Atterberg limits of sediments from DSDP Leg 65 Holes

Atterberg limits have been determined for 32 unconsolidated sediment samples, ranging in composition from silty clay to sandy silt and recovered from four sites drilled at the mouth of the Gulf of California during DSDP Leg 65. The liquid limit of the samples ranged from 41.5% to 157.5%, and the plastic limit from 32.8% to 65.1%. The plasticity index ranged from 5.9% to 102.0%. In some samples, the water content was less than the liquid limit. The liquidity index averaged 76% while the flow and toughness indices averaged 35% and 2.18%, respectively. On the basis of these limits, the sediments analyzed can be classified as inorganic clays of high plasticity, organic clays of moderate to high plasticity, and diatomaceous sands, silts, and silty clays of low plasticity.