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Arctic Ocean (arctic + ocean)

Distribution by Scientific Domains

Earth and Environmental Science	55%
Life Sciences	35%
Humanities and Social Sciences	10%

Distribution within Earth and Environmental Science

Geology & Geophysics	63%
Atmospheric Sciences	18%

Selected Abstracts

The structure of bacterial communities in the western Arctic Ocean as revealed by pyrosequencing of 16S rRNA genes

ENVIRONMENTAL MICROBIOLOGY, Issue 5 2010
David L. Kirchman
Summary Bacterial communities in the surface layer of the oceans consist of a few abundant phylotypes and many rare ones, most with unknown ecological functions and unclear roles in biogeochemical processes. To test hypotheses about relationships between abundant and rare phylotypes, we examined bacterial communities in the western Arctic Ocean using pyrosequence data of the V6 region of the 16S rRNA gene. Samples were collected from various locations in the Chukchi Sea, the Beaufort Sea and Franklin Bay in summer and winter. We found that bacterial communities differed between summer and winter at a few locations, but overall there was no significant difference between the two seasons in spite of large differences in biogeochemical properties. The sequence data suggested that abundant phylotypes remained abundant while rare phylotypes remained rare between the two seasons and among the Arctic regions examined here, arguing against the ,seed bank' hypothesis. Phylotype richness was calculated for various bacterial groups defined by sequence similarity or by phylogeny (phyla and proteobacterial classes). Abundant bacterial groups had higher within-group diversity than rare groups, suggesting that the ecological success of a bacterial lineage depends on diversity rather than on the dominance of a few phylotypes. In these Arctic waters, in spite of dramatic variation in several biogeochemical properties, bacterial community structure was remarkably stable over time and among regions, and any variation was due to the abundant phylotypes rather than rare ones. [source]

Evidence that viral abundance across oceans and lakes is driven by different biological factors

FRESHWATER BIOLOGY, Issue 6 2008
JESSICA L. CLASEN
Summary 1. Samples from 16 lakes in central (n = 145) and western (n = 12) North America, the coastal northeast Pacific (n = 302) and the western Canadian Arctic Oceans (n = 142) were collected and analysed for viral, bacterial and cyanobacterial abundances and chlorophyll- a concentration. 2. Viral abundance was significantly different among the environments. It was highest in the coastal Pacific Ocean and lowest in the coastal Arctic Ocean. The abundances of bacteria and cyanobacteria as well as chlorophyll- a concentrations also differed significantly among the environments, with both bacterial abundance and chlorophyll- a concentration highest in lakes. As a consequence, the association of these variables with viral abundance varied among the environments. 3. Discriminant analyses with the abundance data indicated that the marine and freshwater environments were predictably different from each other. Multiple-regression analysis included bacterial and cyanobacterial abundances, and chlorophyll- a concentration as significant variables in explaining viral abundance in lakes. In regression models for the coastal Pacific Ocean, bacterial and cyanobacterial abundances were significant variables, and for the coastal Arctic Ocean viral abundance was predicted by bacterial abundance and chlorophyll- a concentration. 4. The relationship of viral and bacterial abundance differed between the investigated freshwater and marine environments, probably because of differences in viral production and loss rates. However, freshwaters had fewer viruses compared to bacteria, despite previously documented higher burst sizes and frequencies of infected cells, suggesting that loss rates may be more important in lakes. 5. Together, these findings suggest that there are different drivers of viral abundance in different aquatic environments, including lakes and oceans. [source]

Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic Ocean

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010
H. Ruth Jackson
SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source]

Seamount volcanism along the Gakkel Ridge, Arctic Ocean

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2008
James R. Cochran
SUMMARY The Gakkel Ridge in the Arctic Ocean is the slowest spreading portion of the global mid-ocean ridge system. Total spreading rates vary from 12.8 mm yr,1 near Greenland to 6.5 mm yr,1 at the Siberian margin. Melting models predict a dramatic decrease in magma production and resulting crustal thickness at these low spreading rates. At slow spreading ridges, small volcanic seamounts are a dominant morphologic feature of the rift valley floor and an important mechanism in building the oceanic crust. This study quantitatively investigates the extent, nature and distribution of seamount volcanism at the ultraslow Gakkel Ridge, the manner in which it varies along the ridge axis and the relationship of the volcanoes to the larger scale rift morphology. A numerical algorithm is used to identify and characterize isolated volcanic edifices by searching gridded swath-bathymetry data for closed concentric contours protruding above the surrounding seafloor. A maximum likelihood model is used to estimate the total number of seamounts and the characteristic height within different seamount populations. Both the number and size of constructional volcanic features is greatly reduced at the Gakkel Ridge compared with the Mid-Atlantic Ridge (MAR). The density of seamounts (number/area) on the rift valley floor of the Western Volcanic Zone (WVZ) is ,55% that of the MAR. The observed volcanoes are also much smaller, so, the amount of erupted material is greatly reduced compared with the MAR. However, the WVZ is still able to maintain a MAR-like morphology with axial volcanic ridges, volcanoes scattered on the valley floor and rift valley walls consisting of high-angle faults. Seamount density at the Eastern Volcanic Zone (EVZ) is ,45% that of the WVZ (,25% that of the MAR). Seamounts are clustered at the widely spaced magmatic centres characteristic of the EVZ, although some seamounts are found between magmatic centres. These seamounts tend to be located at the edge of the rift valley or on the valley walls rather than on the valley floor. Seamounts in the Sparsely Magmatic Zone (SMZ) are located almost entirely at the 19°E magmatic centre with none observed within a 185 km-long portion of the rift valley floor. The EVZ and SMZ appear to display a mode of crustal accretion, characterized by extreme focusing of melt to the magmatic centres. Magmas erupted between the magmatic centres appear to have ascended along faults. This is very different from what is observed at the WVZ (or the MAR), and there is a threshold transition between the two modes of crustal accretion. At the Gakkel Ridge, the location of the transition appears to be localized by a boundary in mantle composition. [source]

The sedimentary structure of the Lomonosov Ridge between 88°N and 80°N

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005
Wilfried Jokat
SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87°36,N and 80°N perpendicular to and along the LR show a sediment starved continental margin with a variety of geological structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities <3.0 km s,1 are considered to represent Cenozoic sediments deposited after the ridge subsided below sea level. Velocities >4.0 km s,1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155°E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81°N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85°N the seismic data indicate the presence of a bottom simulating reflector along all lines. [source]

Storage and mobility of black carbon in permafrost soils of the forest tundra ecotone in Northern Siberia

GLOBAL CHANGE BIOLOGY, Issue 6 2008
GEORG GUGGENBERGER
Abstract Boreal permafrost soils store large amounts of organic carbon (OC). Parts of this carbon (C) might be black carbon (BC) generated during vegetation fires. Rising temperature and permafrost degradation is expected to have different consequences for OC and BC, because BC is considered to be a refractory subfraction of soil organic matter. To get some insight into stocks, variability, and characteristics of BC in permafrost soils, we estimated the benzene polycarboxylic acid (BPCA) method-specific composition and storage of BC, i.e. BPCA-BC, in a 0.44 km2 -sized catchment at the forest tundra ecotone in northern Siberia. Furthermore, we assessed the BPCA-BC export with the stream draining the catchment. The catchment is composed of various landscape units with south-southwest (SSW) exposed mineral soils characterized by thick active layer or lacking permafrost, north-northeast (NNE) faced mineral soils with thin active layer, and permafrost-affected raised bogs in plateau positions showing in part thermokarst formation. There were indications of vegetation fires at all landscape units. BC was ubiquitous in the catchment soils and BPCA-BC amounted to 0.6,3.0% of OC. This corresponded to a BC storage of 22,3440 g m,2. The relative contribution of BPCA-BC to OC, as well as the absolute stocks of BPCA-BC were largest in the intact bogs with a shallow active layer followed by mineral soils of the NNE aspects. In both landscape units, a large proportion of BPCA-BC was stored within the permafrost. In contrast, mineral soils with thick active layer or lacking permafrost and organic soils subjected to thermokarst formation stored less BPCA-BC. Permafrost is, hence, not only a crucial factor in the storage of OC but also of BC. In the stream water BPCA-BC amounted on an average to 3.9% of OC, and a yearly export of 0.10 g BPCA-BC m,2 was calculated, most of it occurring during the period of snow melt with dominance of surface flow. This suggests that BC mobility in dissolved and colloidal phase is an important pathway of BC export from the catchment. Such a transport mechanism may explain the high BC concentrations found in sediments of the Arctic Ocean. [source]

Variability of total and solid precipitation in the Canadian Arctic from 1950 to 1995

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2002
Rajmund Przybylak
Abstract Trends in solid and total precipitation, as well as in the ratio of solid to total precipitation (hereinafter S/T ratio), in the Canadian Arctic in recent decades have been investigated. In addition, the influence of air temperature and circulation factors (atmospheric and oceanic) on the above-mentioned precipitation characteristics have been examined. Recently updated and adjusted data by the Canadian Climate Centre from 16 stations located in the Canadian Arctic and two stations from the sub-Arctic were used for the investigation. The southern boundary of the study area was taken after Atlas Arktiki (Tresjinkov, A. 1985. Glavnoye Upravlenye Geodeziy i Kartografiy: Moscow; 204 pp). The majority of the data cover the period from 1950 to 1995. A statistically significant increase in all kinds of areally averaged seasonal and annual precipitation for the Canadian Arctic over the period 1950,95 has been found. On the other hand, the S/T ratio did not change significantly, except for summer values, and its behaviour was also in accord with small variations noted in air temperature. An increase in air temperature in the Canadian Arctic most often led to a rise in all kinds of annual precipitation sums, but only when the warmest and coldest years were chosen based on individual stations. The pattern of the relationship is significantly more complicated, and can even be opposite to that presented above, when the sets of the warmest and coldest years are chosen based on the areally averaged annual temperature for the Canadian Arctic. Significantly more stable results of changes were found for the S/T ratio, which in warmer periods was usually lower. However, more detailed and reliable investigations of temperature,precipitation relationships conducted for individual stations showed that though the S/T ratio in warmer periods may well be lower, this only applies to the southern (warmer) part of the Canadian Arctic (<70 °N). During periods with high positive values of the North Atlantic Oscillation Index (NAOI), a decrease in precipitation is observed in the south-eastern part of the Canadian Arctic, i.e. in the area where strong cooling was also observed. During El Niño events most of the Canadian Arctic had both greater precipitation and a higher S/T ratio than during La Niña events. The most unequivocal results of precipitation and S/T ratio changes were found for changes in the Arctic Ocean circulation regimes. In almost the whole study area, a lower precipitation and S/T ratio were noted during the anticyclonic circulation regime in the Arctic Ocean. Copyright © 2002 Royal Meteorological Society [source]

Late-glacial and Holocene palaeovegetation zonal reconstruction for central and north-central North America

JOURNAL OF BIOGEOGRAPHY, Issue 6 2005
W. L Strong
Abstract Aim, The purpose of this study is to develop palaeovegetation zonation models for central and north-central North America, based on late-Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis (Strong & Hills, 2003) to explain the disjunct distribution of species in western Alberta. Location, Hudson Bay-Lake Michigan to the Rocky Mountains region, north of 36° N to the Arctic Ocean (c. 70° N). Methods, Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000-year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon 14C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near-surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically-based palaeovegetation zonation models at 2000-year intervals from 14,000 to 4000 yr bp (radiocarbon years before present). Results, The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory,Alaska ice-free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49° N latitude in the Alberta,Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp, Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54° N and 59° N latitude in Alberta, respectively. Between 6000 and 4000 yr bp, a 5° and 1° latitudinal southward shift of the northern Boreal Forest and Grassland/Aspen Parkland boundaries occurred, respectively, near their contemporary positions with corresponding expansions of the Subarctic and Arctic zones. Modern Canadian Cordilleran Forests along the eastern slopes of the Rocky Mountains were interpreted as originating from the north-central Montana,south-western Alberta area. Jack pine (Pinus banksiana Lamb.), a common Boreal Forest species, appears to have entered central Canada via the north side of Lake Superior after 11,000 yr bp. Main conclusions, Modern vegetation in central Canada evolved from biomes located in the northern USA during the late-Quaternary. The Boreal Forest biome contained the same arboreal taxa as the modern vegetation, except it lacked jack pine. The proposed regional palaeovegetation models support the hypothesis of Strong & Hills (2003), but new independent palaeoecological data will be needed for a proper evaluation. [source]

THE STRUCTURAL STYLE OF SEDIMENTARY BASINS ON THE SHELVES OF THE LAPTEV SEA AND WESTERN EAST SIBERIAN SEA, SIBERIAN ARCTIC

JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2005
D. Franke
A total of 11,700 km of multichannel seismic reflection data were acquired during three recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas in the Siberian Arctic Ocean. Three seismic marker horizons were defined and mapped in both shelf areas. Their nature and age were predicted on the basis of regional tectonic and palaeoenvironmental events and corroborated using onshore geology. To the north of the Laptev Sea, the Gakkel Ridge, an active mid-ocean ridge which separates the North American and Eurasian Plates, abruptly meets the steep slope of the continental shelf which is curvilinear in plan view. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north-south trending rift basins: the Ust'Lena Rift, the Anisin Basin and the New Siberian Basin. The Ust'Lena Rift has a minimum east-west width of 300km at latitude 75°N and a Cenozoic infill up to 6 s (twt) in thickness. Further to the NW of the Laptev Shelf, the downthrown and faulted basement is overlain by a sub-parallel layered sedimentary succession with a thickness of 4 s (twt) that thins towards the west. Although this area was affected by extension as shown by the presence of numerous faults, it is not clear whether this depression on the NW Laptev Shelf is continuous with the Ust'Lena Rift. The Anisin Basin is located in the northern part of the Laptev Shelf and has a Cenozoic sedimentary fill up to 5 s (twt) thick. The deepest part of the basin trends north-south. To the west is a secondary, NW-SE trending depression which is slightly shallower than the main depocentre. The overall structure of the basin is a half-graben with the major bounding fault in the east. The New Siberian Basin is up to 70 km wide and has a minimum NW-SE extent of 300 km. The sedimentary fill is up to 4.5 s (twt) thick. Structurally, the basin is a half-graben with the bounding fault in the east. Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, as manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick. [source]

Microbial colonisation of artificial and deep-sea sediments in the Arctic Ocean

MARINE ECOLOGY, Issue 4 2009
Corinna Kanzog
Abstract Although environmental factors such as grain size and organic carbon content may influence the distribution of microbes in marine sediments, there has been little experimental study of the topic to date. To investigate how those sediment variables affect microbial colonisation under in situ conditions, deep-sea sediments and artificial sediments (glass beads, sands) were incubated in the Arctic deep sea at 2500 m water depth with or without chitin, one of the most important carbon polymers in marine environments. Microbial abundance, biomass, chitobiase activity and changes in community structure were monitored after 7 days and 1 year. In control sediments without chitin addition, no significant changes in microbial abundance, biomass and activity were observed after 1 year. In the presence of chitin, however, considerable increases in these parameters were recorded in all three sediment types tested. Regardless of chitin addition, natural deep-sea sediments were always associated with higher values of microbial abundance, biomass and activity compared with artificial sediments. Sediment type was always found to be the most significant factor explaining variation in enzymatic activity and bacterial community structure as compared to the effects of chitin amount, incubation time, and changes in cell number or biomass. Overall, this is the first in situ study that has addressed the effects of multiple factors and their interactions on abundance, biomass, activity and community structure of microbial communities in the deep Arctic Ocean. [source]

Water balance modelling of (Sub-)Arctic rivers and freshwater supply to the Barents Sea Basin

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2005
Eduard Koster
Abstract Recently, changes in the freshwater supply by rivers to the Arctic Ocean have attracted a great deal of attention. However, quantitative assessments of changes in the annual and seasonal discharge regime of (Sub-)Arctic rivers resulting from climate change are still far from accurate. The sensitivity of discharge to potential changes in climate in two river catchments of intermediate size (104,105,km2), the Tana River in northern Fennoscandia and the Usa River in northern Russia, both draining into the Barents Sea Basin, was evaluated using a spatially distributed water balance model. The tentative results show that discharge amounts during peak flow might remain more or less the same or show a slight increase. However, peakflow events are expected to occur about 20 days or more earlier in spring. Concerning annual discharge amounts a strong increase of 25% for the Usa River and even 39% for the Tana River is simulated in conformity with projected increases in precipitation. Obviously, the resulting increases of the annual freshwater influx from the Tana River (from 5.3 to 7.3,km3) and that of the Usa River (from 42 to 52,km3) into the Barents Sea are insignificant in absolute terms. But in relative terms they agree remarkably well with earlier estimates of changes in freshwater inflow by the very large (Sub-)Arctic rivers. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009
II: Multilayer cloud
Abstract Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multilayered, mixed-phase cloud system observed during the Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-levels. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate liquid water path and strongly underestimate ice water path, although there is a large spread among models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. These results suggest important differences in the ability of models to simulate deeper Arctic mixed-phase clouds versus the shallow, single-layered mixed-phase clouds in Part I. The observed liquid-ice mass ratios were much smaller than in Part I, despite the similarity of cloud temperatures. Thus, models employing microphysics schemes with temperature-based partitioning of cloud liquid and ice masses are not able to produce results consistent with observations for both cases. Models with more sophisticated, two-moment treatment of cloud microphysics produce a somewhat smaller liquid water path closer to observations. Cloud-resolving models tend to produce a larger cloud fraction than single-column models. The liquid water path and cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by long-wave flux. Copyright © 2009 Royal Meteorological Society [source]

Towards ground truthing exploration in the central Arctic Ocean: a Cenozoic compaction history from the Lomonosov Ridge

BASIN RESEARCH, Issue 2 2010
M. O'Regan
ABSTRACT The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10,30 m Myr,1) and high permeability values (10,15,10,18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A,C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A,C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean. [source]

Deglacial and Holocene conditions in northernmost Baffin Bay: sediments, foraminifera, diatoms and stable isotopes

BOREAS, Issue 3 2008
KAREN LUISE KNUDSEN
A multiproxy study of palaeoceanographic and climatic changes in northernmost Baffin Bay shows that major environmental changes have occurred since the deglaciation of the area at about 12 500 cal. yr BP. The interpretation is based on sedimentology, benthic and planktonic foraminifera and their isotopic composition, as well as diatom assemblages in the sedimentary records at two core sites, one located in the deeper central part of northernmost Baffin Bay and one in a separate trough closer to the Greenland coast. A revised chronology for the two records is established on the basis of 15 previously published AMS 14C age determinations. A basal diamicton is overlain by laminated, fossil-free sediments. Our data from the early part of the fossiliferous record (12 300,11 300 cal. yr BP), which is also initially laminated, indicate extensive seasonal sea-ice cover and brine release. There is indication of a cooling event between 11 300 and 10 900 cal. yr BP, and maximum Atlantic Water influence occurred between 10 900 and 8200 cal. yr BP (no sediment recovery between 8200 and 7300 cal. yr BP). A gradual, but fluctuating, increase in sea-ice cover is seen after 7300 cal. yr BP. Sea-ice diatoms were particularly abundant in the central part of northernmost Baffin Bay, presumably due to the inflow of Polar waters from the Arctic Ocean, and less sea ice occurred at the near-coastal site, which was under continuous influence of the West Greenland Current. Our data from the deep, central part show a fluctuating degree of upwelling after c. 7300 cal. yr BP, culminating between 4000 and 3050 cal. yr BP. There was a gradual increase in the influence of cold bottom waters from the Arctic Ocean after about 3050 cal. yr BP, when agglutinated foraminifera became abundant. A superimposed short-term change in the sea-surface proxies is correlated with the Little Ice Age cooling. [source]