OS41C-01 INVITED
Damocles and related modelling and observing activities in the Eastern Arctic Ocean
DAMOCLES is an European Union "Integrated Project" (December 2005-December 2009) representing a major contribution of the EU to the International Polar Year. Essentially this ambitious project concerns the fate of Arctic Sea-Ice under changing atmospheric and oceanic conditions based on innovative in situ and space observations and the use of the most advanced numerical models for data integration and assimilation for sensitivity studies and prediction. DAMOCLES observing activities involve the development of new High Technology required for collecting the missing data we need related to sea-ice thickness distribution, atmospheric inversion and boundary layers, ocean surface mixed layers, the cold halocline and the atlantic layer and the radiative balance. Dedicated in situ observations in the lower atmosphere, in the upper oceanand through the sea-ice, as well as remote sensing from space and High-tech developments represent a major contribution to the project. DAMOCLES modelling activities aim at understanding processes relevant for the reduction of Arctic sea-ice extent, which is currently observed and predicted from climate scenario simulations. Regional, global and process models are further developed and utilized (1) to explore the sensitivities of the Arctic climate system, (2) to assess the predictability of Arctic variability, (3) to quantify model sensitivities, and (4) to carry out regional Arctic climate scenarios. In addition, data assimilation methods are further developed for an Arctic Ocean reanalysis and better predictive capabilities of ocean, sea-ice and atmosphere conditions. The reanalysis makes use of different kinds of data such as T/S profiles, sea ice observations and drifter data from DAMOCLES and other IPY projects as well as from pre-IPY campaigns. In this presentation we will select some preliminary results both in the domain of modelling and observations in the context of DAMOCLES.
OS41C-02 INVITED
Circulation and water mass transformations in the Eurasian Basin and on the adjacent shelves
The Eurasian Basin, through its connections with the Nordic Seas via Fram Strait and the Barents Sea, is the most ventilated of the Arctic Ocean basins but also the part of the Arctic Ocean where the most profound transformations in water mass properties occur. In recent decades large variations in water mass characteristics have been observed. Due to the strong stratification these changes have largely been caused by variations in properties of the waters advected to the Nordic Seas and the Arctic Ocean from the south, driven by the atmospheric forcing of the large-scale circulation beyond the Arctic. The fact that temperature and salinity anomalies, advected into the Arctic Ocean through Fram Strait, now can be identified in the different basins and traced through different circulation loops suggests that the strength of the water mass transformation processes in the Arctic Ocean has weakened, the cause being mainly higher atmospheric temperature, implying less cooling, and to a smaller degree a larger atmospheric freshwater transport to the Arctic. This reduces the dense water production on the shelves and thus the ventilation of the deeper layers of the Arctic Ocean. This could signal a larger change, where the deep water formation areas in the Arctic Mediterranean Sea eventually cease to operate, and the circulation shifts from one strongly affected by thermohaline processes to one dominated by the wind field, being only modified by the thermodynamics. The Atlantic water crossing the Greenland-Scotland Ridge would then, driven by the prevailing winds, circulate around the Arctic Mediterranean Seas, tracing the loops in the different basins, and gradually becoming dense enough to supply the Greenland-Scotland overflow and the North Atlantic deep water, while the water in the deep basins would become stagnant. Observations, especially from the last 10-15 years, are used to examine the variations in the water mass characteristics, mainly in the Eurasian Basin, to determine if such changes in the water mass transformations have taken place, and if a shift between circulation modes is possible.
OS41C-03
Lomonosov Ridge off Greenland (LOMROG) 2007
The Lomonosov Ridge off Greenland was the primary focus for the LOMROG expedition. This part of the Arctic is virtually unexplored as difficult sea ice conditions have made it inaccessible for surface vessels. With Swedish icebreaker /Oden/ supported by new Russian nuclear icebreaker /50 Let Pobedy/, LOMROG managed to reach the southern most tip of the Lomonosov Ridge off Greenland to carry out multibeam mapping, subbottom and seismic reflection profiling, gravity measurements, geological coring and oceanographic station work. The LOMROG expedition is a Swedish/Danish collaboration project with participating scientists also from Canada, Finland, and USA. The data collection was made for the purpose of studying paleoceanography/oceanography, glacial history and the tectonic evolution of the of the Arctic Ocean as well as for Denmark's Continental Shelf Project under the United Nations Convention on the Law of the Sea Article 76. One of the reasons for targeting the ice-infested area north of Greenland was that it likely holds answers to key questions regarding the glacial history of the Arctic Ocean, such as whether immense ice shelves existed in the Arctic Ocean during past glacial periods./ /Previous expeditions with /Oden/ in 1996 and the US nuclear submarine /Hawkbill/ in 1999, have demonstrated the occurrence of ice grounding down to 1000 m present water depth at about 87°N 145°E on the Lomonosov Ridge crest. If this ice grounding event resulted from a much debated, but supposedly coherent and large floating ice shelf, the Lomonosov Ridge north of Greenland must also be scoured. To test the hypothesis of a huge Arctic Ocean ice shelf LOMROG mapped the areas of the Lomonosov Ridge north of Greenland using the new EM120 multibeam bathymetry and SBP120 subbottom profiling system installed on the /Oden/ during the spring of 2007. Glacial erosion was indeed found at water depth shallower than approximately 800 m and two sediment cores retrieved from the glacially scoured sea floor contain diamicton. These new results will help reconstructing the glacial models of the Arctic Ocean. The oceanographic component of LOMROG investigated (see presentation by Bjork et al) the pathways of the Atlantic water and deep water. Water masses originating from the Canadian Basin side, which have crossed the Lomonosov Ridge at about 88°30'N 154°E, were found following the slope along the southern Lomonosov Ridge slope on the Amundsen Basin side. This presentation is on behalf of the entire LOMROG Scientific Partly.
OS41C-04
The Passage of Canadian Basin Deep Water Over the Lomonosov Ridge and Through the Eurasian Basin of the Arctic Ocean: Results From the LOMROG-2007 Icebreaker Expedition
During the LOMROG-2007 icebreaker expedition to the area where the Lomonosov Ridge attaches to the Greenland shelf, we observed a well defined signal in water mass properties of clear CBDW origin. The major part of CBDW passes the Lomonosov Ridge at the 1870 m deep channel near the North Pole (88 25' N, 150 E) as was discovered during the Beringia/Hotrax 2005 exploration of the sill area. During the LOMROG expedition we observed the signal of CBDW along the Amundsen Basin side of the Lomonosov Ridge slope north of Greenland and further along the Greenland shelf towards east and south. The signal with Canadian Basin properties is clearly seen in the TS structure as well as in the oxygen, silicate and CFC signals around 2000 m depth. No indication of a deep overflow across the Lomonosov Ridge at the channel just north of Greenland was seen.
OS41C-05
Hydrothermal activity and core complex formation at the Arctic Mid-Ocean Ridge: An overview of preliminary results of the H2DEEP expedition to the southern Knipovich Ridge at 73N
The oblique spreading Mohns Ridge passes into the highly oblique spreading Knipovich Ridge through a near 90 degree bend in the ridge axis at 73-74N. Multibeam mapping of this area shows that a 30 km long axial volcanic ridge (AVR) with a 500m high summit occupy the rift valley floor in the central part of the bend where the axis is perpendicular to the spreading direction. The volcanic activity decreases northwards as the obliquity of the spreading increases and this is associated with an increase in the water depth from 2000-2500 m to 3000-3500 m. A hydrothermal plume was located at the eastern side of the AVR with methane values reaching 260 nmol/l and hydrogen values 53 nmol/l. These anomalies are associated with small positive temperature anomaly, but no significant particle anomaly could be detected. The rift valley in the area is partly filled with sediments derived from the nearby Bjornoya fan, and reflection seismic profiles across the ridge demonstrate that sediments thicknesses in the rift valley locally exceeds several hundred meters. Gravity cores of the upper 4 m of these sediments show multiple glass- and iron-rich laminas and layers, demonstrating that these sediments represent a record of hydrothermal and volcanic activity in the area. Seamounts at the western flank of the ridge extend to 600 m below sea level and are limited by low angle detachment faults to the east. A flat summit area suggests that one of the seamounts has been at or close to sea level. Gabbros, troctolites and serpentinites were sampled from the fault surfaces, demonstrating that lower crust and mantle rocks have been exhumed in the area, and bathymetry data indicates that this oceanic core complex cover an area of about 500 km2. A younger detachment fault appears to develop at the inner rift wall just west of the AVR. The rift valley sediments are affected by the faulting and the seismic stratigraphy of these sediments constrain the history of core complex formation.
OS41C-06 INVITED
From Mantle to Microbes: The Cycling of Volatiles in Slow- and Ultraslow Ridge Environments
Olivine-rich gabbros and mantle peridotites are significant components of the seafloor in slow- and ultraslow- spreading ridge environments. The alteration of these rocks has fundamental geophysical and biogeochemical consequences for the global marine system and is critical in cycling volatiles from the mantle to the biosphere. Thus, it is important to understand the extent and conditions of alteration (e.g., temperature, fluid flux, oxidation states) and the impact of these processes for the formation and speciation of C-O-H-S fluids as nutrients for biological activity. This presentation is intended to provide an overview of magmatic and hydrothermal processes that control hydrothermal fluid compositions and the formation of hydrocarbons in submarine environments at the lower end of the spreading rate spectrum and with variable tectonic histories. Emphasis will be placed on how fluid chemistries in peridotite-hosted hydrothermal systems (Rainbow, Logatchev, Lost City and Saldanha along the MAR) differ from those in black smoker systems, and on the role of serpentinization in generating highly reduced, volatile-rich hydrothermal fluids and in the biological communities they may support. In addition to directly influencing the geophysical properties of the oceanic lithosphere, serpentinization processes provide an important sink for many major and minor elements from seawater (e.g., H2O, Mg, B, U, SO4, DIC, and DOC) and result in major changes in the isotopic compositions of O, H, S, C, B, Sr, and Nd in the rocks. Serpentinization also produces elevated concentrations of primarily abiogenic methane (up to 2.5 mmol/kg) and hydrogen (up to 16 mmol/kg) that have important consequences for vent microbial communities and for the existence of a deep H2-based biosphere. Varying fluid fluxes influence redox conditions and the stabilities of oxides, sulfides, and FeNi alloys, which together with microbial activity, can significantly affect C-H-S cycles in these systems. In addition, recent experimental studies and vent fluid data provide evidence for abiotic synthesis of organic compounds through Fischer-Tropsch type reactions during serpentinization and provide constraints on alternative pathways for the formation of early membranes and the origin of life. At moderate temperatures, such as at Lost City, serpentinization produces high pH fluids that promote carbonate precipitation and produce large, porous hydrothermal structures. The production of reduced volatiles and variable mixing with ambient seawater in the subsurface and in near-vent environments is an important process in creating strong chemical gradients that provide micro-niches for distinct communities of H-, S- and CH 4-utilizing archaea, bacteria as well as eubacteria, and which results in high organic carbon contents (up to 1 wt%) in the hydrothermal structures. The ultraslow-spreading Arctic ridges are characterized by a variable degree of volcanism, a lack of transform faults, and the juxtaposition of crustal and mantle rocks along magmatic and amagmatic ridge segments. These ridges are potential sites in which moderate-temperature, peridotite-hosted hydrothermal systems, similar to Lost City, may occur in close proximity to basalt-hosted, black smoker systems - and are thus areas with potentially highly variable volatile contents and fluid compositions which could support a large range of micro-organisms in the subsurface and in near-vent environments. http://www.oceanexplorer.noaa.gov/explorations/05lostcity/welcome.html
OS41C-07
Scientific Scope and Summary of the Arctic Gakkel Vents (AGAVE) Expedition
The AGAVE project is an international collaboration between scientists in the United States, Sweden, Japan, and Germany with the overarching scientific objective of studying the geological, chemical, and biological characteristics of hydrothermal venting on the Gakkel Ridge, the most slowly diverging tectonic plate boundary on Earth. The AGAVE expedition took place on the IB Oden from July 1 - August 10, 2007, and occupied two field sites where evidence of hydrothermal venting had been detected in the water column during the 2001 Arctic Mid-Ocean Ridge Experiment (AMORE). The first site (~85N, 7.5E) is characterized by peridotite outcrops on normal fault scarps, while the second site (~85.5N, 85E) is characterized by constructional basaltic volcanism, thereby allowing for a comparative study of hydrothermal processes at two segments of an ultra-slow spreading ridge with contrasting geological and tectonic settings. Five primary oceanographic assets were employed during the expedition; a high-resolution, ship-mounted multi-beam bathymetry system, a CTD-rosette system for surveying and sampling the water column, the PUMA autonomous underwater vehicle (AUV) for fine-scale water column surveys, the JAGUAR AUV for near-bottom geophysical and photographic surveys, and the CAMPER wireline system for acquiring digital images and samples of the deep seafloor. The combined results from the expedition are significantly expanding our understanding of volcanic and hydrothermal processes on the Gakkel Ridge. Important initial results include the discovery of the Asgard volcanic chain at the 85E segment, the discovery of extensive microbial mats covering these volcanoes, the discovery of basaltic glass fragments covering large portions of the seafloor near the volcanoes, and detailed mapping and sampling of water column plumes.
OS41C-08 INVITED
Biological and Geological Characteristics of the Gakkel Ridge
The Gakkel Ridge (Arctic Ocean) is one of the slowest (1.0 cm per yr), deepest (5000 m axial depth), and most hydrographically and tectonically isolated mid-ocean ridge systems on earth. This isolation from the global ridge system should have profound implications for the evolution and ecology of resident chemosynthetic fauna. The July 2007 Arctic GAkkel Vents Expedition (AGAVE) sought to define this Arctic biogeographic province and the relationship of Arctic vent fauna to Atlantic, Pacific, and hydrocarbon seep fauna through the use of an new under- ice vehicle `Camper', a fiber-optic video-guided sampling system drift towed 1 to 3 m above the seafloor. The imaging, sampling, and sensing capabilities were used to obtain high-resolution seafloor imagery to identify and collect benthic samples with a clamshell `grab' sampler and a suction 'slurp' sampler. Imagery from five video cameras, including obliquely-mounted video and downlooking digital high-definition color cameras were used to construct maps of seafloor features and faunal composition during 3 dives in the peridotite-hosted 7°E region and 13 dives in the volcanic 85°E region. The 7°E site was dominated by an almost continuous cover of pelagic sediment with abundant animal tracks, brittle stars, anemones, and shrimp. The explored 85°E area was dominated by relatively diverse and young lava morphologies- from large pillows hosting delicate surface ornamentation to lobates, long lava tubes, and fresh sheet flows, all with the upper surfaces covered (often cm thick) of fresh volcanic glass 'sediment' suggestive of explosive volcanic activity in the `recent' past. Fauna in these areas consisted mainly of sponges, anemones, amphipods and shrimp. Characterization of the newly-discovered Asgard volcanic chain, including `Oden', `Thor', and `Loke' volcanoes, in the 85°E axial valley revealed extensive microbial mats in the form of: 1) yellow `fluffy' material (often >5 cm thick) in places; and 2) yellow `pebbly' material that may represent older microbial byproducts or inorganic material remnant of past microbial activity. The microbial mats were often associated with weak temperature (e.g., 0.07°C) and Eh anomalies (up to 80 mV) less than 3 meters above the mats, suggesting that they live in regions where reducing and slightly warm fluids are seeping through cracks in the fresh volcanic terrain. The rock margins adjacent to the microbial mats were orange-brown suggesting bio-chemical alteration. The microbial mat material may be sustained by weak fluid discharge from cracks in the young volcanic surfaces. Biological samples, including mat material, sponges, and amphipods were preserved for shore-based taxonomic, phylogenetic, and biogeographic analyses. http://www.divediscover.whoi.edu/expedition11/index.html