Major element concentrations in spinel, olivine and pyroxene from peridotites of ODP Hole 210-1277 of the Newfoundland margin

Serpentinized spinel peridotites of the Newfoundland margin drilled during ODP Leg 210 at Site 1277 have preserved, relic mineral compositions similar to the most depleted abyssal peridotites worldwide and different from those of the conjugate Iberian margin. The samples are derived from mass flows containing clasts of peridotite and gabbro and from in-situ basement, and are mostly mylonitic cpx-poor spinel harzburgites with Cr-rich spinels (Cr#0.35-0.66). Melting of the Newfoundland mantle occurred in the spinel peridotite field and probably exceeded the cpx-out phase boundary for some samples. Using proposed spinel peridotite melting models and experimentally derived phase diagrams, the Newfoundland harzburgites can be modeled as a residue after extraction of 14 to 20-25% melting. Basalts that are interleaved with mass flow deposits on top of the peridotite basement resemble normal to transitional mid-ocean ridge basalt. This, together with the unusually high Cr# of some spinel harzburgites suggest that the formation of basalts and partial melting of the underlying peridotite are not cogenetic. Among mantle samples some of the Newfoundland harzburgites approach mineral compositions of the Bay of island ophiolite and ophiolites from Japan that represent peridotites formed in an arc-setting. Thus, the peridotites drilled at Site 1277 may represent inherited (Caledonian or older) subarc mantle that was exhumed close to the ocean floor during the rifting evolution of the Atlantic. Compared to the spinel harzburgites from Newfoundland, the peridotites from the conjugate Iberian margin are, on average, less depleted and provide evidence for local equilibration in the plagioclase stability field. This can either be explained by an inherited, primary, Ca-richer composition of the Iberia peridotite, or, alternatively, by local melt impregnation and stagnation during continental rifting, and thus refertilizing previously depleted (arc-related) peridotite.

Major, trace and rare earth element concentration of ODP Site 210-1277 basalts, Newfoundland margin

Drilling of the distal Newfoundland margin at Ocean Drilling Program Site 1277 recovered part of the transition between exhumed sub-continental mantle lithosphere and normal mid-ocean-ridge basalt (N-MORB) volcanism perhaps related to the initiation of seafloor spreading, which may have occurred near the Aptian/Albian boundary, coincident with the final separation of subcontinental mantle lithosphere. Subcontinental mantle lithosphere was recovered near the crest of a basement high, the Mauzy Ridge. This ridge lies near magnetic Anomaly M1 and is inferred to be of Barremian age. The recovered section is dominated by serpentinized spinel harzburgite, with subordinate dunite and minor gabbroic intrusives, and it includes inferred high-temperature ductile shear zones. The serpentinite is capped by foliated gabbro cataclasite that is interpreted as the product of a major seafloor extensional detachment. The serpentinized harzburgite beneath is highly depleted subcontinental mantle lithosphere that was exhumed to create new seafloor within the ocean-continent transition zone. After inferred removal of overlying brittle crust, the detachment was eroded, producing multiple mass flows that were dominated by clasts of serpentinite and gabbro in a lithoclastic and calcareous matrix. Basaltic lavas were erupted spasmodically, mainly as sheet flows, with subordinate lava breccia, hyaloclastite, and possible pillow lava. The sedimentary-volcanic succession and the exhumed mantle lithosphere experienced later high-angle extensional fracturing and probably faulting. Extensional fissures opened incrementally and were filled with silt-sized carbonate, basalt-derived clastic sediment, and hyaloclastite, forming neptunian dykes and geopetal structures. Chemical analysis of representative basalts for major elements and trace elements were made using a high-precision, high-accuracy X-ray fluorescence method (utilizing increased count times) and by whole-rock inductively coupled plasma-mass spectrometry that yielded additional evidence for rare earth elements. The analyses indicate N-MORB to slightly enriched compositions. The MORB was produced by relatively high degree melting of a fertile mantle source that differed strongly from the cored serpentinized peridotites. The basalts exhibit a distinct negative Nb anomaly on MORB-normalized plots that can be explained by prior extraction of melt from upper mantle that had previously been affected by subduction, possibly during closure of the Iapetus or Rheic oceans. In the proposed interpretation, mantle lithosphere was exhumed to the seafloor and experienced mass wasting to form serpentinite-rich mass flows. The interbedded MORB records the beginning of a transition to "normal" seafloor spreading. This interpretation takes into account drilling results from the Iberia-Galicia margin and the Jurassic Alps-Apennines.

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

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

Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.