Late Quaternary sediment accumulation in the Baffin Bay

Piston cores from fiords, shelf troughs, and the deep-sea off eastern Baffin Island, N.W.T., Canada, have been sampled for texture and detrital carbonate in the <2 mm fraction. The sediments consist primarily of silty clays usually containing <5% sand. Estimates are made for sediment accumulation (kg/m**2/ka) over the last ca. 10 ka. Three sets, of two cores each, lie on a fiord-shelf transect and thus define variations in sediment accumulation gradients. These continental margin data are compared with cruder estimates of Holocene sediment accumulation at three sites farther offshore in Baffin Bay, Davis Strait and the northern Labrador Sea. Minimum accumulation in a 2 ka interval was 200 kg/m2 with a maximum estimate of 8,800 kg/m2. Detrital carbonate accumulation varies between 0 and 1,300 kg/m**2. Median accumulation for a typical fiord-shelf-deep-sea transect over the last 10 ka have been 10,340, 3493 and 820 kg/m**2. At DSDP Leg, site 645 in central Baffin Bay, the sedimentation rate ranged between 40 and 130 m/Ma (ca. 400 and 1200 kg/m**2/2ka); that is, comparable with the Late Quaternary input into Baffin Bay.

Foraminiferal assemblages of the Mackenzie-Beaufort Sea Slope and Amundsen Gulf

Two cores, one from the Beaufort Sea Slope at 1000 m water depth (core 750) and one from the Amundsen Gulf at 426 m (core 124), were collected to help determine paleo-ice cover in the Holocene and late glacial of this area. Site 750 is particularly sensitive to changes in paleo-ice cover because it rests beneath the present ice margin of the permanent Arctic ice pack. Core 124 was sampled just in front of the former glacier that moved out into the Amundsen Gulf and started to recede about 13 ka B.P. Both cores have a strong occurrence of calcareous foraminifera in the upper few centimeters, but these disappear throughout most of the Holocene, suggesting more open water in that time period than present. In the sediments representing the end of the last glacial period (dated at ~11,500-14,000 calibrated years B.P. (cal B.P.)) a calcareous fauna with an abundant planktic foraminiferal fauna suggests a return to almost permanent ice cover, much like the central Arctic today. Together with the foraminifera there was also abundant ice-rafted debris (IRD) in both cores between 12,000 cal B.P. and ~14,000 cal B.P., but those units are of different ages between cores, suggesting different events. The IRD in both cores appears to have the same magnetic and chemical signals, but their origins cannot be determined exactly until clay mineralogy is completed. There is abundant organic debris in both cores below the IRD units: the organics in core 750 are very diffuse and not visually identifiable, but the organic material in core 124 is clearly identifiable with terrestrial root fragments; these are 14C dated at over 37,000 years B.P. This is a marine unit as it also has glacial front foraminifera in the sediment with the organic debris that must have been originating from subglacial streams. The seismic and multibeam data both indicate glaciers did not cross the core 124 site.

Contents and isotopic speciation of sedimentary carbon and nitrogen in sediment core MD01-2404, the Okinawa Trough

Total organic carbon to total nitrogen ratio (C/N) and their isotopic composition (d13CTOC vs. d15NTN) are oft-applied proxies to discern terrigenous from marine sourced organics and to unravel the ancient environmental information. In high depositional Asian marginal seas, matrixes, including N-bearing minerals, dilution leads to illusive and even contradictive interpretations. We use KOH-KOBr to separate operationally defined total organic matter into oxidizable (labile) and residual fractions for content and isotope measurements. In a sediment core in the Okinawa Trough, significant amounts of carbon and nitrogen existed in the residual phase, in which the C/N ratio was ~9 resembling most documented sedimentary bulk C/N ratios in the China marginal seas. Such similarity creates a pseudo-C/N interrupting the application of bulk C/N. The residual carbon, though composition unknown, it displayed a d13C range (-22.7 to -18.9 per mil, mean -20.7 per mil) similar to black carbon (-24.0 to -22.8 per mil) in East China Sea surface sediments. After removing residual fraction, we found the temporal pattern of d13CLOC in labile fraction (LOC) was more variable but broadly agreed with the atmospheric pCO2-induced changes in marine endmember d13C. Thus, we suggested adding pCO2-induced endmember modulation into two-endmember mixing model for paleo-environment reconstruction. Meanwhile, the residual nitrogen revealed an intimate association with illite content suggesting its terrestrial origin. Additionally, d15N in residual fraction likely carried the climate imprint from land. Further studies are required to explore the controlling factors for carbon and nitrogen isotopic speciation and to retrieve the information locked in the residual fraction.

Granulometry and Bulk Geochemistry of Nearshore Sediments, Herschel Island, Yukon Territory, Canada

This dataset contains the results of granulometric and bulk geochemical analyses of Van Veen surface samples obtained by the Alfred Wegener Institute (AWI) in the course of the 2012 and 2013 summer field seasons. The sampling was performed along transects in depths generally <13 m, to a distance of about <5 km off Herschel Island. In 2012, 75 samples in Pauline Cove and in the vicinity of Simpson Point were obtained. Sample collection was expanded in 2013, on transects established the previous year, with additional locations in Tetris Bay and Workboat Passage. Samples consisted of approximately 100 g of the top 3-6 cm of sediment, and were frozen in the field and freeze dried at the AWI before undergoing analytical procedures. Sample locations were recorded with the onboard global positioning system (GPS) unit. Grain size distributions in our study were obtained using laser diffractometry at the AWI (Beckman Coulter LS200) on the <1 mm fraction of samples oxidized with 30% H2O2 until effervescence ceased to remove organics. Some samples were also sieved using a sieve stack with 1 phi intervals. GRADISTAT (Blott and Pye, 2001) was used to calculate graphical grain size statistics (Folk and Ward, 1957). Grain diameters were logarithmically transformed to phi values, calculated as phi=-log2d, where d is the grain diameter in millimeters (Blott and Pye, 2001; Krumbein, 1934). Freeze dried samples were ground and ground using an Elemetar Vario EL III carbon-nitrogen-sulphur analyzer at the AWI to measure total carbon (TC) and total nitrogen (TN). Tungsten oxide was added to the samples as a catalyst to the pyrolysis. Following this analysis, total organic carbon (TOC) was determined using an Elementar VarioMax. Stable carbon isotope ratios of 13C/12C of 118 samples were determined on a DELTAplusXL mass spectrometer (ThermoFisher Scientific, Bremen) at the German Research Centre for Geosciences (GFZ) in Potsdam, Germany . An additional analysis on 69 samples was carried out at the University of Hamburg with an isotope ratio mass spectrometer (Delta V, Thermo Scientific, Germany) coupled to an elemental analyzer (Flash 2000, Thermo Scientific, Germany). Prior to analysis, soil samples were treated with phosphoric acid (43%) to release inorganic carbon. Values are expressed relative to Vienna Peedee belemnite (VPDB) using external standards (USGS40, -26.4 per mil VPDB and IVA soil 33802153, -27.5 per mil VPDB).

Geochemistry and stable isotope record of black shales and inoceramids from the Demerara Rise

The bulk rock geochemistry and inoceramid isotopic composition from Cenomanian to Santonian, finely laminated, organic-rich black shales, recovered during Ocean Drilling Program Leg 207 on Demerara Rise (western tropical North Atlantic), suggest persistent anoxic (free H2S) conditions within the sediments and short-term variations within a narrow range of anoxic to episodically dysoxic bottom waters over a ~15 Ma time interval. In addition to being organic-rich, the 50-90 m thick sections examined exhibit substantial bulk rock enrichments of Si, P, Ba, Cu, Mo, Ni, and Zn relative to World Average Shale. These observations point to high organic burial fluxes, likely driven by high primary production rates, which led to the establishment of intensely sulfidic pore waters and possibly bottom waters, as well as to the enrichments of Cr, Mo, U, and V in the sediments. At the same time, the irregular presence of benthic inoceramids and foraminifera in this facies demonstrates that the benthic environment could not have been continuously anoxic. The d13C and d15N values of the inoceramid shell organics provide no evidence of chemosymbiosis and are consistent with pelagic rain as being a significant food source. Demerara Rise inoceramids also exhibit well-defined, regularly spaced growth lines that are tracked by d13C and d18O variations in shell carbonate that cannot be simply explained by diagenesis. Instead, productivity variations in surface waters may have paced the growth of the shells during brief oxygenation events suitable for benthic inoceramid settlement. These inferences imply tight benthopelagic coupling and more dynamic benthic conditions than generally portrayed during black shale deposition. By invoking different temporal scales for geochemical and paleontological data, this study resolves recent contradictory conclusions (e.g., sulfidic sedimentary conditions versus dysoxic to suboxic benthic waters) drawn from studies of either sediment geochemistry or fossil distributions alone on Demerara Rise. This variability may be relevant for discussions of black shales in general.