We use geochemical and petrographic data from anoxic sequences of the Nicobar Fan to document extensive marine silicate weathering (MSiW) in the input sediment of the Sumatra subduction zone and the ...conditions that result in authigenic minerals originating from this reaction: precipitation of authigenic carbonate—which sequesters carbon—and formation of authigenic clay—which releases CO2. Increase in 87Sr/86Sr in pore fluids from International Ocean Discovery Program Expedition 362 (Site U1480 to 0.71376 and Site U1481 to 0.71296) reveals a radiogenic strontium contribution from alteration of the Himalayan continental sediment that dominates the Nicobar Fan. Peaks in the dissolved strontium isotope data coincide with zones of methane presence, consistent with MSiW reactions driven by CO2 generation during methanogenesis. Later‐stage fan sequences from 24 to 400 mbsf (meters below seafloor) contain only minor carbonate with 87Sr/86Sr ratios that deviate only slightly from the co‐eval seawater values (0.70920–0.70930); geochemical data in this zone point to a contribution of authigenic clay formation. In contrast, microscopy and elemental mapping of the carbonate‐cemented zones in the earliest fan deposits (>780 mbsf) show replacement of feldspars and dense minerals by carbonate, which ranges in volume from a few percent of the grain to near total grain obliteration. This deeper authigenic carbonate is significantly enriched in radiogenic 87Sr (0.71136–0.71328). Thus, MSiW leads to distinct products, likely in response to a weathering‐derived supply of silica in the younger setting versus calcium enrichment via diffusion from oceanic basement in the older sequence.
Plain Language Summary
Unstable minerals in sediments shed from the continents continue to undergo weathering in the early stages of burial, which is more pronounced in zones where methane generation increases the sediment acidity. Materials derived from dissolution of continent‐derived silicates may appear as newly formed (authigenic) silicates (mostly clay minerals) and also contribute to the nucleation and composition of authigenic carbonates. The authigenic mineral reactions documented here in the input sediments of the Sumatra subduction zone provide constraints on global elemental budgets and the characteristics of materials before they are subducted.
Key Points
Continent‐derived minerals shed from the Himalayas undergo weathering in anoxic sequences of the Nicobar Fan
Co‐occurring peaks of dissolved radiogenic strontium and methane support coupling of silicate weathering and methanogenesis
Silicates in the early fan are replaced by carbonate; geochemical data in the later‐stage fan point to formation of authigenic clays
Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between ...orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) “stack” from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.
•Analyzed cyclostratigraphy of microfossil density in central Arctic Ocean sediments.•Used microfossil density as a proxy for Arctic paleoclimate over the last 550 ka.•Microfossil density varies during interglacial and interstadial periods every ∼20 kyr.•Results suggest strong Arctic cryosphere response to orbital cycles.
Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40°C account for roughly half the marine sediment volume, but the processes mediated by ...microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120°C hot sediments in the Nankai Trough subduction zone. Above 45°C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80° to 85°C. In 100° to 120°C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45°C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.
During Integrated Ocean Drilling Program Expedition 311 five boreholes were drilled across the accretionary prism of the northern Cascadia subduction zone. Logging‐while‐drilling borehole images are ...utilized to determine breakout orientations to define maximum horizontal compressive stress orientations. Additionally, wireline logging data at two of these sites and from Site 889 of Ocean Drilling Program Leg 146 are used to define breakouts from differences in the aperture of caliper arms. At most sites, the maximum horizontal compressive stress SHmax is margin‐normal, consistent with plate convergence. Deviations from this trend reflect local structural perturbations. Our results do not constrain stress magnitudes. If the margin‐normal compressional stress is greater than the vertical stress, the margin‐normal SHmax direction we observe may reflect current locking of a velocity‐weakening shallow megathrust and thus potential for trench‐breaching, tsunamigenic rupture in a future megathrust earthquake.
Key Points:
Logging‐while‐drilling and wireline data at the northern Cascadia margin are used to measure breakout orientations
Maximum horizontal compressive stress SHmax is generally margin‐normal and consistent with plate convergence
If SHmax is greater than the vertical stress, a margin‐normal SHmax is consistent with locking of a velocity‐weakening megathrust
The sediment sequence from Integrated Ocean Drilling Program (IODP) Site U1304 (53°03.40′N, 33°31.78′W; water depth, 3024 m) on the southern Gardar Drift, North Atlantic Ocean, covers the last ...∼1.8 Myr with a mean sedimentation rate of ∼15 cm/kyr. At Site U1304, paleomagnetic directional and relative paleointensity (RPI) records have been generated for the last ∼1.5 Myr, and benthic oxygen isotope data for the last ∼1 Myr. The age model for Site U1304 was established by matching δ18O and RPI data to calibrated reference records. Prominent intervals of diatom mats at Site U1304 are associated with the latter stages of interglacial marine isotope stages (MIS) 9, 11, 13, 15, 21, 27 and 35, and with the weak glacial of MIS 14. The deposition of diatom mats, and associated diluted magnetic mineral concentrations, leads to weak magnetizations and susceptibilities in these intervals. Comparison of histograms of paleomagnetic directions and RPI from diatom-rich sediments and from surrounding silty clays indicates that, although results from diatom-rich sediments are more scattered, the occurrence of diatom mats does not appreciably distort the paleomagnetic directional and RPI records. Site U1304 sediments record the Matuyama/Brunhes boundary (∼772 ka), the Jaramillo Subchron (∼993–1071 ka) and the Cobb Mountain Subchron (∼1193–1219 ka), as well as three apparent geomagnetic excursions in the Matuyama Chron, interpreted as the “Kamikatsura/Santa Rosa”, “Punaruu”, and “Gardar” excursions, at ∼888 ka, ∼1124 ka, and ∼1463 ka, respectively. The Site U1304 RPI record can be correlated with the PISO-1500 RPI stack and with other high-resolution RPI records from the North Atlantic Ocean. Wavelet analyses performed on the Site U1304 RPI record and a new high-resolution North Atlantic paleointensity stack for the last 1500 kyr (HINAPIS-1500), comprising Ocean Drilling Program (ODP) Sites 983, 984 and IODP Sites U1306 and U1304, did not reveal significant orbital power.
•IODP Site U1304 recorded 5 reversals and 3 possible excursions in the last 1.5 Myr.•Major diatom mat intervals at the site occur during latter stages of interglacials.•Diatom mats dilute magnetic content with little distortion of paleomagnetic records.•New N. Atlantic paleointensity (RPI) stack matches the PISO stack at few kyr scales.•RPI records show high coherence and power at periods of ∼64–100 and ∼256 kyr.
Nine new records of plants from Bhutan Jigme Wangchuk; Tsethup Tshering; Dorji Dorji ...
Sigmul bunryu hag-hoeji = Korean journal of plant taxonomy,
06/2023, Letnik:
53, Številka:
2
Journal Article
Odprti dostop
Discoveries and new records of plants specifically provide a basis for empirical data to enable in-depth studies of the ecology, distribution, conservation, applications, and threats to such plants. ...However, many unexplored regions of Bhutan exist in which several plants have yet to be described and documented. Several species reported elsewhere in the Himalayan region with similar climatic conditions are likely to occur in Bhutan as well, indicating a need to corroborate their presence. To explore this, an opportunistic survey was employed, and we provide nine new records of plant species for Bhutan. Of the nine species, three belonged to the Lauraceae family, with the rest from the Aristolochiaceae, Asparagaceae, Lamiaceae, Phyllanthaceae, Sapindaceae, and Urticaceae families. This paper adds nine additional species of plants to the flora of Bhutan. We also report here ethnobotanical applications of these species, providing insight into how communities interact with environmental resources and have the potential to integrate traditional knowledge into scientific understanding, ultimately to reinforce sustainable biocultural conservation at the local level.
Macrostructures preserved in deformed rocks are essential for the understanding of their evolution, especially when the deformation is weak and hard to discriminate in regional scale or purely ...through geophysical data. In order to resolve the inconsistency between NS trending fracture zones and NE oriented spreading fabrics of the South China Sea during the latest spreading stage, we analyzed macrostructures identifiable from the basalt and consolidated sediment samples of the Integrated Ocean Drilling Program (IODP) Sites U1431 and U1433. These two sites are close to the East and Southwest relict spreading ridges and provide critical information on the latest spreading stages. The structures in the basalt of both sites suggest two dominant orientations of NS and NE. At U1431, sediments show mainly WNW trending slickensides, different from that of basalt. At U1433, no structures were found in postspreading sediment. Thus, NE and NS trending structures in basalt are most possibly formed by seafloor spreading. Crosscutting relationship suggests that NE trending structures formed first, followed by NS and finally WNW trending structures. These observations are consistent with geophysical features. Magnetic anomalies and ocean bottom seismometer velocity suggest that the latest relict ridge of the East Subbasin coincides with the EW trending seamount chain. Located between the relict ridges of East and Southwest Subbasins, NS trending Zhongnan‐Liyue Fracture Zone had acted as the latest transform fault. Based on the above evidences, we proposed that the South China Sea may have experienced a short period of NS oriented spreading after earlier SE spreading. These results resolve the previous inconsistencies.
Key Points
Basalt and sediment show different macrostructure orientations, indicating different stress fields between the synspreading and postspreading stages
Magnetic anomalies and low upper crust P wave velocities indicate that the youngest relict ridge in the East Subbasin may coincide with a seamount chain
Cross‐cutting relationship of fractures suggests a short period of roughly NS trending spreading after a SE trending spreading
It has previously been shown that EpiPen® autoinjectors are likely to activate normally following up to five excursions to -25°C but data about the post-freezing performance of other brands of ...adrenaline autoinjectors has not previously been published. Additionally, conditions experienced by polar medics may be substantially colder than this and the performance of adrenaline autoinjectors following more extreme freeze-thaw cycles remains uncharacterised. Investigators in Antarctica and the United Kingdom performed laboratory testing on two brands of adrenaline autoinjector, EpiPen® and Jext® (12 devices of each type). A single freeze-thaw cycle involved freezing the device to -80°C then allowing it to come to room temperature. Devices were exposed to 0, 1, 5 or 15 freeze-thaw cycles. The mass of liquid ejected from each device, when activated, was then measured. No significant differences in the mass of the liquid ejected was found between the test groups. Multiple freeze-thaw cycles to -80°C are unlikely to significantly impact the amount of adrenaline solution expelled from EpiPen® and EpiPen® autoinjectors. This preliminary finding encourages further work investigating the safety and effectiveness of adrenaline autoinjectors after exposure to very low temperatures. This information would be valuable for future polar medics planning and delivering medical provision in extreme environments.It has previously been shown that EpiPen® autoinjectors are likely to activate normally following up to five excursions to -25°C but data about the post-freezing performance of other brands of adrenaline autoinjectors has not previously been published. Additionally, conditions experienced by polar medics may be substantially colder than this and the performance of adrenaline autoinjectors following more extreme freeze-thaw cycles remains uncharacterised. Investigators in Antarctica and the United Kingdom performed laboratory testing on two brands of adrenaline autoinjector, EpiPen® and Jext® (12 devices of each type). A single freeze-thaw cycle involved freezing the device to -80°C then allowing it to come to room temperature. Devices were exposed to 0, 1, 5 or 15 freeze-thaw cycles. The mass of liquid ejected from each device, when activated, was then measured. No significant differences in the mass of the liquid ejected was found between the test groups. Multiple freeze-thaw cycles to -80°C are unlikely to significantly impact the amount of adrenaline solution expelled from EpiPen® and EpiPen® autoinjectors. This preliminary finding encourages further work investigating the safety and effectiveness of adrenaline autoinjectors after exposure to very low temperatures. This information would be valuable for future polar medics planning and delivering medical provision in extreme environments.
A multidisciplinary mineralogical, geochemical and biomarker study of Indus Fan sediments cored during International Ocean Discovery Program (IODP) Expedition 355 to the Laxmi Basin was carried out ...to define the different compositional signatures of sand, silt and clay. Upper Pliocene - lower Pleistocene turbidites from sites U1456 and U1457 were selected as the best candidates for this study. The integrated dataset presented here was obtained by coupling traditional and innovative bulk-sediment and single-mineral techniques on the same samples. Turbiditic deposits mostly consist of medium to fine silt, including rich and diverse heavy-mineral assemblages. Such a fine grain size forced us to push the limits of high-resolution quantitative heavy-mineral analysis down to as low as 5 µm. Heavy-mineral analysis allowed us to establish a Himalayan origin of the detritus in the studied turbidites. Heavy-mineral concentrations are higher in channel-fill than in overbank deposits. Mineralogical and geochemical data concur in revealing that fast-settling ultradense minerals such as zircon are preferentially concentrated in channel-fill deposits, whereas the top of overbank deposits are notably enriched with slow-settling platy phyllosilicates. Biomarker analysis represents a most suitable complementary technique that is able to investigate the provenance signature of the finer sediment fraction, largely consisting of clay. This technique allowed us to identify a largely terrigenous origin of organic matter at Site U1456 and an open marine origin at Site U1457. The latter site lies closer to the Laxmi Ridge, where thermal maturity increases with depth to reach the early oil window (127°C at c. 320 m below the seafloor).
During International Ocean Discovery Program (IODP) Expedition 368, a series of drillings were conducted in the northern South China Sea (SCS). At the abyssal drilling Site 1502 Hole A (3764 m below ...sea level), successive core sections were recovered from 442 to 497 m below sea floor. These cores were placed into the late Miocene period, and the most remarkable feature of these ~50-m-long cores were the consecutive occurrences of the rhythmic reddish-brown and greenish-gray sediments. Such color transitions during the late Miocene period were not remarkable for the cores at the adjacent shallower IODP 368 Sites 1501 and 1505. In this study, we aimed to determine the origin of these cyclicity-like color transitions at Site 1502 in the abyssal SCS. We conducted experiments dealing with sediment color reflectance, nannofossil, key element content, and clay minerals. We inferred that the in-situ formed amorphous hematite caused the coloration of the reddish sediments, in which ferrum and manganese contents were high and carbonate was not poorly preserved. We suggest that the occurrence of the cyclicity-like color transitions could result from the extent of deep-water ventilation in the abyssal SCS. Such changes in deep-water ventilation were possibly related to an orbital-forced rearrangement of deep oceanic circulation in the Pacific Ocean.
•Rhythmic reddish-brown and greenish-gray sediments were found at IODP site 1502 in the abyssal South China Sea.•Coloration of the reddish sediments could be the in-situ formed amorphous hematite.•The reddish sediments were subject to low sedimentation rates and well-ventilated conditions.•The cyclicity-like color changes could result from the changes in the Pacific deep oceanic circulation.
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