21 research outputs found
Late Miocene Submarine Volcanism in the Ross Embayment, Antarctica
Abstract: The ANDRILL McMurdo Ice Shelf (MIS) initiative recovered a 1285 m-long core (MIS AND-1B) composed of cyclic glacimarine sediments with interbedded volcanic deposits. By far the thickest continuous volcanic sequence is about 175 m long and is found at midcore depths from 584.19 to 759.32 meters below sea floor (mbsf). The sequence was logged and initial interpretations of lithostratigraphic subdivisions were made on-ice during drilling in late 2006. Subsequent observations, based on image, petrographic, and SEM-EDS analyses, provide a more detailed, revised interpretation of a thick submarine to emergent volcanic succession. The sequence is subdivided into two main subsequences on the basis of sediment composition, texture and alteration style. The ~70 m thick lower subsequence consists mostly of monothematic stacked volcanic-rich mudstone and sandstone deposits, which are attributed to epiclastic gravity flow turbidite processes. This subsequence is consistent with abundant active volcanism that occurred at a distal site with respect to the drill site. The ~105 m thick upper subsequence consists mainly of interbedded tuff, lapilli tuff, and volcanic diamictite. A late Miocene (6.48 Ma) 2.81 m-thick subaqueously emplaced lava flow occurs within the second subsequence. This second subsequence is attributed to recurring cycles of submarine to emergent volcanic activity that occurred proximal to the drill site. This new dataset provides 1) the first rock evidence of significant late Miocene submarine volcanic activity in the Ross Embayment during a period of no to limited glaciation , and 2) a rich stratigraphic record that elucidates submarine volcano-sedimentary processes in an off-shore setting
Glaciovolcanic evidence for a polythermal Neogene East Antarctic Ice Sheet
A paradigm has existed for more than 30 years that the basal
thermal regime of the East Antarctic Ice Sheet in Victoria Land made
a fundamental transition from wet-based to cold-based either at
ca. 14 Ma or after ca. 2.5 Ma. The basal thermal regime is important
because it determines the potential for unstable behavior in an ice
sheet. We have studied the environmental characteristics of subglacially
erupted volcanic centers scattered along 800 km of the Ross Sea
fl ank of the Transantarctic Mountains. The volcanoes preserve evidence
for the coeval paleo-ice thicknesses and contain features diagnostic
of both wet-based and cold-based ice conditions. By dating the
sequences we are able to demonstrate that the basal thermal regime
varied spatially and with time between ca. 12 Ma and present. It was
polythermal overall and probably comprised a coarse temperature
patchwork of frozen-bed and thawed-bed ice, similar to the East Antarctic
Ice Sheet today. Thus, an important shift is required in the prevailing
paradigm describing its temporal evolution
Allele-Specific Impairment of GJB2 Expression by GJB6 Deletion del(GJB6-D13S1854)
Mutations in the GJB2 gene, which encodes connexin 26, are a frequent cause of congenital non-syndromic sensorineural hearing loss. Two large deletions, del(GJB6-D13S1830) and del(GJB6-D13S1854), which truncate GJB6 (connexin 30), cause hearing loss in individuals homozygous, or compound heterozygous for these deletions or one such deletion and a mutation in GJB2. Recently, we have demonstrated that the del(GJB6-D13S1830) deletion contributes to hearing loss due to an allele-specific lack of GJB2 mRNA expression and not as a result of digenic inheritance, as was postulated earlier. In the current study we investigated the smaller del(GJB6-D13S1854) deletion, which disrupts the expression of GJB2 at the transcriptional level in a manner similar to the more common del(GJB6-D13S1830) deletion. Interestingly, in the presence of this deletion, GJB2 expression remains minimally but reproducibly present. The relative allele-specific expression of GJB2 was assessed by reverse-transcriptase PCR and restriction digestions in three probands who were compound heterozygous for a GJB2 mutation and del(GJB6-D13S1854). Each individual carried a different sequence variant in GJB2. All three individuals expressed the mutated GJB2 allele in trans with del(GJB6-D13S1854), but expression of the GJB2 allele in cis with the deletion was almost absent. Our study clearly corroborates the hypothesis that the del(GJB6-D13S1854), similar to the larger and more common del(GJB6-D13S1830), removes (a) putative cis-regulatory element(s) upstream of GJB6 and narrows down the region of location
Spectrum of Genetic Changes in Patients with Non-Syndromic Hearing Impairment and Extremely High Carrier Frequency of 35delG GJB2 Mutation in Belarus
The genetic nature of sensorineural hearing loss (SNHL) has so far been studied for many ethnic groups in various parts of the world. The single-nucleotide guanine deletion (35delG) of the GJB2 gene coding for connexin 26 was shown to be the main genetic cause of autosomal recessive deafness among Europeans. Here we present the results of the first study of GJB2 and three mitochondrial mutations among two groups of Belarusian inhabitants: native people with normal hearing (757 persons) and 391 young patients with non-syndromic SNHL. We have found an extremely high carrier frequency of 35delG GJB2 mutation in Belarus â5.7%. This point deletion has also been detected in 53% of the patients with SNHL. The 312del14 GJB2 was the second most common mutation in the Belarus patient cohort. Mitochondrial A1555G mt-RNR1 substitution was found in two SNHL patients (0.55%) but none were found in the population cohort. No individuals carried the A7445G mutation of mitochondrial mt-TS1. G7444A as well as T961G substitutions were detected in mitochondrial mt-RNR1 at a rate of about 1% both in the patient and population cohorts. A possible reason for Belarusians having the highest mutation carrier frequency in Europe 35delG is discussed
Late Miocene submarine volcanism in ANDRILL AND-1B drill core, Ross Embayment, Antarctica
The ANDRILL McMurdo Ice Shelf initiative recovered a 1285-m-long core (AND-1B) composed of cyclic glacimarine sediments with interbedded volcanic deposits. The thickest continuous volcanic sequence by far is âź175 m long and is found at mid-core depths from 584.19 to 759.32 m below seafloor. The sequence was logged, and initial interpretations of lithostratigraphic subdivisions were made on ice during drilling in late 2006. Subsequent observations, based on image, petrographic, and scanning electron microscopyâenergy dispersive spectroscopy analyses, provide a more detailed, revised interpretation of a thick submarine to emergent volcanic succession.
The sequence is subdivided into two main subsequences on the basis of sediment composition, texture, and alteration style. The âź70-m-thick lower subsequence consists mostly of monothematic stacked volcanic-rich mudstone and sandstone deposits, which are attributed to epiclastic gravity flow turbidite processes. This subsequence is consistent with abundant active volcanism that occurred at a distal site with respect to the drill site. The âź105-m-thick upper subsequence consists mainly of interbedded tuff, lapilli tuff, and volcanic diamictite. A Late Miocene (6.48 Ma) 2.81-m-thick subaqueously emplaced lava flow occurs within the second subsequence. This second subsequence is attributed to recurring cycles of submarine to emergent volcanic activity that occurred proximal to the drill site. This new data set provides (1) the first rock evidence of significant Late Miocene submarine volcanic activity in the Ross Embayment during a period of no to limited glaciation, and (2) a rich stratigraphic record that elucidates submarine volcano-sedimentary processes in an offshore setting
A recent volcanic eruption beneath the West Antarctic ice sheet
Indirect evidence suggests that volcanic activity occurring beneath the West Antarctic ice sheet influences ice flow and sheet stability(1-3). However, only volcanoes that protrude through the ice sheet(4) and those inferred from geophysical techniques(1,2) have been mapped so far. Here we analyse radar data from the Hudson Mountains, West Antarctica(5), that contain reflections from within the ice that had previously been interpreted erroneously as the ice-sheet bed. We show that the reflections are present within an elliptical area of about 23,000km(2) that contains tephra from an explosive volcanic eruption. The tephra layer is thickest at a subglacial topographic high, which we term the Hudson Mountains Subglacial Volcano. The layer depth dates the eruption at 207 BC +/- 240 years, which matches exceptionally strong but previously unattributed conductivity signals in nearby ice cores. The layer contains 0.019 - 0.31 km(3) of tephra, which implies a volcanic explosive index of 3-4. Production and episodic release of water from the volcano probably affected ice flow at the time of the eruption. Ongoing volcanic heat production may have implications for contemporary ice dynamics in this glacial system
Obliquity-paced Pliocene West Antarctic ice sheet oscillations
Thirty years after oxygen isotope records frommicrofossils deposited in ocean sediments confirmed the hypothesis that variations in the Earthâs orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine based
West Antarctic ice sheet (WAIS) during the âwarmerthan-
presentâ early-Pliocene epoch ( 5â3Myr ago) is needed to
better constrain the possible range of ice-sheet behaviour in the
context of future global warming3. Here we present a marine glacial record from the upper 600mof theAND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earthâs axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to 3 6C warmer than today4 and atmospheric CO2 concentration was as high as 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to 17min equivalent sea level associated with the loss of the WAIS and
up to13min equivalent sea level from the EastAntarctic ice sheet, in response to ocean-induced melting paced by obliquity.During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt 8 under conditions of elevated CO2
Neogene tectonic and climatic evolution of the Western Ross Sea, Antarctica â Chronology of events from the AND-1B drill hole
Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600 m and 40Ar/39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with wellâdated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of preâexisting strata. The combined age model implies relatively rapid (1 m/2â5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately
50% of the record. Three of the longer hiatuses coincide with basinâwide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies:
1. The base of the cored succession (1275â1220 mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5 Ma by several reworked volcanic clasts;
2. A late-Miocene sub-polar orbitally controlled glacialâinterglacial succession (1220â760 mbsf) bounded by two unconformities correlated with basinâwide reflectors associated with early development of the terror rift;
3. A late Miocene volcanigenic succession (760â596 mbsf) terminating with a ~1 my hiatus at 596.35 mbsf which spans the MioceneâPliocene boundary and is not recognised in regional seismic data;
4. An early Pliocene obliquity-controlled alternating diamictite and diatomite glacialâinterglacial succession(590â440 mbsf), separated from;
5. A late Pliocene obliquity-controlled alternating diamictite and diatomite glacialâinterglacial succession (440â150 mbsf) by a 750 ky unconformity interpreted to represent a major sequence boundary at other
locations;
6. An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150â80 mbsf), and;
7. A late Pleistocene glacigene succession (80â0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment