Tuesday 1st May at 3pm we have the pleasure to welcome Dr. Zvika Steiner, from the University of Cambridge, for our next G3 seminar.
Zvika’s talk will be entitled: “The effects of ocean acidification and eutrophication on the CaCO3 cycle of the Red Sea”.
Zvika’s talk will be presented in node room 064/03 at 3pm.
“Experimental and field evidence support the assumption that global warming and ocean acidification is decreasing calcification rates in the oceans. Measured differences in conservation of total-alkalinity with salinity of the Red Sea surface water indicate a 26±16% decline in CaCO3 precipitation rates from 1998 to 2015 and stability during 2015-2018. Strontium-to-alkalinity ratios reveal that the net contribution of hermatypic corals to the CaCO3 budget of the southern and central Red Sea declined from ~20% to nearly 0, while pelagic calcification rates decreased by 7.5±7.5%. The decline in coral calcification rates is much larger than expected based on warming and acidification. Part of this change is possibly associated with eutrophication which can promote ecological change and enhance dissolution of calcium carbonate. Commercial fish-farming in the oligotrophic northern Gulf of Aqaba between 1997 and 2008 provided an opportunity to test the effect of long-term fertilization supplying nitrogen and phosphate on CO2 sequestration by the sea through changes in the CaCO3 cycle which I will explore using sedimentary and ecological observations.”
Tomorrow (Tuesday 6th March) at 10 am, we have the pleasure to welcome Dr. Marianne Conin from Universite de Lorraine, France for our next G3 seminar. Marianne is one of the ECORD / IODP distinguished lecturers and her talk will be entitled,
“10 years of thrilling advances on the understanding of the seismogenic zone behaviour in subduction zones from IODP drilling”.
Marianne’s talk will be presented in the John Swallow Room (054/06) at 10 am.
Prof. Andrew Frederiksen (U. Manitoba) will visit us next Tuesday 8 April and give a G3 talk at NOC Southampton – Node Room (074/02) (Waterfront Campus).
“On Continental Rifts, Lithospheric Structure, and Whether Deconvolution is a Waste of Time”
“The stable interiors of continents preserve long historical records of tectonic and convective processes, both in the crust and in the lithosphere. A particularly good example of this is the Superior Province, North America, which is the largest stable Archean crustal block in existence, and which abuts upon the failed Proterozoic Mid-Continent Rift (MCR). The Superior’s apparently uniform long-term stability conceals considerable crustal and lithospheric complexity. Through data from Canadian and American seismic networks, including early results from the SPREE temporary deployment, we have delineated domains with radically different seismic properties: the Western Superior Mantle Anomaly (WSMA), a high-velocity, strongly anisotropic block, is abutted by lower-velocity features related to post-accretionary events: magmatism in the Nipigon Embayment, rifting in the MCR, the Great Meteor hotspot track, and an enigmatic channel-likelinear feature beneath Minnesota and the Dakotas that may be related to a purely lithospheric failed arm of the MCR. We also detect variations in Precambrian tectonic styles: the strongly anisotropic WSMA underlies a region of the Superior consisting of narrow belts with a strong plate-tectonic signature, while the Minnesota River Valley Terrane, which has been attributed to a vertical tectonic regime, shows no horizontal fabric.
To relate these lithospheric features to crustal properties, we introduce a new method for deriving crustal properties from the P coda. The traditional H-k stacking approach involves deconvolving teleseismic data to form receiver functions, then stacking Moho conversions and reverberations assuming a single crustal layer. Both of these steps can break down in deep sedimentary basins, such as the Williston basin in our study area; the deconvolution can yield “ringy” receiver functions without clear individual arrivals, and the stacking can be problematic in the presence of a strong interface at the base of the sedimentary basin. We replace H-k stacking with a grid-search approach in which the transfer function between vertical and radial components is calculated for an assumed model (which can include a sedimentary layer), and then used to predict the radial component from the vertical. Our results show thickening sediments into the Williston Basin, crustal thinning at the western edge of the Superior (perhaps related to crustal erosion during the Trans-Hudson orogeny), and unusual crustal P/S velocity ratios associated with an offset in the MCR. We do not, however, see a crustal feature corresponding to the low-velocity “channel” observed in the lithosphere, suggesting that this feature is either not rift-related or is confined to the lithosphere alone.”
“Adventures of Curiosity in Gale Crater, Mars”
Prof Sanjeev Gupta from Imperial College
Please note the room change (064/03, 15:00h).
NASA’s car-sized rover, Curiosity is actively exploring Gale Crater on Mars in search of ancient habitable environments. This talk will describe the rover’s explorations and adventures, and discuss the latest findings.
The 155-km diameter Gale Crater was chosen as Curiosity’s field site based on several attributes including an interior mound of ancient flat-lying strata extending almost 5 km above the elevation of the landing site. The lower few hundred meters of the mound show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata. The landing ellipse is characterized by a mixture of alluvial fan, high thermal inertia/high albedo stratified deposits, and a number of stratigraphically/geomorphically distinct fluvial features. Curiosity landed just below the base of the alluvial fan deposit and very close to the high thermal inertia unit. Gale’s regional context and strong evidence for a progression through multiple potentially habitable environments, represented by a stratigraphic record of extraordinary extent, ensure preservation of a rich record of the environmental history of early Mars.
This week’s G3 seminar series will host Dr Oscar Branson on Tuesday, February 17 at 15:00h (Room 074/02), who will give a talk on:
“Bright lights reveal palaeoproxy mechanisms”
His abstract, along with future G3 talks, can be viewed here:
There will be a G3 seminar as follows but not on the normal day, hence advertising early – please put in your diaries and all welcome. Hans Nelson has had an extensive career in sedimentology and marine geology, much of it in the USGS, working on submarine fan processes, turbidite systems, and more recently on the role of earthquake triggering on sediment gravity flows.
Monday February 24th, 3pm, NOCS 074/02
Instituto Andaluz de Ciencias de la Tierra (CSIC), Granada, Spain and University of Leeds
Seismo-turbidite sedimentology: Implications for active tectonic margin stratigraphy, lithology and petroleum reservoirs
Earthquakes generate mass transport deposits (MTDs) plus megaturbidite, multi-pulsed, stacked, homogenite, tsunamite and seiche seismo-turbidites. The strongest (Mw 9) earthquake shaking signatures (e.g. Cascadia) create multi-pulsed individual turbidites, that correlate with seismogram rupture patterns of historic earthquakes. The weaker (Mw = or < 8) earthquakes (e.g. San Andreas) generate dominantly uni-pulsed upstream and stacked turbidites downstream below channel confluences. Both multi-pulsed and stacked turbidites create potentially thick amalgamated-like reservoir sands. Petroleum reservoirs in unconfined basin settings of active tectonic margins may be enhanced because multiple great earthquakes cause seismic strengthening of margin sediment that result in minor MTDs in basin floor turbidite system deposits. In confined basin settings, earthquake triggering results in potential reservoirs with coeval megaturbidites in proximal settings, thick stacked turbidites downstream, and ponded homogenite turbidites in basin centers.
The next G3 seminar will be given on Tuesday, December 3, 2013: 2pm in Room 074/02. This will be the upgrade talk by Ryan Gallacher on: Mantle Structure beneath the Afar triple junction derived from surface wave tomography
Mechanisms describing melt generation during continental breakup are poorly constrained due to the paucity of direct observations. The Ethiopian rift system presents an opportunity to investigate current melt generation and specifically whether active or passive mantle upwelling is dominant during the transition from continental to oceanic rifting. To address this issue, we use Rayleigh-wave tomography to construct the first absolute 3-D shear velocity model for the region, utilising 290 stations from seismic deployments over the past 10 years. Within the rift, shear velocities are 5-12 % slower relative to the regional average. We attribute the crustal low velocity anomalies to magmatic intrusion and partial melt. In the mantle the lowest velocities (<4 km/s) are unlikely solely due to thermal anomalies in a peridotite mantle, rather the presence of partial melt is required. In Northern Afar we estimate ~0.5 % partial melting at 75-150 km depth, based on theoretical predictions of melt effects (Hammond and Humphreys, 2000). The mantle anomalies are offset from the magmatic segments with segmented upwelling between the mantle and the crust. We estimate up to ~2 % partial melt in the mantle, from 40-160 km, beneath the NMER. The diapiric shaped anomalies suggest 3-D melt focusing and pre-rift thinning assist melting, generating active upwelling beneath the rifts due to the effect of melt buoyancy.
G3 Seminar by Bedanta K Goswami, Tuesday 8th October from 15:00 hrs in room 074/02, NOCS.
Preliminary interpretation of CSEM data over gas hydrates in the West Svalbard continental margin
Vestnesa Ridge (1200-1350m water depth) marks the northern boundary of the gas hydrate province in West Svalbard margin. Numerous pockmarks with active seeps on the seafloor are located at the south eastern part of the ridge where fluid migration in the area is impacted by gas hydrates in shallow sediments. Upward migrating free gas is reported to topographically migrate and focus below the ridge crest at the base of the gas hydrate stability zone (GSHZ). Excess pore pressure then forces gas through the GSHZ leading to the formation of pockmarks. Apparent resistivity obtained from controlled source electromagnetic (CSEM) data provide an independent parameter to predict hydrate and gas saturations in the area. In July 2012, a CSEM survey was conducted over an active pockmark at Vestnesa Ridge during cruise JCR269B to allow joint interpretation of CSEM and seismic data. A pseudosection approach adopted for the preliminary analysis due to uncertainty in source receiver geometry show an elevated apparent resistivity of sediments. Assuming 50% porosity of sediments, partial pore saturation are calculated using Archie’s empirical parameters from other hydrate regions with similar sediments. Using a=1, m=2 & n=2, Archie’s law suggest hydrates occupy 12-15% of sediment pores, and in the pipe-like structure 60% of pores are filled with free gas below the pockmark. The results show good agreement with predictions from seismic reflection data while providing new information about gas concentration within the fluid escape features.