Past studies have suggested a statistical connection between explosive volcanic eruptions and subsequent El Niño climate events. This connection, however, has remained controversial. Here we present support for a response of the El Niño/Southern Oscillation (ENSO) phenomenon to forcing from explosive volcanism by using two different palaeoclimate reconstructions of El Niño activity and two independent, proxy-based chronologies of explosive volcanic activity from ad 1649 to the present. We demonstrate a significant, multi-year, El Niño-like response to explosive tropical volcanic forcing over the past several centuries. The results imply roughly a doubling of the probability of an El Niño event occurring in the winter following a volcanic eruption. Our empirical findings shed light on how the tropical Pacific ocean-atmosphere system may respond to exogenous (both natural and anthropogenic) radiative forcing.
[1] It is widely recognized that a significant negative excursion in carbon isotopic (d 13 C) differences between planktic and benthic foraminiferal tests occurred at the Cretaceous-Tertiary (K-T) boundary. We applied parametric and nonparametric breakpoint tests and statistical comparisons of different recovery models to assess the timing and pattern of recovery from this negative excursion at South Atlantic Deep Sea Drilling Project (DSDP) Site 528 and equatorial Pacific DSDP Site 577. Our results indicate a two-stage recovery with an initial recovery to an intermediate state of planktic-to-benthic d 13 C differences followed by a discontinuous shift to a final state with planktic-to-benthic d 13 C differences similar to preextinction values. The final discontinuous shift in both the Pacific and Atlantic Ocean sites occurred several million years after the K-T collapse of planktic-tobenthic d 13 C differences. Both the first and second stages of recovery are best described by damped exponential relaxations. The pattern and timing of this carbon cycle recovery may have been contingent on the occurrence of key biological events.
The oil and gas industry is constantly moving into greater Water depths. Determining the seafloor's ability to Support offshore structures, templates and pipelines is Among the numerous challenges. In deep water Geotechnical investigations have traditionally been Conducted using expensive drilling vessels or semi submersible rigs. Greater water depths require new Technology for the efficient, how cost acquisition of soil Design data. Lye Tethered Seafloor Platoons (TSP) Prototype was developed and tested for the purpose of Obtaining in situ soil property measurements in water Depths as great as 3,000 meters. INTRODUCTION Anticipating its future needs in deep water, Mobil Launched the TSP project in the fall of 1989. The Concept was to design and build a subset module that could continuously measure geotechnical properties fromThe seafloor down to approximately 70 meters. This Would be accomplished by using a remotely-operated package to push specially designed probes downwards through the seabed. The TSP system would be operated From vessels-of-opportunity equipped with dynamic Positioning facilities and would have a water depth Capability up to 3,000 meters. It would be simple in Operation, requires minimal maintenance, and provide Reduced operating cost. The ambitious project described above was the result of About thirteen years of dreaming, planning and Designing. The original idea was conceived by Researchers from Mobil and McClelland Engineers. In August 1981, the conceptual study was initiated by Mobil Research and Development Corporation in Dallas, Texas, and resulted in McClelland Engineers' report in March 1982, which recommended the TSP approach for? Deep water geotechnical data collection. A more detailed Feasibility study was authorized in January 1983 and a Report was issued the following December entitled "A New Approach" to Offshore Geotechnical Investigations - A Compact, Deep Penetration Tethered Seafloor Platform'. This study included yard and field testing of a standard Coiled tubing injector as a means for pushing Geotechnical test probes into the soil. Field testing was Conducted in Venice, Louisiana and nearly vertical penetrations to 53 meters were achieved in marine type Soil conditions. The results of the tests were encouraging and recommendations were made to proceed with building a prototype TSP. Progress on the implementation of the idea fell victim to The downturn in the offshore oil industry and a lack of funding for research projects during the mid 1980's. Work was suspended until the latter part of 1987, when The project was revived by Mobil Exploration Norway Inc.(MENI). This lead to the formation of the joint-venture Nonvoting company, Seabed Exploration A/S (SEAS), to Execute the development contract and begin work. Established in Bed, Norway during September 1989, Seabed Exploration is jointly owned and staffed by the Parent companies Rapp Marine in Bed, Norway and Forgo-McClelland Marine Geosciences, in Houston, Texas. The work was performed by an integrated team with personnel from mechanical system RappMarine providing expertise in Design, construction, and testing. And personnel from Forgo-McClelland, Houston, Providing geotechnical expertise and overall project Management. Forgo Engineers B.V., Holland, was Responsible for probe and data acquisition system Development.
Summary An unprecedented intrusion of the Loop Current into the northern Gulf of Mexico severely affected expiration drilling in areas where water depths are asshallow as 450 ft. At Mobil E and P U.S. Inc.'s well, drilling was discontinuedowing to rig offset and resultant high riser angle. Safe disconnect of theriser required modeling of the mooring system and riser, building necessaryequipment, and proper planning. Introduction In Aug. 1989, the Loop Current unexpectedly moved into the northern Gulf of Mexico, severely affecting exploration drilling in several lease block areas. At least six operators were forced to shut down operations. The affected blockswere primarily in deep water; however, strong currents were found at sites withwater depths as shallow as 450 ft. At Mobil's well in 770 ft of water at EwingBank 871, drilling from the Sedco Forex 601 rig was discontinued owing to rigoffset, vortex-induced vibrations, and resultant high riser angle on Aug. 11. The riser was safely disconnected on Aug. 19 and was not reconnected until Aug.27, when current speeds had diminished greatly. Data on currents measured atthe rig were entered into models of the mooring system and riser that were usedat the rig to ensure a safe disconnect. The Loop Current and Eddies The Loop Current is a portion of the Gulf Stream system that enters the Gulfof Mexico between Cuba and the Yucatan, loops through the eastern Gulf of Mexico, and exits between Florida and Cuba. The path of the Loop Current variesconsiderably. At intervals of 6 to 17 months, large clockwisecirculating eddiesbreak from the current, as shown in Fig. 1. Eddies generally translate to thewest and southwest, but occasionally move northwest onto the Louisiana shelf. The Loop Current and its eddies have the potential to produce currents inexcess of 4 knots near the surface and up to 1 knot at depths to 1,000 ft. Tracking the Loop Current and eddies is possible from November through May bypossible from November through May by use of satellite thermal images availableat no cost from government agencies. The images show the strong temperaturegradients that occur at the edge of the Loop Current and eddies. Certainfactors affect the accuracy of thermal images. Cloud cover often obscures thesea surface, and the location of currents can vary with respect to surfacetemperature gradients. If the edge of the Loop Current is near a site ofinterest, detailed tracking must be undertaken from ships. During June through October, the entire Gulf of Mexico becomes uniformly warm at the surface. Therefore, surface contrasts disappear, making satellite imagery of littlevalue and more costly in-situ measurements necessary. Strategic seeding of the Gulf of Mexico with satellite-tracked drifting buoys is used to infer grossmovements, and ship-deployed instruments are required to delineate the edge ofthe highcurrent features. Time Series of Data at the Drillsite. Measurements on the rig, shown in Fig. 2, began on Aug. 17 and continueduntil Sept. 7. Owing to instrument failures, two major data breaks convenientlyseparate the record into three segments for discussion:Aug. 17–19,Aug. 21–28, andSept. 1–7. Currents during Period 1 were strong with aminimum speed of 1.75 knots and a maximum of 2.68 knots, with the directionrelatively steady at about 70 deg. At the beginning of Period 2, currentscontinued to be strong; however, the direction was almost due north. Thisstrong northward flow is questionable because steerage by the bottom topographyis typically in a more eastward direction. Visual estimates from the rig, however, support the northward direction; the direction change is similar to ameander passage. Current speeds decreased linearly from 2.25 knots on Aug. 24at 5 p.m. to a speed of 0.26 knots on Aug. 26 at 7 p.m., a decrease of about0.25 knots every 6 hours. The current direction change was much more abrupt. Direction changed nearly 90 deg., from 356 to 77 deg., in 4 hours (the changemay have been quicker, but data are not available between the two readingsseparated by hours). The reduction in speeds allowed the riser to bereconnected on Aug. 27. The measured current data in Period 3 are indicative ofcurrents normally experienced at the site. Speeds are generally less than 0.5knot, and direction is continually changing in response to tides and/orinertial oscillations. The vector plots indicate a slow westward flowsuperimposed on the rotational currents during this period. JPT P. 1038
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