Bush Hill Research Articles

Thermal and visual time-series at a seafloor gas hydrate deposit on the Gulf of Mexico slope

Ambient temperature is a critical factor determining the stability of gas hydrate deposits on continental margins. To study this process directly under varying conditions, a monitoring array comprising a time-lapse camera and in-situ temperature probes was deployed at a hydrocarbon seep known as Bush Hill, where gas hydrates deposits are exposed at the seafloor in a water depth of 570 m. For intervals of 91 days and 30 days, the digital camera recorded several daily images of a prominent gas hydrate mound consisting of structure II gas hydrate. The temperature probes were constructed with one autonomous thermistor at each end of a 50-cm PVC wand and recorded temperatures with precision of better than 0.1 °C at 30-min intervals over 327 days. One probe was implanted with a tight seal into a drill hole about 7 cm deep in the top of the gas hydrate mound. The second was inserted about 50 cm deep into the adjacent sediments. For each probe, the top thermistor recorded the ambient water temperature, while the bottom thermistor synoptically recorded the internal temperature of the hydrate or sediment. The bottom water temperatures ranged from 6.64 to 9.73 °C with a mean of 7.90 °C and standard deviation of 0.437. Photographic results showed no dramatic changes in the size, shape or gas venting from the mound. By comparing the temperatures recorded at the tips of the probes with the synoptic water temperature, we estimate that thermal diffusivity for the gas hydrate deposit was 7.14·10 −8 to 8.33·10 −8 m 2 s −1 and was 1.77·10 −7 to 3.01·10 −7 m 2 s −1 for the sediments at the sites where temperatures were recorded. The diffusivity measured in gas hydrate was lower than that measured under laboratory conditions. Stability of gas hydrate in this setting is not likely to be affected by short-term changes in bottom water temperature within the range observed.

Fluid and chemical cycling at Bush Hill: Implications for gas‐ and hydrate‐rich environments

The results of a deployment of aqueous flux meters at the Bush Hill hydrate mound show that persistent hydrologic instability is a primary feature of the globally abundant gas‐ and hydrate‐rich cold seep environment. Seven flux meters were deployed for 14 weeks in the area of the Bush Hill hydrate mound. Instruments were deployed on microbial mats, bivalves, adjacent to the surface hydrate mound, and a site without visible fauna. Flow rates were observed to range from downflow of 0.01 mm/day to upflow of >15 mm/day. Temporal variability and a major hydrological event were observed to occur on all instruments. There is evidence that this event was related to a gas expulsion episode. The two instruments which exhibited downflow during the event were near surface hydrates and bubbling vents. Nearby instruments recorded a rapid increase in flow rates at the time of the event with a subsequent decrease in rates to the previous background values. Two instruments showed significant output of seawater‐like fluids, while the others output typical methane seep‐type pore fluids. These results at a passive margin site, along with our previously published convergent margin results at gas‐rich northeast Pacific cold seeps (Hydrate Ridge, Eel River margin), illustrate the hydrologic complexity of these environments. We now propose that these and our earlier results are characteristic of seafloor environments which have abundant free gas and hydrates. These mechanisms have major consequences for the near‐surface geochemical and microbial environment and for the way we interpret measurements made in these areas.

A compositional kinetic model of hydrate crystallization and dissolution

Hydrates are crystallizing near and at the seafloor from gas vents on shelves where the sedimentation rate is high and hydrocarbons are being generated. When seafloor temperature, vent rate, or vent gas composition changes, these hydrates may become unstable and decompose. We have constructed a compositional kinetic model of hydrate crystallization and dissolution that can address these issues. The model crystallizes hydrate in compositional bins and allows each to dissolve at either a kinetically or compositionally controlled rate if vent gas composition or temperature causes it to become unstable. We empirically calibrate the model to venting at the Bush Hill hydrate mound in the offshore Louisiana Gulf of Mexico, show how variations in venting rate crystallize hydrate of diverse composition in the subsurface, and investigate how bottom water temperature variations similar to those measured could increase the rate of gas venting by destabilizing hydrates within a few meters of the seafloor. We show that increases in bottom water temperature can cause gas venting rates to increase ∼100%, as suggested by recent measurements, only if the dissolution kinetics are fast compared to the empirically calibrated crystallization kinetics and dissolution gases are removed rapidly enough that they do not thermodynamically inhibit the rate of dissolution. Model characteristics required to further investigate hydrate mound construction are identified.

The geochemical signatures of variable gas venting at gas hydrate sites

Diverse evidence suggests that gas-venting rates at sites of hydrate crystallization are variable in space and time, but the magnitude of these variations has been difficult to quantify. The hydrate crystallization model of Chen and Cathles [J. Geophys. Res. (Solid Earth) 108 (2003)] is used here to analyze 10 years of vent gas chemistry measurements at the Bush Hill hydrate mound and gas-venting site, Green Canyon 185, offshore Louisiana, Gulf of Mexico. The analysis suggests that, at any instant of time, gas vents at variable rates in different gas channels at the same site, and that the compositional differences in these vent gases are nearly as large as can be produced by hydrate crystallization. Almost two orders of magnitude differences in venting rate between individual gas channelways are suggested. Changes in the average vent gas composition over the last 10 years suggest the average venting rate varied by a factor of ∼2 or more over a few years. The average C 3+C 4 composition of Bush Hill hydrates are leaner than could be crystallized from vent gases sampled over the last decade, indicating that the venting gas flux was slower in the past by a factor of ∼2. This is compatible with geologic generalizations that venting evolves from fast (mud volcano), to intermediate (hydrate crystallization), to slow (carbonate precipitation) if venting organized into more discrete vents with time.

A kinetic model for the pattern and amounts of hydrate precipitated from a gas steam: Application to the Bush Hill vent site, Green Canyon Block 185, Gulf of Mexico

We construct a linear kinetic model of hydrate crystallization from a gas stream. We use this model to predict the fraction of gas that crystallizes as hydrate in the subsurface of Bush Hill, and the depth profile of subsurface hydrate accumulation. This is possible because the Bush Hill vent is fed by reservoir gas from the nearby Jolliet field whose composition is known. On the average, ∼9% of the vent gas is precipitated as hydrate in the subsurface. Although other explanations are possible, the observed vent gas compositions and the greater range of hydrate gas compositions are consistent with a single source gas whose venting rate varies by a factor of at least 3 over periods of a few years or less. The predicted depth profile of hydrate accumulation and the hydrate content of the Bush Hill mound suggest that between ∼1.1 × 109 and 2.8 × 109 m3 (STP) of gas may have accumulated as hydrate between the seafloor and ∼614‐m depth. For the radiometrically and geologically suggested system age of 10,000 years, the time average venting rate is ∼106 m3/yr (0.7 × 106 kg/yr). If distributed evenly across the 600 m diameter mound, as suggested by echo sounder images, the methane flux is >3.2 kg/m2 yr. This is >103 times that inferred for hydrates associated with bottom‐simulating seismic reflectors. The subsurface hydrate accumulation and the cumulative methane venting are related. We show how both may be estimated from measurements of vent gas composition, bottom water temperature, and geothermal gradient.

ABSTRACT: Estimation of the Hydrate Gas Content of the Bush Hill Vent Site, Green Canyon Block 185, Gulf of Mexico

ABSTRACT: Estimation of the Hydrate Gas Content of the Bush Hill Vent Site, Green Canyon Block 185, Gulf of Mexico

Testing the Link Between Hydrocarbon Seepage, Sea Level Stands, and Salt Diapirism in Deepwater Gulf of Mexico: ABSTRACT

ABSTRACT Hydrocarbon seepage in both liquid (crude oil) and gas (principally methane) forms has been amply documented over the past decade from submersible dives on the northern Gulf of Mexico seafloor overlying salt diapirs. These seepage sites are inhabited by a remarkably diverse chemosynthetic fauna and are associated with massive carbonate buildups formed through bacterially-mediated processes of hydrocarbon oxidation coupled with sulfate reduction. This study addresses questions concerning the timing and longevity of seepage from four representative sites in the Green Canyon area (27°50'N; 91°30'W) on the basis of radiometric dating assays of massive carbonates that act as time keepers of hydrocarbon seeps. 230Th dates from GC-140 and GC-184 blocks place the initiation and termination of massive seepage there at 195 ±25 Ka and 13.3 ±2.7 Ka, respectively, and are in agreement with the chronology of the salt dome emplacement at shallow depth during mid to late Pleistocene low sea-level stands. The prolific seepage activity to the southeast in GC-185 (Bush Hill) and the 230Th dates of 3.2 to 1.4 Ka are attributed to a recent episode of subsidence caused by salt withdrawal which created late normal faults. When multiple dates, subsurface imaging of the salt domes by 3-D seismics, and high resolution subsurface chronostratigraphy are available from the same site, a link is apparent between the incidence of low sea level stands, salt diapirism, and enhanced hydrocarbon seepage. End_of_Record - Last_Page 471-------

Organic geochemistry of sediments from chemosynthetic communities, Gulf of Mexico slope

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H2S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C1–C5 hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C1–C5 hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O2 in sediments and triggers bacterial sulfate reduction to produce the H2S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C1–C5 hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H2S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C1–C5 concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C1) is present (8829 ppm).

Bring out your dead: the great plague of yellow fever in Philadelphia in 1793

List of Illustrations Introduction to the 1993 Edition Preface to the 1949 Edition Acknowledgments A Merry, Sinful Summer Infection in Water Street Fever, Domestic and Foreign Prevention, Personal and Civic Crisis Panic This Excellent Physician Bush Hill The Committee Sangrado The Fugitives Height of the Plague October Frost Afterwards Notes Index

Among-site differences in seedling size, growth, and survivorship in Solidago flexicaulis

Seedling and juvenile size, growth, and survivorship in Solidago flexicaulis L. were compared among three sites in southern Ontario in an attempt to evaluate environmental versus population effects on phenotype. In 1983, seedlings at the Eden Mills site were the largest in size, while survivorship was the lowest at the Guelph site ("Dairy Bush Hill"). When seedlings from Eden Mills were transplanted into the other two sites in 1984, among-site differences in growth and survivorship were predominantly due to environmental differences between sites rather than population differences between seedlings from Eden Mills and the seedlings resident at the site. However, at Dairy Bush Hill, seedlings transplanted within the site grew proportionally more than did the seedlings transplanted from Eden Mills, suggesting that the resident population was better adapted to the conditions. Mortality was again greatest at this site in 1984. Size-dependent mortality was not a factor at the Belfountain site, but was important at the other two sites. Herbivory was an important factor determining whether size-dependent mortality was exhibited at a site.

CONTRIBUTIONS OF PHILIP SYNG PHYSICK.

a frail, 17-year-old boy, ... a faithful, scrupulous, toiling soul, something of a prig, and not popular with his mates, but readily devouring any mental pabulum offered him. x His name was Philip Syng Physick, and he was to become one of the outstanding American eye surgeons and teachers of ophthalmology of his time. After his graduation, Physick studied under Dr. Adam Kuhn, Professor of Materia Medica and Botany at the University of Pennsylvania, and then with Dr. John Hunter in London. In 1792, at 24 years of age, he received his Doctor of Medicine degree from the University of Edinburgh. Physick then returned home to Philadelphia, a flourishing community of over 50,000 people, where he was soon appointed to the staffs of the Bush Hill Hospital and the Pennsylvania Hospital. In 1800 he was taken into the Medical Department of the University of Pennsyl¬ vania and five years later became Professor of Surgery. Like the other surgeons of his day, Philip Syng Physick treated infectious dis¬ eases, reduced and splinted fractures, amputated legs, incised breasts, tapped chests and abdomens, operated for stones in the bladder, and attended difficult confine¬ ments. In addition, he became interested in surgery of the eye, particularly for cataract. According to his son-in-law, Dr. Jacob Randolph, it was this latter opera¬ tion, together with his operation for stones in the bladder, that was foremost in establishing his reputation as a surgeon.2 In 1795, Physick began to keep a journal of his most interesting and unusual cases, and the first patient he described was a blind woman whose vision was re¬ stored by cataract operation. Whereas couching was the usual procedure of that day, Physick's skill permitted him to extract the cataract. Physick used a method similar to that of Baron Wenzel. He described his operation as follows:

The Black Redstart

IN his interesting article on the black redstart in NATURE of May 27, Mr. Fitter says that it "was not known to breed anywhere in the British Isles before 1923". It is well over forty years ago that I watched a pair of these birds throughout their nesting activities at Bush Hill Park, near Enfield in Middlesex. I regret that in the end I took the clutch of four eggs. These eggs were sold at Stevens' auction on July 16, 1918 (Sale No. 12,981, Lot 53) on my leaving England and after this interval I can give no more precise data.

Rev. Lewis Way

Journal Article Rev. Lewis Way Get access E. P. Bird E. P. Bird 153, Millais Road, Bush Hill Park Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s11-XI, Issue 270, 27 February 1915, Page 176, https://doi.org/10.1093/nq/s11-XI.270.176 Published: 27 February 1915

Palæolithic Implements—New Localities in the Thames Valley, near London

IN NATURE, for July 15, 1880, p. 253, Mr. P. H. Pepys drew attention to a section then being made through beds of river gravel and brick earth near the West Drayton Station of the Great Western Railway. I had an opportunity of going to West Drayton on July 27, 1880, so I walked through the cutting towards Langley. My quest was for relics of primæval man, and I was rewarded by finding not only several flint flakes, but the batt end of a massive implement broken in Palæolithic times. This was just north of Langley Station, in Buckinghamshire, and the first Palæolithic relics, as far as I know, detected in that county. The workmen in the cutting for the new canal were such a rough lot that I found it impossible to fraternise with them, so my subsequent visits were all made on Sundays. During these walks I lighted on ten implements and a large number of flakes at Langley and Iver, all in the valley of the Coin, and a river until now (as far as I know) not described as implementiferous. In gravel brought from the pit close to Taplow Station I found a single implement, a large trimmed flake, and numerous simple flakes; this position is also in the county of Buckingham. At West Drayton, in Middlesex, in the valley of the Coln, I lighted on five implements and numerous flakes. East of West Drayton, in a pit near Botwell, in the valley of the Yedding Brook, hitherto undescribed as implement-bearing, I found a single implement; this was in the pit near Bull's Bridge. In the same valley at Hillington, and other places I have found several other implements. In all the excavations from Slough to Acton I have found both implements and flakes. In the new railway cutting from Gunnersbury to Hounslow I have found four implements, one close to Hounslow, a massive butt, and many flakes. This cutting has been a very interesting one, from the abundance of the fossil shells of fresh-water molluscs found in the sands, especially near the bridge under the Hanwell Road. One shell very abundant, and, as far as my observation goes, absent from the sands of North-east London, is Achatina acicula, Müll., kindly named for me by Dr. J. Gwyn Jeffreys. I believe this is the first record of fresh-water shells from the Palæolithic sands of the Ealing district. Since my paper on the Valley of the Brent was read before the Anthropological Institute, in June, 1879, I have found many more implements in the positions there mentioned. At North-east London, and especially in the Valley of the Lea, I have been able to greatly extend the range of Palæolithic man. In addition to the localities mentioned in my paper read before the Anthropological Institute, in June, 1878, and published in February, 1879, I am now able to mention London Fields, Homerton, in the south, a position south of Dalston Junction, and nearer the Thames than the places first given by me, Hackney, near the railway station, Abney Park Cemetery, South Hornsey, Highbury, Stamford Hill, Upper Edmonton, Lower Edmonton, Bush Hill Park, Forty Hill, Enfield, and Cheshunt; the pit at the last place, which formerly produced flakes only, has since furnished three implements—one an example of the first class. On the east side of the Lea I have found implements in the gravels of Stratford, Leyton, Leytonstone, Wanstead, Walthamstow, and Higham Hill—a magnificent example from the last place. Further east, and in the Valley of the Roding (first pointed out by me as a river bearing implements in its gravels)—at Barking—I have found two implements, and elsewhere in the neighbourhood, as at Ilford and Upton, numerous flakes. Still further east, at Gray's Thurrock, West Tilbury, and Southend, I have evidence of the presence of primæval man; at the latter place, a rude make-shift implement, and a scrapingtool with twin bulbs of percussion. These were found by my two sons. I have not mentioned all the positions I know in this letter, or re-mentioned those given in my two papers, but rather the positions I can afford to dispense with. It shows, however, especially when considered with the discoveries at Reading and Oxford, what a vast cohort of men once lived all along the Thames and its northern tributaries in Palæolithic times.

Explosion of the locomotive engine “Bush Hill,” on the portage railroad

Explosion of the locomotive engine “Bush Hill,” on the portage railroad