Gary M. McMurtry

Bio: Gary M. McMurtry is an academic researcher from University of Hawaii. The author has contributed to research in topics: Seamount & Hydrothermal circulation. The author has an hindex of 29, co-authored 60 publications receiving 2705 citations. Previous affiliations of Gary M. McMurtry include University of Hawaii at Manoa.

Loihi Seamount, Hawaii: a mid-plate volcano with a distinctive hydrothermal system

Abstract: The initial discovery of deep-sea hydrothermal vents at the Galapagos Rift1,2 has resulted in a decade of exploration and experimentation. Subsequent discoveries in the Pacific3–8 and Atlantic9 ocean basins have established the importance of these features as sources of mantle-derived gases and solutes10–2, and as loci for heat dissipation13,14, polymetallic sulphide mineral deposition15,16 and geochemical exchange17–19. The presence of dense communities of bacteria and specialized macrofauna20–22 has called into question the absolute role of sunlight as the principal energy source for marine organisms. Until recently, these deep-sea vents were known only at, or near, plate boundaries, but recent dredging23,24, near-bottom-water sampling25–27 and sea-floor camera survey28 programmes have indicated that hydrothermal vents are present at the summit of Loihi Seamount, a mid-plate, hotspot submarine volcano at the southern end of the Hawaiian island chain29. Here we report results obtained from sampling two active vent fields. The fluid chemistry (especially high CO2 and Fe), presence of alkalic lavas and iron-depositing bacteria, and absence of macrofauna suggest that mid-plate vents may differ from the hydrothermal vents found at mid-ocean ridges.

Sediment slump likely caused 1998 Papua New Guinea tsunami

Abstract: Two major marine surveys off northern Papua New Guinea (PNG) earlier this year now suggest, when survivors' reports are taken into account, that last summer's disastrous tsunami there was caused by a sediment slump 25 km offshore. The slump was probably the result of seabed shaking from an earthquake. Not only was a sediment slump, or submarine landslide, responsible for the tsunami, according to the data, but the magnitude and wave-height distribution of the tsunami along the coast were the result of focusing by local seabed morphology. The conclusions are based on new off-shore bathymetry, remote operated vehicle (ROV) dive investigations, the time delay between the source earthquake and when the tsunami struck, computer simulation models, and earthquake aftershock distribution. The most critical evidence is in survivors' accounts of the timing of the tsunami relative to the initially felt earthquake and aftershock [see Davies, 1998a].

Variations in bioturbation across the oxygen minimum zone in the northwest Arabian Sea

Abstract: Oxygen minimum zones are expected to alter substantially the nature, rates and depths of bioturbation along continental margins, yet these effects remain poorly studied. Using excess 210 Pb profiles, sediment X-radiography and box-core samples for macrofauna, we examined bioturbation processes at six stations (400, 700, 850, 1000, 1250 and 3400 m deep) along a transect across the oxygen minimum zone (OMZ) on the Oman margin. Bottom-water oxygen concentrations ranged from ∼0.13 ml l−1 at 400 m to ∼2.99 ml l−1 at 3400 m. 210 Pb mixed-layer depth and bioturbation intensity (Db) exhibited high within-station variance, and means did not differ significantly among stations. However, the mean mixed-layer depth (4.6 cm) for pooled OMZ stations (400–1000 m depths, 0.13–0.27 ml l−1 bottom-water oxygen) was half that for stations from similar water depths along well-oxygenated Atlantic and Pacific slopes (11.1 cm), suggesting that oxygen stress reduced 210 Pb mixing depth on the Oman margin. Modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom-water oxygen concentration from the edge to the core of the Oman OMZ (Spearman's rho⩾0.89, p⩽0.02), suggesting that these parameters are useful proxies for bottom-water oxygen concentrations under dysaerobic conditions. In contrast, neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen-related patterns along the transect. Reduced 210 Pb mixing depth within the Oman-margin OMZ appeared to result from a predominance of surface-deposit feeders and tube builders within this zone, rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass. The number of burrow types per station was highly correlated with macrofaunal species diversity, suggesting that burrow diversity may be a good proxy for species diversity in paleo-dysaerobic assemblages. We conclude that bottom-water oxygen concentrations of 0.13–0.27 ml l−1 substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins.

Inter-laboratory note. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation

Abstract: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) produces complex, time-dependent signals. These require significantly different treatment both during data acquisition and reduction from the more steady-state signals produced by solution sample introduction. This paper discusses, in detail, data acquisition and reduction considerations in LA-ICP-MS analysis. Optimum data acquisition parameters are suggested. Equations are derived for the calculation of sample concentrations and LOD when time-resolved data acquisition is employed, sensitivity calibration is obtained from reference materials with known analyte concentrations and naturally occurring internal standards are used to correct for the multiplicative correction factors of drift, matrix effects and the amount of material ablated and transported to the ICP.

Volatiles in subduction zone magmas : concentration and fluxes based on melt inclusion and volcanic gas data

Abstract: Abstract Owing to advances in microanalytical techniques over the last 15 years, there is a growing database on the volatile contents of subduction-related magmas as recorded in melt (glass) inclusions trapped in phenocrysts in volcanic rocks. Basaltic magmas from subduction zones show a wide range of water contents, ranging from as high as 6–8 to 3000 ppm, suggesting that no melt inclusions sample undegassed arc magmas. The Cl and S contents of arc basaltic magmas are greater than midocean ridge basalts, indicating that these volatiles are also recycled from subducted sediment and altered oceanic crust back into the mantle wedge. Comparison of the fluxes of volatiles subducted back into the mantle along subduction zones and returned from the mantle to the surface reservoir (crust, ocean, and atmosphere) via magmatism suggests that there is an approximate balance for structurally bound H2O and Cl. In contrast, ∼50% of subducted C appears to be returned to the deep mantle by subduction, but uncertainties are relatively large. For S, the amount returned to the surface reservoir by subduction zone magmatism is only ∼15–30% of the total amount being subducted. Dacitic and rhyolitic magmas in arcs contain 1–6 wt.% H2O, a range that overlaps considerably with the values for basaltic magmas. Either basaltic parents for these differentiated magmas are relatively H2O-poor, or intermediate to silicic arc magmas form through open-system processes involving variable amounts of crustal melting, mixing with basalt and basaltic differentiates, and fluxing of CO2-rich vapor from mafic magma recharged into silicic magma bodies. Consideration of H2O–CO2 relations and gaseous SO2 emissions for intermediate to silicic arc magmas shows that such magmas are typically vapor-saturated during crystallization in the middle to upper crust. Gas emissions thus reflect migration and accumulation of volatiles within complex open magmatic systems.