ALBERT

Description: The Australian-Antarctic Ridge (AAR) is one of the largest unexplored regions of the global mid-ocean ridge system. Here, we report a multi-year effort to locate and characterize hydrothermal activity on two 1 st -order segments of the AAR: KR1 and KR2. To locate vent sites on each segment, we used profiles collected by Miniature Autonomous Plume Recorders on rock corers during R/V Araon cruises in March and December of 2011. Optical and oxidation-reduction-potential anomalies indicate multiple active sites on both segments. Seven profiles on KR2 found 3 sites, each separated by ∼25 km. Forty profiles on KR1 identified 13 sites, some within a few km of each other. The spatial density of hydrothermal activity along KR1 and KR2 (plume incidence of 0.34) is consistent with the global trend for a spreading rate of ∼70 mm/yr. The densest area of hydrothermal activity, named “Mujin”, occurred along the 20-km-long inflated section near the segment center of KR1. Continuous plume surveys conducted in January-February of 2013 on R/V Araon found CH 4 / 3 He (1-15 × 10 6 ) and CH 4 /Mn (0.01-0.5) ratios in the plume samples, consistent with a basaltic-hosted system and typical of ridges with intermediate spreading rates. Additionally, some of the plume samples exhibited slightly higher ratios of H 2 / 3 He and Fe/Mn than others, suggesting that those plumes are supported by a younger hydrothermal system that may have experienced a recent eruption. The Mujin-field was populated by Kiwa crabs and seven-armed Paulasterias starfish previously recorded on the East Scotia Ridge, raising the possibility of circum-Antarctic biogeographic connections of vent fauna. This article is protected by copyright. All rights reserved.

Description: This study presents the outcome of an inverse modeling inter-comparison experiment on the use of total column CO 2 retrievals from GOSAT for quantifying global sources and sinks of CO 2 . Eight research groups submitted inverse modeling results for the first year of GOSAT measurements. Inversions were carried out using only GOSAT data, a combination of GOSAT and surface measurements, and using only surface measurements. As expected, the most robust flux estimates are obtained at large scales (e.g. within 20% of the annual flux at the global scale), and they quickly diverge towards the scale of the sub-continental TRANSCOM regions and beyond (to〉100% of the annual flux). We focus our analysis on a shift in the CO 2 uptake over land from the Tropics towards the Northern Hemisphere Extra tropics of ~1 PgC/yr when GOSAT data are used in the inversions. This shift is largely driven by TRANSCOM regions Europe and Northern Africa, showing, respectively, an increased uptake and release of 0.7 and 0.9 PgC/yr. Inversions using GOSAT data show a reduced gradient between mid latitudes of the Northern Hemisphere and the Tropics, consistent with the latitudinal shift in carbon uptake. However, the reduced gradients degrade the agreement with background aircraft and surface measurements. To narrow the range of inversion-derived flux estimates will require further efforts to understand the differences not only between the retrieval schemes but also between inverse models, as their contributions to the overall uncertainty are estimated to be of similar magnitude.

Description: East Asian Summer Monsoon (EASM) rainfall impacts the world's most populous regions. Accurate EASM rainfall prediction necessitates robust palaeoclimate reconstructions from proxy data and quantitative linkage to modern climatic conditions. Many precisely-dated oxygen isotope records from Chinese stalagmites have been interpreted as directly reflecting past EASM rainfall amount variability, but recent research suggests such records instead integrate multiple hydroclimatic processes. Using a Lagrangian precipitation moisture source diagnostic, we demonstrate that EASM rainfall is primarily derived from the Indian Ocean. Conversely, Pacific Ocean moisture export peaks during winter and the moisture uptake area does not differ significantly between summer and winter, and is thus a minor contributor to monsoonal precipitation. Our results are substantiated by an accurate reproduction of summer and winter spatial rainfall distributions across China. We also correlate modern EASM rainfall oxygen isotope ratios with instrumental rainfall amount and our moisture source data. This analysis reveals that the strength of the source effect is geographically variable, and differences in atmospheric moisture transport may significantly impact the isotopic signature of EASM rainfall at the Hulu, Dongge and Wanxiang Cave sites. These results improve our ability to isolate the rainfall amount signal in palaeomonsoon reconstructions and indicate that precipitation across central and eastern China will directly respond to variability in Indian Ocean moisture supply.

Description: We investigate the upper tropospheric distribution of methane (CH4) at low latitudes based on the analysis of air samples collected from aboard passenger aircraft. The distribution of CH4 exhibits spatial and seasonal differences, such as the pronounced seasonal cycles over tropical Asia and elevated mixing ratios over central Africa. Over Africa, the correlations of methane, ethane, and acetylene with carbon monoxide indicate that these high mixing ratios originate from biomass burning as well as from biogenic sources. Upper tropospheric mixing ratios of CH4 were modeled using a chemistry transport model. The simulation captures the large-scale features of the distributions along different flight routes, but discrepancies occur in some regions. Over Africa, where emissions are not well constrained, the model predicts a too steep interhemispheric gradient. During summer, efficient convective vertical transport and enhanced emissions give rise to a large-scale CH4 maximum in the upper troposphere over subtropical Asia. This seasonal (monsoonal) cycle is analyzed with a tagged tracer simulation. The model confirms that in this region convection links upper tropospheric mixing ratios to regional sources on the Indian subcontinent, subtropical East Asia, and Southeast Asia. This type of aircraft data can therefore provide information about surface fluxes.

Description: The Woodlark Basin is one of the rare places on earth where the transition from continental breakup to seafloor spreading can be observed. The potential juxtaposition of continental rocks, a large magmatic heat source, crustal-scale faulting, and hydrothermal circulation has made the Woodlark Basin a prime target for seafloor mineral exploration. However, over the past 20 years, only two locations of active hydrothermalism had been found. In 2009 we surveyed 435 km of the spreading axis for the presence of hydrothermal plumes. Only one additional plume was found, bringing the total number of plumes known over 520 km of ridge axis to only 3, much less than at ridges with similar spreading rates globally. Particularly the western half of the basin (280 km of axis) is apparently devoid of high temperature plumes despite having thick crust and a presumably high magmatic budget. This paucity of hydrothermal activity may be related to the peculiar tectonic setting at Woodlark, where repeated ridge jumps and a re-location of the rotation pole both lead to axial magmatism being more widely distributed than at many other, more mature and stable mid-ocean ridges. These factors could inhibit the development of both a stable magmatic heat source and the deeply penetrating faults needed to create long-lived hydrothermal systems. We conclude that large seafloor massive sulfide deposits, potential targets for seafloor mineral exploration, will probably not be present along the spreading axis of the Woodlark Basin, especially in its younger, western portion.

Description: Carbon monoxide (CO) and other atmospheric trace constituents were measured from onboard an Airbus 340-600 passenger aircraft in the upper troposphere (UT) between south China and the Philippines during Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) flights from May 2005 until March 2008. A total of 132 events having CO enhancements were observed in the UT over the region during the 81 CARIBIC flights from Frankfurt, Germany, to Manila, Philippines, with a stopover in Guangzhou, China. Among these, 51 high-CO events with enhancements more than 50 ppb above background were observed. For these events enhancements ranged from 52.7 to 221.3 ppb and persisted for 3 to 78 min (∼40 to 1200 km), indicating an influence of strong pollution from biomass/biofuel/fossil fuel burning on the trace gas composition of the UT. Back trajectory analysis shows that south China, the Indochinese Peninsula, and the Philippines/Indonesia are the main source regions of the high-CO events. The composition of air parcels originating from south China was found to be primarily influenced by anthropogenic urban/industrial emissions, while emissions from biomass/biofuel burning contributed substantially to CO enhancements from the Indochinese Peninsula. During the Philippines/Indonesia events, air parcel composition suggests contributions from both biomass/biofuel burning and urban/industrial sources. Long-range transport of air parcels from northeast Asia and India also contributed to CO enhancements in the UT over the region. The general features of regional influence, typical cases, and the contributions of biomass/biofuel burning and anthropogenic emissions are presented and discussed to characterize the air parcels during the observed high-CO events.

Description: Magma mixing plays a prominent role in the origins of intermediate magmas in subduction zones. However, the conditions and timescales of magma mixing and how these are linked to subsequent eruption are unclear. Mount Tauhara is the largest dacitic volcanic complex in the Taupo Volcanic Zone, New Zealand. Dacites from Tauhara Volcano have a complex petrography (Qtz + Plag + Amph + OPx + CPx + Oxi ± Oli) that can only have been produced by magma mixing and offer an ideal opportunity to investigate the processes and timescales involved in assembling dacite magmas in a continental subduction zone. Here we present whole-rock and mineral-specific major and trace element and isotopic data for the Tauhara dacites in order to identify the magma mixing end-members, constrain the physical conditions of mixing, and estimate the timescales and relationships between magma mixing, ascent and eruption. These data reveal that four separate mixing events between crystal-rich rhyolites (77–80 wt.% SiO 2 ; 40 ppm Sr) and crystal-poor mafic magmas of basaltic (48 wt.% SiO 2 ; 1340 ppm Sr) to andesitic (55–59 wt.% SiO 2 ; 490–580 ppm Sr) composition occurred to produce the Tauhara dacites. Mixing took place in well-stirred magma chambers located at mid-crustal depths (8–13 km) at temperatures from 840 to 900ºC. The timescales of magma mixing obtained from Ti diffusion in quartz appear to be largely dependent on the temperature and viscosity contrast between the end-members as andesite and rhyolite magma mixed on timescales of 2–7 months, whereas basalt and rhyolite magmas mixed on timescales of 1–2 years. The short magma mixing timescales, combined with the physical properties (e.g., viscosity and density) of the mixed dacite magmas, as compared with those of the end-member magmas, facilitated the ascent and eruption of dacite magmas at Tauhara volcano.

Description: The creation of ocean crust by lava eruptions is a fundamental Earth process, involving immediate and immense transfers of heat and chemicals from crust to ocean. This transfer creates event plumes (“megaplumes”), massive ellipsoidal eddies with distinctive and consistent chemical signatures. Here we report the discovery of unique event plumes associated with a 2008 eruption on the Northeast Lau Spreading Center. Instead of a large plume hundreds of meters thick, we detected at least eight individual plumes, each ∼50 m thick and apparently only 1–3 km in diameter, yet still rising 200–1000 m above the eruption site. Low and uniform 3He/heat (0.041 × 10−17 mol/J) and dissolved Mn/heat (0.04 nmol/J) ratios in water samples were diagnostic of event plumes. High H2 concentrations (up to 9123 nM) and basalt shards confirmed extensive interactions between molten lava and event plume source fluids. Remote vehicle observations in 2009 mapped a new, small (1.5–5.8 × 106 m3) lava flow. Our results suggest that event plumes are more variable, and thus perhaps more common, than previously recognized. Small event plumes may be preferentially associated with small or sheet-flow eruptions, and massive event plumes with slowly extruding pillow mounds 25–75 m thick. Despite this correlation, and high H2 concentrations, existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes. The creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation.

Description: Flask samples from two sites in East Asia, Tae-Ahn Peninsula, Korea (TAP), and Shangdianzi, China (SDZ), were measured for trace gases including CO2, CO and fossil fuel CO2 (CO2ff, derived from Δ14CO2 observations). The five-year TAP record shows high CO2ff when local air comes from the Korean Peninsula. Most samples, however, reflect air masses from Northeastern China with lower CO2ff. Our small set of SDZ samples from winter 2009/2010 have strongly elevated CO2ff. Biospheric CO2 contributes substantially to total CO2 variability at both sites, even in winter when non-fossil CO2 sources (including photosynthesis, respiration, biomass burning and biofuel use) contribute 20–30% of the total CO2 enhancement. Carbon monoxide (CO) correlates strongly with CO2ff. The SDZ and TAP far-field (China influenced) samples have CO: CO2ff ratios (RCO:CO2ff) of 47 ± 2 and 44 ± 3 ppb/ppm respectively, consistent with recent bottom-up inventory estimates and other observational studies. Locally influenced TAP samples fall into two distinct data sets, ascribed to air sourced from South Korea and North Korea. The South Korea samples have low RCO:CO2ff of 13 ± 3 ppb/ppm, slightly higher than bottom-up inventories, but consistent with emission ratios for other developed nations. We compare our CO2ff observations with modeled CO2ff using the FLEXPART Lagrangian particle dispersion model convolved with a bottom-up CO2ff emission inventories. The modeled annual mean CO2ff mole fractions are consistent with our observations when the model inventory includes the reported 63% increase in Chinese emissions from 2004 to 2010, whereas a model version which holds Chinese emissions flat is unable to replicate the observations.

Description: Indian Ocean ridges north of the Rodriguez Triple Junction remain poorly explored for seafloor hydrothermal activity, with only two active sites confirmed north of 25°S. We conducted water column surveys and sampling in 2007 and 2009 to search for hydrothermal plumes over a segment of the Carlsberg Ridge. Here we report evidence for two separate vent fields, one near 3°42′N, 63°40′E and another near 3°41.5′N, 63°50′E, on a segment that is apparently sparsely magmatic. Both sites appear to be located on off-axis highs at the top of the southern axial valley wall, at depths of ∼3600 m or shallower (∼1000 m above the valley floor). At the 63°40′E site, plume sampling found local maxima in light scattering, temperature anomaly, oxidation-reduction potential (ORP), dissolved Mn, and 3He. No water samples are available from the 63°50′E site, but it showed robust light-scattering and ORP anomalies at multiple depths, implying multiple sources. ORP anomalies are very short-lived, so the strong signals at both sites suggest that fluid sources lie within a few kilometers or less from the plume sampling locations. Although ultramafic rocks have been recovered near these sites, the light-scattering and dissolved Mn anomalies imply that the plumes do not arise from a system driven solely by exothermic serpentinization (e.g., Lost City). Instead, the source fluids may be a product of both ultramafic and basaltic/gabbroic fluid-rock interaction, similar to the Rainbow and Logatchev fields on the Mid-Atlantic Ridge.