Temporal variability of gas seeps offshore New Zealand: Multi-frequency geoacoustic imaging of the Wairarapa area, Hikurangi margin

Cold seeps of the Wairarapa area situated around 1000 metres water depth on the Hikurangi margin offshore New Zealand’s North Island have been investigated using multibeam bathymetry, 75 and 410 kHz sidescan sonar imagery as well as 2-8 kHz Chirp sediment echosounder data. Towed video camera observations allowed groundtruthing the various geoacoustic data. At least eight different seep locations displaying various degrees of seep activity have been identified in the study area which consists of an elongated, northward-widening ridge that is part of the Hikurangi margin accretionary complex and well separated from direct terrigenous input by margin channels surrounding the ridge. The geoacoustic signature of individual cold-seep sites range from smooth areas with slightly elevated backscatter intesity resulting from high gas content or the presence of near-surface gas hydrates to rough areas with widespread patches of carbonates at the seafloor. Two cold seeps also show indications for active gas emissions in form of acoustic plumes in the water column. Repeated sidescan sonar imagery of the plumes indicates they are highly variable in intensity and directivity in the water column reflecting a likely control of gas emission by tides and currents. Although gas emission appears strongly focused in the Wairarapa area the actual extent of the cold seep structures are slightly wider in the subsurface as shown by sediment echosounder profiles. On a larger scale, however, fluid seepage at the Wairarapa area is still highly focused

The experimental-methodical geophysical studies in the RV POSEIDON cruise 405

The main results of experimental and methodological geophysical studies in the 405th cruise of the NIS "Poseidon" from 8 to 22 December 2010 in the northwestern part of the Black Sea are presented. The purpose of the POS-405 cruise is the testing of new geophysical equipment developed within the framework of the SUGAR target project. The new multi-beam sounder SBE 3050 Multibeam company ELAC Nautik was installed on the NIS "Poseidon" during the last stay of the ship in dry dock. The sounder is able to record the water column and display gas bubbles on the display screen using the image viewer (WCI). In comparison with the bathymetric map of the canyon, the Danube test gave a positive result. For the first time, a new deep-seated, towed multichannel streamer was deployed. With the help of a deep-water winch, the first seismic signals were completed and recorded. After replacing the members of the scientific crew, a new electromagnetic system with a controlled source (CSEM) was tested. For the first time a 1000 m long receiver was towed. Due to weather conditions (wind of more than 25 m / s), the Poseidon VAT 3.5 days out of 15 workers was in a storm situation. These limitations prevented intensive tests of towed instruments. By agreement with the Institute of Geophysics of the National Academy of Sciences of Ukraine, electromagnetic research was conducted for 15 days using an innovative method for analyzing spontaneous electromagnetic radiation (ASEMI)

Quantifying in-situ gas hydrates at active seep sites in the eastern

www.biogeosciences.net/8/3555/2011

The experimental-methodical geophysical studies in the RV POSEIDON cruise 405

Наведено основні результати експериментально-методичних геофізичних досліджень у 405-му рейсі НДС “Посейдон” з 8 по 22 грудня 2010 р. у північно-західній частині Чорного моря. Мета круїзу POS-405 — дослідження нового геофізичного обладнання, розробленного в межах цільового проекту “SUGAR”. Нову систему багатопроменевого ехолоту SBE 3050 Multibeam компанії ELAC Nautik було встановлено на НДС “Посейдон” під час останньої стоянки корабля в сухому доці. Ехолот здатний записувати водну товщу та відображувати газові бульбашки на екрані дисплея за допомогою переглядача зображень (WCI). У ході зіставлення з батиметричною картою каньйону Дунаю тестування дало позитивний результат. Вперше було розгорнуто новий глибинний буксируваний багатоканальний стример. За допомогою глибоководної лебідки були завершені і записані перші сейсмічні сигнали. Після заміни членів наукового екіпажу було випробувано нову електромагнітну систему з контрольованим джерелом (CSEM). Вперше буксировано приймач завдовжки 1000 м. У зв’язку з погодними умовами (вітер силою понад 25 м/с) НДС “Посейдон” 3,5 дні з 15 робочих перебував у штормовому положенні. Ці обмеження не дали змоги провести інтенсивні випробування буксированих приладів. За домовленістю з Інститутом геофізики НАН України протягом 15 днів було проведено електромагнітні дослідження за інноваційним методом аналізу спонтанного електромагнітного випромінювання (АСЕМВ).Представлены основные результаты экспериментально-методических геофизических исследований в 405-м рейсе НИС "Посейдон" с 8 по 22 декабря 2010 г. в северо-западной части Черного моря. Цель круиза POS-405 - испытание новой геофизической аппаратуры, разработанной в рамках целевого проекта "SUGAR". Новая система многолучевого эхолота SBE 3050 Multibeam компании ELAC Nautik была установлена на НИС "Посейдон" во время последней стоянки корабля в сухом доке. Эхолот способен записывать водную толщу и отображать газовые пузырьки на экране дисплея с помощью программы просмотра изображений (WCI). В ходе сопоставления с батиметрической картой каньона Дуная тестирование дало положительный результат. Впервые был развернут новый глубинный буксированный многоканальный стример. С помощью глубоководной лебедки были завершены и записаны первые сейсмические сигналы. После замены членов научного экипажа была испытана новая электромагнитная система с контролируемым источником (CSEM). Впервые буксировался приемник длиной 1000 м. В связи с погодными условиями (ветер силой свыше 25 м/с) НДС "Посейдон" 3,5 дня из 15 рабочих находился в штормовом положении. Эти ограничения не дали возможности провести интенсивные испытания буксированных приборов. По договоренности с Институтом геофизики НАН Украины на протяжении 15 дней проводились электромагнитные исследования с помощью инновационного метода анализа спонтанного электромагнитного излучения (АСЭМИ)

Crustal structure of the Niuafo’ou Microplate and Fonualei Rift and Spreading Center in the northeastern Lau Basin, Southwestern Pacific

Key points: First insights into the crustal structure of the northeastern Lau Basin, along a 290 km transect at 17°20’S. Crust in southern Fonualei Rift and Spreading Center was created by extension of arc crust and variable amount of magmatism. Magmatic underplating is present in some parts of the southern Niuafo’ou Microplate The northeastern Lau Basin is one of the fastest opening and magmatically most active back‐arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood, the internal structure and evolution of the back‐arc crust are not. We present new geophysical data from a 290 km long east‐west oriented transect crossing the Niuafo’ou Microplate (back‐arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17°20’S. Our P‐wave tomography model and density modelling suggests that past crustal accretion inside the southern FRSC was accommodated by a combination of arc crustal extension and magmatic activity. The absence of magnetic reversals inside the FRSC supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion. The back‐arc crust constituting the southern Niuafo’ou Microplate reveals a heterogeneous structure comprising several crustal blocks. Some regions of the back‐arc show a crustal structure similar to typical oceanic crust, suggesting they originate from seafloor spreading. Other crustal blocks resemble a structure that is similar to volcanic arc crust or a ‘hydrous’ type of oceanic crust that has been created at a spreading center influenced by slab‐derived water at distances < 50 km to the arc. Throughout the back‐arc region we observe a high‐velocity (Vp 7.2‐7.5 km s‐1) lower crust, which is an indication for magmatic underplating, which is likely sustained by elevated upper mantle temperatures in this region

Ionian Abyssal Plain: a window into the Tethys oceanic lithosphere

The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. A NNE–SSW-oriented 131&thinsp;km long seismic refraction and wide-angle reflection profile, consisting of eight ocean bottom seismometers and hydrophones, was acquired in 2014. The profile was designed to univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys and to confute its interpretation as a strongly thinned part of the African continental crust. A P-wave velocity model developed from travel-time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6–7&thinsp;km thick crust with velocities ranging from 5.1 to 7.2&thinsp;km&thinsp;s−1, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina seamounts at the southern IAP boundary, the crust thickens to about 9&thinsp;km and seismic velocities decrease to 6.8&thinsp;km&thinsp;s−1 at the crust–mantle boundary. The seismic velocity distribution and depth of the crust–mantle boundary in the IAP document its oceanic nature and support the interpretation of the IAP as a remnant of the Tethys lithosphere with the Malta Escarpment as a transform margin and a Tethys opening in the NNW–SSE direction.</p

Dengue disease outbreak definitions are implicitly variable.

Infectious diseases rarely exhibit simple dynamics. Outbreaks (defined as excess cases beyond response capabilities) have the potential to cause a disproportionately high burden due to overwhelming health care systems. The recommendations of international policy guidelines and research agendas are based on a perceived standardised definition of an outbreak characterised by a prolonged, high-caseload, extra-seasonal surge. In this analysis we apply multiple candidate outbreak definitions to reported dengue case data from Brazil to test this assumption. The methods identify highly heterogeneous outbreak characteristics in terms of frequency, duration and case burden. All definitions identify outbreaks with characteristics that vary over time and space. Further, definitions differ in their timeliness of outbreak onset, and thus may be more or less suitable for early intervention. This raises concerns about the application of current outbreak guidelines for early warning/identification systems. It is clear that quantitatively defining the characteristics of an outbreak is an essential prerequisite for effective reactive response. More work is needed so that definitions of disease outbreaks can take into account the baseline capacities of treatment, surveillance and control. This is essential if outbreak guidelines are to be effective and generalisable across a range of epidemiologically different settings

Emission of volatile halogenated compounds, speciation and localization of bromine and iodine in the brown algal genome model Ectocarpus siliculosus

This study explores key features of bromine and iodine metabolism in the filamentous brown alga and genomics model Ectocarpus siliculosus. Both elements are accumulated in Ectocarpus, albeit at much lower concentration factors (2-3 orders of magnitude for iodine, and < 1 order of magnitude for bromine) than e.g. in the kelp Laminaria digitata. Iodide competitively reduces the accumulation of bromide. Both iodide and bromide are accumulated in the cell wall (apoplast) of Ectocarpus, with minor amounts of bromine also detectable in the cytosol. Ectocarpus emits a range of volatile halogenated compounds, the most prominent of which by far is methyl iodide. Interestingly, biosynthesis of this compound cannot be accounted for by vanadium haloperoxidase since the latter have not been found to catalyze direct halogenation of an unactivated methyl group or hydrocarbon so a methyl halide transferase-type production mechanism is proposed