Variations in the total column amounts of carbon monoxide and methane in the Antarctic atmosphere

The results of measuring the total contents of carbon monoxide and methane via the method of solar-absorption spectroscopy are presented. The measurements were performed at the Molodezhnaya Station in 1977–1978, at the Mirny Observatory from 1982 to 1992, and at the Novolazarevskaya Station from 2003 to 2006. The character of seasonal variations in the contents of these gases in the Antarctic atmosphere is described and compared to the intra-annual variation of their surface concentrations measured at the Syowa Station (Japan). Synchronous intra-annual variations in the contents of carbon monoxide in the atmospheric column and in its surface concentrations are observed, while the spring maximum content of methane is observed three months after the maximum of its surface concentration. Synchronous seasonal variations in the total content of methane and ozone are observed, which makes it possible to suggest that the Antarctic circumpolar vortex has a significant influence on the characteristics of the vertical distribution of methane during Antarctic spring. Quantitative estimates of the parameters of multiyear variations in the contents of CO and CH₄ are given. The content of methane was increasing (although with different rates) during the entire observation period 1977–2006. The content of CO was observed to increase until 1992 and to decrease during 2003–2006.     

Probability distribution of the Murty‐Loomis tsunami magnitude

Abstract

In 1980, Murty and Loomis proposed a new, objective tsunami magnitude scale based on total tsunami energy. A list of 178 tsunamigenic earthquakes during the period 1815 to 1974 was given along with estimated tsunami magnitudes. In this study, we derived the probability distribution function of tsunami magnitudes based on the assumptions that (1) the occurrences of tsunamigenic earthquakes are a Poisson process, and (2) tsunami energy is a polynomial function of tsunami recurrence time. Using the data given by Murty and Loomis, the parameters of the distribution function are estimated. Comparison with the data shows that the derived distribution is a good representation of the distribution of the Murty‐Loomis tsunami magnitude.     

Wind-Wave Characteristics and Climate Variability in the Indian Ocean Region Using Altimeter Data

The significant wave height and wind speed derived for the period 1993–2010 from altimeter data sets over the Arabian Sea, Bay of Bengal, and the Indian Ocean categorized as six zones has been analyzed. The average variation of both significant wave height and wind speed is found to be almost stable for the period of study. The study reveals that the average wind speed increases by about 6cm/sec/year during monsoon and post monsoon in the southern Indian Ocean. The distribution of wind and waves was studied in the context of seasonal variations. In addition, the average inter-annual and intra-annual variations along with the statistical parameters such as standard deviation, and root mean square wave height for the six zones are also reported in this paper.     

Differences in seasonal variations in the patterns of diurnal earthquake periodicity in the southern and northern hemispheres

Seasonal variations in the form of diurnal periodicity are compared in three regions of the world, two of which (Alaska and Japan) are located in the Northern Hemisphere and one (New Zealand) is in the Southern Hemisphere. It is found that, in the Northern Hemisphere, the duration of the night interval of an increased number of earthquakes in December is greater than in June, while in the Southern Hemisphere it is smaller. The intra-annual character of variations in the form of diurnal earthquake periodicity agrees with the seasonal variations in the length of the day.     

Distinguishing features of the seismicity in South Kamchatka in the 20th century with regard to the Avacha Bay seismic gap

The distinguishing features of the seismicity throughout South Kamchatka and within the Avacha Bay seismic gap in the 20th century are considered. The evolution of the evaluation of the magnitudes of the strongest earthquakes for this gap from M = 7.25–7.5 in 1965–1980 to 7.75–8.0 after 1980 is discussed. On the basis of the method for studying the characteristic features of the seismicity within a seismic gap developed for the Central Kuriles, the seismicity of South Kamchatka is considered for depths of 0–100, 101–200, and more than 200 km according to the data from the New Catalog [6] for the period from 1901 to 1974 (M ≥ 6.1), the Special Catalog for North Eurasia [3] for the period from 1975 to 1993 (M ≥ 4.5), and additional data from the Kamchatka stations for the period from 1994 to 1997. It was found that the seismic process within the region of South Kamchatka is typical of the island arcs; i.e, most of the earthquakes considered and the maximum of the seismic energy released are concentrated in the lithosphere at depths of 0–100 km. The seismological situation in the zone of Avacha Bay is found to be similar to that within the second kind of the seismic gap during the precursory seismic quiescence of the 1978 Oaxac earthquake with M = 7.8 in Central Mexico. This allows us to consider the zone of Avacha Bay as a possible seismic gap of the second kind. Such a result can be considered as a suggestion of the possibility of the occurrence in Avacha Bay of an earthquake with M ～ 8 according to the long-term forecast for the region of the Kuriles and Kamchatka made by S.A. Fedotov.     

Ocean bottom seismometer detection of earthquakes on the Gorda Rise near 41.5° north

The spatial and temporal distribution of microearthquake activity associated with the southern section of the Gorda Rise was monitored during a three week period using an array of four ocean bottom seismometers (OBS's) located at 41.5° N, 127.5° W on the rise axis. Sixty-two events were detected, of which roughly half occurred during a seismic swarm following an event of magnitude 4.9 that was well-recorded on land. A total of eighteen earthquakes could be located, seventeen of which originated from the valley floor, walls, and crestal mountains while the remaining event was located to the east of the rise in the Gorda plate. Well-constrained focal depths for four earthquakes ranged from roughly 4 to 12 km. Depths in excess of 10 km for two of the events provide strong evidence for the absence of a shallow steady-state magma chamber beneath the slow-spreading portion of the Gorda rise. Most of the events are believed to be the result of uplift of the crustal blocks comprising the valley walls. Four events located at an offset of the rise near 41.5° N may be related to strike-slip movement on a developing transform fault. Two of the events that occurred during the survey were large enough to be detected and located by land-based instruments. Comparison of these locations with the OBS locations indicates that well-recorded events having magnitudes of at least 4.5 are routinely mislocated 40–50 km to the east of their actual locations in this area while lower magnitude, poorly recorded earthquakes may have significantly larger location errors.     

Intra-annual recruitment events of a shelf species around an island system in the NW Mediterranean

Seasonal pattern of fish recruitment can vary over years, and the coupling of such pattern with favourable trophic-environmental conditions may trigger non-stationary and non-linear effects on the yearly recruitment variability. The relative contribution of intra-annual discrete recruitment events (REs) to recruitment is often the basis of the inter-annual fluctuations in abundance and biomass of exploited fish populations which are based on a small number of age classes. In this study, REs of European hake (Merluccius merluccius L.) were identified in the north and south of the Balearic Islands (NW Mediterranean) during the 2004 recruitment season and investigated for growth and physiological and morphological condition. Five REs were identified with different contributions in abundance to the annual recruitment in each area coming from different intra-annual spawning batches. Growth rates were similar between the REs with the exception of the last event of the season. Conversely, large differences in morphological and physiological condition were observed between REs and were due to: different environmental-trophic scenarios encountered, and ontogenetic changes related to the recruitment to the shelf-break grounds (ca. 11 cm, 5–6 months of life) which triggered a trade-off in the energy allocation strategy. The spatial-temporal variability in the physiological condition among REs at the beginning of the recruitment season might be explained in the basis on a ‘condition expanded match–mismatch hypothesis’. We advance that individuals recruiting in the north, which were in better condition and temporally and spatially differenced from the south, have most probably hatched in separated locations with different food availability for larvae and early life stages. We propose that hake recruiting to the north and south of the island are from different origins, mainland and the islands respectively, and have benefited from different environmental conditions. This results in a different condition but not in different growth rates.     

Some Features of the Intra-Annual Variability of Heat Fluxes in the North Atlantic

Izvestiya, Atmospheric and Oceanic Physics - In this paper, statistical regularities of the intra-annual variability of heat fluxes in the North Atlantic during the ocean–atmosphere...     

High <Emphasis Type="Italic">S</Emphasis>-wave attenuation anomalies and ringlike seismogenic structures in the lithosphere beneath Altai: Possible precursors of large earthquakes

This paper addresses inhomogeneities in the short-period S-wave attenuation field in the lithosphere beneath Altai. A technique based on the analysis of the amplitude ratios of Sn and Pn waves is used. High S-wave attenuation areas are identified in the West Altai, which are related to the source zones of recent large earthquakes, viz., the 1990 Zaisan earthquake and the 2003 Chuya earthquake. Associated with the Chuya earthquake, a large ringlike seismogenic structure had been formed since 1976. It is also found that ringlike seismogenic structures are confined to high S-wave attenuation areas unrelated to large historical earthquakes. It is supposed that processes paving the way for strong earthquakes are taking place in these areas. The magnitudes of probable earthquakes are estimated using the earlier derived correlation dependences of the sizes of ringlike seismogenic structures and the threshold values of magnitudes on the energy of principal earthquakes with prevailing focal mechanisms taken into consideration. The sources of some earthquakes are likely to occur near to the planned gas pipeline route from Western Siberia to China, which should be taken into account. The relationship of anomalies in the S-wave attenuation field and the ringlike seismogenic structures to a high content of deep-seated fluids in the lithosphere is discussed.     

Temporal fluctuations of water temperature in aSargassum forest

This paper examines the influence of aSargassum forest on temporal fluctuations in temperatures of surrounding water in relation to the thermal structure of water in and above theSargassum forest. Water temperature records were obtained at about one-minute intervals for almost two days in May 1977 during the season of luxuriant seaweed growth, and in August 1977 during the season of little growth. The fluctuations were divided into two types. (1) A diurnal fluctuation under the forest with about a three hour lag behind that above the forest during the season of luxuriant growth but with about a 30 min lag during the season of little growth. (2) Sharp spike-like fluctuations with periods shorter than five minutes appearing only in the dense canopy or floating seaweeds in the surface and subsurface layers during the period of luxuriant growth. The luxuriant forest ofSargassum seems to influence the spatial distribution of water temperature and consequently seems to induce the fluctuations mentioned above. The relationship between short period fluctuations and behaviours of larval fishes are discussed.     

鲁中南隆起区第四纪晚期断裂活动特征

根据野外调查，并综合前人的研究资料，对鲁中南地区第四纪晚期断裂活动进行了分析，研究表明，鲁中南隆起区第四纪断裂活动具有时空不均匀性，主要表现为第四纪时期断层活动强度变化和断裂活动的群集性以及第四纪晚期断裂活动段分布的局限性上。对于鲁中南地区而言，活动断层可以分为中更新世中期（500kaBP)至晚更新世初期（90kaBP)活断层和晚更新世中、晚期至全新世早期活断层两类；其中前一类（主要是中更新世断裂）断裂数量较多，分布较为广泛，而晚更新世晚期以来的活动断裂段的数量较少，分布较局限。它们对地震的控制能力不同，前者可控制5．5级左右的地震，而后一类可控制6－7级地震的发生。     

Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents

Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru–Chile Trench off Southern Central Chile (36°S–39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175–450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope.     

Retrospective analysis of seismic regime features before the Taiwan earthquakes of 1999 and 2002

The features of the seismic regime before the strongest earthquakes of Taiwan in the late 20th (Chi-Chi on September 21, 1999, M_w = 7.6) and the early 21st century (March 31, 2002, M_w = 7.4) are analyzed. Based on 1990–1999 and 1994–2002 data, respectively, retrospective analysis of three seismic regime parameters are studied: the total annual number of earthquakes N_Σ in the range of M_L = 2.5–5.5 and M_w = 3.0–7.0; the total annual quantity of released seismic energy ΣE, J; and angular coefficient b of earthquake recurrence graphs. Two explicit subperiods are revealed in the course of the seismic regime: quiescence in 1990–1996 before the Chi-Chi earthquake and in 1994–1997 before the March 2002 earthquake; in 1997–1999 and 1998–2002, respectively, seismic activation is observed. Due to the predominance of weak earthquakes during the Chi-Chi earthquake preparation, factor b appeared relatively higher (–1.16 on average); in contrast, before the March 2002 earthquake, due to the occurrence of foreshocks with M_w = 6.8–7.0, the factor b values appeared relatively lower (–0.55 and–0.74 for the quiescence and activation subperiods, respectively). Despite the fundamental difference in the seismotectonic situation between the domains where two mainshocks occurred and significantly difference energy ranges of the initial seismic events, the analysis results are similar for both earthquakes. In both cases, the mainshock occurred at the peak of released energy, which can be considered a coincidence. Solid verification of this positive tendency requires the accumulation of seismological statistics.     

Wave climate off northern Norway

The wave climate off northern Norway is considered and the investigation is based on wave measurements made at Tromsøflaket by means of a waverider buoy during the years 1977–1981. Data quality of waverider measurements is briefly commented upon; however, more emphasis is given to an evaluation of the long-term representativity of the actual measuring period and to a procedure accounting approximately for a lack of representativity. The wave climate is presented in terms of a smoothed joint probability density function of the significant wave height, H_s, and the spectral peak period, T_p. Based on this distribution a consistent design curve in the H_s, T_p space is established.     

Changes in zooplankton diversity and distribution pattern under varying precipitation regimes in a southern temperate estuary

The influence of climate variability on the diversity and distribution patterns of zooplankton communities was investigated in the Mondego estuary (Portugal) during four consecutive years characterized by highly variable precipitation and, consequently, river flow regime. Monthly samples were collected along the estuarine gradient at five sampling stations. Seasonal, inter-annual and spatial distributions were evaluated by multivariate analyses and three diversity indices were applied (Species number, Shannon Diversity and Average Taxonomic Distinctness). A two-year drought period presented significant differences in salinity values, especially in 2005 (extreme drought event). During the study period, copepoda was the main dominant group and Acartia tonsa the most abundant species, with the exception of autumn 2006, where high abundances of the cladoceran Penilia avirostris were noticed. Multivariate analysis indicated that zooplankton communities changed from a pre- to a post-drought period indicating the influence of hydrological parameters in communities' structure. The dry period was associated with an increase in zooplankton density, a reduction in seasonality and higher abundance and prevalence of marine species throughout the year. Seasonally, winter/spring communities were distinct from those in summer/autumn. Spatially, salinity-associated differences between upstream and downstream communities were reduced during the drought years, but during the post-drought year, these differences were detected again.     

Mesoscale variability in the South China Sea from the TOPEX/Poseidon altimetry data

Using wavelet transform we studied the mesoscale variability in the South China Sea (SCS) by analyzing 5-yr (October 1992 to August 1997) TOPEX/Poseidon (T/P) altimetry data. Our analysis suggests that mesoscale variability inside the SCS is weaker than that outside the SCS in the Kuroshio. It is found that despite the large temporal variation in the mesoscale variability, there are two narrow bands of significant mesoscale variability north of 10°N throughout much of the 5-yr period. The stronger one lies along the western boundary, while the weaker one is oriented in a southwest-to-northeast direction across the central SCS. In the rest of the SCS, the mesoscale variability is much weaker. In light of the numerical simulation by Metzger and Hurlburt (1996, Journal of Geophysical Research, 101, 12,331–12,352) and an XBT section along 15°N, the broad characteristic structure of the mesoscale variability indicates that the large-scale mean circulation in the SCS is primarily a cyclonic gyre north of about 10°N. In addition to the mesoscale variability, analysis of both the T/P and the XBT data indicates that there also exists significant intra-annual variability within similar geographic locations. The intra-annual variability is found to be primarily a subsurface feature with a very weak surface signature.     

Relocation of two earthquakes in the Southwest Indian Ridge area combining land seismic stations’ with OBSs’ data

Two earthquakes were recorded by 20 ocean bottom seismometers (OBS) deployed in the Southwest Indian Ridge (SWIR) area during a three-dimensional seismic survey in 2010. Their magnitudes (both M _b = 4.4) and hypocenters have been determined by National Earthquake Information Center (NEIC) only using land seismic stations onset times. After the frequency analysis and the band-pass filtering of the OBSs’ data, 7 and 13 P-phase onset times from OBSs were successfully picked for these two events, respectively. Then these two events were relocated by HYPOSAT program with onset times together from OBSs and land seismic stations using different velocity models. These relocation experiments confirm both the importance of adding OBSs’ onset data and the need to apply a local oceanic velocity model for the location of these two events happened on the SWIR. This research has accumulated a wealth of experience for earthquakes observation and research using OBSs in the ocean.     

Tendencies in Coccolithophorid Blooms in Some Marine Environments of the Northern Hemisphere according to the Data of Satellite Observations in 1998–2013

Based on the method developed for the delineation of E. huxleyi blooms, a new technique is achieved for (1) the automated detection of E. huxleyi blooms among coexisting massive blooms of microalgae species of other phytoplankton groups and (2) quantifying the boom surface of this type of coccolithophores. As a result, according to the data of the Climate Change Initiative Ocean Colour (OC CCI) for 1998–2013, we have obtained multiyear time series of variability in both the incidence of E. huxleyi bloom and its area in the North, Norwegian, Greenland, Barents, and Bering seas. It is found that E. huxleyi blooms propagate within the intra-annual cycle from the studied middle-latitude marine areas towards the northern areas of the Northern Atlantic Ocean (NAO) and the Arctic Ocean (AO) following the pathways of the main Gulfstream and its branches. It is also found that E. huxleyi blooms are formed annually, initially in the vicinity of the British Islands; then they successively emerge in the northward direction following the western coast of the Great Britain, turn over its northern extremity to reach, firstly, the North Sea (in May), the Norwegian Sea, and finally the Greenland Sea (in June). Then they burst out in the Barents Sea, where the typical period of blooming lasts until late August and, in some years, even to mid-September. We determine the patterns of maximal rates and duration of blooms for each of the seas studied in the Atlantic and Arctic Oceans. As for the Bering Sea, the temporal and spatial variability in the growth of E. huxleyi has an irregular pattern: after a period of remarkably high expression of this phenomenon in 1998–2001, there was an abrupt decrease in both the number and, especially, extent of bloom areas.     

On vertical particle fluxes in the Caspian Sea

The first results of studies of vertical fluxes of sediment particles using the sediment traps at the Trans-Caspian section are presented. The flux values and distribution regularities are established. The fluxes of particles forming the sediment are also determined. The intra-annual variability in the fluxes corresponds to the seasonal variability of the biological activity. Above the northern slope of the Derbent Basin, the maximum vertical fluxes are recorded in the winter, which is caused by the intensification of the near-bottom currents.