Nitrate-nitrogen isotopic patterns in surface waters of the western and central equatorial pacific

To understand the processes transporting nitrate to the surface layer of the western and central equatorial Pacific, we measured the nitrogen isotopic ratio of nitrate (δ ¹⁵NO ₃ ⁻ ), which is a very useful tracer of the source of nitrate, above 200 m depth in this region in December 1999. δ ¹⁵NO ₃ ⁻ is higher (about 13.0‰) in the surface water than in the subsurface water (where it is about 6.5‰) due to isotopic fractionation during nitrate uptake by phytoplankton. The δ ¹⁵NO ₃ ⁻ value has a roughly linear relationship with the natural logarithm of nitrate concentration (ln[NO ₃ ⁻ ]). However, for values above 150 m depth, the intercept of this linear relationship varies with position from east to west. On the other hand, the data at 200 m depth at all observation stations are concentrated around a single point (ln[NO ₃ ⁻ ] = 2.5 and δ ¹⁵NO ₃ ⁻ = 6.5‰) and do not fit the linear relationships for the shallower values. To examine the meaning of the observed distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration we developed a box model including nitrogen and nitrogen isotopic cycles. By reproducing the observed relationship between δ ¹⁵NO ₃ ⁻ and nitrate concentration using this model we found that most nitrate is transported horizontally from the eastern equatorial Pacific. We also conducted case studies and investigated the effects of differences in pathways of nitrate transport on the distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration. From these studies we concluded that the observed linear relationships between δ ¹⁵NO ₃ ⁻ and ln[NO ₃ ⁻ ], having a common slope around 6‰ but different intercepts at each station, are evidence of the significant horizontal transport of nitrate to the surface water in this area.     

Study of organic-calcium interactions: gypsum precipitation in tropical surface waters

This paper demonstrates the involvement of dissolved organic compounds in the precipitation of gypsum from near-surface seawater. The general solubility and oxidation behavior of these compounds is discussed. Qualitatively different results have been obtained between samples collected from remote areas and those collected from areas of intensive human use.     

Variation of the southern Subtropical Countercurrent related to sea surface height and eddies in the northwest tropical pacific

The ADCP records obtained at about 18°N, 135°E show the southern branch of the Subtropical Countercurrent (STCC). The sea surface heights (SSH) show that there is a tendency to increase and decrease in the south/north of STCC, respectively. So the variability of SSH ultimately contributes to the strengthening of STCC through geostrophic balance. The southern STCC branch distinctly persists from winter to spring. Since 2005, the southern STCC exists almost throughout the year, and the STCC is clearly stronger to the east of 145°E. Anticyclonic and cyclonic eddies exist seemingly as bands around 17.5°N and 20.5°N, respectively. The STCC flowing eastward, which is formed by the geostrophic balance, is maintained with the interaction between geostrophic currents and anticyclonic-cyclonic eddies. The rotating eddies exert an additional driving force to maintain the eastward flow of STCC, and then the STCC reveals a meandering movement due to the interaction with the eddies. The trajectories of surface drifters together with the altimeter data analysis in June 2009 dictate the variability of the STCC induced by the interaction between eddies and the eastward flow. These results suggest that the southern STCC slowly changes from an intra-seasonal event an annual one with time duration of over 21 months.     

The characteristics of signal versus noise sst variability in the north pacific and the tropical pacific ocean

Total sea surface temperature (SST) in a coupled GCM is diagnosed by separating the variability into signal variance and noise variance. The signal and the noise is calculated from multi-decadal simulations from the COLA anomaly coupled GCM and the interactive ensemble model by assuming both simulations have a similar signal variance. The interactive ensemble model is a new coupling strategy that is designed to increase signal to noise ratio by using an ensemble of atmospheric realizations coupled to a single ocean model. The procedure for separating the signal and the noise variability presented here does not rely on any ad hoc temporal or spatial filter. Based on these simulations, we find that the signal versus the noise of SST variability in the North Pacific is significantly different from that in the equatorial Pacific. The noise SST variability explains the majority of the total variability in the North Pacific, whereas the signal dominates in the deep tropics. It is also found that the spatial characteristics of the signal and the noise are also distinct in the North Pacific and equatorial Pacific.     

Enhanced concentrations of dissolved gaseous mercury in the surface waters of the Arctic Ocean

During an almost three months long expedition in the Arctic Ocean, the Beringia 2005, dissolved gaseous mercury (DGM) was measured continuously in the surface water. The DGM concentration was measured using an equilibrium system, i.e. the DGM in the water phase equilibrated with a stream of gas and the gas was thereafter analysed with respect to its mercury content. The DGM concentrations were calculated using the following equation, DGM = Hg_eq / k_H' where Hg_eq is the equilibrated concentration of elemental mercury in the gas phase and k_H' is the dimensionless Henry's law constant at desired temperature and salinity. During the expedition several features were observed. For example, enhanced DGM concentration was measured underneath the ice which may indicate that the sea ice acted as a barrier for evasion of mercury from the Arctic Ocean to the atmosphere. Furthermore, elevated DGM concentrations were observed in water that might have originated from river discharge. The gas-exchange of mercury between the ocean and the atmosphere was calculated in the open water and both deposition and evasion were observed. The measurements showed significantly enhanced DGM concentrations, compared to more southern latitudes.     

First record of the pacific fanfishpteraclis aesticola (jordan and snyder, 1901) in the tropical eastern pacific

One specimen ofPteraclis aesticola was collected off San José del Cabo, Baja California Sur, México (22°54′N, 109°45′W), in March 2007. Present record is the first reported occurrence of the species in the Tropical Eastern Pacific biogeographic region (Gulf of California to southern Ecuadorian waters). Its large fan-like anal and dorsal fins and its counts of fin rays and vertebrae can distinguish the Pacific fanfish from the other species in the genus. This fish may have not yet been recorded in the region because its presence has been overlooked in the past because of rarity and lack of commercial value.     

Tidal currents in the coastal waters east of Hainan Island in winter

Using the 25-h continuing hydrographic observations at three successive stations in February 2012 and the mooring time series of current observations from January to March 2015, the tidal currents and tidal energy fluxes in the coastal waters east of Hainan Island in the northwestern South China Sea were analyzed. The diurnal and semidiurnal(using K 1 and M 2 as proxies, respectively) tidal currents and associated isopycnal undulations were derived with harmonic analysis. Results show that the v...     

Isotopic fractionation of dissolved nitrate during denitrification in the eastern tropical north pacific ocean

The isotopic composition (δ¹⁵N) of dissolved nitrate was measured at five stations within the oxygen-deficient region of the eastern tropical North Pacific Ocean (ETNP) and at one station 900 km northeast of Hawaii, which was considered to be representative of all major water masses of the Pacific. At this last station, the δ¹⁵N composition of dissolved nitrate decreased systematically from about +6‰ at 400 m to approximately +5‰ at 5,000 m; these results are consistent with other estimates from the western Pacific.In contrast, vertical profiles of δ¹⁵N of dissolved nitrate from the ETNP showed marked departure from the above observed trend and correlated with losses of nitrate arising from denitrification. Instantaneous fractionation factors (α) were estimated, using the one dimensional vertical diffusion-advection model. These results suggest that ¹⁴NO₃⁻ is consumed 3–4% faster than ¹⁵NO₃⁻, significantly larger than fractionations (2%) observed under laboratory conditions.Maximum rates of denitrification at 100 m were also evaluated and ranged from 0.6 to 8 μg-at 1⁻¹ yr⁻¹ for the stations investigated. The above upper limit is probably excessive, but the average maximum for the four stations analyzed is estimated to be 3.5 μg-at NO₃⁻ 1⁻¹ yr⁻¹. These results compare favorably with suitably corrected oxygen utilization rates derived from electron transport activity measurements.     

Synoptic variability of the acoustic characteristics in tropical Atlantic waters

Synoptic variability of the sound speed and parameters of the SOFAR channel in the tropical Atlantic are considered. The synoptic component of the temporal and spatial dispersions of sound speed is singled out. The synoptic processes are shown to essentially affect the vertical hydroacoustic structure on a 1-month scale. It has been found that synoptic variations in the sound speed field penetrate as far as the SOFAR channel axis and deform it considerably.Translated by V. Puchkin.     

First investigations of massive ferromanganese crusts in the NE Atlantic in comparison with hydrogenetic pacific occurrences

Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hydrogenetic crusts from a central Pacific seamount revealed lower concentration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly increased terrigenous input of Fe, Pb, Al, and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crust ages average at 10 My. The old phosphatized crust generation that started to grow about 20 My ago on the Pacific seamounts is not pronounced at the Tropic Seamount. The typical hydrographic and morphological parameters for hyrogenetic crust growth have also been found at the Tropic Seamount, which implies that the Tropic Seamount crusts have developed according to the hydrogenetic growth model. There are no indications of hydrothermal influence.     

Comparison of community structures between particle-associated and free-living prokaryotes in tropical and subtropical Pacific Ocean surface waters

The subtropical and tropical regions of the Pacific Ocean are less productive than other oceanic regions. Although particle association should be an important strategy for heterotrophic prokaryotes to survive in such environments, we have little information on particle-associated (PA) prokaryotes in these regions. The specific aim of this study was to determine bacterial and archaeal community structures in the PA assemblage in comparison to the free-living (FL) assemblage in the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and an eastern equatorial region of the Pacific Ocean. Community profiles and phylogenetic identities were obtained by denaturing gradient gel electrophoresis, 454-pyrosequencing, and cloning followed by Sanger sequencing of 16Sr RNA gene amplicons. The distribution patterns of some abundant groups in three regions and two lifestyles (PA and FL) are shown in this study. Also, the PA community structures of bacteria differed from the FL ones and exhibited higher diversity than the FL ones, while the archaeal community structures did not show significant differences between PA and FL assemblages. We found that specific phylotypes of Gammaproteobacteria and Flavobacteria were abundant in PA bacterial assemblages, suggesting that they prefer to attach and consume particulate organic matter. In summary, the surface seawater PA assemblages represent very different bacterial and archaeal community structures between three different oceanic regions, each of which had distinct PA and FL community structures. These results imply that environmental factors determine microbial community structures.     

Copper concentrations in surface waters off the south-eastern atlantic coast,U.S.A.

Copper concentrations in surface waters off the southeastern United States coast range from 0.02 to 0.33 μg/kg (0.3–5.2 nmol/kg). Mean concentrations are lowest in Onslow Bay (0.07 μg/kg) and highest over the Blake Plateau (0.20 μg/kg). An explanation, compatible with the hydrography and hydrodynamics of the area, is proposed for the observed regional variations.     

Similarity in microbial amino acid uptake in surface waters of the North and South Atlantic (sub-)tropical gyres

The Earth’s most extensive biomes – the oceanic subtropical gyres – are considered to be expanding with current surface ocean warming. Although it is well established that microbial communities control gyre biogeochemistry, comparisons of their metabolic activities between gyres are limited. In order to estimate metabolic activities including production of microbial communities, the uptake rates of amino acids leucine, methionine and tyrosine at ambient concentrations were estimated in surface waters of the Atlantic Ocean using radioisotopically labelled tracers. Data were acquired during six research cruises covering main oceanic provinces herein termed: North and South Atlantic Gyres, Bermuda Atlantic Time-series Study site (BATS), Equatorial region, and Mauritanian Upwelling (off Cape Blanc). Data were divided between provinces, the extents of which were identified by ocean colour data, in order to achieve provincial mean uptake rates. Leucine and methionine uptake rates did not differ between sampling periods, and were comparable between the North and South subtropical gyres. Furthermore, variation in uptake rates measured throughout the two oligotrophic gyres, where sampling covered ∼4 × 10⁶ km², was considerably lower than that measured within the Mauritanian Upwelling and Equatorial regions, and even at the BATS site. Tyrosine was generally the slowest of the amino acids to be taken up, however, it was assimilated faster than methionine within the Mauritanian Upwelling region. Thus, we propose that one value for leucine (12.6 ± 3.2 pmol L⁻¹ h⁻¹) and methionine (10.0 ± 3.3 pmol L⁻¹ h⁻¹) uptake could be applied to the oligotrophic subtropical gyres of the Atlantic Ocean. However, with the significantly lower uptake rates observed at the BATS site, we would not advise extrapolation to the Sargasso Sea.     

Response of subsurface waters in the eastern Arabian Sea to tropical cyclones

Thermister chain data at different depths for June 1998 cyclone in the Arabian Sea at a location (69.2 E,15.5 N) which is about 60 km to the left of the cyclone track indicates subsurface warming below 60 m and inertial oscillations of temperature with a periodicity of about 2 days. The oscillations continued for ∼15 days even after the cyclone crossed the coast. The analysis of the buoy, DS1 located at the same position also suggests a stabilized southward flow after about two weeks of the cyclone crossed the coast. Analysis of the buoy data for May 1999 cyclone in the same region also indicates similar pattern. In order to investigate the effect of cyclone–ocean interaction and primarily to understand the process for the subsurface warming, 3-dimensional Princeton Ocean Model is configured for the eastern part of the Arabian Sea. The model uses high horizontal resolution of about 6 km near the coast and a terrain following sigma coordinate in the vertical with 26 levels. The study focuses on surface cooling and temperature rise in the underlying waters and explains its mechanism through upwelling and downwelling respectively. The simulations in concurrence with the observations suggest that the occurrence of subsurface warming precedes the surface cooling with a lag of ˜a day as the cyclone advances DS1. The simulations also demonstrate local temperature stratification plays an important role for cooling of the upper ocean and warming of the subsurface waters and extent of warming is directly related to the depth of the thermocline.     

Methane, carbon monoxide, and carbon dioxide concentrations measured in the atmospheric surface layer over continental Russia in the TROICA experiments

The principal statistical regularities typical of the behaviors of the CH₄, CO, and CO₂ concentrations in the atmospheric surface layer over the continental Russian territory are revealed from the measurements performed in 1997–2004 along the Trans-Siberian Railroad from Moscow to Khabarovsk with a mobile laboratory. The data obtained under the conditions of the atmosphere free of anthropogenic pollutants are analyzed. For near-background conditions, the typical continental methane, carbon monoxide, and carbon dioxide concentrations and characteristic features of their large-scale spatial distributions and daily variations, including those caused by surface inversions, are determined. Variations in the concentrations of these trace gases over industrial regions are analyzed. Our results are compared to the data obtained at background stations of the world network of atmospheric monitoring and to the data of a numerical simulation.     

Intense hydrothermal activity at the axis of the east pacific rise near 13°N: Sumbersible witnesses the growth of sulfide chimney

A submersible study of a fast spreading (12 cm yr^-1) Mid-Ocean ridge segment (East Pacific Rise near 12°50′ N) led to the discovery of intense hydrothermal activity. Twenty four sites with active vents and sixty inactive hydrothermal deposits were found within a narrow graben averaging about 300 m in width along a 20 km long segment of the ridge crest. The graben is floored with fresh basaltic sheet flows including collapsed pits or lava lake structures. From both deep towed camera stations and manned submersible observations, it is estimated that the average spacing between the ridge axis hydrothermal deposits averaging in size 10–50 m in diameter lies between 100 to 200 m. The hydrothermal deposits found in the central graben are believed to have formed rapidly (on the order of a few decades). Detailed investigations of one active site have enabled us to witness the growth of an active chimney which increased its height by 40 cm in 5 days i.e. 8 cm per day. Extensive hydrothermal deposits were discovered on an off-axis seamount located 6 km East of the ridge axis. The hydrothermal deposits found on both the ridge axis and on the seamount are similar in composition and consist essentially of zinc, copper and iron mineral phases. Chemical studies conducted on the venting fluids (320°C) showed that the concentration of the dissolved major metal ions (Fe, Mn, and Zn) is about 0.10–0.13 gl^-1. If we accept an average flow rate of 10ls^-1 based on visual observations the mass of metallic products spewing out from an active chimney must be about 100 kg per day.     

国际海上救援效率比较研究 ——以东海特定水域为例

为研究东海海域海上救援效率和国际协作的协调性,以国际救援为视角,基于ArcGIS构建了海事救援效率评价模型。根据巡逻船舶密度数据确定了救援船舶的概率分布,得出了救援船舶与遇险船舶的可能距离,同时考虑了风浪影响下遇险船舶的漂移以及巡逻船舶失速的情况,分别计算了常风向和次常风向下中国、日本和韩国在东海特定水域的海上救援效率。结果表明:以各国现有的巡逻船舶配备对研究区内漂移的遇险船舶展开救援时,常风向下先后抵达的顺序为韩国、日本和中国,驰援时间分别为5.14、8.18和9.67 h;次常风向下抵达的顺序为韩国、日本和中国,驰援时间分别为5.45、8.25和10.08 h;为提高我国的救援效率,需要在东海海域部署9～10艘巡逻船舶开展常态化巡逻。本文研究可为我国有关部门科学制定和完善海上救援方案,调整海上救援力量配备,进一步加强国际间的协调与合作提供参考。     

Seasonal variability in the recruitment of macrofouling community in Kudankulam waters, east coast of India

The seasonal variability in fouling community recruitment on submerged artificial substratum was studied in Kudankulam coastal water, Gulf of Mannar, East coast of India for a period of two years, from May 2003 to April 2005. The results indicated that the fouling community recruitment occurred throughout the year with varying intensities. Barnacles, ascidians, polychaetes, bivalves and seaweeds were the major fouling groups observed from the test panels. Maximum fouling biomass of 9.17 g dm⁻² was observed during August 2004 and a minimum value of 0.233 g dm⁻² in February 2004. The biomass build-up on test panels was relatively high during the premonsoon season and low during the postmonsoon months. The number of barnacles settled on the panels varied from 1 to 4460 no. dm⁻². The maximum percentage of the ascidian coverage (72%) on test panels was observed during March 2005. In general, July–December was the period of intense recruitment for barnacles and March–May was the period for ascidians.     

Temperature variability caused by internal tides in the coastal waters of east coast of Peninsular Malaysia

The effects of tidal currents (i.e., barotropic and internal tides) are important in the biogeochemistry of a coastal shelf sea. The high-frequency of currents and near-bottom temperatures collected in three consecutive southwest monsoon seasons (May, June, July and August of 2013 until 2015) is presented to reveal the role of the tidal currents to the temperature variability in the coastal shelf sea of the east coast of Peninsular Malaysia (ECPM), south of the South China Sea (SCS). The results of a spectral density and harmonic analysis demonstrate that the near-bottom temperature variability and the tidal currents are influenced by diurnal (O₁ and K₁) and semidiurnal (M₂) tidal currents. The spectral density of residual currents (detided data) at 5, 10 and 16 m depth also shows significant peaks at the diurnal tidal frequency (K₁) and small peaks at the semidiurnal tidal frequency (M₂) indicating the existence of internal tides. The result of the horizontal kinetic energy (HKE) shows a strong intermittent energy of internal tides in the ECPM with the strongest energy is found at 16 m depth during a sporadic cooling event in June and July. A high horizontal cross-shore heat flux (16 m) also indicates strong intrusions of cooler water into the ECPM in June and July. During the short duration of cold pulse water observed in June and July, a cross-wavelet analysis also reveals the strong relationship between the near-bottom temperatures and the internal tidal currents at the diurnal tidal frequency. The intrusion of this cooler water is probably related to the monsoon-induced upwelling in June. It is loosely interpreted that the interaction between the strong barotropic tides and the steep slope in the central basin of the SCS under the stratified condition in southwest monsoon has generated these internal tides. The dissipation of internal tides from the slope area probably has driven the cold-upwelled water into the ECPM coastal shelf sea when the upwelling intensity is the highest in June and July.     

Copper complexation capacity in surface waters of the Venice Lagoon

Total copper (Cu(T)), copper ion activity (pCu) and the copper complexation capacity (CuCC) were determined in samples of seawater collected in July 2003 from the Venice Lagoon. Cu(T) and CuCC showed considerable spatial variability: Cu(T) ranged from 1.8 to 70.0nM, whereas the CuCC varied from 195 to 573nM. pCu values varied from 11.6 to 12.6 and are consistent with those previously reported in estuarine and coastal areas (10.9-14.1). The range of Cu(T) values compares well with those reported in the past in the lagoon and in the adjacent Adriatic Sea. The highest concentrations of Cu(T) were found in samples collected near the industrial area of Porto Marghera, whereas the lowest were measured near the Chioggia and Malamocco inlets, where an intense tidally-driven renewal of seawater takes place. Although CuCC showed a high degree of spatial variability, the values recorded in the Venice Lagoon are comparable to those reported in other estuarine systems. In addition, CuCC was positively correlated with dissolved organic carbon (DOC), suggesting that organic ligands responsible for Cu complexation are part of the bulk organic matter pool in the lagoon. The CuCC:Cu(T) molar ratio was, on average 55:1, indicating that a large excess of complexation capacity exists in the Venice Lagoon. The high levels of CuCC and the narrow range of pCu indicates the importance of the role played by organic ligands in controlling the free ion Cu concentrations in the lagoon, and as a consequence, regulating its availability and/or toxicity.