Spatiotemporal variability of thermal front features in the Baltic Sea 2010–2011

Regions of the formation of the thermal front in the Baltic Sea (a direct manifestation of the lacustrine thermal bar), and its specific features, were analyzed on the basis of subsurface temperature and salinity. Data were obtained from 25 horizontal tows along sections in the southern and central parts of the Baltic Sea during spring 2010 and autumn/winter 2010/2011. The width of the front was approximately 5?C30 km, and the front lifetime was 1.5 months. Horizontal temperature ranged from 0.7 to 2.5°C; thus, the temperature gradient was one- to twofold larger than the long-term monthly mean equivalent. Analysis of hourly temperature and salinity data from the Arkona basin and at the Darss Sill, obtained at 2 m depth, indicated that the surface temperature increased during the transition through temperatures of maximum density at a rate of approximately 0.01?C0.02°C/h between 3?C5 days; which is 1.4- to 5-fold higher than values before and after this period. The thermal front simultaneously propagated along the main sea axis (due to the significant salinity and buoyancy flux variations from south to north), and from the shallow parts towards the deep parts of the Baltic Sea. Therefore, the horizontal advection of the cold/warm waters clearly contributes to the speed increase of the thermal front at the end of the respective season. The speed of the thermal front propagation from south to north was approximately 28 km/day at the end of the spring period of 2010 (based on field data). This was considerably higher in comparison with the typical values of the lacustrine thermal bar speeds; however, it accords with estimates for a basin with depth/salinity horizontal variation.     

Analysis of current–topography interaction in remote sensing imaging procedures for shallow water topography

Underwater topography can be imaged using remote sensing methods. Numerous studies have been conducted to understand the imaging mechanism of shallow water topography. However, current–topography interaction constitutes the weakest link in the remote sensing imaging mechanism of underwater topography. In addition, few studies focused on different topography patterns. Current velocity is highly correlated with bathymetry, and velocity gradient is used as an indicator of sea surface roughness. In this research, we analyzed the distribution characteristics of current velocity and velocity gradient in different cases using a 3-dimensional (3-D) hydrodynamic model to discuss the current–topography interaction part of the remote sensing imaging mechanism, especially the modulation by current parallel or normal to the underwater topography, both positive and negative. Results showed remarkable agreement between 3-D current analysis and surface velocity analysis. Parallel and normal currents had different responses to different topography types. The distribution of surface current gradient showed opposite features over negative and positive topography in parallel and normal current fields. This can be used to distinguish negative topography from positive topography with different current directions to a certain extent.     

Biogeochemical transformations of dissolved organic matter at the sediment–water interface: results from in situ incubations within benthic chambers

Biogeochemical transformations of dissolved organic matter at the sediment–water interface were investigated by the use of benthic chambers in the western Gulf of Lions. The experimental approach used for this study consisted of in situ incubations of radiolabeled glutamic acid (¹⁴C-Glu), followed by a sequential extraction allowing the quantification of the radioactivity associated to different chemical fractions, representative of different biogeochemical processes. This technique was devised to simulate the fate of simple dissolved compounds resulting from the degradation of particulate organic matter near the seafloor. In our experiment the substrate underwent both biotic (mineralization, bacterial incorporation) and abiotic (geopolymerization) transformations. Significant spatial variations were put in relation with sediment characteristics (e.g. fine-grained fraction, Eh, CaCO₃ contents) and biological activities, such as bacterial respiration and infaunal burrowing. Biologically mediated processes decreased from onshore to deep sites, with mineralization always accounting for the bulk of transformations of the injected ¹⁴C-Glu. Geopolymerization did not display a clear spatial trend and appeared to be a quantitatively important process on the Gulf of Lions margin.     

Spring thermocline formation in the coastal zone of the southeastern Baltic Sea based on field data in 2010–2013

The transition from winter vertical mixing to the formation of the spring thermocline in the southeastern Baltic Sea is studied based on data from the hydrophysical measurements program (11 expeditions) in the Russian part of Gdansk Bay in March–June 2010, 2011, and 2013. CTD measurements were taken along the standard 18-km transect across the isobaths with a 500-m step abeam the city of Baltiysk. A set of frequently measured data was collected in a 1–2 week interval from the end of March to the beginning of May, which made it possible to analyze the transformation of the vertical thermal structure of water from inverse winter type to the summer stratification with the transition of temperature over the temperature of the density maximum. Series of repeated measurements at the deep and coastal stations as well as surface and subsurface towed measurements were carried out. The fact that lenses of freshened warmer water appear at the surface almost simultaneously with intensification of cold intrusions in intermediate (10–40 m) layers makes it possible not only to confirm the advective nature of the formation of the spring thermocline in the Baltic Sea, but also to hypothesize about the intensification of intrabasin exchange when winter-time vertical mixing ceases: the potential energy excess supported by vertical mixing in the 60-m upper quasi-homogeneous layer (UQL) of the Baltic Proper, in which the horizontal estuarine salinity gradient is significant, is converted to kinetic energy of exchange currents as the mixing process terminates. Such water dynamics makes it possible to explain the intensification of intrusions in the Baltic in spring and the formation of the cold intermediate layer due to the fast propagation of late-winter UQL water from the Bornholm Basin to the Baltic Proper. The results agree well with earlier published studies of other authors.     

Interannual variations and trend of the production of inorganic carbon by coccolithophores in the arctic in 2002–2010 based on satellite data

Based on MODIS data, a significant decline in the intensity and spatial extension of blooms of coccolithophore E. huxleyi in Arctic waters in 2002–2010 is revealed and quantified. This 9-year tendency has been unfolding against a background of negative trends in the dynamics of SST and levels of incident PAR and summer-time NAO, which collectively, but with a predominance of the NAO influence, are believed to be the main drivers of the decline of E. huxleyi blooms and the associated decline in inorganic carbon production in the Arctic Basin.     

High-resolution observations of dissolved isoprene in surface seawater in the Southern Ocean during austral summer 2010–2011

We measured dissolved isoprene (2-methyl-1,3-butadiene; C₅H₈) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35°S to 64°S and from 37°E to 111°E during austral summer 2010–2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L^?1 and from 181 to 313 nmol m^?2 day^?1, respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll-a concentrations (r ² = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (>53°S) we identified a significant negative correlation (r ² = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO₂), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO₂ are similar within a physically stable water column.     

Contribution of siderite–water interaction for the unconventional generation of hydrocarbon gases in the Solimões basin,north-west Brazil

Hydrocarbon gases with unconventional carbon isotopic signatures were observed in the Solimões sedimentary basin in north-west Brazil. Siderite contents measured with a new Rock-Eval methodology in the drill-cuttings samples of the Famenian source rock were found to decrease with the increase of gas maturity and with the occurrence of the gas isotopic anomalies. Triassic diabase intrusions induced heating of the source rock, which likely resulted in the gradual oxidative dissolution of siderite as suggested by the observation of etch pits on the siderite surfaces. It is proposed that ferrous iron from the carbonate was involved in a redox reaction with water producing ferric iron and H₂, then reducing CO₂ and yielding an inverse correlation between siderite content and gas maturity. Alternatively, hydrogenation of highly mature kerogen by H₂ derived from siderite could explain the production of ¹³C-rich CH₄. Mass balance considerations suggest that these mechanisms may account for a significant fraction of the hydrocarbon gases generated from the Famenian source rock in the Solimões basin.     

Service vessel activity in the U.S. Gulf of Mexico in support of the oil and gas industry using AIS data, 2009–2010

Offshore exploration and production in the U.S. Gulf of Mexico is supported by a large number of service vessels characterized by complex logistical patterns and demand points distributed across an expansive geographic area. No quantitative data on the spatial and temporal distributions of service vessel activity in the region is available due to the size, complexity and dynamics of the network. The purpose of this paper is to apply Automatic Identification System position data to quantify service vessel activity in the U.S. Gulf of Mexico from 2009 to 2010. A total of 1.1 million vessel arrivals and departures were recorded in 2009–2010, and in 2010, the number of vessel events increased by 40% due in part to the Macondo oil spill and cleanup response. Port-to-port movements comprise the majority of events and about 30% of activity relates to movements offshore. Port Fourchon, Venice, New Orleans, Sabine-Neches, and Lake Charles were the most active ports during the period. A detailed breakdown of vessel counts and the limitations of the analysis are outlined.     

Estimation of annual variation of water vapor in the Arctic Ocean between 80°–87°N using shipborne GPS data based on kinematic precise point positioning

The measurement of atmospheric water vapor(WV) content and variability is important for meteorological and climatological research. A technique for the remote sensing of atmospheric WV content using ground-based Global Positioning System(GPS) has become available, which can routinely achieve accuracies for integrated WV content of 1–2 kg/m2. Some experimental work has shown that the accuracy of WV measurements from a moving platform is comparable to that of(static) land-based receivers. Extending this technique into the marine environment on a moving platform would be greatly beneficial for many aspects of meteorological research, such as the calibration of satellite data, investigation of the air-sea interface, as well as forecasting and climatological studies. In this study, kinematic precise point positioning has been developed to investigate WV in the Arctic Ocean(80°–87°N) and annual variations are obtained for 2008 and 2012 that are identical to those related to the enhanced greenhouse effect.     

Making sense of censuses and dealing with missing data: trends in pup counts of Cape fur seal Arctocephalus pusillus pusillus for the period 1972–2004

Trends in the population of Cape fur seals Arctocephalus pusillus pusillus were estimated from counts of pups on aerial photographs of colonies taken between 1972 and 2004 to determine trends in the overall population and subpopulations. Incomplete coverage resulted in missing data in some years. Various methods of determining proxy values for missing data were assessed, and it was concluded that different methods were applicable to Namibian and South African colonies. This reflected variation in trends of pup counts between the countries, which was associated with differences in productivity between the southern and northern Benguela ecosystems. In Namibia, temporal changes in pup numbers were non-linear in some years and there was correspondence in fluctuations at most colonies. This appeared to be on account of an effect of periodic, wide-scale prey shortages that reduced birth rates. There was a northward shift in the distribution of seals in the northern Benguela system. In South Africa, pup counts were much less variable between years, probably on account of a relative stability of food supply. A linear approach was therefore suitable for determining proxy values for missing data at South African colonies. Pup counts suggest that there has been little change in the overall population of the Cape fur seals since 1993, when it was estimated at about two million animals.