The distribution of chlorophyll-a and dominant planktonic components in the coastal transition zone off Concepción, central Chile, during different oceanographic conditions

The oceanographic setting and the planktonic distribution in the coastal transition zone off Concepción (∼35-38°S, ∼73-77°W), an area characterized by its high biological production, were assessed during two different seasons: austral spring with equatorward upwelling favorable winds and austral winter with predominately northerly winds. Oceanographic and biological data (total chlorophyll-a, particulate organic carbon, microplankton, large mesozooplankton >500 μm as potential consumers of microplankton) were obtained during two cruises (October 1998, July 1999) together with satellite imagery for wind stress, geostrophic flow, surface temperature, and chlorophyll-a data. The physical environment during the spring sampling was typical of the upwelling period in this region, with a well-defined density front in the shelf-break area and high concentrations of surface chlorophyll-a (>5 mg m⁻³) on the shelf over the Itata terrace. During the winter sampling, highly variable though weakly upwelling-favorable winds were observed along with lower surface chlorophyll-a values (<2 mg m⁻³) on the shelf. In the oceanic area (>100 km from the coast), cyclonic and anti-cyclonic eddies were evident in the flow field during both periods, the former coinciding with higher chlorophyll-a contents (∼1 mg m⁻³) than in the surrounding waters. Also, a cold, chlorophyll-a rich filament was well defined during the spring sampling, extending from the shelf out to 350-400 km offshore. Along a cross-shelf transect, the micro- and meso-planktonic assemblages displayed higher coastal abundances during the spring cruise but secondary peaks appeared in the oceanic area during the winter cruise, coinciding with the distribution of the eddies. These results suggest that the mesoscale features in this region, in combination with upwelling, play a role in potentially increasing the biological productivity of the coastal transition zone off Concepción.     

Seasonal and inter-annual variation of mesozooplankton in the coastal upwelling zone off central-southern Chile

Zooplankton sampling at Station 18 off Concepción (36°30′S and 73°07′W), on an average frequency of 30 days (August 2002 to December 2005), allowed the assessment of seasonal and inter-annual variation in zooplankton biomass, its C and N content, and the community structure in relation to upwelling variability. Copepods contributed 79% of the total zooplankton community and were mostly represented by Paracalanus parvus, Oithona similis, Oithona nana, Calanus chilensis, and Rhincalanus nasutus. Other copepod species, euphausiids (mainly Euphausia mucronata), gelatinous zooplankton, and crustacean larvae comprised the rest of the community. Changes in the depth of the upper boundary of the oxygen minimum zone indicated the strongly seasonal upwelling pattern. The bulk of zooplankton biomass and total copepod abundance were both strongly and positively associated with a shallow (<20 m) oxygen minimum zone; these values increased in spring/summer, when upwelling prevailed. Gelatinous zooplankton showed positive abundance anomalies in the spring and winter, whereas euphausiids had no seasonal pattern and a positive anomaly in the fall. The C content and the C/N ratio of zooplankton biomass significantly increased during the spring when chlorophyll-a was high (>5 mg m⁻³). No major changes in zooplankton biomass and species were found from one year to the next. We concluded that upwelling is the key process modulating variability in zooplankton biomass and its community structure in this zone. The spring/summer increase in zooplankton may be largely the result of the aggregation of dominant copepods within the upwelling region; these may reproduce throughout the year, increasing their C content and C/N ratios given high diatom concentrations.     

Onshore Neogene stratigraphy in the North of the Alboran Sea (Betic Internal Zones): Paleogeographic implications

The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations.     

Phosphate adsorption and desorption in a tropical estuary (Maracaibo system)

The Maracaibo Estuary is of particular interest because of its location in the tropics, its large size (over 12,000 km²), the economic importance of its underlying hydrocarbon deposits and its increasing rate of pollution. Sediments from this estuary were studied in order to characterise their capacity to adsorb and desorb phosphorus. Considerable variability in capacity for phosphate sorption was found among the seventeen samples studied. This variability can be attributed first to the differences among the samples in total P content and, secondly, to their differences in free iron content. Also, it appears that P retention contributes to the control of P concentration in the water and therefore the sediments serve as a buffer in controlling P eutrophication in the estuary.     

The Huelva (Spain) Tsunami-Ready Station and Its Interaction with Storm Emma (March 2018)

Abstract

The sea level station operating since 1996 at Mazagón (Huelva, Spain) has been progressively upgraded to fit tsunami warning requirements, due to its location in one of the main regions at risk. Its radar water level sensor was complemented in 2017, with the addition of a pressure sensor. The performance of both sea level sensors and their response to sea level oscillations, at different frequencies, is assessed. Particular emphasis is put on the effect of extreme events, such as Storm Emma, when alternative methods to obtain 1-min data are tested, in contrast to the one based on arithmetic means. The overall differences are small, for the whole period of study (centered-root-mean-square-error below 1?cm, for 5-min, and hourly data; similar tidal parameters and sea level oscillations with periods between 30?s and 5?min). However, during Storm Emma, the pressure sensor presents sensibly lower readings than the radar, with the centered-root-mean-square-error rising to 80?mm on the March 2^nd 2018. A new method to compute 1-min data, based on medians, reduced this value to 10?mm for the same day.     

Three-Dimensional Velocity Field and Cross-Frontal Water Exchange in the Kuroshio Extension

A spread of warm water from the first crest of the Kuroshio Extension is periodically enhanced by northward warm water intrusions from the main current. The water type in the spread area was previously found to be the same as that in the Kuroshio front at depth. In looking for the possible mechanism responsible for the northward warm water intrusions, a dynamic analysis in the Kuroshio front was carried out by using CTD, ADCP, AVHRR and ARGOS buoy data, obtained in 1996 by the R.V. Hakuho Maru. Downstream, cross-stream and vertical velocities in the Kuroshio Extension were found by using a "stream coordinate system". The velocity field in the Kuroshio front at the first crest showed a double structure with two surface velocity maxima. In the inner part of the front, relatively high cross-stream (northward) and vertical (upward) velocities were found. Thus, this study suggests that while water particles flow downstream along the first stationary meander of the Kuroshio Extension, they also experience lateral and vertical movements which allow the deeper water from an upstream location to rise to the surface layer, and in certain locations to deflect northward. By assuming isopycnal movement and conservation of potential vorticity, it was found that in those locations where anticyclonic curvature of the meander increases, warm water is more likely to deflect northward. High ageostrophic components observed in the first 300 m of the water column are probably related to the relatively high cross-stream and vertical velocities in the inner part of the front.     

In Situ Measurement of Pinna nobilis Shells for Age and Growth Studies: A New Device

Abstract. Pinna nobilis Linnaeus 1758 is an endemic bivalve mollusc in the Mediterranean Sea, where it inhabits seagrass meadows, especially Posidonia oceanica (L.) Delile. It is the largest bivalve in the Mediterranean, reaching lengths up to 120 cm. In its natural habitat, P. nobilis lives with the anterior part of the valve buried in the seabed, attached to Posidonia rhizomes by byssus threads.
This habit makes it impossible to measure its total length directly in situ. As the only way to determine the individual age is the relationship between age and total length, several equations have been proposed to estimate total length by relating it to the unburied parts of the shell. Such measurements are essential to ecological studies that consider age, growth, and population dynamics, and that evaluate the environmental factors that affect this species.
Accurately estimating total length depends on the accuracy and precision of the method employed to measure the unburied shell parts. In this paper, we point out the lack of precision of the instruments and methods used until now; we also demonstrate the reason for this imprecision. A new device to measure unburied parts of Pinna nobilis with a precision comparable to that obtained when measuring extracted valves is described. This device is unaffected by substratum type and reduces measurement time. The latter is a very important feature, because these procedures are usually performed whilst SCUBA diving. Finally, a growth equation has been fitted to the measurements obtained with the new device from a population located in Moraira (Alicante, western Mediterranean).     

On the estimation of mooring line characteristic resistance for reliability analysis

The main aim of this work is to derive a correct formulation for the characteristic resistance of a mooring line segment with lognormally distributed component resistances and substitute an equation proposed by Vazquez-Hernandez et al. [Vazquez-Hernandez AO, Ellwanger GB, Sagrilo LVS. Reliability-based comparative study for mooring lines design criteria. Appl Ocean Res 2006; 28(6):398–406] in a paper published in this journal, which is not correct. The mooring line is considered as a series system and the resistances of individual components of a line segment are statistically independent and identically distributed; furthermore, the case of normally distributed component resistances is also discussed. A comparison with the corresponding equation proposed by DNV-OS-E301 is given. Results show that the formula proposed by Vazquez-Hernandez et al. [Vazquez-Hernandez AO, Ellwanger GB, Sagrilo LVS. Reliability-based comparative study for mooring lines design criteria. Appl Ocean Res 2006; 28(6):398–406] overestimates quite significantly the characteristic resistance of a mooring line segment.     

Spatial and temporal variability of microplankton and detritus, and their export to the shelf sediments in the upwelling area off Concepción, Chile (∼36°S), during 2002-2005

Seasonal variations in diversity and biomass of diatoms, tintinnids, and dinoflagellates and the contribution of microplankton and faecal material to the vertical flux of particulates were investigated at one time series station T (station 18) between 2002 and 2005 and at a grid of stations during November 2004 in the coastal and oceanic area off Concepción (36°S), Chile. The variations were analysed in relation to water column temperature, dissolved oxygen, nutrient concentration, offshore Ekman transport, and chlorophyll-a concentration. Abundance was estimated as cell numbers per litre and biomass in terms of biovolume and carbon units.A sharp decrease with depth was observed in the abundance of both phytoplankton and microzooplankton during the whole annual cycle; over 70% of their abundance was concentrated in the upper 10 m of the water column. Also, a clear seasonality in microplankton distribution was observed at station T, with maxima for diatoms, tintinnids, and dinoflagellates every summer (centred on January) from 2002 to 2005.On the grid of stations, the maximum integrated (0-50 m) micro-phytoplankton abundances (>1 × 10⁹ cells m⁻²) occurred at the coastal stations, an area directly influenced by upwelling. A similar spatial distribution was observed for the integrated (0-200 m) faecal carbon (with values up to 632 mg C m⁻²). Tintinnids were distributed in all the first 300 miles from the coast and dinoflagellates were more abundant in oceanic waters.At station T, the average POC export production (below 50 m depth) was 16.6% (SD = 17%; range 2-67%; n = 16). The biological-mediated fluxes of carbon between the upper productive layer and the sediments of the continental shelf off Concepción depend upon key groups of phytoplankton (Thalassiosira spp., Chaetoceros spp.) and zooplankton (euphausiids) through the export of either cells or faecal material, respectively.     

The Equatorial Atlantic Mid-Ocean Channel: An Ultra High-Resolution Image of Its Burial History Based on TOPAS Profiles

Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC.