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Llaveria G.,CSIC - Institute of Marine Sciences | Garces E.,CSIC - Institute of Marine Sciences | Ross O.N.,Unitat de Tecnologia Marina | Figueroa R.I.,CSIC - Institute of Marine Sciences | And 2 more authors.
Marine Ecology Progress Series

Small-scale turbulence and parasite infection are 2 important factors that govern the dynamics and fate of phytoplankton populations. We experimentally investigated the influence of turbulent mixing on the infectivity of the parasite Parvilucifera sinerae to dinoflagellates. Natural phytoplankton communities were collected during 3 stages of a bloom event in Arenys de Mar Harbour (NW Mediterranean). The 15 to 60 μm size fraction was used as the inoculum and distributed into spherical flasks. Half of the recipients were exposed to turbulence while the rest were kept still. In the experiments, the dinoflagellate assemblage was mainly composed of Prorocentrum micans, Scrippsiella trochoidea and Alexandrium minutum. We observed a collapse of A. minutum and S. trochoidea populations in the unshaken flasks, which coincided with an increase in parasite infectivity. After a short exposure to turbulence, the development of the dinoflagellate populations slowed down and stabilised as expected. In the shaken treatments, the infectivity was lower and the decay in the host cells numbers was delayed compared to the still treatments. The degree of interference of the turbulence with infectivity varied among the experiments, due to differences in cell abundances and possibly their physiological state. Results from a numerical model suggest that turbulence could lead to a 25 to 30% decrease in the maximum infection rate, which could be due to host population dispersion and/or reduced host-parasite contact times. Turbulence may thus be effective in delaying the initial infection, but not in preventing it. © Inter-Research 2010, www.int-res.com. Source

Hackert E.,The Interdisciplinary Center | Ballabrera-Poy J.,Unitat de Tecnologia Marina | Busalacchi A.J.,The Interdisciplinary Center | Zhang R.-H.,The Interdisciplinary Center | Murtugudde R.,The Interdisciplinary Center
Journal of Geophysical Research: Oceans

In this paper, we assess the impact of sea surface salinity (SSS) observations on seasonal variability of tropical dynamics as well as on dynamical El Nio-Southern Oscillation (ENSO) forecasts using a hybrid coupled model (HCM). The HCM is composed of a primitive equation ocean model coupled with a singular value decomposition-based statistical atmospheric model. An Ensemble Reduced Order Kalman Filter (EROKF) is used to assimilate observations to constrain tropical Pacific dynamics and thermodynamics for initialization of the HCM. Rather than trying to produce the best possible operational forecasts, point-wise subsurface temperature (sTz) has been assimilated separately and together with gridded observed sea surface salinity (SSS) from optimal interpolation to more efficiently isolate the impact of SSS. Coupled experiments are then initiated from these EROKF initial conditions and run for 12 months for each month, 1993-2007. The results show that adding SSS to sTz assimilation improves coupled forecasts for 6-12 month lead times. The main benefit of SSS assimilation comes from improvement to the spring predictability barrier (SPB) period. SSS assimilation increases correlation for 6-12 month forecasts by 0.2-0.5 and reduces RMS error by 0.3C-0.6C for forecasts initiated between December and March, a period key to long-lead ENSO forecasts. The positive impact of SSS assimilation originates from warm pool and Southern Hemisphere salinity anomalies. Improvements are brought about by fresh anomalies at the equator which increases stability, reduces mixing, and shoals the thermocline which concentrates the wind impact of ENSO coupling. This effect is most pronounced in June-August, helping to explain the improvement in the SPB. In addition, we show that SSS impact on coupled forecasts is more pronounced for the period 1993-2001 than for the period 2002-2007 due to the improved inherent predictability associated with the strong 1997-1998 ENSO. Rather than being the final say for the issue of SSS assimilation, this study should be considered as a necessary first step. Future work is still required to assess issues such as SSS satellite data coverage and the complementary nature of satellite/in situ assimilation. However, these results foreshadow the important positive potential impact that gridded satellite SSS provided by missions such as SMOS and Aquarius/SAC-D will have on coupled model predictions. Copyright 2011 by the American Geophysical Union. Source

Cartes J.E.,CSIC - Institute of Marine Sciences | LoIacono C.,CSIC - Institute of Marine Sciences | LoIacono C.,National Oceanographic Center | Mamouridis V.,CSIC - Institute of Marine Sciences | And 2 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers

We analyzed what are the best ecological conditions for megafauna associated with the bamboo coral Isidella elongata based on the geomorphological, physical and trophic information taken in 3 stations (St1, St2, St3) off the southern Catalonian coasts at 620m depth in June 2011. Results were compared with assemblage compositions recorded in past cruises (May 1992, 1994) at the same 3 stations. St1 was in a fishing ground exploited since the 1940s over a relatively wide slope at ca. 22km from the nearest canyon head; St2 and St3 were on a narrower slope closer to canyon heads and to the Ebro river mouth than St1. I. elongata had formed (to May 1994, at least) a dense coral forest at St2-St3 (to ca. 255 colonies/ha at St3), and some isolated colonies (to ca. 0.9 colonies/ha) were still collected in 2011. Fish and invertebrate communities significantly differed between St1 and St2/St3, with two macrourid fishes (Trachrhynchus trachyrhynchus and Nezumia aequalis) and two decapods (Plesionika martia and Plesionika acanthonotus) more abundant at St2/St3. The following ecological indicators imply better food conditions for megafauna at St2-St3 and for I. elongata itself: (i) greater density of zooplankton (copepods, euphausiids, and others) as potential prey for planktivores (including I. elongata); (ii) greater biomass and mean weight of epifaunal and infaunal deposit feeders; (iii) higher feeding intensity, F, at St3 for benthos feeders (Phycis blennoides, N. aequalis and Aristeus antennatus). Also, at St2-St3 we found higher near-bottom turbidity (indicating particle resuspension: food for suspension feeders) and finer and more reduced (Eh) sediments. The results let us suggest that corals and accompanying fauna preferently found optimal ecological conditions in the same habitat, while habitat-forming capacity by I. elongata seemed weak to generate these conditions. Coral forests may enhance detritus accumulations around them, improving habitat conditions for benthos feeders (e.g. macrourid fish). At St3 our side-scan sonar recorded three types of tracks produced by trawler doors, which match with three identified vessels occasionally operating in the area. After this low fishing activity off the Ebro Delta since the mid-1990s, almost all colonies of I. elongata has been removed. However, this impact has hardly altered fish and invertebrate composition without any significant loss of diversity, pointing also toward a rather low capacity of I. elongata facies in forming habitat for megafauna on muddy bottoms of the Mediterranean slope. © 2013 Elsevier Ltd. Source

Miensopust M.P.,Dublin Institute for Advanced Studies | Miensopust M.P.,National University of Ireland | Jones A.G.,Dublin Institute for Advanced Studies | Muller M.R.,Dublin Institute for Advanced Studies | And 2 more authors.
Journal of Geophysical Research: Solid Earth

Within the framework of the Southern African Magnetotelluric Experiment a focused study was undertaken to gain improved knowledge of the lithospheric geometries and structures of the westerly extension of the Zimbabwe craton (ZIM) into Botswana, with the overarching aim of increasing our understanding of southern African tectonics. The area of interest is located in northeastern Botswana, where Kalahari sands cover most of the geological terranes and very little is known about lithospheric structures and thicknesses. Some of the regional-scale terrane boundary locations, defined based on potential field data, are not sufficiently accurate for local-scale studies. Investigation of the NNW-SSE orientated, 600 km long ZIM line profile crossing the Zimbabwe craton, Magondi mobile belt, and Ghanzi-Chobe belt showed that the Zimbabwe craton is characterized by thick (∼220 km) resistive lithosphere, consistent with geochemical and geothermal estimates from kimberlite samples of the nearby Orapa and Letlhakane pipes (∼175 km west of the profile). The lithospheric mantle of the Ghanzi-Chobe belt is resistive, but its lithosphere is only about 180 km thick. At crustal depths a northward dipping boundary between the Ghanzi-Chobe and the Magondi belts is identified, and two middle to lower crustal conductors are discovered in the Magondi belt. The crustal terrane boundary between the Magondi and Ghanzi-Chobe belts is found to be located further to the north, and the southwestern boundary of the Zimbabwe craton might be further to the west, than previously inferred from the regional potential field data. Copyright 2011 by the American Geophysical Union. Source

Lo Iacono C.,CSIC - Institute of Marine Sciences | Lo Iacono C.,UK National Oceanography Center | Gracia E.,CSIC - Institute of Marine Sciences | Ranero C.R.,Catalan Institution for Research and Advanced Studies | And 8 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography

A new mound field, the West Melilla mounds, interpreted as being cold-water coral mounds, has been recently unveiled along the upper slope of the Mediterranean Moroccan continental margin, a few kilometers west of the Cape Tres Forcas. This study is based on the integration of high-resolution geophysical data (swath bathymetry, parametric sub-bottom profiler), CTD casts, Acoustic Doppler Current Profiler (ADCP), ROV video and seafloor sampling, acquired during the TOPOMED GASSIS (2011) and MELCOR (2012) cruises. Up to 103 mounds organized in two main clusters have been recognized in a depth range of 299-590m, displaying a high density of 5mounds/km2. Mounds, 1-48m high above the surrounding seafloor and on average 260m wide, are actually buried by a 1-12m thick fine-grained sediment blanket. Seismic data suggest that the West Melilla mounds grew throughout the Early Pleistocene-Holocene, settling on erosive unconformities and mass movement deposits. During the last glacial-interglacial transition, the West Melilla mounds may have suffered a drastic change of the local sedimentary regime during the late Holocene and, unable to stand increasing depositional rates, were progressively buried. At the present day, temperature and salinity values on the West Melilla mounds suggest a plausible oceanographic setting, suitable for live CWCs. Nonetheless, more data is required to groundtruth the West Melilla mounds and better constrain the interplay of sedimentary and oceanographic factors during the evolution of the West Melilla mounds. © 2013 Elsevier Ltd. Source

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