Mesoscale eddies: Hotspots of prokaryotic activity and differential community structure in the ocean

[EN] To investigate the effects of mesoscale eddies on prokaryotic assemblage structure and activity, we sampled two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) in the permanent eddy-field downstream the Canary Islands. The eddy stations were compared with two far-field (FF) stations located also in the Canary Current, but outside the influence of the eddy field. The distribution of prokaryotic abundance (PA), bulk prokaryotic heterotrophic activity (PHA), various indicators of single-cell activity (such as nucleic acid content, proportion of live cells, and fraction of cells actively incorporating leucine), as well as bacterial and archaeal community structure were determined from the surface to 2000m depth. In the upper epipelagic layer (0?200 m), the effect of eddies on the prokaryotic community was more apparent, as indicated by the higher PA, PHA, fraction of living cells, and percentage of active cells incorporating leucine within eddies than at FF stations. Prokaryotic community composition differed also between eddy and FF stations in the epipelagic layer. In the mesopelagic layer (200?1000 m), there were also significant differences in PA and PHA between eddy and FF stations, although in general, there were no clear differences in community composition or single-cell activity. The effects on prokaryotic activity and community structure were stronger in AE than CE, decreasing with depth in both types of eddies. Overall, both types of eddies show distinct community compositions (as compared with FF in the epipelagic), and represent oceanic ?hotspots? of prokaryotic activity (in the epi- and mesopelagic realms).

Carbon flux, nutrient retention efficiency and the curvature of respiration depth-profiles in the ocean water column

Trabajo realizado por: Packard, T. T., Osma, N., Fernández Urruzola, I., Gómez, M

Role of slowly settling particles in the ocean carbon cycle

[EN] Here we present results from sediment traps that separate particles as a function of their settling velocity, which were moored in the Canary Current region over a 1.5-year period. This study represents the longest time series using “in situ” particle settling velocity traps to date and are unique in providing year-round estimates. We find that, at least during half of the year in subtropical waters (the largest ocean domain), more than 60% of total particulate organic carbon is contained in slowly settling particles (0.7–11 m d−1). Analyses of organic biomarkers reveal that these particles have the same degradation state, or are even fresher than rapidly sinking particles. Thus, if slowly settling particles dominate the exportable carbon pool, most organic matter would be respired in surface waters, acting as a biological source of CO2 susceptible to exchange with the atmosphere. In the context of climate change, if the predicted changes in phytoplankton community structure occur, slowly settling particles would be favored, affecting the strength of the biological pump in the ocean.

Regional and temporal variability of sinking organic matter in the subtropical northeast Atlantic Ocean: a biomarker diagnosis

Sinking particles through the pelagic ocean have been traditionally considered the most important vehicle by which the biological pump sequesters carbon in the ocean interior. Nevertheless, regional scale variability in particle flux is a major outstanding issue in oceanography. 5 Here, we have studied the regional and temporal variability of total particulate organic matter fluxes, as well as chloropigment and total hydrolyzed amino acid (THAA) compositions and fluxes in the Canary Current region, between 20–30 N, during two contrasting periods: August 2006, characterized by warm and stratified waters, but also intense winds which enhanced eddy development south of the Canary Islands, 10 and February 2007, characterized by colder waters, less stratification and higher productivity. We found that the eddy-field generated south of the Canary Islands enhanced by >2 times particulate organic carbon (POC) export with respect to stations (FF; farfield) outside the eddy-field influence. We also observed flux increases of one order of magnitude in chloropigment and 70% in THAA in the eddy-field relative to FF stations. 15 Principal Components Analysis (PCA) was performed to assess changes in particulate organic matter composition between stations. At eddy-field stations, higher chlorophyll enrichment reflected “fresher” material, while at FF stations a higher proportion of pheophytin indicated greater degradation due to microbes and microzooplankton. PCA also suggests that phytoplankton community structure, particularly the dominance of 20 diatoms versus carbonate-rich plankton, is the major factor influencing the POC export within the eddy field. In February, POC export fluxes were the highest ever reported for this area, reaching values of 15 mmolCm−2 d−1 at 200m depth. Compositional changes in pigments and THAA indicate that the source of sinking particles varies zonally and meridionally and suggest that sinking particles were more degraded at 25 near-coastal stations relative to open ocean stations.

Daily ration and feeding chronology of dominant diel vertical migrant fishes in the Subtropical Eastern North Atlantic Ocean

[EN] Diel Vertical Migrants (DVMs) are mainly zooplankton and micronekton which migrate upward from 400-500 m depth every night to feed on the productive epipelagic zone, coming back at dawn to the mesopelagic zone, where they defecate, excrete, and respire the ingested carbon. DVMs should contribute to the biological pump in the ocean and, accordingly, to the global CO2 balance. Although those migrants are mainly small fishes, cephalopods and crustaceans, the lanternfishes (myctophidae) usually contribute up to 80% of total DVMs biomass. Thus, myctophids may represent a pathway accounting for a substantial export of organic carbon to the deep ocean. However, the magnitude of this transport is still poorly known. In order to assess this active flux of carbon, we performed a preliminary study of mesopelagic organisms around the Canary Islands. Here we present the results of diet, daily rations and feeding chronology of Lobianchia dofleini, Hygophum hygomii and Ceratoscopelus maderensis, 3 dominant species of myctophids performing diel vertical migrations in the Subtropical Eastern North Atlantic Ocean. Samples were obtained on board the RV La Bocaina during June 2009. Myctophids were sorted and fixed in 4% buffered formalin and the stomach contents of target species were examined and weighted. Feeding chronology was approached by studying stomach fullness and state of digestion of prey items in individuals from hauls performed at different times and depths. Our results provide further information about lanternfishes feeding ecology in relation to their vertical migration patterns as well as their contribution to the biological carbon pump.

Labile Fe(II) concentrations in the Atlantic sector of the Southern Ocean along a transect from the subtropical domain to the Weddell Sea Gyre

[EN]Labile Fe(II) distributions were investigated in the Sub-Tropical South Atlantic and the Southern Ocean during the BONUS-GoodHope cruise from 34 to 57_ S (February? March 2008). Concentrations ranged from below the detection limit (0.009 nM) to values as high 5 as 0.125 nM. In the surface mixed layer, labile Fe(II) concentrations were always higher than the detection limit, with values higher than 0.060nM south of 47_ S, representing between 39% and 63% of dissolved Fe (DFe). Biological production was evidenced. At intermediate depth, local maxima were observed, with the highest values in the Sub-Tropical domain at around 200 m, and represented more than 70% of DFe. Remineralization processes were likely responsible for those sub-surface maxima. Below 1500 m, concentrations were close to or below the detection limit, except at two stations (at the vicinity of the Agulhas ridge and in the north of the Weddell Sea Gyre) where values remained as high as _0.030?0.050 nM. Hydrothermal or sediment inputs may provide Fe(II) to these deep waters. Fe(II) half life times (t1/2) at 4 _C were measured in the upper and deep waters and ranged from 2.9 to 11.3min, and from 10.0 to 72.3 min, respectively. Measured values compared quite well in the upper waters with theoretical values from two published models, but not in the deep waters. This may be due to the lack of knowledge for some parameters in the models and/or to organic complexation of Fe(II) that impact its oxidation rates. This study helped to considerably increase the Fe(II) data set in the Ocean and to better understand the Fe redox cycle.

Regional and temporal variability of sinking organic matter in the subtropical northeast Atlantic Ocean: A biomarker diagnosis

[EN] Sinking particles through the pelagic ocean have been traditionally considered the most important vehicle by which the biological pump sequesters carbon in the ocean interior. Nevertheless, regional scale variability in particle flux is a major outstanding issue in oceanography. Here, we have studied the regional and temporal variability of total particulate organic matter fluxes, as well as chloropigment and total hydrolyzed amino acid (THAA) compositions and fluxes in the Canary Current region, between 20?30_ N, during two contrasting periods: August 2006, characterized by warm and stratified waters, but also intense winds which enhanced eddy development south of the Canary Islands, and February 2007, characterized by colder waters, less stratification and higher productivity. We found that the eddyfield generated south of the Canary Islands enhanced by >2 times particulate organic carbon (POC) export with respect to stations (FF; far-field) outside the eddy-field influence. We also observed flux increases of one order of magnitude in chloropigment and 2 times in THAA in the eddy-field relative to FF stations. Principal Components Analysis (PCA) was performed to assess changes in particulate organic matter composition between stations. At eddy-field stations, higher chlorophyll enrichment reflected ?fresher? material, while at FF stations a higher proportion of pheophytin indicated greater degradation due to microbes and microzooplankton. PCA also suggests that phytoplankton community structure, particularly the dominance of diatoms versus carbonate-rich plankton, is the major factor influencing the POC export within the eddy field. In February, POC export POC export within the eddy field. In February, POC export fluxes were the highest ever reported for this area, reaching values of _15 mmolCm?2 d?1 at 200m depth. Compositional changes in pigments and THAA indicate that the source of sinking particles varies zonally and meridionally and suggest that sinking particles were more degraded at near-coastal stations relative to open ocean stations.

Regional differences in modelled net production and shallow remineralization in the North Atlantic subtropical gyre

[EN] We used 5-yr concomitant data of tracer distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection, and then compute net production and shallow remineralization rates for both sites. Our main goal was to verify if differences in these rates are consistent with the lower export rates of particulate organic carbon observed at ESTOC. Net production rates computed below the mixed layer to 110m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34±0.79 molO2 m?2, ?1.73±0.52 molCm?2 and ?125±36 mmolNm?2) were slightly higher for oxygen and carbon compared to ESTOC (1.03±0.62 molO2 m?2, ?1.42±0.30 molCm?2 and ?213±56 mmolNm?2), although the differences were not statistically significant. Shallow remineralization rates between 110 and 250m computed at ESTOC (?3.9±1.0 molO2 m?2, 1.53±0.43 molCm?2 and 38±155 mmolNm?2) were statistically higher for oxygen compared to BATS (?1.81±0.37 molO2 m?2, 1.52± 0.30 molCm?2 and 147±43 mmolNm?2). The lateral advective flux divergence of tracers, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. According to these results, the differences in net production and shallow remineralization cannot fully explain the differences in the flux of sinking organic matter observed between both stations, suggesting an additional consumption of nonsinking organic matter at ESTOC.

B-vitamins : past, present and future in the study of the coenzymes that built and maintain a habitable planet

Trabajo realizado por Sergio Sañudo-Wilhelmy, Danielle Monteverde and Laura Gomez-Consarnau

Estimating the contribution of terrestrial organic matter in the South-Western margin of Baja California during the late Holocene

Universidad de Las Palmas de Gran Canaria. Facultad de Ciencias del Mar. Trabajo Fin de Título para la obtención del Graduado en Ciencias del Mar, 2013-2014

A preview of the ocean acidification’s impact on potential respiratory activity

[EN]The increase in the anthropogenic CO2 released to the atmosphere, induces an increase in the dissolved CO2 in the ocean, causing elevated pCO2 values and a pH decrease. Due to the increasing atmospheric CO2, several on-going research programs are evaluating the impact of acidification on marine organisms, intent to predict their future. In this mesocosm experiment (KOSMOS 14GC), we assessed the effect of different CO2 concentrations on metabolism in microplankton (0.7-50μm size) and in biogenic particles harvested by sediment traps.