Prochlorococcus as a Possible Source for Transparent Exopolymer Particles (TEP)

Transparent exopolymer particles (TEP), usually associated with phytoplankton blooms, promote the formation of marine aggregates. Their exportation to deep waters is considered a key component of the biological carbon pump. Here, we explored the role of solar radiation and picocyanobacteria in the formation of TEP in oligotrophic surface waters of the Atlantic and Pacific Oceans in ten on-deck incubation experiments during the Malaspina 2010 Expedition. TEP concentrations were low on the ocean’s surface although these concentrations were significantly higher on the surface of the Pacific (24.45 ± 2.3 μg XG Eq. L-1) than on the surface of the Atlantic Ocean (8.18 ± 4.56 μg XG Eq. L-1). Solar radiation induced a significant production of TEP in the on-deck experiments from the surface water of the Pacific Ocean, reaching values up to 187.3 μg XG Eq. L-1 compared with the low production observed in the dark controls. By contrast, TEP production in the Atlantic Ocean experiments was lower, and its formation was not related to the light treatments. Prochlorococcus sp. from the surface ocean was very sensitive to solar radiation and experienced a high cell decay in the Pacific Ocean experiments. TEP production in the on-deck incubation experiments was closely related to the observed cell decay rates of Prochlorococcus sp., suggesting that this picocyanobacteria genus is a potential source of TEP. The evidence to propose such potential role was derived experimentally, using natural communities including the presence of several species and a variety of processes. Laboratory experiments with cultures of a non-axenic strain of Prochlorococcus marinus were then used to test TEP production by this genus. TEP concentrations in the culture increased with increasing cell abundance during the exponential phase, reaching the highest TEP concentration at the beginning of the stationary phase. The average TEP concentration of 1474 ± 226 μg XG Eq. L-1 (mean ± SE) observed at the stationary phase of P. marinus cultures is comparable with the values reported in the literature for diatom cultures, also growing in non-axenic as well as axenic cultures. Our results identify Prochlorococcus sp. as a possible relevant source of TEP in the oligotrophic ocean.This research was funded by the Expedición Malaspina 2010 project of the CONSOLIDER program (ref. CSD2008-00077), the project Stress-X (ref. CTM2012-32603) of the Spanish Minister of Economy and Competitiveness, and King Abdullah University of Science and Technology baseline funding to SA. FI was supported by a CSIC JAE-preDOC fellowship

Patterns and drivers of UV absorbing chromophoric dissolved organic matter in the euphotic layer of the open ocean

The global distribution of chromophoric dissolved organic matter (CDOM) in the euphotic layer of the Atlantic, Indian, and Pacific oceans (between 35° N and 40° S) was analyzed by absorption spectroscopy during the Malaspina 2010 circumnavigation. Absorption coefficients at 254 nm (a254) and 325 nm (a325), indices (a254/a365) and spectral slopes (between 275 and 295 nm, S275-295) were calculated from the dissolved fraction of the UV absorption spectra to describe the amount and quality of CDOM. Generalized Additive Models (GAMs) were applied to evaluate the relevance of physical and biogeochemical drivers for the variability of CDOM. Besides the low CDOM values, a first division of our data following the Longhurst’s biogeographic classification showed significant differences in CDOM levels among provinces. The lowest values of a254 and a325 were found in the oligotrophic gyres, particularly in the Indian Ocean, and the highest in the upwelling areas, particularly in the Equatorial Pacific. Opposite distributions were obtained for S275-295 and a254/a365, indicative of higher photobleaching in the gyres. Within each province, whereas a254 was constant through the photic layer, a325 increased significantly with depth as a result of the dominance of photobleaching over biological production in the surface layer and the opposite at depth. The Pacific provinces, including the subtropical gyres, showed, however, significantly higher a325 values, indicative of lower photobleaching/higher biological production. The GAM analysis indicates that a254 and a325 were primarily related to chlorophyll a (Chl a), exhibiting a significant positive linear response. Interestingly, Prochlorococcus and Synechococcus abundances were related to these absorption coefficients. Apparent oxygen utilization also contributed to explain the distributions of these absorption coefficients, being inversely related to a254 and directly related to a325. These results are consistent with the premise that a254 could be a proxy for the concentration of dissolved organic carbon and a325 for the aromatic by-products of biological degradation. The GAM analysis also shows that a254/a365 and S275-295 exhibited inverse relationships with solar radiation, indicating that the biological production of CDOM counteracts photodegradation as solar radiation increases. In summary, whereas photobleaching dictates the vertical distribution of CDOM, Chl a explains the CDOM differences among the photic layer of the tropical and subtropical ocean provinces visited during the circumnavigationMinisterio de Economía y Competitividad | Ref. CDS2008-0007

Primary marine aerosol emissions from the Mediterranean Sea during pre-bloom and oligotrophic conditions: Correlations to seawater chlorophyll a from a mesocosm study

Allison N. Schwier et al.© Author(s) 2015. The effect of ocean acidification and changing water conditions on primary (and secondary) marine aerosol emissions is not well understood on a regional or a global scale. To investigate this effect as well as the indirect effect on aerosol that changing biogeochemical parameters can have, ∼ 52 m3 pelagic mesocosms were deployed for several weeks in the Mediterranean Sea during both winter pre-bloom and summer oligotrophic conditions and were subjected to various levels of CO2 to simulate the conditions foreseen in this region for the coming decades. After seawater sampling, primary bubble-bursting aerosol experiments were performed using a plunging water jet system to test both chemical and physical aerosol parameters (10-400 nm). Comparing results obtained during pre-bloom and oligotrophic conditions, we find the same four log-normal modal diameters (18.5 ± 0.6, 37.5 ± 1.4, 91.5 ± 2.0, 260 ± 3.2 nm) describing the aerosol size distribution during both campaigns, yet pre-bloom conditions significantly increased the number fraction of the second (Aitken) mode, with an amplitude correlated to virus-like particles, heterotrophic prokaryotes, TEPs (transparent exopolymeric particles), chlorophyll a and other pigments. Organic fractions determined from kappa closure calculations for the diameter, Dp ∼ 50 nm, were much larger during the pre-bloom period (64 %) than during the oligotrophic period (38 %), and the organic fraction decreased as the particle size increased. Combining data from both campaigns together, strong positive correlations were found between the organic fraction of the aerosol and chlorophyll a concentrations, heterotrophic and autotrophic bacteria abundance, and dissolved organic carbon (DOC) concentrations. As a consequence of the changes in the organic fraction and the size distributions between pre-bloom and oligotrophic periods, we find that the ratio of cloud condensation nuclei (CCN) to condensation nuclei (CN) slightly decreased during the pre-bloom period. The enrichment of the seawater samples with microlayer samples did not have any effect on the size distribution, organic content or the CCN activity of the generated primary aerosol. Partial pressure of CO2, pCO2, perturbations had little effect on the physical or chemical parameters of the aerosol emissions, with larger effects observed due to the differences between a pre-bloom and oligotrophic environment.This work was supported by the MISTRALS/ChArMEx project and by the EC FP7 project “Mediterranean Sea Acidification in a changing climate” (MedSeA; grant agreement 265103).Peer Reviewe

Chromophoric dissolved organic matter (cdom) in the epipelagic global ocean

Trabajo presentado en la ASLO Aquatic Science Metting, celebrada en Granada, España, del 22 al 27 de febrero de 2015Peer Reviewe

Posidonia oceanica as a Source of Chromophoric Dissolved Organic Matter for the Oligotrophic NW Mediterranean Coast

This article belongs to the Special Issue Advances in Marine Dissolved Organic Matter Dynamics.Posidonia oceanica is a well-recognized source of dissolved organic matter (DOM) derived from exudation and leaching of seagrass leaves, but little is known about its impact on the chromophoric fraction of DOM (CDOM). In this study, we monitored for two years the optical properties of CDOM in two contrasting sites in the Mallorca Coast (Balearic Islands). One site was a rocky shore free of seagrass meadows, and the second site was characterized by the accumulation of non-living seagrass material in the form of banquettes. On average, the integrated color over the 250–600 nm range was almost 6-fold higher in the beach compared with the rocky shore. Furthermore, the shapes of the CDOM spectra in the two sites were also different. A short incubation experiment suggested that the spectral differences were due to leaching from P. oceanica leaf decomposition. Furthermore, occasionally the spectra of P. oceanica was distorted by a marked absorption increase at wavelength < 265 nm, presumably related to the release of hydrogen sulfide (HS−) associated with the anaerobic decomposition of seagrass leaves within the banquettes. Our results provide the first evidence that P. oceanica is a source of CDOM to the surrounding waters.This work is a contribution to the StressX project, funded by the Spanish Ministry of Economy and Innovation (MICINN CTM2012-32603). F.I. was supported by a fellowship from the “Junta para la Ampliación de Estudios” (JAE-preDOC program 2011) from Consejo Superior de Investigaciones Científicas (CSIC)

Penetration of Ultraviolet-B Radiation in Oligotrophic Regions of the Oceans During the Malaspina 2010 Expedition

21 pages, 4 tables, 8 figures.-- This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs LicenseFew studies have investigated ultraviolet (UV) radiation in the open ocean besides its harmful effects on organisms and influence on biogeochemical processes. Here, we assessed UV attenuation, with particular focus on UV-B, across the (sub)tropical ocean during the Malaspina 2010 Circumnavigation. Vertical UV radiometer profiles together with Chl-a concentration, and UV absorption by CDOM (aCDOM(λ)) and by suspended particulate matter (ap(λ)) were measured at 117 stations. At photosynthetically active radiation (PAR) and across UV-A and UV-B wavelengths, the lowest downwelling attenuation coefficients (Kd) during the expedition were recorded in ultra-oligotrophic regions at 5°–15°S (mean Kd(305 nm): 0.129 m−1, mean Kd(313 nm): 0.107 m−1) in the Indian and South Pacific Oceans. The waters here were comparatively more transparent than at 5°–15°N (mean Kd(305 nm): 0.239 m−1, mean Kd(313 nm): 0.181 m−1) where equatorial upwelling occurs. Kd was highest near the Costa Rica Dome (Kd(313 nm): 0.226 m−1) and at the confluence of the Benguela and Agulhas currents (Kd(313 nm): 0.251 m−1). The contribution of ap(λ) toward nonwater absorption (anw(λ)) was significantly lower at 305 nm than at 313 and 320 nm, suggesting the contribution of absorption by detritus and phytoplankton particles decreases compared with that of CDOM absorption as UV-B wavelength decreases. Both aCDOM(λ) and ap(λ) at UV-B wavelengths were lowest in the Indian Ocean whereas Kd was lowest in the South Pacific. This finding emphasizes that other factors besides absorption, such as scattering by reflective phytoplankton or inorganic particles, strongly influence UV-B attenuation in open ocean watersThis study was funded by the Spanish Ministry of Economy and Competitiveness through the Malaspina 2010 Expedition project (Consolider-Ingenio 2010; MICINN CSD2008-00077). The PhD fellowship of SO was supported by the baseline funding from KAUST to S. Agustí under award number BAS/1/1072-01-01Peer reviewe

MALASPINA 2010 optical data: aCDOM_aParticles_Kd_Z10%

The dataset is comprised of: downwelling diffuse attenuation coefficients, Z10%, aCDOM and apPeer reviewe

MALASPINA 2010 optical data: aCDOM_aParticles_Kd_Z10%

The dataset is comprised of: downwelling diffuse attenuation coefficients, Z10%, aCDOM and ap.Peer reviewe

Ultraviolet radiation enhances Arctic net plankton community production

In this study we report the response of net community production (NCP) of plankton communities in the Arctic surface waters exposure to natural ultraviolet radiation (UVR) conditions. A possible bias in previous measurements performed using borosilicate glass bottles (opaque to most UVR) can underestimate NCP. Here we show that 77% of the sampled communities suffer, on average, 38.5% of net increase in NCP when exposed to natural UV-B condition, relative to values when UV-B radiation is excluded. UV-B tends to shift communities toward autotrophy, with the most autotrophic communities responding the strongest. This is likely explained by the inhibition of bacterial respiration during the continuous day period of the Arctic summer, corroborated by experiments where bacterial production influenced by UV-B directly affect NCP. Whereas Arctic warming is expected to lead to lower NCP, our results show that increased UV-B radiation may partially compensate this negative effect in surface waters. ©2014. American Geophysical Union.This research is a contribution to projects ARCTICMET and ATOS, funded by the Spanish Ministry of Economy and Competitiveness (CTM2011-15792-E and POL2006-00550/CTM, respectively), the ATP project funded by the FP-7 of the EU (CTM2009-07781-E) and the CarbonRidge project funded by the Norwegian Research Council. L.S.G.-C. was funded by a JAE-Predoc Malaspina fellowship (CSIC-FBBVA, Spain)Peer Reviewe