Influence of microbial community composition and metabolism on air.sea ΔpCO 2 variation off the western Antarctic Peninsula

We studied CO 2 and O 2 dynamics in the western Antarctic Peninsula (WAP) waters in relation to (1) phytoplankton biomass, (2) microbial community primary production and respiration, and (3), for the first time, phytoplankton composition, during summer and fall in 3 consecutive years (2002, 2003 and 2004). The areal average of ΔpCO 2 (the difference between surface seawater and atmospheric partial pressure of CO 2) for the 3 yr was significantly negative (.20.04 ± 44.3 μatm, p < 0.01) during the summer to fall period in the region, possibly indicating a CO 2 sink. In the southern WAP (i.e. south of Anvers Island), ΔpCO 2 was significantly negative (.43.60 ± 39.06 μatm) during fall. In the northern WAP (north of Anvers Island), ΔpCO 2 values showed a more complex distribution during summer and fall (.4.96 ± 37.6 and 21.71 ± 22.39 μatm, respectively). Chlorophyll a (chl a) concentration averaged 1.03 ± 0.25 μg l.1 and was higher in the south of the peninsula. Phytoplankton composition influenced chl a concentration with higher and lower values for diatom-and phytoflagellate-dominated communities, respectively. A significant negative correlation existed between chl a and ΔpCO 2. From incubation experiments performed in the northern WAP, respiration was low (averaging 5.1 mmol O 2 m.3 d.1), and the net community production (NCP) correlated negatively with ΔpCO 2 and positively with %O 2 saturation. However, despite the high NCP values measured, ΔpCO 2 was significantly positive in the northern WAP during the summer to fall period. Strong mixing and lower chl a concentration may explain this result. In contrast, ΔpCO 2 was significantly negative in the southern WAP, possibly because of high surface water chl a concentration.Facultad de Ciencias Naturales y Muse

Influence of microbial community composition and metabolism on air.sea ΔpCO 2 variation off the western Antarctic Peninsula

We studied CO 2 and O 2 dynamics in the western Antarctic Peninsula (WAP) waters in relation to (1) phytoplankton biomass, (2) microbial community primary production and respiration, and (3), for the first time, phytoplankton composition, during summer and fall in 3 consecutive years (2002, 2003 and 2004). The areal average of ΔpCO 2 (the difference between surface seawater and atmospheric partial pressure of CO 2) for the 3 yr was significantly negative (.20.04 ± 44.3 μatm, p < 0.01) during the summer to fall period in the region, possibly indicating a CO 2 sink. In the southern WAP (i.e. south of Anvers Island), ΔpCO 2 was significantly negative (.43.60 ± 39.06 μatm) during fall. In the northern WAP (north of Anvers Island), ΔpCO 2 values showed a more complex distribution during summer and fall (.4.96 ± 37.6 and 21.71 ± 22.39 μatm, respectively). Chlorophyll a (chl a) concentration averaged 1.03 ± 0.25 μg l.1 and was higher in the south of the peninsula. Phytoplankton composition influenced chl a concentration with higher and lower values for diatom-and phytoflagellate-dominated communities, respectively. A significant negative correlation existed between chl a and ΔpCO 2. From incubation experiments performed in the northern WAP, respiration was low (averaging 5.1 mmol O 2 m.3 d.1), and the net community production (NCP) correlated negatively with ΔpCO 2 and positively with %O 2 saturation. However, despite the high NCP values measured, ΔpCO 2 was significantly positive in the northern WAP during the summer to fall period. Strong mixing and lower chl a concentration may explain this result. In contrast, ΔpCO 2 was significantly negative in the southern WAP, possibly because of high surface water chl a concentration.Facultad de Ciencias Naturales y Muse

Complementary support for the new ecological concept of ‘bacterial independence on contemporary phytoplankton production’ in oceanic waters

International audienc

Revisited phytoplanktonic carbon dependency of heterotrophic bacteria in freshwaters, transitional, coastal and oceanic waters

International audienc

Combined effects of global warming and UVB Radiation on the composition and metabolism of the western Antarctic Peninsula microbial community (potential impact on the carbon cycle)

Le réchauffement régional de l'ouest de la Péninsule Antarctique (WAP) combiné à la diminution attendue de glace de mer et à l'apparition printanière du trou d'ozone pourrait modifier la composition et la structure de la communauté microbienne. De plus, ces variations environnementales pourraient modifier le potentiel de la WAP en tant que puits de CO2. Dans ce contexte, cette thèse visait à évaluer les effets combinés du changement climatique sur la production primaire et sur la composition et la structure de la communauté microbienne de la WAP. Cette thèse visait également à évaluer le rôle de la structure, de la composition, de la production primaire et de la respiration de la communauté microbienne sur les échanges de CO2 entre l'atmosphère et l'océan. Cette étude a premièrement permis de décrire les variations de l'étendue de glace de mer, de l'épaisseur de la couche d'ozone et de la température de surface de l'eau dans la WAP au cours des 30 dernières années (1972-2007) et notamment d'observer le retrait de plus en plus précoce de la glace de mer en relation avec le réchauffement des eaux de la WAP. L'évolution de ces paramètres environnementaux offre une nouvelle fenêtre temporelle de production primaire. Ainsi, cette étude a permis de montrer que la production primaire annuelle a augmenté de 1997 à 2007, et ceci, en relation avec l'anomalie de glace de l'hiver précédent. En effet, la production primaire journalière était négativement et positivement corrélée avec, respectivement, l'étendue de glace de mer et la température de l'eau de septembre à novembre et de février à mars, suggérant que le réchauffement régional de la WAP favorise plus de production primaire durant le printemps et l'automne. En revanche, le retrait précoce de la glace de mer en coïncidence avec l'apparition printanière du trou d'ozone a provoqué l'augmentation de la photoinhibition au printemps (avec 11,6 +- 2,8 % de la production primaire journalière en moyenne). En conséquence, le changement climatique régional de la WAP a, à la fois, un effet positif et un effet négatif sur la production primaire. Cette étude a également permis de décrire la dynamique de la communauté microbienne marine dans l'archipel de Melchior (dans la WAP) de l'automne au printemps 2006. En raison des conditions environnementales extrêmes, l'abondance et la biomasse de la communauté microbienne étaient faibles durant l'automne et l'hiver et dominées par les petites cellules (< 2 m) et donc par un réseau trophique microbien. En effet, la biomasse phytoplanctonique était faible durant l'automne et l'hiver (avec une concentration moyenne en chlorophylle a, Chl-a, de 0,3 et 0,13 g l-1, respectivement). La biomasse phytoplanctonique a augmenté au printemps (avec un maximum de Chl-a de 1,13 g l-1), mais, en dépit des conditions de croissance favorables, est restée faible et le phytoplancton était toujours dominé par de petites cellules (2-20 m) et donc par le réseau trophique microbien ou multivore. De plus, la disparition précoce de glace de mer durant le printemps 2006 a exposé les eaux de la WAP à de fortes radiations ultraviolettes B (RUVB, 280-320 nm), qui ont eu un effet négatif sur la communauté microbienne des eaux de surface. Cette étude a également mis en évidence la relation existante entre les échanges CO2 et d'O2 entre l'atmosphère et l'océan dans la WAP et la biomasse, la composition, la production primaire et la respiration de la communauté microbienne. Il existait tout d'abord une relation positive entre la concentration en Chl-a et la proportion de diatomées dans la communauté phytoplanctonique. De plus, il existait une corrélation négative significative entre la Chl-a et le pCO2. La production primaire nette de la communauté (NCP) était principalement contrôlée par la production primaire et était négativement et positivement reliée avec le pCO2 et le pourcentage de saturation de l'O2, respectivement, suggérant que la production primaire joue un rôle majeur dans les échanges de CO2 et d'O2 entre l'atmosphère et l'océan dans la WAP. Par ailleurs, le pCO2 moyen au cours des trois années étudiées était de -20,04 +- 44,3 atm, menant à un puits de CO2 potentiel durant l'été et l'automne dans la région. Le sud de la WAP était un puits potentiel de CO2 (-43,60 +- 39,06 atm) durant l'automne alors que le nord de la WAP était principalement une source potentielle de CO2 durant l'été ou l'automne (-4,96 +- 37,6 et 21,71 +- 22,39 atm, respectivement). Les plus fortes concentrations en Chl-a mesurées dans le sud de la WAP pourraient expliquer cette distribution spatiale.Regional warming in the western Antarctic Peninsula (WAP), along with the expected decrease in sea-ice cover and the seasonal ozone layer breakdown could modify the composition and the structure of the microbial community. In addition, these environmental changes could modify the potential of the WAP as a CO2 sink. In this context, this thesis aimed at evaluating the combined effects of regional climatic changes on the primary production and the composition and structure of the microbial community in the WAP. In a second time, this thesis aimed at evaluating the role of the microbial community structure, composition, primary production and respiration on air-sea CO2 gas exchanges.First, the variations in sea-ice cover, stratospheric ozone layer thickness and sea surface temperature over the last 30 years (1972-2007) were described. Related to the warming of WAP waters, the retreat of sea-ice was happening earlier each decade in the WAP. The observed changes in these environmental parameters offer a new temporal window for primary production. Indeed, the annual primary production increased from 1997 to 2007, in relation with the sea-ice cover anomaly for the previous winter. In addition, daily primary production was negatively and positively correlated to, respectively, sea-ice cover and sea-water temperature from September to November and from February to March, suggesting that regional warming favoured more primary production during spring and fall. On the contrary, the early retreat of sea-ice in spring, in coincidence with the spring ozone layer breakdown, led to an increase in photoinhibition (with an average of 11.6 +- 2.8 % of the daily primary production being photoinhibited). Therefore, regional climatic changes in the WAP had both a positive and a negative impact on primary production.The microbial community variability was also described in the Melchior Archipelago (in the WAP) from fall to spring 2006. Because of the extreme environmental conditions, the microbial community abundance and biomass were low in fall and winter and the community was dominated by small cells (< 2 m), hence by a microbial food-web. Indeed, phytoplanktonic biomass was low during fall and winter (with respective chlorophyll a concentration, Chl-a, of 0.3 and 0.13 g l-1). Phytoplankton biomass increased in spring (with a maximum Chl-a of 1.13 g l-1) but, despite favourable growth conditions, phytoplankton was still dominated by small cells (2-20 m), hence by a microbial or multivorous food-web. In addition, the early retreat of sea-ice in the spring 2006 exposed the WAP waters to strong ultraviolet B radiations (UVBR, 280-320 nm) that had a negative impact on the microbial community in surface waters.Finally, the relationship between air-sea CO2 and O2 exchanges in the WAP with the phytoplankton community biomass and composition and with the microbial community primary production and respiration was described. A positive relationship existed between Chl-a and the proportion of diatoms in the phytoplankton community. In addition, a negative relationship existed between Chl-a and pCO2. The net community production (NCP) was mainly controlled by primary production and was negatively and positively related to pCO2 and the %O2 saturation, respectively, suggesting that primary production was the main driver of air-sea CO2 and O2 gas exchanges in the WAP. In addition, the average pCO2 for the summers and falls 2002 to 2004 was -20.04 +- 44.3 atm, leading to a potential CO2 sink during this period in the WAP. The southern WAP was a potential CO2 sink (-43.60 +- 39.06 atm) during fall while the northern part of the Peninsula was mainly a potential CO2 source during summer and fall (-4.96 +- 37.6 and 21.71 +- 22.39 atm, respectively). The higher Chl-a concentrations measured in the southern WAP may explain this spatial distribution.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

High-Frequency physical, biogeochemical and meteorological data of Coastal Mediterranean Thau Lagoon Observatory. SEANOE. https://doi.org/10.17882/58280

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Functional Stability of a Coastal Mediterranean Plankton Community During an Experimental Marine Heatwave

WOS:000760642700001International audienceAs heatwaves are expected to increase in frequency and intensity in the Mediterranean Sea due to global warming, we conducted an in situ mesocosm experiment for 20 days during the late spring and early summer of 2019 in a coastal Mediterranean lagoon to investigate the effects of heatwaves on the composition and function of coastal plankton communities. A heatwave was simulated by elevating the water temperature of three mesocosms to +3 degrees C while three control mesocosms had natural lagoon water temperature, for 10 days. Further, the heating procedure was halted for 10 days to study the resilience and recovery of the system. Automated high frequency monitoring of dissolved oxygen concentration and saturation, chlorophyll-a fluorescence, photosynthetic active radiation, salinity, and water temperature was completed with manual sampling for nutrient and phytoplankton pigment analyses. High-frequency data were used to estimate different functional processes: gross primary production (GPP), community respiration (R), and phytoplankton growth (mu), and loss (l) rates. Ecosystem stability was assessed by calculating resistance, resilience, recovery, and temporal stability in terms of the key functions (GPP, R, mu, and l). Meanwhile, the composition of phytoplankton functional types (PFT) was assessed through chemotaxonomic pigment composition. During the heatwave, GPP, R, mu, and l increased by 31, 49, 16, and 21%, respectively, compared to the control treatment. These positive effects persisted several days after the offset of the heatwave, resulting in low resilience in these key functions. However, GPP and R recovered almost completely at the end of the experiment, suggesting that the effect of the heatwave on these two rates was reversible. The heatwave also affected the PFT composition, as diatoms, prymnesiophytes, and cyanobacteria were favored, whereas dinoflagellates were negatively affected. By highlighting important effects of a simulated marine heatwave on the metabolism and functioning of a coastal Mediterranean plankton community, this study points out the importance to extend this type of experiments to different sites and conditions to improve our understanding of the impacts of this climate-change related stressor that will grow in frequency and intensity in the future

Rassoulzadegan in Villefranche-sur-Mer and the 'evolution' of marine microbial ecology over the last three decades

International audienc

Functional and structural responses of plankton communities toward consecutive experimental heatwaves in Mediterranean coastal waters

The frequency of marine heatwaves (HWs) is projected to increase in the Mediterranean Sea over the next decades. An in situ mesocosm experiment was performed in a Mediterranean lagoon for 33 days. Three mesocosms were used as controls following the natural temperature of the lagoon. In three others, two HWs of + 5 °C compared to the controls were applied from experimental day (d) 1 to d5 (HW1) and from d11 to d15 (HW2). High-frequency data of oxygen, chlorophyll-a (chl-a), temperature, salinity and light from sensors immersed in all mesocosms were used to calculate gross primary production (GPP), respiration (R) and phytoplankton growth (µ) and loss (L) rates. Nutrients and phytoplankton community structure from pigments were also analyzed. HW1 significantly increased GPP, R, chl-a, µ and L by 7 to 38%. HW2 shifted the system toward heterotrophy by only enhancing R. Thus, the effects of the first HW resulted in the attenuation of those of a second HW on phytoplankton processes, but not on community respiration, which was strongly regulated by temperature. In addition, natural phytoplankton succession from diatoms to haptophytes was altered by both HWs as cyanobacteria and chlorophytes were favored at the expense of haptophytes. These results indicate that HWs have pronounced effects on Mediterranean plankton communities