The role of phytoplankton composition and microbial community metabolism in sea-air Delta pCO₂ variation in the Weddell Sea

The Weddell Sea is known to be a CO2 sink due to active biological and physical pumps. Here we study the relationships of phytoplankton biomass and composition and microbial community metabolism, estimated from simulated in situ incubations and from nutrient's difference between surface and subsurface waters, with ?pCO2 in the Weddell Sea, during four austral summers (2002–2005). The ?pCO2 was significantly negative throughout the Weddell Sea in 2002 (-17.2±28.1 µatm), 2003 (-64.1±31.3 µatm), 2004 (-54.9±61.8 µatm) and 2005 (-63.8±60 µatm), indicating that the Weddell Sea acted as an atmospheric CO2 sink during those summers. The ?pCO2 was significantly lower in the south than in the center or north of the Weddell Sea. This was consistent with the significantly higher Chlorophyll-a concentrations (Chl-a) observed in the south (2.3±1.9 µg l-1) than in the center (1.3±1.2 µg l-1) or north (1.4±1.7 µg l-1). In contrast, waters were mainly undersaturated in O2, due to the upwelling of oxygen poor Warm Deep Water (WDW). The negative relationship between the ?pCO2 and the %O2 saturation suggested that planktonic metabolic activities played a role in these gases dynamics, along with the upwelling of WDW. However, these relationships could not be observed from the results of the incubation experiments, probably because of different temporal scales between gas exchanges in incubation experiments and in situ CO2 and O2 dynamics. The dynamics of CO2 and O2 were solely related to the net community production (NCP) and to the gross primary production (GPP) when only stations with Chl-a > 1 µg l-1 were considered. A significant relationship was, however, found between ?pCO2 and the primary production until the time of sampling for all stations when estimated from nutrients depletion between surface and subsurface waters. Finally, the distribution of CO2 and O2 were related to the biomass of diatoms and, contrarily to other seas, to the biomass of phytoflagellates

Effects of enhanced temperature and ultraviolet B radiation on a natural plankton community of the Beagle Channel (Southern Argentina): A mesocosm study

Marine planktonic communities can be affected by increased temperatures associated with global climate change, as well as by increased ultraviolet B radiation (UVBR, 280-320 nm) through stratospheric ozone layer thinning. We studied individual and combined effects of increased temperature and UVBR on the plankton community of the Beagle Channel, southern Patagonia, Argentina. Eight 2 m3 mesocosms were exposed to 4 treatments (with 2 replicates) during 10 d: (1) control (natural temperature and UVBR), (2) increased UVBR (simulating a 60% decrease in stratospheric ozone layer thickness), (3) increased temperature (+ 3°C), and (4) simultaneous increased temperature and UVBR (60% decrease in stratospheric ozone; + 3°C). Two distinct situations were observed with regard to phytoplankton biomass: bloom (Days 1-4) and post-bloom (Days 5-9). Significant decreases in micro-sized diatoms (>20 µm), bacteria, chlorophyll a, and particulate organic carbon concentrations were observed during the post-bloom in the enhanced temperature treatments relative to natural temperature, accompanied by significant increases in nanophytoplankton (10-20 µm, mainly prymnesiophytes). The decrease in micro-sized diatoms in the high temperature treatment may have been caused by a physiological effect of warming, although we do not have activity measurements to support this hypothesis. Prymnesiophytes benefited from micro-sized diatom reduction in their competition for resources. The bacterial decrease under warming may have been due to a change in the dissolved organic matter release caused by the observed change in phytoplankton composition. Overall, the rise in temperature affected the structure and total biomass of the communities, while no major effect of UVBR was observed on the plankton community

On the phytoplankton bloom in coastal waters of southern King George Island (Antarctica) in January 2010: An exceptional feature?

Since the early 1990s, phytoplankton has been studied and monitored in Potter Cove (PC) and Admiralty Bay (AB), King George/25 de Mayo Island (KGI), South Shetlands. Phytoplankton biomass is typically low compared to other Antarctic shelf environments, with average spring–summer values below 1 mg chlorophyll a (Chl a) m23. The physical conditions in the area (reduced irradiance induced by particles originated from the land, intense winds) limit the coastal productivity at KGI, as a result of shallow Sverdrup’s critical depths (Zc) and large turbulent mixing depths (Zt). In January 2010 a large phytoplankton bloom with a maximum of around 20 mg Chl a m23, and monthly averages of 4 (PC) and 6 (AB) mg Chl a m23, was observed in the area, making it by far the largest recorded bloom over the last 20 yr. Dominant phytoplankton species were the typical bloom-forming diatoms that are usually found in the western Antarctic Peninsula area. Anomalously cold air temperature and dominant winds from the eastern sector seem to explain adequate light : mixing environment. Local physical conditions were analyzed by means of the relationship between Zc and Zt, and conditions were found adequate for allowing phytoplankton development. However, a multiyear analysis indicates that these conditions may be necessary but not sufficient to guarantee phytoplankton accumulation. The relation between maximum Chl a values and air temperature suggests that bottom-up control would render such large blooms even less frequent in KGI under the warmer climate expected in the area during the second half of the present century

A review and meta-analysis of the impact of intestinal worms on child growth and nutrition

More than a half of the world's population are infected with one or more species of intestinal worms of which the nematodes Ascaris lumbricoides, Trichuris trichiura and the hookworms are the most common and important in terms of child health. This paper: (1) introduces the main species of intestinal worms with particular attention to intestinal nematodes; (2) examines how such worms may affect child growth and nutrition; (3) reviews the biological and epidemiological factors that influence the effects that worms can have on the growth and nutrition of children; (4) considers the many factors that can affect the impact of treatment with anthelmintic drugs; (5) presents the results of a meta-analysis of studies of the effect of treating worm infections on child growth and nutrition; (6) discusses the results in terms of what is reasonable to expect that deworming alone can achieve; (7) describes some important characteristics of an ideal study of the effects of deworming; and (8) comments on the implications for programmes of recommendations concerning mass deworming