Response of three krill species to hypoxia and warming: An experimental approach to oxygen minimum zones expansion in coastal ecosystems

To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZ), respiratory response and stress experiments combining hypoxia/reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current system (HCS, Chilean coast), and the Northern California Current system (NCCS, Oregon). Euphausia mucronata from the HCS shows oxyconforming or oxygen partial pressure (pO2)-dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a "high oxygen stress" for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba maintain respiration rates constant down to low critical pO2 values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had the lowest antioxidant enzyme activities, but the highest concentrations of the molecular antioxidant glutathione (GSH) and was not affected by 6 h exposure to moderate hypoxia. Temperate krill species had higher SOD (superoxide dismutase) values in winter than in summer, which relate to higher winter metabolic rate (E. pacifica). In all species, antioxidant enzyme activities remained constant during hypoxic exposure at habitat temperature. Warming by 7°C above habitat temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4°C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2°C). In this season, experimental warming by +4°C reduced antioxidant activities and the hypoxia combination again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.

Surface temperature measurements near Ny-Ålesund, Svalbard, Norway in 2008 with links to data files

The ground surface temperature is one of the key parameters that determine the thermal regime of permafrost soils in arctic regions. Due to remoteness of most permafrost areas, monitoring of the land surface temperature (LST) through remote sensing is desirable. However, suitable satellite platforms such as MODIS provide spatial resolutions, that cannot resolve the considerable small-scale heterogeneity of the surface conditions characteristic for many permafrost areas. This study investigates the spatial variability of summer surface temperatures of high-arctic tundra on Svalbard, Norway. A thermal imaging system mounted on a mast facilitates continuous monitoring of approximately 100 x 100 m of tundra with a wide variability of different surface covers and soil moisture conditions over the entire summer season from the snow melt until fall. The net radiation is found to be a control parameter for the differences in surface temperature between wet and dry areas. Under clear-sky conditions in July, the differences in surface temperature between wet and dry areas reach up to 10K. The spatial differences reduce strongly in weekly averages of the surface temperature, which are relevant for the soil temperature evolution of deeper layers. Nevertheless, a considerable variability remains, with maximum differences between wet and dry areas of 3 to 4K. Furthermore, the pattern of snow patches and snow-free areas during snow melt in July causes even greater differences of more than 10K in the weekly averages. Towards the end of the summer season, the differences in surface temperature gradually diminish. Due to the pronounced spatial variability in July, the accumulated degree-day totals of the snow-free period can differ by more than 60% throughout the study area. The terrestrial observations from the thermal imaging system are compared to measurements of the land surface temperature from the MODIS sensor. During periods with frequent clear-sky conditions and thus a high density of satellite data, weekly averages calculated from the thermal imaging system and from MODIS LST agree within less than 2K. Larger deviations occur when prolonged cloudy periods prevent satellite measurements. Futhermore, the employed MODIS L2 LST data set contains a number of strongly biased measurements, which suggest an admixing of cloud top temperatures. We conclude that a reliable gap filling procedure to moderate the impact of prolonged cloudy periods would be of high value for a future LST-based permafrost monitoring scheme. The occurrence of sustained subpixel variability of the summer surface temperature is a complicating factor, whose impact needs to be assessed further in conjunction with other spatially variable parameters such as the snow cover and soil properties.

Organic carbon, reduced sulfur, and iron in Miocene to Holocene sediments from the Oman and Beguela upwelling systems

We examined sediments from Neogene and Quaternary sections of the Benguela and Oman upwelling systems (DSDP Site 532, ODP Sites 723 and 722) to determine environmental and geochemical factors which control and limit pyrite formation in organic-carbon-rich marine sediments. Those samples from the upwelling sites, which contained low to moderate concentrations of total organic carbon (0.7%-3%), had C/S ratios typical of normal marine sediments, i.e., around 2.8. In these sediments, TOC availability probably limited pyrite formation. Results that do not conform with accepted models were found for the sediments high in TOC (3^0-12.4%). The organic matter was of marine origin and contained considerable pyrolytic hydrocarbons, a fact that we take as a sign of low degradation, yet significant concentrations of dissolved sulfate coexisted with it (> 5 mmol/L in the case of Sites 532 and 723). Detrital iron was probably not limiting in either case, because the degree of pyritization was always less than 0.65. Therefore, controls on sulfate reduction and pyrite formation in the organic matter-rich sediments do not appear to conform simply to generally accepted diagenetic models. The data from these thermally immature, old, and organic-rich marine sediments imply that (1) the total reduced sulfur content of organic-rich marine upwelling sediments rarely exceeds an approximate boundary of 1.5% by weight, (2) the C/S ratio of these sediments is not constant and usually much higher than the empirical values proposed for marine sediments. We conclude that sedimentary pyrite formation in upwelling sediments is limited by an as yet unknown factor, and that caution is advised in using C/S ratios and C vs. S diagrams in paleoenvironmental reconstructions for organic-rich sediments.

Immunomodulating effects of environmentally realistic copper concentrations in Mytilus edulis adapted to naturally low salinities, link to supplementary material

The monitoring of organisms' health conditions by the assessment of their immunocompetence may serve as an important criterion for the achievement of the Good Environmental Status (GES) as defined in the Marine Strategy Framework Directive (EU). In this context, the complex role of natural environmental stressors, e.g. salinity, and interfering or superimposing effects of anthropogenic chemicals, should be carefully considered, especially in scenarios of low to moderate contamination. Organisms from the Baltic Sea have adapted to the ambient salinity regime, however energetically costly osmoregulating processes may have an impact on the capability to respond to additional stress such as contamination. The assessment of multiple stressors, encompassing natural and anthropogenic factors, influencing an organisms' health was the main aim of the present study. Immune responses of Mytilus edulis, collected and kept at natural salinities of 12 per mil (LS) and 20 per mil (MS), respectively, were compared after short-term exposure (1, 7 and 13 days) to low copper concentrations (5, 9 and 16 µg/L Cu). A significant interaction of salinity and copper exposure was observed in copper accumulation. LS mussels accumulated markedly more copper than MS mussels. No combined effects were detected in cellular responses. Bacterial clearance was mostly achieved by phagocytosis, as revealed by a strong positive correlation between bacterial counts and phagocytic activity, which was particularly pronounced in LS mussels. MS mussels, on the other hand, seemingly accomplished bacterial clearance by employing additional humoral factors (16 µg/L Cu). The greatest separating factor in the PCA biplot between LS and MS mussels was the proportion of granulocytes and hyalinocytes while functional parameters (phagocytic activity and bacterial clearance) were hardly affected by salinity, but rather by copper exposure. In conclusion, immune responses of the blue mussel may be suitable and sensitive biomarkers for the assessment of ecosystem health in brackish waters (10-20 per mil S).