Showing papers by "Thomas Mock published in 2002"
TL;DR: Regulation of photosynthesis in a mixed culture of three diatom species, which grew in chemostats at -1 degrees C, revealed that lipids are important components, required to sustain membrane structure under a deficiency of integral membrane bound proteins and pigments.
124 citations
TL;DR: Investigation of sea ice diatoms found three species coexisting in chemostats illuminated with 15 and 2 micromol photons m(-2) s(-1) caused a 50% increase in monogalactosyldiacylglycerols (MGDG) thylakoid membrane related 20:5 n-3 fatty acids and increased the ratio of MGDG:DGDG ratio.
95 citations
TL;DR: Oxygen micro-optodes were used to measure oxygen dynamics directly within the microstructure of sea ice by freezing the sensors into the ice during its formation as discussed by the authors, and the final ice thickness was 27 cm.
Abstract: Oxygen micro-optodes were used to measure oxygen dynamics directly within the microstructure of sea ice by freezing the sensors into the ice during its formation. The experiment was conducted in a 4 m 3 mesocosm filled with artificial seawater and inoculated with a unialgal culture of the common Antarctic ice diatom Fragilariopsis cylindrus (Bacillariophyceae) to a final chlorophyll a (chl a) concentration of 11 µg l -1 . Ice growth was initiated 7 d after inoculation by reducing the air temperature to -10 ± 2°C and terminated 17 d later. The final ice thickness was 27 cm. One optode was frozen into grease ice and 2 others into the skeletal layer of the growing ice sheet. Increasing oxygen concentrations during ice crystal formation at the water surface and the ice-water interface revealed a strong inclusion of oxygen, which was either physically trapped and/or the result of photosynthesising diatoms. The major portion of oxygen was present as gas bubbles due to super- saturation as a result of increasing salinity and oxygen production by diatoms. An increase in salinity due to a concurrent decrease in ice temperatures during subsequent sea ice development reduced the maximum concentration of dissolved oxygen within brine. Thus, dissolved oxygen concentrations decreased over time, whereas gaseous oxygen was released to the atmosphere and seawater. The sensors are a significant advance on more conventional microelectrodes, because the recordings can be temperature and salinity compensated in order to obtain precise measurements of oxygen dynam- ics with regard to total (dissolved and gaseous) and dissolved oxygen in sea ice. Optodes do not consume oxygen during measurement over a long period under extreme conditions, which is another advantage for long-term deployment in the field.
50 citations
TL;DR: The new device enabled some of the first precise measurements of in situ photosynthetic carbon assimilation in newly formed Antarctic sea ice, which is an important component in the sea ice ecosystem of the Antarctic Ocean.
Abstract: An in situ incubation technique used successfully to measure the photosynthetic carbon assimilation of internal algal assemblages within thick multiyear Arctic ice was developed and improved to measure the photosynthetic carbon assimilation within young sea ice only 50 cm thick (Eastern Weddell Sea, Antarctica). The light transmission was improved by the construction of a cylindrical frame instead of using a transparent acrylic-glass barrel. The new device enabled some of the first precise measurements of in situ photosynthetic carbon assimilation in newly formed Antarctic sea ice, which is an important component in the sea ice ecosystem of the Antarctic Ocean. The rates of carbon assimilation of the interior algal assemblage (top to 5 cm from bottom) was 0.25 mg C m−2 d−1 whereas the bottom algal community (lowest 5 cm) attained only 0.02 mg C m−2 d−1. Chl a specific production rates (PChl) for bottom algae (0.020 – 0.056 μg C μg chl a−1 h−1) revealed strong light limitation, whereas the interior algae (PChl = 0.7 – 1.2 μg C μg chl a−1 h−1) were probably more limited by low temperatures (< –5 °C) and high brine salinities.
34 citations
01 Nov 2002
TL;DR: In this paper, the authors review the concept of melting probes, i.e. small probes with a heated tip ("hot point"), that melt through the ice. But they do not discuss the means of exploring such an environment.
Abstract: Signatures indicative of a subglacial ocean on the Jovian satellite Europa have been discovered by the Galileo spaceprobe. The structure and chemistry of this postulated ocean, have received considerable attention, and its exploration is seen as an important goal for the fields of comparative planetology and astrobiology. Terrestrial subglacial lakes (e.g., Lake Vostok) have been considered as analogues for several aspects of a Europan ocean and the means of exploring such an environment will be discussed. We review the concept of melting probes, i.e. small probes with a heated tip ("hot point"), that melt through the ice. Such devices can carry instruments for in-situ measurements, or act as sample-return probes by the new concept of melting "upwards" once the sampling in the liquid ocean has been performed. Experience with melting probes in Antarctica exists; a demonstration mission to, e.g., Lake Vostok is proposed, and a possible design for a mission to Europa is outlined. Although, for a Europan mission, a probe capable of in-situ analysis might differ substantially from the terrestrial 'sample-return' version.
14 citations