Impacts of passive warming chambers on soil parameters in Antarctica

Passive chambers are used to examine the impacts of summer warming in Antarctica but, so far, impacts occurring outside the growing season, or related to extreme temperatures, have not been reported, despite their potentially large biological significance. In this review, we synthesise and discuss the microclimate impacts of passive warming chambers (closed, ventilated and Open Top Chamber-OTC) commonly used in Antarctic terrestrial habitats, paying special attention to seasonal warming, during the growing season and outside, extreme temperatures and freeze-thaw events. Both temperature increases and decreases were recorded throughout the year. Closed chambers caused earlier spring soil thaw (8-28 days) while OTCs delayed soil thaw (3-13 days). Smaller closed chamber types recorded the largest temperature extremes (up to 20°C higher than ambient) and longest periods (up to 11 h) of above ambient extreme temperatures, and even OTCs had above ambient temperature extremes over up to 5 consecutive hours. The frequency of freeze-thaw events was reduced by ~25%. All chamber types experienced extreme temperature ranges that could negatively affect biological responses, while warming during winter could result in depletion of limited metabolic resources. The effects outside the growing season could be as important in driving biological responses as the mean summer warming. We make suggestions for improving season-specific warming simulations and propose that seasonal and changed temperature patterns achieved under climate manipulations should be recognised explicitly in descriptions of treatment effects.

Absolute abundances of dinoflagellate cysts in surface sediment samples from four sites: Lycopodium marker-grain method

Absolute abundances (concentrations) of dinoflagellate cysts are often determined through the addition of Lycopodium clavatum marker-grains as a spike to a sample before palynological processing. An inter-laboratory calibration exercise was set up in order to test the comparability of results obtained in different laboratories, each using its own preparation method. Each of the 23 laboratories received the same amount of homogenized splits of four Quaternary sediment samples. The samples originate from different localities and consisted of a variety of lithologies. Dinoflagellate cysts were extracted and counted, and relative and absolute abundances were calculated. The relative abundances proved to be fairly reproducible, notwithstanding a need for taxonomic calibration. By contrast, excessive loss of Lycopodium spores during sample preparation resulted in non-reproducibility of absolute abundances. Use of oxidation, KOH, warm acids, acetolysis, mesh sizes larger than 15 µm and long ultrasonication (> 1 min) must be avoided to determine reproducible absolute abundances. The results of this work therefore indicate that the dinoflagellate cyst worker should make a choice between using the proposed standard method which circumvents critical steps, adding Lycopodium tablets at the end of the preparation and using an alternative method.