Anthropogenic climate change is projected to exacerbate midlatitude aridity. Here, we analyze newly developed multi‐century tree‐ring records for a long‐term perspective on drought in Tunisia and Algeria. We use a new set of 13 Cedrus atlantica and Pinus halepensis chronologies with a strong signal for warm‐season drought (May–August) to generate a robust, well‐validated reconstruction of the Palmer Drought Severity Index (PDSI) for the period AD 1456–2002. Key features of the reconstruction reveal the magnitude of pre‐instrumental droughts from the historic record. Remarkably, the most recent drought (1999–2002) appears to be the worst since at least the middle of the 15th century. This drought is consistent with the early signature of a transition to more arid midlatitude conditions, as projected by general circulation models.
The present study examines how climatic conditions and pond design affect the growth performance of microalgae. From January to April of 2011, outdoor batch cultures ofNannochloropsis salinawere grown in three replicate 780 L conventional raceways, as well as in an experimental 7500 L algae raceway integrated design (ARID) pond. The ARID culture system utilizes a series of 8–20 cm deep basins and a 1.5 m deep canal to enhance light exposure and mitigate temperature variations and extremes. The ARID culture reached the stationary phase 27 days earlier than the conventional raceways, which can be attributed to its superior temperature management and shallower basins. On a night when the air temperature dropped to −9°C, the water temperature was 18°C higher in the ARID pond than in the conventional raceways. Lipid and fatty acid content ranged from 16 to 25% and from 5 to15%, respectively, as a percentage of AFDW. Palmitic, palmitoleic, and eicosapentaenoic acids comprised the majority of fatty acids. While the ARID culture system achieved nearly double the volumetric productivity relative to the conventional raceways (0.023 versus 0.013 g L−1day−1), areal biomass productivities were of similar magnitude in both pond systems (3.47 versus 3.34 g m−2day−1), suggesting that the ARID pond design has to be further optimized, most likely by increasing the culture depth or operating at higher cell densities while maintaining adequate mixing.
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