Environmental Factors Controlling Ostracod Distribution on the Tibetan Plateau and Adjacent Areas

Abstract:

Non-marine ostracods represent a reliable tool to reconstruct past climate conditions. The investigation of environmental tolerances of modern ostracod species is therefore vital to estimate past climate conditions based on fossil assemblages. To determine the climate range of individual ostracod species their modern geographical distribution is combined with climate data sets. The overlap of modern ecological tolerances of ostracod species found in a fossil assemblage yield information about past air temperatures [1].

In our study we establish ecological tolerances of species from the Tibetan Plateau and adjacent areas and indicate which environmental parameter is most important for species distribution. Therefore the point biserial correlation coefficient is applied on the species distribution of 34 taxa from 364 locations based on the presence/absence of species. We use a 0.93 km gridded climate database that pairs climate parameters with modern collection sites. In total we investigated the influence of 20 different environmental parameters, such as annual temperature amplitude, July and January temperatures, precipitation, salinity and altitude. The yearly temperature range is the most important factor defining the distribution for Candona candida and Fabaeformiscandona gyirongensis. The distribution of Eucypris mareotica is also influenced by the yearly temperature range, but in addition is restricted by low salinities. Species showing no correlation to temperature variations in their distribution were also identified. The distribution of Limnocythere inopinata and Heterocypris salina is restricted by the amount of precipitation, especially during winter months, and low salinities. On the other hand, Candona neglectaseems to be unaffected by any of the studied parameters and probably only is limited by extremely high salinities. The calculated mutual climate ranges of the investigated ostracod species will be applied to ostracod assemblage data from a long sediment sequence of Lake Nam Co, southern Tibetan Plateau, to estimate past air temperatures and allow for the reconstruction of climate variability.

References: [1] Horne, D., 2007. A Mutual Temperature Range method for Quaternary palaeoclimatic analysis using European nonmarine Ostracoda. Quat. Sci. Rev. 26, 1398-1415.