Ostracod distribution in Ulungur Lake (Xinjiang, China) and a reassessed Holocene record

Abstract

Ostracod shells in surface sediments from Ulungur Lake (Xinjiang, China) belong mainly to Limnocythere inopinata as the dominant species, and Candona neglecta and Darwinula stevensoni as accompanying, less abundant taxa. Shells of an additional nine species were recorded only sporadically. The three most abundant ostracods have wide tolerance ranges in terms of salinity, substrate and water depth. The similarly recorded bivalve Pisidium subtruncatum, and the gastropods Gyraulus chinensis and Radix auricularia belong to the most tolerant representatives of the genera. The bivalve and gastropods, in addition to the ostracod assemblage, reflect the fact that Ulungur Lake has experienced strong lake level and salinity variations due to water withdrawal in the catchment and the counteracting diversion of river waters to the lake in recent decades. The substrate in Ulungur Lake is typically finegrained, apart from the delta region of the Ulungur River channel, which is marked by relatively coarsegrained detrital sediments barren of ostracod shells. This channel was created 40 years ago to divert water to Ulungur Lake and support its local fisheries and recreational facilities. A reassessed Holocene ostracod record from the lake shows that a significantly higher salinity and lower lake level existed in the early Holocene before 6.0 ka in response to the regional climate. In contrast, a higher lake level and lowest salinity is inferred for the late Holocene period between ca. 3.6 and 1.3 ka before present. Afterwards, the lake level declined and salinity increased in response to regional moisture reduction, although conditions similar to the early Holocene lake status were not re-established. Our surface-sedimentderived data provide a baseline for analysis of future environmental variations due to global climate change and regional water management.

TheIlyocyprispuzzle: A multidisciplinary approach to the study of phenotypic variability

“…Since then many authors have analyzed the marginal ripplets on the inner lamella of the left valve but not always they seem to resemble the pattern illustrated by Janz () (Anadón et al, ; Mischke and Zhang, ) or they respect it partially, giving rise to several subtypes within the same population (Mischke et al, ). In studies on the quaternary lacustrine and fluvio‐lacustrine deposits, the marginal ripplets and the surface ornamentation have sometimes been successfully used to distinguish between different Ilyocypris species (Wrozyna et al, ; Lord et al, ; Mischke and Zhang, ; Mischke et al, , ). In some cases, however, the simultaneous use of the two diagnostic criteria led to controversial species attribution and eventually to a supra‐specific identification (Gliozzi and Mazzini, ; Anadón et al, ; Van der Meeren et al, ).…”

“…In his investigation, the marginal ripplets seem to have a constant pattern within the same species. Since then many authors have analyzed the marginal ripplets on the inner lamella of the left valve but not always they seem to resemble the pattern illustrated by Janz (1994) (Anadón et al, 2012;Mischke and Zhang, 2010) or they respect it partially, giving rise to several subtypes within the same population (Mischke et al, 2014). In studies on the quaternary lacustrine and fluvio-lacustrine deposits, the marginal ripplets and the surface ornamentation have sometimes been successfully used to distinguish between different Ilyocypris species (Wrozyna et al, 2009;Lord et al, 2011;Mischke and Zhang, 2010;Mischke et al, 2012Mischke et al, , 2014.…”

Late Pleistocene to Holocene climate and limnological changes at Lake Karakul (Pamir Mountains, Tajikistan)

“…The study by Ricketts et al (2001) suggests increased biological productivity at Lake Issyk-Kul during the second half of the Holocene, after the shift to a closed system, corresponding to our findings from Lake Karakul for the last 6.7 cal kyr BP. A trend towards cooler conditions from about 3.5 to 1.9 cal kyr BP is reported for Lake Karakul by Mischke et al (2010) and Taft et al (2014), who investigated the last 4.2 kyr BP at high resolution. Low TOC values and low Fe/Mn ratios in core KK12-1 support these assumptions, implying decreased bioproductivity and increased mixing and ventilation of the lake floor.…”

“…A relatively stable high lake level with sufficient inflow prevailed at Lake Issyk-Kul until 6.9 cal kyr BP, coinciding with our findings for the early and mid-Holocene. On the other hand, Lake Ulungur experienced low lake levels between 10 and 6 cal kyr BP with a minimum around 7.6 cal kyr BP (Mischke and Zhang, 2010), while Boston Lake did not exist before approx. 8 kyr BP (Wünnemann et al, 2006;Huang et al, 2009).…”

Temporally changing drivers for late-Holocene vegetation changes on the northern Tibetan Plateau

“…The lake's internal variables, such as TIC content, show the highest levels of correlation with pollen assemblages. Since aragonite dominates the carbonate minerals of Lake Kusai and possibly has a biogenic origin (e.g., from ostracod shells) (Wang, 2008;Yao et al, 2011), the decreasing TIC content may relate to unfavourable living conditions for ostracods such as high salinity levels in the lake-water, as has been reported for Lake Ulungur in northern China since 1200 cal a BP (Jiang et al, 2008;Mischke and Zhang, 2011).…”