| Otoliths are biogenic carbonate minerals controlling hearing and balance inteleost fish, whose microchemistry has been used to trace fish’s migration pathwaysand water environmental change. The otoliths of modern naked carp and ancientnaked carp excavated near the Bird Island offshore Lake Qinghai are the objects of inthis research. The microchemistry of modern and ancient otoliths were analyzed andcompared, in order to reveal the migration pathways of the naked carp, and to addresshow the water chemistry changes in Lake Qinghai in future.Otolith microchemistry of the modern naked carp was obtained by LA–ICP–MS.The results indicated that both of Li/Ca and B/Ca are basically consist with Sr/Ca as aresult of their similar geochemical behavior, such that both Li/Ca and B/Ca can beused to trace the migratory behavior of naked carp as Sr/Ca. As nutrition elements, Na,K, and P are controlled by the physiological function of fish, so Na/Ca, K/Ca, P/Caare not suitable for tracing migration behavior of fish. The Mg/Ca and Ba/Ca could beaffected by both water environmental change and physiological function of fish, sothat to a certain extent they can be used likely to trace fish’s migration as well. Thetemporal variation of Fe/Ca and Mn/Ca keep basically consistent.Furthermore, the δ18O and87Sr/88 Sr of the modern otolith zones were analyzed bySHRIMP Ⅱ and LA–MC–ICP–MS, respectively. The otolith incremental zones arecharacterized by lower δ18O which recorded the fish’s migration to ambient riversduring spring and summer. Combined δ18O with the 87Sr/88 Sr, the O – Sr isotopecomposition of the otoliths undoubtly indicated that the majority naked carps are morelikely to migrate and spawn in a fix river.The AMS–14C dating results of ancient fishbones and otoliths indicated that theseancient naked carps lived from 680 to 300 years ago, and the OSL ages of the overlainsediments were dated to about 230 to 420 calendar years. The well agreementbetween two independent datings confirms that these ancient naked carp lived in arelict lake across the Ming Dynasty.The microchemistry of ancient otoliths were compared with those of modernotoliths, the results show(1) that the δ18O of the ancient otoliths(1.76 ± 1.03 ‰) aresignificantly higher than those of the modern ones(–4.82 ± 0.96 ‰) by about 6‰.This can be attributed to the 18 O enrichment in the relict lake which experiencedstrong evaporation(low P/E) and authigenic carbonate precipitation. In constrast, theδ13C of the ancient otoliths(–10.06 ± 0.41 ‰) were significantly lower than those ofthe modern ones(–4.05 ± 1.35 ‰) by about 6‰, probably because of the authigeniccarbonate precipitation, organic matter degradation, and/or the food source changeunder shallow water conditions.(2) Mg/Ca, Li/Ca, and B/Ca of the ancient otolithswere higher than those of modern ones, as a result of their similar geochemicalbehaviours. After isolated from the main lake, the relict lake where the ancient nakedcarp lived enriched in Mg, Li, and B. By constrast, the Sr/Ca of ancient and modernotoliths were nearly equal and consistent low, probably resulting from uniform andlow Sr/Ca in lake water itself owing to authigenic carbonate precipitation. The slightdifference of Ba/Ca between the ancient and modern otoliths could be due to thesimilar uptake of Ba by fish body or to somewhat enrichment of Ba in the relict lake.Based upon the elemental enrichment or depletion as recorded in the ancient otoliths,relative to modern Lake Qinghai, combining with the location latitude and ages ofancient carp remains, we conclude that there was a high lake level during the theLittle Ice Age whose level was higher ~8 meters and lake area was larger 5% than themodern one than. According to the otolith microchemistry, if there were no abundantfresh water supply and exchange, the water in Lake Qinghai is likely to enrich more18 O and trace elements(Mg, B, Li, and potentially Ba) and deplete more13 C and Srrelative to the modern main and satellite lakes.This study about the otolith microchemistry of the naked carp in Lake Qinghaiand its trace for environmental change, not only makes us further understanding themigration on this precious fish, but also provides a new insight into Lake Qinghaiwater level change during the Little Ice Age and the water chemical evolution. |
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