The Exploration For The Indices Of Paleotemperature And Paleosalinity In The South Yellow Sea

A successive 13-month seasonal study from May 2014 to May 2015 in an intertidal flat, Qingdao Bay and several culture experiments were conducted on the dominant species Ammonia aomoriensis. MPS(mean proloculus size) of A. aomoriensis is correlated to salinity variation, also, calcite Mg/Ca ratio responses to both temperature and salinity in this study. In addition, the aforementioned relationships were applied to a sediment core CSDP-01 collected from the South Yellow Sea to estimate the bottom water temperature and salinity fluctuations in the past.MPS value of A. aomoriensis from field study is inversely proportional to salinity: MPS = 214.7030(±20.7783)- 5.4215(±0.6902) S(r =-0.6979, p<0.0001), salinity range 29~31. While the formula obtained from the offspring of A. aomoriensis in culture displays a lower sensitivity: MPS = 65.2737(±4.3334)- 0.3357(±0.1468) S(r =-0.3908, p = 0.0297), salinity 24~33. The steeper slope(-5.4215 vs-0.3357) might be attributed to the appearance of trimorphism(higher density of microspheric agamont and megalospheric schizont) in A. aomoriensis induced by the fluctuant unstable environment in nature. As a result, the culture equation might be more appropriate in optimum stable condition, where meglospheric gamont is exclusively dominant; while the field one might be more appropriate in unstable environment where trimorphism is observed by using MPS of A. aomoriensis in paleoenvironmental reconstruction. Temperature has no significant effect on proloculus size of A. aomoriensis.In laboratory cultures, Mg/Ca of A. aomoriensis is correlated with temperature: Mg/Ca = 0.5565(±0.3897) + 0.1279(±0.0242) T(r =0.7715, p<0.0001); Mg/Ca = 1.0980(±0.2073) e0.0510(±0.0097) T(r=0.7782, p<0.0001), 6~24℃, salinity 30, with an exponential sensitivity 5.10±0.97%/℃. Moreover, salinity also make a contribution to the Mg2+ incorporation with a lower sensitivity of 1.91±0.55%/unit: Mg/Ca =1.1379(±0.3801) + 0.0459(±0.0137) S(r = 0.7648,p = 0.01); Mg/Ca = 1.4171(±0.2218) e0.0191(±0.0055)S(r = 0.7690, p = 0.0093), salinity 24~33, 18℃. This implies that a salinity increase of 3 unit results in enhanced Mg incorporation equivalent to 1℃ temperature increase. A. aomoriensis belongs to low-Mg calcite species, and also has lower sensitivity relative to other planktonic and benthic foraminifera. A new formula is expressed as follows when combine both temperature and salinity contribution: Mg/Ca =-0.622(±0.8945) + 0.091(±0.0134) T + 0.0513(±0.0285) S(r = 0.8008, p<0.0001), standard error of estimate is 0.3553mmol/mol.By comparing the 10 samples of A. aomoriensis in sediment core CSDP-01, and calibrating the specific difference of Mg/Ca of several species from upper 48 meters, the results show that the linear regression Mg/Ca = 0.5565(±0.3897) + 0.1279(±0.0242) T is more appropriate than the exponential one. The estimate Holocene bottom water temperature by the linear formula fitted well with the recent annal temperature data, which indicates that the Mg/Ca-thermometer and MPS-salinity relationship of A.aomoriensis obtained in this study could be used to estimate the past bottom water temperature and salinity change in the South Yellow Sea.