Research On Paleoenvironment Inferred From Early Pleistocene Planktonic Foraminifera In North Atlantic

This paper samples from site U1313 on Expedion 306 in the north Atlantic,and synthetic depth for 69.93-115.1 meters, from 1471.5319 kaBP to 2414.1978 kaBP. This research use Mg/Ca ratios, Sr/Ca ratios,Carbon and oxygen stable isotope in planktonic Foraminifera(Globigerinoides ruber(white)), ancien- t oceanic environment during the period.There are six parts of this dissertation:Part I Introduce my research purpose and meaning.Both domestic and foreign research progress on the ancient environments using Mg/Ca ratios, Sr/Ca ratios ,Carbon and oxygen isotope in planktonic foraminifera(Globigerinoides ruber white).Part II Detailing research theory foundation and technical route.Partâ…¢Introduced comprehensively study area and the status of the area in paleoenvironment studies.Partâ…£This part maintly introduces sample source, sample pretreatment, cleaning procedures before computer test.Part V According to the experimental obtain Mg/Ca ratios, Sr/Ca ratios, Carbon and oxygen isotope, analyzing regularity and cycle, estimate the sea surface temperature, ancient salinity, seawater nutritional status and the atmosphere-ocean exchange in the period.Partâ…¥The main conclusions.The main conclusions are as follows:(1) The Mg/Ca ratios and Sr/Ca ratios in Globigerinoides ruber have approximate rule of variation in the 2253.765kaBP²414.198kaBP, but Mg/Ca ratios were greater sensitivity than Sr/Ca ratios on the Marine environment change.The Mg/Ca ratios haven't significant cycle. Using Elderfield and Ganssen (2000) established the Mg/Ca and SST relationship equation: Mg/Ca = 0.52exp(0.10*SST), got these SST with 41 time points in research area , the maximum temperature was 3.25℃。(2)Theδ¹⁸O in G.ruber have change since 2414kaBP,however, the whole was rising trend. According to the theory of oxygen isotope fractionation, Theδ¹⁸O was higher in the sea , Theδ¹⁸O was lower in the ice coverage, the ice coverage had relative increase.So, since 2414kaBP to 2253kaBP, the whole of SST was drop. Theδ¹⁸O in G.ruber had only 21.170882ka cycle, and through 95% confidence of the inspection,With consistent the earth orbit parameters about 21,000 years (two cycles: 19,000 years and 23,000 years ). Combining G.ruber(white) with Mg/Ca, using the estimated SST Bemis(1998):δ¹⁸Oseawater(SMOW)=δ¹⁸Oshell(PDB)+ï½›T(℃)-16.5｝/4.8+0.27, estimated ancient SST since 2253kaBP to 1471kaBP.Comparative analysis Estimate of SST,According to G.ruber and Mg/Ca estimating, foundδ¹⁸O in G.ruber (white) are more sensitive to Temperature changes.(3)Using Jennifer Arbuszewski(2010) established equation: S=34.28+1.97ln(Mg/Ca)+0.59*(δ¹⁸Oshell) and Fairbanks(1992) established equation:δ¹⁸Ow=-5.21+0.17×(S), respectively estimated ancient ocean Salinity since 2253kaBP to 2414kaBP in all time points.Since 1471kaBP to 2253kaBP period, using Fair- banks formula and estimatedδ¹⁸O in the ocean, the overall salinity was 35.94‰in this period.(4) Since 2414kaBP to 1471kaBP, Theδ¹⁸O and theδ¹³C in G.ruber (white) had opposite influence by environment, and display of high value and low value is relative.It was closed to D-value of in time and the earth's orbit cycles.The overall of theδ¹³C in G.ruber(white) was downtrend since 2414kaBP to 1471kaBP, so seawater nutritive condition of the seawater were ascendant trend. But in 2414.1978kaBP²350.5567 kaBP,2067.8571kaBP²011.9211kaBP,1859.3889kaBP¹835.3519kaBP,1649.6056kaBP¹590.5083 kaBP,1531.0862kaBP¹504.5345kaBP period were downtrend, and atmosphere-ocean exchange action were ascendant trend.