Q-Mode and R-Mode Factor Analysis in Quantitative Studies of ...

TERRÆ 7(1-2):41-49, 2010Hirama, M. V., Toledo, F. A. de L., Junior, E. C., Costa, K. B., Quadros, J. P. dedepths during their reproduction period in winter,when the vertical density gradient is reduced. G.ruber (pink) and G. inflata were also associated tofactor 3 to stratified waters (Hilbrecht, op.cit.). Asa consequence of G. truncatulinoides and G. inflatatolerance to little variation in salinity, factor 3 canbe related to salinity as well. Both forms of Globigerinoidessacculifer, which have a preference for themixed layer (Fairbanks et al. 1982; Ravelo et al.,1990; Andreasen e Ravelo, 1997), were the greatestcontribution to factor 5. Thus it was interpreted asmixed layer factor. Finally, factor 9 was regarded astemperature influenced because of warm speciesG. menardii tumida and G. menardii flexuosa relationship(Hemleben et al., 1989). When taken factorscores into account along with biostratigraphiczones Y and Z and oxygen isotopic data (Figure 8)thermocline (factor 1) seems to go along with theoxygen trend. Thermocline factor behaviour followedthe temperate water conditions (factor 2)in the course of biozone Y. The factor interpretedas stratification or salinity variation (factor 3) presentedan opposite tendency to factor 4 (linked toGlobigerinella digitata and Hastigerina digitata). Frombase-core to about 20,000 years ago (biozone Y)mixed layer control (factor 5) seems to mirror factor6 (Turborotalia quinqueloba and Globoturborotalitatenella), from then on, the two curves appearedcoincident. There were not comparative patternsobserved among the other factors.Figure 7 – SAN-76 Q-mode factor 1 and 2 histogramsindicating factor scores of the taxa analysed5. Conclusionthe application of Q- and R-mode factor analysisto microfossil compositional data sets was usefulto reconstruct the most prominent environmentalparameters inherent to planktonic foraminifera orcalcareous nannofossils fluctuations in the past.Greater correlation coefficients (0.9 to average)confers more reliability to the Q-mode techniquecompared to the R-mode for which only a third ofthe correlation coefficients were higher than 0.3.Additionally, the amount of R-mode statisticallysignificant factors was larger. This is consistentwith natural conditions where several parametersact simultaneously in a given community. However,interpretations of these factors could be ahard task since factors correlate to species whoseecological preferences are unclear or unknown. Areduced amount of retained factors of Q-modeshow a relationship with the most abundant species,yielding easier interpretation parameters.Comparing the application of both techniqueson calcareous nannofossils and planktonicforaminifera it was possible to recognize some similaritiesamong factors. The significance of PC-01factor 1 and SAN-76 factor 2 Q-mode results areanalogous and related to the same time interval:glacial period influenced by surface water productivity.Along these lines PC-01 factor 2 (nutricline/thermocline) and SAN-76 factor 1 (mixed layer)indicates the control of water stratification duringthe interglacial.Temperature-related R-mode factors (PC-01factor 1; SAN-76 factor 2 and 9) attend to the samebiota response although any temporal connectioncould be found. In this way PC-01 factor 2 andSAN-76 factor 1 and 5 linked to water stratification.These factors showed oscillating curves throughoutthe cores, but could be associated to majorrelevance in biozone Y. Finally PC-01 factor 4 andSAN-76 factor 3 should be considered indicatingequivalent conditions since they dwell on productivityinductions (lower vertical gradient) or salinityissues for both groups of organisms.The lack of correspondence between Q-moderetained factor and those from R-mode approach47a5_t7.indd 47 27/01/2011 11:28:06