The Use of R-Mode Factor Analysis in the Study of Palaeoclimatic and Palaeoceanographic Changes in SW Aegean Sea, Greece

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1 The Use of R-Mode Factor Analysis in the Study of Palaeoclimatic and Palaeoceanographic Changes in SW Aegean Sea, Greece Maria Geraga, Patras University, Greece, Stella Tsaila Monopoli, Patras University, Greece, George Papatheodorou, Patras University, Greece, George Ferentinos, Patras University, Greece, Chrisanthi Ioakim, Institute of Geology and Mineral Exploration, Greece INTRODUCTION Within the last decades many studies have been carried out in order to delineate the evaluation of Quaternary palaeoclimate (e.g. Emilliani, 1955, Bond et al., 1992). More specifically the studies at the eastern Mediterranean, on one hand focus on the understanding of palaeoclimatic changes and on the other hand they deal with the understanding of palaeoceanographic conditions which caused the formation of the sapropels (organic rich sediments) (e.g. Cita et al., 1977, Aksu et al., 1995). The formation of the sapropels seems to be a combination of (a) reduced surficial density (by an increasing temperature of the sea surface and/ or a reduction of sea surface salinity) which caused decrease bottom water ventilation and (b) increased organic material flows (terrigenous and/or marine origin) which caused increased demands of dissolved oxygen used for the oxidation of organic matter in the water column. Planktonic and benthonic foraminifera faunas have been studied extensively, as indicators of Quaternary climatic and oceanographic changes since they can provide useful information for the temperature and salinity of the sea surface, the marine productivity, the seawater circulation and the oxygen consecration in seawater column (Thunell, 1978). This study refers to the palaeoclimatic and palaeoceanographic evaluation of eastern Mediterranean and more specifically at SW Aegean Sea. The deductions are based on the application of factor analysis (R-mode) to high resolution microfauna data consisting of planktonic and benthonic fauna analyses. This method enabled us to examine the interactions among the variables (foraminifera species) and to identify a series of palaeoclimatic and palaeoceanographic events of long and short duration that took place at SW Aegean Sea, within the last years

2 MATERIALS AND METHODS The present paper is based on the micropalaeontological examination of two cores, C40 and C69 collected from the Myrtoon basin and the SW Cretan basin respectively, in the southwestern Aegean Sea (Fig.1) (Table 1). Table 1 Core Longitude Latitude Water depth (m) Core length (cm) C , , C , , Fig. 1:. Location map of the study area in the SW Aegean Sea M.B: Myrtoon basin, C.T: Cretan basin, N.A.T: North Aegean Trough, S.K : Skopelos Basin, N.S.B: North Skyros basin, S.S.B: South Skyros basin, N.I.B: North Ikaria basin and S.I.B: South Ikaria basin. For the foraminiferal studies the samples were disintegrated in hydrogen peroxide and were then sieved through the 150µm size sieve. The dry and weighed samples were split into aliquots. The planktonic and benthonic forams were identified and counted. Each studied sample consisted of at least 200 specimen of planktonic or benthonic foraminifera. The planktonic forams analyses are based on a total number of 148 samples (54 samples along the C40 and 94 along C69). The benthonic forams analyses are based on 49 samples along the core C69, since the low abundance of benthic forams (<200 specimen) at C40 didn t allow for a quantitative benthic analysis. The mean sampling interval is between 1 and 5 cm. Approximately, each sample covered approximately a 1cm depth interval in each core. The organic carbon content (Corg) was determined by the K 2 Cr 2 O 7 Fe(NH 4 ) 2 6(H 2 O) titration method according to Gaudette et al. (1974).

3 A total number of 79 samples along the two cores (34 samples from C40 and 45 from C69) were analyzed for the determination of the oxygen isotopes in the tests of the planktonic foraminifera Globigerinoides ruber (>125 µm). The analyses for the core C40 were carried out at the Laboratory of Geology and Geophysics in Edinburgh University whilst the analyses for the core C69 at the Southampton Oceanographic Center. The measured isotopic values were used to support the results in the palaeoclimate as determined by the planktonic forams. The chronological framework is based on 5 samples (3 for C40 and 2 for C69) (Table 2) which have been dated by the method of Accelerator Mass Spectrometry (AMS) at the laboratories of Beta Analytic. In this work the dating will be given in terms of uncorrected 14 C years ( 14 C nc ) for reservoir Table 2 Core Depth (cm) 72,5 C40 82,5 131,0 C Age (kyrs BP) Factor analysis was subjected to the results of microfauna analyses (Davis, 1987, Reyment and Joreskog, 1993). Two data matrix were exploited during this procedure. The first matrix [148 12] includes the percentages of the main planktonic foraminifera species as they were derived from the micropalaeontological examinations of the two cores whilst the second [49 16] contains the percentages of the main benthonic foraminifera species, as a result of the micropalaeontological examinations of the C69 core. In addition, both matrixes include the percentages of the organic mater content of each sample. All the foraminifera species used as variables in the application, are all indicators of specific climatic and oceanographic conditions. More precisely, the planktonic species selected among others for this procedure, are: Globigerinoides ruber, Gs. sacculifer, Orbulina universa, Globigerinella spp (G. aequilateralis, G. calida),

4 Globigerina bulloides, Globigerinita glutinata, Turborotalita quinqueloba, Globorotalia inflata, Gr. scitula, Neogloboquadrina dutertrei, N. pachyderma. Furthermore, the following benthonic species were applied: Bolivina spp (B. spathulata, B. dilatata, B.alata), Bulimina costata, B. marginata, Cassidulina spp. (C. crassa, C.laevigata, C.subglobosa), Cassidulinoides bradyi, Chilostomella sp., Cibicides spp., Fursenkoina sp., Globobulimina spp., Gyroidina spp. (G. orbicularis, G. altiformis, G. neosoldanii), Hoegludina sp., Miliolidae, Nonion sp, Uvigerina spp. (Uv. peregrina, Uv. aculeata, Uv. mediterranea, Uv.auberiana) whilst the epifauna species Asterigerinata sp., Dentalina sp., Discorbis spp., Gravelinopsis sp., Hanzawaia sp., Neocorbina sp., Ophthalmidium acutimargo Patellina sp., Rosalina sp., Spirillina sp., Spirophthalimidium spp. Valvulineria sp. consist the association of Group A. RESULTS-DISCUSSION Sediments Five lithological units mainly consisting of mud were identified at C40 core. One of them represents the sapropel sequence of S1 which is regarded as the youngest sapropel layer in eastern Mediterranean and is dated between 6-9ka (Geraga, et al., 2000). The core C69 contain six lithological units which are also mainly consisting of mud. One of the six units represents the sapropel sequence of S1 whilst another one the sapropelic sequence of S2. It is noteworthy, that S2 occurs rarely in marine sediments of eastern Mediterranean and that is the reason why it is commonly called the ghost sapropel (Vergnaud-Grazzini et al., 1977). In both cores S1 appears in two sublayers, S1a and S1b. The interruption in the deposition of S1 has been observed in many cores from the eastern Mediterranean and it is attributed to climatic causes (De Rijk S., et al., 1997, Geraga et al., 2000). Based on the radiometric ages, the mean sedimentation rate in the C40 core is estimated at 10.3cm/kyr whilst in the core C69 at 4.3cm/kyr. The basis of the C40 is

5 estimated at 18.3kyrs whilst the basis of C69 at 45.5kyrs. Furthermore the time interval between the samples studied ranges between 100 to 500yrs. Planktonic foraminifera R-mode analysis Factor analysis yielded a five-factor solution, since (a) this number of factors accounted for the 74.6% of the total variance (Table 3), (b) all the variables have a high communality ( ) (Table 4) and (c) 5 factors remained after the drawing of the straight line at the bottom portion of the Catell s scree test plot (Fig. 2). Table 3: Eigenvalues, percent of Variance, Cumulative percent of Variance for the Factor analysis (R-mode) of planktonic foraminifera Factors Eigenvalues Percent of trace (%) Cumulative percent of trace Eigenvalues Factors Fig. 2: Catell s sree test plot for the selection of factors at the application of R-mode analysis to planktonic forams

6 Table 4: Loadings for the Varimax rotated 5-Factors model and Communalities Variables Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Communality G. bulloides -0,415-0,346 0,213 0,625-0,237 0,784 Corg -0,051-0,208-0,109 0,761-0,199 0,676 G.inflata -0,013-0,098-0,084-0,067 0,931 0,888 G.glutinata -0,097-0,269-0,455-0,667-0,280 0,812 Or.universa -0,234-0,125 0,672 0,304-0,303 0,706 T.quinqueloba 0,919-0,029-0,150 0,058-0,133 0,889 Gs.ruber -0,687-0,451 0,256 0,283 0,043 0,621 Gs. Sacculifer -0,022-0,198 0,788 0,056-0,129 0,686 G. scitula 0,648 0,303-0,115-0,158 0,249 0,612 Globigerinella -0,347-0,183 0,657-0,173 0,054 0,618 N.dutertrei 0,118 0,871-0,147-0,115-0,002 0,807 N.pachyderma 0,186 0,832-0,221-0,088-0,099 0,793 The vertical distribution of the revealed factor scores (: the contribution of each factor at each sample) along the C40 and C69 cores, are presented Fig 3 and Fig 4 respectively. The 1 st factor accounts for the 35% of the total variance and exhibits bipolar character: one pole is dominated by T. quinqueloba and Gr. scitula (0,919 and 0,648 respectively) and the other is dominated by Gs. ruber (-0,687). T. quinqueloba and Gr. scitula are considered as indicative of cool-subpolar conditions whilst Gs. ruber indicates warm subtropical and oligotrophic conditions (Boltovskoy and Wright, 1976). Thus the 1 st factor can be regarded as an index of the sea surface temperature variability and the downcore fluctuation of the factor scores in both cores can be compared with the δ 18 O vertical distribution. Between 14-18ka, at the C40 core, the low factor scores coincide with the heavy values of δ 18 O and indicate the cold conditions during the Last Glacial Period, on the other hand the gradual increase of the scores compared with the reduction of δ 18 O indicate the gradual improvement of the climate during the Late Glacial period (Thunell and Williams, 1989). Furthermore two short lived events at 13.8ka and 11ka imply a shift to colder climatic conditions as shown by the low factor scores and the heavy δ 18 O values. These events probably correspond to the stadials Heinrich 1 and Younger Dryas respectively (Bond et al., 1992).

7 Fig. 3: Downcore variation of δ 18 Ο values and factor scores (FS), as they revealed after the application of factor analysis at the planktonic data of C40. Fig. 4: Downcore variation of δ 18 Ο values and factor scores (FS), as they revealed after the application of factor analysis at the planktonic data of C69. In the last years the factor scores remained high constantly and together with the depleted values of δ 18 O suggest the warm climate of Holocene. The low scores at 8.9ka and 7.1ka probably were caused by the increase of the percentage of T.

8 quinqueloba. This species flourish at low salinity surficial waters as these which established at eastern Mediterranean region during the formation of S1a and S1b (Laurens, 1994). Similar results concerning climate variability are also proved by the downcore variation of the factor scores at core C69. Between 21-45ka the relatively high factor scores together with the relatively low δ 18 O values indicate the mild climate during ST3. The reduction of the factor scores at 36-38ka, 26-2ka and 21ka coincide with the establishment of the cold events Heinrich 4, 3 and 2 respectively whilst the increased values around 36ka coincide with the establishment of the Alesund interglacial and the formation of S2 (Bond et al., 1992, Larsen et al., 1987). Between 10-21ka, relatively low factor scores occur which combined with the high δ 18 O values, imply the cold climatic conditions of isotopic stage ST2. During this period, the lower factor scores take place at 18ka and 13.8ka and probably correspond to Last Glacial Maximum and to Heinrich 1 event, respectively. The 2 nd factor accounted for the 11.7% of the total variance and showed an average fauna of N. dutertrei (0,871) and N. pachyderma (0,832). N. dutertrei and N. pachyderma flourish at waters with enhanced marine primary productivity caused by the shoaling of the pycnocline into the euthotic zone and the subsequent development of Deep Chlorophyll Maximum layer (DCM) (Fairbanks et al., 1982). Therefore the 2 nd factor indicates the periods where the oceanographic conditions over SW Aegean Sea were suitable for the formation of DCM layer. Such conditions seem to be established between 32-36ka (C69) and between 12-18ka (C40 and C69) as shown by the high values of the scores. Today a pycnocline is developed at the eastern Mediterranean waters at around 150m of depth, separating the warm and high salinity surficial waters from the cool and low salinity intermediate ones (Theoharis, et al., 1993). The shoaling of the pycnocline at the first period (32-36ka) probably was incurred by the reduction of surface salinity as indicated by the extremely depleted values of δ 18 O -on the contrary, within the second interval (12-18ka), it seems to be attributed to the reduction of sea surface temperature during the Last Glacial Period. The 3 rd factor accounted for the 10.3% of the total variance and calculated an average fauna of Or. universa (0,672), Gs. sacculifer (0,788) and Globigerinella spp. (0,657). These species are considered as warm climate indicators and thus the 3 rd

9 factor emphasizes some intervals of enhanced warm conditions (Boltovskoy and Wright, 1976). The fluctuation of the scores of this factor shows, as in the case of the 1 st factor also, indicate climatic variability and must be studied in relation to the 1 st factor. High values of the scores occur between 6-9ka (C40 and C69) and around 41ka. The first interval coincides with the formation of S1 whereas the high values during S1a and S1b show the significant role that the increased sea surface temperature played for their formation (Geraga et al., 2000). On the contrary, during the deposition of S2 the relative low values of this factor suggest that temperature did not play a determinant role for the formation of S2. The second interval maybe corresponds to an interstadial event which preceded the establishment of the Heinrich 4 event on 38ka The 4 th factor represents the 9.0% of the total variance and displays bipolic character with positive loadings at G. bulloides and Corg and negative loadings at G. glutinata (-0,667). G. bulloides is a species of subpolar water masses but highly dependent on enhanced food levels caused by strong fresh-water inputs, upwelling or strong seasonal mixing (Lourens, 1994). Thus high values of the 4 th factor can be indicative of periods where the increase of organic material (Corg) is caused by such oceanographic conditions. The high values of factor 4 during the formation of S1a and S1b imply riverborne organic material whilst the low values of factor 4 during S2 suggest that the organic material in this case is probably of marine origin. The 5 th factor accounted for the 8.5% of the total variance and exhibits positive loadings only at G. inflata (0,931). Gr. inflata is a mainly transitional species that thrives in well mixed eutrophicated environments under deep stirring (Lourens, 1994). Thus the 5 th factor portraits periods of enhanced primary productivity. In this case the mechanism which produced the eutrophism at the sea water differs from those proposed at the 2 nd and 4 th factors and this explains the dissimilarity between the vertical distribution of the equivalent factor scores. High values of factor scores occur after the deposition of S1 (C40 and C69) and of S2 (C69), between 22-25ka and at 40ka (C69).

10 Benthonic foraminifera The application of factor analysis to benthonic foraminifera revealed 5 factors since (a) this number of factors accounted for the 75,3% of the total variance (Table 5), (b) all the variables have a high communality ( ) (Table 6) and (c) 5 factors remained after the drawing of the straight line at the bottom portion of the Catell s scree test plot (Fig. 5). Table 5: Eigenvalues, percent of Variance, Cumulative percent of Variance for the Factor analysis (R-mode) of benthonic foraminifera Factors Eigenvalues Percent of trace (%) Cumulative percent of trace E igenvalues Factors Fig. 5: Catell s sree test plot for the selection of factors at the application of R-mode analysis to benthonic forams

11 Table 6: Loadings for the Varimax rotated 5-Factors model and Communalities Variables Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Communalities Bolivina 0,301 0,454 0,696 0,043-0,036 0,784 B.marginata -0,037-0,015 0,870 0,169-0,044 0,789 Bulimina -0,325 0,087 0,368 0,770-0,077 0,743 Cass/des -0,194-0,128-0,140 0,010 0,891 0,868 Cassidulina 0,509 0,543 0,382-0,051-0,081 0,710 Chilostomella -0,280-0,203 0,324 0,650 0,343 0,765 Cibicides -0,051 0,863-0,085-0,127-0,105 0,782 Corg -0,619-0,633-0,183-0,077 0,168 0,851 Fursenkoina spp -0,176-0,191 0,621-0,073 0,350 0,581 Gyroidina 0,344-0,059-0,283 0,809-0,142 0,877 Globobulimina -0,105-0,077 0,218-0,074 0,871 0,829 GroupA 0,844 0,068-0,078-0,048-0,123 0,740 H.elegans 0,761-0,044-0,138-0,045-0,083 0,800 Miliolidae 0,768 0,236 0,221 0,017-0,163 0,721 Nonion 0,532 0,449-0,201 0,287-0,100 0,617 Uvigerina 0,214 0,567 0,026 0,550-0,120 0,685 The vertical distribution of the revealed factor scores along the core C69 are shown at Fig. 6. The 1 st factor accounted for the 30.4% of the total variance and displays a bipolar character with positive loadings at H. elegans (0,761), Group A (0,844), Miliolidae (0,768), Nonion spp. (0,732) and Cassidulina spp. (0,509) and negative loadings at the organic mater content of the sediments, Corg(-0,619). The 2 nd factor accounted the 17% of the total variance has also bipolar character with positive loadings at Cibicides spp. (0,862), Uvigerina spp. (0,567) and Cassidulina spp. (0,543) and negative loadings at the organic mater content (Corg) (-0,633). The 3 rd, 4 th and 5 th factors represent the 12%, 8.7% and 7.2% of the total variance and calculated benthonic assemblages consisting of (a) Bolivina spp. (0,696), B. marginata (0,870) and Fursenkoina spp. (0,621), (b) Bulimina spp. (0,770), Chilostomella sp. (0,650), Gyroidina spp. (0,809) and Uvigerina spp. (0,550) and (c) Cassidulinoides spp. (0,891) and Globobulimina spp. (0,871) respectively. The species which comprised the 1 st and 2 nd factors are mainly epifauna and are indicate of well-oxygenated bottom waters (Murray, 1991). Thus high factor scores suggest periods of high oxygen concentration at bottom waters. The strong negative correlation of the organic matter content (Corg) suggest the inability of

12 Fig. 4: Downcore variation of factor scores (FS), as they revealed after the application of factor analysis at the benthonic data of C69. these species to survive under dysoxic or anoxic environments like those developed during the deposition of the two sapropel sequences. The vertical distribution of the factor scores suggests that, the oxygen concentration was sufficient within the last years and that the water circulation was constant, except of the periods of sapropel depotition. Although both the 1 st and 2 nd factors indicate bottom water environments with sufficient oxygen supply, the vertical distributions of their scores differ as far as the the following points are concerned: (a) the benthonic association of the 2 nd factor exhibits faster expansion immediately after S2 compared to the one of the 1 st factor, (b) the benthonic assemblage of the 1 st factor is abundant just before the deposition of S1 while the benthonic assemblage of factor 2 during the first stages of S1 and (c) their vertical fluctuations along the core exhibit mirror-image effect. What is mentioned above implies that the benthonic assemblage of the 2 nd factor is more tolerant to the reduction of O 2 and it can profit by the food supply in eutrophicated environments like those established during and just after the deposition of S2 as well as at the first stage of deposition of S1

13 The benthonic species of the 3 rd factor in aerobic bottom waters are shallow infauna (Bolivina spp., B. marginata) and deep infauna (Fursenkoina spp.) and they emigrate on the seafloor surface under conditions of reduced oxygen concentration or increased food availability (Jorissen, 1999). Thus the high scores of this factor suggest periods of dysoxic or enhanced eutrophicated seafloor environments. Based on their vertical fluctuations such environments were developed during the formation of S2, and just before the deposition of S1a and S1b. Furthermore the variability of the scores during the deposition of S2 implies analogous variability of oxygen concentration or food availability. The species of the 4 th factor are epifauna (Gyroidina spp.), shallow infauna (Bulimina spp. and Uvigerina spp.) or deep infauna (Chilostomella sp) (Murray, 1991). The common characteristics of this association are: (a) the resistance to low oxygen conditions and (b) the capacity to profit very easyly by the food supply (Jorissen, 1999). This benthonic association seems to be abundant at eutrophicated seafloor environments which start to recover after an anoxic event. The vertical distribution of the scores indicates that such conditions were developed between ka, at the interruption of S1 and just after the deposition of S1. The species of the 5 th factor are deep infauna species and their concentration in benthonic assemblages increase with the reduction of dissolved O 2 at bottom waters, where all the other benthonic species are unable to survive. Consequently, these species indicate extremely dysoxic environments which usually precede anoxic conditions. Such conditions seem to develop at the seafloor during the first stages of the S1a and S1b depositions as well as at the central part of S2. CONCLUSIONS The application of factor analysis to planktonic forams revealed 5 factors. Two of these factors cluster the planktonic species which are indicators of temperature changes and they can be considered as sea surface temperature depended. The variation of their high resolution scores compared with the δ 18 O data showed a sequence of palaeoclimatic changes of long and short duration, which may correspond to global events such as Heinrich 1, 2, 3, 4 and Younger Dryas. The other three factors cluster planktonic species which prefer high eutrophicated waters and the variation of their scores revealed the periods where the marine productivity was improved by (i) the development of Deep Chlorophyl

14 Maximum (DCM) layer, (ii) the increase of river outflows and (iii) the well mixed surface waters. The application of factor analysis also showed that the organic mater during the deposition of S1 is associated to the second type of enhanced productivity whilst the organic mater of S2 can be related to with the first type. The application of the factor analysis to benthonic forams revealed 5 factors which appear to correspond to five stages of bottom water enrichment. The variation of the scores of the 1st factor showed that the last 45kyrs SW Aegean Sea was characterized by well oxidized bottom waters except of the periods of sapropel depotition. When the trophic level of the sea bottom increases such as it happens during the deposition of S2, the dominated benthic fauna is represented by the 2nd factor whilst environments of reduced oxygen supply and/or of increased organic flows (like those developed during the interruption of the sapropelic deposition of S1) are implied by the high values of the 4th factor scores. Even more dysoxic environments such as those developed exactly before the deposition of S1a and S1b are represented by the 3th factor. Furthermore, highly dysoxic, almost anoxic environments like those formed at the begging of S1a and S1b are represented by the 5th factor. References Aksu A.E., Yasar D., Mudie P.J. (1995): Paleoclimatic and paleoceangraphic conditions leading to the development of sapropel layer S1 in Aeagean Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 116: Boltovskoy E. and Wright R. (1976): Recent foraminferan. (Ed. Junk W.). The Hague: pp 515. Bond G., Heinrich H., Broecker W., Labeyrie L., McManus J., Andrews J., Huon S., Jantschik R., Clasen S., Simet C., Tedesco K., Klas M., Bonani G., Ivy S., (1992): Evidence for massive discharges of icebergs into the NorthAtlantic ocean during the last glacial period. Nature: 360: Cita B.M., Vergnaud-Grazzini C., Robert C., Chamley H., Ciaranfi N., D' Onofrios (1977): Paleoclimatic Record of a long deep sea core from the Eastern Mediterranean. Quaternary Research 8: Davis, J.C. (1987): Statistics and data anlysis in geology (2 nd ed.): John Wiley & Sons, New York, 656 p. De Rijk S., Rohling E.J., Hayes A. (1999): Eastern Mediterranean sapropel S1 interruption: an expression of the onset of climatic deterioration around 7kyrs BP. Marine Geology 153: Emilliani C, (1955): Pleinstocene temperatures. Journal of Geology 63: Fairbanks R.G., Sverdlove M., Free R., Wiebe P.H., Be A.W.H. (1982): Vertical Panama Basin. Nature 298:

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