SPATIAL AND SEASONAL VARIABILITY OF ELEMENT CONCENTRATIONS OF SUSPENDED PARTICULATE MATTER IN THE CRETAN ARC STRAITS <B>SPATIAL AND SEASONAL VARIABILITY OF ELEMENT CONCENTRATIONS OF SUSPENDED PARTICULATE MATTER IN THE CRETAN ARC STRAITS</B> <HR><P> Varnavas, S.<BR> University of Patras, Department of Geology, 26110 Patras Greece</B><P><P> The analysis of suspended particulate matter (SPM) from the Straits and the northern Cretan Margin showed significant spatial, vertical and seasonal element variability. Marked enrichments in SPM were observed in the upper water column, being associated probably with primary productivity. Sr increases at this water level being controlled by light transmittance suggesting its biogenic origin. Sr enrichments are greater in the NW Cretan Margin than in the Antikythira Strait. The variability of Cu is controlled by salinity. Cu enrichments are related to adsorption on Fe-Mn hydroxides and/or to bioaccumulation processes. In winter at 50 m depth Cu values tend to decrease from higher to lower latitudes and in the NW Cretan Margin. Both in autumn and winter Mn shows its highest values at the Rhodes Strait being decreased towards the Kasos Strait and the open sea. On the basis of the Li distribution it is suggested that the lithogenous contribution to the total SPM is very limited. <B><P><P> Introduction</B><P><P> The chemical composition of suspended particulate matter in sea water is controlled by a number of factors such as the rate of primary productivity, the amount of lithogenous input to the sea, the rate of its sink etc. (Noriki and Tsunogai, 1992). Biogeochemical processes leading to release and/or uptake of elements from sea water during the horizontal or vertical fluxes of suspended particulate matter are also responsible for its composition. The biodegradation of the organic fraction of SPM at certain water levels results in the enrichment of its inorganic constituents. Similarly the dissolution of its carbonate fraction in deeper waters may result in the depletion of the elements associated with the carbonate fraction (i.e. Sr) and the enrichment of its non-carbonate constituents (i.e. Fe, Li) (Chester, 1990) .<BR> <BR> Adsorption-desorption process being controlled by physical oceanographic and physicochemical conditions is also an important controlling process of the compositional variability of SPM (Regnier <I>et al</I>., 1990; Paucot, <I>et al</I>., 1993; Price <I>et al</I> 1993). In this work the spatial vertical and seasonal variations of element concentrations of SPM in the Cretan Straits and the Southern Cretan Sea are studied and the above processes are deduced (Fig. 1).<B><P><P> Methodology</B><P><P> After the filtration of the water samples the membrane filters were treated with HCl and they were placed on a hot plate for 1 hour. Subsequently Acetone was added (to dissolve the filter) to form a single phase. Atomic Absorption methods were applied with the operation of a Perkin-Elmer 2100 Spectrometer, and 700 HGA Graphite Tube Atomiser. The analyses were carried out using the appropriate parameters and standards for each element. The precision was checked by replicate analyses while accuracy was checked using sensitivity check standards. <B><P><P> Results & Discussion</B><I><P><P> Vertical variations of suspended particulate matter</I><BR> An investigation into the vertical variations of SPM shows that in autumn there is a distinct peak at 100 m water depth at the Kithyra Strait, the Karpathos Strait and at the Mirtoan Basin. The SPM value at 100 m is greater at the Karpathos Strait intermediate at the Mirtoan Basin and lower at the Kithyra Strait showing a decrease from east to west.<P><P> The significant peak in the SPM content found in autumn at 100 m water depth at Kithyra Strait, Karpathos Strait and western open Cretan Sea would suggest high biological activity and/or a trap of lithogenous material at this water level. The same phenomenon is also observed in the same general area in winter. The decrease of SPM at this water level from east to west both in winter and in autumn implies that these processes should be more intense in the eastern part of the area studied. Moreover the higher SPM values found in winter than in autumn at this level at the Karpathos Strait would further suggest that these processes are more intense in winter than in autumn.<P><P> Distinct SPM peaks were found in winter at 50 m depth at Rhodes Strait, at the Kamilonisi Margin and the NW Cretan Sea which should be related to primary productivity. This is consistent with chlorophyll maxima and higher concentrations of phytoplankton cells reported at 50 m water depth in the investigated area (Balopoulos 1995). The highest concentrations of SPM found at 50 m at Rhodes Strait compared with its values in the central and western part of the Study area implies higher primary productivity in the former region. This is also consistent with the spatial distribution of the levels of primary production according to which the north-eastern part of the Cretan Sea is characterised by lower levels compared to the remaining area investigated (Balopoulos, 1995).<I><P><P> Spatial and seasonal element variability at different water levels </I><BR> At 50 m water depth in autumn 94 Sr decreases in the eastern straits from Rhodes to Kasos, whereas in the open sea it increases from east to west. In the western straits Sr increases from north to south showing its highest concentration at the Antikythira Strait. In winter the spatial variations of Sr at 50 m water depth are similar to those observed in autumn.<P><P> At 100 m water depth the spatial variations of Sr are comparable to those observed at 50 m water depth during the same sampling period. In autumn at 50 m water depth negligible amounts of Cu were detected in SPM, while its values tend to increase at the western straits. During the same sampling period at 100 m water depth the Cu values in the eastern part of the study area are higher than at 50 m water depth tending to increase westwards. The highest Cu values are encountered at NW Cretan Margin. In winter at 100 m water depth the Cu values tend to decrease from higher to lower latitudes.<P><P> The highest Mn value at 50 m water depth both in autumn and winter is observed at the Rhodes Strait with decreasing values towards the Kasos Strait and the open Sea. Elevated Mn values are observed also at both sampling periods at the Elafonisos Strait. In winter there is a distinct trend showing decrease in Mn from the Elafonisos to Antikythira Straits. Overall, at the 50 m water level the SPM in winter contains higher amounts of Mn than in autumn. At 100 m water level in autumn two maxima in Mn are observed at Elafonisos and at Karpathos Straits with lower values in between. In winter the highest Mn value is observed at Rhodes Strait with a tendency for Mn to decrease South-westwards to the open sea.<P><P> Both in autumn and winter at 50 m water level Pb exhibits elevated values at the Mirtoan Basin. In winter elevated Pb values are also observed at the Kythira, Antikythira and Karpathos straits. In autumn Pb decreases from Elafonisos to Antikythira Strait. In autumn at 100 m water level Pb decreases from the northern to the southern straits both in the east and west. In winter Pb shows a maximum at the western open Cretan Sea while at the remaining stations it remains at generally low levels.<P><P> Iron in autumn at 100 m water level exhibits two maxima, one at the Kythira Strait and another in the open Cretan Sea. Generally lower Fe values are found in the eastern part of the study area. In winter the highest Fe values occur at the Rhode Strait being decreased south-westwards in the Karpathos and Kasos Straits. It then also decreases westwards exhibiting a low in the open Cretan Sea. At the Mirtoan Basin Fe shows a maximum being decreased southwards.<BR> Lithium in autumn at 100 m shows a maximum at the Antikythira Strait being decreased both in the remaining western straits and to the open Cretan Sea. Very low Li values are observed in the eastern part of the study area. In winter at this water level a different Li distribution pattern is obtained. A maximum in Li is found in the open Cretan Sea its values being decreased both eastwards and westwards.<I><P><P> Statistical analysis of analytical data</I><BR> In order to investigate the mode of incorporation of the elements in the suspended particulate mater (SPM) R - mode factor analysis has been applied on the data. The application of factor analysis on the data obtained from the analysis of the samples from 100 m water depth showed that the elements are grouped in three factors, which account for 87.7% of the total date variance.<P><P> The first factor which accounts for 42.3 % of the total data variance shows high positive loadings of Li, Sr and Cu. The highest loading in this factor is that of Li. It is therefore concluded that this factor represents the lithogenous fraction of the SPM.<P><P> The second factor accounts for 26.1% of the total data variance and shows high positive loadings of Fe and Mn. This factor represents the Fe-Mn hydroxide fraction of the SPM. Lower positive loadings are also observed for Cu. Therefore it is suggested that a portion of Cu is adsorbed onto the Fe and Mn hydroxides.<P><P> The third factor which accounts for 19.3% of the total data variance shows high positive loadings of Pb and Sr. This factor should represent the biogenic fraction of the SPM.<P><P> The application of factor analysis on all data from Antikythira Strait showed that the first factor which accounts for 33.4% of the total data variance shows high loadings of Fe, Mn, and Pb. The second factor which accounts for 27.0% of the total data variance shows high loadings of Li and Cu. The third factor which accounts for 15.9% of the total data variance shows negative loading of Sr.<P><P> The results of application of factor analysis on all data from north west Cretan Margin showed that the first factor exhibits high loadings of Mn, Fe, Pb and lower loading of Li. The second factor is highly loaded with Sr, while the third factor shows positive loading of Li.<I><P><P> Behaviour of Elements in relation to physical oceanographic conditions.</I><BR> An examination of the element variability in relation to physical oceanographic conditions showed that in the NW Cretan Margin Sr is largely controlled by light transmittance. A similar behaviour of Sr was also observed at Antikythira Strait suggesting its probable biogenic origin. Also it was revealed that the variability of Cu was controlled by salinity.<B><P><P> Conclusions</B><P><P> ISignificant vertical spatial and seasonal variations in the concentrations of SPM are observed in the area investigated.<BR> IISignificant enrichments in SPM are encountered at the upper part of the water column.<BR> IIISuch enrichments are observed at the same water level in different seasons.<BR> IVStrontium enrichments associated with SPM increase in the upper part of the water column are indicative of biogenic carbonate contribution to the total SPM.<BR> VOn the basis of the spatial variations of Sr it is suggested that the biogeochemical process being responsible for the Sr enrichment is more intense in the NW Cretan Margin than in the Antikythira Strait.<BR> VIDissolution of carbonates may be partly responsible for the decrease in Sr observed at deeper waters.<BR> VIIThe biogeochemical behaviour of Cu is similar to that of Sr. Bioaccumulation by marine micro-organisms and/or adsorption on biogenic remains are the probable processes responsible for the Cu enrichments.<BR> VIIIOn the basis of the Li distribution it is suggested that the lithogenous contribution to the total SPM is very limited.<BR> IXSignificant SPM enrichments found at the bottom waters at the NW Cretan Margin are associated with negligible amounts of Li.<BR> XIt is revealed that the compositional variability of suspended particulate matter is strongly controlled by the prevailing physical oceanographic conditions.<BR> XIThe variability of Cu is influenced by salinity.<BR> XIIThe variability of Sr is influenced by the light transmittance.<B><P><P> References</B><P><P> Balopoulos, E.Th. (1995). Hydrodynamics and Biogeochemical fluxes in the Straits of the Cretan Arc (Aegean Sea Eastern Mediterranean Basin). In Proceedings of MAST DAYS Conference (in press).<BR> Brooks, R. R., Presley, B. J. & Kaplan, I. R. (1967). Determination of Metal in Particulate Matter. Talanta 14, 309.<BR> Chester, R. (1990). Marine Geochemistry . Academic Press London-New York.<BR> Noriki, S. And Tsunogai, S. (1992). Directly observed Particulate fluxes of Cd, Ni and Cu in Pelagic Oceans: Implications of two different settling particles. Mar. Chem., 37:105-115.<BR> Paucot, H. <I>et al</I>. (1993). Particulate Trace Metals in the Suspended Matter in Regions of the Straits of Gibraltar and Sicily. Water Pollution Res. Rept., 30, (J. M. Martin and H. Barth, eds.) EEC, Brussels, 171-181. <BR> Price, N. B., Mowbray, S. R., Giordani, P. And Frignani, M. (1993). Transfer of Iron and related Elements on Adriatic Shelf. In: MAST DAYS & EUROMARKET 1993, Project Reports, V. 1., editors K. G. Barthel, M. Bohle-Carbonell, C. Fragakis, M. Weydert, Commission of the European Communities pp 383-396.<BR> Regnier, P., <I>et al</I>. (1990). Trace Metals in the Suspended Matter collected in the Mixing Zone of the Rhone Estuary. Water Pollution Res. Rept,. 20, (J. M. Martin and H. Barth, eds.) EEC, Brussels, 385-396<P><P>