palaeoecology of akebiconcha kawamurai bivalvia vesicomyidae from the pliocene tamari silt formation in the kakegawa area central japan abstract the japanese vesicomyid clam akebiconcha kawamurai is taxonomically very close to calyptogena species living specimens of a kawamurai have been collected from bathyal depths but its ecology is not clear a fossil akebiconcha kawamurai assemblage is found in the uppermost part of the tamari silt formation early pliocene in age cropping out in the kakegawa area central japan the assemblage occurs in several shell beds scattered through the massive silt the silt matrix between shell beds yields sporadic shells of another molluscan fossil assemblage an empleconia sp a neilonella coix assemblage the akebiconcha kawamurai assemblage commonly is associated with solemya johnsoni conchocele bisecta and lucinoma aff acutilineata these three genera prefer a reducing environment and possess endosymbiotic sulphide oxidising bacteria therefore the co occurrence and the large biomass suggest that akebiconcha kawamurai possesses such endosymbiotic bacteria as do many other calyptogena species by contrast the species composition of the empleconia sp a neilonella coix assemblage indicates an oxic environment in the bathyal zone we do not think that the ecosystem of the akebiconcha assemblage was supported by cold seepage water from a subduction zone because the assemblage is enclosed by the massive fine silt the mode of fossil occurrence and the living depth of recent akebiconcha kawamurai make us presume rather that conditions supporting akebiconcha kawamurai colonies are a reducing mud bottom at bathyal hypoxic depths alternation between the reducing and oxic assemblages in the outcrop is likely to have been formed by fluctuation of the water mass controlling the dissolved oxygen in the water

spatial productivity variations during formation of sapropels s5 and s6 in the mediterranean sea evidence from ba contents abstract we investigated five time equivalent core sections 180 110 kyr bp from the balearic sea menorca rise the easternmost levantine basin and southwest south and southeast of crete to reconstruct spatial patterns of productivity during deposition of sapropels s5 and s6 in the mediterranean sea our indicators are ba total organic carbon and carbonate contents we found no indications of ba remobilization within the investigated core intervals and used the accumulation rate of biogenic ba to compute paleoproductivity maximum surface water productivity up to 350 g c m2 yr was found during deposition of s5 isotope stage 5e but pronounced spatial variability is evident coeval sediment intervals in the balearic sea show very little productivity change suggesting that chemical and biological environments in the eastern and western mediterranean basins were decoupled in this interval we interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone river derived nutrient input and shoaling of the pycnocline nutricline to the photic zone the productivity increase during the formation of s6 was moderate compared to s5 and had a less marked spatial variability within the study area of the eastern mediterranean sea given that s6 formed during a glacial interval glacial boundary conditions such as high wind stress and or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the eastern mediterranean sea ems observed for s5 a non sapropel sediment interval with elevated ba content and depleted 18o 16o ratios in planktonic foraminifer calcite was detected between s6 and s5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr at this time productivity apparently increased up to five times over surrounding intervals but abundant benthic fauna show that the deep water remained oxic following our interpretation the interval denotes a failed sapropel when a weaker monsoon did not force the ems into permanent stratification the comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the ems

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

nile water as a cause of eastern mediterranean sapropel formation evidence for and against during the late pleistocene sapropels layers of organic carbon rich sediment formed throughout the entire eastern mediterranean basin in close association with glacial interglacial transitions the current theory for the mechanism of sapropel formation involves a density stratification of the water column due to the invasion of a large quantity of low saline water which resulted in oxygen depletion of the bottom waters most workers believe that this low salinity water was glacial meltwater that entered the mediterranean via the black sea and a series of interconnected glacial lakes but the suggestion also has been made that the freshwater originated from the nile river in this study the oxygen isotope values of planktonic foraminifera globigerinoides ruber have been examined in six gravity cores and one piston core from the southern levantine basin and compared with the oxygen isotope records ofg ruber from other areas of the eastern mediterranean this study deals mainly with the latest sapropel which was deposited approximately 7000 to 9000 years ago results indicate that nile discharge probably does reduce salinities somewhat in the immediate area surrounding the mouth of the nile but this water is rapidly mixed with the highly saline waters of the easternmost mediterranean using a mixing equation and surface water salinity limitations an approximate oxygen isotope balance of surface waters was calculated for the time of latest sapropel deposition this calculation shows that neither nile river discharge nor black sea input nor both together are large enough to account for the large scale oxygen isotope depletion associated with latest sapropel deposition in the eastern mediterranean this suggests that part of the isotopic change at termination i is probably due to increased surface water salinities during the last glacial maximum in addition evidence from the timing of sapropel 1 deposition and the dissolved oxygen balance indicates that deposition of the latest sapropel is associated with increased surface water production of biogenic material as much as three times higher than that of present day

origin of rhythmic albian black shales piobbico core central italy calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions 1 the mid cretaceous 120 90 ma was a time of excess atmospheric co2 greenhouse climate and widespread o2 deficiency in the ocean the albian is punctuated by brief intermittent episodes of anoxia dysoxia recorded as cyclic black shales in the western tethys and atlantic oceans the albian section of the piobbico core central italy contains 30 m 10 ma of rhythmic black shales that were sampled at a high resolution and examined for calcareous nannofossil assemblages and c and o stable isotopes unlike oceanic anoxic events productivity was not the primary factor controlling the deposition of albian rhythmic black shales it is suggested that during warm humid climatic cycles higher temperatures and or increased precipitation and runoff produced density stratification at a regional scale recurrent lowered salinity in the early albian and warming in the late albian are credited with causing development of a pycnocline resulting in slower rates of deep water renewal and consequent anoxia

the nature distribution and origin of a sapropelic layer in sediments of the silicia basin northeastern mediterranean a sapropelic layer with organic carbon contents of 1 0 1 5 in contrast to the usual 0 2 0 5 of adjacent normal basin sediments is found to be widespread in sediment cores collected from the cilicia basin northeastern mediterranean the horizon is thought to be equivalent to the s1 sapropel of other workers it is finely laminated with no evidence of bioturbation has a very markedly low magnetic susceptibility and contains a significantly higher content of pollen and plant debris than is found in the normal basin sediment the stable oxygen and carbon isotope values suggest that the layer formed during post glacial climatic warming when fresh nutrient rich surface water flowed into the cilicia basin from the surrounding land to produce a stratified water mass which allowed the development of anoxic bottom waters the distribution of the sapropelic layer indicates that anoxic conditions extended to within approximately 350 m of sea level during deposition a depth shallower than previously recorded in the eastern mediterranean

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

shoaling of the eastern mediterranean pycnocline due to reduction of excess evaporation implications for sapropel formation a simple two layered model is applied to assess the relation between variations in the depth of the permanent pycnocline and changes in the excess of evaporation over freshwater input in the eastern mediterranean this study is performed to estimate the magnitude of the excess evaporation at times of sapropel formation in the eastern mediterranean pycnocline shoaling from a depth below the euphotic layer to a depth within that layer at times of sapropel formation has been inferred from the planktonic foraminiferal record by rohling and gieskes 1989 the model suggests that a decrease in the eastern mediterranean excess evaporation defined as evaporation minus total freshwater input by about 8 5 1011 m yr 1 would suffice to invoke shoaling of the pycnocline to a depth within the euphotic layer a consideration of the effects exerted by concomitant changes in the thermal balance suggests that the necessary decrease of excess evaporation may even be smaller than the above estimate

role of sea level forced sedimentary processes on the distribution of organic carbon rich marine sediments a review of the late quaternary sapropels in the mediterranean sea abstract the 124 ka to present sapropel s5 s1 series in the eastern mediterranean sea correspond to the last glacial interglacial period and permit detailed investigation of 5th order sedimentary frequencies the sapropel layers are clustered in high frequency milankovian cycle that occur within sequence stratigraphic 4th order cycles of late pleistocene holocene sea level oscillations the sea level changes had an amplitude exceeding 120 m and have been correlated to the glacial interglacial cycles modulated by the 100 ka eccentricity using published data we examined occurrences of the complete s5 s1 series in the mediterranean sea and then we focussed on two stratigraphic sequences in the central adriatic shelf and middle adriatic depression where sapropels s5 and s1 were deposited during periods of sea level rise recorded by the transgressive systems tract marine isotopic stage 5 and 1 respectively sapropels s4 and s3 were deposited during the highstand systems tract that developed throughout mis 5 of the late pleistocene sequence sapropel s2 should have been deposited during the warm mis 3 3 and followed the mis 4 sea level drop when sediment supply was enhanced during the late highstand and falling stage of sea level of the late pleistocene sequence the pronounced mis 2 cold stage led to a lowstand and to the regional erosional surface sequence boundary we also compared the adriatic sapropel s5 s2 sequence 4th order to the mid pliocene cluster o sequence 3rd order in both cases sapropels are well formed before the increase of sediment supply due to progradation of the shelf wedge that occurs in the late high stand and initial falling stage in sea level finally we considered the influence of sea level lowering which could cause a weakening of north adriatic deep water formation therefore influencing the mediterranean deep water circulation this condition would favour oxygen depletion but it does not correspond to a well developed sapropel as in the case of s2 based on the assumption that productivity increases related to insolation play a dominant role in their sedimentation sapropel s2 is the result of low amplitude insolation maxima that were unable to generate a productivity increase leading to the burial of conspicuous amount of organic matter therefore in the adriatic sea the absence of the s2 sapropel is correlated to the high sedimentation rate diluting the signal whereas in the eastern mediterranean basin this sapropel is virtually absent because of a weak orbital forcing combined with oxidation that erased its record

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

late quaternary changes in mediterranean intermediate water density and formation rate three recently acquired eastern mediterranean cores containing late quaternary sediments display a marked faunal contrast between the holocene and older sapropels it is suggested that the absence of neogloboquadrinids in the holocene sapropel and their abundance in older sapropels reflect differences in food availability related to the extent of development of a deep chlorophyll maximum layer dcm and the intensity of new primary production associated with this layer the depth of such a layer which consists of phytoplankton with a characteristic taxonomic composition is determined by the vertical hydrodynamical structure during deposition of the older sapropels the pycnocline was apparently positioned well above the base of the euphotic layer a situation that favors a pronounced dcm and an associated relatively high rate of new production shallowing of the pycnocline implies a relatively low density of the mediterranean intermediate water miw on the other hand during deposition of the holocene sapropel the pycnocline had apparently vanished due to termination of miw formation

buffered lagged or cooled disentangling hyporheic influences on temperature cycles in stream channels 1 we monitored summertime base flow water temperatures of hyporheic discharge to surface water in main side and spring channels located within the bank full scour zone of the gravel and cobble bedded umatilla river oregon usa diel temperature cycles in hyporheic discharge were common but spatially variable relative to the main channel s diel cycle hyporheic discharge locations typically had similar daily mean temperatures but smaller diel ranges compressed by 2 to 6 c and desynchronized phases offset by 0 to 6 h in spring channels which received only hyporheic discharge surface water diel cycles were also compressed by 2 to 6 c and desynchronized by 4 to 6 h relative to the main channel creating diverse daytime and nighttime mosaics of surface water temperatures across main side and spring channels despite only minor differences 1 c in daily mean temperatures among the channels the river s hyporheic zone received and stored heat from the channel yet hyporheic return flows carried heat back to the channel minutes to months after removal associated surface water temperature dynamics were therefore complex hyporheic discharge was not simply cooler or warmer than main channel water instead instantaneous temperature differences between channel water and hyporheic discharge typically arose from diel temperature cycles in hyporheic discharge that were buffered and lagged relative to diel cycles in the main channel

identifying distinct thermal components of a creek 1 statistical and heat budget methods for analyzing temperature dynamics of creeks are limited by the ability to resolve thermal processes and fine grained thermal structures respectively here we describe a hybrid method that identifies distinct thermal components in a stream s heat budget using only temperature data and an algorithm that employs mutual information to unmix signals in the temperature data spatial resolution is limited only by the number of temperature logging sensors which can be quite high for distributed temperature sensors process resolution is at the level of thermal components defined as distinct collections of heat flux elements sharing coordinated nonindependent dynamics inference can be used to relate thermal components to meteorological forcing and structural heterogeneity in the fluvial system and to suggest novel hypotheses for further testing with targeted heat budget studies applying the method to a small arid land creek produced two novel hypotheses 1 lateral conduction of heat from adjacent dry land bed terraces appeared to cause a substantial heating of the stream augmented by off channel flow paths and 2 riparian vegetation was associated with a subtraction of heat from the stream at a rate proportionate to solar insolation exceeding the maximum decoupling effect of shade by at least 2 c at midday and suggesting upwelling heat flux from water to tree canopy proportional to sunlight the method appears useful for generating new hypotheses for selecting informative sites for detailed heat budgets for determining the dimensionality of heat budgets in natural streams and more broadly for associating thermal components to fluvial structure and processes

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

geochemical and micropaleontological characterisation of a mediterranean sapropel s5 a case study from core ban89gc09 south of crete several geochemical and micropaleontological proxies were studied in a well developed sapropel s5 from a core collected south of crete to investigate the causes and the mechanisms of its deposition to reconstruct the paleoenvironmental and paleoceanographical conditions at time of its formation and to detect the roles played by productivity and anoxia the geochemical proxies are also used to unravel the sediment provenance and therefore to help tracing water circulation patterns and freshwater sources the multiproxy approach reveals that the sapropel layer has high internal variability and five different depositional phases can be identified four within the visible sapropel layer an increase in temperature and the development of a deep chlorophyll maximum characterise the onset of the sapropel phase 1 with enhanced productivity being favoured by local riverine input not clearly ascribable to nile river freshwater discharge and by the shoaling of the pycnocline nutricline surface water stratification and productivity develop together with strong seafloor dysoxia anoxia phase 2 is characterised by lower stratification slightly lower temperature and or higher seasonal contrast and still high productivity phase 3 records high productivity high temperature and high stratification probably more sustained by the nile input a sudden partial re oxygenation takes place at the end of this phase changing the main features of the sapropel in the fourth phase productivity starts to decrease water stratification seems to be partially broken down and sediment oxygenation increases a transitional phase phase 5 occurs between the end of the visible sapropel and the normal pelagic post sapropel sedimentation where productivity is still high and oxygenation improves compared to the visible sapropel layer the massive occurrence of polysphaeridium zoharyi cyst of a red tide forming dinoflagellate also characterises this phase the geochemical proxies indicate that pre sapropel and post sapropel sediments are quite different from each other and the provenance shifts from a more mixed to a more markedly southern origin of sediments

late pleistocene holocene sedimentation in the nw aegean sea a palaeoclimatic palaeoceanographic reconstruction sedimentological particle size organic carbon calcium carbonate clay mineralogy and radiocarbon dating and micropalaeontological investigation of 9 cores from the nw aegean sea eastern mediterranean have enabled five main lithological units to be identified the units cover a period from the late pleistocene to the present day on the basis of these results and reference to other studies a palaeo reconstruction is presented for the area the reconstruction takes into account the increase in sea level during the period the decrease in fluvial inputs issuing to the area from the north mediterranean coastline and the possible influence of water issuing from the black sea it is concluded that the sedimentological and oceanographic regimes of the area were strongly influenced by a fluvial component during the late pleistocene and early holocene whereas today the sedimentary record is more indicative of an open oceanic environment

high frequency climate fluctuations over the last deglaciation in the alboran sea western mediterranean evidence from calcareous plankton assemblages abstract a high resolution study with a centennial scale resolution has been performed on the calcareous plankton assemblage coccolithophores and planktonic foraminifera at ocean drilling program site 976 alboran sea western mediterranean focusing on the interval between 20 and 9 ka in order to reconstruct changes in surface and subsurface water dynamics and productivity the biotic surface water proxies integrate the extremely detailed multi decadal scale geochemical data set and the pollen record already available at the core thus providing a complete paleoenvironmental paleoceanographic reconstruction the results highlight the sensitivity of the calcareous plankton in recording stadial interstadial phases and higher frequency climatic events that produced changes in sea water features wind induced upwelling and river discharge during the last glacial period favored nutrient availability and moderate productivity during heinrich stadial 1 hs1 the arrival of cold and fresher waters from iceberg melting in the north atlantic significantly hampered productivity at its lowest values of the whole investigated interval calcareous plankton behavior supports the hypothesis that hs1 is a composite event marked by three phases hs1a characterized by the coldest sst polar atlantic water inflow into the basin and a first step toward a dry climate on the continent hs1b recording enhanced freshwater inflow and drought on land and hs1c indicating reduced polar water influx the bolling allerod ba interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of organic rich layer 1 during the ba coccolithophore assemblage also marks higher frequency changes in hydrographic conditions apparently in relation with greenland interstadial i gi i high variability the younger dryas stadial yd is characterized by refunding cold and dry conditions although not as severe as during hs1 and by enhanced detrital input in surface water during drier conditions on land the holocene onset records climate amelioration both in the marine and continental environment although coccolithophore productivity is not as high as during the ba the rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases subphases is characterized by a complex pattern forced by strong interaction between ice sheet instability meltwater discharge entering the gibraltar strait north atlantic westerlies and moisture availability clearly impacting over surface water temperature productivity and land masses

paleoenvironmental changes during sapropel 19 i cycle 90 deposition evidences from geochemical mineralogical and micropaleontological proxies in the mid pleistocene montalbano jonico land section southern italy an integrated micropaleontological geochemical and mineralogical study has been performed across the mid pleistocene sapropel 19 i cycle 90 from the montalbano jonico land section southern italy to reconstruct the paleoenvironmental conditions at time of its formation the sapropel interval is characterized by two oxygen depletion phases phase a and c interrupted by a temporary re oxygenation interval phase b the beginning and the end of sapropel deposition are dated at 957 0 81 kyr and 950 0 86 kyr respectively the duration of the interruption is estimated to 0 350 0 32 kyr the multiproxy approach highlights that deposition of sapropel 19 reflects a period of enhanced freshwater runoff induced by a wetter climate as a consequence of a more efficient fluvial erosion a higher terrigenous input mostly ascribable to a southern apennines source and an increased turbidity of surface waters accompanied most of sapropel deposition biotic and abiotic proxies document that different paleoenvironmental conditions occur through phases a c the beginning of phase a is characterized by warm on land paleoclimate as well as warm and oligotrophic surface water conditions during the upper part of phase a temperature starts decreasing and surface waters appear more productive this change probably represents the prelude to cooler and drier conditions characterizing phase b which displays a river supply reduction and an eolian input increase sahara dust during phase c the restored depleted oxygen environment at the bottom sediments is clearly coupled with the re establishment of humid conditions and increased river supply at the same time enhanced mixing of water column a cooler paleoclimate and increased productivity of surface waters are recorded the latter likely favored by the enhanced mixing of water column and also increased delivery of land derived nutrients the end of phase c is marked by a restored normal run off enhanced productivity in surface waters and low oxygen conditions at the bottom sediments persist slightly above phase c the overall results suggest that the onset of sapropel deposition is related to water stratification that caused low oxygen exchanges with the sea bottom although enhanced productivity characterizes most of the sapropel deposition it was not the primary factor triggering sapropel deposition

paleoenvironmental conditions at core kc01b ionian sea through mis 13 9 evidence from calcareous nannofossil assemblages quantitative analyses on calcareous nannofossil assemblages on high temporal resolution 600e800 years have been carried out from core kc01b in the ionian sea eastern mediterranean throughout marine isotope stage mis 13e9 between 500 and 300 ka this is an interval of considerable climate changes known as the mid brunhes event which includes mis 11 considered as a possible analogue for future interglacial conditions in the mediterranean core the interval is characterized by the dominance of gephyrocapsaspp as also known fromocean records calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity water stratification and temperature specifically the increase in abundance of gephyrocapsa caribbeanica and small gephyrocapsa coupled with decreases of florisphaera profunda syracosphaera spp and rhabdosphaera spp suggests enhanced primary productivity mixed surface waters during interglacial stages and at the terminations which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation on the other hand distributions of calciosolenia spp oolithotus spp and umbilicosphaera sibogae which are inphase with d 18 o curve showing higher abundances at the lighter values of the marine

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

recent sapropel formation in the eastern mediterranean during the 1983 expedition of the rv tyro in the eastern mediterranean a combined programme of seismological micropalaeontological and geochemical research was performed the geochemical research focused mainly on the interstitial water and the chemical composition and origin of sapropels for this purpose box cores piston cores and bottom water samples were collected we report here that some of these cores showed clear evidence of long term stagnant bottom water conditions in a small basin south of crete for which we propose the name tyro basin 1 the bottom water is strongly anoxic whereas the sediment down to at least 400 cm is sapropel to sapropelic as salt concentrations in the bottom water are eight times higher than in normal seawater the anoxic conditions in this basin are probably due indirectly to dissolution of salt from a nearby diapir

mediterranean pluvial periods and sapropel formation over the last 200 000 years abstract three mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200 60 kyr bp the isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water w in the tyrrhenian sea and levantine basin our results show a strong w salinity decrease in both basins associated with each sapropel these w decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel s 1 centred at ca 8 kyr bp a strong precipitation increase transformed the whole mediterranean sea into a non concentration basin the low surface salinity was responsible for the water column stratification while nutrients brought in by the runoff enhanced productivity it resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin in addition the mediterranean sea 18 o record is very similar to that of the bay of bengal as the latter is very sensitive to the summer monsoon rain this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon like precipitation due to an increase in summer insolation driven by precession variations

the formation of eastern mediterranean sapropels abstract sapropel formation in the eastern mediterranean is explained by an oceanographic approach it is suggested that sapropels are not only a consequence of eustatic sea level changes as earlier proposed by olausson a model which is widely accepted but rather a result of a very sensitive reaction of the eastern mediterranean to any small climatic amelioration present day aeration of the deep eastern mediterranean basin results from circulation of oxygen rich deep water originating mainly in the adriatic assuming present day conditions a climatic amelioration towards more humid and warmer conditions leading to an increase of the water temperature in the adriatic basin by 0 7 c or to a decrease of its salinity by only 0 2 will cause stratification of water masses and enhance sapropel formation