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

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

a complex trace fossil from the spitskop member terminal ediacaran lower cambrian of southern namibia streptichnus narbonnei igen et isp nov a new trace fossil from the upper part of the spitskop member of the urusis formation southern namibia consists of clusters of unidirectionally curved radial elements in which individual elements typically are composed of imbricated sickle shaped segments somewhat comparable to those of treptichnus pedum such complex trace fossils generally are found only in cambrian or younger strata this opens to question the position of the ediacaran cambrian boundary in the nama group suggesting that it may locally be within the uppermost part of the urusis formation rather than at the base of the nomtsas formation

hydrogen isotopic compositions of long chain alkenones record freshwater flooding of the eastern mediterranean at the onset of sapropel deposition sapropels are organic rich sediment layers that were intermittently deposited in the mediterranean sea especially in its eastern basin during the last 10myr the associated anoxic events that gave rise to sapropel formation resulted indirectly from the impact of african monsoon maxima on the basin s hydrography sharp shifts in oxygen isotopes 18o to values more depleted in the heavy isotope 18o in carbonates from surface dwelling planktonic foraminifera slightly preceding sapropel deposition suggest that the mediterranean was flooded by large amounts of freshwater leading to the development of a low salinity of the surface water and a strong density stratification of the water column however the degree of freshwater flooding and concomitant drop in sea surface salinity sss remain elusive recent work has shown that the hydrogen isotope d values of long chain alkenones produced by haptophyte algae depend mainly on the d of the water and on salinity and may therefore offer a new tool for salinity reconstructions our analysis of the d of alkenones from last interglacial sapropel s5 from the aegean sea shows a large decrease in d of 25 at the onset of sapropel formation suggesting a drop in sss of 6 from 39 to 33 although the absolute sss estimates should be interpreted with care as they are subject to relatively large uncertainties the estimated sss values appear quite reasonable as they for example yield sss before sapropel deposition similar to that of the present day aegean sea to reduce uncertainties in sss estimates the d salinity relationship has to be better constrained with cultures and also tested in field studies however our results do illustrate the promise of a combined use of d of alkenones u37k of alkenones and 18o of surface dwelling planktonic foraminifera for sss reconstructions

nitrogen isotope dynamics of the cariaco basin venezuela 1 we report 15n 14n measurements of water column nitrate and ammonium sinking particles and sediments from the cariaco basin an anoxic marine basin off the coast of venezuela water column denitrification occurring in the basin has only a very small isotopic imprint on nitrate in the basin because nitrate consumption is nearly complete in the actively denitrifying water near the oxic anoxic interface 275 m being free of a large denitrification signal the 15n of shallow thermocline nitrate is 3 5 significantly lower than the mean deep ocean nitrate 15n of 5 this may be due to the nitrification of newly fixed n whether it occurs within the basin or in open atlantic waters that flow into the cariaco over the sill the 15n 14n of the sinking flux in the deepest trap 1250 m is similar to that of thermocline nitrate as expected given the complete consumption of nitrate in the surface layer moreover the 15n 14n of the seafloor sediment is similar to that of the sinking flux as is common in environments of high export production low o2 and good organic matter preservation thus the modern cariaco basin records the 15n 14n of the thermocline nitrate which in turn may record the input of newly fixed n to the upper ocean be it local or more regional in origin

biological productivity during sapropel s5 formation in the eastern mediterranean sea evidence from stable isotopes of nitrogen and carbon we determined 15n 14n ratios in modern surface and sapropel s5 sediments of the mediterranean sea to clarify differences in the nutrient regime associated with sapropel formation in the modern situation high 15n of unused nitrate 15 20 remaining in the surface waters during the winter phytoplankton bloom evidences p limitation of biological production in winter 15n of surface sediments decrease towards the east of the basin 5 to 2 5 this is a consequence of either eastward increasing nitrogen fixation during the summer months or of particulate matter being supplied predominantly by the p limited winter bloom very low 1 1 15n values in sapropel s 5 from four locations require a very light source of nutrient n assimilated at a minimum of ten times the modern export flux because the isochronous records show no spatial gradient in 15n we exclude both ekman type upwelling and direct riverine discharge as likely sources of nutrients our data are consistent with an anti estuarine thermohaline circulation in the upper 500m during s5 time allowing for the trapping of nutrients in the eastern basin the most likely scenario for s5 is that phosphorus release from a relatively shallow redox boundary resulted in an imbalanced supply of n p 16 1 to the photic zone the result was a slow assimilation of carbon during summer stratification and extensive n2 fixation providing the majority of the export flux from a n limited system

evidence from burial sediments for prehistoric burial practice and ritual in monte claro chambered tombs micromorphology mineralogy and geochemistry abstract the burial matrix in archaeological graves is seldom subject to detailed examination for evidence of its potential interaction with the interred remains sediments adjacent to skeletal remains resting on a marl platform in a subterranean chambered burial dated to the third millennium bc were investigated using micromorphological archaeobotanical and chemical methods micromorphological features in the tombs typical of caco3 depletion appeared more abundant in positions close to the skeletal remains than in positions further away suggesting that the carbonate dissolution was caused by acidification resulting from the body decay as well as from environmental factors organic signatures around the remains were dominated by background sedimentary organic matter of the marl attesting to the exposed style of burial being unfavourable for the preservation of organic remains red concentrates present in a distinct region of the resting platform were distinguishable from similar coloured deposits formed by debris from the vault they were identified as haematite ochre deposits matching features observed in other prehistoric sites including those of the same culture and attesting to ritual associated with the treatment of the dead greyish fibrous contexts found on the burial resting platforms were identified as silicified sedge probably remnants of the combustible parts of torches the position and nature of the sedge derived material suggests their use for illuminating the graves at depth and or as a possible votive ritual the detailed scientific examination of the burial matrix can reveal unique perspectives and add interpretative value to the archaeological investigation of graves

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

nile river sediment fluctuations over the past 7000 yr and their key role in sapropel development the provenance pattern of nile river sediments can be used as a proxy for paleoclimatic changes in east africa the 87sr 86sr ratios are particularly appropriate for such provenance investigations because the white nile drains predominantly crystalline basement rocks whereas the blue nile and atbara flow off the ethiopian highlands which consist of tertiary volcanic rocks a high resolution profile of 87sr 86sr and ti al ratios from a well dated core in the nile delta shows a close correspondence with known changes in nile flow over the past 7000 yr at times of higher river flow there was markedly decreased input of blue nile derived and total sediment this change was caused by northward movement of the inter tropical convergence zone resulting in increased vegetative cover in the ethiopian highlands due to higher rainfall and a longer wet season this inverse relationship between nile river flow and sediment flux may have had important implications in the development of agricultural technology in ancient egypt the marked minimum in 87sr 86sr at 4200 4500 yr b p is coincident with the end of the old kingdom in egypt and provides independent evidence that demise of the old kingdom might have been associated with an extended period of catastrophic low floods during the quaternary and late neogene there was periodic deposition of organic rich sediments sapropels in the eastern mediterranean that represent important indicators of major environmental change evidence from the ti al ratio suggests that the pattern of erosion and sediment supply from the nile catchment observed in this study also occurred throughout much of the neogene and quaternary the reduced inputs of blue nile sediment during times of sapropel formation contributed to the increased primary productivity by reducing the amount of phosphate removed on particles and to the observed change to n limitation in the eastern mediterranean which are important characteristics of sapropel deposition

evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the eastern mediterranean sea abstract nitrogen isotopes of chlorins degradation products of chlorophyll reflect the isotopic composition of nutrient n utilized by marine phytoplankton communities here we show that in sediments of the eastern mediterranean pleistocene and holocene values of 15n for chlorins and total nitrogen vary in concert with a consistent offset of 5 reflecting the fractionation imparted during chlorophyll biosynthesis samples from the integrated ocean drilling program sites 964 and 969 were analyzed at a sampling resolution of 4 10 cm clustered around sapropel events 2 3 4 and 5 100 170 ka in low organic content sediments chlorin values of 0 coincident with total nitrogen values of 5 indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment in sapropel horizons the chlorin and total nitrogen values are 5 more negative 5 and 0 respectively resembling previously reported modern day water column particulates 0 we suggest that nutrient conditions in the eastern mediterranean correspond to three scenarios and that the similarity between sapropel and modern day bulk 15n is coincidental organic poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of atlantic sourced nitrate sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine p fluxes to surface waters present day conditions are dominated by anthropogenic n sources these scenarios agree with a model of sapropel formation in which stratification caused by increased fresh water inputs led to n fixation due to p n nutrient imbalance enhanced production combined with stratification promoted and maintained anoxic deep waters consequently increasing organic matter preservation such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

carbon and nitrogen isotope excursions in mid pleistocene sapropels from the tyrrhenian basin evidence for climate induced increases in microbial primary production the modern mediterranean sea is oligotrophic yet its sediment record contains layers of organic carbon rich sapropels at 21 ky precessional spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important we have made a high resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3 m sequence that corresponds to 1001 to 946 ka organic 13c values systematically increase from 26 to 21 and 15n values systematically decrease from 4 to 0 as organic carbon mass accumulation rates increase in the sapropel layers the increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates the decrease in nitrogen isotope values implies major contributions of nitrogen fixing cyanobacteria to the total marine productivity the precessional minima with which sapropels coincide were times of wetter climate that stratified the surface mediterranean sea increased delivery of soil derived phosphorus and evidently amplified microbial primary production our high resolution study reveals several relatively rapid excursions into and out of the high productivity mode that suggest that sapropel deposition was a climate sensitive surface driven phenomenon that was not accompanied by basin wide stagnation

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

seasonal salinity changes during mediterranean sapropel deposition 9000 years b p evidence from isotopic analyses of individual planktonic foraminifera using stable isotopic analyses of individual tests of planktonic foraminifera with different seasonal and depth habitats we have investigated temporal variations in surface water salinities in the eastern mediterranean during the past 13 000 years low oxygen isotopic values document the presence of anomalously low salinity conditions in the eastern mediterranean at about 13 000 years b p 4000 years before the deposition of the youngest sapropel by 11 000 years b p during the deposition of presapropel sediments low salinity surface waters were more pervasive but were restricted to summer months and only affected the surface of the water column at the onset of sapropel deposition about 9000 years b p surface salinities in the eastern mediterranean had decreased by almost 4 and had extended to depths of at least 75 m the low salinity surface lens was not however a permanent feature of the eastern mediterranean during sapropel deposition low salinity surface conditions occurred in the fall and winter seasons but normal sea surface salinities returned during spring months on a seasonal and or interannual basis thus a low salinity surface lens could have existed continuously for months or decades at a time but would have been interrupted intermittently by a return to normal conditions any triggering mechanism proposed for mediterranean sapropels must account for the seasonal fluctuations and ephemeral nature of low salinity conditions in the eastern mediterranean despite normal salinities returning occasionally during spring months a low salinity surface lens may have greatly inhibited the production of levantine intermediate water prevented the formation of adriatic deep water and consequently reduced ventilation of the eastern mediterranean

neogene sapropels in the mediterranean a review for 50 years the existence of sapropels organic carbon rich sediments deposited within plio pleistocene sediments of the mediterranean sea has been known initially research concentrated on material recovered in relatively short gravity piston cores taken from the eastern basins where sequences were found to be well developed preserved and had extensive spatial coverage in the main previous studies concentrated upon establishing a workable stratigraphy spatial correlation of individual layers and determining the probable depositional mechanisms however despite a plethora of research papers some issues still remain unresolved this is in part due to a lack of agreement between investigators sampling and analytical short comings restricted sample size and the fact that in many instances like was not being compared with like recently the limit of sapropels in the western basin has been further extended as a result the palaeoceanographic palaeoclimate models which had previously been developed for deposition of sapropels in the eastern basin have been modified most recently strong links have been established between astronomical cyclicity and sapropel formation this review paper provides a summary of sapropel research to date and ongoing sapropel research in the mediterranean some of which appears in this thematic issue of marine geology it is fitting that this thematic issue of marine geology be dedicated to the memory of colette vergnaud grazzini and rob kidd who in many ways helped to initiate the resurgence in sapropel studies in the 1970s in the mediterranean perhaps in 50 more years we will know all of the answers 1999 elsevier science b v all rights reserved

glacial holocene δ15n record from the gulf of tehuantepec mexico implications for denitrification in the eastern equatorial pacific and changes in atmospheric n2o 1 the intensity of denitrification in the gulf of tehuantepec along the mexican margin of the eastern tropical north pacific etnp was reconstructed for the last 23 000 years using the nitrogen isotopic composition of sediment organic matter 15norg in conjunction with other geochemical tracers of water column productivity during the last glacial period 15norg values ranged from 6 5 to 8 6 with values increasing between 23 and 17 ka deglaciation was marked by an abrupt increase in 15norg with maximum values 9 9 occurring during the bolling allerod period and the earliest holocene a decline in 15norg values occurred over the last 10 000 years with late holocene values being similar to those of the glacial period our data suggest that denitrification in this region was minimal during the last glacial and is consistent with the deposition of bioturbated sediments at the study site the intensity of denitrification increased dramatically during deglaciation and the early holocene signaling the presence of a strong oxygen minimum zone this period is also marked by the deposition of laminated sediments in the region the 15norg records display similar temporal trends to those seen in the greenland ice core record of atmospheric n2o concentrations at present denitrification within the eastern tropical pacific and arabian sea accounts for a major portion of the global marine loss of fixed nitrogen and a significant fraction of the ocean atmosphere n2o flux originates from these areas large changes in n2o emissions from these regions in the past would have directly impacted global greenhouse gas concentrations

a large abrupt change in the abyssal water masses of the eastern mediterranean 1 in this letter we report observations showing for the first time the occurrence of a new major transformation in the thermohaline cell of the eastern mediterranean sea after 2 decades during which waters of aegean origin dominated the abyssal layers of that basin the adriatic sea has returned to represent a major source of eastern mediterranean deep water emdw the observed characteristics of such water however profoundly differ from those observed previously in the abyssal layers of the ionian basin in fact the newly formed emdw we observed there is saltier warmer and denser than emdw observed before and during the eastern mediterranean transient emt thus during the past 2 decades the thermohaline cell of the eastern mediterranean once considered steady showed two large abrupt somehow opposite fluctuations as in the case of the first one origins climatic implications and fate of this second fluctuation have to be clarified

improved preservation of organic matter and pollen in eastern mediterranean sapropels here we investigate the processes leading to high organic content and high pollen concentration in pelagic marine sediments three marine cores near the base of the nile river cone display the classical quaternary sequence of sapropels and hemipelagic muds large variations in total pollen concentration as well as in percentage composition of the pollen assemblage are clearly linked to the two lithological types all pollen types have much higher concentration in sapropels than in muds by 3 or 4 orders of magnitude within sapropels the percentages of gymnosperms pinus and cedrus pollen and pteridophyte spores are very low and the pollen spectrum is dominated by various angiosperms these variations in total pollen concentration as well as in percentages cannot be accounted for by variations in pollen production or in efficiency of transport because they similarly involve pollen of different areas and climates transported to the sea by different means the cause for these variations can only be a difference in preservation of pollen preservation is good in sapropels for all pollen types but generally poor in muds we believe that sapropels were deposited under reducing bottom waters which allowed a better preservation of the organic matter including pollen

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

water column dynamics during the last interglacial anoxic event in the mediterranean sapropel s5 1 marine organic rich sediments are important for long term carbon sequestration and as a source of fossil hydrocarbons but the processes underlying their formation remain elusive we present a multiproxy analysis of a relatively recent well preserved mediterranean organic rich deposit known as sapropel s5 which formed 124 119 thousand years ago ka b p where b p references year 1950 combining planktonic foraminiferal abundance records with stable isotope and organic biomarker data we reconcile the apparently contradicting coexistence of deep dwelling foraminiferal faunas with green sulphur bacteria that indicate photic zone euxinia s5 started with a rapid freshwater induced increase of density stratification that inhibited vertical mixing and deepwater ventilation through the first 900 years anoxic to euxinic deepwater conditions developed and extended up to roughly 200 m water depth then followed a 4100 year period of variability in the depth intensity of winter mixing with a roughly 1400 year periodicity coincident with fluctuations in water column stability s5 terminated with a marked decrease in density stratification and consequently renewed convective overturn

the role of atmospheric deposition in the biogeochemistry of the mediterranean sea abstract estimates of atmospheric inputs to the mediterranean and some coastal areas are reviewed and uncertainities in these estimates considered both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important 50 or even dominant 80 contribution to sediments in the offshore waters of the entire mediterranean basin model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen one third of total phosphorus and 10 of the zinc entering the entire basin measured data in sub basins such as the north western mediterranean and northern adriatic indicate an even greater proportions of atmospheric versus riverine inputs when dissolved fluxes are compared the form most likely to impinge on surface water biogeochemical cycles the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes neglecting co limitation by other nutrients new production supported by atmospheric nitrogen deposition ranges from 2 4 g c m 2 yr 1 whereas atmospheric phosphorus deposition appears to support less than 1 g c m 2 yr 1 in spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of n p or fe future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric oceanographic forcing functions a scientific program aimed at elucidating the possible biogeochemical effects of saharan outbreaks in the mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

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

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

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