organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

peak last glacial weathering intensity on the north american continent recorded by the authigenic hf isotope composition of north atlantic deep sea sediments we have retrieved radiogenic hafnium hf isotope compositions hf from authigenic fe mn oxyhydroxides of deep northwest atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from ne america during the last deglaciation the extraction of seawater derived hf isotopic compositions from fe mn oxyhydroxides is not a standard procedure comparisons between the al hf ratios and hf isotopic compositions of the chemically extracted authigenic phase on the one hand and those of the corresponding detrital fractions on the other provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures this is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper blake ridge for which consistent replicates were produced throughout the hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central north atlantic seawater comparison with previously published seawater nd and pb isotope compositions obtained on the same cores shows that both hf and pb were released incongruently during incipient chemical weathering but responded differently to the deglacial retreat of the laurentide ice sheet hafnium was released more congruently during peak glacial conditions of the last glacial maximum lgm and changed to typical incongruent interglacial hf signatures either during or shortly after the lgm this indicates that some zircon derived hf was released to seawater during the lgm conversely there is no clear evidence for an increase in the influence of weathering of lu rich mineral phases during deglaciation possibly since relatively unradiogenic hf contributions from feldspar weathering were superimposed while the authigenic pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental north america during the transition to the holocene a similar incongruent excursion is notably absent in the hf isotope record the early change towards more radiogenic hf in relation to the lgm may provide direct evidence for the transition from a cold based to a warm based laurentide ice sheet on the atlantic sector of north america

history of laurentide meltwater flow to the gulf of mexico during the last deglaciation as revealed by reworked calcareous nannofossils the history of meltwater flow from the laurentide ice sheet to the gulf of mexico during the last deglaciation which holds possible implications for the cause of the younger dryas cold episode is not well understood we propose a new chronology based on using the percentage of reworked calcareous nannofossils in orca basin sediments as a proxy for erosion the period of greatest meltwater flow to the gulf was between 12 7 and 12 1 ka during the bolling warm interval and flow remained high until the beginning of the younger dryas cold episode at 11 3 ka this corresponds to meltwater pulse ia a sharp meltwater decrease at 12 2 ka may represent the older dryas glacial readvance little or no meltwater is inferred to have flowed to the gulf from 10 to 9 ka which is the time of the second major meltwater pulse ib therefore meltwater must have been permanently diverted away from the gulf of mexico at the beginning of the younger dryas

the cretaceous tertiary boundary cocktail chicxulub impact triggers margin collapse and extensive sediment gravity flows a distinctive mixture of reworked microfossils impact derived materials and lithic fragments occurs in sediments at the cretaceous tertiary boundary in the basinal gulf of mexico and caribbean we have named this mixture the cretaceous tertiary boundary cocktail lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows apparently triggered by the collapse of continental margins around the gulf of mexico as a result of the chicxulub impact as most microfossils in the gravity flow units are reworked biostratigraphy provides only maximum ages recognition of the cocktail is a reliable way to identify cretaceous tertiary boundary deposits in the basinal gulf of mexico and caribbean

relationships between anoxia glacial meltwater and microfossil preservation in the orca basin gulf of mexico abstract the isotopic and microfossil records from piston core en32 pc6 from the orca basin gulf of mexico reveal that various factors have moderated the sediment composition of the basin during the last 29 000 yrs 29 ka b p coincident with the introduction of isotopically depleted glacial meltwater into the gulf approximately 16 ka b p anoxic conditions commenced within the intraslope basin as evidenced by sedimentary laminations and improved microfossil pteropod planktonic foraminifera and radiolaria preservation the increased delivery of terrigenous organic matter with the glacial meltwater may have been responsible for inducing the anoxia also at this time the water of the orca basin was most likely somewhat stratified due to elevated salinities and the increased supply of organic matter onto the continental slope from the continent would have depleted the oxygen supply of the orca basin by oxidative consumption about 13 ka b p oxygenated conditions resumed and microfossil abundance preservation decreased when meltwater input diminished at 8 5 ka b p the orca basin again became anoxic due to the development of the orca basin brine

alternative routing of lake agassiz overflow during the younger dryas new dates paleotopography and a re evaluation abstract overflow from glacial lake agassiz has been implicated in affecting late glacial ocean circulation and climate the timing of the diversion of lake agassiz overflow away from its southern routing to the gulf of mexico correlates closely with the younger dryas ca 11 10 14 c ka new models of paleotopography in the eastern outlet region of lake agassiz adjusted for differential isostatic rebound show that overflow to the superior basin would have occurred when the lake formed its herman norcross and tintah beaches just after 10 9 14 c ka if the laurentide ice sheet lis had retreated from the thunder bay ontario region by that time however the absence of coarse flood deposits normally associated with large overflows plus the morphology of possible overflow channels in the thunder bay region suggest that agassiz overflow may not have been routed into the great lakes during the younger dryas as previously believed in addition non carbonate radiocarbon dates in the thunder bay area are all younger than 10 14 c ka suggesting that this area may not have been deglaciated until after the younger dryas thus preventing lake agassiz overflow through this area an alternative route of overflow from lake agassiz during the younger dryas could have been through the northwestern clearwater outlet to the arctic ocean although all research to date shows that this region was covered by ice until 10 14 c ka on the other hand it is possible that older and coarser overflow sediment may now lie buried beneath finer deposits associated with the 10 14 c ka marquette readvance of the lis which ponded waters in valleys between lake agassiz and lake superior or that eastward overflow in this area was not catastrophic

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

hydrodynamic sorting and transport of terrestrially derived organic carbon in sediments of the mississippi and atchafalaya rivers abstract over the course of two years four cruises were conducted at varying levels of discharge in the lower mississippi and atchafalaya rivers mr and ar where grab samples were collected from sand and mud dominated sediments the tetramethylammonium hydroxide tmah thermochemolysis method was used to determine sources of terrestrially derived organic carbon oc in these two sediment types to examine the effects of hydrodynamic sorting on lignin sources in river sediments average lignin concentrations in the lower mr were 1 4 1 1 mg goc 1 at english turn et and 10 4 27 4 mg goc 1 at venice using these concentrations annual lignin fluxes to the gulf of mexico from tidal and estuarine mud remobilization at et and venice were 3 1 2 5 10 5 kg and 11 4 30 0 10 5 kg respectively much of the lignin derived materials in muddy sediments appeared to be derived from non woody grass like sources which should decay more quickly than the woody materials typically found in the sandy deposits the average total oc 1 93 0 47 of english turn sands yields an annual flux of 0 34 0 09 10 9 kg lignin flux in the english turn sands 3 6 2 6 mg gc 1 using the numbers above would be 12 2 9 4 10 5 kg the extensive amounts of sand sized woody materials coffee grinds found in the sandy sediments in both the ar and mr are likely derived from woody plant materials this is the first time it has been demonstrated that sandy sediments in the mr provide an equally important pathway compared to muds for the transport of terrestrially derived organic matter to the northern gulf of mexico using the ar average oc in sand 1 16 0 72 we estimated an annual flux of oc to the shelf of 0 13 0 07 10 9 kg lignin flux for ar sands was estimated to be 12 4 12 1 10 5 kg despite the high error associated with these numbers we observe for the first time that the flux of lignin in sandy sediments in the ar to the northern gulf of mexico is comparable to that found in the mr these results further support the likelihood of grain size related hydrodynamic sorting of terrestrially derived organic carbon in the lower mississippi and atchafalaya rivers suggesting that there is a distinct sandy sediment organic fraction contributed by major rivers to the global carbon cycle

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

a low extinction rate of intermediate water benthic foraminifera at the cretaceous tertiary boundary the contrast between the high extinction rates of calcareous marine plankton and low extinction rates of deep water calcareous benthic foraminifera across the cretaceous tertiary k t boundary is now recognized however the water depth at which the vertical change in extinction rates of marine organisms occurred at the k t boundary is not yet known because of the lack of data on the extinction rates of intermediate water organisms the extinction rate of intermediate water benthic foraminiferal species from kawaruppu hokkaido japan was determined by distinguishing locally extinct species a distinctly low extinction rate 10 for calcareous benthic foraminiferal fauna from the upper part of the intermediate water is documented for the first time this rate is almost equal to the extinction rate of deep water benthic foraminifera 10 and is much smaller than the planktic foraminiferal extinction rate 81 the extinction rate curve for calcareous foraminifera in a vertical water column indicates that a rapid change from a high extinction rate 80 to a low extinction rate 10 took place at a water depth of about 150 m this depth of change is equivalent to the boundary depth between the surface and intermediate waters and between the euphotic and aphotic zones furthermore this coincidence is consistent with the hypothesis that acid rain and a darkness induced breakdown of the marine food chain produced by a cometary or asteroidal impact at the k t boundary were the main causes of the mass extinction of calcareous planktic organisms in surface waters

chronology of glacial lake agassiz meltwater routed to the gulf of mexico abstract sediment cores with new radiocarbon dates from the southern outlet of glacial lake agassiz indicate that meltwater delivery to the mississippi valley was disrupted at 10 800 14 c yr b p and the outlet was abandoned by 9400 14 c yr b p these findings confirm the timing of generally accepted terminations of the lockhart and emerson phases of lake agassiz additionally the radiocarbon chronology indicates that the spillway was fully formed by 10 800 14 c yr b p and that the occupancy in late emerson time was likely short lived with minimal spillway erosion

provenance of freshwater pulses in the gulf of mexico during the last deglaciation during the last deglaciation the decaying laurentide ice sheet lis delivered huge volumes of meltwater toward the gulf of mexico the present investigation of clay mineralogy and grain size characteristics of terrigenous sediments deposited in the orca basin gulf of mexico offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns five peculiar sedimentary levels characterized by high smectite content and low caco3 content were identified and occurred simultaneously with major meltwater floods according to recently published clay mineral distribution maps for north america these results help to pinpoint the southwestern margin of the lis as a main contributor to most of the meltwater discharges in addition the peculiar mineralogical composition illite and chlorite rich of the sediments characterizing the meltwater episode associated with heinrich event 1 suggests a provenance from the great lakes area supporting the interpretation of destabilization of the lis southeastern margin during this event decreased terrigenous contribution associated with changing provenance of sediments after 12 9 cal ka bp suggests strong modifications of the continental hydrography in relation to lake agassiz history and changes in the morphology of mississippi delta due to rising sea level

the ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

origins and accumulation of organic matter in expanded albian to santonian black shale sequences on the demerara rise south american margin ocean drilling program leg 207 recovered thick sequences of albian to santonian organic carbon rich claystones at five drill sites on the demerara rise in the western equatorial atlantic ocean dark colored finely laminated cenomanian santonian black shale sequences contain between 2 and 15 organic carbon and encompass oceanic anoxic events 2 and 3 high rock eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin however d 13 corg values lie mostly between 30 and 27 and toc tn ratios range from 15 to 42 which both mimic the source signatures of modern c3 land plants the contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations the low d 13 corg values which are actually common in mid cretaceous marine organic matter are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle the elevated c n ratios which are also typical of black shales indicate depressed organic matter degradation associated with low oxygen conditions in the water column that favored preservation of carbon rich forms of marine organic matter over nitrogen rich components underlying the laminated cenomanian santonian sequences are homogeneous dark colored lower to middle albian siltstones that contain between 0 2 and 9 organic carbon the organic matter in these rocks is mostly marine in origin but it occasionally

the effects of retrograde reactions and of diffusion on 40ar 39ar ages of micas the effects of metamorphic reactions occurring during decompression were explored to understand their influence on the ar ar ages of micas monometamorphic metasediments from the lepontine alps switzerland reached lower amphibolite facies during the barrovian metamorphism related to the collision between european and african adria continental plates mineral assemblages typically composed of garnet plagioclase biotite muscovite and paragonite or margarite were screened for petrological equilibrium to focus on samples that record a minimum degree of retrogression x ray diffraction data indicate that some mineral separates prepared for ar ar stepwise heating analysis are monomineralic whereas others are composed of two white micas muscovite with paragonite or margarite or biotite and chlorite in monomineralic samples ar ar and ar ar proportional to ca k and cl k ratios did not change and the resulting ages can be interpreted unambiguously in mineral separates containing two white micas ca k and cl k ratios were variable reflecting non simultaneous laboratory degassing of the two heterochemical ar reservoirs these ratios were used to identify each ar reservoir and to unravel the age in a chlorite margarite biotite calcschist equilibrated near 5608c and 0 65 gpa biotite margarite and muscovite all yield ages around 18ma at slightly higher grade 560 5808c 0 8 0 9 gpa the assemblage muscovite paragonite plagioclase is in equilibrium and remains stable during retrogression in this case muscovite and paragonite yield indistinguishable ages around 16 5ma above 5908c paragonite was mostly consumed to form plagioclase 45908c whereby the relict mica yields an age up to 5 6 ma younger than muscovite this partial or total resetting of the ar clock in paragonite is interpreted to reflect plagioclase growth during decompression where biotite is present within this same assemblage it systematically yields a younger age than muscovite by 0 5 2 ma however these biotites all show small amounts of retrograde chlorite formation we conclude that even very minor chloritization of biotite is apparently a more effective process than temperature in resetting the ar clock as is the formation of plagioclase from paragonite decomposition multi equilibrium thermobarometry is an excellent means to ensure that equilibrium in investigated samples is preserved and this helps to obtain geologically meaningful metamorphic ages however even samples passing such equilibrium tests may still show retrograde effects that affect the ar retention of micas a more robust interpretation of such ar ar results may require use of a second geochronometer such as u pb on monazite

stable carbon isotope ratio variations of organic matter in orca basin sediments abstract orca basin is a highly reducing basin on the slope of the gulf of mexico stable carbon isotope ratios and total organic carbon percentages were determined for two cores within the basin and one control core outside the basin the results show that the organic carbon content of the basin cores is consistently 2 3 times greater than that of the control core the pleistocene holocene boundary indicated by a break in the 13 c depth profile occurs at a greater sediment depth in the basin cores than in the control core a small sampling interval has made it possible to detect an unexplained fine structure in the 13 c profile not previously observed

carbon stable isotope δ13c and elemental toc tn geochemistry in saltmarsh surface sediments western brittany france a useful tool for reconstructing holocene relative sea level providing a dense network of holocene relative sea level rsl records still faces some challenges such as the paucity of microfossil assemblages within some holocene sedimentary sequences recently the isotopic 13c and elemental geochemistry total organic carbon toc total nitrogen tn and c n ratios of saltmarsh sediments has showed potential for rsl reconstruction this study presents the results of new 13c toc and tn measurements obtained on surface sediments of two marshes of the brittany region france overall the distribution of 13c toc tn and c n values shows clear dependencies with elevation sediments from above and below the high tide level show contrasting tn contents clustering analyses identified three elevation dependent groups characterized by specific values of 13c toc and tn the use of this geochemical reference for rsl reconstruction is tested on a core retrieved from one of the marshes the sea level index points obtained plot in good accordance with the microfauna based rsl positions previously obtained in the region some diagenetic losses in tn are observed between modern and holocene sediments this does not appear to be harmful to the accuracy of the rsl reconstructions but suggests that c n ratios may be unreliable palaeoenvironmental proxies in this specific context

seasonal laurentide ice sheet melting during the mystery interval 17 5 14 5 ka the last deglaciation in the northern hemisphere was interrupted by two major stadials the so called mystery interval 17 5 14 5 ka and the younger dryas 12 9 11 7 ka during these events the north atlantic region was marked by cold surface conditions yet simultaneous glacier and snowline retreat rerouting of laurentide ice sheet meltwater from the gulf of mexico to an eastern or northern spillway may have reduced meridional overturning circulation at the onset of the younger dryas however this hypothesis has not been tested for the mystery interval paired mg ca and 18 o measurements on foraminifera from laminated orca basin sediments in the gulf of mexico constrained by 35 14 c dates document the timing of meltwater input with subcentennial resolution isolating the 18 o of seawater termed 18 o gom reveals three major melting episodes from ca 17 5 ka until 12 9 ka followed by a rapid cessation consistent with meltwater rerouting at the onset of the younger dryas conversely inferred meltwater fl ow to the gulf of mexico during the mystery interval does not support a simple routing event but is consistent with glacier and snowline retreat we suggest that summer melting of northern hemisphere ice sheets during this stadial may have been an important mechanism for enhanced winter sea ice formation hypercold winter conditions and enhanced seasonality in the north atlantic region

oxygen isotope geochemistry of laurentide ice sheet meltwater across termination i abstract we present a new method that quantifies the oxygen isotope geochemistry of laurentide ice sheet lis meltwater across the last deglaciation and reconstruct decadal scale variations in the 18o of lis meltwater entering the gulf of mexico between 18 and 11 ka we employ a technique that combines laser ablation icp ms la icp ms and oxygen isotope analyses on individual shells of the planktic foraminifer orbulina universa to quantify the instantaneous 18owater value of mississippi river outflow which was dominated by meltwater from the lis for each individual o universa shell we measure mg ca a proxy for temperature and ba ca a proxy for salinity with la icp ms and then analyze the same o universa for 18o using the remaining material from the shell from these proxies we obtain 18owater and salinity estimates for each individual foraminifer regressions through data obtained from discrete core intervals yield 18ow vs salinity relationships with a y intercept that corresponds to the 18owater composition of the freshwater end member our data suggest that from 15 5 through 14 6 ka estimated 18ow values of mississippi river discharge from discrete core intervals range from 11 to 21 vsmow which is consistent with 18o values from both regional precipitation and the low elevation southern margin of the lis during the bolling and allerod 14 0 through 13 3 ka estimated 18ow values of mississippi river discharge from discrete core intervals range from 22 to 38 vsmow these values suggest a dynamic melting history of different parts of the lis with potential contributions to mississippi river outflow from both the low elevation southern margin of the lis and high elevation high latitude domes in the lis interior that were transported to the ablation zone prior to 15 5 ka the 18owater value of the mississippi river was similar to that of regional precipitation or low latitude lis meltwater but the ba concentration in the mississippi basin was affected by changes in weathering within the watershed complicating ba salinity relationships in the gulf of mexico after 13 ka our data suggest mississippi river outflow did not influence surface salinity above our gulf of mexico orca basin core site rather we hypothesize that open ocean conditions prevailed as sea level rose and the paleoshoreline at the southern edge of north america retreated northward

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

chemical evidence of differential particle dispersal in the southern washington coastal environment aliphatic hydrocarbons cupric oxide oxidation products of lignin and polycyclic aromatic hydrocarbons pah were analyzed by capillary gas chromatography in sediments from the southern washington continental shelf and slope the concentration of diploptene relative to plantwax n alkanes increased systematically in surface sediments with distance offshore along east west transects of the study area and remained constant in surface sediments along the midshelf silt deposit analogous trends were also observed for the concentration of cinnamyl phenols relative to vanillyl phenols and total methylphenanthrenes relative to phenanthrene these changes in sedimentary composition are evidence that diploptene from some terrestrial source lignin characteristic of non woody vascular plant tissue and a fossil organic material contained within weathered rock debris disperse across the washington continental shelf and slope in geographic patterns distinct from that for other river derived chemically related materials the compositional variations are explained by the particulate associations of the land derived chemicals and differential hydraulic dispersion of their respective carrier particles after discharge at the mouth of the columbia river

slumping and a sandbar deposit at the cretaceous tertiary boundary in the el tecolote section northeastern mexico an impact induced sediment gravity flow slumps affecting uppermost mendez formation marls as well as the spherulitic layer and basal part of the sandy deposits of the cretaceous tertiary k t boundary clastic unit are described at the new k t el tecolote section northeastern mexico these k t clastic deposits represent sedimentation at middle bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional high to low density turbidite flow we emphasize the development and accretion of a lateral bar in a channel area from a surging low density turbidity current and under a high flow regime the slumps discovered on land and the sedimentary processes of the k t clastic unit reflect destabilization and collapse of the continental margin support the mechanism of gravity flows in the deep sea and represent important and extensive evidence for the impact effects in the gulf of mexico triggered by the chicxulub event

glacial to holocene terrigenous organic matter input to sediments from orca basin gulf of mexico a combined optical and biomarker approach in this study we assessed changes in the contribution of terrigenous organic matter om to the gulf of mexico over the course of the last deglaciation the last 25 kyr to this end we combined optical kerogen analyses with bulk sedimentary biomarker and compound specific carbon isotope analyses samples were obtained from core md02 2550 from orca basin 2249 m water depth at 26 56 77n 91 20 74w with temporal resolution ranging from multi decadal to millennial scale depending on the proxy all proxies confirmed larger terrigenous input during glacial times compared to the holocene in addition the kerogen analyses suggest that much of the glacial om is reworked at least 50 of spores and pollen grains and 40 of dinoflagellate cysts the holocene sediments in contrast contain mainly marine om which is exceptionally well preserved during the deglaciation terrigenous input was generally high due to large meltwater fluxes whereby discrepancies between different proxies call for additional influences such as the change in distance to the river mouth local productivity changes and hydrodynamic particle sorting it is possible that kerogen particles and the terrigenous biomarkers studied here represent distinct pools of land derived om with inputs varying independently

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

the relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration abstract a study of organic biomarker compounds which could serve as tracers of terrigenous and marine sedimentary organic matter sources was performed on samples from a 208 7 m hydraulic piston core hole dsdp hole 619 from the hemipelagic pigmy basin in the northern gulf of mexico organic carbon normalized concentrations of total long chain c37 c39 alkenones and some individual c27 c29 desmethyl sterols were determined to be useful proportional indicators tracers of preserved marine and terrigenous organic carbon respectively the alkenones whose only known source is marine phytoplankton of the class prymnesiophyceae generally occurred in higher concentrations in interglacial isotope stages 1 and 5a b than in the intervening glacial stages sterols c27 c29 apparently of a dominantly terrigenous origin occurred in lower concentrations during interglacial stages than in glacial stages tracers of both terrigenous and marine organic matter appear to be affected by the differential diagenetic alteration of the biomarker corg ratios as indicated by a simple first order kinetic model the lack of any desmethylor 4a methylsterol which is linearly related to the proportion of marine sedimentary organic matter as scaled by 13corg indicates that either 1 1 sedimentary diagenesis has obscured the biomarker corg vs 13corg record 2 2 phytoplanktonic assemblage changes caused variations in the biomarker corg ratio of the primary input preferential preservation of terrigenous sterols may result in a biased sedimentary record of sterol input which could be misinterpreted as indicating solely terrigenous sterol sources a simple model which characterizes the effects of sedimentary diagenesis on the relationship between corg normalized biomarker ratios and 13corg demonstrates the potential problems of long term differential diagenetic skewing on those tracer records

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

deglacial nitrogen isotope changes in the gulf of mexico evidence from bulk sedimentary and foraminifera bound nitrogen in orca basin sediments 1 constraining variations in marine n2 fixation over glacial interglacial timescales is crucial for determining the role of the marine nitrogen cycle in modifying ocean productivity and climate yet paleo records from n2 fixation regions are sparse here we present new nitrogen isotope 15n records of bulk sediment and foraminifera test bound fb nitrogen extending back to the last ice age from the oligotrophic gulf of mexico gom previous studies indicate a substantial terrestrial input during the last ice age and early deglacial for which we attempt to correct the bulk sediment 15n using its observed relationship with the c n ratio both corrected bulk and fb 15n reveal a substantial glacial to holocene decrease of 15n toward holocene values of around 2 5 similar to observations from the caribbean this 15n change is most likely due to a glacial to holocene increase in regional n2 fixation a deglacial peak in the fb 15n of thermocline dwelling foraminifera orbulina universa probably reflects a whole ocean increase in the 15n of nitrate during deglaciation the 15n of the surface dwelling foraminifera globigerinoides ruber and the corrected bulk 15n show little sign of this deglacial peak both decreasing from last glacial values much earlier than does the 15n of o universa this may indicate that g ruber and bulk n reflect the euphotic zone signal of an early local increase in n2 fixation our results add to the evidence that during the last ice age the larger iron input from dust did not lead to enhanced n2 fixation in this region rather the glacial to holocene decrease in 15n is best explained by a response of n2 fixation within the atlantic to the deglacial increase in global ocean denitrification

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

megaflood erosion and meltwater plumbing changes during last north american deglaciation recorded in gulf of mexico sediments submicrometer variations in the median diameter of siliciclastic mud in orca basin northern gulf of mexico sensitively monitor laurentide ice sheet runoff to the gulf during early stages of the last deglaciation grain size data document a prominent pulse of very fine grained sediment to the northern gulf from 12 6 to 12 0 ka corresponding with the well known sea surface meltwater spike in 18 o records meltwater megafloods at this time eroded and transported large volumes of clay to the gulf via the mississippi river system the nonquartzose megaflood sediments appear to have been derived from clay rich midcontinental terrace deposits rather than from glacial outwash supplied by the laurentide ice margin sediment grain size data in combination with other terrigenous proxies clay minerals and reworked calcareous nannofossils indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff this variability reflects changes in continental plumbing consistent with terrestrial records of north american deglaciation

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

age stratigraphy and deposition of near k t siliciclastic deposits in mexico relation to bolide impact examination of 10 k t boundary sections in northeastern and east central mexico and new data presented from 7 sections permit the following conclusions 1 the globally recognized k t boundary and mass extinction in planktic foraminifera is stratigraphically above and separated by a thin marl layer of maastrichtian age from the siliciclastic deposit that is commonly interpreted as a short term hours to days k t impact generated tsunami deposit a similar relationship between the k t boundary and siliciclastic or breccia deposits is observed at brazos river in texas beloc in haiti and poty quarry in brazil 2 stratigraphic control indicates that deposition of the siliciclastic member occurred sometime during the last 150 k y of the maastrichtian and ended at least several thousand years prior to the k t boundary 3 at least four discrete horizons of bioturbation have been observed within the siliciclastic deposit that indicate episodic colonization by invertebrates over an extended time period 4 the glass and spherule rich unit which has been linked to the haiti spherule layer and the chicxulub structure is at the base of the siliciclastic deposit and thus significantly predates the k t boundary event the stratigraphic separation of the k t boundary and siliciclastic deposits and the evidence of long term deposition between them suggests the presence of two events 1 a globally recognized k t boundary impact event marked by ir anomaly and the mass extinction and 2 a caribbean event impact or volcanic and probably linked to the chicxulub structure that predates the k t boundary and is marked by glass and siliciclastic or breccia deposits

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

impact induced mass wasting at the k t boundary blake nose western north atlantic seismic reflection data combined with results from ocean drilling document regional scale slumping associated with the cretaceous tertiary k t impact event the k t boundary is biostratigraphically complete at three ocean drilling program sites 1049 1050 and 1052 located on blake nose 30 n 75 w off eastern florida in water depths of 1300 2600 m maastrichtian chalk is folded and fractured below the k t boundary at all three sites whereas lowermost paleocene clays and chalks are undeformed deformation is pervasive in maastrichtian at the deepest water site site 1049 whereas at the shallower water sites sites 1050 and 1052 thick intervals of structurally intact maastrichtian chalk are separated by thinner intervals of highly deformed sediments correlation of core to seismic reflection data indicates that the k t boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the 55 km distance of the depth transect maastrichtian sediments appear to have moved as large slump blocks on the upper part of blake nose but deformed more uniformly in the deeper water parts of the transect we suggest that mass wasting occurred on the blake nose 1600 km from the chicxulub crater in response to the cataclysmic seismicity generated by the impact

benthic foraminifera at the cretaceous tertiary boundary around the gulf of mexico cretaceous tertiary k t boundary sections in northeastern mexico contain marly formations separated by a controversial clastic unit benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls with the exception of the upper bathyal northernmost section mixed neritic bathyal faunas were present in the clastic unit indicating redeposition in the deep basin by mass wasting processes resulting from the k t bolide impact in the gulf of mexico benthic foraminifera in the mexican sections and at other deep sea locations were not subject to major extinction at the time of impact but there were temporary changes in assemblage composition benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late maastrichtian and increased food supply during the latest maastrichtian the food supply decreased drastically just after the k t boundary possibly because of the collapse of surface productivity cretaceous and early paleogene benthic foraminifera however did not exhibit the benthic pelagic coupling of present day faunas as documented by the lack of significant extinction at the k t collapse of surface productivity much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions the decrease in food supply at the k t boundary might be associated with the processes of mass wasting which removed surface food rich sediment benthic faunas show a staggered pattern of faunal recovery in the lowermost paleogene consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

the impact of ice sheet dynamics in western mediterranean environmental conditions during terminations an approach based on terrestrial long chain n alkanes deposited in the upper slope of the gulf of lions abstract during the promess campaign summer 2004 a borehole prgl1 was drilled in the upper slope of the gulf of lions previous studies showed that the deposition of the sedimentary units at borehole prgl1 was determined by changes in the discharge of the rhone river induced by sea level and climate variability with a strong 100 ka imprint however there are no detailed studies that focus on the glacial interglacial transitions i e terminations that define 100 ka quaternary ice age cycles here we present a high resolution record of terrestrial long chain n alkanes c21 to c33 from mis 3 to mis 11 in order to monitor changes in the sediments deposited on the upper slope of the gulf of lions with the aim to provide new insight into the climatic events occurring during terminations in the western mediterranean sea principal component analysis grouped n alkane on the basis of the degree of maturation of organic matter fresh degraded that allowed to monitor past variability in the source of the sediment deposited in the upper slope as a consequence of sea level and climate change this information was used to estimate the impact that northern ice sheet variability had on the western mediterranean basin as sea level started to fall fresh terrestrial organic matter increased owing to the seaward migration of rhone s mouth simultaneously the decrease in sea level exposed old and reworked organic material from the rhone s catchment including the delta plain and the continental shelf that was eroded and transported into our study site this resulted in an increase in the proportion of degraded terrestrial organic matter together with sea level decrease aside from sea level changes the proportion of fresh vs degraded organic matter seems to be affected by the amount of continental runoff with an increasing proportion of fresh terrestrial organic matter occurring at times of reduced continental runoff during the last glacial the increase of fresh terrestrial organic matter was contemporaneous with heinrich events hes suggesting dry and cold conditions on the western mediterranean basin these dry and cold millennial scale episodes were reproduced during terminations ii iii and iv preceding flood events most probably due to weakening reinforcement of atlantic meridional overturning circulation amoc that caused dry humid conditions in western mediterranean