sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

spatial variations of magnetic susceptibility of chinese loess for the last 600 kyr implications for monsoon evolution 1 we examine spatial variations in magnetic susceptibility ms over the loess plateau in china based on 50 sections in order to identify spatial changes in monsoon climate at key glacial interglacial and interstadial intervals for the last 600 kyr the results indicate strong coherence between ms variations during the interglacial periods and present day precipitation and temperature patterns this suggests that the strength of the summer monsoon had a dominant influence on the ms signals in soils through modulating pedogenic intensity the distribution of ms during glacial periods is characterized by weak s n gradients and rough w e zonal patterns indicating a negligible effect of the summer monsoon interstadial patterns are intermediate between the glacial and interglacial ones interglacial patterns for the last 600 kyr are essentially similar suggesting that the climate regime during these periods has not undergone significant changes and that the east asian summer monsoon has remained the main moisture carrier our estimates of the relative amplitudes of climate oscillations during these time slices are consistent with earlier paleoclimate studies these data associated with the available susceptibility based climofunctions may be used to estimate spatial changes of paleorainfall and paleotemperature for these key periods and hence to test climate models

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

effect of channel bifurcation on residual estuarine circulation winyah bay south carolina the residual circulation pattern of winyah bay the fourth largest estuary on the eastern coast of the us is examined using stationary and shipborne current measurements during periods of low freshwater discharge the estuary has a complex morphology with a single channel and narrow banks at the river entrance and the bay mouth and a bifurcated channel system main and western channels respectively in the middle part that appears to affect the residual circulation overall the upper single channel morphology and middle dual channel morphology parts of the estuary exhibit a baroclinic residual circulation the presence of bifurcated channels in the middle part of the estuary modifies the typical gravitational circulation the near bed landward directed residual flow is stronger in the deeper main channel than the shallower western channel this is the result of the fact that the magnitude of residual flow scales with the water depth of the channel and it is also influenced by the opposing patterns of channel alignment in the northern and southern junctions analytical modeling confirms that the observed residual currents in the upper and middle estuary are density induced in the lower estuary residual flow is directed seaward throughout the water column of the channel while in the adjacent shoals the residual flow is directed landward suggesting that in contrast to the upper and middle estuary the residual flow near the mouth is barotropic controlled by the tides and the channelbank morphology 2005 published by elsevier ltd

field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera we determined the 18o and 13c of individual globigerinoides ruber and pulleniatina obliquiloculata from sediment traps located from 5 n to 12 s along 140 w in the pacific ocean to evaluate the effects of varying co3 on shell 18o and 13c variations in the offset between shell 13c and 13cdic 13cs dic are attributed to differences in co3 temperature and shell size between sample sites when 13cs dic of g ruber was corrected for variations in co3 using the experimental slope of bijma et al 1998 the residual 13cs dic was correlated with mixed layer temperature 0 10 0 04 c 1 the slope of this temperature effect is consistent with experimental results in p obliquiloculata 13cs dic and temperature were strongly anticorrelated 0 14 0 03 c 1 we are unable to separate the influences of co3 and temperature in this species without independent experimental data correcting for co3 variability on 18os of g ruber improves the accuracy of estimated sea surface temperatures

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

phytoliths as quantitative indicators for the reconstruction of past environmental conditions in china ii palaeoenvironmental reconstruction in the loess plateau abstract quantitative reconstruction of the climatic history of the chinese loess plateau is important for understanding present and past environment and climate changes in the northern hemisphere here we reconstructed mean annual temperature mat and mean annual precipitation map trends during the last 136 ka based on the analysis of phytoliths from the weinan loess section 34 24 n 109 30 e near the southern part of the loess plateau in northern china the reconstructions have been carried out using a chinese phytolith climate calibration model based on weighted averaging partial least squares regression a series of cold and dry events as indicated by the reconstructed mat and map are documented in the loess during the last glacial periods which can be temporally correlated with the north atlantic heinrich events our mat and map estimations show that the coldest and or driest period occurred at the upper part of l2 unit late mis 6 where mat dropped to ca 4 4 c and map to ca 100 mm two other prominent cold dry periods occurred at lower ll 5 ca 77 62 ka and l1 1 ca 23 10 5 ka where the mat and map decreased to about 6 1 6 5 c and 150 370 mm respectively ca 6 6 6 2 c and 400 200 mm lower than today however the highest mat average 14 6 c max 18 1 c and map average 757 mm max 1000 mm occurred at sl interval mis 5 during the interstadial of l1 4 l1 2 mis 3 and during the holocene warm wet period the mat was about 1 2 c and map 100 150 mm higher than today in the weinan region the well dated mat and map reconstructions from the chinese loess plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial interglacial timescale that is based on phytolith data this study also reveals a causal link between climatic instability in the atlantic ocean and climate variability in the chinese loess plateau

the importance of solar insolation on the temperature variations for the past 110 kyr on the chinese loess plateau abstract the late quaternary temperature history on the chinese loess plateau clp is little known due to the absence of suitable paleothermometers here we present a quantitative temperature record for the last 110 kyr from lantian county southern clp based on the distributions of bacterial tetraethers lantian loess temperature variations display significant correlation with the northern hemisphere insolation 35 n as well as the cave monsoon records at the precession band we attribute such correlation to both the latent heat release from the east asian summer monsoon and the direct influence of sun s sensible heat over the semi arid landscape the long term cooling during the marine isotope stage mis 3 and the modest temperature drop of 5 c from 79 to 65 ka are best explained by interactions among multiple climate forcings including insolation atmospheric co 2 concentration global ice volume and regional glacier activities the cold and modestly wet climate during mis 3 may have promoted maximum regional glacial advances whereas the minimal temperature during local lgm reduced moisture transfer and led to glacial recession the unusually early deglacial warming at 22 5 ka highlights the importance of regional climate records to decipher the complex continental climate dynamics

seasonal changes in species composition numbers mass size and isotopic composition of planktonic foraminifera settling into the deep sargasso sea abstract planktonic foraminifera recovered from six successive sediment trap samples collected over fourteen months at a depth of 3200 m near bermuda show varied responses to seasonal changes in the near surface hydrography these include changes in species composition and within species changes in number of individuals collected per unit time average size and weight of individuals and in oxygen and carbon isotopic composition a total of seventeen species were identified and eleven were sufficiently abundant for isotopic analysis in at least some of the samples the accumulations on the sea floor of some of these species can be expected to contain a strong seasonal component in their oxygen isotopic composition which may be utilized in paleoclimatic and paleo oceanographic reconstructions best suited to this purpose are those species which form their tests in isotopic equilibrium with surface water and whose abundance is confined to a portion of the year only the best examples are pulleniatina o bliguiloculata globigerinoides conglobatus and neogloboquadrina dutertrei globigerinoides ruber is a good estimator of the average surface water temperature because it occurs in rather even abundance throughout the year hastigerina pelagica though very abundant in surface water is practically eliminated even before arrival on the sea floor by partial resorption and structural weakening of the tests during gametogenesis orbulina universa globorotalia truncaltulinoides and globorotalia hirsuta show morphological and istopic evidence for contibnued calcification in deeper water after initial test formation near ther surface globigerina bulloides represents the most striking example of oxygen isotopic disequilibrium with sea water

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

continental shelf landscapes of the southeastern united states since the last interglacial abstract the wide sediment starved continental shelf and modern coastal areas of the southeastern united states retain well preserved but scattered remnants of a submerged paleolandscape this paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of south carolina with portions of north carolina georgia and florida usa data for this study include multibeam bathymetry surveys sidescan sonar mosaics high resolution subbottom profiles and ground truth surveys from 250 m to the modern tidewater region four bathymetric zones are recognized with eleven landforms and landform indicators the described zones range in depths from the modern shoreline across the shelf and over the shelf edge to 250 m msl relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events the potential for preservation of paleoamerican sites is high at the shelf edge between 130 m and 45 m with archaic and later occupations likely in depths of less than 25 m prominent vantage points for paleoamericans 11 kya would have existed at the shelf edge and tidewater resources would have been available nearby for a period of almost 6 ka rapid transgression rates 60 km ka after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf searches for the earliest paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists coastal managers fishery scientists and marine spatial planners over the next several decades

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

oxygen and carbon isotopic composition and biogeographic distribution of planktonic foraminifera in the indian ocean five planktonic foraminiferal assemblages were encountered along a north south transect in the indian ocean with the following dominant species globorotalia truncatulinoides in the southern subtropical assemblage globigerinoides ruber globigerinella aequilateralis and globorotalia menardii in the northern subtropical assemblage globigerinoides sacculifer and pulleniatina obliquiloculata in the tropical assemblage neogloboquadrina dutertrei and globigerina bulloides in the tropical upwelling assemblage and globigernoides conglobatus in the tropical arabian sea assemblage oxygen and carbon isotopic analyses were performed on three surface dwelling species of planktonic foraminifera in tropical and subtropical waters 22 30 c the 18o of globigerinoides ruber and g sacculifer varies with surface water temperature and the slope of the isotope temperature regression line is similar to that of epstein et al 1953 for marine molluscs however foraminiferal 18o values are significantly lighter than those of molluscs indicating isotopic disequilibrium comparison between plankton tows taken within and below the mixed layer at the same stations shows that g ruber has similar low 18o values in both sets suggesting that it secretes its shell within the mixed layer by contrast g sacculifer has slightly higher 18o values below than within the mixed layer because it continues to secrete calcite below the thermocline no significant 18o variations with shell size were found on the other hand 13c values were strongly size dependent i e the smaller the size the lighter the 13c comparison of living g ruber and g sacculifer with recent specimens from the surface sediment shows that the living foraminifera are generally lighter in 18o than the fossils supporting independent observations that the latter have secreted additional calcite during gametogenesis when the organisms settle freely from the euphotic zone for about 12 h and pass through waters lower in temperature than the epipelagic waters where the foraminifera form the bulk of their shells

correlations between microbial tetraether lipids and environmental variables in chinese soils optimizing the paleo reconstructions in semi arid and arid regions the bacterial membrane lipid based continental paleothermometer the mbt cbt or mbt cbt proxy methylation index of branched tetraethers cyclization of branched tetraethers results in a large temperature deviation when applied in semiarid and arid regions here we propose new calibration models based on the investigation of 100 surface soils across a large climatic gradient with a particular focus on semiarid and arid regions of china and apply them to a loess paleosol sequence as reported elsewhere mbt values exhibit a much higher correlation with maat than with summer temperature suggesting a minimal seasonality bias however mbt is apparently insensitive to temperature 20 degrees c additional complexities are apparent in alkaline and arid soils which are characterized by different relationships to climatic parameters than those in the complete chinese or global dataset for example mbt and cbt indices exhibit a negative correlation in alkaline and arid soils in contrast to their positive correlation in acid soils moreover the cyclization ratio of bgdgts cbt previously defined as a proxy for soil ph is apparently primarily controlled by maat in these alkaline soils thus we propose 1 a local chinese calibration of the mbt cbt proxy and 2 an alternative temperature proxy for use in semiarid and arid regions based on the fractional abundances of bgdgts the latter has a markedly higher determination factor and lower root mean square error in alkaline soils than the chinese local calibration and is suggested to be preferred for paleotemperature reconstruction in chinese loess paleosol sequences these new bgdgt proxies have been applied to the weinan holocene paleosol section of the chinese loess plateau clp the fractional abundance calibration when applied in the weinan holocene paleosol produces a total holocene temperature variation of 5 2 degrees c and a temperature for the topmost sample that is consistent with the modern temperature previously we showed that the ratio of archaeal isoprenoid gdgts to bgdgts r i b increases at map 0 5 in the clp suggest the presence of enhanced aridity in the late holocene in north china in combination the high r i b ratios 0 5 and the associated low mbt values 0 4 reveal the co occurrence of dry and cold events especially in the latest holocene in the loess paleosol sequences in clp and probably also in cold and arid regions outside of clp c 2013 elsevier ltd all rights reserved

migration of the pee dee river system inferred from ancestral paleochannels underlying the south carolina grand strand and long bay inner shelf several generations of the ancestral pee dee river system have been mapped beneath the south carolina grand strand coastline and adjacent long bay inner shelf deep boreholes onshore and high resolution seismic reflection data offshore allow for reconstruction of these paleochannels which formed during glacial lowstands when the pee dee river system incised subaerially exposed coastal plain and continental shelf strata paleochannel groups representing different generations of the system decrease in age to the southwest where the modern pee dee river merges with several coastal plain tributaries at winyah bay the southern terminus of long bay positions of the successive generational groups record a regional southwestward migration of the river system that may have initiated during the late pliocene the migration was primarily driven by barrier island deposition resulting from the interaction of fluvial and shoreline processes during eustatic highstands structurally driven subsurface paleotopography associated with the mid carolina platform high has also indirectly assisted in forcing this migration these results provide a better understanding of the evolution of the region and help explain the lack of mobile sediment on the long bay inner shelf migration of the river system caused a profound change in sediment supply during the late pleistocene the abundant fluvial source that once fed sand rich barrier islands was cut off and replaced with a limited source supplied by erosion and reworking of former coastal deposits exposed at the shore and on the inner shelf

a preliminary sediment budget for the winyah bay estuary south carolina usa abstract winyah bay a 65 km2 coastal plain estuary in south carolina has an average freshwater input of 557 m3 s 1 and presently receives 0 43 106 t yr 1 of suspended sediments from its watershed corresponding to a yield of 12 7 t km 2 yr 1 however 20 dams have been constructed on the upper rivers primarily on the yadkin and pee dee rivers which serve to capture an additional 0 40 106 t yr 1 of sediment implying a gross sediment yield of 24 5 t km2 yr 1 for the watershed although almost 50 never reaches the coast continuous dredging in the estuarine channels removes 0 107 106 t yr 1 of silt and clay from the estuary sediment coring and 210 pb analysis indicate that the sedimentation rate in mud bay a high accretion area in the lower estuary is 5 5 mm yr 1 which together with previous estimates of marsh sedimentation rates of 2 7 mm yr 1 in the tidal marshes surrounding the estuary leads to a total estuarine mud sedimentation estimate of 0 24 106 t yr 1 thus 80 of the fine grained sediment reaching winyah bay is either accumulating in adjacent marshes or on estuarine mud flats or is being dredged and deposited offshore although these budget calculations need further confirmation by direct measurements and additional coring winyah bay apparently delivers only a minimal amount of suspended fine grained sediments to the coastal ocean

isotopic analysis of foraminifera shells interference from chemical treatment abstract foraminifera shells were soaked in solutions of formalin ethanol tetrachlorethylene and hydrogen peroxide also crushed solnhofen limestone was exposed to formalin formalin treatment caused a significant change in the results of stable isotope analysis the effect is interpreted as a result of partial dissolution soaking other than those with formalin did not affect isotopic analysis

sea surface temperature estimates from the southwest pacific based on planktonic foraminifera and oxygen isotopes planktonic foraminiferal census data were collected on 34 surficial sediment samples from east of new zealand sea surface temperature estimates were derived from the data using the modern analogue technique mat and compared to data from climap s fa 20 equation they were also computed from oxygen isotope analyses of globigerina bulloides the temperature estimates compared well between the three methods and were found to correlate closely with the appropriate seasonal sea surface temperature as measured by satellite the foraminiferal assemblages and derivative temperatures clearly identify the major watermasses and oceanic fronts in the region and thus can be applied to palaeoceanographic analysis of southwest pacific sediments

suspended sediment variability on seasonal and tidal time scales in the winyah bay estuary south carolina usa a transient estuarine turbidity maximum etm was observed in winyah bay during field sampling in 1996 the core of this turbidity maximum migrated 8 km seaward of its traditional location at the saltefreshwater interface in response to very high river discharge events in 1996 in response to the semidiurnal tidal cycle there was a well defined variation in the suspended sediment concentration within the turbidity maximum zone between ebb and flood tides as a result of differences in tidal velocities the suspended sediment inventory in the water column during the flood tide was greater than suspended sediment inventory during the ebb tide during slack water the water column was characterized by 0 03 kg m 3 sediment concentrations whereas at times of maximum boundary shear stress near the bottom the water column was highly turbid indicating that bottom sediments were resuspended by the strong tidal currents typical of the bay throughout a tidal cycle the vertical extension of high suspended sediment concentration in the water column within the etm was well developed during the flood tide and inhibited during the ebb tide internal tidal asymmetry with well mixed conditions during the flood tide near the bottom and with stratification in the water column during the ebb tide was probably the process responsible for the enhancement of turbulence during the flood tide and inhibition of turbulence during the ebb tide with implications for the etm 2003 elsevier ltd all rights reserved

analysis of fluvial suspended sediment load contribution through anthropocene history to the south atlantic bight coastal zone u s a abstract discerning the effects of anthropogenic activities i e reservoir construction land use change as opposed to those of natural processes i e climate variability on suspended sediment flux has become an increasingly difficult challenge this contribution presents water and suspended sediment flux from five major watersheds that discharge into the southeastern u s atlantic a region that is currently considered sediment starved three periods of anthropocene time were defined and evaluated 1 pre european conditions 1680 1700 2 pre dam conditions 1905 1925 and 3 post dam conditions 1985 2005 physical and hydrologic watershed data were used to run a climate driven hydrological transport numerical model hydrotrend to estimate suspended sediment flux for each period results indicate that the suspended sediment contribution to the south atlantic bight coastal zone increased by up to 145 as a result of accelerated soil erosion conditions caused by the arrival of europe

detecting the intertidal morphologic change using satellite data abstract the objectives of this study were a to generate an intertidal digital elevation model dem using waterlines extracted from landsat tm and in situ ground levelling data b to quantitatively estimate morphologic change from the generated dems for the years 1991 and 2000 and c to evaluate the chenier migration in the tidal flats of gomso bay korea on extracting the waterlines we considered the tidal flat environments such as tidal conditions remnant surface water suspended sediment and exposure time ground levelling was carried out along one line in 1991 and two lines in 2000 from the extracted waterlines and ground levelling data we succeeded in generating intertidal dems with an accuracy of 10 9 cm r m s overall and 7 3 cm r m s in the lower tidal flats the morphologic changes estimated by subtracting the two dems showed an erosion rate of 9 0 cm over 9 yr that corresponds to an annual mean morphologic change budget of 309 865 m 3 yr overall the gomso tidal flats can be defined as an erosion dominant environment the changes with respect to the sedimentary facies were also evaluated as a the sandy silt flat had a sedimentation rate of 3 4 cm over 9 yr that corresponds to an annual mean budget of 52 552 m 3 yr b the silty sand flat had a sedimentation rate of 14 3 cm over 9 yr that corresponds to a mean erosion of 197 927 m 3 yr and c the sand flat had a sedimentation rate of 11 8 cm over 9 yr that corresponds to a mean change of 58 808 m 3 yr the results comply with the general rules of sedimentology we also investigated the chenier migration which is the most dynamic geomorphologic change in the tidal flats chenier is usually composed by sand and shell as a result of coastal progradation in sand and it is dominantly fed by sediments transported by long shore currents the chenier was found to have migrated about 148 m landward over 6 yr the results demonstrate that satellite remote sensing is an efficient and effective tool for a long term morphologic change estimation in tidal flats

shoreline erosion and decadal sediment accumulation in the tar pamlico estuary north carolina usa a source to sink analysis abstract estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea level rise and wave attack as estuarine shorelines erode or become modified with hard structures there is potential for significantly altering the availability of sediment and the filling of coastal systems this study used a source to sink approach and quantified rates of shoreline erosion in the tar pamlico sub estuary a tributary of the larger albemarle pamlico estuarine system apes the average shoreline change rate scr determined using an end point method was 0 5 0 9 m yr 1 for the tar pamlico incorporating bulk density estimates this contributes 0 6 105 tons of fine sediment to the system annually or after accounting for fluvial input about 40 of the total sediment supply to the sub estuary the role of the tar pamlico as a sink for these sediments was addressed using the radionuclide tracers 210pb and 137cs radionuclide activities and sediment accumulation rates identified several depositional regions in particular in the middle of the estuary linear sediment accumulation rates ranged from 0 10 0 02 to 0 38 0 02 g cm 2 yr 1 and total storage of fine sediment in the system was 1 6 105 t yr 1 it was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation a preliminary budget for fine sediments grain size

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

variation in 6 methyl branched glycerol dialkyl glycerol tetraethers in lantian loess paleosol sequence and effect on paleotemperature reconstruction abstract the distribution of branched glycerol dialkyl glycerol tetraethers brgdgts has been increasingly used as a proxy in paleoclimate studies of marine lacustrine and loess environments a paleothermometer was subsequently quantified using a combination of the methylation and cyclization index of branched tetraethers mbt cbt on the basis that mbt was related to mean annual air temperature and to a lesser extent soil ph whereas cbt correlated only with soil ph as newly described 6 methyl brgdgts seemed to introduce a dependence on soil ph of this temperature proxy we investigated the effect of the 6 methyl brgdgts on an existing paleotemperature reconstruction we describe the evolution in temperature and ph recorded in the lantian loess paleosol sequence for the last 120 kyr using a new analytical method the results show that 6 methyl brgdgts were abundant comprising on average 26 of the total amount of brgdgts in the sequence the fractional abundance of 6 methyl brgdgts generally tracked the change in soil ph at the same soil section a considerable delay up to ca 7 kyr in the variation in fractional abundance of 6 methyl brgdgts vs that of 5 methyl brgdgts was observed possibly resulting from the different environmental factors to which they respond we also found that variation in the reconstructed mat values using different calibrations could be up to 7 c possibly due to soil moisture variation since soil moisture may have a significant impact on the distribution of brgdgts our results further indicate that early warming occurred on the southern chinese loess plateau relative to a monsoonal precipitation increase as reported elsewhere

microbial lipid records of highly alkaline deposits and enhanced aridity associated with significant uplift of the tibetan plateau in the late miocene saline alkaline sediments and soils are widespread in arid and semiarid regions but their occurrence in ancient dry periods remains unknown due to the lack of a suitable proxy on the basis of investigations of modern chinese soils with a wide ph range of 3 5 9 1 we suggest that the microbial lipid ratio r i b i e the abundance ratio of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers to bacterial branched gdgts indicates the presence of drought induced alkaline deposits in terrestrial settings the r i b is invariant in modern soils with ph 600 mm but it increases sharply at higher ph values and lower mean annual precipitation i b ratio in a fluviolacustrine section in the zhada basin of the southwestern tibetan plateau covering the time period 9 2 2 6 m y ago the r i b ratio remains relatively stable in most intervals but exhibits maxima in some horizons indicative of the occurrence of severe drought and alkaline deposits in the basin catchment these occur in fluvial sediments deposited 9 m y ago a critical time with respect to the intensification of the east asian and indian monsoons and the significant uplift of the plateau that has previously been associated with enhanced aridity in central asia

environmental evolution recorded by lipid biomarkers from the tawan loess paleosol sequences on the west chinese loess plateau during the late pleistocene this study provides a reconstruction of the environmental evolution since 128 ka recorded by the lipid biomarkers of the c15 c35n alkanes the c13 c33n alkan 2 ones and the c12 c30n alkanols isolated from the tawan loess section northwest china variations in paleoenvironment are reconstructed from the values of the carbon preference index cpi the average chain length acl the l h ratio of lower molecular weight to higher molecular weight homologues the n alkane c27 c31 ratios and the n alkan 2 one c27 c31 ratio these parameters indicate the dominance of grasses over the west chinese loess plateau clp during the late pleistocene lower values of the cpi and the acl values respectively indicate stronger microbial reworking of organic matter and changes in plant species which are both indicative of a warmer wetter environment furthermore the fluctuations of environment recorded in the tawan section exhibit ten phases that show obvious cycles between warm periods and cold intervals this study reveals that changes in the biomarker proxies agree well with changes in the magnetic susceptibility and grain size and it indicates a huge potential for paleoenvironmental reconstructions by using the n alkan 2 one and n alkanol proxies

temperature changes reconstructed from branched gdgts on the central loess plateau during the past 130 5 ka abstract this study investigated the glycerol dialkyl glycerol tetraethers gdgts in a loess paleosol sequence lps to quantitatively reconstruct the mean annual air temperature mat on the central chinese loess plateau clp during the past 130 5 ka the results show that 1 mat variations reconstructed by global mbt methylation index of branched tetraethers and cbt cyclisation ratio of branched tetraethers transfer functions at xifeng range from 7 3 c to 28 4 c the mat variation on the central clp xifeng site is between the previously reported mat variations on the western yuanbao site and eastern clp mangshan site in agreement with the pattern that temperature increases from the northwestern clp to the southeastern clp 2 mat variations estimated by transfer functions of global mbt cbt global mbt cbt and chinese mbt cbt for lps are nearly all higher than the modern mat at xifeng indicating that the reconstructed mat values are probably overestimated 3 the maximum value of magnetic susceptibility at xifeng lagged that of the mat derived by mbt cbt proxy during the last interglacial 9 ka lag and since the last deglacial 6 ka lag

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

a test of different factors influencing the isotopic signal of planktonic foraminifera in surface sediments from the northern south china sea abstract the stable isotope composition of planktonic foraminifera is one of the most important proxies in paleoenvironmental research in this study three parameters affecting the stable isotope values of globigerinoides ruber from surface sediment from the northern south china sea were tested different cleaning methods different morphotypes and different size fractions our results show that in the small size fraction there is a small but significant effect on 13c by oxidizing the tests prior to measurement our data also confirm a small but significant difference between different morphotypes of g ruber however the variability caused by the seasonal effect stable isotope value is larger than the effect caused by different cleaning protocols or different morphotypes the large spread of the isotope values up to 2 have some implications to paleoceanographic reconstructions when measurements are performed on a small number of foraminiferal tests the isotope value does not necessarily reflect yearly average or a certain season but is a random value of the seasonal variability in that region

temperature dependent variation in the distribution of tetraether membrane lipids of marine crenarchaeota implications for tex86 paleothermometry 1 recently a new geochemical temperature proxy the tex86 was introduced this proxy is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraethers gdgts of the membrane lipids of marine crenarchaeota which changes as a response to temperature however until now only sediment data have been used to establish this proxy and experimental work is missing we performed mesocosm studies with marine crenarchaeota incubated at temperatures ranging from 5 to 35 c and salinities of 27 and 35 to test the validity of the tex86 proxy growth of marine crenarchaeota in these mesocosms was evident from the substantial increase in the concentration of marine crenarchaeotal membrane lipids with amounts up to 3400 ng l with increasing temperature an increase in the number of cyclopentane moieties in the crenarchaeotal membrane lipids was observed different salinities did not show any effect on the gdgt distribution the tex86 showed a significant linear correlation to incubation temperature tex86 0 015 t 0 10 r2 0 79 this equation has a similar slope to the correlation obtained from core tops but differs in the intersection tex86 0 015 t 0 28 r2 0 92 this difference is mainly determined by the smaller amount of the regioisomer of crenarchaeol in the incubation series compared to core top samples these incubation experiments indicates that water temperature is indeed the major controlling factor for the membrane distribution of marine crenarchaeota and confirms that the tex86 proxy depends on a physiological response to regulate membrane fluidity

climate reconstruction based on gdgt based proxies in a paleosol sequence in japan postdepositional effect on the estimation of air temperature abstract we investigated branched and isoprenoid glycerol dialkyl glycerol tetraethers gdgts in surface soils and a paleosol sequence to understand the effects of environmental and postdepositional factors on branched gdgt composition in different soil types and to reconstruct the past changes in the mean annual air temperature maat in southwestern japan during the last 15 ka the estimated maat was overestimated by 6 c and 2 c when the global and regional soil calibrations were applied respectively additionally the estimated maat increased downward by a maximum of 4 c in the upper 30 cm of the soil sequence this is likely to reflect the addition of newly produced branched gdgts in subsurface soils the estimated maats in a paleosol sequence are thus 10 c and 6 c higher than those expected when the global and regional soil calibrations were applied respectively but the variation agrees with the holocene variation in the maat estimated by the pollen assemblage this indicates that the mbt cbt derived maat is biased but the variation reflects the past changes in maat

delayed build up of arctic ice sheets during 400 000 year minima in insolation variability an east asian winter monsoon proxy record using grain size variations in chinese loess over the past 900 000 years shows that for up to 20 000 years after the interglacials at 400 000 year intervals the weak monsoon winds maintain a mild non glacial climate at high northern latitudes qingzhen hao and colleagues present a record of grain size variations in the chinese loess plateau a proxy of variations in the strength of the east asian winter monsoon and show that relatively high insolation at 400 000 year intervals held off the inception of the subsequent ice age for about 20 000 years relative to other glacial inceptions mechanistically the extension of warm conditions was probably linked to a weak siberian high pressure system associated with a delayed build up of northern ice and snow the authors speculate that these observations imply that arctic climate may remain in non glacial mode for more than 40 000 years even in the absence of anthropogenic greenhouse gases knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial1 may help to inform our understanding of future climate change unfortunately long term continuous records of ice sheet variability in the northern hemisphere only are scarce because records of benthic 18o content represent an integrated signal of changes in ice volume in both polar regions2 however variations in northern hemisphere ice sheets influence the siberian high3 an atmospheric pressure system so variations in the east asian winter monsoon eawm as recorded in the aeolian dust deposits on the chinese loess plateau can serve as a useful proxy of arctic climate variability before the ice core record begins here we present an eawm proxy record using grain size variations in two parallel loess sections representative of sequences across the whole of the chinese loess plateau over the past 900 000 years the results show that during periods of low eccentricity and precessional variability at approximately 400 000 year intervals the grain size inferred intensity of the eawm remains weak for up to 20 000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis in contrast there is a rapid increase in the eawm after the end of most other interglacials we conclude that for both the 400 000 year interglacials the weak eawm winds maintain a mild non glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records during these times the less severe summer insolation minima at 65 n ref 4 would have suppressed ice and snow accumulation leading to a weak siberian high and consequently weak eawm winds

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

sources and distribution of organic matter in a river dominated estuary winyah bay sc usa abstract the sources and distribution of organic matter om in surface waters and sediments from winyah bay south carolina usa were investigated using a variety of analytical techniques including elemental stable isotope and organic biomarker analyses several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range the dissolved organic carbon doc concentrations of surface waters ranged from 7 mg l 1 in the lower bay stations closest to the ocean to 20 mg l 1 in the river and upper bay samples there was a general linear relationship between doc concentrations and salinity in three of the four sampling periods in contrast particulate organic carbon poc concentrations were significantly lower 0 1 3 mg l 1 and showed no relationship with salinity the high molecular weight dissolved om hmw dom isolated from selected water samples collected along the bay displayed atomic carbon nitrogen ratios c n a and stable carbon isotopic compositions of organic carbon 13coc that ranged from 10 to 30 and from 28 to 25 respectively combined such compositions indicate that in most hmw dom samples the majority of the om originates from terrigenous sources with smaller contributions from riverine and estuarine phytoplankton in contrast the c n a ratios of particulate om pom samples varied significantly among the collection periods ranging from low values of 5 to high values of 20 overall the trends in c n a ratios indicated that algal sources of pom were most important during the early and late summer whereas terrigenous sources dominated in the winter and early spring in winyah bay bottom sediments the concentrations of the mineral associated om were positively correlated with sediment surface area the c n a ratios and 13coc compositions of the bulk sedimentary om ranged from 5 to 45 and from 28 to 23 respectively these compositions were consistent with predominant contributions of terrigenous sources and lesser but significant inputs of freshwater estuarine and marine phytoplankton the highest terrigenous contents were found in sediments from the river and upper bay sites with smaller contributions to the lower parts of the estuary the yields of lignin derived cuo oxidation products from winyah bay sediments indicated that the terrigenous om in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil om based on the lignin phenol compositions most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region a few samples displayed lignin compositions that suggested a more significant contribution from marsh c3 grasses however there was no evidence of inputs of spartina alterniflora a c4 grass remains from the salt marshes that surround the lower sections of winyah bay

molecular records of continental air temperature and monsoon precipitation variability in east asia spanning the past 130 000 years our current understanding of past changes in east asian summer monsoon easm precipitation intensity derives from several loess paleosol sequences and oxygen isotope 18o records of well dated stalagmites although temperature is generally presumed to have had minimal impact on easm records past air temperature dynamics over east asia are so far relatively poorly understood mainly due to the lack of tools to reconstruct continental paleotemperatures here we report a high resolution record of east asian air temperature over the past 130 000 years based on soil bacterial lipid signatures preserved in a loess paleosol sequence from the mangshan loess plateau in china we find that maximum local insolation is the main driver of air temperature although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak causing a decoupling with easm precipitation intensity direct comparison of our temperature record with precipitation induced changes in past soil ph derived from the same suite of lipids confirms this decoupling subsequent cross spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band the length of this lag is variable however and increases as glaciation develops this observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of easm response to insolation forcing during ice ages

quantitative relationships between magnetic enhancement of modern soils and climatic variables over the chinese loess plateau environmental magnetism has been widely employed to reconstruct past climate changes on the chinese loess plateau clp and several climofunctions based on the magnetic properties of loess have been developed however systematic investigation of the quantitative relationship between topsoil magnetic enhancement and modern climate remains uncommon in this study we obtained surface soil samples from 257 sites over the clp and adjacent regions from this set we used 180 samples from sites unaffected by potential contamination to investigate the relationship between the commonly measured magnetic properties of magnetic susceptibility and magnetic remanence and modern climatic variables the spatial distribution of the results demonstrates a strong nw se gradient of the magnetic enhancement of surface soils the results of more detailed magnetic parameters indicate that pedogenic viscous superparamagnetic and stable single domain particles are mainly responsible for the magnetic enhancement of the soils in the studied region and that the magnetic grain size distribution of the ferrimagnetic components of pedogenic origin remains almost constant independent of pedogenic intensity the uniform mechanism of magnetic enhancement mainly linked with the concentration of the pedogenic components rather than with variations in magnetic grain size decreases the level of ambiguity in climate reconstructions based on magnetic measurements of chinese loess statistical analyses including correlation principal component analysis pca and multiple regression analysis suggest that annual rainfall rather than temperature exerts the dominant effect on soil magnetic enhancement finally we used the results to develop several transfer functions to reconstruct mean annual precipitation map transfer functions based on frequency dependent susceptibility fd and anhysteretic remanent magnetization arm provide the most reliable estimates of map this study significantly improves the understanding of the relationship between soil magnetic properties and climate

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

comparison of isotopic composition of planktonic foraminifera in plankton tows sediment traps and sediments planktonic foraminifera from plankton tows sediment traps and sediments in the central north atlantic were studied in order to understand what determines their oxygen and carbon isotope composition a clear separation of species and genera on a 18o vs 13c plot for all samples suggests that their isotopic composition is controlled to a certain degree by biological factors within a species population the globorotaliids show a positive linear correlation between 18o and 13c while the shallow dwelling spinose species mostly globigerinoides species do not show a definite trend the latter species when collected in plankton tows often show slight negative deviations from isotopic equilibrium with respect to oxygen all species deviate from carbon isotope equilibrium by 1 5 to 6 these deviations from equilibrium are probably caused by incorporation of isotopically light metabolic co2 into the skeleton which is enhanced by the activity of symbiotic algae during their ontogeny the average weight per individual of most species increases which indicates that calcification continues to a depth of about 100 m this additional skeleton roughly 50 by weight is isotopically heavier because temperatures are lower and photosynthesis of symbiotic algae stops below the photic zone therefore the skeleton of foraminifera collected in sediment traps below 400 m has an overall oxygen isotope composition that seems to be in equilibrium for caco3 deposited in the upper 100 m