1997 1998 el nino off peru a numerical study an eddy resolving numerical simulation for the peru chile system between 1993 and 2000 is analyzed mainly for the 1997 1998 el nino atmospheric and lateral oceanic forcings are realistic and contain a wide range of scales from days to interannual the solution is validated against altimetric observations and the few in situ observations available the simulated 1997 1998 el nino closely resembles the real 1997 1998 el nino in its time sequence of events the two well marked sea level peaks in may june and november december 1997 are reproduced with amplitudes close to those observed other sub periods of the el nino seem to be captured adequately simple dynamical analyses are performed to explain the 1997 1998 evolution of the upwelling in the model the intensity of the upwelling appears to be determined by an interplay between alongshore poleward advection related to coastal trapped waves and wind intensity but also by the cross shore geostrophic flow and distribution of the water masses on a scale of 1000 km or more involving rossby waves westward propagation and advection from equatorial currents in particular the delay of upwelling recovery until fall 1998 i e well after the second el nino peak is partly due to the persistent advection of offshore stratified water toward the coast of peru altimetry data suggest that these interpretations of the numerical solution also apply to the real ocean

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

enhancement of wind driven upwelling and downwelling by alongshore bathymetric variability steady wind driven flow along a shelf of changing width is described with a frictional barotropic model valid in the limit of small rossby and burger number in these limits an alongshore wind drives enhanced onshelf transport in a coastal ocean if the shelf widens downwind and the change in shelf width only affects the flow in the direction of kelvin wave propagation downwave from the change in shelf width there is enhanced onshore transport of cold nutrient laden bottom water if the winds favor upwelling and the shelf narrows in the direction of kelvin wave propagation this enhanced transport extends a considerable distance away from the change in shelf width but becomes concentrated near the shelf break far from the change in width isobath curvature on the scale of the shelf width significantly modifies local cross shelf transport the cross shelf transport of nutrient rich water during upwelling is expected to be enhanced from point eugenia to la jolla san luis obispo to monterey and point reyes to cape mendocino on the west coast of north america

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

late quaternary glacial interglacial cyclicity models of the red sea the benthic foraminiferal faunas from samples of two piston cores retrieved along a north south transect in the red sea were studied the northern core was collected during meteor cruise m 31 2 while the southern one was collected during the sonne cruise 121 benthic foraminiferal faunas from both sites exhibit large variability with respect to density diversity species composition and assemblages combined with stable oxygen and carbon isotope records of planktic and benthic foraminifera one hundered thirty benthic foraminiferal species were identified in the investigated cores the faunal data set of the northern core was reduced to five assemblages factors while the southern one was reduced to four assemblages all assemblages were ranked according to their ecological significance besides relative abundance of major benthic foraminiferal suborders textulariina agglutinating foraminifera miliolina and rotaliina in addition to infaunal epifaunal relative abundance were used as paleoenvironmental proxies allowing the reconstruction of past changes in deep water salinity ventilation and organic carbon fluxes at the sea floor four distinct glacial interglacial cycle during the past 380 kyr have been recognized in the red sea the identified four cycles reveal deviation in deep sea ecosystem between the northern and southern red sea in the northern red sea salinity fluctuations productivity and deep water ventilation and formation had the major impact on benthic foraminiferal pattern corresponding to glacial interglacial cycles and glacio eustatic sea level changes coupled with the impact of mediterranean climate regime on the otherhand in the southern red sea region the oscillation trend of benthic foraminiferal pattern within the glacials and interglacials stages indicates a high frequency environmental alternation this alternation is consistent with the extent of ne monsoonal wind that controls the intensity and extension of the productivity which in turn determine organic matter fluxes and oxygen level at the sea floor

paleoceanographic record of the last glacial interglacial cycle in the red sea and gulf of aden abstract hydrographic conditions in the red sea are strongly controlled by regional climatic conditions and the restricted water exchange with the gulf of aden indian ocean in turn intermediate and deep water masses in the gulf of aden reflect the nature of red sea outflow planktonic and benthic foraminiferal faunas and the lithology and mineralogy of red sea and gulf of aden sediments were studied in order to evaluate changes in water mass conditions in the two basins during the last 18 000 years the results indicate that changes in the local climate and circulation regime during this period resulted in significant hydrographic changes in surface and bottom waters in the red sea and intermediate waters in the gulf of aden during the last glacial maximum high aridity and glacio eustatic sea level lowering resulted in surface and bottom water salinities in the red sea which were considerably higher than at present in the gulf of aden glacial surface salinities and temperatures remained similar to holocene values while surface water productivity may have been lower surface salinities in the red sea decreased after 18 000 years b p as the connection between the red sea and gulf of aden was reestablished however bottom water salinities remained high until at least 11 000 years b p pluvial conditions during deglaciation enhanced the density difference between surface and bottom waters in the red sea and resulted in a decrease in the oxygen content of the bottom waters hydrographic conditions in the western gulf of aden reflect a change in the properties of outflowing red sea water during deglaciation

south atlantic and benthic foraminifer δ13c deviations implications for reconstructing the late quaternary deep water circulation abstract benthic foraminifer species cibicidoides wuellerstorfi and related genera are assumed to secrete calcite very close to the carbon isotope values of the ambient bottom water co2 recently attention has been focused on substantial productivity linked 13c depletions to examine further the productivity effect on benthic 13c deviations we present data from the south atlantic between 15 and 35 s including water samples from 10 hydrographic stations and related surface sediment measurements on c wuellerstorfi we compare open ocean data with observations in the namibia upwelling area as a result 13c co2 values as well as phosphate concentrations in water samples of the upwelling realm differ significantly from those of the open ocean realm at least in the upper and mid depth water masses sacw aaiw ucdw however deviations from the redfield fractionation caused by air sea fractionation remain constant within each water mass which means that the carbon isotope changes toward upwelling areas are exclusively determined by biological cycling in addition to lower 13c co2 values in upwelling areas a depletion in the 13c of epibenthic foraminifer calcite is observed which is most likely explained by the decay of organic matter reducing the 13c 12c ratio in the pore water and influencing the carbon isotopic composition of the c wuellerstorfi shells of highly productive areas the paleoceanographic implication of this effect for reconstructing the late quaternary deep water circulation is discussed using carbon isotope records of several sediment cores within and outside the namibia upwelling area

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence slowly accumulated 5 cm kyr 1 and rapidly accumulated 5 20 cm kyr 1 sediments have been compared to define the initiation and termnation times of the most recent sapropel s1 in the eastern mediterranean sea the ba a1 ratio has been employed as a more persistent index of productivity than cg accelerator mass spectrometry radiocarbon dating of pelagic foraminifera indicates a maximum duration for increased ba a1 levels in s 1 from 9500 6000 uncorrected radiocarbon convention years b p in the rapidly accumulated sediments and 9500 5300 years b p in the slowly accumulated sediments this difference is ascribed to bioturbation affecting the slower accumulated s1 sediments in the two most rapidly accumulated s1 units from the adriatic and aegean seas there is a saddle of lower values centered on 7500 years b p in the corg and ba ai profiles so that the visual s 1 unit appears as a doublet geochemical evidence indicates that this intervening period is best interpreted as an episode of increased ventilation and bottom water oxygenation during the period of sapropel accumulation

evaluation of thermobarometers for garnet peridotites the accuracy and precision of a large number of combinations of geothermometers and geo barometers for garnet lherzolites have been evaluated with a suite of well equilibrated xenoliths from kimberlites of northern lesotho accuracy was tested by comparison of p t estimates for a diamond bearing and a graphite bearing xenolith with the experimentally determined diamond graphite univariant curve and by comparison of p t estimates for phlogopite bearing xenoliths to the high temperature stability limit of phlogopite eggler and wendlandt 1979 precision was evaluated by measuring the scatter of p t estimates for each of four xenoliths from a wide range of p and t when many point analyses of the constituent minerals are used for p t estimation a thermobarometer composed of the uncorrected diopside enstatite miscibility gap of lindsley and dixon 1976 combined with the uncorrected isopleths for aluminum in enstatite coexisting with pyrope of macgregor 1974 is most satisfactory correction schemes such as those of wells 1977 and wood 1974 will ultimately provide a better means of p t estimation but at the present stage of development they serve to decrease precision without a demonstrable increase in accuracy thermometers based on fe2 mg exchange reactions are imprecise because of variable and unknown fe2 fe3 in minerals and xenoliths the inflection observed in the northern lesotho paleogeotherm cannot be an artifact of the method of temperature estimation

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

benthic foraminiferal response to variations in surface water productivity and oxygenation in the northern arabian sea abstract a benthic foraminiferal record of 120 000 year obtained from the base of the oxygen minimum zone omz at a site in the northern arabian sea was studied quantitative benthic foraminiferal data were compared with palaeoproductivity indices corg and globigerina bulloides and indices for bottom water oxygen concentration pteropod preservation index mo al v al and mn al the benthic foraminiferal record revealed two distinct assemblages that show variations in the precession frequency band a high diversity low equitability assemblage proliferates in isotopic stages 1 4 and 5 and has been interpreted to reflect relatively oxygenated bottom water conditions this assemblage shows a strong covariance with minima in summer monsoon productivity a low diversity low equitability fauna typically with a few species showing high dominances is considered to reflect low bottom water oxygen conditions related to eutrophic surface water conditions dominating species in this assemblage are bolivinids buliminids and globobuliminids this assemblage dominates during precession driven maxima in summer surface water productivity and also during isotopic stages 2 and 3 we suggest that an intensified and colder glacial winter ne monsoon led to increased winter production which superimposed on the precession driven changes in surface water productivity resulted in overall poorly oxygenated bottom water during glacial stages 2 and 3 a promising proxy for tracing winter productivity in the northern arabian sea is the planktonic foraminifer globigerina falconensis the benthic foraminiferal species rotaliatinopsis seminvoluta in particular is prolific under glacial conditions

sst patterns and dynamics of the southern senegal gambia upwelling center the southern end of the canary current system comprises of an original upwelling center that has so far received little attention the southern senegal gambia upwelling center ssuc we investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the ssuc dynamical functioning as manifested by the recurrence and persistence of particular sst patterns the analyses also reveal subtle aspects of its upwelling structure shelf break cooling of surface waters consistent with internal tide breaking mixing complex interplay between local upwelling and the mauritanian current off the cape verde headland complexity of the inner shelf mid shelf frontal transition the amplitude of the diurnal cycle suggests that large uncertainties exist in the ssuc heat budget the studies limitations underscore the need for continuous in situ measurement in the ssuc particularly of winds

three hundred eighty thousand year long stable isotope and faunal records from the red sea influence of global sea level change on hydrography stable isotope and faunal records from the central red sea show high amplitude oscillations for the past 380 000 years positive 18o anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the arabian sea was reduced due to a reduced geometry of the bab el mandeb strait salinities as high as 53 and 55 are inferred from pteropod and benthic foraminifera 18o respectively for the last glacial maximum during this period all planktonic foraminifera vanished from this part of the red sea environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level the foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka spectral analysis of the planktonic 18o record documents highest variance in the orbital eccentricity obliquity and precession bands indicating a dominant influence of climatically driven sea level change on environmental conditions in the red sea variance in the precession band is enhanced compared to the global mean marine climate record specmap suggesting an additional influence of the indian monsoon system on red sea climates

the importance of the oxygen minimum zone and sediment geochemistry in the distribution of recent benthic foraminifera in the northwest indian ocean abstract the relationship between the distribution of benthic foraminifera and sediment type and depositional environment in the arabian sea is discussed the benthic foraminiferal fauna were sampled in nineteen recent surface sediment samples and geochemical variables of the sediment of the same samples were measured the water depths for the box core samples varies from 440 to 4040 m a total of 103 species and six species complexes were identified the geochemical properties were found to correspond well to the sediment type and depositional environment and six different sediment depositional environment types could be distinguished analysis of the benthic foraminiferal fauna reveals specific faunal assemblages that are closely related to these sediment depositional environment types

mantle derived spinel lherzolite xenoliths from the deccan volcanic province india implications for the thermal structure of the lithosphere underlying the deccan traps abstract petrography mineral and host rock chemistry of the mantle derived spinel lherzolite xenoliths in the nephelinites of kutch a late variant of the deccan traps province india are reported the xenoliths register equilibration temperatures between 920 70 c and 1060 50 c and an ascent time between 19 and 168 days representing a palaeogeotherm of minimum heat flow between 60 and 70 mw m 2 the xenoliths possibly came from the oceanic lithosphere under the deccan field following the cretaceous eocene fragmentation of gondwanaland

observations of upwelling and relaxation events in the northern monterey bay during august 2000 1 the interplay between the point ano nuevo upwelling center an offshore anticyclonic mesoscale eddy and the waters of the monterey bay was studied during a series of up and downwelling favorable wind events during august 2000 the upwelling events were characterized by the appearance of cold salty water at point ano nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued during the downwelling relaxation events the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself the circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing the icon model a nested data assimilating sigma coordinate model was used to simulate the upwelling and relaxation events and calculate the subsurface current and density fields the model reproduced the dominant current and temperature patterns outside the bay including the southward flowing upwelling filament the movement of the offshore eddy the poleward flow off point sur and the circulation within the bay the model salinity fields at the surface and 100 m levels show that during upwelling the bay was filled with higher salinity water stemming from the point ano nuevo upwelling center to the north during downwelling the source water for both the surface and 100 m levels was the colder fresher california current water offshore which had advected southward well past point pinos during the previous upwelling event

effect of municipal wastewaters on bottom sediment geochemistry and benthic foraminifera of two red sea coastal inlets jeddah saudi arabia al arbaeen and al shabab inlets are two red sea coastal inlets lying on the mid coast of jeddah city saudi arabia forty four surface sediment samples were collected from these inlets and surrounding areas during june 2010 water depths and the overlying environmental parameters temperature salinity ph and dissolved oxygen of these samples were measured sediment samples were analyzed for variables such as loss on ignition loi organic matter caco3 heavy metals fe mn cu zn cd ni cr and pb and benthic foraminifera to assess any changes in the environment of the inlets and surrounding areas variables distribution patterns indicated that mud sediments dominated the inlets and enriched by loi heavy metals and ammonia tepida quinqueloculina seminula assemblage whereas coarse sand gravel sediments dominated the substrates of surrounding areas and enriched by caco3 and coscinospira hemprichii peneroplis planatus varidentella neostriatula assemblage with low values of loi and heavy metals highest concentrations of cu zn cd ni cr and pb were recorded inside the inlets especially near the discharge points and they were positively correlated with the loi and mud fraction indicating their affinity to anthropogenic materials however highest concentrations of fe and mn were typically recorded in the whole study area these metals were positively correlated with the loi values of the surrounding area but in the inlets they were negatively correlated with the loi indicating an existence of reducing conditions caused by limited dissolved oxygen conditions at bottom waters of the inlets changing the environment within the inlets according to higher concentrations of heavy metals and loi is probably responsible for the existence of the low density and diversity of benthic foraminifera and the absence of reefal symbiont bearing species

glacial conditions in the red sea in this paper results from previous studies on planktonic foraminifera 6 o and global sea level are combined to discuss climatic conditions in the red sea during the last glacial maximum 18 000 b p first the influence of 120 m sea level lowering on the exchange transport through the strait of bab el mandab is considered this strait is the only natural connection of the red sea to the open ocean next glacial red sea outflow salinity is estimated about 48 parts per thousand from the foraminiferal record combined these results yield an estimate of the glacial net water deficit which appears to have been quite similar to the present about 2 rn yf finally budget calculation of 6 o fluxes suggests that the glacial 6 o value of evaporation was about 50 of the present value this is considered to have resulted from substantially increased mean wind speeds over the glacial red sea which would have caused a rapid drop in the kinematic fractionation factor foro the sensitivity of the calculated values for water deficit and isotopic fractionation to the various assumptions and estimates is evaluated in the discussion improvents are to be expected especially through research on the glacial salinity contrast between the red sea and gulf of aden it is argued however that such future improvement will likely result in a worsening of the isotopic discrepancy thus increasing the need for an additional mechanism that influenced fractionation such as mean wind speed this study demonstrates the need for caution when calculating pal osaliniti s from 5 so records under the assumption that the modem s 5 so relation has remained constant through time previously overlooked factors such as mean wind speed may have significantly altered that relation in the past

subsurface recirculation and larval retention in the lee of a small headland a variation on the upwelling shadow theme 1 the interaction of alongshore coastal currents with large headlands has been shown to increase the retention of planktonic organisms through the formation of headland eddies or upwelling shadows in their lee this study investigates the circulation within bodega bay in the lee of a small headland in an upwelling region and the potential for retention of plankton during the upwelling season of 2004 time series of temperature and velocity were recorded throughout bodega bay conductivity temperature depth ctd surveys were conducted and surface drifters were released during upwelling downwelling and relaxation conditions postlarval settlement was monitored daily over two periods coinciding with ctd surveys under strong upwelling favorable conditions wind driven surface currents were equatorward both offshore and throughout the bay however there was significant current shear along the eastern shore of the bay where cold bottom waters move poleward counter to the direction of the wind driven surface flow during downwelling and relaxation conditions flow was poleward throughout the water column along the eastern shore of the bay postlarvae settled during all wind conditions but greatest settlement was observed at the onset of upwelling favorable conditions while no typical upwelling shadow is evident in the lee of the bodega headland subsurface recirculation driven by the alongshore flow past bodega head may facilitate the retention of plankton in the bay previous studies have generally focused on large headlands however it is likely that other small embayments in the lee of small headlands may also provide retention opportunities for planktonic organisms in upwelling regions

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

water level fluctuations of lake tanganyika in phase with oceanic changes during the last glaciation and deglaciation there has been considerable controversy about the magnitude of fluctuations of the levels of lake tanganyika the earth s second deepest lake 1 470 m following the discovery of submerged valleys extending down to 550 m below present lake levels1 these fluctuations register changes in the precipitation evaporation evapotranspiration ratio in a large equatorial tropical area of catchment south of the equator here we report new palaeohydrological data back to 40 kyr bp from carbon dating of the total organic matter in two diatomaceous cores the results constrain the vertical lake level fluctuations more than has hitherto been possible2 5 and show that the fluctuations from 26 kyr bp are correlated with changes in global sea level and ice volume surpris ingly fluctuations seem to be in phase with those of the african lakes north of the equator which are clearly linked to the milankovitch mechanisms

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

on the sources formation and circulation of red sea deep water red sea deep water is renewed from sources in the far north of the red sea upwelling of deep water throughout the basin maintains the sharp pycnocline with its base near the depth of the sill at bab el mandeb before now deep water renewal was thought to occur mainly by means of convective deep water formation in the north which renews the bottom water and gives rise to a southward flowing bottom current carbon 14 and 3he data from the geosecs indian ocean expedition lead to the identification of an additional volumetrically larger mode of northern deep water formation in which new deep water is injected immediately beneath the pycnocline this mode of deep water formation to be called the isopycnal mode also gives rise to a southward flowing current in this case at the top of the deep water mass geosecs data also demonstrate the existence at intermediate depths in the deep water of a return flow to the north the surface history in the nuclear era of the 14c in the deep water source region was reconstructed by direct radiocarbon measurements on annual growth bands of corals calculation then shows that new deep water forms in the convective mode at a rate of 0 05 0 01 sverdrup sv expressed as if the flow were continuous and is due principally to processes occurring in the mouth of the gulf of suez the injection beneath the pycnocline of new deep water formed in the isopycnal mode is 0 11 0 02 sv this new deep water appears to originate mainly in the extreme open northern red sea the gulf of aqaba makes a modest but significant contribution to both modes the total deep water renewal rate is about 0 16 sv yielding a bulk deep water residence time of about 36 years oxygen consumption in the deep water shows approximately exponential decrease of consumption rate with depth as expected on geological and geophysical grounds hydrographically significant fluxes of heat and salt from the sea floor into the red sea deep water are discernible in the hydrography helium 3 flux from the sea floor into the deep water is about 69 1 stp year

middle late quaternary palaeoclimate variability from lake and wetland deposits in the nefud desert northern arabia abstract records of former lake and wetland development in present day arid hyper arid environments provide an important source of information for palaeoclimatic and palaeoenvironmental studies in arabia such records are typically confined to eccentricity modulated insolation maxima and are often spatially and temporally discontinuous here we present records from a single locality in northern arabia of wetter interludes during both global interglacial and glacial conditions providing a unique opportunity to examine the nature of these events in a common setting at jubbah in the southern nefud desert lake and wetland deposits reveal the repeated formation of a water body within a large endorheic basin over the past ca 360 kyr lake wetland formation occurred during mis 11 9 7 5 3 and the early holocene assisted by local topographic controls and spring recharge palaeoenvironmental and palaeoecological data reveal the existence of a large still water body formed during either mis 11 or 9 ca 363 ka and basin wide alluviation followed by lake formation during mis 7 ca 212 ka during mis 5e ca 130 ka a large freshwater lake occupied the basin while during mis 5a ca 80 ka the basin contained a shallow wetland and freshwater lake complex lake wetland formation also occurred during early mis 3 ca 60 ka at the terminal pleistocene holocene transition ca 12 5 ka and the early middle holocene ca 9 6 5 ka phases of lake and wetland development coincided with human occupation of the basin during the middle palaeolithic epipalaeolithic and neolithic periods highlighting the significance of the region for early demographic change

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

palhydaf palaeohydrology in africa program objectives methods major results abstract the palhydaf program aims to reconstruct the late quaternary 130 ka b p to present environmental and hydrological changes of northwest africa and to interpret them in terms of palaeoclimate for testing coupled atmospheric ocean circulation models lacustrine sequences were obtained from closed basins which lie along two meridional transects southern tunisia southern niger and algeria mali particular attention is given to groundwater storage and periods of recharge of the aquifers the chronological framework is based on 14c dates conventional and ams methods and or the th u disequilibrium method in favourable cases e g mali correlations can be made between the chronology of surface palaeohydrology and that of aquifer recharge various environmental markers mineralogy elemental chemistry stable isotopes biological remains are used for palaeoenvironmental purposes quantitative estimates of palaeoclimatic variables e g air humidity may be attempted through the combination of geochemical and palaeobiological data the major results already obtained are summarized for the following individual sectors 1 southern tunisia 1 northern algeria 2 southern algeria 3 northern niger 3 mali 4 southern niger at the present stage of investigation the following new inferences can be drown one or several humid episode s occurred in the northern sahara between 150 and 75 ka b p several factors suggest that these humid conditions also affected lower latitudes although their southern extent cannot be given precisely at present the previously postulated existence of large lakes at 20 35 ka b p is not confirmed this time interval seems to coincide with raised water tables but not to a major humid phase in all cases the 14c chronologies obtained for the late pleistocene have to be checked by comparison with other dating methods e g th u disequilibrium after the arid period of the last glacial maximum the return of humid conditions occurred in two major steps at 12 and 9 5 9 ka b p for both the southern and the northern sahara

impact of climatic changes on the benthic foraminiferal fauna in the ionian sea during the last 330 0000 years to reconstruct paleoceanographic changes in the eastern mediterranean during the last 330 000 years we studied benthic foraminifera in a piston core from the ionian sea the fauna exhibits large fluctuations in foraminiferal number diversity and species composition interglacials are characterized by low foraminiferal number and diversity indicating oligotrophic conditions directly below or above interglacial sapropels increased numbers of low oxygen tolerant species indicate a strong reduction of deep water circulation glacials are characterized by increased foraminiferal number and diversity and faunas that are dominated by shallow infaunal species indicating mesotrophic conditions around glacial sapropel s6 very high foraminiferal numbers and the dominance of shallow and deep infaunal species suggest enhanced organic matter fluxes these faunal results provide information about changes in the african and north atlantic climate systems monsoon and westerlies controlling the humidity and wind stress in the mediterranean region

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

dynamics of a low enrichment high retention upwelling center over the southern senegal shelf senegal is the southern tip of the canary upwelling system its coastal ocean hosts an upwelling center which shapes sea surface temperatures between latitudes 12 and 15 n near this latter latitude the cape verde headland and a sudden change in shelf cross shore profile are major sources of heterogeneity in the southern senegal upwelling sector ssus ssus dynamics is investigated by means of regional ocean modeling system simulations configuration realism and resolution x 2 km are sufficient to reproduce the ssus frontal system our main focus is on the 3 d upwelling circulation which turns out to be profoundly different from 2 d theory cold water injection onto the shelf and upwelling are strongly concentrated within a few tens of kilometers south of cape verde and largely arise from flow divergence in the alongshore direction a significant fraction of the upwelled waters are retained nearshore over long distances while travelling southward under the influence of northerly winds another source of complexity regional scale alongshore pressure gradients also contributes to the overall retention of upwelled waters over the shelf varying the degree of realism of atmospheric and oceanic forcings does not appreciably change these conclusions this study sheds light on the dynamics and circulation underlying the recurrent sea surface temperature pattern observed during the upwelling season and offers new perspectives on the connections between the ssus physical environment and its ecosystems it also casts doubt on the validity of upwelling intensity estimations based on simple ekman upwelling indices at such local scales

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

constraints on the collision and the pre collision tectonic configuration between india and asia from detrital geochronology thermochronology and geochemistry studies in the lower indus basin pakistan abstract knowledge of the timing of india asia collision is a fundamental prerequisite for understanding the evolution of the himalayan tibetan orogen and its role in global climate oceanic chemistry and ecological evolution despite much active research the basic pre collision tectonic configuration and the timing of terminal india asia suturing remain debated for example debates regarding when and how the intervening kohistan ladakh arc was sutured with india and asia still remain elusive some models propose the arc collided with asia at about 100 ma with india asia collision at ca 55 ma whilst a newer model proposed the arc s collision with india at 50 ma and subsequently with asia at 40 ma another example is the recent proposition that an oceanic greater india basin separated the tethyan himalaya microcontinent from the remaining indian plate until 20 25 ma with the consumption of this oceanic basin marking the final collision at this time these controversies relate to whether the commonly documented 50 ma contact represents the terminal india asia suturing or the amalgamation between various arcs or microcontinents with india or asia here we present an integrated provenance study of geochronology thermochronology and geochemistry on the late cretaceous pleistocene sediments from the lower indus basin on the indian plate the detrital zircon u pb and fission track data show a reversal in sediment source from a pure indian signature to increasing inputs from the suture zone and the asian plate between the middle paleocene and early oligocene the nd and sr isotopes narrow down this change to 50 ma by revealing input of asian detritus and the establishment of a nd sr isotopic pattern similar to the present day indus fan by 50 ma with no significant variations up section contrary to what might be expected if later major collisions had occurred our isotopic data indicate that greater india was occupied by a fluvial deltaic system analogous to the present day indus and named as the paleo indus which has been transporting asian detritus southward across the suture zone and kohistan ladakh arc since 50 ma suggesting no other ocean basins intervened between india and asia after this time in this region our data require that in the west the india asia collision were accomplished by 50 ma

simulation of intense monsoons under glacial conditions paleoenvironmental and paleoclimatological proxy data indicate that strong continental monsoons took place under glacial conditions during marine isotopic stage 6 5 175 ka bp so far no climate model has explored the possible coexistence of glacial conditions at mid and high latitudes and of interglacial monsoons in the tropics here we use an atmospheric general circulation model and clearly demonstrate that high insolation can generate increased monsoon activity even with surface glacial conditions our experiments show that indian and african monsoons at 175 ka were stronger than nowadays and induced an increase in outflow of the nile river to the mediterranean sea this freshwater supply combined with the local low glacial evaporation may explain the stagnation of the eastern mediterranean sea leading to the deposit of sapropel s6 our simulations show also increased surface winds in the northern atlantic and pacific oceans which may have affected the bioproductivity in these areas

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

response of red sea deep water agglutinated foraminifera to water mass changes during the late quaternary abstract the distribution of deep water agglutinated foraminifera was determined in core material taken in the central red sea by the r v meteor cruise 5 leg 2 the sedimentary record represents the last 380 kyr which includes four glacial interglacial cycles the agglutinate assemblage is of low diversity and in general is a minor component of the benthic foraminifera it comprises 14 species belonging to the following genera ammobaculites lagenammina plotnikovina pseudogaudryina reophax sahulia siphotextularia spiroplectinella textularla and a doubtful genus of unknown taxonomic position psammosphaera three sub groups were identified in the core according to their occurrence either in interglacial stages or in both glacial and interglacial intervals reflecting mainly tolerance to salinity variations exceptional bottom water conditions during the last 60 kyr caused a remarkable decrease in the abundance and diversity of this group the development of dysaerobic bottom water between approx 60 and 26 kyr the presence of a deep water mass of extremely high salinity ca 55 between 26 and 13 kyr and the occurrence of anoxic bottom sediments between 12 9 and 9 6 kyr seem to have caused the extreme impoverishment during the last 9 6 kyr the agglutinated foraminifera gradually recolonized the deep water a diverse assemblage composed of the above mentioned genera is found in holocene sediments only in the core top sample in addition small 63 149 m noncanaliculate organic cemented agglutinated foraminifera belonging to the genera ammodiscus cribrostomoides eggerella glomospira haplophragmoides morulaeplecta spiroplectammina paratrochammina and trochammina are preserved preferentially only in the uppermost part of the core 0 28 cm depth in sediments younger than 3 kyr

benthic foraminifera as proxies of organic matter flux and bottom water oxygenation a case history from the northern arabian sea abstract benthic foraminifera have been quantified in two sediment cores from a topographic high murray ridge in the northern arabian sea one core is from a station within the present day oxygen minimum zone omz the other from a station below the omz changes in the intensity of the omz linked to monsoonal climate variability had a strong impact on benthic foraminiferal composition and accumulation rates at the shallower omz station 920 m an intensification of the omz resulted in lower diversities and high dominances of low oxygen tolerant species the deeper station 1470 m was far less affected though at least once during the last 225 000 years the benthic faunal composition and accumulation rates show evidence for a deepening of the base of the omz to a level close to or even below 1470 m we suggest that percentages of miliolids can be used for rapid reconstruction of periods of increased ventilation in the northern arabian sea and are a promising proxy for tracing changes in bottom and pore water oxygenation in general omz conditions are characterised by high abundances of deep infaunal species and increased burial efficiency of organic matter the proportion of deep infaunal species appears to be a measure for the anoxic burial efficiency of organic matter and not a direct measure for the arriving flux at the seabed results furthermore show that benthic foraminiferal accumulation rates cannot be used as a proxy for surface water productivity under the prevalence of severe dysoxia

benthic foraminiferal successions across late quaternary mediterranean sapropels abstract benthic foraminiferal records across late quaternary mediterranean sapropels s6 s5 and s1 are reviewed and re considered in the light of recent advances in foraminiferal ecology it is suggested that the main factor controlling the foraminiferal successions that occur immediately before and after sapropel deposition is the amount of time involved in the onset of anoxic conditions and in the re oxygenation of the benthic environment faunas dominated by deep infaunal taxa such as globobulimina and chilostomella reflect a very gradual decrease or increase of bottom water oxygenation post sapropel faunas dominated by small biconvex trochospiral taxa which are inferred to have a much more opportunistic life strategy are typical of a very rapid re oxygenation of the benthic environment after sapropel deposition the time involved in re oxygenation depends upon the mechanism causing sapropel formation the faunal succession found above sapropel s5 suggests a basin with a strong density gradient in the upper part of the water column during sapropel deposition followed by a rapid turnover of the following column and quick re oxygenation of the benthic environment in contrast the faunal succession above sapropel s6 suggests a water column with a more gradual density gradient deeper in the basin a progressive deepening of the halocline and a very slow increase of bottom water oxygenation

mesoscale eddies in the gulf of aden and their impact on the spreading of red sea outflow water abstract the gulf of aden goa in the northwestern indian ocean is the receiving basin for red sea outflow water rsow one of the world s few high salinity dense overflows but relatively little is known about spreading pathways and transformation of rsow through the gulf here we combine historical data satellite altimetry new synoptic hydrographic surveys and the first in situ direct observations of subsurface currents in the goa to identify the most important processes in the spreading of rsow the new in situ data sets were collected in 2001 2003 as part of the red sea outflow experiment redsox and consist of two ctd ladcp surveys and 49 one year trajectories from acoustically tracked floats released at the depth of rsow the results indicate that the prominent positive and negative sea level anomalies frequently observed in the goa with satellite altimetry are associated with anticyclonic and cyclonic eddies that often reach to at least 1000 m depth i e through the depth range of equilibrated rsow the eddies dominate rsow spreading pathways and help to rapidly mix the outflow water with the background eddies in the central and eastern gulf are basin scale 250 km diameter and have maximum azimuthal speeds of about 30 cm s at the rsow level in the western gulf smaller eddies not detectable with satellite altimetry appear to form as the larger westward propagating eddies impale themselves on the high ridges flanking the tadjura rift both the hydrographic and lagrangian observations show that eddies originating outside the gulf often transport a core of much cooler fresher water from the arabian sea all the way to the western end of the goa where the highest salinity outflow water is found this generates large vertical and horizontal gradients of temperature and salinity setting up favorable conditions for salt fingering and diffusive convection both of these mixing processes were observed to be active in the gulf two new annually appearing anticyclonic eddies are added to the previously identified gulf of aden eddy gae prasad and ikeda 2001 and somali current ring scr fratantoni et al 2006 these are the summer eddy se and the lee eddy le both of which form at the beginning of the summer monsoon when strong southwest winds blowing through socotra passage effectively split the gae into two smaller eddies the se strengthens as it propagates westward deeper in the goa while the lee eddy remains stationary in the lee of socotra island both eddies are strengthened or sustained by ekman convergence associated with negative wind stress curl patches caused by wind jets through or around high orography the annual cycle in the appearance propagation and demise of these new eddies and those described in earlier work is documented to provide a comprehensive view of the most energetic circulation features in the goa the observations contain little evidence of features that have been shown previously to be important in the spreading of mediterranean outflow water mow in the north atlantic namely a wall bounded subsurface jet the mediterranean undercurrent and submesoscale coherent lenses containing a core of mow meddies this is attributed to the fact that the rsow enters the open ocean on a western boundary high background eddy kinetic energy typical of western boundary regimes will tend to shear apart submesoscale eddies and boundary undercurrents even if a submesoscale lens of rsow did form in the goa westward self propagation would transport the eddy and its cargo of outflow water back toward rather than away from its source

paleoenvironmental events during the last 13 000 years in the central red sea as recorded by pteropoda a high resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central red sea r v meteor cruise 5 leg 2 the numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr the results indicate the existence of a highly stratified water column during deglaciation and early holocene 13 8 5 ka during this period the depth of the mixed layer varied between less than 50 100 m at most and productivity was markedly reduced in comparison to the recent situation the intermediate and deep water were constantly highly depleted in oxygen a pronounced younger dryas event was recognized at 10 4 ka which coincides with an arid phase on the border land the oxygenation of the intermediate water improved remarkably after 7 5 ka and peaked during the period between 4 6 and 2 0 ka during this period the mixed layer reached its present depth and the productivity which was maximal during middle holocene attained present level during the last 4 6 kyr

understanding the red sea response to sea level here we outline a new pragmatic methodology to derive relative sea level estimates from central red sea oxygen isotope records based on a previously published model in this paper the methodology is described in detail and it is shown that sea level change is the dominant factor responsible for the recorded variability in red sea 18o pdb for sea level changes greater than 12 m variables such as temperature or net evaporation are shown to have relatively small effects on the oxygen isotope record the modelled 18o pdb to sea level relationship is given in terms of a fifth order polynomial which may be used to describe relative sea level from central red sea oxygen isotope records we show how established sea level records from fossil reef terraces for the last 20 kyr are successfully simulated from central red sea oxygen isotope records we also examine the spatial variability of 18o pdb in the basin over the last 13 kyr

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

changes in beach gravel lithology caused by anthropogenic activities along the southern coast of lake michigan usa the southern coast of lake michigan is the most urbanized and most densely populated area in the great lakes region development of steel mills harbors and municipalities in nw indiana and in ne illinois in the last century and a half altered the nearshore environment so much that native beach gravel 8 mm now exist only in the exhumed paleo beach remnants from the nipissing phase 4 500 years ago of lake michigan native gravel collected from paleo beach remnants at mount baldy dune and beach house blowout contain predominantly beach shingle very platy siltstones 71 78 with secondary crystalline pebbles 18 in the east and carbonate pebbles 12 in the west a large amount of anthropogenic fill steel industry waste waste from power generating plants construction debris railroad and road fill has been added since the late 1800s to fill lake michigan and expand industrial land four areas of major coastal structures michigan city pier and breakwater burns harbor pier and breakwater gary works pier and indiana harbor peninsula altered the natural littoral drift and created four independent sectors on indiana s coast northeastern eastern central and western between which no natural transfers of coarse sediments occur downdrift from the coastal structures severe beach erosion has prompted extensive beach nourishment with non native sandy gravel four distinct populations of modern beach gravel now exist along indiana s coast of lake michigan 1 native gravel with diluted beach nourishment influence 2 native gravel with a minor industrial influence 3 compact gravel of nourished origin and 4 anthropogenic gravel of industrial origin native gravel with diluted nourishment influence is found in the western downdrift areas of the northeastern from long beach to washington park beach and eastern sectors from eastern indiana dunes state park to western dune acres and contains up to 40 compact carbonate and crystalline pebbles in addition to native beach shingle native gravel with minor industrial influence is found in the central sector of indiana s coast from central ogden dunes to marquette beach and contains predominantly beach shingle platy clastic lithology but also up to 30 of chert and other pebbles released by industry compact gravel of nourished origin contains 60 90 of carbonate and crystalline pebbles and is found in the eastern updrift areas of the northeastern michiana beach and duneland beach and eastern sectors from crescent beach to the western beverly shores anthropogenic gravel of industrial origin contains 70 90 compact chert and slag and is found in every beach of the western sector and in the westernmost beach of the central sector streams draining into southern lake michigan generally contain little coarse sediment except in their channels near the roads and railroads where angular to subangular anthropogenic pebbles predominate 70 90 however streams have very little influence on gravel lithology along the coast because they seldom discharge anthropogenic gravel into lake michigan recent changes in gravel lithology along the southern lake michigan coast may affect changes in nearshore benthic flora and fauna as well as algal and bacterial blooms during warm summer months

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

the paleolimnology of haynes lake oak ridges moraine ontario canada documenting anthropogenic and climatic disturbances haynes lake is a small kettle lake located on the oak ridges moraine and is within the greater metropolitan area of toronto ontario canada s most populous region lake sedimentation flux rates diatoms and thecamoebians extracted from a benthic core were used as biological proxies to evaluate changes in water quality through time as a function of anthropogenic activity and changing climate there were two periods of disturbance to the haynes lake ecosystem from ca 8 500 years before present ybp through to ca a d 2003 which were significant enough to cause changes in lake sedimentation the diatom flora and thecamoebian fauna the first disturbance was concomitant with the decline in global temperatures following the hypsithermal climate optimum ca 4 700 ybp the most significant disruption to haynes lake over the last 8 500 years however was the settlement of europeans and subsequent urban development ca a d 1875 including the construction of a road immediately adjacent to the lake anthropogenic disturbance of inorganic clays in the recent paleosediment record 5 cm is indicative of more recent eutrophication events

palaeoceanographic evolution of the central red sea during the late holocene three multicores were studied in the central red sea off port sudan at a w e transect in order to reconstruct palaeoceanographic conditions of the past 6000 years downcore fluctuations in the rel

aplanktonic zones in the red sea abstract we use micropalaeontological and stable isotope results for a series of cores from north to south through the red sea to assess temporal and spatial patterns of change in planktonic foraminiferal faunas leading up to the remarkable full glacial red sea aplanktonic zones aplanktonic zones reflect salinities in the red sea in excess of the lethal 49 p s u limit caused by reduced exchange transport through the strait of bab el mandab due to glacial sea level lowering concerning the last glacial cycle aplanktonic conditions began at 39 ka bp in the north where salinities eventually reached 55 57 p s u paradoxically planktonic faunas are reported to have survived the last glacial maximum in the northern gulf of aqaba suggesting a poorly understood freshwater dilution at that time aplanktonic conditions s 49 p s u reached the south central red sea by 22 ka bp while planktonic foraminiferal faunas continued albeit in very low abundances and limited diversity s 45 p s u in the southernmost red sea during marine isotope stage mis 6 the 49 p s u isohaline appears to have resided in the central red sea between cores kl11 and md921017 we observe a systematic sequence of species disappearances before all glacial maxima of the last 500 kyr absence of a logical relationship with sea levels suggests that the disappearance sequences are not related to a general salinity increase instead we argue that the sequences were driven by complex reorganisations in hydrography stratification productivity food availability and subsurface oxygenation reproduction habitats the onset is marked by dramatic basin wide expansion of conditions that today are restricted to only the southern red sea suggesting an expansion of the dominance of ne monsoonal circulation over the entire red sea this expansion occurred 15 or more kyr before the aplanktonic zones of mis 12 6 and 2 and also before mis 10 and 8 which never reach the aplanktonic stage regarding the last glacial cycle this event occurred as early as 75 ka bp mis 4 5 boundary after this major climatic reorganisation we reconstruct progressive intensification of the new conditions especially marked by northward expansion and intensification of the subsurface oxygen minimum zone omz during the last glacial cycle a shallow and very distinct omz affected the central red sea as early as 68 ka bp and the north as late as 55 ka bp the omz expansion intensification appears to have been interrupted by episodes of increased ventilation

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

the last 140 ka in the afro asian arid semi arid transitional zone abstract during the last ten years a great number of geological or other proxy records provided radiocarbon u th or tl dated information on the past climatic oscillations in the arid semi arid zones extending between the atlantic and the pacific comparisons and a synthetic view of these results can now be attempted for the last 140 ka and compared with global changes as registered in oceanic or ice cores and with palaeomonsson models for this purpose wide spatial and time scales have to be used on the whole arid humid alternations roughly fit global changes cold phases corresponding to an extension of the arid areas to the south warm phases corresponding to the shrinking of the same to the north the last interglacial is associated with an increase of precipitation throughout the area considered isotopic stage 4 brings no evidence whatsoever of humid conditions two wetter episodes are registrated during stage 3 a major rainfall decrease is everywhere associated with the last glacial maximum 21 15 ka in most regions the arid or semi arid zones extending several hundred kilometers southwards relative to the present day pattern the two abrupt deglaciation steps and the younger dryas are recorded in all of the most sensitive regions at the margins of the present day monsoonal range during the holocene the precipitation increases everywhere by 100 400 mn relative to the present day values the optimum being at 8 5 6 5 ka a climatic deterioration follows with an irregular pattern of dry wet episodes according to the different geographic conditions the humid phase terminates at 3 5 3 ka in the whole transitional zone the major southward shift of the monsoonal precipitation range since its optimum some 8000 years ago fits the astronomical neoglacial trend and may possibly be correlated with past stage 5d although its rapidity and spatial importance may just reflect one of the sharp successive cold warm variations registered by grip during the whole stage 5

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

relocations and local earthquake tomography implications toward the mafic pluton induced crustal seismicity in kachchh gujarat india for last 18 years abstract the study presents new probable crustal model based on precise double difference relocations of 2420 aftershocks of the 2001 bhuj earthquake mw7 7 during 2001 16 and combining other geophysical and geological studies in the region which will lead to a better understanding of the cause of uninterrupted aftershock activities in the region relocations of aftershocks delineate two main seismic clusters in the central aftershock zone caz i e eastern a1 and western a2 the alignments of relocated hypocenters of the aftershocks delineate three main fault segments viz the south dipping north as well as south wagad faults and north dipping kachchh mainland fault relocations also detect some zones of devoid of aftershocks with a typical dimension of 3 9 km within the caz which could be related to locales of future earthquakes seismic velocity tomograms depict that both seismic clusters a1 and a2 are associated with high velocity anomalies inferred to be mafic plutons below the wagad and banni regions respectively the e w depth section of relocated hypocenters delineates an 18 km variation of the seismogenic base which could be attributed to the increase in crustal maficness due to the intrusion of mafic plutons below the caz stress inversions of selected focal mechanisms depict a rotation of 44 in the 1 orientation within the caz which could be attributed to large local stresses induced by mafic plutons the continued seismicity at kachchh is proposed to be caused by the presence of large stresses associated with mafic plutons owing to the n s plate compression associated with northward movement of the indian plate wherein crustal fluid flows aqueous metamorphic fluids or volatile co2 might provide the triggering to generate continued aftershock activities at kachchh india

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

late quaternary biostratigraphy and paleotemperatures of the red sea and the gulf of aden based on planktonic foraminifera and pteropods abstract the quantitative distributions of planktonic foraminifera and pteropods were analyzed in seven red sea cores and two deep sea cores from the gulf of aden and off sokotra island biostratigraphic intervals were distin guished corresponding to oxygen isotope stages 1 5 in the red sea and stages 1 3 in the gulf of aden the faunal assemblages demonstrate that in the red sea hydrological conditions changed significantly during the late quaternary especially at the last glacial maximum when water exchange at the bab el mandeb straits was at a minimum and at the pleistocene holocene boundary at the end of deglaciation water exchange renewal and pluvial conditions resulted in surface salinity decrease and stable stratification which was followed by a rise in planktonic fauna abundance and stagnation of bottom waters the more constant composition of rather cold water subtropical faunal assemblages in the gulf of aden during the last 40 000 50 000 yrs points to more stable hydrological parameters and to local upwelling or influx of arabian upwelling waters during the last stadial mean annual sea surface temperatures fell by at least 5 c compared to the present in the central part of the red sea and by 3 5 c in the western gulf of aden

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

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

a numerical modeling study of the upwelling source waters along the oregon coast during 2005 abstract regional ocean circulation along the oregon coast is studied numerically for forcing fields derived from year 2005 and climatological mean conditions the primary object is to study directly the lagrangian pathways by which fluid arrives in the oregon upwelling zone roughly half of the upwelling fluid is found to arrive in the regional domain from alongshelf source points primarily north but also south of the oregon upwelling zone while the other half ultimately arrives from points offshore and west of the zone for both the year 2005 and the climatological simulations different regimes of dominant alongshelf source waters are found with cape blanco being a dividing point for northern versus southern sources and with the water parcels coming primarily from depths below 100 m for the offshore sources most upwelling fluid originates from depths between 150 and 250 m during 2005 but from within the upper 150 m for the climatological simulations in both cases there are specific regions alon

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

on the dynamics of the southern senegal upwelling center observed variability from synoptic to superinertial scales upwelling off southern senegal and gambia takes place over a wide shelf with a large area where depths are shallower than 20 m this results in typical upwelling patterns that are distinct e g more persistent in time and aligned alongshore from those of other better known systems including oregon and peru where inner shelves are comparatively narrow synoptic to superinertial variability of this upwelling center is captured through a 4 week intensive field campaign representing the most comprehensive measurements of this region to date the influence of mesoscale activity extends across the shelf break and far over the shelf where it impacts the midshelf upwelling e g strength of the upwelling front and circulation possibly in concert with wind fluctuations internal tides and solitary waves of large amplitude are ubiquitous over the shelf the observations suggest that these and possibly other sources of mixing play a major role in the overall system dynamics through their impact upon the general shelf thermohaline structure in particular in the vicinity of the upwelling zone systematic alongshore variability in thermohaline properties highlights important limitations of the 2d idealization framework that is frequently used in coastal upwelling studies