nannoplankton successions in the northern red sea during the last glaciation 60 to 14 5 ka bp reactions to climate change abstract due to its restricted connection with the indian ocean the desert enclosed red sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation the understanding of its glacial history is however still limited a serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities here we present a continuous and well dated calcareous nannoplankton record from the northern red sea covering the interval from 60 14 5 ka bp our investigation shows that the composition of the calcareous nannoplankton community varied between 32 ka bp and 14 5 ka bp in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the north atlantic region heinrich events h3 h2 and h1 are dominated by emiliania huxleyi gephyrocapsa oceanica and especially gephyrocapsa ericsonii are abundant between h3 h2 and h2 h1 a less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to 32 ka bp suggesting that a strong atmospheric coupling between the northern red sea and the north atlantic realm was established in the late marine isotope stage 3 in contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial red sea we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition

paleoclimatic implications of late quaternary lacustrine sediments in western nubia sudan abstract owing to the hypercontinental location of western nubia secular fluctuations of climate have been filtered and wet phases can be considered as representative of conditions throughout the southeastern sahara the study area is crossed by the 20 mm isohyet between 9300 and about 4000 yr b p however there were widespread lake and swamp environments with freshwater molluscs ostracods and diatoms and a species rich savanna mammal fauna the center of the west nubian basin approx 18 n an area of about 20 000 km 2 was occupied by a semiaquatic landscape which was situated at the same latitude as paleolake chad from extensive lake carbonates up to about 4 m thick a long term rise of the groudwater table is inferred environments developed that now exist at about latitude 13 n radiocarbon dates from lake sediment sequences cluster between 30 000 and 21 000 yr b p indicating a pleistocene wet phase a gap in radiocarbon dates between 21 000 and 11 000 yr b p signals a phase of hyperaridity similar to the present hyperarid phase with eolian deflation and deposits of sand being the dominant forms of erosion and accumulation

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

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

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

direct observations of seasonal exchange through the bab el mandab strait the exchange flow between the red sea and the gulf of aden indian ocean through the bab el mandab strait was measured continuously for 10 months june 1995 march 1996 adcp and temperature salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the gulf of aden and the high salinity outflow layer from the red sea the timing structure and evolution of the summer season mid depth intrusion of cold low salinity water into the red sea from the gulf of aden is measured for the complete intrusion cycle of 1995 we unexpectedly find the deep outflow still strong in june 1995 with speeds of 0 6 m sec and transport of 0 4 sv 1 sv 106 m sec from july to mid september the deep outflow persists but is attenuated to speeds of 0 2 m sec and transport of 0 05 sv the dominant summer feature the cold low salinity intermediate layer intrusion persists for 3 months occupies 70 of the water column in the strait and carries approximately 1 7 1012 m of cold nutrient rich water into the red sea the winter regime begins in mid september is fully developed by early november and continues to the end of our first observation interval in march 1996 speeds in the lower layer are 0 8 1 0 m sec and 0 4 0 6 m sec in the upper layer at maximum exchange in mid february outflow transport reaches 0 7 sv ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along channel wind forcing and perhaps to coastally trapped waves

mediterranean moisture source for an early holocene humid period in the northern red sea paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost red sea were used to infer hydrological changes at the southern margin of the mediterranean climate zone during the holocene between approximately 9 25 and 7 25 thousand years ago about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff which thereafter decreased to modern values the northern red sea humid interval is best explained by enhancement and southward extension of rainfall from mediterranean sources possibly involving strengthened early holocene arctic oscillation patterns and a regional monsoon type circulation induced by increased land sea temperature contrasts we conclude that afro asian monsoonal rains did not cross the subtropical desert zone during the early to mid holocene

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

distribution of crenarchaeota tetraether membrane lipids in surface sediments from the red sea abstract the red sea represents an extreme marine environment with high salinity high temperature and low level of nutrients complicating the application of standard geochemical palaeotemperature proxies in order to investigate the applicability of the tex 86 tetraether index of gdgts with 86 carbons proxy for sea surface temperature sst in the red sea the distribution of glycerol dialkyl glycerol tetraether membrane lipids gdgts in sediments from the red sea and the gulf of aden were examined against expectations tex 86 values for the red sea do not show a simple linear relationship with sst and deviate from the global core top calibration in the northern red sea at temperatures between 25 and 28 c the values increase linearly with sst whereas in the southern red sea at temperatures above 28 c tex 86 decreases with increasing temperature factors like seasonality and depth of production salinity and nutrient availability as well as diagenetic overprint or influence of allochtonous terrestrial lipids cannot explain this pattern however the observed tex 86 relationship with sst could be explained by the presence of a hypothetical endemic crenarchaeota population in the red sea with a specific tex 86 vs sst relationship in the southern red sea a two component mixing model implies an exponential decrease in the endemic population towards the gulf of aden thus the application of the tex 86 as a palaeotemperature proxy in the red sea is likely only possible for the northern red sea area with the specific sst vs tex 86 relationship determined in this study and potentially for the whole red sea basin during glacials when water exchange with the indian ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the indian ocean our results suggest that distinct populations of crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition necessitating application of another calibration than the global core top calibration for tex 86 palaeothermometry

isotopic composition of conomurex fasciatus shells as an environmental proxy for the red sea abstract the marine gastropod conomurex fasciatus born 1778 is the main component of thousands of shell middens on the farasan islands in the southern red sea the middens date from 6500 to 4500 cal bp and cover the period of increased aridification over the region no general research on c fasciatus has been carried out before and basic information about the species is mostly speculative to test if c fasciatus shells can be used as a recorder of climate variability we collected living specimens from the farasan islands in saudi arabia over a 1 5 year period this area receives almost no precipitation and sea surface salinity is extremely high 38 39 psu and sea surface temperature sst ranges from 26 5 c to 34 9 c raman spectroscopy results on modern c fasciatus shell samples show these specimens to be aragonitic ground fragments from archaeological c fasciatus shells used for isotope analyses were also measured by raman spectroscopy and shown to be well preserved against diagenetic alterations leading to aragonite to calcite transformation measured shell edge 18o values range from 0 5 to 1 7 calculated modern shell edge temperatures from these 18o values correlate with modern sst measured on site with an error of 2 4 c two different growth rates occurred in the shells of c fasciatus the measurement of growth increments in the lip part of adult specimens indicates a tide related growth rate of 13 mm year sequential 18o data from juvenile parts of the shell indicates a faster growth rate of 90 mm year this growth rate and the correlation of 18o with measured temperatures allows the use of c fasciatus shell 18o as a palaeoclimate proxy

millennial scale variability in red sea circulation in response to holocene insolation forcing in order to assess how insolation driven climate change superimposed on sea level rise and millennial events influenced the red sea during the holocene we present new paleoceanographic records from two sediment cores to develop a comprehensive reconstruction of holocene circulation dynamics in the basin we show that the recovery of the planktonic foraminiferal fauna after the younger dryas was completed earlier in the northern than in the central red sea implying significant changes in the hydrological balance of the northern red sea region during the deglaciation in the early part of the holocene the environment of the red sea closely followed the development of the indian summer monsoon and was dominated by a circulation mode similar to the current summer circulation with low productivity throughout the central and northern red sea the climatic signal during the late holocene is dominated by a faunal transient event centered around 2 4 ka bp its timing corresponds to that of north atlantic bond event 2 and to a widespread regionally recorded dry period this faunal transient is characterized by a more productive foraminiferal fauna and can be explained by an intensification of the winter circulation mode and high evaporation the modern distribution pattern of planktonic foraminifera reflecting the prevailing circulation system was established after 1 7 ka bp

renewal of deep water in the red sea during 1982 1987 between october 1982 and may 1983 the deep water in the northern red sea was ventilated through slope convection the deep water became cooler fresher and more oxygenated dense bottom water formed in the gulf of suez during winter cooling sank down the continental slope thereby entraining near surface and intermediate depth waters from the application of a one dimensional plume model a vertical transport of 0 58 106 m3 s 1 over a period of 7 months was estimated long term time series of atmospheric heat fluxes show that such a major convection event can occur every 4 7 years the corresponding renewal time of the red sea deep water is thus of the order of 40 90 years in agreement with previous estimates

moment tensor solutions estimated using optimal filter theory global seismicity 2001 abstract moment tensor solutions estimated using optimal filter theory are listed for 290 moderate to large size earthquakes that occurred during 2001

moment tensor solutions estimated using optimal filter theory global seismicity 1991 moment tensor solutions estimated using optimal filter theory are listed for 108 moderate to large size earthquakes occurring during 1991

amplitude spectra moment tensor inversion of shallow earthquakes in spain summary the study of focal mechanisms for shallow earthquakes of low to moderate magnitude at regional distances requires a proper inversion technique one of the major problems is the correct separation of path effects from source effects the method used should take into account problems arising from errors in the definition of crustal structure and inclusion of the high frequency content of the waveforms in this study a method of frequency domain moment tensor inversion to determine deviatoric moment tensor solutions from body wave amplitude spectra is described the method has been tested with synthetic data to define instabilities that are due to mismodelling of several parameters the inversion technique is applied to broadband seismic data of shallow 10 km depth earthquakes in spain solutions are obtained for a range of depths and compared with solutions obtained with different methods such as first motion polarities and moment tensor inversion in the time domain a combined fit of amplitude spectra first motion polarities and double couple component is introduced as a method which resolves better the non uniqueness of solution the proposed method can be implemented in fast moment tensor inversion when a green functions database has been created in advance for the studied area

modes of subsurface intermediate and deep water renewal in the red sea a linear box model of the red sea is presented the model which inverts hydrographic and 3he data for the main features of the width integrated circulation is able to describe a large part of the seasonal and annual mean circulation by combining and reconciling major elements of current theories of the red sea circulation available flow measurements and tracer data the model provides a unified conceptual framework for the understanding of the circulation of the red sea the model forms deep water in the extreme north in two modes as first suggested by cember 1988 the convective mode renews the bottom water at an annual mean rate of 0 04 sv in the winter the isopycnal mode water renews the uppermost part of the deep water mass it flows to the south along the bottom of the pycnocline at an annual mean rate of 0 02 0 04 sv a new feature in the model s near surface circulation scheme is the ventilation of the thermocline in the winter at a mean rate of 0 04 sv also from the extreme north there is also a middepth return flow to the north at an annual mean rate of 0 07 sv this flow has been suggested but never rigorously quantified before

mid holocene land surface conditions in northern africa and the arabian peninsula a data set for the analysis of biogeophysical feedbacks in the climate system large changes in the extent of northern subtropical arid regions during the holocene are attributed to orbitally forced variations in monsoon strength and have been implicated in the regulation of atmospheric trace gas concentrations on millenial timescales models that omit biogeophysical feedback however are unable to account for the full magnitude of african monsoon amplification and extension during the early to middle holocene 9500 5000 years b p a data set describing land surface conditions 6000 years b p on a 1 1 grid across northern africa and the arabian peninsula has been prepared from published maps and other sources of palaeoenvironmental data with the primary aim of providing a realistic lower boundary condition for atmospheric general circulation model experiments similar to those performed in the palaeoclimate modelling intercomparison project the data set includes information on the percentage of each grid cell occupied by specific vegetation types steppe savanna xerophytic woods scrub tropical deciduous forest and tropical montane evergreen forest open water lakes and wetlands plus information on the flow direction of major drainage channels for use in large scale palaeohydrological modeling the data set is available in digital form by anonymous ftp

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

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

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

moment tensor solutions estimated using optimal filter theory global seismicity 1988 1989 moment tensor solutions estimated using optimal filter theory are listed for 201 moderate to large earthquakes occurring from 1988 to 1989

large woody debris structures for sand bed channels described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris this method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand in these types of environments buoyancy forces are typically more important factors in woody debris stability than fluid drag buoyant forces are counteracted by the weight of the structure earth anchors and sediment deposits design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37 km watershed large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention construction costs per unit channel length were 23 58 of costs for recent stone bank stabilization projects within the same region during the second year following construction 31 of the structures failed during high flows probably due to inadequate anchoring

physical and biological characteristics of the winter summer transition in the central red sea the central red sea crs lies between two distinct hydrographic and atmospheric regimes in the southern red sea seasonal monsoon reversal regulates the exchange of water between the red sea and the indian ocean in the northern red sea intermediate and occasionally deep water are formed during winter to sustain the basin s overturning circulation highly variable mesoscale eddies and the northward flowing eastern boundary current ebc determine the physical and biogeochemical characteristics of the crs ship based and glider observations in the crs between march and june 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the ebc flow less saline and relatively warmer water of indian ocean origin reaches the crs via the ebc initially an anticyclonic eddy with diameter of 140km penetrating to 150m depth with maximum velocities up to 30 35 cm s 1 prevails in the crs this anticyclonic eddy appears to block or at least redirect the northward flow of the ebc dissipation of the eddy permits the near coastal northward flow of the ebc and gives place to a smaller cyclonic eddy with a diameter of about 50km penetrating to 200m depth by the end of may as the northerly winds become stronger and persistent throughout the basin characteristic of the summer southwest monsoon wind regime the ebc and its associated lower salinity water became less evident replaced by the saltier surface water that characterizes the onset of the summer stratification in the crs

red sea circulation during marine isotope stage 5e we have employed a regional massachusetts institute of technology oceanic general circulation model of the red sea to investigate its circulation during marine isotope stage mis 5e the peak of the last interglacial approximately 125 ka before present compared to present day conditions mis 5e was characterized by higher northern hemisphere summer insolation accompanied by increases in air temperature of more than 2 c and global sea level approximately 8 m higher than today as a consequence of the increased seasonality intensified monsoonal conditions with increased winds rainfall and humidity in the red sea region are evident in speleothem records and supported by model simulations to assess the dominant factors responsible for the observed changes we conducted several sensitivity experiments in which the mis 5 boundary conditions or forcing parameters were used individually overall our model simulation for the last interglacial maximum reconstructs a red sea that is colder less ventilated and probably more oligotrophic than at present day the largest alteration in red sea circulation and properties was found for the simulation of the northward displacement and intensification of the african tropical rain belt during mis 5e leading to a notable increase in the fresh water flux into the red sea such an increase significantly reduced the red sea salinity and exchange volume of the red sea with the gulf of aden the red sea reacted to the mis 5e insolation forcing by the expected increase in seasonal sea surface temperature amplitude and overall cooling caused by lower temperatures during deep water formation in winter

sensitivity of red sea circulation to monsoonal variability during the holocene an integrated data and modeling study received 20 october 2009 revised 6 march 2010 accepted 30 june 2010 published 4 november 2010 1 we used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the red sea in response to reduced sea level and modified atmospheric conditions during the holocene with holocene sea level close to the modern level the red sea was sensitive to changes in atmospheric conditions and it only shows a relatively mild response to sea level change changes in the monsoon system influence the exchange flow through the strait of bab el mandab the meridional overturning circulation of the red sea and its hydrography forced by humid conditions the modeled red sea temperature increased by 1 5 c while when arid conditions were imposed the temperature decreased by 2 5 c similar heating and cooling events during the early and late holocene are seen in a sea surface temperature record from the northern red sea derived from the temperature sensitive tex86 molecular biomarker which suggests that humid conditions prevailed during the early holocene and more arid conditions prevailed during the late holocene the gradual decline in red sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength this monsoon trend and the resulting changes in the red sea circulation are supported by the distribution of crenarchaea fossil lipids in red sea sediments from this period monsoon driven changes in the exchange flow through the strait of bab el mandab affected the crenarchaea population structure and therefore their molecular fossil distribution in the sediments of the red sea potentially provides an index for the summer monsoon strength during the holocene

possible reverse trend in asian summer monsoon strength during the late holocene holocene climate change is characterized as generally cooling in high latitudes and drying in tropical and asian summer monsoonal regions following the gradual decrease in northern hemisphere summer insolation over the last 12 000 years however some recent high resolution well dated monsoon reconstructions seem to suggest an abnormal increase in asian summer monsoon strength during the late holocene against the generally weakening holocene trend here we synthesize marine and terrestrial moisture records from asian monsoonal regions that span most of the holocene period late holocene strengthening of asian summer monsoon identified from a wealth of the synthesized monsoon records appears to be a robust feature which warrants further consideration of its possible causes the possible reverse trend in asian summer monsoon strength preceding insolation minima seems to have also occurred during previous interglacial periods based on speleothem records we further show a similar late holocene reverse trend in tropical hydrological changes suggesting that the asian summer monsoon behavior might be internally linked to the movement of the average position of the itcz and enso variability during the late holocene on the other hand we suggest that even though several holocene temperature records indeed show a reverse trend in the late holocene the overall evidence for a link between the late holocene reverse trend in asian summer monsoon and global temperature changes is insufficient the reverse trend in asian summer monsoon during the late holocene is difficult to be explained with the traditional boreal insolation driven view we suggest that this phenomenon might be linked to austral summer insolation changes and or greenhouse gas increase however we caution that additional paleoclimate reconstructions and model simulations are needed to systematically study the spatial pattern and understand underlying mechanism of the late holocene reverse trend in asian summer monsoon strength

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

climatic changes in the northern red sea during the last 22 000 years as recorded by calcareous nannofossils 1 we present a high resolution record of calcareous nannofossils from the northern red sea for the last 22 kyr extreme conditions with enhanced salinities during the last glacial maximum are characterized by high values of gephyrocapsa ericsonii the dominance of emiliania huxleyi in heinrich event 1 indicates a climatic cooling favoring the bloom of opportunistic species the calcareous nannofossils record a two step onset of the postglacial humid climate punctuated by the younger dryas both steps show an early oligotrophic phase dominated by florisphaera profunda and gladiolithus flabellatus and a subsequent fertile phase characterized by e huxleyi the younger dryas is described by high values of gephyrocapsa oceanica indicating an increased mixing of the water column in the late holocene repetitive increases in abundance of f profunda and g flabellatus reflect restricted oligotrophic conditions caused by the high aridity following the holocene humid period

the 1992 cape mendocino earthquake broadband determination of source parameters the april 25 1992 cape mendocino earthquake ms 7 1 has renewed speculation about the nature of subduction along the cascadia subduction zone and the associated seismic hazard this event may represent the first large m 6 thrust event along the entire cascadia subduction zone in historic times last 200 years we analyze long period surface waves and broadband body waves in order to estimate the mainshock source parameters we also examine broadband body waves from the nearby 1991 honeydew earthquake m 6 in order to assess the contributions of both rupture complexity and unmodeled source and receiver structure in the cape mendocino waveforms from both body and surface wave inversions as well as forward modeling of body waves we estimate a best double couple mechanism for the cape mendocino earthquake strike 330 10 dip 12 2 rake 75 15 seismic moment 1 93 1019 n m and mw 6 8 this mechanism contains a significant component of slip in the estimated direction of gorda north america plate convergence although this earthquake had suitable geometry for relieving strain accumulated by gorda north america plate convergence we cannot resolve whether it occurred on the interplate megathrust or on a fault within the overriding accretionary prism we find evidence for southwest offshore rupture toward an azimuth of 240 in addition we find evidence for early aftershocks in both the teleseismically recorded body waves and in locally recorded strong motions we model one aftershock delayed 13 s from the mainshock with a mechanism that is different from the mainshock mechanism but is consistent with the north south trending horizontal compression found offshore within the gorda plate we postulate that this aftershock and two additional large strike slip aftershocks that ruptured the gorda plate within 24 hours of the mainshock were caused by the transfer of stress accumulated across the cascadia subduction zone and accretionary prism far offshore to the gorda plate where it reduced the normal stress across nw se oriented faults triggering failure the complexity of fault interactions near the mendocino triple junction needs to be understood before potential seismic hazards of the southern cascadia subduction zone can be quantified

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

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

moment tensor solutions estimated using optimal filter theory global seismicity 1990 moment tensor solutions estimated using optimal filter theory are listed for 114 moderate to large size earthquakes occurring during 1990

observations of the summer red sea circulation 1 aiming at exploring and understanding the summer circulation in the red sea a cruise was conducted in the basin during the summer of 2001 involving hydrographic meteorological and direct current observations the most prominent feature characteristic of the summer circulation and exchange with the indian ocean is a temperature salinity and oxygen minimum located around a depth of 75 m at the southern end of the basin associated with gulf of aden intermediate water inflowing from the gulf of aden during the summer season as an intruding subsurface layer stirring and mixing with ambient waters lead to marked increases in temperature from 16 5 to almost 33 c and salinity from 35 7 to more than 38 psu in this layer by the time it reaches midbasin the observed circulation presents a very vigorous pattern with strong variability and intense features that extend the width of the basin a permanent cyclone detected in the northern red sea verifies previous observations and modeling studies while in the central sector of the basin a series of very strong anticyclones were observed with maximum velocities exceeding 1 m s the three layer flow pattern representative of the summer exchange between the red sea and the gulf of aden is observed in the strait of bab el mandeb in the southern part of the basin the layer flow is characterized by strong banking of the inflows and outflows against the coasts both surface and intermediate water masses involved in the summer red sea circulation present prominent spatial variability in their characteristics indicating that the eddy field and mixing processes play an important role in the summer red sea circulation

glacio eustatic sea level control on red sea salinity previous studies of the red sea demonstrated that glacial surface and bottom water salinities in the basin were significantly higher than at present the very low abundance of planktonic foraminifera the so called aplanktonic zone during the last glacial indicates that surface water conditions approached or exceeded the tolerance limits of this plankton group1 2 glacial sediments are also characterized by high concentrations of magnesian calcite3 4 dolomite3 inorganically precipitated aragonite4 5 and benthic foraminifera typical of hypersaline environments3 6 additional evidence from oxygen isotope records of planktonic2 7 and benthic foraminifera8 9 as well as pteropods2 demonstrate that glacial interglacial contrasts in the red sea have an amplitude much larger than typically observed in open ocean records here we use both oxygen isotope data and a fractional overmixing model to estimate the impact of the most recent 18 000 yr bp pleistocene glacio eustatic sea level lowering on red sea salinity we estimate that during the last glacial maximum surface salinities in the central red sea were more than 10 0 higher than at present deep water salinities were also higher during the last glaciation and remained unusually high through deglaciation the combination of very high bottom salinities and the onset of pluvial conditions during deglaciation in the red sea region prevented ventilation of red sea bottom waters and resulted in the accumulation of organic rich sediments

holocene strengthening of the oxygen minimum zone in the northwestern arabian sea linked to changes in intermediate water circulation or indian monsoon intensity abstract a high resolution 14 000 year old record of benthic foraminifera from odp hole 723a was produced to understand changing intensity of the nw arabian sea oxygen minimum zone omz and its links with intermediate water circulation and indian monsoon intensity during the latest pleistocene the omz was very weak marked by the abundance of oxic species from early to mid holocene period up to 6500 years bp intense sw monsoon related high surface productivity led to the development of an omz in the arabian sea however presence of oxic and suboxic species indicate that omz intensification was minimized by cyclic incursions of oxygen rich intermediate waters from the south the middle holocene was a transitional period to intense omz conditions the intensification of the omz could be due to replacement of oxygen rich southern source sub antarctic mode and antarctic intermediate waters samw aaiw with oxygen poor red sea water rsw from the north during the middle holocene as the intensity of the summer monsoon weakened during the late holocene 4200 years bp onwards the arabian sea omz intensified suggesting total cut off from the oxygenated samw aaiw spectral analysis of information function h benthic foraminifer bolivina spp and oxic species of benthic foraminifera indicate that the intensity of the omz and deep water conditions respond closely to solar cycles

recent environmental change and prehistoric human activity in egypt and northern sudan abstract this paper reviews the various late quaternary records that are available from western egypt and northern sudan which includes more than 500 published radiocarbon dates and various sedimentary archives from local landscape components including palaeolakes soils drainages wadis and archaeological sites this palaeoenvironmental compilation frames the spatial and temporal context of local cultural activities when the region was most hospitable 9000 6000 bp at this time monsoonal weather influenced the portion of the african continental interior creating enough convective rainfall for occasional surface water storage in this part of the modern sahara rapid hydroclimatic changes play a key role in geomorphic evolution and resource availability as watering holes formed and dried up in the early to middle holocene neolithic people developed various subsistence strategies including opportunistic hunting of small animals e g gazelle and hare and food related e g wild sorghum millet and legumes activities gathering plant cultivation and livestock rearing during its wettest phases during the monsoonal maximum the area was drought prone sustaining a meager steppe shrub desert flora further desertification and aeolian deflation during the middle and late holocene fostered technological innovation migration and settlement as well as the further development of agrarian communities and complex culture

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

an entropy based method for determining the flow depth distribution in natural channels a methodology for determining the bathymetry of river cross sections during floods by the sampling of surface flow velocity and existing low flow hydraulic data is developed similar to chiu 1988 who proposed an entropy based velocity distribution the flow depth distribution in a cross section of a natural channel is derived by entropy maximization the depth distribution depends on one parameter whose estimate is straightforward and on the maximum flow depth applying to a velocity data set of five river gage sites the method modeled the flow area observed during flow measurements and accurately assessed the corresponding discharge by coupling the flow depth distribution and the entropic relation between mean velocity and maximum velocity the methodology unfolds a new perspective for flow monitoring by remote sensing considering that the two main quantities on which the methodology is based i e surface flow velocity and flow depth might be potentially sensed by new sensors operating aboard an aircraft or satellite

palaeoenvironment palaeoclimate and sea level changes in the shuaiba lagoon during the late holocene last 3 6 ka eastern red sea coast saudi arabia multi proxy investigations of sediment lithology geochemistry benthic foraminifera and 18o and 13c of elphidium striatopunctatum were carried out on a sediment core shua3 2 2 m long spanning

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

moment tensor solutions estimated using optimal filter theory global seismicity 1992 abstract moment tensor solutions estimated using optimal filter theory are listed for 133 moderate to large earthquakes occurring during 1992

on the crossover of boundary currents in an idealized model of the red sea the west to east crossover ofboundarycurrents has been seen in mean circulationschemes fromseveral past models of the red sea this study investigates the mechanisms that produce and control the crossover in an idealized eddy resolving numerical model of the red sea the authors also review the observational evidence and derive an analytical estimate for the crossover latitude the surface buoyancy loss increases northward in the idealized model and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonicgyreinthenorth in themidbasin thenorthwardsurfaceflow crossesfromthewestern boundarytothe eastern boundary numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0 b and the meridional gradient of surface buoyancy forcing in the analytical estimate which is based on quasigeostrophic b plane dynamics the crossover is predicted to lie at the latitude where the net potential vorticity advection including an eddy component is zero various terms in the potential vorticity budget can be estimated using a buoyancy budget a thermal wind balance and a parameterization of baroclinic instability

moment tensor solutions estimated using optimal filter theory global seismicity 1993 abstract moment tensor solutions estimated using optimal filter theory are listed for 130 moderate to large size earthquakes occurring during 1993

estimation of bathymetry and discharge in natural river cross sections by using an entropy approach summary this paper presents a new method for reconstructing the bathymetric profile of a cross section based on the application of the principle of maximum entropy and proposes a procedure for its parameterization the method can be used to characterize the bathymetry of a cross section based on a reduced amount of data exclusively of a geometric type namely the elevation of the lowest point of the channel cross section the observed georeferenced flow widths and the corresponding water levels measured during the events the procedure was parameterized and applied on two actual river cross sections characterized by different shapes and sizes in both cases the procedure enabled us to describe the real bathymetry of the cross sections with reasonable precision and to obtain an accurate estimate of the flow areas with reference to the same two cases we show finally that combining the bathymetry reconstruction method proposed here and an entropy based approach for estimating the cross sectional mean velocity previously proposed farina et al 2014 enables a good estimate of discharge

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

climate of the last 53 000 years in the eastern mediterranean based on soil sequence stratigraphy in the coastal plain of israel abstract in this paper we present a detailed record of proxy climatic events in the coastal belt of the eastern mediterranean during the past 53 000 years a sequence of alternating palaeosols aeolianites and dune sands which have been dated by luminescence and by 14c was studied by the magnetic susceptibility particle size distribution clay mineralogy and soil micromorphology thirteen proxy climatic events demonstrating fluctuations of relatively dry and wet episodes were recognized the soil parent materials as well as the different soil types were rated in a semi quantitative dry to wet scale the palaeosol sequence is compared to a proxy climatic record of oxygen and carbon isotopes in speleothems from a karstic cave in central israel and to a record of lake levels of lake lisan and its successor which is known as the dead sea a genuine red mediterranean soil rhodoxeralfs localy designated as hamra soil developed during the last glacial stage from 40 to 12 5 thousand calendar years bp climatic fluctuations that were recorded in speleothems and in changing lake levels were not preserved in this soil during the cold and dry younger dryas ca 12 5 to 11 5 calendar ka bp a thick bed of loess material deriving from atmospheric dust of the sahara and arabian deserts covered the entire coastal belt during this phase lake lisan was desiccated and turned into the modern smaller dead sea during the early holocene some 10 7 5 calendar ka bp a second red hamra soil developed in warm and wet environments associated with a relatively high stand of the dead sea level a depletion of 18o and a significant enrichment of 13c in the speleothems were recorded during this episode this event was in phase with the widespread distribution of freshwater lakes in the sahara desert and the accumulation of the s1 sapropel in the eastern mediterranean several small scale dry and somewhat wet fluctuations of the late holocene from 7 5 calendar ka bp to the present were recorded in the coastal belt changes in human history as reflected in archaeological records are associated with proxy climatic fluctuations periods of desertification and deterioration are coupled with dry episodes periods of relative human prosperity are coupled with wetter episodes

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

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

scenarios regarding the lead of equatorial sea surface temperature over global ice volume 1 recent proxy evidences indicate that the equatorial sea surface temperature sst may have led global ice volume by 3 kyr during the late pleistocene glacial cycles given the short timescales of equatorial dynamics equatorial climate variability is characterized by a timescale of no more than a few years it would seem somewhat surprising therefore that the equatorial ocean and atmosphere can determine and lead the long timescale 100 kyr glacial cycles two scenarios are presented according to which such a lead may be observed even when the equatorial ocean and atmosphere are not necessarily responsible for leading the glacial cycles they may still act as a strong amplifier first it is shown that if the plankton based proxy reflects the warm season temperature rather than an annual temperature it may lead the global temperature although the dynamics of the glacial cycles may still be dominated by the northern hemisphere ice sheets it is noted that a present day seasonal bias of the equatorial proxy record is still inconclusive and the possibility of a proxy bias only during glacial times is considered as well a second scenario is suggested in which global sea level rises before equatorial sst yet the later evolution of factors such as the atmospheric co2 and equatorial sst is faster and takes the lead over global ice volume if the initial rise of sea level is masked by a sufficiently large proxy noise because of instrumental and natural noise it may not be seen and the lead may be attributed to the equatorial sst and co2

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

geomorphological changes in the coastal area of farasan al kabir island saudi arabia since mid holocene based on a multi proxy approach abstract the geomorphological evolution of the southeastern coastal area of farasan al kabir island saudi arabia is revealed by the mapping of modern landforms and a multi proxy and high spatial resolution study including grain size particulate organic carbon mineralogy element geochemistry benthic foraminifera analysis and radiocarbon dating of a 3 3 m long sediment core the modern geomorphological features comprise a variety of arid landforms such as plateau cliffs and pediments of pleistocene coral limestones playa depressions located on plateau surfaces alluvial fans butte and sandy beaches the mid holocene evolution of the borehole area is resulted from the detailed analysis of five sedimentary units detected along the core matar 1 and includes three distinct stages a from 5253 223 y cal bp to 3138 223 y cal bp carbonate coarse grained material consisting of coral fragments molluscs calcareous algae and benthic foraminifera are deposited on a shallow marine fringing reefal platform which becomes progressively a nearshore backreef around 3675 215 y cal bp and later around 3138 223 y cal bp a reef ramp b since 3040 220 y cal bp the borehole area obtains the characteristics of a high energy beach that receives increasing inputs of terrigenous material c subsequently a supratidal backshore setting is established influenced mostly by terrestrial processes and occasionally by marine processes as it is indicated by the decreasing and sometimes sporadic presence of benthic foraminifera and recently a sedimentary veneer consisting of terrigenous carbonate and evaporite material is formed by terrestrial mainly wadi and aeolian processes

importance of the gulf of aqaba for the formation of bottom water in the red sea received 30 march 2000 revised 8 may 2001 accepted 13 september 2001 published 16 august 2002 1 conductivity temperature depth tracer and direct current measurements collected in the northern red sea in february and march 1999 are used to study the formation of deep and bottom water in that region historical data showed that open ocean convection in the red sea can contribute to the renewal of intermediate or deep water but cannot ventilate the bottom water the observations in 1999 showed no evidence for open ocean convection in the red sea during the winter 1998 1999 the overflow water from the gulf of aqaba was found to be the densest water mass in the northern red sea an anomaly of the chlorofluorocarbon component cfc 12 observed in the gulf of aqaba and at the bottom of the red sea suggests a strong contribution of this water mass to the renewal of bottom water in the red sea the cfc data obtained during this cruise are the first available for this region because of the new signal it is possible for the first time to subdivide the deep water column into deep and bottom water in the northern red sea the available data set also shows that the outflow water from the gulf of suez is not dense enough to reach down to the bottom of the red sea but was found about 250 m above the bottom index terms 4875 oceanography biological and chemical trace elements 4283 oceanography general water masses 4243 oceanography general marginal and semienclosed seas 4271 oceanography general physical and chemical properties of seawater keywords gulf of aqaba red sea formation of bottom water tracer oceanography cfc overflow

circulation and exchange in choked marginal seas a theory for the exchange between a rotating buoyancy forced marginal sea and an ocean is developed and tested numerically cooling over the marginal sea leads to sinking and sets up a two layer exchange flow with a warm surface layer entering from the ocean and a cool layer exiting at depth the connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled the incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies consistent with the overall heat and volume balances for the marginal sea there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait included in this family is a limiting maximal exchange solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section the state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or in some cases the ocean depending on the configuration of the exchange long wave information may be blocked from entering the strait from the marginal sea from the open ocean or both the scenario that holds determines what is predicted and what needs to be input numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill the comparison is reasonable in most cases though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values the analytical model is an alternative to the price and yang and siddall et al models of a marginal sea outflow

response characteristics of a buoyancy driven sea abstract the authors consider the flow in a semienclosed sea or basin subjected to a destabilizing surface buoyancy flux and separated from a large adjoining reservoir by a sill a series of numerical experiments were conducted to quantify the energetics of the flow within the basin that is the amount of kinetic and potential energy stored within the basin and the rate at which these quantities are transported to and from the reservoir via the exchange flow over the sill the numerical experiments were formulated at laboratory scales and conducted using a boundary fitting clustered grid to resolve the entrainment and mixing processes within the flow and to facilitate quantitative comparison with previous laboratory experiments volume and boundary integrated energetics were computed for both steady and time varying flows in the steady state limit the rate of energy flux through the surface is balanced by dissipation within the basin and advection of potential energy over the sill and into the reser

source depth dependence of micro tsunamis recorded with ocean bottom pressure gauges the january 28 2000 mw 6 8 earthquake off nemuro peninsula japan abstract micro tsunami waves with a maximum amplitude of 4 6 mm were detected with the ocean bottom pressure gauges on a cabled deep seafloor observatory south of hokkaido japan following the january 28 2000 earthquake m w 6 8 in the southern kuril subduction zone we model the observed micro tsunami and estimate the focal depth and other source parameters such as fault length and amount of slip using grid searching with the least squares method the source depth and stress drop for the january 2000 earthquake are estimated to be 50 km and 7 mpa respectively with possible ranges of 45 55 km and 4 13 mpa focal depth of typical inter plate earthquakes in this region ranges from 10 to 20 km and stress drop of inter plate earthquakes generally is around 3 mpa the source depth and stress drop estimates suggest that the earthquake was an intra slab event in the subducting pacific plate rather than an inter plate event in addition for a prescribed fault width of 30 km the fault length is estimated to be 15 km with possible ranges of 10 20 km which is the same as the previously determined aftershock distribution the corresponding estimate for seismic moment is 2 7 10 19 nm with possible ranges of 2 3 10 19 3 2 10 19 nm standard tide gauges along the nearby coast did not record any tsunami signal high precision ocean bottom pressure measurements offshore thus make it possible to determine fault parameters of moderate sized earthquakes in subduction zones using open ocean tsunami waveforms

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

relation between mean and maximum velocities in a natural river the cross sectional mean velocity is an important variable in open channel hydraulics whereas the maximum velocity in a channel cross section is mentioned very little however the maximum velocity in a channel cross section might be as important as the cross sectional mean velocity this is because the measurable maximum velocity can be considered as a signal from which one can know the range of the velocity in a channel cross section this study explored the relation between the cross sectional mean and maximum velocities in a natural river by using velocity data collected from the mississippi river the relation of the maximum velocity to the cross sectional mean velocity on different straight reaches in the mississippi river is perfectly linear the relation of the maximum velocity to the cross sectional mean velocity on different river bends is still linear and changes with the rc b value slightly the conclusions are preliminary because of the limited amount of data

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

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

a pronounced dry event recorded around 4 2 ka in brine sediments from the northern red sea partly laminated sediments were sampled from the brine filled anoxic shaban deep basin in the northern red sea at about 4200 cal yr bp more than two millennia of anoxic sedimentation is replaced by a sub oxic facies strongly suggesting the episodic absence of the brine at the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase within less than 100 yr pointing to a strong positive salinity anomaly at the sea surface this major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small shaban deep basin the timing and strength of the reconstructed environmental changes around 4200 cal yr bp suggest that this event is the regional expression of a major drought event which is widely observed in the neighboring regions and which strongly affected middle east agricultural civilizations

influence of northern hemisphere climate and global sea level rise on the restricted red sea marine environment during termination i 1 we present high resolution paleoceanographic records of surface and deep water conditions within the northern red sea covering the last glacial maximum and termination i using alkenone paleothermometry stable oxygen isotopes and sediment compositional data paleoceanographic records in the restricted desert surrounded northern red sea are strongly affected by the stepwise sea level rise and appear to record and amplify well known millennial scale climate events from the north atlantic realm during the last glacial maximum lgm sea surface temperatures were about 4 c cooler than the late holocene pronounced coolings associated with heinrich event 1 2 c below the lgm level and the younger dryas imply strong atmospheric teleconnections to the north atlantic owing to the restricted exchange with the indian ocean red sea salinity is particularly sensitive to changes in global sea level paleosalinities exceeded 50 psu during the lgm a pronounced freshening of the surface waters is associated with the meltwater peaks mwp1a and mwp1b owing to an increased surface near inflow of normal saline water from the indian ocean vertical 18o gradients are also increased during these phases indicating stronger surface water stratification the combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers which were deposited under almost anoxic condition in a stagnant water body

source mechanism of the 1992 roermond earthquake from surface wave inversion of regional data summary the dutch german border region near the city of roermond the netherlands was hit by a rather strong crustal earthquake at 1 20 ut 1992 april 13 the epicentre is located within the roer valley graben a region currently undergoing extension the centroidal source mechanism of this event has been retrieved by moment tensor inversion of broad band long period surface waves recorded at regional distances 100 1500 km the double couple contribution of the moment tensor corresponds to almost pure normal faulting rake 262 on a steeply south westward dipping fault dip 58 with a nw se trend strike 138 this result is consistent with local tectonics but violates some first motion p wave polarity data the deduced seismic moment is 9 2 1016 n m corresponding to a moment magnitude of 5 3 a centroidal depth of 18 km fits slightly better than 13 km however the differences are small and other methods are necessary to constrain the depth further it is now possible to access a number of broad band three component seismic stations in europe via phone line e g german regional seismic network and the orfeus data centre i e global digital seismic network this allows retrieval of waveform data immediately after an earthquake in this paper we present a potentially fast and reliable procedure for extracting the moment tensor from low frequency surface waves using the roermond earthquake as an example detailed knowledge of the velocity depth structure along the travel paths seems unnecessary with our procedure further testing is required on all future moderate to strong earthquakes in europe using rapidly accessible stations to investigate the procedure s usefulness and possible limitations as a tool for rapid moment tensor estimation

hydraulic control of three layer exchange flows application to the bab al mandab two layer hydraulic models have proven to be extremely useful in understanding a number of exchange flows through straits for example the strait of gibraltar there are though some strait flows that cannot be represented by a two layer model a very striking example is the bab al mandab in the exchange between the red sea and the gulf of aden three distinct water masses are observed in the strait during summer the wintertime flow is though very different with only two layers observed in the strait in this paper a three layer model of hydraulically controlled exchange flows is described the model can represent exchange flows that are controlled with respect to either the first or second or both internal modes a number of different examples are discussed the model is able to explain the qualitative features of the seasonal variation of the flow in the bab al mandab in particular the reversal of the direction of flow of the surface layer and the intrusion into the red sea of cold intermediate water from the gulf of aden during the summer months can be explained by upwelling in the gulf of aden forced by the southwest monsoon

millennial scale sea surface temperature changes in the eastern mediterranean nile river delta region over the last 27 000 years 1 in this study we utilize two organic geochemical proxies the u37k index and tex86 to examine past sea surface temperatures sst from a site located near the nile river delta in the eastern mediterranean em sea the u37k and tex86 records generally are in agreement and indicate sst ranges of 14 c 26 c and 14 c 28 c respectively during the last 27 cal ka during the holocene tex86 based sst estimates are usually higher than u37k based sst estimates which is likely due to seasonal differences between the timing of the haptophyte and crenarchaeota blooms in the em and is related to the onset of the modern flow regime of the nile river both records show that sst varied on centennial to millennial timescales in response to global climate events i e cooling during the last glacial maximum lgm heinrich event 1 h1 and the younger dryas yd and warming during the bolling allerod and in the early holocene during deposition of sapropel s1 the h1 cooling was particularly severe and is marked by a drop in sst of 4 5 c in comparison to pre h1 sst with temperatures 1 c cooler than during the lgm in contrast to high latitude and western mediterranean records which indicate both an abrupt onset and termination of the yd event the transition from the yd to the holocene was much more gradual in the em

dominant northern hemisphere climate control over millennial scale glacial sea level variability abstract based on a radiocarbon and paleomagnetically dated sediment record from the northern red sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea level dependent water exchange with the indian ocean we provide a new global sea level reconstruction spanning the last glacial period the sea level record has been extracted from the temperature corrected benthic stable oxygen isotopes using coral based sea level data as constraints for the sea level oxygen isotope relationship although the general features of this millennial scale sea level records have strong similarities to the rather symmetric and gradual southern hemisphere climate patterns we observe in constrast to previous findings pronounced sea level rises of up to 25 m to generally correspond with northern hemisphere warmings as recorded in greenland ice core interstadial intervals whereas sea level lowstands mostly occur during cold phases corroborated by climber 2 model results the close connection of millennial scale sea level changes to northern hemisphere temperature variations indicates a primary climatic control on the mass balance of the major northern hemisphere ice sheets and does not require a considerable antarctic contribution

two layer hydraulics a functional approach a new approach for investigating two layer hydraulic exchange flows in channels is introduced the approach is based on the functional formalism of gill 1977 and applied to the flow through a contraction in width and to flow over a simple sill the sill geometry is an extension of that looked at by earlier workers in particular farmer armi 1986 who used a froude number plane approach in the present paper a simple relationship between the composite froude number and the hydraulic functional is derived though the functional approach may also be applied to channels where a froude number is not readily defined the ability to trace roots of this functional from one reservoir to the other is a prerequisite for the flow to be realizable two hydraulic transitions are required for the flow to be fully controlled and the exchange flow rate to be maximal if only one hydraulic transition is present the flow is governed by the conditions in one of the reservoirs and the exchange flow rate is found to be submaximal the flow along a channel is found to be very sensitive to small departures from symmetry about a horizontal plane the response of the interface to the introduction of a net barotropic flow is found to be a discontinuous function of the strength of the forcing for some range of sill heights

convectively driven exchange flow in a stratified sill enclosed basin laboratory experiments are used to investigate the processes governing steady convectively driven circulation in a basin that communicates with a large external reservoir over a shallow sill the motion is maintained by a steady loss of buoyancy distributed over the surface of the basin turbulent convection associated with the forcing produces a horizontal buoyancy gradient across the sill and the resulting mean flow consists of a layer directed into the basin near the surface with a dense counter flow below to first order the magnitude of the exchange flow over the sill is determined by the horizontal momentum balance within the basin measurements of the mean and turbulent flow fields are used to show that inertia buoyancy and friction may each contribute significantly to the balance the interior flow produces a horizontal pressure gradient near the surface which must also contribute to the momentum balance the density of the lower layer at the sill reflects the cumulative effect of interior processes such as mixing and these in turn influence the hydraulically controlled exchange flow over the sill the basin dynamics are therefore coupled in a nonlinear fashion with the submaximal sill exchange this coupling is investigated first by showing how interior processes are affected by changes in the magnitude of the forcing and then by observing the associated variation of the flow state at the sill the flow state is defined in terms of its relative proximity to the theoretical maximal exchange limit results show that the exchange flows are submaximal with flow rate approximately 85 of the maximal limit this state appears to change very little in response to increasing forcing for a stratified basin which exhibits a deep stagnant layer under the convectively driven near surface exchange flow the possibility of basin ventilation or erosion of deep fluid exists in the long term this process and its dependence on external parameters is also explored