response of diatom and silicoflagellate assemblages in the central gulf of california to regional climate change during the past 55 kyrs abstract high resolution studies of diatoms and silicoflagellates of the past 55 kyrs in cores md02 2517 2515 from the central gulf of california goc reveal profound changes in goc surface waters roperia tesselata a diatom proxy for late winter early spring upwelling and dictyocha stapedia a subtropical silicoflagellate indicative of goc sea surface temperatures ssts 24 c are common during the holocene but rare during marine isotope stage mis 2 and most of mis 3 a relationship that likely reflects a more northerly position of the north pacific high nph during the holocene in contrast during most of mis 2 27 15 ka the persistent presence of distephanus speculum a silicoflagellate associated with ssts during mis 3 55 27 ka increased dominance of azpeitia nodulifera diatom implies that stratified tropical waters were present year round whereas silicoflagellate assemblages suggest that stratified tropical conditions alternated with more productive upwelling conditions on millennial timescales reduced biosiliceous productivity during heinrich events likely reflected a reduction in both surface water nutrient levels and in the strength of northwest winds due to a weakened and more southerly nph conversely enhanced biosiliceous productivity during mis 3 interstadials was probably linked to heightened nutrient levels and a strengthened nph abrupt relative abundance increases of the silicoflagellate dictyocha aculeata approximate the termination of mis3 heinrich events and may signal times when nutrient rich deep waters associated with the resumption of enhanced atlantic meridional overturning circulation penetrated into the central gulf

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

silica burial enhanced by iron limitation in oceanic upwelling margins marine sediments deposited beneath the eastern pacific upwelling margin are a substantial sink for silica the geochemistry of these sediments suggests that periods of intense upwelling result in iron limitation which enhances the export of silica from the surface to the deep ocean and sediments

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

climate forcing primary production and the distribution of holocene biogenic sediments in the gulf of california abstract the gulf of california is a marginal seaway under the influence of a monsoon climate that produces cool dry winters and warm humid summers winds tidal mixing and coastal trapped waves forced by climate and the pacific ocean control nutrient advection and primary productivity pp strong northwest winds from the subtropical east pacific high pressure system begin in november and last until april and drive coastal upwelling along the mainland margin especially in the central and southern gulf in the northern gulf particularly around the midrift island tidal mixing and turbulence occurs year round advecting nutrients into the mixed layer and high productivity during summer and early fall months winds are variable of less intensity and mainly blow cross basin except in the most northern gulf summer pp is generally low in the central and southern gulf except along the mainland where coastal trapped waves associated with tropical surges and hurricanes generate mixing over the continental shelf mesoscale eddies or gyres often associated with jets and filaments extend to depths of 1000 m and transport nutrient enriched upwelled waters and plankton detritus across the gulf the largest and most persistent gyres rotate in an anti cyclonic direction east to west and are a principal source of the plankton export to the peninsula margin two major biogenic sediment patterns are present in core top sediments hemipelagic biosiliceous rich muds are accumulating beneath upwelling areas of high productivity in the central gulf and along the mainland margin calcium carbonate and organic carbon rich oc sediments are concentrated along the peninsula margin generally beneath lower productivity waters with the highest oc content in areas with the lowest productivity the high uniform biosiliceous content in guaymas basin extending southward into carmen basin reflects the redistribution by mesoscale gyres of phytoplankon debris produced in mainland coastal upwelling and tidally forced areas around the midrift islands holocene biogenic patterns are similar to the present day with the major difference in rates of accumulation phytoplankton production prior to about 8200 yr bp was significantly higher in the central and southern gulf decreased though the mid holocene and has been reasonably steady for the past 2500 yr the strong north south and east west gradients in present day phytoplankton productivity patterns are also reflected in the holocene sediment record a series of depositional cycles occur in the biogenic record with the strongest peaks of variability at about 150 144 18 200 198 5 and 350 350 40 yrs longer periodicities are present prior to 3200 yr bp but the 350 yr cycle dominates in the late holocene where it is best expressed as productivity dissolution cycles in the carbonate record

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

paleoceanographic history of the guaymas basin gulf of california during the past 15 000 years based on diatoms silicoflagellates and biogenic sediments high resolution records of calcium carbonate biogenic opal diatoms and silicoflagellates from western guaymas basin gravity core ggc55 and piston core jpc56 and eastern guaymas basin dsdp site 480 reveal a complex paleoceanographic history of the central gulf of california during the past 15 000 years prior to 6 2 ka the eastern and western guaymas basin proxy records were remarkably similar after conditions similar to those of today during the bolling allerod the younger dryas yd saw a major drop in diatom production coincident with increased calcium carbonate and tropical microfossils suggestive of el nino like conditions biosiliceous productivity began increasing during the latter part of the yd but it was only during the earliest holocene 11 6 to 11 0 ka that conditions similar to those of the bolling allerod returned to the central gulf between around 11 0 and 6 2 ka tropical diatoms and silicoflagellates were virtually absent from the central gulf as relatively cooler and fresher surface waters resembling those of the modern northern gulf were present in the central gulf beginning at about 6 2 ka tropical diatoms and silicoflagellates began increasing in the central gulf and coccoliths returned to western gulf sediments the onset of modern day monsoon conditions in the american southwest required the presence of warm ssts in the northern gulf which probably did not occur until after about 5 4 ka when tropical diatoms and silicoflagellates became relatively common in the central gulf modern east west contrasts which arise from late winter early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the gulf commenced between 6 2 and 5 4 ka possibly due to a shift in the direction of late winter early spring winds more towards the southeast or down the axis of the gulf this proposed wind shift might have ultimately been due to a late holocene strengthening of enso like conditions in the eastern equatorial pacific published by elsevier b v

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

experimental insights into laser diffraction particle sizing of fine grained sediments for use in palaeoceanography grain size measurements of fine grained sediments based on laser diffraction may contain spurious information due to the over estimation of the size and proportion of platy particles consequently some regard the use of laser diffraction particle sizing in palaeoceanography inappropriate here it is shown experimentally that such concerns are not warranted laser diffraction particle sizing is known to be fast precise and allows for detailed particle sizing over a broad size range it is therefore potentially a very powerful technique if the complications associated with it can be overcome as most sediments are mixtures of different components transported by different mechanisms inferences of past environmental parameters require decomposition of the grain size record in question useful decomposition can only be performed if changes in the contribution of the components are registered predictably by the measuring device this study reports on mixing experiments which show that the fritsch a22 laser diffraction particle sizer does indeed register small changes in the contribution of the mixing components in a predictable way mixing proportions estimated from the measurements do however differ from the initial mixing proportions but these can be converted with only small errors application of the conversion equations to a north atlantic grain size record that showed consistent slowdown of deep ocean circulation in response to millennial scale ice rafting events during the last glacial does not quantitatively affect the original inferences laser diffraction particle sizing of fine grained sediments therefore yields reproducible and useful data for palaeoceanographic reconstructions

steering of westerly storms over western north america at the last glacial maximum the last glacial maximum hydroclimate over western north america differed from the modern climate a proxy model comparison suggests that the glacial storm track was squeezed and steered by atmospheric high pressure systems

late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico a high resolution record of organic walled dinoflagellate cyst production in guaymas basin gulf of california mexico reveals a complex paleoceanographic history over the last 40 ka guaymas basin is an excellent location to perform high resolution studies of changes in late quaternary climate and paleo productivity because it is characterized by high primary productivity high sedimentation rates and low oxygen bottom waters these factors contribute to the deposition and preservation of laminated sediments throughout large portions of the core md02 2515 in this study we document dinoflagellate cyst production at a centennial to millennial scale throughout the late quaternary based on the cyst assemblages three dinoflagellate cyst zones were established and roughly correspond to marine isotope stages miss 1 to 3 miss 1 and 3 are dominated by cysts of heterotrophic dinoflagellates whereas mis 2 is characterized by enhanced variability and a greater proportion of cysts produced by autotrophic taxa the most dominant dinoflagellate cyst taxa found throughout the core were brigantedinium spp and operculodinium centrocarpum dansgaard oeschger event 8 is observed in the dinoflagellate cyst record where it is characterized by an increase in warm taxa such as spiniferites pachydermus other intervals of interest are the younger dryas where warmer conditions are recorded and the holocene which is characterized by the consistent presence of tropical species stelladinium reidii tuberculodinidum vancampoae bitectatodinium spongium and an increase in quinquecuspis concreta changes in cyst assemblages concentrations and species diversity along with geochemical data reflect major orbital to millennial scale climatic and oceanographic changes reference price a m k n mertens v pospelova t f pedersen and r s ganeshram 2013 late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico paleoceanography 28 doi 10 1002 palo 20019

slowly moving thermal mineral waters in deep crystalline basement crystalline basement can contain notable quantities of thermal mineral waters knowledge about their movement and it characteristics fluxes velocities trajectories is of great relevance for subjects like waste disposal or geothermal resources geothermal methods enable to quantify these flow characteristics the use and potential of several methods is demonstrated at three sites all from hercynian basement in western europe the results show rather uniform characteristics darcy flow velocities on the order of 10 11 10 10 m s 1 the domain of flow ranges down to 5 7 km depth

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

a 190 ky record of lithogenic grain size on the namibian slope forging a tight link between past wind strength and coastal upwelling dynamics abstract we inferred wind strength variations at the namibian coast and its effect on upwelling intensity over the last 190 ky by comparing grain size data and alkenone based sea surface temperatures ssts from one sediment core located on the upper slope off luderitz 25 6 s 13 38 e the wind strength proxy was defined by partitioning terrigenous grain size distributions gsds into two sub populations owing to a simple statistical model the fine poorly sorted component is assumed to include both fine aeolian dust and hemipelagic mud carried by rivers or winnowed from the shelf those two fractions are assumed to have been identically sorted during settling in the water column and are not distinguished by our approach the mode of the coarse well sorted sub population displays rapid high amplitude variations through time we ascribe a strictly aeolian origin to this component and consider that low altitude winds are able to carry coarse grained particles to the ocean as shown by grain size measurements of present dust material from the adjacent continent stuut j b w prins m a schneider r r weltje g j jansen j h f postma g 2002 a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic mar geol 180 221 233 variations in the coarse grained dust diameter are closely correlated with sst changes past ssts records from the namibian upper slope have been previously hypothesized as reflecting upwelling intensity combined with occasional injection of warm water from the angola dome we challenge this view in considering that past long term ssts variations are primarily induced by the wind strength and witness coastal upwelling intensity early mis 6 is the only period with evidences of warm poleward water intrusion at the core site the windiest conditions occurred during isotopic stages 3 and 4 the wind strength proxy defined in this study can be used confidently as an independent proxy for past upwelling intensity over the last two climatic cycles

new insights into productivity and redox controlled trace element ag cd re and mo accumulation in a 55 kyr long sediment record from guaymas basin gulf of california a high resolution 55 kyr long record of chalcophile and redox sensitive trace element accumulation ag cd re and mo from md02 2515 western guaymas basin is investigated in conjunction with patterns in stratigraphy and productivity high opal concentrations 59 wt representing increased diatom production coincide with laminated sediments and dilute the concentrations of organic carbon corg and metals a similarity between opal and normalized corg ag and cd concentrations suggests delivery to the sediments by diatom export production while patterns in normalized re and mo accumulation suggest a different emplacement mechanism although mo enrichment in organic rich laminated sediments typically represents anoxic conditions at other locations mo and re in guaymas basin is enriched in nonlaminated and bioturbated sediments that are representative of oxygenated conditions adsorption onto fe and or mn oxyhydroxide surfaces during oxygenation inadequately explains both the re and mo enrichments thus recently published mechanisms invoking direct re and mo removal from the water column and bioturbation assisted irrigation of re into the sediments are used to explain the counterintuitive observations in guaymas basin the md02 2515 stratigraphic and proxy records are also different from other records in the northeast pacific in that there is little correspondence with greenland dansgaard oeschger interstadials there is some correlation with heinrich events suggesting that ventilation of intermediate waters and or reduced productivity may be important in controlling stratigraphy and trace element accumulation the results question whether md02 2515 records can be compared to northeast pacific open margin records especially before 17 kyr b p

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

reconstruction of past climate variability and enso like fluctuations in the southern gulf of california alfonso basin since the last glacial maximum abstract nannofossil assemblages from core md02 2510 provide a 22 ka record of past oceanographic variability in alfonso basin gulf of california east subtropical pacific in this area environmental conditions depend on a monsoonal system heavily influenced by changes in the location of the itcz and nearby atmospheric pressure centers to reconstruct nutricline depth and enso like variability two ecological indexes were calculated based on the relative abundance of the three dominant coccolith species the late glacial period is characterized by intensified wind driven upwelling high primary productivity and la nina like conditions an environmental shift occurs during the glacial interglacial transition el nino like conditions intensify nutricline deepens and surface productivity declines the late holocene is characterized by a persistent increase in nutricline depth and dominance of el nino like conditions the fluctuations in the composition of the coccolith assemblages can be related to orbital scale fluctuations in the average position of the itcz however while the enso like signal that overprints the record varies in response to orbital forcing on suborbital time scales the relation between enso like conditions and the average position of the itcz and the north pacific high changes suggesting that the development of persistent el nino like conditions is strongly dependent on the specific climatic background

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

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