trends in river flow affecting the northeastern reach of the san francisco bay estuary over the past 7000 years abstract a variety of stratigraphic analyses particle grain size iron concentration loss on ignition and macrofossils from sediments obtained from two marsh sites are used to reconstruct a middle to late holocene record of stream flow into san francisco bay browns island a freshwater brackish site is located at the confluence of the sacramento and san joaquin rivers and is dominated by stands of scirpus americanus peyton hill is a brackish site located near carquinez straits and is dominated by stands of scirpus robustus twenty five ams 14c dates provide chronostratigraphic control during the holocene discharge from the sacramento and san joaquin rivers was broadly comparable to modern flows however an extended period of higher flow began 3800 cal yr b p and continued for almost two millennia at this time browns island supported phragmites communis a freshwater species and peyton hill supported s americanus at least two floods recognized by discrete increases in sand and silt occurred at 3600 and 530 cal yr b p

origin and availability of organic matter leading to arsenic mobilisation in aquifers of the red river delta vietnam abstract groundwater arsenic as concentrations in the red river delta vietnam are often patchy and related to the microbially induced reduction of fe oxy hydroxides in this study we explored the influence of the origin composition and availability of natural organic matter on the hydrochemical variability in the aquifers of van phuc carbon isotope signatures 13corg and c n ratios were assessed in combination with lithology geochemistry hydrochemistry hydrology and the distribution of specific biomarkers the elationship of c n ratios and 13corg distinguished four groups of sediment types that differ in their organic carbon sources this includes organic carbon originating predominantly from vascular c3 plants c n 15 4 21 0 13corg 28 6 to 26 7 c4 plants c n 10 6 13corg 14 8 freshwater derived particulate organic carbon c n 8 13corg 24 as well as mixtures incorporating both sources at the high as sites we found particulate organic carbon poc being 1 2 less depleted in 13corg than at low as sites more importantly however our assessment shows that the availability of organic matter has to be considered decisive with regard to groundwater as contamination fine grained clayey sediments overlaying sands generally protect organic matter from substantial degradation and its leaching into an adjacent aquifer however at the sites that are high in dissolved as in van phuc sediment layers rich in organic matter are hydraulically connected to the underlying aquifer here soluble organic matter seeping into the aquifer can induce and or enhance reducing conditions thereby mobilising as from fe oxy hydroxides our study shows that both the clay content as well as the origin of organic matter are largely controlled by the depositional environment of the sediments

assessing δ13c and c n ratios from organic material in archived cores as holocene sea level and palaeoenvironmental indicators in the humber estuary uk organic 13c and c n analyses of estuarine deposits provide proxies for changes in the source of organic matter which can be driven by fluctuations in relative sea level river discharge and catchment disturbance here we present the results of a comprehensive vegetation and sediment 13c and c n survey of welwich marsh outer humber estuary uk together with high resolution 13c and c n analyses of holocene cores collected nine years previously from the humber estuary and the lincolnshire marshes eastern england uk the contemporary intertidal 13c and c n dataset shows a gradual increase in surface sediment 13c with decreasing marsh height and suggests that 13c is controlled by the degree of tidal inundation and thus reflects organic matter source however sediment c n ratios are less sensitive to tidal changes and the recent introduction of c4 salt marsh species complicates the contemporary analogue the holocene 13c and c n records are in general agreement with existing microfossil data and provide additional palaeoenvironmental information this includes support for an estuary wide expansion of marine conditions from c 3 3 ka cal yr bp followed by a contraction of marine conditions after c 2 7 ka cal yr bp and evidence for an increase in delivery of terrigenous organic matter to the inner estuary in the late holocene bulk organic 13c and c n analysis is shown to be a reliable and independent indicator of coastal environmental change and is therefore a complementary technique to the more commonly used microfossil approach however this study also shows that in some circumstances the technique may be compromised when applied to sediments from cores that have been stored for a period of time

brackish water foraging isotopic landscapes and dietary reconstruction in suisun marsh central california while bone stable isotope signatures of humans foraging in open coastal and fully terrestrial environments have been relatively well documented the signature of foraging near brackish water estuaries is less well known this study examines the central california isotopic landscape or isoscape showing how foods in different ecosystems have distinctive isotopic compositions we present new bone collagen and apatite stable isotope data from two late holocene sites ca sol 11 and ca sol 69 near suisun marsh a low salinity brackish water estuary upstream from san francisco bay faunal remains at the sites include significant numbers of aquatic resources including fish and shellfish in addition to terrestrial mammals while paleobotanical remains suggest mainly terrestrial nuts and seeds stable isotope data at the population level corroborate this finding and show consumption of significant levels of brackish water nutrients including both dietary protein and dietary carbohydrates and fats paired with terrestrial foods this dietary focus generates a unique brackish water isotopic signature that is distinct from others in central california the documentation of an isoscape with strong regional gradients can be of tremendous help in reconstructing ancient patterns in subsistence migration and trade

a review of coastal palaeoclimate and relative sea level reconstructions using δ13c and c n ratios in organic material holocene reconstructions of relative sea level rsl and environmental change in the coastal zone have become progressively more numerous since the importance of assessing possible future sea level rises has become apparent traditionally this has been achieved using a combination of biological and physical indicators e g pollen diatoms foraminifera grain size etc in some circumstances microfossils can be rare or absent from holocene sediments and in these cases carbon isotope ratios 13c and organic carbon to total nitrogen ratios c n can be used because they have the potential to provide information as to the origin of organic material preserved in coastal environments the distinction in 13c and c n of the various sources of carbon to estuarine sediments has led to its wide use as a tracer of carbon pathways and storage in estuaries more recently these techniques have been applied to holocene sediments to decipher changes in palaeocoastal environments and thus position relative to sea level and or palaeoriver discharge which have direct relevance to palaeoclimate this paper reviews the studies that have utilised this technique and explores examples from a wide range of coastal environments saltmarshes estuaries lagoons isolation basins and fjords it also discusses the potential alteration of geochemical signatures as a result of decompositional processes organic matter decomposition has been shown to change sediment 13c and c n values and thus an understanding of the processes involved is necessary in order to have confidence in the palaeoenvironmental interpretation of holocene 13c and c n decompositional shifts in c n and particularly 13c can occur over a relatively short time period however it is the direction of change in 13c and c n rather than absolute values that is key for interpreting changes in relative sea level and thus such changes are commonly preserved

evidence for temporal fluctuations in marine radiocarbon reservoir ages in the santa barbara channel southern california abstract differences in the 14 c ages of closely associated marine shell and carbonized plant material from stratified archaeological deposits on san miguel island california suggest holocene 10 000 present fluctuations in marine 14 c reservoir ages these fluctuations coincide with 18 o and 13 c shifts measured in mytilus californianus shells from the same stratigraphic contexts and general atmospheric oceanic circulation models for the region based on these data we make three primary observations 1 significant changes appear to have occurred in the radiocarbon reservoir during the holocene 2 these fluctuations appear to correlate with regional oceanographic changes and 3 high resolution 14 c dating of marine shells may require different r values for different periods of time

c3 c4 variations in salt marsh sediments an application of compound specific isotopic analysis of lipid biomarkers to late holocene paleoenvironmental research in salt marshes bulk carbon isotope values reflect organic matter contributions not only from salt marsh plants but also from algal and bacterial inputs as well as allochthonous terrestrial organic matter in the present study compound specific isotope analysis was applied to a core and modern plant samples collected from a machiasport maine salt marsh we sampled 10 plant species common to the marsh including spartina alterniftora spartina patens juncus gerardi solidago sempervirens salicornia europa potentilla anserina atriplex patula plantago maritima suaeda maritima and limonium nashii isolation of two n alkanes c 27 and c 29 present in marsh plant samples allowed for the reconstruction of past plant communities present in the cored deposits for the c 27 and c 29 homologues there is a 3 10 separation in carbon isotopic composition between c3 and c4 species carbon isotopic values down core show a transition from a c4 dominated plant community to a c3 dominated community attributable to the migration of lower marsh zones onto brackish freshwater marsh zones during a late holocene relative sea level rise the two homologues used have the potential to provide paleoenvironmental information in future core work where the sea level variable will be controlled

environmental changes in shamei lagoon hainan island china interactions between natural processes and human activities abstract the sources and burial patterns of organic matter in shamei lagoon hainan china were investigated by analyzing the collected sediment cores in terms of the variations in total organic carbon toc total nitrogen tn stable carbon isotopic composition 13c and 15n and the ratio of total organic carbon to total nitrogen toc tn on such a basis the environmental evolution and primary productivity changes of the lagoon were revealed and the impacts of both natural environmental changes and human activities were identified downcore variation patterns of the parameters representing sources and burial flux of organic matter were predominantly related to natural evolution of the lagoon from 1800 to 1950 and they were increasingly affected by human activities afterwards in the period 1800 1900 the water exchange capacity of the lagoon declined substantially but it was still suitable for the growth of marine phytoplankton as is indicated by relatively high proportion and burial flux of organic matter originated from marine sources during 1900 1950 the lagoon was transformed into a freshwater environment after 1950 due to strong influence by human activities the local freshwater phytoplankton became the major source of buried organic matter at the same time marine lost its niche and its burial flux was much lower than that of its freshwater counterpart the large increment of buried freshwater organic matter also indirectly reflects the eutrophication trend since 1950

late holocene δ13c and pollen records of paleosalinity from tidal marshes in the san francisco bay estuary california abstract records of stable carbon isotopes 13c are presented from cores collected from four san francisco bay marshes and used as a proxy for changes in estuary salinity the 13c value of organic marsh sediments are a reflection of the relative proportion of c3 vs c4 plants occupying the surface and can thus be used as a proxy for vegetation change on the marsh surface the four marshes included in this study are located along a natural salinity gradient that exists in the san francisco bay and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity the 13c values complement pollen data from the same marsh sites producing a paleoclimate record for the late holocene period in the san francisco bay estuary the data indicate that there have been periods of higher than average salinity in the bay estuary reduced fresh water inflow including 1600 1300 cal yr b p 1000 800 cal yr b p 300 200 cal yr b p and ca a d 1950 to the present periods of lower than average salinity increased fresh water inflow occurred before 2000 cal yr b p from 1300 to 1200 cal yr b p and ca 150 cal yr b p to a d 1950 a comparison of the timing of these events with records from the california coast watershed and beyond the larger drainage of the bay reveals that the paleosalinity variations reflected regional precipitation

stable isotope record of late holocene salinity and river discharge in san francisco bay california abstract oxygen and carbon isotopic measurements of fossil mollusks from san francisco bay are used to derive a record of paleosalinity and paleostreamflow for the past 5 900 years the 18 o and 13 c values of river water 12 and 9 are markedly different than seawater 0 and 1 and vary systematically as a function of salinity in the estuary the data show that annually averaged salinity in the south central part of the bay was very close to the modern diversion corrected value of 26 8 over the past 2 700 years and 4 lower than modern between 3 800 and 5 100 yr b p based on those salinities the average annual river inflow to san francisco bay is calculated to have been 1290 m 3 s over the past 2 400 years and 1990 m 3 s between 3 800 and 5 100 yr b p 1 8 times greater than the modern diversion corrected value of 1100 m 3 s assuming a constant bay volume the inferred river discharge record generally corroborates independent paleohydrologic records in california including tree ring treeline and lake level records

some aspects of viscous stress relaxation and intraplate seismicity abstract considerable evidence suggests that the lithosphere has a maxwellian rheology with an effective viscosity of 1026 poise or less in a maxwellian lithosphere viscous stress dissipation limits the maximum attainable stresses due to mechanisms providing a constant stress buildup to a value max given by the product of stress buildup rate c and viscous relaxation time max c where is the ratio of viscosity to rigidity the effectiveness of several intraplate stress building mechanisms in a maxwellian lithosphere was analysed with the following results 1 1 the maximum stress produced by the latitudinal drift of lithospheric plates is 27 bars or less 2 2 the maximum stress produced by the cooling of uplifted eroded regions is 90 bars or less 3 3 lithospheric flexure due to isostatic rebound causes maximum stresses of 68 bars or less for the appalachian rebound and approximately 150 bars for the laurentide rebound it is concluded that none of the mechanisms considered are likely to cause earthquakes if the mechanical strength of the lithosphere is on the order of 1 kb if the strength of the lithosphere is on the order of 100 bars then intraplate earthquakes may result from the laurentide deglaciation as well as from the cooling of uplifted eroded regions but if the lithospheric viscosity is on the order of 1025 poise then only the laurentide deglaciation may produce adequate stresses the fact that a stress buildup rate of 74 bars 200 yrs along the san andreas fault generates earthquakes requires a minimum lithospheric viscosity on the order of 1022 poise

carbon isotope diatom and pollen evidence for late holocene salinity change in a brackish marsh in the san francisco estuary analysis of diatoms pollen and the carbon isotopic composition of a sediment core from a brackish marsh in the northern part of the san francisco estuary has provided a paleosalinity record that covers the past 3000 yr changes in marsh composition and diatom frequencies are assumed to represent variations in freshwater inflow to the estuary three periods of relatively high salinity low freshwater inflow are indicated 3000 to 2500 cal yr b p 1700 to 730 cal yr b p and ca a d 1930 to the present the most recent period of high salinity is primarily due to upstream storage and water diversion within the sacramento san joaquin watershed although drought may also have been a factor the two earlier high salinity periods are likely the result of reduced precipitation low salinity high freshwater flow is indicated for the period 750 cal yr b p to a d 1930 c 2001 university of washington

a 2000 yr record of sacramento san joaquin river inflow to san francisco bay estuary california oxygen and carbon isotopic measurements of fossil bivalves macoma naarfa contained in estuarine sediment are used to reconstruct a late llolocene record of sitlinity and stream flow in san francisco bay discharge into the bay is a particularly good indicator of paleoclin ate in california because the bay s influent streams drain 40 of the state the isotopic record suggests that hetween al oul 1670 ant1 1900 calcnd r yc trs yr cal 1i i inflow to the bay was sul stantially greirler tlian the cstinli tecl precliversion inllow ol 1100 m3 s an unconforn ity representing a 900 yr hiatus is present in the core between 1670 ancl 750 yr cirl ii 13 possil ly r lusc cl by i n tjor 11ydrologic rl event over the p ist 750 yr strcitn ilow to s iii i ril cisco ikty ii is vitrirtl wit11 i pcriotl ol 200 yr i1lter11itte wet iltttl tlry i tlrougl t intc r rls typiritlly 11 rvc i lstecl 40 to 100 yr

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

a 4300 year strontium isotope record of estuarine paleosalinity in san francisco bay california abstract strontium isotopic compositions of carbonate mollusk shells from estuarine sediments cored beneath san francisco bay are used to derive a record of mean annual salinity and average freshwater inflow to the estuary for intervals during the past 4300 yrs the large difference in the 87sr 86sr ratio between seawater 0 7092 and the average freshwater entering the estuary 0 7065 produces a correlation between 87sr 86sr and salinity in bay waters that can be detected with high precision measurements paleosalinity is inferred from the 87sr 86sr ratio measured in fossil carbonate shells of bivalves preserved in the sediment because salinity in san francisco bay is primarily controlled by the freshwater inflow from the sacramento and san joaquin rivers the paleosalinity record can be converted to a paleodischarge record using a transfer function derived from historical data salinity data are referenced to modern values estimated for the estuary after correcting for the lower discharge caused by diversion since 1850 a d data are presented from richardson bay located near the estuary mouth modern mear arrival salinity mas of ca 24 and from san pablo bay located about 30 km upstream modern mas of ca 18 20 for richardson bay the data cover the periods 0 600 yrs b p and 2200 4300 yrs b p based on radiocarbon dating for san pablo bay the periods 0 130 yrs b p and 2500 2800 yrs b p are represented the richardson bay data indicate extended periods of low salinity relative to modern indicating higher freshwater inflow at ca 80 220 310 440 500 3100 3400 and 4300 yrs ago the data indicate high salinity relative to modern hence lower freshwater inflow at about 40 140 210 270 2100 and 3450 3700 yrs b p for san pablo bay where salinity resolution is better salinity was lower than modern during the period at ca 50 and 2550 2650 yrs b p and higher than modern at ca 90 110 155 and 2510 2530 yrs b p the data suggest that mean annual discharge to san francisco bay typically varies between values that are below the modern value 600 m3 s and values 2 to 3 times as high the average paleosalinity is typically substantially lower than the modern values the 4300 yr average freshwater inflow is estimated to be 1200 200 m3 s the record indicates that quasi cyclic variations in mean annual discharge occur naturally with a period of about 200 yrs or less

234u 238u and δ87sr in peat as tracers of paleosalinity in the sacramento san joaquin delta of california usa abstract the purpose of this study was to determine the history of paleosalinity over the past 6000 years in the sacramento san joaquin delta the delta which is the innermost part of the san francisco estuary we used a combination of sr and u concentrations 87sr values and 234u 238u activity ratios ar in peat as proxies for tracking paleosalinity peat cores were collected in marshes on browns island franks wetland and bacon channel island in the delta cores were dated using 137cs the onset of pb and hg contamination from hydraulic gold mining and 14c a proof of concept study showed that the dominant emergent macrophyte and major component of peat in the delta schoenoplectus spp incorporates sr and u and that the isotopic composition of these elements tracks the ambient water salinity across the estuary concentrations and isotopic compositions of sr and u in the three main water sources contributing to the delta seawater sacramento river water and san joaquin river water were used to construct a three end member mixing model delta paleosalinity was determined by examining variations in the distribution of peat samples through time within the area delineated by the mixing model the delta has long been considered a tidal freshwater marsh region but only peat samples from franks wetland and bacon channel island have shown a consistently fresh signal

paleoclimate variability in central taiwan during the past 30 kyrs reflected by pollen δ13ctoc and n alkane δd records in a peat sequence from toushe basin abstract a total of 233 samples from the upper 16 m of the toushe peat core retrieved in central taiwan were measured for toc and 13ctoc values from these samples 17 selected samples with large 13ctoc fluctuations were analyzed for n alkane and d of the c27 and c29 n alkanes combining with the detailed high resolution pollen and geochemical records this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30 kyrs before the last glacial maximum lgm climate was cold and damp with predominantly woodland vegetation in toushe basin and turned to cold and dry after 25 kyr bp climatic conditions there were the worst during lgm over the past 30 kyrs especially around 23 and 18 kyr bp when the woodland was diminished and c4 grass was dominated although short durations of relatively wet conditions could be found at 17 16 and 14 kyr bp cold and dry climates were prevailing during 29 5 28 24 22 17 15 and 13 11 5 kyr bp corresponding to heinrich h events 3 2 1 and younger dryas yd respectively during the early holocene dry climate occurred at 11 10 9 7 9 2 and 8 kyr bp whereas wet condition appeared at 10 3 9 8 9 7 5 kyr bp in the middle holocene climate kept warm and moderate wet in the first half period but many dry events existed in the second half following a cold and dry event at 6 kyr bp after a sharply warm peak at 5 2 kyr bp the climate in toushe turned to cold quickly and tree shrub vegetation disappeared completely with the replacement of c3 grasses in the late holocene climate was relatively wetter with predominant c3 grasses in the basin our climatic interpretations based on the peat records agree well with the greenland ice core and chinese speleothem records on millennium time scales during the last glacial period dry climates corresponding to weakening of the east asian summer monsoon easm during the heinrich events and younger dryas in central taiwan and eastern china demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate however the discrepancies exist between our peat record and the dongge hulu stalagmite record on 1 the age of h2 2 climate intensities of lgm and h1 and 3 wetness condition during holocene these observations call for further study on high resolution climatic changes especially on moisture budget in the east asian monsoonal region

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

stable carbon isotopes as potential sea level indicators in salt marshes north carolina usa we compared the use of 13c values and c n ratios from salt marsh sediments to reconstruct relative sea level rsl with an established approach using foraminifera analysis of bulk organic sediment and plant samples collected along transects at two sites in north carolina usa demonstrates that sediment 13c values can be used to distinguish between spartina alterniflora dominated low marsh c photosynthetic pathway 13c values from 17 6 to 16 1 and juncus roemerianus dominated high marsh c 3 photosynthetic pathway 13c values from 28 2 to 21 8 environments juncus roemerianus plants undergo little decompositional change in 13c average 0 8 although there is a clear difference between spartina alterniflora tissue and bulk organic sediments approximately 4 c n ratios on bulk organic sediment from freshwater upland and salt marsh environments converge during early diagenesis rendering them of little use in reconstructing rsl the utility of 13c values as a sea level indicator is limited by the elevational range of c4 plants making it difficult to recognize salt marsh subenvironments and improve the precision of rsl reconstructions furthermore juncus roemerianus dominated high marsh and freshwater upland sediments cannot be adequately distinguished with 13c values

the application of δ13c toc and c n geochemistry to reconstruct holocene relative sea levels and paleoenvironments in the thames estuary uk we examined the use of d 13 c toc and c n geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data the modern distribution of d 13 c toc and c n of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the thames estuary and norfolk uk are described the d 13 c toc and c n geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae which was controlled primarily by tidal inundation we reviewed published and unpublished studies to produce an english database of vegetation n 257 and sediment n 132 d 13 c toc and c n geochemistry four elevation dependent environments in the database had statistically distinct d 13 c toc and c n values 1 tidal flat low marsh d 13 c 24 9 1 2 toc 3 6 1 7 c n 9 9 0 8 2 middle marsh high d 13 c 26 2 1 0 toc 9 8 6 7 c n 12 1 1 8 3 reed swamp d 13 c 27 9 0 7 toc 36 5 11 5 c n 13 9 1 2 and 4 fen carr d 13 c 29 0 0 6 toc 41 6 5 7 c n 17 4 3 1 the d 13 c toc and c n geochemistry database was applied to a holocene sediment core collected from the thames estuary to produce three new sea level index points and one limiting date illustrating the utility of d 13 c toc and c n values to reconstruct holocene relative sea levels copyright 2015 john wiley sons ltd

application of stable carbon isotopes for reconstructing salt marsh floral zones and relative sea level new jersey usa we investigated use of 13c in bulk organic sediment to define the botanical origin of samples preserved in coastal sediment as a means to reconstruct relative sea level in new jersey usa modern transects at three sites demonstrated that low and high salt marsh floral zones dominated by c4 species spartina alterniflora and spartina patens were associated with sediment 13c values between 18 9 and 15 8 and occurred from mean tide level mtl to mean higher high water mhhw brackish transitional settings vegetated by phragmites australis with iva fructescens and typha sp c3 species and freshwater upland samples c3 species were characterized by bulk sediment 13c values of 27 0 to 22 0 and existed above mhhw parallel transects at one site suggested that intra site variability was not discernible the utility of 13c values for reconstructing relative sea level in new jersey is limited by an inability to differentiate between brackish sediments related to sea level and freshwater upland samples to facilitate this distinction in a 4 4 m core we used a multi proxy approach 13c values with presence or absence of agglutinated foraminifera to recognize indicative meanings for four sample types sediment with 13c values greater than 18 9 was derived from a vegetated salt marsh and formed between mtl and mhhw sediment with 13c values less than 22 0 and containing agglutinated foraminifera formed in a brackish transitional zone between mhhw and highest astronomical tide hat this is the narrowest elevational range of the four sample types and most precise sea level indicator sediment with 13c values less than 22 0 and lacking foraminifera can only constrain the upper bound of former sea level samples with intermediate values 22 0 to 18 9 formed between mtl and hat using these indicative meanings and radiocarbon dates we suggest that a transition from brackish to salt marsh 13c values recorded in the core took approximately 350 years from 1800 to 1450 cal a bp

differences in radiocarbon age between shell and charcoal from a holocene shellmound in northern california abstract the west berkeley shellmound the oldest well dated archaeological site in the san francisco bay region contains shell and charcoal ranging in age from ca 1200 to 5700 cal yr b p radiocarbon ages of marine shell and charcoal collected from fifteen stratigraphic levels in the west berkeley shellmound suggest changes in the 14 c content of san francisco bay surface waters relative to the atmosphere the oceanic reservoir age over the past 5000 yr the reservoir age of san francisco bay waters fluctuated between 870 and 170 14 c yr over the past 5000 yr with the lowest values occurring 2900 to 3800 cal yr b p and the highest values between 1200 and 2000 cal yr b p changes in the radiocarbon reservoir age may be due to changes in the strength of seasonal wind driven upwelling off coastal california where upwelling brings 14 c depleted waters to the surface the period of lowest r values at 3500 to 3900 cal yr b p is coincident with relatively low salinity in san francisco bay indicating high freshwater inflow and wet climate in california based on lake level records the period of high r values 1200 2000 cal yr b p is coincident with one of the driest periods in california during the late holocene these data suggest a link between coastal upwelling and precipitation over central california the age of the top of west berkeley mound and several other mounds in the san francisco bay region 1100 to 1300 cal yr b p coincides with a prolonged dry period in california and low river inflow to san francisco bay perhaps the sites were abandoned because of the drought

holocene paleoecology of an estuary on santa rosa island california abstract the middle to late holocene history and early anglo european settlement impacts on santa rosa island california were studied through the analysis of sediments in a small estuarine marsh a 5 4 m long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr three major zones are distinguishable in the core the lowermost zone 5200 to 3250 yr b p represents a time of arid climate with predominantly marine sediment input and high chenopodiaceae and ambrosia pollen values the intermediate zone 3250 yr b p to 1800 a d is characterized by greater fresh water input and high values for asteraceae and cyperaceae pollen and charcoal particles the uppermost zone 1800 a d to present documents the unprecedented erosion sedimentation and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during anglo european settlement the identification of pollen grains of torrey pine pinus torreyana documents the persistence of this endemic species on the island throughout the middle to late holocene

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record

oxygen isotope seasonality in a temperate estuarine shell midden a case study from ca ala 17 on the san francisco bay california abstract seasonality determination using stable oxygen isotope 18 o analyses in archaeological mollusk shell has been largely limited to aquatic settings where one of the two factors that control shell 18 o water 18 o or salinity and temperature is assumed to be constant open coastal marine environments reflect the former situation and tropical estuaries constitute the latter in an effort to expand stable isotope seasonality to an ecological setting where neither variable remains constant we present a model of annual shell 18 o cycle of aragonite deposition derived from instrumental data on salinity and temperature from san francisco bay california the predicted range of modeled shell 18 o is consistent with observed 18 o values in prehistoric and modern shells when local conditions are considered measurements of 18 o taken at 0 mm and 2 mm from the terminal growth margin were made on 36 archaeological specimens of macoma nasuta from a late holocene hunter gatherer site ca ala 17 and season of collection was inferred using the shell 18 o model we conclude that shellfish exploitation occurred through the year with the exception of fall which may indicate scheduling conflicts with acorn harvesting or other seasonally abundant resources elsewhere the model supports the feasibility of stable isotope seasonality studies in temperate estuaries provided that instrumental records are available to quantify the relevant water conditions at appropriate spatial and temporal scales