the 13c12c ratios of siderite and organic matter of a modern metalliferous hydrothermal sediment and their implications for banded iron formations abstract a hydrothermal ferruginous sediment precipitated by the activity of the microaerophilic chemolithotrophic bacterium galionella ferruginea has been sampled in a bay of nea kameni island santorini greece due to high fugacity of carbon dioxide precipitation of siderite also occurred the 13c value pdb was determined to be 6 5 in the siderite and 26 8 in the organic matter of mainly microbiological origin the enrichment of isotopically light carbon in carbonates of banded iron formations 13 c 10 has recently been discussed in literature the dilution of these marine carbonates by isotopically light carbon is suggested to have resulted from bacterial oxidation of reduced organic carbon during early diagenesis it is further suggested that fe iii in the newly precipitated sediment served as electron acceptor during oxidation in a hydrothermal model for the origin of banded iron formations this is consistent with the data presented here it is therefore postulated from the results presented that the reduced organic carbon in banded iron formations originates from microaerophilic chemolithotrophic bacteria

ballast brook and beaufort formations late tertiary on northern banks island arctic canada abstract excellent exposures of late tertiary terrestrial sediments occur in the ballast brook region of northwestern banks island canadian arctic archipelago these sediments contain abundant concentrations of organic detritus as well as autochthonous peats which can be traced for some kilometres all of these deposits were previously assigned to the beaufort formation in this paper the deposits formerly grouped as the beaufort formation are subdivided into two formations the newly named ballast brook formation and the beaufort formation the ballast brook formation is characterized by alluvial sand silt clay and peat with compressed altered wood paleobotanical evidence indicates an early to mid miocene age with mid miocene being the most probable this formation is believed to overlie the eureka sound group and is in erosional contact with the overlying beaufort formation plant macrofossils from the ballast brook formation include a number of taxa now found in northern hardwood and southern boreal forests while the prominent peat which characterizes the formation contains a number of taxa that now grow or could be expected to grow in a cypress swamp type of environment for example the conifer glyptostrobus is well represented in the peat the beaufort formation at ballast brook consists of alternating sands and gravels and silt in the lower part it is characterized by an abundance of unaltered wood and other plant materials paleobotanical evidence indicates an early pliocene to early late pliocene age i e approx 5 3 ma like the ballast brook formation the beaufort formation contains an abundance of fossils of conifers but in contrast with the ballast brook formation nearly all of them belong to pinaceae a group well represented in the present boreal forest the beaufort formation also contains insect fossils which are very rare in the ballast brook formation together the insect and plant macrofossils suggest an environment similar to but richer in species some extinet others now found only in asia than present boreal forest and taiga the ballast brook formation flora resembles the flora from mary sachs gravel formerly beaufort formation on southwestern banks island and the flora from the west river beds on the northwest territories mainland it also is similar to a 40 ar 39 ar dated mid miocene flora from east central alaska and to the mamontova gora mid miocene flora from russia

intraseasonal variability in the upper layer currents observed in the eastern equatorial indian ocean 1 direct observations of the upper ocean velocity in the eastern equatorial indian ocean by an acoustic doppler current profiler from november 2000 to october 2001 on the equator at 90 e demonstrate that the dominant periods of variability in the upper layer zonal and meridional currents are in intraseasonal frequency bands with periods of 30 to 50 days and 10 to 20 days respectively the strong intraseasonal variability in the zonal current obscures the semiannual wyrtki jets which can be seen clearly in the monthly averaged field in addition a zone of strong vertical shear of the zonal current and a distinct equatorial undercurrent with semiannual period are observed the results provide us with a new perspective on importance of the energetic intraseasonal variability in the eastern equatorial indian ocean which indicates strong correlation with the wind variability near the mooring location

oceanic precondition and evolution of the 2006 indian ocean dipole 1 details of subsurface ocean conditions associated with the indian ocean dipole event iod were observed for the first time by mooring buoys in the eastern equatorial indian ocean large scale sea surface signals in the tropical indian ocean associated with the positive iod started in august 2006 and the anomalous conditions continued until december 2006 data from the mooring buoys however captured the first appearance of the negative temperature anomaly at the thermocline depth with strong westward current anomalies in may 2006 about three months earlier than the development of the surface signatures these subsurface evolutions within the ocean would be a key factor for better understanding of iod mechanisms and its predictability and are providing a fundamental dataset for validation of modeling outputs

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

bio physical coupling and ocean dynamics in the central equatorial indian ocean during 2006 indian ocean dipole the high frequency times series data collected during 28 th october to 21 st november 2006 onboard r v mirai provided the first evidence of short term bio physical coupling in the central equatorial indian ocean eio the predominant feature of the thermal structure was the down sloping of 28 o c isotherm and up sloping of 14 o c isotherm indicating deepening of surface layer and shoaling of lowerthermocline respectively concomitant with the deepening of surface layer nitracline and subsurface chlorophyll maximum scm also deepened from the prominent bi weekly periodicity in the 14 o cisotherm and the upward phase propagation in the meridional current velocity we infer that shoaling was the response of mixed rossby gravity mrg waves based on temperature and currents we propose that deepening of surface layer was caused by the eastward advection of warmer waters associated with the weakening of indian ocean dipole iod this made the upper ocean more nutrientdepleted and biologically less productive an indication that the central eio is returning to its pre iod condition

subsurface equatorial zonal current in the eastern indian ocean 1 variations of subsurface zonal current in the eastern equatorial indian ocean are investigated by examining 6 year data december 2000 november 2006 from acoustic doppler current profiler adcp mooring at 0 s 90 e the analysis indicates the presence of an eastward equatorial subsurface current between 90 and 170 m depths during both boreal winter and summer during boreal winter the generation of eastward pressure gradient which drives an eastward flow in the thermocline is caused primarily by upwelling equatorial kelvin waves excited by prevailing easterly winds on the other hand the downwelling rossby waves generated by the reflection of the spring downwelling kelvin waves in the eastern boundary as well as the upwelling equatorial kelvin waves triggered by easterlies create an oceanic state that favors the generation of the eastward pressure gradient during boreal summer the subsurface current reveals a distinct seasonal asymmetry the maximum eastward speed of 63 cm s 1 is observed in april and secondary maximum of 49 cm s 1 is seen in october the zonal transport per unit width within depth of the subsurface current exhibits similar variations reaching maximum eastward transport of 35 m2 s 1 in april and secondary maximum of 29 m2 s 1 in october moreover the subsurface current during boreal summer undergoes significant interannual variations it was absent in 2003 but it was anomalously strong during 2006

fe ii oxidation processes at the surface of bacterially colonized iron deposits abstract fe ii oxidation processes at the surfaces of bacterially colonized iron deposits are examined at three hot springs in japan for which the chemical profiles of the ph redox and o2 and fe ii concentrations at the water deposit interface are measured via microelectrodes the three hot springs share similar bulk chemistry with a weakly acidic ph of 5 7 6 3 a high iron concentration of 50 130 m and a high dissolved inorganic carbon concentration of 20 60 mm at the sambe and shionoha hot springs where the bulk water o2 concentration is ca 80 m abiotic fe ii oxidation via autocatalysis prevails at the okuoku hachikurou hot spring where the bulk water o2 concentration is ca 50 m autocatalytic fe ii oxidation is suppressed and biotic fe ii oxidation induced by cyanobacterial photosynthesis is effective these observations indicate that an o2 concentration of ca 50 m is the threshold of reversing the relative contribution of biotic and abiotic fe ii oxidation protons from fe ii oxidation are compensated by reactions among the dissolved inorganic carbon species which sustain the ph condition and continuous fe ii oxidation at the deposit surface the observations of this study provide implications for understanding the deposition of banded iron formations in the geological past

a comparison of intuitive and objective interpretations of miocene plant assemblages from north bohemia abstract an extensive corpus of semi quantitatively described geobotanical analyses from the early miocene of north bohemia has been examined by parametrical and non parametrical multivariate statistical methods the results of these analyses have been compared with traditional geobotanical interpretations that are based on uniformitarian assumptions the statistical analyses show that there are patterns of relationships inherent in the raw geobotanical analyses that are very similar to the traditional interpretations but the statistical analyses define seventeen groups where tradition recognises eight the objective picture from the statistical study however throws a fresh perspective on the familiar evidence and implies that montane colline and riparian forest associations often sub divided on edaphic lines can be recognised in addition to the lowland marsh ecologies implicit in a major brown coal deposit the present day ecological patterns recognisable in ecosystems more than twenty million years old suggest that most of the components retained their ecological preferences throughout this time the statistical analyses offer fresh insights into aspects of the processes transporting the specimens to their place of burial the success of the statistical analyses indicates that the methods used are potentially capable of identifying ecological associations in older geological systems

decoupling photochemical fe ii oxidation from shallow water bif deposition abstract oxidized fe minerals in archean paleoproterozoic banded iron formations bifs are commonly taken to indicate the presence of biogenic o 2 or photosynthetic fe ii oxidizing bacteria in the oceans photic zone however at least one viable abiogenic oxidation mechanism has been proposed prior to the rise of atmospheric oxygen and the development of a protective ozone layer the earth s surface was subjected to high levels of ultraviolet radiation bulk ocean waters that were anoxic at this time could have supported high concentrations of dissolved fe ii under such conditions dissolved ferrous iron species such as fe 2 and fe oh would have absorbed radiation in the 200 400 nm range leading to the formation of dissolved ferric iron fe iii which in turn would have hydrolyzed to form ferric hydroxide fe oh 3 at circumneutral ph cairns smith a g 1978 precambrian solution photochemistry inverse segregation and banded iron formations nature 76 807 808 braterman p s cairns smith a g and sloper r w 1983 photo oxidation of hydrated fe 2 significance for banded iron formations nature 303 163 164 this process has been invoked to account for bif deposition without need for biology francois l m 1986 extensive deposition of banded iron formations was possible without photosynthesis nature 320 352 354 here we evaluate the potential importance of photochemical oxidation using a combination of experiments and thermodynamic models the experiments simulate the chemistry of ambient precambrian seawater mixing with fe ii rich hydrothermal fluids with and without uv irradiation we find that if fe ii was effused from relatively shallow seamount type vent systems directly into an anoxic photic zone the photochemical contribution to solid phase precipitation would have been negligible instead most of the fe ii would have precipitated rapidly as an amorphous precursor phase to the ferrous silicate mineral greenalite fe 3 si 2 o 5 oh 4 and or the ferrous carbonate siderite feco 3 depending on different simulated atmospheric pco 2 levels conversely in experiments where fe ii was exposed either to phototrophic fe ii oxidizing bacteria or to o 2 ferric hydroxide formed rapidly and the precipitation of ferrous iron phases was not observed if as suggested on mass balance grounds bif deposition requires that fe be sourced from shallow seamount type systems then we are driven to conclude that oxide facies bif are the product of a rapid non photochemical oxidative process the most likely candidates being direct or indirect biological oxidation and that a significant fraction of bif could have initially been deposited as ferrous minerals

short term upper ocean variability in the central equatorial indian ocean during 2006 indian ocean dipole event 1 intensive observations using an array of surface and subsurface moored buoys are conducted around 80 5 e in the equatorial indian ocean during october november 2006 an intriguing data set of atmospheric and oceanic variables during a peak phase of a positive indian ocean dipole is obtained the ocean observation data shows relatively shallow thermocline which intensifies with time during the one month period and eastward subsurface zonal flow under westward flowing surface current generating unusually strong vertical shear above the thermocline intraseasonal meridional current variability is also observed upper ocean volume budget analysis indicates that a strong upwelling event larger than 10 m day and associated upward movement of the isotherms below the thermocline occur for a few days in early november these observed data demonstrates unusual conditions of the upper ocean during boreal autumn in 2006

indian ocean response to anomalous conditions in 2006 1 the equatorial indian ocean eio exhibited anomalous conditions characteristic of an indian ocean dipole iod during 2006 the eastern eio had cold sea surface temperature anomalies ssta lower sea level shallow thermocline and higher chlorophyll than normal the anomalies in the east restricted to the south of the equator were highest off sumatra the western pole of the iod was marked by warm ssta and deeper thermocline with maxima on either side of the equator an ocean general circulation model of the indian ocean forced by quikscat winds reproduces the iod of 2006 remarkably well the switch over to cooling in the east and warming in the west happened during may and july respectively in the east airsea heat flux initiated cold ssta in the model which were sustained later by oceanic processes in the west surface heat fluxes and horizontal advection caused warm ssta and contribution by the latter decreased after august citation vinayachandran p n j kurian and c p neema 2007 indian ocean response to anomalous conditions in 2006 geophys res lett 34 l15602 doi 10 1029 2007gl030194

relationship between optimal precursors for indian ocean dipole events and optimally growing initial errors in its prediction using the geophysical fluid dynamics laboratory climate model version 2p1 we explored the precursory disturbances that are most likely to develop into a positive indian ocean dipole iod the dominant spatial patterns of these precursors are defined as the optimal precursors oprs of positive iod as they are more inclined to cause a positive iod than other superimposed initial perturbations in the experiments specifically there are two types of oprs with opposite patterns the surface component of opr 1 opr 2 is an indistinctive west east dipole pattern with a small area of negative positive perturbations to the coast of sumatra and java correspondingly there is a significant west east dipole pattern in the subsurface component of the oprs with the largest values located in the eastern equatorial indian ocean the dominant mode of the time dependent evolutions of the precursors features rapid development of positive iod furthermore the oprs are similar to the optimally growing initial errors oges associated with iod predictions that have been presented in previous studies the shortwave radiation latent heat flux and westward rossby waves play an important role in the time dependent evolution of oges moreover the large values of the oprs are located in the same areas as the sensitive areas of targeted observations identified by the oges this infers that intensive observations over these areas would not only reduce initial errors improve the accuracy of initial fields and decrease the prediction errors but would also detect the precursory signals in advance which substantially improves the forecast skill of iod this article is protected by copyright all rights reserved

the dynamics of zonal current variations in the central equatorial indian ocean 1 this paper examines the depth integrated zonal momentum balance in the central equatorial indian ocean 0 80 5 e for two periods in 1993 1994 and 2004 2006 using a combination of in situ and satellite observations one to two year record length mean balances are approximately linear and steady state monthly to seasonal time scale variations are also governed by linear dynamics with imbalances between the pressure gradient force and surface wind stress leading to zonal mass transport variations along the equator interannual variations in zonal transports along the equator associated with indian ocean dipole events in 1994 and 2006 are likewise consistent with linear dynamics these results provide a valuable benchmark for evaluating models of equatorial indian ocean circulation on seasonal time scales

intraseasonal vertical velocity variation caused by the equatorial wave in the central equatorial indian ocean intraseasonal vertical velocity variation in the central equatorial indian ocean was investigated using observations from the field experiment mirai indian ocean cruise for the study of the mjo convection onset mismo and from the research moored array for african asian australian monsoon analysis and prediction rama in october november 2006 using an array of four subsurface moored acoustic doppler current profilers adcps we estimated vertical velocity by applying the continuity equation results indicated alternating downwelling and upwelling episodes at around thermocline depth with maximum amplitudes larger than 8 0 10 5 m s 1 or about 7 m per day the vertical velocity variation was mainly produced by the divergence convergence of meridional currents with a quasi biweekly period of 11 16 days the temporal changes in temperature around thermocline depth were consistent with variations in vertical velocity whereas upwelling had less impact on the surface layer temperature intraseasonal variations in the ocean may be a part of biweekly fluctuations by remotely forced mixed rossby gravity waves which have a meridional current maximum at the equator accompanied by divergence convergence in the surface layer a few degrees from the equator

dynamics of wind forced intraseasonal zonal current variations in the equatorial indian ocean 1 this study examines the structure and dynamics of wind forced intraseasonal zonal current variability in the equatorial indian ocean we take advantage of a variety of satellite and in situ data sets including unprecedented 4 8 year long velocity time series records from the research moored array for african asian australian monsoon analysis and prediction rama program spectral analysis reveals prominent intraseasonal zonal currents variations along the equator with periods of 30 70 days these oscillations are vertically in phase above the thermocline and propagate eastward with the local zonal winds in the thermocline intraseasonal zonal velocity variations also propagate eastward across a broad range of phase speeds expected for low baroclinic equatorial kelvin waves amplitudes decrease with depth with deeper levels leading those near surface collectively these results suggest that the near surface layer responds directly to intraseasonal zonal wind stress forcing and that subsequently energy radiates downward and eastward in the thermocline in the form of wind forced equatorial kelvin waves in addition intraseasonal zonal current variability on the equator is coherent with off equatorial sea surface height fluctuations in the eastern and central of the basin this coherence is primarily due to the fact that equatorial zonal wind variations are associated with off equatorial wind stress curls that can generate local ekman pumping and westward propagating rossby waves

deposition of banded iron formations by anoxygenic phototrophic fe ii oxidizing bacteria the mechanism of banded iron formation bif deposition is controversial but classically has been interpreted to reflect ferrous iron fe ii oxidation by molecular oxygen after cyanobacteria evolved on earth anoxygenic photoautotrophic bacteria can also catalyze fe ii oxidation under anoxic conditions calculations based on experimentally determined fe ii oxidation rates by these organisms under light regimes representative of ocean water at depths of a few hundred meters suggest that even in the presence of cyanobacteria anoxygenic phototrophs living beneath a wind mixed surface layer provide the most likely explanation for bif deposition in a stratified ancient ocean and the absence of fe in precambrian surface waters

argo profiles a rare occurrence of three consecutive positive indian ocean dipole events 2006 2008 1 during 2006 2008 the indian ocean io experienced a rare realization of three consecutive positive io dipoles piods including an unusual occurrence with a la nina in 2007 common to all three piods is an early excitation of equatorial easterly anomalies argo profiles reveal that for the 2008 and 2006 piods the wind anomalies are generated by the following process upwelling rossby waves propagating into the western io and their subsequent reflection as equatorial upwelling kelvin waves enhance the seasonal upwelling changing sea surface temperature sst gradients for the 2007 piod coastal upwelling kelvin waves off the sumatra java coast associated with the 2006 piod el nino radiate into the io as upwelling rossby waves they curve sharply equatorward to arrive at the central equatorial io inducing easterly anomalies upwelling kelvin waves and the unusual piod our results suggest that real time argo observations when assimilated into predictive systems will enhance iod forecasting skills

microbiological processes in banded iron formation deposition banded iron formations have been studied for decades particularly regarding their potential as archives of the precambrian environment in spite of this effort the mechanism of their deposition and specifically the role that microbes played in the precipitation of banded iron formation minerals remains unresolved evidence of an anoxic earth with only localized oxic areas until the great oxidation event ca 2 45 to 2 32 ga makes the investigation of o2 independent mechanisms for banded iron formation deposition relevant recent studies have explored the long standing proposition that archean banded iron formations may have been formed and diagenetically modified by anaerobic microbial metabolisms these efforts encompass a wide array of approaches including isotope ecophysiological and phylogeny studies molecular and mineral marker analysis and sedimentological reconstructions herein the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post depositional alteration are described the main findings of recent years are summarized and compared here and suggestions are made regarding cross disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition

improved prediction of the indian ocean dipole mode by use of subsurface ocean observations abstractthe numerical seasonal prediction system using the scale interaction experiment frontier version 1 sintex f ocean atmosphere coupled model has so far demonstrated a good performance for prediction of the indian ocean dipole mode iod despite the fact that the system adopts a relatively simple initialization scheme based on nudging only the sea surface temperature sst however it is to be expected that the system is not sufficient to capture in detail the subsurface oceanic precondition therefore the authors have introduced a new three dimensional variational ocean data assimilation 3dvar method that takes three dimensional observed ocean temperature and salinity into account since the new system has successfully improved iod predictions the present study is showing that the ocean observational efforts in the tropical indian ocean are decisive for improvement of the iod predictions and may have a large impact on important socioeconomic activities particularly in the indian ocean rim co

rapid termination of the 2006 el nino and its relation to the indian ocean 1 we investigated the rapid termination of the 2006 el nino using observed data and a coupled ocean atmosphere general circulation model cgcm observed data showed development of an anomalous south indian ocean sio anticyclone associated with the concurrent indian ocean dipole during september november 2006 at the end of 2006 the eastward retreat of the sio anticyclone in response to the indian ocean warming generated an easterly anomaly over the western pacific and the resultant oceanic upwelling kelvin wave terminated the el nino cgcm experiments indicated that the formation of the sio anticyclone was influenced remotely by the pacific ocean sst anomalies and that the easterly anomaly over the western pacific at the end of 2006 was reinforced by the indian ocean sst anomalies these results suggest that interactive feedback between the indian and pacific oceans helped the rapid termination of the 2006 event