No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Extraterrestrial 3He in Paleocene sediments from Shatsky Rise: Constraints on sedimentation rate variability
Abstract
We attempt to constrain the variability of the flux of extraterrestrial 3 He in the Paleocene by studying sediments from Shatsky Rise (Ocean Drilling Program, ODP Leg 198) that have tight orbital age control. 3 He concentrations in Shatsky Rise sediments vary periodically at high frequency by about a factor of 6 over the 800-ka record analyzed. Virtually all of the sedimentary 3 He (N99.98%) is of extraterrestrial origin. The total helium in the sediments can be explained as a binary mixture of terrestrial and extraterrestrial components. We calculate an average 3 He/ 4 He ratio for the extraterrestrial endmember of 2.41 ± 0.29 × 10 − 4 , which is, remarkably, equal to that measured in present-day interplanetary dust particles. We determine a constant extraterrestrial 3 He flux of 5.9 ± 0.9 × 10 − 13 cm 3 STP . cm − 2 ka − 1 for our 800-ka Paleocene record at ~ 58 Ma. This value is identical within error to those for the late Paleocene in sediments from the northern Pacific and the Weddell Sea. Bulk sediment MARs (derived using a constant extraterrestrial 3 He flux) respond to climate-forced carbonate preservation cycles and changes in eolian flux over the late Paleocene. This is the first direct evidence for significant changes in dust accumulation in response to eccentricity forcing during a greenhouse climate interval.
Supplementary resource (1)
Data
January 2009
... Dust flux reconstructions from marine sediments require an accurate estimate of the concentration of windblown dust in the sediment. In the past decade, several studies have used the dominant isotopes of helium and thorium, 4 He and 232 Th, to infer dust concentrations in sediments (e.g., Patterson et al., 1999;Marcantonio et al., 2001aMarcantonio et al., , 2009Anderson et al., 2006;McGee et al., 2007;Winckler et al., 2008;Serno et al., 2014Serno et al., , 2015. Both isotopes are highly enriched in lithogenic minerals relative to marine biogenic sediments, and they are less susceptible to contamination by volcanic inputs than other markers of lithogenic inputs (e.g., Al, Ti). ...
... In settings in which 4 He or 232 Th are dominantly derived from eolian dust, both dust concentration and bulk sediment flux can then be derived from a single analysis, allowing calculation of the dust flux (Marcantonio et al., 2001a(Marcantonio et al., , 2009Winckler et al., 2005Winckler et al., , 2008Anderson et al., 2006;McGee et al., 2007;Serno et al., 2014) using the following equation: ...
... 4 He as a dust proxy 4 He has been used as a dust proxy in a variety of settings. It was first used in marine sediments ranging in age from the Quaternary (Patterson et al., 1999;Winckler et al., 2005Winckler et al., , 2008Serno et al., 2014Serno et al., , 2015 to the early Cenozoic (Marcantonio et al., 2009), and more recently it has been employed as a dust tracer in Antarctic ice (Winckler and Fischer, 2006) and corals (Mukhopadhyay and Kreycik, 2008). Additionally, 4 He/Ca ratios have been interpreted as a dust provenance tracer in Antarctic ice (Winckler and Fischer, 2006). ...
Despite its potential linkages with North Atlantic climate, the variability in Saharan dust transport to the western North Atlantic over the past two millennia has not been well-characterized. A factor of 4 increase in dust production in sub-Saharan Africa has been attributed to the onset of Sahelian agriculture 200 yr ago. The regional extent of this anthropogenic dust increase, however, remains uncertain. Additionally, while millennial-scale cold periods of the last deglaciation have been associated with strong increases in North African dust emissions, few adequate records exist to observe dustiness during the Little Ice Age, a century-scale cooling of the North Atlantic (AD 1400–1800). In this study, we develop a new technique for the paired use of ²³⁰Th-normalized ²³²Th fluxes and ³He-normalized ⁴He fluxes in Bahamian tidal flat sediments. After justifying the fact that ²³⁰Th and ³He have had relatively constant sources to tidal flat and banktop waters, and accounting for the smoothing effect of bioturbation, a factor of 4 change in far-field dust transport to the western North Atlantic between the pre-industrial and modern era is not supported by our dust proxies over the past 2000 yr. Furthermore, we speculate why the response of western North Atlantic dust deposition associated with the Little Ice Age climate anomalies may have been modest compared to prior climatic events of the early Holocene or the last deglaciation.
... He and 232 Th, to infer dust concentrations in sediments (e.g., Patterson et al., 1999; Marcantonio et al., 2001a Marcantonio et al., , 2009 Anderson et al., 2006; McGee et al., 2007; Winckler et al., 2008; Serno et al., 2014 Serno et al., , 2015). Both isotopes are highly enriched in lithogenic minerals relative to marine biogenic sediments, and they are less susceptible to contamination by volcanic inputs than other markers of lithogenic inputs (e.g., Al, Ti). ...
... An additional reason for their use is convenience: 4 He and 232 Th are measured as a part of routine analysis for the minor isotopes 3 He and 230 Th, respectively, both of which are used for determining accumulation rates in marine sediments (Francois et al., 2004; McGee and Mukhopadhyay, 2013). In settings in which 4 He or 232 Th are dominantly derived from eolian dust, both dust concentration and bulk sediment flux can then be derived from a single analysis, allowing calculation of the dust flux (Marcantonio et al., 2001aMarcantonio et al., , 2009 Winckler et al., 2005 Winckler et al., , 2008 Anderson et al., 2006; McGee et al., 2007; Serno et al., 2014) using the following equation: where F dust is dust flux, MAR is the mass accumulation rate (or flux) of the sediment (derived from 3 He or 230 Th data), [X] sed is the 4 He or 232 Th concentration measured in the sediment and [X] At present, we have a limited understanding of the mean values and variability of these concentrations between source areas or grain size fractions. Constraints on dust provenance are essential to the interpretation of dust flux records. ...
... He has been used as a dust proxy in a variety of settings . It was first used in marine sediments ranging in age from the Quaternary (Patterson et al., 1999; Winckler et al., 2005 Winckler et al., , 2008 Serno et al., 2014 Serno et al., , 2015) to the early Cenozoic (Marcantonio et al., 2009), and more recently it has been employed as a dust tracer in Antarctic ice (Winckler and Fischer, 2006) and corals (Mukhopadhyay and Kreycik, 2008). Additionally, 4 He/Ca ratios have been interpreted as a dust provenance tracer in Antarctic ice (Winckler and Fischer, 2006). ...
... Dust flux reconstructions from marine sediments require an accurate estimate of the concentration of windblown dust in the sediment. In the past decade, several studies have used the dominant isotopes of helium and thorium, 4 He and 232 Th, to infer dust concentrations in sediments (e.g., Patterson et al., 1999;Marcantonio et al., 2001aMarcantonio et al., , 2009Anderson et al., 2006;McGee et al., 2007;Winckler et al., 2008;Serno et al., 2014Serno et al., , 2015. Both isotopes are highly enriched in lithogenic minerals relative to marine biogenic sediments, and they are less susceptible to contamination by volcanic inputs than other markers of lithogenic inputs (e.g., Al, Ti). ...
... In settings in which 4 He or 232 Th are dominantly derived from eolian dust, both dust concentration and bulk sediment flux can then be derived from a single analysis, allowing calculation of the dust flux (Marcantonio et al., 2001a(Marcantonio et al., , 2009Winckler et al., 2005Winckler et al., , 2008Anderson et al., 2006;McGee et al., 2007;Serno et al., 2014) using the following equation: ...
... 4 He as a dust proxy 4 He has been used as a dust proxy in a variety of settings. It was first used in marine sediments ranging in age from the Quaternary (Patterson et al., 1999;Winckler et al., 2005Winckler et al., , 2008Serno et al., 2014Serno et al., , 2015 to the early Cenozoic (Marcantonio et al., 2009), and more recently it has been employed as a dust tracer in Antarctic ice (Winckler and Fischer, 2006) and corals (Mukhopadhyay and Kreycik, 2008). Additionally, 4 He/Ca ratios have been interpreted as a dust provenance tracer in Antarctic ice (Winckler and Fischer, 2006). ...
Reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates. Dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples. More recently, dust fluxes have been estimated from measurements of helium and thorium, as rare isotopes of these elements (He-3 and Th-230) allow estimates of sediment flux, and the dominant isotopes (He-4 and Th-232) are uniquely associated with the lithogenic fraction of marine sediments. In order to improve the fidelity of dust flux reconstructions based on He and Th, we present a survey of He and Th concentrations in sediments from dust source areas in East Asia, Australia and South America. Our data show systematic relationships between He and Th concentrations and grain size, with He concentrations decreasing and Th concentrations increasing with decreasing grain size. We find consistent He and Th concentrations in the fine fraction (<5μm) of samples from East Asia, Australia and Central South America (Puna-Central West Argentina), with Th concentrations averaging 14μg/g and He concentrations averaging 2μccSTP/g. We recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine-grained, and suggest that previous studies may have systematically overestimated Th-based dust fluxes by 30%. Source areas in Patagonia appear to have lower He and Th contents than other regions, as fine fraction concentrations average 0.8μccSTP/g and 9μg/g for 4He and 232Th, respectively. The impact of grain size on lithogenic He and Th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably. Our data also have important implications for the hosts of He in long-traveled dust and for the 3He/4He ratio used for terrigenous He in studies of extraterrestrial He in sediments and ice.We also investigate the use of He/Th ratios as a provenance tracer. Our results suggest differences in fine fraction He/Th ratios between East Asia, Australia, central South America and Patagonia, with ratios showing a positive relationship with the geological age of source rocks. He/Th ratios may thus provide useful provenance information, for example allowing separation of Patagonian sources from Puna-Central West Argentina or Australian dust sources. He/Th ratios in open-ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas. He/Th ratios in mid-latitude South Atlantic sediments suggest that dust in this region primarily derives from the Puna-Central West Argentina region (23-32°S) rather than Patagonia (>38°S). In the equatorial Pacific, He/Th ratios are much lower than in extratropical Pacific sediments or potential source areas measured as a part of this study (East Asia, South America, Australia) for reasons that are at present unclear, complicating their use as provenance tracers in this region.
... This approach has proved particularly valuable in portions of the sedimentary record marked by dramatic changes in sedimentation (e.g., Mukhopadhyay et al. 2001b;Farley and Eltgroth 2003;Murphy et al. 2010). Even in periods of more typical pelagic sedimentation, 3 He ET -based accumulation rates allow calculation of fluxes for paleoclimate studies with sub-orbital resolution that are largely independent of age model errors, changes in carbonate preservation and lateral advection of sediments (Winckler et al. 2005;Marcantonio et al. 2009;McGee et al. 2010;Torfstein et al. 2010). ...
... The first assumption does not hold during the late Eocene and late Miocene (see Sect. 4.1), and the second may not be appropriate in transitions between oxic and anoxic sediments, but in much of the late Cretaceous and Cenozoic they appear reasonable. In the carbonate-rich sections that have been studied, 3 He ET concentrations are relatively constant with respect to the non-carbonate fraction, a rough indicator of relative sedimentation rates, supporting an approximately constant 3 He ET flux (e.g., Mukhopadhyay et al. 2001a, b;Farley and Eltgroth 2003;Marcantonio et al. 2009). ...
... These 3 He ET fluxes are then applied to the interval of interest, which is often a time of substantial changes in sedimentation when orbital signals are in doubt. Absolute 3 He ET fluxes for a given time period vary from site to site due to differences in 3 He ET preservation or sediment focusing (Fig. 5); for example, 3 He ET fluxes for the late Eocene and early Paleocene are a factor of 3 or more higher in sediment cores from the central and western North Pacific, South Atlantic and Southern Ocean (Farley 1995;Farley and Eltgroth 2003;Marcantonio et al. 2009;Murphy et al. 2010) than in a sediment core from Blake Nose in the North Atlantic (Farley and Eltgroth 2003). To the extent that these differences reflect differences in sediment focusing (which increases 3 He ET fluxes during a dated interval by laterally advecting IDPs to a core site), 3 He ET -based MARs will be systematically biased low in sites with high focusing but relative changes in accumulation rates will still be robust. ...
Most 3 He in deep-sea sediments is derived from fine-grained extraterres-trial matter known as interplanetary dust particles (IDPs). These particles, typically \50 lm in diameter, are sufficiently small to retain solar wind-implanted He with high 3 He/ 4 He ratios during atmospheric entry heating. This extraterrestrial 3 He (3 He ET) is retained in sediments for geologically long durations, having been detected in sedimentary rocks as old as 480 Ma. As a tracer of fine-grained extraterrestrial material, 3 He ET offers unique insights into solar system events associated with increased IDP fluxes, including asteroid break-up events and comet showers. Studies have used 3 He ET to identify IDP flux changes associated with a Miocene asteroid break-up event and a likely comet shower in the Eocene. During much of the Cenozoic, 3 He ET fluxes have remained relatively constant over million-year timescales, enabling 3 He ET to be used as a constant flux proxy for calculating sedimentary mass accumulation rates and constraining sedi-mentary age models. We review studies employing 3 He ET -based accumu-lation rates to estimate the duration of carbonate dissolution events associated with the K/Pg boundary and Paleocene-Eocene Thermal Maximum. Additionally, 3 He ET has been used to quantify sub-orbital variability in fluxes of paleoproductivity proxies and windblown dust. In order to better interpret existing records and guide the application of 3 He ET in novel settings, future work requires constraining the carrier phase(s) of 3 He ET responsible for long-term retention in sediments, better characterizing the He isotopic composition of the terrigenous
... We, thus, explored the use of two For the He-based age model and for calculation of terrigenous 4 He mass accumulation rates (MAR) we require knowledge of the local extraterrestrial 3 He ( 3 He ET ) flux. In the absence of a suitable calibration interval at our site, we used the 3 He ET flux of 5.91E−13 cm 3 STP cm −2 ky −1 for the central Pacific (Marcantonio et al., 2009) and 2.2E−13 cm 3 STP cm −2 ky −1 for the North Atlantic region (Farley and Eltgroth, 2003) as endmembers. These endmembers cover nearly the entire range of values published for the Paleocene-Eocene boundary interval so far. ...
... However, there are a number of arguments suggesting that the upper limit of our age-model is likely to be the more realistic estimate. If we choose to calibrate our 3 He ET age-model using the 3 He ET flux for the Pacific (Marcantonio et al., 2009), the estimated duration of the CIE core is much too short (∼10 kyr), whereas this interval has been estimated to have a duration at least six-times longer (66-113 kyr; Murphy et al., 2010;Röhl et al., 2007). Use of the Pacific 3 He ET flux in our age model would imply that the entire sequence between ∼195 and 202.5 mbsf represents the PETM as conventionally-recognized, but this finding is not only contradicted by the δ 13 C record (which confines the CIE core to the interval ∼201.5-202.5 mbsf), but would also require a very high average sedimentation rate of ∼3.7 cm kyr −1 , compared to typical pelagic sedimentation rates in the Paleocene of <1 cm kyr −1 as obtained by using the 3 He ET flux value from the Atlantic. ...
... [21] For a short interval at Shatsky Rise (230-234 rmcd; about 9 eccentricity cycles) helium isotope data [Marcantonio et al., 2009] and dust flux estimates [Woodard et al., 2011] show that changes in eolian dust flux are synchronous with Fe intensity data and thus likely eccentricity driven. In addition, the extraterrestrial 3 He data from Site 1209 point to climateforced changes in carbonate preservation anti-phased to the [Bornemann et al., 2009], and ODP Site 761B (offshore NW Australia) [Quillévéré et al., 2002] and bulk rock d 13 C from Zumaia (Spain) [Arenillas et al., 2008] across the Top Chron 27n event or Latest Danian Event (LDE). ...
... Red lines mark correlation ties between Zumaia and Site 1209. dust flux [Marcantonio et al., 2009]. Coarse fraction data presented here document enhanced preservation of calcium carbonate in eccentricity minima, supporting the helium isotope results. ...
The late Cretaceous and Paleogene paleoclimate reveals a rather complex history of gradual as well as rapid warming and cooling transitions and events. In particular, the early Paleogene is thought to contain unique and critical records of greenhouse conditions that could provide valuable insights into past as well as future greenhouse worlds. The Zachos et al. (2001) benthic isotope compilation includes data from more than 40 DSDP and ODP sites, from which the Paleocene interval is a combined record of mainly Atlantic Ocean, S Ocean, and Indian Ocean sites. Detailed insight into the Paleocene climate record was hampered until the first continuous and complete records covering the entire early Paleogene have been retrieved from the equatorial Pacific (ODP Leg 198, Shatsky Rise) and the South Atlantic (ODP Leg 208, Walvis Ridge). Here we present the first complete high-resolution benthic foraminiferal stable isotope record from a single Pacific site (ODP Site 1209) covering the entire Paleocene (magnetic polarity chrons C24r to C30n). The record provides unprecedented insight into the sensitivity of climate system and carbon cycle to orbital and other forcing over the entire Paleocene including detailed characteristics of the early Late Paleocene Biotic event (ELPE), the Chron 27n event and the K/Pg boundary. The pronounced beat of the global carbon cycle in the Paleocene as recorded in the d13C record is related to the long (405 kyr) eccentricity cycle. In addition, we show that the Chron 27n event at 61.7 Ma is characterized by a clear negative excursion in d13C and d18O associated with a decreased in carbonate content. The abrupt warming of 2°C in the deep equatorial Pacific supports the hypothesis that this event may represent an early Paleocene hyperthermal.
... Alternatively, knowledge of the cosmic dust flux over a period of time can be used to estimate sediment mass accumulation rates (e.g. Farley and Eltgroth, 2003;Marcantonio et al., 2009;Mukhopadhyay et al., 2001;Murphy et al., 2010). However, diffusion experiments in the magnetic fraction of marine sediment (Hiyagon, 1994a(Hiyagon, , 1994b and bulk pelagic clays (Mukhopadhyay and Farley, 2006) suggest that a significant proportion of the helium of extraterrestrial origin would escape from the sediments for times >10 6 yrs. ...
Sediments contain interplanetary dust particles (IDPs) carrying extraterrestrial noble gases, such as 3He, which have previously been used to estimate the IDP accretion flux over time and the duration of past environmental events. However, due to its high diffusivity, He can be lost by diffusion either due to frictional heating during entry in the atmosphere, or once it has been incorporated in the sediments. Therefore the absolute values of 3He IDP fluxes cannot be known. Due to its lower diffusivity, Ne is less likely to be lost by diffusion than He and can potentially provide an absolute IDP flux value. Here, we studied the Ne and He isotopic composition of 21 sediments of different ages (3 to 38 Myr, 56 Myr and 183 Myr) in order to better constrain the retention of 3He in such deposits. The samples are carbonates from 2 sites of the Integrated Ocean Drilling Program (IODP), which previously showed evidence of detectable extraterrestrial 3He, and from the Sancerre core in the Paris basin. The 3He/4He, 20Ne/22Ne and 21Ne/22Ne ratios of decarbonated residues vary respectively from 0.09×10-6 to 76.5×10-6, 9.54±0.08 to 11.30±0.60 and from 0.0295±0.0001 to 0.0344±0.0003. These isotopic compositions can be explained by a mixing between two terrestrial components (atmosphere and radiogenic He and nucleogenic Ne present in the terrigenous fractions) and an extraterrestrial component. The linear relationship between 20Ne/22Ne and 3He/22Ne ratios shows that the extraterrestrial component has a unique composition and is similar to the He and Ne composition of implanted solar wind. This composition is different from the individual stratospheric IDPs for which the Ne and He isotopic compositions have been measured. We suggest that this difference is due to a bias in the sampling of the individual IDPs previously analyzed toward the largest ones that are more likely to lose He during entry in the atmosphere. Our data further constrains the size of the majority of the IDPs to be less than 10 μm in diameter. In addition, the constant 3He/22Ne ratio of the extraterrestrial component present in the samples, which is similar to the implanted solar wind composition, suggests that no diffusive loss of 3He occurred in the atmosphere or on the seafloor. Thus, neglecting any non-fractionating He and Ne loss by weathering and/or alteration of the host phases on the seafloor, the extraterrestrial 3He and 20Ne fluxes between 3 to 38 Myr ago are respectively 0.2±0.1×10-12 cm3cm-2kyr-1 and 0.2±0.1×10-11 cm3cm-2kyr-1. During the sharp increases of the late Eocene and late Miocene, the IDP 3He and 20Ne fluxes reach values up to five times higher.
... Terrestrial 4 He ( 4 He terr ) has been successfully used as an eolian dust proxy in marine sediments [Patterson et al., 1999;Mukhopadhyay et al., 2001;Winckler et al., 2005Winckler et al., , 2008Marcantonio et al., 2009;Serno et al., 2014], Antarctic ice [Winckler and Fischer, 2006], and corals [Mukhopadhyay and Kreycik, 2008;Bhattacharya, 2012]. 4 He in continental crust material is produced by α-decay of U/Th-series elements. ...
We present a new record of eolian dust flux to the western Subarctic North Pacific (SNP) covering the past 27,000 years based on a core from the Detroit Seamount. Comparing the SNP dust record to the North Greenland Ice Core Project (NGRIP) ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation, while the timing of abrupt changes is synchronous. If dust deposition in the SNP faithfully records its mobilization in East Asian source regions, then the difference in the relative amplitude must reflect climate-related changes in atmospheric dust transport to Greenland. Based on the synchronicity in the timing of dust changes in the SNP and Greenland, we tie abrupt deglacial transitions in the 230Th-normalized 4He flux record to corresponding transitions in the well-dated NGRIP dust flux record to provide a new chronostratigraphic technique for marine sediments from the SNP. Results from this technique are complemented by radiocarbon dating, which allows us to independently constrain radiocarbon paleoreservoir ages. We find paleoreservoir ages of 745 ± 140 years at 11,653 year B.P., 680 ± 228 years at 14,630 year B.P., and 790 ± 498 years at 23,290 year B.P. Our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western SNP. Good temporal synchronicity between eolian dust records from the Subantarctic Atlantic and equatorial Pacific and the ice core record from Antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions.
... The base of LDE bed I is 8.20 m above the base of the section (Fig. 2) in lower planktic foraminifer Zone P3b (LO of I. albeari at 8.05 m: Sprong et al., 2009), in calcareous nannofossil Zone NP4 (Martini, 1971) and in Subzone NTp7B (Varol, 1989 (Westerhold et al., 2008(Westerhold et al., , 2011Marcantonio et al., 2010). ...
The Latest Danian Event (LDE) is a proposed early Palaeogene transient warming event similar to the Paleocene–Eocene Thermal Maximum, albeit of smaller magnitude. The LDE can be correlated with a carbon isotope excursion ('CIE-DS1') at Zumaia, Spain, and the 'top Chron C27n event' defined recently from ocean drilling sites in the Atlantic and Pacific, supporting a global extent. Yet, records of environmental change during the LDE (e.g. warming and sea-level fluctuations) are still rare. In this study, we focus on the micropalaeontology (calcareous nannofossils and benthic foraminifera), mineralogy and trace element geochemistry of the LDE in the Qreiya 3 section from the southern Tethyan margin in Egypt. In this section, the LDE is characterized by the occurrence of anomalous beds intercalated within upper Danian shales and marls. The event beds of the LDE are situated above an unconformity on top of a shallowing-upwards sequence deposited in a well-oxygenated outer neritic to upper bathyal marine palaeoenvironment. The lower LDE bed is barren of benthic foraminifera, but contains pyrite and fish remains, and is interpreted as an anoxic level formed during rapid relative sea-level rise. Incursion of a Neoeponides duwi (Nakkady, 1950) benthic assemblage in LDE bed II is interpreted as repopulation of the seafloor after anoxia. The sea-level cycle associated with the LDE is estimated at about 50 m maximum in the Qreiya 3 section. The environmental changes at Qreiya 3 are of supra-regional extent, since a similar sequence of events has been observed at other southern Tethyan locations.
... Excess 40 Ar* and 4 He have only two possible sources in seafloor serpentinites: (1) mantle-derived rocks with 40 Ar/ 36 Ar of up to $ 30,000 and 3 He/ 4 He of $ 8 Ra (where Ra is the atmospheric 3 He/ 4 He ratio of 1.4 Â 10 À 6 ; Graham, 2002); and, (2) marine sediments, which typically have 40 Ar/ 36 Ar ratios of between 296 and $ 1500, and 3 He/ 4 He ratios ranging from crustal values of $ 0.02 Ra near continental margins to values of $ 170 Ra in sediments that host Interplanetary Dust Particles (e.g. Marcantonio et al., 2009;Matsuda and Nagao, 1986;Podosek et al., 1980;Staudacher and All egre, 1988). ...
Serpentinites form by hydration of ultramafic lithologies in a range of seafloor and shallow subduction zone settings. Serpentinites are recognised as major reservoirs of fluid mobile elements and H2O in subducting oceanic lithosphere, and together with forearc serpentinites formed in the mantle wedge, provide critical information about shallow-level volatile fluxes during subduction. The current study provides new Cl, as well as the first comprehensive Br, I and noble gas analyses reported for seafloor and forearc chrysotile–lizardite serpentinites. The samples were recovered from IODP drilling campaigns of mid-ocean ridge, passive margin and forearc settings (n=17), and ophiolites in the Italian Alps and Apennines (n=10). The aims of this study were to determine the compositional variability of noble gases and halogens in serpentinites entering subduction zones and evaluate the efficiency of gas loss during the early stages of serpentinite subduction.
Ongoing CO2 emissions are expected to increase global temperatures and affect ocean chemistry better known as ‘ocean acidification’. This latter is a major threat for marine calcifying biota (corals, foraminifera, coccolithophorids). However, recent works identify a particular resilience of coccolithophorids to past ocean acidification events, whereas temperature limits biocalcification. Studies on cultured coccolithophorids or surface-water samples allow understanding the response to short-term temperature, pCO2 or pH variations, but long-term species-specific resilience to environmental changes is crucial to evaluate the respective role of ocean acidification and temperature on fossil calcifying biota. We approach the long-term response of coccolithophorids to these parameters by analyzing the fossil record of two past global events showing perturbation of the carbon cycle associated to CO2 fluctuations and global warming: these are the Toarcian Oceanic Anoxic Event (T-OAE; 183 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; 56 Ma). Firstly, I present new high resolution biostratigraphy for both events in order to link the bioevents to the carbon stable isotopes curve and hence to the carbon isotopes excursion defining the T-OAE and the PETM. We quantify the response of fossil cocoliths to past hyperthermal events by quantifying nannofossils accumulation rate. Both are hyperthermals, but only the former records organic matter accumulations (black shales). Besides ocean acidification, the carbonate saturation and alkalinity of the oceans have an impact on coccolithophorids; we will thus use the calcium isotope composition of the test of planktonic foraminifera to track changes in CO32- concentration across the PETM, where ocean acidification is inferred, and compare these data with analogue records for the T-OAE
Subduction plate boundaries are commonly weak owing to fluid overpressure. The generation of fluid overpressure has been invoked for compaction disequilibrium and mineral dehydration in subducting sediments and altered oceanic crust. The subduction mélange in the Shimanto accretionary complex, southwest Japan, preserves the quartz-calcite-filled shear veins and sigmoidal extension veins formed under fluid overpressure near the downdip limit of the thermally-controlled seismogenic zone. The shear veins record the repeated low-angle brittle thrusting under fluid overpressure, while the extension veins constitute the Riedel shear zones developed during subduction under vertical maximum principle stress. To examine the origin of overpressured fluids, we conducted fluid inclusion and noble gas analyses on the shear and extension veins. The result of fluid inclusion analysis shows various fluid pressures between lithostatic to hydrostatic pressures during the vein formation, which were associated with warm fluid infiltration. ³He/⁴He values of shear veins and extension veins range 1.6–2.5 Ra and 1.6–2.3 Ra, respectively, indicating the presence of mantle helium. ⁴⁰Ar/³⁶Ar values and ⁸⁴Kr/³⁶Ar and ¹³⁰Xe/³⁶Ar ratios of the veins are similar to those of serpentinized mantle, suggesting that mantle helium originated from serpentinized mantle. Because the mantle-derived rocks such as peridotite and serpentinite are absent in the mélange, the results of noble gas analyses represent the infiltration of fluids from the serpentinized mantle into the mélange shear zone. Our results show that an infiltration of fluids derived from serpentinized mantle contributed the fluid overpressure in the mélange shear zone near the downdip limit of the seismogenic zone.
This work is about the identification of modern cosmic dust that had survived heating during its high-velocity passage through the Earth’s atmosphere from ³He isotope concentrations in marine (Gulf of Finland) ferromanganese nodules (FMNs). The measured bulk composition of helium includes components of various origins, enabling the determination of the age (1800 years) of the shallow-water Baltic FMNs and the average time of exposure (8 × 10⁷ years) of cosmic dust particles during their existence in space. The concentration of cosmic dust per gram of FMN material is found to be 0.036 μg. The contribution of solar-wind helium to the Earth’s atmospheric helium is found to be small. The experiments are conducted by the stepheating method in vacuo with the subsequent mass-spectrometric analysis of the helium released from the samples.
Eolian dust in pelagic deep sea sediments can be used to reconstruct ancient wind patterns and paleoenvironmental response to climate change. Traditional methods to determine dust accumulation involve isolating the non-dissolvable aluminosilicate minerals from deep sea sediments through a series of chemical leaches, but cannot differentiate between minerals from eolian, authigenic and volcanogenic sources. Other geochemical proxies, such as sedimentary 232Th and crustal 4He content, have been used to construct high-resolution records of atmospheric dust fluxes to the deep sea during the Quaternary. Here we use sedimentary Th content as a proxy for terrigenous material (eolian dust) in ∼58 Myr-old sediments from the Shatsky Rise (ODP Site 1209) and compare our results with previous dust estimates generated using the traditional chemical extraction method and sedimentary 4Hecrustal concentrations. We find excellent agreement between Th-based dust estimates and those generated using the traditional method. In addition our results show a correlation between sedimentary Th and 4Hecrustal content, which suggests a source older than present day Asian loess supplied dust to the central subtropical Pacific Ocean during the early Paleogene.
1] We have compiled the first stratigraphically continuous high‐resolution benthic foraminiferal stable isotope record for the Paleocene from a single site utilizing cores recovered at Pacific ODP Site 1209. The long‐term trend in the benthic isotope record suggests a close coupling of volcanic CO 2 input and deep‐sea warming. Over the short‐term the record is characterized by slow excursions with a pronounced periodic beat related to the short (100 kyr) and long (405 kyr) eccentricity cycle. The phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the Oligocene and Miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on Milankovitch time scales. In addition, the record documents an unusual transient warming of 2°C coeval with a 0.6‰ carbon isotope excursion and a decrease in carbonate content at 61.75 Ma. This event, which bears some resemblance to Eocene hyperthermals, marks the onset of a long‐term decline in d 13 C. The timing indicates it might be related to the initiation of volcanism along Greenland margin.
1] The accumulation of wind blown (eolian) dust in deep‐sea sediments reflects the aridity/humidity con-ditions of the continental region supplying the dust, as well as the "gustiness" of the climate system. Detailed studies of Pleistocene glacial‐interglacial dust fluxes suggest changes in accumulation rates cor-responding to orbital variations in solar insolation (Milankovitch cycles). While the orbital cycles found in sedimentary archives of the Pleistocene are intricately related to glacial growth and decay, similar global orbital signals recognized in deep‐sea sediments of early Paleogene age, the last major greenhouse interval ∼65–45 million years ago, could not have been linked to the waxing and waning of large ice sheets. Thus orbital signals recorded in early Paleogene sediments must reflect some other climate response to changes in solar insolation. To explore the potential connection between orbital forcing and the climate processes that control dust accumulation, we generated a high‐resolution dust record for ∼58 Myr old sediments from Shatsky Rise (ODP Site 1209, paleolatitude ∼15°N–20°N). The dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early Paleogene, indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate. Furthermore, the relative amplitude of the dust flux response during the early Paleogene greenhouse was comparable to that during icehouse climates. Thus, subtle variations in solar insolation driven by changes in Earth's orbit about the Sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial‐interglacial states. Components: 12,300 words, 6 figures, 3 tables.
The study focuses on the grain-size dependent distribution of particle-reactive, natural radionuclides (230Th, 231Pa, 10Be) in marine sediments from the Southern Ocean, the South East Atlantic, and the Equatorial Pacific. Particle-size specific isotope analyses show that a large amount (53-89 %) of the total 230Th is concentrated in clay-size material. It is discussed to what extent a lateral transport of fine particles could generate a biasing to particle flux calculations based on 230Th. In the Southern Ocean sediment the distribution of 231Pa and 10Be strongly depends on the concentration of biogenic silica of particles. 231Pa/230Th and 10Be/230Th in opal-rich particles largely exceed their production ratio in seawater. This supports the application of bulk 231Pa/230Th as a proxy for past opal fluxes to Southern Ocean sediments. The study of compound-specific 231Pa/230Th and 10Be/230Th, as conducted here, allows a more detailed picture of the origin of the isotopic signatures.
We show that helium-4 (4He) concentrations in a modern Porites coral from Cape Verde provides a robust reconstruction of mineral dust loading over the Eastern Tropical Atlantic from mid-1950's to mid-1990's. The 4He record demonstrates pronounced increases in dust emission from North Africa associated with the severe droughts in the Sahel. Our record provides direct evidence that dust emission rates in the 1950's, prior to the onset of the Sahel droughts, were a factor of nine lower than during 1980-84. This large change in dust emission rate indicates global aerosol contents would have increased by ~45% over this period, which may have contributed to a reduction in solar radiation reaching the Earth's surface. We find that dust emission from North Africa is most closely related to drought patterns, rather than to changes in atmospheric circulation patterns resulting from climate oscillations, such as North Atlantic Oscillations and El Nino/Southern Oscillation.
At four sites in the central equatorial Pacific Ocean the flux of extraterrestrial 3He, determined using the excess 230Th profiling method, is 8×10-13cm3STPcm-2ka-1. This supply rate is constant to within 30%. At these same sites, however, the burial rate of 3He, determined using chronostratigraphic accumulation rates, varies by more than a factor of 3. The lowest burial rates, which occur north of the equator at 1°N, 139°W are lower than the global average rate of supply of extraterrestrial 3He by 20% and indicate that sediment winnowing may have occurred. The highest burial rates, which are recorded at the equator and at 2°S, are higher than the rate of supply of extraterrestrial 3He by 100%, and these provide evidence for sediment focusing. By analyzing several proxies measured in core PC72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of 230Th,3He,10Be, Ti, and barite, with a maximum peak-to-trough amplitude of a factor of 6, take place systematically during glacial time. However, the ratio of any one proxy to another is constant to within 30% over the entire length of the records. Given that each proxy represents a different source (234U decay in seawater, interplanetary dust, upper atmosphere, continental dust, or upper ocean), our preferred interpretation for the covariation is that the climate-related changes in burial rates are driven by changes in sediment focusing.
Measurements of helium isotopes in particles separated from polar ice demonstrate that extraterrestrial ³He dominates the ³He flux at the GISP2 (Greenland) and Vostok (Antarctica) ice core sites. Replicate measurements of late Holocene ice samples yield ³He fluxes of 0.62±0.27×10−12 cm³ STP cm−2 ka−1 (GISP2) and 0.77 ± 0.25 × 10−12 cm³ STP cm−2 ka−1 (Vostok), similar to results from marine sediments. These are the first detailed measurements of ³He in particles from ice core samples, and they demonstrate the utility of the ice core record for evaluating the temporal history of the extraterrestrial dust flux. Results from Vostok samples from 1096–1403 m depth (75–97 ka B.P.) are similar to the late Holocene data, with the exception of two highly anomalous results from 1307 m. The latter probably indicate the presence of rare, large or gas-rich extraterrestrial particles.
1] We present a helium isotope record for core TT013-114PC from the central equatorial Pacific (140°W, 4°N, 4432 m water depth) spanning a period of 1 million years. We focus on the time interval from 560 to 800 kyr, largely coinciding with the mid-Pleistocene climate transition (MPT) when the dominant period of the Earth's climate variability shifted from 41 kyr to 100 kyr. The terrigenous 4 He concentrations from our study correlate very well with published titanium concentrations in this core strongly supporting the use of terrigenous 4 He as a monitor of continental dust. Normalizing titanium and terrigenous 4 He concentrations to 3 He suggests that the dust supply during the MPT was approximately 30% lower compared to the subsequent period (560–100 kyr). The 3 He-normalized barium, aluminum and phosphorus concentrations, trace elements with a predominantly biogenic source in these sediments, are relatively constant. This is in contrast to previous studies that reported an apparent rise of titanium-normalized productivity proxies. Rather than a significant increase in productivity during the MPT, we conclude that the dust flux to the central equatorial Pacific was reduced and that the export productivity was approximately constant during this period of climate reorganization.
Today, the ocean is characterized by pools of warm tropical–subtropical water bounded poleward and at depth by cold water. In the tropics and subtropics, the warm waters are floored at depth by the thermocline–pycnocline, which crops out on the ocean surface between the subtropical and polar frontal systems that form the poleward boundary. It is along and between the frontal systems that the thermocline waters enter the ocean interior. These frontal systems form beneath the maxima of the zonal component of the westerly winds. Today, the location of the westerly winds is stabilized by the persistent high-pressure systems at the polar regions produced by the ice cover of the Antarctic and sea-ice cover of the Arctic.
We present a detailed down-core analysis of helium isotope ratios and concentrations for bulk sediments from the central Equatorial Pacific that span the last two glacial-interglacial cycles. Measured ratios range from 1.0 × 10−5 to 2.1 × 10−4, or 7.4 to 149 times the atmospheric ratio. The 3He from interplanetary dust particles (IDPs) constitutes virtually all of the 3He measured within the sediment. Because carbonate accumulation rates are high in the Equatorial Pacific, the measured 3He concentrations are lower than have been measured elsewhere, and range from 4.7 × 10−13 to 3.0 × 10−12 cm3STP · g−1.If the cosmic dust 3He-flux is constant with time, sediment mass accumulation rates can be determined from the 3He concentration in sediments. The excess 230Th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in-situ decay of 234U in seawater. To first order, initial excess 230Th activities correlate with 3He concentrations within this core. Based on the 230Th results, we estimate the 3He-flux to the Earth's surface as (9.6 ± 2.0) × 10−16 cm3STP · cm−2 · a−1. If this flux has remained constant over extended periods of time, it can be used to determine sediment accumulation rates beyond the 230Th range (300,000 yr).
Analyses of marine carbonates through the interval 63.9 to 65.4 million years ago indicate a near-constant flux of extraterrestrial helium-3, a tracer of the accretion rate of interplanetary dust to Earth. This observation indicates that the bolide associated with the Cretaceous-Tertiary (K-T) extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower. The use of helium-3 as a constant-flux proxy of sedimentation rate implies deposition of the K-T boundary clay in (10 +/- 2) x 10(3) years, precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover.
Dust plays a critical role in Earth's climate system and serves as a natural source of iron and other micronutrients to remote regions of the ocean. We have generated records of dust deposition over the past 500,000 years at three sites spanning the breadth of the equatorial Pacific Ocean. Equatorial Pacific dust fluxes are highly correlated with global ice volume and with dust fluxes to Antarctica, which suggests that dust generation in interhemispheric source regions exhibited a common response to climate change over late-Pleistocene glacial cycles. Our results provide quantitative constraints on the variability of aeolian iron supply to the equatorial Pacific Ocean and, more generally, on the potential contribution of dust to past climate change and to related changes in biogeochemical cycles.
A continuous age model for the brief climate excursion at the Paleocene–Eocene boundary has been constructed by assuming a constant flux of extraterrestrial ^3He (^3He_(ET)) to the seafloor. ^3He_(ET) measurements from ODP Site 690 provide quantitative evidence for the rapid onset (<few kyr) and short duration (<120 kyr) of global warming and of the associated disturbance to the Earth’s surficial carbon budget at this time. These observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon, possibly from seafloor methane hydrate, as the proximal cause of the event. However, the ^3He_(ET) technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre-event values. The ^3He_(ET)-based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle, and so may indicate additional or accelerated mechanisms of carbon removal from the ocean–atmosphere system during this period. ^3He_(ET) was also measured at ODP Site 1051 to test the validity of the Site 690 chronology. Comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at Site 1051, an observation consistent with sediment structures and previous age modeling efforts. The Site 1051 age model shows a ∼30 kyr period in which climate proxies return toward pre-event values, after which they remain invariant for ∼80 kyr. If this rise represents the recovery interval identified at Site 690, then the ^3He_(ET)-based age models of the two sites are in good agreement. However, alternative interpretations are possible, and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion. Regardless of these details, this work shows that the ^3He_(ET) technique can provide useful independent evidence for the development and testing of astronomically calibrated age models.
We have determined the helium concentration and isotopic composition of a suite of early Maastrichtian through middle Eocene pelagic limestones in the Italian Apennines. The results provide a 35 Myr record of the implied flux of extraterrestrial ^3He, which is a proxy for the accretion rate of interplanetary dust particles (IDPs).
Our measurements show that the ^3He flux was fairly constant in the Maastrichtian, except for possible minor increases (factor of two or less) from ∼70.5 Ma to 68 Ma and at ∼66 Ma, which probably reflect transient increases in the accretion rate of asteroidal and/or cometary IDPs. We find no evidence for an increase in IDP accretion at or immediately before the K/T boundary, implying that the K/T impact was not associated with enhanced solar system dustiness. This observation precludes the possibility that the K/T impactor was a member of a major comet shower, and is more consistent with impact of a lone comet or asteroid. Our data suggest a 2 to 4 fold increase in IDP accretion between 57 and 54 Ma, followed by a factor of three decrease over an ∼4 Myr period in the early to middle Eocene. The duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets, and is more likely the result of collisions in the asteroid belt/and or Kuiper belt. In the entire 35 Myr record we find no evidence for major enhancements of the IDP accretion rate of the type expected from comet showers. Our results, in combination with earlier ^3He measurements, do not support models that predict recurrent comet showers with periods of <38 Myrs. If there is a periodicity in the cratering record that is caused by periodic modulation of the Oort cloud, it is not evident in the Apennine sediment data.
Along with the ^3He measurements we also obtained ^4He concentrations, which record temporal changes in the flux or composition of terrigenous matter. The most significant change in ^4He occurs in the last 4 Myrs of the Cretaceous, over which the concentration of ^4He in the detrital component rises by 300%. This rise tracks a strong increase in the seawater ^(87)Sr/^(86)Sr ratio, suggesting a globally significant change in the composition of continental detritus delivered to the oceans, possibly arising from increased continental weathering.
Samples collected from a depth transect of eight sites during Ocean Drilling Program Leg 198 to Shatsky Rise contain a remarkable sedimentary record of surface and deepwater circulation in the tropical Pacific over the past 120 m.y. In addition, basement sills recovered provide valuable constraints on the age and origin of the volcanic foundations of the rise. The sediments recovered contain evidence of the long-term transition from greenhouse to icehouse climate state and of several abrupt climate change events. Shatsky Rise cores contain an exceptional record of an Oceanic Anoxic Event (OAE1a) in the early Aptian (120 Ma), with some of the highest organic carbon contents measured in pelagic sediments. These strata contain exceptionally preserved organic compounds including the oldest known alkenones. Organic geochemistry suggests that bacterial activity played a significant role in sequestering organic carbon. Stable isotope data from Upper Cretaceous and Paleogene sediments reveal several abrupt switches in the sources of intermediate waters bathing Shatsky Rise. Neodymium isotopes also show evidence for these changes and help to identify source regions in the North Pacific, Southern Ocean, and, possibly, Tethys. Strong evidence exists in Shatsky cores for the mid-Maastrichtian (∼69 Ma) global extinction of inoceramids, a long-ranging, widespread group of bottom-dwelling clams. Stable and neodymium isotopes combined with biotic data show changes in intermediate water sources at this time as well as significant changes in surface water oceanography. Shatsky Rise sites contain high-quality records of the Cretaceous/Tertiary boundary event. Detailed nannofossil assemblage studies demonstrate that the survivor taxa are those that were adapted to unstable environmental conditions of shelves, including taxa that have cyst stages. The Paleogene sedimentary record from Shatsky Rise is strongly cyclic with variations in the amount of dissolution. Superimposed on this record are "hyperthermal" episodes including the Paleocene/Eocene Thermal Maximum (PETM; ∼55.0 Ma) and events in the early late Paleocene (∼58.4 Ma) and early Eocene (52.7 Ma). The PETM on Shatsky Rise contains evidence for 5°C warming of tropical sea-surface temperatures, major reorganization of benthic and planktonic communities, and pronounced short-term shoaling of the lysocline. Oxygen isotope and Mg/Ca data demonstrate warming of surface and intermediate waters (possibly combined with decreasing salinity) during the early Eocene and help constrain the timing of the acceleration of Antarctic glaciation during the middle Eocene. Recovery of basaltic sills provides valuable age and geochemical constraints for interpreting the origin of Shatsky Rise. Radiometric ages confirm previous suggestions that this large igneous province was emplaced rapidly. Isotope geochemistry shows a mid-ocean-ridge basalt signature that argues against a mantle plume origin. However, alternative origins are difficult to prove unequivocally.
We have measured the isotope ratios of helium contained in various terrigenous materials that contribute to deep-sea sediments. These materials include ice-rafted debris from the North Atlantic, Chinese Loess, and sediment collected at or near the mouths of three large rivers: the Amazon, the Ganges, and the Yangtze. We observe terrigenous 3He/4He ratios that vary from 1.8 × 10−9 to 4.6 × 10−7, i.e., values that are higher than the theoretically-derived range of 10−9 to 10−8.Atlantic and Pacific deep-sea sediment 3He/4He ratios can be explained by mixing of helium from similar extraterrestrial but different terrigenous sources. Terrigenous sources for North Atlantic and North Pacific sediments are characterized by 3He and 4He contents that are higher, and 3He/4He ratios that are lower, than those for central and eastern equatorial Pacific sediments. This is consistent with the supply to the North Atlantic and North Pacific oceans of older cratonic continental material that contains high amounts of in situ-produced nucleogenic and radiogenic helium. Terrigenous material transported to central and eastern equatorial Pacific sediments contains lower amounts of 3He and 4He and higher 3He/4He ratios, indicative of supply from a more juvenile Andean source.In the equatorial Atlantic (core V31-135), we have used previously-published 230Th data to determine an extraterrestrial 3He flux of (1.16 ± 0.15) × 10−12 cm3STP · cm−2 · ka−1, within error of that previously determined in sediments from the equatorial Pacific Ocean ([0.78 ± 0.29] × 10−13 cm3STP · cm−2 · ka−1; Marcantonio et al., 1996).
Thirty-nine sediments from 12 different sites, 10 sites in the western to central Pacific and two sites in the Atlantic Ocean, have been examined for He-3/He-4 ratios. The ratio is found to be larger than 5 x 10 to the -5th at six sites, well above the values generally observed in common terrestrial materials. This result is probably due to the input of extraterrestrial materials. Input of stratospheric dust of 1 ppm or less, which corresponds to a fallout rate of about 2000 tons per year, can explain the observations.
THE deposition rate of deep-sea sediments, and their focused redeposition by deep-sea currents, can be evaluated from analyses of sedimentary 230Th with a temporal resolution limited only by bioturbation6,7,10,11. 230Th is produced uniformly throughout the ocean by radioactive decay of dissolved 234U and is removed sufficiently fast by sorption onto sinking particles to act as a 'constant-flux' tracer of sedimentation rates. But the half-life of 230Th (75 kyr) limits its use for this purpose to the past 200–250 kyr. Here we explore the use of extraterrestrial 3He from interplanetary dust particles1–4 (IDPs) as a constant-flux proxy that is free from this limitation. A comparison of 3He with 230Th in two cores from the equatorial Pacific Ocean indicates that the variability in the mean flux of IDPs over the past 200 kyr is less than 75%. But in contrast to this relatively constant rate of supply of 3He to the deep sea, the local burial rates of 3He and 230Th have varied by a factor of five over the past 450 and 200 kyr, respect-ively. We interpret this variability as reflecting sediment focusing, with a temporal pattern that suggests regular cycles of climate-driven reorganization of near-bottom currents in the deep Pacific Ocean.
HELIUM-S concentrations and 3He/4He ratios in modern pelagic sediments are known to be far in excess of terrestrial values as a result of micrometeorite fallout1-3. Here I report that extraterrestrial helium is easily detected in a pelagic clay core dating back more than 70 Myr. The remarkable preservation of the extraterrestrial signature arises from high retention of 3He within interplanetary dust particles, coupled with loss of radiogenic 4He from terrestrial mineral grains. The core provides a continuous record of the fallout of extraterrestrial helium for the Cenozoic era. This record suggests that there have been significant variations in the influx of interplanetary dust through time, probably related to asteroidal breakup events or the passage of comets through the inner Solar System. The results also show 3He to be a far more sensitive tracer of the interplanetary dust flux than is iridium.
The cause of the 100 kyr glacial–interglacial cycles during the past 800 kyr is one of the fundamental puzzles in paleoclimatology. The widely accepted Milankovitch theory, relating earth's climate cycles to variations in insolation caused by periodic changes in orbital parameters, has difficulties to explain the predominant 100 kyr rhythm. Although earth's eccentricity varies with a period of 100 kyr, the resulting change in insolation is too small to produce the corresponding climate cycle by direct forcing (Imbrie et al., Paleoceanography 8 (1993) 699). In order to solve the '100 kyr problem', Muller and MacDonald (Nature 377 (1995) 107; Science 277 (1997a) 215; Proc. Nat. Acad. Sci. USA 94 (1997b) 8329) proposed an alternative orbital but non-Milankovitch mechanism attributing the glacial cycles to regular variations in the accretion of interplanetary dust particles (IDP) caused by 100 kyr cycles in the orbital inclination of the earth. To test this controversial hypothesis, we study the IDP accumulation in deep-sea sediments from a period in the early Pleistocene. We find apparent 41 kyr cycles but no 100 kyr periodicity in the IDP accumulation rate. As there is no known mechanism to produce 41 kyr cycles in IDP supply from space, we conclude that the 41 kyr cycles are caused by the dynamics of sediment accumulation, and that changes in the IDP flux do not drive the Pleistocene glacial cycles.
Abstract— Measurements of He isotopes in cluster interplanetary dust particles (IDPs) from stratospheric dust collector L2009 reveal anomalous 3He/4He ratios comparable to those seen earlier, up to ∼40x the solar wind ratio, in particles from the companion collector L2011. These overabundances of 3He in the L2009 samples are masked by much higher 4He contents compared to the L2011 particles, and are visible only in minor gas fractions evolved by stepwise heating at high temperatures.
Cosmic-ray induced spallogenic reactions are efficient producers of 3He. The majority of this paper is devoted to a detailed assessment of the possible role of spallation in generating the 3He excesses in these and other cluster IDPs. A model of collisional erosion and fragmentation during inward transit through the interplanetary dust environment is used to estimate space lifetimes of particles from asteroidal and Edgeworth–Kuiper Belt sources. Results of the modeling indicate that Poynting–Robertson orbital evolution timescales of IDPs small enough to elude destruction on their way to Earth from either location are far shorter than the cosmic-ray exposure ages required to account for observed 3He overabundances. Grains large enough to have sufficiently long space residence times are fragmented close to their sources.
An alternative to long in-space exposure could be prolonged irradiation of particles buried in parent body regoliths prior to their ejection as IDPs. A qualitative calculation suggests, however, that collisional erosion of asteroidal upper-regolith materials is likely to occur on timescales shorter than the > 1 Ga burial times needed for accumulation of spallogenic 3He to the levels seen in several cluster particles. In contrast, regoliths on Edgeworth–Kuiper Belt objects may be stable enough to account for the 3He excesses, and delivery of heavily pre-irradiated IDPs to the inner solar system by short-period Edgeworth–Kuiper Belt comets remains a possibility. A potential problem is that the expected associated abundances of spallation-produced 21Ne appear to be absent, although here the present IDP data base is too sparse and for the most part too imprecise to rule out a spallogenic origin. Relatively short periods of pre-ejection residence in asteroidal regoliths may be responsible for the curiously broad exposure age distributions reported for micrometeorites extracted from Greenland and sea-floor sediments.
Abstract— We report mass-spectrometric measurements of light noble gases pyrolytically extracted from 28 interplanetary dust particles (IDPs) and discuss these new data in the context of earlier analyses of 44 IDPs at the University of Minnesota. The noble gas database for IDPs is still very sparse, especially given their wide mineralogic and chemical variability, but two intriguing differences from isotopic distributions observed in lunar and meteoritic regolith grains are already apparent. First are puzzling overabundances of 3He, manifested as often strikingly elevated 3He/4He ratios—up to >40x the solar-wind value—-and found primarily but not exclusively in shards of some of the larger IDPs (“cluster particles”) that fragmented on impact with the collectors carried by high-altitude aircraft. It is difficult to attribute these high ratios to 3He production by cosmic-ray-induced spallation during estimated space residence times of IDPs, or by direct implantation of solar-flare He. Minimum exposure ages inferred from the 3He excesses range from ∼50 Ma to an impossible >10 Ga, compared to Poynting-Robertson drag lifetimes for low-density 20–30 μm particles on the order of ∼0.1 Ma for an asteroidal source and ∼10 Ma for origin in the Kuiper belt. The second difference is a dominant contribution of solar-energetic-particle (SEP) gases, to the virtual exclusion of solar-wind (SW) components, in several particles scattered throughout the various datasets but most clearly and consistently observed in recent measurements of a group of individual and cluster IDPs from three different collectors. Values of the SEP/SW fluence ratio in interplanetary space from a simple model utilizing these data are ∼1% of the relative SEP/SW abundances observed in lunar regolith grains, but still factors of approximately 10–100 above estimates for this ratio in low-energy solar particle emission.
Fluxes of continental mineral aerosols (dust) were greater during glacial periods than during interglacials throughout most regions of the Earth. The equatorial Pacific Ocean was a possible exception to this pattern in that previous studies have reported either greater dust fluxes during interglacials or no consistent glacial–interglacial pattern of dust flux. We have applied the 230Th-normalization technique to derive five new records of dust flux from central equatorial Pacific Ocean sediments. In contrast to previous studies, which relied on stratigraphic accumulation rates, the 230Th-normalization technique produces internally consistent results, revealing fluxes to this region of continental lithogenic material that were positively correlated with global ice volume throughout the past 300,000 yr. Maximum glacial fluxes of continental mineral aerosols exceed minimum interglacial fluxes by about a factor of 2, similar to changes found elsewhere at low and mid-latitudes. This amplitude of variability is substantially smaller than that seen in some recent models, and these observations provide a calibration point for future model development.
A continuous age model for the brief climate excursion at the Paleocene–Eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3He (3HeET) to the seafloor. 3HeET measurements from ODP Site 690 provide quantitative evidence for the rapid onset (<few kyr) and short duration (<120 kyr) of global warming and of the associated disturbance to the Earth’s surficial carbon budget at this time. These observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon, possibly from seafloor methane hydrate, as the proximal cause of the event. However, the 3HeET technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre-event values. The 3HeET-based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle, and so may indicate additional or accelerated mechanisms of carbon removal from the ocean–atmosphere system during this period. 3HeET was also measured at ODP Site 1051 to test the validity of the Site 690 chronology. Comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at Site 1051, an observation consistent with sediment structures and previous age modeling efforts. The Site 1051 age model shows a ∼30 kyr period in which climate proxies return toward pre-event values, after which they remain invariant for ∼80 kyr. If this rise represents the recovery interval identified at Site 690, then the 3HeET-based age models of the two sites are in good agreement. However, alternative interpretations are possible, and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion. Regardless of these details, this work shows that the 3HeET technique can provide useful independent evidence for the development and testing of astronomically calibrated age models.
In the eastern equatorial Indian Ocean, the flux of extraterrestrial 3He, a proxy of interplanetary dust particles (IDPs), has been relatively constant over the past 200 ka. The flux is equal to (1.1±0.4)×10−12 cm3 STP cm−2 ka−1, a value obtained using the xs230Th profiling method. Variations in mass accumulation rates (MARs) derived assuming a constant extraterrestrial 3He flux have a 40-ka periodicity similar to that observed in the δ18O-derived MARs. This frequency is similar to that of the Earth's obliquity. Measured 187Os/188Os ratios are less radiogenic than present-day seawater (0.49–0.98), reflecting the mixing of Os derived from extraterrestrial, terrigenous and hydrogenous sources. When coupled with He data measured on the same samples, Os isotope data yield important information about the terrigenous component supplied to the eastern equatorial Indian Ocean. The amount of Os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics. Once corrected for the extraterrestrial component of Os, Os isotope signatures, in conjunction with the 4He concentrations, suggest a supply of terrigenous material from Indonesian ultramafic and Himalayan crustal sources that clearly varies through time.
Sediments from western Arabian Sea core 74KL representing the last 23 ka were analyzed for helium, thorium, and protactinium isotopes. Assuming global average fluxes of extraterrestrial 3He and 230Th, the average 3He-derived sediment mass accumulation rate (MAR) is a factor of 1.8 higher than the average 230Th-derived MAR. 3He- and 230Th-derived MARs converge, however, during the Younger Dryas (YD) and during the peak of the early Holocene humid interval. These features, not seen anywhere else in the world, probably reflect a combination of climate-driven changes in the flux of 230Th and 3He. Ratios of xs231Pa/xs230Th, proxies of paleoproductivity, are lowest during the last glacial maximum (LGM), and increase abruptly during the Bolling–Allerod. Later, following a sudden decrease to near-LGM values during the YD, they rise abruptly to maximum values for the entire record in the early Holocene. We hypothesize that low xs231Pa/xs230Th ratios reflect low productivity due to the decreased intensity of the SW monsoon, whereas the opposite is true for high ratios. The correlation between Arabian Sea productivity and monsoonal upwelling, on the one hand, and North Atlantic climate variability, on the other, suggests a linkage between high- and low-latitude climates caused by changing patterns of atmospheric circulation.
Atmospheric dust levels may play important roles in feedbacks linking continental source areas, tropical convection, marine productivity, and global climate. These feedbacks appear to be particularly significant in the tropical Pacific, where variations in local convection and productivity have been demonstrated to have impacts on climate at higher latitudes. Modeling of past dust levels and related feedbacks has been limited, however, by a paucity of observational data. In this study we present a temporal and spatial survey of dust fluxes to the eastern equatorial Pacific over the past 30 kyr. Glacial and Holocene fluxes of 232Th, a proxy for continental material, were calculated by normalization to 230Th from a north–south transect of cores along 110°W between 3°S and 7°N (ODP sites 848–853). Fluxes were 30–100% higher during the last glacial, suggesting increased dustiness in both hemispheres during the glacial period. In both time periods, dust fluxes decrease towards the south, reflecting scavenging of Northern Hemisphere dust by precipitation at the ITCZ. The Holocene meridional dust flux gradient between 7°N and 3°S is characterized by a steep drop in dust levels at the southern edge of the modern range of the ITCZ, while the gradient is shallower and more nearly linear during the last glacial. This change may indicate that the glacial ITCZ in this region was a less effective barrier to inter-hemispheric dust transport, most likely due to a decrease in convective intensity and precipitation during the last glacial; alternatively, the change in gradient may be explained by increased variability in the location of the glacial ITCZ. Our data do not appear to require a mean southerly displacement of the glacial ITCZ, as suggested by the results of other studies.
We have determined the helium concentration and isotopic composition of a suite of early Maastrichtian through middle Eocene pelagic limestones in the Italian Apennines. The results provide a 35 Myr record of the implied flux of extraterrestrial 3He, which is a proxy for the accretion rate of interplanetary dust particles (IDPs).Our measurements show that the 3He flux was fairly constant in the Maastrichtian, except for possible minor increases (factor of two or less) from ∼70.5 Ma to 68 Ma and at ∼66 Ma, which probably reflect transient increases in the accretion rate of asteroidal and/or cometary IDPs. We find no evidence for an increase in IDP accretion at or immediately before the K/T boundary, implying that the K/T impact was not associated with enhanced solar system dustiness. This observation precludes the possibility that the K/T impactor was a member of a major comet shower, and is more consistent with impact of a lone comet or asteroid. Our data suggest a 2 to 4 fold increase in IDP accretion between 57 and 54 Ma, followed by a factor of three decrease over an ∼4 Myr period in the early to middle Eocene. The duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets, and is more likely the result of collisions in the asteroid belt/and or Kuiper belt. In the entire 35 Myr record we find no evidence for major enhancements of the IDP accretion rate of the type expected from comet showers. Our results, in combination with earlier 3He measurements, do not support models that predict recurrent comet showers with periods of <38 Myrs. If there is a periodicity in the cratering record that is caused by periodic modulation of the Oort cloud, it is not evident in the Apennine sediment data.Along with the 3He measurements we also obtained 4He concentrations, which record temporal changes in the flux or composition of terrigenous matter. The most significant change in 4He occurs in the last 4 Myrs of the Cretaceous, over which the concentration of 4He in the detrital component rises by 300%. This rise tracks a strong increase in the seawater 87Sr/86Sr ratio, suggesting a globally significant change in the composition of continental detritus delivered to the oceans, possibly arising from increased continental weathering.
The first complete cyclic sedimentary successions for the early Paleogene from drilling multiple holes have been retrieved during two ODP expeditions: Leg 198 (Shatsky Rise, NW Pacific Ocean) and Leg 208 (Walvis Ridge, SE Atlantic Ocean). These new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the Atlantic and the Pacific Oceans covering the entire Paleocene epoch based on the identification of the stable long-eccentricity cycle (405-kyr). High resolution X-ray fluorescence (XRF) core scanner and non-destructive core logging data from Sites 1209 through 1211 (Leg 198) and Sites 1262, 1267 (Leg 208) are the basis for such a robust chronostratigraphy. Former investigated marine (ODP Sites 1001 and 1051) and land-based (e.g., Zumaia) sections have been integrated as well. The high-fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into Greenhouse climate variability in the early Paleogene. We demonstrate that the Paleocene epoch covers 24 long eccentricity cycles. We also show that no definite absolute age datums for the K/Pg boundary or the Paleocene–Eocene Thermal Maximum (PETM) can be provided by now, because of still existing uncertainties in orbital solutions and radiometric dating. However, we provide two options for tuning of the Paleocene which are only offset by 405-kyr. Our orbitally calibrated integrated Leg 208 magnetostratigraphy is used to revise the Geomagnetic Polarity Time Scale (GPTS) for Chron C29 to C25. We established a high-resolution calcareous nannofossil biostratigraphy for the South Atlantic which allows a much more detailed relative scaling of stages with biozones. The re-evaluation of the South Atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron C28r, C27n, and C26n.
The accumulation of extraterrestrial 3He, a tracer for interplanetary dust particles (IDPs), in sediments from the Ontong Java Plateau (OJP; western equatorial Pacific Ocean) has been shown previously to exhibit a regular cyclicity during the late Pleistocene, with a period of ∼100 ka. Those results have been interpreted to reflect periodic variability in the global accretion of IDPs that, in turn, has been linked to changes in the inclination of Earth’s orbit with respect to the invariable plane of the solar system. Here we show that the accumulation in OJP sediments of authigenic 230Th, produced by radioactive decay of 234U in seawater, exhibits a 100-ka cyclicity similar in phase and amplitude to that evident in the 3He record. We interpret the similar patterns of 230Th and 3He accumulation to reflect a common origin within the ocean–climate system. Comparing spatial and temporal patterns of sediment accumulation against regional patterns of biological productivity and against the well-established pattern of CaCO3 dissolution in the deep Pacific Ocean leads to the further conclusion that a common 100-ka cycle in accumulation of biogenic, authigenic and extraterrestrial constituents in OJP sediments reflects the influence of climate-related changes in sediment focusing, rather than changes in the rate of production or supply of sedimentary constituents.
To better understand the composition, characteristics of helium diffusion, and size distribution of interplanetary dust particles (IDPs) responsible for the long-term retention of extraterrestrial 3He, we carried out leaching, stepped heating, and sieving experiments on pelagic clays that varied in age from 0.5 Ma to ∼90 Myr. The leaching experiments suggest that the host phase(s) of 3He in geologically old sediments are neither organic matter nor refractory phases, such as diamond, graphite, Al2O3, and SiC, but are consistent with extraterrestrial silicates, Fe–Ni sulfides, and possibly magnetite. Stepped heating experiments demonstrate that the 3He release profiles from the magnetic and non-magnetic components of the pelagic clays are remarkably similar. Because helium diffusion is likely to be controlled by mineral chemistry and structure, the stepped heating results suggest a single carrier that may be magnetite, or more probably a phase associated with magnetite. Furthermore, the stepped outgassing experiments indicate that about 20% of the 3He will be lost through diffusion at seafloor temperatures after 50 Myrs, while sedimentary rocks exposed on the Earth’s surface for the same amount of time would lose up to 60%. The absolute magnitude of the 3He loss is, however, likely to depend upon the 3He concentration profile within the IDPs, which is not well known. Contrary to previous suggestions that micrometeorites in the size range of 50–100 μm in diameter are responsible for the extraterrestrial 3He in geologically old sediments [Stuart, F.M., Harrop, P.J., Knott, S., Turner, G., 1999. Laser extraction of helium isotopes from Antarctic micrometeorites: source of He and implications for the flux of extraterrestrial 3He flux to earth. Geochim. Cosmochim. Acta63, 2653–2665], our sieving experiment demonstrates that at most 20% of the 3He is carried by particles greater than 50 μm in diameter. The size-distribution of the 3He-bearing particles implies that extraterrestrial 3He in sediments record the IDP flux rather than the micrometeorite flux.
The mass accumulation rates (MARs) of aeolian dust in the ocean basins provide an important record of climate in the continental source regions of atmospheric dust and of the prevailing wind patterns responsible for dust transport in the geologic past. The incorporation of other terrigenous components such as volcanic ashes in seafloor sediments, however, often obscures the aeolian dust record. We describe a new approach which uses the delivery rate of crustal ⁴He to seafloor sediments as a proxy for the mass accumulation rate of old continental dust which is unaffected by the addition of other terrigenous components.
The influx of extraterrestrial (ET) matter on the Earth results in appreciable fluxes of 3He originating from several different processes. We have analyzed the published data on the observed concentrations of 3He in interplanetary dust particles (IDPs) sampled in the stratosphere, in polar ice samples, and in meteorites. This information, considered together with production of secondary fragments during the atmospheric entry of meteoroids, allows us to make plausible estimates of fluxes of the extra-terrestrial fluxes of the two principal 3He types accreted along with the extraterrestrial materials: (i) solar wind (SW) and solar energetic particle (SEP) 3He implanted in ET particles, and (ii) 3He produced in the ET matrix by interactions of galactic cosmic ray (GCR) particles. An appreciable fraction of 3He brought to the Earth by ET particles is expected to be lost from the particles during ablation and fragmentation of the particles during their transit through the atmosphere. By comparing the measured 3He fluxes in two terrestrial archives, polar ice and marine sediments, and based on supplementary data (3He / 4He and 20Ne / 22Ne ratios), we have attempted to determine the relative fluxes of solar (SW and SEP) and GCR 3He that are preserved in them.
We have modeled atmospheric entry heating of interplanetary dust to characterize the population of particles carrying extraterrestrial He to the seafloor. We find that ∼0.5% of the mass and ∼4% of the surface area of the infalling dust transits the atmosphere at temperatures lower than that required for He release (∼600°C). Size-dependent heating causes the particles which retain He to be far smaller than those in the parental interplanetary dust population. The particle-size distribution of He-bearing dust is such that most of the mass is delivered by particles of ∼20 μm diameter, while most of the surface area (relevant for surface-correlated constituents, e.g., implanted solar wind He) is carried by particles of ∼7 μm diameter. Knowledge of these size distributions allows us to evaluate the possibility of sedimentary redistribution of extraterrestrial dust in the atmosphere and ocean. The size distributions also have important consequences for interpretation of He abundances in seafloor sediment samples that integrate over fairly small areas and times. Sediment samples generally will not record a representative distribution of interplanetary dust but will have a strong tendency to undersample rare large particles. We predict a high degree of variability in replicate He analyses of a single sediment sample, with a mass-correlated He component yielding greater variability than a surface-correlated component. Comparison with sediment measurements confirms such variability and demonstrates excellent agreement with the statistical distribution expected for a surface correlated component, consistent with suggestions that seafloor extraterrestrial He is surface-correlated implanted solar wind or solar flare He. A second important statistical effect is that sediment measurements systematically underestimate the true extraterrestrial He flux, typically by 50%.
We have measured the helium abundance and isotopic composition of a suite of Lower Ordovician marine limestones and associated fossil meteorites from Kinnekulle, Sweden. Limestone 3He/4He ratios as high as 11.5 times the atmospheric value in fused samples and up to 23 times atmospheric in a single step-heat fraction indicate the presence of extraterrestrial helium, and demonstrate that at least a fraction of the extraterrestrial 3He carried by interplanetary dust particles must be retained against diffusive and diagenetic losses for up to 480 Ma. The carrier phase has not been identified but is not magnetic. Extrapolation of high-temperature 3He diffusivities in these sediments is consistent with strong retention of extraterrestrial 3He under ambient Earth-surface conditions. Combination of the observed helium concentrations with sedimentation rates estimated from conodont biostratigraphy suggest that the flux of extraterrestrial 3He in the Early Ordovician was about 0.5 x 10(-12) cm3 STP cm-2 ka-1, ignoring potential post-deposition helium loss. This value is indistinguishable from the average 3He flux estimated for the Cenozoic Era. In contrast, previous studies of fossil meteorites, Ir abundances, and Os isotopic ratios in the limestone suggest that the total accretion rate of extraterrestrial material during the studied interval was at least an order of magnitude higher than the Cenozoic average. This disparity may reflect significant post-depositional loss of 3He from IDPs within these old limestones; if so, the match between the Ordovician flux and the Cenozoic average would be fortuitous. Alternatively, the size distribution of infalling objects during the Early Ordovician may have been enriched only in extraterrestrial material too large to retain 3He during atmospheric entry heating (> approximately 30 micrometers). The fossil meteorites themselves also preserve extraterrestrial helium. Meteorite 3He concentrations of 2 to 9 x 10(-12) cm3 STP g-1 are several orders of magnitude lower than found in most modern meteorites, suggesting very substantial helium loss (probably >99.9%) from these chemically altered objects. The Meteorites carry 3He concentrations only a factor of a few higher than the host limestones. The meteorites themselves cannot be the source of the extraterrestrial 3He observed in the limestones.
Polar ice provides an archive for the influx of cosmic dust. Here, we present a high-resolution, glacial-to-interglacial record of cosmic dust using helium isotope analysis of the European Project for Ice Coring in Antarctica (EPICA) ice core drilled in Dronning Maud Land. We obtained a relatively constant 3He flux over the past 30,000 years. This finding excludes 3He as a pacemaker of late Pleistocene glacial cycles. Rather, it supports 3He as a constant flux parameter in paleoclimatic studies. A last glacial-to-Holocene shift of the 4He/non-sea salt Ca2+ ratio appears to indicate a glacial-to-interglacial change in the terrestrial dust source.
Fragments from 20 individual particles, collected in the earth's stratosphere and believed to be interplanetary dust particles (IDPs), were subjected to step-heating to see if differences in the release pattern for He-4 could be observed which might provide clues to the origin of the particles. Comparisons were made to the release pattern for 18 individual lunar surface grains heated in the same manner. Twelve of the IDP fragments contained an appreciable amount of He-4, 50 percent of which was released by the time the particles were heated to approximately 630 C. For the 18 individual lunar grains, the corresponding average temperature was 660 C. The He-3/He-4 ratios found for these fragments agreed well with those found for deep Pacific magnetic fines believed to be of extraterrestrial origin, and were comparable to those which have been observed for the solar wind and lunar surface soil grains. Four of the IDP fragments contained appreciably less He-4, and this was released at a higher temperature. The remaining four fragments had too little He-4 to permit a determination. From Flynn's analyses of the problem of the heating of IDPs in their descent in the atmosphere, the present results suggest that the parent IDPs of the 12 particles which contained an appreciable amount of He-4 suffered very little heating in their descent and are likely of asteroidal origin, although one cannot rule out the possibility that at least some of them had a cometary origin and entered the earth's atmosphere at a grazing angle.
He and Ne isotope ratios were determined for 16 interplanetary dust particles (IDPs) collected in the stratosphere. The observed He concentration varied greatly from particle to particle, with the highest values approaching those found for lunar surface fines and some gas-rich meteorites. The average Ne-20/Ne-22 ratio was 12.0 + or - 0.5. The data suggest that the observed IDPs could have entered the atmosphere at relatively low velocities, and hence may be primarily of asteroidal rather than cometary origin.
Leg 198 synthesis: a remarkable 120-m.y. record of climate and oceanography from Shatsky Rise, northwest Pacific Ocean Accretion of interplanetary dust in polar ice
- T J Bralower
- I P Silva
- M J Malone
- Tx
- E J Brook
- M D Kurz
- J Curtice
- S Cowburn
Bralower, T.J., Silva, I.P., Malone, M.J., 2002. Leg 198 synthesis: a remarkable 120-m.y. record of climate and oceanography from Shatsky Rise, northwest Pacific Ocean. Ocean Drilling Program, College Station, TX. Brook, E.J., Kurz, M.D., Curtice, J., Cowburn, S., 2000. Accretion of interplanetary dust in polar ice. Geophys. Res. Lett. 27 (19), 3145–3148.
Extraction of helium from individual interplanetary dust Ozima High 3He/4He ratios in ocean sediments
- A O Nier
- D J Schlutter
Nier, A.O., Schlutter, D.J., 1992. Extraction of helium from individual interplanetary dust Ozima, M., Takayanagi, M., Zashu, S., Amari, S., 1984. High 3He/4He ratios in ocean sediments. Nature 31, 448–450.
Depth variations in the flux of 4 He crustal derived using the 3 He-calculated MARs. The flux of 4 He crustal is an estimate of the flux of windblown dust from the continents. For the most part, highest 4 He crustal fluxes coincide with peaks in eccentricity
- Fig Marcantonio
Fig. 5. Depth variations in the flux of 4 He crustal derived using the 3 He-calculated MARs.
The flux of 4 He crustal is an estimate of the flux of windblown dust from the continents.
For the most part, highest 4 He crustal fluxes coincide with peaks in eccentricity.
F. Marcantonio et al. / Earth and Planetary Science Letters 287 (2009) 24–30
High 3He/4He ratios in ocean sediments
- Ozima