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1.
Records of the past neodymium (Nd) isotope composition of the deep ocean can resolve ambiguities in the interpretation of other tracers. We present the first Nd isotope data for sedimentary benthic foraminifera. Comparison of the ?Nd of core-top foraminifera from a depth transect on the Cape Basin side of the Walvis Ridge to published seawater data, and to the modern dissolved SiO2–?Nd trend of the deep Atlantic, suggests that benthic foraminifera represent a reliable archive of the deep water Nd isotope composition. Neodymium isotope values of benthic foraminifera from ODP Site 1264A (Angola Basin side of the Walvis Ridge) from the last 8 Ma agree with Fe–Mn oxide coatings from the same samples and are also broadly consistent with existing fish teeth data for the deep South Atlantic, yielding confidence in the preservation of the marine Nd isotope signal in all these archives. The marine origin of the Nd in the coatings is confirmed by their marine Sr isotope values. These important results allow application of the technique to down-core samples.The new ?Nd datasets, along with ancillary Cd/Ca and Nd/Ca ratios from the same foraminiferal samples, are interpreted in the context of debates on the Neogene history of North Atlantic Deep Water (NADW) export to the South Atlantic. In general, the ?Nd and δ13C records are closely correlated over the past 4.5 Ma. The Nd isotope data suggest strong NADW export from 8 to 5 Ma, consistent with one interpretation of published δ13C gradients. Where the ?Nd record differs from the nutrient-based records, changes in the pre-formed δ13C or Cd/Ca of southern-derived deep water might account for the difference. Maximum NADW-export for the entire record is suggested by all proxies at 3.5–4 Ma. Chemical conditions from 3 to 1 Ma are totally different, showing, on average, the lowest NADW export of the record. Modern-day values again imply NADW export that is about as strong as at any stage over the past 8 Ma.  相似文献   

2.
While ocean circulation is driven by the formation of deep water in the North Atlantic and the Circum-Antarctic, the role of southern-sourced deep water formation in climate change is poorly understood. Here we address the balance of northern- and southern-sourced waters in the South Atlantic through the last glacial period using neodymium isotope ratios of authigenic ferromanganese oxides in thirteen deep sea cores from throughout the South Atlantic. The data indicate that northern-sourced water did not reach the Southern Ocean during the late glacial, and was replaced by southern-derived intermediate and deep waters. The high-resolution neodymium isotope record (~ 300 yr sample spacing) from two spliced deep Cape Basin sites indicates that over the last glacial period northern-sourced water mass export to the Southern Ocean was stronger during the major Greenland millennial warming intervals (and Southern Hemisphere cool periods), and particularly during the major interstadials 8, 12, and 14. Northern-sourced water mass export was weaker during Greenland stadials and reached minima during Heinrich Events. The benthic foraminiferal carbon isotopes in the same Cape Basin core reflect a partial control by Southern Hemisphere climate changes and indicate that deep water formation and ventilation occurred in the Southern Ocean during major Greenland cooling intervals (stadials). Together, neodymium isotopes and benthic carbon isotopes provide new information about water mass sourcing and circulation in deep Southern Ocean waters during rapid glacial climate changes. Combining carbon and neodymium isotopes can be used to monitor the relative proportion of northern- and southern-sourced waters in the Cape Basin to gain insight into the processes which control the carbon isotopic composition of deep waters. In this study we show that deep water formation and circulation was more important than biological productivity and nutrient regeneration changes for controlling the carbon isotope chemistry of Antarctic Bottom Water during millennial-scale glacial climate cycles. This observation also lends support to the hypothesis that ocean circulation is linked to interhemispheric climate changes on short timescales, and that ventilation in the glacial ocean rapidly switched between the northern and Southern Hemisphere on millennial timescales.  相似文献   

3.
Based on the oxygen and carbon stable isotopic records of benthic foraminifera in nine deep-sea cores of the South China Sea (SCS), the bathymetric profiles of δ18O and δ13C since the last glacial maximum (LGM) are preliminarily established. The bathymetric gradients of deep-water δ18O and δ13C in the SCS are obviously greater during the LGM than during the Holocene, showing the existence of the deep thermocline and nutricline at water depth of about 2 000 m. Particularly, the differences in δ18O and δ13C between the LGM and Holocene, from which the ice-volume effect and the global mean shift have been subtracted respectively, are positive values at water depths of 1 000–2 500 m in the SCS. This indicates the existence of deep-water mass with relatively cool temperature or higher salinity, better ventilation and more δ13C within the water depth range of the SCS during the LGM, which is distinctly different from that at present. These changes further confirm the existence of the glacial “North Pacific Deep Water” which, however, is possibly confined to the water depth range of 1 000–2 500 m. Project supported by the National Natural Science Foundation of China (Grant Nos. 49576286 and 49732060).  相似文献   

4.
High resolution benthic foraminiferal stable isotopes (δ18O, δ13C) and molecular biomarkers in the sediments are used here to infer rapid climatic changes for the last 8200 years in the Ría de Muros (NW Iberian Margin). Benthic foraminiferal δ18O and δ13C potentially register migrations in the position of the hydrographic front formed between two different intermediate water masses: Eastern North Atlantic Central Water of subpolar origin (ENACWsp) and subtropical origin (ENACWst). The molecular biomarkers in the sediment show a strong coupling between continental organic matter inputs and negative δ13C values in benthic foraminifera. The rapid centennial and millennial events registered in these records have been compared with two well known North Atlantic Holocene records from the subtropical Atlantic sea surface temperatures (SST) anomalies off Cape Blanc, NW Africa and the subpolar Atlantic (Hematite Stained Grains percentage, subpolar North Atlantic). Comparison supports a strong link between high- and low-latitude climatic perturbations at centennial–millennial time scales during the Holocene. Spectral analyses also points to a pole-to-equator propagation of the so-called 1500 yr cycles. Our results demonstrate that during the Holocene, the NW Iberian Margin has undergone a series of rapid events which are likely triggered at high latitudes in the North Atlantic and are rapidly propagated towards lower latitudes. Conceivably, the propagation of these rapid climatic changes involves a shift in atmospheric and oceanic circulatory systems.  相似文献   

5.
Carbon and oxygen isotopic determinations have been made of 29 species of Recent Indian Ocean planktonic foraminifera. Fourteen core-top samples were used and as many as 18 species were chosen from a single core-top sample. The δ13C of the foraminifera was compared with that of total dissolved CO2 (ΣCO2) and of calcite precipitated in isotopic equilibrium with ΣCO2. The foraminiferal calcite is always at least 1.2‰ less than the value estimated for equilibrium calcite. This carbon isotopic disequilibrium suggests the partial utilization of13C-depleted metabolic CO2. The calcite tests of several species, however, have δ13C values which are similar to the δ13C of ΣCO2 in seawater. This relationship suggests that important paleohydrographic information may be obtained from carbon isotope records based on analyses of several foraminiferal species from single deep-sea sediment samples.  相似文献   

6.
Seven Miocene Pacific Ocean Deep Sea Drilling Project sites from four different water masses (planktonic foraminiferal biogeographic regions) have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal δ13C records in DSDP Site 289. The correlations are based on the assumption that there are global or at least Pacific-wide controls on the δ13C of deep-water HCO3?. Each of the individual δ13C records is correlated to Site 289 based on the shape of the curves in a manner analogous to that used to correlate sea-floor magnetic anomaly patterns.The results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to ±100,000 years. Correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than ±200,000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences. Carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized, globally applicable, correlation tool (with an interregional precision of ±100,000 years or better) as more continuous and undisturbed deep-sea sections become available as a result of the Hydraulic Piston Coring Program.  相似文献   

7.
The evolution of interocean carbon isotopic gradients over the last 2.5 m.y. is examined using high-resolution δ13C records from deep sea cores in the Atlantic and Pacific Oceans. Over much of the Northern Hemisphere ice ages, relative reductions in North Atlantic Deep Water production occur during ice maxima. From 2.5 to 1.5 Ma, glacial reductions in NADW are less than those observed in the late Pleistocene. Glacial suppression of NADW intensified after 1.5 Ma, earlier than the transition to larger ice sheets around 0.7 Ma. At a number of times during the Pleistocene, δ13C values at DSDP Site 607 in the North Atlantic were indistinguishable from eastern equatorial Pacific δ13C values from approximately the same depth (ODP Site 677), indicating significant incursions of low δ13C water into the deep North Atlantic. Atlantic/Pacific δ13C values converge during glaciations between 1.13-1.05 m.y., 0.83-0.70 m.y., and 0.46-0.43 m.y. This represents a pseudo-periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing. This partial decoupling, at low frequencies, of the δ18O and δ13C signals at Site 607 indicates that variations in North Atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing.  相似文献   

8.
To constrain short-term changes of climate and oceanography in the northern South China Sea(SCS)over interglacial marine isotope stage(MIS)5.5,we studied planktic and benthic 18O records of seven marine sediment cores with a time resolution of70–700 yr.Using 6–8 tie points the planktic records were tuned to the U/Th chronology of speleothem 18O records in China and Europe.The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11(HS-11)near 128.4 ka.HS-11 matches a 2300-yr long positive 18O excursion by 1.5/0.8‰both in planktic and benthic 18O records.Hence half of the planktic 18O signal was linked to increased upwelling of18O-and12C-enriched deep waters in the southwestern SCS.The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait,that form a boundary current along the northern slope of the SCS,building a major sediment drift.At its lower margin near 2300–2400 m water depth(w.d.)Parasound records reveal a belt of modern erosion.At the end of glacial termination 2,stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144.Likewise hiatuses probably earmarked all preceding glacial terminations at Site 1144 back to 650 ka.Accordingly,boundary current erosion then shifted~300 m upslope to~2040–2060 m w.d.These vertical shifts imply a rise in boundary current buoyancy,that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.  相似文献   

9.
We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ18Osw from the pore water δ18O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ18Osw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ18Osw of 1.0-1.1‰.Using the calculated bottom-water δ18Osw, we have extracted the temperature component from the benthic foraminiferal δ18O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern.  相似文献   

10.
New data from three Tasman Sea cores support Keigwin's [1] observation that the δ13C of Pacific benthic foraminifera (and by inference bottom-water TCO2) decreased by 0.7‰ at about 6.5 Myr B.P. Simple box models are developed and used to test several hypotheses about the cause of the δ13C decrease. We favor the idea that the δ13C shift was due to a rapid change in TCO2 cycling within the oceans (such as would result from either a decrease in upwelling rate, or an increase in the fraction of PO43? reaching the deep oceans in particulate organic matter and a corresponding drop in the preformed PO43? concentration). The δ13C decrease across the shift might reflect either a global decrease in upwelling rate, or a different abyssal circulation pattern before the shift.  相似文献   

11.
A comparison of the oxygen isotope signal in deep-sea benthic foraminifera with the record of glacio-eustatic sea level for the last 160,000 years reveals that the amplitude of the benthic δ18O records predicts more continental ice volume than appears to be reflected in lowered sea level stands. These differences between the benthic δ18O ice volume estimates and radiometrically-dated records of eustatic sea level are consistent with the presence of a large floating Arctic Ocean ice mass during glacial intervals. The presence of an Arctic Ocean ice sheet during glacial intervals may account for the two climatic modes observed in oxygen isotope records which span the entire Pleistocene. The early Pleistocene (1.8 to 0.9 Myr B.P.) interval is characterized by low-amplitude, high-frequency δ18O fluctuations between glacial and interglacial periods, while the late Pleistocene (0.9 Myr B.P. to present) is characterized by large-amplitude, low-frequency δ18O changes. These two climatic modes can be explained by the initiation of earth orbital conditions favoring the co-occurrence of glacial period Arctic Ocean ice sheets and large continental ice sheets approximately 900,000 years before present.  相似文献   

12.
New data for the direct measurement of the isotopic composition of neodymium in Atlantic Ocean seawater are compared with previous measurements of Pacific Ocean seawater and ferromanganese sediments from major ocean basins. Data for Atlantic seawater are in excellent agreement with Nd isotopic measurements made on Atlantic ferromanganese sediments and are distinctly different from the observed compositions of Pacific samples. These results clearly demonstrate the existence of distinctive differences in the isotopic composition of Nd in the waters of the major ocean basins and are characteristic of the ocean basin sampled. The average εNd(0) values for the major oceans as determined by data from seawater and ferromanganese sediments are as follows: Atlantic Ocean,εNd(0) ? ?12 ± 2; Indian Ocean,εNd(0) ? ?8 ± 2; Pacific Ocean,εNd(0) ? ?3 ± 2. These values are considerably less than εNd(0) value sources with oceanic mantle affinities indicating that the REE in the oceans are dominated by continental sources. The difference in the absolute abundance of143Nd between the Pacific and Atlantic Oceans corresponds to ～106 atoms143Nd per gram of seawater. The correspondence between the143Nd/144Nd in seawater and in the associated sediments suggests the possible application of this approach to paleo-oceanography.Distinctive differences in εNd(0) values are observed in the Atlantic Ocean between deep-ocean water associated with North Atlantic Deep Water and near-surface water. This suggests that North Atlantic Deep Water may be relatively well mixed with respect to Nd isotopic composition whereas near-surface water may be quite heterogeneous, reflecting different sources for surface waters relative to deep water. This suggests that it may be possible to distinguish the sources of water masses within an ocean basin on the basis of Nd isotopic composition.The Nd isotopic variations in seawater are used to relate the residence time of Nd and mixing rates between the oceans.  相似文献   

13.
Carbon isotope stratigraphy of the Late Jurassic and earliest Cretaceous was revealed from Torinosu‐type limestone, which was deposited in a shallow‐marine setting in the western Paleo‐Pacific, in Japan. Two sections were examined; the Nakanosawa section of the late Kimmeridgian to early Tithonian age (Fukushima Prefecture, Northeast Japan), and the Furuichi section of the late Kimmeridgian to early Berriasian age (Ehime Prefecture, Southwest Japan). The age‐model was established using Sr isotope ratio and fossil occurrence. The limestone samples have a low Mn/Sr ratio (mostly <0.5) and lack a distinct correlation between δ13C and δ18O, indicating a low degree of diagenetic alteration. Our composite δ13C profile from the two limestone sections shows three stratigraphic correlation points that can be correlated with the profiles of relevant ages from the Alpine Tethyan region: a large‐amplitude fluctuation (the lower upper Kimmeridgian, ～152 Ma), a positive anomaly (above the Kimmeridgian/Tithonian boundary, ～150 Ma), and a negative anomaly (the upper lower Tithonian, ～148 Ma). In addition, we found that δ13C values of the Torinosu‐type limestone are ～1‰ lower than the Tethyan values in the late Kimmeridgian. This inter‐regional difference in δ13C values is likely to have resulted from a higher productivity and/or an organic burial in the Tethyan region. The difference gradually reduces and disappears in the late Tithonian, where the Tethyan and our δ13C records show similar stable values of 1.5–2.0‰. This isotopic homogenization is probably due to changes in the continental distribution and the global ocean circulation, which propagated the 13C‐depleted signature from the larger Paleo‐Pacific to the smaller Tethys Ocean during this time.  相似文献   

14.
Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial–interglacial change in deep North Pacific phosphate (PO4) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation – and thus respired carbon storage – over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO2) by sequestering CO2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO2.  相似文献   

15.
The coastal confined aquifer in the Gulf of Urabá (Colombia) is an important water source for the banana agro‐industry as well as for urban and rural communities. However, the main processes controlling recharge and mixing in the aquifer are still poorly understood. Hydrochemical analyses and stable isotope monitoring were conducted to (a) determine groundwater recharge origin, mean groundwater age, and the main processes governing groundwater chemistry and the potential mixing of marine water and the influence of diffusive processes from the two surrounding aquitard layers. Hydrochemical data indicate that the main processes affecting the dissolved chemical composition include cation exchange, dissolution of carbonated and CO2, and silicate weathering. δ18O and δ2H compositions combined with 14C data highlight the differences in climatic conditions between the recharge zone and the confined section of the aquifer, which is close to the Atlantic Ocean. Groundwater samples with 14C ages from recent to 28,300 years BP show a depleted isotopic trend ranging from ?6.43‰ to ?9.14‰ in δ18O and from ?43.2‰ to ?65.7‰ in δ2H. The most depleted δ18O and δ2H compositions suggest a cooler recharge climate than the current conditions (corresponding to the last glacial period of the late Pleistocene). Depleted δ13C values in the total dissolved inorganic carbon indicate the existence of organic material oxidation processes within the geologic formation. These results can be used or transferred to enhance groundwater modelling efforts in other confined coastal aquifers of South America where scarcity of long‐term monitoring data limits water resources planification under a changing climate.  相似文献   

16.
Ocean Drilling Program Leg 199 Site 1220 provides a continuous sedimentary section across the Paleocene/Eocene (P/E) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ13C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH. A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P/E transition at Site 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at Site 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, pCO2 must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P/E transition. The calculated increased pCO2 coincides with paleo‐botanical evidence. The current global emission rate (～7.3 peta (1015) gC/y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water.  相似文献   

17.
13C and ΣCO2 data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ13C of the ΣCO2 in the deep water (～3000m) decreases from 1.7‰ in the North Atlantic to ?0.10‰ in the North Pacific. This change is attributed to the addition of about 158 μmoles of CO2 per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO2, while the remainder is attributed to dissolution of calcium carbonate.The δ13C of the dissolved CO2 in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO2 at a mean temperature of 16°C. The δ13C and ΣCO2 values of Antarctic surface water samples suggest that these waters are derived from a mixture of North Atlantic deep water and equilibrated surface water.  相似文献   

18.
The high-resolution quantitative analysis of the planktonic foraminifera and the δ18O records of the section between 96.49– 137.6 mcd at ODP Site 1144 on the continental slope of northern South China Sea reveals an abrupt cooling event of sea surface temperature (SST) during the last interglacial (MIS 5.5, i.e. 5e). The dropping range of the winter SST may come to 7.5°C corresponding to 1.2‰ of the δ18O value of sea surface water. This event is comparable with those discovered in the west Europe and the northern Atlantic Ocean, but expressed in a more intensive way. It is inferred that this event may have been induced by middle- to low-latitude processes rather than by polar ice sheet change. Since the Kuroshio-index speciesPulleniatina obliquiloculata displayed the most distinct change at the event, it may also be related to the paleoceanographic change of the low-latitude area in the western Pacific Ocean. This event can be considered as one of “Younger Dryas-style coolings” and is indicative of climate variability of the last interglacial stage.  相似文献   

19.
In order to derive a radiometric age marker for the end of the penultimate glacial–interglacial transition, we compiled published U-series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial, and computed the corresponding open-system ages using Thompson et al. model (Thompson, W.G., Spiegelman, M.W., Goldstein, S.L., Speed, R.C., An open-system model for U-series age determinations of fossil corals. Earth Planet. Sci. Lett. 210 (2003) 365–381). We obtain a global mean age of 126 calendar kyr BP (ka) ± 1.7kyr (2σ) for the beginning of the last interglacial sea level high stand. After showing that the phase relationships observed between changes in sea level, North Atlantic benthic and planktonic foraminifera oxygen isotopic records, and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation, we derive an age of 131.2ka ± 2kyr (2σ) for the abrupt increase in atmospheric CH4 and North Atlantic surface temperature marking the end of the penultimate glacial–interglacial transition. This age is consistent with U–Th dates of the penultimate glacial–interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with North Atlantic temperature records over the last deglaciation. Finally, we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from Termination II to Termination I, implying that northern hemisphere summer insolation alone cannot explain the timing of terminations.  相似文献   

20.
3/He4He measurements at two stations in the Atlantic show that the deep water (> 2 km) contains far less excess3He than our previous measurements have shown for the Pacific Ocean. The3/He4He ratio anomaly (relative to atmospheric3/He4He) is approximately 5% for the deep Atlantic compared to about 20% for the deep Pacific. The North Atlantic3He profile shows much more structure than the South Atlantic profile, with maxima observed at 500 m, 1900 m, and 3200 m. The maxima at 500 m and 1900 m are probably due to in situ tritium decay, whereas the 3200 m maximum cannot be due to tritium, and is probably due to leakage of3He into the Atlantic water from the mantle. It seems significant that maxima in the trace elements Cu, Zn and Fe have also been observed at 3200 m at this station by Brewer, Spencer and Robertson.  相似文献   

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