Radium in the near-surface Caribbean Sea

Recent radium measurements from the near-surface Caribbean Sea are presented. The surface horizontal and vertical distributions of²²⁶Ra are essentially the same as reported by Szabo et al. (1967) for the early 1960's. The²²⁶Ra activity at the surface is relatively uniform across the Caribbean, with an average of8.2±0.4dpm/100kg. The subsurface distribution to ～200 m averages7.8±0.4dpm/100kg and increases slowly below 200 m. reaching ～9.5 dpm/100 kg at 560 m. In contrast to²²⁶Ra, the surface concentration of²²⁸Ra was much more variable in both time and space. An average increase of 33% was found between 1968 and 1976 in the western Caribbean and during both years an anomalously high²²⁸Ra activity was found in the eastern Caribbean. These data support previous hypotheses that water entering the eastern Caribbean has been enriched in²²⁸Ra prior to entry and that variable mixing of the Atlantic water masses found to the northeast and southeast of the Lesser Antilles may produce temporal variations in the near-surface²²⁸Ra activity. Scatter plots of²²⁸Ra vs. salinity and sigma-t indicate that the near-surface vertical distribution of²²⁸Ra in the Caribbean Sea is predominantly influenced by advection. Thus²²⁸Ra cannot be used to study near-surface vertical mixing rates in this region.     

New production in the South China Sea

Measurement of²²⁸Ra activities in the upper 300 m water column was conducted at two stations in the South China Sea using an MnO₂-fiber extraction/β-counting technique of²²⁸Ac. Results showed that²²⁸Ra activities ranged from 0.38 to 3.60 Bq · m^-3. The vertical profiles of²²⁸Ra at the time-series station favored a steady state assumption. Based on a one-dimensional steady state model,²²⁸Ra-nitrate coupled approach was applied to stations NS97-43, NS99-53 (T₁), NS99-53 (T₂). New production thus quantified were 4.4, 5.1 and 5.7 mmolC · m^-2 · d^-1, respectively,f ratios in the South China Sea were estimated from the derived new production and the documented primary productivity in the regime, to be 0.12–0.15.     

Investigating Bermuda's pollution history through stable isotope analyses of modern and museum-held gorgonian corals

For centuries, Bermuda has been challenged with wastewater management for the protection of human and environmental health. By quantifying the δ¹⁵N of the common sea fan Gorgonia ventalina sampled from 30 sites throughout Bermuda we show that sewage-derived nitrogen is detectable on nearshore coral reefs and declines across the lagoon to the outer rim. We also sampled gorgonians from two museum collections representing a 50y time-series (1958–2008). These samples revealed an increase in δ¹⁵N of > 4.0‰ until the mid-1970s, after which δ¹⁵N values slowly declined by ~ 2.0‰. A δ¹⁵N chronology from a gorgonian skeleton exhibited a similar decline over the last 30–40 years of approximately 0.6‰. We conclude that policies have been effective in reducing sewage impacts to Bermudian reefs. However, significant sources of sewage pollution persist and are likely have a strong impact on harbor and nearshore coral communities and human health.     

The effects of alteration and the interpretation of heat flow and radioactivity data—a reply to R.U.M. Rao

The first²²⁴Ra (t_1/2 = 3.64days) measurements from mixing zones of estuarine systems are presented for the Pee Dee River-Winyah Bay and Delaware Bay Estuaries. High-resolution gamma-ray spectrometry was used to determine²²⁴Ra,²²⁸Ra (t_1/2 = 5.7years), and²²⁶Ra (t_1/2 = 1622years) activity ratios. Desorption and diffusion from suspended and bottom sediments contributes to the non-conservative increases of the three isotopes in each systems. In Delaware Bay²²⁴Ra concentrations were nearly constant over the 2.5‰ to 15‰ salinity range where two turbidity maximum zones are located.²²⁸Th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of²²⁴Ra in this system. Samples collected on the ebb and flood tide from a salt marsh along Delaware Bay have a 5-fold increase in²²⁴Ra from flood to ebb and 3- and 2-fold increases for²²⁸Ra and²²⁶Ra respectively, indicating salt marshes are another source of radium to estuarine waters.     

Synthetic coral-reef terraces and variations of Quaternary sea level

Coral-reef terraces on tectonically elevated coasts provide important data on variations of sea level. In this paper a systematic approach is presented for the construction of synthetic reef terraces. Idealized reef terraces are generated assuming a constant rate of tectonic uplift ν and a harmonic variation of sea level with amplitudeh_wo and period τ. It is further assumed that coral terraces grow only during periods of relative sea-level rise. The behavior is governed by the parameter u = τυ/2π h_wo. If u > 1 no reef terraces form. If 0.217 < u < 1 a discontinuous series of terraces form on the uplifting basement. If 0 < u < 0.217 the basement is covered with coral and a series of coral terraces forms on this coral. Uplifted coral-reef terraces on the Huon Peninsula, Papua New Guinea, compare reasonably well with terraces generated by our model with τ = 20,000 years andh_wo = 21.4 m. We also compare the observed terraces with model terraces using the paleo sea level inferred from¹⁸O/¹⁶O data. The observed terraces are qualitatively similar to those predicted using the oxygen isotope data, however, the model terraces require larger relative sea-level variations with a near 20,000 year period than those inferred directly from the¹⁸O/¹⁶O data.     

Excess228Th in the airborne dust: an indicator of continental dust from the East Asian deserts

Thorium isotopes in the airborne dust collected at Tsukuba Science City in Japan from January 1981 to December 1982 show clear seasonal variations. Especially²²⁸Th in the airborne particles have a typical maximum cincentration between February and April, which is about an order of magnitude higher than during the remainder of the year. According to the result of size distribution of thorium isotope-bearing particles in the air, about 53% of²²⁸Th is associated with the particles less than 1.6 μm aerodynamic diameter. These results reveal that²²⁸Th in the airborne particles is present in fine soily matters originating from the East Asian deserts.     

Resistance of Lophelia pertusa to coverage by sediment and petroleum drill cuttings

In laboratory experiments, the cold-water coral Lophelia pertusa was exposed to settling particles. The effects of reef sediment, petroleum drill cuttings and a mix of both, on the development of anoxia at the coral surface were studied using O₂, pH and H₂S microsensors and by assessing coral polyp mortality. Due to the branching morphology of L. pertusa and the release of coral mucus, accumulation rates of settling material on coral branches were low. Microsensors detected H₂S production in only a few samples, and sulfate reduction rates of natural reef sediment slurries were low (<0.3 nmol S cm⁻³ d⁻¹). While the exposure to sediment clearly reduced the coral’s accessibility to oxygen, L. pertusa tolerated both partial low-oxygen and anoxic conditions without any visible detrimental short-term effect, such as tissue damage or death. However, complete burial of coral branches for >24 h in reef sediment resulted in suffocation.     

Correlation between δ~(18)O,Sr/Ca and Mg/Ca of coral Acropora and seawater temperature from coral culture experiments

To be used as proxies of seawater surface temperature(SST), the δ 18Oc values and Sr/Ca and Mg/Ca ratios of scleractinian coral skeletons must be verified by coral culture experiments in the laboratory. This paper describes a coral culture experiment that was conducted at several seawater temperatures T(21–28°C) using a tandem aquarium system and the new method for depositing coral skeletons grown under controlled conditions. The δ 18Oc values and the Sr/Ca and Mg/Ca ratios of the cultured coral were measured. We concluded that the δ 18Oc values and Sr/Ca and Mg/Ca ratios of the cultured coral are clearly correlated with T. The linear regression curve is δ18Oc(‰)=δ0.1427δT(°C)δ0.1495(n=18, r=0.955, p0.0001), and the slope of δ0.1427‰/°C is at the low end of the range of published values(δ0.13–δ0.29‰/°C). The Sr/Ca ratio decreases with increasing T, whereas the Mg/Ca ratio increases with increasing T, indicating a negative correlation between Sr/Ca and Mg/Ca. Their linear regression curves are Sr/Ca(mmol/mol)=δ0.04156δT+10.59(n=15, r=0.789, p0.005) and Mg/Ca(mmol/mol)= 0.04974δT+2.339(n=17, r=0.457, p0.05), respectively, which demonstrate that when Mg/Ca and Sr/Ca are increased by one unit, T increases by 5.19°C and decreases by 15.62°C, respectively. These variations are significantly lower than published values.     

UUThTh systematics and the precise measurement of time over the past 500,000 years

We have developed techniques to measure the²³⁰Th abundance in corals by isotope dilution mass spectrometry. This, coupled with our previous development of mass spectrometric techniques for²³⁴U and²³²Th measurement, has allowed us to reduce significantly the analytical errors in²³⁸U²³⁴U²³⁰Th dating and greatly reduce the sample size. We show that 6 × 10⁸ atoms of²³⁰Th can be measured to ±30‰ (2σ) and 2 × 10¹⁰ atoms of²³⁰Th to ±2‰. The time over which useful age data on corals can be obtained ranges from a few years to 500 ky. The uncertainty in age, based on analytical errors, is ±5 y (2σ) for a 180 year old coral (3 g), ±44 y at 8294 years and ±1.1 ky at 123.1 ky (250 mg of coral). We also report²³²Th concentrations in corals (0.083–1.57 pmol/g) that are more than two orders of magnitude lower than previous values. Ages with high analytical precision were determined for several corals that grew during high sea level stands 120 ky ago. These ages lie specifically within or slightly postdate the Milankovitch insolation high at 128 ky and support the idea that the dominant cause of Pleistocene climate change is Milankovitch forcing.     

Temporal variation of228Ra in the near-surface Gulf of Mexico

The Mn-fiber technique for extracting radium from seawater has proved useful for studying the marine geochemistry of²²⁸Ra. In the Gulf of Mexico, this technique was used to measure the surface and near-surface distribution of²²⁶Ra and²²⁸Ra. The observed surface distribution of²²⁸Ra, and particularly the radium activity ratio (228/226) can be explained by known circulation patterns, or, when local surface currents are not well understood, may provide insight into their general characteristics.The radium activity ratio has increased from 0.5 in 1968 to 0.7 in 1973 in the surface Gulf of Mexico. This observed increase cannot be attributed to known anthropogenic or natural source perturbations within the Caribbean Sea-Gulf of Mexico system. Possible causes include a change in the residence time for near-surface water, or variations in the relative dominance of the two sources for water entering the eastern Caribbean; the North Equatorial Current and the Guiana Current.The temporal distribution of²²⁸Ra is unstable and naturally variable over a time period less than or equal to five years in the Gulf of Mexico and by extrapolation, the Caribbean Sea. Therefore, its usefulness in calculations of eddy diffusion coefficients for these regions is greatly diminished.     

Tropical Indian Ocean Basin Mode recorded in coral oxygen isotope data from the Seychelles over the past 148 years

The tropical Indian Ocean(TIO) displays a uniform basin-wide warming or cooling in sea surface temperature(SST) during the decay year of El Niδo-Southern Oscillation(ENSO) events. This warming or cooling is called the tropical Indian Ocean Basin Mode(IOBM). Recent studies showed that the IOBM dominates the interannual variability of the TIO SST and has impacts on the tropical climate from the TIO to the western Pacific. Analyses on a 148-year-long monthly coral δ 18 O record from the Seychelles Islands demonstrate that the Seychelles coral δ 18 O not only is associated with the local SST but also indicates the interannul variability of the basin-wide SST in the TIO. Moreover, the Seychelles coral δ 18 O shows a dominant period of 3–7 years that well represents the variability of the IOBM, which in return is modulated by the inter-decadal climate variability. The correlation between the Seychelles coral δ 18 O and the SST reveals that the coral δ 18 O lags the SST in the eastern equatorial Pacific by five months and reaches its peak in the spring following the mature phase of ENSO. The spatial pattern of the first EOF mode indicates that the Seychelles Islands are located at the crucial place of the IOBM. Thus, the Seychelles coral δ 18 O could be used as a proxy of the IOBM to investigate the ENSO teleconnection on the TIO in terms of long-time climate variability.     

The diurnal and semidiurnal barometric oscillations global distribution and annual variation

Summary The global distributions of the annual and seasonal means of the diurnal (S ₁) and semidiurnal (S ₂) surface pressure oscillations are investigated by spherical harmonic analysis. The main waves are,S ₁ ¹ (with wave number 1) forS ₁ andS ₂ ² forS ₂.S ₁ ¹ is much less predominant among the waves ofS ₁ thanS ₂ ² among those ofS ₂. As in the case of the lunar semidiurnal barometric tideL ₂ the pressure maxima occur earlier in the Southern than in the Northern Hemisphere. In the case ofS ₂ the standing waveS ₂ ⁰ and the waveS ₂ ³ are also of interest besidesS ₂ ². Although the present analysis extends only from 60°N to 60°S, whileS ₂ ⁰ is largest at polar latitudes, its results show thatS ₂ ⁰ should be smaller at high southerly than at high northerly latitudes, as has been observed. Thus this observed asymmetrical distribution ofS ₂ ⁰ may be due to causes outside the polar regions rather than to their geographical differences. The best approximation to the observed distribution ofS ₂ ⁰ is obtained by including a mode representing an oscillation independent of longitude and latitude indicating a small semidiurnal variation of the mean global surface presure, which is an unlikely result on physical grounds.The seasonal variation ofS ₁ ¹ expressed in percent of the annual mean is smaller than that ofS ₂ ², and both are less than the unexplained seasonal variation ofL ₂ ².The main wavesS ₁ ¹ andS ₂ ² are expressed not only by associated Legendre functions, but also by Hough functions.National Center for Atmospheric Research, Boulder, Colorado, U.S.A., sponsored by the National Science Foundation.     

Variability in luminescent lamination and initial 230Th/232Th activity ratios in a late Holocene stalagmite from northern Norway

Luminescent lamination in a stalagmite from northern Norway is used to construct a ～2780-year long, floating record of annual growth rate. Thermal ionisation mass-spectrometric (TIMS) U–Th ages (n = 12) were determined along the growth axis and three subsample locations and ages (corrected and uncorrected for initial ²³⁰Th/²³²Th activity) were selected as anchor points for the floating chronology. On the basis of these anchor points, termination of growth occurred between AD 1729 and AD 1826. The annual banding records are used to evaluate the initial ²³⁰Th/²³²Th activity ratio adopted for correction of the U–Th ages. To achieve a reasonable fit between U–Th ages and estimates predicted by the anchored annual band age models, mean initial ²³⁰Th/²³²Th activity ratios of between 0.44 and 1.47 must be invoked. However, there remains a reasonable degree of scatter about the expected linear relationship between annual bands and U–Th chronology for individual subsamples indicating that the use of a single correction factor for Holocene stalagmites should be applied with caution.Stalagmite growth rate fluctuates on annual to centennial scale. The growth termination of the stalagmite presented here could have been a result of environmental change associated with the Little Ice Age, or, possibly local percolation pathway changes after an M_s ～ 6 earthquake in the region in AD 1819. Stable-isotope data from the same axis of growth show a pattern similar to the large-scale growth rate variations, and these combined proxy records are interpreted as showing gradual cooling and/or shortening of the vegetation growth season for the last 3000 years.     

Natural and anthropogenic radionuclide distributions in the northwest Atlantic Ocean

We have used in-situ pumps which filter large volumes of sea water through a 1 μm cartridge prefilter and two MnO₂-coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans. Two sites in the northwest Atlantic show subsurface maxima of the fallout radionuclides¹³⁷Cs,^239,240Pu and²⁴¹Am. Although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions, comparison of predicted and measured water column inventories suggests that at least 35–50% of the Pu and²⁴¹Am are supplied to the deep water by advection.The depth distributions of the naturally occurring radionuclides²³²Th,²²⁸Th and²³⁰Th reflect their sources to the oceans.²³²Th shows high dissolved concentrations in surface waters, presumably as a result of atmospheric or riverine supply. Activities of²³²Th decrease with depth to values 0.01 dpm/1000 l.²²⁸Th shows high activities in near surface and near bottom water, due to the distribution of its parent,²²⁸Ra. Dissolved²³⁰Th, produced throughout the water column from²³⁴U decay, increases with depth to 3000 m. Values in the deep water (> 3000 m) are nearly constant ( 0.6–0.7 dpm/1000 l), and the distribution of this tracer (and perhaps other long-lived particle-reactive tracers as well) may be affected by the advection inferred from Pu and²⁴¹Am data.The ratio of particulate to dissolved activity for both²³⁰Th and²²⁸Th is 0.15–0.20. This similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium. Moreover, in mid-depths²²⁸Th tends to have a higher particulate/dissolved ratio than²³⁰Th, suggesting uptake and release of²³⁰Th and²²⁸Th by different processes. This could occur if²²⁸Th, produced in surface water, were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking.²³⁰Th, produced throughout the water column, may more closely approach a sorption equilibrium at all depths.²³⁰Th,²⁴¹Am and^239,240Pu are partitioned onto particles in the sequence Th > Am > Pu with 15% of the²³⁰Th on particles compared with 7% for Am and 1% for Pu. Distribution coefficients (K_d) are 1.3–1.6 × 10⁷ for Th, 5–6 × 10⁶ for Am and 7–10 × 10⁵ for Pu. The lower reactivity for Pu is consistent with analyses of Pu oxidation states which show 85% oxidized (V + VI) Pu. However, theK_d value for Pu may be an upper limit because Pu, like²²⁸Th, may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase.     

Uranium and thorium series nuclides in oriented ferromanganese nodules: growth rates,turnover times and nuclide behavior

Three ferromanganese nodules handpicked from the tops of 2500 cm² area box cores taken from the north equatorial Pacific have been analysed for their U-Th series nuclides.²³⁰Th_exc concentrations in the surface 1–2 mm of the top side of the nodules indicate growth rates of 1.8–4.6 mm/10⁶ yr. In two of the nodules a significant discontinuity in the²³⁰Th_exc depth profile has been observed at ～0.3 m.y. ago, suggesting that the nodule growth has been episodic. The concentration profiles of²³¹Pa_exc (measured via²²⁷Th) yield growth rates similar to the²³⁰Th_exc data. The bottom sides of the nodules display exponential decrease of²³⁰Th_exc/²³²Th activity ratio with depth, yielding growth rates of 1.5–3.3 mm/10⁶ yr.The²³⁰Th_exc and²³¹Pa_exc concentrations in the outermost layer of the bottom face are significantly lower than in the outermost layer of the top face. Comparison of the extrapolated²³⁰Th_exc/²³²Th and²³⁰Th_exc/²³¹Pa_exc activity ratios for the top and bottom surfaces yields an “age” of (5?15) × 10⁴ yr for the bottom relative to the top. This “age” most probably represents the time elapsed since the nodules have attained the present orientation.The²¹⁰Pb concentration in the surface ～0.1 mm of the top side is in large excess over its parent²²⁶Ra. Elsewhere in the nodule, up to ～1 mm depth in both top and bottom sides,²¹⁰Pb is deficient relative to²²⁶Ra, probably due to²²²Rn loss. The absence of²¹⁰Pb_exc below the outermost layer of the top face rules out the possibility of a sampling artifact as the cause of the observed exponentially decreasing²³⁰Th_exc and²³¹Pa_exc concentration profiles. The flux of²¹⁰Pb_exc to the nodules ranges between 0.31 and 0.58 dpm/cm² yr. The exhalation rate of²²²Rn, estimated from the²²⁶Ra-²¹⁰Pb disequilibrium is ～570 dpm/cm² yr from the top side and >2000 dpm/cm² yr from the bottom side.²²⁶Ra is deficient in the top side relative to²³⁰Th up to ～0.5–1 mm and is in large excess throughout the bottom. The data indicate a net gain of²²⁶Ra into the nodule, corresponding to a flux of (24?46) × 10^?3 dpm/cm² yr. On a total area basis the gain of²²⁶Ra into the nodules is <20% of the²²⁶Ra escaping from the sediments. A similar gain of²²⁸Ra into the bottom side of the nodules is reflected by the high²²⁸Th/²³²Th activity ratios observed in the outermost layer in contact with sediments.     

The residence time of thorium in surface sea water and its implications regarding the rate of reactive pollutants

The activity ratio of²²⁸Th/²²⁸Ra in the open surface ocean averages 0.21. This suggests that thorium is removed from surface water in about 0.7 yr. As plant matter is cycled within the surface sea on a similar time scale, the suggestion is made that highly reactive compounds are inadvertently removed by plants in their quest for the critical nutrients nitrate and phosphate. Combined with the coefficient for horizontal eddy diffusivity obtained from the distribution of²²⁸Ra in surface sea water this result provides a basis for the prediction of the distribution of “reactive” pollutants released to the surface sea from coastal areas.     

The lunar barometric tide,its global distribution and annual variation

Summary The global distribution of the lunar barometric tideL ₂ is investigated by spherical harmonic analysis, based on 104 stations for the annual mean, and on 85 stations for the three seasons. The main wave ofL ₂ is the one with wave number 2, but for a detailed study of the irregularities of the global distribution ofL ₂, waves with other wave numbers have also to be considered. Even the main wave ofL ₂ is asymmetric to the equator with the two lunar-daily pressure maxima occurring earlier in the Southern than in the Northern Hemisphere. The amplitudes at the same distances from the equator are greater in the Southern than in the Northern Hemisphere. These hemispheric differences are most pronounced during the D season. As found in earlier investigations the phase consiant ofL ₂ is always greater during the J season than during the D season. But the amplitudes are greatest during the J season only north of 30^oS. Farther south the amplitude maximum occurs during the D season.sponsored by the National Science Foundation     

Meridional distribution of226Ra in the eastern Pacific along GEOSECS cruise tracks

We present the distribution of²²⁶Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface²²⁶Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the²²⁶Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of²²⁶Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary²²⁶Ra can be traced up to at least 1–1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic²²⁶Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2–4 km)²²⁶Ra data give the following set of best fits: upwelling velocity(V_z) = 3.5m/yr, vertical eddy diffusivity(K_z) = 0.6cm²/s, horizontal (north-south) eddy diffusivity(K_y) = 1 × 10⁷cm²/s, and water-column regeneration flux of²²⁶Ra(J) = 3.3 × 10^?5dpmkg^?1yr^?1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of²²⁶Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constantV_z and K_z. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities.     

Seasonal and annual variation of CO<Subscript>2</Subscript> flux above a broad-leaved Korean pine mixed forest

Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO₂ profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F _NEE, F _GPP and R _E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO₂ uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux.L_AI and soil temperature determined the seasonal and annual dynamics of F_GPP and R_E separately. V_PD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.The forest was a net sink of atmospheric CO₂ and sequestered ?449 g C·m^?2 during the study period; ?278 and ?171 gC·m^?2 for 2003 and 2004 respectively. F _GPP and F _RE over 2003 and 2004 were ?1332, ?1294 g C·m^?2. and 1054, 1124 g C·m^?2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO₂.There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO₂. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F _GPP, and 60.4, 62.1% of R _E of the entire year.     

The water column distributions of thorium isotopes in the western North Pacific

Four vertical profiles of²³⁰Th and²²⁸Th were determined using large volume water samples in the western North Pacific. An almost linear increase of²³⁰Th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain. We developed a model which included a dissolved-particulate transformation as well as parameters of the scavenging model. Application of the model to the vertical distributions of total and the GEOSECS particulate Th isotopes (²³⁰Th and²³⁴Th) yielded the residence time of dissolved Th with respect to adsorption to particles and the turnover time of particulate Th to be 235 days and 57 days, respectively. The Th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m/day which continually release Th into sea water as well as pick up Th from the water along their journey to the bottom.For²²⁸Th, a large excess over²³²Th was observed throughout the water column with pronounced high concentrations in surface and bottom waters, suggesting that the²²⁸Th was derived from²²⁸Ra diffused out of sediments. The vertical distributions of²²⁸Th seemed to be significantly influenced by lateral mixing along isopycnals.