Progress in the determination of Ac in sea water

²²⁷Ac is a naturally occurring radioisotope with a unique combination of properties that make it suitable for the determination of deep ocean mixing and upwelling rates. Here, we present a method for the determination of ²²⁷Ac in sea water on sample sizes of 20–80 L. The measurement is based on co-precipitation of ²²⁷ Ac with MnO₂, followed by chemical isolation of actinium in the presence of an artificial Ac isotope. Actinium is then electrodeposited onto silver discs. In two alpha-spectrometric counting periods, first the artificial ²²⁵Ac isotope is counted, then after > 100 days five daughters of ²²⁷Ac. The first counting period gives a total yield for the procedure, integrating chemical recovery and detector efficiency. The total yield was found here to be on average 15 ± 5%, the chemical yield on average about 50%. The counting of five decay products of ²²⁷Ac in the second period makes the method particularly sensitive. Using appropriate decay corrections, the initial ²²⁷Ac activity can be determined to better than 10% relative error for concentrations < 10,000 atoms/L. We compare data acquired by the new method to a data set from in-situ pumps, from a parallel sampling campaign in the Eastern Weddell Gyre, and we can show excellent agreement. Repeated determinations of ²²⁷Ac in a uranium reference material (UREM-11) demonstrate the accuracy of the method.     

Comparison of techniques for pre-concentrating radium from seawater

In the framework of the KEOPS project (KErguelen: compared study of the Ocean and the Plateau in Surface water), we aimed to provide information on the water mass pathways and vertical mixing on the Kerguelen Plateau, Southern Ocean, based on ²²⁸Ra profiles. Because ²²⁸Ra activities are extremely low in this area (~ 0.1 dpm/100 kg or ~ 2.10^− 18 g kg^− 1), the filtration of large volumes of seawater was required in order to be able to detect it with minimal uncertainty. This challenging study was an opportunity for us to test and compare methods aimed at removing efficiently radium isotopes from seawater. We used Mn-fiber that retains radium and that allows the measurement of all four radium isotopes (²²⁶Ra, ²²⁸Ra, ²²³Ra, ²²⁴Ra). First, we used Niskin bottles or the ship's seawater intake to collect large volumes of seawater that were passed onto Mn-fiber in the laboratory. Second, we filled cartridges with Mn-fiber that we placed in tandem on in situ pumps. Finally, we fixed nylon nets filled with Mn-fiber on the frame of in situ pumps to allow the passive filtration of seawater during the pump deployment.Yields of radium fixation on the cartridges filled with Mn-fiber and placed on in situ pumps are ca. 30% when combining the two cartridges. Because large volumes of seawater can be filtered with these pumps, this yields to effective volumes of 177–280 kg (that is, higher than that recovered from fourteen 12-l Niskin bottles). Finally, the effective volume of seawater that passed through Mn-fiber placed in nylon nets and deployed during 4 h ranged between 125 and 364 kg. Consequently, the two techniques that separate Ra isotopes in situ are good alternatives for pre-concentrating radium from seawater. They can save ship-time by avoiding repeated CTD casts to obtain the large volumes of seawater. This is especially true when in situ pumps are deployed to collect suspended particles. However, both methods only provide ²²⁸Ra/²²⁶Ra ratios. The determination of the ²²⁸Ra specific activity is obtained by multiplying this ratio by the ²²⁶Ra activity measured in a discrete sample collected at the same water depth.     

Marine ecosystem approaches to management: challenges and lessons in the United States

This study examined how the United States’ largest marine resource management agency, the National Oceanic and Atmospheric Administration (NOAA), has begun to change its management strategy away from traditional marine resource management approaches towards an Ecosystem Approach to Management (EAM). Surveys were conducted with 57 NOAA scientists and resource managers in nine NOAA programs in 8 different geographic regions across the United States in 2005. A qualitative analysis examined the attitudes and experiences of participants with respect to implementing EAM and identified four major challenges to enhancing cooperation and understanding of EAM. We conclude with recommendations for concrete initiatives that future efforts in EAM that any management agency can undertake to facilitate further ecosystem management opportunities.     

First and second baroclinic mode responses of the tropical Indian Ocean to interannual equatorial wind anomalies

The combined and individual responses of the first and second baroclinic mode dynamics of the tropical Indian Ocean to the well-known Indian Ocean Dipole mode (IOD) wind anomalies are investigated. The IOD forced first baroclinic Rossby waves arrive at the western boundary in three months, while the reflected component from the eastern boundary with opposite phase arrives in five to six months, both carry input energy to the west. The inclusion of the second baroclinic mode slows down the wave propagation by mode coupling and stretches the energy spectrum to a relatively longer time scale. The total energy exists in the equatorial wave guide for at least five months from the forcing, as much as 10% of that of the atmospheric input, which mainly dissipates at the western boundary. The individual responses of the ocean to IOD interannual wind anomaly show that the significant modes of oceanic anomalies are confined to a wave guide of 10° on either side of the equator.     

Primary production and implications for metabolic balance in Hawaiian lee eddies

Recent discrepancies between geochemical and biological approaches for determining whether ocean ecosystems are net heterotrophic or net autotrophic have led to uncertainty in the net metabolic state of open ocean ecosystems. Geochemical approaches indicate that the oceans are net positive autotrophic, but direct observations based on short-term incubation techniques suggest that the ocean is in a state of net heterotrophy. One hypothesis for the apparent discrepancy is that net autotrophic production occurs in aperiodic “bursts,” which are superimposed on a more constant background state of net heterotrophy. Mixing events, which introduce new nutrients to the surface ocean, provide one mechanism for fueling such aperiodic bursts of net production. In conjunction with the Eddy Flux (E-Flux) program in the lee of the Hawaiian Islands during winter 2004–2005, we examined the relationship between photosynthesis and irradiance (P vs. E) in surface waters inside and outside of two cold-core, cyclonic eddies, and conducted five incubation experiments to examine the metabolic response of mixed-layer plankton communities to nutrient-rich deep-sea water additions. Our results showed that in the mixed layer, maximum rates of light-saturated photosynthesis, derived from photosynthesis–irradiance experiments were not significantly different inside vs. outside the eddies (p=0.35 and 0.44 for E-Flux I and E-Flux III, respectively). Addition of nutrients to mixed-layer water showed that (1) gross primary production (GPP) became decoupled from a more constant rate of respiration and (2) net system metabolism shifted from approximate balance, or slight net heterotrophy, to a demonstrably net autotrophic system. From these results, we determined that the threshold GPP for net autotrophic production for the mixed layer of the study region was 1.65 mmol O₂ m⁻³ d⁻¹, which is consistent with previous estimates for the oligotrophic open ocean.     

富钴结核粒径分形特征

利用分形理论,对我国在中、西太平洋国际海底区域获得富钴结核的粒径特征进行了研究.结果显示富钴结核的粒径具有分段分形的特点,计算得到了它们的各自的分维数,并对其意义进行了探讨.     

Open boundary conditions for nonlinear channel flow

Open boundary conditions are derived for the one-dimensional nonrotating two-layer shallow-water equations. The conditions are based on characteristics of the external and internal modes. It is possible to find exact nonlinear characteristic conditions for the external mode, as well as approximate nonlinear conditions for the internal mode. These conditions can also be linearised by Taylor expansion; the approximate linear conditions are similar to those used in several previous studies. Both of the nonlinear and linearised conditions perform well, indicating that either the nonlinear or linearised conditions may potentially be extended to the more general case of multi-layer flows.     

Height variability from the MIROC – IPCC model for the 20th century compared to that of the TOPEX/POSEIDON altimeter

Planetary waves are key to large-scale dynamical adjustment in the global ocean as they transfer energy from the east to the west side of oceanic basins; they connect the forcing in the ocean interior with the variability at its boundaries; and they change the local heat content, thus coupling oceanic, atmospheric, and biological processes. Planetary waves, mostly of the first baroclinic mode, are observed as distinctive patterns in global time series of sea surface height anomaly (SSHA) and heat storage. The goal of this study is to compare and validate large-scale SSHA signals from coupled ocean-atmosphere general circulation Model for Interdisciplinary Research on Climate (MIROC) with TOPEX/POSEIDON satellite altimeter observations. The last decade of the models’ time series is selected for comparison with the altimeter data. The wave patterns are separated from the meso- and large-scale SSHA signals by digital filters calibrated to select the same spectral bands in both model and altimeter data. The band-wise comparison allows for an assessment of the model skill to simulate the dynamical components of the observed wave field. Comparisons regarding both the seasonal cycle and the Rossby wave field differ significantly among basins. When carried within the same basin, differences can occur between equal latitudes in opposite hemispheres. Furthermore, at some latitudes the MIROC reproduces biannual, annual and semiannual planetary waves with phase speeds and average amplitudes similar to those observed by the altimeter, but with significant differences in phase.     

Fluctuation in Ommastrephe bartrami yield in the North Pacific

The fluctuation in Ommastrephe bartrami yield from 1995 to 2001 in the North Pacific was shown obvious, on which this study was conducted using data of sea surface temperature (SST), chlorophyll-a (chl-a) and statistical production. The study shows that, cool water and low food abundance caused by abnormal Kuroshio resulted in the reduction in abundance of O. bartrami, which was worsened by excessive catch and the unawareness to local fishery resources protection.