The flux of water from the mixed layer into the thermocline/intermediate layers of the Pacific Ocean is quantified using chlorofluorocarbon (CFC) and hydrographic data. The total ventilation flux of at least 123 Sv for the South Pacific (SP) only slightly exceeds that of at least 111 Sv for the North Pacific (NP). Although the overall ventilation flux (to 27.3 σ θ ) is similar in the NP and SP, the partitioning amongst the water masses is markedly different. In the NP the partitioning is equal between the wind‐driven (≤26.5 σ θ ) and thermohaline (>26.5–27.3 σ θ ) layers. While in the SP the ventilation flux of the thermohaline layers exceeds by nearly 2:1 the wind‐driven layers. The wind‐driven subtropical gyre thermocline ventilation flux for the NP (41 Sv) exceeds the SP (25 Sv), and both agree well with literature estimates of Sverdrup transports. The ventilated volumes and ages are related to the wind stress curl and surface buoyancy fluxes. In the thermocline ventilation of Shallow Salinity Minimum Water (22 m yr −1 in the NP, 15 m yr −1 in the SP) and Subtropical Mode Water is more effective in the NP than in the SP. In contrast, in the thermohaline layers direct air‐sea exchange during convective formation of Subantarctic Mode and Antarctic Intermediate Water is more effective in ventilating the SP than processes in the NP. These same differences are also used to explain the larger volume of the shadow zone in the NP. In the subpolar regions the ventilation fluxes can be used to infer formation rates of 8 Sv for the NP Intermediate Water and 9 Sv for the Subantarctic Mode Water. Into the tropical Pacific there is a substantial flux of 35 Sv of extratropical water for the wind‐driven layers and 36 Sv for the thermohaline layers. The relatively young (5–20 years increasing with increasing density) CFC‐derived ages show that a climate anomaly introduced into the subtropical thermocline could be transported into the tropics relatively quickly.
In 1995, concentrations of the chlorofluorocarbon compound CFC‐12 in the outflow water from the Persian Gulf were 8–40 fold higher than normally caused by air‐sea gas exchange. At that time, the anomaly was restricted to the Gulf of Oman north of 20°N, while in 1998 the signal had spread southwestward to 12°N. The sources of this CFC‐12 input of about 6400 kg are most likely the fire extinguishers and solvents used during and after the Gulf War in 1991. This CFC‐12 signal is a new feature of the Persian Gulf Water (PGW) which can be used to track and quantify the spreading and dilution of PGW in the northern Indian Ocean. The contaminated PGW spreads southward with a mean velocity of 0.02–0.025 m s −1 . At 20°N, the anomaly is diluted by a factor of more than two, and east of the island Socotra by a factor of four. A mean transport of less than 0.5·10 6 m³ s −1 is calculated for PGW assuming a mean dilution rate of 30% from the source signal in the Gulf of Oman to the western Arabian Sea.
Abstract. A high-quality dataset of surface water fugacity of CO2 (fCO2w)1, consisting of over a million observations, and derived products are presented for the northern Caribbean Sea, covering the time span from 2002 through 2018. Prior to installation of automated pCO2 systems on cruise ships of Royal Caribbean International and subsidiaries, very limited surface water carbon data were available in this region. With this observational program, the northern Caribbean Sea has now become one of the best-sampled regions for pCO2 of the world ocean. The dataset and derived quantities are binned and averaged on a 1∘ monthly grid and are available at http://accession.nodc.noaa.gov/0207749 (last access: 30 June 2020) (https://doi.org/10.25921/2swk-9w56; Wanninkhof et al., 2019a). The derived quantities include total alkalinity (TA), acidity (pH), aragonite saturation state (ΩAr) and air–sea CO2 flux and cover the region from 15 to 28∘ N and 88 to 62∘ W. The gridded data and products are used for determination of status and trends of ocean acidification, for quantifying air–sea CO2 fluxes and for ground-truthing models. Methodologies to derive the TA, pH and ΩAr and to calculate the fluxes from fCO2w temperature and salinity are described.
The CENP-W/T complex was previously reported to be required for mitosis. HeLa cells depleted of CENP-W displayed profound mitotic defects, with mitotic timing delay, disorganized prometaphases and multipolar spindles as major phenotypic consequences. In this study, we examined the process of multipolar spindle formation induced by CENP-W depletion. Depletion of CENP-W in HeLa cells labeled with histone H2B and tubulin fluorescent proteins induced rapid fragmentation of originally bipolar spindles in a high proportion of cells. CENP-W depletion was associated with depletion of Hec1 at kinetochores. The possibility of promiscuous centrosomal duplication was ruled out by immunofluorescent examination of centrioles. However, centrioles were frequently observed to be abnormally split. In addition, a large proportion of the supernumerary poles lacked centrioles, but were positively stained with different centrosomal markers. These observations suggested that perturbation in spindle force distribution caused by defective kinetochores could contribute to a mechanical mechanism for spindle pole disruption. 'Spindle free' nocodazole arrested cells did not exhibit pole fragmentation after CENP-W depletion, showing that pole fragmentation is microtubule dependent. Inhibition of centrosome separation by monastrol reduced the incidence of spindle pole fragmentation, indicating that Eg5 plays a role in spindle pole disruption. Surprisingly, CENP-W depletion rescued the monopolar spindle phenotype of monastrol treatment, with an increased frequency of bipolar spindles observed after CENP-W RNAi. We overexpressed the microtubule cross-linking protein TPX2 to create spindle poles stabilized by the microtubule cross-linking activity of TPX2. Spindle pole fragmentation was suppressed in a TPX2-dependent fashion. We propose that CENP-W, by influencing proper kinetochore assembly, particularly microtubule docking sites, can confer spindle pole resistance to traction forces exerted by motor proteins during chromosome congression. Taken together, our findings are consistent with a model in which centrosome integrity is controlled by the pathways regulating kinetochore-microtubule attachment stability.
The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.
Gas transfer velocities were determined in the Southern Ocean during the Southern Ocean Iron Fertilization experiment (SOFex) using the dual deliberate tracer technique. The decrease of the purposefully injected tracers, sulfur hexafluoride and helium‐3, could be well described by gas exchange parameterizations with wind speed that satisfy global constraints based on bomb‐ 14 C uptake. The concentration decrease of tracers could be predicted slightly better with established relationships if gas transfer was modeled as a function of the cube rather than the square of the wind speed, particularly over a time interval with high and variable winds. However, both fits can model the concentration decrease within the uncertainty of the observations. This suggests that it will be singularly difficult to definitively determine if a quadratic or cubic dependence of gas exchange with wind is more appropriate based on deliberate tracer measurements. However, these results show that gas exchange rates in the Southern Ocean are not anomalous when compared with the rest of the ocean. Thus this cannot account for discrepancy between observational and model‐based estimates of uptake of CO 2 in the Southern Ocean. Using a high‐quality wind speed field obtained from the QuikSCAT satellite Seawinds scatterometer and an established surface water pCO 2 climatology, the CO 2 uptake in the Southern Ocean (>34°S) is reassessed. The total uptake rates are similar to previous observation‐based estimates, but the analysis shows that the uptake rate is sensitive to wind speed product used and the wind speed distribution.
We report the determination of the complete sequences for two chicken beta tubulin genes, beta 3 and beta 5. Taken with the previously published efforts, we have determined the primary structures of five of the seven beta tubulin genes in this vertebrate species. A comparison of these sequences unambiguously reveals that amino acid sequence variations among different beta tubulin gene products are distinctly clustered within an otherwise highly conserved framework of the beta tubulin molecule. To determine the extent to which this pattern of structural heterogeneity is conserved among vertebrates, we have isolated novel beta tubulin sequences from human and mouse cDNA libraries and compared these and all other known vertebrate beta tubulin sequences with the family of chicken polypeptide sequences. What emerges from such comparison is the recognition of distinct, evolutionarily conserved isotypes of beta tubulin that are distinguished primarily by their characteristic carboxyl-terminal variable region sequence and, to a lesser extent, by sequence in an amino-terminal variable domain as well. These correlations represent a convincing demonstration that multiple beta tubulin genes in vertebrates encode a family of closely related but structurally distinct beta tubulin isotypes and further serve to define the sequences of four classes of polypeptide isotypes that constitute that family.
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