Equatorial Atlantic variability and its relation to mean state biases in CMIP5

Coupled general circulation model (GCM) simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to their performance in the equatorial Atlantic. In terms of the mean state, 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial SST gradient whose sign is opposite to observations. Westerly surface wind biases in boreal spring play an important role in the reversed SST gradient by deepening the thermocline in the eastern equatorial Atlantic and thus reducing upwelling efficiency and SST cooling in the following months. Both magnitude and seasonal evolution of the biases are very similar to what was found previously for CMIP3 models, indicating that improvements have only been modest. The weaker than observed equatorial easterlies are also simulated by atmospheric GCMs forced with observed SST. They are related to both continental convection and the latitudinal position of the intertropical convergence zone (ITCZ). Particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability. The dependence of equatorial easterlies on ITCZ latitude shows a marked asymmetry. From the equator to 15°N, the equatorial easterlies intensify approximately linearly with ITCZ latitude. When the ITCZ is south of the equator, on the other hand, the equatorial easterlies are uniformly weak. Despite serious mean state biases, several models are able to capture some aspects of the equatorial mode of interannual SST variability, including amplitude, pattern, phase locking to boreal summer, and duration of events. The latitudinal position of the boreal spring ITCZ, through its influence on equatorial surface winds, appears to play an important role in initiating warm events.     

Phenocryst-bulk rock composition relations of abyssal tholeiites and their petrogenetic significance

In order to infer equilibrium phase relations of abyssal tholeiites, olivine, plagioclase, augite, and pigeonite tholeiites from the ocean floor are plotted in terms of the CIPW norm proportions in the tetrahedron olivine-plagioclase-diopside-quartz. The phase relations of abyssal tholeiites have a general similarity in form to those of the experimentally studied relevant systems. Experimental studies on natural basalts allow the pressure of crystallization for abyssal tholeiitic magmas to be evaluated approximately. It appears that the pressure at which the phenocryst-stage crystallization of abyssal tholeiites takes place is as high as 2 or 3 kbar, provided that abyssal tholeiitic magmas are ‘dry’.Abyssal tholeiites could be derived from liquids that are in equilibrium with Ca-poor pyroxene in the pressure range of about 5–8 kbar. Major element chemistry of abyssal tholeiites is incompatible with the view that these tholeiitic basalts are derived from picritic magma by olivine fractionation.     

Age constraints on the Palaeoproterozoic Lomagundi–Jatuli Event in Zimbabwe: Zircon geochronology of the Magondi Supergroup

The ca. 2.2–2.1 Ga Magondi Supergroup on the Zimbabwe Craton in Southern Africa is mainly composed of sedimentary rocks deposited in a rift basin/passive continental margin, which record a unique episode in carbon isotope perturbation called the Lomagundi–Jatuli Event (LJE). This study reports new U–Pb ages of detrital zircons from the Deweras and Lomagundi groups of the Magondi Supergroup, and of igneous zircons from underlying granitoids, to constrain the timing of the LJE and to identify the provenance of the Magondi Supergroup. Most analysed detrital zircon grains range in ages between ca. 2.9 and 2.6 Ga. Three ca. 2.3–2.2 Ga detrital zircons from sandstone of the Deweras Group, with the youngest ²⁰⁷Pb‐²⁰⁶Pb age of 2,216 ± 22 Ma, indicate the onset of LJE in the Zimbabwe Craton was almost simultaneous to that in Fennoscandia and the Superior Craton, supporting the global synchronicity of the LJE.     

Overview and current status of the VSOP mission

An overview and status report of the VLBI Space Observatory Programme is presented.     

Temperature evolution from the <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O record of Hani peat,Northeast China,in the last 14000 years

From the last deglaciation to the Holocene, the Greenland Ice Core (GISP2) δ ¹⁸O records as well as the records of ice-rafted debris on the surface of the North Atlantic have revealed a succession of sudden cooling events on the centennial to millennial scales. However, the temperature proxy records are rarely studied systematically and directly to ensure that this air temperature cooling pattern simultaneously existed in the East Asian Region, in addition to the repeated pattern occurring in the Greater Atlantic Region. A peat cellulose δ ¹⁸O temperature proxy record proximately existing for 14000 years was picked up from the Hani peat in Jilin Province, China. It suggests by comparison that the sudden cooling events, such as the Older Dryas, Inter-Allerød, Younger Dryas, and nine ice-rafted debris events of the North Atlantic, are almost entirely reiterated in the temperature signals of Hani peat cellulose δ ¹⁸O. These cooling events show that the repeatedly occurring temperature cooling pattern not only appeared in the North Atlantic Region in the high latitudes, but also in the Northwest Pacific Region in the middle latitudes. The climate change events marking the start of the Holocene Epoch, the Holocene Megathermal, the “8.2 kyr” event, the “4.2 kyr” event, the Medieval Warm Period, and the Little Ice Age are further discussed. The sensitivity response of Hani peat cellulose δ ¹⁸O to the land surface temperature and the reason for the age accuracy of peat cellulose ¹⁴C are also discussed based on the characteristics of the peat bog environment.     

Seasonal variations of the Hawaiian Lee Countercurrent induced by the meridional migration of the trade winds

Seasonal variations of the Hawaiian Lee Countercurrent (HLCC) are investigated using satellite observations of sea surface height and wind stress as well as eddy-resolving ocean model simulations. The HLCC is strong from summer to winter and weak in spring between the dateline and the Hawaiian Islands. In response to the seasonal migration of the northeast trade winds in the meridional direction, the wind curl dipole lee of Hawaii varies in strength, exciting westward-propagating Rossby waves. The analyses of both observations and simulations show that the propagation of Rossby waves south of the HLCC, driven by the southern pole of the wind curl dipole in the lee of the islands, contributes the most to the seasonal variations of the HLCC. Unlike the wind-driven seasonal variations, our analysis suggests that other mechanisms such as mode water intrusion or air–sea interaction may cause the interannual variations of the HLCC.     

Diffusion and sorption of Cs, I and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Clay-based modeling approach

Diffusion and sorption behaviors of cationic Cs⁺, anionic I⁻ and neutral HTO in samples of the Wakkanai Formation from the Horonobe underground research laboratory (URL), Japan, were investigated as a function of ionic strength (I) of synthetic groundwater by through-diffusion and batch sorption experiments and mechanistic modeling. The effective diffusivities (D_e) measured by through-diffusion experiments showed cation excess and anion exclusion effects, which were strongly dependent on I; D_e for Cs⁺ decreased as I increased, D_e for I⁻ showed the opposite dependency and D_e for HTO showed no dependence. The sorption of Cs⁺ measured by through-diffusion and batch sorption experiments were described by Freundlich isotherms with consistent parameters and decreased with I as a result of competitive ion exchange.Diffusion and sorption behaviors were interpreted by assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The component additive (CA) sorption model, which includes illite and smectite contents and their ion exchange constants, provided a reasonable account of the Cs⁺ sorption trends measured as functions of I and Cs concentration. The diffusion model was developed by coupling the electrical double layer (EDL) model, describing the change of ionic concentrations (cation excess and anion deficit) and viscoelectric effects caused by electrostatic interaction at negatively charged clay surfaces, and a simplified pore model assuming one type of pore shape and includes their size distribution. When averaging the electrostatic effects by using the pore surface area distribution, the model could predict the cation excess and anion exclusion effects, and its dependence on I reasonably well. This result implies the nanoscale pores dominating the pore surface area can strongly impact on ionic diffusion in argillaceous rocks. The clay-based modeling approach described here provides a useful tool to predict ionic diffusion and sorption in argillaceous rocks.     

Synchronous climate anomalies in the western North Pacific and North Atlantic regions during the last 14,000 years

A peat cellulose δ¹⁸O record spanning around 14,000 years from the Hani peat mire in northeastern China reveals several abrupt temperature anomalies in the period from the last deglaciation through the Holocene. The timing of these anomalies coincides well with the notable cooling events recorded respectively using the GISP2 ice core and ice-rafted sediment of the North Atlantic Ocean, such as the Older Dryas, Inter-Allerød, Younger Dryas, and the nine ice-rafted debris events. The results demonstrate that this repeating pattern of abrupt temperature deterioration is not limited to the North Atlantic area at high latitude but also exists in the western North Pacific region at middle latitude. The synchronous temperature anomalies possibly are resulted from the joint effects of meltwater discharge into the North Atlantic Ocean and reduced solar activity. In the period from around 8600 to 8200 cal. yrs BP the Hani peat record shows a broad δ¹⁸O peak that may reflect compound climate signals resulting from the two kinds of forcing factors: the temperature drop related to reduced solar activity at around 8600–8250 cal. yrs BP, and the temperature anomaly attributed to the meltwater effect at around 8220 ± 70 cal. yrs BP. This result may provide palaeo-temperature evidence for existence of the sharp “8.2 k” event in the western North Pacific region. In addition, our results have revealed that in the period from the last deglaciation through the Holocene the synchronous temperature anomalies before and after the “8.2 k” event seem to be related to meltwater outflow and reduced solar activity, respectively. It is important that the all temperature anomalies—whether because of reduced solar activity in the late Holocene or from meltwater discharge in the early Holocene—are accompanied by an abrupt decline in the Indian Ocean summer monsoon and abrupt strengthening of the East Asian summer monsoon. It is likely that reduced solar activity and meltwater outflow appear to modulate Earth system changes in the same direction. The influences could be compounded. Reduced solar activity and meltwater outburst both appear to act as triggers for occurrence of the El Niño phenomenon in the equatorial Pacific Ocean, which may result in broad teleconnections between the temperature anomaly in the Northern Hemisphere and abrupt variation of the Asian monsoon.     

First observations with the 64-m Kalyazin telescope included in a ground-based—space interferometer: The quasar 3C 147

The 64-m radio telescope equipped with an S-2 recording system in the town of Kalyazin was involved in an international fine-structure survey of quasars and active galactic nuclei carried out with a ground-based—space radio interferometer. The HALCA Japanese satellite in an orbit with an altitude of up to 24 000 km with an 8-m antenna was used as a space element of the interferometer. A radio image of the inner region of the CSS-type quasar 3C 147 was obtained with an angular resolution of ～0.3 mas at 6 cm. The image exhibits a core and several jet components mostly arranged in the main jet direction, but one of the components moves across the jet. No evidence was found for the superluminal separation of jet components. The estimated brightness temperature,～10¹¹ K, is consistent with the theoretical limit imposed by synchro-Compton radiation.