Spectral analysis and modeling of microcyclostratigraphy in late Paleozoic glaciogenic rhythmites, Parana Basin, Brazil

We investigate the depositional time scale of lithological couplets (fine sandstone/siltstone-siltstone/mudstone) from two distinctive outcrops of Permo-Carboniferous glacial rhythmites in the Itarare Group (Parana Basin, Brazil). Resolving the fundamental issue of time scale for these rhythmites is important in light of recent evidence for paleosecular variation measured in these sequences. Spectral analysis and tuning of high-resolution gray scale scans of sediment core microstratigraphy, which comprises pervasive laminations, reveal a comparable spectral content at both localities, with a frequency suite interpreted as that of short-term climate variability of Recent and modern times. This evidence for decadal- to centennial-scale deposition of these lithological couplets is discussed in light of the `varvic` character, i.e., annual time scale that was previously assumed for the rhythmites.

Community structure and dynamics in climate networks

We consider climate networks constructed from observed and model simulated fields of three climate variables and investigate their community structure. We find that for all fields the number of effective communities is rather small (four to five). We are able to trace the origin of these communities to certain dynamical properties of climate. Our results suggest that the complete complexity of the climate system condenses beyond the `weather` time scales into a small number of low-dimensional interacting components and provide clues as to the nature of the climate subsystems underlying these components.

Orbitally driven east-west antiphasing of South American precipitation

The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales. This antiphasing arises through the alternating strength of incoming solar radiation in the two hemispheres, which affects monsoon intensity and hence the position of the meridional atmospheric circulation of the Hadley cells(1-4). Here we compare an oxygen isotopic record recovered from a speleothem from northeast Brazil for the past 26,000 years with existing reconstructions of precipitation in tropical South America(5-8). During the Holocene, we identify a similar, but zonally oriented, antiphasing of precipitation within the same hemisphere: northeast Brazil experiences humid conditions during low summer insolation and aridity when summer insolation is high, whereas the rest of southern tropical South America shows opposite characteristics. Simulations with a general circulation model that incorporates isotopic variations support this pattern as well as the link to insolation-driven monsoon activity. Our results suggest that convective heating over tropical South America and associated adjustments in large-scale subsidence over northeast Brazil lead to a remote forcing of the South American monsoon, which determines most of the precipitation changes in the region on orbital timescales.

REPRODUCTIVE BIOLOGY IN FEMALES OF AEGLA STRINATII (DECAPODA: ANOMURA: AEGLIDAE)

Females of Aegla strinatii (n = 466) were sampled monthly (September 2003 to September 2005) by means of sieves and traps from Rio das Ostras (24 degrees 38'16.2 '' S; 48 degrees 24'05.2 '' W), at Jacupiranga State Park, South of Sao Paulo State, Brazil. The reproductive period was markedly seasonal (from May to September) encompassing the Austral late autumn through late winter. This is in accordance to the pattern of reproductive period variations in relation to the latitudinal climate variability verified in species of Aegla. The proportion of adult females exhibiting the ovigerous condition was higher in young/small specimens as compared to old/large ones, and suggests the occurrence of senescence in the latter group. Average size at the onset of functional maturity in females was estimated as 16.66 mm of carapace length (rostrum excluded). The number of eggs per ovigerous females ranged from 1 to 325. Eggs are slightly elliptical and average size varied according to embryonic stage. Mean (+/- standard deviation) carapace length of juveniles (n = 118) was 1.50 +/- 0.05 mm (range: 1.40-1.65mm).

The impact of El Nino Southern Oscillation phases on off-season maize yield for a subtropical region of Brazil

In recent years, maize has become one of the main alternative crops for the autumn winter growing season in the central-western and southeastern regions of Brazil. However, water deficits, sub-optimal temperatures and low solar radiation levels are common problems that are experienced during this growing season by local farmers. One methodology to assess the impact of variable weather conditions on crop production is the use of crop simulation models. The goal of this study was to evaluate the effect of climate variability on maize yield for a subtropical region of Brazil. Specific objectives for this study were (1) to analyse the effect of El Nino Southern Oscillation (ENSO) on precipitation and air temperature for four locations in the state of Sao Paulo and (2) to analyse the impact of ENSO on maize grown off-season for the same four locations using a crop simulation model. For each site, historical weather data were categorised as belonging to one of three phases of ENSO: El Nino (warm sea surface temperature anomalies in the Pacific), La Nina (cool sea surface temperature anomalies) or neutral, based on an index derived from observed sea surface temperature anomalies. During El Nino, there is a tendency for an increase in the rainfall amount during May for the four selected locations, and also during April, mainly in three of the locations, resulting in an increase in simulated maize yield planted between February 15 and March 15. In general, there was a decrease in the simulated yield for maize grown off-season during neutral years. This study showed how a crop model can be used to assess the impact of climate variability on the yield of maize grown off-season in a subtropical region of Brazil. The outcomes of this study can be very useful for both policy makers and local farmers for agricultural planning and decision making. Copyright (C) 2009 Royal Meteorological Society

Annual growth rings in the mangrove Laguncularia racemosa (Combretaceae)

Stem discs from trees of known age were used to determine the periodic nature of the growth rings formed in Laguncularia racemosa and to describe the anatomical features of these rings. The growth rings were scarcely distinct on microscopic examination, but they were well distinguishable macroscopically, with alternating light brown and dark brown layers. Cross-dating analysis revealed the occurrence of annual growth rings in L. racemosa. The existence of annual growth rings in L. racemosa suggests that it may have great potential for dendrochronology and should encourage age-related studies on the dynamics of mangrove forests. These studies can be important for the evaluation of climate change impact on mangrove ecosystems, as well as for the analysis of effects related to climate variability on plant communities.