Low-latitude Locations Research Articles

Planktic foraminiferal response to early Eocene carbon cycle perturbations in the southeast Atlantic Ocean (ODP Site 1263)

At low latitude locations in the northern hemisphere, striking changes in the relative abundances and diversity of the two dominant planktic foraminifera genera, Morozovella and Acarinina, are known to have occurred close to the Early Eocene Climatic Optimum (EECO; ~49–53Ma). Lower Eocene carbonate-rich sediments at Ocean Drilling Program (ODP) Site 1263 were deposited on a bathymetric high (Walvis Ridge) at ~40° S, and afford an opportunity to examine such planktic foraminiferal assemblage changes in a temperate southern hemisphere setting. We present here quantified counts of early Eocene planktic foraminiferal assemblages from Hole 1263B, along with bulk sediment stable isotope analyses and proxy measurements for carbonate dissolution. The bulk sediment δ13C record at Site 1263 resembles similar records generated elsewhere, such that known and inferred hyperthermal events can be readily identified. Although some carbonate dissolution has occurred, the well-preserved planktic foraminiferal assemblages mostly represent primary changes in environmental conditions. Our results document the permanent decrease in Morozovella abundance and increase in Acarinina abundance at the beginning of the EECO, although this switch occurred ~165kyr after that at low-latitude northern hemisphere locations. This suggests that unfavourable environmental conditions for morozovellids at the start of the EECO, such as sustained passage of a temperature threshold or other changes in surface waters, occurred at lower latitudes first. The remarkable turnover from Morozovella to Acarinina was widely geographically widespread, although the causal mechanism remains elusive. In addition, at Site 1263, we document the virtual disappearance within the EECO of the biserial chiloguembelinids, commonly considered as inhabiting intermediate water depths, and a reduction in abundance of the thermocline-dwelling subbotinids. We interpret these changes as signals of subsurface water properties, perhaps warming, and the associated contraction of ecological niches.

Self-reported discomfort associated with Daylight Saving Time in Brazilian tropical and subtropical zones

Background: Daylight Saving Time (DST) annually moves clocks 1 hour forward, when daytime is longer than night. Previous studies from medium and high latitude locations have pointed to a disruptive effect of DST on human circadian rhythms. Since Brazil is an equatorial country implementing DST, a different relationship between photic and social synchronisers may interfere with DST effects.Aim: To explore the prevalence and duration of self-reported discomfort related to DST among Brazilian residents (latitude 12–33° S, longditude 39–57° W). It was hypothesised that an elevated prevalence of self-reported discomfort would be found in Brazil, due to the pronounced uncoupling between social and geophysical synchronisers.Subjects and methods: In total, 12 467 volunteers completed a web-based, Brazilian version of Horne-Östberg Morningness-Eveningness Questionnaire, provided demographic information, and answered questions related to DST complaints (discomfort, duration of discomfort).Results: Of the total sample, 45.43% reported no discomfort related to DST, with meaningful proportions for all chronotypes. However, eveningness was most associated with discomfort. About one fourth of the total sample reported discomfort over the whole DST period. Gender interaction is largely supported by these results.Conclusions: DST at low latitude locations may be disruptive for circadian rhythms, since seasonality of sunrise near the equator is negligible or very mild.

Analytic modeling of parabolic trough solar thermal power plants

We derive, evaluate and validate comprehensive analytic modeling of the energy flows in parabolic trough solar thermal power plants. The analytic formulae are straightforward to implement and evaluate, relating to the heat transfer within and from the solar concentrators (including transients, mainly overnight heat losses), and the impact of solar field operation on turbine power and efficiency. Prior numerical simulations used to design solar thermal power systems have either been proprietary or devoid of a fully-reported source code - hence inaccessible or problematic for widespread use. Also, the dependence of these simulations on extensive numerical procedures does not provide a transparent physical picture that grants a clear understanding of how component and system performance vary with the principal operating and input variables - a drawback overcome by the analytic approach presented here. Published experimental measurements of sufficient extent to permit meaningful comparisons between theory and experiment for such solar thermal power plants are exceptionally limited. This narrow data base is used for model validation on both a monthly and an hourly basis. The analytic model is then applied to evaluating a solar power plant now being planned for northeast Brazil, also highlighting the energy-delivery advantages of low-latitude locations.

Probing the infrared counterparts of diffuse far-ultraviolet sources in the Galaxy

Recent availability of high quality infrared (IR) data for diffuse regions in the Galaxy and external galaxies have added to our understanding of interstellar dust. A comparison of ultraviolet (UV) and IR observations may be used to estimate absorption, scattering and thermal emission from interstellar dust. In this paper, we report IR and UV observations for selective diffuse sources in the Galaxy. Using archival mid-infrared (MIR) and far-infrared (FIR) observations from Spitzer Space Telescope, we look for counterparts of diffuse far-ultraviolet (FUV) sources observed by the Voyager, Far Ultraviolet Spectroscopic Explorer (FUSE) and Galaxy Evolution Explorer (GALEX) telescopes in the Galaxy. IR emission features at 8µm are generally attributed to Polycyclic Aromatic Hydrocarbon (PAH) molecules, while emission at 24µm are attributed to Very Small Grains (VSGs). The data presented here is unique and our study tries to establish a relation between various dust populations. By studying the FUV-IR correlations separately at low and high latitude locations, we have identified the grain component responsible for the diffuse FUV emission.

A comprehensive optical characterization of linear Fresnel collectors by means of an analytic study

Linear Fresnel collectors lead to a reduction of investment costs compared to parabolic trough collectors, but it is not yet certain whether this implies a reduction of levelyzed cost of electricity or not. In order to analyze the optical behavior of concentrators ray trace models are often used. However, such methodology leads to time-consuming codes that make difficult to optimize all design variables. In this work an analytic method is used in order to characterize the effect of the design variables on the annual energy impinging onto the reflecting surface, and results for two different locations are compared. The paper leads to the notable conclusion that the ratio of energy impinging onto the reflecting surface of Fresnel collectors is closer to that of parabolic troughs at low latitude locations.

Global warming impact on floral phenology of fruit trees species in Mediterranean region

This study was carried out in three geographically contrasting countries of the Mediterranean region. It aims to understand the impact of climate change, particularly the temperature increases, on phenological stage of three taxonomically different species (early and late-spring-flowering species). Three species, namely olive (Olea europaea), apple (Malus domestica Borkh.) and almond (Prunus dulcis (Mill.)) were investigated to highlight the phenological behavior of one species at different locations and different species at one location. Climatic and phenological data were collected from Morocco, France and Italy over the last 40 years. Analysis of data on temperature showed a strong warming in the northern locations (coldest areas), particularly in Nîmes, compared to the southern ones (warmer locations) during the period October to May. The marked spring warming in all locations since the end of 1980s in France (the beginning of 1990s in Italy and Morocco) resulted in blooming earliness, with regional patterns in terms of impact. The late-spring-flowering species (olive and apple) showed a remarkable sensitivity to continuous warming in different areas. No flowering earliness was observed in early-spring-flowering species (almond), due to the stability of mean temperature during February. Thus, a strong control of mean temperature during the forcing period on flowering earliness of apple was found in all areas. Physiological processes (dormancy and dormancy release) of trees during the dormant and growth period explain, in part, the regional differences observed in flowering dates among sites and species. Overall, the pronounced warming in the southern France reflects a relative trend toward aridity of climate at this site, and consequently some vulnerability of fruit trees. As result, the process of flowering in a high latitude locations (northern areas) in the future can be represented by that in a low latitude locations at present (southern areas), particularly for apple.

Was the Late Paleocene-Early Eocene Hot Because Earth Was Flat? An Ocean Lithium Isotope View of Mountain Building, Continental Weathering, Carbon Dioxide, and Earth's Cenozoic Clima

Hothouse climates in Earth’s geologic past, such as the Eocene epoch, are thought to have been caused by the release of large amounts of carbon dioxide and/or methane, which had been stored as carbon in biogenic gases and organic matter in sediments, to the ocean-atmosphere system. However, to avoid runaway temperatures, there must be long-term negative feedbacks that consume CO 2 on time scales longer than the ~ 100,000 years generally ascribed to ocean uptake of CO 2 and burial of marine organic carbon. Here, we argue that continental chemical weathering of silicate rocks, the ultimate long-term (multi-million year) sink for CO 2 , must have been almost dormant during the late Paleocene and early Eocene, allowing buildup of atmospheric CO 2 to levels exceeding 1,000 ppm. This reduction in the strength of the CO 2 sink was the result of minimal global tectonic uplift of silicate rocks that did not produce mountains susceptible to physical and chemical weathering, an inversion of the Uplift-Weathering Hypothesis. There is lack of terrestrial evidence for absence of uplift; however, the δ 7 Li chemistry of the Paleogene ocean indicates that continental relief during this period of the Early Cenozoic was one of peneplained (flat) continents characterized by high chemical weathering intensity and slow physical and chemical weathering rates, yielding low river fluxes of suspended solids, dissolved cations, and clays delivered to the sea. Only upon re-initiation of mountain building in the Oligocene-Miocene (Himalayas, Andes, Rockies) and drifting of these continental blocks to low-latitude locations near the Inter-Tropical Convergence Zone and monsoonal climate belts did continental weathering take on modern characteristics of rivers with high suspended loads and incongruent weathering, with much of the cations released during weathering being sequestered into secondary clay minerals. The δ 7 Li record of the Cenozoic ocean provides another piece of circumstantial evidence in support of the Late Cenozoic Uplift-Weathering Hypothesis.

Estimation of $hmF2$ and $foF2$ Communication Parameters of Ionosphere $F2$-Layer Using GPS Data and IRI-Plas Model

F2-layer is the most important and characteristic layer of the ionosphere in the propagation of high frequency (HF) waves due to the highest level of conductivity in the propagation path. In this study, the relation of Total Electron Content (TEC) with the maximum ionization height (hmF2) and the critical frequency (foF2) of F2-layer are investigated within their defined parametric range using the IRI model extended towards the plasmasphere (IRI-Plas). These two parameters are optimized using daily observed GPS-TEC (IONOLAB-TEC) in an iterational loop through Non-Linear Least Squares (NLSQ) optimization while keeping the physical correlation between hmF2 and foF2 parameters. Optimization performance is examined for daily (24-hour) and hourly TEC optimizations separately. It is observed that hourly TEC optimization produces results with much smaller estimation errors. As a result of the hourly optimization, we obtain the hourly hmF2 and foF2 estimates as they are the optimization parameters. Obtained hmF2 and foF2 estimates are compared with the ionosonde estimates for various low, middle and high latitude locations for both quite and disturbed days of ionosphere. The results show that hmF2 and foF2 estimates obtained from IRI-Plas optimization (IRI-Plas-Opt) and ionosonde are very much in agreement with each other. These results also signify that IRI-Plas provides a reliable background model for ionosphere. With the proposed method, it is possible to build a virtual ionosonde via optimization of IRI-Plas model using the observed TEC values.

Importance of local vs. geographic variation in salt marsh plant quality for arthropod herbivore communities

Summary An important recent advance in food web ecology has been the application of theory regarding spatial gradients to studies of the factors that affect animal population dynamics. Building on extensive studies of the Spartina alterniflora food web at the local scale, we hypothesized that geographic variation in S. alterniflora quality is an important bottom-up control on food web structure and that geographic variation in S. alterniflora quality would interact with the presence of predators and top omnivores to mediate herbivore densities. We employed a four-factor fully crossed experiment in which we (i) collected plants from high- and low-latitude locations and grew them in a common garden and varied (ii) plant fertilization status (mimicking the plant quality differences due to marsh elevation), (iii) mesopredator density and (iv) omnivore density. Our results suggest that the single most important factor mediating insect herbivore densities is local variation in plant quality – induced in our experiment by fertilization and demonstrated repeatedly as a consequence of marsh elevation. Top-down effects were generally weak and in those cases where predators did exert a significant suppressing effect on herbivores, that impact was itself mediated by host-plant characteristics. Finally, despite observed variation in plant quality with latitude, and the separately measurable effects of this variation on herbivores, geographic-scale variation in plant quality was overwhelmed by local conditions in our experiments. Synthesis. We suggest that a first-order understanding of variation across large latitudinal ranges in the Spartina alterniflora arthropod food web must begin with local variation in plant quality, which provides strong bottom-up forcing to herbivore populations. A second-order understanding of the arthropod food web should consider the role of predation in controlling herbivores feeding on low-quality plants. Finally, while latitudinal variation in plant quality probably explains some variation in herbivore densities, it is probably more of a response to herbivore pressure than a driver of the herbivore dynamics. Although extrapolating from local to geographic scales presents multiple challenges, it is an essential task in order for us to develop an understanding that is general rather than site-specific.

First bird remains from the Eocene of Algarrobo, central Chile Primeros restos de aves del Eoceno de Algarrobo, Chile central

Paleogene records of birds in the Eastern margin of the Pacific Ocean have increased in recent years, being almost exclusively restricted to fossil Sphenisciformes (penguins). New avian remains (Ornithurae, Neornithes) from Middle-to-Late Eocene levels of the Estratos de Algarrobo unit, in Algarrobo, central Chile, are disclosed in the present work. These new finds are significant in representing the first non-spheniscid bird remains of Middle to Late Eocene age, recovered in mid-latitudes of the eastern Pacific and probably belonging to a procelarid. It complements the regional record of Eocene birds, previously known only at high-latitudes such as Seymour Island (Antarctica) and Magallanes (Chile), and low-latitude locations in Peru.

Low-latitude mesospheric vertical winds observed using VHF radar

[1] Using long-term data (January 1998 to December 2009) collected from Mesosphere-Stratosphere-Troposphere (MST) radar located at a tropical station, Gadanki (13.5°N, 79.2°E), India, variability of low-latitude mesospheric vertical wind is investigated for the first time. The emphasis is on sub-daily, monthly, seasonal and annual variabilities in vertical wind in the altitude region 65–85 km. Possible sources of errors in the vertical wind measurement at mesospheric altitudes from the MST radar are discussed. The observed mesospheric vertical wind is generally upward in all the seasons. During winter and summer, significant sub-daily variations are noticed followed by spring and fall equinoxes. The vertical wind can reach occasionally values as high as 5 ms−1 but most of the time (95%) it is, in general, less than ∼2.63 ms−1. The present observations are consistent with the general circulation features in recent models for low latitude locations with northward and upward wind prevailing throughout the year representing part of meridional circulation.

Bimodal breeding seasonality of an understorey bird, Premnoplex brunnescens, in an Ecuadorian cloud forest

Despite the aseasonality of temperature and day length of many tropical regions, especially when compared with temperate latitudes, most tropical animals show fairly pronounced seasonal shifts in foraging, movement patterns and reproduction (Flecker & Feifarek 1994, Saul 1975, Wolda & Fisk 1981). Understanding reproductive seasonality in tropical avian communities involves distinguishing among complex interactions between weather, resource abundance, hormones, behaviour and other life-history traits (Wikelski et al. 2003). While there is a great deal of evidence that many tropical bird species breed seasonally (Hau 2001, Marchant 1959, Miller 1963, Snow & Snow 1964), we still understand little of the causes which drive observed patterns (Wikelski et al. 2003). Most studies which address the seasonality of reproduction in tropical birds have focused on locations with fairly extreme temporal changes in rainfall (Cruz & Andrews 1989, Lack 1950, Marchant 1959, Poulin et al. 1992, Voous 1950), and comparatively few have looked at relatively aseasonal low-latitude locations (Miller 1963, Moreau 1950). Similarly, though a few studies have pointed out slight variation in the within-species initiation of breeding based on microhabitat (Wikelski et al. 2003), we know very little about how micro-habitat choice for nesting may affect (or be affected by) breeding seasonality. In this study I describe the nesting cycle of the spotted barbtail (Premnoplex brunnescens), from the Ecuadorian Andes to better understand how reproduction may be seasonal when climatic cues are subtle or absent.

Medical Problems Requiring Mountain Rescues from 1985 to 2007 in Yu-Shan National Park, Taiwan

Wang, Shih-Hao(1,2) Tai-Yi Hsu,(1,2) Jen-Tse Kuan,(1,2) Jih-Chang Chen,(1,2) Wei-Fong Kao,(3) Te-Fa Chiu,(1,2) Yu-Cheng Chen,(1,2) and Hang-Cheng Chen.(1,2) Medical problems requiring mountain rescues from 1985 to 2007 in Yu-Shan National Park, Taiwan. High Alt. Med Biol. 10:77-82, 2009.-Medical problems requiring mountain rescue in densely populated and low-latitude locations like Taiwan have rarely been studied or discussed. The purpose of this research was to examine mountain-rescue operations that occurred in Yu-Shan National Park Taiwan from 1985 to 2007. Of 186 mountain-rescue operations, 128 involved medical problems (illnesses or injuries). Of the medical problems, 62% involved trauma and 41% involved illness. Ninety-nine ground rescues, 14 helicopter rescues, 38 combination ground and helicopter rescues, and 20 rescues using unclear methods were conducted, and the remaining 15 rescue operations did not involve visitors. In the 186 rescue operations, 330 visitors were rescued, 240 of them survived, 66 were dead, and 24 had an unclear outcome. Factors that affected the type of injury or the probability of survival included the activity, altitude, composition of the visitor group, weather, and occurrence of natural disasters. Mountain-rescue operations in which both ground and helicopter rescue were utilized were more successful. Our retrospective findings indicate that wilderness emergency services should have the capability of performing rescues in rugged terrain and be flexible in their approach to any situation arising in mountainous regions; proper training of onboard helicopter medical personnel is also necessary. In conclusion, we recommend setting up a standard system for reporting mountain- rescue operations, with statistics compiled annually.

Solar flux effects on equatorial ionization anomaly and total electron content over Brazil: Observational results versus IRI representations

The F layer critical frequency (foF2) as measured by Digisondes in the equatorial and low latitude locations in Brazil is analyzed to investigate the seasonal and solar flux controls of the intensity of the equatorial ionization anomaly (EIA) in the equinoctial month of March. The analysis also included the total electron content (TEC) as measured by a GPS receiver operated at the EIA crest location. The foF2 data set covered a period of large solar flux variation from 1996 to 2003, while the GPS TEC data was for a period in 2002–2003 when the solar flux parameter F10.7 underwent large variations, permitting in both cases an examination of the solar flux effects on these parameters. The seasonal variation pattern in TEC shows a maximum in equinoctial months and a minimum in June solstice, with similar variations for foF2. The solar flux dependence of the TEC is a maximum during equinoxes, especially for post-sunset TEC values at times when the latitudinal distribution is controlled by the equatorial evening plasma fountain processes. Significant variations with local time are found in the degree of solar flux dependence for both the TEC and EIA. The EIA intensity shows large dependence on F10.7 during post-sunset to midnight hours. These results are discussed in comparison with their corresponding IRI representations.

Latitudinal symbiont zonation in Stylophora pistillata from southeast Africa

Studies on latitudinal gradients in Symbiodinium diversity on scleractinian corals are largely restricted to warm-water low latitude locations, and it appears that there is a shift in symbiont distributions with increasing latitude. The Symbiodinium assemblages of high latitude coral communities have largely been undocumented despite occupying an important transitional zone between tropical and temperate regions. Using a combination of the internal transcribed spacer region 2 (ITS2) and denaturing gradient gel electrophoresis (DGGE), we assessed the cladal and subcladal variability of Symbiodinium in the widely distributed species Stylophora pistillata along a latitudinal transect in southeast African waters which extended into high latitude locations. All colonies examined belonged to clade C. Six unique ITS2-DGGE banding profiles (designated Cspa to Cspf) were observed, which showed a latitudinal distribution from north to south, most likely a result of a gradient in water temperature and irradiance driven by riverine input in the southern regions. Sequence analysis revealed that all sequences except one did not match previously identified clade C sub-types, probably due to the lack of regional information in the Western Indian Ocean when compared to the Caribbean and Pacific. This study further supports the applicability of ITS2-DGGE in studies on Symbiodinium diversity, and highlights that potentially ecologically informative biogeographic patterns may be overlooked when only cladal designations are employed.

Variability of equatorial ionospheric electron density at fixed heights below the F2 peak

Abstract A study on variability of the equatorial ionosphere was carried out at fixed heights below the F2 peak for two different levels of solar activity. The study covered height range of 100 km up to the peak of F2 layer using a real height step increase of 10 km. The variability index used is the percentage ratio of standard deviation over the average value for the month. Daytime minimum variability of between 3% and 10% was observed at height range of about 150–210 km during low solar activity and between 2% and 7% at height range of 160–220 km during high solar activity. The nighttime maximum of between 70% and 187% was observed at height range of about 210–250 km during low solar activity and between 42% and 127% at height range of 210–250 km during high solar activity. The height range at which daytime minimum was observed falls within the F1 height of the ionosphere. The result obtained is consistent with previous works carried out in the low latitude locations for American sector.

Day-to-day variability in the occurrence characteristics of Sq focus during d-months and its association with diurnal changes in the Declination component

AbstractScrutiny of the geomagnetic observations of the Declination component “D” from equatorial and low-latitude locations in the Indian longitude revealed anomalous variations during d-months. Examination of the Quiet day (Ap≤7) variations in the Declination component (Yin nT =HsinD) and Horizontal component (H) during the d-months (November, December, January, February) of the low solar activity year 1977 revealed the salient features associated with the day-to-day changes observed in Sq current system over the latitude chain in the Indo-Russian longitude. Diurnal variations in the east-west componentYand north-south componentHwere used to depict the effect of changes in the Sq current pattern for a selected set of Quiet days, which are classified into normal and abnormal days based on the trend in the variation of the Declination component. Normal days designated in the study clearly showed the expected pattern of variation in ΔY(eastward-directed field) in the morning hours and westward-directed field in the afternoon hours, and diurnal variation of ΔHsimultaneously showed the presence of northern Sq focus within the low-latitude range. In contrast, the abnormal days projected by the variation in ΔYand ΔHon certain days of d-months showed an almost complete absence of the focus formation within the expected latitude extent. Day-to-day variability characteristics of the Declination component discussed in the study are illustrated in relation to modifications in the expected Sq current system by the invasion of the prevalent southern hemisphere current whorl to the northern hemisphere during the winter months. Some of the anomalous changes observed in the day-to-day variation in the latitudinal pattern of ΔYand ΔHcomponents are also interpreted as suggesting an influence of high-latitude magnetospheric current systems on certain quiet days.

Formation of an F3 layer in the equatorial ionosphere: A result from strong IMF changes

We analyzed ionospheric observations made with digisondes in Jicamarca, Ramey, Wallops Island, Ascension Island, and Kwajalein Island during the major magnetic storm of November 9–10, 2004, which was associated with rapid interplanetary magnetic field (IMF) Bz changes. The strongest ionospheric responses to the southward IMF Bz turning were observed at the dip equator at Jicamarca where during the magnetic disturbance a dramatic F2 peak density depletion occurred at around 15:00 local time, accompanied by a fast upward motion of the plasma. In this process, an additional ionospheric layer, the F3 layer, formed with peak densities NmF3 exceeding NmF2. This observation may be considered evidence of an equatorial plasma fountain enhancement caused by the magnetic field disturbance. Responses were observed in a large range of latitudes and local times. The best indicator of the responses appears to be the peak height of the F layer, since competing processes determine the peak densities. The observed responses at low latitude locations in the morning and dusk sectors pose challenges to the simple penetrating electric field model because the upward motion is inconsistent with the E× B drift associated with a dawn–dusk electric field. Clear responses in the Jicamarca local time sector occurred at latitudes as high as 28°, at Ramey, Puerto Rico. This latitude range appears to be beyond the range of the flux tube corresponding to the 900 km F3 layer peak height at Jicamarca, indicating a more extended uplifting of flux tubes.

Comment on “Anomalous radiocarbon ages for foraminifera shells” by W. Broecker et al.: A correction to the western tropical Pacific MD9821‐81 record

[1] The effort to obtain high-resolution paleoceanographic data often leads to continental margin settings where the flux of clastic sediments produces higher sediment accumulation rates. However, on continental margins the possibility for down-slope transport of reworked sediment is a concern. This is particularly true in tectonically active settings such as the western Pacific, which includes the maritime islands of the Philippines and the adjacent archipelago. The continental margins of the western tropical Pacific are strategically located within the Pacific Warm Pool, and detailed paleoceanographic information from this region is a valuable asset in efforts to improve our understanding of what factors contribute to large and sometimes abrupt changes in global climate. The acquisition of data sets such as sea surface temperatures from the tropical Pacific warm pool through the last glacial cycle has indeed added measurably to a growing array of data from lowlatitude locations. Certainly, there is much left to be learned from the high deposition rate records located in continental margin settings. However, over the past 2 years, there have been concerns that one of the high deposition rate sequences in the western tropical Pacific, R/V Marion Dufresne core MD98-2181, is composed of down-slope transport of reworked material or slumping [Broecker et al., 2006]. Because this site has provided one of the highest-resolution data sets of sea surface temperature and salinity information for the Pacific warm water pool through the last glacial cycle [Stott et al., 2002, 2004], it is important to assess the stratigraphic integrity of the sequence and to identify where there may be problems with the record. [2] The MD98-2181 core was collected from a depth of 2114 m on the continental slope south of Mindanao Island. During the last glacial and Holocene sediments accumulated at this site at rates of between 50 and 80 cm/kyr making this an ideal location to collect high-resolution paleoceanographic information from the Pacific Warm Pool [Stott et al., 2004]. We have worked on the MD98-2181 core for the past eight years, conducting stable isotope and Mg/Ca measurements on planktonic and benthic foraminifers in an effort to document the timing and the magnitude of sea surface temperature and salinity changes in the western tropical Pacific Warm Pool through the last glacial cycle [Stott et al., 2002, 2004]. In doing so we have obtained C ages for 42 planktonic foraminifer samples from the Holocene and late glacial portions of the core (Table 1 and Figure 1). The majority of our MD98-2181 samples were taken from u-channel subcores. These subcores were sectioned continuously at 2 cm increments in Stott’s laboratory and the samples were washed in buffered DI water over a 63 mm sieve to remove fine clays. The planktonic Globigeriniodes ruber used for stable isotope and Mg/Ca measurements and also for C determinations was picked from the >150 mm fraction whereas Globigerinoides sacculifer was picked from the >250 mm fraction. In some instances other more robust planktonic species have also been C dated including, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei, which were picked from the >250 mm fractions. M. Rincon, who has been Stott’s laboratory manager for the past 15 years, picked each sample used in these studies. The G. ruber dO stratigraphy for MD98-2181 is shown in Figure 2. [3] The late glacial to Recent dO stratigraphy from this core matches other high-resolution sequences from this region with the exception of a 20 cm interval between 941 and 961 cm. The samples from the 941–961 cm interval exhibit dO values that are clearly higher than adjacent intervals immediately above and below (Figure 2). The interval centered at 950 cm would have been deposited during the last deglaciation and the apparent timing of the anomalously high dO values would put it close to the time of the Younger Dryas. For this reason it was not initially clear whether these values represented the presence of reworked glacial age material or if the values were indicative of a brief return to glacial-like conditions during the deglaciation. The intervals directly below 961 cm do not exhibit such high dO values as those at 950 cm and the isotope stratigraphy appears to closely match that of other high-resolution records from the western tropical Pacific region [Stott et al., 2004]. [4] In 2003, W. Broecker approached Stott about a collaboration that involved C dating of planktonic and PALEOCEANOGRAPHY, VOL. 22, PA1211, doi:10.1029/2006PA001379, 2007 Click Here for Full Article

Forage production of tropical grasses under extended daylength at subtropical and tropical latitudes

Decreased growth of warm-season forage grasses during subtropical winters has been shown to be a response to short-daylength during those months. The objective of this research was to evaluate the influence of short-daylength on growth of forage grasses in low latitude locations. Three grasses (Argentine bahiagrass, Paspalum notatum Flügge; Common guineagrass, Panicum maximum Jacq.; Tifton-85 bermudagrass, Cynodon spp. Pers.) were grown at three locations (south Florida, Puerto Rico, and St. Croix) under extended (15 h) and natural daylength during 2 years. Plots were harvested at 5-week (October–February) and 4-week (March–April) intervals to measure dry matter (DM) yield and nutritive value of the herbage. Daylength effects were found on DM harvested for all grasses in south Florida ( P < 0.01). At that location, grasses exposed to increased daylength averaged a 44% increase in DM harvested compared to those grown under natural daylength. Daylength effects were consistent for bahiagrass at the other two locations as well. However, guineagrass and bermudagrass did not respond to extended daylength in Puerto Rico and St. Croix. These results showed that bahiagrass is capable of producing additional forage during the cool season at all locations tested if sensitivity to photoperiod is genetically removed or attenuated.