Variations In Length Of Day Research Articles

Effects of daylength and temperature on the growth and photosynthesis of an Arctic cyanobacterium, Schizothrix calcicola (Oscillatoriaceae)

Cyanobacteria are often the dominant phototrophs in high-latitude lakes and streams where they must experience continuously low temperature and extreme variations in daylength. The present study examined the interaction between these two variables for the growth and physiology of an Arctic isolate of the mat-forming species Schizothrix calcicola (Agardh) Gomont. Growth rates (μ), photosynthesis (P), respiration (R), pigment composition and in vivo absorption characteristics were measured under 15 combinations of daylengths (8:16, 12:12, 16:8, 20:4 and 24:0 L/D) and temperatures (5, 15 and 25 °C). μ increased with increasing temperature (μmax at 5 °C = 0.12 d−1, μmax at 25 °C = 0.28 d−1) and a similar trend was observed in photosynthetic capacity (average P B max at 5 °C = 4.42 mg C (mg Chl a)−1 h−1, average P B max at 25 °C = 5.74 mg C (mg Chl a)−1 h−1), pigment content and absorbance. Daylength had a positive effect on μ and pigment absorption, but not pigment content. The shape of the μ–daylength curve varied with temperature: μ was a linear function of daylength at 5 °C, but at 15 and 25 °C the relationship resembled a rectangular hyperbola and μ saturated at 16:8 and 12:12 L/D, respectively. The non-linear relationship between μ and daylength at high temperature was related to a reduction in net photosynthesis under extended daylength; at 25 °C, net P under 24:0 L/D was 0.82 ± 0.37 mg O2 (mg Chl a)−1 h−1, while under 8:16 L/D, it was 6.54 ± 0.69 mg O2 (mg Chl a)−1 h−1. The constant increase in growth with increasing daylength at low temperature may reflect an adaptive tolerance to the combination of cold temperature and continuous daylight during the Arctic summer.

Effects of daylength and temperature on the growth and photosynthesis of an Arctic cyanobacterium, Schizothrix calcicola (Oscillatoriaceae)

Cyanobacteria are often the dominant phototrophs in high-latitude lakes and streams where they must experience continuously low temperature and extreme variations in daylength. The present study examined the interaction between these two variables for the growth and physiology of an Arctic isolate of the mat-forming species Schizothrix calcicola (Agardh) Gomont. Growth rates (μ), photosynthesis (P), respiration (R), pigment composition and in vivo absorption characteristics were measured under 15 combinations of daylengths (8:16, 12:12, 16:8, 20:4 and 24:0 L/D) and temperatures (5, 15 and 25 °C). μ increased with increasing temperature (μmax at 5 °C = 0.12 d−1, μmax at 25 °C = 0.28 d−1) and a similar trend was observed in photosynthetic capacity (average P B max at 5 °C = 4.42 mg C (mg Chl a)−1 h−1, average P B max at 25 °C = 5.74 mg C (mg Chl a)−1 h−1), pigment content and absorbance. Daylength had a positive effect on μ and pigment absorption, but not pigment content. The shape of the μ–daylength curve varied with temperature: μ was a linear function of daylength at 5 °C, but at 15 and 25 °C the relationship resembled a rectangular hyperbola and μ saturated at 16:8 and 12:12 L/D, respectively. The non-linear relationship between μ and daylength at high temperature was related to a reduction in net photosynthesis under extended daylength; at 25 °C, net P under 24:0 L/D was 0.82 ± 0.37 mg O2 (mg Chl a)−1 h−1, while under 8:16 L/D, it was 6.54 ± 0.69 mg O2 (mg Chl a)−1 h−1. The constant increase in growth with increasing daylength at low temperature may reflect an adaptive tolerance to the combination of cold temperature and continuous daylight during the Arctic summer.

Wind contributions to the Earth's angular momentum budgets in seasonal variation

The atmospheric contributions to seasonal variations in length of day (LOD) and wobble are discussed for the period 1988–1997. The data sets used here are SPACE97 and EOP97C04 for LOD and wobble, respectively. Two atmospheric angular momentum (AAM) functions are calculated from the operational objective analysis data of the Japan Meteorological Agency (JMA) and the reanalysis data of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR). Both the axial AAM functions agree well in annual variation and roughly in semiannual variation, with the function inferred from the observed LOD. The two equatorial AAM functions show the different wind contributions to the function inferred from the observed wobble, in both annual and semiannual variations, which are attributable in part to the different vertical wind integration methods between NCEP/NCAR and JMA. The equatorial tropospheric wind contributions, calculated by the same method, are found to show discrepancies arising from the different tropospheric regional winds associated with the Asian monsoon.

Length of day decade variations, torsional oscillations and inner core superrotation: evidence from recovered core surface zonal flows

We consider the core surface flow derived from geomagnetic models [Bloxham, J., Jackson, A., 1992. Time-dependent mapping of the magnetic field at the core–mantle boundary. J. Geophys. Res. 97, 19537–19563.] under the frozen flux and tangentially geostrophic assumptions, and focus on the significance of its toroidal zonal component. This component represents a small fraction of the whole flow, but is believed to contain important information concerning core dynamics and the way the liquid core interacts with both the mantle and the inner core. We consider the 150-year period 1840–1990 for which the best data is available. Our results show that with the current methodology and data, recovered core surface zonal flows can successfully be used to address three issues in core dynamics, provided that one properly takes data and methodology uncertainties into account. The first issue deals with the possibility of testing the theory of Jault et al. [Jault, D., Gire, C., Le Mouël, J.-L., 1988. Westward drift, core motions and exchanges of angular momentum between core and mantle. Nature 333, 353–356.] which predicts a relationship between core surface zonal flows and length of day (LOD) variations on decade time scales. We recover the known fact that this theory leads to a successful prediction of LOD variations after 1920 and not early on, and show that this failure can entirely be attributed to the (partly correlated) uncertainties affecting the t 1 0 and t 3 0 flow components required to carry on the prediction. The second issue deals with the possibility of detecting torsional oscillations of the kind that Braginsky [Braginsky, S.I., 1970. Torsional magnetohydrodynamics vibrations in the Earth's core and variations in day length. Geomagn. Aeron. 10, 3–12 (Eng. transl. 1–8).] predicted should occur in the core on decade time scales. We show that the large scale component of the relevant equatorial symmetric zonal flow ( t 1 0, t 3 0, t 5 0 and very marginally t 7 0) displays significant time variations that can be attributed to such oscillations. But uncertainties affecting these coefficients are quite large and should therefore be taken into account. The third and final issue deals with the possibility of identifying a surface signature of the inner core superrotation that some seismologists claim to have detected and that is predicted by most dynamo numerical simulations. We show that the average zonal flow recovered over the 1840–1990 period displays a strong westward rotation (at 0.3–1°/yr) within the inner core tangent cylinder, which can possibly be interpreted as the surfacic counterpart of an opposite eastward inner core superrotation.

Variations in length of day and inner core differential rotation from gravitational coupling

Gravitational coupling between the inner core (IC) and mantle exchanges angular momentum between them and causes variations in the length of day (LOD) and the IC differential rotation. We simulate the coupled rotation of a triaxial ellipsoidal Earth — IC, outer core (OC) and mantle — using gravitational and pressure coupling torques and integrate the angular momentum equations in the time domain. The IC differential rotation is found directly from the resulting time series, whereas LOD oscillations are determined from a spectral analysis of the mantle rotation. The LOD oscillation period depends on the choice of triaxiality model for the IC, and varies between 4 and 18 years. We show that a previous formulation of this problem, in which the IC rotates about a fixed axis, is a special case of the present approach which adopts a general rotation allowing both axial rotation and wobble-nutation motions. The differences in the IC gravitational torque between the two formulations are that there is only one torque term in the simple rotation while there are two terms (called p-related and q-related torques) in the general rotation. It is found that the q-related torque corresponds to that in the case of simple rotation, and the p-related torque can be larger than the q-related torque. We also find that a differential rotation of the IC with respect to the mantle, caused by the gravitational torque, is controlled by the IC obliquity. Although it is unlikely that the gravitational torque alone creates a super rotation similar to that reported from some of the recent seismic observations, the gravitational torque effect should probably not be neglected. A few degrees in the IC obliquity produces an IC differential rotation larger than that suggested by seismology, implying that the figure axis of the IC probably deviates from that of the mantle by less than 1°. If that is correct, it may suggest that the IC anisotropy axis is not aligned with the IC figure axis (a difficult and unresolved issue), since it is observed from conventional seismology that the former deviates from the earth's rotation axis by 5–10°. One of the advantages of our time domain approach is that the problems of LOD, IC differential rotation, and wobble-nutation can be investigated consistently. Triaxiality of the earth (in particular, the IC) is necessary to produce axial gravitational torques between the IC and mantle, and hence LOD variations and IC differential rotation, but triaxiality does not change the periods of wobble-nutation modes obtained in previous studies for small obliquities ≪1°.

Electromagnetic core–mantle coupling: III. Laterally varying mantle conductance

We consider the implications of lateral variations in deep-mantle conductance for electromagnetic core–mantle coupling and the consequent decadal variations in length of day. Large scale variations in conductance can alter long-term trends in the torque, but do not on average enhance its magnitude or alter its decadal variation. Many previous estimates of the torque predict an unobserved negative trend during this century; this trend may result from modelling assuming an incorrect conductance structure. By suitable choice of this structure, the trend can be removed, but there is no correlation between such a structure and seismological observations of lower mantle heterogeneity. Runcorn argued that a highly conducting layer in the deep mantle beneath the Pacific could account for features of the observed secular variation, and also preferred palaeomagnetic VGP reversal paths. We argue that the conductance customarily advocated for this mechanism is inconsistent with core–mantle angular momentum exchange on decadal time scales.

Control of inner core rotation by electromagnetic, gravitational and mechanical torques

We compute the polar rotation of the Earth's inner core in response to the combined effects of electromagnetic, gravitational and mechanical torques. We obtain electromagnetic torques between 10 18 and 10 20 Nm, compared to gravitational torques between 10 19 and 10 21 Nm estimated by Xu et al. [Xu, S., Crossley D., Szeto, A.M.K., 1999. Variations in length of day and inner core differential rotation from gravitational coupling. Phys. Earth Planet. Inter., 116, 95–110] and Buffett [Buffett, B.A., 1996b. A mechanism for decade fluctuations in the length of day. Geophys. Res. Lett., 23, 3803–3806.], respectively. We obtain mechanical torques on the order of 10 15 Nm. Gravitationally dominated cases produce inner core oscillations with periods between 1 and 10 years. In electromagnetically dominated cases, the inner core rotates close to the imposed rotation rate of the outer core fluid. Modulations in the rotation rate are produced as the inner core passes through successive gravitational wells. These modulations occur over roughly 90 year timescales for outer core flow rates of 1°/year. When the electromagnetic torques are only marginally stronger than the gravitational torques, the inner core slowly rotates prograde by 90° relative to the mantle, escaping a gravitational well in roughly 100 years, then falls into the next gravitational well, rotating through 90° in just 4 years. Finite inner core viscosity is modeled using a relaxation time for the inner core topography. With relaxation, the gravitational torque reduces but does not eliminate the anomalous inner core rotation. Because of the short timescales of many of the irregularities in inner core rotation, it may be possible to observe them in presently-available seismic data.

Phenology of Atlantic Rain Forest Trees: A Comparative Study1

This paper describes the phenology of leaf, flower, and fruit phenology in the Atlantic rain forests of southeastern Brazil. For 17 months, we observed the phenological patterns of trees from two Atlantic forest types at four sites: pre-montane forest (Sites I and IV; the “typical” Atlantic rain forest) and coastal plain forest (Sites II and III). All sites experience a nonseasonal, tropical wet climate, characterized by an annual rainfall usually > 2000 mm and lacking a dry season. We tested for the occurrence (or absence) of seasonal phenological patterns within each site and compared the patterns detected among the four different forest sites using circular statistics. The expected weakly seasonal phenological patterns were not observed for these forests. Flowering and leaf flush patterns of Atlantic rain forest trees were significantly seasonal, concentrated at the beginning of the wettest season, and were significantly correlated with day length and temperature. These results stress the influence that seasonal variation in day length has on ever-wet forest tree phenology. Fruiting phenologies were aseasonal in all four forests. Flowering patterns did not differ significantly among three of the four forest sites analyzed, suggesting the occurrence of a general flowering pattern for Atlantic rain forest trees.

On High Frequency Polar Motion and Length of Day Variations

AbstractThe 0.042-day Earth rotation data (diurnal and semidiurnal) computed by the International GPS Service were used to analyze the daily/sub-daily variations of polar motion (PM) and length of day (LOD). Systematic and advanced spectral analytical investigations of the degree of periodic variability have been carried out. They show that the prominent periodical components can be found at the tidal frequencies of zonal, tesseral and sectorial waves. These investigations should give better insight into the physical processes, which influence Earth orientation (i.e. due to the atmospheric and oceanic motions, tidal forces etc.). It should be the basis for the detailed modeling of excitation functions in the sub-diurnal range of the high-frequency spectrum.

Regulation of emotional behaviour by day length in mice: implication of melatonin.

Pineal melatonin secretion occurs at night in all vertebrates and the duration of its secretion is negatively correlated with day length. As short-day exposure was previously shown to decrease emotional behaviour of mice toward an unfamiliar environment, the present study was designed to determine whether such behavioural changes could be mediated by melatonin. In a first experiment, the effects of a 3-week exposure to various day lengths (18h-6h, 12h-12h and 6h-18h light-dark conditions) on neophobic behaviour (free-exploratory paradigm) were examined in both BALB/c mice, which exhibit a very transitory melatonin peak of low amplitude in a 12h light-12h dark cycle, and C3H/He mice, which present a clear melatonin rise during the night-time. A second experiment was designed to determine if the decrease of emotional reactivity induced by a short-day exposure (6h-18h light-dark cycle during 3 weeks) in C3H/He mice could be counteracted by a daily treatment with a melatonin antagonist, S 22153 (1, 5 and 25 mg/kg/day). The short-day exposure was found to decrease neophobic reactions in both C3H/He and BALB/c mice. In contrast, the long-day exposure enhanced neophobia in C3H/He mice only. S 22153 was found to counteract, in a dose-dependent manner, the anxiolytic-like effects induced by the short-day exposure in C3H/He mice. The present results provide evidence that the modulation of circulating melatonin could be involved in the emotional changes related to day-length variations. Further studies are needed to investigate whether pinealectomy could counteract the photoperiod-related changes in anxiety.

Oceanic angular momentum variability estimated from the Parallel Ocean Climate Model, 1988–1998

This paper describes the use of a global numerical model of the oceans to estimate variations in both the equatorial and axial components of angular momentum resulting from oceanic mass redistribution and circulation. The Parallel Ocean Climate Model, driven by daily wind fields and monthly heat fluxes from the European Centre for Medium‐Range Weather Forecasts for 1988–1998, provides insight into variations in the transport and exchange of angular momentum, a quantity which is essentially conserved within the Earth system. Exchange of angular momentum between the oceans and the solid Earth should be manifest as changes in the Earth's rotation (both polar motion and length of day), and it is possible to compare predicted Earth rotation changes with actual geodetic observations. Using an inverted barometer assumption for oceans, the numerical model predictions of rotation change agree in sign and magnitude and are significantly correlated with observed polar motion and length of day variations after subtracting the dominant atmospheric contributions. The correlation has a seasonal variation which suggests that the role of the oceans in the excitation polar motion is more important during the Northern Hemisphere summer. Our results indicate that the oceans, to a different extent, account for a significant part of the nonatmospheric angular momentum budget for the Earth, and its fluid envelopes on interannual to submonthly timescales.

Length of day variations due to zonal tides for an inelastic earth in non-hydrostatic equilibrium

We present a refined theoretical model for length-of-day (lod) variations induced by the zonal part of the tide-generating potential. The model is computed from a numerical integration, from the Earth's centre up to the surface, of the equation of motion, the rheological equation of state and Poisson's equation. The Earth is modelled as a three-layered body, with an inelastic inner core, an inviscid fluid core and an inelastic mantle sustaining convection, which,induces deviations from hydrostatic equilibrium. The model also incorporates ocean corrections deduced from dynamic ocean models. It is shown that the non-hydrostatic structure inside the Earth has an effect of less than 0.1 per cent on the transfer functions, while the different modellings of mantle inelasticity (different combinations of possible values for the inelastic parameters) can lead to a wide range of results. Finally, we show that the precision of the geodetic observations of UT1 and the precision of the oceanic and atmospheric corrections are not yet sufficient to obtain information about mantle inelasticity from the comparison between theoretical models and geodetic observations.

Water temperature sensitivity of EOD waveform in Brachyhypopomus pinnicaudatus

The mechanisms that trigger the onset of the breeding season depend on geographical latitude. At the edge of Gymnotiform distribution in America, variations in day length and water temperature are likely cues to initiate breeding. In this study we aim to clarify the role of temperature and the interaction between temperature and hormonal state upon electric organ discharge waveform. In breeding ponds, we measured naturally occurring changes of water temperature and of electric organ discharge waveform during two 48-h periods in a sample of identified mature males and females of Brachyhypopomus pinnicaudatus. Water temperature, day-night cycle, and sexual maturity each modified electric organ discharge waveform. Temperature sensitivity was also evaluated in the laboratory in adult sexually-differentiated individuals, adult non-differentiated fish, juveniles, and testosterone-treated fish. Our data strongly suggest an interaction between the effects of temperature and steroid hormones upon electric organ discharge waveform. High temperature (30 °C) induced a significant decay of head negative phase amplitude in temperature-sensitive fish. This sensitivity was observed in physiological conditions that coincide with low levels of steroid hormones: juveniles and adult fish kept in captivity at 20–21 °C. Conversely, temperature resistance was observed in mature fish in the breeding habitat and was induced by testosterone treatment and by captivity at 27–28 °C.

Photoperiodic Responsiveness of Equatorial and Temperate-Zone Stonechats

The gonads of equatorial stonechats in East Africa (African Stonechats, Saxicola torquata axillaris) develop in anticipation of the short rainy season, the major reproductive period. After the breeding season, gonads regress and birds undergo a complete molt. This annual cycle of reproduction and molt is based on an endogenous circannual rhythmicity that is highly sensitive to photoperiodic changes. By exposing birds to sinusoidal day-length variations with an amplitude of 7 hr, simulating in shape and amplitude those occurring at 47.5°N, gonadal and molt cycles could be synchronized to periods of either 12 or 6 months. In this respect, equatorial birds behaved essentially like temperate-zone stonechats (S. t. rubicola). In both subspecies, photoperiodic synchronization results from seasonal changes in responsiveness to photoperiodic stimuli, reflected in the alternation between a state of photosensitivity and a state of photore-fractoriness. When exposed to a 6-month photoperiodic cycle with an amplitude of only I hr and 10 min, birds of both subspecies no longer synchronized their rhythms with it. Under these conditions, the two subspecies differed in the way testis size changed after the initial phase of testicular growth: whereas the testes of most of the temperate-zone birds stayed enlarged for 6 to 11 months, those of most equatorial birds started to regress within only 2 to 3 months. This difference probably reflects evolutionary adjustments of the two subspecies to the different photoperiodic conditions prevailing in their respective breeding grounds: the equatorial birds appear to initiate refractoriness under shorter photoperiods than do the temperate-zone stonechats. It is not clear as yet whether the very small photoperiodic changes that occur at the equator are sufficient to synchronize circannual rhythms of birds in this region. Possibly the photoperiodic responsiveness of equatorial stonechats is only the unavoidable consequence of gene flow from adjacent, more northerly or more southerly populations.

Constraining electromagnetic core–mantle coupling

Electromagnetic core–mantle coupling is one candidate for explaining length of day (LOD) variations on decadal time scales. This coupling has traditionally been calculated from models of core surface flow U → , but core flow inversions are not unique. Unfortunately, the main torque contribution depends on the toroidal part ∇× r → Φ of the vector field ( U → B r ), which is left undetermined by the radial induction equation that links core flows to magnetic field data under the frozen-flux hypothesis. ( B r is the radial magnetic field at the core surface.) We have developed a new method that bypasses flow inversions. Using the vector field ( U → B r ) directly, we estimate its toroidal part by imposing that ( U → B r ) vanishes where B r=0. The calculation of the electromagnetic torque is also hindered by the uncertainty in the conductivity structure of the lower mantle. However, we conclude that the conductivity of the lower mantle has to be much larger than current estimates derived from diamond anvil cell experiments to make the electromagnetic torque significant. The region beneath Africa and the mid-Atlantic (where there is the most significant ( B r=0) curve apart from the magnetic equator) is particularly important. Here, the field Φ is relatively well constrained, and this is the single region that contributes most to the torque. Following Holme [Holme, R., 1998a. Electromagnetic core–mantle coupling 1: explaining decadal changes in the length of day. Geophys. J. Int. (132) 167–180.], we show nevertheless that small changes to Φ suffice to recover the torque Γ LOD required to explain LOD variations provided that the lower mantle conductivity is high enough. We find a value similar to Holme [Holme, R., 1998b. Electromagnetic core–mantle coupling 2: probing deep mantle conductance. In: Gunis, M., Wysession, M.E., Knittel, E., Buffett, B.A. (Eds.), The Core–Mantle Boundary Region. AGU, pp. 139–151.] for the minimum conductance (10 8 S). However, we were not able to simultaneously recover Γ LOD and constrain U → to be tangentially geostrophic.

Seasonality, but not prevalence of sudden infant death syndrome varies by region in mainland Britain

This study aimed to investigate whether seasonal variation in day length contributed to winter/summer variation in sudden infant death syndrome (SIDS) at different latitudes in mainland Britain. Over 11 yrs 13,973 deaths were studied. Using appropriate analytic techniques a sine curve was fitted to monthly rates with the amplitude indicating magnitude of seasonal change. The rate of SIDS per 1,000 live births was the same (1.73) in the north as in the south. The amplitude was a quarter less in the north (41.3%) than in the south (54.2%) (p<0.001). While annual rates did not differ, the within year distribution did. The findings for seasonality of SIDS births were similar (amplitudes: north 213%, south 32.3%). Correlations were made between SIDS amplitude and individual environmental factors, particularly temperature and day length. These complex issues, while reported briefly, do not allow firm conclusions. In the north the winter day length is shorter, sunshine hours are less and temperature is lower, but the winter increment in SIDS is less. The extent of seasonal variation of sudden infant death syndrome is greater in the south as compared with the colder, darker north but this has no effect on sudden infant death syndrome rates. Changing photoperiod by latitude, amongst other environmental influences, may hold clues to the aetiology of sudden infant death syndrome.

Seasonal variations in length of day and atmospheric angular momentum

The seasonal variations of the Earth’s rotation are still not sufficiently well explained in terms of their causes. Quantitative estimates of the variability of the oscillations in length of day (LOD) and atmospheric angular momentum (AAM) have been applied very seldom. Therefore, the problem is re-examined. In particular, the axial AAM component labelled χ3 is related to changes in LOD. For this reason, the following series of data at one-day intervals is used in this study: (a) LOD from the series EOP (IERS) C04 from 1962 to 1996, (b) χ3 (W ), χ3(P) and χ3 (P + IB) from the series AAM (NMC) from 1976 to 1995 and (c) χ3 (W ), χ3 (P) and χ3 (P + IB) from the series AAM (JMA) from 1983 to 1995. Here, χ3 (W ) is the wind term, χ3 (P) the pressure term and χ3 (P + IB) the pressure term with inverted-barometer response. First, the seasonal oscillations are separated from the various time-series by filtering. To illustrate their characteristics, the amplitudes, periods and phases of the annual and semi-annual oscillations are then derived and presented in terms of their temporal variability. The discrepancies between the magnitudes of the annual and semi-annual components of LOD without the tidal effects Sa and without Ssa and of χ3 (W ), χ3(W ) + χ3 (P) and χ3 (W ) + χ3 (P + IB) show to what extent uncertainties are present in the data, which portions of AAM originate from χ3(W ), χ3 (P) and χ3 (P + IB), and whether another excitation source contributes to seasonal LOD variations. At the annual frequency, the wind term from the upper stratosphere that is neglected is evidently responsible for the imbalance between the LOD and AAM data. However, at the semi-annual frequency, the discrepancy is not fully explained by the missing stratospheric wind term, and a contribution from the global surface water redistribution is likely.

Meteorological excitation of interannual polar motion by the North Atlantic Oscillation

Variations of the atmospheric angular momentum (AAM) is responsible for almost all of the observed length-of-day (LOD) variation on time scales from several days to several years, and much of the observed polar motion on the intra-seasonal time scale. El Niño–Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO) have been singled out to successfully explain interannual LOD variations. However, excitation sources for the interannual polar motion, including the 14 month Chandler wobble, have not been positively identified. This paper studies the correlation of the observed polar motion Ψ with the North Atlantic Oscillation (NAO), an interannual, mid-latitude, north-south seesaw in the atmosphere-ocean system. An index (NAOI) used as a proxy to measure the strength of NAO is compared with the observed interannual polar motion excitation during 1964–1994. Cross-correlation functions and coherence spectra demonstrate significant correlations between NAOI and Ψ, especially in the x component as expected from NAOs location and general pattern. This constitutes a positive identification of excitation of interannual polar motion by a meteorological system. Furthermore, our corresponding results with respect to ENSO strongly suggest that a combination of meteorological systems will better explain the observed interannual polar motion and perhaps the Chandler wobble.

Detection and modeling of NonTidal oceanic effects on Earth's rotation rate

Subdecadal changes in Earth's rotation rate, and hence in the length of day (LOD), are largely controlled by variations in atmospheric angular momentum. Results from two oceanic general circulation models (OGCMs), forced by observed wind stress and heat flux for the years 1992 through 1994, show that ocean current and mass distribution changes also induce detectable LOD variations. The close similarity of axial oceanic angular momentum (OAM) results from two independent OGCMs, and their coherence with LOD, demonstrate that global ocean models can successfully capture the large-scale circulation changes that drive OAM variability on seasonal and shorter time scales.

Influence of daylength on metabolic rate and daily water loss in the male prosimian primate Microcebus murinus

In its natural habitat, Microcebus murinus, a small malagasy prosimian primate, is exposed to seasonal shortage of water and resources. During the winter dry season, animals enter a pronounced fattening period with concurrent decrease in behavioural/physiological activities, whereas the breeding season is restricted to the rainy summer months. To determine the role of daylength on metabolic rate and water loss in this nocturnal primate, we measured body mass, oxygen consumption at 25°C (RMR), circadian water loss through urine output (UO) and evaporation (EWL) in eight males exposed to either short days (8L:16D SD) or long days (14L:10D LD), under controlled captive conditions. Exposure to SD led to a ponderal increase (maximal body mass: 125±4 g, N=8), and to significant changes in RMR and water loss, both reaching lowest values after 3 months under SD (0.84±0.04 ml O 2 h −1 g −1 and 38±0.3 mg H 2O g −1 day −1, respectively). Following exposure to LD, body mass decreased to 77±3 g ( N=8), whereas both RMR and water loss, mainly through EWL, significantly increased ( P<0.001), the highest value occurring after 2 months (1.51±0.08 ml O 2 h .−1 g −1 and 87±7 mgH 2O g −1 day −1, respectively). Moreover, independent of daylength, circadian changes in EWL were characterized by significantly reduced values during the diurnal rest. The results demonstrate that daylength variations affect the physiology of this tropical primate, allowing anticipatory adaptation to seasonal environmental constraints.