Mass Anomalies Research Articles

The strength of gravitational core-mantle coupling

Gravitational coupling between Earth's core and mantle has been proposed as an explanation for a 6 year variation in the length-of-day (ΔLOD) signal and plays a key role in the possible superrotation of the inner core. Explaining the observations requires that the strength of the coupling, Γ, falls within fairly restrictive bounds; however, the value of Γ is highly uncertain because it depends on the distribution of mass anomalies in the mantle. We estimate Γ from a broad range of viscous mantle flow models with density anomalies inferred from seismic tomography. Requiring models to give a correlation larger than 70% to the surface geoid and match the dynamic core-mantle boundary ellipticity inferred from Earth's nutations, we find that 3 × 10 19 < Γ < 2 × 10 20 N m, too small to explain the 6 year ΔLOD signal. This new constraint on Γ has important implications for core-mantle angular momentum transfer and on the preferred mode of inner core convection.

Structure and dynamics of Titan’s outer icy shell constrained from Cassini data

The Cassini–Huygens mission has brought evidence for an internal ocean lying beneath an outer icy shell on Titan. The observed topography differs significantly from the reference hydrostatic shape, while the measured geoid anomalies (estimated up to degree three) remain weak. This suggests compensation either by deflections of the ocean/ice interface or by density variations in an upper crust. However, the observed degree-three gravity signal indicates either that the topography is not perfectly compensated, or that mass anomalies exist in the deep interior, or a combination of both. To investigate the compensation mechanisms, we developed an interior structure model satisfying simultaneously the surface gravity and long-wavelength topography. We quantified the excess deflection of ocean/ice I interface, the density anomalies in the upper crust, or the deflection of the ice/rock interface needed to explain the observed degree-three anomalies. Finally, we tested the long-term mechanical stability of the internal mass anomalies by computing the relaxation rate of each internal interface in response to interface mass load. We showed that the computed deflection of the ocean/ice I interface is stable only for a conductive highly viscous layer above a relatively cold ocean (T<250K). Solutions with a moderately convecting ice shell are possible only for models with crustal density variations. Due to fast relaxation, the high pressure ice layer cannot be the source of the degree three geoid anomalies. The existence of mass anomalies in the rocky core remains a possible explanation. Estimation of the degree-four gravity signal by future Cassini flybys will further constrain the compensation mechanism and the source of gravity anomalies.

The Phobos geodetic control point network and rotation model

A new global control point network was derived for Phobos, based on SRC (Mars Express), Phobos-2, and Viking Orbiter image data. We derive 3-D Cartesian coordinates for 813 control points as well as improved pointing data for 202 SRC and Viking images in the Phobos-fixed coordinate system. The point accuracies vary from 4.5m on the Phobos nearside, to up to 67.0m on the farside, where we rely on Viking images (average point accuracy: 13.7m). From tracking of the control points we detect a librational motion synchronous to the Phobos orbital period and measure libration amplitude of 1.09°, in agreement with predictions from shape information assuming a uniform interior. This suggests that the interior of Phobos is homogeneous – but small local mass anomalies, e.g., associated with crater Stickney, cannot be ruled out. Our new control point network has a higher number of data points and higher point accuracy than previous data products and will be an important basis for accurate shape models and maps.

Perturbing effects of sub-lithospheric mass anomalies in GOCE gravity gradient and other gravity data modelling: Application to the Atlantic-Mediterranean transition zone

The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission, launched on March 2009, included a new type of satellite instrument, an on-board three-axis gradiometer able to measure the Earth's gravity gradients at the satellite height (255km). The potential of this new type of measurement and its derived products (i.e., global gravity field models), together with other land-based geophysical observables (Bouguer and geoid anomalies), to image sub-lithospheric thermal and compositional anomalies is evaluated in this study. We focus on the Atlantic-Mediterranean Transition Region (AMTR), the diffuse, transpressive contact between the Iberian Peninsula and North Africa. The present-day lithospheric structure in the area is characterized by a wide band of active deformation, large lateral variations in the lithosphere and the presence of a positive seismic-velocity anomaly in the uppermost mantle beneath the Betics and the westernmost Alboran Basin-Gibraltar Arc. Here, the perturbing effects of deep, sub-lithospheric density anomalies in GOCE gravity gradients and other land-based geophysical data are assessed, and its impact in lithospheric-scale geophysical-petrological modeling within a thermodynamically consistent framework analyzed. Some of the gravity gradients computed at the satellite altitude are rather sensitive to the presence of even a relatively small sub-lithospheric cold slab, like the one observed in the AMTR, showing the potential of the new GOCE data to map upper mantle anomalies. Lithospheric models ignoring the AMTR sub-lithospheric heterogeneities could be significantly biased. In particular, extreme changes of 4–6km and 60–70km in the crustal and lithospheric thickness, respectively, are required to include sub-lithospheric mantle contributions to land-based and satellite gravity data.

Mass anomaly visualisation and depth estimation from full tensor gradient gravity data

SUMMARY Full Tensor Gradient (FTG) gravity data measures the derivatives of the Earth's gravitational field. Such variations in the gravitational field may be due to the presence of bodies of higher or lower density relative to the surrounding rock. As the gravity tensor contains 5 independent components, effective visualisation of this high-dimensional dataset is advantageous for efficient processing of the FTG data. We present two aspects of visualising mass anomalies in FTG gravity datasets. First, we create a textured image where the orientations of the resulting texture reflect local lateral orientations encoded in the FTG data. It uses a colour map to highlight geologically significant structures such as linear features and radially symmetric points by identifying different geological features and using colour components to represent different feature types. This visualisation method is shown to be robust to significant levels of modelled noise, and we demonstrate its applicability to a field FTG survey. Second, we present an algorithm for estimating the depths of mass anomalies in FTG data. A voxel representation of the subsurface is created and voxels are voted for according to gravitational curvature properties encoded in the FTG tensor. A visualisation of the volume at successive depths highlights 3D locations of mass anomalies at local maxima of the volume. The algorithm is evaluated on a forward-modelled FTG dataset where the depths of mass anomalies are known. The depths of mass anomalies are shown to be accurately located in the presence of noise.

Nonseasonal fluctuations of the Arctic Ocean mass observed by the GRACE satellites

Time variable gravity observations from the GRACE satellites reveal strong nonseasonal fluctuations of bottom pressure in the Arctic Ocean on the time scales from 2 to 6 months and a record‐high bottom pressure anomaly in February of 2011. Here, we examine the nature and driving forces behind those fluctuations. We find that the nonseasonal variability of the Arctic Ocean mass is strongly coupled to wind forcing. The zonal wind pattern is correlated with a dipole pattern of Arctic Ocean mass changes. Westerly wind intensification over the North Atlantic at about 60°N as well as over the Russian Arctic continental shelf break cause the ocean mass to decrease in the Nordic seas and in the central Arctic, and to increase over the Russian Arctic shelf. Basin‐wide Arctic Ocean mass fluctuations are correlated with northward wind anomalies over the northeastern North Atlantic and Nordic seas, and over the Bering Sea. We show that positive (negative) Arctic Ocean mass anomalies are associated with anticyclonic (cyclonic) anomalies of the large‐scale ocean circulation pattern. Based on ocean model simulations, we conclude that the observed nonseasonal Arctic Ocean mass variability is mostly explained by the net horizontal wind‐driven transports, and the contribution of fresh water fluxes is negligible. We demonstrate that transport anomalies across both the Atlantic and Pacific gateways were equally important for generating large Arctic Ocean mass anomalies in 2011.

Antarctic ice-mass balance 2003 to 2012: regional reanalysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment based on GPS uplift rates

Abstract. We present regional-scale mass balances for 25 drainage basins of the Antarctic Ice Sheet (AIS) from satellite observations of the Gravity and Climate Experiment (GRACE) for time period January 2003 to September 2012. Satellite gravimetry estimates of the AIS mass balance are strongly influenced by mass movement in the Earth interior caused by ice advance and retreat during the last glacial cycle. Here, we develop an improved glacial-isostatic adjustment (GIA) estimate for Antarctica using newly available GPS uplift rates, allowing us to more accurately separate GIA-induced trends in the GRACE gravity fields from those caused by current imbalances of the AIS. Our revised GIA estimate is considerably lower than previous predictions, yielding an estimate of apparent mass change of 53 ± 18 Gt yr−1. Therefore, our AIS mass balance of −114 ± 23 Gt yr−1 is less negative than previous GRACE estimates. The northern Antarctic Peninsula and the Amundsen Sea sector exhibit the largest mass loss (−26 ± 3 Gt yr−1 and −127 ± 7 Gt yr−1, respectively). In contrast, East Antarctica exhibits a slightly positive mass balance (26 ± 13 Gt yr−1), which is, however, mostly the consequence of compensating mass anomalies in Dronning Maud and Enderby Land (positive) and Wilkes and George V Land (negative) due to interannual accumulation variations. In total, 6% of the area constitutes about half the AIS imbalance, contributing 151 ± 7 Gt yr−1 (ca. 0.4 mm yr−1) to global mean sea-level change. Most of this imbalance is caused by ice-dynamic speed-up expected to prevail in the near future.

Numerical simulations of global‐scale high‐resolution hydrological crustal deformations

High‐resolution load‐induced crustal deformations calculated from numerical models are tested for their ability to predict hydrologically‐induced station height variability, as they are known to be large enough to affect epoch‐wise parameters obtained from the analysis of global geodetic networks. Loading contributions due to terrestrial water storage as given by global hydrological models are calculated on a 0.5° global regular grid with daily temporal resolution. Apart from the dominant seasonal variations, the hydrological loading signal discloses also rapid changes exceeding 1 mm in several regions that can be associated with major precipitation events and river floods. Locally strong loading signals with exceptionally high amplitudes, in many cases even with nonseasonal nature, occur along the major river channels. Only high‐resolution loading calculations considering also the water mass anomalies stored in the model river flow can resolve the correct amplitudes in the surrounded area up to 100 km distance. The comparison of the modeled hydrological surface deformation with GPS station time series shows that high‐resolution hydrological loading estimates based on global‐scale models are able to explain a considerable fraction (up to 54%) of the observed vertical station movements caused by continental water storage variations.

Toward 1-mGal accuracy in global marine gravity from CryoSat-2, Envisat, and Jason-1

More than 60% of the Earth's land and shallow marine areas are covered by &gt; 2 km of sediments and sedimentary rocks, with the thickest accumulations on rifted continental margins (Figure 1). Free-air marine gravity anomalies derived from Geosat and ERS-1 satellite altimetry (Fairhead et al., 2001; Sandwell and Smith, 2009; Andersen et al., 2009) outline most of these major basins with remarkable precision. Moreover, gravity and bathymetry data derived from altimetry are used to identify current and paleo-submarine canyons, faults, and local recent uplifts. These geomorphic features provide clues to where to look for large deposits of sediments. While current altimeter data delineate large offshore basins and major structures, they do not resolve some of the smaller geomorphic features and basins (Yale et al., 1998; Fairhead et al., 2001). Improved accuracy and resolution is desirable: to facilitate comparisons between continental margins; as an exploration tool and to permit extrapolation of known structures from well-surveyed areas; to follow fracture zones out of the deep-ocean basin into antecedent continental structures, to define and compare segmentation of margins along strike and identify the position of the continent-ocean boundary; and to study mass anomalies (e.g., sediment type and distribution) and isostatic compensation at continental margins. In this article, we assess the accuracy of a new global marine gravity model based on a wealth of new radar altimetry data and demonstrate that these gravity data are superior in quality to the majority of publicly available academic and government ship gravity data.

Gravitational Gradients at Satellite Altitudes in Global Geophysical Studies

Due to the ESA’s satellite mission GOCE launched in March 2009, gravitational gradients sampled along the orbital trajectory approximately 250 km above the Earth’s surface have become available. Since 2010, gravitational gradients have routinely been applied in geodesy for the derivation of global Earth’s gravitational models provided in terms of fully normalized coefficients in a spherical harmonic series representation of the Earth’s gravitational potential. However, in geophysics, gravitational gradients observed by spaceborne instruments have still been applied relatively seldom. This contribution describes their possible geophysical applications in structural studies where gravitational gradients observed at satellite altitudes are compared with those derived by a spectral forward modeling technique using available global models of selected Earth’s mass components as input data. In particular, GOCE gravitational gradients are interpreted in terms of a superposition principle of gravitation as combined gravitational effects generated by a homogeneous reference ellipsoid of revolution, mean topographic and ice mass density distributions, depth-dependent mass density contrasts within bathymetry and lateral mass density anomalies with sediments and crustal layers. Respective gravitational effects are one by one removed from gravitational gradients observed at approximately 250 km elevation above ground. Removing respective gravitational gradients from observed gravitational gradients gradually reveals problematic geographic areas with model deficiencies. For the full interpretation of observed gravitational gradients, deficiencies of CRUST2.0 must be corrected and effects of deeper laying mass anomalies not included in the study considered. These findings are confirmed by parameters describing spectral properties of the gravitational gradients. The methodology can be applied for validating Earth’s gravitational models and for constraining crustal models in the development phase.

Radiological findings in Currarino syndrome

ObjectiveTo describe the clinical, radiological and genetic findings of a family affected by Currarino syndrome (CS) (agenesis of the sacrum, presacral mass, and anal-rectal anomalies), and to familiarize the radiologist with this condition that, although uncommon, could be suspected by its characteristic images. Materials and methodsA study was made of 8 out of 9 family members (the parents, 7 siblings, 4 males and 3 females) suspected of having CS. The clinical and genetic findings are described. Using simple X-rays, ultrasound and magnetic resonance imaging, the presence of agenesis of the sacrum, a presacral mass and anal-rectal anomalies were investigated. Furthermore, a genetic analysis of the HLBX9 gene was performed. Permission by the Ethics Committee was not requested as all the family members gave their consent by signing a document. ResultsThe mother with a scimitar-shaped sacrum confirmed that she was the transmitter of the genetic mutation. One of the seven siblings had complete CS (sacral agenesis, anorectal stenosis, and anterior meningocele). Four siblings had an incomplete CS: 3 with sacral agenesis and a presacral mass (two anterior meningoceles and one teratoma) and the fourth with sacral agenesis and anorectal stenosis. One sibling had no anomalies. The mother, as well as four siblings, did not have the HLXB9 gene mutation. ConclusionWhen there is sacral agenesis, the possibility of presacral masses and anorectal changes should be investigated. Likewise, if there is familial association, they should be investigated for a CS.

Crustal thickness and support of topography on Venus

The topography of a terrestrial planet can be supported by several mechanisms: (1) crustal thickness variations, (2) density variations in the crust and mantle, (3) dynamic support, and (4) lithospheric stresses. Each of these mechanisms could play a role in compensating topography on Venus, and we distinguish between these mechanisms in part by calculating geoid‐to‐topography ratios and apparent depths of compensation. By simultaneously inverting for mass anomalies at two depths, we solve for the spatial distribution of crustal thickness and a similar map of mass anomalies in the mantle, thus separating the effects of shallow and deep compensation mechanisms on the geoid. The roughly circular regions of mantle mass deficit coincide with the locations of what are commonly interpreted to be buoyant mantle plumes. Additionally, there is a significant geographic correlation between patches of thickened crust and mass deficits in the mantle, especially for spherical harmonic degree l &lt; 40. These mass deficits may be interpreted either as lateral thermal variations or as Mg‐rich melt residuum. The magnitudes of mass deficits under the crustal highlands are roughly consistent with a paradigm in which highland crust is produced by melting of upwelling plumes. The mean thickness of the crust is constrained to a range of 8–25 km, somewhat lower than previous estimates. The best two‐layered inversion of gravity incorporates a dynamic mantle load at a depth of 250 km.

Irreversible mass loss of Canadian Arctic Archipelago glaciers

AbstractThe Canadian Arctic Archipelago (CAA) contains the largest volume of glacier ice on Earth outside of Antarctica and Greenland. In the absence of significant calving, CAA glacier mass balance is governed by the difference between surface snow accumulation and meltwater runoff—surface mass balance. Here we use a coupled atmosphere/snow model to simulate present‐day and 21st century CAA glacier surface mass balance. Through comparison with Gravity Recovery and Climate Experiment mass anomalies and in situ observations, we show that the model is capable of representing present‐day CAA glacier mass loss, as well as the dynamics of the seasonal snow cover on the CAA tundra. Next, we force this model until 2100 with a moderate climate warming scenario (AR5 RCP4.5). We show that enhanced meltwater runoff from CAA glaciers is not sufficiently compensated by increased snowfall. Extrapolation of these results toward an AR5 multimodel ensemble results in sustained 21st century CAA glacier mass loss in the vast majority (&gt;99%) of the ~7000 temperature realizations.

Regional surface mass anomalies from GRACE KBR measurements: Application of L‐curve regularization anda priori hydrological knowledge

We present a method of directly estimating surface mass anomalies at regional scales using satellite‐to‐satellite K‐band Ranging (KBR) data from the Gravity Recovery and Climate Experiment (GRACE) twin‐satellite mission. Geopotential differences based primarily on KBR measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements. Surface mass anomalies are computed based on a downward continuation process, with optimal regularization parameters estimated using the L‐curve criterion method. We derive the covariance functions in both space‐ and space‐time domains and use them as light constraints in the regional gravity estimation process in the Amazon basin study region. The space‐time covariance function has a time‐correlation distance of 1.27 months, which is evident that observations between neighboring months are correlated and the correlation should be taken into account. However, most of the current GRACE solutions did not consider such temporal correlations. In our study, the artifact in the regional gravity solution is mitigated by using the covariance functions. The averaged commission errors are estimated to be only 6.86% and 5.85% for the solutions based on the space‐covariance function (SCF) and the space‐time covariance function (STCF), respectively. Our regional gravity solution in the Amazon basin study region, which requires no further post‐processing, shows enhanced regional gravity signatures, reduced gravity artifacts, and the gravity solution agrees with NASA/GSFC's GRACE MASCON solution to about 1 cm RMS in terms of water thickness change over the Amazon basin study region. The regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors.

Single-hole imaging using borehole gravity gradiometry

We study the feasibility of imaging density variations away from boreholes using gravity gradient measurements in a single borehole. The objective is to develop numerical interpretation tools and to understand the utility and limitations of borehole gravity gradiometry in anticipation of the development of such instruments for the exploration and production of minerals, oil, and gas. We develop an analytic solution for directly locating discrete off-hole mass anomalies and apply a generalized inverse approach to image anomalous density distribution. In the analytic approach, we solve for the distance and direction angles to a point source using the multiple components of the gravity gradient tensor from a set of observations in a single borehole; and then apply this approach to the scenarios of prismatic sources. In the generalized inverse approach, we invert multiple gradient tensor components to construct 3D density contrast distributions around the borehole. As few as two independent gravity gradient components in a single borehole can be used to locate and image isolated anomalous density bodies.

Independent patterns of water mass anomalies over Australia from satellite data and models

The Gravity Recovery and Climate Experiment (GRACE) products allow the quantification of total water storage (TWS) changes at global to regional scales. However, the quantity measured by GRACE represents mass signals integrated over vertical columns, requiring their separation into their original sources. Such a separation is vital for Australia, for which GRACE estimates are affected by leakage from the surrounding oceans. The independent component analysis (ICA) method that uses higher-order statistics, is implemented here to separate GRACE-derived water storage signals over the Australian continent from its surrounding oceans, covering from October 2002 to May 2011. The performance of ICA applied to GRACE is then compared to the ICA of WaterGAP Global Hydrology Model (WGHM) and the ICA of the Australian Water Resources Assessment (AWRA) system. To study the influence of rainfall variability on the derived independent patterns, use is made of Tropical Rainfall Measuring Mission (TRMM) data set, from January 2000 to May 2011. Implementing ICA on GRACE-TWS showed a remarkable improvement in separating the continental hydrological signals from the surrounding oceanic anomalies, which was not achievable using a conventional principle component analysis. Reconstructing the continental TWS changes using only those independent components of GRACE that were located over the continent showed a high correlation with WGHM-TWS and AWRA-TWS. Mass concentrations over the oceans and particularly S2 semi-diurnal aliased pattern were separated as independent modes. Correlation analysis between the independent components of GRACE and climate teleconnections showed that the mass anomalies over the northern ocean, Gulf of Carpentaria and north-eastern parts of Australia were significantly correlated with the El Niño-Southern Oscillation, while those over south and south-eastern parts of Australia were mainly linked to the Indian Ocean Dipole.

An EOF and SVD analysis of interannual variability of GPS coordinates, environmental parameters and space gravity data

Eleven years, 1999–2010, of GPS positions of stations located in Europe and the Mediterranean were analyzed together with time series of atmospheric pressure, terrestrial water storage, and surface mass anomalies provided by the GRACE gravity mission. The Empirical Orthogonal Functions (EOF) technique was applied to single variables data series detrended and de-seasoned to identify the main modes of interannual variability in both time and space. For the GPS coordinates, the analysis has revealed the presence of significant interannual fluctuations which were also identified in the time series of the environmental parameters and of the space gravity data. A prominent feature common to the main modes of the time components of all variables is a slope inversion occurring around 2003–2004. During 2003 most of the European continent was affected by a severe drought. A second type of analysis was performed by applying the Singular Value Decomposition (SVD) approach to a few series of variable pairs to study the coupled space/time variability. This mathematical tool is used to examine possible cause-effect physical relationships between variables pairs. The analysis shows, for example, for the atmospheric pressure and the up coordinate that the first two SVDs account for about 97% of the total covariance. The clear anticorrelation observed between the two SVD1 spatial patterns represents the vertical crustal displacements associated with variations in atmospheric pressure. East–West (EW) and North–South (NS) gradients of the environmental parameters and of the GRACE surface mass anomalies were computed and compared to the EOFs of the east and north GPS coordinates respectively. Significant correlations were found, in particular, between the EW atmospheric pressure gradient and the east EOFs and between the GRACE EW and NS gradients and the east and north EOFs respectively. Significant correlations were also identified between the Multivariate ENSO Index (MEI) and the EOFs of GPS coordinates.

Hallazgos radiológicos en el síndrome de Currarino

ObjectiveTo describe the clinical, radiological and genetic findings of a family affected by Currarino syndrome (CS) (agenesis of the sacrum, presacral mass, and anal-rectal anomalies), and to familiarise the radiologist with this condition that, although uncommon, could be suspected by its characteristic images. Material and methodsA study was made of 8 out of 9 family members (the parents, 7 siblings; 4 males and 3 females) suspected of having CS. The clinical and genetic findings are described. Using simple X-rays, ultrasound and magnetic resonance imaging, the presence of agenesis of the sacrum, a presacral mass and anal-rectal anomalies were investigated. Furthermore, a genetic analysis of the HLBX9 gene was performed. Permission by the Ethics Committee was not requested as all the family members gave their consent by signing a document. ResultsThe mother with a scimitar-shaped sacrum confirmed that she was the transmitter of the genetic mutation. One of the seven siblings had complete CS (sacral agenesis, anorectal stenosis, and anterior meningocele). Four siblings had an incomplete CS: 3 with sacral agenesis and a presacral mass (two anterior meningoceles and one teratoma) and the fourth with sacral agenesis and anorectal stenosis. One sibling had no anomalies. The mother, as well as four siblings, did not have the HLXB9 gene mutation. ConclusionWhen there is sacral agenesis, the possibility of presacral masses and anorectal changes should be investigated. Likewise, if there is familial association, they should be investigated for a CS.

On the relationship between the postmidnight thermospheric equatorial mass anomaly and equatorial ionization anomaly under geomagnetic quiet conditions

The equatorial mass anomaly (EMA) in the thermosphere and equatorial ionization anomaly (EIA) in the ionosphere are two interesting phenomena in low-equatorial latitude regions. Previous studies have shown that the EMA appears between 1000 and 2000 local time (LT) and its location of trough is aligned with dip equator, indicating the plausible role of the EIA structure in the development of EMA. In this report, we conducted a statistical study of the occurrence of postmidnight EMA and EIA on the basis of the CHAMP in situ measurements during 2002-2008. Our results revealed that clear EMA and EIA structures are sometimes visible in the postmidnight sector (0100-0600 LT) during geomagnetic quiet periods (Kp < 3). The postmidnight EMA is not necessarily accompanied by the EIA signature in both case study and statistics sense being distinct from the daytime situation. In addition, the occurrence rates of postmidnight EMA and EIA display contrasting behavior with respect to their local time, longitudinal and solar activity dependences. The highest occurrence rate for EMA is 8% at around 0300 LT, while the occurrence rate of the EIA decreases gradually from about 30% at around 2300 LT to similar to 5% at 0600 LT. Longitudinal occurrence of postmidnight EIA presents a wave-like pattern; however, no salient feature appears for the longitudinal occurrence of EMA. Postmidnight EMA is more likely to occur at lower solar activity, whereas an opposite trend presents in the EIA. On the basis of above results, our findings imply that a simple EIA-EMA cause-effect relationship does not hold in the postmidnight sector.

Suppression of the 2010 Alexandrium fundyense bloom by changes in physical, biological, and chemical properties of the Gulf of Maine.

For the period 2005-2009, the abundance of resting cysts in bottom sediments from the preceding fall was a first-order predictor of the overall severity of spring-summer blooms of Alexandrium fundyense in the western Gulf of Maine and southern New England. Cyst abundance off mid-coast Maine was significantly higher in fall 2009 than it was preceding a major regional bloom in 2005. A seasonal ensemble forecast was computed using a range of forcing conditions for the period 2004-2009, suggesting that a large bloom was likely in the western Gulf of Maine in 2010. This did not materialize, perhaps because environmental conditions in spring-summer 2010 were not favorable for growth of A.fundyense. Water mass anomalies indicate a regional-scale change in circulation with direct influence on A. fundyense's niche. Specifically, near-surface waters were warmer, fresher, more stratified, and had lower nutrients than during the period of observations used to construct the ensemble forecast. Moreover, a weaker-than-normal coastal current lessened A. fundyense transport into the western Gulf of Maine and Massachusetts Bay. Satellite ocean color observations indicate the 2010 spring phytoplankton bloom was more intense than usual. Early-season nutrient depletion may have caused a temporal mismatch with A. fundyense's endogenous clock that regulates the timing of cyst germination. These findings highlight the difficulties of ecological forecasting in a changing oceanographic environment, and underscore the need for a sustained observational network to drive such forecasts.