1,929 research outputs found
Polarimetric Multi-View Inverse Rendering
A polarization camera has great potential for 3D reconstruction since the
angle of polarization (AoP) of reflected light is related to an object's
surface normal. In this paper, we propose a novel 3D reconstruction method
called Polarimetric Multi-View Inverse Rendering (Polarimetric MVIR) that
effectively exploits geometric, photometric, and polarimetric cues extracted
from input multi-view color polarization images. We first estimate camera poses
and an initial 3D model by geometric reconstruction with a standard
structure-from-motion and multi-view stereo pipeline. We then refine the
initial model by optimizing photometric and polarimetric rendering errors using
multi-view RGB and AoP images, where we propose a novel polarimetric rendering
cost function that enables us to effectively constrain each estimated surface
vertex's normal while considering four possible ambiguous azimuth angles
revealed from the AoP measurement. Experimental results using both synthetic
and real data demonstrate that our Polarimetric MVIR can reconstruct a detailed
3D shape without assuming a specific polarized reflection depending on the
material.Comment: Paper accepted in ECCV 202
The potential role of Antarctic krill faecal pellets in efficient carbon export at the marginal ice zone of the South Orkney Islands in spring
Antarctic krill (Euphausia superba) play a central
role in the food web of the Southern Ocean, forming
a link between primary production and large predators.
Krill produce large, faecal pellets (FP) which can form a
large component of mesopelagic particulate organic carbon
(POC) fluxes. However, the patchy distribution of krill
swarms, highly variable pellet composition, and variable
sinking and attenuation rates means that these episodic,
but potentially large, carbon fluxes are difficult to sample
or model. We measured particle flux and type using Marine
Snow Catchers (MSC) in the marginal ice zone near the
South Orkneys, Antarctica. Krill FP were the dominant
component of the POC flux in the upper 200 m (typically
60â85%). FP sinking velocities measured onboard were
highly variable (15â507 m dâ
1) but overall high, with
mean equivalent velocities of 172, 267, and 161 m dâ
1 at
our three stations. The high numbers of krill FP sinking
through the mesopelagic suggest that krill FP can be transferred
efficiently and/or that rates of krill FP production are
high. We compared our direct MSC-derived estimates of krill FP POC flux (33â154 mg C mâ
2 dâ
1) and attenuation
to estimates of krill FP production based on previous measurements
of krill density and literature FP egestion rates,
and estimated net krill FP attenuation rates in the upper
mesopelagic. Calculated attenuation rates are sensitive to
krill densities in the overlying water column but suggest
that krill FP could be transferred efficiently through the
upper mesopelagic, and, in agreement with our MSC attenuation
estimates, could make large contributions to bathypelagic
POC fluxes. Our study contrasts with some others
which suggest rapid FP attenuation, highlighting the need
for further work to constrain attenuation rates and assess
how important the contribution of Antarctic krill FP could
be to the Southern Ocean biological carbon pump
Krill faecal pellets drive hidden pulses of particulate organic carbon in the marginal ice zone
The biological carbon pump drives a flux of particulate organic carbon (POC) through the ocean and affects atmospheric levels of carbon dioxide. Short term, episodic flux events are hard to capture with current observational techniques and may thus be underrepresented in POC flux estimates. We model the potential hidden flux of POC originating from Antarctic krill, whose swarming behaviour could result in a major conduit of carbon to depth through their rapid exploitation of phytoplankton blooms and bulk egestion of rapidly sinking faecal pellets (FPs). Our model results suggest a seasonal krill FP export flux of 0.039 GT C across the Southern Ocean marginal ice zone, corresponding to 17â61% (mean 35%) of current satellite-derived export estimates for this zone. The magnitude of our conservatively estimated flux highlights the important role of large, swarming macrozooplankton in POC export and, the need to incorporate such processes more mechanistically to improve model projections
Fitting a 3D Morphable Model to Edges: A Comparison Between Hard and Soft Correspondences
We propose a fully automatic method for fitting a 3D morphable model to
single face images in arbitrary pose and lighting. Our approach relies on
geometric features (edges and landmarks) and, inspired by the iterated closest
point algorithm, is based on computing hard correspondences between model
vertices and edge pixels. We demonstrate that this is superior to previous work
that uses soft correspondences to form an edge-derived cost surface that is
minimised by nonlinear optimisation.Comment: To appear in ACCV 2016 Workshop on Facial Informatic
Krill (Euphausia superba) distribution contracts southward during rapid regional warming
High-latitude ecosystems are among the fastest warming on the planet1. Polar species may be sensitive to warming and ice loss, but data are scarce and evidence is conflicting2,3,4. Here, we show that, within their main population centre in the southwest Atlantic sector, the distribution of Euphausia superba (hereafter, âkrillâ) has contracted southward over the past 90âyears. Near their northern limit, numerical densities have declined sharply and the population has become more concentrated towards the Antarctic shelves. A concomitant increase in mean body length reflects reduced recruitment of juvenile krill. We found evidence for environmental controls on recruitment, including a reduced density of juveniles following positive anomalies of the Southern Annular Mode. Such anomalies are associated with warm, windy and cloudy weather and reduced sea ice, all of which may hinder egg production and the survival of larval krill5. However, the total post-larval density has declined less steeply than the density of recruits, suggesting that survival rates of older krill have increased. The changing distribution is already perturbing the krill-centred food web6 and may affect biogeochemical cycling7,8. Rapid climate change, with associated nonlinear adjustments in the roles of keystone species, poses challenges for the management of valuable polar ecosystems3
Growth and shrinkage in Antarctic krill Euphausia superba is sex-dependent
ABSTRACT: The ability of Antarctic krill Euphausia superba Dana to withstand the overwintering
period is critical to their success. Laboratory evidence suggests that krill may shrink in body
length during this time in response to the low availability of food. Nevertheless, verification that
krill can shrink in the natural environment is lacking because winter data are difficult to obtain.
One of the few sources of winter krill population data is from commercial vessels. We examined
length-frequency data of adult krill (>35 mm total body length) obtained from commercial vessels
in the Scotia-Weddell region and compared our results with those obtained from a combination of
science and commercial sampling operations carried out in this region at other times of the year.
Our analyses revealed body-length shrinkage in adult females but not males during overwinter,
based on both the tracking of modal size classes over seasons and sex-ratio patterns. Other
explanatory factors, such as differential mortality, immigration and emigration, could not explain
the observed differences. The same pattern was also observed at South Georgia and in the Western
Antarctic Peninsula. Fitted seasonally modulated von Bertalanffy growth functions predicted
a pattern of overwintering shrinkage in all body-length classes of females, but only stagnation in
growth in males. This shrinkage most likely reflects morphometric changes resulting from the
contraction of the ovaries and is not necessarily an outcome of winter hardship. The sex-dependent
changes that we observed need to be incorporated into life cycle and population dynamic
models of this species, particularly those used in managing the fishery.
KEY WORDS: Southern Ocean · Population dynamics · Production · Life cycle · Fisher
North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift
In the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show,however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7â13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a âhabitat squeezeâ with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that,
as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the âAtlantificationâ of the sub-Arctic
Increasing picocyanobacteria success in shelf waters contributes to long-term food web degradation
Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biotaâlarge diatoms, dinoflagellates and copepodsâthat traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico- and nanophytoplankton biomass in coastal areas. Among the pico-fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico- and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light-harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega-3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition-related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters
Successful ecosystem-based management of Antarctic krill should address uncertainties in krill recruitment, behaviour and ecological adaptation
Antarctic krill, Euphausia superba, supports a valuable commercial ïŹshery in the Southwest Atlantic, which holds the highest krill densities and is warming rapidly. The krill catch is increasing, is concentrated in a small area, and has shifted seasonally from summer to autumn/winter. The ïŹshery is managed by the Commission for the Conservation of Antarctic Marine Living Resources, with the main goal of safeguarding the large populations of krilldependent predators. Here we show that, because of the restricted distribution of successfully spawning krill and high inter-annual variability in their biomass, the risk of direct ïŹshery impacts on the krill stock itself might be higher than previously thought. We show how management beneïŹts could be achieved by incorporating uncertainty surrounding key aspects of krill ecology into management decisions, and how knowledge can be improved in these key areas. This improved information may be supplied, in part, by the ïŹshery itself
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