Sea floor topography modeling by cumulating different types of gravity information

<p>We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.</p>

Community structure of Harpacticoida and Canuelloida (Crustacea, Copepoda) on the Great Meteor Seamount (North-east Atlantic Ocean)

During the expedition POS397 ‘GroMet’ in 2010 the sediments of the Great Meteor Seamount (GMS) plateau were sampled quantitatively for the first time, allowing statistical analysis of the community structure of Harpacticoida and Canuelloida. Analysis of similarity revealed no differences between three geographic regions at family/species level. Analysis of diversity indicated slightly greater diversity in the south, with more species belonging to more genera/families. Dispersal opportunities possibly occurring at the plateau (emergence, erosion, rafting) are discussed. Of 18 investigated families 106 species were identified, but only 5.66% were already scientifically known and widely distributed. Within the investigated families, 37.74% of the species belonged to shallow-water genera, leading to the conclusion that the plateau was once connected to shallow-water habitats, perhaps functioning as a stepping stone, but is now geographically isolated. This isolation is most likely due to seafloor spreading of the Atlantic Ocean and descending of the GMS. On the plateau, six species with wider distribution ranges were present, indicating that species may arrive accidentally, but their means of settlement remains unknown. Comparisons of the identified GMS plateau fauna with that of other seamounts and mid-oceanic islands revealed similar communities at family level, but at species level the GMS shares only one species with the Seine Seamount; all other elevations had more species in common. Hence, the GMS plateau is considered to be isolated regarding benthic Copepoda but may play an important role in meiofaunal species distribution, as it represents a shallow-water habitat within the deep sea.

A new tardigrade species of the genus Neostygarctus Grimaldi de Zio et al., 1982 (Tardigrada, Arthrotardigrada) from the Great Meteor Seamount, Northeast Atlantic

A new species of Neostygarctus Grimaldi de Zio et al., 1982 is described from the Great Meteor Seamount summit plateau in the Northeast Atlantic. Neostygarctus grossmeteori sp. nov. is characterized by the number and position of dorsomedian spines (five spines on the cephalic plate and each body plate and on the caudal plate, the spines decreasing in length backwards); the presence of eyes and of one or two pairs of ventral cervical spines; a transversal row of two to five short but strong spikes on the ventral side of the lateral body processes; only the internal claws of each leg provided with a normal accessory spine. The new species is related to N. acanthophorus Grimaldi de Zio et al., 1982 but differs by details of the dorsal body spines and the sculptures, the presence of ventral neck spines and ventral spikes on lateral body projections. Neostygarctus grossmeteori sp. nov. differs from two other known species of Neostygarctus, N. oceanopolis Kristensen et al., 2015 (Condor Seamont, NE Atlantic) and N. lovedeluxe Fujimoto & Miyazaki, 2013 (submarine cave NW Pacific), even more obviously by the number and position of dorsal body spines.

Laophontodes typicus T. Scott (Copepoda, Harpacticoida, Laophontodinae) – discovering a species complex by morphology

It appeared necessary to undertake a redescription of Laophontodes typicus T. Scott, 1894, but with the absence of the type specimen, several additional individuals collected from a number of regions were studied. The specimens chosen were from the western coast of Sussex and the Scottish Firth of Forth (UK), the Skjerstad fjord (Norway), the Patagonian continental slope (Chile) and the Great Meteor Seamount (subtropical north-eastern Atlantic Ocean). All specimens examined had been previously determined as L. typicus and deposited in the collections of renowned research institutions. However, detailed morphological comparison revealed that only the Sussex material can be assigned to L. typicus; the remaining specimens represent distinct species whose original assignment to L. typicus was erroneous, due to a morphological ambiguity. Thus, the current status of L. typicus must be regarded as a species complex. The Sussex material enabled a detailed redescription of L. typicus. Additionally, five new species are described, namely L. scottorum sp. nov., L. sarsi sp. nov., L. gertraudae sp. nov., L. monsmaris sp. nov. and L. norvegicus sp. nov. They exhibit some morphological similarity, but equally present discrete characters justifying their establishment as distinct taxa. The descriptions are accompanied by a detailed discussion that explains the justification of the splitting of L. typicus.

Uroptychus tuerkayi sp. nov. (Anomura, Chirostylidae), a new squat lobster from the Atlantis-Great Meteor Seamount Chain in the eastern Atlantic

A new species of chirostylid squat lobster,Uroptychus tuerkayisp. nov., is described based upon material collected by the French “Seamount 2” project (1993) from the Atlantis-Great Meteor Seamount Chain south of the Azores Islands, at a depth of 340-730 m.Uroptychus tuerkayiresemblesU. maroccanusTürkay, 1976 from the Moroccan coast, but it can be readily distinguished by the eyes being distinctly longer instead of as long as broad (globular inU. maroccanus), the antennal article 5 with a small instead of prominent distomesial spine, the anterolateral spine of the carapace slightly smaller than or subequal to, instead of much smaller than the lateral orbital spine, the pterygostomian flap anteriorly acuminate and not strongly produced to a spine as inU. maroccanus, and in having pereopod 1 with obsolescent instead of distinct spines on the merus and carpus. This is the sixth species ofUroptychusfrom the eastern Atlantic. A key to the eastern Atlantic species ofUroptychusis provided.

On a hexactinellid sponge aggregation at the Great Meteor seamount (North-east Atlantic)

Hexactinellids or glass sponges constitute a predominantly deep-sea sponge group typically occurring at bathyal and abyssal depths. Some species form dense populations along the European and African continental slope but the distribution and extent of these populations remains ill known and the driving factors behind their occurrence poorly understood. Here we report an aggregation of the hexactinellid sponge Poliopogon amadou Thomson, 1878 at ~2700 m depth on the Great Meteor seamount, a large seamount located southern of the Azores archipelago. A description of the species, along with scanning electron microscopy of its spicules, is provided.