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R S Lampitt - One of the best experts on this subject based on the ideXlab platform.
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links between surface productivity and deep ocean particle flux at the porcupine Abyssal Plain sustained observatory
Biogeosciences, 2015Co-Authors: Helene Frigstad, Stephanie A Henson, Susan E Hartman, Abdirahman M Omar, Emil Jeansson, Harriet Cole, Corinne Pebody, R S LampittAbstract:Abstract. In this study we present hydrography, biogeochemistry and sediment trap observations between 2003 and 2012 at Porcupine Abyssal Plain (PAP) sustained observatory in the Northeast Atlantic. The time series is valuable as it allows for investigation of the link between surface productivity and deep ocean carbon flux. The region is a perennial sink for CO2, with an average uptake of around 1.5 mmol m−2 day−1. The average monthly drawdowns of inorganic carbon and nitrogen were used to quantify the net community production (NCP) and new production. Seasonal NCP and new production were found to be 4.57 ± 0.85 mol C m−2 and 0.37 ± 0.14 mol N m−2, respectively. The C : N ratio was high (12) compared to the Redfield ratio (6.6), and the production calculated from carbon was higher than production calculated from nitrogen, which is indicative of carbon overconsumption. The export ratio and transfer efficiency were 16 and 4 %, respectively, and the site thereby showed high flux attenuation. Particle tracking was used to examine the source region of material in the sediment trap, and there was large variation in source regions, both between and within years. There were higher correlations between surface productivity and export flux when using the particle-tracking approach, than by comparing with the mean productivity in a 100 km box around the PAP site. However, the differences in correlation coefficients were not significant, and a longer time series is needed to draw conclusions on applying particle tracking in sediment trap analyses.
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biogeochemical variations at the porcupine Abyssal Plain sustained observatory in the northeast atlantic ocean from weekly to inter annual timescales
Biogeosciences, 2015Co-Authors: Susan E Hartman, R S Lampitt, Helene Frigstad, Zongpei Jiang, Daniela Turk, Clare Ostle, Ute SchusterAbstract:Abstract. We present high-resolution autonomous measurements of carbon dioxide partial pressure p(CO2) taken in situ at the Porcupine Abyssal Plain sustained Observatory (PAP-SO) in the northeast Atlantic (49° N, 16.5° W; water depth of 4850 m) for the period 2010–2012. Measurements of p(CO2) made at 30 m depth on a sensor frame are compared with other autonomous biogeochemical measurements at that depth (including chlorophyll a fluorescence and nitrate concentration data) to analyse weekly to seasonal controls on p(CO2) flux in the inter-gyre region of the North Atlantic. Comparisons are also made with in situ regional time series data from a ship of opportunity and mixed layer depth (MLD) measurements from profiling Argo floats. There is a persistent under-saturation of CO2 in surface waters throughout the year which gives rise to a perennial CO2 sink. Comparison with an earlier data set collected at the site (2003–2005) confirms seasonal and inter-annual changes in surface seawater chemistry. There is year-to-year variability in the timing of deep winter mixing and the intensity of the spring bloom. The 2010–2012 period shows an overall increase in p(CO2) values when compared to the 2003–2005 period as would be expected from increases due to anthropogenic CO2 emissions. The surface temperature, wind speed and MLD measurements are similar for both periods of time. Future work should incorporate daily CO2 flux measurements made using CO2 sensors at 1 m depth and the in situ wind speed data now available from the UK Met Office Buoy.
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the porcupine Abyssal Plain fixed point sustained observatory pap so variations and trends from the northeast atlantic fixed point time series
Ices Journal of Marine Science, 2012Co-Authors: Susan E Hartman, Henry A Ruhl, R S Lampitt, Corinne Pebody, Kate E Larkin, Maureen Pagnani, J M Campbell, Thanos Gkritzalis, Zongpei Jiang, Andrew J GoodayAbstract:The Porcupine Abyssal Plain sustained observatory (PAP-SO) in the Northeast Atlantic (49°N 16.5°W; 4800 m) is the longest running open-ocean multidisciplinary observatory in the oceans around Europe. The site has produced high-resolution datasets integrating environmental and ecologically relevant variables from the surface to the seabed for >20 years. Since 2002, a full-depth mooring has been in place with autonomous sensors measuring temperature, salinity, chlorophyll-a fluorescence, nitrate, and pCO2. These complement ongoing mesopelagic and seabed observations on downward particle flux and benthic ecosystem structure and function. With national and European funding, the observatory infrastructure has been advanced steadily, with the latest development in 2010 involving collaboration between the UK's Meteorological Office and Natural Environment Research Council. This resulted in the first simultaneous atmospheric and ocean datasets at the site. All PAP-SO datasets are open access in near real time through websites and as quality-controlled datasets for a range of remote users using ftp sites and uploaded daily to MyOcean and the global telecommunications system for use in modelling activities. The combined datasets capture short-term variation (daily–seasonal), longer term trends (climate-driven), and episodic events (e.g. spring-bloom events), and the data contribute to the Europe-wide move towards good environmental status of our seas, driven by the EU's Marine Strategy Framework Directive (http://ec.europa.eu/environment/water/marine).
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the sustained observatory over the porcupine Abyssal Plain pap insights from time series observations and process studies
Deep-sea Research Part Ii-topical Studies in Oceanography, 2010Co-Authors: R S Lampitt, D S M Billett, Adrian MartinAbstract:Oceanographic research in the past 20 years has highlighted the importance of understanding decadal-scale variation in the oceans in order to predict how the ocean will respond to climate change. Climate factors control many of the processes that regulate the input of nutrients to the euphotic zone, primary productivity, zooplankton responses, the downward flux of organic matter, the biomass and composition of seabed communities and, ultimately, the burial of carbon in deep-sea sediments. A critical part of our understanding of the interdependence of these many elements comes from long-term eulerian observations, such as the Hawaii Ocean Time series (HOT) (Karl et al., 2003), the Bermuda Atlantic Time Series (BATS) (Steinberg et al., 2001), the NE Pacific Station M (Smith and Druffel, 1998) and the NE Atlantic Porcupine Abyssal Plain site (PAP) ([Billett and Rice, 2001] and [Lampitt et al., 2001]). Each time series site is considered as representing a different oceanic setting and each has a different suite of observations and history. However, the unifying theme of them all is to understand the time varying properties and processes of the oceanic environment. Only at Station M and PAP have water column and seabed observations been integrated, a feature of some considerable advantage. This special issue presents the latest work at PAP.
D S M Billett - One of the best experts on this subject based on the ideXlab platform.
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the sustained observatory over the porcupine Abyssal Plain pap insights from time series observations and process studies
Deep-sea Research Part Ii-topical Studies in Oceanography, 2010Co-Authors: R S Lampitt, D S M Billett, Adrian MartinAbstract:Oceanographic research in the past 20 years has highlighted the importance of understanding decadal-scale variation in the oceans in order to predict how the ocean will respond to climate change. Climate factors control many of the processes that regulate the input of nutrients to the euphotic zone, primary productivity, zooplankton responses, the downward flux of organic matter, the biomass and composition of seabed communities and, ultimately, the burial of carbon in deep-sea sediments. A critical part of our understanding of the interdependence of these many elements comes from long-term eulerian observations, such as the Hawaii Ocean Time series (HOT) (Karl et al., 2003), the Bermuda Atlantic Time Series (BATS) (Steinberg et al., 2001), the NE Pacific Station M (Smith and Druffel, 1998) and the NE Atlantic Porcupine Abyssal Plain site (PAP) ([Billett and Rice, 2001] and [Lampitt et al., 2001]). Each time series site is considered as representing a different oceanic setting and each has a different suite of observations and history. However, the unifying theme of them all is to understand the time varying properties and processes of the oceanic environment. Only at Station M and PAP have water column and seabed observations been integrated, a feature of some considerable advantage. This special issue presents the latest work at PAP.
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Long-term changes in reproductive patterns of the holothurian Oneirophanta mutabilis from the Porcupine Abyssal Plain
Marine Biology, 2005Co-Authors: E. Ramirez-llodra, W. D. K. Reid, D S M BillettAbstract:Time-series studies (1989–2002) in the NE Atlantic have shown large-scale changes in the composition and structure of the benthic community on the Porcupine Abyssal Plain. Radical changes in the abundance of some species in 1996 led to a significant shift in the way in which organic matter was reprocessed at the seabed. This article examines the reproductive processes of the holothurian Oneirophanta mutabilis collected during the time series. The reproductive biology of O . mutabilis is reviewed. No males were evident in any of the samples. The sex ratio (females: ‘no gender’) was biased significantly towards no-gender individuals. The maximum egg size was 650 μm and there was no evidence of synchrony in reproduction. Significant changes in the oocyte-size distribution and the fecundity of O . mutabilis were noted through time, coinciding with the time of greatest faunal change in the benthic community. There was an increase in the proportion of previtellogenic oocytes and a decrease in the proportion of mature vitellogenic oocytes in 1997 and 1998, in parallel with a significant decrease in fecundity of the post-1996 samples. Samples from 2002 showed a reversal in the reproductive trends, with an increase in the proportion of mature vitellogenic oocytes and fecundity. The results are discussed in relation to large changes in abundance of the epibenthos on the Porcupine Abyssal Plain. It is suggested that the superabundance of certain megafaunal species on the Abyssal seafloor affected the availability of trophic resources for O . mutabilis , leading to the changes in its reproductive effort.
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depth related distribution and abundance of seastars echinodermata asteroidea in the porcupine seabight and porcupine Abyssal Plain n e atlantic
Deep Sea Research Part I: Oceanographic Research Papers, 2002Co-Authors: Kerry L Howell, D S M Billett, Paul A TylerAbstract:The depth-related distribution of seastar (Echinodermata: Asteroidea) species between 150 and 4950 m in the Porcupine Seabight and Porcupine Abyssal Plain is described. 47 species of asteroid were identified from ~14,000 individuals collected. The bathymetric range of each species is recorded. What are considered quantitative data, from an acoustically monitored epibenthic sledge and supplementary data from otter trawls, are used to display the relative abundance of individuals within their bathymetric range. Asteroid species are found to have very narrow centres of distribution in which they are abundant, despite much wider total adult depth ranges. Centres of distribution may be skewed. This might result from competition for resources or be related to the occurrence of favourable habitats at particular depths. The bathymetric distributions of the juveniles of some species extend outside the adult depth ranges. There is a distinct pattern of zonation with two major regions of faunal change and six distinct zones. An upper slope zone ranges from 150 to ~700 m depth, an upper bathyal zone between 700 and 1100 m, a mid-bathyal zone from 1100 to1700 m and a lower bathyal zone between 1700 and 2500 m. Below 2500 m the lower continental slope and continental rise have a characteristic asteroid fauna. The Abyssal zone starts at about 2800 m. Regions of major faunal change are identified at the boundaries of both upper and mid-bathyal zones and at the transition of bathyal to Abyssal fauna. Diversity is greatest at ~1800 m, decreasing with depth to ~2600 m before increasing again to high levels at ~4700 m.
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long term change in the megabenthos of the porcupine Abyssal Plain ne atlantic
Progress in Oceanography, 2001Co-Authors: D S M Billett, Brian J Bett, A L Rice, Michael H Thurston, Joelle Galeron, Myriam Sibuet, George A WolffAbstract:A radical change in the abundance of invertebrate megafauna on the Porcupine Abyssal Plain is reported over a period of 10 years (1989–1999). Actiniarians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increased significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977–1999) show that prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a localised event. Several dominant holothurian species show a distinct trend in decreasing body size over the study period. The changes in megafauna abundance may be related to environmental forcing (food supply) rather than to localised stochastic population variations. Inter-annual variability and long-term trends in organic matter supply to the seabed may be responsible for the observed changes in abundance, species dominance and size distributions.
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organic matter in deep sea sediments from the porcupine Abyssal Plain in the north east atlantic ocean i lipids
Deep Sea Research Part I: Oceanographic Research Papers, 1994Co-Authors: Vera L C S Santos, D S M Billett, A L Rice, George A WolffAbstract:Abstract The extractable lipids of four undisturbed sediment cores from the Porcupine Abyssal Plain, in the north-eastern Atlantic Ocean, have been analysed. Several compound classes including n-alkanes, n-alcohols, alkanoic and alkenoic acids, sterols, triterpenoids and alkenones were present in most of the samples. Surficial sediments showed evidence of mixed marine and terrigenous organic matter, the latter presumably being higher plant-derived. There was, however, considerable variability in the distributions of lipids in the surficial sediments; this is consistent with photographic evidence of the patchiness of the Porcupine Abyssal Plain sediments, which are strongly influenced by the benthic faunal community. In general, the concentrations of most compounds (with respect to total organic carbon) are attenuated with depth in the sediments, although the “higher plant” signal is apparently more recalcitrant thanthe “marine” signal. There is also evidence of significant down-core variability in some of the cores.
R. B. Whitmarsh - One of the best experts on this subject based on the ideXlab platform.
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the peridotite ridge province in the southern iberia Abyssal Plain seismic constraints revisited
Journal of Geophysical Research, 2014Co-Authors: Timothy A. Minshull, S. M. Dean, R. B. WhitmarshAbstract:The west Iberia margin has become the type example of a magma-starved margin in which extension during breakup led to the exhumation of mantle rocks apparently over a broad area. Much of our understanding of this process is based on geophysical and drilling data from the southern Iberia Abyssal Plain, where the seaward part of the region of exhumed mantle is comprised of a series of margin-parallel basement ridges. Here we analyse wide-angle and normal incidence seismic data from a series of intersecting profiles across this peridotite ridge province and develop a three-dimensional picture of its structure. Using these seismic data, we infer a location and age (magnetic anomaly M1; 125-127?Ma) of first-formed oceanic crust in this region that are consistent with Ocean Drilling Program data and data from the conjugate margin. We infer that the peridotite ridge province is about 70?km wide with strong serpentinization (>75%) at the top of basement reducing to much lower degrees (< 25%) around 2?km below. We map the geometry of some prominent reflectors on the landward margin of the peridotite ridge province that likely represent detachment faults and show that one of these has a domal structure similar to that of detachment faults at slow- to ultra-slow-spreading mid-ocean ridges.
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tectonic implications of exposure of lower continental crust beneath the iberia Abyssal Plain northeast atlantic ocean geophysical evidence
Tectonics, 2000Co-Authors: R. B. Whitmarsh, Timothy A. Minshull, S. M. Dean, Michael J TompkinsAbstract:We present new seismic data from a basement high beneath the southern Iberia Abyssal Plain that appears, from the latest Ocean Drilling Program (ODP) results and indirectly from various seismic observations, to consist of lower continental crustal material. This is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks. We infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting. Our results lead to the following new observations: low-angle detachment faults, previously reported along the east-west Lusigal-12 profile across the southern Iberia Abyssal Plain, penetrate both the 3–10 km thick continental crust and, unusually, the uppermost mantle. Processing of new multichannel seismic reflection profiles across the basement high on which ODP Sites 900, 1067, and 1068 are located reveals that the high is bounded by a previously unsuspected steep, landward dipping normal fault on its east flank. Basement cores from the above ODP sites also reveal that the high is not capped by the previously predicted early syn-rift sediment but by rocks from the lower continental crust. These unexpected observations are incorporated into a new tectonic model of the development of this part of the west Iberia margin which is also consistent with other geophysical observations. A novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3–6 km by a currently poorly understood process. The model implies three stages of deformation: (1) lithospheric extension, principally by symmetric pure shear, which leads to a ∼10 km thick crust in which the lower crust is largely absent over the axial zone and the crust-mantle boundary forms a shear zone, (2) further thinning and then dissection of the most distal continental crust by seaward dipping, low-angle normal faults, (3) inception of a high-angle, landward dipping normal fault that offsets the tectonized crust-mantle boundary and uplifts the lower crust to the crest of the basement high on which ODP Sites 900, 1067, and 1068 were drilled.
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Deep structure in the vicinity of the ocean-continent transition zone under the southern Iberia Abyssal Plain
Geology, 1998Co-Authors: Timothy A. Minshull, R. B. Whitmarsh, S. M. Dean, S. M. Russell, Keith E. Louden, D. ChianAbstract:We present results from a seismic and magnetic study of acoustic basement beneath the southern Iberia Abyssal Plain. An ocean-continent transition zone (OCT), characterized by subdued basement relief and weak magnetization, lies seaward of thinned continental crust. Its western edge is a region with isochron-parallel ridges and generally higher basement magnetizations. The width of the OCT decreases to the north. The seaward change in basement morphology coincides with changes in seismic velocity structure, but in both regions, anomalously high velocities at shallow depths within acoustic basement suggest that the OCT consists largely of serpentinized peridotite. Our magnetic and seismic data support the hypothesis of exhumed upper mantle, more than that of ultraslow sea-floor spreading, for the origin of the OCT.
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47 the ocean continent transition beneath the iberia Abyssal Plain and continental rifting to seafloor spreading processes 1
Proceedings of the Ocean Drilling Program. Scientific results, 1996Co-Authors: R. B. Whitmarsh, D S SawyerAbstract:The west Iberia continental margin is a nonvolcanic rifted margin which, following rifting that began in the Late Triassic, broke away from Newfoundland in the Early Cretaceous as rifting propagated from south to north. The ocean/continent transition off Newfoundland seems to occur ~50 km seaward of the shelf edge near the base of the continental slope. Off west Iberia, the ocean/continent transition is defined by an 80- to 130-km-wide region beneath the Iberia Abyssal Plain between the most oceanward-tilted basement fault blocks (continental crust?) and a 300-km-long narrow peridotite ridge parallel to the margin. Leg 149 drilled a west-to-east transect of holes across the ocean/continent transition, and three of these reached acoustic basement, beginning at the peridotite ridge. Sites 897 (over the peridotite ridge) and 899 (19 km further east) sampled serpentinized peridotites with similar, but not identical, petrologies that experienced a similar history of exhumation from the deep mantle to the surface. They crystallized at 1170°-1230°C, and this was followed by ductile shear deformation at 880°-1000°C. After limited partial melting, secondary minerals crystallized at about 30 km depth. Mylonitization, and then low-temperature deformation and serpentinization, followed as the rocks were exhumed at the seabed. One possibly important, but unexPlained, difference between the two sites is the fivefold greater strength of remanent magnetization of the Site 899 cores, which is reflected in the amplitudes of magnetic anomalies observed over the sites. The peridotites are neither clearly subcontinental nor suboceanic. Further landward, Site 900 sampled a flasered cumulate gabbro basement. The rare-earth element (REE) patterns of the gabbros are ambiguous and have been matched by different authors to both island arc and N-MORB basalts. The light REE patterns fit a transitional MORB parent magma whereas Nd and Pb isotope ratios strongly suggest a MORB parent. The gabbro therefore likely formed in a magma chamber from a melt that was little contaminated, if at all, by continental crust. Traces of the primary mineralogy indicate dynamic crystallization at depths of at least 13 km and temperatures typical of granulite facies conditions. During exhumation to the seabed the rocks underwent retrograde metamorphism at 280 ± 20°C followed by crystallization of some plagioclases at 136.4 ± 0.3 Ma. Late Barremian- to late Aptian-age debris-flow and mass-flow deposits were encountered above acoustic basement at Sites 897 and 899, both of which are now situated on substantial basement elevations hundreds of meters above basement of the adjacent basins. They are overlain by poorly fossiliferous uppermost Maastrichtian to Eocene thin claystones and conglomerates (lag deposits) of similar age to the sediments at the same level in the flanking basins. We exPlain these deposits by rapid Aptian uplift (or relative uplift), about 10 m.y. after the onset of 10 mm/yr seafloor spreading west of the peridotite ridge, followed in Eocene time by blanketing by the sediments of the Iberia Abyssal Plain. This also exPlains the long history of seawater alteration of serpentinized peridotite at both sites. The above drilling results are exPlained here by two possible hypotheses, that also take account of geophysical constraints on the development of the west Iberia ocean/continent transition, neither of which exPlains all the observations. The first hypothesis is that the ocean/continent transition is underlain by crust formed by ultraslow (~5 mm/yr half-rate) seafloor spreading which, by analogy with the slow-spreading Mid-Atlantic Ridge, leads to the seabed exposure of peridotite and gabbro by extensive faulting. This hypothesis exPlains the drilling results but has difficulty in exPlaining the magnetic anomalies and the minute volume of basalt encountered in the cores. The second hypothesis envisages an ocean/continent transition of tectonically and magmatically disrupted continental crust. It exPlains the Site 900 MORB gabbro as material underplated beneath thinned continental crust or as an aborted point-of-initiation of seafloor spreading, and the alkaline to transitional characters of igneous clasts in Site 897 and 899 deposits as evidence of continental rifting. Its main problem is the lack of unambiguous continental basement samples although there is evidence of re-worked continental sediments in the cores. Both hypotheses predict a highly heterogeneous crust, which will be hard to characterize without further basement sampling.
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the ocean continent boundary off the western continental margin of iberia ii crustal structure in the tagus Abyssal Plain
Geophysical Journal International, 1992Co-Authors: L M Pinheiro, R. B. Whitmarsh, P R MilesAbstract:SUMMARY An 80 km long reversed seismic refraction line (Line 5) was shot over the Tagus Abyssal Plain off Portugal. The main P-wave reflected and refracted phases were modelled both for traveltime and amplitude. The resulting P-wave velocity/depth model has the following features: (a) an extremely thin crust of about 2 km; (b) the absence of oceanic layer 3; and (c) very low upper mantle velocities between 7.6 and 7.9 km s-'. This very unusual seismic velocity crustal structure is quite unlike thinned continental crust but is remarkably similar to the seismic crustal structures found at Atlantic fracture zones, and in particular to the structures found in profiles shot along the transform valley and near ridge-transform intersections. A magnetic anomaly chart seems to allow the possibility of several fracture zones one of which could intersect the centre of Line 5. As an alternative to the fracture zone hypothesis we show that if the oceancontinent transition in the Tagus Abyssal Plain is located at about 11"30'W, in a symmetric position with respect to the ocean-continent transition in the conjugate South Newfoundland Basin, then magnetic anomalies can be modelled simply by assuming sea-floor spreading west of 11'45'W at 10 mm yr-' beginning at M11 time (133 Myr BP), and blocks of rifted continental crust to the east. The location of the proposed ocean-continent transition in the Tagus Abyssal Plain is marked by a well-defined N-S linear magnetic anomaly which is adjacent to the oldest sea-floor spreading block. East of the proposed ocean-continent transition there is an increase in the depth to basement similar to that found east of the ocean-continent transition in the Iberia Abyssal Plain and elsewhere. This model also allows us to exPlain why Purdy's (1975) seismic refraction line A-AR in the Tagus Abyssal Plain cannot be interpreted as a conventional reversed pair because most of Line A was shot over the ocean-continent transition zone and most of Line AR over thinned continental crust. Remarkably similar velocity/depth structures to that under Line 5 are found close to the ocean-continent transition zone off the whole of western Iberia, in areas which show no clear evidence of fracture zones. Therefore it appears more likely that the seismic structure of Line 5 is due to its proximity to the ocean-continent transition than to a local association with a fracture zone and further, that its structure is typical of this transition off the western margin of Iberia. We also suspect that the low upper mantle velocities associated with the ocean-continent transition indicate the widespread occurrence of serpentinized peridotite.
Brian J Bett - One of the best experts on this subject based on the ideXlab platform.
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Agglutination of benthic foraminifera in relation to mesoscale bathymetric features in the Abyssal NE Atlantic (Porcupine Abyssal Plain)
Marine Micropaleontology, 2016Co-Authors: Paris V. Stefanoudis, Brian J Bett, Jennifer M Durden, Ralf Schiebel, Romain Mallet, Andrew J GoodayAbstract:Abyssal hills, small topographic features rising above the Abyssal seafloor (< 1000 m altitude), have distinct environmental characteristics compared to Abyssal Plains, notably the presence of coarser-grained sediments. As a result, they are a major source of habitat heterogeneity in the deep sea. The aim of this study was to investigate whether there is a link between Abyssal hills and the test characteristics of selected agglutinated benthic foraminiferal species. We analysed 1) the overall morphometry, and 2) the granulometric and chemical (elemental) characteristics of the agglutinated tests of ten common foraminiferal species (Adercotryma glomerata, Ammobaculites agglutinans, Cribrostomoides subglobosus, Lagenammina sp.1, Nodulina dentaliniformis, Portatrochammina murrayi, three Reophax sp. and Recurvoides sp. 9) at four sites (two on top of Abyssal hills and two on the adjacent Plain) in the area of the Porcupine Abyssal Plain Sustained Observatory, northeast Atlantic. The foraminiferal test data were compared with the particle size distribution and elemental composition of sediments from the study sites in order to explore possible grain size and mineral selectivity. We found differences in the visual appearance of the tests (i.e. the degree of irregularity in their shape), which was confirmed by morphometric analyses, related to seafloor topography. The agglutinated foraminifera selected different sized particles on hills and Plains, reflecting the distinct granulometric characteristics of these settings. These characteristics (incorporation of coarse particles, test morphometry) could provide evidence for the recognition of ancient Abyssal hill environments, as well as other palaeoceanographic settings that were characterised by enhanced current flow. Furthermore, analyses of sediment samples from the hill and Plain sites using wavelength dispersive X-ray fluorescence (WD-XRF) yielded different elemental profiles from the Plains, probably a result of winnowing on the hills, although all samples were carbonate-rich. In contrast, the majority of the agglutinated tests were rich in silica, suggesting a preferential selection for quartz.
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the hemisessile lifestyle and feeding strategies of iosactis vagabunda actiniaria iosactiidae a dominant megafaunal species of the porcupine Abyssal Plain
Deep Sea Research Part I: Oceanographic Research Papers, 2015Co-Authors: Jennifer M Durden, Brian J Bett, Henry A RuhlAbstract:Iosactis vagabunda Riemann-Zurneck, 1997 (Actiniaria, Iosactiidae) is a small endomyarian anemone, recently quantified as the greatest contributor to megafaunal density (48%; 2372 individuals ha?1) on the Porcupine Abyssal Plain (PAP). We used time-lapse photography to observe 18 individuals over a period of approximately 20 months at 8-h intervals, and one individual over 2 weeks at 20-mine intervals, and report observations on its burrowing activity, and both deposit and predatory feeding behaviours. We recorded the apparent subsurface movement of an individual from an abandoned burrow to a new location, and burrow creation there. Raptorial deposit feeding on settled phytodetritus particles was observed, as was predation on a polychaete 6-times the estimated biomass of the anemone. Though essentially unnoticed in prior studies of the PAP, I. vagabunda may be a key component of the benthic community, and may make a critical contribution to the carbon cycling at the PAP long-term time-series study site.
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temporal changes 1989 1999 in deep sea metazoan meiofaunal assemblages on the porcupine Abyssal Plain ne atlantic
Deep-sea Research Part Ii-topical Studies in Oceanography, 2010Co-Authors: V Kalogeropoulou, Brian J Bett, Andrew J Gooday, Nikolaos Lampadariou, Martinez P Arbizu, Ann VanreuselAbstract:Trends among major metazoan meiofaunal taxa were investigated based on 56 deployments of a multicorer at 10 time points over a period of 11 years (1989–1999) at the Porcupine Abyssal Plain Sustained Observatory site (PAP-SO: 48°50′N 16°30′W, 4850 m depth). This area is characterised by a strong seasonality in the deposition of organic matter to the seafloor and by the massive increase in the density of holothurian species since 1996, the so-called ‘Amperima event’. Total meiofaunal densities ranged from 346 to 1074 ind.×10 cm−2 and showed a significant increase with time when time was represented by cruises, years and the ‘Amperima period’ (1996–1999) vs. the pre-Amperima period (1989–1994). This pattern was driven mainly by the nematodes, which were the dominant taxon (not, vert, similar90% of total abundance). The third most abundant group, the polychaetes, also increased significantly in abundance over the time series, while the ostracods showed a significant decrease. Most other taxa, including the second-ranked group, the copepods (harpacticoids and nauplii), did not exhibit significant temporal changes in abundance. Ordination of taxon composition showed a shift from the pre-Amperima to the Amperima periods, a trend supported by the significant correlation between the x-ordinate and time. The majority (52–75%) of meiofaunal animals inhabited the top 2 cm of the 5 cm sediment cores analysed. There were significant increases in the proportion of total meiofauna, nematodes and copepods (but not polychaetes) inhabiting the 0–1 cm layer over time (represented by cruises) and between the pre-Amperima and Amperima periods in the case of copepods and polychaetes. During the intensively sampled period (1996–1997), there were indications of seasonal changes in the vertical distribution patterns of total meiofauna and nematodes within the sediment. We discuss the potential link between temporal variations in organic matter flux to the seafloor and meiofaunal populations, considering both qualitative and quantitative changes in fluxes and how they may be linked to climate variations.
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long term change in the megabenthos of the porcupine Abyssal Plain ne atlantic
Progress in Oceanography, 2001Co-Authors: D S M Billett, Brian J Bett, A L Rice, Michael H Thurston, Joelle Galeron, Myriam Sibuet, George A WolffAbstract:A radical change in the abundance of invertebrate megafauna on the Porcupine Abyssal Plain is reported over a period of 10 years (1989–1999). Actiniarians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increased significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977–1999) show that prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a localised event. Several dominant holothurian species show a distinct trend in decreasing body size over the study period. The changes in megafauna abundance may be related to environmental forcing (food supply) rather than to localised stochastic population variations. Inter-annual variability and long-term trends in organic matter supply to the seabed may be responsible for the observed changes in abundance, species dominance and size distributions.
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patterns in polychaete abundance and diversity from the madeira Abyssal Plain northeast atlantic
Deep Sea Research Part I: Oceanographic Research Papers, 2001Co-Authors: Adrian G Glover, Brian J Bett, Myriam Sibuet, Gordon L J Paterson, John D Gage, Martin Sheader, Lawrence E HawkinsAbstract:Polychaete abundance and diversity patterns from the Madeira Abyssal Plain (MAP) were studied together with data from three other sites on the northeastern Atlantic Abyssal Plains. Polychaete abundance at MAP was significantly lower than at any of the other sites, including those lying under comparable productivity regimes. Analysis of diversity, using rarefaction and species counts per unit area, suggests that MAP is extremely species poor and shows dominance by a few common species. The MAP site is characterised by a superficial layer of turbidite sediment, and the hypothesis is put forward that the unusual sediment characteristics at MAP have affected macrofaunal abundance over a vast area (>2000 km2). Analysis of species composition indicates that the MAP site is not faunistically unique; rather it contains a high proportion of widespread, abundant, cosmopolitan species. We suggest that these are the opportunists of the Abyssal benthic habitat. Differences in abundance between the other Abyssal sites are the result of both productivity and local environmental conditions. Equitability at the other north Atlantic sites is not affected by productivity, although the actual number of species per unit area is affected, showing a south–north gradient.
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links between surface productivity and deep ocean particle flux at the porcupine Abyssal Plain sustained observatory
Biogeosciences, 2015Co-Authors: Helene Frigstad, Stephanie A Henson, Susan E Hartman, Abdirahman M Omar, Emil Jeansson, Harriet Cole, Corinne Pebody, R S LampittAbstract:Abstract. In this study we present hydrography, biogeochemistry and sediment trap observations between 2003 and 2012 at Porcupine Abyssal Plain (PAP) sustained observatory in the Northeast Atlantic. The time series is valuable as it allows for investigation of the link between surface productivity and deep ocean carbon flux. The region is a perennial sink for CO2, with an average uptake of around 1.5 mmol m−2 day−1. The average monthly drawdowns of inorganic carbon and nitrogen were used to quantify the net community production (NCP) and new production. Seasonal NCP and new production were found to be 4.57 ± 0.85 mol C m−2 and 0.37 ± 0.14 mol N m−2, respectively. The C : N ratio was high (12) compared to the Redfield ratio (6.6), and the production calculated from carbon was higher than production calculated from nitrogen, which is indicative of carbon overconsumption. The export ratio and transfer efficiency were 16 and 4 %, respectively, and the site thereby showed high flux attenuation. Particle tracking was used to examine the source region of material in the sediment trap, and there was large variation in source regions, both between and within years. There were higher correlations between surface productivity and export flux when using the particle-tracking approach, than by comparing with the mean productivity in a 100 km box around the PAP site. However, the differences in correlation coefficients were not significant, and a longer time series is needed to draw conclusions on applying particle tracking in sediment trap analyses.
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biogeochemical variations at the porcupine Abyssal Plain sustained observatory in the northeast atlantic ocean from weekly to inter annual timescales
Biogeosciences, 2015Co-Authors: Susan E Hartman, R S Lampitt, Helene Frigstad, Zongpei Jiang, Daniela Turk, Clare Ostle, Ute SchusterAbstract:Abstract. We present high-resolution autonomous measurements of carbon dioxide partial pressure p(CO2) taken in situ at the Porcupine Abyssal Plain sustained Observatory (PAP-SO) in the northeast Atlantic (49° N, 16.5° W; water depth of 4850 m) for the period 2010–2012. Measurements of p(CO2) made at 30 m depth on a sensor frame are compared with other autonomous biogeochemical measurements at that depth (including chlorophyll a fluorescence and nitrate concentration data) to analyse weekly to seasonal controls on p(CO2) flux in the inter-gyre region of the North Atlantic. Comparisons are also made with in situ regional time series data from a ship of opportunity and mixed layer depth (MLD) measurements from profiling Argo floats. There is a persistent under-saturation of CO2 in surface waters throughout the year which gives rise to a perennial CO2 sink. Comparison with an earlier data set collected at the site (2003–2005) confirms seasonal and inter-annual changes in surface seawater chemistry. There is year-to-year variability in the timing of deep winter mixing and the intensity of the spring bloom. The 2010–2012 period shows an overall increase in p(CO2) values when compared to the 2003–2005 period as would be expected from increases due to anthropogenic CO2 emissions. The surface temperature, wind speed and MLD measurements are similar for both periods of time. Future work should incorporate daily CO2 flux measurements made using CO2 sensors at 1 m depth and the in situ wind speed data now available from the UK Met Office Buoy.
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the porcupine Abyssal Plain fixed point sustained observatory pap so variations and trends from the northeast atlantic fixed point time series
Ices Journal of Marine Science, 2012Co-Authors: Susan E Hartman, Henry A Ruhl, R S Lampitt, Corinne Pebody, Kate E Larkin, Maureen Pagnani, J M Campbell, Thanos Gkritzalis, Zongpei Jiang, Andrew J GoodayAbstract:The Porcupine Abyssal Plain sustained observatory (PAP-SO) in the Northeast Atlantic (49°N 16.5°W; 4800 m) is the longest running open-ocean multidisciplinary observatory in the oceans around Europe. The site has produced high-resolution datasets integrating environmental and ecologically relevant variables from the surface to the seabed for >20 years. Since 2002, a full-depth mooring has been in place with autonomous sensors measuring temperature, salinity, chlorophyll-a fluorescence, nitrate, and pCO2. These complement ongoing mesopelagic and seabed observations on downward particle flux and benthic ecosystem structure and function. With national and European funding, the observatory infrastructure has been advanced steadily, with the latest development in 2010 involving collaboration between the UK's Meteorological Office and Natural Environment Research Council. This resulted in the first simultaneous atmospheric and ocean datasets at the site. All PAP-SO datasets are open access in near real time through websites and as quality-controlled datasets for a range of remote users using ftp sites and uploaded daily to MyOcean and the global telecommunications system for use in modelling activities. The combined datasets capture short-term variation (daily–seasonal), longer term trends (climate-driven), and episodic events (e.g. spring-bloom events), and the data contribute to the Europe-wide move towards good environmental status of our seas, driven by the EU's Marine Strategy Framework Directive (http://ec.europa.eu/environment/water/marine).