Depth dependence of westward-propagating North Atlantic features diagnosed from altimetry and a numerical 1/6° model

International audienceA 1/6° numerical simulation is used to investigate the vertical structure of westward propagation between 1993 and 2000 in the North Atlantic ocean. The realism of the simulated westward propagating signals, interpreted principally as the signature of first-mode baroclinic Rossby waves (RW), is first assessed by comparing the simulated amplitude and zonal phase speeds of Sea Level Anomalies (SLA) against TOPEX/Poseidon-ERS satellite altimeter data. Then, the (unobserved) subsurface signature of RW phase speeds is investigated from model outputs by means of the Radon Transform which was specifically adapted to focus on first-mode baroclinic RW. The analysis is performed on observed and simulated SLA and along 9 simulated isopycnal displacements spanning the 0-3250 m depth range. Simulated RW phase speeds agree well with their observed counterparts at the surface, although with a slight slow bias. Below the surface, the simulated phase speeds exhibit a systematic deceleration with increasing depth, by a factor that appears to vary geographically. Thus, while the reduction factor is about 15-18% on average at 3250 m over the region considered, it appears to be much weaker (about 5-8%) in the eddy-active Azores Current, where westward propagating structures might be more coherent in the vertical. In the context of linear theories, these results question the often-made normal mode assumption of many WKB-based theories that the phase speed is independent of depth. Alternatively, these results could also suggest that the vertical structure of westward propagating signals may significantly depend on their degree of nonlinearity, with the degree of vertical coherence possibly increasing with the degree of nonlinearity

On the Variability of the DWBC Transport Between 26.5°N and 16°N in an Eddy‐Rich Ocean Model

The southward flow of North Atlantic Deep Water makes up the major component of the deepwater limb of the Atlantic Meridional Overturning Circulation (AMOC). In the subtropical North Atlantic, it's flow is concentrated along the continental slope, forming a coherent Deep Western Boundary Current (DWBC). Both, observations and models show a high variability of the flow in this region. Here we use an eddy-rich ocean model to show that this variability is mainly caused by eddies and meanders. Their formation process involves an important contribution from energy transfer by barotropic instability. They occur along the entire DWBC pathway and introduce several recirculation gyres that result in a decorrelation of the DWBC transport at 26.5°N and 16°N, despite the fact that a considerable mean transport of 20 Sv connects the two latitudes. Water in the DWBC at 26.5°N is partly returned northward. Because the amount of water returned depends on the DWBC transport itself, a stronger DWBC does not necessarily lead to an increased amount of water that reaches 16°N. Along the pathway to 16°N, the transport signal is altered by a broad and temporally variable transit time distribution. Thus, advection in the DWBC cannot account for coherent AMOC changes on interannual timescales seen in the model

A conceptual and empirical framework for the social distribution of cognition: The case of memory

In this paper, we aim to show that the framework of embedded, distributed, or extended cognition offers new perspectives on social cognition by applying it to one specific domain: the psychology of memory. In making our case, first we specify some key social dimensions of cognitive distribution and some basic distinctions between memory cases, and then describe stronger and weaker versions of distributed remembering in the general distributed cognition framework. Next, we examine studies of social influences on memory in cognitive psychology, and identify the valuable concepts and methods to be extended and embedded in our framework; we focus in particular on three related paradigms: transactive memory, collaborative recall, and social contagion. Finally, we sketch our own early studies of individual and group memory developed within our framework of distributed cognition, on social contagion of autobiographical memories, collaborative flashbulb memories, and memories of high school at a high school reunion. We see two reciprocal benefits of this conceptual and empirical framework to social memory phenomena: that ideas about distributed cognition can be honed against and tested with the help of sophisticated methods in the social cognitive psychology of memory; and conversely, that a range of social memory phenomena that are as yet poorly understood can be approached afresh with theoretically motivated extensions of existing empirical paradigms

A componential approach to individual differences in hypnotizability

Although responsiveness to hypnotic suggestions (hypnotizability) typically is conceptualized and studied as a singular homogeneous capability, numerous lines of evidence suggest instead that it is a hierarchically structured cognitive capacity comprising a core superordinate ability and ancillary subordinate component abilities. After reviewing current approaches to the measurement of hypnotizability and componential approaches to other cognitive capabilities, we highlight outstanding questions in the field and argue for a componential approach to the study of hypnotizability. Such an approach assumes that hypnotizability is not a unitary construct but is rooted in multiple subabilities that interact to give rise to individual differences that are expressed within specific contexts. We revisit previous componential work on hypnotizability and propose a series of steps by which a componential model can be more rigorously interrogated and integrated with contemporary advances in our understanding of human cognition

Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

International audienceThree hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Dono-hue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations

Proteolytic enzyme and inhibitor levels in reindeer (Rangifer tarandus tarandus L.) vs. bovine longissimus muscle, as they relate to ageing rate and response

Eight reindeer bulls (age 1.5 years) and six Friesian bulls (age 1.5 years) were included in the study for comparison of tenderness. The reindeer were slaughtered at a commercial reindeer slaughter plant in northern Sweden and the Friesian bulls at a commercial slaughter plant in The Netherlands. Samples for determination of calpain/calpastatin activity were taken from the M. longtssimus (LO) within 1 h post mortem (p.m.), and at various times p.m. pH and temperature were registered in LO; ultimate pH values were measured at 24 h p.m. for beef and at 35 h p.m. for reindeer. At day 1 p.m., samples of LO from both carcass sides were excised, divided in two parts, vacuum packaged and stored at 0-2 °C. One part of each muscle was randomly sampled at 1, 3, 7 and 14 days p.m. for determination of shear force, proteolytic enzyme activity, myofibrillar protein degradation, collagen content and heat solubility. pH and temperature fall was faster in reindeer than in beef. Collagen content in reindeer muscle was found to be low but collagen was 4 times less soluble as compared with beef. Reindeer LO was found to be extremely tender, at 3 days p.m. shear force values were only 2-3 kg/cm2 (8-12 kg/cm2 for beef LO). In reindeer meat, the jJ.-calpain levels dropped to about 55% within 3 days. Troponin T and 30 kDa values were not related to changes in tenderness in reindeer meat. Cathepsin activities in reindeer were up to ten times higher than in beef. As in beef, cathepsin B+L levels in reindeer increased during storage, which is probably associated with a decrease in cystatin-like inhibitor levels

Transfer of particulate matter from the Northwestern Mediterranean continental margin: Variability and controlling factors

International audienceLong-term observations of monthly downward particle fluxes and hourly currents and temperaturewere initiated in 1993 in two canyons of the continental margin of the Gulf of Lion. The goals of thissurvey were to estimate its contribution to the CO 2 global budget and to understand the role offorcing factors in the control of present-day particle exchange across this margin. A previousstatistical analysis of the long-term time series suggested that variability in the transfer of particulatematter to the deep ocean could be the result of the effect of the meandering of the Northern Currentand by dense water formation in winter rather than variations in the sources of matter. Numericalsimulations have been carried out to consider these hypotheses. A model is used to examine theimpact of local atmospheric forcing (wind stress, heat fluxes, precipitation–evaporation budget) onthe variability of the oceanic circulation and of mass fluxes within the canyons from December toApril, for five consecutive years between 1996 and 2001. Results show an east-west gradient of massexport on the shelf and a positive correlation between anomalies of dense water formation rates andinterannual variability of particle fluxes. However, in the eastern part of the Gulf, the simulated massexport from the shelf is not significant, even during a winter of strong convection, when the measuredparticle fluxes are at maxima. Moreover, although the model suggests that the dense water formationcould be the major hydrodynamic forcing factor, this process is not sufficient to completely explainthe space and time variations of observed particle fluxes, especially at depth

Simulations of a Line W-based observing system for the Atlantic meridional overturning circulation

In a series of observing system simulations, we test whether the Atlantic meridional overturning circulation (AMOC) can be observed based on the existing Line W deep western boundary array. We simulate a Line W array, which is extended to the surface and to the east to cover the basin to the Bermuda Rise. In the analyzed ocean circulation model ORCA025, such an extended Line W array captures the main characteristics of the western boundary current. Potential trans-basin observing systems for the AMOC are tested by combining the extended Line W array with a mid-ocean transport estimate obtained from thermal wind "measurements" and Ekman transport to the total AMOC (similarly to Hirschi et al., Geophys Res Lett 30(7):1413, 2003). First, we close Line W zonally supplementing the western boundary array with several "moorings" in the basin (Line W-32A degrees N). Second, we supplement the western boundary array with a combination of observations at Bermuda and the eastern part of the RAPID array at 26A degrees N (Line W-B-RAPID). Both, a small number of density profiles across the basin and also only sampling the eastern and western boundary, capture the variability of the AMOC at Line W-32A degrees N and Line W-B-RAPID. In the analyzed model, the AMOC variability at both Line W-32A degrees N and Line W-B-RAPID is dominated by the western boundary current variability. Away from the western boundary, the mid-ocean transport (east of Bermuda) shows no significant relation between the two Line W-based sections and 26A degrees N. Hence, a Line W-based AMOC estimate could yield an estimate of the meridional transport that is independent of the 26A degrees N RAPID estimate. The model-based observing system simulations presented here provide support for the use of Line W as a cornerstone for a trans-basin AMOC observing system

Basin-scale pCO2 maps estimated from ARGO float data: A model study

A novel method for mapping surface pCO(2) on a basin scale using ARGO floats is presented and tested in the framework of an eddy-resolving biogeochemical model of the North Atlantic. Voluntary observing ship (VOS) and ARGO float coverage of the year 2005 is applied to the model to generate synthetic "observations." The model-generated VOS line "observations'' of pCO(2), SST, and SSS form a training data set for a self-organizing neural network. The trained neural network is subsequently applied locally to estimate pCO(2) from the model-generated ARGO float SST and SSS data. The local pCO(2) estimates at the simulated float positions are extrapolated using objective mapping. The accuracy of the nearly basinwide pCO(2) estimates is assessed by comparing against the pCO(2) output of the model that serves as synthetic "ground truth.'' For an ARGO float coverage of the year 2005, the resulting monthly mean pCO(2) maps cover 70% of the considered area (15 degrees N to 65 degrees N) with an RMS error of 15.9 mu atm. Compared to remote sensing-based estimates that suffer from large regional gaps in optical satellite data coverage, the RMS error in reproducing the annual cycle of pCO(2) can be reduced by 42% when the more evenly distributed ARGO float-based data are used