Prominent renewal of Weddell Sea Deep Water from a remote source

Three transient tracer sections of CFC-11 across the Weddell Sea are presented, collected during "Polarstern" cruises ANT X/4 (July 1992), ANT XIII/4 (May 1996) and ANT XV/4 (April 1998). The corresponding sections of silicate, a quasi-steady state tracer, are displayed for comparison and as a supplement. Two distinct CFC-11 maximum layers are found in the deep water, one centred near 2200 m and another near 3500 m. These layers, noticed previously also by other investigators, represent recently ventilated Weddell Sea Deep Water. The deeper, more pronounced core occurs along the southern continental slope, whereas the shallower core occurs in the northern Weddell Sea. The deeper CFC-11 maximum layer coincides with a pronounced silicate minimum layer. Quantitatively, the deeper core constitutes a ventilation route for the Weddell Sea of utmost importance, the amount of ventilated surface water involved being 2.7 ± 0.9 Sv. Most of the deep interior Weddell Sea appears to be ventilated by this external source. The ventilation rate of the Weddell Sea due to the inflow from the east is at least as high as that from the local southern and western sources that produce bottom water. Associated with the deep CFC-11 maximum core are discontinuities in the potential temperature-property diagrams of silicate, oxygen, total carbon dioxide, nitrate and salinity. The recently ventilated deep water is characterized by low concentrations of silicate, total carbon dioxide and nitrate, and by high oxygen content and salinity as compared to the deep water at the same potential temperature formed by mixing of Warm Deep Water and Weddell Sea Bottom Water

Ocean/ice shelf interaction in the southern Weddell Sea: results of a regional numerical helium/neon simulation

Ocean/ice interaction at the base of deep drafted Antarctic ice shelves modifies the physical properties of inflowing shelf waters to become Ice Shelf Water (ISW).In contrast to the conditions at the atmosphere/ocean interface, the increased hydrostaticpressure at the glacial base causes gases embedded in the ice to solve completely after being released by melting. Helium and neon with an extremely low solubility are supersatured in glacial meltwater by more than 1000%. At the continentalslope in front of the large Antarctic caverns ISW mixes with ambient waters toform different precursors of Antarctic Bottom Water. A regional ocean circulation model is presented which uses an explicit formulation of the ocean/ice shelf interaction to describe for the first time the input of noble gases to the Southern Ocean. The results reveal a long-term variability of the basal mass loss solely controlled by the interaction between waters of the continental shelf and the ice shelf cavern. Modeled helium and neon supersaturations from the Filchner-Ronne Ice Shelf front reveal a "low-pass" filtering of the inflowing signal due to cavern processes. On circumpolar scales the helium and neon distributions in the Southern Ocean quantify the ISW contribution to bottom water which spreads with the coastal current connecting the major formation sites in Ross and Weddell Seas

Interindividual Differences in Mid-Adolescents in Error Monitoring and Post-Error Adjustment

A number of studies have concluded that cognitive control is not fully established until late adolescence. The precise differences in brain function between adults and adolescents with respect to cognitive control, however, remain unclear. To address this issue, we conducted a study in which 185 adolescents (mean age (SD) 14.6 (0.3) years) and 28 adults (mean age (SD) 25.2 (6.3) years) performed a single task that included both a stimulus-response (S-R) interference component and a task-switching component. Behavioural responses (i.e. reaction time, RT; error rate, ER) and brain activity during correct, error and post-error trials, detected by functional magnetic resonance imaging (fMRI), were measured. Behaviourally, RT and ER were significantly higher in incongruent than in congruent trials and in switch than in repeat trials. The two groups did not differ in RT during correct trials, but adolescents had a significantly higher ER than adults. In line with similar RTs, brain responses during correct trials did not differ between groups, indicating that adolescents and adults engage the same cognitive control network to successfully overcome S-R interference or task switches. Interestingly, adolescents with stronger brain activation in the bilateral insulae during error trials and in fronto-parietal regions of the cognitive control network during post-error trials did have lower ERs. This indicates that those mid-adolescents who commit fewer errors are better at monitoring their performance, and after detecting errors are more capable of flexibly allocating further cognitive control resources. Although we did not detect a convincing neural correlate of the observed behavioural differences between adolescents and adults, the revealed interindividual differences in adolescents might at least in part be due to brain development

Brain response during correct trials.

<p>A) Main effect of task transition: Regions of the brain that respond more strongly during switch compared to repeat trials in adolescents and adults (threshold T = 2.11, p<0.05, FDR-corrected, in 25 contiguous voxels, yellow colour scale). B) Main effect of congruence: Regions of the brain respond more strongly during congruent compared to incongruent trials in adolescents and adults (threshold T = 2.64, p<0.05, FDR-corrected, in 25 contiguous voxels, blue colour scale), and regions of the brain that respond more strongly during incongruent compared to congruent trials in adolescents and adults (threshold T = 2.97, p<0.05, FDR-corrected, in 25 contiguous voxels, red colour scale). C) Main effect of group in the subsample analysis (N = 45 error-prone adolescents and N = 28 adults): Regions of the brain that respond weaker in adolescents compared to adults (threshold T = 2.87, p<0.05, FDR-corrected, in 25 contiguous voxels, yellow colour scale).</p

Brain response during error trials.

<p>Note that only 181 adolescents and 22 adults who made at least 3 mistakes were considered for this analysis. A) Regions of the brain during error trials that show a significant negative correlation with overall ER (threshold T = 3.84, p<0.05, FDR-corrected, in 25 contiguous voxels) in adolescents. B) Correlation coefficients for the negative correlation between brain response during error trials and overall ER for adolescents (blue) and adults (orange) in the peak voxels (please see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088957#pone.0088957.s003" target="_blank">Table S3</a>). The correlation only reached significance in adolescents.</p

Procedure of the interference and switch task with two out of 16 possible stimuli.

<p>Procedure of the interference and switch task with two out of 16 possible stimuli.</p

Brain response during correct post-error/post-missing trials.

<p>Note that only 181 adolescents and 22 adults which made at least three mistakes were considered for this analysis. A) Regions of the brain during post-error/post-missing trials that show a significant negative correlation with overall ER (threshold T = 2.77, p<0.05, FDR-corrected, in 25 contiguous voxels) in adolescents. B) Correlation coefficients for the correlation between brain response during post-error/post-missing trials and overall ER for adolescents (blue) and adults (orange) in the peak voxels (sorted by t-values, please see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088957#pone.0088957.s004" target="_blank">Table S4</a>). The correlations only reached significance in adolescents.</p

Mean reaction times (A) and error rates (B) for the four different conditions resulting from the factors task transition and congruence in adolescents (blue) and adults (orange).

<p>Notes: rp – repeat, sw – switch, C – congruent, I – incongruent. The error bars indicate the area of one standard deviation around the mean.</p