A coral perspective on last interglacial tropical Atlantic temperature and hydroclimate variability

The warming envisaged by future climate change scenarios contains a natural climate variability component that must be disentangled from the contribution of anthropogenic sources. High resolution records are also required in order to document societally relevant climate events, such as hurricanes, droughts and other climate phenomena that occur on sub-seasonal to multi-decadal time-scales. Large, long lived, Diploria Strigosa corals offer such records through the geochemical and isotopic records, reflective of the shallow seawaters they inhabit, found within their annually banded aragonitic skeletons. D. Strigosa colonies that grew during the last interglacial (LIG, MIS 5e, 127-117 ka) were obtained form the uplifted fossil reef terraces of the southern Caribbean island of Bonaire (Caribbean Netherlands). This thesis discusses the background and techniques used to successfully obtain and interpret palaeoclimate records from this delicate coral material. Results are presented in three manuscripts that explore distinct aspects of monthly resolved coral Sr/Ca and A 18O records and provide insights into LIG tropical Atlantic climate variability

Stress Induces Contextual Blindness in Lotteries and Coordination Games

In this paper, we study how stress affects risk taking in three tasks: individual lotteries, Stag Hunt (coordination) games, and Hawk-Dove (anti-coordination) games. Both control and stressed subjects take more risks in all three tasks when the value of the safe option is decreased and in lotteries when the expected gain is increased. Also, subjects take longer to take decisions when stakes are high, when the safe option is less attractive and in the conceptually more difficult Hawk-Dove game. Stress (weakly) increases reaction times in those cases. Finally, our main result is that the behavior of stressed subjects in lotteries, Stag Hunt and Hawk-Dove are all highly predictive of each other (p-value < 0.001 for all three pairwise correlations). Such strong relationship is not present in our control group. Our results illustrate a “contextual blindness” caused by stress. The mathematical and behavioral tensions of Stag Hunt and Hawk-Dove games are axiomatically different, and we should expect different behavior across these games, and also with respect to the individual task. A possible explanation for the highly significant connection across tasks in the stress condition is that stressed subjects habitually rely on one mechanism to make a decision in all contexts whereas unstressed subjects utilize a more cognitively flexible approach

Resource allocation in the brain

When an individual performs several tasks simultaneously, processing resources must be allocated to different brain systems to produce energy for neurons to fire. Following the evidence from neuroscience, we model the brain as an organization in which a coordinator allocates limited resources to the brain systems responsible for the different tasks. Systems are privately informed about the amount of resources necessary to perform their task and compete to obtain the resources. The coordinator arbitrates the demands while satisfying the resource constraint. We show that the optimal mechanism is to impose to each system with privately known needs a cap in resources that depends negatively on the amount of resources requested by the other system. This allocation can be implemented using a biologically plausible mechanism. Finally, we provide some implications of our theory: (i) performance can be flawless for sufficiently simple tasks, (ii) the dynamic allocation rule exhibits inertia (current allocations are increasing in past needs), and (iii) different cognitive tasks are performed by different systems only if the tasks are sufficiently important

Information Gatekeepers: Theory and Experimental Evidence

We consider a model where two adversaries can spend resources in acquiring public information about the unknown state of the world in order to influence the choice of a decision maker. We characterize the sampling strategies of the adversaries in the equilibrium of the game. We show that, as the cost of information acquisition for one adversary increases, that person collects less evidence whereas the other adversary collects more evidence. We then test the results in a controlled laboratory setting. The behavior of subjects is close to the theoretical predictions. Mistakes are relatively infrequent (15%). They occur in both directions, with more over-sampling (39%) than under-sampling (8%). The main difference with the theory is the smooth decline in sampling around the theoretical equilibrium. Comparative statics are also consistent with the theory, with adversaries sampling more when their own cost is low and when the other adversary’s cost is high. Finally, there is little evidence of learning over the 40 matches of the experiment