The Pliocene closure fo the Central American Seaway : reconstructing surface-, intermediate- and deep-water connections

Timing of Gateway Closure The shoaling of the Isthmus of Panama and the associated reorganisation of deep-ocean circulation have been controversially reported as contributing to both a warming and a cooling of global climate. A resulting increase in moisture supply to the northern hemisphere, through the initiation or strengthening of the Gulf Stream, may have been an important precondition for Northern Hemisphere Glaciation. A robust timeframe for the closure of this major ocean gateway is essential for understanding its direct and indirect effects on global climate. Method We use radiogenic isotopes of Nd and Pb to reconstruct the history of shallow, intermediate and deep water connections between the Caribbean Sea and the eastern Equatorial Pacific Ocean from 5.0 to 2.0 million years ago. Surface water exchange is characterised using the Nd isotope composition of planktonic foraminiferal calcite. The Nd and Pb isotope compositions of early diagenetic ferromanganese coatings of the same sediment samples are employed to reconstruct intermediate and deep water exchange. Results and Conclusion Our results indicate that Caribbean Intermediate Water continued to diverge from a relatively constant Pacific deepwater Nd composition from 5.0 to 2.0 Ma. Comparison with published stable isotope and Mg/Ca records from the same ODP Sites 999, 1000 and 1241 suggest that Caribbean Intermediate Water composition continued to change even after a decrease in surface water exchange with the Pacific (4.5 Ma onwards [1]). A more rapid restriction of mixing between the Pacific and Caribbean at intermediate depths from 4 to 3.5 Ma clearly preceeded the major increase in ice-rafted-debris north of Iceland [2]. [1] Groeneveld et al. (2008) G3 9, Q01P23. [2] Jansen et al. (2000) Paleoceanography 15, 709-721

PARTY FORMATION INCOLLECTIVE DECISION-MAKING

We study party formation in a general model of collective decisionmaking, modeling parties as agglomerations of policy positions championed by decision-makers. We show that if there are economies of party size and the policy chosen is not beaten by another policy in pairwise voting, then players agglomerate into exactly two parties. This result does not depend on the magnitude of the economies of party size or sensitively on the nature of the individuals' preferences. Our analysis encompasses a wide range of models, including decision-making in committees with costly participation and representative democracy in which the legislature is elected by citizens.

Party formation in single-issue politics [revised]

We study the implications of economies of party size in a model of party formation. We show that when the policy space is one-dimensional, candidates form at most two parties. This result does not depend on the magnitude of the economies of party size or sensitively on the nature of the individuals' preferences. It does depend on our assumptions that the policy space is one-dimensional and that uncertainty is absent; we study how modifications of these assumptions affect our conclusions.Political parties, party formation, economies of party size

Cost benefit analysis vs. referenda

We consider a planner who chooses between two possible public policies and ask whether a referendum or a cost benefit analysis leads to higher welfare. We find that a referendum leads to higher welfare than a cost benefit analyses in "common value" environments. Cost benefit analysis is better in "private value" environments.Cost benefit analysis, elections, referenda, project evaluation

Understanding Caesar’s Ethnography: A Contextual Approach to Protohistory

The Celts of western and central Europe1 flourished during the height of Greek and Roman civilization, and yet there is a methodological schism between the study of the Mediterranean world and that of the “peripheral” Europeans. Our appreciation of classical society stems primarily from the plentiful written texts – texts that provide us with minute details of society, religion, and politics from the words of the people who actively participated in that culture. The study of the Celts, on the other hand, is more oblique: our primary source is archaeology, and what little textual evidence we do have derives from Mediterranean historians and geographers. In anthropological terms, classicists study sources written from an emic perspective, while archaeologists study sources written from the etic. The European Iron Age is unusual because it requires a methodology that bridges the familiar divisions between historian and archaeologist. In early investigations of the Celts, archaeological excavation was seen as a tool used to give physical illustration to classical accounts of Celtic life. The ancient texts were thought to hold the real truth of Celtic society – a truth that was archaeology’s job to unearth. In the past two decades, however, this perception has changed dramatically, and archaeologists use Greek and Roman texts rarely, if at all. This is in part a reaction to criticisms of the reliability of ancient sources and a realization of how these texts have been used to distort our perceptions of the archaeological record. Much ink has been spilled on this topic, with the result that many archaeologists now choose to gloss over or simply ignore documentary evidence. This is not a result of ignorance but rather a result of methodology having failed to keep pace with theory. I would like to try to redress this imbalance and begin a debate on how to use the ancient texts correctly, so that they are a help rather than a hindrance to the archaeologist

Equilibria for a Three-Person Location Problem

We find all the mixed strategy equilibria, within a certain class, of the simplified three-firm location model of Hotelling (in which the price variable is ignored)

Profit-Sharing in a Collusive Industry

We study a model in which collusive duopolists divide up the monopoly profit according to their relative bargaining power. We are particularly interested in how the negotiated profit shares depend on the sizes of the firms. If each can produce at the same constant unit cost up to its capacity, we show that the profit per unit of capacity of the small firm is higher than that of the large one. We also study how the ratio of the negotiated profits depends on the size of demand relative to industry capacity, and how this ratio changes with variations in demand