Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Neogene diatoms from the western Antarctic Peninsula

During Ocean Drilling Program Leg 178 we cored nine sites on the continental rise (Sites 1095, 1096, and 1101), continental shelf (Sites 1097, 1100, 1102, and 1103), and in an inner shelf basin, Palmer Deep (Sites 1098 and 1099), along the Pacific margin of the Antarctic Peninsula. Fossil diatoms are a key group that provides age constraint for these shelf site sediments to allow reconstruction of Antarctic Peninsula glacial history. This paper provides the systematic paleontology of diatoms applied in biostratigraphic and paleoceanographic studies and includes a total of 33 plates. Taxonomic confusion in previous reports, including biostratigraphically useful species such as Thalassiosira inura and Thalassiosira complicata, is discussed. These systematics and taxonomic discussions help to provide a reference for Neogene diatoms in the Southern Ocean.

Paleoceanography of sediment cores SO202-27-6 during MIS 3

The modern subarctic Pacific is characterized by a steep salinity-driven surface water stratification, which hampers the supply of saline and nutrient-rich deeper waters into the euphotic zone, limiting productivity. However, the strength of the halocline might have varied in the past. Here, we present diatom oxygen (d18Odiat) and silicon (d30Sidiat) stable isotope data from the open subarctic North-East (NE) Pacific (SO202-27-6; Gulf of Alaska), in combination with other proxy data (Neogloboquadrina pachydermasin d18O, biogenic opal, Ca and Fe intensities, IRD), to evaluate changes in surface water hydrography and productivity during Marine Isotope Stage (MIS) 3, characterized by millennial-scale temperature changes (Dansgaard-Oeschger (D-O) cycles) documented in Greenland ice cores.

Radiocarbon ages and diatom abundance in cores GA306-BC4 and GA306-GC4 obtained during Galathea 3 cruise, West Greenland

Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at AD 750-1330, although with some oceanographic variability after AD 1000. A pronounced oceanographic shift occurred at AD 1330, corresponding in time to the transition from the so-called 'Medieval Warm Period' (MWP) to the 'Little Ice Age' (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at AD 1330-1350, AD 1400-1575 and AD 1660-1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations.

Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Diatom biostratigraphy of sediments from the Kerguelen Plateau, Southern Ocean

The biostratigraphic distribution and abundance of lower Oligocene to Pleistocene diatoms is documented from Holes 747A, 747B, 748B, 749B, and 751A drilled during Ocean Drilling Program Leg 120 on the Kerguelen Plateau in the southeast Indian Ocean. The occurrence of middle and upper Eocene diatoms is also documented, but these are rare and occur in discrete intervals. The recovery of several Oligocene to Pleistocene sections with minimal coring gaps, relatively good magnetostratigraphic signatures, and mixed assemblages of both calcareous and siliceous microfossils makes the above four Leg 120 sites important biostratigraphic reference sections for the Southern Ocean and Antarctic continent. A high-resolution diatom zonation divides the last 36 m.y. into 45 zones and subzones. This zonation is built upon an existing biostratigraphic framework developed over the past 20 yr of Southern Ocean/Antarctic deep-sea coring and drilling. After the recent advances from diatom biostratigraphic studies on sediments from Legs 113, 114, 119, and 120, a zonal framework for the Southern Ocean is beginning to stabilize. The potential age resolution afforded by the high-diversity diatom assemblages in this region ranks among the highest of all fossil groups. In addition to the 46 datum levels that define the diatom zones and subzones, the approximate stratigraphic level, age, and magnetic anomaly correlative of more than 150 other diatom datums are determined or estimated. These total 73 datum levels for the Pliocene-Pleistocene, 67 for the Miocene, and 45 for the Oligocene. Greater stratigraphic resolution is possible as the less common and poorly documented species become better known. This high-resolution diatom stratigraphy, combined with good to moderately good magnetostratigraphic control, led to the recognition of more than 10 intervals where hiatuses dissect the Oligocene-Pleistocene section on the Kerguelen Plateau. We propose 12 new diatom taxa and 6 new combination

Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Diatoms and Silicoflagellates from ODP Hole 114-699A and Site 114-704

The stratigraphic ranges and relative abundances of selected diatoms and silicoflagellates are presented from three Neogene sedimentary sequences from the subantarctic South Atlantic. These data were compiled from Hole 699A in the southwest South Atlantic and Holes 704A and 704B in the southeast South Atlantic. Thirty-five samples were examined from a 67.5-m section of Hole 699A, which is mostly late Miocene or younger in age. A total of 225 samples was examined from the upper 569.1-m lower Miocene to Quaternary section in Holes 704A and 704B. Although the partial census of the Site 704 sequences is only preliminary, it reveals that the Neogene is remarkably complete and serves as a reference for further detailed examination of an important biostratigraphic-magnetostratigraphic reference section for the Neogene record of the Southern Ocean.

Diatom abundance in ODP Leg 178 holes

This paper documents the biostratigraphic distribution and abundance of diatoms from sites drilled during Ocean Drilling Program Leg 178, off the Pacific margin of the Antarctic Peninsula. Drift sediments cored on the continental rise at Sites 1095, 1096, and 1101 have good recovery and a well-defined paleomagnetic record. Well-preserved diatoms are present throughout the upper Miocene to middle Pliocene and in the upper Quaternary section of these sites. The stratigraphic occurrence of diatom species through these intervals defines numerous datum levels. Diatom events are given absolute age estimates through direct correlation to the established paleomagnetic stratigraphy of Sites 1095, 1096, and 1101. Leg 178 diatom biostratigraphic results enable the development of a regional stratigraphic framework for the Pacific sector of the Southern Ocean and record the interaction of open-ocean and shelf-margin diatom floras.

Marine diatoms in deep sea sediments

Long-term evolution is thought to take opportunities that arise as a consequence of mass extinction (as argued, for example, by Gould, 2002) and the following biotic recovery, but there is absolutely no evidence for this being the case. However, our study shows that eutrophication by oceanic mixing also played a part in the enhancement of several evolutionary events amongst marine organisms, and these results could indicate that the rates of oceanic biodiversification may be slowed if upwelling becomes weakened by future global warming. This paper defines three distinct evolutionary events of resting spores of the marine diatom genus Chaetoceros, to reconstruct past upwelling through the analysis of several DSDP, ODP and land-based successions from the North, South and equatorial Pacific as well as the Atlantic Ocean during the past 40 million years. The Atlantic Chaetoceros Explosion (ACE) event occurred across the E/O boundary in the North Atlantic, and is characterized by resting spore diversification that occurred as a consequence of the onset of upwelling following changes in thermohaline circulation through global cooling in the early Oligocene. Pacific Chaetoceros Explosion events-1 and -2 (PACE-1 and PACE-2) are characterized by relatively higher occurrences of iron input following the Himalayan uplift and aridification at 8.5 Ma and ca. 2.5 Ma in the North Pacific region. These events not only enhanced the diversification and increased abundance of primary producers, including that of Chaetoceros, other diatoms and seaweeds, but also stimulated the evolution of zooplankton and larger predators, such as copepods and marine mammals, which ate these phytoplankton and plants. Current thinking suggests new evolutionary niches open up after a mass extinction, but our study finds that eutrophication can also stimulate evolutionary diversification. Moreover, in the opposite fashion, our results show that as thermohaline circulation abates, global warming progresses and the ocean surface becomes warmer, many marine organisms will be affected by the environmental degradation.

Middle Miocene to Quaternary diatom biostratigraphy of DSDP Site 90-594

A diatom biostratigraphy is presented for middle Miocene through Quaternary sediments recovered from the Chatham Rise east of New Zealand's South Island. The upper 590 m of the 639.5-m composite-section Site 594 represents approximately 16 m.y. and is characterized by moderately to very poorly preserved diatoms of antarctic to temperate affinity. Pliocene through Quaternary assemblages are poorly preserved and dominated by antarctic-subantarctic species which provide detailed biostratigraphic control. Recognized are 11 of 14 zones of the middle upper Miocene to Quaternary Neogene Southern Ocean diatom zonation (NSD 7-NSD 20) of Ciesielski (1983; this chapter). Four Neogene Southern Ocean diatom zones (NSD 3-NSD 6) are recognized in the lower middle Miocene to middle upper Miocene of Site 594. Assemblages of this interval have a mixed high-latitude and temperate affinity; however, poor preservation limits correlation to high- and temperate-latitude zonal schemes. Neogene North Pacific diatom zones and subzones of NNPD 3 through NNPD 5 (Barron, in press, b) are correlated to Neogene Southern Ocean diatom zones NSD 3 through NSD 7: the upper portions of the Actinocyclus ingens Zone (NNPD 3) is correlative to the upper Nitzschia maleinterpretaria Zone (NSD 3); the Denticulopsis lauta Zone (NNPD 4) and Subzones a and b are correlative to the lower Coscinodiscus lewisianus Zone (NSD 4); and the D. hustedtü-D. lauta Zone (NNPD 5) and its Subzones a through d encompass the upper C. lewisianus Zone (NSD 4), N. grossepunctata Zone (NSD 5), N. denticuloides Zone (NSD 6), and the lower D. hustedtii-D. lauta Zone (NSD 7). A major disconformity spans the late Gilbert to early Gauss Chron (3.9-2.8 Ma). A second disconformity brackets the Miocene/Pliocene boundary; the section missing covers late Chron 5 and the early Gilbert chron (5.5-4.6 Ma). The remainder of the siliceous-fossil-bearing Miocene sediments at Site 594 appear to be correlative to lower paleomagnetic Chronozone 5 through upper Chronozone 16. Uppermost lower Miocene or lowermost middle Miocene sediments in the basal 50 m of Hole 594A are barren of diatoms.

Neogene diatoms of the Japan Sea

A series of excellent upper Miocene through Quaternary diatomaceous sequences recovered at four sites during Leg 127 was examined for diatoms. The diagenetic transition from opal-A to opal-CT is a diachronic horizon from the uppermost part of the Denticulopsis katayamae Zone (8.5 Ma) at Hole 797B to the uppermost part of the Neodenticula kamtschatica Zone (5.73 Ma) at Hole 795A. The diatom zonation of Koizumi (1985) best divides the upper Miocene to Quaternary sequences above the opal-A/opal-CT boundary and also is useful to date carbonate concretions including diatoms below the boundary. Forty diatom datum levels were evaluated biostratigraphically based on the sediment accumulation rate curve, and several isochronous datum levels are newly proposed for the Japan Sea area. A warm-water current did not penetrated into the Japan Sea through the Tsushima strait during the late Miocene and Pliocene time, because subtropical warm-water diatoms are essentially not present in such sediment samples. The occurrences of diatom are cyclic throughout the Quaternary sediments and are affected by eustatic sea level changes.

Miocene to Holocene diatom biostratigraphy of ODP Leg 105 sites

Diatoms occur sporadically in lower Miocene to Holocene sediments recovered at ODP Site 645 and in upper Pliocene to Holocene sediments at ODP Site 646. The diatom assemblage at Site 645 contains rare stratigraphic indicators. Fragmentation of frustules and the occurrence of species characteristic of high-latitude shelf, upper-slope environments suggest current transportation from the shelf. The diatom abundance and preservation at Site 646 probably reflect climatic changes and are also affected by dissolution, but it is not possible to detect the dominant factor. Therefore, the stratigraphic ranges of the primary and secondary biostratigraphic indicators are often unreliable.

Distribution of Pliocene diatom faunas in the Northwest Pacific

High-resolution quantitative diatom data are tabulated for the early part of the late Pliocene ( 3.25 to 2.08 Ma ) at DSDP Site 580 in the northwestern Pacific. Sample spacing averages 11 k.y. between 3.1 and 2.8 Ma, but increases to 14 to 19 k.y. prior to 3.1 Ma and after 2.8 Ma. Q-mode factor analysis of the middle Pliocene assemblage reveals four factors which explain 92.4% of the total variance of the 47 samples studied between 3.25 and 2.55 Ma. Three of the factors are closely related to modern subarctic, transitional, and subtropical elements, while the fourth factor, which is dominated by Coscinodiscus marginatus and the extinct Pliocene species Neodenticula kamtschatica, appears to correspond to a middle Pliocene precursor of the subarctic water mass. Knowledge of the modern and generalized Pliocene paleoclimatic relationships of various diatom taxa is used to generate a paleoclimate curve ("Twt") based on the ratio of warm-water (subtropical) to cold-water diatoms with warm-water transitional taxa (Thalassionema nitzschioides, Thalassiosira oestrupii, and Coscinodiscus radiatus) factored into the equation at an intermediate (0.5) value. The "Twt" ratios at more southerly DSDP Sites 579 and 578 are consistently higher (warmer) than those at Site 580 throughout the Pliocene, suggesting the validity of the ratio as a paleoclimatic index. Diatom paleoclimatic data reveal a middle Pliocene (3.1 to 3.0 Ma) warm interval at Site 580 during which paleotemperatures may have exceeded maximum Holocene values by 3 °- 5.5 °C at least three times. This middle Pliocene warm interval is also recognized by planktic foraminifers in the North Atlantic, and it appears to correspond with generalized depleted oxygen isotope values suggesting polar warming. The diatom "Twt" curve for Site 580 compares fairly well with radiolarian and silicoflagellate paleoclimatic curves for Site 580, planktic foraminiferal sea-surface temperature estimates for the North Atlantic, and benthic oxygen isotope curves for late Pliocene, although higher resolution studies on paired samples are required to test the correspondence of these various paleoclimatic indices.

Distribution of diatoms in Oligocene to Pleistocene sediments of the tropical Pacific

According to the drilling probes of the Deep Waier Drilling Project, Neogene sediments in a tropical area of the Pacific Ocean are divided into 15 zones based on diatoms. The author shows that a unique zonation may be applied for the entire region. Identification of diatoms zones boundaries was conducted through their direct correlation with nannoplancton, radiolarian and foraminiferal zonal sceals. Their ultra-structure and morphological relationship are being analysed. The mode of siliceous accumulation within the equatorial belt differed through the western central and eastern region since the early Miocene and the difference become more evident from the end of Middle Miocene. The distribution of Neogene diatomaceous silt in the tropical area is controlled by the character of gyre-water circulation and agrees with the modern geographical zonation.