Cheilostome Bryozoans As Indicators Of Seasonality In Two Neogene Epicontinental Seas Of Western Europe
نویسندگان
چکیده
The amount of variation in zooid length within colonies of Recent cheilostome bryozoans has been shown to be a function of the seasonal temperature regime prevailing during a colony’s growth, and has been formulated in a regression equation which may be used to estimate absolute values of palaeoseasonality. Using this technique, data on intracolony zooid lengths from colonies from the lower Pliocene Coralline Crag in southern England and the Middle Miocene ‘Falun’ in Northwest France reveal changes in the seasonal regimes of western European epicontinental seas through the Neogene. An estimated mean annual range of temperature of 5.8oC (±2.2oC) during the Pliocene indicates a seasonal regime less pronounced than the seas around western Europe today. This result is supported by independent estimates of palaeoseasonality and is inferred here to be a consequence of an enhanced Gulf Stream and a warmer winter atmosphere. A low mean annual range of temperature of only 2.8oC (±0.1oC) estimated for the Middle Miocene implies that a much more ‘equable’ climate existed on land than at present.
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Intracolony variation in zooid size in cheilostome bryozoans as a new technique for investigating palaeoseasonality
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