ALBERT

Description: Stratigraphic units representing high-sea-level events in Britain, northern France, Belgium, The Netherlands, northwest Germany, Denmark, Sweden and Norway, are correlated by aminostratigraphy (D (alloisoleucine)/L (isoleucine) (ratios from Littorina littorea, Macoma balthica, Macoma calcarea and Arctica islandica). The eight sea-level events recognized are modelled with the constraints provided by the oxygenisotope signal of sea-level variability, and available geochronometric age determinations for calibrating the D/L data. These data are used to constrain the timing and extent of glaciations in the British Isles and Scandinavia during the Middle and Late Pleistocene.

Description: The late Pliocene phase of large-scale climatic deterioration about 3.2-2.4 Ma BP is well documented in a number of (benthic) 〈latex〉$\delta^{18}$〈/latex〉O records. To test the global implications of this event, we have mapped the distribution patterns of various sediment variables in the Pacific and Atlantic Oceans during two time slices, 3.4-3.18 and 2.43-2.33 Ma BP. The changes of bulk sedimentation and bulk sediment accumulation rates are largely explained by the variations of CaCO〈latex〉$_3$〈/latex〉-accumulation rates (and the accumulation rates of the complementary siliciclastic sediment fraction near continents in higher latitudes). During the late Pliocene, the CaCO〈latex〉$_3$〈/latex〉-accumulation rate increased along the equatorial Pacific and Atlantic and in the northeastern Atlantic, but decreased elsewhere. The accumulation rate of organic carbon (C〈latex〉$_{org}$〈/latex〉) and net palaeoproductivity also increased below the high-productivity belts along the equator and the eastern continental margins. From these patterns we may conclude that (trade-) wind-induced upwelling zones and upwelling productivity were much enhanced during that time. This change led to an increased transfer of CO〈latex〉$_2$〈/latex〉 from the surface ocean to the ocean deep water and to a reduction of evaporation, which resulted in an aridification of the Saharan desert belt as depicted in the dust sediments off northwest Africa.

Description: Young Sepia officinalis (0-5 months) were studied in the laboratory and in the sea, and their appearance and behaviour compared with that of adult animals. Cuttlefish lay large eggs and the hatchlings are miniature replicas of the adults. From the moment of hatching they show body patterns as complex as those of adults and far more elaborate than those shown by most juvenile cephalopods. There are 13 body patterns: 6 of these are `chronic' (lasting for minutes or hours) and 7 are `acute' (lasting for seconds or minutes). The patterns are built up from no fewer than 34 chromatic, 6 textural, 8 postural and 6 locomotor components, used in varying combinations and intensities of expression. Nearly all these components occur in young animals: 26 of the chromatic, all the textural and locomotor, and 6 of the postural components. Nevertheless, patterning does change with age and we have recorded this and correlated the changes with behaviour. The components are built up from units, which themselves comprise four elements organized in precise relation to one another: chromatophores, iridophores, leucophores and skin muscles. The chromatophores are always especially important: they are muscular organs innervated directly from the brain and controlled ultimately by the highest centres (optic lobes). The areas in the Sepia brain that control patterning are already well developed at hatching, for the appearance of the skin is as much part of the brain's motor program as is the attitude of the arms or fins, or the posture of the entire animal. The iridophores and leucophores develop later and are especially important constituents of many adult patterns, notably the Intense Zebra of the mature male. Experiments confirm that patterning is neurally controlled and apparently mediated exclusively by the visual system. Young cuttlefish use patterning primarily for concealment, utilizing such strategies as general colour resemblance, disruptive coloration, obliterative shading, shadow elimination, disguise and adaptive behaviour. Older animals also conceal themselves but increasingly use patterns for signalling, both interspecifically (warning or `deimatic' displays) and intraspecifically (sexual signalling). Laboratory-reared cuttlefish were released in the sea and observed underwater. They quickly and effectively concealed themselves on the substrate; it was easy for the human observer to lose them and many passing fish behaved as if they were not there. One local predator, Serranus cabrilla, was observed to attack them and no fewer than 35 attacks were recorded, only six of which were successful. Laboratory-reared cuttlefish apparently distinguished between these predators and other, non-predatory, fish the first time they encountered them in nature.

Description: The 100 ka rhythm of orbital eccentricity has dominated large-amplitude climatic variations in the high-latitude North Atlantic during the Brunhes magnetic chron (0-0.735 Ma BP). Earlier, during the Matuyama chron (0.735-2.47 Ma BP), climatic variations in this region were lower in amplitude and concentrated mainly at the 41 ka rhythm of orbital obliquity. These rhythmic climatic responses to orbital forcing are evident both in stable isotopic (δ18O) indicators of ice volume or temperature and in biotic and lithologic indicators of local North Atlantic surfaceocean variability. The synchronous responses of these indicators are consistent with results from atmospheric general circulation models showing that the North American ice sheet directly controls North Atlantic surface-ocean responses via strong cold winds that are generated on the northern ice-sheet flanks and blow out across the ocean, chilling its surface. Before 2.47 Ma BP, smaller-scale quasiperiodic oscillations of the planktonic fauna and flora occurred, but the cause of these variations in the absence of significant ice sheets is unclear.