ALBERT

Description: In Moreton Bay, Queensland, the catch obtained using monofilament polyamide (PA) otter trawl-nets with multifilament polyethylene (PE) cod ends was compared with that obtained using multifilament PE trawl-nets of identical mesh opening (38 mm). Monofilament PA otter trawl-nets retained fewer small prawns ( 〈 24 mm carapace length) than conventional multifilament PE nets, but both nets caught similar quantities of larger prawns ( 〉 24 mm carapace length). The higher retention rate of small prawns by multifilament PE gear was reflected in the greater catch weights of Peraeus plebejus, Metapenaeus bennettae and Metapenaeopsis novaeguineae in those nets. Catch weights of larger prawn species such as Penaeus esculentus and Metapenaeus endeavouri did not differ between nets. Winter whiting (Sillago maculata) and squid (Loligo spp.) were trawled in similar abundance in both nets, although the monofilament retained fewer squid 〈 50 mm mantle length. More marketable ( 〉 15 cm carapace width) sand crabs (Portunus pelagicus) were caught in the monofilament net. There was not significant difference in the trash (noncommercial component) weight caught in both nets. Over the range of towing speeds tested (1.7–2.3 kn), use of monofilament nets significantly reduced total gear drag.

Description: RECENT advances in 40Ar/39Ar dating1,2 have made it possible to date individual K-feldspar grains from Pleistocene tephra, a capability that greatly improves the reliability and temporal resolving power of the method. Here we apply these new techniques to the dating of a phonolite tephra from the East Eifel volcanic field in West Germany, which is sandwiched between loess and palaeosol (alfisol) deposits, and which was therefore erupted during the transition from a glacial to an interglacial period. Our age estimate for this transition is 215±4 kyr (1 σ), which has important implications for the marine δ18O timescale and for models of global climate change during the Pleistocene. The results show that single-grain dating can detect and compensate for the large quantities of xenocrystic contaminants which are found in many tephra deposits. This technique could be used to date the tephra layers found in marine sediment cores and the results could greatly enhance the reliability of the marine δ18O timescale for more rigorous Fourier analysis testing of the Milankovitch hypothesis.

Description: Sediments on high Arctic shelves result from modern processes and the effect of former glaciations. Based on data from the northern Barents Sea, an area with input from large and numerous surging glaciers, we define two principal zones with different environmental regimes and corresponding sedimentary facies: (1) a glacier-proximal zone influenced by grounding-line processes and the immediately adjacent areas affected by glacial sediment input, and (2) a glacier-distal, sea-ice and current-controlled zone, which also includes a wide sediment-starved region dominated by biogenic carbonate accumulation. Characteristic of the glacier-proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea-floor morphologies. Extensive ice gouging causes a homogeneous sediment texture. In the glacier-distal zone, fine-grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes. On shallow banks, in 30–50 m of water, carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply.

Description: Clay- and silt-size mineral assemblages are described from eight piston cores from the fiords and shelf on the western margin of Baffin Bay, Arctic Canada. Radiocarbon dates indicate that all the cores extend back in time to the last local glacial/interglacial transition (i.e. 8–10 ka); four extend back to between 10 and 12 ka, and HU77-021-156, located on the Southeast Baffin Island shelf, includes the entire late Foxe glacial stage. Silt- and clay-size particles constitute ca 40 and 55%, respectively, by weight of the bulk sediment. The clay-size fraction is dominated by mica; feldspars and quartz are the main constituents of the silt fraction. The fiord sediments are mainly composed of local mineralogies, but on the shelf, and at times in the fiords, exotic mineral species occur. The most important of these are detrital carbonates, derived from erosion of the Paleozoic basins in Arctic Canada and/or northwest Greenland. Both calcite and dolomite occur; calcite is the major carbonate mineral in the “southern” cores, whereas dolomite is the most abundant in cores north of 66°N. Higher inputs of carbonate species occur during regional deglaciation, 7–10 ka, and during the last 5 ka (probably reflecting increased iceberg production from northwest Greenland). Thus variations in the precentages of the carbonate minerals indicate significant shifts in Late Quaternary glacial-sediment source areas and oceanographic regimes.

Description: Changes in composition of modern benthic ostracod faunas across the continental margin of southwestern Africa occur at boundaries between and within major water masses: a Mixed Layer-Antarctic Intermediate Water (AAIW) boundary at 200 m, an AAIW salinity minimum zone at 650 m, an AAIW bathyal thermocline at 1000 m, and the AAIW/North Atlantic Deep Water (NADW) boundary at 1500 m. In addition, two population changes occur within the NADW at 1.8–2.0 km and 2.0–3.0 km. The Antarctic Bottom Water assemblage is sparse and poorly preserved.

Description: Measurements in the mixing zone of the Elbe estuary were performed during three consecutive tidal cycles with three types of instruments—a moored tripod with velocity and temperature/conductivity/light attenuation sensors, a profiling sonde with similar sensors lowered from an anchored vessel, and instrumented moorings. Acoustic-travel-time sensors were used for velocity measurements. Spectral analysis of 12·8 min pieces of the obtained time series gives results that are consistent with isotropic turbulence for part of the frequency space. Temporal changes of turbulent kinetic energy are correlated with tidal current velocity. A retardation is found between changes in tidal current and turbulent energy. Not all shear stress terms are in similar phase with tidal flow. Mean gradients, Reynolds stress terms, and turbulent salt flux terms are combined to determine eddy viscosity and eddy diffusion coefficients.

Description: ROOTH proposed that the Younger Dryas cold episode, which chilled the North Atlantic region from 11,000 to 10,000 yr BP, was initiated by a diversion of meltwater from the Mississippi drainage to the St Lawrence drainage system. The link between these events is postulated to be a turnoff, during the Younger Dryas cold episode, of the North Atlantic's conveyor-belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the North Atlantic region2. This turnoff is attributed to a reduction in surface-water salinity, and hence also in density, of the waters in the region where North Atlantic Deep Water (NADW) now forms. Here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from Orca Basin core EN32-PC4 which reveal a significant reduction in meltwater flow through the Mississippi River to the Gulf of Mexico from about 11,200 to 10,000 radiocarbon years ago. This finding is consistent with the record for Lake Agassiz which indicates that the meltwater from the southwestern margin of the Laurentide Ice Sheet was diverted to the northern Atlantic Ocean through the St Lawrence valley during the interval from ~11,000 to 10,000 years before present (yr BP).

Description: Compressional-wave (P-wave) velocities and magnetic susceptibilities were measured on gravity (GGC) and piston cores (PC) and Ocean Drilling Program (ODP) Leg 108 advanced piston cores (APC) from the equatorial Atlantic to test our hypothesis that climatically driven changes in terrigenous and biogenic fluxes, and in carbonate dissolution control the interrelationships between the two signals. In Pleistocene sediments deposited above the calcium compensation depth (CCD) we observed changes in P-wave velocity and magnetic susceptibility that are (1) inversely correlated, and (2) coherent to changes in glacial-interglacial climate. Glacials show low P-wave velocities and relatively high magnetic susceptibilities. In contrast, interglacials show high P-wave velocities and relatively low magnetic susceptibilities. These temporal changes in P-wave velocity and magnetic susceptibility reflect the climatic history recorded in the sediments and are related to: (1) the production of biogenic carbonate, mainly planktonic foraminifera, and (2) the terrigenous sediment supply that contains magnetic minerals. Below the CCD this pattern disappears and consistently low P-wave velocities and distinctly higher magnetic susceptibilities prevail. The distinct decrease of large P-wave velocity fluctuations is due to the dissolution of carbonate sediments which cause a distinct decrease in sand grain sizes and a consistently low carbonate content (〈 10%). Dilution of magnetic material by the carbonate fraction is minor and the high magnetic susceptibility values and the relatively high amplitude variations in magnetic susceptibility are due to changes in the magnetic mineral concentration of the terrigenous (non-carbonate) fraction. In early Pliocene sediments we also observed covarying velocity and magnetic susceptibility signals that may reflect a predominatly terrigenous control on sedimentation. Our preliminary results demonstrate that a combined use of non-destructive measurements of acoustic and rock-magnetic signals provides a potential paleoceanographic tool for characterizing: (1) glacial-interglacial pelagic sedimentation, (2) pelagic sedimentation above the CCD, (3) increases in carbonate dissolution, and (4) areas below the CCD. Furthermore, rock magnetic fluctuations in sediments below the CCD may provide an important stratigraphic tool for the deep carbonate-free basins of the world's oceans.

Description: The life cycle of loliginid squids has been completed in recirculating seawater systems. Two systems were required: a 2 m diameter circular culture tank (CT) with adjoining 2 m circular filter tank (3000 liters total volume of natural seawater) for culture of hatchlings, 1–60 days old; and a 6 × 2·6 × 1 m raceway culture tank (RW) with a smaller adjoining rectangular filter tank (14 850 liters total volume of artificial seawater) for the grow-out of adults. Both systems were equipped with temperature control apparatus, modular filter units (particle filters and activated carbon), foam fractionators, biological filters (crushed oyster shell) and UV sterilizers. The systems carried low bioloads, 〈 1·0 g/m3 and as high as 0·8 kg/m3, respectively. Water quality was excellent: NH4N was below 0·01 mg/liter in the CT and 0·10 mg/liter in the RW: NO2N was below 0·01 mg/liter in the CT and 0·03 mg/liter in the RW; NO3N was below 12 mg/liter in the CT and below 50 mg/liter in the RW; and pH was above 8·0 in both systems. The design of the systems proved to be behaviorally and physiologically suitable for squids and two species grew to adult size and produced viable young. These systems are compared to other squid maintenance and rearing systems and marine recirculating seawater systems.

Description: A comparative study of isodideimnine-1 and didemnin B is presented using spcctroecopic methods, partial degradation and partial synthesis. This leads to the conclusion of the presence of a single depsipeptide, namely didemnin B, with (3S,4R,5S) isostatine instead of the previous statine residue. An attempt to determine the whole conformation in solution of didemnin B by using 2D-NMR is also described.

Description: Seismic refraction investigations along a 440-km long profije on the northern Baltic Shield have resolved the crustal structure in this area of Archaean to Early Proterozoic lithosphere formation. The profile, called the POLAR Profile, extends approximately along a SW-NE-oriented line from the Karelian Province in northern Finland across the Lapland Granulite Belt and the Kola Peninsula Province to the Varanger Peninsula in northeastern Norway. At six shotpoints, large explosions (200–1680 kg), and at three shotpoints, small explosions (80 kg) were detonated and recorded at an average station spacing of 2 km, providing high-quality record sections. A two-dimensional cross section of the crust was obtained by forward modelling using ray-tracing techniques. High-velocity bodies are found in the upper crust related to the Karasjok-Kittilä Greenstone Belt and the Lapland Granulite Belt. They extend to a depth of 6–13 km. In the Karelian Province in the southwest, a low-velocity zone was found between the depths of 8 and 14 km. The middle crust shows a slight increase in the average velocities from the southwest to the northeast, and a small velocity jump is found along a mid-crustal boundary between 18 and 21 km. The thickness of the middle crust varies between 16 and 18 km. The lower crust and the crust-mantle boundary (Moho) show considerable lateral variation. The top of the lower crust lies between 26 and 33 km, while its thickness decreases from 21 km in the southwest to 10–14 km beneath the Lapland Granulite Belt and the Inari Terrain, reaching 20 km again in the extreme northeast. The velocities also change laterally. The thin lower crust is characterized by rather low velocities (6.8–6.9 km/s), whereas in the southwest and northeast the velocities (6.9–7.3 km/s) resemble more typical shield structures. The Moho is found at 47 km in the Karelian Province, rises to 40 km beneath the Lapland Granulite Belt and descends to 46 km in the northeastern part of the Kola Peninsula Province. The upper mantle velocities at the Moho range from 8.1 km/s in the region of the thin crust, to 8.5 km/s and more beneath the Karelian Province. It is tempting to suggest that the anomalous lower crust underlying the Lapland Granulite Belt and the Inari Terrain may represent the remnants of an Early Proterozoic back-arc basin that was active prior to the 2.0 to 1.9 Ga plate convergence event, during which the Lapland Granulite Belt was thrust onto the Archaean basement of the Karelian Province. Another explanation is to assume that the velocity reduction in the anomalous lower crust was caused by a rather pronounced uplift of this region following the 1.9-Ga collision event.

Description: Pore fluid venting associated with subduction-induced sediment deformation causes precipitation of calcium carbonate as prominent carbonate chimneys or cement in the accreted sediments across the active continental margin off Oregon and Washington. A depletion of interstitial Ca2+ with a maximum decrease of 50% relative to seawater Ca2+ over only 1.5m depth and reduction in porosity in the deformed sediments suggest that interstitial Ca2+ is removed to form calcium carbonate cement. In contrast, the pore waters of the undeformed abyssal plain sediments show no depletion in dissolved Ca2+. They are either enriched to a maximum of 5% or show no change in dissolved Ca2+. Here the background level of CaCO3 content in the sediment is only 0.1 to 1%. Calcium carbonate precipitation in the deformed sediments probably occurs as the result of upward migration and oxidation of biogenic methane and of the increase in carbonate saturation due to release of excess pore pressure during fluid venting. Upward advection of fluids at rates of 1–28 cm y−1 is predicted from diffusion-advection-reaction models applied to the downcore concentration profiles of dissolved Ca2+ and NH4+ in the tectonically-deformed sediments. The range of predicted flow rates is related to the type of calcium carbonate lithification; i.e. slow rates generate cement and fast rates generate chimneys. Carbonate mineral precipitation associated with pore fluid venting requires direct transfer of Ca2+ from the oceanic basement to the accretionary complex. Such a mechanism leads us to propose that the accretionary complexes of the global plate subduction zones are a major sink for crustal Ca2+. A global flux of crustal Ca2+ that is removed by carbonate mineral precipitation may be as muc3 as the hydrothermal Ca-input. This significant Ca-flux, not previously considered in the global geochemical budget, implies that pore fluid venting in subduction zones may also act as a global sink or source for other elements.

Description: Ocean crustal carbon uptake during seafloor alteration at DSDP Sites 417A, 417D, and 418A exceeds the estimated loss of carbon during magmatic ridge outgassing. If these sites are representative for oceanic crust in general, 2.2–2.9 × 1012 moles of carbon are removed from the oceans per year as a net flux of carbon between the oceanic crust and seawater. Although most of this carbon occurs as calcium carbonate, this ocean crustal carbonate probably cannot be considered part of the marine calcium carbonate sink since much of the Ca in these carbonates must be derived from basalt alteration that is not balanced by a concomitant uptake of seawater Mg. Our present estimate cannot be satisfactorily applied to global carbon budgets, because of uncertainties in the bulk budget of ocean floor alteration and because of the uniqueness of our estimate. Yet, our data document that the formation of ocean crust provides a significant sink for carbon that should be included in models of the global cycling of carbon. Furthermore, magmatic outgassing during ocean crust emplacement and seafloor basalt alteration may provide a buffering mechanism for atmospheric carbon.

Description: The imaging of a multichannel seismic record was improved by reprocessing using pre-stack techniques. The reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the Japan Trench margin. Much of the lower slope appears to be underlain by a detached, coherent block of continental crust. The lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone. Slumping continues as long as debris is removed from the front of the margin by subduction, and the apron cannot build up sufficiently to stabilize the failing lower slope. Truncated beds at the base of the upper plate indicate subcrustal erosion as well, this probably being the main cause of massive subsidence of the margin. Subsidence was the cause of oversteepening, destabilization and subsequent gravity collapse of the leading edge of the upper plate.

Description: The ice-proximal environment of the Nordaustlandet tidewater ice cap, Svalbard Archipelago, is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial Pleistocene deglaciation. Investigations of the proglacial region in 1980–1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment-laden water from subglacial meltwater streams during the summer. Two large, stable meltwater outflows were observed in embayments along the southern part of the ice front. Landsat images show that both outflows have been in approximately the same position since at least 1976. They are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock. An “outflow valley” extending away from the ice front was observed in front of the western meltwater outflow. Sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow, probably caused by meltwater effluence. Enhanced sediment accumulations in this region, observed as a ≈ 3 ms sediment drape in front of the outflow, and large arcuate ridges in the outflow valley, testify to the transport efficiency of the subglacial meltwater stream. Several mounds, up to about 25 m high and 200 m wide, are observed on sidescan and 3.5 kHz profiles directly in front of the outflow. Although samples from these structures are absent, they are most likely composed of sediment and are similar to beaded eskers observed in Pleistocene glacimarine sequences indicating locally very high sedimentation rates. Fine-grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current. Elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern Barents Sea.

Description: Cephalopods are exclusively marine molluscs and should be included among the organisms that are of general interest to marine biologists. As to experimental embryology, Naef has already stressed the suitability of cephalopod embryos for experimental work. The whole body of information accumulated in this field during the past half century since Naef published his monograph was reviewed by Marthy. This field of research is clearly underrated by many developmental biologists who could profit by the topological simplicity of the blastulation pattern in cephalopods, which contrasts with the spiralian mode of other molluscs. Questions raised by comparative/evolutionary embryology, following the tradition of descriptive developmental morphology, are truly stimulating to the field of experimental embryology, and vice versa. However, experimental studies are generally possible with only a limited number of models, which, in the case of cephalopods, appear to be embryos of medium to small size. On the other hand, some of the most intriguing questions in cephalopod biology are related to those forms that produce eggs of extremely large size. This chapter gives a brief overview of these recent studies placing them in the chronological sequence of embryogenesis. Studies covering early stages of embryonic development as well as later ones will be cited at least once in the section dealing with the earliest stage considered. Most of these investigations ultimately rest on the basic work by Naef.

Description: Sediment fluxes were highest in the Norwegian Sea during late glacial/early deglacial periods, i.e., at oxygen isotope transition 43, below transition 65, at various levels within stage 6, and below stage 9. Dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea. The high organic carbon content (0.5–1.3%) in these layers reflects input from erosion of terrigenious matter-rich sediments outcropping on the shelves. Partial oxidation of organic matter and decreased deep-water renewal may explain the strong carbonate dissolution observed during these periods. Interglacial environments were strongly variable throughout the last 350 ka. Circulation patterns of stage 5e best resemble modern conditions, while stage 7 and 9 sediments record a much weaker Norwegian Current.

Description: 19 samples (1189 individuals) of the commercially fished Patagonian squid Loligo gahi d'Orbigny were collected from Falkland waters between March 1987 and April 1988 and subjected to starch gel electrophoresis. 41 enzyme-coding loci were screened for polymorphism. Clearly resolved enzyme phenotypes were obtained at 21 loci of which six exhibited polymorphism (glutamate oxaloacetate transaminase, GOT-II, E.C. 2.6.1.1.; α-glycerophosphate dehydrogenase, α-GPDH, E.G. 1.1.1.8; isocitrate dehydrogenase, ICD, E.C. 1.1.1.42; malate dehydrogenase, MDH-II, E.G. 1.1.1.37; phosphogluconate dehydrogenase, PGD, E.C. 1.1.1.44; and phosphoglucose mutase, PGM, E.G. 2.7.5.1). Routine scoring at the 21 loci revealed moderate levels of genetic variability, with the proportion of polymorphic loci, P = 0.273, mean heterozygosities per locus = 0.0693, and the effective number of alleles, Ne, with values of 1.13–1.83.

Description: Genetic population structure of the commercially fished Patagonian squid Loligo gahi d'Orbigny was examined by collecting 19 samples (1189 individuals) from Falkland waters between March 1987 and April 1988 and subjecting individuals to electrophoretic and morphometric analysis. Morphological features (dorsal mantle length, fin length oblique, fin width, interorbital width, tentacle length, length of arms I and II, and mid-mantle circumference), sex and stage of reproductive maturity (Lipinski's universal scale) were recorded prior to electrophoresis. Analyses of allele frequencies at six polymorphic loci provided no evidence of stock separation, and the frequency distribution of genotypic classes almost exclusively fitted Hardy-Weinberg expectations for a randomly interbreeding population. Nei's mean genetic distances and identities between samples ranged from 0.000–0.002 and 0.997–1.00, respectively, supporting the contention of a genetically homogeneous breeding unit. Multivariate analyses revealed significant differences in the morphometrics among certain samples collected at approximately the same time, especially of interorbital width, first arm length and fin width. This morphological differentiation was not correlated with differences at the genetic level. The frequency distribution of dorsal mantle length and stages of reproductive maturity through the year were compatible with two alternative interpretations of population structure: (i) the existence of two temporally distinct separate spawning populations, one autumn- and the other spring-spawning, or, (ii) that slow-growing or late spawned individuals spawn at 18 months old while most squid spawn at 1 yr old in the austral spring and summer. Although it is not possible to discount either interpretation unequivocally, the latter hypothesis of population structure is more congruent with existing genetic evidence.

Description: Pore fluids extracted from near-surface sediments of the deformation front along the Oregon subduction zone have, in general, the dissolved nutrient pattern characteristic of bacterial sulfate reduction. However, in certain locations there are peculiar ammonium distributions and anomalously 13C-depleted dissolved ΣCO2. These carbon isotope and nutrient patterns are attributed to the concurrent microbially-mediated oxidation of sedimentary organic matter (POC) and methane (CH4) originating from depth. In contrast to the oxidation of sedimentary organic matter in the sulfate zone, utilization of methane as the carbon source by sulfate-reducing bacteria would generate only half as much total carbon dioxide for each mole of sulfate consumed and would not generate any dissolved ammonium. The isotopically light ΣCO2 released from methane oxidation depletes the total metabolic carbon dioxide pool. Therefore, NH4+, ΣCO2 and δ13C of interstitial carbon dioxide in these pore fluids distintcly reflect the combined contributions of each of the two carbon substrates undergoing mineralization; i.e. methane and sedimentary organic matter. By appropriately partitioning the nutrient and substrate relationships, we calculate that in the area of the marginal ridge of the Oregon subduction zone as much as 30% of the ΣCO2 in pore fluids may result from methane oxidation. The calculation also predicts that the carbon isotope signature of the carbon dioxide derived from methane is between −35‰ and −63‰ PDB. Such an isotopically light gas generated from within the accretionary complex could be the residue of a biogenic methane pool. Fluid advection is required to carry such methane from depth to the present near-surface sediments. This mechanism is consistent with large-scale, tectonically-induced fluid transport envisioned for accreted sediments of the world's convergent plate boundaries.

Description: Petrographic, mineralogic, and geochemical data are reported for lavas from two of the major shield volcanoes of the Santorini volcanic complex (Skaros and Micro Profitis Ilias), both of which were active prior to the well-known Minoan eruption with associated caldera collapse. Field work and whole-rock chemical analyses indicate four cycles of eruptive activity within the Skaros sequence and three within the Micro Profitis Ilias (M P1) sequence. SiO2 and LIL-element contents decrease from the base to the top of all cycles except for the uppermost cycle of Skaros. Chemical variations within cycles are interpreted to result from eruption from compositionally and thermally zoned magma chambers. Major oxide data and the results of least-squares, mass balance modeling indicate that fractional crystallization played an important role in the development of the observed chemical variations. However, observed systematic variations in groundmass compositions within each cycle, observed irregular variations in total phenocryst content and the results of density calculations require that generation of the chemical zonation did not involve crystal settling but reflects unstable density stratification, probably resulting from sidewall crystallization. Some of the primitive lavas erupted on Santorini preserve phenocryst and xenocryst evidence for a stage of high-pressure fractional crystallization (involving removal of olivine, clinopyroxene, orthopyroxene, and Cr-spinel). Trace element data combined with petrographic data (i.e. the occurrence of abundant phenocrysts with resorption textures) is taken as evidence that magma mixing was also important in the development of cyclic variations. Most basaltic andesites from Skaros appear to be hybrids derived by mixing of basalt and andesite/dacite. Mineralogic data demonstrate that mixing was also important in the development of zonation in the chambers beneath MPI, but trace element data cannot be explained by combined fractionation and mixing alone. Specifically, incompatible, and compatible element abundances are lower than predicted if fractionation and mixing occurred and it is suggested that the anomalous trace element behaviour of especially LIL elements reflects the simultaneous operation of assimilation, for which there is support from isotopic studies. It is concluded that inter- cyclic chemical variations are explicable in terms of fractionation, mixing and assimilation. The LIL element and highly compatible element concentrations in the most primitive lavas erupted in each cycle of Skaros and MPI increase with time, indicating that mixing became more important with time.