A geological constraint on relative sea level in Marine Isotope Stage 3 in the Larsemann Hills, Lambert Glacier region, East Antarctica (31 366–33 228 cal yr BP)

In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 ¹⁴C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change.     

Variations in abundances and distributions of isoprenoid chromans and long-chain alkylbenzenes in sediments of the Mulhouse Basin: a molecular sedimentary record of palaeosalinity

The abundances and distribution patterns of mono-, di- and trimethylated 2-methyl-2-(4,8,12-trimethyltridecyl) chromans (MTTCs) and long-chain alkylbenzenes in extracts of marl (66 samples), anhydrite (15) and halite (1) strata of the Salt IV Formation of the Oligocene Mulhouse Basin are reported. The distributions of the methylated MTTCs indicate salinity changes of the upper part of a density stratified water column of the basin. These variations are explained by a tectonically or climatically induced change in the supply of water of relative lower salinity to form a layer overlying the deeper water brine. Hence, it is suggested that mesohaline (3.5–15%) conditions in the surface waters were established as a result of periodic incursions of marine water and subsequent evaporation. Conversely, during periods when the surface water was derived mainly from fresh water from the hinterland, lower average salinity in the surface layer resulted. The distributions of long-chain alkylbenzenes also appear to record these changes.     

THE ROLE OF ATMOSPHERIC CIRCULATION PATTERNS IN AGROCLIMATE VARIABILITY IN FINLAND, 1961–2011

This study evaluates interannual variations and trends in growing season daily temperature sum and daily precipitation sum in Finland during 1961–2011, and their connections to well known atmospheric circulation patterns. Changes in summer (June–August) climate partially explain changes in growing season daily temperature sum and daily precipitation sum over Finland, which naturally decreased from south to north. On a national scale, growing season warmed and became wetter during 1961–2011, as growing season daily temperature sum and daily precipitation sum significantly (p < 0.05) increased by 5.01 ± 3.17°C year^–1 and 1.39 ± 0.91 mm year^–1, respectively. The East Atlantic pattern was the most influential atmospheric circulation pattern for variations in growing season daily temperature sum (rho = 0.40) across Finland and the East Atlantic/West Russia pattern was most influential for growing season daily precipitation sum variability (rho = –0.54). There were significant (p < 0.05) increasing trends in growing season daily temperature sum and daily precipitation sum throughout Finland during 1961–2011. Increased growing season daily temperature sum was mainly observed in northern, central, western, eastern and coastal areas of south‐western Finland. This warming was positively associated with the East Atlantic pattern in the north, centre and south, but negatively associated with the East Atlantic/West Russia pattern in eastern Finland. Increased GSP mostly occurred in southern, eastern, western, central, northern and north‐western Finland. These wetting trends were positively correlated with the East Atlantic pattern in the north and negatively correlated with the Polar pattern in the south and the East Atlantic/West Russia pattern in the east, west, centre and north‐east of Finland. The overall agroclimatic year‐to‐year variability in Finland between 1961 and 2011 was mostly linked to variations in the East Atlantic and East Atlantic/West Russia patterns.     

Sedimentary pigments as markers for environmental change in an Antarctic lake

Fossil pigments were identified in a sediment core from Kirisjes Pond, a small lake in the Larsemann Hills, east Antarctica, using reversed-phase HPLC and LC–MS/MS. Chlorophyll a- and b-derived components indicate the presence of oxygenic primary producers; steryl chlorin esters provide evidence of grazing, while shifts in their esterifying sterol composition record changes in the primary producer community. Bacteriochlorophyll c- and d-derived components, indicative of photic zone anoxia, were identified with structural variations including extensive alkylation in the macrocycle up to C₆. The pigment distribution reveals a change from oxygenated freshwater to a stratified water body with development of photic zone anoxia. This coincides with a marine incursion identified from diatom records and is followed by re-isolation and reversion to oxygenated freshwater conditions.     

Structures and profiles of novel sulfur-linked chlorophyll derivatives in an Antarctic lake sediment

High performance liquid chromatography-mass spectrometry has permitted the identification of a homologous series of novel alkylsulfide derivatives of chlorophyll a containing between one and five carbon atoms, in sediment from a coastal Antarctic lake. The sulfur-containing compounds are present in varying abundance in stratigraphic horizons representing a phase when the lake was a marine basin. Throughout this marine phase photic zone anoxia is recorded by the presence of bacteriochlorophyll c and d-derivatives. Distributional variations between sulfurised and non-sulfurised chlorophyll a-derivatives throughout the sediment section studied indicate that the extent of sulfurisation is not controlled by chlorophyll a abundance alone.     

Melting of a Hydrous Mantle: I. Phase Relations of Natural Peridotite at High Pressures and Temperatures with Controlled Activities of Water, Carbon Dioxide, and Hydrogen

Four natural peridotite nodules ranging from chemically depletedto Fe-rich, alkaline and calcic (SiO₂ = 43.7–45.7 wt.per cent, A1₂O₃ = 1.6O–8.21 wt. per cent, CaO = 0.70–8.12wt. per cent, alk = 0.10–0.90 wt. per cent and Mg/(Mg+Fe²⁺)= 0.94–0.85) have been investigated in the hypersolidusregion from 800? to 1250?C with variable activities of H₂O,CO₂, and H₂. The vapor-saturated peridotite solidi are 50–200?Cbelow those previously published. The temperature of the beginningof melting of peridotite decreases markedly with decreasingMg/(Mg+SFe) of the starting material at constant CaO/Al₂O₃.Conversely, lowering CaO/Al₂O₃ reduces the temperature at constantMg/(Mg+Fe) of the starting material. Temperature differencesbetween the solidi up to 200?C are observed. All solidi displaya temperature minimum reflecting the appearance of garnet. Thisminimum shifts to lower pressure with decreasing Mg/(Mg + Fe)of the starting material. The temperature of the beginning ofmelting decreases isobarically as approximately a linear functionof the mol fraction of H₂O in the vapor (X_H2O^v). The data alsoshow that some CO₂ may dissolve in silicate melts formed bypartial melting of peridotite. Amphibole (pargasitic hornblende) is a hypersolidus mineralin all compositions, although its P/T stability field dependson bulk rock chemistry. The upper pressure stability of amphiboleis marked by the appearance of garnet. The vapor-saturated (H₂O) liquidus curve for one peridotiteis between 1250? and 1300?C between 10 and 30 kb. Olivine, spinel,and orthopyroxene are either liquidus phases or co-exist immediatelybelow the temperature of the peridotite liquidus. The data suggest considerable mineralogical heterogeneity inthe oceanic upper mantle because the oceanic geotherm passesthrough the P/T band covering the appearance of garnet in variousperidotites. The variable depth to the low-velocity zone is explained byvariable aHjo conditions in the upper mantle and possibly alsoby variations in the composition of the peridotite itself. Itis suggested that komatiite in Precambrian terrane could formby direct melting of hydrous peridotite. Such melting requiresabout 1250?C compared with 1600?C which is required for drymelting. The genesis of kimberlite can be related to partial meltingof peridotite under conditions of X_H2O^v = 0.5–0.25 (X_CO2^v= 0.5–0.75). Such activities of H₂O result in meltingat depths ranging between 125 and 175 km in the mantle. Thisrange is within the minimum depth generally accepted for theformation of kimberlite.     

Quantitative study of the distributary braidplain of the Preboreal ice-contact Gardermoen delta complex, southeastern Norway

This raised delta structure is an ice-contact deltaic complex with a volume of c. 4.4.10⁹ m³, deposited c . 9500 yr BP in a shallow wide 'fjord' during the retreat of the Scandinavian ice cap. The delta plain lies at an altitude of 200–223 m. It aggraded c . 20 m above the contemporaneous sea level during a regional marine regression. The braidplain palaeochannel characteristics indicate a peak meltwater discharge of 7–9 10³ m³/s. Calculations based on a glacial ablation model indicate a mid-summer discharge of c . 5.5 10³ m³/s. However, the fluvial topset of the delta has an erosive base whose altitude decreases upstream and indicates stream incision by more the 6 m below the contemporaneous sea level. The deep scour is ascribed to episodic floods over the relatively short delta plain, which exceeded direct ablation-associated discharges. The depositional time-span of the delta is assessed to have been 70 years, calculated from coastal gradient and shoreline displacement curves. The average sedimentation rate of the delta is thereby inferred to have been extremely high, c . 6. 10⁷ m³/yr. The sedimentation is thought to reflect 'extreme' ice-margin conditions, where the sediment and water discharge was maximized by full-scale ablation, with simultaneous subglacial, englacial and supraglacial sediment and water supply. These conditions might further coincide with an abundant rainfall in the catchment area or the drainage of dammed waters, initiating episodic floods which eroded deep beneath sea level. As a whole, the study illustrates the hydrological conditions of proglacial sedimentation at the front of the rapidly retreating last Scandinavian ice cap.