Plasma chemistry of the chinstrap penguin Pygoscelis antarctica during fasting periods: A case of poor adaptation to food deprivation?

The chinstrap penguin (Pygoscelis antarctica) is the smallest penguin species to be used to study the physiology of fasting. We analysed body-mass change and plasma chemistry of five non-breeding chinstraps during an experimental fasting period in the breeding season. We also analysed the same parameters in six fasting birds under natural conditions (during an incubation shift, which lasts about 10 days). Both groups presented similar patterns of change, showing a rapid increase in urea and uric acid plasma concentrations. Urea surpassed 3 mmol/l after 5 fasting days, while uric acid reached 1 mmol/l after 9 days. Plasma glucose levels decreased after 11 days, whereas cholesterol also showed a clear reduction during fasting. These results as a whole suggest that chinstrap penguins reached phase III after a short period in comparison with other Pygoscelis species. Body size and ecological factors could explain these inter-specific differences.Peer Reviewe

Relative sea-level rise around East Antarctica during Oligocene glaciation

During the middle and late Eocene (∼48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarcticainduced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rosedespite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an icesheet grounding line

Eocene cooling linked to early flow across the Tasmanian Gateway

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO(2)). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO(2) forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling

ANISOTROPY OF MAGNETIC HYSTERESIS PROPERTIES OF AUDIO-TAPE SAMPLES : ITS APPLICATION FOR THE MAGNETIC ANISOTROPY OF GNEISSIC ROCKS

The magnetic anisotropy of hysteresis properties of audio-tape samples which were made from single domain (SD) of γ-hematite were measured using a vibration sample magnetometer (VSM). Subsequently after alternating field demagnetization (AF demagnetization) of natural remanent magnetization (NRM) up to 60mT, the anhysteretic remanent magnetization (ARM) was produced by applying an external alternating field up to 120mT under the geomagnetic field in the laboratory. After these ARM acquisitions, these ARMs were demagnetized by AF field up to 70mT. On the hysteresis properties of audio-tape, H_C (coercivity) and I_R (saturation isothermal remanent magnetization) were found to be more anisotropic than χ_ (differential susceptibility at low field); these anisotropic maximum axes were parallel to the length of the tape. The anisotropic maximum axis of χ_ was perpendicular to that of I_R and H_C in the tape plane. The most stable remanent magnetization after AF demagnetization remained parallel to the maximum axis of H_C and of I_R. On the basis of the similarity of the magnetic properties between the tape sample and the gneissic rocks from the Skarvsnes area, East Antarctica, it is clear that SD alignment in rocks shows the perpendicular anisotropic maximum axis of χ_ to that of I_R and H_C. Therefore, this anti-phase of the anisotropy may be an important index to determine SD alignment in metamorphic rocks. The present study suggests that the NRM from old rocks not always shows the ancient geomagnetic field

THE MAGNETIC ANISOTROPY OF GNEISSIC ROCKS FROM THE SKARVSNES AREA, EAST ANTARCTICA

The relationship between magnetic anisotropy and natural remanent magnetization (NRM) was investigated in the gneissic rocks collected from Skarvsnes, Lutzow-Holm Bay, East Antarctica. About 60% of the samples show clear gneissosity, but 40% of the samples have less clear gneissosity. The samples with gneissic fabric show magnetic anisotropy. The maximum value of H_C and I_R, and the minimum values of X_ coincide with the lineation within a foliation plane. During thermal demagnetization of the samples having stable NRM\u27s, the NRM declinations are gradually shifted toward the direction of lineation, and they are stabilized in a plane, within the rock, having well developed foliation. The anisotropy tendency is more clearly observed by using the H_C and I_R values than X_ values. Two kinds of virtual geomagnetic pole (VGP) positions are identified from the Skarvsnes area. The former is consistent (latitude 11.2°S, longitude 16.0°E) with the previous results reported from the Lutzow-Holm Bay area, and the latter (latitude 2.5°S, longitude 63.2°E) reflects the magnetic anisotropy resulting from the lineation

磁気履歴特性の異方性についての岩石磁気学的研究

　古い地質時代の岩石の古地磁気学的研究を行う際の最大の問題は，岩石の持つ自然残留磁化（NRM: natural remanent magnetization）から，いかにして正確な古地磁気が再現できるかという点にある．東南極大陸を代表とする大陸の基盤を構成する古い地質時代の岩石には変成岩類が多いが，変成岩のような粒子配列の顕著な岩石の古地磁気研究をおこなう場合には，この粒子配列がNRM獲得時やその後のNRMに及ぼす影響はないのか，という問題がある．したがって，東南極大陸からの信頼できる古地磁気データを増やしていくためには，変成岩類の古地磁気調査法を確立することが必要となる．本研究の目的は，変成岩類のような粒子配列のある岩石の古地磁気学研究手法についての，岩石磁気学的な手法を開発することであり，そのために，"岩石中の粒子配列の岩石磁気学的解析"についての基礎的研究をおこなった．　岩石中の粒子配列解析方法を開発するため，振動型磁力計（VSM: Vibrating Sample Magnetometer）を用いで磁気履歴特性（ヒシテリシス曲線から得た磁気特性）の異方性についての基礎的実験をおこなった．従来よく使われている磁気特性の異方性は，帯磁率異方性（AMS）や残留磁化異方性（AMR）である．それに対して，磁気履歴特性の異方性は，複数の磁気特性の異方性について，同物理条件下で測定した結果を比較できるという利点がある．この磁気履歴特性の異方性についての基礎的研究をおこなうために，粒子サイズや粒子形状の異なる数種類の磁性鉱物を組み合わせて，人工配列試料を約40個作製した．磁気特性の異方性容易軸は，岩石中の磁性粒子が単磁区（SD）粒子か多磁区（MD）粒子かによって変化する．そのため，人工配列試料は，SD，MD双方の粒子から作成したものが必要である．SD粒子の試料としてはオーディオテープを使用し，MD粒子の場合は，大きさの異なるさまざまな鉱物種の磁性粒子を組み合わせた試料を作製した．さらに，二方向の粒子配列を持つ試料や粒子サイズや粒子形状の異なる二種類の磁性粒子を配列させた試料を作製した．これらの人工配列試料について，VSMを使って得られたヒシテリシス曲線から，磁気履歴特性をよみとり，磁気履歴特性の異方性について解析した．加えて，複数得られる磁気履歴特性の中でも，最もNRMへの影響が大きいと推定されるにも関わらず，岩石におけるその異方性については未だ研究報告のない、"保磁力の異方性"についての検討をおこなった．　以上の人工配列試料の実験に基づき，以下に述べる磁気履歴特性の異方性解析方法を考案した．また，従来よく使われているAMSやAMRと区別するために，この方法を磁気履歴特性の異方性（AMH: anisotropy of magnetic hysteresis properties）解析法と名付けた．AMHとは，従来一種類の磁気特性の異方性のみで粒子配列解析手段としていたAMSやAMRに対して，ヒジテリシス曲線から読みとれるいくつかの磁気履歴特性（本論文では，飽和残留磁化:IR，保磁力：HC，低磁場下の微分帯磁率：χL，高磁場下の微分帯磁率：χPの4種類を採用している）を組み合わせた複数の磁気異方性の総称である．AMH解析法とは、どの磁気履歴特性のanisotropy degree（異方性容易軸の強度1異カ性難易軸の強度）が大きいかという特徴と，AMHの各磁気履歴特性の異方性の強度変化の増減の相関関係から，岩石中の粒子配列解析をおこなうという方法である．anisotropy degreeの大きさを比較する場合には，前述の４種類の磁気履歴特性を用いる．AMHの各磁気履歴特性の異方性の強度変化の増減の相関関係を表すためには，IR，HC，χLの3種類を用いる．　人工配列試料についての基礎的実験，および，岩石試料についての実験の結果，以下のような結論が得られた．　岩石中にSD粒子の配列があった場合には，"IR //HC⊥χL"という磁気履歴特性の強度の増減の相関が観察でき，IR，HCの異方性容易軸は粒子配列の方向と一致し，χLの異方性容易軸は，粒子の配列方向と直交する．また，SD粒子の配列が顕著である時は，HCのanisotropy degreeは大きくなる．HCのanisotropy degreeが大きい場合，消磁後のNRM（ChNRM）は，HCの異方性容易軸の方向のNRMの残留磁化成分が他の方向より残りやすいため，信頼できる古地磁気方位を示さない．この現象は，SD粒子配列試料であるオーディオテープでも，SD粒子が配列している相関関係を表す岩石試料からも見いだされる．したがって，粒子配列のある岩石中のSD粒子の配列があるかどうかは，SDタイプのAMH相関関係（"IR //HC⊥χL"）が見られるかどうかで判定できる．すなわち，SD粒子の配列があって，HCが大きい時には，この岩石は古地磁気用試料としてふさわしくない．　ＭＤ粒子の配列があるときは、"IR //χL ⊥HC"という磁気履歴特性の強度の増減の相関が観察でき，IR，χLの異方性容易軸は粒子配列の方向と一致し，HCの異方性容易軸は，粒子の配列方向と直交する．この相関関係をMDタイプのAMH相関関係と呼ぶ．MD粒子から作製した人工試料の場合は，MD粒子が配列していてもHCのanisotropy degreeは小さくなる．また，SD粒子とMD粒子の混合試料の場合は"IR //HC⊥χL"という磁気特性の強度の増減の相関関係がみられる．MD粒子の配列のある岩石，または，SD粒子とMD粒子の配列のある岩石の場合は，HCのanisotropy degreeが小さければ，古地磁気用試料として採用できる．　上述のハ侶解析法の有効性を確かめるために，南極スカルブスネス地域の古生代の片麻岩について，NRMとAMHの比較をした．その結果，AMH相関関係がMDタイプのもの，あるいは，AMH相関関係がSDタイプでもHCの異カ性が小さい岩石ならば，粒子配列がNRMに影響は与えないことが判明した．したがって，野外で採取された多数の試料の中から代表的なものを選び，あらかじめAMH解析法で検討することによって，より効率的に，また，確実な古地磁気調査をすることができる．以上のように，AMH解析法は，信頼できる古地磁気研究をおこなうために有効な方法である