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

Integrated Ocean Drilling Program Expedition 318 Preliminary Report Wilkes Land Glacial History Cenozoic East Antarctic Ice Sheet Evolution from Wilkes Land Margin Sediments

Understanding the evolution and dynamics of the Antarctic cryosphere, from its inception during the Eocene-Oligocene transition (∼34 Ma) through the significant subsequent periods of likely coupled climate and atmospheric CO2 changes, is not only of major scientific interest but also is of great importance for society. Drilling the Antarctic Wilkes Land margin was designed to provide a long-term record of the sedimentary archives along an inshore to offshore transect of Cenozoic Antarctic glaciation and its intimate relationships with global climatic and oceanographic change. The principal goals were 1. To obtain the timing and nature of the first arrival of ice at the Wilkes Land margin inferred to have occurred during the earliest Oligocene (reflecting Oligocene isotope Event 1), 2. To obtain the nature and age of the changes in the geometry of the prograda- tional wedge interpreted to correspond with large fluctuations in the extent of the East Antarctic Ice Sheet and possibly coinciding with the transition from a wet-based to a cold-based glacial regime, 3. To obtain a high-resolution record of Antarctic climate variability during the late Neogene and Quaternary, and 4. To obtain an unprecedented ultrahigh resolution (i.e., annual to decadal) Holocene record of climate variability. The Wilkes Land drilling program was developed to constrain the age, nature, and paleoenvironment of deposition of the previously only seismically inferred glacial sequences. Drilling the Wilkes Land margin has a unique advantage in that seismic Unconformity WL-U3, inferred to separate preglacial strata below from glacial strata above in the continental shelf, can be traced to the continental rise deposits, allowing sequences to be linked from shelf to rise. Integrated Ocean Drilling Program Expedition 318, carried out in January-March 2010 (Wellington, New Zealand to Hobart, Australia), occupied seven sites that recovered ∼2000 m of high-quality middle Eocene-Holocene sediments at proposed Sites WLRIS-6A, WLRIS-7A, WLRIS-4A, and WLRIS-5A (Sites U1355, U1356, U1359, and U1361) on the Wilkes Land rise and Sites WLSHE-8A, WLSHE-9A, and ADEL-01B (Sites U1358, U1360, and U1357) on the Wilkes Land shelf at water depths between ∼400 and 4000 m. Together, the cores represent ∼53 m.y. of Antarctic history. Recovered cores successfully date the inferred seismic units (WL-S4-WL-S9). The cores reveal the history of the Wilkes Land Antarctic margin from an ice-free greenhouse Antarctica, to the first cooling, to the onset and erosional consequences of the first glaciation and the subsequent dynamics of the waxing and waning ice sheets, all the way to thick, unprecedented tree ring style records with seasonal resolution of the last deglaciation that began ∼10,000 y ago. The cores also reveal details of the tectonic history of the so-called Australo-Antarctic Gulf (at 53 Ma) from the onset of the second phase of rifting between Australia and Antarctica, to ever subsiding margins and deepening, all the way to the present continental and ever widening ocean/continent configuration. Tectonic and climatic change turned the initially shallow broad subtropical Antarctic Wilkes Land shelf into a deeply subsided basin with a narrow, iceinfested margin. Thick Oligocene and notably Neogene deposits, including turbidites, contourites, and larger and smaller scaled debris mass flows witness the erosional power of the waxing and waning ice sheets and deep ocean currents. The recovered clays, silts, and sands and their microfossils also reveal the transition of subtropical ecosystems and a vegetated Antarctica into sea ice-dominated ecosystems bordered by calving glaciers

Sedimentology of lower Pliocene to Upper Pleistocene diamictons from IODP Site U1358, Wilkes Land margin, and implications for East Antarctic Ice Sheet dynamics

AbstractDuring the early Pliocene a dynamic marine-based ice sheet retreated from the Wilkes Land margin with periodic ice advances beyond Last Glacial Maximum position. A change in sand provenance is indicative of a more stable Mertz Glacier system during the Late Pleistocene. East Antarctic Ice Sheet (EAIS) dynamics were evaluated through the analysis of marine diamictons from Integrated Ocean Drilling Program (IODP) site U1358 on the Adélie Land continental shelf. The warmer than present conditions of the early Pliocene coupled with the site's proximity to the landward sloping Wilkes Subglacial Basin provided the rationale for the investigations at this site. Based on visual core descriptions, particle size distributions, and major and trace element ratios, we interpret the origin of lower Pliocene strata by intermittent glaciomarine sedimentation with open-marine conditions and extensive glacial advances to the outer shelf. Heavy mineral analyses show that sand-sized detritus in the lower Pliocene strata was sourced from local intermediate to high-grade metamorphic rocks near Mertz Glacier. In contrast, Pleistocene diamictons exhibit a larger contribution from a prehnite-pumpellyite greenschist facies suggesting supply via iceberg rafting from northern Victoria Land. From this sedimentological evidence, we postulate a shift from a dynamic EAIS margin in the early Pliocene to possible stabilization in the Pleistocene

Integrated ocean drilling program expedition 318 preliminary report wilkes land glacial history cenozoic east antarctic ice sheet evolution from wilkes land margin sediments

Understanding the evolution and dynamics of the Antarctic cryosphere, from its inception during the Eocene-Oligocene transition (∼34 Ma) through the significant subsequent periods of likely coupled climate and atmospheric CO2 changes, is not only of major scientific interest but also is of great importance for society. Drilling the Antarctic Wilkes Land margin was designed to provide a long-term record of the sedimentary archives along an inshore to offshore transect of Cenozoic Antarctic glaciation and its intimate relationships with global climatic and oceanographic change. The principal goals were 1. To obtain the timing and nature of the first arrival of ice at the Wilkes Land margin inferred to have occurred during the earliest Oligocene (reflecting Oligocene isotope Event 1), 2. To obtain the nature and age of the changes in the geometry of the prograda- tional wedge interpreted to correspond with large fluctuations in the extent of the East Antarctic Ice Sheet and possibly coinciding with the transition from a wet-based to a cold-based glacial regime, 3. To obtain a high-resolution record of Antarctic climate variability during the late Neogene and Quaternary, and 4. To obtain an unprecedented ultrahigh resolution (i.e., annual to decadal) Holocene record of climate variability. The Wilkes Land drilling program was developed to constrain the age, nature, and paleoenvironment of deposition of the previously only seismically inferred glacial sequences. Drilling the Wilkes Land margin has a unique advantage in that seismic Unconformity WL-U3, inferred to separate preglacial strata below from glacial strata above in the continental shelf, can be traced to the continental rise deposits, allowing sequences to be linked from shelf to rise. Integrated Ocean Drilling Program Expedition 318, carried out in January-March 2010 (Wellington, New Zealand to Hobart, Australia), occupied seven sites that recovered ∼2000 m of high-quality middle Eocene-Holocene sediments at proposed Sites WLRIS-6A, WLRIS-7A, WLRIS-4A, and WLRIS-5A (Sites U1355, U1356, U1359, and U1361) on the Wilkes Land rise and Sites WLSHE-8A, WLSHE-9A, and ADEL-01B (Sites U1358, U1360, and U1357) on the Wilkes Land shelf at water depths between ∼400 and 4000 m. Together, the cores represent ∼53 m.y. of Antarctic history. Recovered cores successfully date the inferred seismic units (WL-S4-WL-S9). The cores reveal the history of the Wilkes Land Antarctic margin from an ice-free greenhouse Antarctica, to the first cooling, to the onset and erosional consequences of the first glaciation and the subsequent dynamics of the waxing and waning ice sheets, all the way to thick, unprecedented tree ring style records with seasonal resolution of the last deglaciation that began ∼10,000 y ago. The cores also reveal details of the tectonic history of the so-called Australo-Antarctic Gulf (at 53 Ma) from the onset of the second phase of rifting between Australia and Antarctica, to ever subsiding margins and deepening, all the way to the present continental and ever widening ocean/continent configuration. Tectonic and climatic change turned the initially shallow broad subtropical Antarctic Wilkes Land shelf into a deeply subsided basin with a narrow, iceinfested margin. Thick Oligocene and notably Neogene deposits, including turbidites, contourites, and larger and smaller scaled debris mass flows witness the erosional power of the waxing and waning ice sheets and deep ocean currents. The recovered clays, silts, and sands and their microfossils also reveal the transition of subtropical ecosystems and a vegetated Antarctica into sea ice-dominated ecosystems bordered by calving glaciers