Abundance and biomass of planktonic diatom Proboscia alata and associated species, chlorophyll a, organic carbon and nitrogen concentrations in waters over the Bering Sea middle shelf in August 2001

During most of the vegetation season from late May to early September large-sized diatom alga Proboscia alata forms local patches with high abundances and biomasses in different oceanographic domains of the eastern Bering Sea shelf. For 0-25 m layer average abundance and biomass of species in these patches are 700000 cells/l and 5 g/m**3 (wet weight), while corresponding estimates for the layer of maximal species concentrations are 40000000 cells/l and 38 g/m**3 (wet weight) or 1.6 g C/m**3. These levels of abundance and biomass are typical for the spring diatom bloom in the region. Outbursts of P. alata mass development are important for the carbon cycle in the pelagic zone of the shelf area in the summer season. The paradox of P. alata summertime blooms over the middle shelf lies in their occurrences against the background of the sharp seasonal pycnocline and deficiency in nutrients in the upper mixed layer. Duration of the outbursts in P. alata development is about two weeks and size of patches with high abundances can be as large as 200 km across. Degradation of the P. alata summertime outbursts may occur during 4-5 days. Rapid sinking of cells through the seasonal pycnocline results in intense transport of organic matter to bottom sediments. One of possible factors responsible for rapid degradation of the blooms is affect on the population by ectoparasitic flagellates. At terminal stages of the P. alata blooms percentage of infected cells can reach 70-99%.

Corrected ICESat altimetry data, surface mass balance, and firn elevation change on Antarctic ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Floating ice shelves buttress the flow of grounded tributary glaciers and their thickness and extent are particularly susceptible to changes in both climate and ocean forcing. Recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. However, the extent and magnitude of ice-shelf thickness change, its causes and its link to glacier flow rate are so poorly understood that its influence on the future of the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal for the first time the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary driver of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet that has led to accelerated glacier flow. The highest thinning rates (~7 m/a) occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen Seas and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic Ice Sheet mass balance, and hence global sea-level, on annual to decadal timescales.

Hydrate abundances at the high-flux Batumi seep area in the southeastern Black Sea

Submarine gas hydrates are a major global reservoir of the potent greenhouse gas methane. Since current assessments of worldwide hydrate-bound carbon vary by one order of magnitude, new technical efforts are required for improved and accurate hydrate quantifications. Here we present hydrate abundances determined for surface sediments at the high-flux Batumi seep area in the southeastern Black Sea at 840 m water depth using state-of-the art autoclave technology. Pressure sediment cores of up to 2.65 m in length were recovered with an autoclave piston corer backed by conventional gravity cores. Quantitative core degassing yielded volumetric gas/bulk sediment ratios of up to 20.3 proving hydrate presence. The cores represented late glacial to Holocene hemipelagic sediments with the shallowest hydrates found at 90 cmbsf. Calculated methane concentrations in the different cores surpassed methane equilibrium concentrations in the two lowermost lithological Black Sea units sampled. The results indicated hydrate fractions of 5.2% of pore volume in the sapropelic Unit 2 and mean values of 21% pore volume in the lacustrine Unit 3. We calculate that the studied area of ~ 0.5 km**2 currently contains about 11.3 kt of methane bound in shallow hydrates. Episodic detachment and rafting of such hydrates is suggested by a rugged seafloor topography along with variable thicknesses in lithologies. We propose that sealing by hydrate precipitation in coarse-grained deposits and gas accumulation beneath induces detachment of hydrate/sediment chunks. Floating hydrates will rapidly transport methane into shallower waters and potentially to the sea-atmosphere boundary. In contrast, persistent in situ dissociation of shallow hydrates appears unlikely in the near future as deep water warming by about 1.6 °C and/or decrease in hydrostatic pressure corresponding to a sea level drop of about 130 m would be required. Because hydrate detachment should be primarily controlled by internal factors in this area and in similar hydrated settings, it serves as source of methane in shallow waters and the atmosphere which is mainly decoupled from external forcing.

Bulk stable carbon and oxygen isotopes from ODP Site 1258, and Fe intensities from ODP Site 1262, and minimal tuning age model options for ODP Site 1258 and 1262

Timing is crucial to understanding the causes and consequences of events in Earth history. The calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating. Uncertainties in the computations of Earth's orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 Ma. Attempts to construct a robust astronomically tuned time scale for the early Paleogene by integrating radioisotopic and astronomical dating are only partially consistent. Here, using the new La2010 and La2011 orbital solutions, we present the first accurate astronomically calibrated time scale for the early Paleogene (47-65 Ma) uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the Fish Canyon standard. Comparison with geological data confirms the stability of the new La2011 solution back to ~54 Ma. Subsequent anchoring of floating chronologies to the La2011 solution using the very long eccentricity nodes provides an absolute age of 55.530 {plus minus} 0.05 Ma for the onset of the Paleocene/Eocene Thermal Maximum (PETM), 54.850 {plus minus} 0.05 Ma for the early Eocene ash -17, and 65.250 {plus minus} 0.06 Ma for the K/Pg boundary. The new astrochronology presented here indicates that the intercalibration and synchronization of U/Pb and 40Ar/39Ar radiometric geochronology is much more challenging than previously thought.