Geochemistry of sediments from the continental slope of the Ross Sea, Antarctica

A sediment core, collected from the western part of the continental slope of the Ross Sea at 2380 m water depth, records events of the last two climatic cycles (250 kyr). A 230Thex-based chronology was obtained and boundaries of the isotope stages were set assuming that biological productivity was enhanced during periods of less ice cover. Then, 230Thex0, organic carbon, biogenic silica and biogenic Ba distributions were compared to the glacial-interglacial stage boundaries and corresponding ages of the delta18O record of Martinson et al. [Martinson et al., 1987, doi:10.1016/0033-5894(87)90046-9]. Sediment accumulation rates ranged between 1.2 cm kyr**-1 in the isotope stage 6 and 3.8 cm kyr**-1 during the Holocene. Variations in the concentrations and fluxes of organic carbon, biogenic Ba, biogenic silica and Mn gave information on palaeoclimate changes. Processes of sediment redistribution in the Ross Sea margin were enlightened from a comparison of the measured and expected fluxes of 230Thex. Calculation of the focusing-corrected accumulation rates of biogenic Ba enabled us to evaluate the export palaeoproductivity. Corrected accumulation rates of biogenic components and calculated palaeoproductivities were low, compared to the Antarctic Polar Front in the Atlantic sector, throughout the last two climatic cycles. Glacial-interglacial changes of sea ice cover and ventilation of the Ross Sea were probably major causes of variations in biogenic particle flux and distribution of redox-sensitive elements within the sediment column.

Radionuclides measured on three sediment cores from the Weddell Sea, Antarctica

High resolution 230Thex and 10Be and biogenic barium profiles were measured at three sediment gravity cores (length 605-850 cm) from the Weddell Sea continental margin. Applying the 230Thex dating method, average sedimentation rates of 3 cm/kyr for the two cores from the South Orkney Slope and of 2.4 cm/kyr for the core from the eastern Weddell Sea were determined and compared to delta18O and lithostratigraphic results. Strong variations in the radionuclide concentrations in the sediments resembling the glacial/interglacial pattern of the delta18O stratigraphy and the 10Be stratigraphy of high northern latitudes were used for establishing a chronostratigraphy. Biogenic Ba shows a pattern similar to the radionuclide profiles, suggesting that both records were influenced by increased paleoproductivity at the beginning of the interglacials. However, 230Thex0 fluxes (0 stands for initial) exceeding production by up to a factor of 4 suggest that sediment redistribution processes, linked to variations in bottom water current velocity, played the major role in controlling the radionuclide and biogenic barium deposition during isotope stages 5e and 1. The correction for sediment focusing makes the 'true' vertical paleoproductivity rates, deduced from the fluxes of proxy tracers like biogenic barium, much lower than previously estimated. Very low 230Thex0 concentrations and fluxes during isotope stage 6 were probably caused by rapid deposition of older, resedimented material, delivered to the Weddell Sea continental slopes by the grounded ice shelves and contemporaneous erosion of particles originating from the water column.

Biogenic opal, carbonat concentrations and stable oxygen isotope ratios of foraminifera from sediment cores of the Southern Ocean

We present records of biogenic opal percentage and burial rate in 12 piston cores from the Atlantic and Indian sectors of the Southern Ocean. These records provide a detailed, quantitative description of changing patterns of opal deposition over the last 450 kyr. The striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal, and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the Southern Ocean under different global climate conditions. Three broad depositional patterns can be distinguished. Northernmost records (39°-42°S latitude) are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity. Records from cores just north of the present Antarctic Polar Front (46°-49°S) show even larger increases in opal burial rate during glacial intervals, but have variance concentrated in the 100 and 23 kyr bands. Southernmost records (51°-55°S) are completely out of phase with those to the north, with greatly reduced opal burial rates during glacial periods. Taken as a whole, the opal records show no evidence for the increased total Antarctic productivity predicted by recent geochemical models of atmospheric CO2 variability. The areal expansion of Southern Ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial-interglacial opal patterns. The excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region. However, local circulation changes may act to modify this basic signal, possibly accounting for the observed differences in the opal variance spectra.

Pedro Piñero Ramírez et al. (eds.), Romancero de la Provincia de Sevilla, Sevilla: Universidad - Diputación, 2013, 935 pp.

Fil: Chicote, Gloria. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina.

Trace elements in benthic foraminifera of sediment core V30-49

Eastern tropical Atlantic benthic foraminiferal Ba/Ca and Cd/Ca data from core V30-949 (3093 m) reveal large inferred changes in nutrient concentrations of deep Atlantic waters during the last 250 kyr. Relative changes in North Atlantic Deep Water contribution to this site are estimated by scaling the V30-49 Cd/Ca record to values of modern end-member water masses; these estimates agree well with the relative structure and timing of circulation changes in the eastern tropical Atlantic reconstructed from a d13C record-based mixing model (Raymo et al., 1997, doi:10.1029/97PA01019). Temporal differences between V30-49 Cd/Ca and Ba/Ca records suggest that the Ba/Ca record reflects changes in circulation with an additional increase in the Ba composition of deep Atlantic water masses during glacial episodes, possibly resulting from increased productivity. Similarity between the d13C and Ba/Ca records suggests that carbon isotopes in the deep glacial Atlantic also reflect productivity increases.

Sea surface temperature and export productivity reconstructions of sediments off the western Iberian margin

Present day hydrographic conditions along the western Iberian margin are characterized by seasonal upwelling with filaments that can penetrate more than 200 km into the open ocean and constitute areas of cold and highly productive waters. In order to investigate spatial and temporal gradients in temperature and productivity conditions during the last 150 ky, high-resolution proxy records were generated in 3 cores (SU92-03, MD95-2040, MD95-2042), located along the Iberian coast between 43°12'N and 37°48'N and forming a N-S profile. In all cores, planktonic foraminifera census counts are used to reconstruct summer sea surface temperature (SSTsu) and export productivity (Pexpsu) using the modern analog technique SIMMAX 28. SSTsu and Pexpsu values similar to the present are observed throughout the Holocene and MIS 5e periods for each site, respectively, indicating fairly stable conditions equivalent to the modern ones. On glacial/interglacial timescales, SSTsu increases by 2-3 °C from the northern to southernmost site. Pexpsu, on the other hand, shows a decrease of 30-40 gC/m**2/yr from North to South at present time and during interglacial periods, and no significant variation (90-100 gC/m**2/yr) during glacial periods. The northernmost core SU92-03 reveals the coldest conditions with records more similar to MD95-2040 than to MD95-2042, the later of which is, as at present, more affected by subtropical waters. Core SU92-03 shows higher interglacial productivity similar to open ocean mid- to high latitude sites, while the other two cores monitor higher glacial productivity conform with other upwelling sites off NW Africa. A boundary between differences in glacial/interglacial productivity appears to be present in our study between 43°12'N and 40°35'N. Especially north of 40°N, coldest SSTsu and lowest Pexpsu are found during Heinrich events (H)1-H8 and H10-H11. In contrast, lowest Pexpsu do not coincide with these events at site MD95-2042, but appear to be related to the presence of relatively warm and nutrient-poor subtropical Eastern North Atlantic Central Water advected with the Azores Current.

Comments on “High-temperature creep resistance and effects on the austenite reversion and precipitation of 18 Ni (300) maraging steel” by dos Reis et al. [Materials Characterization 107 (2015) 350- 357]

This letter attempts to comment on an article by dos Reis et al., in the aspects of creep considerationand chemical analysis in maraging steels.

Feasibility, normative heuristics and the proper place of historical responsibility – a reply to Ohndorf et al.

In this comment, we pick up three points raised by Ohndorf et al. (2015) in their reply to our ethical assessment of the German Advisory Council’s Budget Approach (WBGUBA). First, we discuss and clarify the relationship between ethics and political feasibility, highlighting that the way Ohndorf et el. use feasibility creates an unwarranted status quo bias. Second, we explain the proper place historical responsibility should have within the WBGUBA, stressing the fact that the reasons why we choose one policy proposal over another matter. Third, we analyze the limited extent to which a normative heuristic should motivate an ethically ambitious policy proposal like the WBGUBA.

Supporting data for Blossey et al (2016): CGILS Phase 2 LES intercomparison of response of subtropical marine low cloud regimes to CO2 quadrupling and a CMIP3-composite forcing change

This archive provides supporting data with forcings, data and plotting scripts for the paper P. N. Blossey, C. S. Bretherton, A. Cheng, S. Endo, T. Heus, A. Lock and J. J. van der Dussen, 2016. CGILS Phase 2 LES intercomparison of response of subtropical marine low cloud regimes to CO2 quadrupling and a CMIP3-composite forcing change. J. Adv. Model. Earth Syst., Under revision.