High-resolution isotope stratigraphy of ODP Site 184-1144

Narrow-spaced oxygen and carbon stable isotope records of the planktonic foraminifer Globigerinoides ruber (white) were obtained at Ocean Drilling Program Leg 184 Site 1144 to establish a first record of high-resolution Pleistocene monsoon variability on orbital to centennial timescales in the northern South China Sea. The new records extend from the Holocene back to marine isotope Stage (MIS) 34 (1.1 Ma). Sedimentation rates average 0.56 m/k.y. for the upper Matuyama and Brunhes Chrons and increase to 1.8 m/k.y. over the last 100 k.y. Stable isotope records thus reach an average time resolution of 270-500 yr for the last 375 k.y. and 570 yr further back to 700 ka. On the other hand, major stratigraphic gaps were identified for peak warm Stages 5.5, 7.5 (down to 8.4), 11.3, and 15.5. These gaps probably resulted from short-lasting events of contour current erosion induced by short-term enhanced incursions of Upper Pacific Deep Water near the end of glacial terminations. A further major hiatus extends from MIS 34 to MIS 73(?). The long-term variations in monsoon climate were largely dominated by the 100-k.y. eccentricity cycle. Planktonic delta13C values culminated near 30, 480, and 1035 ka and reflect an overlying 450-k.y. eccentricity cycle of minimum nutrient concentrations in the surface ocean. Superimposed on the orbital variations, millennial-scale cycles were prominent throughout the last 700 k.y., mainly controlled by short-term changes in monsoon-driven precipitation and freshwater input from mainland China. During the last 110 k.y. these short-lasting oscillations closely match the record of 1500-yr Dansgaard-Oeschger climate cycles in the Greenland ice core record.

Stable carbon and oxygen isotope compositions of bulk rock samples analyzed from the Zumaia section

Astronomical tuning of sedimentary records to precise orbital solutions has led to unprecedented resolution in the geological time scale. However, the construction of a consistent astronomical time scale for the Paleocene is controversial due to uncertainties in the recognition of the exact number of 405-kyr eccentricity cycles and accurate correlation between key records. Here, we present a new Danian integrated stratigraphic framework using the land-based Zumaia and Sopelana hemipelagic sections from the Basque Basin and deep-sea records drilled during Ocean Drilling Program (ODP) Legs 198 (Shatsky Rise, North Pacific) and 208 (Walvis Ridge, South Atlantic) that solves previous discrepancies. The new coherent stratigraphy utilises composite images from ODP cores, a new whole-rock d13C isotope record at Zumaia and new magnetostratigraphic data from Sopelana. We consistently observe 11 405-kyr eccentricity cycles in all studied Danian successions. We achieve a robust correlation of bioevents and stable isotope events between all studied sections at the ~100-kyr short-eccentricity level, a prerequisite for paleoclimatic interpretations. Comparison with and subsequent tuning of the records to the latest orbital solution La2011 provides astronomically calibrated ages of 66.022 ± 0.040 Ma and 61.607 ± 0.040 Ma for the Cretaceous-Paleogene (K-Pg) and Danian-Selandian 105 (D-S) boundaries respectively. Low sedimentation rates appear common in all records in the mid-Danian interval, including conspicuous condensed intervals in the oceanic records that in the past have hampered the proper identification of cycles. The comprehensive interbasinal approach applied here reveals pitfalls in time scale construction, filtering techniques in particular, and indicates that some caution and scrutiny has to be applied when building orbital chronologies. Finally, the Zumaia section, already hosting the Selandian Global Boundary Stratotype Section and Point (GSSP), could serve as the global Danian unit stratotype in the future.

Late Pleistocene oxygen isotope record of biognic silica

We determined the isotopic composition of oxygen in marine diatoms in eight deep-sea cores recovered from the Atlantic sector of the Southern Ocean. The analytical reproducibility and core-to-core consistency of the isotopic signal suggests that diatom delta18O can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18O -isotope-based stratigraphy for the Southern Ocean. The data indicate that diatom delta18O reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka. The delta18O analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common Antarctic species have the same water-opal fractionation. The transition from the last glacial maximum (LGM) to the Holocene is fully recorded in high sedimentation rate cores. An 18O enrichment during the LGM, a post-LGM meltwater spike and an input of meltwater during the late Holocene are the main isotopic features observed in down core records. The origin of this meltwater was very likely melting icebergs and/or continental ice or by melting sea ice that had accumulated snow. The most pronounced meltwater effects are recorded in cores that are associated with the Weddel gyre. Our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate; further, isotopic stratigraphies may be constructed for records and regions where they were previously not possible.

Stable carbon and oxygen isotope record of planktonic foraminifera across the Paleocene-Eocene boundary

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic 'events' near the Paleocene-Eocene boundary provide strati-graphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera bio-stratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean's carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO2. As a consequence of this exchange of 12C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.