Mg/Ca and stable oxygen measurement of the past 27 Ma of ODP Hole 120-747A

We explore the applicability of paired Mg/Ca and 18O/16O measurements on benthic foraminifera from Southern Ocean site 747 to paleoceanographic reconstructions on pre-Pleistocene timescales. We focus on the late Oligocene through Pleistocene (27-0 Ma) history of paleotemperatures and the evolution of the d18O values of seawater (d18Osw) at a temporal resolution of ~100-200 kyr. Absolute paleotemperature estimates depend on assumptions of how Mg/Ca ratios of seawater have changed over the past 27 Myr, but relative changes that occur on geologically brief timescales are robust. Results indicate that at the Oligocene to Miocene boundary (23.8 Ma), temperatures lag the increase in global ice-volume deduced from benthic foraminiferal d18O values, but the smaller-scale Miocene glaciations are accompanied by ocean cooling of -1°C. During the mid-Miocene phase of Antarctic ice sheet growth (~15-13 Ma), water temperatures cool by ~3°C. Unlike the benthic foraminiferal d18O values, which remain relatively constant thereafter, temperatures vary (by 3°C) and reach maxima at ~12 and ~8.5 Ma. The onset of significant Northern Hemisphere glaciation during the late Pliocene is synchronous with an ~4°C cooling at site 747. A comparison of our d18Osw curve to the Haq et al. (1987, doi:10.1126/science.235.4793.1156 ) sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18O/16O ratios. At ~12-11 Ma in particular, when benthic foraminiferal d18O values do not support a further increase in ice volume, the d18Osw curve comes to a maximum that corresponds to a major mid-Miocene sea level regression. The agreement between the character of our Mg/Ca-based d18Osw curve and sequence stratigraphy demonstrates that benthic foramaniferal Mg/Ca ratios can be used to trace the d18Osw on pre-Pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater Mg/Ca ratios. The Mg/Ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes, which can lead to misinterpretations of the d18O record.

Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Properties of seawater (pH total scale) from a Satlantic SeaFET instrument mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous pH measurements made during 2013 expedition with a Satlantic SeaFET instrument that was connected to the flowthrough system. Data calibration was performed according to Bresnahan et al. (2014) (using spectrophotometric pH measurements on discrete samples (Clayton and Byrne 1993). pH_internal values were taken to calibrate the data (rather than pH_external) because of the better calibration coefficient (there was no trend associated with it). The equations of Clayton and Byrne (1993) was used to compute pH from the measured absorbance values at the temperature of measurement. The data was converted to in situ temperature using the "CO2-sys" program which can be downloaded from http://cdiac.ornl.gov/ftp/co2sys/.

(Table 2) Ice, snow and freeboard statistics from measurement transects at 11 ice stations during Aurora Australis cruise SIPEX in 2007

The Sea Ice Physics and Ecosystem experiment (SIPEX) was conducted in the East Antarctic pack ice zone between 115-130°E from 9 September - 11 October, 2007. In situ measurements of sea-ice and snow properties were conducted at 15 ice stations, together with ship-based ASPeCt observations. The ice and snow thickness varied considerably in different regions of the pack ice, with particularly thick ice associated with deformation and a strong slope jet in the southwest of the study region. The mean ice thickness was 0.99 m (1.57 m excluding the northern marginal ice zones), but varied from 0.61 m along the southern leg to 1.80 m along the western leg, with pockets of considerably thicker ice in some regions. Swell was observed on two occasions penetrating more than 330 km south of the ice edge into regions with 80-100% ice concentration. Ice thicknesses calculated from near coincident ICESat laser altimetry (1.74 m) are similar to the in-situ observations in the central pack (1.57 m).