ALBERT

Description: The circulation and internal structure of the oceans exert a strong influence on Earth's climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss (Sigman et al., 2010, doi:10.1038/nature09149). Circulation change, particularly in the Atlantic Ocean, is widely suggested (Bartoli et al., 2005, doi:10.1016/j.epsl.2005.06.020; Haug and Tiedemann, 1998, doi:10.1038/31447; Woodard et al., 2014, doi:10.1126/science.1255586; McKay et al., 2012, doi:10.1073/pnas.1112248109) to have been instrumental in the intensification of Northern Hemisphere glaciation when large ice sheets first developed on North America and Eurasia during the late Pliocene, approximately 2.7 million years ago (Bailey et al., 2013, doi:10.1016/j.quascirev.2013.06.004). Yet the mechanistic link and cause/effect relationship between ocean circulation and glaciation are debated. Here we present new records of North Atlantic Ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the Last Glacial to Holocene (35-5 thousand years ago) and the late Pliocene to earliest Pleistocene (3.3-2.4 million years ago). Our data show no secular change. Instead we document major southern-sourced water incursions into the deep North Atlantic during prominent glacials from 2.7 million years ago. Our results suggest that Atlantic circulation acts as a positive feedback rather than as an underlying cause of late Pliocene Northern Hemisphere glaciation. We propose that, once surface Southern Ocean stratification (Sigman, et al., 2004, doi:10.1038/nature02357) and/or extensive sea-ice cover (McKay et al., 2012, doi:10.1073/pnas.1112248109) was established, cold-stage expansions of southern-sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean, helping to increase the amplitude of glacial cycles.

Description: Atmospheric _p_CO~2~ is a critical component of the global carbon system and is considered to be the major control of Earth's past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document _p_CO~2~ for the past 800 kyrs, but at no point during this interval were CO~2~ levels higher than today. Interpretation of older _p_CO~2~ has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct _p_CO~2~: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ^11^B) of foraminifer shells. Here we present alkenone and δ^11^B-based _p_CO~2~ reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to _p_CO~2~ in the alkenone record compared to contemporaneous ice core and δ^11^B records, suggesting caution in the interpretation of alkenone-based records at low _p_CO~2~ levels. This is possibly caused by the physiology of CO~2~ uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of _p_CO~2~.

Description: Over the last deglaciation there were two transient intervals of pronounced atmospheric CO2 rise; Heinrich Stadial 1 (17.5-15 kyr) and the Younger Dryas (12.9-11.5 kyr). Leading hypotheses accounting for the increased accumulation of CO2 in the atmosphere at these times invoke deep ocean carbon being released from the Southern Ocean and an associated decline in the global efficiency of the biological carbon pump. From core ODP1090 we present new G. bulloidies carbon and oxygen isotope records. These stable isotopic analyses were performed on a Thermo Finnigan MAT253 coupled with a Kiel IV carbonate device at the University of Southampton.

Description: Over the last deglaciation there were two transient intervals of pronounced atmospheric CO2 rise; Heinrich Stadial 1 (17.5-15 kyr) and the Younger Dryas (12.9-11.5 kyr). Leading hypotheses accounting for the increased accumulation of CO2 in the atmosphere at these times invoke deep ocean carbon being released from the Southern Ocean and an associated decline in the global efficiency of the biological carbon pump. From core TAN1106-28 we present new G. bulloidies boron isotope and Mg/Ca derived sea surface pH and pCO2 concentrations. Trace element analysis was performed on a ThermoScientific Element 2 ICP-MS at the University of Southampton using the method described by Henehan et al. (2015). Isotopic analysis was performed on a ThermoScientific Neptune MC-ICPMS at the University of Southampton following the methods of Foster (2008) and Foster et al. (2013).

Description: Over the last deglaciation there were two transient intervals of pronounced atmospheric CO2 rise; Heinrich Stadial 1 (17.5-15 kyr) and the Younger Dryas (12.9-11.5 kyr). Leading hypotheses accounting for the increased accumulation of CO2 in the atmosphere at these times invoke deep ocean carbon being released from the Southern Ocean and an associated decline in the global efficiency of the biological carbon pump. From core ODP1090 we present new G. bulloidies boron isotope and Mg/Ca derived sea surface pH and pCO2 concentrations. Trace element analysis was performed on a ThermoScientific Element 2 ICP-MS at the University of Southampton using the method described by Henehan et al. (2015). Isotopic analysis was performed on a ThermoScientific Neptune MC-ICPMS at the University of Southampton following the methods of Foster (2008; doi:10.1016/j.epsl.2008.04.015) and Foster et al. (2013; doi:10.1016/j.chemgeo.2013.08.027).

Description: Over the last deglaciation there were two transient intervals of pronounced atmospheric CO2 rise; Heinrich Stadial 1 (17.5-15 kyr) and the Younger Dryas (12.9-11.5 kyr). Leading hypotheses accounting for the increased accumulation of CO2 in the atmosphere at these times invoke deep ocean carbon being released from the Southern Ocean and an associated decline in the global efficiency of the biological carbon pump. From core TAN1106-28 we present new deglacial alkenone and n-alkane records. Analysis and characterization of total lipid content were performed at Institut de Ciències del Mar in Barcelona following published methods (Villanueva et al., 1997; doi:10.1016/S0021-9673(96)00669-3, Calvo et al., 2003; doi:10.1016/S0021-9673(03)00119-5, Kornilova and Rosell-Melé, 2003; doi:10.1016/S0146-6380(03)00155-4) on an Agilent 7890 Gas Chromatograph with a flame ionization detector equipped with a HP-1 capillary column (60 m, 0.25 mm I.D. and 0.25 µm film thickness).

Description: This dataset includes measurements on mixed layer planktonic foraminifera from IODP/ODP sites for boron isotopes and trace elements. Boron isotopes were measured after column chemistry and solution analyses on a Neptune multi collector ICPMS, while trace elements were measured on pre-columned aliquots of the same samples, using Element XR ICP-MS. Furthermore, the dataset includes the seawater pH and atmospheric CO2 calculated from B isotopes measurements and Mg/Ca-temperature estimates, for no-vital effect treatment (T. sac-vital effect corrections at Eocene d11Bsw conditions result in d11B offsets within analytical uncertainty), and no pH correction on Mg/Ca-temperature relationship (assuming T. sac like species). Carbonate system calculations incorporate MyAMI ion-pairing corrections (https://github.com/MathisHain/MyAMI), and surface Omega values specific for the Eocene and the paleo-latitude of the core location. Propagation of uncertainties for pH and CO2 is completed through 1000 Monte Carlo simulations.