Palaeoceanography

  • Article |

    A record of flow-speed variations from an ocean core shows that a key component of Indian Ocean circulation rapidly accelerated 2.1 million years ago, coincident with intensification of Pacific Walker circulation.

    • H. J. L. van der Lubbe
    • , I. R. Hall
    •  & J. C. A. Joordens
  • Article |

    New proxy data for ocean pH and an ocean–atmosphere model show that a radically different ocean circulation led to decoupling of ocean productivity and upwelling in the equatorial Pacific Ocean 3–6 million years ago.

    • Madison G. Shankle
    • , Natalie J. Burls
    •  & Pincelli M. Hull
  • Article |

    Unexpected intervals of low 230Th concentration in marine sediment cores are explained by considering that during at least two such periods, the Arctic Ocean and Nordic seas were composed entirely of fresh water and covered by a thick ice shelf.

    • Walter Geibert
    • , Jens Matthiessen
    •  & Ruediger Stein
  • Article |

    Analysis of dust from marine sediments in the North Pacific shows that warm periods during the Pliocene witnessed weaker and more poleward westerlies than during subsequent glacial periods.

    • Jordan T. Abell
    • , Gisela Winckler
    •  & Timothy D. Herbert
  • Letter |

    After the Cretaceous/Palaeogene mass extinction event, nannoplankton communities exhibited volatility for 1.8 million years before a more stable community emerged, coinciding with restoration of the carbon cycle and a fully functioning biological pump between the surface and deep sea.

    • Sarah A. Alvarez
    • , Samantha J. Gibbs
    •  & Andy Ridgwell
  • Letter |

    Using phreatic overgrowths on speleothems, sea level during the mid-Piacenzian Warm Period, which was about two to three degrees Celsius warmer than the pre-industrial period, is shown to have been about 16 metres higher than today.

    • Oana A. Dumitru
    • , Jacqueline Austermann
    •  & Bogdan P. Onac
  • Letter |

    A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.

    • Margot J. Cramwinckel
    • , Matthew Huber
    •  & Appy Sluijs
  • Letter |

    Micro- and nannofossil, trace fossil and geochemical evidence from the Chicxulub impact crater demonstrates that proximity to the asteroid impact site did not determine rates of recovery of marine ecosystems after the end-Cretaceous mass extinction.

    • Christopher M. Lowery
    • , Timothy J. Bralower
    •  & William Zylberman
  • Article |

    Noble gases trapped in ice cores are used to show that the mean global ocean temperature increased by 2.6 degrees Celsius over the last glacial transition and is closely correlated with Antarctic temperature.

    • Bernhard Bereiter
    • , Sarah Shackleton
    •  & Jeff Severinghaus
  • Letter |

    A reconstruction of changes in ocean oxygenation throughout the last glacial cycle shows that respired carbon was removed from the deep Southern Ocean during deglaciation and Antarctic warm events, consistent with a prominent role of reduced iron fertilization and enhanced ocean ventilation, modifying atmospheric carbon dioxide concentrations over the past 80,000 years.

    • Samuel L. Jaccard
    • , Eric D. Galbraith
    •  & Robert F. Anderson
  • Letter |

    Core isotope measurements in the equatorial Pacific Ocean reveal that although atmospheric dust deposition during the last ice age was higher than today’s, the productivity of the equatorial Pacific Ocean did not increase; this may have been because iron-enabled greater nutrient consumption, mainly in the Southern Ocean, reduced the nutrients available in the equatorial Pacific Ocean, and hence also productivity there.

    • K. M. Costa
    • , J. F. McManus
    •  & A. C. Ravelo
  • Letter |

    The processes responsible for driving the expansion of the ocean's oxygen minimum zones remain uncertain; here sediment core data from the Gulf of Alaska suggest that reduced oxygen solubility was a result of ocean warming initiating the expansion of the North Pacific oxygen minimum zone, leading to increased marine productivity and carbon export and, in turn, further reductions in dissolved oxygen levels.

    • S. K. Praetorius
    • , A. C. Mix
    •  & F. G. Prahl
  • Letter |

    A synthesis of new and existing data allows Heinrich Stadial 11 (HS11), a prominent Northern Hemisphere cold event, to be linked to the timing of peak sea-level rise during glacial termination T-II, whereas rapid sea-level rise in T-I is shown to clearly post-date Heinrich Stadial 1, so fundamentally different mechanisms seem to be at work during glacial terminations.

    • G. Marino
    • , E. J. Rohling
    •  & J. Yu
  • Letter |

    A delay between surface cooling and the arrival of ice-rafted debris at a site southwest of Iceland over the past four glacial cycles implies that icebergs typically arrived too late to have triggered cooling, although the freshwater derived from melting icebergs may provide a positive feedback for cold stadial conditions.

    • Stephen Barker
    • , James Chen
    •  & David Thornalley
  • Letter |

    A new ice core from West Antarctica shows that, during the last ice age, abrupt Northern Hemisphere climate variations were followed two centuries later by a response in Antarctica, suggesting an oceanic propagation of the climate signal to the Southern Hemisphere high latitudes.

    • Christo Buizert
    • , Betty Adrian
    •  & Thomas E. Woodruff
  • Letter |

    The boron isotope pH proxy in sediment-core planktic foraminifera is used as a tracer of oceanic CO2 outgassing to show that surface waters which derive partly from deep water upwelled in the Southern Ocean became a significant source of carbon to the atmosphere during the last deglaciation.

    • M. A. Martínez-Botí
    • , G. Marino
    •  & D. Vance
  • Letter |

    Reconstruction of the Atlantic meridional overturning circulation from a highly resolved marine sedimentary record shows that a deep, vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, but that a shallower glacial mode prevailed during glacial maxima.

    • E. Böhm
    • , J. Lippold
    •  & M. Deininger
  • Letter |

    Analysis of radiocarbon and uranium-series dates and clumped isotope temperature estimates from water column profiles of fossil deep-sea corals in the North Atlantic shows that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling–Allerød warming and reinvigoration of the Atlantic meridional overturning circulation 14,700 years ago.

    • Nivedita Thiagarajan
    • , Adam V. Subhas
    •  & Jess F. Adkins
  • Letter |

    The isotopic composition of glacial sediment discharged into the ocean from south Greenland is used to identify a major reduction in the amount of that sediment derived from erosion of Greenland’s Precambrian bedrock, probably indicating the cessation of subglacial erosion and sediment transport during Marine Isotope Stage 11 as a result of the almost complete deglaciation of south Greenland.

    • Alberto V. Reyes
    • , Anders E. Carlson
    •  & David J. Ullman
  • Letter |

    New sea surface temperature and oxygen isotope records, combined with climate modelling experiments, show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation.

    • Mahyar Mohtadi
    • , Matthias Prange
    •  & Andreas Lückge
  • Article |

    A novel approach to the estimation of sea level and deep-sea temperature has been used to determine these quantities over the past 5.3 million years; this approach, based on oxygen isotope records from the eastern Mediterranean, shows that temperature and sea-level histories are broadly correlated but also show intriguing temporal offsets.

    • E. J. Rohling
    • , G. L. Foster
    •  & F. Williams
  • Letter |

    Chemical, isotopic and physical evidence indicate that some of the groundwater in the Chesapeake Bay crater is remnant Early Cretaceous North Atlantic sea water, probably 100–145 million years old, with an average salinity of about 70‰, which is twice that of modern sea water.

    • Ward E. Sanford
    • , Michael W. Doughten
    •  & Thomas D. Bullen
  • Letter |

    Four reconstructions of North American ice-sheet history are tested using oxygen isotope records from the Gulf of Mexico in a water-mixing model; the one based on ice physics is the best match to the isotopic data and to the observed Last Glacial Maximum fall in sea level due to melting of the Laurentide ice sheet.

    • Andrew D. Wickert
    • , Jerry X. Mitrovica
    •  & Robert S. Anderson
  • Letter |

    Reconstructed changes in North Atlantic nitrogen fixation over the past 160,000 years have a 23,000-year cycle that is interpreted to result from precession-paced changes in the supply of phosphorus to surface waters by equatorial Atlantic upwelling.

    • Marietta Straub
    • , Daniel M. Sigman
    •  & Gerald H. Haug
  • Article |

    A synthesis of geochemical proxy records of sea surface temperature shows that the early Pliocene climate was little different from today in terms of maximum ocean temperatures but had substantially lower meridional and zonal temperature gradients.

    • A. V. Fedorov
    • , C. M. Brierley
    •  & A. C. Ravelo
  • Letter |

    Records of biogenic opal export in the North Atlantic Ocean show pronounced maxima during each glacial termination over the past 550,000 years, consistent with a strong deglacial reduction in the formation of silicate-poor glacial North Atlantic intermediate water and a consequent increase in upward silicate transport.

    • A. N. Meckler
    • , D. M. Sigman
    •  & G. H. Haug
  • Letter |

    Model simulations show that in response to insolation changes only, southern westerlies and feedbacks between sea ice, temperature, evaporation and salinity caused vigorous Southern Ocean ventilation and cooler deep ocean during the interglacials before the mid-Brunhes transition, suggesting that this transition may in fact have resulted from a series of individual interglacial responses to various combinations of insolation conditions.

    • Qiuzhen Yin
  • Letter |

    Data are presented that support the idea of an oxygenation event in the immediate aftermath of the Marinoan glaciation, pre-dating previous estimates for post-Marinoan oxygenation by more than 50 million years.

    • Swapan K. Sahoo
    • , Noah J. Planavsky
    •  & Ganqing Jiang