Seawater Nd and Pb isotopic record in central Pacific and Caribbean sediments

The shoaling and final closure of the Central American Seaway (CAS) resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of Atlantic Meridional Overturning Circulation (AMOC). The exact timing of CAS closure is key to interpreting its importance. Here we present a reconstruction of deep and intermediate water Nd and Pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial Pacific (Ocean Drilling Program (ODP) Site 1241) and the Caribbean (ODP Sites 998, 999, and 1000) covering the final stages of CAS closure between 5.6 and 2.2 Ma. The data for the Pacific site indicate no significant Atlantic/Caribbean influence over this entire period. The Caribbean sites show a continuous trend to less radiogenic Nd isotope compositions during the Pliocene, consistent with an enhancement of Upper North Atlantic Deep Water (UNADW) inflow and a strengthening of the AMOC. Superimposed onto this long-term trend, shorter-term changes of intermediate Caribbean Nd isotope signatures approached more UNADW-like values during intervals when published reconstructions of seawater salinity suggested complete closure of the CAS. The data imply that significant deep water exchange with the Pacific essentially stopped by 7 Ma and that shallow exchange, which still occurred at least periodically until approximately 2.5 Ma, may have been linked to the strength of the AMOC but did not have any direct effect on the intermediate and deep Caribbean Nd isotope signatures through mixing with Pacific waters.

Annotated record of the detailed examination of Mn deposits from RIDA cruise stations

The cores and dredges described at this site were taken on the RIDA cruise from 1 May until 25 May 1984 by the Muséum National d'Histoire Naturelle from the R/V Marion Dufresne. A total of 45 cores and dredges were recovered along with underwater camera runs. They are available at MNHN for sampling and study.

(Table 2) Revised stacked record on magnetic susceptibility of ODP Site 162-984 sediments

Magnetic field and susceptibility data were collected using the geological high-resolution magnetometer tool string (GHMT) at three sites during Ocean Drilling Program Leg 162. Postcruise processing of the magnetic field data yielded a polarity stratigraphy for Holes 986C and 987E. A magnetic susceptibility record was measured at Hole 984B. Detailed analysis of the core and log susceptibility records at Hole 984B yielded an empirical tool resolution of the susceptibility measurement tool (SUMT) of 53 cm. At Site 984, where sedimentation rates were typically >10 cm/k.y., this gave a resolution of at least ~5000 yr. This data report summarizes the GHMT postcruise processing, method of interpretation, and analysis of the SUMT resolution.

Benthic foraminiferal stable isotope record for the equatorial Pacific

Stable oxygen and carbon isotope (d18O and d13C) values measured in foraminiferal calcite are one of the primary tools used in paleoceanography. Diagenetic recrystallization of foraminiferal calcite can act to reset primary isotopic values, but its effects are typically poorly quantified. Here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial Pacific Ocean recovered during Ocean Drilling Program Leg 199 and Integrated Ocean Drilling Program Expedition 320. Our selected sites form paleowater and burial depth transects, with excellent stratigraphic control allowing us to confidently correlate our records. We observe large intersite differences in the preservation state of benthic foraminiferal calcite, implying very different recrystallization histories, but negligible intersite offsets in benthic d18O and d13C values. We infer that diagenetic alteration of benthic foraminiferal calcite (in sedimentary oozes) must predominantly occur at shallow burial depths (<100 m) where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small. Our results suggest that even extensive recrystallization of benthic foraminiferal calcite results in minimal shifts from primary d18O and d13C values. This finding supports the long-held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep-sea sediments routinely employed for paleoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record.

Annotated record of the detailed examination of Mn deposits from the H.M.S. Egeria, H.M.S. Fling Fish and H.M.S. Investigator expeditions in the Indian Ocean and Southern Seas

Captain Wharton, the Hydrographer of the Admiralty sent to the author a series of the deposit-samples collected in the Indian and Antarctic Oceans during the expeditions in 1887 of H.M.S. Flying Fish, H.M.S. Egeria and H.M.S. Investigator. These deposits were submitted to careful microscopical examination and chemical analysis.

The record of stable isotope composition of surface and thermocline planktic foraminifera from sediment core 64PE-174P13 for the last 460,000 years

The upper branch of the Atlantic Meridional Overturning Circulation predominantly enters the Atlantic Ocean through the southeast, where the subtropical gyre is exposed to the influence of the Agulhas leakage (AL). To understand how the transfer of Indian Ocean waters via the AL affected the upper water column of this region, we have generated new proxy records of planktic foraminifera from a core on the central Walvis Ridge, on the eastern flank of the South Atlantic Gyre (SAG). We analyzed the isotopic composition of subsurface dweller Globigerinoides ruber sensu lato, and thermocline Globorotalia truncatulinoides sinistral, spanning the last five Pleistocene glacial-interglacial (G-IG) cycles. The former displays a response to obliquity, suggesting connection with high latitude forcing, and a warming tendency during each glacial termination, in response to the interhemispheric seesaw. The d18O difference between the two species, interpreted as a proxy for upper ocean stratification, reveals a remarkably regular sawtooth pattern, bound to G-IG cyclicity. It rises from interglacials until glacial terminations, with fast subsequent decrease, appearing to promptly respond to deglacial peaks of AL. Stratification, however, bears a different structure during the last cycle, being minimal at Last Glacial Maximum, and peaking at Termination I. We suggest this to be the result of the intensified glacial wind field over the SAG and/or of the invasion of the South Atlantic thermocline by Glacial North Atlantic Intermediate Waters. The d13C time series of the two species have similar G-IG pattern, whereas their difference is higher during interglacials. We propose that this may be the result of the alternation of intermediate water masses in different circulation modes, and of a regionally more efficient biological pump at times of high pCO2.

Annotated record of the detailed examination of Mn deposits from the TRANSINDIK R/V Valdivia (VA 07) cruise stations

The studied material was taken from Central Indian Ocean central, during the "TRANSINDIK" campaign of the R/V Valdivia. The campaign was conducted from 14 December 1973 until 23 January 1974, between Beira (Mozambique) and Singapore via Port Louis (Mauritius). The samples were taken on 14 stations aligned on a profile trending West, following approximately the 15th parallel (south). This profile cuts through the Mascarene plateau Basin. The preliminary study presented in this report was carried out as part of a study into the genesis and diagenesis the ocean deposits of the central and southern areas of the Indian Ocean (Laboratoire de GÈologie du MusÈum d'Histoire Naturelle - R.C.P. 212) and under the CNEXO No. 74/1017 contract. The data collected supplements the results of the OSIRIS campaign (R/V Marion Dufresne - TAAF) concerning relations existing between morphostructure and sedimentation and, more particularly, the nature and age of metalliferous deposits associated with Mn concretions.

Annotated record of the detailed examination of Mn deposits from the VERMILION SEA Expedition stations

On Vermilion Sea Expedition two research vessels among which the R/V Spencer F. Baird conducted a geological and geophysical exploration of the Gulf of California from February to May, 1959. Support was obtained from the Office of Naval Research and the Bureau of Ships of the U. S. Navy and from a grant of the American Petroleum Institute. Study of the canyons was one feature of the first part of the expedition. Submarine canyon studies were directed by Francis P. Shepard, Professor of Submarine Geology, aboard the research vessel Spencer F. Baird. The expedition found that the narrow channel between Angel de la Guarda Island, toward the head of the Gulf, and the peninsula is scoured almost free of sediments by strong currents. On the other side of Angel de la Guarda Island, between it and the mainland, one of the dredge hauls brought up a manganese nodule. It came from a depth of approximately 1500 feet. This is the shallowest water in which the nodules have been found. Studies have been under way some time on the feasibility of mining such nodules from the sea floor. They contain cobalt, nickel, copper and other valuable metals. (also in, Scripps Institution of Oceanography Vermilion Sea Expedition to the Gulf of California, http://library.ucsd.edu/dc/object/bb34484017)