Age models of upper Pliocene samples of the North Atlantic

Abundance variations of six Pliocene species of discoasters have been analyzed over the time interval from 1.89 to 2.95 Ma at five contrasting sites in the North Atlantic: Deep Sea Drilling Project Sites 552 (56°N) and 607 (41°N) and Ocean Drilling Program 658 (20°N), 659 (18°N), and 662 (1°S). A sampling interval equivalent to approximately 3 k.y. was used. Total Discoaster abundance showed a reduction with increasing latitude and from the effects of upwelling. This phenomenon is most obvious in Discoaster brouweri, the only species that survived over the entire time interval studied. Prior to 2.38 Ma, Discoaster pentaradiatus and Discoaster surculus are important components of the Discoaster assemblage: Discoaster pentaradiatus increases slightly with latitude up to 41°N, and its abundance relative to D. brouweri increases up to 56°N; D. surculus increases in abundance with latitude and with upwelling conditions relative to both D. brouweri and D. pentaradiatus and is dominant to the latter species at upwelling Site 658 and at the highest latitude sites. Discoaster asymmetricus and Discoaster tamalis appear to increase in abundance with latitude relative to D. brouweri. Many of the abundance changes observed appear to be connected with the initiation of glaciation in the North Atlantic at 2.4 Ma. The long-term trend of decreasing Discoaster abundance probably reflects the fall of sea-surface temperatures. This trend of cooling is overprinted by short-term variations that are probably associated with orbital forcing. Evidence for the astronomical elements of eccentricity and obliquity periodicities were found at all sites; however, only at Sites 607, 659, and 662 were precessional periodicities detected. Furthermore, only at Site 659 was precession found to be dominant to obliquity. Abundance peaks of individual species were found to cross-correlate between sites. The distinct abundance fluctuations observed especially in the tropics suggest that temperature is not the only factor responsible for this variation. This study reveals for the first time the importance of productivity pressure on the suppression of Discoaster abundance.

Age model and Plio-Pleistocene benthic stable oxygen isotope ratios of ODP Site 184-1143 in the Sourh China Sea

Based on benthic foraminiferal delta18O from ODP Site 1143, a 5-Myr astronomical timescale for the West Pacific Plio-Pleistocene was established using an automatic orbital tuning method. The tuned Brunhes/Matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0.78 Ma. The tuned ages for several planktonic foraminifer bio-events also agree well with published dates, and new ages for some other bio-events in the South China Sea were also estimated. The benthic delta18O from Site 1143 is highly coherent with the Earth's orbit (ETP) both at the obliquity and precession bands for the last 5 Myr, and at the eccentricity band for the last 2 Myr. In general, the 41-kyr cycle was dominant through the Plio-Pleistocene although the 23-kyr cycle was also very strong. The 100-kyr cycle became dominant only during the last 1 Myr. A comparison of the benthic delta18O between the Atlantic (ODP 659) and the East and West Pacific (846 and 1143) reveals that the Atlantic-Pacific benthic oxygen isotope difference ratio (Delta delta18OAtl-Pac) displays an increasing trend in three time intervals: 3.6-2.7 Ma, 2.7-2.1 Ma and 1.5-0.25 Ma. Each of the intervals begins with a rapid negative shift in Delta delta18OAtl-Pac, followed by a long period with an increasing trend, corresponding to the growth of the Northern Hemisphere ice sheet. This means that all three intervals of ice sheet growth in the Northern Hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the Atlantic as compared to that of the Pacific, followed by its gradual relative cooling. This general trend, superimposed on the frequent fluctuations with glacial cycles, should yield insights into the processes leading to the boreal glaciation. Cross-spectral analyses of the Delta delta18OAtl-Pac with the Earth's orbit suggests that after the initiation of Northern Hemisphere glaciation at about 2.5 Ma, obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo-ocean.

Diversity of abyssal agglutinated foraminifera from Cenomanian to Santonian sediments of the North Atlantic

Benthic foraminiferal assemblages of distinctive taxonomic composition occur at the top of benthic fossil-free black shales which correspond to the anoxic event at the Cenomanian/Turonian boundary in the North Atlantic abyssal DSDP/ODP sites 386, 398, 603 and 641. These assemblages consist of minute, thin-walled agglutinated foraminifera with low specific diversity of 2 to 4 species, variable abundance and dominance of few taxa (Haplophragmoides, Rhizammina and Glomospira). The species are inferred to be opportunistic, able to survive in low-oxygen environments and to be pioneers recolonizing the seafloor after cessation of bottom-water anoxia. Most species are characterized by test morphologies with high surface/volume ratios and single-layered wall structures, with loosely agglutinated grains, and small amounts of organic cement for agglutination. These features are best observed in material from ODP Hole 641A which has exceptional foraminiferai preservation because of its shallow burial depth. The successive appearance of benthic foraminifera after the anoxic event is probably controlled by the continuous reoccurrence of more oxygenated bottom- and interstitial-water conditions. With the final development of oxic bottom-water conditions in the Turonian, a rapid radiation of deep-water agglutinated foraminifera occurred in the North Atlantic.

Data collection of depth and time integrated Calanus finmarchicus abundances, averaged temperatures, and integrated Chlorophyll concentration in the North Atlantic Ocean

Here we present a new, pan-North-Atlantic compilation of data on key mesozooplankton species, including the most important copepod, Calanus finmarchicus. Distributional data of eight representative zooplankton taxa, from recent (2000-2009) Continuous Plankton Recorder data, are presented, along with basin-scale data of the phytoplankton colour index. Then we present a compilation of data on C. finmarchicus, including observations of abundance, demography, egg production and female size, with accompanying data on temperature and chlorophyll. . This is a contribution by Canadian, European and US scientists and their institutions.