Neogene calcareous nannofossil abundance and datums of ODP Site 186-1150 and 186-1151 sediments

Calcareous nannofossil assemblages were studied from Ocean Drilling Program Holes 1150A, 1150B, 1151A, 1151C, and 1151D in order to estimate the age of sediments drilled in the Japan Trench of the western Pacific Ocean. The abundance and species diversity of nannofossil flora are generally low but are sufficient to show that the sedimentary sequences range from Quaternary to Miocene in age (nannofossil Zones CN15-CN3). The abundance of Coccolithus pelagicus, a cold-water indicator, was studied from sediments younger than 3.83 Ma from both Holes 1150A and 1151A in order to elucidate past climate conditions. Between 3.83 and 2.82 Ma, the abundance of C. pelagicus was generally low, but abundance increased significantly after 2.82 Ma. In agreement with previous studies, this increase appears to be related to a change in the current system around the western Pacific Ocean and eastern Atlantic Ocean that occurred in response to the final elevation of the Isthmus of Panama.

Chlorophyll a concentration and zooplankton abundance and biomass below melting sea ice in the Amundsen Gulf

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic-pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind./m**3) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5-2.3 mg Chl-a/m**3) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind./m**2) and wet biomass (<0.2 g/m**2). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.