posted on 2015-10-01, 15:21authored byAdeyinka Oluyemi Aturamu
The taxonomy of benthic foraminifera recovered from 160 core samples over depth
20.59 m and representing the past ~597 Kyr (sedimentary deposit of the Tarantian and
Ionian stages) at Bowers Ridge, Bering Sea IODP site U1342, includes some 52 species
from 41 genera and 22 families: these species are given formal taxonomic treatment
with detailed illustration. A further 16 species are discussed in open nomenclature.
Foraminifer assemblages are dominated by species of Takayanagia delicata, Uvigerina
bifurcata, Islandiella norcrossi and Alabaminella weddellensis accounting for more
than 58 % of all specimens recovered. In addition to their taxonomic identification, this
study interrogates the relationship between benthic foraminifera and interpreted changes
in oxygen concentration and productivity during a series of late Quaternary glacial–
interglacial cycles at site U1342. In particular, the species Bolivina spissa (Cushman) –
thought to record changes in seabed oxygen level, shows no correlation between test
pore density and interpreted bottom water oxygen level (BW-O2), suggesting that
oxygen is not the sole driver influencing the distribution and morphology of this
species. Further assessment of the total foraminiferal assemblages at site U1342 - using
the sedimentological context and the proportion of deep infaunal species as a proxy for
low oxygen conditions at the seabed, and shallow infaunal species as a proxy for a welloxygenated
seabed, identify eight broadly defined temporally successive benthic
foraminiferal intervals through the sampled core. Three of these intervals, between
depths 0 - ~5.40, ~ 6.50 - 9.00 and ~16.90 - 18.67 m-CCSF, signal a well-oxygenated
sea bed, whilst the other five intervals suggest increased phytodetritus flux to the
seabed, coupled with variations in seabed oxygen level. In general, there is no clear
connexion between these intervals and the glacial-interglacial oscillation at the site
during the past ~597 ka, suggesting that ecological influences on foraminiferal
distribution at Bowers are complex.