Core top and near-surface core catcher samples from eight drill sites in the Eastern Tropical Pacific were investigated for ostracod assemblage composition. Integrated Ocean Drilling Program (IODP) Sites U1337 and U1338 (4200-4463 m water depth) are almost devoid of Ostracoda. Ocean Drilling Program (ODP) Sites 1237, 1238, 1239, 1240, 1241 and 1242 (depth range of 1400-3200 m) exhibit a similar taxonomic composition with a predominance of
Krithe spp. Site 1238 located similar to 200 km west of Ecuador at a water depth of 2203 m had the highest total abundance and was selected for the downcore assemblage study of glacial-interglacial variations over the last 460 ka. A total of three different assemblages were distinguished: glacial, interglacial and background. The glacial assemblage is characterized by higher total ostracod abundance, ostracod valve accumulation rates, and species diversity. The typical glacial taxa are
Krithe spp.,
Legitimocythere castanea,
Bradleya mesembrina,
Cytheropteron spp. and
Fallacihowella sol. Interglacial intervals are characterized by low abundance and diversity and the characteristic taxa are
Pseudobosquetina mucronalata,
Bradleya sp. 1,
Agrenocythere hazelae and
Poseidonamicus major. A background assemblage is found throughout the entire record and consists of
Parakrithe sp.,
Ambocythere cf.
sturgio and
Rugocythereis sp. During glacial intervals (Marine Isotope Stages [MIS] 6, 8, 10, 12), Site 1238 was more strongly influenced by the colder, higher oxygenated Circum-Polar Deep Water. Interglacial intervals (MIS 7, 9, 11) were characterized by climate warming, increased bottom water corrosiveness and decrease in dissolved oxygen. The upper part of the record at Site 1238, MIS 1-5, is characterized by increased biogenic sedimentation rates and possible intensification of upwelling.
