A BENTHIC FORAMINIFERAL RECORD OF HOLOCENE CLIMATIC CHANGE: ADMIRALTY SOUND, ANTARCTIC PENINSULA

Sediment cores JKC-62 and KC-63, collected from the southern margin of James Ross Island, (JRI) northern Weddell Sea during cruise NBP10-01, were analyzed for benthic foraminifera to reconstruct environmental and glacial conditions through the late Holocene. Two lithologic units were identified in both cores; Unit 1 was comprised of sand to gravel size sediments while Unit 2 was comprised of silty-clay sized sediments.

Benthic foraminiferal analysis of JKC-62 revealed two major environmental changes represented by foraminiferal abundances. Unit 2 (37 cm to 320 cm) of JKC-62 was overwhelmingly dominated by Nonionella iridea indicating non-corrosive bottom waters. Within Unit 2 are three intervals of rapid decrease in the abundance of N. iridea and increase in abundance of Globocassidulina subglobosa, which suggests ice shelf and sea-ice formation and the input of corrosive bottom waters inhibiting the preservation of N. iridea. Unit 2 (130 cm to 246 cm) of KC-63 was characterized by the abundance of Portatrochammina rossensis, an agglutinated species, which indicates the sustained presence of corrosive bottom waters. However, the increase in abundance of N. iridea in the lower part of Unit 2 (216 cm to 234 cm) indicates an input of fresher, non-corrosive waters, possibly due to ice shelf and sea-ice melt. Though this environmental change was short lived, it represents similar conditions to what was suggested for Unit 2 of JKC-62.

The uppermost lithologic unit (Unit 1) seen in both JKC-62 and KC-63 (0 cm to 37 cm and 0 cm to 130 cm respectively) was dominated by reworked Cretaceous foraminifera, the majority being identified as Bolivina incrassata. The occurrence of the reworked Cretaceous foraminifera suggests significant erosion of Cretaceous sediments off of James Ross Island by Swift Glacier into the adjacent marine environment, which coincides with a record of late Holocene warming interpreted from the JRI ice core.