Abstract
Reconstruction of intermediate water properties is important for understanding feedbacks within the ocean-climate system, particularly since these water masses are capable of driving high–low latitude teleconnections. Nevertheless, information about intermediate water mass evolution through the late Pleistocene remains limited. This paper examines changes in Antarctic Intermediate Water (AAIW), the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition (δ18O and δ13C) and trace element concentration (Mg/Ca and B/Ca) of two benthic foraminiferal species from the same samples: epifaunal Planulina wuellerstorfi and infaunal Uvigerina peregrina. Our results confirm that the most reasonable estimates of AAIW temperature and Δ[CO2−3] are generated by Mg/CaU. peregrina and B/CaP. wuellerstorfi, respectively. We present a 400 kyr record of intermediate water temperature and Δ[CO2−3] from a sediment core from the Southwest Pacific (DSDP site 593; 40°30′S, 167°41′E, 1068 m water depth), which lies within the core of modern AAIW. Our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late Pleistocene. When combined with two nearby records of water properties from deeper depths, our data demonstrate that during interglacial stages of the late Pleistocene, AAIW and Circumpolar Deep Water (CPDW) have more similar water mass properties (temperature and δ13C), while glacial stages are typified by dissimilar properties between AAIW and CPDW in the Southwest Pacific. Our new Δ[CO2−3] record shows short time-scale variations, but a lack of coherent glacial–interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods.
Highlights
The Southern Ocean is a critical component of the oceanclimate system since it is capable of substantial carbon storage and variable CO2 fluxes across the air–sea interface (Burke and Robinson, 2012; Anderson et al, 2009)
We examine changes in two Antarctic Intermediate Water (AAIW) properties through the late Pleistocene using benthic foraminiferal stable isotopic and trace elemental ratios to characterize the intermediate waters that are exported from the Southern Ocean to the Pacific
We have evaluated several methods for using foraminiferal geochemistry to reconstruct past changes in intermediate water temperatures (IWT) and [CO23−] over the last 400 kyr, and demonstrate above that Mg/CaU. peregrina and B/CaP. wuellerstorfi are the best proxies for estimating paleotemperature and [CO23−], respectively
Summary
The Southern Ocean is a critical component of the oceanclimate system since it is capable of substantial carbon storage and variable CO2 fluxes across the air–sea interface (Burke and Robinson, 2012; Anderson et al, 2009). Analysis of millennial-scale climate variability during the late Pleistocene demonstrates the potential for AAIW to be a driver in high–low latitude teleconnections on shorter time scales owing to transportation of heat and storage of CO2 (Bostock et al, 2010; Pahnke and Zahn, 2005). Generating these records is complicated due to the limited development of geochemical proxies at intermediate water depths. We examine changes in two AAIW properties through the late Pleistocene using benthic foraminiferal stable isotopic and trace elemental ratios to characterize the intermediate waters that are exported from the Southern Ocean to the Pacific. We investigate: 1) if the Mg/CaU. peregrina paleotemperature proxy (Elderfield et al, 2010) is viable and devoid of carbonate ion effects at intermediate water depths; 2) the utility of B/CaU. peregrina to reconstruct past changes in intermediate water [CO23−]; and 3) changes to the paleoceanographic history of AAIW over the last 400 kyr
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