Radiolarian-based paleotemperatures during the last 160 kyr at ODP Site 1089 (Southern Ocean, Atlantic Sector)

Abstract

Two cores, Site 1089 (ODP Leg 177) and PS2821-1, recovered from the same location (40 ‡56PS; 9 ‡54PE) at the Subtropical Front (STF) in the Atlantic Sector of the Southern Ocean, provide a high-resolution climatic record, with an average temporal resolution of less than 600 yr. A multi-proxy approach was used to produce an age model for Core PS2821-1, and to correlate the two cores. Both cores document the last climatic cycle, from Marine Isotopic Stage 6 (MIS 6, ca. 160 kyr BP, ka) to present. Summer sea-surface temperatures (SSSTs) have been estimated, with a standard error of ca. þ 1.16 ‡C, for the down core record by using Q-mode factor analysis (Imbrie and Kipp method). The paleotemperatures show a 7 ‡C warming at Termination II (last interglacial, transition from MIS 6 to MIS 5). This transition from glacial to interglacial paleotemperatures (with maximum temperatures ca. 3 ‡C warmer than present at the core location) occurs earlier than the corresponding shift in N 18 O values for benthic foraminifera from the same core; this suggests a lead of Southern Ocean paleotemperature changes compared to the global ice-volume changes, as indicated by the benthic isotopic record. The climatic evolution of the record continues with a progressive temperature deterioration towards MIS 2. High-frequency, millennial-scale climatic instability has been documented for MIS 3 and part of MIS 4, with sudden temperature variations of almost the same magnitude as those observed at the transitions between glacial and interglacial times. These changes occur during the same time interval as the Dansgaard^Oeschger cycles recognized in the N 18 O ice record of the GRIP and GISP ice cores from Greenland, and seem to be connected to rapid changes in the STF position in relation to the core location. Sudden cooling episodes ('Younger Dryas (YD)-type' and 'Antarctic Cold Reversal (ACR)-type' of events) have been recognized for both Termination I (ACR-I and YD-I events) and II (ACR-II and YD-II events), and imply that our core is located in an optimal position in order to record events triggered by phenomena occurring in both hemispheres. Spectral analysis of our SSST record displays strong analogies, particularly for high, sub-orbital frequencies, to equivalent records from Vostok (Antarctica) and from the Subtropical North Atlantic ocean. This implies that the climatic variability of widely separated areas (the Antarctic continent, the Subtropical North Atlantic, and the Subantarctic South Atlantic) can be strongly coupled and co-varying at millennial time scales (a few to 10-ka periods), and eventually induced by the same triggering mechanisms. Climatic variability has also been documented for supposedly warm and stable interglacial intervals (MIS 1 and 5), with several cold events which can be correlated to other Southern Ocean and North Atlantic sediment records. ß

Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)

“…Additional age markers for the MIS 1 to MIS 5 interval were obtained from radiolarian abundance stratigraphy of Cycladophora davisiana (Cortese and Abelmann, 2002). Ages and stage boundaries refer to the time scales of Imbrie et al (1984), for the 590^300-ka interval, and to Martinson et al (1987), for the younger interval ( 6 300 ka).…”

The last five glacial‐interglacial transitions: A high‐resolution 450,000‐year record from the subantarctic Atlantic

“…[7] In this paper, we extend down to $430 ka the previously published radiolarian-based SST estimates for the spliced Site 1089 and PS2821-1 cores, covering last 160 ka [Cortese and Abelmann, 2002]. The time series produced represents a high-resolution climatic record of last five glacial-interglacial cycles located at the boundary between two oceanic regions: the subtropical Indian Ocean and the subantarctic Atlantic Ocean (Figure 1).…”

“…[4] Transfer functions applied to microfossil assemblages have been successfully used to reconstruct past sea surface temperatures (SST) [CLIMAP Project Members, 1981;Pisias et al, 1997;Zielinski et al, 1998;Abelmann et al, 1999;Cortese and Abelmann, 2002;Niebler et al, 2003]. Radiolarians are particularly promising in this respect for the study area, as they are highly diversified and well preserved in Southern Ocean sediments Cortese and Abelmann, 2002].…”

“…Radiolarians are particularly promising in this respect for the study area, as they are highly diversified and well preserved in Southern Ocean sediments Cortese and Abelmann, 2002].…”

Sedimentary record of radiolarian biogeography, offshore eastern New Zealand

“…Large populations can be obtained from small sediment samples that are readily collected from core tops or other sediment sampling devices, and these populations are time-averaged assemblages that are more appropriate for comparison with down-core assemblages than are plankton populations. Radiolarian assemblages in sea-floor sediments have been shown to accurately reflect watermass characteristics in numerous regional studies in the Pacific (Molina-Cruz 1977;Moore 1978;Boltovskoy 1987;Pisias & Mix 1997;Chang et al 2003), Atlantic (Goll & Bjørklund 1972, 1974Morley 1979;Dolven et al 2002;Bjørklund & Krugilova 2003), Indian (Dow 1978;Johnson & Nigrini 1980,1982Morley 1989), and Antarctic (Lozano & Hays 1976;Abelmann et al 1999;Cortese & Abelmann 2002) Oceans. The majority of these studies (e.g., Lozano & Hays 1976;Moore 1978;Pisias & Mix 1997;Chang et al 2003) have used variations of the Imbrie & Kipp (1971) transfer function method, involving Q-mode factor and regression analysis, to translate biogeographic information on modern assemblages into paleo-temperature estimates based on fossil assemblages in sediment cores.…”