Abstract
The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its climatic impact. Deciphering the chemical composition of Circumpolar Deep Water (CDW) within the ACC can provide critical insights about its development and evolution. Here we present new fossil fish teeth/bone debris neodymium isotope (εNd) records from Deep Sea Drilling Project (DSDP) Sites 278 and 274 in the southwest Pacific Ocean, with the aim to trace changes in deep water masses across the Tasmanian Gateway between the early Oligocene and early Miocene (~ 33–22 Ma). Site 274 provides the first Nd isotope record proximal to the Ross Sea during the Oligocene (33.5–23.4 Ma). Its Nd isotope composition shows excursions to very radiogenic values, εNd(t) = −3.1 and εNd(t)= − 3.7, at 33.5 Ma and 23.8 Ma, respectively, in response to major steps in Antarctic ice sheet expansion. A shift to lower, more unradiogenic εNd(t) values between 29.7 and 29.1 Ma is linked to an increased influence of proto-CDW upwelling at the site. In contrast, the Nd isotope record from Site 278 in the southern Emerald Basin shows little variability (εNd(t) = −6.0 to −6.7) throughout the Oligocene and early Miocene (30.9–21.8 Ma). Comparison with published data north of the ACC path, demonstrates the presence of two deep water masses in the South Pacific prior to the inferred onset of the ACC (33–30 Ma), one occupying depths between ~2500 and 3000 m (εNd(t)= ~ −3 to −5) and a deep/bottom water mass (> 3000 m) with a more unradiogenic Nd isotope composition (εNd(t)= ~ −6). Site 278 located close to the proto-polar front (proto-PF) indicates that following the inferred onset of the ACC, deep waters bathing the southern Emerald Basin remained more radiogenic in the Southwest Pacific compared to sites along the proto-PF in the South Atlantic and Indian Ocean (εNd(t)= ~ −8.1). This indicates a provinciality in Nd isotope compositions of deep waters along the proto-PF across the Tasmanian Gateway. Our data are incompatible with the existence of a modern-like homogenous (lateral and vertical) Nd isotope composition of CDW along the main flow path of the ACC in all oceanic basins in the Oligocene to early Miocene. We attribute distinct Nd isotope compositions of deep waters across the Tasmanian Gateway to reflect a less deep reaching and weaker ACC (proto-ACC) than today. Our findings suggest that the modern strong and deep-reaching ACC flow must have been developed at a later point in the Neogene.
Original language | English |
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Article number | 103718 |
Pages (from-to) | 1-12 |
Journal | Global and Planetary Change |
Volume | 208 |
DOIs | |
Publication status | Published - Jan 2022 |
Bibliographical note
Funding Information:This research used samples provided by the International Ocean Discovery Program (IODP). We acknowledge the staff and shipboard party from Legs 28 and 29. We thank the staff at the Gulf Coast core repository (GCR) for curating these cores and assistance in core handling and shipping. We also acknowledge the Paleomagnetic Laboratory of Barcelona (CSIC-CCiTUB). We also thank Denise Kulhanek and an anonymous reviewer for their constructive comments, which improved this paper. Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), co-funded by the European Union through FEDER funds; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme.
Funding Information:
This research used samples provided by the International Ocean Discovery Program (IODP). We acknowledge the staff and shipboard party from Legs 28 and 29. We thank the staff at the Gulf Coast core repository (GCR) for curating these cores and assistance in core handling and shipping. We also acknowledge the Paleomagnetic Laboratory of Barcelona (CSIC-CCiTUB). We also thank Denise Kulhanek and an anonymous reviewer for their constructive comments, which improved this paper. Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016 ; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P ), co-funded by the European Union through FEDER funds ; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme.
Publisher Copyright:
© 2021 Elsevier B.V.
Funding
This research used samples provided by the International Ocean Discovery Program (IODP). We acknowledge the staff and shipboard party from Legs 28 and 29. We thank the staff at the Gulf Coast core repository (GCR) for curating these cores and assistance in core handling and shipping. We also acknowledge the Paleomagnetic Laboratory of Barcelona (CSIC-CCiTUB). We also thank Denise Kulhanek and an anonymous reviewer for their constructive comments, which improved this paper. Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), co-funded by the European Union through FEDER funds; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme. This research used samples provided by the International Ocean Discovery Program (IODP). We acknowledge the staff and shipboard party from Legs 28 and 29. We thank the staff at the Gulf Coast core repository (GCR) for curating these cores and assistance in core handling and shipping. We also acknowledge the Paleomagnetic Laboratory of Barcelona (CSIC-CCiTUB). We also thank Denise Kulhanek and an anonymous reviewer for their constructive comments, which improved this paper. Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016 ; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P ), co-funded by the European Union through FEDER funds ; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme.
Keywords
- ACC
- CDW
- Deep ocean circulation
- Neodymium isotope ratios
- Oligocene-early Miocene
- Tasmanian Gateway