IODP Expedition 351, Philippine Sea: Neogene NW Pacific Deep Water Circulation
Lead Research Organisation:
University of Nottingham
Department Name: Sch of Geography
Abstract
Deep thermohaline circulation of the world's oceans, specifically in relation to meridional (from polar to polar regions) overturning circulation, is closely linked to long and short term climate changes in the geological past. As circulation pathways, flow speeds, and upwelling of the oceans changes, the amount of CO2 (which is held in ocean water) in contact with the atmosphere changes, and heat (also held in ocean water) transport between high and low latitudes changes. Climate both impacts deep ocean circulation (e.g. growth of sea ice in the Quaternary), and is impacted by oceanic changes (e.g. glacial CO2 storage in the deep Southern Ocean; transport of warm water through the Isthmus of Panama). Despite its importance, however, the history of deep (greater than about 4 km water depth) Pacific Ocean circulation, the most extensive of the world's oceans, has not yet been constrained for the Neogene (the last 26 million years).
Modern Pacific circulation is composed largely of lower salinity surface water flowing broadly southwards, driven by Circumpolar Deep Water from the south (greater than about 4 km water depth) flowing northwards. This important Circumpolar Deep Water is composed of a mixture of Antarctic Bottom Water and North Atlantic Deep Water, formed by cold dense sinking high latitude water masses outside of the Pacific. Circumpolar Deep Water fills the deep Pacific, and is a source of the shallower (~1-3 km water depth) return southern flow Pacific Central Water.
The Neogene (~23 Ma to Recent) has seen large changes in global climate, from a mid Miocene warm world (before 14 million years ago), to the 'ice-house' of Northern Hemisphere Glaciation (after 3 million years ago). Understanding the strength of the Pacific meridional overturning circulation in a warmer world is yet to be resolved, with some studies suggesting enhanced circulation and others reduced in the Eocene (around 50 million years ago). Several studies have attempted to reconstruct Pacific deep circulation over the Miocene (23 to 5 million yeas ago), but have focussed on intermediate depth Pacific Central Water largely due to available material. Some studies suggest there was a waning influence of Atlantic waters as the Isthmus of Panama closed through the Neogene. Others suggest the mid Miocene Pacific had a slower circulation, but with a similar southern source to today. If true, we would expect bottom waters in the North Pacific to have a greater Circumpolar Deep Water 'signature' after 14 Ma. This hypothesis can be tested with new International Ocean Discovery Program cores from the Philippine Sea (NW Pacific), that were monitoring deep waters (4.5 km water depth) throughout the Neogene, and have an excellent record of fish teeth with which to measure Nd isotopes as a water mass tracer proxy. Southern Ocean water Nd isotopes have a more negative value (-8) than Pacific Central Water (-3.5), and the Southern Ocean's influence on Circumpolar Deep Water is shown in modern Nd isotope profiles from the NW Pacific.
Modern Pacific circulation is composed largely of lower salinity surface water flowing broadly southwards, driven by Circumpolar Deep Water from the south (greater than about 4 km water depth) flowing northwards. This important Circumpolar Deep Water is composed of a mixture of Antarctic Bottom Water and North Atlantic Deep Water, formed by cold dense sinking high latitude water masses outside of the Pacific. Circumpolar Deep Water fills the deep Pacific, and is a source of the shallower (~1-3 km water depth) return southern flow Pacific Central Water.
The Neogene (~23 Ma to Recent) has seen large changes in global climate, from a mid Miocene warm world (before 14 million years ago), to the 'ice-house' of Northern Hemisphere Glaciation (after 3 million years ago). Understanding the strength of the Pacific meridional overturning circulation in a warmer world is yet to be resolved, with some studies suggesting enhanced circulation and others reduced in the Eocene (around 50 million years ago). Several studies have attempted to reconstruct Pacific deep circulation over the Miocene (23 to 5 million yeas ago), but have focussed on intermediate depth Pacific Central Water largely due to available material. Some studies suggest there was a waning influence of Atlantic waters as the Isthmus of Panama closed through the Neogene. Others suggest the mid Miocene Pacific had a slower circulation, but with a similar southern source to today. If true, we would expect bottom waters in the North Pacific to have a greater Circumpolar Deep Water 'signature' after 14 Ma. This hypothesis can be tested with new International Ocean Discovery Program cores from the Philippine Sea (NW Pacific), that were monitoring deep waters (4.5 km water depth) throughout the Neogene, and have an excellent record of fish teeth with which to measure Nd isotopes as a water mass tracer proxy. Southern Ocean water Nd isotopes have a more negative value (-8) than Pacific Central Water (-3.5), and the Southern Ocean's influence on Circumpolar Deep Water is shown in modern Nd isotope profiles from the NW Pacific.
Planned Impact
Beneficiaries from the proposed research over different timescales:
Undergraduate community: Over a short timescale, including whilst sailing on IODP Exp. 351, students studying Earth Sciences within Universities worldwide will be able to follow the expedition through IODP outreach blogs and websites (which will include contributions from me) to gain an understanding of the International Ocean Discovery Program in particular, the life of a research scientist, and possible careers within the Earth Sciences.
School children: Over a shorter timescale, it is hoped that my contribution to IODP outreach activities, including blogs and websites showcasing the IODP programme, will help school children to gain an understanding of the importance of studying science. This is in terms of practical applications beyond studying in class, the potential careers for those studying science, and the importance of science to the global community.
The general public: On shorter and medium timescales, it is envisioned that my contribution to IODP outreach activities, including websites and online publications, will help the general public through engagement with the media in understanding that extreme environmental changes have occurred in Earth's past, and that ralative 'climate stability' is not necessarily the only state.
Interested scientific lay-community: Over a longer timescale, via my contribution to online publications aimed at engaging with the non-specialist (including for example New Scientist, NERC Planet Earth, the UK IODP Newsletter), it is hoped that the interested scientific lay-community will benefit from a better understanding of what happened during particularly interesting times in the history of the Earth.
Policy-makers: Over longer timescales, after my publication of research results from this proposal, it is envisioned that a better understanding of the causal mechanisms of global ocean circulation will be achieved, which will have implications for our understanding and modelling of possible future changes to deep water circulation (which has already been detected in recent decades in the North Atlantic). This research my therefore lead to policy changes in relation to regional oceanic, ecologic and climatic changes.
Undergraduate community: Over a short timescale, including whilst sailing on IODP Exp. 351, students studying Earth Sciences within Universities worldwide will be able to follow the expedition through IODP outreach blogs and websites (which will include contributions from me) to gain an understanding of the International Ocean Discovery Program in particular, the life of a research scientist, and possible careers within the Earth Sciences.
School children: Over a shorter timescale, it is hoped that my contribution to IODP outreach activities, including blogs and websites showcasing the IODP programme, will help school children to gain an understanding of the importance of studying science. This is in terms of practical applications beyond studying in class, the potential careers for those studying science, and the importance of science to the global community.
The general public: On shorter and medium timescales, it is envisioned that my contribution to IODP outreach activities, including websites and online publications, will help the general public through engagement with the media in understanding that extreme environmental changes have occurred in Earth's past, and that ralative 'climate stability' is not necessarily the only state.
Interested scientific lay-community: Over a longer timescale, via my contribution to online publications aimed at engaging with the non-specialist (including for example New Scientist, NERC Planet Earth, the UK IODP Newsletter), it is hoped that the interested scientific lay-community will benefit from a better understanding of what happened during particularly interesting times in the history of the Earth.
Policy-makers: Over longer timescales, after my publication of research results from this proposal, it is envisioned that a better understanding of the causal mechanisms of global ocean circulation will be achieved, which will have implications for our understanding and modelling of possible future changes to deep water circulation (which has already been detected in recent decades in the North Atlantic). This research my therefore lead to policy changes in relation to regional oceanic, ecologic and climatic changes.
People |
ORCID iD |
| Sev Kender (Principal Investigator) |
Publications
Arculus R
(2016)
Reply to 'Unclear causes for subduction'
in Nature Geoscience
Arculus R
(2015)
A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc
in Nature Geoscience
Kender S
(2018)
Neodymium Evidence for Increased Circumpolar Deep Water Flow to the North Pacific During the Middle Miocene Climate Transition
in Paleoceanography and Paleoclimatology
| Description | During our expedition to the IBM Arc, we successfully collected 1.5 km of borehole through the overlying sediments and into the Philippine Sea crust, dating the rocks with microscopic fossils and magnetic field reversals. We found the crust to be much younger than expected, a discovery based on microfossil and thermal subsidence evidence. Our ideas of how the subduction zone formed needed to readjust to account for this information. The crust was found to have chemical characteristics indicating it was formed at the time the subduction zone started, rather than much earlier. The crust may have formed in an extensional setting through seafloor spreading, in some ways similar to that formed at mid-ocean ridges today, although in this case near the newly-formed subduction zone. One idea is that the subduction zone formed along a previous line of weakness in one of these fracture zones, although it is not proven. Our new records show that the initiation was probably 'spontaneous' rather than 'induced', as the crust was formed in an extensional setting and did not become uplifted before formation. The tectonic history of the past 20 Ma has been such that the palaeo water-depth did not change significantly, allowing us to reconstruct North Pacific Deep Water (>4.5 km water depth) properties over this time period for the first time. We did this by measuring Nd isotopes in fish teeth and ferro-manganese coatings which is the most powerful water circulation proxy that exists. Remarkably, we found that NPDW did not travel this far northwards before the Middle Miocene climate transition (14 Ma), and we tie this change in Pacific Ocean circulation to climate events. |
| Exploitation Route | Our findings will significantly contribute to the debate about subduction zone formation, and be used by others in the field to build new models. Our ocean circulation findings are published in the peer reviewed literature, and provide powerful boundary condition changes for coupled ocean-atmosphere climate models. |
| Sectors | Education,Other |
| URL | https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2017PA003309 |