Investigating Past Ocean Dynamics – iPODS

MOC Drivers Cartoon

Cartoon illustrating the main ‘drivers’ of the ocean’s overturning circulation (credit, for mistakes, L.Skinner).

iPODS (Investigating Past Ocean Dynamics) is an INQUA international focus group, and a part of PALCOMM.

The deep ocean circulation affects climate and cycles of biogeochemical elements such as carbon and nutrients. iPODS is aimed at improving our understanding of past deep ocean circulation changes and its effects on biogeochemical tracer distributions.  While iPODS focuses on radiocarbon and oxygen isotopes (δ18O), it is linked to a sister PAGES working group ‘Ocean Circulation and Carbon Cycling’ (OC3) that focuses on stable carbon isotopes (δ13C).

iPODS Logo

Scientific Questions:
How did the deep ocean circulation change during the last deglaciation (both in terms of transport pathways and transit times)?

What were the effects of these changes on carbon cycling in the ocean and atmospheric CO2?

Specific Goals:
Compilation of published and unpublished benthic and planktic radiocarbon data (with a focus on age-models, past reservoir age variability, ‘ventilation metrics’ and associated uncertainties).

Compilation of published and unpublished Nd isotope and Pa/Th data (with a focus on emerging issues and novel developments).

Integration of these sparsely sampled non-conservative and pseudo-conservative tracer proxies with compiled conservative proxy data from stable oxygen isotopes.
Forward, and inverse modelling of radiocarbon, and auxiliary tracers (incl. δ18O, εNd).

The first IPODS meeting was held at the Oeschger Centre for Climate Change Research at the University of Bern (29 September – 3 October 2014), in conjunction with the sister PAGES working group ‘OC3’ that focuses on the compilation and study of past stable carbon isotope data, also with a view to better understanding past ocean dynamics. Over 60 scientists, from a wide range of backgrounds and origins, attended the meeting to discuss over four days the objectives of IPODS and of OC3. The Bern IPODS meeting had three main objectives: 1) to consider the use of radiocarbon as a relatively sparsely sampled proxy/tracer that may yet provide invaluable information on past ocean dynamical changes of direct relevance to the marine carbon cycle; 2) to consider similarly the utility of long-lived radiogenic isotopes (e.g. Nd isotopes, sedimentary Pa/Th ratios), for which there is also a relative paucity of data; and 3) to consider opportunities for applying numerical models of varying complexity to the study of these tracers and their implications for ocean dynamics and carbon cycling. Finally, the group also discussed what activities IPODS might motivate in the immediate and medium-term future that might contribute to the more effective use of such proxies/models towards a greater understanding of their implications for past ocean dynamical- (and marine carbon cycle) change.  For more information about this meeting go here.

The two main outputs from this meeting are to be: 1) a review article on the use of radiocarbon as a tracer and dating tool in palaeoceanography (this is in preparation); 2) a compilation of radiocarbon data from the LGM (see Skinner et al., 2017 for an initial take on this); and 3) a compilation of surface reservoir ages spanning the last deglaciation (work in progress).

The second IPODS meeting was held in Utrecht, the Netherlands August 26 – 27(2016), prior to ICP12. This meeting brought together 29 scientists from around the world to discuss the role of the ocean circulation in glacial-interglacial and millennial CO2 change, and to review numerical model perspectives on this question. Two review papers are to emerge from the discussions at the Utrecht meeting, one focusing on the ocean’s role in deglacial carbon cycle change (Schmittner lead), and another on the ocean’s role in millennial CO2 change (Gottschalk lead).

Michael Sarnthein presenting at the 2nd IPODS meeting, Utrecht, NL., 2016.

The third IPODS meeting is planned, again as a joint meeting with the PAGES group OC3, to take place in Cambridge UK in September 2018. More details will be posted here soon, or contact me for information.