Speakers

Maureen Raymo (Lamont Doherty Earth Observatory, Columbia University)

Luke Skinner (University of Cambridge, Cambridge)

What can we learn from oceans?

Palaeoceanography is a vital part of Quaternary science, as oceans contain a vast amount of sediment.  Reconstructing global ice volume (and there for global climate) and ocean temperatures using proxy records from these sediments was not possible before these methods were used.  These long records stretch back through the Quaternary and beyond, and contain very important information about the climate, and allow an investigation of climate interactions over long time-scales.  It is from these records that we were able to clearly see glacial-interglacial cycles.

 

Luke Skinner and Maureen Raymo discussing the importance of oceans in Quaternary Science

Luke Skinner and Maureen Raymo discussing the importance of oceans in Quaternary Science

What have been the major developments in oceanography?

Much of pioneering work into long marine cores was led by Nick Shackleton.  These long sediment records could be dated by stretching and compressing them to fit with known records of orbital forcing, as this was known to have driven climate change on this scale.

As the number of long marine cores increased through the 1990s, numerous records with different timescales were released, making it difficult to select a single timescale to work from.  By taking 57 of these long ocean records of δ18O (which measure global ice volume and also deep ocean temperature), Lorraine Lisiecki and Maureen Raymo were able to produce a single record covering the past 5.3 Ma, called the LR04 stack.  This acted as an important stratigraphic tool for the palaeoclimatic community.  Despite its use, averaging these records from across the globe has caused some problems.  Due to meltwater input, the d18O records from the Pacific Ocean lag those from the Atlantic by an average of 1600 years and sometimes up to 4000 years.

Another important development was the use of δ13C records to investigate temperature gradients in the ocean, thereby inferring ocean circulation.  From this you can reconstruct δ13C in the past (i.e. during a glacial period) and investigate ocean circulation variability.

 

Our understanding of the oceans’ large scale overturning has evolved significantly over the past 50 years, to a better understanding of ocean mixing.  Now that developments have been made, it is vital that future palaeoceanographic interpretation incorporate these developments, including: energy budgets, diapycnal mixing (vertical mixing – this has a control on the rate deep water reaches the surface), winds, and buoyance effects.  In turn, the investigation of palaeoceanograpic conditions can help improve our current conceptual framework.

 

What are the major challenges?

Future progress in this field will rely upon new methods and proxies, and their application to new methods.  It is likely that these will involve novel combinations of numerical model simulations and palaeoceanographic data.  How the vast amount of data is managed and used effectively will be a challenge in the future.

The long-term ocean record still presents some challenges.  The δ18O signal which is recorded in sediment cores represents changes in both deep ocean temperature and global ice volume.  The importance of each of these factors for the overall δ18O is thought to be 1/3 and 2/3 respectively.  However, it is not known if this ratio has changed in the past.  It is also unknown is the δ18O fluctuations reflect change in northern or southern hemisphere ice volume.

 

Despite the recent advances in understanding how these processes work, several specific questions remain unaddressed with regard to ocean circulation:

  • what are the roles of wind vs dispersal mixing in ocean circulation.
  • what are the energy budgets available to drive ocean mixing.
  • the stability properties of the Meridional Overturning Circulation (MOC), and how does variability in the Atlantic Meridional Overturning Circulation (AMOC) link to buoyancy both forcing and regional climate change.