The PRISM (Pliocene palaeoclimate) reconstruction: time for a paradigm shift

Abstract

Global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change, but single-temperature representations of the oceanic mixed layer for data–model comparisons are outdated, and the time for a paradigm shift in marine palaeoclimate reconstruction is overdue. The new paradigm in marine palaeoclimate reconstruction stems the loss of valuable climate information and instead presents a holistic and nuanced interpretation of multi-dimensional oceanographic processes and responses. A wealth of environmental information is hidden within the US Geological Survey's P liocene R esearch, I nterpretation and S ynoptic M apping (PRISM) marine palaeoclimate reconstruction, and we introduce here a plan to incorporate all valuable climate data into the next generation of PRISM products. Beyond the global approach and focus, we plan to incorporate regional climate dynamics with emphasis on processes, integrating multiple environmental proxies wherever available in order to better characterize the mixed layer, and developing a finer time slice within the Mid-Piacenzian Age of the Pliocene, complemented by underused proxies that offer snapshots into environmental conditions. The result will be a proxy-rich, temporally nested, process-oriented approach in a digital format—a relational database with geographic information system capabilities comprising a three-dimensional grid representing the surface layer, with a plethora of data in each cell.

On the identification of a Pliocene time slice for data–model comparison

“…The current PRISM SST dataset has 115 sites [17] (figure 6 a ) focused on a time slab of approximately 240 ka based on the warm peak averaging technique [35,55]. The next PRISM SST reconstruction, which is in development (PRISM4), represents more than a two order-of-magnitude increase in resolution with palaeoceanographic reconstruction 56. Preliminary analysis of available material for reanalysis from the PRISM project suggests that no fewer than 30 globally distributed SST sites may contribute to the first phase of time slice reconstruction for 3.204–3.207 Ma BP (figure 6 a and table 3).…”

The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction

“…8b) also lend themselves to a different approach to paleoenvironmental reconstruction, which in turn provides an alternative for data-model comparison. Dowsett et al (2013b) outlined challenges to conventional paleoclimate reconstruction citing as rationale information loss due to underutilization of multivariate data sets capable of a more holistic reconstruction. They called for new methods focused on regional and/or process-oriented reconstructions similar to those being developed for PRISM4.…”

“…By providing uncertainty ranges and paleoenvironmental estimates in terms of cold/dry and warm/wet (terrestrial) and maximum, mean, and minimum warming (marine), the data sets provide guidelines and realistic limits for a robust Piacenzian global paleoenvironmental reconstruction. For the purposes of verifying paleoclimate model simulations, the time slab would ideally need to collapse (temporally) as much as possible toward a true time slice, like the 3.205 Ma datum proposed by Dowsett et al (2013b) and . At that time, correlative with MIS KM5c, orbital forcing was close to presentday forcing.…”

“…In an effort to reduce uncertainty, PlioMIP2 experimental protocols now call for sub-orbital resolution verification data around a specific stratigraphic target of interest that exhibits orbital forcing close to that of present day (Dowsett et al, 2013b;). An initial time slice centered at 3.205 Ma (Fig.…”

Warm climates of the past—a lesson for the future?

“…A dataset that has been developed with the purpose of providing a synthesis of past temperature data is presented by Dowsett et al [24], who describe a vision for ‘PRISM4’—the next generation of global temperature database for the mid-Pliocene warm period (approx. 3 Ma), including, critically, assessment of confidence in all the proxies.…”