Estimating the radiocarbon distribution in the glacial and deglacial ocean

Mea Cook

Abstract

Radiocarbon is a useful tracer of ocean circulation. Unlike tracers such as d13C and nutrient concentration, the decay of radiocarbon is a clock that provides information about the rates of movement of water mases. Estimates of D14C in the past ocean can illuminate the relationship between ocean circulation and climate change, and the partitioning of carbon between the ocean and atmosphere. The D14C in the glacial and deglacial ocean is poorly known, the existing data are sparse in time and space, and key areas of the ocean are completely unconstrained. Estimates of D14C in the past ocean are typically made using deep-water corals or coeval planktonic and benthic foraminifera. To date, relatively few corals suitable for paleoceanographic study have been collected. In addition it is difficult to find sediment cores with abundant enough benthic foraminifera for analysis. Many of the foraminifer radiocarbon measurements in the literature are difficult to compare. Different investigators use different approaches to interpreting the raw radiocarbon mesurements. In addition, measurements of radiocarbon in foraminifera can be significantly biased because of post-depositional processes. Another difficulty is that the uncertainty in the radiocarbon age-calendar age relationship is large during the last glacial maximum and deglaciation. In this talk I'll discuss various approaches to collecting and interpreting foraminiferal radiocarbon measurements. I will also present a synthesis of published and unpublished radiocarbon data, where all the data are treated identically and are subject to a careful error analysis. The unpublished data are new results from a depth transect of sediment cores from the subpolar North Pacific.