Inferring surface water equilibrium calcite δ¹⁸O during the last deglacial period from benthic foraminiferal records: Implications for ocean circulation

Abstract

The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed "upstream" (by planktonic foraminifera) and "downstream" (by benthic foraminifera) to constrain how tracer signals are modified by the intervening circulation and, by extension, to constrain properties of that circulation.

Reconstructing deglacial ocean ventilation using radiocarbon : data and inverse modeling

“…Overall, my results echo those from previous studies that similarly illustrated the difficulty to reject the consistency of sediment data for the LGM and the deglaciation with the modern circulation, given the data uncertainties and paucity (e.g., Amrhein, 2016;Amrhein et al, 2015;Burke et al, 2011;Dail and Wunsch, 2014;Gebbie, 2014;Gebbie and Huybers, 2006;LeGrand and Wunsch, 1995;Marchal and Curry, 2008).…”

“…First I examine the extent to which the box model of modern ocean ventilation can be fitted to the deep water Δ 14 C data (bin Δ 14 C values); the surface Δ 14 C values that lead to the fit are considered next. This analysis of residuals provides an avenue to test H0, because large differences between the fitted and observed Δ 14 C values are expected if the observed values are jointly incompatible with modern ocean ventilation (for similar approaches using benthic δ 18 O data, see Amrhein et al, 2015;Gebbie, 2012). To derive the fitted Δ 14 C values, the deep water Δ 14 C anomalies in that are implied by the fit of the model to the data are computed from…”

“…from (19) for a number of -dimensional vectors ! , where each vector has the elements corresponding to a given surface box set to 1 for all times while the other elements (corresponding to other surface boxes) are set to 0 (Amrhein et al (2015). The values of !…”

A Synthesis of Deglacial Deep‐Sea Radiocarbon Records and Their (In)Consistency With Modern Ocean Ventilation

“…Departures of from can thus be investigated from the matrix T v . One approach for such investigation is to repeatedly calculate from for a number of vectors , where each vector has the elements corresponding to a given surface box set to 1 for all times while the elements corresponding to other surface boxes are set to 0 (Amrhein et al, ). The elements of calculated in this way provide a measure of the ability of the deep water Δ 14 C data to resolve Δ 14 C in the different surface boxes of the model, with a value near 0 indicating poor resolvability and a value near 1 indicating high resolvability.…”

Last Glacial Maximum and deglacial abyssal seawater oxygen isotopic ratios

“…A growing literature (e.g. Marchal and Curry, 2008;Huybers and Wunsch, 2010;Burke et al, 2011;Gebbie, 2012;Amrhein et al, 2015;W16;M15) attempting to quantify inferred circulation differences between the LGM and the modern period increasingly finds it difficult to distinguish any qualitative or even quantitative changes. Such findings do not disprove hypotheses of major change to water mass volumes, including cold, strong abyssal salinities during the LGM, but only reinforce the need for far more data than are now available -if the hypotheses are to become factual.…”