Enough is enough, or more is more? Testing the influence of foraminiferal count size on reconstructions of paleo-marsh elevation

Andrew C. Kemp*, Alexander J. Wright, Niamh Cahill

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Salt-marsh foraminifera are sea-level proxies used to quantitatively reconstruct Holocene paleo-marsh elevations (PME) and subsequently relative sea level (RSL). The reliability of these reconstructions is partly dependent upon counting enough foraminifera to accurately characterize assemblages, while counting fewer tests allows more samples to be processed. We test the influence of count size on PME reconstructions by repeatedly subsampling foraminiferal as-semblages preserved in a core of salt-marsh peat (from Newfoundland, Canada) with unusually large counts (up to 1595). Application of a single, weighted-averaging transfer function developed from a regional-scale modern training set to these ecologically-plausible simulated assemblages gener-ated PME reconstructions at count sizes of 10-700. Recon-structed PMEs stabilize at counts sizes greater than ~50 and counts exceeding ~250 tests show little return for the additional time invested. The absence of some rare taxa in low counts is unlikely to markedly influence results from weighted-averaging transfer functions. Subsampling of mod-ern foraminifera indicates that cross-validated transfer func-tion performance shows only modest improvement when more than ~40 foraminifera are counted. Studies seeking to understand multi-meter and millennial scale RSL trends should count more than ~50 tests. The precision sought by studies aiming to resolve decimeter- and decadal-scale RSL variability is best achieved with counts greater than ~75. In most studies seeking to reconstruct PME, effort is more productively allocated by counting relatively fewer foraminifera in more core samples than in counting large numbers of individuals. Target count sizes of 100-300 in existing studies are likely conservative and robust. Given the low diversity of salt-marsh foraminiferal assemblages, our results are likely applicable throughout and beyond northeastern North America.

Original languageEnglish
Pages (from-to)266-278
Number of pages13
JournalJournal of Foraminiferal Research
Volume50
Issue number3
Early online date1 Jul 2020
DOIs
Publication statusPublished - Jul 2020

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