Publication Date:
2022-05-25
Description:
© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 125 (2017): 26-39, doi:10.1016/j.dsr.2017.04.006.
Description:
Bamboo corals, long-lived cold water gorgonin octocorals, offer unique paleoceanographic archives of the
intermediate ocean. These Isididae corals are characterized by alternating gorgonin nodes and high Mg-calcite
internodes, which synchronously extend radially. Bamboo coral calcite internodes have been utilized to obtain
geochemical proxy data, however, growth rate uncertainty has made it difficult to construct precise
chronologies for these corals. Previous studies have relied upon a tie point from records of the anthropogenic
Δ14C bomb spike preserved in the gorgonin nodes of live-collected corals to calculate a mean radial extension
rate for the outer ~50 years of skeletal growth. Bamboo coral chronologies are typically constructed by
applying this mean extension rate to the entire coral record, assuming constant radial extension with coral age.
In this study, we aim to test this underlying assumption by analyzing the organic nodes of six California margin
bamboo corals at high enough resolution (〈0.5 mm) to identify the Δ14C bomb spike, including two tie points
at 1957 and 1970, plus coral collection date (2007.5) for four samples. Radial extension rates between tie points
ranged from 10 to 204 μm/year, with a decrease in growth rate evident between the 1957-1970 and 1970-
2007.5 periods for all four corals. A negative correlation between growth rate and coral radius (r = -0.7; p =
0.03) was determined for multiple bamboo coral taxa and individuals from the California margin,
demonstrating a decline in radial extension rate with specimen age and size. To provide a mechanistic basis for
these observations, a simple mathematical model was developed based on the assumption of a constant
increase in circular cross sectional area with time to quantify this decline in radial extension rate with coral size
between chronological tie points. Applying the area-based model to our Δ14C bomb spike time series from
individual corals improves chronology accuracy for all live-collected corals with complete Δ14C bomb spikes.
Hence, this study provides paleoceanographers utilizing bamboo corals with a method for reducing age model
uncertainty within the anthropogenic bomb spike era (~1957-present). Chronological uncertainty is larger for
the earliest portion of coral growth, particularly for skeleton precipitated prior to bomb spike tie points,
meaning age estimations for samples living before 1957 remain uncertain. Combining this technique with
additional chronological markers could improve age models for an entire bamboo coral. Finally, the relative
consistency in growth rate in similarly-aged corals of the same depth and location supports the hypothesis that
skeletal growth may be limited by local environmental conditions.
Description:
This research was made possible
by National Science Foundation Award #1420984 to M. LaVigne and a Clare Boothe Luce Fellowship to M.
Frenkel.
Keywords:
Bamboo coral
;
Gorgonin
;
Paleoceanography
;
Chronologies
;
Radiocarbon
;
Growth rate
;
14C nuclear bomb spike
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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